Mic60/mitofilin overexpression alters mitochondrial dynamics and attenuates vulnerability of dopaminergic cells to dopamine and rotenone

Mitofilin in cardiovascular diseases: Insights into the pathogenesis and potential pharmacological interventions

The impact of mitochondrial dysfunction on the pathogenesis of cardiovascular disease is increasing. However, the precise underlying mechanism remains unclear. Mitochondria produce cellular energy through oxidative phosphorylation while regulating calcium homeostasis, cellular respiration, and the production of biosynthetic chemicals. Nevertheless, problems related to cardiac energy metabolism, defective mitochondrial proteins, mitophagy, and structural changes in mitochondrial membranes can cause cardiovascular diseases via mitochondrial dysfunction. Mitofilin is a critical inner mitochondrial membrane protein that maintains cristae structure and facilitates protein transport while linking the inner mitochondrial membrane, outer mitochondrial membrane, and mitochondrial DNA transcription. Researchers believe that mitofilin may be a therapeutic target for treating cardiovascular diseases, particularly cardiac mitochondrial dysfunctions. In this review, we highlight current findings regarding the role of mitofilin in the pathogenesis of cardiovascular diseases and potential therapeutic compounds targeting mitofilin.

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.

Mitochondrial Proteomes in Neural Cells: A Systematic Review

Mitochondria are ancient endosymbiotic double membrane organelles that support a wide range of eukaryotic cell functions through energy, metabolism, and cellular control. There are over 1000 known proteins that either reside within the mitochondria or are transiently associated with it. These mitochondrial proteins represent a functional subcellular protein network (mtProteome) that is encoded by mitochondrial and nuclear genomes and significantly varies between cell types and conditions. In neurons, the high metabolic demand and differential energy requirements at the synapses are met by specific modifications to the mtProteome, resulting in alterations in the expression and functional properties of the proteins involved in energy production and quality control, including fission and fusion. The composition of mtProteomes also impacts the localization of mitochondria in axons and dendrites with a growing number of neurodegenerative diseases associated with changes in mitochondrial proteins. This review summarizes the findings on the composition and properties of mtProteomes important for mitochondrial energy production, calcium and lipid signaling, and quality control in neural cells. We highlight strategies in mass spectrometry (MS) proteomic analysis of mtProteomes from cultured cells and tissue. The research into mtProteome composition and function provides opportunities in biomarker discovery and drug development for the treatment of metabolic and neurodegenerative disease.

Mitochondrial Volume Regulation and Swelling Mechanisms in Cardiomyocytes

Mitochondrion, known as the "powerhouse" of the cell, regulates ion homeostasis, redox state, cell proliferation and differentiation, and lipid synthesis. The inner mitochondrial membrane (IMM) controls mitochondrial metabolism and function. It possesses high levels of proteins that account for ~70% of the membrane mass and are involved in the electron transport chain, oxidative phosphorylation, energy transfer, and ion transport, among others. The mitochondrial matrix volume plays a crucial role in IMM remodeling. Several ion transport mechanisms, particularly K+ and Ca2+, regulate matrix volume. Small increases in matrix volume through IMM alterations can activate mitochondrial respiration, whereas excessive swelling can impair the IMM topology and initiates mitochondria-mediated cell death. The opening of mitochondrial permeability transition pores, the well-characterized phenomenon with unknown molecular identity, in low- and high-conductance modes are involved in physiological and pathological increases of matrix volume. Despite extensive studies, the precise mechanisms underlying changes in matrix volume and IMM structural remodeling in response to energy and oxidative stressors remain unknown. This review summarizes and discusses previous studies on the mechanisms involved in regulating mitochondrial matrix volume, IMM remodeling, and the crosstalk between these processes.

Caenorhabditis elegans as a Model System to Study Human Neurodegenerative Disorders

In recent years, advances in science and technology have improved our quality of life, enabling us to tackle diseases and increase human life expectancy. However, longevity is accompanied by an accretion in the frequency of age-related neurodegenerative diseases, creating a growing burden, with pervasive social impact for human societies. The cost of managing such chronic disorders and the lack of effective treatments highlight the need to decipher their molecular and genetic underpinnings, in order to discover new therapeutic targets. In this effort, the nematode Caenorhabditis elegans serves as a powerful tool to recapitulate several disease-related phenotypes and provides a highly malleable genetic model that allows the implementation of multidisciplinary approaches, in addition to large-scale genetic and pharmacological screens. Its anatomical transparency allows the use of co-expressed fluorescent proteins to track the progress of neurodegeneration. Moreover, the functional conservation of neuronal processes, along with the high homology between nematode and human genomes, render C. elegans extremely suitable for the study of human neurodegenerative disorders. This review describes nematode models used to study neurodegeneration and underscores their contribution in the effort to dissect the molecular basis of human diseases and identify novel gene targets with therapeutic potential.

Carnosic acid attenuated cytochrome c release through the mitochondrial structural protein Mic60 by PINK1 in SH-SY5Y cells

Mitochondrial dysfunction has been implicated in Parkinson's disease. Mic60 is a critical component of mitochondrial crista remodeling and participates in maintaining mitochondrial structure and function. This study investigated whether the carnosic acid (CA) of rosemary protects the mitochondria of SH-SY5Y cells against the neurotoxicity of 6-hydroxydopamine (6-OHDA) by regulating Mic60. Our results showed that CA pretreatment reversed the reduction in the Mic60 and citrate synthase proteins, as well as the protein induction of PKA caused by 6-OHDA. Moreover, Mic60 and PINK1 siRNAs blocked the ability of CA to lessen the release of mitochondrial cytochrome c by 6-OHDA. As shown by immunoprecipitation assay, in 6-OHDA-treated cells, the interaction of Mic60 with its phosphorylated threonine residue was decreased, but the interaction with its phosphorylated serine residue was increased. PINK1 siRNA and forskolin, a PKA activator, reversed these interactions. Moreover, forskolin pretreatment prevented CA from rescuing the interaction of PINK1 and Mic60 and the reduction in cytochrome c release and mitophagy impairment in 6-OHDA-treated cells. In conclusion, CA prevents 6-OHDA-induced cytochrome c release by regulating Mic60 phosphorylation by PINK1 through a downregulation of PKA. The regulation of Mic60 by CA can be considered as a protective mechanism for the prevention of Parkinson's disease.

A CHCHD6-APP axis connects amyloid and mitochondrial pathology in Alzheimer's disease

The mechanistic relationship between amyloid-beta precursor protein (APP) processing and mitochondrial dysfunction in Alzheimer's disease (AD) has long eluded the field. Here, we report that coiled-coil-helix-coiled-coil-helix domain containing 6 (CHCHD6), a core protein of the mammalian mitochondrial contact site and cristae organizing system, mechanistically connects these AD features through a circular feedback loop that lowers CHCHD6 and raises APP processing. In cellular and animal AD models and human AD brains, the APP intracellular domain fragment inhibits CHCHD6 transcription by binding its promoter. CHCHD6 and APP bind and stabilize one another. Reduced CHCHD6 enhances APP accumulation on mitochondria-associated ER membranes and accelerates APP processing, and induces mitochondrial dysfunction and neuronal cholesterol accumulation, promoting amyloid pathology. Compensation for CHCHD6 loss in an AD mouse model reduces AD-associated neuropathology and cognitive impairment. Thus, CHCHD6 connects APP processing and mitochondrial dysfunction in AD. This provides a potential new therapeutic target for patients.

CHCHD2 maintains mitochondrial contact site and cristae organizing system stability and protects against mitochondrial dysfunction in an experimental model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's dementia. Mitochondrial dysfunction is involved in the pathology of PD. Coiled-coil-helix-coiled-coil-helix domain-containing 2 (CHCHD2) was identified as associated with autosomal dominant PD. However, the mechanism of CHCHD2 in PD remains unclear.

METHODS

Short hairpin RNA (ShRNA)-mediated CHCHD2 knockdown or lentivirus-mediated CHCHD2 overexpression was performed to investigate the impact of CHCHD2 on mitochondrial morphology and function in neuronal tumor cell lines represented with human neuroblastoma (SHSY5Y) and HeLa cells. Blue-native polyacrylamide gel electrophoresis (PAGE) and two-dimensional sodium dodecyl sulfate-PAGE analysis were used to illustrate the role of CHCHD2 in mitochondrial contact site and cristae organizing system (MICOS). Co-immunoprecipitation and immunoblotting were used to address the interaction between CHCHD2 and Mic10. Serotype injection of adeno-associated vector-mediated CHCHD2 and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration were used to examine the influence of CHCHD2 in vivo.

RESULTS

We found that the overexpression of CHCHD2 can protect against methyl-4-phenylpyridinium (MPP+)-induced mitochondrial dysfunction and inhibit the loss of dopaminergic neurons in the MPTP-induced mouse model. Furthermore, we identified that CHCHD2 interacted with Mic10, and overexpression of CHCHD2 can protect against MPP+-induced MICOS impairment, while knockdown of CHCHD2 impaired the stability of MICOS.

CONCLUSION

This study indicated that CHCHD2 could interact with Mic10 and maintain the stability of the MICOS complex, which contributes to protecting mitochondrial function in PD.

Oxidative phosphorylation mediated pathogenesis of Parkinson's disease and its implication via Akt signaling

Substantia Nigra Pars-compacta (SNpc), in the basal ganglion region, is a primary source of dopamine release. These dopaminergic neurons require more energy than other neurons, as they are highly arborized and redundant. Neurons meet most of their energy demand (∼90%) from mitochondria. Oxidative phosphorylation (OxPhos) is the primary pathway for energy production. Many genes involved in Parkinson's disease (PD) have been associated with OxPhos, especially complex I. Abrogation in complex I leads to reduced ATP formation in these neurons, succumbing to death by inducing apoptosis. This review discusses the interconnection between complex I-associated PD genes and specific mitochondrial metabolic factors (MMFs) of OxPhos. Interestingly, all the complex I-associated PD genes discussed here have been linked to the Akt signaling pathway; thus, neuron survival is promoted and smooth mitochondrial function is ensured. Any changes in these genes disrupt the Akt pathway, which hampers the opening of the permeability transition pore (PTP) via GSK3β dephosphorylation; promotes destabilization of OxPhos; and triggers the release of pro-apoptotic factors.

Metabolic Features of Brain Function with Relevance to Clinical Features of Alzheimer and Parkinson Diseases

Brain metabolism is comprised in Alzheimer’s disease (AD) and Parkinson’s disease (PD). Since the brain primarily relies on metabolism of glucose, ketone bodies, and amino acids, aspects of these metabolic processes in these disorders—and particularly how these altered metabolic processes are related to oxidative and/or nitrosative stress and the resulting damaged targets—are reviewed in this paper. Greater understanding of the decreased functions in brain metabolism in AD and PD is posited to lead to potentially important therapeutic strategies to address both of these disorders, which cause relatively long-lasting decreased quality of life in patients.

MICOS and the mitochondrial inner membrane morphology - when things get out of shape

Mitochondria play a key role in cellular signalling, metabolism and energetics. Proper architecture and remodelling of the inner mitochondrial membrane are essential for efficient respiration, apoptosis and quality control in the cell. Several protein complexes including mitochondrial contact site and cristae organizing system (MICOS), F₁ F_O -ATP synthase, and Optic Atrophy 1 (OPA1), facilitate formation, maintenance and stability of cristae membranes. MICOS, the F₁ F_O -ATP synthase, OPA1 and inner membrane phospholipids such as cardiolipin and phosphatidylethanolamine interact with each other to organize the inner membrane ultra-structure and remodel cristae in response to the cell's demands. Functional alterations in these proteins or in the biosynthesis pathway of cardiolipin and phosphatidylethanolamine result in an aberrant inner membrane architecture and impair mitochondrial function. Mitochondrial dysfunction and abnormalities hallmark several human conditions and diseases including neurodegeneration, cardiomyopathies and diabetes mellitus. Yet, they have long been regarded as secondary pathological effects. This review discusses emerging evidence of a direct relationship between protein- and lipid-dependent regulation of the inner mitochondrial membrane morphology and diseases such as fatal encephalopathy, Leigh syndrome, Parkinson's disease, and cancer.

Increase of complex I and reduction of complex II mitochondrial activity are possible adaptive effects provoked by fluoride exposure

Fluoride (F) can induce changes in the expression of several liver proteins, most of them localized in the mitochondria and its effect is dose- and time-dependent. This study analyzed the effect of distinct F concentrations and exposure periods on the mitochondrial activity of complex I-III and II-III in the liver. Thirty-six 21-day-old male Wistar rats were divided into 2 groups (n = 18) according to the duration of the treatment (20 or 60 days). They were subdivided into 3 subgroups (n = 6) according to the concentration of F (0 mg/L, 15 mg/L or 50 mg/L). After the experimental periods, the animals were anesthetized, liver mitochondria were isolated and stored for activity analyses. The determination of complexes II-III and I-III was based on the reduction of cytochrome c³⁺ to cytochrome c²⁺ performed spectrophotometrically. Bioinformatics analyses were performed using data from a previous study (Pereira et al., 2018). The mitochondrial complex I-III was significantly activated in the groups treated with 50 mgF/L for 20 days and 15 mgF/L for 60 days. The complex II-III was significantly reduced in the group treated with the higher F dose for 60 days. The networks indicated more changes in mitochondrial proteins in the group treated with the higher dose for 20 days; the reduction is probably linked to the activation of the complex I-III. The reduction in the complex II-III upon exposure to the higher F dose in the long term might be part of an adaptative mechanism of the body to counteract the deleterious effects of this ion on the energy metabolism.

Parkin interacts with Mitofilin to increase dopaminergic neuron death in response to Parkinson's disease-related stressors

Mitochondrial dysfunction plays a critical role in the pathophysiology of Parkinson's disease (PD). The inner mitochondrial membrane (IMM) protein, Mitofilin or Mic60, has been shown to play a key role in controlling and maintaining mitochondrial cristae morphology, and its dysregulation induces cyto-deleterious effects. Here, we investigated the mechanism underlying Mitofilin degradation in dopaminergic neuron death using N27-A cells, and Human Dopamine Neuronal Primary cells treated with PD stressors, Dopamine (DA) or Rotenone (Rot). We found that both PD stressors increased mitochondrial Parkin translocation and interaction with Mitofilin that promotes Mitofilin degradation via ubiquitination, which is responsible for reduced mitochondrial membrane potential and increased ROS production. These effects were concomitant with abnormal mitochondrial structure and increased neuronal death. DA-induced degradation of Mitofilin enhances mitochondrial calpain activity, increases the release of AIF into the cytosol, and promotes apoptosis via an AIF-PARP dependent mechanism. We found that Rot-treated cells exhibit excessive mitophagy, while DA does not trigger mitophagy. In addition, overexpressing USP30, a mitochondrial deubiquitinase, attenuated cell death induced by Rot, but not by DA-treated cells. Together, our study reveals the impact of Parkin-Mitofilin interaction in PD stressor-induced neurotoxicity, which leads to the degradation of Mitofilin, resulting in mitochondrial structural damage and dysfunction that is responsible for neuronal death by apoptosis via an AIF-PARP pathway.

Global Interactome Mapping of Mitochondrial Intermembrane Space Proteases Identifies a Novel Function for HTRA2

A number of unique proteases localize to specific sub-compartments of the mitochondria, but the functions of these enzymes are poorly defined. Here, in vivo proximity-dependent biotinylation (BioID) is used to map the interactomes of seven proteases localized to the mitochondrial intermembrane space (IMS). In total, 802 high confidence proximity interactions with 342 unique proteins are identified. While all seven proteases co-localized with the IMS markers OPA1 and CLPB, 230 of the interacting partners are unique to just one or two protease bait proteins, highlighting the ability of BioID to differentiate unique interactomes within the confined space of the IMS. Notably, high-temperature requirement peptidase 2 (HTRA2) interacts with eight of 13 components of the mitochondrial intermembrane space bridging (MIB) complex, a multiprotein assembly essential for the maintenance of mitochondrial cristae structure. Knockdown of HTRA2 disrupts cristae in HEK 293 and OCI-AML2 cells, and leads to increased intracellular levels of the MIB subunit IMMT. Using a cell-free assay it is demonstrated that HTRA2 can degrade recombinant IMMT but not two other core MIB complex subunits, SAMM50 and CHCHD3. The IMS protease interactome thus represents a rich dataset that can be mined to uncover novel IMS protease biology.

The MICOS complex, a structural element of mitochondria with versatile functions

Mitochondria perform a plethora of functions in various cells of different tissues. Their architecture differs remarkably, for instance in neurons versus steroidogenic cells. Furthermore, aberrant mitochondrial architecture results in mitochondrial dysfunction. This indicates strongly that mitochondrial architecture and function are intimately linked. Therefore, a deep knowledge about the determinants of mitochondrial architecture and their function on a molecular level is of utmost importance. In the past decades, various proteins and protein complexes essential for formation of mitochondrial architecture have been identified. Here we will review the current knowledge of the MICOS complex, one of the major structural elements of mitochondria. MICOS is a multi-subunit complex present in the inner mitochondrial membrane. Multiple interaction partners in the inner and outer mitochondrial membrane point to participation in a multitude of important processes, such as generation of mitochondrial architecture, lipid metabolism, and protein import into mitochondria. Since the MICOS complex is highly conserved in form and function throughout evolution, we will highlight the importance of MICOS for mammals. We will emphasize in particular the current knowledge of the association of MICOS with severe human diseases, including Charcot–Marie–Tooth disease type 2, Alzheimer's disease, Parkinson's disease, Frontotemporal Dementia and Amyotrophic Lateral Sclerosis.

The role of mitochondrial dynamics in human cancers

Mitochondria are crucial cellular organelles. Under extracellular stimulations, mitochondria undergo constant fusion and fission dynamics to meet different cellular demands. Mitochondrial dynamics is regulated by specialized proteins and lipids. Dysregulated mitochondrial dynamics has been linked to the initiation and progression of diverse human cancers, affecting aspects such as cancer metastasis, drug resistance and cancer stem cell survival, suggesting that targeting mitochondrial dynamics is a potential therapeutic strategy. In the present review, we summarize the molecular mechanisms underlying fusion and fission dynamics and discuss the effects of mitochondrial dynamics on the development of human cancers.

Knockdown of mitofilin inhibits autophagy and facilitates starvation-induced apoptosis in HeLa cells

Objectives

Mitofilin contributes to the maintenance of mitochondrial structure and functions. This study was undertaken to determine the mechanisms underlying its regulation of apoptosis.

Materials and Methods

Mitofilin was knockdowned by specific short hairpin RNA (shRNA) and the stable HeLa cell clone was selected. The autophagy activity were assessed with LC3-II conversion and puncta formation by western blot and fluorescence imaging in starved and normal cultured HeLa cells. Autophagy flux was measured in the presence of NH₄Cl. Wortmannin was used to inhibit autophagy. Cell viability and apoptosis were detected with cell counting kit-8 (CCK-8) and fluorescence-activated cell sorting (FACS) assay, respectively.

Results

Mitofilin expression was down-regulated in starved HeLa cells. In established mitofilin stable knockdown cell lines, LC3-II conversion and puncta formation were detected, which are both hallmarks of autophagy, under both basal and starvation conditions. Mitofilin down-regulation decreased LC3-II conversion and puncta formation, which indicates that loss of mitofilin function inhibits both basal and starvation-induced autophagy activity. CCK-8 and FACS analysis confirmed mitofilin involvement in the regulation of cell survival since mitofilin down-regulation facilitated starvation-induced apoptosis in HeLa cells.

Conclusion

Taken together, mitofilin is a potent regulator of autophagy and it may modulate cell survival through regulation of autophagy.

The ‘mitochondrial contact site and cristae organising system’ (MICOS) in health and human disease

The ‘mitochondrial contact site and cristae organising system’ (MICOS) is an essential protein complex that promotes the formation, maintenance and stability of mitochondrial cristae. As such, loss of core MICOS components disrupts cristae structure and impairs mitochondrial function. Aberrant mitochondrial cristae morphology and diminished mitochondrial function is a pathological hallmark observed across many human diseases such as neurodegenerative conditions, obesity and diabetes mellitus, cardiomyopathy, and in muscular dystrophies and myopathies. While mitochondrial abnormalities are often an associated secondary effect to the pathological disease process, a direct role for the MICOS in health and human disease is emerging. This review describes the role of MICOS in the maintenance of mitochondrial architecture and summarizes both the direct and associated roles of the MICOS in human disease.

Pediatric ependymoma: GNAO1, ASAH1, IMMT and IPO7 protein expression and 5-year prognosis correlation

OBJECTIVE

The aim of this work was to evaluate a pediatric ependymoma protein expression that may be useful as a molecular biomarker candidate for prognosis, correlated with clinical features such as age, gender, histopathological grade, ependymal tumor recurrence and patient survival.

PATIENTS AND METHODS

Immunohistochemistry assays were performed for GNAO1, ASAH1, IMMT, IPO7, Cyclin D1, P53 and Ki-67 proteins. Kaplan-Meier and Cox analysis were performed for age, gender, histopathological grade, relapse and survival correlation.

RESULTS

We found that three proteins correlate with histopathological grade and relapse; two proteins correlate with survival; one protein does not correlate with any clinical feature.

CONCLUSION

Our results suggest that, out of the proteins analyzed, five may be considered suitable prognostic biomarkers and one may be considered a predictive biomarker for response to treatment of pediatric ependymoma.

Potential Role of Mic60/Mitofilin in Parkinson's Disease

There are currently no treatments that hinder or halt the inexorable progression of Parkinson's disease (PD). While the etiology of PD remains elusive, evidence suggests that early dysfunction of mitochondrial respiration and homeostasis play a major role in PD pathogenesis. The mitochondrial structural protein Mic60, also known as mitofilin, is critical for maintaining mitochondrial architecture and function. Loss of Mic60 is associated with detrimental effects on mitochondrial homeostasis. Growing evidence now implicates Mic60 in the pathogenesis of PD. In this review, we discuss the data supporting a role of Mic60 and mitochondrial dysfunction in PD. We will also consider the potential of Mic60 as a therapeutic target for treating neurological disorders.

Mitochondrial inner membrane protein, Mic60/mitofilin in mammalian organ protection

The identification of the mitochondrial contact site and cristae organizing system (MICOS) in the inner mitochondrial membrane shed light on the intricate components necessary for mitochondria to form their signature cristae in which many protein complexes including the electron transport chain are localized. Mic60/mitofilin has been described as the core component for the assembly and maintenance of MICOS, thus controlling cristae morphology, protein transport, mitochondrial DNA transcription, as well as connecting the inner and outer mitochondrial membranes. Although Mic60 homologs are present in many species, mammalian Mic60 is only recently gaining attention as a critical player in several organ systems and diseases with mitochondrial-defect origins. In this review, we summarize what is currently known about the ever-expanding role of Mic60 in mammals, and highlight some new studies pushing the field of mitochondrial cristae organization towards potentially new and exciting therapies targeting this protein.

Reactive Oxygen Species and Mitochondrial Dynamics: The Yin and Yang of Mitochondrial Dysfunction and Cancer Progression

Mitochondria are organelles with a highly dynamic ultrastructure maintained by a delicate equilibrium between its fission and fusion rates. Understanding the factors influencing this balance is important as perturbations to mitochondrial dynamics can result in pathological states. As a terminal site of nutrient oxidation for the cell, mitochondrial powerhouses harness energy in the form of ATP in a process driven by the electron transport chain. Contemporaneously, electrons translocated within the electron transport chain undergo spontaneous side reactions with oxygen, giving rise to superoxide and a variety of other downstream reactive oxygen species (ROS). Mitochondrially-derived ROS can mediate redox signaling or, in excess, cause cell injury and even cell death. Recent evidence suggests that mitochondrial ultrastructure is tightly coupled to ROS generation depending on the physiological status of the cell. Yet, the mechanism by which changes in mitochondrial shape modulate mitochondrial function and redox homeostasis is less clear. Aberrant mitochondrial morphology may lead to enhanced ROS formation, which, in turn, may deteriorate mitochondrial health and further exacerbate oxidative stress in a self-perpetuating vicious cycle. Here, we review the latest findings on the intricate relationship between mitochondrial dynamics and ROS production, focusing mainly on its role in malignant disease.

Optic Atrophy 1 Is Epistatic to the Core MICOS Component MIC60 in Mitochondrial Cristae Shape Control

The mitochondrial contact site and cristae organizing system (MICOS) and Optic atrophy 1 (OPA1) control cristae shape, thus affecting mitochondrial function and apoptosis. Whether and how they physically and functionally interact is unclear. Here, we provide evidence that OPA1 is epistatic to MICOS in the regulation of cristae shape. Proteomic analysis identifies multiple MICOS components in native OPA1-containing high molecular weight complexes disrupted during cristae remodeling. MIC60, a core MICOS protein, physically interacts with OPA1, and together, they control cristae junction number and stability, OPA1 being epistatic to MIC60. OPA1 defines cristae width and junction diameter independently of MIC60. Our combination of proteomics, biochemistry, genetics, and electron tomography provides a unifying model for mammalian cristae biogenesis by OPA1 and MICOS.

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Complexes containing OPA1 and MIC60 are targeted during cristae remodeling

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OPA1 lies upstream of MIC60 in regulating cristae junction number and stability

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OPA1 is the sole regulator of cristae junction width

Apolipoprotein O expression in mouse liver enhances hepatic lipid accumulation by impairing mitochondrial function

Apolipoprotein O (ApoO) was recently observed in the cellular mitochondrial inner membrane, which plays a role in mitochondrial function and is associated with myocardiopathy. Empirical information on the physiological functions of apoO is therefore limited. In this study, we aimed to elucidate the effect of apoO on hepatic fatty acid metabolism. An adenoviral vector expressing hApoO was constructed and introduced into chow diet and high-fat diet induced mice and the L02 human hepatoma cell line. High levels of hApoO mRNA and protein were detected in the liver, and the expression of lipid metabolism genes was significantly altered compared with negative controls. The liver function indices (serum ALT and AST) were clearly elevated, and the ultrastructure of cellular mitochondria was distinctly altered in the liver after apoO overexpression. Further, mitochondrial membrane potential decreased with hApoO treatment in L02 cells. These results establish a link between apoO and lipid accumulation and could suggest a new pathway for regulating non-alcoholic fatty liver disease progression.