The Good and the Bad of Mitochondrial Breakups

Morphometric analysis of the sperm midpiece during capacitation

In mammalian sperm, mitochondria are very densely packed and form a helical sheath in the midpiece of the flagellum. Mitochondria from somatic cells can rapidly change shape to adapt to environmental conditions. During capacitation, mammalian spermatozoa undergo morphological and physiological changes to acquire fertilization ability, evidenced by changes in sperm motility patterns (hyperactivation) and the ability to perform the acrosome reaction. Whether there are changes in sperm mitochondrial morphology during capacitation is unknown. This work aimed to quantify morphometric changes in the sperm midpiece during capacitation. Using mitochondrial fluorescent probes and a combination of freely available software, we quantified the dimensions and fluorescence intensity of the midpiece. After capacitation, the area occupied by the mitochondria decreased due to a reduction in the width but not the length of the midpiece. The decrease in the area of the midpiece occurred in spermatozoa that underwent the acrosome reaction, suggesting a reorganization of the mitochondria during capacitation. Ultrastructural analysis supported these results. The application of image processing to fluorescence microscopy images may help to identify morphological changes during capacitation.

Fibroblast growth factor 8 (FGF8) induces mitochondrial remodeling in chondrocytes via ERK/AMPK signaling pathway

Osteoarthritis (OA) is a disease characterized by articular cartilage degeneration, and its pathogenic mechanisms are associated with mitochondrial homeostasis disorders. Fibroblast growth factor 8 (FGF8) is a multipotent protein ligand which is upregulated in OA cartilage. However, the molecular mechanisms by which FGF8 regulates mitochondria in chondrocytes are not yet fully understood. Here, we treated chondrocytes with FGF8 and detected the effects of FGF8 on mitochondrial morphology in the cytoplasm using transmission electron and confocal laser scanning microscopy. ATP levels were measured to determine the cellular energy status. Western blotting and immunofluorescence staining experiments were employed to detect the fusion-fission proteins mitofusin 1 (MFN1), mitofusin 2 (MFN2), optic atrophy 1 (OPA1), dynamin-related protein 1 (DRP1), mitochondrial fission 1 protein (FIS1), and related signaling pathways. The FGF receptor (FGFR) inhibitor, AZD4547, and the ERK inhibitor, U0126, were used to verify the specific effects of the FGFR and ERK pathways. We found that FGF8 regulated mitochondrial morphology and dynamics in chondrocytes by inducing mitochondrial elongation. While it upregulated fusion proteins MFN1, MFN2, and OPA1, FGF8 downregulated fission proteins DRP1 and FIS1. ERK and AMPK pathways were activated in chondrocytes after FGF8 treatment. In contrast, both AZD4547 and U0126 inhibitors abolished mitochondrial elongation as well as the alteration of fusion-fission proteins induced by FGF8, and U0126 also inhibited the FGF8-triggered activation of AMPK. This study is the first to reveal that FGF8 remodels mitochondria through ERK/AMPK signaling in chondrocytes, offering novel insights into the potential role of FGF8 in OA.

Control of Mitochondrial Quality: A Promising Target for Diabetic Kidney Disease Treatment

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD), affecting over 40% of patients with diabetes. DKD progression involves fibrosis and damage to glomerular and tubulointerstitial regions, with mitochondrial dysfunction playing a critical role. Impaired mitochondria lead to reduced adenosine triphosphate (ATP) production, damaged mitochondria accumulation, and increased reactive oxygen species (ROS), contributing to renal deterioration. Maintaining mitochondrial quality control (MQC) is essential for preventing cell death, tissue injury, and kidney failure. Recent clinical trials show that enhancing MQC can alleviate DKD. However, current treatments cannot halt kidney function decline, underscoring the need for new therapeutic strategies. Mitochondrial-targeted drugs show potential; however, challenges remain because of adverse effects and unclear mechanisms. Future research should aim to comprehensively explore therapeutic potential of MQC in DKD. This review highlights the significance of MQC in DKD treatment, emphasizing the need to maintain mitochondrial quality for developing new therapies.

Senolysis by GLS1 Inhibition Ameliorates Kidney Aging by Inducing Excessive mPTP Opening Through MFN1

Cellular senescence is a pivotal contributor to aging and age-related diseases. The targeted elimination of senescent cells, known as senolysis, has emerged as a promising therapeutic strategy for mitigating these conditions. Glutaminase 1 (GLS1), a key enzyme in the glutaminolysis pathway, has been implicated in various cellular senescence processes. However, its specific role in senescent renal tubular epithelial cells (TECs) remains unclear. This study investigates the role and underlying mechanisms of GLS1 in senescent TECs. Using d-galactose (d-gal)-induced senescence of HK-2 cells, we found that GLS1 inhibition eliminated senescent TECs by promoting excessive mitochondrial permeability transition pore (mPTP) opening. Mechanistically, the excessive mPTP opening is associated with the upregulation of mitofusin 1 (MFN1). Inhibition of GLS1 in d-gal-treated HK-2 cells induced a shift in mitochondrial dynamics from fission to fusion, accompanied by a significant increase in MFN1 expression. Knocking down MFN1 reduced the mPTP opening and the expression of mPTP-related genes (PPIF, VDAC, and BAX) in cells co-treated with d-gal and the GLS1 inhibitor BPTES. Moreover, treatment of aged mice with BPTES specifically eliminated senescent TECs and ameliorated age-associated kidney disease. These findings reveal that GLS1 inhibition eliminate senescent TECs by promoting excessive mPTP opening, suggesting that targeting GLS1 may be a novel senolytic strategy for alleviating aging-related kidney diseases.

Cocaine Differentially Affects Mitochondrial Function Depending on Exposure Time

Cocaine use is a rising global concern, and increased use is accompanied by a significant increase in people entering treatment for the first time. However, there are still no complete therapies, and preclinical tools are necessary to both understand the action of cocaine and mitigate for its effects. Cocaine exposure rapidly impacts cellular and mitochondrial health, leading to oxidative stress. This study evaluated the effects of acute, repeated, and chronic cocaine exposure on C17.2 neural precursor cells. A single exposure to high concentrations of cocaine caused rapid cell death, with lower concentrations increasing markers of oxidative stress and mitochondrial dysfunction within 4 h of exposure. Alterations in cellular bioenergetics and mitochondrial fusion and fission gene expression (OPA1, DRP1) were also observed, which returned to baseline by 24 h after insult. Repeated exposure over 3 days reduced cell proliferation and spare mitochondrial respiratory capacity, suggesting compromised cellular resilience. Interestingly, chronic exposure over 4 weeks led to cellular adaptation and restoring mitochondrial bioenergetics and ATP production while mitigating for oxidative stress. These findings highlight the time-dependent cellular effects of cocaine, with initial toxicity and mitochondrial impairment transitioning to adaptive responses under chronic exposure.

Mitochondrial dysfunction is a hallmark of woody breast myopathy in broiler chickens

The woody breast (WB) myopathy poses significant economic and welfare concerns to the poultry industry, however, there is no effective strategy to mitigate this pathology due to its unknown etiology. After showing previously that hypoxia is a key factor in WB progression, we used here various techniques demonstrating dysregulated mitochondria (morphology, biogenesis, tethering, function, and bioenergetics) in WB-affected muscles and in hypoxic myoblasts compared to healthy tissues and normoxic cells, respectively. The increased levels of calcium (Ca2+) in both WB-affected tissues and hypoxic myoblasts suggested that mitochondrial Ca2+ overload is likely a leading cause for mitochondrial dysfunction that merits further in-depth investigation. These findings are the first, to the best of our knowledge, to provide fundamental insights into the underlying molecular mechanisms of WB and open new vistas for understanding the interplay between calcium, mitochondrial (dys)function, and avian muscle health for subsequent development of effective preventative/corrective strategies.

Pharmacologic activation of integrated stress response kinases inhibits pathologic mitochondrial fragmentation

Excessive mitochondrial fragmentation is associated with the pathologic mitochondrial dysfunction implicated in the pathogenesis of etiologically diverse diseases, including many neurodegenerative disorders. The integrated stress response (ISR) - comprising the four eIF2α kinases PERK, GCN2, PKR, and HRI - is a prominent stress-responsive signaling pathway that regulates mitochondrial morphology and function in response to diverse types of pathologic insult. This suggests that pharmacologic activation of the ISR represents a potential strategy to mitigate pathologic mitochondrial fragmentation associated with human disease. Here, we show that pharmacologic activation of the ISR kinases HRI or GCN2 promotes adaptive mitochondrial elongation and prevents mitochondrial fragmentation induced by the calcium ionophore ionomycin. Further, we show that pharmacologic activation of the ISR reduces mitochondrial fragmentation and restores basal mitochondrial morphology in patient fibroblasts expressing the pathogenic D414V variant of the pro-fusion mitochondrial GTPase MFN2 associated with neurological dysfunctions, including ataxia, optic atrophy, and sensorineural hearing loss. These results identify pharmacologic activation of ISR kinases as a potential strategy to prevent pathologic mitochondrial fragmentation induced by disease-relevant chemical and genetic insults, further motivating the pursuit of highly selective ISR kinase-activating compounds as a therapeutic strategy to mitigate mitochondrial dysfunction implicated in diverse human diseases.

MCU expression in hippocampal CA2 neurons modulates dendritic mitochondrial morphology and synaptic plasticity

Neuronal mitochondria are diverse across cell types and subcellular compartments in order to meet unique energy demands. While mitochondria are essential for synaptic transmission and synaptic plasticity, the mechanisms regulating mitochondria to support normal synapse function are incompletely understood. The mitochondrial calcium uniporter (MCU) is proposed to couple neuronal activity to mitochondrial ATP production, which would allow neurons to rapidly adapt to changing energy demands. MCU is uniquely enriched in hippocampal CA2 distal dendrites compared to proximal dendrites, however, the functional significance of this layer-specific enrichment is not clear. Synapses onto CA2 distal dendrites readily express plasticity, unlike the plasticity-resistant synapses onto CA2 proximal dendrites, but the mechanisms underlying these different plasticity profiles are unknown. Using a CA2-specific MCU knockout (cKO) mouse, we found that MCU deletion impairs plasticity at distal dendrite synapses. However, mitochondria were more fragmented and spine head area was diminished throughout the dendritic layers of MCU cKO mice versus control mice. Fragmented mitochondria might have functional changes, such as altered ATP production, that could explain the structural and functional deficits at cKO synapses. Differences in MCU expression across cell types and circuits might be a general mechanism to tune mitochondrial function to meet distinct synaptic demands.

Epithelial OPA1 links mitochondrial fusion to inflammatory bowel disease

Dysregulation at the intestinal epithelial barrier is a driver of inflammatory bowel disease (IBD). However, the molecular mechanisms of barrier failure are not well understood. Here, we demonstrate dysregulated mitochondrial fusion in intestinal epithelial cells (IECs) of patients with IBD and show that impaired fusion is sufficient to drive chronic intestinal inflammation. We found reduced expression of mitochondrial fusion-related genes, such as the dynamin-related guanosine triphosphatase (GTPase) optic atrophy 1 (OPA1), and fragmented mitochondrial networks in crypt IECs of patients with IBD. Mice with Opa1 deficiency in the gut epithelium (Opa1i∆IEC) spontaneously developed chronic intestinal inflammation with mucosal ulcerations and immune cell infiltration. Intestinal inflammation in Opa1i∆IEC mice was driven by microbial translocation and associated with epithelial progenitor cell death and gut barrier dysfunction. Opa1-deficient epithelial cells and human organoids exposed to a pharmacological OPA1 inhibitor showed disruption of the mitochondrial network with mitochondrial fragmentation and changes in mitochondrial size, ultrastructure, and function, resembling changes observed in patient samples. Pharmacological inhibition of the GTPase dynamin-1-like protein in organoids derived from Opa1i∆IEC mice partially reverted this phenotype. Together, our data demonstrate a role for epithelial OPA1 in regulating intestinal immune homeostasis and epithelial barrier function. Our data provide a mechanistic explanation for the observed mitochondrial dysfunction in IBD and identify mitochondrial fusion as a potential therapeutic target in this disease.

Gestational exposure to carbon black nanoparticles triggered fetal growth restriction in mice: The mediation of inactivating autophagy-lysosomal degradation system in placental ferroptosis

Carbon black nanoparticles (CBNPs) are ubiquitous in our daily ambient environment, either resulting from tobacco combustion or constituting the core of PM2.5. Despite the potential risk of trafficking CBNPs to the fetus, the underlying toxicity of nano-sized carbon black particles in the placenta remains unambiguous. Pregnant C57BL/6 mice received intratracheal instillation of 30 nm or 120 nm CBNPs. CBNPs deposited in the lungs could infiltrate the red blood cells, further cross into the placenta, and cause fetal growth restriction. Mechanistically, we proposed a two-hit hypothesis in placenta response to CBNPs. The first hit was that CBNPs caused mitochondrial damage, reflected in the reduced mitochondrial matrix, the excessive mitochondrial fission, and the decreased mitochondrial membrane potential and mtDNA copy number. The second hit was that CBNPs disrupted the autophagy-lysosomal degradation system, impeding the removal of dysfunctional mitochondria and resulting in ferroptosis. Ferrestatin-1, a ferroptosis inhibitor, and rapamycin, an autophagy promotor, reversed ferroptosis and further confirm our suspicion. The findings suggested that CBNPs-triggered double-hit evoked placental ferroptosis, leading to fetal growth restriction. The study raised concerns about the potential placental toxicity of CBNPs and its impact on the fetal adverse outcome, which may propose potential targets for interventions in placental damage.

Outer mitochondrial membrane E3 Ub ligase MARCH5 controls de novo peroxisome biogenesis

We report that the outer mitochondrial membrane (OMM)-associated E3 Ub ligase MARCH5 is vital for generating mitochondria-derived pre-peroxisomes. In human immortalized cells, MARCH5 knockout leads to the accumulation of immature peroxisomes, reduced fatty-acid-induced peroxisomal biogenesis, and abnormal peroxisome biogenesis in MARCH5/Pex14 and MARCH5/Pex3 dko cells. Upon fatty-acid-induced peroxisomal biogenesis, MARCH5 redistributes to peroxisomes, and ubiquitination activity-deficient mutants of MARCH5 accumulate on peroxisomes containing high levels of the OMM protein Tom20 (mitochondria-derived pre-peroxisomes). Similarly, depletion of peroxisome biogenesis factor Pex14 leads to the accumulation of MARCH5- and Tom20-positive pre-peroxisomes, whereas no peroxisomes are detected in MARCH5/Pex14 dko cells. Inconsistent with MARCH5 merely acting as a quality factor, mitochondrial decline is not evident in tested models. Furthermore, reduced expression of peroxisomal proteins is detected in MARCH5-/- cells, whereas some of these proteins are stabilized in peroxisome biogenesis deficiency models lacking MARCH5 expression. Thus, MARCH5 is central for mitochondria-dependent peroxisome biogenesis.

Rnd3 protects against doxorubicin-induced cardiotoxicity through inhibition of PANoptosis in a Rock1/Drp1/mitochondrial fission-dependent manner

Doxorubicin, a representative drug of the anthracycline class, is widely used in cancer treatment. However, Doxorubicin-induced cardiotoxicity (DIC) presents a significant challenge in its clinical application. Mitochondrial dysfunction plays a central role in DIC, primarily through disrupting mitochondrial dynamics. This study aimed to investigate the impact of Rnd3 (a Rho family GTPase 3) on DIC, with a focus on mitochondrial dynamics. Cardiomyocyte-specific Rnd3 transgenic mice (Rnd3-Tg) and Rnd3LSP/LSP mice (N-Tg) were established for in vivo experiments, and adenoviruses harboring Rnd3 (Ad-Rnd3) or negative control (Ad-Control) were injected in the myocardium for in vitro experiments. The DIC model was established using wild-type, N-Tg, and Rnd3-Tg mice, with subsequent intraperitoneal injection of Dox for 4 weeks. The molecular mechanism was explored through RNA sequencing, immunofluorescence staining, co-immunoprecipitation assay, and protein-protein docking. Dox administration induced significant mitochondrial injury and cardiac dysfunction, which was ameliorated by Rnd3 overexpression. Further, the augmentation of Rnd3 expression mitigated mitochondrial fragmentation which is mediated by dynamin-related protein 1 (Drp1), thereby ameliorating the PANoptosis (pyroptosis, apoptosis, and necroptosis) response induced by Dox. Mechanically, the interaction between Rnd3 and Rho-associated kinase 1 (Rock1) may impede Rock1-induced Drp1 phosphorylation at Ser616, thus inhibiting mitochondrial fission and dysfunction. Interestingly, Rock1 knockdown nullified the effects of Rnd3 on cardiomyocytes PANoptosis, as well as Dox-induced cardiac remodeling and dysfunction elicited by Rnd3. Rnd3 enhances cardiac resilience against DIC by stabilizing mitochondrial dynamics and reducing PANoptosis. Our findings suggest that the Rnd3/Rock1/Drp1 signaling pathway represents a novel target for mitigating DIC, and modulating Rnd3 expression could be a strategic approach to safeguarding cardiac function in patients undergoing Dox treatment. The graphical abstract illustrated the cardioprotective role of Rnd3 in DIC. Rnd3 directly binds to Rock1 in cytoplasm and ameliorates mitochondrial fission by inhibiting Drp1 phosphorylation at ser616, thereby alleviating PANoptosis (apoptosis, pyroptosis, and necroptosis) in DIC.

Morphological diversification and functional maturation of human astrocytes in glia-enriched cortical organoid transplanted in mouse brain

Astrocytes, the most abundant glial cell type in the brain, are underrepresented in traditional cortical organoid models due to the delayed onset of cortical gliogenesis. Here we introduce a new glia-enriched cortical organoid model that exhibits accelerated astrogliogenesis. We demonstrated that induction of a gliogenic switch in a subset of progenitors enabled the rapid derivation of astroglial cells, which account for 25-31% of the cell population within 8-10 weeks of differentiation. Intracerebral transplantation of these organoids reliably generated a diverse repertoire of cortical neurons and anatomical subclasses of human astrocytes. Spatial transcriptome profiling identified layer-specific expression patterns among distinct subclasses of astrocytes within organoid transplants. Using an in vivo acute neuroinflammation model, we identified a subpopulation of astrocytes that rapidly activates pro-inflammatory pathways upon cytokine stimulation. Additionally, we demonstrated that CD38 signaling has a crucial role in mediating metabolic and mitochondrial stress in reactive astrocytes. This model provides a robust platform for investigating human astrocyte function.

Mitochondrial Dynamics in Brain Cells During Normal and Pathological Aging

Mitochondrial dynamics significantly play a major role in the pathogenesis of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. The dysregulation of mitochondrial biogenesis and function, characterized by impaired fission and fusion processes mediated by a number of proteins, in particular, Drp1, Mfn1, Mfn2, Opa1, and PGC-1α, contributes to neuronal vulnerability and degeneration. Insufficient mitophagy and disrupted mitochondrial transport exacerbate oxidative stress and neurotoxicity. Emerging therapeutic strategies that target mitochondrial dynamics, including various pharmacological agents, demonstrate potential for restoring mitochondrial balance and enhancing neuroprotection. This growing body of research underscores the importance of mitochondrial health in developing effective interventions for neurodegenerative conditions. This review highlights well-established links between the disruption of mitochondrial dynamics and the development of neurodegenerative processes. We also discuss different therapeutic strategies that target mitochondrial function in neurons that have been proposed as perspective neuroprotective treatments.

Protein kinase A and local signaling in cancer

Protein kinase A (PKA) is a basophilic kinase implicated in the modulation of many cell-signaling and physiological processes. PKA also contributes to cancer-relevant events such as growth factor action, cell cycle control, cell migration and tumor metabolism. Germline and somatic mutations in PKA, gene amplifications, and chromosome rearrangements that encode kinase fusions, are linked to a growing number of malignant neoplasms. Mislocalization of PKA by exclusion from A-Kinase Anchoring Protein (AKAP) signaling islands further underlies cancer progression. This article highlights the influence of AKAP signaling and local kinase action in selected hallmarks of cancer. We also feature the utility of kinase inhibitor drugs as frontline and future anti-cancer therapies.

Pharmacologic Activation of Integrated Stress Response Kinases Inhibits Pathologic Mitochondrial Fragmentation

Excessive mitochondrial fragmentation is associated with the pathologic mitochondrial dysfunction implicated in the pathogenesis of etiologically-diverse diseases, including many neurodegenerative disorders. The integrated stress response (ISR) - comprising the four eIF2α kinases PERK, GCN2, PKR, and HRI - is a prominent stress-responsive signaling pathway that regulates mitochondrial morphology and function in response to diverse types of pathologic insult. This suggests that pharmacologic activation of the ISR represents a potential strategy to mitigate pathologic mitochondrial fragmentation associated with human disease. Here, we show that pharmacologic activation of the ISR kinases HRI or GCN2 promotes adaptive mitochondrial elongation and prevents mitochondrial fragmentation induced by the calcium ionophore ionomycin. Further, we show that pharmacologic activation of the ISR reduces mitochondrial fragmentation and restores basal mitochondrial morphology in patient fibroblasts expressing the pathogenic D414V variant of the pro-fusion mitochondrial GTPase MFN2 associated with neurological dysfunctions including ataxia, optic atrophy, and sensorineural hearing loss. These results identify pharmacologic activation of ISR kinases as a potential strategy to prevent pathologic mitochondrial fragmentation induced by disease-relevant chemical and genetic insults, further motivating the pursuit of highly selective ISR kinase-activating compounds as a therapeutic strategy to mitigate mitochondrial dysfunction implicated in diverse human diseases.

The Large GTPase Guanylate-Binding Protein-1 (GBP-1) Promotes Mitochondrial Fission in Glioblastoma

Glioblastomas (aka Glioblastoma multiformes (GBMs)) are the most deadly of the adult brain tumors. Even with aggressive treatment, the prognosis is extremely poor. The large GTPase Guanylate-Binding Protein-1 (GBP-1) contributes to the poor prognosis of GBM by promoting migration and invasion. GBP-1 is substantially localized to the cytosolic side of the outer membrane of mitochondria in GBM cells. Because mitochondrial dynamics, particularly mitochondrial fission, can drive cell migration and invasion, the potential interactions between GBP-1 and mitochondrial dynamin-related protein 1 (Drp1) were explored. Drp1 is the major driver of mitochondrial fission. While GBP-1 and Drp1 both had punctate distributions within the cytoplasm and localized to regions of the cytoplasmic side of the plasma membrane of GBM cells, the proteins were only molecularly co-localized at the mitochondria. Subcellular fractionation showed that the presence of elevated GBP-1 promoted the movement of Drp1 from the cytosol to the mitochondria. The migration of U251 cells treated with the Drp1 inhibitor, Mdivi-1, was less inhibited in the cells with elevated GBP-1. Elevated GBP-1 in GBM cells resulted in shorter and wider mitochondria, most likely from mitochondrial fission. Mitochondrial fission can drive several important cellular processes, including cell migration, invasion, and metastasis.

Ribosomes hibernate on mitochondria during cellular stress

Cell survival under nutrient-deprived conditions relies on cells' ability to adapt their organelles and rewire their metabolic pathways. In yeast, glucose depletion induces a stress response mediated by mitochondrial fragmentation and sequestration of cytosolic ribosomes on mitochondria. This cellular adaptation promotes survival under harsh environmental conditions; however, the underlying mechanism of this response remains unknown. Here, we demonstrate that upon glucose depletion protein synthesis is halted. Cryo-electron microscopy structure of the ribosomes show that they are devoid of both tRNA and mRNA, and a subset of the particles depicted a conformational change in rRNA H69 that could prevent tRNA binding. Our in situ structural analyses reveal that the hibernating ribosomes tether to fragmented mitochondria and establish eukaryotic-specific, higher-order storage structures by assembling into oligomeric arrays on the mitochondrial surface. Notably, we show that hibernating ribosomes exclusively bind to the outer mitochondrial membrane via the small ribosomal subunit during cellular stress. We identify the ribosomal protein Cpc2/RACK1 as the molecule mediating ribosomal tethering to mitochondria. This study unveils the molecular mechanism connecting mitochondrial stress with the shutdown of protein synthesis and broadens our understanding of cellular responses to nutrient scarcity and cell quiescence.

Cyclin-dependent Kinase 5 and Neurodegenerative Diseases

Neurodegenerative diseases are a group of diseases characterized by the progressive loss of neurons, including Alzheimer's disease, Parkinson's disease, and Amyotrophic lateral sclerosis. These diseases have a high incidence and mortality rate globally, placing a heavy burden on patients and their families. The pathogenesis of neurodegenerative diseases is complex, and there are no effective treatments at present. Cyclin-dependent kinase 5 is a proline-directed serine/threonine protein kinase that is closely related to the development and function of the nervous system. Under physiological conditions, it is involved in regulating the process of neuronal proliferation, differentiation, migration, and synaptic plasticity. Moreover, there is increasing evidence that cyclin-dependent kinase 5 also plays an important role in the pathogenesis of neurodegenerative diseases. In this review, we address the biological characteristics of cyclin-dependent kinase 5 and its role in neurodegenerative diseases. In particular, this review highlights the underlying mechanistic linkages between cyclin-dependent kinase 5 and mitochondrial dysfunction, oxidative stress and neuroinflammation in the context of neurodegeneration. Finally, we also summarize the currently available cyclin-dependent kinase 5 inhibitors and their prospects for the treatment of neurodegenerative diseases. Taken together, a better understanding of the molecular mechanisms of cyclin-dependent kinase 5 involved in neurodegenerative diseases can lead to the development of new strategies for the prevention and treatment of these devastating diseases.

Investigating the interplay between mitophagy and diabetic neuropathy: Uncovering the hidden secrets of the disease pathology

Mitophagy, the cellular process of selectively eliminating damaged mitochondria, plays a crucial role in maintaining metabolic balance and preventing insulin resistance, both key factors in type 2 diabetes mellitus (T2DM) development. When mitophagy malfunctions in diabetic neuropathy, it triggers a cascade of metabolic disruptions, including reduced energy production, increased oxidative stress, and cell death, ultimately leading to various complications. Thus, targeting mitophagy to enhance the process may have emerged as a promising therapeutic strategy for T2DM and its complications. Notably, plant-derived compounds with β-cell protective and mitophagy-stimulating properties offer potential as novel therapeutic agents. This review highlights the intricate mechanisms linking mitophagy dysfunction to T2DM and its complications, particularly neuropathy, elucidating potential therapeutic interventions for this debilitating disease.

Neuro-intestinal acetylcholine signalling regulates the mitochondrial stress response in Caenorhabditis elegans

Neurons coordinate inter-tissue protein homeostasis to systemically manage cytotoxic stress. In response to neuronal mitochondrial stress, specific neuronal signals coordinate the systemic mitochondrial unfolded protein response (UPRmt) to promote organismal survival. Yet, whether chemical neurotransmitters are sufficient to control the UPRmt in physiological conditions is not well understood. Here, we show that gamma-aminobutyric acid (GABA) inhibits, and acetylcholine (ACh) promotes the UPRmt in the Caenorhabditis elegans intestine. GABA controls the UPRmt by regulating extra-synaptic ACh release through metabotropic GABAB receptors GBB-1/2. We find that elevated ACh levels in animals that are GABA-deficient or lack ACh-degradative enzymes induce the UPRmt through ACR-11, an intestinal nicotinic α7 receptor. This neuro-intestinal circuit is critical for non-autonomously regulating organismal survival of oxidative stress. These findings establish chemical neurotransmission as a crucial regulatory layer for nervous system control of systemic protein homeostasis and stress responses.

GPCR Screening Reveals that the Metabolite Receptor HCAR3 Regulates Epithelial Proliferation, Migration, and Cellular Respiration

Epithelial cells in the skin and other tissues rely on signals from their environment to maintain homeostasis and respond to injury, and GPCRs play a critical role in this communication. A better understanding of the GPCRs expressed in epithelial cells will contribute to understanding the relationship between cells and their niche and could lead to developing new therapies to modulate cell fate. This study used human primary keratinocytes as a model to investigate the specific GPCRs regulating epithelial cell proliferation and differentiation. We identified 3 key receptors-HCAR3, LTB4R, and GPR137-and found that knockdown of these receptors led to changes in numerous gene networks that are important for maintaining cell identity and promoting proliferation while inhibiting differentiation. Our study also revealed that the metabolite receptor HCAR3 regulates keratinocyte migration and cellular metabolism. Knockdown of HCAR3 led to reduced keratinocyte migration and respiration, which could be attributed to altered metabolite use and aberrant mitochondrial morphology caused by the absence of the receptor. This study contributes to understanding the complex interplay between GPCR signaling and epithelial cell fate decisions.

lncRNA Oip5-as1 inhibits excessive mitochondrial fission in myocardial ischemia/reperfusion injury by modulating DRP1 phosphorylation

BACKGROUND

Aberrant mitochondrial fission, a critical pathological event underlying myocardial ischemia/reperfusion (MI/R) injury, has emerged as a potential therapeutic target. The long non-coding RNA (lncRNA) Oip5-as1 is increasingly recognized for its regulatory roles, particularly in MI/R injury. However, its precise mechanistic role in modulating mitochondrial dynamics remains elusive. This study aims to elucidate the mechanistic role of Oip5-as1 in regulating mitochondrial fission and evaluate its therapeutic potential against MI/R injury.

METHODS

To simulate in vitro MI/R injury, HL-1 cardiomyocytes were subjected to hypoxia/reoxygenation (H/R). Lentiviral vectors were employed to achieve overexpression or knockdown of Oip5-as1 in HL-1 cells by expressing Oip5-as1 or shRNA targeting Oip5-as1, respectively. The impact of Oip5-as1 on mitochondrial dynamics in HL-1 cells was assessed using CCK-8 assay, flow cytometry, immunofluorescence staining, and biochemical assays. MI/R injury was induced in mice by ligating the left anterior descending coronary artery. Conditional knockout mice for Oip5-as1 were generated using the CRISPR/Cas9 genome editing technology, while overexpression of Oip5-as1 in mice was achieved via intramyocardial administration of AAV9 vectors. In mice, the role of Oip5-as1 was evaluated through echocardiographic assessment, histopathological staining, and transmission electron microscopy. Furthermore, Western blotting, RNA pull-down, RNA immunoprecipitation, and co-immunoprecipitation assays were conducted to investigate Oip5-as1's underlying mechanisms.

RESULTS

The expression levels of Oip5-as1 are significantly decreased in MI/R-injured HL-1 cells and myocardium. In HL-1 cells undergoing H/R injury, overexpression of Oip5-as1 attenuated excessive mitochondrial fission, preserved mitochondrial functionality, and reduced cellular apoptosis, while knockdown of Oip5-as1 exhibited the opposite effects. Furthermore, in a mouse model of MI/R injury, overexpression of Oip5-as1 diminished mitochondrial fission, myocardial infarct size and improved cardiac function. However, knockout of Oip5-as1 exacerbated myocardial injury and cardiac dysfunction, which were significantly reversed by treatment with a mitochondrial division inhibitor-1 (Mdivi-1). Mechanistically, Oip5-as1 selectively interacts with AKAP1 and CaN proteins, inhibiting CaN activation and subsequent DRP1 dephosphorylation at Ser637, thereby constraining DRP1's translocation to the mitochondria and its involvement in mitochondrial fission.

CONCLUSIONS

Our study underscores the pivotal role of Oip5-as1 in mitigating excessive mitochondrial fission during MI/R injury. The findings not only enhance our comprehension of the molecular mechanisms underlying MI/R injury but also identify Oip5-as1 as a potential therapeutic target for ameliorating MI/R injury.

TGF-β3 mediates mitochondrial dynamics through the p-Smad3/AMPK pathway

It is well recognized that mitochondrial dynamics plays a vital role in cartilage physiology. Any perturbation in mitochondrial dynamics could cause disorders in cartilage metabolism and even lead to the occurrence of cartilage diseases such as osteoarthritis (OA). TGF-β3, as an important growth factor that appears in the joints of OA disease, shows its great potential in chondrocyte growth and metabolism. Nevertheless, the role of TGF-β3 on mitochondrial dynamics is still not well understood. Here we aimed to investigate the effect of TGF-β3 on mitochondrial dynamics of chondrocytes and reveal its underlying bio-mechanism. By using transmission electron microscopy (TEM) for the number and morphology of mitochondria, western blotting for the protein expressions, immunofluorescence for the cytoplasmic distributions of proteins, and RNA sequencing for the transcriptome changes related to mitochondrial dynamics. We found that TGF-β3 could increase the number of mitochondria in chondrocytes. TGF-β3-enhanced mitochondrial number was via promoting the mitochondrial fission. The mitochondrial fission induced by TGF-β3 was mediated by AMPK signaling. TGF-β3 activated canonical p-Smad3 signaling and resultantly mediated AMPK-induced mitochondrial fission. Taken together, these results elucidate an understanding of the role of TGF-β3 on mitochondrial dynamics in chondrocytes and provide potential cues for therapeutic strategies in cartilage injury and OA disease in terms of energy metabolism.

Mitochondrial energy state controls AMPK-mediated foraging behavior in C. elegans

Organisms surveil and respond to their environment using behaviors entrained by metabolic cues that reflect food availability. Mitochondria act as metabolic hubs and at the center of mitochondrial energy production is the protonmotive force (PMF), an electrochemical gradient generated by metabolite consumption. The PMF serves as a central integrator of mitochondrial status, but its role in governing metabolic signaling is poorly understood. We used optogenetics to dissipate the PMF in Caenorhabditis elegans tissues to test its role in food-related behaviors. Our data demonstrate that PMF reduction in the intestine is sufficient to initiate locomotor responses to acute food deprivation. This behavioral adaptation requires the cellular energy regulator AMP-activated protein kinase (AMPK) in neurons, not in the intestine, and relies on mitochondrial dynamics and axonal trafficking. Our results highlight a role for intestinal PMF as an internal metabolic cue, and we identify a bottom-up signaling axis through which changes in the PMF trigger AMPK activity in neurons to promote foraging behavior.

Contribution of the Type III Secretion System (T3SS2) of Vibrio parahaemolyticus in Mitochondrial Stress in Human Intestinal Cells

Vibrio parahaemolyticus is an important human pathogen that is currently the leading cause of shellfish-borne gastroenteritis in the world. Particularly, the pandemic strain has the capacity to induce cytotoxicity and enterotoxicity through its Type 3 Secretion System (T3SS2) that leads to massive cell death. However, the specific mechanism by which the T3SS2 induces cell death remains unclear and its contribution to mitochondrial stress is not fully understood. In this work, we evaluated the contribution of the T3SS2 of V. parahaemolyticus in generating mitochondrial stress during infection in human intestinal HT-29 cells. To evaluate the contribution of the T3SS2 of V. parahaemolyticus in mitochondrial stress, infection assays were carried out to evaluate mitochondrial transition pore opening, mitochondrial fragmentation, ATP quantification, and cell viability during infection. Our results showed that the Δvscn1 (T3SS2+) mutant strain contributes to generating the sustained opening of the mitochondrial transition pore. Furthermore, it generates perturbations in the ATP production in infected cells, leading to a significant decrease in cell viability and loss of membrane integrity. Our results suggest that the T3SS2 from V. parahaemolyticus plays a role in generating mitochondrial stress that leads to cell death in human intestinal HT-29 cells. It is important to highlight that this study represents the first report indicating the possible role of the V. parahaemolyticus T3SS2 and its effector proteins involvement in generating mitochondrial stress, its impact on the mitochondrial pore, and its effect on ATP production in human cells.

Leflunomide Treatment Does Not Protect Neural Cells following Oxygen-Glucose Deprivation (OGD) In Vitro

Neonatal hypoxia-ischemia (HI) affects 2-3 per 1000 live births in developed countries and up to 26 per 1000 live births in developing countries. It is estimated that of the 750,000 infants experiencing a hypoxic-ischemic event during birth per year, more than 400,000 will be severely affected. As treatment options are limited, rapidly identifying new therapeutic avenues is critical, and repurposing drugs already in clinical use offers a fast-track route to clinic. One emerging avenue for therapeutic intervention in neonatal HI is to target mitochondrial dysfunction, which occurs early in the development of brain injury. Mitochondrial dynamics are particularly affected, with mitochondrial fragmentation occurring at the expense of the pro-fusion protein Optic Atrophy (OPA)1. OPA1, together with mitofusins (MFN)1/2, are required for membrane fusion, and therefore, protecting their function may also safeguard mitochondrial dynamics. Leflunomide, an FDA-approved immunosuppressant, was recently identified as an activator of MFN2 with partial effects on OPA1 expression. We, therefore, treated C17.2 cells with Leflunomide before or after oxygen-glucose deprivation, an in vitro mimic of HI, to determine its efficacy as a neuroprotection and inhibitor of mitochondrial dysfunction. Leflunomide increased baseline OPA1 but not MFN2 expression in C17.2 cells. However, Leflunomide was unable to promote cell survival following OGD. Equally, there was no obvious effect on mitochondrial morphology or bioenergetics. These data align with studies suggesting that the tissue and mitochondrial protein profile of the target cell/tissue are critical for taking advantage of the therapeutic actions of Leflunomide.

MCU-enriched dendritic mitochondria regulate plasticity in distinct hippocampal circuits

Mitochondria are dynamic organelles that are morphologically and functionally diverse across cell types and subcellular compartments in order to meet unique energy demands. Mitochondrial dysfunction has been implicated in a wide variety of neurological disorders, including psychiatric disorders like schizophrenia and bipolar disorder. Despite it being well known that mitochondria are essential for synaptic transmission and synaptic plasticity, the mechanisms regulating mitochondria in support of normal synapse function are incompletely understood. The mitochondrial calcium uniporter (MCU) regulates calcium entry into the mitochondria, which in turn regulates the bioenergetics and distribution of mitochondria to active synapses. Evidence suggests that calcium influx via MCU couples neuronal activity to mitochondrial metabolism and ATP production, which would allow neurons to rapidly adapt to changing energy demands. Intriguingly, MCU is uniquely enriched in hippocampal CA2 distal dendrites relative to neighboring hippocampal CA1 or CA3 distal dendrites, however, the functional significance of this enrichment is not clear. Synapses from the entorhinal cortex layer II (ECII) onto CA2 distal dendrites readily express long term potentiation (LTP), unlike the LTP-resistant synapses from CA3 onto CA2 proximal dendrites, but the mechanisms underlying these different plasticity profiles are unknown. We hypothesized that enrichment of MCU near ECII-CA2 synapses promotes LTP in an otherwise plasticity-restricted cell type. Using a CA2-specific MCU knockout (cKO) mouse, we found that MCU is required for LTP at distal dendrite synapses but does not affect the lack of LTP at proximal dendrite synapses. Loss of LTP at ECII-CA2 synapses correlated with a trend for decreased spine density in CA2 distal dendrites of cKO mice compared to control (CTL) mice, which was predominantly seen in immature spines. Moreover, mitochondria were significantly smaller and more numerous across all dendritic layers of CA2 in cKO mice compared to CTL mice, suggesting an overall increase in mitochondrial fragmentation. Fragmented mitochondria might have functional changes, such as altered ATP production, that might explain a deficit in synaptic plasticity. Collectively, our data reveal that MCU regulates layer-specific forms of plasticity in CA2 dendrites, potentially by maintaining proper mitochondria morphology and distribution within dendrites. Differences in MCU expression across different cell types and circuits might be a general mechanism to tune the sensitivity of mitochondria to cytoplasmic calcium levels to power synaptic plasticity.

Quantitative imaging and semiotic phenotyping of mitochondrial network morphology in live human cells

The importance of mitochondria in tissue homeostasis, stress responses and human diseases, combined to their ability to transition between various structural and functional states, makes them excellent organelles for monitoring cell health. There is therefore a need for technologies to accurately analyze and quantify changes in mitochondrial organization in a variety of cells and cellular contexts. Here we present an innovative computerized method that enables accurate, multiscale, fast and cost-effective analysis of mitochondrial shape and network architecture from confocal fluorescence images by providing more than thirty features. In order to facilitate interpretation of the quantitative results, we introduced two innovations: the use of Kiviat-graphs (herein named MitoSpider plots) to present highly multidimensional data and visualization of the various mito-cellular configurations in the form of morphospace diagrams (called MitoSigils). We tested our fully automated image analysis tool on rich datasets gathered from live normal human skin cells cultured under basal conditions or exposed to specific stress including UVB irradiation and pesticide exposure. We demonstrated the ability of our proprietary software (named MitoTouch) to sensitively discriminate between control and stressed dermal fibroblasts, and between normal fibroblasts and other cell types (including cancer tissue-derived fibroblasts and primary keratinocytes), showing that our automated analysis captures subtle differences in morphology. Based on this novel algorithm, we report the identification of a protective natural ingredient that mitigates the deleterious impact of hydrogen peroxide (H2O2) on mitochondrial organization. Hence we conceived a novel wet-plus-dry pipeline combining cell cultures, quantitative imaging and semiotic analysis for exhaustive analysis of mitochondrial morphology in living adherent cells. Our tool has potential for broader applications in other research areas such as cell biology and medicine, high-throughput drug screening as well as predictive and environmental toxicology.

Mitochondrial deoxyguanosine kinase is required for female fertility in mice

Mitochondrial homeostasis plays a pivotal role in oocyte maturation and embryonic development. Deoxyguanosine kinase (DGUOK) is a nucleoside kinase that salvages purine nucleosides in mitochondria and is critical for mitochondrial DNA replication and homeostasis in non-proliferating cells. Dguok loss-of-function mutations and deletions lead to hepatocerebral mitochondrial DNA deletion syndrome. However, its potential role in reproduction remains largely unknown. In this study, we find that Dguok knockout results in female infertility. Mechanistically, DGUOK deficiency hinders ovarian development and oocyte maturation. Moreover, DGUOK deficiency in oocytes causes a significant reduction in mitochondrial DNA copy number and abnormal mitochondrial dynamics and impairs germinal vesicle breakdown. Only few DGUOK-deficient oocytes can extrude their first polar body during in vitro maturation, and these oocytes exhibit irregular chromosome arrangements and different spindle lengths. In addition, DGUOK deficiency elevates reactive oxygen species levels and accelerates oocyte apoptosis. Our findings reveal novel physiological roles for the mitochondrial nucleoside salvage pathway in oocyte maturation and implicate DGUOK as a potential marker for the diagnosis of female infertility.

Super-Resolution Microscopy Unveils Synergistic Structural Changes of Organelles Upon Point Mutation

Ethyl methanesulphonate (EMS), is a widely used chemical mutagen that causes high-frequency germline null mutation by inserting an alkyl group into the nucleotide guanine in eukaryotic cells. The effect of EMS on the dynamics of the aneuploid genome, increased cellular instability, and carcinogenicity in relation to benign and malignant tumors are reported, but the molecular level understanding of morphological changes of higher-order chromatin structure has poorly been understood. This is due to a lack of sufficient resolution in conventional microscopic techniques to see small structures below the diffraction limit. Here, using super-resolution radial fluctuation, a largely fragmented, decompaction, and less dense heterochromatin structure upon EMS treatment to HEK 293A cells without any change in nuclear DNA domains is observed. This result suggests an early stage of carcinogenicity happened due to the point mutation. In addition, the distinct structural changes with an elongated morphology of lysosomes are also observed. On the other hand, fragmented and increased heterogeneous populations with an increased cytoplasmic occupancy of mitochondria are observed.

Brown adipose tissue CoQ deficiency activates the integrated stress response and FGF21-dependent mitohormesis

Coenzyme Q (CoQ) is essential for mitochondrial respiration and required for thermogenic activity in brown adipose tissues (BAT). CoQ deficiency leads to a wide range of pathological manifestations, but mechanistic consequences of CoQ deficiency in specific tissues, such as BAT, remain poorly understood. Here, we show that pharmacological or genetic CoQ deficiency in BAT leads to stress signals causing accumulation of cytosolic mitochondrial RNAs and activation of the eIF2α kinase PKR, resulting in activation of the integrated stress response (ISR) with suppression of UCP1 but induction of FGF21 expression. Strikingly, despite diminished UCP1 levels, BAT CoQ deficiency displays increased whole-body metabolic rates at room temperature and thermoneutrality resulting in decreased weight gain on high-fat diets (HFD). In line with enhanced metabolic rates, BAT and inguinal white adipose tissue (iWAT) interorgan crosstalk caused increased browning of iWAT in BAT-specific CoQ deficient animals. This mitohormesis-like effect depends on the ATF4-FGF21 axis and BAT-secreted FGF21, revealing an unexpected role for CoQ in the modulation of whole-body energy expenditure with wide-ranging implications for primary and secondary CoQ deficiencies.

PLAAT1 expression triggers fragmentation of mitochondria in an enzyme activity-dependent manner

The phospholipase A and acyltransferase (PLAAT) family is a protein family consisting of five members (PLAAT1-5), which acts as phospholipid-metabolizing enzymes with phospholipase A1/A2 and N-acyltransferase activities. Since we previously reported that the overexpression of PLAAT3 in mammalian cells causes the specific disappearance of peroxisomes, in the present study we examined a possible effect of PLAAT1 on organelles. We prepared HEK293 cells expressing mouse PLAAT1 in a doxycycline-dependent manner and found that the overexpression of PLAAT1 resulted in the transformation of mitochondria from the original long rod shape to a round shape, as well as their fragmentation. In contrast, the overexpression of a catalytically inactive point mutant of PLAAT1 did not generate any morphological change in mitochondria, suggesting the involvement of catalytic activity. PLAAT1 expression also caused the reduction of peroxisomes, while the levels of the marker proteins for ER, Golgi apparatus and lysosomes were almost unchanged. In PLAAT1-expressing cells, the level of dynamin-related protein 1 responsible for mitochondrial fission was increased, whereas those of optic atrophy 1 and mitofusin 2, both of which are responsible for mitochondrial fusion, were reduced. These results suggest a novel role of PLAAT1 in the regulation of mitochondrial biogenesis.

Proteomic analysis of gene expression in the prefrontal cortex in infant rhesus macaques after multiple sevoflurane exposures

PURPOSE

Repeated exposure of infant rhesus macaques to sevoflurane induces neurotoxicity and is associated with neurocognitive impairment in later life. We aimed to investigate the effect of repeated sevoflurane exposure on the expression of proteins in the prefrontal cortex of infant rhesus macaques by proteomics.

METHODS

Rhesus macaques were exposed to sevoflurane three times, on postnatal days 7, 21 and 35. Quantitative proteomics employing LC-MS with isobaric labeling (TMT10plex), western blotting, and transmission electron microscopy (TEM) were utilized in the studies.

RESULTS

The results of a proteomics investigation of the brain revealed that the proteins that were differentially expressed in rhesus macaques after sevoflurane exposures were associated mainly with mitochondrial respiration. Following multiple sevoflurane exposures, the prefrontal cortices of rhesus macaques exhibited increases in NDUFA8 and COX IV protein levels, while no alterations in mitochondrial morphology were observed through TEM.

CONCLUSION

Multiple exposures to sevoflurane increased the mitochondrial protein levels in rhesus macaques.

3D reconstructions of parasite development and the intracellular niche of the microsporidian pathogen Encephalitozoon intestinalis

Microsporidia are an early-diverging group of fungal pathogens with a wide host range. Several microsporidian species cause opportunistic infections in humans that can be fatal. As obligate intracellular parasites with highly reduced genomes, microsporidia are dependent on host metabolites for successful replication and development. Our knowledge of microsporidian intracellular development remains rudimentary, and our understanding of the intracellular niche occupied by microsporidia has relied on 2D TEM images and light microscopy. Here, we use serial block-face scanning electron microscopy (SBF-SEM) to capture 3D snapshots of the human-infecting species, Encephalitozoon intestinalis, within host cells. We track E. intestinalis development through its life cycle, which allows us to propose a model for how its infection organelle, the polar tube, is assembled de novo in developing spores. 3D reconstructions of parasite-infected cells provide insights into the physical interactions between host cell organelles and parasitophorous vacuoles, which contain the developing parasites. The host cell mitochondrial network is substantially remodeled during E. intestinalis infection, leading to mitochondrial fragmentation. SBF-SEM analysis shows changes in mitochondrial morphology in infected cells, and live-cell imaging provides insights into mitochondrial dynamics during infection. Our data provide insights into parasite development, polar tube assembly, and microsporidia-induced host mitochondria remodeling.

Mitoribosomal synthetic lethality overcomes multidrug resistance in MYC-driven neuroblastoma

Mitochondria are central for cancer responses to therapy-induced stress signals. Refractory tumors often show attenuated sensitivity to apoptotic signaling, yet clinically relevant molecular actors to target mitochondria-mediated resistance remain elusive. Here, we show that MYC-driven neuroblastoma cells rely on intact mitochondrial ribosome (mitoribosome) processivity and undergo cell death following pharmacological inhibition of mitochondrial translation, regardless of their multidrug/mitochondrial resistance and stem-like phenotypes. Mechanistically, inhibiting mitoribosomes induced the mitochondrial stress-activated integrated stress response (ISR), leading to downregulation of c-MYC/N-MYC proteins prior to neuroblastoma cell death, which could be both rescued by the ISR inhibitor ISRIB. The ISR blocks global protein synthesis and shifted the c-MYC/N-MYC turnover toward proteasomal degradation. Comparing models of various neuroectodermal tumors and normal fibroblasts revealed overexpression of MYC proteins phosphorylated at the degradation-promoting site T58 as a factor that predetermines vulnerability of MYC-driven neuroblastoma to mitoribosome inhibition. Reducing N-MYC levels in a neuroblastoma model with tunable MYCN expression mitigated cell death induction upon inhibition of mitochondrial translation and functionally validated the propensity of neuroblastoma cells for MYC-dependent cell death in response to the mitochondrial ISR. Notably, neuroblastoma cells failed to develop significant resistance to the mitoribosomal inhibitor doxycycline over a long-term repeated (pulsed) selection. Collectively, we identify mitochondrial translation machinery as a novel synthetic lethality target for multidrug-resistant MYC-driven tumors.

Quantitative assessment of mitochondrial morphology relevant for studies on cellular health and environmental toxicity

Mitochondria are essential organelles that play crucial roles in cellular energy metabolism, calcium signaling and apoptosis. Their importance in tissue homeostasis and stress responses, combined to their ability to transition between various structural and functional states, make them excellent organelles for monitoring cellular health. Quantitative assessment of mitochondrial morphology can therefore provide valuable insights into environmentally-induced cell damage. High-content screening (HCS) provides a powerful tool for analyzing organelles and cellular substructures. We developed a fully automated and miniaturized HCS wet-plus-dry pipeline (MITOMATICS) exploiting mitochondrial morphology as a marker for monitoring cellular health or damage. MITOMATICS uses an in-house, proprietary software (MitoRadar) to enable fast, exhaustive and cost-effective analysis of mitochondrial morphology and its inherent diversity in live cells. We applied our pipeline and big data analytics software to assess the mitotoxicity of selected chemicals, using the mitochondrial uncoupler CCCP as an internal control. Six different pesticides (inhibiting complexes I, II and III of the mitochondrial respiratory chain) were tested as individual compounds and five other pesticides present locally in Occitanie (Southern France) were assessed in combination to determine acute mitotoxicity. Our results show that the assayed pesticides exhibit specific signatures when used as single compounds or chemical mixtures and that they function synergistically to impact mitochondrial architecture. Study of environment-induced mitochondrial damage has the potential to open new fields in mechanistic toxicology, currently underexplored by regulatory toxicology and exposome research. Such exploration could inform health policy guidelines and foster pharmacological intervention, water, air and soil pollution control and food safety.

Impaired mitophagosome-lysosome fusion mediates olanzapine-induced aging

The lifespan of schizophrenia patients is significantly shorter than the general population. Olanzapine is one of the most commonly used antipsychotic drugs (APDs) for treating patients with psychosis, including schizophrenia and bipolar disorder. Despite their effectiveness in treating positive and negative symptoms, prolonged exposure to APDs may lead to accelerated aging and cognitive decline, among other side effects. Here we report that dysfunctional mitophagy is a fundamental mechanism underlying accelerated aging induced by olanzapine, using in vitro and in vivo (Caenorhabditis elegans) models. We showed that the aberrant mitophagy caused by olanzapine was via blocking mitophagosome-lysosome fusion. Furthermore, olanzapine can induce mitochondrial damage and hyperfragmentation of the mitochondrial network. The mitophagosome-lysosome fusion in olanzapine-induced aging models can be restored by a mitophagy inducer, urolithin A, which alleviates defective mitophagy, mitochondrial damage, and fragmentation of the mitochondrial network. Moreover, the mitophagy inducer ameliorated behavioral changes induced by olanzapine, including shortened lifespan, and impaired health span, learning, and memory. These data indicate that olanzapine impairs mitophagy, leading to the shortened lifespan, impaired health span, and cognitive deficits. Furthermore, this study suggests the potential application of mitophagy inducers as therapeutic strategies to reverse APD-induced adverse effects associated with accelerated aging.

Therapeutic Effects of Mesenchymal Stromal Cells Require Mitochondrial Transfer and Quality Control

Due to their beneficial effects in an array of diseases, Mesenchymal Stromal Cells (MSCs) have been the focus of intense preclinical research and clinical implementation for decades. MSCs have multilineage differentiation capacity, support hematopoiesis, secrete pro-regenerative factors and exert immunoregulatory functions promoting homeostasis and the resolution of injury/inflammation. The main effects of MSCs include modulation of immune cells (macrophages, neutrophils, and lymphocytes), secretion of antimicrobial peptides, and transfer of mitochondria (Mt) to injured cells. These actions can be enhanced by priming (i.e., licensing) MSCs prior to exposure to deleterious microenvironments. Preclinical evidence suggests that MSCs can exert therapeutic effects in a variety of pathological states, including cardiac, respiratory, hepatic, renal, and neurological diseases. One of the key emerging beneficial actions of MSCs is the improvement of mitochondrial functions in the injured tissues by enhancing mitochondrial quality control (MQC). Recent advances in the understanding of cellular MQC, including mitochondrial biogenesis, mitophagy, fission, and fusion, helped uncover how MSCs enhance these processes. Specifically, MSCs have been suggested to regulate peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α)-dependent biogenesis, Parkin-dependent mitophagy, and Mitofusins (Mfn1/2) or Dynamin Related Protein-1 (Drp1)-mediated fission/fusion. In addition, previous studies also verified mitochondrial transfer from MSCs through tunneling nanotubes and via microvesicular transport. Combined, these effects improve mitochondrial functions, thereby contributing to the resolution of injury and inflammation. Thus, uncovering how MSCs affect MQC opens new therapeutic avenues for organ injury, and the transplantation of MSC-derived mitochondria to injured tissues might represent an attractive new therapeutic approach.

Mitochondrial transport in neurons and evidence for its involvement in acute neurological disorders

Ensuring mitochondrial quality is essential for maintaining neuronal homeostasis, and mitochondrial transport plays a vital role in mitochondrial quality control. In this review, we first provide an overview of neuronal mitochondrial transport, followed by a detailed description of the various motors and adaptors associated with the anterograde and retrograde transport of mitochondria. Subsequently, we review the modest evidence involving mitochondrial transport mechanisms that has surfaced in acute neurological disorders, including traumatic brain injury, spinal cord injury, spontaneous intracerebral hemorrhage, and ischemic stroke. An in-depth study of this area will help deepen our understanding of the mechanisms underlying the development of various acute neurological disorders and ultimately improve therapeutic options.

Role of Mitochondrial Dynamics in Heart Diseases

Mitochondrial dynamics, including fission and fusion processes, are essential for heart health. Mitochondria, the powerhouses of cells, maintain their integrity through continuous cycles of biogenesis, fission, fusion, and degradation. Mitochondria are relatively immobile in the adult heart, but their morphological changes due to mitochondrial morphology factors are critical for cellular functions such as energy production, organelle integrity, and stress response. Mitochondrial fusion proteins, particularly Mfn1/2 and Opa1, play multiple roles beyond their pro-fusion effects, such as endoplasmic reticulum tethering, mitophagy, cristae remodeling, and apoptosis regulation. On the other hand, the fission process, regulated by proteins such as Drp1, Fis1, Mff and MiD49/51, is essential to eliminate damaged mitochondria via mitophagy and to ensure proper cell division. In the cardiac system, dysregulation of mitochondrial dynamics has been shown to cause cardiac hypertrophy, heart failure, ischemia/reperfusion injury, and various cardiac diseases, including metabolic and inherited cardiomyopathies. In addition, mitochondrial dysfunction associated with oxidative stress has been implicated in atherosclerosis, hypertension and pulmonary hypertension. Therefore, understanding and regulating mitochondrial dynamics is a promising therapeutic tool in cardiac diseases. This review summarizes the role of mitochondrial morphology in heart diseases for each mitochondrial morphology regulatory gene, and their potential as therapeutic targets to heart diseases.

Responsive calcium-derived nanoassemblies induce mitochondrial disorder to promote tumor calcification

Physiological calcification of the treated tumor area is considered to be a predictor of good prognosis. Promoting tumor calcification by inducing mitochondrial metabolic disorder and destroying calcium equilibrium has a potential inhibitory effect on tumor proliferation. Here, by promoting calcification by inducing mitochondrial dysfunction combined with triggering a surge of reactive oxygen species, we construct a bioresponsive calcification initiator, termed CaP-AA, using CaHPO4 covalently doped l-ascorbic acid. CaHPO4 releases Ca2+ within the cytoplasm of tumor cells to trigger calcium overload. Meanwhile, exogenous l-ascorbic acid indirectly enhances metabolic balance disruption via pro-oxidant effects. Such Ca2+ overload increases the likelihood of tumor calcification in vivo for tumor inhibition by perturbing mitochondrial homeostasis. The introduction of responsive calcium sources that would, in turn, trigger intratumoral calcification mediated by perturbing mitochondrial homeostasis would be an effective regulatory strategy for tumor therapy.

Ruscogenin Alleviates Myocardial Ischemia via Myosin IIA-Dependent Mitochondrial Fusion and Fission Balance

Ruscogenin (RUS), a major effective steroidal sapogenin derived from Ophiopogon japonicas, has been reported to alleviate myocardial ischemia (MI), but its cardioprotective mechanism is still not completely clear. In this study, we observed that RUS markedly reduced MI-induced myocardial injury, as evidenced by notable reductions in infarct size, improvement in biochemical markers, alleviation of cardiac pathology, amelioration of mitochondrial damage, and inhibition of myocardial apoptosis. Moreover, RUS notably suppressed oxygen-glucose deprivation (OGD)-triggered cell injury and apoptosis. Notably, RUS demonstrated a considerable decrease of the interaction between myosin IIA and F-actin, along with the restoration of mitochondrial fusion and fission balance. We further confirmed that the effects of RUS on MI were mediated by myosin IIA using siRNA and overexpression techniques. The inhibition of myosin IIA resulted in a significant improvement of mitochondrial fusion and fission imbalance, while simultaneously counteracting the beneficial effects of RUS. By contrast, overexpression of myosin IIA aggravated the imbalance between mitochondrial fusion and fission and partially weakened the protection of RUS. These findings suggest that myosin IIA is essential or even a key functional protein in the cardioprotection of RUS. Overall, our results have elucidated an undiscovered mechanism involving myosin IIA-dependent mitochondrial fusion and fission balance for treating MI. Furthermore, our study has uncovered a novel mechanism underlying the protective effects of RUS.

PGAM5 is an MFN2 phosphatase that plays an essential role in the regulation of mitochondrial dynamics

Mitochondrial morphology is regulated by the post-translational modifications of the dynamin family GTPase proteins including mitofusin 1 (MFN1), MFN2, and dynamin-related protein 1 (DRP1). Mitochondrial phosphatase phosphoglycerate mutase 5 (PGAM5) is emerging as a regulator of these post-translational modifications; however, its precise role in the regulation of mitochondrial morphology is unknown. We show that PGAM5 interacts with MFN2 and DRP1 in a stress-sensitive manner. PGAM5 regulates MFN2 phosphorylation and consequently protects it from ubiquitination and degradation. Further, phosphorylation and dephosphorylation modification of MFN2 regulates its fusion ability. Phosphorylation enhances fission and degradation, whereas dephosphorylation enhances fusion. PGAM5 dephosphorylates MFN2 to promote mitochondrial network formation. Further, using a Drosophila genetic model, we demonstrate that the MFN2 homolog Marf and dPGAM5 are in the same biological pathway. Our results identify MFN2 dephosphorylation as a regulator of mitochondrial fusion and PGAM5 as an MFN2 phosphatase.

NRF1-mediated mitochondrial biogenesis antagonizes innate antiviral immunity

Mitochondrial biogenesis is the process of generating new mitochondria to maintain cellular homeostasis. Here, we report that viruses exploit mitochondrial biogenesis to antagonize innate antiviral immunity. We found that nuclear respiratory factor-1 (NRF1), a vital transcriptional factor involved in nuclear-mitochondrial interactions, is essential for RNA (VSV) or DNA (HSV-1) virus-induced mitochondrial biogenesis. NRF1 deficiency resulted in enhanced innate immunity, a diminished viral load, and morbidity in mice. Mechanistically, the inhibition of NRF1-mediated mitochondrial biogenesis aggravated virus-induced mitochondrial damage, promoted the release of mitochondrial DNA (mtDNA), increased the production of mitochondrial reactive oxygen species (mtROS), and activated the innate immune response. Notably, virus-activated kinase TBK1 phosphorylated NRF1 at Ser318 and thereby triggered the inactivation of the NRF1-TFAM axis during HSV-1 infection. A knock-in (KI) strategy that mimicked TBK1-NRF1 signaling revealed that interrupting the TBK1-NRF1 connection ablated mtDNA release and thereby attenuated the HSV-1-induced innate antiviral response. Our study reveals a previously unidentified antiviral mechanism that utilizes a NRF1-mediated negative feedback loop to modulate mitochondrial biogenesis and antagonize innate immune response.

PHLPP1 regulates PINK1-parkin signalling and life span

Adaptability to intracellular or extracellular cues is essential for maintaining cellular homeostasis. Metabolic signals intricately control the morphology and functions of mitochondria by regulating bioenergetics and metabolism. Here, we describe the involvement of PHLPP1, a Ser/Thr phosphatase, in mitochondrial homeostasis. Microscopic analysis showed the enhanced globular structure of mitochondria in PHLPP1-depleted HEK 293T and C2C12 cells, while forced expression of PHLPP1 promoted mitochondrial tubularity. We show that PHLPP1 promoted pro-fusion markers MFN2 and p-DRP1Ser637 levels using over-expression and knockdown strategies. Contrastingly, PHLPP1 induced mitochondrial fragmentation by augmenting pro-fission markers, t-DRP1 and pDrp1Ser616 upon mitochondrial stress. At the molecular level, PHLPP1 interacted with and caused dephosphorylation of calcineurin, a p-DRP1Ser637 phosphatase, under basal conditions. Likewise, PHLPP1 dimerized with PINK1 under basal conditions. However, the interaction of PHLPP1 with both calcineurin and PINK1 was impaired upon CCCP and oligomycin-induced mitochondrial stress. Interestingly, upon mitochondrial membrane depolarization, PHLPP1 promoted PINK1 stabilization and parkin recruitment to mitochondria, and thereby activated the mitophagy machinery providing a molecular explanation for the dual effects of PHLPP1 on mitochondria under different conditions. Consistent with our in-vitro findings, depletion of phlp-2, ortholog of PHLPP1 in C. elegans, led to mitochondrial fission under basal conditions, extended the lifespan of the worms, and enhanced survival of worms subjected to paraquat-induced oxidative stress.

3D reconstructions of parasite development and the intracellular niche of the microsporidian pathogen E. intestinalis

Microsporidia are an early-diverging group of fungal pathogens that infect a wide range of hosts. Several microsporidian species infect humans, and infections can lead to fatal disease in immunocompromised individuals. As obligate intracellular parasites with highly reduced genomes, microsporidia are dependent on metabolites from their hosts for successful replication and development. Our knowledge of how microsporidian parasites develop inside the host remains rudimentary, and our understanding of the intracellular niche occupied by microsporidia has thus far relied largely on 2D TEM images and light microscopy. Here, we use serial block face scanning electron microscopy (SBF-SEM) to capture 3D snapshots of the human-infecting microsporidian, Encephalitozoon intestinalis , within host cells. We track the development of E. intestinalis through its life cycle, which allows us to propose a model for how its infection organelle, the polar tube, is assembled de novo in each developing spore. 3D reconstructions of parasite-infected cells provide insights into the physical interactions between host cell organelles and parasitophorous vacuoles, which contain the developing parasites. The host cell mitochondrial network is substantially remodeled during E. intestinalis infection, leading to mitochondrial fragmentation. SBF-SEM analysis shows changes in mitochondrial morphology in infected cells, and live-cell imaging provides insights into mitochondrial dynamics during infection. Together, our data provide insights into parasite development, polar tube assembly, and microsporidia-induced mitochondrial remodeling in the host cell.

PRKN/parkin-mediated mitophagy is induced by the probiotics Saccharomyces boulardii and Lactococcus lactis

Mitochondrial impairment is a hallmark feature of neurodegenerative disorders, such as Parkinson disease, and PRKN/parkin-mediated mitophagy serves to remove unhealthy mitochondria from cells. Notably, probiotics are used to alleviate several symptoms of Parkinson disease including impaired locomotion and neurodegeneration in preclinical studies and constipation in clinical trials. There is some evidence to suggest that probiotics can modulate mitochondrial quality control pathways. In this study, we screened 49 probiotic strains and tested distinct stages of mitophagy to determine whether probiotic treatment could upregulate mitophagy in cells undergoing mitochondrial stress. We found two probiotics, Saccharomyces boulardii and Lactococcus lactis, that upregulated mitochondrial PRKN recruitment, phospho-ubiquitination, and MFN degradation in our cellular assays. Administration of these strains to Drosophila that were exposed to paraquat, a mitochondrial toxin, resulted in improved longevity and motor function. Further, we directly observed increased lysosomal degradation of dysfunctional mitochondria in the treated Drosophila brains. These effects were replicated in vitro and in vivo with supra-physiological concentrations of exogenous soluble factors that are released by probiotics in cultures grown under laboratory conditions. We identified methyl-isoquinoline-6-carboxylate as one candidate molecule, which upregulates mitochondrial PRKN recruitment, phospho-ubiquitination, MFN degradation, and lysosomal degradation of damaged mitochondria. Addition of methyl-isoquinoline-6-carboxylate to the fly food restored motor function to paraquat-treated Drosophila. These data suggest a novel mechanism that is facilitated by probiotics to stimulate mitophagy through a PRKN-dependent pathway, which could explain the potential therapeutic benefit of probiotic administration to patients with Parkinson disease.

Mitochondrial morphology controls fatty acid utilization by changing CPT1 sensitivity to malonyl-CoA

Changes in mitochondrial morphology are associated with nutrient utilization, but the precise causalities and the underlying mechanisms remain unknown. Here, using cellular models representing a wide variety of mitochondrial shapes, we show a strong linear correlation between mitochondrial fragmentation and increased fatty acid oxidation (FAO) rates. Forced mitochondrial elongation following MFN2 over-expression or DRP1 depletion diminishes FAO, while forced fragmentation upon knockdown or knockout of MFN2 augments FAO as evident from respirometry and metabolic tracing. Remarkably, the genetic induction of fragmentation phenocopies distinct cell type-specific biological functions of enhanced FAO. These include stimulation of gluconeogenesis in hepatocytes, induction of insulin secretion in islet β-cells exposed to fatty acids, and survival of FAO-dependent lymphoma subtypes. We find that fragmentation increases long-chain but not short-chain FAO, identifying carnitine O-palmitoyltransferase 1 (CPT1) as the downstream effector of mitochondrial morphology in regulation of FAO. Mechanistically, we determined that fragmentation reduces malonyl-CoA inhibition of CPT1, while elongation increases CPT1 sensitivity to malonyl-CoA inhibition. Overall, these findings underscore a physiologic role for fragmentation as a mechanism whereby cellular fuel preference and FAO capacity are determined.

A GPCR screening in human keratinocytes identifies that the metabolite receptor HCAR3 controls epithelial proliferation, migration, and cellular respiration

Epithelial cells in the skin and other tissues rely on signals from their environment to maintain homeostasis and respond to injury, and G protein-coupled receptors (GPCRs) play a critical role in this communication. A better understanding of the GPCRs expressed in epithelial cells will contribute to understanding the relationship between cells and their niche and could lead to developing new therapies to modulate cell fate. This study used human primary keratinocytes as a model to investigate the specific GPCRs regulating epithelial cell proliferation and differentiation. We identified three key receptors, hydroxycarboxylic acid-receptor 3 (HCAR3), leukotriene B4-receptor 1 (LTB4R), and G Protein-Coupled Receptor 137 (GPR137) and found that knockdown of these receptors led to changes in numerous gene networks that are important for maintaining cell identity and promoting proliferation while inhibiting differentiation. Our study also revealed that the metabolite receptor HCAR3 regulates keratinocyte migration and cellular metabolism. Knockdown of HCAR3 led to reduced keratinocyte migration and respiration, which could be attributed to altered metabolite use and aberrant mitochondrial morphology caused by the absence of the receptor. This study contributes to understanding the complex interplay between GPCR signaling and epithelial cell fate decisions.