Apoptosis-Inducing Factor (AIF) in Physiology and Disease: The Tale of a Repented Natural Born Killer

An acidic pH environment converts necroptosis to apoptosis

Cardiac ischemia results in anaerobic metabolism and lactic acid accumulation and with time, intracellular and extracellular acidosis. Ischemia and subsequent reperfusion injury (IRI) lead to various forms of programmed cell death. Necroptosis is a major form of programmed necrosis that worsens cardiac function directly and also promotes inflammation by the release of cellular contents. Potential effects of increasing acidosis on programmed cell death and their specific components have not been well studied. While apoptosis is caspase-dependent, in contrast, necroptosis is mediated by the receptor-interacting protein kinases 1 and 3 (RIPK1/3). In our study, we observed that at physiological pH = 7.4, caspase-8 inhibition did not prevent TNFα-induced cell death in mouse cardiac vascular endothelial cells (MVECs) but promoted necroptotic cell death. As expected, necroptosis was blocked by RIPK1 inhibition. However, at pH = 6.5, TNFα induced an apoptosis-like pattern which was inhibited by caspase-8 inhibition. Interestingly phosphorylation of necroptotic molecules RIPK1, RIPK3, and mixed lineage kinase domain-like protein (MLKL) was enhanced in an acidic pH environment. However, RIPK3 and MLKL phosphorylation was self-limited which may have limited their participation in necroptosis. In addition, an acidic pH promoted apoptosis-inducing factor (AIF) cleavage and nuclear translocation. AIF RNA silencing inhibited cell death, supporting the role of AIF in this cell death. In summary, our study demonstrated that the pH of the micro-environment during inflammation can bias cell death pathways by altering the function of necroptosis-related molecules and promoting AIF-mediated cell death. Further insights into the mechanisms by which an acidic cellular micro-environment influences these and perhaps other forms of regulated cell death, may lead to therapeutic strategies to attenuate IRI.

PARP1 inhibition prevents oxidative stress in age-related hearing loss via PAR-Ca2+-AIF axis in cochlear strial marginal cells

Studies have highlighted oxidative damage in the inner ear as a critical pathological basis for sensorineural hearing loss, especially the presbycusis. Poly(ADP-ribose) polymerase-1 (PARP1) activation responds to oxidative stress-induced DNA damage with pro-repair and pro-death effects resembling two sides of the same coin. PARP1-related cell death, known as parthanatos, whose underlying mechanisms are attractive research hotspots but remain to be clarified. In this study, we observed that aged rats showed stria vascularis degeneration and oxidative damage, and PARP1-dependent cell death was prominent in age-related cochlear disorganization and dysfunction. Based on oxidative stress model of primary cultured stria marginal cells (MCs), we revealed that upregulated PARP1 and PAR (Poly(ADP-ribose)) polymers are responsible for MCs oxidative death with high mitochondrial permeability transition pore (mPTP) opening and mitochondrial membrane potential (MMP) collapse, while inhibition of PARP1 ameliorated the adverse outcomes. Importantly, the PARylation of apoptosis-inducing factor (AIF) is essential for its conformational change and translocation, which subsequently causes DNA break and cell death. Concretely, the interaction of PAR and truncated AIF (tAIF) is the mainstream in the parthanatos pathway. We also found that the effects of AIF cleavage and release were achieved through calpain activity and mPTP opening, both of which could be regulated by PARP1 via mediation of mitochondria Ca2+ concentration. In conclusion, the PAR-Ca2+-tAIF signaling pathway in parthanatos contributes to the oxidative stress damage observed in MCs. Targeting PAR-Ca2+-tAIF might be a potential therapeutic strategy for the early intervention of presbycusis and other oxidative stress-associated sensorineural deafness.

Experimental evidence for Parthanatos-like mode of cell death of heat-damaged human skin fibroblasts in a cell culture-based in vitro burn model

The cellular mechanisms of burn conversion of heat damaged tissue are center of many studies. Even if the molecular mechanisms of heat-induced cell death are controversially discussed in the current literature, it is widely accepted that caspase-mediated apoptosis plays a central role. In the current study we wanted to develop further information on the nature of the mechanism of heat-induced cell death of fibroblasts in vitro. We found that heating of human fibroblast cultures (a 10 s rise from 37 °C to 67 °C followed by a 13 s cool down to 37 °C) resulted in the death of about 50% of the cells. However, the increase in cell death started with a delay, about one hour after exposure to heat, and reached the maximum after about five hours. The lack of clear evidence for an active involvement of effector caspase in the observed cell death mechanism and the lack of observation of the occurrence of hypodiploid nuclei contradict heat-induced cell death by caspase-mediated apoptosis. Moreover, a dominant heat-induced increase in PARP1 protein expression, which correlated with a time-delayed ATP synthesis inhibition, appearance of double-strand breaks and secondary necrosis, indicate a different type of cell death than apoptosis. Indeed, increased translocation of Apoptosis Inducing Factor (AIF) and Macrophage Migration Inhibitory Factor (MIF) into cell nuclei, which correlates with the mentioned enhanced PARP1 protein expression, indicate PARP1-induced, AIF-mediated and MIF-activated cell death. With regard to the molecular actors involved, the cellular processes and temporal sequences, the mode of cell death observed in our model is very similar to the cell death mechanism via Parthanatos described in the literature.

Neuroglobin overexpression in cerebellar neurons of Harlequin mice improves mitochondrial homeostasis and reduces ataxic behavior

Neuroglobin, a member of the globin superfamily, is abundant in the brain, retina, and cerebellum of mammals and localizes to mitochondria. The protein exhibits neuroprotective capacities by participating in electron transfer, oxygen supply, and protecting against oxidative stress. Our objective was to determine whether neuroglobin overexpression can be used to treat neurological disorders. We chose Harlequin mice, which harbor a retroviral insertion in the first intron of the apoptosis-inducing factor gene resulting in the depletion of the corresponding protein essential for mitochondrial biogenesis. Consequently, Harlequin mice display degeneration of the cerebellum and suffer from progressive blindness and ataxia. Cerebellar ataxia begins in Harlequin mice at the age of 4 months and is characterized by neuronal cell disappearance, bioenergetics failure, and motor and cognitive impairments, which aggravated with aging. Mice aged 2 months received adeno-associated viral vectors harboring the coding sequence of neuroglobin or apoptosis-inducing factor in both cerebellar hemispheres. Six months later, Harlequin mice exhibited substantial improvements in motor and cognitive skills; probably linked to the preservation of respiratory chain function, Purkinje cell numbers and connectivity. Thus, without sharing functional properties with apoptosis-inducing factor, neuroglobin was efficient in reducing ataxia in Harlequin mice.

Advancements in unravelling the fundamental function of the ATAD3 protein in multicellular organisms

ATPase family AAA domain containing protein 3, commonly known as ATAD3 is a versatile mitochondrial protein that is involved in a large number of pathways. ATAD3 is a transmembrane protein that spans both the inner mitochondrial membrane and outer mitochondrial membrane. It, therefore, functions as a connecting link between the mitochondrial lumen and endoplasmic reticulum facilitating their cross-talk. ATAD3 contains an N-terminal domain which is amphipathic in nature and is inserted into the membranous space of the mitochondria, while the C-terminal domain is present towards the lumen of the mitochondria and contains the ATPase domain. ATAD3 is known to be involved in mitochondrial biogenesis, cholesterol transport, hormone synthesis, apoptosis and several other pathways. It has also been implicated to be involved in cancer and many neurological disorders making it an interesting target for extensive studies. This review aims to provide an updated comprehensive account of the role of ATAD3 in the mitochondria especially in lipid transport, mitochondrial-endoplasmic reticulum interactions, cancer and inhibition of mitophagy.

Exposure to lipid mixture induces intracellular lipid droplet formation and impairs mitochondrial functions in astrocytes

Astrocytes, the predominant glial cells in the central nervous system (CNS), play diverse roles including metabolic support for neurons, provision of neurotrophic factors, facilitation of synaptic neurotransmitter uptake, regulation of ion balance, and involvement in synaptic formation. The accumulation of lipids has been noted in various neurological conditions, yet the response of astrocytes to lipid-rich environments remains unclear. In this study, primary astrocytes isolated from the neonatal rat cortex were exposed to a lipid mixture (LM) comprising cholesterol and various fatty acids to explore their reaction. Our results showed that astrocyte viability remained unchanged following 24 h of 5% or 10% LM treatment. However, exposure to LM for 96 h resulted in reduced cell viability. In addition, LM treatment led to the accumulation of lipid droplets (LDs) in astrocytes, with LD size increasing over prolonged exposure periods. Following 24 h of LM treatment and then 48 h in fresh medium, a significant reduction in intracellular LD size was observed in cultures treated with 5% LM, while no change occurred in cultures exposed to 10% LM. Yet, exposure to 10% LM for 24 h significantly increased the expression of the cholesterol efflux regulatory protein/ATP-binding cassette transporter (ABCA1) gene, responsible for intracellular cholesterol efflux, resulting in reduced cholesterol content within astrocytes. Moreover, LM exposure led to decreased mitochondrial membrane potential (MMP) and increased levels of mature apoptosis-inducing factor (AIF). The smaller LDs were observed to co-localize with microtubule-associated protein 1A/1 B light chain 3 B (LC3) and lysosomal-associated membrane protein-1 (LAMP-1) in LM-treated astrocytes, coinciding with lysosomal acidification. These results indicate that the continuous buildup of LDs in astrocytes residing in lipid-enriched environments may be attributed to disruptions caused by LM in mitochondrial and lysosomal functions. Such disruptions could potentially impede the supportive role of astrocytes in neuronal function.

The Multifaceted Role of miR-21 in Pancreatic Cancers

With the lack of specific signs and symptoms, pancreatic ductal adenocarcinoma (PDAC) is often diagnosed at late metastatic stages, resulting in poor survival outcomes. Among various biomarkers, microRNA-21 (miR-21), a small non-coding RNA, is highly expressed in PDAC. By inhibiting regulatory proteins at the 3' untranslated regions (UTR), miR-21 holds significant roles in PDAC cell proliferation, epithelial-mesenchymal transition, angiogenesis, as well as cancer invasion, metastasis, and resistance therapy. We conducted a systematic search across major databases for articles on miR-21 and pancreatic cancer mainly published within the last decade, focusing on their diagnostic, prognostic, therapeutic, and biological roles. This rigorous approach ensured a comprehensive review of miR-21's multifaceted role in pancreatic cancers. In this review, we explore the current understandings and future directions regarding the regulation, diagnostic, prognostic, and therapeutic potential of targeting miR-21 in PDAC. This exhaustive review discusses the involvement of miR-21 in proliferation, epithelial-mesenchymal transition (EMT), apoptosis modulation, angiogenesis, and its role in therapy resistance. Also discussed in the review is the interplay between various molecular pathways that contribute to tumor progression, with specific reference to pancreatic ductal adenocarcinoma.

Mechanistic Insights into 1,2-bis(2,4,6-tribromophenoxy)ethane-Induced Male Reproductive Toxicity in Zebrafish

The novel brominated flame retardant, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), has increasingly been detected in environmental and biota samples. However, limited information is available regarding its toxicity, especially at environmentally relevant concentrations. In the present study, adult male zebrafish were exposed to varying concentrations of BTBPE (0, 0.01, 0.1, 1, and 10 μg/L) for 28 days. The results demonstrated underperformance in mating behavior and reproductive success of male zebrafish when paired with unexposed females. Additionally, a decline in sperm quality was confirmed in BTBPE-exposed male zebrafish, characterized by decreased total motility, decreased progressive motility, and increased morphological malformations. To elucidate the underlying mechanism, an integrated proteomic and phosphoproteomic analysis was performed, revealing a predominant impact on mitochondrial functions at the protein level and a universal response across different cellular compartments at the phosphorylation level. Ultrastructural damage, increased expression of apoptosis-inducing factor, and disordered respiratory chain confirmed the involvement of mitochondrial impairment in zebrafish testes. These findings not only provide valuable insights for future evaluations of the potential risks posed by BTBPE and similar chemicals but also underscore the need for further research into the impact of mitochondrial dysfunction on reproductive health.

AIF translocation into nucleus caused by Aifm1 R450Q mutation: generation and characterization of a mouse model for AUNX1

Mutations in AIFM1, encoding for apoptosis-inducing factor (AIF), cause AUNX1, an X-linked neurologic disorder with late-onset auditory neuropathy (AN) and peripheral neuropathy. Despite significant research on AIF, there are limited animal models with the disrupted AIFM1 representing the corresponding phenotype of human AUNX1, characterized by late-onset hearing loss and impaired auditory pathways. Here, we generated an Aifm1 p.R450Q knock-in mouse model (KI) based on the human AIFM1 p.R451Q mutation. Hemizygote KI male mice exhibited progressive hearing loss from P30 onward, with greater severity at P60 and stabilization until P210. Additionally, muscle atrophy was observed at P210. These phenotypic changes were accompanied by a gradual reduction in the number of spiral ganglion neuron cells (SGNs) at P30 and ribbons at P60, which coincided with the translocation of AIF into the nucleus starting from P21 and P30, respectively. The SGNs of KI mice at P210 displayed loss of cytomembrane integrity, abnormal nuclear morphology, and dendritic and axonal demyelination. Furthermore, the inner hair cells and myelin sheath displayed abnormal mitochondrial morphology, while fibroblasts from KI mice showed impaired mitochondrial function. In conclusion, we successfully generated a mouse model recapitulating AUNX1. Our findings indicate that disruption of Aifm1 induced the nuclear translocation of AIF, resulting in the impairment in the auditory pathway.

CHCHD4 binding affects the active site of apoptosis inducing factor (AIF): Structural determinants for allosteric regulation

Apoptosis-inducing factor (AIF), which is confined to mitochondria of normal healthy cells, is the first identified caspase-independent cell death effector. Moreover, AIF is required for the optimal functioning of the respiratory chain machinery. Recent findings have revealed that AIF fulfills its pro-survival function by interacting with CHCHD4, a soluble mitochondrial protein which promotes the entrance and the oxidative folding of different proteins in the inner membrane space. Here, we report the crystal structure of the ternary complex involving the N-terminal 27-mer peptide of CHCHD4, NAD+, and AIF harboring its FAD (flavin adenine dinucleotide) prosthetic group in oxidized form. Combining this information with biophysical and biochemical data on the CHCHD4/AIF complex, we provide a detailed structural description of the interaction between the two proteins, validated by both chemical cross-linking mass spectrometry analysis and site-directed mutagenesis.

Synaptic vesicle protein 2A mitigates parthanatos via apoptosis-inducing factor in a rat model of pharmacoresistant epilepsy

AIMS

Synaptic vesicle protein 2A (SV2A) is a unique therapeutic target for pharmacoresistant epilepsy (PRE). As seizure-induced neuronal programmed death, parthanatos was rarely reported in PRE. Apoptosis-inducing factor (AIF), which has been implicated in parthanatos, shares a common cytoprotective function with SV2A. We aimed to investigate whether parthanatos participates in PRE and is mitigated by SV2A via AIF.

METHODS

An intraperitoneal injection of lithium chloride-pilocarpine was used to establish an epileptic rat model, and phenytoin and phenobarbital sodium were utilized to select PRE and pharmacosensitive rats. The expression of SV2A was manipulated via lentivirus delivery into the hippocampus. Video surveillance was used to assess epileptic ethology. Biochemical tests were employed to test hippocampal tissues following a successful SV2A infection. Molecular dynamic calculations were used to simulate the interaction between SV2A and AIF.

RESULTS

Parthanatos core index, PARP1, PAR, nuclear AIF and MIF, γ-H2AX, and TUNEL staining were all increased in PRE. SV2A is bound to AIF to form a stable complex, successfully inhibiting AIF and MIF nuclear translocation and parthanatos and consequently mitigating spontaneous recurrent seizures in PRE. Moreover, parthanatos deteriorated after the SV2A reduction.

SIGNIFICANCE

SV2A protected hippocampal neurons and mitigated epileptic seizures by inhibiting parthanatos via binding to AIF in PRE.

Chemical screening by time-resolved X-ray scattering to discover allosteric probes

Drug discovery relies on efficient identification of small-molecule leads and their interactions with macromolecular targets. However, understanding how chemotypes impact mechanistically important conformational states often remains secondary among high-throughput discovery methods. Here, we present a conformational discovery pipeline integrating time-resolved, high-throughput small-angle X-ray scattering (TR-HT-SAXS) and classic fragment screening applied to allosteric states of the mitochondrial import oxidoreductase apoptosis-inducing factor (AIF). By monitoring oxidized and X-ray-reduced AIF states, TR-HT-SAXS leverages structure and kinetics to generate a multidimensional screening dataset that identifies fragment chemotypes allosterically stimulating AIF dimerization. Fragment-induced dimerization rates, quantified with time-resolved SAXS similarity analysis (kVR), capture structure-activity relationships (SAR) across the top-ranked 4-aminoquinoline chemotype. Crystallized AIF-aminoquinoline complexes validate TR-SAXS-guided SAR, supporting this conformational chemotype for optimization. AIF-aminoquinoline structures and mutational analysis reveal active site F482 as an underappreciated allosteric stabilizer of AIF dimerization. This conformational discovery pipeline illustrates TR-HT-SAXS as an effective technology for targeting chemical leads to important macromolecular states.

Nano-flow cytometry unveils mitochondrial permeability transition process and multi-pathway cell death induction for cancer therapy

Mitochondrial permeability transition (mPT)-mediated mitochondrial dysfunction plays a pivotal role in various human diseases. However, the intricate details of its mechanisms and the sequence of events remain elusive, primarily due to the interference caused by Bax/Bak-induced mitochondrial outer membrane permeabilization (MOMP). To address these, we have developed a methodology that utilizes nano-flow cytometry (nFCM) to quantitatively analyze the opening of mitochondrial permeability transition pore (mPTP), dissipation of mitochondrial membrane potential ( Δ Ψm), release of cytochrome c (Cyt c), and other molecular alternations of isolated mitochondria in response to mPT induction at the single-mitochondrion level. It was identified that betulinic acid (BetA) and antimycin A can directly induce mitochondrial dysfunction through mPT-mediated mechanisms, while cisplatin and staurosporine cannot. In addition, the nFCM analysis also revealed that BetA primarily induces mPTP opening through a reduction in Bcl-2 and Bcl-xL protein levels, along with an elevation in ROS content. Employing dose and time-dependent strategies of BetA, for the first time, we experimentally verified the sequential occurrence of mPTP opening and Δ Ψm depolarization prior to the release of Cyt c during mPT-mediated mitochondrial dysfunction. Notably, our study uncovers a simultaneous release of cell-death-associated factors, including Cyt c, AIF, PNPT1, and mtDNA during mPT, implying the initiation of multiple cell death pathways. Intriguingly, BetA induces caspase-independent cell death, even in the absence of Bax/Bak, thereby overcoming drug resistance. The presented findings offer new insights into mPT-mediated mitochondrial dysfunction using nFCM, emphasizing the potential for targeting such dysfunction in innovative cancer therapies and interventions.

The unfolded protein response-glutathione metabolism axis: A novel target of a cycloruthenated complexes bypassing tumor resistance mechanisms

Platinum-based drugs remain the reference treatment for gastric cancer (GC). However, the frequency of resistance, due to mutations in TP53 or alterations in the energy and redox metabolisms, impairs the efficacy of current treatments, highlighting the need for alternative therapeutic options. Here, we show that a cycloruthenated compound targeting the redox metabolism, RDC11, induces higher cytotoxicity than oxaliplatin in GC cells and is more potent in reducing tumor growth in vivo. Detailed investigations into the mode of action of RDC11 indicated that it targets the glutathione (GSH) metabolism, which is an important drug resistance mechanism. We demonstrate that cycloruthenated complexes regulate the expression of enzymes of the transsulfuration pathway via the Unfolded Protein Response (UPR) and its effector ATF4. Furthermore, RDC11 induces the expression of SLC7A11 encoding for the cystine/glutamate antiporter xCT. These effects lead to a lower cellular GSH content and elevated oxygen reactive species production, causing the activation of a caspase-independent apoptosis. Altogether, this study provides the first evidence that cycloruthenated complexes target the GSH metabolism, neutralizing thereby a major resistance mechanism towards platinum-based chemotherapies and anticancer immune response.

Parthanatos: Mechanisms, modulation, and therapeutic prospects in neurodegenerative disease and stroke

Parthanatos is a cell death signaling pathway that has emerged as a compelling target for pharmaceutical intervention. It plays a pivotal role in the neuron loss and neuroinflammation that occurs in Parkinson's Disease (PD), Alzheimer's Disease (AD), Huntington's Disease (HD), Amyotrophic Lateral Sclerosis (ALS), and stroke. There are currently no treatments available to humans to prevent cell death in any of these diseases. This review provides an in-depth examination of the current understanding of the Parthanatos mechanism, with a particular focus on its implications in neuroinflammation and various diseases discussed herein. Furthermore, we thoroughly review potential intervention targets within the Parthanatos pathway. We dissect recent progress in inhibitory strategies, complimented by a detailed structural analysis of key Parthanatos executioners, PARP-1, AIF, and MIF, along with an assessment of their established inhibitors. We hope to introduce a new perspective on the feasibility of targeting components within the Parthanatos pathway, emphasizing its potential to bring about transformative outcomes in therapeutic interventions. By delineating therapeutic opportunities and known targets, we seek to emphasize the imperative of blocking Parthanatos as a precursor to developing disease-modifying treatments. This comprehensive exploration aims to catalyze a paradigm shift in our understanding of potential neurodegenerative disease therapeutics, advocating for the pursuit of effective interventions centered around Parthanatos inhibition.

The effect of astaxanthin on the alkalinity stress resistance of Exopalaemon carinicauda

Astaxanthin (Axn), a feed additive, can improve growth performance and enhance the environmental stress tolerance of shrimp at all growth stages. High carbonate alkalinity is considered a major stressor that affects the survival, growth, and reproduction of aquatic animals in saline-alkaline waters. In this study, a combined analysis of physiology, transcriptomics, and metabolomics was performed to explore the effected mechanism of Axn on Exopalaemon carinicauda (E. carinicauda) under alkalinity stress. The results revealed that dietary Axn can inhibit oxidative stress damage caused by alkalinity stress and maintain the normal cell structure and mitochondrial membrane potential. Transcriptomic data indicated that differentially expressed genes (DEGs) under alkalinity stress and those under alkalinity stress after Axn feeding were associated with apoptosis. The metabolic data suggested that alkalinity stress has adverse effects on ammonia metabolism, unsaturated fatty acid metabolism, and TCA cycle, and dietary Axn can improve the metabolic processes in E. carinicauda. In addition, transcriptomics and metabolomics analyses showed that Axn could help maintain the cytoskeletal structure and inhibit apoptosis under alkalinity stress; a TUNEL assay further confirmed these effects. Lastly, metabolic responses to alkalinity stress included changes in multiple amino acids and unsaturated fatty acids, and pathways related to energy metabolism were downregulated in the hepatopancreas of E. carinicauda under alkalinity stress. Collectively, all these results provide new insights into the molecular mechanisms underlying alkalinity stress tolerance in E. carinicauda after Axn feeding.

Hepatic transcriptome analyses of juvenile white bass (Morone chrysops) when fed diets where fish meal is partially or totally replaced by alternative protein sources

White bass (Morone chrysops) are a popular sportfish throughout the southern United States, and one parent of the commercially-successful hybrid striped bass (M. chrysops ♂ x M. saxatilis ♀). Currently, white bass are cultured using diets formulated for other carnivorous fish, such as largemouth bass (Micropterus salmoides) or hybrid striped bass and contain a significant percentage of marine fish meal. Since there are no studies regarding the utilization of alternative proteins in this species, we evaluated the global gene expression of white bass fed diets in which fish meal was partially or totally replaced by various combinations of soybean meal, poultry by-product meal, canola meal, soy protein concentrate, wheat gluten, or a commercial protein blend (Pro-Cision™). Six isonitrogenous (40% protein), isolipidic (11%), and isocaloric (17.1 kJ/g) diets were formulated to meet the known nutrient and energy requirements of largemouth bass and hybrid striped bass using nutrient availability data for most of the dietary ingredients. One of the test diets consisted exclusively of plant protein sources. Juvenile white bass (40.2 g initial weight) were stocked into a flow-through aquaculture system (three tanks/diet; 10 fish/tank) and fed the test diets twice daily to satiation for 60 days. RNA sequencing and bioinformatic analyses revealed significant differentially expressed genes between all test diets when compared to fish meal control. A total of 1,260 differentially expressed genes were identified, with major ontology relating to cell cycle and metabolic processes as well as immune gene functions. This data will be useful as a resource for future refinements to moronid diet formulation, as marine fish meal becomes limiting and plant ingredients are increasingly added as a reliable protein source.

Gene therapy for mitochondrial disorders

In this review, we detail the current state of application of gene therapy to primary mitochondrial disorders (PMDs). Recombinant adeno-associated virus-based (rAAV) gene replacement approaches for nuclear gene disorders have been undertaken successfully in more than ten preclinical mouse models of PMDs which has been made possible by the development of novel rAAV technologies that achieve more efficient organ targeting. So far, however, the greatest progress has been made for Leber Hereditary Optic Neuropathy, for which phase 3 clinical trials of lenadogene nolparvovec demonstrated efficacy and good tolerability. Other methods of treating mitochondrial DNA (mtDNA) disorders have also had traction, including refinements to nucleases that degrade mtDNA molecules with pathogenic variants, including transcription activator-like effector nucleases, zinc-finger nucleases, and meganucleases (mitoARCUS). rAAV-based approaches have been used successfully to deliver these nucleases in vivo in mice. Exciting developments in CRISPR-Cas9 gene editing technology have achieved in vivo gene editing in mouse models of PMDs due to nuclear gene defects and new CRISPR-free gene editing approaches have shown great potential for therapeutic application in mtDNA disorders. We conclude the review by discussing the challenges of translating gene therapy in patients both from the point of view of achieving adequate organ transduction as well as clinical trial design.

Vibrio parahaemolyticus thermostable direct haemolysin induces non-classical programmed cell death despite caspase activation

Thermostable direct haemolysin (TDH) is the key virulence factor secreted by the human gastroenteric bacterial pathogen Vibrio parahaemolyticus. TDH is a membrane-damaging pore-forming toxin. It evokes potent cytotoxicity, the mechanism of which still remains under-explored. Here, we have elucidated the mechanistic details of cell death response elicited by TDH. Employing Caco-2 intestinal epithelial cells and THP-1 monocytic cells, we show that TDH induces some of the hallmark features of apoptosis-like programmed cell death. TDH triggers caspase-3 and 7 activations in the THP-1 cells, while caspase-7 activation is observed in the Caco-2 cells. Interestingly, TDH appears to induce caspase-independent cell death. Higher XIAP level and lower Smac/Diablo level upon TDH intoxication provide plausible explanation for the functional inability of caspases in the THP-1 cells, in particular. Further exploration reveals that mitochondria play a central role in the TDH-induced cell death. TDH triggers mitochondrial damage, resulting in the release of AIF and endonuclease G, responsible for the execution of caspase-independent cell death. Among the other critical mediators of cell death, ROS is found to play an important role in the THP-1 cells, while PARP-1 appears to play a critical role in the Caco-2 cells. Altogether, our work provides critical new insights into the mechanism of cell death induction by TDH, showing a common central theme of non-classical programmed cell death. Our study also unravels the interplay of crucial molecules in the underlying signalling processes. Our findings add valuable insights into the role of TDH in the context of the host-pathogen interaction processes.

Parthanatos type programmed cell death and septic patient mortality

OBJECTIVE

Parthanatos is a form of programmed cell death mediated by apoptosis-inducing factor (AIF). However, there are not data on parthanatos in septic patients. The objective of the current study was to explore whether parthanatos is associated with mortality of septic patients.

DESIGN

Observational and prospective study.

SETTING

Three Spanish Intensive Care Units during 2017.

PATIENTS

Patients with sepsis according to Sepsis-3 Consensus criteria.

INTERVENTIONS

Serum AIF concentrations were determined at moment of sepsis diagnosis.

MAIN VARIABLE OF INTEREST

Mortality at 30 days.

RESULTS

There were included 195 septic patients, and non-surviving (n=72) had serum AIF levels (p<0.001), lactic acid (p<0.001) and APACHE-II (p<0.001) that surviving (n=123). Multiple logistic regression analysis showed that patients with serum AIF levels>55.6ng/mL had higher mortality risk (OR=3.290; 95% CI=1.551-6.979; p=0.002) controlling for age, SOFA and lactic acid.

CONCLUSIONS

Parthanatos is associated with mortality of septic patients.

A Missense Variant in AIFM1 Caused Mitochondrial Dysfunction and Intolerance to Riboflavin Deficiency

AIFM1 is a mitochondrial flavoprotein involved in caspase-independent cell death and regulation of respiratory chain complex biogenesis. Mutations in the AIFM1 gene have been associated with multiple clinical phenotypes, but the effectiveness of riboflavin treatment remains controversial. Furthermore, few studies explored the reasons underlying this controversy. We reported a 7-year-old boy with ataxia, sensorimotor neuropathy and muscle weakness. Genetic and histopathological analyses were conducted, along with assessments of mitochondrial function and apoptosis level induced by staurosporine. Riboflavin deficiency and supplementation experiments were performed using fibroblasts. A missense c.1019T > C (p. Met340Thr) variant of AIFM1 was detected in the proband, which caused reduced expression of AIFM1 protein and mitochondrial dysfunction as evidenced by downregulation of mitochondrial complex subunits, respiratory deficiency and collapse of ΔΨm. The proportion of apoptotic cells in mutant fibroblasts was lower than controls after induction of apoptosis. Riboflavin deficiency resulted in decreased AIFM1 protein levels, while supplementation with high concentrations of riboflavin partially increased AIFM1 protein levels in variant fibroblasts. In addition, mitochondrial respiratory function of mutant fibroblasts was partly improved after riboflavin supplementation. Our study elucidated the pathogenicity of the AIFM1 c.1019T > C variant and revealed mutant fibroblasts was intolerant to riboflavin deficiency. Riboflavin supplementation is helpful in maintaining the level of AIFM1 protein and mitochondrial respiratory function. Early riboflavin treatment may serve as a valuable attempt for patients with AIFM1 variant.

The Designer Drug αPHP Affected Cell Proliferation and Triggered Deathly Mechanisms in Murine Neural Stem/Progenitor Cells

Increasing reports of neurological and psychiatric outcomes due to psychostimulant synthetic cathinones (SCs) have recently raised public concern. However, the understanding of neurotoxic mechanisms is still lacking, particularly for the under-investigated αPHP, one of the major MDPV derivatives. In particular, its effects on neural stem/progenitor cell cultures (NSPCs) are still unexplored. Therefore, in the current in vitro study, the effects of increasing αPHP concentrations (25-2000 μM), on cell viability/proliferation, morphology/ultrastructure, genotoxicity and cell death pathways, have been evaluated after exposure in murine NSPCs, using a battery of complementary techniques, i.e., MTT and clonogenic assay, flow cytometry, immunocytochemistry, TEM, and patch clamp. We revealed that αPHP was able to induce a dose-dependent significant decrease of the viability, proliferation and clonal capability of the NSPCs, paralleled by the resting membrane potential depolarization and apoptotic/autophagic/necroptotic pathway activation. Moreover, ultrastructural alterations were clearly observed. Overall, our current findings demonstrate that αPHP, damaging NSPCs and the morpho-functional fundamental units of adult neurogenic niches may affect neurogenesis, possibly triggering long-lasting, irreversible CNS damage. The present investigation could pave the way for a broadened understanding of SCs toxicology, needed to establish an appropriate treatment for NPS and the potential consequences for public health.

Mitochondrial Factors in the Cell Nucleus

The origin of eukaryotic organisms involved the integration of mitochondria into the ancestor cell, with a massive gene transfer from the original proteobacterium to the host nucleus. Thus, mitochondrial performance relies on a mosaic of nuclear gene products from a variety of genomes. The concerted regulation of their synthesis is necessary for metabolic housekeeping and stress response. This governance involves crosstalk between mitochondrial, cytoplasmic, and nuclear factors. While anterograde and retrograde regulation preserve mitochondrial homeostasis, the mitochondria can modulate a wide set of nuclear genes in response to an extensive variety of conditions, whose response mechanisms often merge. In this review, we summarise how mitochondrial metabolites and proteins-encoded either in the nucleus or in the organelle-target the cell nucleus and exert different actions modulating gene expression and the chromatin state, or even causing DNA fragmentation in response to common stress conditions, such as hypoxia, oxidative stress, unfolded protein stress, and DNA damage.

Effects of mitochondria on postmortem meat quality: characteristic, isolation, energy metabolism, apoptosis and oxygen consumption

Meat quality holds significant importance for both consumers and meat producers. Various factors influence meat quality, and among them, mitochondria play a crucial role. Recent studies have indicated that mitochondria can sustain their functions and viability for a certain duration in postmortem muscles. Consequently, mitochondria have an impact on oxygen consumption, energy metabolism, and apoptotic processes, which in turn affect myoglobin levels, oxidative stress, meat tenderness, fat oxidation, and protein oxidation. Ultimately, these factors influence the color, tenderness, and flavor of meat. However, there is a dearth of comprehensive summaries addressing the effects of mitochondria on postmortem muscle physiology and meat quality. Therefore, this review aims to describe the characteristics of muscle mitochondria and their potential influence on muscle. Additionally, a suitable method for isolating mitochondria is presented. Lastly, the review emphasizes the regulation of oxygen consumption, energy metabolism, and apoptosis by postmortem muscle mitochondria, and provides an overview of relevant research and recent advancements. The ultimate objective of this review is to elucidate the underlying mechanisms through which mitochondria impact meat quality.

Advances in exercise to alleviate sarcopenia in older adults by improving mitochondrial dysfunction

Sarcopenia is a chronic degenerative disease affecting primarily older adults. A growing aging population is gradually increasing the number of patients suffering from sarcopenia, placing increasing financial pressure on patients' families and society in general. There is a strong link between mitochondrial dysfunction and sarcopenia pathogenesis. As a result, treating sarcopenia by improving mitochondrial dysfunction is an effective strategy. Numerous studies have demonstrated that exercise has a positive effect on mitochondrial dysfunction when treating sarcopenia. Exercise promotes mitochondrial biogenesis and mitochondrial fusion/division to add new mitochondria or improve dysfunctional mitochondria while maintaining mitochondrial calcium homeostasis, mitochondrial antioxidant defense system, and mitochondrial autophagy to promote normal mitochondrial function. Furthermore, exercise can reduce mitochondrial damage caused by aging by inhibiting mitochondrial oxidative stress, mitochondrial DNA damage, and mitochondrial apoptosis. Exercise effectiveness depends on several factors, including exercise duration, exercise intensity, and exercise form. Therefore, Moderate-intensity exercise over 4 weeks potentially mitigates sarcopenia in older adults by ameliorating mitochondrial dysfunction. HIIT has demonstrated potential as a viable approach to addressing sarcopenia in aged rats. However, further investigation is required to validate its efficacy in treating sarcopenia in older adults.

Apoptotic Factors and Mitochondrial Complexes Assist Determination of Strain-Specific Susceptibility of Mice to Parkinsonian Neurotoxin MPTP

Identification of genetic mutations in Parkinson's disease (PD) promulgates the genetic nature of disease susceptibility. Resilience-associated genes being unknown till date, the normal genetic makeup of an individual may be determinative too. Our earlier studies comparing the substantia nigra (SN) and striatum of C57BL/6J, CD-1 mice, and their F1-crossbreds demonstrated the neuroprotective role of admixing against the neurotoxin MPTP. Furthermore, the differences in levels of mitochondrial fission/fusion proteins in the SN of parent strains imply effects on mitochondrial biogenesis. Our present investigations suggest that the baseline levels of apoptotic factors Bcl-2, Bax, and AIF differ across the three strains and are differentially altered in SN following MPTP administration. The reduction in complex-I levels exclusively in MPTP-injected C57BL/6J reiterates mitochondrial involvement in PD pathogenesis. The MPTP-induced increase in complex-IV, in the nigra of both parent strains, may be compensatory in nature. The ultrastructural evaluation showed fairly preserved mitochondria in the dopaminergic neurons of CD-1 and F1-crossbreds. However, in CD-1, the endoplasmic reticulum demonstrated distinct luminal enlargement, bordering onto ballooning, suggesting proteinopathy as a possible initial trigger.The increase in α-synuclein in the pars reticulata of crossbreds suggests a supportive role for this output nucleus in compensating for the lost function of pars compacta. Alternatively, since α-synuclein over-expression occurs in different brain regions in PD, the α-synuclein increase here may suggest a similar pathogenic outcome. Further understanding is required to resolve this biological contraption. Nevertheless, admixing reduces the risk to MPTP by favoring anti-apoptotic consequences. Similar neuroprotection may be envisaged in the admixed populace of Anglo-Indians.

VERY LONG-CHAIN ACYL-CoA SYNTHETASE-3 (ACSVL3) PROMOTES THE MALIGNANT GROWTH BEHAVIOR OF U87 GLIOMA CELLS VIA CHANGES IN CELL CYCLE WITHOUT AFFECTING APOPTOSIS

Decreasing the expression of very long-chain acyl-CoA synthetase 3 (ACSVL3) in U87MG glioblastoma cells by either RNA interference or genomic knockout (KO) significantly decreased their growth rate in culture, as well as their ability to form rapidly growing tumors in mice. U87-KO cells grew at a 9-fold slower rate than U87MG cells. When injected subcutaneously in nude mice, the tumor initiation frequency of U87-KO cells was 70% of that of U87MG cells, and the average growth rate of tumors that did form was decreased by 9-fold. Two hypotheses to explain the decreased growth rate of KO cells were investigated. Lack of ACSVL3 could reduce cell growth either by increasing apoptosis, or via effects on the cell cycle. We examined intrinsic, extrinsic, and caspase-independent apoptosis pathways; none were affected by lack of ACSVL3. However, significant differences in the cell cycle were seen in KO cells, suggesting arrest in S-phase. Levels of cyclin-dependent kinases 1, 2, and 4 were elevated in U87-KO cells, as were regulatory proteins p21 and p53 that promote cell cycle arrest. In contrast, lack of ACSVL3 reduced the level of the inhibitory regulatory protein p27. γ-H2AX, a marker of DNA double strand breaks, was elevated in U87-KO cells, while pH3, a mitotic index marker, was reduced. Previously reported alterations in sphingolipid metabolism in ACSVL3-depleted U87 cells may explain the effect of KO on cell cycle. These studies reinforce the notion that ACSVL3 is a promising therapeutic target in glioblastoma.

Potential lifetime effects caused by cellular uptake of nanoplastics: A review

Plastics have been used for about 100 years, and daily-use products composed of plastics are now prevalent. As a result, humans are very easily exposed to the plastic particles generated from the daily-use plastics. However, studies on cellular uptake of nanoplastics in "human cells" have only recently begun to attract attention. In previous studies, definitions of nanoplastics and microplastics were vague, but recently, they have been considered to be different and are being studied separately. However, nanoplastics, unlike plastic particles of other sizes such as macro- and microplastics, can be absorbed by human cells, and thus can cause various risks such as cytotoxicity, inflammation, oxidative stress, and even diseases such as cancer^{82, 83.} and diabetes (Fan et al., 2022; Wang et al., 2023). Thus, in this review, we defined microplastics and nanoplastics to be different and described the potential risks of nanoplastics to human caused by cellular uptake according to their diverse factors. In addition, during and following plastic product usage a substantial number of fragments of different sizes can be generated, including nanoplastics. Fragmentation of microplastics into nanoplastics may also occur during ingestion and inhalation, which can potentially cause long-term hazards to human health. However, there are still few in vivo studies conducted on the health effect of nanoplastics ingestion and inhalation.

A novel tumour enhancer function of Insulin-like growth factor II mRNA-binding protein 3 in colorectal cancer

CRC cells evolve a variety of strategies to limit or circumvent apoptosis cell death. RNA binding proteins (RBPs) regulate many of the molecular mechanisms that underlie the development of cancer. The insulin-like growth factor II mRNA-binding proteins (IMP) family are oncofoetal RBPs, consisting of IMP1, IMP2 and IMP3, which have an important role in RNA metabolism. IMP3 is highly expressed in colorectal cancer (CRC) tissue, where its expression often correlates with poor prognosis. However, the role of IMP3 in CRC is not fully understood. IMP3 expression was analysed using a public database and by Western blotting and immunohistochemistry in human colon samples derived from patients with sporadic CRC and healthy subjects. To address whether IMP3 controls cancer cell survival, we analysed cell death pathways in in vitro and in vivo experiments after IMP3 downregulation by siRNA or an antisense oligonucleotide. IMP3 was highly expressed in CRC samples compared to normal control tissues. The knockdown of IMP3 enhanced a caspase-independent cell death in CRC cell lines. Furthermore, the treatment of CRC cells with IMP3 siRNA did not alter the expression of GSDMD, GPX-4 and the activated form of RIP3, three key molecules that govern pyroptosis, ferroptosis and necroptosis, respectively. Abrogation of IMP3 in CRC significantly reduced Bcl-2 and Bcl-xL mRNA and was associated with an altered mitochondrial membrane potential that allowed the nuclear migration of the apoptosis-inducing factor (AIF). Moreover, specific immunoprecipitation experiments on CRC human cell lines indicated that IMP3 binds Bcl-2 and Bcl-xL mRNA, suggesting that IMP3 acts as a regulator of the intrinsic apoptotic pathway through the surveillance of anti-apoptotic Bcl mRNA metabolism. Finally, we showed that IMP3 block inhibited the growth of CRC cell lines in vivo after transplantation into immunodeficient mice. Altogether, these data support a novel role for IMP3 in controlling the intrinsic caspase-independent apoptotic pathway in CRC.

p20BAP31 induces cell apoptosis via both AIF caspase-independent and the ROS/JNK mitochondrial pathway in colorectal cancer

Background

During cell apoptosis, the C-terminus of BAP31 is cleaved by caspase-8 and generates p20BAP31, which has been shown to induce an apoptotic pathway between the endoplasmic reticulum (ER) and mitochondria. However, the underlying mechanisms of p20BAP31 in cell apoptosis remains unclear.

Methods

We compared the effects of p20BAP31 on cell apoptosis in six cell lines and selected the most sensitive cells. Functional experiments were conducted, including Cell Counting Kit 8 (CCK-8), reactive oxygen species (ROS), and mitochondrial membrane potential (MMP) assay. Then, cell cycle and apoptosis were investigated by flow cytometry and verified by immunoblotting. Next, NOX inhibitors (ML171 and apocynin), ROS scavenger (NAC), JNK inhibitor (SP600125), and caspase inhibitor (Z-VAD-FMK) were used to further investigate the underlying mechanisms of p20BAP31 on cell apoptosis. Finally, apoptosis-inducing factor (AIF) translocation from the mitochondria to the nuclei was verified by immunoblotting and immunofluorescence assay.

Results

We found that overexpression of p20BAP31 indeed induced apoptosis and had a much greater sensitivity in HCT116 cells. Furthermore, the overexpression of p20BAP31 inhibited cell proliferation by causing S phase arrest. Further study revealed that p20BAP31 reduced MMP, with a significant increase in ROS levels, accompanied by the activation of the MAPK signaling pathway. Importantly, the mechanistic investigation indicated that p20BAP31 induces mitochondrial-dependent apoptosis by activating the ROS/JNK signaling pathway and induces caspase-independent apoptosis by promoting the nuclear translocation of AIF.

Conclusions

p20BAP31 induced cell apoptosis via both the ROS/JNK mitochondrial pathway and AIF caspase-independent pathway. Compared with antitumor drugs that are susceptible to drug resistance, p20BAP31 has unique advantages for tumor therapy.

Repurposing Dihydroartemisinin to Combat Oral Squamous Cell Carcinoma, Associated with Mitochondrial Dysfunction and Oxidative Stress

Oral squamous cell carcinoma (OSCC), with aggressive locoregional invasion, has a high rate of early recurrences and poor prognosis. Dihydroartemisinin (DHA), as a derivative of artemisinin, has been found to exert potent antitumor activity. Recent studies reported that DHA suppresses OSCC cell growth and viability through the regulation of reactive oxygen species (ROS) production and mitochondrial calcium uniporter. However, the mechanism underlying the action of DHA on OSCCs remains elusive. In the study, we observed that 159 genes were remarkably misregulated in primary OSCC tumors associated with DHA-inhibited pathways, supporting that OSCCs are susceptible to DHA treatment. Herein, our study showed that DHA exhibited promising effects to suppress OSCC cell growth and survival, and single-cell colony formation. Interestingly, the combination of DHA and cisplatin (CDDP) significantly reduced the toxicity of CDDP treatment alone on human normal oral cells (NOK). Moreover, DHA remarkably impaired mitochondrial structure and function, and triggered DNA damage and ROS generation, and activation of mitophagy. In addition, DHA induced leakage of cytochrome C and apoptosis-inducing factor (AIF) from mitochondria, elevated Bax/cleaved-caspase 3 expression levels and compromised Bcl2 protein expression. In the OSCC tumor-xenograft mice model, DHA remarkably suppressed tumor growth and induced apoptosis of OSCCs in vivo. Intriguingly, a selective mitophagy inhibitor Mdivi-1 could significantly reinforce the anticancer activity of DHA treatment. DHA and Mdivi-1 can synergistically suppress OSCC cell proliferation and survival. These data uncover a previously unappreciated contribution of the mitochondria-associated pathway to the antitumor activity of DHA on OSCCs. Our study shed light on a new aspect of a DHA-based therapeutic strategy to combat OSCC tumors.

LACTB induces cancer cell death through the activation of the intrinsic caspase-independent pathway in breast cancer

BACKGROUND

LACTB was recently identified as a mitochondrial tumour suppressor that negatively affects cancer cell proliferation by inducing cell death and/or differentiation, depending on the cell type and tissue. However, the detailed mechanism underlying the LACTB-induced cancer cell death is largely unknown.

METHODS

We used cell-based, either in 2D or 3D conditions, and in vivo experiments to understand the LACTB mechanisms. In this regard, protein array followed by an enrichment analysis, cell proliferation assays using different compounds, western blot analysis, flow cytometry and immunofluorescence were performed. Differences between quantitative variables following normal distribution were valuated using Student t test for paired or no-paired samples according to the experiment. For in vivo experiments differences in tumour growth were analyzed by 2-way ANOVA.

RESULTS

We show, that LACTB expression leads to cell cycle arrest in G1 phase and increase of DNA oxidation that leads to activation of intrinsic caspase-independent cell death pathway. This is achieved by an increase of mitochondrial reactive oxygen species since early time points of LACTB induction.

CONCLUSION

Our work provides a deeper mechanistic insight into LACTB-mediated cancer-cell death and shows the dynamics of the cellular responses a particular tumor suppressive stimulus might evoke under different genetic landscapes.

The natural product dehydrocurvularin induces apoptosis of gastric cancer cells by activating PARP-1 and caspase-3

The natural product dehydrocurvularin (DSE2) is a fungal-derived macrolide with potent anticancer activity, but the mechanism is still unclear. We found that DSE2 effectively inhibited the growth of gastric cancer cells and induced the apoptosis by activating Poly(ADP-ribose) polymerase 1 (PARP-1) and caspase-3. Pharmacological inhibition and genetic knockdown with PARP-1 or caspase-3 suppressed DSE2-induced apoptosis. PARP-1 was previously reported to be cleaved into fragments during apoptosis. However, PARP-1 was barely cleaved in DSE2-induced apoptosis. DSE2 induced PARP-1 activation as indicated by rapid depletion of NAD⁺ and the concomitant formation of poly(ADP-ribosylated) proteins (PARs). Interestingly, the PARP-1 inhibitor (Olaparib) attenuated the cytotoxicity of DSE2. Moreover, the combination of Olaparib and Z-DEVD-FMK (caspase-3 inhibitor) further reduced the cytotoxicity. It has been shown that PARP-1 activation triggers cytoplasm-nucleus translocation of apoptosis-inducing factor (AIF). Caspase-3 inhibitors inhibited PARP-1 activation and suppressed PARP-1-induced AIF nuclear translocation. These results indicated that DSE2-induced caspase-3 activation may occur before PARP-1 activation. The ROS inhibitor, N-acetyl-cysteine, significantly inhibited the activation of caspase-3 and PARP-1, indicating that ROS overproduction contributed to DSE2-induced apoptosis. Using an in vivo approach, we further found that DSE2 significantly inhibited gastric tumor growth and promoted translocation of AIF to the nucleus. In conclusion, DSE2 induces gastric cell apoptosis by activating caspase-3 and PARP-1, and shows potent antitumor activity against human gastric carcinoma in vitro and in vivo.

AIFM1, negatively regulated by miR-145-5p, aggravates hypoxia-induced cardiomyocyte injury

BACKGROUND

Hypoxia-induced apoptosis is linked to the pathogenesis of myocardial infarction. The role of apoptosis-inducing factor mitochondria associated 1 (AIFM1) in cardiomyocyte injury remains unclear. This study was aimed at probing into the role and the underlying regulatory mechanism of AIFM1 in myocardial injury.

METHODS

H9c2 cardiomyocytes and C57BL/6 mice were used for myocardial hypoxic/ischemic injury and myocardial infarction animal models. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to evaluate the expression levels of AIFM1 mRNA and miR-145-5p. Western blot was used for examining the expression levels of AIFM1, caspase-3, cleaved caspase-3, p-53, and γ-H2AX. Cell viability was examined by cell counting kit-8 (CCK-8) assay and BrdU assay. Interaction between AIFM1 and miR-145-5p was determined by bioinformatics analysis, qRT-PCR, Western blot, and dual-luciferase reporter assay.

RESULTS

AIFM1 expression was markedly highly elevated, while miR-145-5p expression was significantly down-regulated in the myocardial infarction animal model and H9c2 cells under hypoxia. Augmentation of AIFM1 led to a dramatic decrease of cell viability, accompanied by an increase of the secretion of the inflammatory cytokines IL-1β, TNF-α, IL-6, and the expression of cleaved caspase-3. Furthermore, AIFM1 was identified as a target of miR-145-5p. In addition, miR-145-5p/AIFM1 axis regulated the expression of p53.

CONCLUSION

AIFM1 may exacerbate myocardial ischemic injury by promoting inflammation and the injury of cardiomyocytes, and its up-regulation may be partly due to the down-regulation of miR-145-5p.

Upregulation of Ca2+-binding proteins contributes to VTA dopamine neuron survival in the early phases of Alzheimer's disease in Tg2576 mice

BACKGROUND

Recent clinical and experimental studies have highlighted the involvement of Ventral Tegmental Area (VTA) dopamine (DA) neurons for the early pathogenesis of Alzheimer's Disease (AD). We have previously described a progressive and selective degeneration of these neurons in the Tg2576 mouse model of AD, long before amyloid-beta plaque formation. The degenerative process in DA neurons is associated with an autophagy flux impairment, whose rescue can prevent neuronal loss. Impairments in autophagy can be the basis for accumulation of damaged mitochondria, leading to disturbance in calcium (Ca²⁺) homeostasis, and to functional and structural deterioration of DA neurons.

METHODS

In Tg2576 mice, we performed amperometric recordings of DA levels and analysis of dopaminergic fibers in the Nucleus Accumbens - a major component of the ventral striatum precociously affected in AD patients - together with retrograde tracing, to identify the most vulnerable DA neuron subpopulations in the VTA. Then, we focused on these neurons to analyze mitochondrial integrity and Apoptosis-inducing factor (AIF) localization by electron and confocal microscopy, respectively. Stereological cell count was also used to evaluate degeneration of DA neuron subpopulations containing the Ca²⁺-binding proteins Calbindin-D28K and Calretinin. The expression levels for these proteins were analyzed by western blot and confocal microscopy. Lastly, using electrophysiology and microfluorometry we analyzed VTA DA neuron intrinsic properties and cytosolic free Ca²⁺ levels.

RESULTS

We found a progressive degeneration of mesolimbic DA neurons projecting to the ventral striatum, located in the paranigral nucleus and parabrachial pigmented subnucleus of the VTA. At the onset of degeneration (3 months of age), the vulnerable DA neurons in the Tg2576 accumulate damaged mitochondria, while AIF translocates from the mitochondria to the nucleus. Although we describe an age-dependent loss of the DA neurons expressing Calbindin-D28K or Calretinin, we observed that the remaining cells upregulate the levels of Ca²⁺-binding proteins, and the free cytosolic levels of Ca²⁺ in these neurons are significantly decreased. Coherently, TUNEL-stained Tg2576 DA neurons express lower levels of Calbindin-D28K when compared with non-apoptotic cells.

CONCLUSION

Overall, our results suggest that the overexpression of Ca²⁺-binding proteins in VTA DA neurons might be an attempt of cells to survive by increasing their ability to buffer free Ca²⁺. Exploring strategies to overexpress Ca²⁺-binding proteins could be fundamental to reduce neuronal suffering and improve cognitive and non-cognitive functions in AD.

Knockout of IL-6 mitigates cold water-immersion restraint stress-induced intestinal epithelial injury and apoptosis

Background

Interleukin-6 (IL-6) is essential for maintaining intestinal epithelial homeostasis. Although cold water-immersion restraint (CWIR) stress is commonly used to induce in vivo gastric injury, it also affects intestinal epithelial permeability. Although IL-6 is increased in response to acute physiological and psychological stress, its exact effects on the pathophysiology of the intestinal epithelium in response to acute CWIR stress remain unknown.

Methods

We used IL-6 knockout (KO) mice with acute CWIR modeling to investigate the effect of IL-6 deficiency on intestinal epithelial morphology and pathological damage using histological staining assays under the acute stress. We detected jejunal epithelial apoptosis using TUNEL and standard molecular experiments.

Results

CWIR caused intestinal epithelial damage, which was alleviated by the absence of IL-6, as evidenced by morphological changes and goblet cell and intestinal permeability alteration. IL-6 KO also reduced CWIR-mediated inflammatory levels and improved stress defense. Meanwhile, IL-6 deficiency decreased the intestinal epithelial apoptosis induced by CWIR administration. This IL-6 KO-led effect depended more on mitochondrial AIF signaling rather than the traditional caspase pathway.

Conclusion

As a result, we concluded that acute CWIR-induced severe intestinal damage and jejunal epithelium apoptosis could be alleviated by IL-6 deficiency, implying a protective effect of IL-6 deficiency on the intestines under acute stress. The findings shed new light on treating CWIR-induced intestinal disorders by inhibiting IL-6 signaling.

Nanosecond PEF Induces Oxidative Stress and Apoptosis via Proteasomal Activity Inhibition in Gastric Adenocarcinoma Cells with Drug Resistance

Nanosecond (ns) pulsed electric field (PEF) is a technology in which the application of ultra-short electrical pulses can be used to disrupt the barrier function of cell plasma and internal membranes. Disruptions of the membrane integrity cause a substantial imbalance in cell homeostasis in which oxidative stress is a principal component. In the present study, nsPEF-induced oxidative stress was investigated in two gastric adenocarcinoma cell lines (EPG85-257P and EPG85-257RDB) which differ by their sensitivity to daunorubicin. Cells were exposed to 200 pulses of 10 ns duration, with the amplitude and pulse repetition frequency at 1 kHz, with electric field intensity varying from 12.5 to 50 kV/cm. The electroporation buffer contained either 1 mM or 2 mM calcium chloride. CellMask DeepRed visualized cell plasma permeabilization, Fluo-4 was used to visualize internal calcium ions content, and F-actin was labeled with AlexaFluor^®488 for the cytoskeleton. The cellular viability was determined by MTT assay. An alkaline and neutral comet assay was employed to detect apoptotic and necrotic cell death. The luminescent method estimated the modifications in GSSG/GSH redox potential and the imbalance of proteasomal activity (chymotrypsin-, trypsin- and caspase-like). The reactive oxygen species (ROS) level was measured by flow cytometry using dihydroethidium (DHE) dye. Morphological visualization indicated cell shrinkage, affected cell membranes (characteristic bubbles and changed cell shape), and the reorganization of actin fibers with sites of its dense concentration; the effect was more intense with the increasing electric field strength. The most significant decrease in cell viability and GSSG/GSH redox potential was noted at the highest amplitude of 50 kV/cm, and calcium ions amplified this effect. nsPEF, particularly with calcium ions, inhibited proteasomal activities, resulting in increased protein degradation. nsPEF increased the percentage of apoptotic cells and ROS levels. The EPG85-257 RDB cell line, which is resistant to standard chemotherapy, was more sensitive to applied nsPEF protocols. The applied nsPEF method disrupted the metabolism of cancer cells and induced apoptotic cell death. The nsPEF ability to cause apoptosis, oxidative stress, and protein degradation make the nsPEF methodology a suitable alternative to current anticancer pharmacological methods.

Human mitochondrial protein complexes revealed by large-scale coevolution analysis and deep learning-based structure modeling

MOTIVATION

Recent development of deep-learning methods has led to a breakthrough in the prediction accuracy of 3D protein structures. Extending these methods to protein pairs is expected to allow large-scale detection of protein-protein interactions (PPIs) and modeling protein complexes at the proteome level.

RESULTS

We applied RoseTTAFold and AlphaFold, two of the latest deep-learning methods for structure predictions, to analyze coevolution of human proteins residing in mitochondria, an organelle of vital importance in many cellular processes including energy production, metabolism, cell death and antiviral response. Variations in mitochondrial proteins have been linked to a plethora of human diseases and genetic conditions. RoseTTAFold, with high computational speed, was used to predict the coevolution of about 95% of mitochondrial protein pairs. Top-ranked pairs were further subject to modeling of the complex structures by AlphaFold, which also produced contact probability with high precision and in many cases consistent with RoseTTAFold. Most top-ranked pairs with high contact probability were supported by known PPIs and/or similarities to experimental structural complexes. For high-scoring pairs without experimental complex structures, our coevolution analyses and structural models shed light on the details of their interfaces, including CHCHD4-AIFM1, MTERF3-TRUB2, FMC1-ATPAF2 and ECSIT-NDUFAF1. We also identified novel PPIs (PYURF-NDUFAF5, LYRM1-MTRF1L and COA8-COX10) for several proteins without experimentally characterized interaction partners, leading to predictions of their molecular functions and the biological processes they are involved in.

AVAILABILITY AND IMPLEMENTATION

Data of mitochondrial proteins and their interactions are available at: http://conglab.swmed.edu/mitochondria.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

AIFM1 beyond cell death: An overview of this OXPHOS-inducing factor in mitochondrial diseases

Apoptosis-inducing factor (AIF) is a mitochondrial intermembrane space flavoprotein with diverse functions in cellular physiology. In this regard, a large number of studies have elucidated AIF's participation to chromatin condensation during cell death in development, cancer, cardiovascular and brain disorders. However, the discovery of rare AIFM1 mutations in patients has shifted the interest of biomedical researchers towards AIF's contribution to pathogenic mechanisms underlying inherited AIFM1-linked metabolic diseases. The functional characterization of AIF binding partners has rapidly advanced our understanding of AIF biology within the mitochondria and beyond its widely reported role in cell death. At the present time, it is reasonable to assume that AIF contributes to cell survival by promoting biogenesis and maintenance of the mitochondrial oxidative phosphorylation (OXPHOS) system. With this review, we aim to outline the current knowledge around the vital role of AIF by primarily focusing on currently reported human diseases that have been linked to AIFM1 deficiency.

Role of Neuropilin 1 in COVID-19 Patients with Acute Ischemic Stroke

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection can trigger the adaptive and innate immune responses, leading to uncontrolled inflammatory reactions and associated local and systematic tissue damage, along with thromboembolic disorders that may increase the risk of acute ischemic stroke (AIS) in COVID-19 patients. The neuropilin (NRP-1) which is a co-receptor for the vascular endothelial growth factor (VEGF), integrins, and plexins, is involved in the pathogenesis of AIS. NRP-1 is also regarded as a co-receptor for the entry of SARS-CoV-2 and facilitates its entry into the brain through the olfactory epithelium. NRP-1 is regarded as a cofactor for binding of SARS-CoV-2 with angiotensin-converting enzyme 2 (ACE2), since the absence of ACE2 reduces SARS-CoV-2 infectivity even in presence of NRP-1. Therefore, the aim of the present study was to clarify the potential role of NRP-1 in COVID-19 patients with AIS. SARS-CoV-2 may transmit to the brain through NRP-1 in the olfactory epithelium of the nasal cavity, leading to different neurological disorders, and therefore about 45% of COVID-19 patients had neurological manifestations. NRP-1 has the potential capability to attenuate neuroinflammation, blood–brain barrier (BBB) permeability, cerebral endothelial dysfunction (ED), and neuronal dysfunction that are uncommon in COVID-19 with neurological involvement, including AIS. Similarly, high NRP-1 serum level is linked with ED, oxidative stress, and the risk of pulmonary thrombosis in patients with severe COVID-19, suggesting a compensatory mechanism to overcome immuno-inflammatory disorders. In conclusion, NRP-1 has an important role in the pathogenesis of COVID-19 and AIS, and could be the potential biomarker linking the development of AIS in COVID-19. The present findings cannot provide a final conclusion, and thus in silico, experimental, in vitro, in vivo, preclinical, and clinical studies are recommended to confirm the potential role of NRP-1 in COVID-19, and to elucidate the pharmacological role of NRP-1 receptor agonists and antagonists in COVID-19.

Methylmercury induced apoptosis of human neuroblastoma cells through the reactive oxygen species mediated caspase and poly ADP-ribose polymerase/apoptosis-inducing factor dependent pathways

Methylmercury (MeHg) is an environmental neurotoxic substance, which can easily cross the blood-brain barrier, causing irreversible damage to the human central nervous system. Reactive oxygen species (ROS) are involved in various ways of intracellular physiological or pathological processes including neuronal apoptosis. This study attempted to explore the role of ROS-mediated poly ADP-ribose polymerase (PARP)/apoptosis-inducing factor (AIF) apoptosis signaling pathway in the process of MeHg-induced cell death of human neuroblastoma cells (SH-SY5Y). Here, we found that SH-SY5Y cells underwent apoptosis in response to MeHg, which was accompanied by the increased levels of ROS and calcium ion, and the activation of caspase cascades and PARP. Inhibiting the production of ROS can reduce the apoptosis rate to a certain extent. PARP/AIF apoptotic pathway is independent of caspase dependent signaling pathway and regulates it. In conclusion, these results suggest that ROS mediated activation of caspase pathway and PARP/AIF signaling pathway are involved in MeHg induced apoptosis, and these two pathways interact with each other.

In search of the Aplysia immunome: an in silico study

The immune repertoires of mollusks beyond commercially important organisms such as the pacific oyster Crassostrea gigas or vectors for human pathogens like the bloodfluke planorb Biomphalaria glabrata are understudied. Despite being an important model for neural aging and the role of inflammation in neuropathic pain, the immune repertoire of Aplysia californica is poorly understood. Recent discovery of a neurotropic nidovirus in Aplysia has highlighted the need for a better understanding of the Aplysia immunome. To address this gap in the literature, the Aplysia reference genome was mined using InterProScan and OrthoFinder for putative immune genes. The Aplysia genome encodes orthologs of all critical components of the classical Toll-like receptor (TLR) signaling pathway. The presence of many more TLRs and TLR associated adapters than known from vertebrates suggest yet uncharacterized, novel TLR associated signaling pathways. Aplysia also retains many nucleotide receptors and antiviral effectors known to play a key role in viral defense in vertebrates. However, the absence of key antiviral signaling adapters MAVS and STING in the Aplysia genome suggests divergence from vertebrates and bivalves in these pathways. The resulting immune gene set of this in silico study provides a basis for interpretation of future immune studies in this important model organism.

AIFM1 is a component of the mitochondrial disulfide relay that drives complex I assembly through efficient import of NDUFS5

The mitochondrial intermembrane space protein AIFM1 has been reported to mediate the import of MIA40/CHCHD4, which forms the import receptor in the mitochondrial disulfide relay. Here, we demonstrate that AIFM1 and MIA40/CHCHD4 cooperate beyond this MIA40/CHCHD4 import. We show that AIFM1 and MIA40/CHCHD4 form a stable long‐lived complex in vitro, in different cell lines, and in tissues. In HEK293 cells lacking AIFM1, levels of MIA40 are unchanged, but the protein is present in the monomeric form. Monomeric MIA40 neither efficiently interacts with nor mediates the import of specific substrates. The import defect is especially severe for NDUFS5, a subunit of complex I of the respiratory chain. As a consequence, NDUFS5 accumulates in the cytosol and undergoes rapid proteasomal degradation. Lack of mitochondrial NDUFS5 in turn results in stalling of complex I assembly. Collectively, we demonstrate that AIFM1 serves two overlapping functions: importing MIA40/CHCHD4 and constituting an integral part of the disulfide relay that ensures efficient interaction of MIA40/CHCHD4 with specific substrates.

Bone morphogenetic protein inhibitors and mitochondria targeting agents synergistically induce apoptosis-inducing factor (AIF) caspase-independent cell death in lung cancer cells

BACKGROUND

Bone morphogenetic proteins (BMP) are evolutionarily conserved morphogens that are reactivated in lung carcinomas. In lung cancer cells, BMP signaling suppresses AMP activated kinase (AMPK) by inhibiting LKB1. AMPK is activated by mitochondrial stress that inhibits ATP production, which is enhanced 100-fold when phosphorylated by LKB1. Activated AMPK can promote survival of cancer cells but its "hyperactivation" induces cell death. The studies here reveal novel cell death mechanisms induced by BMP inhibitors, together with agents targeting the mitochondria, which involves the "hyperactivation" of AMPK.

METHODS

This study examines the synergistic effects of two BMP inhibitors together with mitochondrial targeting agents phenformin and Ym155, on cell death of lung cancer cells expressing LKB1 (H1299), LKB1 null (A549), and A549 cells transfected with LKB1 (A549-LKB1). Cell death mechanisms evaluated were the activation of caspases and the nuclear localization of apoptosis inducing factor (AIF). A769662 was used to allosterically activate AMPK. Knockdown of BMPR2 and LKB1 using siRNA was used to examine their effects on nuclear localization of AMPK. Validation studies were performed on five passage zero primary NSCLC.

RESULTS

Both BMP inhibitors synergistically suppressed growth when combined with Ym155 or phenformin in cells expressing LKB1. The combination of BMP inhibitors with mitochondrial targeting agents enhanced the activation of AMPK in lung cancer cells expressing LKB1. Allosteric activation of AMPK with A769662 induced cell death in both H1299 and A549 cells. Cell death induced by the combination of BMP inhibitors and mitochondrial-targeting agents did not activate caspases. The combination of drugs induced nuclear localization of AIF in cells expressing LKB1, which was attenuated by knockdown of LKB1. Knockdown of BMPR2 together with Ym155 increased nuclear localization of AIF. Combination therapy also enhanced cell death and AIF nuclear localization in primary NSCLC.

CONCLUSIONS

These studies demonstrate that inhibition of BMP signaling together with mitochondrial targeting agents induce AIF caspase-independent cell death, which involves the "hyperactivation" of AMPK. AIF caspase-independent cell death is an evolutionarily conserved cell death pathway that is infrequently studied in cancer. These studies provide novel insight into mechanisms inducing AIF caspase-independent cell death in cancer cells using BMP inhibitors. Video Abstract.

Involvement of the NF-κB and PI3K/Akt/mTOR pathways in cell death triggered by stypoldione, an o-quinone isolated from the brown algae Stypopodium zonale

Multiple myeloma (MM) is a clonal plasma cell malignancy that remains incurable to date. Thus, the aims of this study were to evaluate the involvement of the NF-κB and PI3K/Akt/mTOR pathways in the cytotoxicity of stypoldione, an o-quinone isolated from the brown algae Stypopodium zonale, in MM cells (MM1.S). The cytotoxic effect was evaluated in MM1.S cells and peripheral blood mononuclear cells (PBMCs) by MTT assay. The stypoldione reduced the cell viability of MM1.S cells in a concentration and time-dependent manner (IC50 in MM.1S from 2.55 to 5.38 μM). However, it was also cytotoxic to PBMCs, but at a lower range. Additionally, no significant hemolysis was observed even at concentration up to 10 times the IC50 . Apoptotic cell death was confirmed by cell morphology and Annexin V-FITC assay. Stypoldione induced intrinsic and extrinsic apoptosis by increasing FasR expression and reactive oxygen species (ROS) production, inverting the Bax/Bcl-2 ratio, and inducing ΔΨm loss, which resulted in AIF release and caspase-3 activation. It also increased Ki-67 and survivin expression and inhibited the NF-κB and PI3K/Akt/mTOR pathways. These results suggest that stypoldione is a good candidate for the development of new drugs for MM treatment.

cAMP сoncentrations in cardiac mitochondria and serum in the С57ВL/6 mice under independent melanoma В16/F10 growth versus melanoma В16/F10 growth linked to chronic neurogenic pain

The aim of this research work is to study the cAMP level in the cardiac mitochondria and serum in the С57ВL/6 strain mice of both genders under the independent melanoma В16/F10 growth versus the melanoma В16/F10 growth linked to chronic neurogenic pain (CNP). Materials and methods. Mice of strain С57ВL/6 (n=336) have been grouped as follows: the intact group of the mice (♂n=21; ♀n=21), the reference group (♂n=21; ♀n=21) with the reproduced CNP model, the comparison group (♂n=63; ♀n=63) to include the mice with melanoma В16/F10, and the main test group (♂n=63; ♀n=63) to cover the mice with the melanoma growth against the CNP background. Upon expiration of 1 week, 2 and 3 weeks of the melanoma growth, in the animals of the above experimental groups the cardiac mitochondria have been isolated with the centrifugation using high-performance refrigerated centrifuge Avanti J-E, BECMAN COULTER, USA. With ELISA Kit (RayBio USA) we have determined cAMP concentrations in serum and in the cardiac mitochondria. Results. CNP has induced a decrease in the cAMP level in the cardiac mitochondria by a factor of 3,6 in the female mice only. In the animals of the comparison group the cAMP level in the heart has been increasing beginning with week 2 of the tumor growth on average by a factor of 4, while in the main test group starting from week 1 of the tumor growth it has been recorded 2-4 times higher and was depleted by the end of the experiment. As to the cAMP concentration in serum, the dynamics thereof has not been found to be in correlation with the cardiac mitochondrial data, and its concentration decrease has been recorded both in the females and the males. Conclusion. So, the changes in the cAMP concentration in the cardiac mitochondria demonstrate their gender-specific feature; the female mice as against the males have responded to an independent impact produced by CNP. As to the main test group, CNP has stimulated an increase in the cAMP level in the cardiac mitochondria 1 week earlier than it is the case with the comparison group, and it has resulted in the full cAMP depletion by the 3rd week of the experiment.

CEST-2.2 overexpression alters lipid metabolism and extends longevity of mitochondrial mutants

Mitochondrial dysfunction can either extend or decrease Caenorhabditis elegans lifespan, depending on whether transcriptionally regulated responses can elicit durable stress adaptation to otherwise detrimental lesions. Here, we test the hypothesis that enhanced metabolic flexibility is sufficient to circumvent bioenergetic abnormalities associated with the phenotypic threshold effect, thereby transforming short‐lived mitochondrial mutants into long‐lived ones. We find that CEST‐2.2, a carboxylesterase mainly localizes in the intestine, may stimulate the survival of mitochondrial deficient animals. We report that genetic manipulation of cest‐2.2 expression has a minor lifespan impact on wild‐type nematodes, whereas its overexpression markedly extends the lifespan of complex I‐deficient gas‐1(fc21) mutants. We profile the transcriptome and lipidome of cest‐2.2 overexpressing animals and show that CEST‐2.2 stimulates lipid metabolism and fatty acid beta‐oxidation, thereby enhancing mitochondrial respiratory capacity through complex II and LET‐721/ETFDH, despite the inherited genetic lesion of complex I. Together, our findings unveil a metabolic pathway that, through the tissue‐specific mobilization of lipid deposits, may influence the longevity of mitochondrial mutant C. elegans.

Microplitis bicoloratus bracovirus regulates cyclophilin A-apoptosis-inducing factor interaction to induce cell apoptosis in the insect immunosuppressive process

Microplitis bicoloratus bracovirus (MbBV) induces apoptosis in hemocytes of the host (Spodoptera litura) via the cyclophilin A (CypA)-mediated signaling pathway. However, the mechanisms underlying CypA-mediated signaling during apoptosis remain largely unknown. Therefore, in this study, we investigated how CypA and apoptosis-inducing factor (AIF) interact during MbBV-mediated apoptosis. Our findings showed that MbBV induces apoptosis through the CypA-AIF axis of insect immune suppression. In MbBV-infected Spli221 cells, both the expression of the cypa gene and the release of AIF from the mitochondria increased the number of apoptotic cells. CypA and AIF underwent concurrent cytoplasm-nuclear translocation. Conversely, blocking of AIF release from mitochondria not only inhibited the CypA-AIF interaction but also inhibited the cytoplasmic-nuclear translocation of AIF and CypA. Importantly, the survival of the apoptotic phenotype was significantly rescued in MbBV-infected Spli221 cells. In addition, we found that the cyclosporine A-mediated inhibition of CypA did not prevent the formation of the CypA and AIF complex; rather, this only suppressed genomic DNA fragmentation. In vitro experiments revealed direct molecular interactions between recombinant CypA and AIF. Taken together, our results demonstrate that the CypA-AIF interaction plays an important role in MbBV-induced innate immune suppression. This study will help to clarify aspects of insect immunological mechanisms and will be relevant to biological pest control.

SGPL1 stimulates VPS39 recruitment to the mitochondria in MICU1 deficient cells

Objective

Mitochondrial “retrograde” signaling may stimulate organelle biogenesis as a compensatory adaptation to aberrant activity of the oxidative phosphorylation (OXPHOS) system. To maintain energy-consuming processes in OXPHOS deficient cells, alternative metabolic pathways are functionally coupled to the degradation, recycling and redistribution of biomolecules across distinct intracellular compartments. While transcriptional regulation of mitochondrial network expansion has been the focus of many studies, the molecular mechanisms promoting mitochondrial maintenance in energy-deprived cells remain poorly investigated.

Methods

We performed transcriptomics, quantitative proteomics and lifespan assays to identify pathways that are mechanistically linked to mitochondrial network expansion and homeostasis in Caenorhabditis elegans lacking the mitochondrial calcium uptake protein 1 (MICU-1/MICU1). To support our findings, we carried out biochemical and image analyses in mammalian cells and mouse-derived tissues.

Results

We report that micu-1(null) mutations impair the OXPHOS system and promote C. elegans longevity through a transcriptional program that is independent of the mitochondrial calcium uniporter MCU-1/MCU and the essential MCU regulator EMRE-1/EMRE. We identify sphingosine phosphate lyase SPL-1/SGPL1 and the ATFS-1-target HOPS complex subunit VPS-39/VPS39 as critical lifespan modulators of micu-1(null) mutant animals. Cross-species investigation indicates that SGPL1 upregulation stimulates VPS39 recruitment to the mitochondria, thereby enhancing mitochondria-lysosome contacts. Consistently, VPS39 downregulation compromises mitochondrial network maintenance and basal autophagic flux in MICU1 deficient cells. In mouse-derived muscles, we show that VPS39 recruitment to the mitochondria may represent a common signature associated with altered OXPHOS system.

Conclusions

Our findings reveal a previously unrecognized SGPL1/VPS39 axis that stimulates intracellular organelle interactions and sustains autophagy and mitochondrial homeostasis in OXPHOS deficient cells.

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micu-1(null) nematodes are long-lived mitochondrial mutants.

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MICU-1/MICU1 deficiency stimulates VPS-39/VPS39 and SPL-1/SGPL1 upregulation.

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VPS-39 sustains mitochondrial network expansion in micu-1(null) nematodes.

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VPS39 and SGPL1 expression influences mitochondria-lysosome contact sites in MICU1 deficient cells.

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VPS39/SGPL1 signaling may be a common signature of mitochondrial deficient cells.