Consequences of Folding the Mitochondrial Inner Membrane

The impacts of the mitochondrial myopathy-associated G58R mutation on the dynamic structural properties of CHCHD10

The mitochondria are responsible for producing energy within the cell, and in mitochondrial myopathy, there is a defect in the energy production process. The CHCHD10 gene codes for a protein called coiled-coil-helix-coiled-coil-helix domain-containing protein 10 (CHCHD10), which is found in the mitochondria and is involved in the regulation of mitochondrial function. G58R mutation has been shown to disrupt the normal function of CHCHD10, leading to mitochondrial dysfunction and ultimately to the development of mitochondrial myopathy. The structures of G58R mutant CHCHD10 and how G58R mutation impacts the wild-type CHCHD10 protein at the monomeric level are unknown. To address this problem, we conducted homology modeling, multiple run molecular dynamics simulations and bioinformatics calculations. We represent herein the structural ensemble properties of the G58R mutant CHCHD10 (CHCHD10G58R) in aqueous solution. Moreover, we describe the impacts of G58R mutation on the structural ensembles of wild-type CHCHD10 (CHCHD10WT) in aqueous solution. The dynamics properties as well as structural properties of CHCHD10WT are impacted by the mitochondrial myopathy-related G58R mutation. Specifically, the secondary and tertiary structure properties, root mean square fluctuations, Ramachandran diagrams and results from principal component analysis demonstrate that the CHCHD10WT and CHCHD10G58R proteins possess different structural ensemble characteristics and describe the impacts of G58R mutation on CHCHD10WT. These findings may be helpful for designing new treatments for mitochondrial myopathy.Communicated by Ramaswamy H. Sarma.

Mitochondria and MICOS - function and modeling

An extensive review is presented on mitochondrial structure and function, mitochondrial proteins, the outer and inner membranes, cristae, the role of F1FO-ATP synthase, the mitochondrial contact site and cristae organizing system (MICOS), the sorting and assembly machinery morphology and function, and phospholipids, in particular cardiolipin. Aspects of mitochondrial regulation under physiological and pathological conditions are outlined, in particular the role of dysregulated MICOS protein subunit Mic60 in Parkinson's disease, the relations between mitochondrial quality control and proteins, and mitochondria as signaling organelles. A mathematical modeling approach of cristae and MICOS using mechanical beam theory is introduced and outlined. The proposed modeling is based on the premise that an optimization framework can be used for a better understanding of critical mitochondrial function and also to better map certain experiments and clinical interventions.

Spatiotemporal Distribution and Function of Mitochondria in Oocytes

Mitochondria are energy provider organelles in eukaryotic cells that contain their own specific genome. This review addresses structural and functional properties of mitochondria, focusing on recent discoveries about the changes in quality and number of mitochondria per cell during oocyte development. We highlight how oocyte mitochondria exhibit stage-specific morphology and characteristics at different stages of development, in sharp contrast to the elongated mitochondria present in somatic cells. We then evaluate the latest transcriptomic data to elucidate the complex functions of mitochondria during oocyte maturation and the impact of mitochondria on oocyte development. Finally, we describe the methodological progress of mitochondrial replacement therapy to rescue oocytes with developmental disorders or mitochondrial diseases, hoping to provide a guiding reference to future clinical applications.

Call to action to properly utilize electron microscopy to measure organelles to monitor disease

This review provides an overview of the current methods for quantifying mitochondrial ultrastructure, including cristae morphology, mitochondrial contact sites, and recycling machinery and a guide to utilizing electron microscopy to effectively measure these organelles. Quantitative analysis of mitochondrial ultrastructure is essential for understanding mitochondrial biology and developing therapeutic strategies for mitochondrial-related diseases. Techniques such as transmission electron microscopy (TEM) and serial block face-scanning electron microscopy, as well as how they can be combined with other techniques including confocal microscopy, super-resolution microscopy, and correlative light and electron microscopy are discussed. Beyond their limitations and challenges, we also offer specific magnifications that may be best suited for TEM analysis of mitochondrial, endoplasmic reticulum, and recycling machinery. Finally, perspectives on future quantification methods are offered.

A Comprehensive Approach to Sample Preparation for Electron Microscopy and the Assessment of Mitochondrial Morphology in Tissue and Cultured Cells

Mitochondria respond to metabolic demands of the cell and to incremental damage, in part, through dynamic structural changes that include fission (fragmentation), fusion (merging of distinct mitochondria), autophagic degradation (mitophagy), and biogenic interactions with the endoplasmic reticulum (ER). High resolution study of mitochondrial structural and functional relationships requires rapid preservation of specimens to reduce technical artifacts coupled with quantitative assessment of mitochondrial architecture. A practical approach for assessing mitochondrial fine structure using two dimensional and three dimensional high-resolution electron microscopy is presented, and a systematic approach to measure mitochondrial architecture, including volume, length, hyperbranching, cristae morphology, and the number and extent of interaction with the ER is described. These methods are used to assess mitochondrial architecture in cells and tissue with high energy demand, including skeletal muscle cells, mouse brain tissue, and Drosophila muscles. The accuracy of assessment is validated in cells and tissue with deletion of genes involved in mitochondrial dynamics.

Structural Analysis of Mitochondria in Cardiomyocytes: Insights into Bioenergetics and Membrane Remodeling

Mitochondria in mammalian cardiomyocytes display considerable structural heterogeneity, the significance of which is not currently understood. We use electron microscopic tomography to analyze a dataset of 68 mitochondrial subvolumes to look for correlations among mitochondrial size and shape, crista morphology and membrane density, and organelle location within rat cardiac myocytes. A tomographic analysis guided the definition of four classes of crista morphology: lamellar, tubular, mixed and transitional, the last associated with remodeling between lamellar and tubular cristae. Correlations include an apparent bias for mitochondria with lamellar cristae to be located in the regions between myofibrils and a two-fold larger crista membrane density in mitochondria with lamellar cristae relative to mitochondria with tubular cristae. The examination of individual cristae inside mitochondria reveals local variations in crista topology, such as extent of branching, alignment of fenestrations and progressive changes in membrane morphology and packing density. The findings suggest both a rationale for the interfibrillar location of lamellar mitochondria and a pathway for crista remodeling from lamellar to tubular morphology.

Targeting Mitochondrial Metabolic Reprogramming as a Potential Approach for Cancer Therapy

Abnormal energy metabolism is a characteristic of tumor cells, and mitochondria are important components of tumor metabolic reprogramming. Mitochondria have gradually received the attention of scientists due to their important functions, such as providing chemical energy, producing substrates for tumor anabolism, controlling REDOX and calcium homeostasis, participating in the regulation of transcription, and controlling cell death. Based on the concept of reprogramming mitochondrial metabolism, a range of drugs have been developed to target the mitochondria. In this review, we discuss the current progress in mitochondrial metabolic reprogramming and summarized the corresponding treatment options. Finally, we propose mitochondrial inner membrane transporters as new and feasible therapeutic targets.

How does density of the inner mitochondrial membrane influence mitochondrial performance?

Our current understanding of variation in mitochondrial performance is incomplete. The production of ATP via oxidative phosphorylation is dependent, in part, on the structure of the inner mitochondrial membrane. Morphology of the inner membrane is crucial for the formation of the proton gradient across the inner membrane and, therefore, ATP synthesis. The inner mitochondrial membrane is dynamic, changing shape and surface area. These changes alter density (amount per volume) of the inner mitochondrial membrane within the confined space of the mitochondrion. Because the number of electron transport system proteins within the inner mitochondrial membrane changes with inner mitochondrial membrane area, a change in the amount of inner membrane alters the capacity for ATP production within the organelle. This review outlines the evidence that the association between ATP synthases, inner mitochondrial membrane density, and mitochondrial density (number of mitochondria per cell) impacts ATP production by mitochondria. Furthermore, we consider possible constraints on the capacity of mitochondria to produce ATP by increasing inner mitochondrial membrane density.

Mitochondria in Aging and Alzheimer's Disease: Focus on Mitophagy

Alzheimer's disease (AD) is characterized by the accumulation of amyloid β and phosphorylated τ protein aggregates in the brain, which leads to the loss of neurons. Under the microscope, the function of mitochondria is uniquely primed to play a pivotal role in neuronal cell survival, energy metabolism, and cell death. Research studies indicate that mitochondrial dysfunction, excessive oxidative damage, and defective mitophagy in neurons are early indicators of AD. This review article summarizes the latest development of mitochondria in AD: 1) disease mechanism pathways, 2) the importance of mitochondria in neuronal functions, 3) metabolic pathways and functions, 4) the link between mitochondrial dysfunction and mitophagy mechanisms in AD, and 5) the development of potential mitochondrial-targeted therapeutics and interventions to treat patients with AD.

Inner mitochondrial membrane protein Prohibitin 1 mediates Nix-induced, Parkin-independent mitophagy

Autophagy of damaged mitochondria, called mitophagy, is an important organelle quality control process involved in the pathogenesis of inflammation, cancer, aging, and age-associated diseases. Many of these disorders are associated with altered expression of the inner mitochondrial membrane (IMM) protein Prohibitin 1. The mechanisms whereby dysfunction occurring internally at the IMM and matrix activate events at the outer mitochondrial membrane (OMM) to induce mitophagy are not fully elucidated. Using the gastrointestinal epithelium as a model system highly susceptible to autophagy inhibition, we reveal a specific role of Prohibitin-induced mitophagy in maintaining intestinal homeostasis. We demonstrate that Prohibitin 1 induces mitophagy in response to increased mitochondrial reactive oxygen species (ROS) through binding to mitophagy receptor Nix/Bnip3L and independently of Parkin. Prohibitin 1 is required for ROS-induced Nix localization to mitochondria and maintaining homeostasis of epithelial cells highly susceptible to mitochondrial dysfunction.

Mitochondrial Dynamics during Development

Mitochondria are dynamic membrane-bound organelles in eukaryotic cells. These are important for the generation of chemical energy needed to power various cellular functions and also support metabolic, energetic, and epigenetic regulation in various cells. These organelles are also important for communication with the nucleus and other cellular structures, to maintain developmental sequences and somatic homeostasis, and for cellular adaptation to stress. Increasing information shows mitochondrial defects as an important cause of inherited disorders in different organ systems. In this article, we provide an extensive review of ontogeny, ultrastructural morphology, biogenesis, functional dynamics, important clinical manifestations of mitochondrial dysfunction, and possibilities for clinical intervention. We present information from our own clinical and laboratory research in conjunction with information collected from an extensive search in the databases PubMed, EMBASE, and Scopus.

Maintenance of small molecule redox homeostasis in mitochondria

Compartmentalisation of eukaryotic cells enables fundamental otherwise often incompatible cellular processes. Establishment and maintenance of distinct compartments in the cell relies not only on proteins, lipids and metabolites but also on small redox molecules. In particular, small redox molecules such as glutathione, NAD(P)H and hydrogen peroxide (H₂ O₂ ) cooperate with protein partners in dedicated machineries to establish specific subcellular redox compartments with conditions that enable oxidative protein folding and redox signalling. Dysregulated redox homeostasis has been directly linked with a number of diseases including cancer, neurological disorders, cardiovascular diseases, obesity, metabolic diseases and ageing. In this review, we will summarise mechanisms regulating establishment and maintenance of redox homeostasis in the mitochondrial subcompartments of mammalian cells.

A Cristae-Like Microcompartment in Desulfobacterota

Some Alphaproteobacteria contain intracytoplasmic membranes (ICMs) and proteins homologous to those responsible for the mitochondrial cristae, an observation which has given rise to the hypothesis that the Alphaproteobacteria endosymbiont had already evolved cristae-like structures and functions. However, our knowledge of microbial fine structure is still limited, leaving open the possibility of structurally homologous ICMs outside the Alphaproteobacteria. Here, we report on the detailed characterization of lamellar cristae-like ICMs in environmental sulfate-reducing Desulfobacterota that form syntrophic partnerships with anaerobic methane-oxidizing (ANME) archaea. These structures are junction-bound to the cytoplasmic membrane and resemble the form seen in the lamellar cristae of opisthokont mitochondria. Extending these observations, we also characterized similar structures in Desulfovibrio carbinolicus, a close relative of the magnetotactic D. magneticus, which does not contain magnetosomes. Despite a remarkable structural similarity, the key proteins involved in cristae formation have not yet been identified in Desulfobacterota, suggesting that an analogous, but not a homologous, protein organization system developed during the evolution of some members of Desulfobacterota. IMPORTANCE Working with anaerobic consortia of methane oxidizing ANME archaea and their sulfate-reducing bacterial partners recovered from deep sea sediments and with the related sulfate-reducing bacterial isolate D. carbinolicus, we discovered that their intracytoplasmic membranes (ICMs) appear remarkably similar to lamellar cristae. Three-dimensional electron microscopy allowed for the novel analysis of the nanoscale attachment of ICMs to the cytoplasmic membrane, and these ICMs are structurally nearly identical to the crista junction architecture seen in metazoan mitochondria. However, the core junction-forming proteins must be different. The outer membrane vesicles were observed to bud from syntrophic Desulfobacterota, and darkly stained granules were prominent in both Desulfobacterota and D. carbinolicus. These findings expand the taxonomic breadth of ICM-producing microorganisms and add to our understanding of three-dimensional microbial fine structure in environmental microorganisms.

Hubbing the Cancer Cell

Oncogenic transformation drives adaptive changes in a growing tumor that affect the cellular organization of cancerous cells, resulting in the loss of specialized cellular functions in the polarized compartmentalization of cells. The resulting altered metabolic and morphological patterns are used clinically as diagnostic markers. This review recapitulates the known functions of actin, microtubules and the γ-tubulin meshwork in orchestrating cell metabolism and functional cellular asymmetry.

ANT1 overexpression models: Some similarities with facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder characterized by progressive muscle weakness. Adenine nucleotide translocator 1 (ANT1), the only 4q35 gene involved in mitochondrial function, is strongly expressed in FSHD skeletal muscle biopsies. However, its role in FSHD is unclear. In this study, we evaluated ANT1 overexpression effects in primary myoblasts from healthy controls and during Xenopus laevis organogenesis. We also compared ANT1 overexpression effects with the phenotype of FSHD muscle cells and biopsies. Here, we report that the ANT1 overexpression-induced phenotype presents some similarities with FSHD muscle cells and biopsies. ANT1-overexpressing muscle cells showed disorganized morphology, altered cytoskeletal arrangement, enhanced mitochondrial respiration/glycolysis, ROS production, oxidative stress, mitochondrial fragmentation and ultrastructure alteration, as observed in FSHD muscle cells. ANT1 overexpression in Xenopus laevis embryos affected skeletal muscle development, impaired skeletal muscle, altered mitochondrial ultrastructure and led to oxidative stress as observed in FSHD muscle biopsies. Moreover, ANT1 overexpression in X. laevis embryos affected heart structure and mitochondrial ultrastructure leading to cardiac arrhythmia, as described in some patients with FSHD. Overall our data suggest that ANT1 could contribute to mitochondria dysfunction and oxidative stress in FSHD muscle cells by modifying their bioenergetic profile associated with ROS production. Such interplay between energy metabolism and ROS production in FSHD will be of significant interest for future prospects.

Melatonin: Regulation of Viral Phase Separation and Epitranscriptomics in Post-Acute Sequelae of COVID-19

The relentless, protracted evolution of the SARS-CoV-2 virus imposes tremendous pressure on herd immunity and demands versatile adaptations by the human host genome to counter transcriptomic and epitranscriptomic alterations associated with a wide range of short- and long-term manifestations during acute infection and post-acute recovery, respectively. To promote viral replication during active infection and viral persistence, the SARS-CoV-2 envelope protein regulates host cell microenvironment including pH and ion concentrations to maintain a high oxidative environment that supports template switching, causing extensive mitochondrial damage and activation of pro-inflammatory cytokine signaling cascades. Oxidative stress and mitochondrial distress induce dynamic changes to both the host and viral RNA m6A methylome, and can trigger the derepression of long interspersed nuclear element 1 (LINE1), resulting in global hypomethylation, epigenetic changes, and genomic instability. The timely application of melatonin during early infection enhances host innate antiviral immune responses by preventing the formation of "viral factories" by nucleocapsid liquid-liquid phase separation that effectively blockades viral genome transcription and packaging, the disassembly of stress granules, and the sequestration of DEAD-box RNA helicases, including DDX3X, vital to immune signaling. Melatonin prevents membrane depolarization and protects cristae morphology to suppress glycolysis via antioxidant-dependent and -independent mechanisms. By restraining the derepression of LINE1 via multifaceted strategies, and maintaining the balance in m6A RNA modifications, melatonin could be the quintessential ancient molecule that significantly influences the outcome of the constant struggle between virus and host to gain transcriptomic and epitranscriptomic dominance over the host genome during acute infection and PASC.

Mitochondrial Membranes and Mitochondrial Genome: Interactions and Clinical Syndromes

Mitochondria are surrounded by two membranes; the outer mitochondrial membrane and the inner mitochondrial membrane. They are unique organelles since they have their own DNA, the mitochondrial DNA (mtDNA), which is replicated continuously. Mitochondrial membranes have direct interaction with mtDNA and are therefore involved in organization of the mitochondrial genome. They also play essential roles in mitochondrial dynamics and the supply of nucleotides for mtDNA synthesis. In this review, we will discuss how the mitochondrial membranes interact with mtDNA and how this interaction is essential for mtDNA maintenance. We will review different mtDNA maintenance disorders that result from defects in this crucial interaction. Finally, we will review therapeutic approaches relevant to defects in mitochondrial membranes.

Mitochondrial adaptations throughout the Trypanosoma brucei life cycle

The unicellular parasite Trypanosoma brucei has a digenetic life cycle that alternates between a mammalian host and an insect vector. During programmed development, this extracellular parasite encounters strikingly different environments that determine its energy metabolism. Functioning as a bioenergetic, biosynthetic, and signaling center, the single mitochondrion of T. brucei is drastically remodeled to support the dynamic cellular demands of the parasite. This manuscript will provide an up-to-date overview of how the distinct T. brucei developmental stages differ in their mitochondrial metabolic and bioenergetic pathways, with a focus on the electron transport chain, proline oxidation, TCA cycle, acetate production, and ATP generation. Although mitochondrial metabolic rewiring has always been simply viewed as a consequence of the differentiation process, the possibility that certain mitochondrial activities reinforce parasite differentiation will be explored.

Understanding mitochondria and the utility of optimization as a canonical framework for identifying and modeling mitochondrial pathways

The goal of this paper is to provide an overview of our current understanding of mitochondrial function as a framework to motivate the hypothesis that mitochondrial behavior is governed by optimization principles that are constrained by the laws of the physical and biological sciences. Then, mathematical optimization tools can generally be useful to model some of these processes under reasonable assumptions and limitations. We are specifically interested in optimizations via variational methods, which are briefly summarized. Within such an optimization framework, we suggest that the numerous mechanical instigators of cell and intracellular functioning can be modeled utilizing some of the principles of mechanics that govern engineered systems, as well as by the frequently observed feedback and feedforward mechanisms that coordinate the multitude of processes within cells. These mechanical aspects would need to be coupled to governing biochemical rules. Of course, biological systems are significantly more complex than engineered systems, and require considerably more experimentation to ascertain and characterize parameters and subsequent behavior. That complexity requires well-defined limitations and assumptions for any derived models. Optimality is being motivated as a framework to help us understand how cellular decisions are made, especially those that transition between physiological behaviors and dysfunctions along pathophysiological pathways. We elaborate on our interpretation of optimality and cellular decision making within the body of this paper, as we revisit these ideas in the numerous different contexts of mitochondrial functions.

Targeting regulation of ATP synthase 5 alpha/beta dimerization alleviates senescence

Senescence is a distinct set of changes in the senescence-associated secretory phenotype (SASP) and leads to aging and age-related diseases. Here, we screened compounds that could ameliorate senescence and identified an oxazoloquinoline analog (KB1541) designed to inhibit IL-33 signaling pathway. To elucidate the mechanism of action of KB1541, the proteins binding to KB1541 were investigated, and an interaction between KB1541 and 14-3-3ζ protein was found. Specifically, KB1541 interacted with 14-3-3ζ protein and phosphorylated of 14-3-3ζ protein at serine 58 residue. This phosphorylation increased ATP synthase 5 alpha/beta dimerization, which in turn promoted ATP production through increased oxidative phosphorylation (OXPHOS) efficiency. Then, the increased OXPHOS efficiency induced the recovery of mitochondrial function, coupled with senescence alleviation. Taken together, our results demonstrate a mechanism by which senescence is regulated by ATP synthase 5 alpha/beta dimerization upon fine-tuning of KB1541-mediated 14-3-3ζ protein activity.

Comparative Analysis of the APOL1 Variants in the Genetic Landscape of Renal Carcinoma Cells

Simple Summary

Renal cell carcinoma (RCC) occurs at higher frequency in individuals of African ancestry, with well-recorded documentation in this community. This is most prominent in the context of chronic kidney disease. In turn, many forms of progressive chronic kidney disease are more common in populations of Sub-Saharan African ancestry. This disparity has been attributed to well-defined allelic variants and has risen in the parental populations to high frequency under evolutionary pressure. Mechanisms of increased kidney disease risk and cell injury, causally associated with these APOL1 gene variants, have been extensively studied. Most studies have compared the effects of ectopic overexpression of the parental non-risk APOL1 with the mutated risk variants in cellular and organismal platforms. In the current study, we have used CRISPR/Cas9 genetic engineering to knock out or modify the sequence of endogenous APOL1 in RCC to mimic and examine the effects of these naturally occurring kidney disease risk allelic variants. Remarkably, these modifications to endogenous APOL1 genes in RCC resulted in a set of prominent effects on mitochondrial integrity and metabolic pathways and disrupted tumorigenesis. These findings both clarify pathways of cell injury of APOL1 risk variants in cells of kidney origin and motivate further studies to examine the potential central role of APOL1 in the pathogenesis of renal cell carcinoma and its relation to chronic kidney disease in genotypically at-risk African ancestry individuals.

Abstract

Although the relative risk of renal cell carcinoma associated with chronic kidney injury is particularly high among sub-Saharan African ancestry populations, it is unclear yet whether the APOL1 gene risk variants (RV) for kidney disease additionally elevate this risk. APOL1 G1 and G2 RV contribute to increased risk for kidney disease in black populations, although the disease mechanism has still not been fully deciphered. While high expression levels of all three APOL1 allelic variants, G0 (the wild type allele), G1, and G2 are injurious to normal human cells, renal carcinoma cells (RCC) naturally tolerate inherent high expression levels of APOL1. We utilized CRISPR/Cas9 gene editing to generate isogenic RCC clones expressing APOL1 G1 or G2 risk variants on a similar genetic background, thus enabling a reliable comparison between the phenotypes elicited in RCC by each of the APOL1 variants. Here, we demonstrate that knocking in the G1 or G2 APOL1 alleles, or complete elimination of APOL1 expression, has major effects on proliferation capacity, mitochondrial morphology, cell metabolism, autophagy levels, and the tumorigenic potential of RCC cells. The most striking effect of the APOL1 RV effect was demonstrated in vivo by the complete abolishment of tumor growth in immunodeficient mice. Our findings suggest that, in contrast to the WT APOL1 variant, APOL1 RV are toxic for RCC cells and may act to suppress cancer cell growth. We conclude that the inherent expression of non-risk APOL1 G0 is required for RCC tumorigenicity. RCC cancer cells can hardly tolerate increased APOL1 risk variants expression levels as opposed to APOL1 G0.

Deregulated mitochondrial microRNAs in Alzheimer's disease: Focus on synapse and mitochondria

Alzheimer's disease (AD) is the most common cause of dementia and is currently one of the biggest public health concerns in the world. Mitochondrial dysfunction in neurons is one of the major hallmarks of AD. Emerging evidence suggests that mitochondrial miRNAs potentially play important roles in the mitochondrial dysfunctions, focusing on synapse in AD progression. In this meta-analysis paper, a comprehensive literature review was conducted to identify and discuss the (1) role of mitochondrial miRNAs that regulate mitochondrial and synaptic functions; (2) the role of various factors such as mitochondrial dynamics, biogenesis, calcium signaling, biological sex, and aging on synapse and mitochondrial function; (3) how synapse damage and mitochondrial dysfunctions contribute to AD; (4) the structure and function of synapse and mitochondria in the disease process; (5) latest research developments in synapse and mitochondria in healthy and disease states; and (6) therapeutic strategies that improve synaptic and mitochondrial functions in AD. Specifically, we discussed how differences in the expression of mitochondrial miRNAs affect ATP production, oxidative stress, mitophagy, bioenergetics, mitochondrial dynamics, synaptic activity, synaptic plasticity, neurotransmission, and synaptotoxicity in neurons observed during AD. However, more research is needed to confirm the locations and roles of individual mitochondrial miRNAs in the development of AD.

Effects of Iron and Zinc on Mitochondria: Potential Mechanisms of Glaucomatous Injury

Glaucoma is the most substantial cause of irreversible blinding, which is accompanied by progressive retinal ganglion cell damage. Retinal ganglion cells are energy-intensive neurons that connect the brain and retina, and depend on mitochondrial homeostasis to transduce visual information through the brain. As cofactors that regulate many metabolic signals, iron and zinc have attracted increasing attention in studies on neurons and neurodegenerative diseases. Here, we summarize the research connecting iron, zinc, neuronal mitochondria, and glaucomatous injury, with the aim of updating and expanding the current view of how retinal ganglion cells degenerate in glaucoma, which can reveal novel potential targets for neuroprotection.

Mitochondrial Cristae Architecture and Functions: Lessons from Minimal Model Systems

Mitochondria are known as the powerhouse of eukaryotic cells. Energy production occurs in specific dynamic membrane invaginations in the inner mitochondrial membrane called cristae. Although the integrity of these structures is recognized as a key point for proper mitochondrial function, less is known about the mechanisms at the origin of their plasticity and organization, and how they can influence mitochondria function. Here, we review the studies which question the role of lipid membrane composition based mainly on minimal model systems.

Mitochondrial Contact Site and Cristae Organization System and F1FO-ATP Synthase Crosstalk Is a Fundamental Property of Mitochondrial Cristae

Mitochondrial cristae are polymorphic invaginations of the inner membrane that are the fabric of cellular respiration. Both the mitochondrial contact site and cristae organization system (MICOS) and the F1FO-ATP synthase are vital for sculpting cristae by opposing membrane-bending forces. While MICOS promotes negative curvature at crista junctions, dimeric F1FO-ATP synthase is crucial for positive curvature at crista rims. Crosstalk between these two complexes has been observed in baker's yeast, the model organism of the Opisthokonta supergroup. Here, we report that this property is conserved in Trypanosoma brucei, a member of the Discoba clade that separated from the Opisthokonta ∼2 billion years ago. Specifically, one of the paralogs of the core MICOS subunit Mic10 interacts with dimeric F1FO-ATP synthase, whereas the other core Mic60 subunit has a counteractive effect on F1FO-ATP synthase oligomerization. This is evocative of the nature of MICOS-F1FO-ATP synthase crosstalk in yeast, which is remarkable given the diversification that these two complexes have undergone during almost 2 eons of independent evolution. Furthermore, we identified a highly diverged, putative homolog of subunit e, which is essential for the stability of F1FO-ATP synthase dimers in yeast. Just like subunit e, it is preferentially associated with dimers and interacts with Mic10, and its silencing results in severe defects to cristae and the disintegration of F1FO-ATP synthase dimers. Our findings indicate that crosstalk between MICOS and dimeric F1FO-ATP synthase is a fundamental property impacting crista shape throughout eukaryotes. IMPORTANCE Mitochondria have undergone profound diversification in separate lineages that have radiated since the last common ancestor of eukaryotes some eons ago. Most eukaryotes are unicellular protists, including etiological agents of infectious diseases, like Trypanosoma brucei. Thus, the study of a broad range of protists can reveal fundamental features shared by all eukaryotes and lineage-specific innovations. Here, we report that two different protein complexes, MICOS and F1FO-ATP synthase, known to affect mitochondrial architecture, undergo crosstalk in T. brucei, just as in baker's yeast. This is remarkable considering that these complexes have otherwise undergone many changes during their almost 2 billion years of independent evolution. Thus, this crosstalk is a fundamental property needed to maintain proper mitochondrial structure even if the constituent players considerably diverged.

Ultrastructural Changes of the Mitochondrion During the Life Cycle of Trypanosoma brucei

The mitochondrion is crucial for ATP generation by oxidative phosphorylation, among other processes. Cristae are invaginations of the mitochondrial inner membrane that house nearly all the macromolecular complexes that perform oxidative phosphorylation. The unicellular parasite Trypanosoma brucei undergoes during its life cycle extensive remodeling of its single mitochondrion, which reflects major changes in its energy metabolism. While the bloodstream form (BSF) generates ATP exclusively by substrate-level phosphorylation and has a morphologically highly reduced mitochondrion, the insect-dwelling procyclic form (PCF) performs oxidative phosphorylation and has an expanded and reticulated organelle. Here, we have performed high-resolution 3D reconstruction of BSF and PCF mitochondria, with a particular focus on their cristae. By measuring the volumes and surface areas of these structures in complete or nearly complete cells, we have found that mitochondrial cristae are more prominent in BSF than previously thought and their biogenesis seems to be maintained during the cell cycle. Furthermore, PCF cristae exhibit a surprising range of volumes in situ, implying that each crista is acting as an independent bioenergetic unit. Cristae appear to be particularly enriched in the region of the organelle between the nucleus and kinetoplast, the mitochondrial genome, suggesting this part has distinctive properties.

VDAC-A Primal Perspective

The evolution of the eukaryotic cell from the primal endosymbiotic event involved a complex series of adaptations driven primarily by energy optimization. Transfer of genes from endosymbiont to host and concomitant expansion (by infolding) of the endosymbiont's chemiosmotic membrane greatly increased output of adenosine triphosphate (ATP) and placed selective pressure on the membrane at the host-endosymbiont interface to sustain the energy advantage. It is hypothesized that critical functions at this interface (metabolite exchange, polypeptide import, barrier integrity to proteins and DNA) were managed by a precursor β-barrel protein ("pβB") from which the voltage-dependent anion-selective channel (VDAC) descended. VDAC's role as hub for disparate and increasingly complex processes suggests an adaptability that likely springs from a feature inherited from pβB, retained because of important advantages conferred. It is proposed that this property is the remarkable structural flexibility evidenced in VDAC's gating mechanism, a possible origin of which is discussed.

Mitochondrial protein import dysfunction: mitochondrial disease, neurodegenerative disease and cancer

The majority of proteins localised to mitochondria are encoded by the nuclear genome, with approximately 1500 proteins imported into mammalian mitochondria. Dysfunction in this fundamental cellular process is linked to a variety of pathologies including neuropathies, cardiovascular disorders, myopathies, neurodegenerative diseases and cancer, demonstrating the importance of mitochondrial protein import machinery for cellular function. Correct import of proteins into mitochondria requires the co-ordinated activity of multimeric protein translocation and sorting machineries located in both the outer and inner mitochondrial membranes, directing the imported proteins to the destined mitochondrial compartment. This dynamic process maintains cellular homeostasis, and its dysregulation significantly affects cellular signalling pathways and metabolism. This review summarises current knowledge of the mammalian mitochondrial import machinery and the pathological consequences of mutation of its components. In addition, we will discuss the role of mitochondrial import in cancer, and our current understanding of the role of mitochondrial import in neurodegenerative diseases including Alzheimer's disease, Huntington's disease and Parkinson's disease.

Electrical control of the cell energy metabolism at the level of mitochondrial outer membrane

Energy, generated by the mitochondrial oxidative phosphorylation system, is transferred to the cytosol across the mitochondrial outer membrane (MOM), through the voltage-dependent anion channels (VDACs). The role of the VDAC's voltage-gating process to control the transfer of ATP, creatine phosphate and other negatively charged metabolites across MOM might be crucial for the cell energy metabolism regulation. However, it depends on the probability of the outer membrane potential (OMP) generation by a currently undefined mechanism that has usually been considered doubtful, based on the assumption that VDACs always stay in the electrically open state. Nevertheless, computational analysis of various possible metabolically-dependent mechanisms of OMP generation suggests that MOM is not a "coarse sieve", but in fact it functions as an electrical gatekeeper of cell energy metabolism, due to a probable OMP-dependent VDAC's gating. OMP generation could also be involved in the control of cell death resistance and mechanisms of various diseases.