Dendritic cells power down inside tumors—re-energizing them could help treat cancer

Good news! Cancer is history (soon)!

"Dendritic cells ... By using their long projections to display fragments of protein, they summon other immune cells to attack invaders and destroy diseased cells. But when dendritic cells find themselves inside a tumor, they tend to run out of steam. According to new research, these cells stop working because their mitochondria ... become degraded.

When scientists examined mice with melanoma, they found that some dendritic cells within the animals’ tumors had perfectly healthy mitochondria, while others were debilitated.

As the tumors grew, the number of cells with active mitochondria dwindled. Although it’s unclear exactly why these organelles go on the fritz, the team did determine that a protein called OPA1 appears to be essential to their functioning. Dendritic cells that possessed this protein were much better at rallying other immune cells, while those engineered to lack it were far less effective—leading to more tumor growth.

When the researchers injected the rodents’ dendritic cells with lots of additional mitochondria, the animals were able to mount a strong antitumor response and fared better when treated with a type of immunotherapy. ..."

From the Perspective abstract:

"Dendritic cells are innate immune cells that regulate the quality, magnitude, and duration of antitumor responses. Conventional type 1 dendritic cells (cDC1s) are crucial in this capacity but are paradoxically rare and functionally impaired in most solid tumors. This is a major barrier to effective immunotherapy. The molecular underpinnings of cDC1 dysfunction within the tumor microenvironment are poorly understood. On page 55 of this issue, You et al. (1) report that mitochondrial fitness is important for cDC1 function. They also demonstrate the therapeutic rescue of cDC1 function within the tumor microenvironment in mice, which provides a framework for metabolically reprogramming dendritic cells to restore antitumor immunity."

From the editor's summary and abstract:

"Editor’s summary

Type 1 conventional dendritic cells (cDC1s) promote CD8+ T cell–mediated antitumor responses. However, cDC1s can become dysfunctional in the tumor microenvironment, and the mechanisms governing cDC1 function versus dysfunction in cancer remain unclear. You et al. report that mitochondrial metabolic states and signaling direct cDC1 function in antitumor immunity (see the Perspective by Molina and Haldar). Loss of the mitochondrial protein OPA1 disrupted nuclear respiratory factor 1 (NRF1) activity and electron transport chain integrity, leading to defects in mitochondrial bioenergetics and redox balance in cDC1s, accompanied by reduced tumor control. OPA1-NRF1 signaling progressively declined during tumor progression, and tumor-bearing mice receiving cDC1s with high mitochondrial fitness had improved antitumor responses, especially in combination with immunotherapy. Therefore, “metabolic engineering” of cDC1s may provide a mechanism for cancer immunotherapy. —Priscilla N. Kelly

Structured Abstract

INTRODUCTION

Conventional type 1 dendritic cells (cDC1s) are essential for cytotoxic CD8+ T cell responses in cancer immunity and immunotherapy. Although previous studies have suggested that mitochondrial oxidative phosphorylation (OXPHOS) is dispensable for DC maturation in vitro and represents a hallmark of tolerance in human monocyte–derived DCs, whether and how mitochondrial metabolism regulates cDC1-CD8+ T cell interactions in antitumor immunity remain largely unknown. In this study, we reveal that intratumoral cDC1s have discrete mitochondrial states and that mitochondrial fusion protein OPA1 dictates cDC1 antitumor immunity by facilitating mitochondrial energy and redox metabolism.

RATIONALE

Despite the success of immunotherapy in cancer treatment, therapeutic resistance or relapse occurs in a large subset of patients. cDC1s determine antitumor effects and therapeutic benefits upon immune checkpoint blockade (ICB) by orchestrating CD8+ T cell activation and function. However, cDC1s often experience metabolic stress and exhibit decreased functional fitness within the tumor microenvironment. ...

RESULTS

We established, from both mouse and human tumors, that cDC1s exhibit discrete mitochondrial states.

One subpopulation, referred to as [TMRM/MG]hi cells, contained polarized mitochondria, as demonstrated by the ratio of mitochondrial membrane potential [measured with tetramethylrhodamine methyl ester perchlorate (TMRM)] compared with mitochondrial mass [measured with MitoTracker Green (MG)]; whereas the 

other subpopulation, [TMRM/MG]lo cells, had depolarized mitochondria. Intratumoral cDC1s with polarized mitochondria more effectively primed CD8+ T cell responses than those with depolarized mitochondria.

Using unbiased profiling approaches and experimental validations, we uncovered that OPA1 orchestrates the mitochondrial states and morphology in intratumoral cDC1s.

Notably, OPA1 deletion in cDC1s led to increased tumor growth and impaired antitumor CD8+ T cell responses, corresponding to defective antigen presentation by cDC1s. Mechanistically, we established that OPA1 supports nuclear respiratory factor 1 (NRF1) activity and expression to sustain mitochondrial OXPHOS in cDC1s. OPA1-NRF1 axis–mediated OXPHOS inhibited autophagy and lysosome–dependent degradation of major histocompatibility complex I (MHC-I) and antigen. In addition, OPA1-mediated electron transport chain (ETC) flow contributed to cDC1 immunogenicity by facilitating NADH-to-NAD+ conversion (i.e., conversion from the reduced to the oxidized form of nicotinamide adenine dinucleotide). These OPA1-dependent effects were antagonized by mitochondrial fission protein DRP1.

During tumor progression, intratumoral cDC1s experienced a progressive mitochondrial dysfunction, as revealed by reduction of the [TMRM/MG]hi subpopulation as well as decreased mitochondrial volume and OPA1-NRF1 signaling.

Intratumoral administration of tumor antigen–pulsed cDC1s with polarized mitochondria into tumor-bearing mice resulted in superior tumor control compared with cDC1s with depolarized mitochondria, particularly when combined with ICB therapies. Indeed, a substantial proportion of mice receiving cotreatment of tumor antigen–pulsed cDC1s with polarized mitochondria plus ICB completely rejected tumors and developed durable immune memory responses upon tumor rechallenge.

CONCLUSION

We uncovered discrete mitochondrial states and the underlying mitochondrial metabolic signaling programs in cDC1s that support their functional fitness in antitumor immunity and the establishment of durable ICB responses. These discoveries provide opportunities to reinvigorate cDC1s for improved cancer immunotherapy."

ScienceAdviser

Mitochondria power immunity against cancer (Perspective, no public access)

Mitochondrial metabolism and signaling direct dendritic cell function in antitumor immunity (no public access)

Mitochondrial metabolism and signaling orchestrate cDC1 antitumor responses.

Nanoflowers rejuvenate old and damaged human cells by replacing their mitochondria

Good news! This could be huge!

"Biomedical researchers ... may have discovered a way to stop or even reverse the decline of cellular energy production—a finding that could have revolutionary effects across medicine. ...

The study ... used a combination of microscopic flower-shaped particles—called nanoflowers—and stem cells. In the presence of these nanoflowers, the stem cells produced twice the normal amount of mitochondria. When these boosted stem cells were placed near damaged or aging cells, they transferred their surplus mitochondria to their injured neighbors. ..."

From the significance and abstract:

"Significance

Mitochondrial dysfunction plays a key role in many diseases, yet treatments to restore function remain limited. Cells naturally transfer mitochondria to help repair damage, but this process is inefficient.

Here, we use molybdenum disulfide (MoS2) nanoflowers to boost mitochondrial production, turning donor cells into mitochondrial biofactories.

These cells transfer more mitochondria to damaged cells, significantly improving energy production and function. In disease models, this approach restores cell health, offering a strategy for treating mitochondrial-related disorders. By enhancing the body’s own repair mechanisms, this nanomaterial-based method could pave the way for innovative therapies in regenerative medicine.

Abstract

Intercellular mitochondrial transfer, the spontaneous exchange of mitochondria between cells, is a recently described phenomenon crucial for cellular repair, regeneration, and disease management. Enhancing this natural process holds promise for developing novel therapies targeting diseases associated with mitochondrial dysfunction.

Here, we introduce a nanomaterial-based approach employing molybdenum disulfide (MoS2) nanoflowers with atomic-scale vacancies to stimulate mitochondrial biogenesis in cells to make them mitochondrial biofactories.

Upon cellular uptake, these nanoflowers result in a two-fold increase in mitochondrial mass and enhancing mitochondrial transfer to recipient cells by several-fold.

This enhanced efficiency of transfer significantly improves mitochondrial respiratory capacity and adenosine triphosphate production in recipient cells under physiological conditions.

In cellular models of mitochondrial and cellular damage, MoS2 enhanced mitochondrial transfer achieved remarkable restoration of cell function.

This proof-of-concept study demonstrates that nanomaterial-boosted intercellular mitochondrial transfer can enhance cell survivability and function under diseased conditions, offering a promising strategy for treating mitochondrial dysfunction-related diseases."

Nanoflowers rejuvenate old and damaged human cells by replacing their mitochondria

Nanomaterial-induced mitochondrial biogenesis enhances intercellular mitochondrial transfer efficiency (open access)

Fig. 1 Synthesis and characterization of size-tunable MoS2 nanoflowers.

Fig. 2 Treatment with MoS2 nanoflowers stimulates mitochondrial biogenesis and bioenergetics.

New discovery: Physics of how cell’s mitochondria divide into smaller parts by fission

Amazing stuff! I was previously not aware of mitochondrial fission and fusion.

Apparently, the new discoveries allow for the unification of two competing, but opposite existing models of this fission.

"Key takeaways

• Mitochondria, the tiny structures providing much of the energy that our cells need, can split apart into smaller pieces in a process called fission.
• The mechanics of mitochondrial fission have been poorly understood, holding back efforts to address serious health problems associated with defects in the process, such as cancer, cardiovascular diseases and neurodegenerative disorders.
• A pair of studies ... have revealed the molecular mechanisms behind mitochondrial fission, creating potential for future treatments.

... Less well-known are their roles in cellular signaling and in eliminating defective cells, which is important for stopping cancer before it starts.

As ... mitochondria squirm around inside cells, they split off pieces through a process called fission, and combine with each other, also known as fusion, to keep up with the cell’s complex energy demands.

Too much fission leads to many undersized mitochondria;

too much fusion leads to many oversized ones. 

Imbalances between fission and fusion are associated with serious disorders of the heart, lungs and brain as well as cancer and diabetes. ...

According to the researchers, mitochondria split in a two-stage process. They found that in each phase, the same protein is used in a different way. ...

The researchers used machine learning, experiments with genetic engineering and advanced X-ray imaging, and computer models of molecular interactions. What they found melds together two leading models for explaining the mechanics of mitochondrial fission. 

First, proteins from what scientists refer to as the dynamin superfamily join up to spiral around the mitochondrion like a scaffold and squeeze its elastic membrane to form a narrow neck. This process is in line with a model suggesting fission is driven by the constriction of dynamin proteins. However, constriction by itself has never been experimentally observed to induce fission.

What happens next is in line with the competing, almost opposite model, which holds that fission is driven not by the assembly (and squeezing) but rather the disassembly of the spiral scaffold into free-floating dynamin protein. The research team showed that, indeed, the floating dynamin proteins drive fission, but only when the mitochondria have been pre-squeezed into a narrow tube first. The individual free-floating proteins then flip around and use their own shape to bend the membrane inward even further by pressing against it. 

In fact, at the threshold for fission, something unexpected happens: The membrane buckles suddenly and becomes so narrow that the mitochondrion can no longer remain in one piece. This snap-through instability, studied in physics and mechanical engineering, finalizes fission in a manner like an umbrella abruptly turned inside out by a wind gust. ...

Beyond the discoveries about mitochondria, this research may offer clues into the mechanisms behind other important cellular behaviors. For instance, the process by which a cell takes in a substance from the outside — vital for both communication between cells and the delivery of medicine — employs a similar change in the membrane. The process, called endocytosis, is dependent on dynamin. ..."

From the abstract (1):

"Mitochondrial fission is controlled by dynamin-like proteins, the dysregulation of which is correlated with diverse diseases. Fission dynamin-like proteins are GTP hydrolysis-driven mechanoenzymes that self-oligomerize into helical structures that constrict membranes to achieve fission while also remodeling membranes by inducing negative Gaussian curvature, which is essential for the completion of fission.

Despite advances in optical and electron imaging technologies, the underlying mechanics of mitochondrial fission remain unclear due to the multiple times involved in the dynamics of mechanoenzyme activity, oligomer disassembly, and membrane remodeling.

Here, we examine how multiscale phenomena in dynamin Drp1 synergistically influence membrane fission using a mechanical model calibrated with small-angle X-ray scattering structural data and informed by a machine learning analysis of the Drp1 sequence, and tested the concept using optogenetic mechanostimulation of mitochondria in live cells.

We find that free dynamin-like proteins can trigger a “snap-through instability” that enforces a shape transition from an oligomer-confined cylindrical membrane to a drastically narrower catenoid-shaped neck within the spontaneous hemi-fission regime, in a manner that depends critically on the length of the confined tube.

These results indicate how the combination of assembly and paradoxically disassembly of dynamin-like proteins can lead to diverse pathways to scission."

From the abstract (2):

"Dynamin-related protein (Drp1) drives mitochondrial fission, dysregulation of which leads to neurodegenerative, metabolic, and apoptotic disorders. The precise mechanism of fission completion is unclear.

One prevailing model is based on GTP-driven assembly of Drp1 helices that increase confinement via force generation. However, constriction to nanoscopic tubule radii appears necessary but not sufficient for scission.

The other is based on GTP-driven disassembly of a constricting Drp1 scaffold that drives a membrane disturbance, but the relation of disassembly to scission and GTP hydrolysis remain uncertain.

Elucidation of mitochondrial fission is complicated by the multiple time-involved in the dynamics of mechanoenzyme activity, oligomer disassembly, and membrane remodeling.

Using machine learning, synchrotron X-ray scattering, and a theoretical model, our data support a model where progressive GTP hydrolysis enables free Drp1s to increase their capacity for inducing membrane negative Gaussian curvature (NGC). 

Furthermore, we identify Drp1 variants that diminish this progressive capacity. Machine learning reveals that predicted NGC-generating sequences of the Drp1 oligomer are not in contact with the confined lipid tube and that scission-enhancing membrane remodeling is triggered by free Drp1 released upon disassembly."

New discovery: Physics of how cell’s powerhouse splits | UCLA

1) Dynamin-like Proteins Combine Mechano-constriction and Membrane Remodeling to Enable Two-Step Mitochondrial Fission via a “Snap-through” Instability (open access)

2) Drp1 Proteins Released from Hydrolysis-Driven Scaffold Disassembly Trigger Nucleotide-Dependent Membrane Remodeling to Promote Scission (open access)

Graphical abstract (1)

Graphical abstract (2)

Figure 1. Drp1 has an intrinsic ability to induce negative Gaussian curvature.

Mitochondria: Way More Than ‘Powerhouses’

Recommendable!

"... For example, a one-ounce sparrow will fly hundreds of miles every spring and fall, flapping nonstop for days without stopping for food or water. Two labs independently pinned birds’ seasonal sprints on differences in their mitochondria, which become “turbocharged” only during migration season — and then revert to their normal state during the rest of the year. ...

A body of work from different labs has pointed to mitochondria as the cellular metronome; these studies suggest that the rate at which mitochondria process molecules sets the rate of other cellular processes, such as gene expression and protein synthesis. In lab experiments, speeding up and slowing down the metabolic rates of mitochondria altered developmental rates too. ...

Now developmental biologists are finding that a cell’s metabolism and the products of its mitochondria help determine cell specialization during embryonic development, which shows how, at the molecular level, environment influences life in its earliest stages. ..."

Mitochondria: Way More Than ‘Powerhouses’

Scientists repair damaged mitochondria linked to common diseases

Good news! Already patented!

"... In experiments with human kidney cells, the research team reported, adding a small molecule called SP11 to the fragmented mitochondria made them hale and whole again. 

The team described their work in a May 6 report in Nature Communications, and Stanford has patented SP11 as a potential candidate for drug development. ..."

From the abstract:

"Fis1-mediated mitochondrial localization of Drp1 and excessive mitochondrial fission occur in human pathologies associated with oxidative stress. However, it is not known how Fis1 detects oxidative stress and what structural changes in Fis1 enable mitochondrial recruitment of Drp1.

We find that conformational change involving α1 helix in Fis1 exposes its only cysteine, Cys41. In the presence of oxidative stress, the exposed Cys41 in activated Fis1 forms a disulfide bridge and the Fis1 covalent homodimers cause increased mitochondrial fission through increased Drp1 recruitment to mitochondria.

Our discovery of a small molecule, SP11, that binds only to activated Fis1 by engaging Cys41, and data from genetically engineered cell lines lacking Cys41 strongly suggest a role of Fis1 homodimerization in Drp1 recruitment to mitochondria and excessive mitochondrial fission.

The structure of activated Fis1-SP11 complex further confirms these insights related to Cys41 being the sensor for oxidative stress.

Importantly, SP11 preserves mitochondrial integrity and function in cells during oxidative stress and thus may serve as a candidate molecule for the development of treatment for diseases with underlying Fis1-mediated mitochondrial fragmentation and dysfunction."

Scientists repair damaged mitochondria linked to common diseases | Stanford Report

A hidden cysteine in Fis1 targeted to prevent excessive mitochondrial fission and dysfunction under oxidative stress (open access)

... researchers found a small molecule called SP11 that prevents damage to mitochondria (purple) ... caused by exposure to oxidating chemicals. It has potential for treating mitochondria-associated ailments like ALS, heart disease and diabetes, in which oxidating chemicals are formed in the body. Healthy mitochondria (left) split and unite all the time as a way to exchange components that are required to maintain their quality. Adding an oxidizing agent like hydrogen peroxide (center) kept mitochondria from dividing into equal halves and snipped them into useless fragments instead. The addition of SP11 (right) made the mitochondria healthy and whole again.

Top: A protein called Drp1 (blue) prompts the cell’s power plants, mitochondria (tan), to divide. Drp1 normally acts through a go-between protein called Mff (green).

Bottom: But when exposure to oxidizing chemicals stresses mitochondria, another go-between protein, Fis1 (pink) hijacks the division process, squeezing mitochondria into unequal parts. Those parts fracture into smaller and smaller fragments until they can’t produce enough energy to keep the cell healthy. The damage spreads from cell to cell and causes a variety of human ailments, including Parkinson’s and heart disease.

Fig. 7: SP11 reduces H2O2-induced mitochondrial ROS production and fragmentation and increased Drp1 translocation to the mitochondria.

About the mitochondrial pyruvate carrier in mitochondria

Amazing stuff!

"Scientists ... have worked out the structure of this machine and shown how it operates like the lock on a canal to transport pyruvate – a molecule generated in the body from the breakdown of sugars – into our mitochondria.

Known as the mitochondrial pyruvate carrier, this molecular machine was first proposed to exist in 1971, but it has taken until now for scientists to visualise its structure at the atomic scale using cryo-electron microscopy, a technique used to magnify an image of an object to around 165,000 times its real size.  ...

When [sugars] are broken down inside our cells they produce pyruvate, but to get the most out of this molecule it needs to be transferred inside the cell’s powerhouses, the mitochondria. There, it helps increase 15-fold the energy produced in the form of the cellular fuel ATP.” ...

Using state-of-the-art cryo-electron microscopy, we’ve been able to show not only what this transporter looks like, but exactly how it works. It’s an extremely important process, and understanding it could lead to new treatments for a range of different conditions.

Mitochondria are surrounded by two membranes.

The outer one is porous, and pyruvate can easily pass through, but the 

inner membrane is impermeable to pyruvate.

To transport pyruvate into the mitochondrion, first an outer ‘gate’ of the carrier opens, allowing pyruvate to enter the carrier.

This gate then closes, and the inner gate opens, allowing the molecule to pass through into the mitochondrion. ...

this carrier is now recognised as a promising drug target for a range of conditions, including diabetes, fatty liver disease, Parkinson’s disease, specific cancers, and even hair loss. ..."

From the abstract:

"The mitochondrial pyruvate carrier transports pyruvate, produced by glycolysis from sugar molecules, into the mitochondrial matrix, as a crucial transport step in eukaryotic energy metabolism. The carrier is a drug target for the treatment of cancers, diabetes mellitus, neurodegeneration, and metabolic dysfunction–associated steatotic liver disease.

We have solved the structure of the human MPC1L/MPC2 heterodimer in the inward- and outward-open states by cryo–electron microscopy, revealing its alternating access rocker-switch mechanism.

The carrier has a central binding site for pyruvate, which contains an essential lysine and histidine residue, important for its ΔpH-dependent transport mechanism. We have also determined the binding poses of three chemically distinct inhibitor classes, which exploit the same binding site in the outward-open state by mimicking pyruvate interactions and by using aromatic stacking interactions."

Throwing a ‘spanner in the works’ of our cells’ machinery could help fight cancer, fatty liver disease… and hair loss | University of Cambridge "Fifty years since its discovery, scientists have finally worked out how a molecular machine found in mitochondria, the ‘powerhouses’ of our cells, allows us to make the fuel we need from sugars, a process vital to all life on Earth."

Molecular basis of pyruvate transport and inhibition of the human mitochondrial pyruvate carrier (open access)

Fig. 1. Human MPC [mitochondrial pyruvate carrier] in the outward-open and inward-open states.

Fig. 2. The dynamic motions of the MPC.

Mitochondria are moving between cells on demand or due to cancer

Amazing stuff! A recommendable overview article.

"Mitochondria — the supposedly static energy factories that reside inside cells — seem to actually be expert travellers, skipping from one cell to another.

This ‘mitochondrial transfer’ has been observed in a wide variety of cells and in organisms as diverse as yeast, molluscs and rodents.

Some studies have hinted that cells donate their mitochondria to their neighbours during times of need.

Other research suggests that mitochondrial transfer can be a lethal weapon that cancer cells deploy to gain an advantage.

A handful of researchers have begun developing treatments that would draw on this process to enhance immunotherapies or treat mitochondrial diseases."

"... Ever since they were discovered in the mid-nineteenth century, mitochondria have been known as organelles that reside inside cells.

But that textbook picture now seems to be wrong. An explosion of research is challenging mitochondria’s long-standing image as exclusively cellular organelles. “They may be a multicellular organelle,” ... In other words, the supposedly static energy factories now seem to be expert travellers, skipping from one cell to another on demand. ...

It’s not yet clear why mitochondria are so mobile. Some studies have hinted that cells donate their mitochondria to their neighbours during times of need. In cellular emergencies, newly arrived mitochondria might kick-start tissue repair, fire up the immune system or rescue distressed cells from death. ..."

Nature Briefing: Translational Research

Cells are swapping their mitochondria. What does this mean for our health? "Researchers are studying why the energy factories are moving between cells and whether the process can be harnessed to treat cancer and other diseases."

Mitochondria, visible in red, travel through a tunnelling nanotube from a type of bone marrow cell (top left) to a T cell that fights infections and cancer (bottom right)

High-resolution images discover and capture intricate structure and assembly of the respirasome supercomplex

Amazing stuff!

"... Using cryo-electron tomography, researchers at the University of Basel, Switzerland, have now gained insight into the architecture of mitochondria at unprecedented resolution. ...

They discovered that the proteins responsible for energy generation assemble into large "supercomplexes," which play a crucial role in providing the cell's energy. ...

"Using the electron microscope, individual supercomplexes were clearly visible—we could directly see their structures and how they work. The respiratory supercomplexes pump protons across the mitochondrial membrane. The ATP production complexes, which act similarly to a watermill, use this flow of protons to drive ATP generation." ..."

From the editor's summary and abstract:

"Editor’s summary

The mitochondrial respiratory chain consists of membrane-integral complexes that build up the proton gradient across the membranes of the cristae, thereby powering ATP synthase.

Waltz et al. used cryo–electron tomography to resolve native structures of these complexes directly within the green alga Chlamydomonas reinhardtii. Their findings reveal how respiratory complexes I, III, and IV assemble into a respirasome supercomplex, which is restricted to flat membrane regions apart from rows of ATP synthase at the curved tips of cristae. The work also captures fine structural details of how respirasomes are held together and how electron-carrier proteins bind these assemblies, offering insights into mitochondrial respiration inside native cells. ...

Abstract

Mitochondria regenerate adenosine triphosphate (ATP) through oxidative phosphorylation. This process is carried out by five membrane-bound complexes collectively known as the respiratory chain, working in concert to transfer electrons and pump protons. The precise organization of these complexes in native cells is debated.

We used in situ cryo–electron tomography to visualize the native structures and organization of several major mitochondrial complexes in Chlamydomonas reinhardtii cells. ATP synthases and respiratory complexes segregate into curved and flat crista membrane domains, respectively. Respiratory complexes I, III, and IV assemble into a respirasome supercomplex, from which we determined a native 5-angstrom (Å) resolution structure showing binding of electron carrier cytochrome c. Combined with single-particle cryo–electron microscopy at 2.4-Å resolution, we model how the respiratory complexes organize inside native mitochondria."

High-resolution images capture intricate structure of mitochondrial supercomplexes

The cell’s powerhouses: Molecular machines enable efficient energy production (original news release) "Mitochondria are the powerhouses in our cells, producing the energy for all vital processes. Using cryo-electron tomography, researchers at the University of Basel have now gained insight into the architecture of mitochondria at unprecedented resolution. They discovered that the proteins responsible for energy generation assemble into large “supercomplexes”, which play a crucial role in providing the cell’s energy."

In-cell architecture of the mitochondrial respiratory chain (no public access)

In-cell architecture of the mitochondrial respiratory chain (open access, preprint)

I presume, this image represents the supercomplex (a screenshot take from the linked YouTube video, but the video is without any captions and without any audio, how amateurish)

This is the official image provided. However, I believe this is a sort of artistic rendering and not a real image.

How Flaviviruses Use Mitochondrial Processes to Thrive

Good news! Amazing stuff!

"A team of ... infectious diseases researchers recently conducted an in-depth review of the literature on how one genus of viruses, known as flaviviruses, manipulates mitochondria to evade immune responses. Annually, more than 3 billion people are at risk for flavivirus infection, which includes diseases such as yellow fever and dengue fever.

In their review ... the authors highlighted key mechanisms used by flaviviruses to evade host immune responses, such as the manipulation of mitochondrial fission and fusion processes to enhance replication, modulation of mitochondrial metabolic pathways, and effects on mitochondrial respiration. The work covered a wide scope of viruses within the genus, detailing the mechanisms used by Zika virus, dengue virus, Japanese encephalitis virus, West Nile virus, tick-borne encephalitis, and yellow fever virus. ..."

From the abstract (a disappointing, amateurish abstract):

"Mitochondria are essential eukaryotic organelles that regulate a range of cellular processes, from metabolism to calcium homeostasis and programmed cell death. They serve as essential platforms for antiviral signaling proteins during the innate immune response to viral infections. Mitochondria are dynamic structures, undergoing frequent fusion and fission processes that regulate various aspects of mitochondrial biology, including innate immunity. Pathogens have evolved sophisticated mechanisms to manipulate mitochondrial morphology and function to facilitate their replication. In this review, we examine the emerging literature on how flaviviruses modulate mitochondrial processes."

How Flaviviruses Use Mitochondrial Processes to Thrive < Internal Medicine

Flaviviruses manipulate mitochondrial processes to evade the innate immune response (open access)

Fig. 1: Mitochondria play important roles in innate antiviral immune responses. Under stress conditions, such as those induced by viral infection, DNA is released from the mitochondria (mtDNA) and nucleus (dsDNA).

Fig. 2: Flaviviruses modulate mitochondrial fission and fusion dynamics.

Newly discovered mechanism reveals NAD's role in aging and disease

Good news!

"... "Therefore, dysregulated NAD levels are involved in aging processes as well as many pathologies ranging from cancer to diabetes and neurodegenerative diseases. And the reason for this is that it holds a key position in both energy metabolism and the regulation of vital functions," ...

Based on their new findings, the team of researchers believes that excessive consumption of mitochondrial NAD might constitute a key factor leading to dysfunctional cellular powerhouses and thus aging-associated diseases. ..."

From the abstract:

"The coenzyme NAD+ is consumed by signalling enzymes, including poly-ADP-ribosyltransferases (PARPs) and sirtuins. Ageing is associated with a decrease in cellular NAD+ levels, but how cells cope with persistently decreased NAD+ concentrations is unclear. Here, we show that subcellular NAD+ pools are interconnected, with mitochondria acting as a rheostat to maintain NAD+ levels upon excessive consumption.

To evoke chronic, compartment-specific overconsumption of NAD+, we engineered cell lines stably expressing PARP activity in mitochondria, the cytosol, endoplasmic reticulum or peroxisomes, resulting in a decline of cellular NAD+ concentrations by up to 50%. Isotope-tracer flux measurements and mathematical modelling show that the lowered NAD+ concentration kinetically restricts NAD+ consumption to maintain a balance with the NAD+ biosynthesis rate, which remains unchanged.

Chronic NAD+ deficiency is well tolerated unless mitochondria are directly targeted. Mitochondria maintain NAD+ by import through SLC25A51 and reversibly cleave NAD+ to nicotinamide mononucleotide and ATP when NMNAT3 is present. Thus, these organelles can maintain an additional, virtual NAD+ pool. Our results are consistent with a well-tolerated ageing-related NAD+ decline as long as the vulnerable mitochondrial pool is not directly affected."

Newly discovered mechanism reveals NAD's role in aging and disease

Subcellular NAD+ pools are interconnected and buffered by mitochondrial NAD+ (no public access)

Proposed model for the cooperation of SLC25A51 and NMNAT3 to buffer cellular NAD+ fluctuations.

A new kind of mitochondria

Amazing stuff! Incredible!

Five key blood markers linked to suicide have been identified

Good news! Amazing stuff! So far these discoveries seem to be limited to the presence of depression.

"... researchers have found biomarkers linked to mitochondrial dysfunction, which interrupts how cells ‘talk’ to each other and could be a factor in suicidal ideation. While suicide is complex and includes broad factors such as trauma and stress, being able to identify those most at risk could be a crucial diagnostic tool. ...

Earlier this year, scientists discovered molecular links to suicidal ideation, showing that some people who suffer from depression could be more at risk. And research into blood markers has been under way since 2019. ..."

From the abstract:

"Peripheral blood metabolomics was used to gain chemical insight into the biology of treatment-refractory Major Depressive Disorder with suicidal ideation, and to identify individualized differences for personalized care. The study cohort consisted of 99 patients with treatment-refractory major depressive disorder and suicidal ideation (trMDD-SI n = 52 females and 47 males) and 94 age- and sex-matched healthy controls (n = 48 females and 46 males). The median age was 29 years (IQR 22–42). Targeted, broad-spectrum metabolomics measured 448 metabolites. Fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) were measured as biomarkers of mitochondrial dysfunction. The diagnostic accuracy of plasma metabolomics was over 90% (95%CI: 0.80–1.0) by area under the receiver operator characteristic (AUROC) curve analysis. Over 55% of the metabolic impact in males and 75% in females came from abnormalities in lipids. Modified purines and pyrimidines from tRNA, rRNA, and mRNA turnover were increased in the trMDD-SI group. FGF21 was increased in both males and females. Increased lactate, glutamate, and saccharopine, and decreased cystine provided evidence of reductive stress. Seventy-five percent of the metabolomic abnormalities found were individualized. Personalized deficiencies in CoQ10, flavin adenine dinucleotide (FAD), citrulline, lutein, carnitine, or folate were found. Pathways regulated by mitochondrial function dominated the metabolic signature. Peripheral blood metabolomics identified mitochondrial dysfunction and reductive stress as common denominators in suicidal ideation associated with treatment-refractory major depressive disorder. Individualized metabolic differences were found that may help with personalized management."

Five key blood markers linked to suicide have been identified In a finding that could have a significant impact on personalized medicine and treatment, scientists have identified blood compounds linked to suicidal ideation.

Blood Testing Identifies Biomarkers of Suicidal Thoughts UC San Diego study suggests new way to personalize mental health care

Metabolic features of treatment-refractory major depressive disorder with suicidal ideation (open access)

Wow! What a chart! Fig. 2: Metabolomic analysis of treatment-refractory major depressive disorder with suicidal ideation.

Fig. 3: Biomarkers of mitochondrial dysfunction.

Nuclear DNA influences variation in mitochondrial DNA

Amazing stuff!

"... mitochondria, have their own DNA that’s passed down from mother to child. The mitochondrial genome, which encodes just 13 proteins, is smaller and comparatively less well studied than the genome in the cell’s nucleus, even though mutations in mitochondrial DNA can cause a number of rare diseases. 

Now a new study of both mitochondrial and nuclear genomes from hundreds of thousands of people may change how scientists think about the mitochondrial genome and how it interacts with the nuclear genome. The findings could inform future studies of how this crosstalk helps mitochondria power the cell, and shed light on when they cause disease.

Scientists have long known that cells can have hundreds, even thousands, of copies of the mitochondrial genome, and that this “copy number” can vary widely from one cell type to the next. There is also much variation in the sequences of all that mitochondrial DNA in a single cell, called heteroplasmy, which researchers had previously linked to rare inherited mitochondrial disease. 

The new study ... has shown that the number of copies of the mitochondrial genome is a trait that varies from person to person and is controlled by the nuclear genome. The researchers also found that heteroplasmy is also influenced by mutations in the nuclear genome and is pervasive even among healthy people. ..."

From the abstract:

"Mitochondrial DNA (mtDNA) is a maternally inherited, high-copy-number genome required for oxidative phosphorylation. Heteroplasmy refers to the presence of a mixture of mtDNA alleles in an individual and has been associated with disease and ageing. Mechanisms underlying common variation in human heteroplasmy, and the influence of the nuclear genome on this variation, remain insufficiently explored. Here we quantify mtDNA copy number (mtCN) and heteroplasmy using blood-derived whole-genome sequences from 274,832 individuals and perform genome-wide association studies to identify associated nuclear loci. Following blood cell composition correction, we find that mtCN declines linearly with age and is associated with variants at 92 nuclear loci. We observe that nearly everyone harbours heteroplasmic mtDNA variants obeying two principles: (1) heteroplasmic single nucleotide variants tend to arise somatically and accumulate sharply after the age of 70 years, whereas (2) heteroplasmic indels are maternally inherited as mixtures with relative levels associated with 42 nuclear loci involved in mtDNA replication, maintenance and novel pathways. These loci may act by conferring a replicative advantage to certain mtDNA alleles. As an illustrative example, we identify a length variant carried by more than 50% of humans at position chrM:302 within a G-quadruplex previously proposed to mediate mtDNA transcription/replication switching. We find that this variant exerts cis-acting genetic control over mtDNA abundance and is itself associated in-trans with nuclear loci encoding machinery for this regulatory switch. Our study suggests that common variation in the nuclear genome can shape variation in mtCN and heteroplasmy dynamics across the human population."

Nuclear DNA influences variation in mitochondrial DNA | Broad Institute

Nuclear genetic control of mtDNA copy number and heteroplasmy in humans (open access)

Fig. 4: Pervasive nuclear genetic control over common mtDNA heteroplasmies.

Mitochondria power-supply failure may cause age-related cognitive impairment

Good news! Towards beating the ravages of age!

"... “Fifty percent of people experience loss of working memory with old age, meaning their ability to hold and manipulate information in the short-term decreases,” ... “We set out to understand why some individuals maintain healthy working memory as they age, while others do not. In the process, we discovered a novel mechanism for the synaptic basis of cognitive impairment.” ...
“Investigating these microscopic dysfunctions is uncharted territory that could revolutionize our understanding of aging and its impact on cognition.” ..."

From the abstract:

"Morphology and function of the dorsolateral prefrontal cortex (dlPFC), and corresponding working memory performance, are affected early in the aging process, but nearly half of aged individuals are spared of working memory deficits. Translationally relevant model systems are critical for determining the neurobiological drivers of this variability. The common marmoset (Callithrix jacchus) is advantageous as a model for these investigations because, as a non-human primate, marmosets have a clearly defined dlPFC that enables measurement of prefrontal-dependent cognitive functions, and their short (∼10 year) lifespan facilitates longitudinal studies of aging. Previously, we characterized working memory capacity in a cohort of marmosets that collectively covered the lifespan, and found age-related working memory impairment. We also found a remarkable degree of heterogeneity in performance, similar to that found in humans. Here, we tested the hypothesis that changes to synaptic ultrastructure that affect synaptic efficacy stratify marmosets that age with cognitive impairment from those that age without cognitive impairment. We utilized electron microscopy to visualize synapses in the marmoset dlPFC and measured the sizes of boutons, presynaptic mitochondria, and synapses. We found that coordinated scaling of the sizes of synapses and mitochondria with their associated boutons is essential for intact working memory performance in aged marmosets. Further, lack of synaptic scaling, due to a remarkable failure of synaptic mitochondria to scale with presynaptic boutons, selectively underlies age-related working memory impairment. We posit that this decoupling results in mismatched energy supply and demand, leading to impaired synaptic transmission. We also found that aged marmosets have fewer synapses in dlPFC than young, though the severity of synapse loss did not predict whether aging occurred with or without cognitive impairment. This work identifies a novel mechanism of synapse dysfunction that stratifies marmosets that age with cognitive impairment from those that age without cognitive impairment. ..."

Mitochondria power-supply failure may cause age-related cognitive impairment - Salk Institute for Biological Studies Salk scientists find mitochondria at dysfunctional synapses fail to meet energetic demand, supplying either too much or too little power and potentially causing age-related cognitive impairment

Violation of the ultrastructural size principle in the dorsolateral prefrontal cortex underlies working memory impairment in the aged common marmoset (Callithrix jacchus) (open access)

Normally, the different parts of the synaptic complex grow and shrink together. The researchers found evidence that this process can go awry in aging, which may contribute to cognitive impairment.

Mitochondria metabolic activity influences neurons’ growth rate

Amazing stuff!

"to look at the [mitochondrias]’ respiration rates—basically, how much oxygen they consume, which is also a measure of how much cellular fuel they produce. They used oxygraphy to monitor the oxygen intake of mouse neurons for the first 20 days after their birth—and were stunned to find that after two weeks, the oxygen consumption rate of neurons had grown to nearly ten times that of human neurons.

From there, ... everything fell into place. The team knew they could manipulate mitochondrial respiration pharmacologically, so they sped up metabolism in human cortical neurons in vitro. ... neurons; at only a few weeks old, the accelerated cortical neurons were considerably more mature than a normal human neuron. ...
The scientists tested the same principle in vivo, speeding up the mitochondrial metabolism of human neurons and implanting them into mice, as well as slowing down the mitochondrial metabolism of mouse neurons both in culture and inside the mice’s brains. The results from both in and out of the brain aligned: Human neurons with increased metabolic rates grew faster than normal, and mouse neurons with decreased mitochondrial metabolic rates displayed slower growth. ...
targeting mitochondrial metabolism could one day be considered in the treatment of some developmental disorders ..."

From the abstract:

"Neuronal development in the human cerebral cortex is considerably prolonged compared to that of other mammals. We explored whether mitochondria influence the species-specific timing of cortical neuron maturation. By comparing human and mouse cortical neuronal maturation at high temporal and cell resolution, we found a slower mitochondria development in human cortical neurons compared with that in the mouse, together with lower mitochondria metabolic activity, particularly that of oxidative phosphorylation. Stimulation of mitochondria metabolism in human neurons resulted in accelerated development in vitro and in vivo, leading to maturation of cells weeks ahead of time, whereas its inhibition in mouse neurons led to decreased rates of maturation. Mitochondria are thus important regulators of the pace of neuronal development underlying human-specific brain neoteny."

Mitochondrial Metabolism Dictates Neurons’ Growth Rate | The Scientist Magazine® Altering the rate of respiration in mitochondria changes how fast neurons grow, making mouse neurons grow more like human ones and vice versa, a study finds.

Mitochondria metabolism sets the species-specific tempo of neuronal development (no public access)

A human neuron with mitochondria stained in white

A “door” into the mitochondrial membrane

Amazing stuff!

"Proteins on the outer membrane of mitochondria are especially important; they allow the mitochondria to communicate with the rest of the cell, and play a role in immune functions and a type of programmed cell death called apoptosis. Over the course of evolution, cells evolved a specific mechanism by which to insert these proteins — which are made in the cell’s cytoplasm — into the mitochondrial membrane. But what that mechanism was, and what cellular players were involved, has long been a mystery. 

A new paper ... reveals that a protein called mitochondrial carrier homolog 2, or MTCH2 for short, which has been linked to many cellular processes and even diseases such as cancer and Alzheimer’s, is responsible for acting as a “door” for a variety of proteins to access the mitochondrial membrane. ..."

"How mitochondria handle helical proteins

The essential roles of mitochondria in metabolism and signaling depend on a functionally and structurally diverse class of alpha-helical proteins embedded in the outer mitochondrial membrane. Guna et al. identified the mitochondrial outer membrane protein MTCH2 (mitochondrial carrier homolog 2) and found that it is both necessary and sufficient for the insertion of mitochondrial alpha-helical proteins. MTCH2 is the defining member of a broadly conserved class of insertases that exploit a diverged ancestral solute transporter fold to mediate membrane protein insertion. MTCH2’s role as a gatekeeper for outer mitochondrial membrane biogenesis rationalizes its pleotropic phenotypes and association with human disease."

From the abstract:

"In the mitochondrial outer membrane, α-helical transmembrane proteins play critical roles in cytoplasmic-mitochondrial communication. Using genome-wide CRISPR screens, we identified mitochondrial carrier homolog 2 (MTCH2), and its paralog MTCH1, and showed that it is required for insertion of biophysically diverse tail-anchored (TA), signal-anchored, and multipass proteins, but not outer membrane β-barrel proteins. Purified MTCH2 was sufficient to mediate insertion into reconstituted proteoliposomes. Functional and mutational studies suggested that MTCH2 has evolved from a solute carrier transporter. MTCH2 uses membrane-embedded hydrophilic residues to function as a gatekeeper for the outer membrane, controlling mislocalization of TAs into the endoplasmic reticulum and modulating the sensitivity of leukemia cells to apoptosis. Our identification of MTCH2 as an insertase provides a mechanistic explanation for the diverse phenotypes and disease states associated with MTCH2 dysfunction."

A “door” into the mitochondrial membrane | MIT News | Massachusetts Institute of Technology Study finds the protein MTCH2 is responsible for shuttling various other proteins into the membrane of mitochondria. The finding could have implications for cancer treatments and MTCH2-linked conditions.

MTCH2 is a mitochondrial outer membrane protein insertase (no public access)

Stem cell-based genomic study yields insights on viral infection

Good news! Advances in virology are pouring forth! We are beating the pathogens one step at a time!

The approach applied here may significantly expedite future research!

"A mitochondrial gene plays a crucial role in genetic susceptibility to Zika, dengue and SARS-CoV-2 infections, according to a new study...

The study ... provides proof of principle that cell-based genome-wide association studies (GWAS) could be a valuable tool for studying genetic susceptibility to infections and other diseases. Genome-wide association studies scan the genomes of hundreds or thousands of people looking for genetic changes associated with diseases. ...
built a laboratory platform that is essentially a GWAS study in a dish. Instead of enrolling people, they used cells donated by patients that were coaxed back into a stem-cell like or early developmental state that can grow into any other type of tissue with the appropriate growth factor. Then, they used the platform to screen for genes that increase the likelihood of infection with Zika virus. ...
Over the past decade and a half, GWAS studies have emerged as a powerful tool to study genetic risk factors for disease ...
used CRISPR gene-editing technology to remove the NDUFA4 gene in the cells. He found that the cells lacking this gene are less susceptible to infection with Zika, the dengue virus and the SARS-CoV-2 virus. By contrast, cells from patients with COVID-19 expressed higher levels of NDUFA4 than cells from healthy donors. ... showed that the loss or reduced expression of the NDUFA4 gene stresses the mitochondria, causing mitochondrial proteins to leak into the cell’s cytoplasm and triggers an innate immune response usually reserved to fight infection. ..."

From the abstract:

"Population-based studies to identify disease-associated risk alleles typically require samples from a large number of individuals. Here, we report a human-induced pluripotent stem cell (hiPSC)-based screening strategy to link human genetics with viral infectivity. A genome-wide association study (GWAS) identified a cluster of single-nucleotide polymorphisms (SNPs) in a cis-regulatory region of the NDUFA4 gene, which was associated with susceptibility to Zika virus (ZIKV) infection. Loss of NDUFA4 led to decreased sensitivity to ZIKV, dengue virus, and SARS-CoV-2 infection. Isogenic hiPSC lines carrying non-risk alleles of SNPs or deletion of the cis-regulatory region lower sensitivity to viral infection. Mechanistic studies indicated that loss/reduction of NDUFA4 causes mitochondrial stress, which leads to the leakage of mtDNA and thereby upregulation of type I interferon signaling. This study provides proof-of-principle for the application of iPSC arrays in GWAS and identifies NDUFA4 as a previously unknown susceptibility locus for viral infection."

Stem cell-based genomic study yields insights on viral infection | Cornell Chronicle

A human iPSC-array-based GWAS identifies a virus susceptibility locus in the NDUFA4 gene and functional variants (open access)

Embryos with mitochondrial replacement therapy develop normally in first safety study

Good news!

"When the first baby to be conceived using a technique that mixes genetic material from three people was born, in 2016, scientists worried that the procedure had not been studied to show it was safe. Now, scientists in China have conducted the first comprehensive study of the technique in early-stage human embryos, and report that it does not seem to affect their development.

Techniques for using genetic material from three people to make embryos are designed to prevent mothers with defects in their mitochondria ... from passing them on to their children. Mitochondria contain their own DNA, and children inherit all of their mitochondria from their mother.

“Mitochondrial replacement therapy is a controversial field,” ...
... studied the safety of one of three main types of mitochondrial replacement therapy, called spindle transfer, which was used to make the first baby with genetic material from three people, who was born in Mexico in 2016. In this method, the nuclear DNA from the egg of a woman with faulty mitochondria is transferred to a donor egg with healthy mitochondria that has had its nuclear DNA removed. The egg is then fertilized with the father’s sperm in a test tube. The resulting embryo contains genes from both parents in addition to mitochondrial genes from the donor. ..."

From the abstract:

"Mitochondrial DNA (mtDNA) mutations are often associated with incurable diseases and lead to detectable pathogenic variants in 1 out of 200 babies. Uncoupling of the inheritance of mtDNA and the nuclear genome by spindle transfer (ST) can potentially prevent the transmission of mtDNA mutations from mother to offspring. However, no well-established studies have critically assessed the safety of this technique. Here, using single-cell triple omics sequencing method, we systematically analyzed the genome (copy number variation), DNA methylome, and transcriptome of ST and control blastocysts. The results showed that, compared to that in control embryos, the percentage of aneuploid cells in ST embryos did not significantly change. The epiblast, primitive endoderm, and trophectoderm (TE) of ST blastocysts presented RNA expression profiles that were comparable to those of control blastocysts. However, the DNA demethylation process in TE cells of ST blastocysts was slightly slower than that in the control blastocysts. Collectively, our results suggest that ST seems generally safe for embryonic development, with a relatively minor delay in the DNA demethylation process at the blastocyst stage."

Embryos with DNA from three people develop normally in first safety study

Single-cell multiomics analyses of spindle-transferred human embryos suggest a mostly normal embryonic development (open access)