Loss of OPA1 perturbates the mitochondrial inner membrane structure and integrity, leading to cytochrome c release and apoptosis

Lipid metabolic reprogramming of hepatic CD4+ T cells during SIV infection

While liver inflammation is associated with AIDS, little is known so far about hepatic CD4+ T cells. By using the simian immunodeficiency virus (SIV)-infected rhesus macaque (RM) model, we aimed to characterize CD4+ T cells. The phenotype of CD4+ T cells was assessed by flow cytometry from uninfected (n = 3) and infected RMs, with either SIVmac251 (n = 6) or SHIVSF162p3 (n = 6). After cell sorting of hepatic CD4+ T cells, viral DNA quantification and RNA sequencing were performed.Thus, we demonstrated that liver CD4+ T cells strongly expressed the SIV coreceptor, CCR5. We showed that viremia was negatively correlated with the percentage of hepatic effector memory CD4+ T cells. Consistent with viral sensing, inflammatory and interferon gene transcripts were increased. We also highlighted the presence of harmful CD4+ T cells expressing GZMA and members of TGFB that could contribute to fuel inflammation and fibrosis. Whereas RNA sequencing demonstrated activated CD4+ T cells displaying higher levels of mitoribosome and membrane lipid synthesis transcripts, few genes were related to glycolysis and oxidative phosphorylation, which are essential to sustain activated T cells. Furthermore, we observed lower levels of mitochondrial DNA and higher levels of genes associated with damaged organelles (reticulophagy and mitophagy). Altogether, our data revealed that activated hepatic CD4+ T cells are reprogrammed to lipid metabolism. Thus, strategies aiming to reprogram T cell metabolism with effector function could be of interest for controlling viral infection and preventing liver disorders.IMPORTANCEHuman immunodeficiency virus (HIV) infection may cause liver diseases, associated with inflammation and tissue injury, contributing to comorbidity in people living with HIV. Paradoxically, the contribution of hepatic CD4+ T cells remains largely underestimated. Herein, we used the model of simian immunodeficiency virus (SIV)-infected rhesus macaques to access liver tissue. Our work demonstrates that hepatic CD4+ T cells express CCR5, the main viral coreceptor, and are infected. Viral infection is associated with the presence of inflamed and activated hepatic CD4+ T cells expressing cytotoxic molecules. Furthermore, hepatic CD4+ T cells are reprogrammed toward lipid metabolism after SIV infection. Altogether, our findings shed new light on hepatic CD4+ T cell profile that could contribute to liver injury following viral infection.

An interactive deep learning-based approach reveals mitochondrial cristae topologies

The convolution of membranes called cristae is a critical structural and functional feature of mitochondria. Crista structure is highly diverse between different cell types, reflecting their role in metabolic adaptation. However, their precise three-dimensional (3D) arrangement requires volumetric analysis of serial electron microscopy and has therefore been limiting for unbiased quantitative assessment. Here, we developed a novel, publicly available, deep learning (DL)-based image analysis platform called Python-based human-in-the-loop workflow (PHILOW) implemented with a human-in-the-loop (HITL) algorithm. Analysis of dense, large, and isotropic volumes of focused ion beam-scanning electron microscopy (FIB-SEM) using PHILOW reveals the complex 3D nanostructure of both inner and outer mitochondrial membranes and provides deep, quantitative, structural features of cristae in a large number of individual mitochondria. This nanometer-scale analysis in micrometer-scale cellular contexts uncovers fundamental parameters of cristae, such as total surface area, orientation, tubular/lamellar cristae ratio, and crista junction density in individual mitochondria. Unbiased clustering analysis of our structural data unraveled a new function for the dynamin-related GTPase Optic Atrophy 1 (OPA1) in regulating the balance between lamellar versus tubular cristae subdomains.

Structural mechanism of mitochondrial membrane remodelling by human OPA1

Distinct morphologies of the mitochondrial network support divergent metabolic and regulatory processes that determine cell function and fate1-3. The mechanochemical GTPase optic atrophy 1 (OPA1) influences the architecture of cristae and catalyses the fusion of the mitochondrial inner membrane4,5. Despite its fundamental importance, the molecular mechanisms by which OPA1 modulates mitochondrial morphology are unclear. Here, using a combination of cellular and structural analyses, we illuminate the molecular mechanisms that are key to OPA1-dependent membrane remodelling and fusion. Human OPA1 embeds itself into cardiolipin-containing membranes through a lipid-binding paddle domain. A conserved loop within the paddle domain inserts deeply into the bilayer, further stabilizing the interactions with cardiolipin-enriched membranes. OPA1 dimerization through the paddle domain promotes the helical assembly of a flexible OPA1 lattice on the membrane, which drives mitochondrial fusion in cells. Moreover, the membrane-bending OPA1 oligomer undergoes conformational changes that pull the membrane-inserting loop out of the outer leaflet and contribute to the mechanics of membrane remodelling. Our findings provide a structural framework for understanding how human OPA1 shapes mitochondrial morphology and show us how human disease mutations compromise OPA1 functions.

The Role of Mitophagy in Glaucomatous Neurodegeneration

This review aims to provide a better understanding of the emerging role of mitophagy in glaucomatous neurodegeneration, which is the primary cause of irreversible blindness worldwide. Increasing evidence from genetic and other experimental studies suggests that mitophagy-related genes are implicated in the pathogenesis of glaucoma in various populations. The association between polymorphisms in these genes and increased risk of glaucoma is presented. Reduction in intraocular pressure (IOP) is currently the only modifiable risk factor for glaucoma, while clinical trials highlight the inadequacy of IOP-lowering therapeutic approaches to prevent sight loss in many glaucoma patients. Mitochondrial dysfunction is thought to increase the susceptibility of retinal ganglion cells (RGCs) to other risk factors and is implicated in glaucomatous degeneration. Mitophagy holds a vital role in mitochondrial quality control processes, and the current review explores the mitophagy-related pathways which may be linked to glaucoma and their therapeutic potential.

Preserving and enhancing mitochondrial function after stroke to protect and repair the neurovascular unit: novel opportunities for nanoparticle-based drug delivery

The neurovascular unit (NVU) is composed of vascular cells, glia, and neurons that form the basic component of the blood brain barrier. This intricate structure rapidly adjusts cerebral blood flow to match the metabolic needs of brain activity. However, the NVU is exquisitely sensitive to damage and displays limited repair after a stroke. To effectively treat stroke, it is therefore considered crucial to both protect and repair the NVU. Mitochondrial calcium (Ca2+) uptake supports NVU function by buffering Ca2+ and stimulating energy production. However, excessive mitochondrial Ca2+ uptake causes toxic mitochondrial Ca2+ overloading that triggers numerous cell death pathways which destroy the NVU. Mitochondrial damage is one of the earliest pathological events in stroke. Drugs that preserve mitochondrial integrity and function should therefore confer profound NVU protection by blocking the initiation of numerous injury events. We have shown that mitochondrial Ca2+ uptake and efflux in the brain are mediated by the mitochondrial Ca2+ uniporter complex (MCUcx) and sodium/Ca2+/lithium exchanger (NCLX), respectively. Moreover, our recent pharmacological studies have demonstrated that MCUcx inhibition and NCLX activation suppress ischemic and excitotoxic neuronal cell death by blocking mitochondrial Ca2+ overloading. These findings suggest that combining MCUcx inhibition with NCLX activation should markedly protect the NVU. In terms of promoting NVU repair, nuclear hormone receptor activation is a promising approach. Retinoid X receptor (RXR) and thyroid hormone receptor (TR) agonists activate complementary transcriptional programs that stimulate mitochondrial biogenesis, suppress inflammation, and enhance the production of new vascular cells, glia, and neurons. RXR and TR agonism should thus further improve the clinical benefits of MCUcx inhibition and NCLX activation by increasing NVU repair. However, drugs that either inhibit the MCUcx, or stimulate the NCLX, or activate the RXR or TR, suffer from adverse effects caused by undesired actions on healthy tissues. To overcome this problem, we describe the use of nanoparticle drug formulations that preferentially target metabolically compromised and damaged NVUs after an ischemic or hemorrhagic stroke. These nanoparticle-based approaches have the potential to improve clinical safety and efficacy by maximizing drug delivery to diseased NVUs and minimizing drug exposure in healthy brain and peripheral tissues.

Glaucomatous optic neuropathy: Mitochondrial dynamics, dysfunction and protection in retinal ganglion cells

Glaucoma is a leading cause of irreversible blindness worldwide and is characterized by a slow, progressive, and multifactorial degeneration of retinal ganglion cells (RGCs) and their axons, resulting in vision loss. Despite its high prevalence in individuals 60 years of age and older, the causing factors contributing to glaucoma progression are currently not well characterized. Intraocular pressure (IOP) is the only proven treatable risk factor. However, lowering IOP is insufficient for preventing disease progression. One of the significant interests in glaucoma pathogenesis is understanding the structural and functional impairment of mitochondria in RGCs and their axons and synapses. Glaucomatous risk factors such as IOP elevation, aging, genetic variation, neuroinflammation, neurotrophic factor deprivation, and vascular dysregulation, are potential inducers for mitochondrial dysfunction in glaucoma. Because oxidative phosphorylation stress-mediated mitochondrial dysfunction is associated with structural and functional impairment of mitochondria in glaucomatous RGCs, understanding the underlying mechanisms and relationship between structural and functional alterations in mitochondria would be beneficial to developing mitochondria-related neuroprotection in RGCs and their axons and synapses against glaucomatous neurodegeneration. Here, we review the current studies focusing on mitochondrial dynamics-based structural and functional alterations in the mitochondria of glaucomatous RGCs and therapeutic strategies to protect RGCs against glaucomatous neurodegeneration.

Taurine Protects against the Fatty Liver Hemorrhagic Syndrome in Laying Hens through the Regulation of Mitochondrial Homeostasis

Metabolic-associated fatty liver disease (MAFLD) is a chronic liver disease caused by fat deposition in the liver of humans and mammals, while fatty liver hemorrhagic syndrome (FLHS) is a fatty liver disease in laying hens which can increase the mortality and cause severe economic losses to the laying industry. Increasing evidence has shown a close relationship between the occurrence of fatty liver disease and the disruption of mitochondrial homeostasis. Studies have proven that taurine can regulate hepatic fat metabolism, reduce hepatic fatty deposition, inhibit oxidative stress, and alleviate mitochondrial dysfunction. However, the mechanisms by which taurine regulates mitochondrial homeostasis in hepatocytes need to be further studied. In this study, we determined the effects and mechanisms of taurine on high-energy low-protein diet-induced FLHS in laying hens and in cultured hepatocytes in free fatty acid (FFA)-induced steatosis. The liver function, lipid metabolism, antioxidant capacity, mitochondrial function, mitochondrial dynamics, autophagy, and biosynthesis were detected. The results showed impaired liver structure and function, mitochondrial damage and dysfunction, lipid accumulation, and imbalance between mitochondrial fusion and fission, mitochondrial autophagy, and biosynthesis in both FLHS hens and steatosis hepatocytes. Taurine administration can significantly inhibit the occurrence of FLHS, protect mitochondria in hepatocytes from disease induced by lipid accumulation and FFA, up-regulate the expression levels of Mfn1, Mfn2, Opa1, LC3I, LC3II, PINK1, PGC-1α, Nrf1, Nrf2, and Tfam, and down-regulate the expression levels of Fis1, Drp1, and p62. In conclusion, taurine can protect laying hens from FLHS through the regulation of mitochondrial homeostasis, including the regulation of mitochondrial dynamics, autophagy, and biosynthesis.

In search for mitochondrial biomarkers of Parkinson's disease: Findings in parkin-mutant human fibroblasts

Most cases of Parkinson's disease (PD) are idiopathic, with unknown aetiology and genetic background. However, approximately 10 % of cases are caused by defined genetic mutations, among which mutations in the parkin gene are the most common. There is increasing evidence of the involvement of mitochondrial dysfunction in the development of both idiopathic and genetic PD. However, the data on mitochondrial changes reported by different studies are inconsistent, which can reflect the variability in genetic background of the disease. Mitochondria, as a plastic and dynamic organelles, are the first place in the cell to respond to external and internal stress. In this work, we characterized mitochondrial function and dynamics (network morphology and turnover regulation) in primary fibroblasts from PD patients with parkin mutations. We performed clustering analysis of the obtained data to compare the profiles of mitochondrial parameters in PD patients and healthy donors. This allowed to extract the features characteristic for PD patients fibroblasts, which were a smaller and less complex mitochondrial network and decreased levels of mitochondrial biogenesis regulators and mitophagy mediators. The approach we used allowed a comprehensive characteristics of elements common for mitochondrial dynamics remodelling accompanying pathogenic mutation. This may be helpful in the deciphering key pathomechanisms of the PD disease.

The role of apoptosis in the pathogenesis of osteoarthritis

PURPOSE

Apoptosis is an important physiological process, making a great difference to development and tissue homeostasis. Osteoarthritis (OA) is a chronic joint disease characterized by degeneration and destruction of articular cartilage and bone hyperplasia. This purpose of this study is to provide an updated review of the role of apoptosis in the pathogenesis of osteoarthritis.

METHODS

A comprehensive review of the literature on osteoarthritis and apoptosis was performed, which mainly focused on the regulatory factors and signaling pathways associated with chondrocyte apoptosis in osteoarthritis and other pathogenic mechanisms involved in chondrocyte apoptosis.

RESULTS

Inflammatory mediators such as reactive oxygen species (ROS), nitric oxide (NO), IL-1β, tumor necrosis factor-α (TNF-α), and Fas are closely related to chondrocyte apoptosis. NF-κB signaling pathway, Wnt signaling pathway, and Notch signaling pathway activate proteins and gene targets that promote or inhibit the progression of osteoarthritis disease, including chondrocyte apoptosis and ECM degradation. Long non-coding RNAs (LncRNAs) and microRNAs (microRNAs) have gradually replaced single and localized research methods and become the main research approaches. In addition, the relationship between cellular senescence, autophagy, and apoptosis was also briefly explained.

CONCLUSION

This review offers a better molecular delineation of apoptotic processes that may help in designing new therapeutic options for OA treatment.

Pathological convergence of APP and SNCA deficiency in hippocampal degeneration of young rats

The common pathogenesis of Alzheimer's disease (AD) and Parkinson's disease (PD) has been supported by biochemical, genetic and molecular evidence. Mitochondrial dysfunction is considered to be the common pathology in early AD and PD. The physiological regulation of APP and α-synuclein on mitochondria remains unclear, let alone whether they share common regulatory mechanisms affecting the development of neurodegenerative diseases. By studying gene knockout rats, the commonality of physiological APP and α-synuclein in maintaining mitochondrial function through calcium homeostasis regulation was revealed, which was critical in inhibiting hippocampal degeneration in young rats. APP and α-synuclein both control hippocampal mitochondrial calcium intake and outflow. In the mitochondrial calcium influx regulation, APP and α-synuclein are located on the mitochondrial-associated endoplasmic reticulum membrane (MAM) and converge to regulate the IP₃R1-Grp75-VDAC2 axis. Mitochondrial calcium outflow is redundantly promoted by both α-synuclein and APP. Loss of APP or SNCA leads to mitochondrial calcium overload, thus enhancing aerobic respiration and ER stress, and ultimately causing excessive apoptosis in the hippocampus and spatial memory impairment in young rats. Based on this study, we believe that the physiological function impairment of APP and SNCA is the early core pathology to induce mitochondrial dysfunction at the early stage of AD and PD, while the IP₃R1-Grp75-VDAC2 axis might be the common drug target of these two diseases.

Pancreatic cancer stemness: dynamic status in malignant progression

Pancreatic cancer (PC) is one of the most aggressive malignancies worldwide. Increasing evidence suggests that the capacity for self-renewal, proliferation, and differentiation of pancreatic cancer stem cells (PCSCs) contribute to major challenges with current PC therapies, causing metastasis and therapeutic resistance, leading to recurrence and death in patients. The concept that PCSCs are characterized by their high plasticity and self-renewal capacities is central to this review. We focused specifically on the regulation of PCSCs, such as stemness-related signaling pathways, stimuli in tumor cells and the tumor microenvironment (TME), as well as the development of innovative stemness-targeted therapies. Understanding the biological behavior of PCSCs with plasticity and the molecular mechanisms regulating PC stemness will help to identify new treatment strategies to treat this horrible disease.

Genetically Engineered Triple MAPT-Mutant Human-Induced Pluripotent Stem Cells (N279K, P301L, and E10+16 Mutations) Exhibit Impairments in Mitochondrial Bioenergetics and Dynamics

Pathological abnormalities in the tau protein give rise to a variety of neurodegenerative diseases, conjointly termed tauopathies. Several tau mutations have been identified in the tau-encoding gene MAPT, affecting either the physical properties of tau or resulting in altered tau splicing. At early disease stages, mitochondrial dysfunction was highlighted with mutant tau compromising almost every aspect of mitochondrial function. Additionally, mitochondria have emerged as fundamental regulators of stem cell function. Here, we show that compared to the isogenic wild-type triple MAPT-mutant human-induced pluripotent stem cells, bearing the pathogenic N279K, P301L, and E10+16 mutations, exhibit deficits in mitochondrial bioenergetics and present altered parameters linked to the metabolic regulation of mitochondria. Moreover, we demonstrate that the triple tau mutations disturb the cellular redox homeostasis and modify the mitochondrial network morphology and distribution. This study provides the first characterization of disease-associated tau-mediated mitochondrial impairments in an advanced human cellular tau pathology model at early disease stages, ranging from mitochondrial bioenergetics to dynamics. Consequently, comprehending better the influence of dysfunctional mitochondria on the development and differentiation of stem cells and their contribution to disease progression may thus assist in the potential prevention and treatment of tau-related neurodegeneration.

SLC25A46 promotes mitochondrial fission and mediates resistance to lipotoxic stress in INS-1E insulin-secreting cells

Glucose sensing in pancreatic β-cells depends on oxidative phosphorylation and mitochondria-derived signals that promote insulin secretion. Using mass spectrometry-based phosphoproteomics to search for downstream effectors of glucose-dependent signal transduction in INS-1E insulinoma cells, we identified the outer mitochondrial membrane protein SLC25A46. Under resting glucose concentrations, SLC25A46 was phosphorylated on a pair of threonine residues (T44/T45) and was dephosphorylated in response to glucose-induced Ca2+ signals. Overexpression of SLC25A46 in INS-1E cells caused complete mitochondrial fragmentation, resulting in a mild mitochondrial defect associated with lowered glucose-induced insulin secretion. In contrast, inactivation of the Slc25a46 gene resulted in dramatic mitochondrial hyperfusion, without affecting respiratory activity or insulin secretion. Consequently, SLC25A46 is not essential for metabolism-secretion coupling under normal nutrient conditions. Importantly, insulin-secreting cells lacking SLC25A46 had an exacerbated sensitivity to lipotoxic conditions, undergoing massive apoptosis when exposed to palmitate. Therefore, in addition to its role in mitochondrial dynamics, SLC25A46 plays a role in preventing mitochondria-induced apoptosis in INS-E cells exposed to nutrient stress. By protecting mitochondria, SLC25A46 might help to maintain β-cell mass essential for blood glucose control.

Fish Models for Exploring Mitochondrial Dysfunction Affecting Neurodegenerative Disorders

Neurodegenerative disorders are characterized by the progressive loss of neuronal structure or function, resulting in memory loss and movement disorders. Although the detailed pathogenic mechanism has not been elucidated, it is thought to be related to the loss of mitochondrial function in the process of aging. Animal models that mimic the pathology of a disease are essential for understanding human diseases. In recent years, small fish have become ideal vertebrate models for human disease due to their high genetic and histological homology to humans, ease of in vivo imaging, and ease of genetic manipulation. In this review, we first outline the impact of mitochondrial dysfunction on the progression of neurodegenerative diseases. Then, we highlight the advantages of small fish as model organisms, and present examples of previous studies regarding mitochondria-related neuronal disorders. Lastly, we discuss the applicability of the turquoise killifish, a unique model for aging research, as a model for neurodegenerative diseases. Small fish models are expected to advance our understanding of the mitochondrial function in vivo, the pathogenesis of neurodegenerative diseases, and be important tools for developing therapies to treat diseases.

Hypertension and cellular senescence

Essential or primary hypertension is a wordwide health problem. Elevated blood pressure (BP) is closely associated not only with increased chronological aging but also with biological aging. There are various common pathways that play a role in cellular aging and BP regulation. These include but not limited to inflammation, oxidative stress, mitochondrial dysfunction, air pollution, decreased klotho activity increased renin angiotensin system activation, gut dysbiosis etc. It has already been shown that some anti-hypertensive drugs have anti-senescent actions and some senolytic drugs have BP lowering effects. In this review, we have summarized the common mechanisms underlying cellular senescence and HT and their relationships. We further reviewed the effect of various antihypertensive medications on cellular senescence and suggest further issues to be studied.

Determinants and outcomes of mitochondrial dynamics

Mitochondria are not only central organelles in metabolism and energy conversion but are also platforms for cellular signaling cascades. Classically, the shape and ultrastructure of mitochondria were depicted as static. The discovery of morphological transitions during cell death and of conserved genes controlling mitochondrial fusion and fission contributed to establishing the concept that mitochondrial morphology and ultrastructure are dynamically regulated by mitochondria-shaping proteins. These finely tuned, dynamic changes in mitochondrial shape can in turn control mitochondrial function, and their alterations in human diseases suggest that this space can be explored for drug discovery. Here, we review the basic tenets and molecular mechanisms of mitochondrial morphology and ultrastructure, describing how they can coordinately define mitochondrial function.

Neuroprotective Effects of the Neural-Induced Adipose-Derived Stem Cell Secretome against Rotenone-Induced Mitochondrial and Endoplasmic Reticulum Dysfunction

Mesenchymal stem cells (MSCs) have therapeutic effects on neurodegenerative diseases (NDDs) known by their secreted molecules, referred to as the “secretome”. The mitochondrial complex I inhibitor, rotenone (ROT), reproduces α-synuclein (α-syn) aggregation seen in Parkinson’s disease (PD). In this present study, we examined the neuroprotective effects of the secretome from neural-induced human adipose tissue-derived stem cells (NI-ADSC-SM) during ROT toxicity in SH-SY5Y cells. Exposure to ROT significantly impaired the mitophagy by increased LRRK2, mitochondrial fission, and endoplasmic reticulum (ER) stress (ERS). ROT also increased the levels of calcium (Ca2+), VDAC, and GRP75, and decreased phosphorylated (p)-IP3R Ser1756/total (t)-IP3R1. However, NI-ADSC-SM treatment decreased Ca2+ levels along with LRRK2, insoluble ubiquitin, mitochondrial fission by halting p-DRP1 Ser616, ERS by reducing p-PERK Thr981, p-/t-IRE1α, p-SAPK, ATF4, and CHOP. In addition, NI-ADSC-SM restored the mitophagy, mitochondrial fusion, and tethering to the ER. These data suggest that NI-ADSC-SM decreases ROT-induced dysfunction in mitochondria and the ER, which subsequently stabilized tethering in mitochondria-associated membranes in SH-SY5Y cells.

Evaluation of a Less Invasive Cochlear Implant Surgery in OPA1 Mutations Provoking Deafblindness

Cochlear implantation (CI) for deafblindness may have more impact than for non-syndromic hearing loss. Deafblind patients have a double handicap in a society that is more and more empowered by fast communication. CI is a remedy for deafness, but requires revision surgery every 20 to 25 years, and thus placement should be minimally invasive. Furthermore, failed reimplantation surgery will have more impact on a deafblind person. In this context, we assessed the safety of minimally invasive robotically assisted cochlear implant surgery (RACIS) for the first time in a deafblind patient. Standard pure tone audiometry and speech audiometry were performed in a patient with deafblindness as part of this robotic-assisted CI study before and after surgery. This patient, with an optic atrophy 1 (OPA1) (OMIM#165500) mutation consented to RACIS for the second (contralateral) CI. The applicability and safety of RACIS were evaluated as well as her subjective opinion on her disability. RACIS was uneventful with successful surgical and auditory outcomes in this case of deafblindness due to the OPA1 mutation. RACIS appears to be a safe and beneficial intervention to increase communication skills in the cases of deafblindness due to an OPA1 mutation. The use of RACIS use should be widespread in deafblindness as it minimizes surgical trauma and possible failures.

Identification of AFG3L2 dominant optic atrophy following reanalysis of clinical exome sequencing

Purpose

To highlight the importance of the utility of clinical exome sequencing, and show how it led to the diagnosis of nonsyndromic autosomal dominant optic atrophy arising from an autosomal dominant variant in AFG3L2.

Observations

A healthy father and daughter of East African heritage experienced the onset of vision loss in the first decade of life due to optic atrophy. No additional neurologic or neuroimaging abnormalities were detected. Clinical exome sequencing was initially performed and provided a negative result. Reanalysis of the sequencing data revealed an autosomal dominant pathogenic variant in AFG3L2, c.1064C>T (p.Thr355Met), a gene that was recently identified to be associated with non-syndromic optic atrophy. This variant has previously been reported in a patient with optic atrophy, motor disturbances, and an abnormal brain MRI.

Conclusions

As the causes of dominant optic atrophy continue to expand, accurate genetic diagnosis is aided by an iterative reanalysis process for individuals and families when initial exome and genome testing does not provide an answer.

Long-term blue light exposure impairs mitochondrial dynamics in the retina in light-induced retinal degeneration in vivo and in vitro

Long-term light exposure, especially in the spectrum of blue light, frequently causes excessive oxidative stress in dry age-related macular degeneration (AMD). Here, to gain insight into the underlying mechanism, we focused on mitochondrial dynamics alterations under long-term exposure to blue light in mouse and retinal cells. Six-month-old C57BL/6 mice were exposed to blue light (450 nm, 800 lx) for 2 weeks. The phenotypic changes in the retina were assayed using haematoxylin-eosin staining and transmission electron microscopy. Long-term blue light exposure significantly thinned each retinal layer in mice, induced retinal apoptosis and impaired retinal mitochondria. A retinal pigment epithelial cell line (ARPE-19) was used to verify the phototoxicity of blue light. Flow cytometry, immunofluorescence and MitoSox Red probe experiments confirmed that more total and mitochondria-specific ROS were generated in the blue light group than in the control group. Mito-Tracker Green probe showed fragmented mitochondrial morphology. The western blotting results indicated a significant increase in DRP1, OMA1, and BAX and a decrease in OPA1 and Bcl-2. In conclusion, long-term exposure to blue light damaged the retinas of mice, especially the ONL and RPE cells. There was destruction and dysfunction of mitochondria in RPE cells in vivo and in vitro. Mitochondrial dynamics were disrupted with characteristics of fusion-related obstruction after blue-light irradiation.

Reduced OPA1, Mitochondrial Fragmentation and Increased Susceptibility to Apoptosis in Granular Corneal Dystrophy Type 2 Corneal Fibroblasts

The progressive degeneration of granular corneal dystrophy type 2 (GCD2) corneal fibroblasts is associated with altered mitochondrial function, but the underlying mechanisms are incompletely understood. We investigated whether an imbalance of mitochondrial dynamics contributes to mitochondrial dysfunction of GCD2 corneal fibroblasts. Transmission electron microscopy revealed several small, structurally abnormal mitochondria with altered cristae morphology in GCD2 corneal fibroblasts. Confocal microscopy showed enhanced mitochondrial fission and fragmented mitochondrial tubular networks. Western blotting revealed higher levels of MFN1, MFN2, and pDRP1 and decreased levels of OPA1 and FIS1 in GCD2. OPA1 reduction by short hairpin RNA (shRNA) resulted in fragmented mitochondrial tubular networks and increased susceptibility to mitochondrial stress-induced apoptosis. A decrease in the mitochondrial biogenesis-related transcription factors NRF1 and PGC1α was observed, while there was an increase in the mitochondrial membrane proteins TOM20 and TIM23. Additionally, reduced levels of mitochondrial DNA (mtDNA) were exhibited in GCD2 corneal fibroblasts. These observations suggest that altered mitochondrial fission/fusion and biogenesis are the critical molecular mechanisms that cause mitochondrial dysfunction contributing to the degeneration of GCD2 corneal fibroblasts.

Mitochondrial cristae in health and disease

Mitochondria are centers of energy metabolism. The mitochondrial network is shaped by mitochondrial dynamics, including the processes of mitochondrial fission and fusion and cristae remodeling. The cristae folded by the inner mitochondrial membrane are sites of the mitochondrial oxidative phosphorylation (OXPHOS) system. However, the factors and their coordinated interplay in cristae remodeling and linked human diseases have not been fully demonstrated. In this review, we focus on key regulators of cristae structure, including the mitochondrial contact site and cristae organizing system, optic atrophy-1, mitochondrial calcium uniporter, and ATP synthase, which function in the dynamic remodeling of cristae. We summarized their contribution to sustaining functional cristae structure and abnormal cristae morphology, including a decreased number of cristae, enlarged cristae junctions, and cristae as concentric ring structures. These abnormalities directly impact cellular respiration and are caused by dysfunction or deletion of these regulators in diseases such as Parkinson's disease, Leigh syndrome, and dominant optic atrophy. Identifying the important regulators of cristae morphology and understanding their role in sustaining mitochondrial morphology could be applied to explore the pathologies of diseases and to develop relevant therapeutic tools.

Non-Coding RNA-Dependent Regulation of Mitochondrial Dynamics in Cancer Pathophysiology

Mitochondria are essential organelles which dynamically change their shape and number to adapt to various environmental signals in diverse physio-pathological contexts. Mitochondrial dynamics refers to the delicate balance between mitochondrial fission (or fragmentation) and fusion, that plays a pivotal role in maintaining mitochondrial homeostasis and quality control, impinging on other mitochondrial processes such as metabolism, apoptosis, mitophagy, and autophagy. In this review, we will discuss how dysregulated mitochondrial dynamics can affect different cancer hallmarks, significantly impacting tumor growth, survival, invasion, and chemoresistance. Special emphasis will be given to emerging non-coding RNA molecules targeting the main fusion/fission effectors, acting as novel relevant upstream regulators of the mitochondrial dynamics rheostat in a wide range of tumors.

Targeting Mitochondrial Dysfunction in Neurodegenerative Diseases: Expanding the Therapeutic Approaches by Plant-Derived Natural Products

Mitochondria are the primary source of energy production in neurons, supporting the high energy consumption of the nervous system. Inefficient and dysfunctional mitochondria in the central nervous system have been implicated in neurodegenerative diseases. Therefore, targeting mitochondria offers a new therapeutic opportunity for neurodegenerative diseases. Many recent studies have proposed that plant-derived natural products, as pleiotropic, safe, and readily obtainable sources of new drugs, potentially treat neurodegenerative diseases by targeting mitochondria. In this review, we summarize recent advances in targeting mitochondria in neurotherapeutics by employing plant-derived natural products. We discuss the mechanism of plant-derived natural products according to their mechanism of action on mitochondria in terms of regulating biogenesis, fusion, fission, bioenergetics, oxidative stress, calcium homeostasis, membrane potential, and mitochondrial DNA stability, as well as repairing damaged mitochondria. In addition, we discuss the potential perspectives and challenges in developing plant-derived natural products to target mitochondria, highlighting the clinical value of phytochemicals as feasible candidates for future neurotherapeutics.

Mitochondrial movers and shapers: Recent insights into regulators of fission, fusion and transport

Mitochondria are highly dynamic organelles that undergo rapid morphological adaptations influencing their number, transport, cellular distribution, and function, which in turn facilitate the integration of mitochondrial function with physiological changes in the cell. These mitochondrial dynamics are dependent on tightly regulated processes such as fission, fusion, and attachment to the cytoskeleton, and their defects are observed in various pathophysiological conditions including cancer, cardiovascular disease, and neurodegeneration. Various studies over the years have identified key molecular players and uncovered the mechanisms that mediate and regulate these processes and have highlighted their complexity and context-specificity. This review focuses on the recent studies that have contributed to the understanding of processes that influence mitochondrial morphology including fission, fusion, and transport in the cell.

Current Advances in Gene Therapies of Genetic Auditory Neuropathy Spectrum Disorder

Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing impairments characterized by an impaired transmission of sound from the cochlea to the brain. This defect can be due to a lesion or defect in the inner hair cell (IHC), IHC ribbon synapse (e.g., pre-synaptic release of glutamate), postsynaptic terminals of the spiral ganglion neurons, or demyelination and axonal loss within the auditory nerve. To date, the only clinical treatment options for ANSD are hearing aids and cochlear implantation. However, despite the advances in hearing-aid and cochlear-implant technologies, the quality of perceived sound still cannot match that of the normal ear. Recent advanced genetic diagnostics and clinical audiology made it possible to identify the precise site of a lesion and to characterize the specific disease mechanisms of ANSD, thus bringing renewed hope to the treatment or prevention of auditory neurodegeneration. Moreover, genetic routes involving the replacement or corrective editing of mutant sequences or defected genes to repair damaged cells for the future restoration of hearing in deaf people are showing promise. In this review, we provide an update on recent discoveries in the molecular pathophysiology of genetic lesions, auditory synaptopathy and neuropathy, and gene-therapy research towards hearing restoration in rodent models and in clinical trials.

Ovarian Cancer: A Landscape of Mitochondria with Emphasis on Mitochondrial Dynamics

Ovarian cancer (OC) represents the main cause of death from gynecological malignancies in western countries. Altered cellular and mitochondrial metabolism are considered hallmarks in cancer disease. Several mitochondrial aspects have been found altered in OC, such as the oxidative phosphorylation system, oxidative stress and mitochondrial dynamics. Mitochondrial dynamics includes cristae remodeling, fusion, and fission processes forming a dynamic mitochondrial network. Alteration of mitochondrial dynamics is associated with metabolic change in tumour development and, in particular, the mitochondrial shaping proteins appear also to be responsible for the chemosensitivity and/or chemoresistance in OC. In this review a focus on the mitochondrial dynamics in OC cells is presented.

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.

Humic substances from composted fennel residues control the inflammation induced by Helicobacter pylori infection in AGS cells

Helicobacter pylori (H. pylori) is a common human pathogen causing inflammation. Recent studies have suggested a sophisticated interplay between mitochondria, innate immunity and inflammatory response, thus proposing mitochondrial disfunction as the hallmark of severe inflammatory disorders. In this study, humic substances isolated from composted fennel residues (HS-FEN) were tested as potential therapeutical strategy to restore the mitochondrial physiology and control the inflammation associated with H. pylori infection. The molecular features of HS-FEN were characterized by infrared spectrometry, thermochemolysis-GC/MS, NMR spectroscopy, and high-performance size-exclusion chromatography (HPSEC), which revealed the presence of aromatic polyphenolic components arranged in a rather stable conformation. In vitro results showed antioxidant and anti-inflammatory properties of HS-FEN, that was found to increase the expression level of OPA-1 and SOD-2 genes and in AGS cells stimulated with H. pylori culture filtrate (Hpcf) and concomitantly decrease the expression level of Drp-1 gene and IL-12, IL-17 and G-CSF proteins. The hydrophobic features of HS, their conformational arrangement and large content of bioactive molecules may explain the beneficial effects of HS-FEN, that may potentially become an interesting source of anti-inflammatory agents capable to counteract or prevent the H. pylori-related inflammatory disorders.

The status and trends of mitochondrial dynamics research: A global bibliometric and visualized analysis

BACKGROUND

Mitochondria are remarkably dynamic organelles encapsulated by bilayer membranes. The dynamic properties of mitochondria are critical for energy production.

AIMS

The aim of our study is to investigate the global status and trends of mitochondrial dynamics research and predict popular topics and directions in the field.

METHODS

Publications related to the studies of mitochondrial dynamics from 2002 to 2021 were retrieved from Web of Science database. A total of 4,576 publications were included. Bibliometric analysis was conducted by visualization of similarities viewer and GraphPadPrism 5 software.

RESULTS

There is an increasing trend of mitochondrial dynamics research during the last 20 years. The cumulative number of publications about mitochondrial dynamics research followed the logistic growth model [Formula: see text]. The USA made the highest contributions to the global research. The journal Biochimica et Biophysica Acta (BBA)-Molecular Cell Research had the largest publication numbers. Case Western Reserve University is the most contributive institution. The main research orientation and funding agency were cell biology and HHS. All keywords related studies could be divided into three clusters: "Related disease research", "Mechanism research" and "Cell metabolism research".

CONCLUSIONS

Attention should be drawn to the latest popular research and more efforts will be put into mechanistic research, which may inspire new clinical treatments for the associated diseases.

PD98059 protects SH-SY5Y cells against oxidative stress in oxygen-glucose deprivation/reperfusion

Mitochondria play a key role in the cerebral ischemia-reperfusion injury. Although the extracellular signal-regulated kinase 1/2 inhibitor PD98059 (PD) is a selective and reversible flavonoid that can protect the mitochondria in a rat model of cardiac arrest/cardiopulmonary resuscitation, its role requires further confirmation. In this study, we investigated whether PD could maintain mitochondrial homeostasis and decrease reactive oxygen species (ROS) production in neuroblastoma (SH-SY5Y) cells exposed to oxygen-glucose deprivation/reperfusion (OGD/R). PD improved the mitochondrial morphology and function, reversed the increase in ROS production and cell apoptosis, and reduced total-superoxide dismutase and Mn-superoxide dismutase activities induced by OGD/R. PD decreases ROS production and improves mitochondrial morphology and function, protecting SH-SY5Y cells against OGD/R-induced injury.

mtDNA Maintenance and Alterations in the Pathogenesis of Neurodegenerative Diseases

Considerable evidence indicates that the semiautonomous organelles mitochondria play key roles in the progression of many neurodegenerative disorders. Mitochondrial DNA (mtDNA) encodes components of the OXPHOS complex but mutated mtDNA accumulates in cells with aging, which mirrors the increased prevalence of neurodegenerative diseases. This accumulation stems not only from the misreplication of mtDNA and the highly oxidative environment but also from defective mitophagy after fission. In this review, we focus on several pivotal mitochondrial proteins related to mtDNA maintenance (such as ATAD3A and TFAM), mtDNA alterations including mtDNA mutations, mtDNA elimination, and mtDNA release-activated inflammation to understand the crucial role played by mtDNA in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Our work outlines novel therapeutic strategies for targeting mtDNA.

Exercise and mitochondrial remodeling to prevent age-related neurodegeneration

Healthy brain activity requires precise ion and energy management creating a strong reliance on mitochondrial function. Age-related neurodegeneration leads to a decline in mitochondrial function and increased oxidative stress, with associated declines in mitochondrial mass, respiration capacity, and respiration efficiency. The interdependent processes of mitochondrial protein turnover and mitochondrial dynamics, known together as mitochondrial remodeling, play essential roles in mitochondrial health and therefore brain function. This mini-review describes the role of mitochondria in neurodegeneration and brain health, current practices for assessing both aspects of mitochondrial remodeling, and how exercise mitigates the adverse effects of aging in the brain. Exercise training elicits functional adaptations to improve brain health, and current literature strongly suggests that mitochondrial remodeling plays a vital role in these positive adaptations. Despite substantial implications that the two aspects of mitochondrial remodeling are interdependent, very few investigations have simultaneously measured mitochondrial dynamics and protein synthesis. An improved understanding of the partnership between mitochondrial protein turnover and mitochondrial dynamics will provide a better understanding of their role in both brain health and disease, as well as how they induce protection following exercise.

Melatonin protects oocytes from cadmium exposure-induced meiosis defects by changing epigenetic modification and enhancing mitochondrial morphology in the mouse

Cadmium (Cd) is one major environmental pollutant that can cause detrimental impacts on human as well as animal reproductive systems as a result of oxidative stress. It is widely acknowledged that melatonin secreted principally by the pineal gland is not only a natural potent antioxidant but also a free radical scavenger, whereas concerning how to alleviate the toxic effects of Cd on oocyte maturation remains elusive. In this investigation, it was the first time to explore the protective effects and potential mechanism of melatonin on meiotic maturation of mouse oocytes exposed to Cd in vitro medium. We found that Cd exerts adverse effects on meiotic maturation progression by disrupting the normal function of mitochondrion combined with the aberrant mitochondrial distribution and decreased membrane potential and altering epigenetic modification, including H3K9me2 and H3K4me2. Additionally, it was observed that Cd exposure disrupted the morphology of spindle organization and caused chromosome misalignment, which might be through changing the level of acetylated tubulin, whereas melatonin administration alleviated the toxic impacts of Cd on oocytes. Furthermore, the mitochondrial morphology-related genes mRNA expression and protein expression of autophagy-related genes was also investigated. The results suggested that melatonin supplementation significantly altered the mRNA expression of mitochondrial dynamics-related genes, rather than the expression of mitophagy-related proteins. Taken together, our results validated that melatonin administration has a certain protective impact against oocytes meiosis maturation defects induced by cadmium through changing epigenetic modification and enhancing mitochondrial morphology rather than mitophagy.

Opa1 and Drp1 reciprocally regulate cristae morphology, ETC function, and NAD+ regeneration in KRas-mutant lung adenocarcinoma

Oncogenic KRas activates mitochondrial fission through Erk-mediated phosphorylation of the mitochondrial fission GTPase Drp1. Drp1 deletion inhibits tumorigenesis of KRas-driven pancreatic cancer, but the role of mitochondrial dynamics in other Ras-driven malignancies is poorly defined. Here we show that in vitro and in vivo growth of KRas-driven lung adenocarcinoma is unaffected by deletion of Drp1 but is inhibited by deletion of Opa1, the GTPase that regulates inner membrane fusion and proper cristae morphology. Mechanistically, Opa1 knockout disrupts cristae morphology and inhibits electron transport chain (ETC) assembly and activity, which inhibits tumor cell proliferation through loss of NAD+ regeneration. Simultaneous inactivation of Drp1 and Opa1 restores cristae morphology, ETC activity, and cell proliferation indicating that mitochondrial fission activity drives ETC dysfunction induced by Opa1 knockout. Our results support a model in which mitochondrial fission events disrupt cristae structure, and tumor cells with hyperactive fission activity require Opa1 activity to maintain ETC function.

TMBIM5 is the Ca2+ /H+ antiporter of mammalian mitochondria

Mitochondrial Ca2+ ions are crucial regulators of bioenergetics and cell death pathways. Mitochondrial Ca2+ content and cytosolic Ca2+ homeostasis strictly depend on Ca2+ transporters. In recent decades, the major players responsible for mitochondrial Ca2+ uptake and release have been identified, except the mitochondrial Ca2+ /H+ exchanger (CHE). Originally identified as the mitochondrial K+ /H+ exchanger, LETM1 was also considered as a candidate for the mitochondrial CHE. Defining the mitochondrial interactome of LETM1, we identify TMBIM5/MICS1, the only mitochondrial member of the TMBIM family, and validate the physical interaction of TMBIM5 and LETM1. Cell-based and cell-free biochemical assays demonstrate the absence or greatly reduced Na+ -independent mitochondrial Ca2+ release in TMBIM5 knockout or pH-sensing site mutants, respectively, and pH-dependent Ca2+ transport by recombinant TMBIM5. Taken together, we demonstrate that TMBIM5, but not LETM1, is the long-sought mitochondrial CHE, involved in setting and regulating the mitochondrial proton gradient. This finding provides the final piece of the puzzle of mitochondrial Ca2+ transporters and opens the door to exploring its importance in health and disease, and to developing drugs modulating Ca2+ exchange.

Sericin-mediated improvement of dysmorphic cardiac mitochondria from hypercholesterolaemia is associated with maintaining mitochondrial dynamics, energy production, and mitochondrial structure

CONTEXT

Sericin is a component protein in the silkworm cocoon [Bombyx mori Linnaeus (Bombycidae)] that improves dysmorphic cardiac mitochondria under hypercholesterolemic conditions. This is the first study to explore cardiac mitochondrial proteins associated with sericin treatment.

OBJECTIVE

To investigate the mechanism of action of sericin in cardiac mitochondria under hypercholesterolaemia.

MATERIALS AND METHODS

Hypercholesterolaemia was induced in Wistar rats by feeding them 6% cholesterol-containing chow for 6 weeks. The hypercholesterolemic rats were separated into 2 groups (n = 6 for each): the sericin-treated (1,000 mg/kg daily) and nontreated groups. The treatment conditions were maintained for 4 weeks prior to cardiac mitochondria isolation. The mitochondrial structure was evaluated by immunolabeling electron microscopy, and differential mitochondrial protein expression was determined and quantitated by two-dimensional gel electrophoresis coupled with mass spectrometry.

RESULTS

A 32.22 ± 2.9% increase in the percent striated area of cardiac muscle was observed in sericin-treated hypercholesterolemic rats compared to the nontreatment group (4.18 ± 1.11%). Alterations in mitochondrial proteins, including upregulation of optic atrophy 1 (OPA1) and reduction of NADH-ubiquinone oxidoreductase 75 kDa subunit (NDUFS1) expression, are correlated with a reduction in mitochondrial apoptosis under sericin treatment. Differential proteomic observation also revealed that sericin may improve mitochondrial energy production by upregulating acetyl-CoA acetyltransferase (ACAT1) and NADH dehydrogenase 1α subcomplex subunit 10 (NDUFA10) expression.

DISCUSSION AND CONCLUSIONS

Sericin treatment could improve the dysmorphic mitochondrial structure, metabolism, and energy production of cardiac mitochondria under hypercholesterolaemia. These results suggest that sericin may be an alternative treatment molecule that is related to cardiac mitochondrial abnormalities.

Sirt3 mitigates LPS-induced mitochondrial damage in renal tubular epithelial cells by deacetylating YME1L1

Acute kidney injury (AKI) is often secondary to sepsis. Increasing evidence suggests that mitochondrial dysfunction contributes to the pathological process of AKI. In this study, we aimed to examine the regulatory roles of Sirt3 in Lipopolysaccharide (LPS)-induced mitochondrial damage in renal tubular epithelial cells (TECs). Sirt3 knockout mice were intraperitoneally injected with LPS, and cultured TECs were stimulated with LPS to evaluate the effects of Sirt3 on mitochondrial structure and function in TECs. Electron microscopy was used to assess mitochondrial morphology. Immunofluorescence staining was performed to detect protein expression and examine mitochondrial morphology. Western blotting was used to quantify protein expression. We observed that LPS increased apoptosis, induced disturbances in mitochondrial function and dynamics, and downregulated Sirt3 expression in a sepsis-induced AKI mouse model and human proximal tubular (HK-2) cells in vitro. Sirt3 deficiency further exacerbated LPS-induced renal pathological damage, apoptosis and disturbances in mitochondrial function and dynamics. On the contrary, Sirt3 overexpression in HK-2 cells alleviated these lesions. Functional studies revealed that Sirt3 overexpression alleviated LPS-induced mitochondrial damage and apoptosis in TECs by promoting OPA1-mediated mitochondrial fusion through the deacetylation of i-AAA protease (YME1L1), an upstream regulatory molecule of OPA1. Our study has identified Sirt3 as a vital factor that protects against LPS-induced mitochondrial damage and apoptosis in TECs via the YME1L1-OPA1 signaling pathway.

The mycotoxin viriditoxin induces leukemia- and lymphoma-specific apoptosis by targeting mitochondrial metabolism

Inhibition of the mitochondrial metabolism offers a promising therapeutic approach for the treatment of cancer. Here, we identify the mycotoxin viriditoxin (VDT), derived from the endophytic fungus Cladosporium cladosporioides, as an interesting candidate for leukemia and lymphoma treatment. VDT displayed a high cytotoxic potential and rapid kinetics of caspase activation in Jurkat leukemia and Ramos lymphoma cells in contrast to solid tumor cells that were affected to a much lesser extent. Most remarkably, human hematopoietic stem and progenitor cells and peripheral blood mononuclear cells derived from healthy donors were profoundly resilient to VDT-induced cytotoxicity. Likewise, the colony-forming capacity was affected only at very high concentrations, which provides a therapeutic window for cancer treatment. Intriguingly, VDT could directly activate the mitochondrial apoptosis pathway in leukemia cells in the presence of antiapoptotic Bcl-2 proteins. The mitochondrial toxicity of VDT was further confirmed by inhibition of mitochondrial respiration, breakdown of the mitochondrial membrane potential (ΔΨm), the release of mitochondrial cytochrome c, generation of reactive oxygen species (ROS), processing of the dynamin-like GTPase OPA1 and subsequent fission of mitochondria. Thus, VDT-mediated targeting of mitochondrial oxidative phosphorylation (OXPHOS) might represent a promising therapeutic approach for the treatment of leukemia and lymphoma without affecting hematopoietic stem and progenitor cells.

Berberine mitigates hepatic insulin resistance by enhancing mitochondrial architecture via the SIRT1/Opa1 signalling pathway

The aberrant changes of fussion/fission-related proteins can trigger mitochondrial dynamics imbalance, which cause mitochondrial dysfunctions and result insulin resistance (IR). However, the relationship between the inner mitochondrial membrane fusion protein optic atrophy 1 (Opa1) and hepatic IR as well as the specific molecular mechanisms of signal transduction has not been fully elucidated. In this study, we explore whether abnormalities in the Opa1 cause hepatic IR and whether berberine (BBR) can prevent hepatic IR through the SIRT1/Opa1 signalling pathway. High-fat diet (HFD)-fed mice and db/db mice are used as animal models to study hepatic IR in vivo. IR, morphological changes, and mitochondrial injury of the liver are examined to explore the effects of BBR. SIRT1/Opa1 protein expression is determined to confirm whether the signalling pathway is damaged in the model animals and is involved in BBR treatment-mediated mitigation of hepatic IR. A palmitate (PA)-induced hepatocyte IR model is established in HepG2 cells in vitro. Opa1 silencing and SIRT1 overexpression are induced to verify whether Opa1 deficiency causes hepatocyte IR and whether SIRT1 improves this dysfunction. BBR treatment and SIRT1 silencing are employed to confirm that BBR can prevent hepatic IR by activating the SIRT1/Opa1 signalling pathway. Western blot analysis and JC-1 fluorescent staining results show that Opa1 deficiency causes an imbalance in mitochondrial fusion/fission and impairs insulin signalling in HepG2 cells. SIRT1 and BBR overexpression ameliorates PA-induced IR, increases Opa1, and improves mitochondrial function. SIRT1 silencing partly reverses the effects of BBR on HepG2 cells. SIRT1 and Opa1 expressions are downregulated in the animal models. BBR attenuates hepatic IR and enhances SIRT1/Opa1 signalling in db/db mice. In summary, Opa1 silencing-mediated mitochondrial fusion/fission imbalance could lead to hepatocyte IR. BBR may improve hepatic IR by regulating the SIRT1/Opa1 signalling pathway, and thus, it may be used to treat type-2 diabetes.

Modelling autosomal dominant optic atrophy associated with OPA1 variants in iPSC-derived retinal ganglion cells

Autosomal dominant optic atrophy (DOA) is the most common inherited optic neuropathy, characterized by the preferential loss of retinal ganglion cells (RGCs), resulting in optic nerve degeneration and progressive bilateral central vision loss. More than 60% of genetically confirmed patients with DOA carry variants in the nuclear OPA1 gene, which encodes for a ubiquitously expressed, mitochondrial GTPase protein. OPA1 has diverse functions within the mitochondrial network, facilitating inner membrane fusion and cristae modelling, regulating mitochondrial DNA maintenance and coordinating mitochondrial bioenergetics. There are currently no licensed disease-modifying therapies for DOA and the disease mechanisms driving RGC degeneration are poorly understood. Here, we describe the generation of isogenic, heterozygous OPA1 null induced pluripotent stem cell (iPSC) (OPA1+/-) through clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing of a control cell line, in conjunction with the generation of DOA patient-derived iPSC carrying OPA1 variants, namely, the c.2708_2711delTTAG variant (DOA iPSC), and previously reported missense variant iPSC line (c.1334G>A, DOA plus [DOA]+ iPSC) and CRISPR/Cas9 corrected controls. A two-dimensional (2D) differentiation protocol was used to study the effect of OPA1 variants on iPSC-RGC differentiation and mitochondrial function. OPA1+/-, DOA and DOA+ iPSC showed no differentiation deficit compared to control iPSC lines, exhibiting comparable expression of all relevant markers at each stage of differentiation. OPA1+/- and OPA1 variant iPSC-RGCs exhibited impaired mitochondrial homeostasis, with reduced bioenergetic output and compromised mitochondrial DNA maintenance. These data highlight mitochondrial deficits associated with OPA1 dysfunction in human iPSC-RGCs, and establish a platform to study disease mechanisms that contribute to RGC loss in DOA, as well as potential therapeutic interventions.

LIX1-mediated changes in mitochondrial metabolism control the fate of digestive mesenchyme-derived cells

YAP1 and TAZ are transcriptional co-activator proteins that play fundamental roles in many biological processes, from cell proliferation and cell lineage fate determination to tumorigenesis. We previously demonstrated that Limb Expression 1 (LIX1) regulates YAP1 and TAZ activity and controls digestive mesenchymal progenitor proliferation. However, LIX1 mode of action remains elusive. Here, we found that endogenous LIX1 is localized in mitochondria and is anchored to the outer mitochondrial membrane through S-palmitoylation of cysteine 84, a residue conserved in all LIX1 orthologs. LIX1 downregulation altered the mitochondrial ultrastructure, resulting in a significantly decreased respiration and attenuated production of mitochondrial reactive oxygen species (mtROS). Mechanistically, LIX1 knock-down impaired the stability of the mitochondrial proteins PHB2 and OPA1 that are found in complexes with mitochondrial-specific phospholipids and are required for cristae organization. Supplementation with unsaturated fatty acids counteracted the effects of LIX1 knock-down on mitochondrial morphology and ultrastructure and restored YAP1/TAZ signaling. Collectively, our data demonstrate that LIX1 is a key regulator of cristae organization, modulating mtROS level and subsequently regulating the signaling cascades that control fate commitment of digestive mesenchyme-derived cells.

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LIX1 is tightly anchored to the outer membrane of mitochondria.

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LIX1 mitochondrial localization is mediated by S-palmitoylation on cysteine 84.

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LIX1 knock-down reduces the stability of the mitochondrial proteins PHB2 and OPA1 and impairs cristae organization.

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Redox signaling modulations regulate YAP1/TAZ activity and control fate commitment of digestive mesenchyme-derived cells.

Mitochondrial organization and structure are compromised in fibroblasts from patients with Huntington's disease

Huntington´s disease (HD) is a progressive neurodegenerative disease with onset in adulthood that leads to a complete disability and death in approximately 20 years after onset of symptoms. HD is caused by an expansion of a CAG triplet in the gene for huntingtin. Although the disease causes most damage to striatal neurons, other parts of the nervous system and many peripheral tissues are also markedly affected. Besides huntingtin malfunction, mitochondrial impairment has been previously described as an important player in HD. This study focuses on mitochondrial structure and function in cultivated skin fibroblasts from 10 HD patients to demonstrate mitochondrial impairment in extra-neuronal tissue. Mitochondrial structure, mitochondrial fission, and cristae organization were significantly disrupted and signs of elevated apoptosis were found. In accordance with structural changes, we also found indicators of functional alteration of mitochondria. Mitochondrial disturbances presented in fibroblasts from HD patients confirm that the energy metabolism damage in HD is not localized only to the central nervous system, but also may play role in the pathogenesis of HD in peripheral tissues. Skin fibroblasts can thus serve as a suitable cellular model to make insight into HD pathobiochemical processes and for the identification of possible targets for new therapies.

The Genetics of Ethambutol-Induced Optic Neuropathy: A Narrative Review

Tuberculosis (TB) is a global health problem with the major brunt of disease occurring in developing countries. The cornerstone of treatment of TB is anti-tubercular therapy (ATT), which includes rifampicin, isoniazid, pyrazinamide and ethambutol. Because of emerging drug resistance, treatment failures, defaulters and increasing incidence of disseminated and extrapulmonary TB, the guidelines have been modified in some countries. Ethambutol is prescribed for longer times (in some cases >8 months) and hence the incidence of ethambutol-induced optic neuropathy (EtON) is expected to rise. The fundamental question which needs explanation is why only a small subset of patients on ethambutol are prone to develop loss of vision. This review focuses on available genetic studies which provide evidence that mitochondria are the likely substrates involved in the final pathway of reactive oxidative damage of the papillo-macular bundle. Genetic analysis of mitochondrial mutations encoding genes involved in oxidative phosphorylation pathways may help in isolating the subset of patients who are genetically susceptible. If the groups having high risk of developing EtON are recognised then prolonged duration of ethambutol treatment can be avoided in these susceptible individuals. A better understanding of the pathophysiology will also pave the way for the development of management strategies in this condition.

Cochlear Implantation Outcomes in Patients with Auditory Neuropathy Spectrum Disorder of Genetic and Non-Genetic Etiologies: A Multicenter Study

With diverse etiologies and clinical features, the management of pediatric auditory neuropathy spectrum disorder (ANSD) is often challenging, and the outcomes of cochlear implants (CIs) are variable. This study aimed to investigate CI outcomes in pediatric patients with ANSD of different etiologies. Thirty-six children with ANSD who underwent cochlear implantation between 2001 and 2021 were included. Comprehensive etiological analyses were conducted, including a history review, next-generation sequencing-based genetic examinations, and imaging studies using high-resolution computed tomography and magnetic resonance imaging. Serial behavioral and speech audiometry were performed before and after surgery, and the outcomes with CI were evaluated using the Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) scores. By etiology, 18, 1, 1, and 10 patients had OTOF-related, WFS1-related, OPA1-related, and cochlear nerve deficiency (CND)-related ANSD, respectively. Six patients had no definite etiology. The average CI-aided behavioral threshold was 28.3 ± 7.8 dBHL, and those with CND-related ANSD were significantly worse than OTOF-related ANSD. The patients’ median CAP and SIR scores were 6 and 4, respectively. Favorable CI outcomes were observed in patients with certain etiologies of ANSD, particularly those with OTOF (CAP/SIR scores 5–7/2–5), WFS1 (CAP/SIR score 6/5), and OPA1 variants (CAP/SIR score 7/5). Patients with CND had suboptimal CI outcomes (CAP/SIR scores 2–6/1–3). Identifying the etiologies in ANSD patients is crucial before surgery and can aid in predicting prognoses.

CHCHD10 and SLP2 control the stability of the PHB complex: a key factor for motor neuron viability

CHCHD10 is an amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) gene that encodes a mitochondrial protein whose precise function is unclear. Here we show that CHCHD10 interacts with the Stomatin-Like Protein 2 (SLP2) and participates to the stability of the Prohibitin (PHB) complex in the inner mitochondrial membrane. By using patient fibroblasts and mouse models expressing the same CHCHD10 variant (p.Ser59Leu), we show that SLP2 forms aggregates with prohibitins, found in vivo in the hippocampus and as aggresome-like inclusions in spinal motor neurons of Chchd10S59L/+ mice. Affected cells and tissues display instability of the PHB complex which participates at least in part to the activation of the OMA1 cascade with OPA1 processing leading to mitochondrial fragmentation, abnormal mitochondrial cristae morphogenesis and neuronal death found in spinal cord and the hippocampus of Chchd10S59L/+ animals. Destabilization of the PHB complex leads to the instability of the mitochondrial contact site and cristae organizing system (MICOS) complex, likely via the disruption of OPA1/Mitofilin interaction. Thus, SLP2/PHB aggregates and destabilization of the PHB complex are critical in the sequence of events leading to motor neuron death in CHCHD10S59L-related disease.

Differential Retinal Ganglion Cell Vulnerability, A Critical Clue for the Identification of Neuroprotective Genes in Glaucoma

Retinal ganglion cells (RGCs) are the neurons in the retina which directly project to the brain and transmit visual information along the optic nerve. Glaucoma, one of the leading causes of blindness, is characterized by elevated intraocular pressure (IOP) and degeneration of the optic nerve, which is followed by RGC death. Currently, there are no clinical therapeutic drugs or molecular interventions that prevent RGC death outside of IOP reduction. In order to overcome these major barriers, an increased number of studies have utilized the following combined analytical methods: well-established rodent models of glaucoma including optic nerve injury models and transcriptomic gene expression profiling, resulting in the successful identification of molecules and signaling pathways relevant to RGC protection. In this review, we present a comprehensive overview of pathological features in a variety of animal models of glaucoma and top differentially expressed genes (DEGs) depending on disease progression, RGC subtypes, retinal regions or animal species. By comparing top DEGs among those different transcriptome profiles, we discuss whether commonly listed DEGs could be defined as potential novel therapeutic targets in glaucoma, which will facilitate development of future therapeutic neuroprotective strategies for treatments of human patients in glaucoma.

Drp1-mediated mitochondrial fission promotes carbon tetrachloride-induced hepatic fibrogenesis in mice

Background

Mitochondrial dynamics is essential for the maintenance of healthy mitochondrial network. Emerging evidence suggests that mitochondrial dysfunction is closely linked to the pathogenesis of hepatic fibrogenesis following chronic liver injury. However, the role of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission in the context of liver fibrosis remains unclear.

Methods and Results

In this study, C57BL/6 mice were used to establish a model of liver fibrosis via oral gavage with CCl4 treatment for 8 weeks. Furthermore, mitochondrial fission intervention experiments were achieved by the mitochondrial division inhibitor 1 (Mdivi-1). The results demonstrated that chronic CCl4 exposure resulted in severe hepatic fibrogenesis and mitochondrial damage. By contrast, pharmacological inhibition of mitochondrial division by Mdivi-1 substantially reduced the changes of mitochondrial dynamics and finally prevented the deposition of extracellular matrix proteins. Mechanistically, excessive mitochondrial fission may activate hepatic stellate cells through RIPK1-MLKL-dependent hepatocyte death, which ultimately promotes liver fibrosis.

Conclusion

Our study imply that inhibiting Drp1-mediated mitochondrial fission attenuates CCl4-induced liver fibrosis and may serve as a therapeutic target for retarding progression of chronic liver disease.

Current Understanding of the Pivotal Role of Mitochondrial Dynamics in Cardiovascular Diseases and Senescence

The heart is dependent on ATP production in mitochondria, which is closely associated with cardiovascular disease because of the oxidative stress produced by mitochondria. Mitochondria are highly dynamic organelles that constantly change their morphology to elongated (fusion) or small and spherical (fission). These mitochondrial dynamics are regulated by various small GTPases, Drp1, Fis1, Mitofusin, and Opa1. Mitochondrial fission and fusion are essential to maintain a balance between mitochondrial biogenesis and mitochondrial turnover. Recent studies have demonstrated that mitochondrial dynamics play a crucial role in the development of cardiovascular diseases and senescence. Disruptions in mitochondrial dynamics affect mitochondrial dysfunction and cardiomyocyte survival leading to cardiac ischemia/reperfusion injury, cardiomyopathy, and heart failure. Mitochondrial dynamics and reactive oxygen species production have been associated with endothelial dysfunction, which in turn causes the development of atherosclerosis, hypertension, and even pulmonary hypertension, including pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. Here, we review the association between cardiovascular diseases and mitochondrial dynamics, which may represent a potential therapeutic target.

Clinical and genetic spectrums of 413 North African families with inherited retinal dystrophies and optic neuropathies

Background

Inherited retinal dystrophies (IRD) and optic neuropathies (ION) are the two major causes world-wide of early visual impairment, frequently leading to legal blindness. These two groups of pathologies are highly heterogeneous and require combined clinical and molecular diagnoses to be securely identified. Exact epidemiological studies are lacking in North Africa, and genetic studies of IRD and ION individuals are often limited to case reports or to some families that migrated to the rest of the world. In order to improve the knowledge of their clinical and genetic spectrums in North Africa, we reviewed published data, to illustrate the most prevalent pathologies, genes and mutations encountered in this geographical region, extending from Morocco to Egypt, comprising 200 million inhabitants.

Main body

We compiled data from 413 families with IRD or ION together with their available molecular diagnosis. The proportion of IRD represents 82.8% of index cases, while ION accounted for 17.8%. Non-syndromic IRD were more frequent than syndromic ones, with photoreceptor alterations being the main cause of non-syndromic IRD, represented by retinitis pigmentosa, Leber congenital amaurosis, and cone-rod dystrophies, while ciliopathies constitute the major part of syndromic-IRD, in which the Usher and Bardet Biedl syndromes occupy 41.2% and 31.1%, respectively. We identified 71 ION families, 84.5% with a syndromic presentation, while surprisingly, non-syndromic ION are scarcely reported, with only 11 families with autosomal recessive optic atrophies related to OPA7 and OPA10 variants, or with the mitochondrial related Leber ION. Overall, consanguinity is a major cause of these diseases within North African countries, as 76.1% of IRD and 78.8% of ION investigated families were consanguineous, explaining the high rate of autosomal recessive inheritance pattern compared to the dominant one. In addition, we identified many founder mutations in small endogamous communities.

Short conclusion

As both IRD and ION diseases constitute a real public health burden, their under-diagnosis in North Africa due to the absence of physicians trained to the identification of inherited ophthalmologic presentations, together with the scarcity of tools for the molecular diagnosis represent major political, economic and health challenges for the future, to first establish accurate clinical diagnoses and then treat patients with the emergent therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02340-7.