OMA1-mediated integrated stress response protects against ferroptosis in mitochondrial cardiomyopathy

Opa1 processing is dispensable in mouse development but is protective in mitochondrial cardiomyopathy

Mitochondrial fusion and fission accompany adaptive responses to stress and altered metabolic demands. Inner membrane fusion and cristae morphogenesis depends on optic atrophy 1 (Opa1), which is expressed in different isoforms and is cleaved from a membrane-bound, long to a soluble, short form. Here, we have analyzed the physiological role of Opa1 isoforms and Opa1 processing by generating mouse lines expressing only one cleavable Opa1 isoform or a non-cleavable variant thereof. Our results show that expression of a single cleavable or non-cleavable Opa1 isoform preserves embryonic development and the health of adult mice. Opa1 processing is dispensable under metabolic and thermal stress but prolongs life span and protects against mitochondrial cardiomyopathy in OXPHOS-deficient Cox10-/- mice. Mechanistically, loss of Opa1 processing disturbs the balance between mitochondrial biogenesis and mitophagy, suppressing cardiac hypertrophic growth in Cox10-/- hearts. Our results highlight the critical regulatory role of Opa1 processing, mitochondrial dynamics, and metabolism for cardiac hypertrophy.

Mitochondrial unfolded protein response mechanism and its cardiovascular protective effects

The mitochondrial unfolded protein response (UPRmt) is a cytoprotective response in response to cellular stress that is activated in response to mitochondrial stress to maintain intra-protein homeostasis, thereby protecting the cell from a variety of stimuli. The activation of this response has been linked to cardiovascular diseases. Here, we reviewed the current understanding of UPRmt and discussed its specific molecular mechanism, mainly in mammals, as well as addressing its protective role against cardiovascular diseases, so as to provide direction for further research on UPRmt and therapies targeting cardiovascular diseases in the future.

CALCOCO2 prevents AngII-induced atrial remodeling by regulating the interaction between mitophagy and mitochondrial stress

BACKGROUND

The biological functions of mitochondrial complexes are closely related to the development of atrial fibrillation (AF). Calcium binding and coiled-coil domain 2 (CALCOCO2) is a novel and specific receptor for mitophagy; however, its function in AF remains unknown. Therefore, this study aimed to investigate the role and molecular mechanisms of CALCOCO2 in AF, especially its regulatory mechanism in mitophagy and mitochondrial stress.

METHODS

Mice and HL-1 cells were treated with AngII to establish in vitro and in vivo AF models. Additionally, we examined the effect of CALCOCO2 or DAP3 Binding Cell Death Enhancer 1 (DELE1) overexpression on mitophagy and mitochondrial stress in AF models. To investigate the role of mitophagy in the regulatory effects of CALCOCO2 in AF, HL-1 cells were treated with chloroquine, a mitophagy inhibitor. Moreover, mitochondrial parameters were examined using specific fluorescent probes, transmission electron microscopy, western blotting, immunohistochemistry, and confocal microscopy.

RESULTS

AngII severely impaired the normal morphology and function of mitochondria; inhibited mitophagy; promoted atrial mitochondrial stress, fibrosis, and oxidative stress; and accelerated the progression of atrial remodeling in atrial myocytes. However, CALCOCO2 overexpression reversed/ameliorated these AF-induced changes. Additionally, CALCOCO2 overexpression restored mitochondrial homeostasis in atrial muscle by activating mitophagy and ameliorating mitochondrial stress. Mechanistically, DELE1 overexpression increased mitochondrial reactive oxygen species level and the expression of mitochondrial stress proteins (HRI, eIF2α, and ATF4) even in CALCOCO2-expressing in vitro AF models..

CONCLUSIONS

CALCOCO2 may serve as a potential target for AF therapy to prevent or reverse the progression of atrial remodeling by regulating mitophagy and DELE1-mediated mitochondrial stress.

Epirubicin induces cardiotoxicity through disrupting ATP6V0A2-dependent lysosomal acidification and triggering ferroptosis in cardiomyocytes

Epirubicin (EPI) is effective in the treatment of malignant cancers, but its application is limited by life-threatening cardiotoxicity. Iron homeostasis disturbance has been implicated in anthracycline induced cardiotoxicity (AIC), and ferroptosis is involved in AIC which dependent upon intracellular iron. However, the role and exact mechanisms of ferroptosis in the pathogenesis of epirubicin-induced cardiotoxicity (EIC) remain elusive. In this study, we aimed to investigate mechanisms underlying ferroptosis-driven EIC. Epirubicin triggered ferroptosis both in vivo and in cultured cardiomyocytes, and pretreatment with ferroptosis inhibitor, Ferrostatin-1(Fer-1) alleviates EIC. Microarray analysis was performed to screen for potential molecules involved in EIC in neonatal primary mouse ventricular cardiomyocytes (NMVMs). We found that the transcript level of ATP6V0A2, a subunit of vacuolar ATPase (V-ATPase), was significantly downregulated when NMVMs were subjected to EPI, which was verified in vivo and in vitro as measured by real time quantitative reverse transcription PCR (qRT-PCR) and immunoblotting. Intriguingly, overexpression of ATP6V0A2 effectively decreased excessive oxidative stress and lipid-peroxidation accumulation, thereby inhibiting ferroptosis and protecting cardiomyocytes against EIC, as evidenced by functional, enzymatic, and morphological changes. Mechanistically, forced expression of ATP6V0A2 restored lysosomal acidification in EPI-treated cardiomyocytes and protected cardiomyocytes and mice hearts from ferroptosis-driven EIC. In this study, our data elucidate that ferroptosis is involved in EIC, which is ignited by ATP6V0A2-dependent lysosomal acidification dysfunction. Our study provides a new potential therapeutic target for ameliorating EIC.

ATAD1 prevents clogging of TOM and damage caused by un-imported mitochondrial proteins

Mitochondria require the constant import of nuclear-encoded proteins for proper functioning. Impaired protein import not only depletes mitochondria of essential factors but also leads to toxic accumulation of un-imported proteins outside the organelle. Here, we investigate the consequences of impaired mitochondrial protein import in human cells. We demonstrate that un-imported proteins can clog the mitochondrial translocase of the outer membrane (TOM). ATAD1, a mitochondrial ATPase, removes clogged proteins from TOM to clear the entry gate into the mitochondria. ATAD1 interacts with both TOM and stalled proteins, and its knockout results in extensive accumulation of mitochondrial precursors as well as decreased protein import. Increased ATAD1 expression contributes to improved fitness of cells with inefficient mitochondrial protein import. Overall, we demonstrate the importance of the ATAD1 quality control pathway in surveilling protein import and its contribution to cellular health.

Glutathione determines chronic myeloid leukemia vulnerability to an inhibitor of CMPK and TMPK

Bcr-Abl transformation leads to chronic myeloid leukemia (CML). The acquirement of T315I mutation causes tyrosine kinase inhibitors (TKI) resistance. This study develops a compound, JMF4073, inhibiting thymidylate (TMP) and cytidylate (CMP) kinases, aiming for a new therapy against TKI-resistant CML. In vitro and in vivo treatment of JMF4073 eliminates WT-Bcr-Abl-32D CML cells. However, T315I-Bcr-Abl-32D cells are less vulnerable to JMF4073. Evidence is presented that ATF4-mediated upregulation of GSH causes T315I-Bcr-Abl-32D cells to be less sensitive to JMF4073. Reducing GSH biosynthesis generates replication stress in T315I-Bcr-Abl-32D cells that require dTTP/dCTP synthesis for survival, thus enabling JMF4073 susceptibility. It further shows that the levels of ATF4 and GSH in several human CML blast-crisis cell lines are inversely correlated with JMF4073 sensitivity, and the combinatory treatment of JMF4073 with GSH reducing agent leads to synthetic lethality in these CML blast-crisis lines. Altogether, the investigation indicates an alternative option in CML therapy.

Mitochondrial Structure and Function in Human Heart Failure

Despite clinical and scientific advancements, heart failure is the major cause of morbidity and mortality worldwide. Both mitochondrial dysfunction and inflammation contribute to the development and progression of heart failure. Although inflammation is crucial to reparative healing following acute cardiomyocyte injury, chronic inflammation damages the heart, impairs function, and decreases cardiac output. Mitochondria, which comprise one third of cardiomyocyte volume, may prove a potential therapeutic target for heart failure. Known primarily for energy production, mitochondria are also involved in other processes including calcium homeostasis and the regulation of cellular apoptosis. Mitochondrial function is closely related to morphology, which alters through mitochondrial dynamics, thus ensuring that the energy needs of the cell are met. However, in heart failure, changes in substrate use lead to mitochondrial dysfunction and impaired myocyte function. This review discusses mitochondrial and cristae dynamics, including the role of the mitochondria contact site and cristae organizing system complex in mitochondrial ultrastructure changes. Additionally, this review covers the role of mitochondria-endoplasmic reticulum contact sites, mitochondrial communication via nanotunnels, and altered metabolite production during heart failure. We highlight these often-neglected factors and promising clinical mitochondrial targets for heart failure.

The integrated stress response promotes neural stem cell survival under conditions of mitochondrial dysfunction in neurodegeneration

Impaired mitochondrial function is a hallmark of aging and a major contributor to neurodegenerative diseases. We have shown that disrupted mitochondrial dynamics typically found in aging alters the fate of neural stem cells (NSCs) leading to impairments in learning and memory. At present, little is known regarding the mechanisms by which neural stem and progenitor cells survive and adapt to mitochondrial dysfunction. Using Opa1-inducible knockout as a model of aging and neurodegeneration, we identify a decline in neurogenesis due to impaired stem cell activation and progenitor proliferation, which can be rescued by the mitigation of oxidative stress through hypoxia. Through sc-RNA-seq, we identify the ATF4 pathway as a critical mechanism underlying cellular adaptation to metabolic stress. ATF4 knockdown in Opa1-deficient NSCs accelerates cell death, while the increased expression of ATF4 enhances proliferation and survival. Using a Slc7a11 mutant, an ATF4 target, we show that ATF4-mediated glutathione production plays a critical role in maintaining NSC survival and function under stress conditions. Together, we show that the activation of the integrated stress response (ISR) pathway enables NSCs to adapt to metabolic stress due to mitochondrial dysfunction and metabolic stress and may serve as a therapeutic target to enhance NSC survival and function in aging and neurodegeneration.

Regulation of FSP1 myristoylation by NADPH: A novel mechanism for ferroptosis inhibition

Excitotoxicity is a prevalent pathological event in neurodegenerative diseases. The involvement of ferroptosis in the pathogenesis of excitotoxicity remains elusive. Transcriptome analysis has revealed that cytoplasmic reduced nicotinamide adenine dinucleotide phosphate (NADPH) levels are associated with susceptibility to ferroptosis-inducing compounds. Here we show that exogenous NADPH, besides being reductant, interacts with N-myristoyltransferase 2 (NMT2) and upregulates the N-myristoylated ferroptosis suppressor protein 1 (FSP1). NADPH increases membrane-localized FSP1 and strengthens resistance to ferroptosis. Arg-291 of NMT2 is critical for the NADPH-NMT2-FSP1 axis-mediated suppression of ferroptosis. This study suggests that NMT2 plays a pivotal role by bridging NADPH levels and neuronal susceptibility to ferroptosis. We propose a mechanism by which the NADPH regulates N-myristoylation, which has important implications for ferroptosis and disease treatment.

ISRIB improves white matter injury following TBI by inhibiting NCOA4-mediated ferritinophagy

Traumatic brain injury (TBI) often results in persistent neurological dysfunction, which is closely associated with white matter injury. The mechanisms underlying white matter injury after TBI remain unclear. Ferritinophagy is a selective autophagic process that degrades ferritin and releases free iron, which may cause ferroptosis. Although ferroptosis has been demonstrated to be involved in TBI, it is unclear whether ferritinophagy triggers ferroptosis in TBI. Integrated stress response inhibitor (ISRIB) has neuroprotective properties. However, the effect of ISRIB on white matter after TBI remains uncertain. We aimed to investigate whether ferritinophagy was involved in white matter injury following TBI and whether ISRIB can mitigate white matter injury after TBI by inhibiting ferritinophagy. In this study, controlled cortical impact (CCI) was performed on rats to establish the TBI model. Ferritinophagy was measured by assessing the levels of nuclear receptor coactivator 4 (NCOA4), which regulates ferritinophagy, ferritin heavy chain 1(FTH1), LC3, ATG5, and FTH1 colocalization with LC3 in the white matter. Increased NCOA4 and decreased FTH1 were detected in our study. FTH1 colocalization with LC3 enhanced in the white matter after TBI, indicating that ferritinophagy was activated. Immunofluorescence co-localization results also suggested that ferritinophagy occurred in neurons and oligodendrocytes after TBI. Furthermore, ferroptosis was assessed by determining free iron content, MDA content, GSH content, and Perl's staining. The results showed that ferroptosis was suppressed by NCOA4 knockdown via shNCOA4 lentivirus infection, indicating that ferroptosis in TBI is triggered by ferritinophagy. Besides, NCOA4 deletion notably improved white matter injury following TBI, implying that ferritinophagy contributed to white matter injury. ISRIB treatment reduced the occurrence of ferritinophagy in neurons and oligodendrocytes, attenuated ferritinophagy-induced ferroptosis, and alleviated white matter injury. These findings suggest that NCOA4-mediated ferritinophagy is a critical mechanism underlying white matter injury after TBI. ISRIB holds promise as a therapeutic agent for this condition.

Mitochondrial proteases modulate mitochondrial stress signalling and cellular homeostasis in health and disease

Maintenance of mitochondrial homeostasis requires a plethora of coordinated quality control and adaptations' mechanisms in which mitochondrial proteases play a key role. Their activation or loss of function reverberate beyond local mitochondrial biochemical and metabolic remodelling into coordinated cellular pathways and stress responses that feedback onto the mitochondrial functionality and adaptability. Mitochondrial proteolysis modulates molecular and organellar quality control, metabolic adaptations, lipid homeostasis and regulates transcriptional stress responses. Defective mitochondrial proteolysis results in disease conditions most notably, mitochondrial diseases, neurodegeneration and cancer. Here, it will be discussed how mitochondrial proteases and mitochondria stress signalling impact cellular homeostasis and determine the cellular decision to survive or die, how these processes may impact disease etiopathology, and how modulation of proteolysis may offer novel therapeutic strategies.

Is mitochondrial morphology important for cellular physiology?

Mitochondria are double membrane-bound organelles the network morphology of which in cells is shaped by opposing events of fusion and fission executed by dynamin-like GTPases. Mutations in these genes can perturb the form and functions of mitochondria in cell and animal models of mitochondrial diseases. An expanding array of chemical, mechanical, and genetic stressors can converge on mitochondrial-shaping proteins and disrupt mitochondrial morphology. In recent years, studies aimed at disentangling the multiple roles of mitochondrial-shaping proteins beyond fission or fusion have provided insights into the homeostatic relevance of mitochondrial morphology. Here, I review the pleiotropy of mitochondrial fusion and fission proteins with the aim of understanding whether mitochondrial morphology is important for cell and tissue physiology.

The cell biology of ferroptosis

Ferroptosis is a non-apoptotic cell death mechanism characterized by iron-dependent membrane lipid peroxidation. Here, we review what is known about the cellular mechanisms mediating the execution and regulation of ferroptosis. We first consider how the accumulation of membrane lipid peroxides leads to the execution of ferroptosis by altering ion transport across the plasma membrane. We then discuss how metabolites and enzymes that are distributed in different compartments and organelles throughout the cell can regulate sensitivity to ferroptosis by impinging upon iron, lipid and redox metabolism. Indeed, metabolic pathways that reside in the mitochondria, endoplasmic reticulum, lipid droplets, peroxisomes and other organelles all contribute to the regulation of ferroptosis sensitivity. We note how the regulation of ferroptosis sensitivity by these different organelles and pathways seems to vary between different cells and death-inducing conditions. We also highlight transcriptional master regulators that integrate the functions of different pathways and organelles to modulate ferroptosis sensitivity globally. Throughout this Review, we highlight open questions and areas in which progress is needed to better understand the cell biology of ferroptosis.

Apoptotic Bodies Derived from Fibroblast-Like Cells in Subcutaneous Connective Tissue Inhibit Ferroptosis in Ischaemic Flaps via the miR-339-5p/KEAP1/Nrf2 Axis

Preventing and treating avascular necrosis at the distal end of the flaps are critical to surgery success, but current treatments are not ideal. A recent study shows that apoptotic bodies (ABs) generated near the site of apoptosis can be taken up and promote cell proliferation. The study reveals that ABs derived from fibroblast-like cells in the subcutaneous connective tissue (FSCT cells) of skin flaps promoted ischaemic flap survival. It is also found that ABs inhibited cell death and oxidative stress and promoted M1-to-M2 polarization in macrophages. Transcriptome sequencing and protein level testing demonstrated that ABs promoted ischaemic flap survival in endothelial cells and macrophages by inhibiting ferroptosis via the KEAP1-Nrf2 axis. Furthermore, microRNA (miR) sequencing data and in vitro and in vivo experiments demonstrated that ABs inhibited KEAP1 by delivering miR-339-5p to exert therapeutic effects. In conclusion, FSCT cell-derived ABs inhibited ferroptosis, promoted the macrophage M1-to-M2 transition via the miR-339-5p/KEAP1/Nrf2 axis and promoted ischaemic flap survival. These results provide a potential therapeutic strategy to promote ischaemic flap survival by administering ABs.

Inhibition of mammalian mtDNA transcription acts paradoxically to reverse diet-induced hepatosteatosis and obesity

The oxidative phosphorylation system1 in mammalian mitochondria plays a key role in transducing energy from ingested nutrients2. Mitochondrial metabolism is dynamic and can be reprogrammed to support both catabolic and anabolic reactions, depending on physiological demands or disease states. Rewiring of mitochondrial metabolism is intricately linked to metabolic diseases and promotes tumour growth3-5. Here, we demonstrate that oral treatment with an inhibitor of mitochondrial transcription (IMT)6 shifts whole-animal metabolism towards fatty acid oxidation, which, in turn, leads to rapid normalization of body weight, reversal of hepatosteatosis and restoration of normal glucose tolerance in male mice on a high-fat diet. Paradoxically, the IMT treatment causes a severe reduction of oxidative phosphorylation capacity concomitant with marked upregulation of fatty acid oxidation in the liver, as determined by proteomics and metabolomics analyses. The IMT treatment leads to a marked reduction of complex I, the main dehydrogenase feeding electrons into the ubiquinone (Q) pool, whereas the levels of electron transfer flavoprotein dehydrogenase and other dehydrogenases connected to the Q pool are increased. This rewiring of metabolism caused by reduced mtDNA expression in the liver provides a principle for drug treatment of obesity and obesity-related pathology.

High fat diet ameliorates mitochondrial cardiomyopathy in CHCHD10 mutant mice

Mutations in CHCHD10, a mitochondrial protein with undefined functions, are associated with autosomal dominant mitochondrial diseases. Chchd10 knock-in mice harboring a heterozygous S55L mutation (equivalent to human pathogenic S59L) develop a fatal mitochondrial cardiomyopathy caused by CHCHD10 aggregation and proteotoxic mitochondrial integrated stress response (mtISR). In mutant hearts, mtISR is accompanied by a metabolic rewiring characterized by increased reliance on glycolysis rather than fatty acid oxidation. To counteract this metabolic rewiring, heterozygous S55L mice were subjected to chronic high-fat diet (HFD) to decrease insulin sensitivity and glucose uptake and enhance fatty acid utilization in the heart. HFD ameliorated the ventricular dysfunction of mutant hearts and significantly extended the survival of mutant female mice affected by severe pregnancy-induced cardiomyopathy. Gene expression profiles confirmed that HFD increased fatty acid utilization and ameliorated cardiomyopathy markers. Importantly, HFD also decreased accumulation of aggregated CHCHD10 in the S55L heart, suggesting activation of quality control mechanisms. Overall, our findings indicate that metabolic therapy can be effective in mitochondrial cardiomyopathies associated with proteotoxic stress.

Cardiac-specific deletion of heat shock protein 60 induces mitochondrial stress and disrupts heart development in mice

Congenital heart diseases are the most common birth defects around the world. Emerging evidence suggests that mitochondrial homeostasis is required for normal heart development. In mitochondria, a series of molecular chaperones including heat shock protein 60 (HSP60) are engaged in assisting the import and folding of mitochondrial proteins. However, it remains largely obscure whether and how these mitochondrial chaperones regulate cardiac development. Here, we generated a cardiac-specific Hspd1 deletion mouse model by αMHC-Cre and investigated the role of HSP60 in cardiac development. We observed that deletion of HSP60 in embryonic cardiomyocytes resulted in abnormal heart development and embryonic lethality, characterized by reduced cardiac cell proliferation and thinner ventricular walls, highlighting an essential role of cardiac HSP60 in embryonic heart development and survival. Our results also demonstrated that HSP60 deficiency caused significant downregulation of mitochondrial ETC subunits and induced mitochondrial stress. Analysis of gene expression revealed that P21 that negatively regulates cell proliferation is significantly upregulated in HSP60 knockout hearts. Moreover, HSP60 deficiency induced activation of eIF2α-ATF4 pathway, further indicating the underlying mitochondrial stress in cardiomyocytes after HSP60 deletion. Taken together, our study demonstrated that regular function of mitochondrial chaperones is pivotal for maintaining normal mitochondrial homeostasis and embryonic heart development.

Mitochondria at the crossroads of health and disease

Mitochondria reside at the crossroads of catabolic and anabolic metabolism-the essence of life. How their structure and function are dynamically tuned in response to tissue-specific needs for energy, growth repair, and renewal is being increasingly understood. Mitochondria respond to intrinsic and extrinsic stresses and can alter cell and organismal function by inducing metabolic signaling within cells and to distal cells and tissues. Here, we review how the centrality of mitochondrial functions manifests in health and a broad spectrum of diseases and aging.

Mild therapeutic hypothermia upregulates the O-GlcNAcylation level of COX10 to alleviate mitochondrial damage induced by myocardial ischemia-reperfusion injury

OBJECTIVE

Mild therapeutic hypothermia (MTH) is an important method for perioperative prevention and treatment of myocardial ischemia-reperfusion injury (MIRI). Modifying mitochondrial proteins after protein translation to regulate mitochondrial function is one of the mechanisms for improving myocardial ischemia-reperfusion injury. This study investigated the relationship between shallow hypothermia treatment improving myocardial ischemia-reperfusion injury and the O-GlcNAcylation level of COX10.

METHODS

We used in vivo Langendorff model and in vitro hypoxia/reoxygenation (H/R) cell model to investigate the effects of MTH on myocardial ischemia-reperfusion injury. Histological changes, myocardial enzymes, oxidative stress, and mitochondrial structure/function were assessed. Mechanistic studies involved various molecular biology methods such as ELISA, immunoprecipitation (IP), WB, and immunofluorescence.

RESULTS

Our research results indicate that MTH upregulates the O-GlcNACylation level of COX10, improves mitochondrial function, and inhibits the expression of ROS to improve myocardial ischemia-reperfusion injury. In vivo, MTH effectively alleviates ischemia-reperfusion induced cardiac dysfunction, myocardial injury, mitochondrial damage, and redox imbalance. In vitro, the OGT inhibitor ALX inhibits the OGT mediated O-GlcNA acylation signaling pathway, downregulates the O-Glc acylation level of COX10, promotes ROS release, and counteracts the protective effect of MTH. On the contrary, the OGA inhibitor ThG showed opposite effects to ALX, further confirming that MTH activated the OGT mediated O-GlcNAcylation signaling pathway to exert cardioprotective effects.

CONCLUSIONS

In summary, MTH activates OGT mediated O-glycosylation modified COX10 to regulate mitochondrial function and improve myocardial ischemia-reperfusion injury, which provides important theoretical basis for the clinical application of MTH.

Integration of single-cell RNA sequencing of endothelial cells and proteomics to unravel the role of ICAM1-PTGS2 communication in apical periodontitis: A laboratory investigation

AIM

Endothelial cells (EDs) play a key role in angiogenesis and are associated with granulomatous lesions in patients with chronic apical periodontitis (CAP). This study aimed to investigate the diversity of EDs using single-cell ribonucleic acid sequencing (scRNA-seq) and to evaluate the regulation of intercellular adhesion molecule 1 (ICAM1) on the ferroptosis-related protein, prostaglandin-endoperoxide synthase 2 (PTGS2), in CAP.

METHODOLOGY

EDs from the uploaded scRNA-seq data of five CAP samples (GSE181688 and GSE197680) were categorized using distinct marker genes. The interactions between vein EDs (veinEndo) and other cell types were analysed using CellPhoneDB. Differentially expressed proteins in the proteomics of human umbilical vein EDs (HUVECs) and THP-1-derived macrophages infected with Porphyromonas gingivalis were compared with the differentially expressed genes (DEGs) of VeinEndo in scRNA-seq of CAP versus healthy control periodontal tissues. The protein-protein interaction of ICAM1-PTGS2 in macrophages and HUVECs was validated by adding recombinant ICAM1, ICAM1 inhibitor and PTGS2 inhibitor using real-time polymerase chain reaction (PCR), western blotting, and immunofluorescence staining.

RESULTS

EDs in patients with CAP were divided into eight subclusters: five vein ED, capillaries, arterials and EC (PLA). There were 29 mutually upregulated DEGs and two mutually downregulated DEGs in vein cells in the scRNA-seq data, as well as differentially expressed proteins in the proteomics of HUVECs. Real-time PCR and immunofluorescence staining showed that ICAM1 and PTGS2 were highly expressed in CAP, infected HUVECs, and macrophages. Recombinant protein ICAM1 may improve PTGS2 expression, reactive oxygen species (ROS), and Fe2+ levels and decrease glutathione peroxidase 4 (GPX4) and SLC7A11 protein levels. ICAM1 inhibitor may inverse the above changes.

CONCLUSIONS

scRNA-seq revealed the diversity of EDs in CAP and identified the possible regulation of ICAM1 by the ferroptosis-related protein, PTGS2, in infected HUVECs and macrophages, thus providing a basis for therapeutic approaches that target the inflammatory microenvironment of CAP.

Research advances on molecular mechanism and natural product therapy of iron metabolism in heart failure

The progression of heart failure (HF) is complex and involves multiple regulatory pathways. Iron ions play a crucial supportive role as a cofactor for important proteins such as hemoglobin, myoglobin, oxidative respiratory chain, and DNA synthetase, in the myocardial energy metabolism process. In recent years, numerous studies have shown that HF is associated with iron dysmetabolism, and deficiencies in iron and overload of iron can both lead to the development of various myocarditis diseases, which ultimately progress to HF. Iron toxicity and iron metabolism may be key targets for the diagnosis, treatment, and prevention of HF. Some iron chelators (such as desferrioxamine), antioxidants (such as ascorbate), Fer-1, and molecules that regulate iron levels (such as lactoferrin) have been shown to be effective in treating HF and protecting the myocardium in multiple studies. Additionally, certain natural compounds can play a significant role by mediating the imbalance of iron-related signaling pathways and expression levels. Therefore, this review not only summarizes the basic processes of iron metabolism in the body and the mechanisms by which they play a role in HF, with the aim of providing new clues and considerations for the treatment of HF, but also summarizes recent studies on natural chemical components that involve ferroptosis and its role in HF pathology, as well as the mechanisms by which naturally occurring products regulate ferroptosis in HF, with the aim of providing reference information for the development of new ferroptosis inhibitors and lead compounds for the treatment of HF in the future.

OMA1 competitively binds to HSPA9 to promote mitophagy and activate the cGAS-STING pathway to mediate GBM immune escape

BACKGROUND

Immunotherapy with checkpoint inhibitors, especially those targeting programmed death receptor 1 (PD-1)/PD-1 ligand (PD-L1), is increasingly recognized as a highly promising therapeutic modality for malignancies. Nevertheless, the efficiency of immune checkpoint blockade therapy in treating glioblastoma (GBM) is constrained. Hence, it is imperative to expand our comprehension of the molecular mechanisms behind GBM immune escape (IE).

METHODS

Protein chip analysis was performed to screen aberrantly expressed OMA1 protein in PD-1 inhibitor sensitive or resistant GBM. Herein, public databases and bioinformatics analysis were employed to investigate the OMA1 and PD-L1 relation. Then, this predicted relation was verified in primary GBM cell lines through distinct experimental methods. To investigate the molecular mechanism behind OMA1 in immunosuppression, a series of experimental methods were employed, including Western blotting, co-immunoprecipitation (Co-IP), mass spectrometry (MS), immunofluorescence, immunohistochemistry, and qRT-PCR.

RESULTS

Our findings revealed that OMA1 competitively binds to HSPA9 to induce mitophagy and mediates the IE of GBM. Data from TCGA indicated a significant correlation between OMA1 and immunosuppression. OMA1 promoted PD-L1 levels in primary cells from patients with GBM. Next, the results of Co-IP and MS conducted on GBM primary cells revealed that OMA1 interacts with HSPA9 and induces mitophagy. OMA1 promoted not only cGAS-STING activity by increasing mitochondrial DNA release but also PD-L1 transcription by activating cGAS-STING. Eventually, OMA1 has been found to induce immune evasion in GBM through its regulation of PD-1 binding and PD-L1 mediated T cell cytotoxicity.

CONCLUSIONS

The OMA1/HSPA9/cGAS/PD-L1 axis is elucidated in our study as a newly identified immune therapeutic target in GBM.

Regulation of proteostasis and innate immunity via mitochondria-nuclear communication

Mitochondria are perhaps best known as the "powerhouse of the cell" for their role in ATP production required for numerous cellular activities. Mitochondria have emerged as an important signaling organelle. Here, we first focus on signaling pathways mediated by mitochondria-nuclear communication that promote protein homeostasis (proteostasis). We examine the mitochondrial unfolded protein response (UPRmt) in C. elegans, which is regulated by a transcription factor harboring both a mitochondrial- and nuclear-targeting sequence, the integrated stress response in mammals, as well as the regulation of chromatin by mitochondrial metabolites. In the second section, we explore the role of mitochondria-to-nuclear communication in the regulation of innate immunity and inflammation. Perhaps related to their prokaryotic origin, mitochondria harbor molecules also found in viruses and bacteria. If these molecules accumulate in the cytosol, they elicit the same innate immune responses as viral or bacterial infection.

miR-15b-5p promotes HgCl2-induced chicken embryo kidney cells ferroptosis by targeting β-TrCP-mediated ATF4 ubiquitin degradation

Mercuric chloride (HgCl2), a widespread environmental pollutant, induces ferroptosis in chicken embryonic kidney (CEK) cells. Whereas activating transcription factor 4 (ATF4), a critical mediator of oxidative homeostasis, plays a dual role in ferroptosis, but its precise mechanisms in HgCl2-induced ferroptosis remain elusive. This study aims to investigate the function and molecular mechanism of ATF4 in HgCl2-induced ferroptosis. Our results revealed that ATF4 was downregulated during HgCl2-induced ferroptosis in CEK cells. Surprisingly, HgCl2 exposure has no significant impact on ATF4 mRNA level. Further investigation indicated that HgCl2 enhanced the expression of the E3 ligase beta-transducin repeat-containing protein (β-TrCP) and increased ATF4 ubiquitination. Subsequent findings identified that miR-15b-5p as an upstream modulator of β-TrCP, with miR-15b-5p downregulation observed in HgCl2-exposed CEK cells. Importantly, miR-15b-5p mimics suppressed β-TrCP expression and reversed HgCl2-induced cellular ferroptosis. Mechanistically, HgCl2 inhibited miR-15b-5p, and promoted β-TrCP-mediated ubiquitin degradation of ATF4, thereby inhibited the expression of antioxidant-related target genes and promoted ferroptosis. In conclusion, our study highlighted the crucial role of the miR-15b-5p/β-TrCP/ATF4 axis in HgCl2-induced nephrotoxicity, offering a new therapeutic target for understanding the mechanism of HgCl2 nephrotoxicity.

Sustained OMA1-mediated integrated stress response is beneficial for spastic ataxia type 5

AFG3L2 is a mitochondrial protease exerting protein quality control in the inner mitochondrial membrane. Heterozygous AFG3L2 mutations cause spinocerebellar ataxia type 28 (SCA28) or dominant optic atrophy type 12 (DOA12), while biallelic AFG3L2 mutations result in the rare and severe spastic ataxia type 5 (SPAX5). The clinical spectrum of SPAX5 includes childhood-onset cerebellar ataxia, spasticity, dystonia and myoclonic epilepsy. We previously reported that the absence or mutation of AFG3L2 leads to the accumulation of mitochondria-encoded proteins, causing the overactivation of the stress-sensitive protease OMA1, which over-processes OPA1, leading to mitochondrial fragmentation. Recently, OMA1 has been identified as the pivotal player communicating mitochondrial stress to the cytosol via a pathway involving the inner mitochondrial membrane protein DELE1 and the cytosolic kinase HRI, thus eliciting the integrated stress response. In general, the integrated stress response reduces global protein synthesis and drives the expression of cytoprotective genes that allow cells to endure proteotoxic stress. However, the relevance of the OMA1-DELE1-HRI axis in vivo, and especially in a human CNS disease context, has been poorly documented thus far. In this work, we demonstrated that mitochondrial proteotoxicity in the absence/mutation of AFG3L2 activates the OMA1-DELE1-HRI pathway eliciting the integrated stress response. We found enhanced OMA1-dependent processing of DELE1 upon depletion of AFG3L2. Also, in both skin fibroblasts from SPAX5 patients (including a novel case) and in the cerebellum of Afg3l2-/- mice we detected increased phosphorylation of the α-subunit of the eukaryotic translation initiation factor 2 (eIF2α), increased levels of ATF4 and strong upregulation of its downstream targets (Chop, Chac1, Ppp1r15a and Ffg21). Silencing of DELE1 or HRI in SPAX5 fibroblasts (where OMA1 is overactivated at basal state) reduces eIF2α phosphorylation and affects cell growth. In agreement, pharmacological potentiation of integrated stress response via Sephin-1, a drug that selectively inhibits the stress-induced eIF2alpha phosphatase GADD34 (encoded by Ppp1r15a), improved cell growth of SPAX5 fibroblasts and cell survival and dendritic arborization ex vivo in primary Afg3l2-/- Purkinje neurons. Notably, Sephin-1 treatment in vivo extended the lifespan of Afg3l2-/- mice, improved Purkinje neuron morphology, mitochondrial ultrastructure and respiratory capacity. These data indicate that activation of the OMA1-DELE1-HRI pathway is protective in the context of SPAX5. Pharmacological tuning of the integrated stress response may represent a future therapeutic strategy for SPAX5 and other cerebellar ataxias caused by impaired mitochondrial proteostasis.

DELE1 promotes translation-associated homeostasis, growth, and survival in mitochondrial myopathy

Mitochondrial dysfunction causes devastating disorders, including mitochondrial myopathy. Here, we identified that diverse mitochondrial myopathy models elicit a protective mitochondrial integrated stress response (mt-ISR), mediated by OMA1-DELE1 signaling. The response was similar following disruptions in mtDNA maintenance, from knockout of Tfam, and mitochondrial protein unfolding, from disease-causing mutations in CHCHD10 (G58R and S59L). The preponderance of the response was directed at upregulating pathways for aminoacyl-tRNA biosynthesis, the intermediates for protein synthesis, and was similar in heart and skeletal muscle but more limited in brown adipose challenged with cold stress. Strikingly, models with early DELE1 mt-ISR activation failed to grow and survive to adulthood in the absence of Dele1, accounting for some but not all of OMA1's protection. Notably, the DELE1 mt-ISR did not slow net protein synthesis in stressed striated muscle, but instead prevented loss of translation-associated proteostasis in muscle fibers. Together our findings identify that the DELE1 mt-ISR mediates a stereotyped response to diverse forms of mitochondrial stress and is particularly critical for maintaining growth and survival in early-onset mitochondrial myopathy.

A guideline on the molecular ecosystem regulating ferroptosis

Ferroptosis, an intricately regulated form of cell death characterized by uncontrolled lipid peroxidation, has garnered substantial interest since this term was first coined in 2012. Recent years have witnessed remarkable progress in elucidating the detailed molecular mechanisms that govern ferroptosis induction and defence, with particular emphasis on the roles of heterogeneity and plasticity. In this Review, we discuss the molecular ecosystem of ferroptosis, with implications that may inform and enable safe and effective therapeutic strategies across a broad spectrum of diseases.

Inhibition of ferroptosis reverses heart failure with preserved ejection fraction in mice

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) accounts for approximately 50% of heart failure cases. The molecular mechanisms by which HFpEF leads to impaired diastolic function of the heart have not been clarified, nor have the drugs that target the clinical symptoms of HFpEF patients.

METHODS

HFpEF chip data (GSE180065) was downloaded from the National Center for Biotechnology Information (NCBI) database. Differentially expressed genes (DEGs) were filtered by the limma package in R and processed for GO and KEGG pathway analyses. Then, ferroptosis-related genes in HFpEF were identified by taking the intersection between DEGs and ferroptosis-related genes. CytoHubba and MCODE were used to screen ferroptosis-related hub DEGs in the protein-protein interaction (PPI) network. Establishment of a mouse HFpEF model to validate the transcript levels of ferroptosis-related hub DEGs and ferroptosis-related phenotypes. Transcript levels of ferroptosis-related hub DEGs and HFpEF phenotypic changes in the hearts of HFpEF mice were further examined after the use of ferroptosis inhibitors.

RESULTS

GO and KEGG enrichment analyses suggested that the DEGs in HFpEF were significantly enriched in ferroptosis-related pathways. A total of 24 ferroptosis-related DEGs were identified between the ferroptosis gene dataset and the DEGs. The established PPI network was further analyzed by CytoHubba and MCODE modules, and 11 ferroptosis-related hub DEGs in HFpEF were obtained. In animal experiments, HFpEF mice showed significant abnormal activation of ferroptosis. The expression trends of the 11 hub DEGs associated with ferroptosis, except for Cdh1, were consistent with the results of the bioinformatics analysis. Inhibition of ferroptosis alters the transcript levels of 11 ferroptosis-related hub DEGs and ameliorates HFpEF phenotypes.

CONCLUSIONS

The present study contributes to a deeper understanding of the specific mechanisms by which ferroptosis is involved in the development of HFpEF and suggests that inhibition of ferroptosis may mitigate the progression of HFpEF. In addition, eleven hub genes were recognized as potential drug binding targets.

Mitochondrial entry gate as regulatory hub

Mitochondria import 1000-1300 different precursor proteins from the cytosol. The main mitochondrial entry gate is formed by the translocase of the outer membrane (TOM complex). Molecular coupling and modification of TOM subunits control and modulate protein import in response to cellular signaling. The TOM complex functions as regulatory hub to integrate mitochondrial protein biogenesis and quality control into the cellular proteostasis network.

Ferroptosis in mitochondrial cardiomyopathy

Ferroptosis is a form of necrotic cell death characterized by iron-dependent lipid peroxidation culminating in membrane rupture. Accumulating evidence links ferroptosis to multiple cardiac diseases and identifies mitochondria as important regulators of ferroptosis. Mitochondria are not only a major source of reactive oxygen species (ROS) but also counteract ferroptosis by preserving cellular redox balance and oxidative defense. Recent evidence has revealed that the mitochondrial integrated stress response limits oxidative stress and ferroptosis in oxidative phosphorylation (OXPHOS)-deficient cardiomyocytes and protects against mitochondrial cardiomyopathy. We summarize the multiple ways in which mitochondria modulate the susceptibility of cells to ferroptosis, and discuss the implications of ferroptosis for cardiomyopathies in mitochondrial disease.

Inhibition of cisplatin-induced Acsl4-mediated ferroptosis alleviated ovarian injury

Given that the severity of the chemotherapy-induced ovarian damage, effective fertility preservation is a necessary part of the treatment process. Ferroptosis is a regulated cell death triggered by excessive phospholipid peroxidation caused by iron and the role of ferroptosis in chemotherapy-induced ovarian damage remains unclear. In this study, we demonstrated that cisplatin treatment caused the accumulation of iron ions which induced ferroptosis in ovarian tissue. And our results show that ferrostatin-1 was able to suppress the ovarian injury and granulosa cell death caused by cisplatin (Cis) in vivo and in vitro. At the same time, we observed significant changes in the expression levels of Acyl-CoA synthetase long-chain family member 4 (Acsl4) and glutathione peroxidase 4 (GPX4). Similarly, Rosiglitazone, an inhibitor of Acsl4, administration alleviated the ovary damage of the mice undergoing chemotherapy. Further mechanistic investigation showed that cisplatin increased the expression level of specificity protein 1 (SP1), and SP1 could bind to the promoter of Acsl4 to increased Acsl4 transcription. Overall, ferroptosis plays an important role in Cis induced ovarian injury, and inhibition of ferroptosis protects ovarian tissues from damage caused by cisplatin, and for the first time, we have identified the potential of Fer-1 and Rosi to protect ovarian function in female mice undergoing chemotherapy.

PKD knockdown mitigates Ang II-induced cardiac hypertrophy and ferroptosis via the JNK/P53 signaling pathway

BACKGROUND

Cardiac hypertrophy is studied in relation to energy metabolism, autophagy, and ferroptosis, which are associated with cardiovascular adverse events and chronic heart failure. Protein kinase D (PKD) has been shown to play a degenerative role in cardiac hypertrophy. However, the role of ferroptosis in PKD-involved cardiac hypertrophy remains unclear.

METHODS

A cardiac hypertrophy model was induced by a subcutaneous injection of angiotensin II (Ang II) for 4 weeks. Adeno-associated virus serotype 9 (AAV9)-PKD or AAV9-Negative control were injected through the caudal vein 2 weeks prior to the injection of Ang II. The degree of cardiac hypertrophy was assessed using echocardiography and by observing cardiomyocyte morphology. Levels of ferroptosis and protein expression in the Jun N-terminal kinase (JNK)/P53 signaling pathway were measured both in vivo and in vitro.

RESULTS

The results indicated that PKD knockdown reduces Ang II-induced cardiac hypertrophy, enhances cardiac function and inhibits ferroptosis. The involvement of the JNK/P53 pathway in this process was further confirmed by in vivo and in vitro experiments.

CONCLUSION

In conclusion, our findings suggest that PKD knockdown mitigates Ang II-induced cardiac hypertrophy and ferroptosis via the JNK/P53 signaling pathway.

High fat diet ameliorates mitochondrial cardiomyopathy in CHCHD10 mutant mice

Mutations in CHCHD10 , a mitochondrial protein with undefined functions, are associated with autosomal dominant mitochondrial diseases. Chchd10 knock-in mice harboring a heterozygous S55L mutation (equivalent to human pathogenic S59L) develop a fatal mitochondrial cardiomyopathy caused by CHCHD10 aggregation and proteotoxic mitochondrial integrated stress response (mtISR). In mutant hearts, mtISR is accompanied by a metabolic rewiring characterized by increased reliance on glycolysis rather than fatty acid oxidation. To counteract this metabolic rewiring, heterozygous S55L mice were subjected to chronic high fat diet (HFD) to decrease insulin sensitivity and glucose uptake and enhance fatty acid utilization in the heart. HFD ameliorated the ventricular dysfunction of mutant hearts and significantly extended the survival of mutant female mice affected by severe pregnancy-induced cardiomyopathy. Gene expression profiles confirmed that HFD increased fatty acid utilization and ameliorated cardiomyopathy markers. Importantly, HFD also decreased accumulation of aggregated CHCHD10 in the S55L heart, suggesting activation of quality control mechanisms. Overall, our findings indicate that metabolic therapy can be effective in mitochondrial cardiomyopathies associated with proteotoxic stress.

Improving lysosomal ferroptosis with NMN administration protects against heart failure

Myocardial mitochondria are primary sites of myocardial energy metabolism. Mitochondrial disorders are associated with various cardiac diseases. We previously showed that mice with cardiomyocyte-specific knockout of the mitochondrial translation factor p32 developed heart failure from dilated cardiomyopathy. Mitochondrial translation defects cause not only mitochondrial dysfunction but also decreased nicotinamide adenine dinucleotide (NAD+) levels, leading to impaired lysosomal acidification and autophagy. In this study, we investigated whether nicotinamide mononucleotide (NMN) administration, which compensates for decreased NAD+ levels, improves heart failure because of mitochondrial dysfunction. NMN administration reduced damaged lysosomes and improved autophagy, thereby reducing heart failure and extending the lifespan in p32cKO mice. We found that lysosomal damage due to mitochondrial dysfunction induced ferroptosis, involving the accumulation of iron in lysosomes and lipid peroxide. The ameliorative effects of NMN supplementation were found to strongly affect lysosomal function rather than mitochondrial function, particularly lysosome-mediated ferroptosis. NMN supplementation can improve lysosomal, rather than mitochondrial, function and prevent chronic heart failure.

Sorting nexin 3 exacerbates doxorubicin-induced cardiomyopathy via regulation of TFRC-dependent ferroptosis

The clinical utilization of doxorubicin (Dox) in various malignancies is restrained by its major adverse effect: irreversible cardiomyopathy. Extensive studies have been done to explore the prevention of Dox cardiomyopathy. Currently, ferroptosis has been shown to participate in the incidence and development of Dox cardiomyopathy. Sorting Nexin 3 (SNX3), the retromer-associated cargo binding protein with important physiological functions, was identified as a potent therapeutic target for cardiac hypertrophy in our previous study. However, few study has shown whether SNX3 plays a critical role in Dox-induced cardiomyopathy. In this study, a decreased level of SNX3 in Dox-induced cardiomyopathy was observed. Cardiac-specific Snx3 knockout (Snx3-cKO) significantly alleviated cardiomyopathy by downregulating Dox-induced ferroptosis significantly. SNX3 was further demonstrated to exacerbate Dox-induced cardiomyopathy via induction of ferroptosis in vivo and in vitro, and cardiac-specific Snx3 transgenic (Snx3-cTg) mice were more susceptible to Dox-induced ferroptosis and cardiomyopathy. Mechanistically, SNX3 facilitated the recycling of transferrin 1 receptor (TFRC) via direct interaction, disrupting iron homeostasis, increasing the accumulation of iron, triggering ferroptosis, and eventually exacerbating Dox-induced cardiomyopathy. Overall, these findings established a direct SNX3-TFRC-ferroptosis positive regulatory axis in Dox-induced cardiomyopathy and suggested that targeting SNX3 provided a new effective therapeutic strategy for Dox-induced cardiomyopathy through TFRC-dependent ferroptosis.

Inhibition of CARM1-Mediated Methylation of ACSL4 Promotes Ferroptosis in Colorectal Cancer

Ferroptosis, which is caused by iron-dependent accumulation of lipid peroxides, is an emerging form of regulated cell death and is considered a potential target for cancer therapy. However, the regulatory mechanisms underlying ferroptosis remain unclear. This study defines a distinctive role of ferroptosis. Inhibition of CARM1 can increase the sensitivity of tumor cells to ferroptosis inducers in vitro and in vivo. Mechanistically, it is found that ACSL4 is methylated by CARM1 at arginine 339 (R339). Furthermore, ACSL4 R339 methylation promotes RNF25 binding to ACSL4, which contributes to the ubiquitylation of ACSL4. The blockade of CARM1 facilitates ferroptosis and effectively enhances ferroptosis-associated cancer immunotherapy. Overall, this study demonstrates that CARM1 is a critical contributor to ferroptosis resistance and highlights CARM1 as a candidate therapeutic target for improving the effects of ferroptosis-based antitumor therapy.

Mitohormesis

Perturbation of mitochondrial function can trigger a host of cellular responses that seek to restore cellular metabolism, cytosolic proteostasis, and redox homeostasis. In some cases, these responses persist even after the stress is relieved, leaving the cell or tissue in a less vulnerable state. This process-termed mitohormesis-is increasingly viewed as an important aspect of normal physiology and a critical modulator of various disease processes. Here, we review aspects of mitochondrial stress signaling that, among other things, can rewire the cell's metabolism, activate the integrated stress response, and alter cytosolic quality-control pathways. We also discuss how these pathways are implicated in various disease states from pathogen challenge to chemotherapeutic resistance and how their therapeutic manipulation can lead to new strategies for a host of chronic conditions including aging itself.

Mitochondrial quality control in health and cardiovascular diseases

Cardiovascular diseases (CVDs) are one of the primary causes of mortality worldwide. An optimal mitochondrial function is central to supplying tissues with high energy demand, such as the cardiovascular system. In addition to producing ATP as a power source, mitochondria are also heavily involved in adaptation to environmental stress and fine-tuning tissue functions. Mitochondrial quality control (MQC) through fission, fusion, mitophagy, and biogenesis ensures the clearance of dysfunctional mitochondria and preserves mitochondrial homeostasis in cardiovascular tissues. Furthermore, mitochondria generate reactive oxygen species (ROS), which trigger the production of pro-inflammatory cytokines and regulate cell survival. Mitochondrial dysfunction has been implicated in multiple CVDs, including ischemia-reperfusion (I/R), atherosclerosis, heart failure, cardiac hypertrophy, hypertension, diabetic and genetic cardiomyopathies, and Kawasaki Disease (KD). Thus, MQC is pivotal in promoting cardiovascular health. Here, we outline the mechanisms of MQC and discuss the current literature on mitochondrial adaptation in CVDs.

Temporal dynamics of muscle mitochondrial uncoupling-induced integrated stress response and ferroptosis defense

Mitochondria play multifaceted roles in cellular function, and impairments across domains of mitochondrial biology are known to promote cellular integrated stress response (ISR) pathways as well as systemic metabolic adaptations. However, the temporal dynamics of specific mitochondrial ISR related to physiological variations in tissue-specific energy demands remains unknown. Here, we conducted a comprehensive 24-hour muscle and plasma profiling of male and female mice with ectopic mitochondrial respiratory uncoupling in skeletal muscle (mUcp1-transgenic, TG). TG mice are characterized by increased muscle ISR, elevated oxidative stress defense, and increased secretion of FGF21 and GDF15 as ISR-induced myokines. We observed a temporal signature of both cell-autonomous and systemic ISR in the context of endocrine myokine signaling and cellular redox balance, but not of ferroptotic signature which was also increased in TG muscle. We show a progressive increase of muscle ISR on transcriptional level during the active phase (night time), with a subsequent peak in circulating FGF21 and GDF15 in the early resting phase. Moreover, we found highest levels of muscle oxidative defense (GPX and NQO1 activity) between the late active to early resting phase, which could aim to counteract excessive iron-dependent lipid peroxidation and ferroptosis in muscle of TG mice. These findings highlight the temporal dynamics of cell-autonomous and endocrine ISR signaling under skeletal muscle mitochondrial uncoupling, emphasizing the importance of considering such dissociation in translational strategies and sample collection for diagnostic biomarker analysis.

Mitochondrial DNA breaks activate an integrated stress response to reestablish homeostasis

Mitochondrial DNA double-strand breaks (mtDSBs) lead to the degradation of circular genomes and a reduction in copy number; yet, the cellular response in human cells remains elusive. Here, using mitochondrial-targeted restriction enzymes, we show that a subset of cells with mtDSBs exhibited defective mitochondrial protein import, reduced respiratory complexes, and loss of membrane potential. Electron microscopy confirmed the altered mitochondrial membrane and cristae ultrastructure. Intriguingly, mtDSBs triggered the integrated stress response (ISR) via the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) by DELE1 and heme-regulated eIF2α kinase (HRI). When ISR was inhibited, the cells experienced intensified mitochondrial defects and slower mtDNA recovery post-breakage. Lastly, through proteomics, we identified ATAD3A-a membrane-bound protein interacting with nucleoids-as potentially pivotal in relaying signals from impaired genomes to the inner mitochondrial membrane. In summary, our study delineates the cascade connecting damaged mitochondrial genomes to the cytoplasm and highlights the significance of the ISR in maintaining mitochondrial homeostasis amid genome instability.

The mechanism of ferroptosis and its related diseases

Ferroptosis, a regulated form of cellular death characterized by the iron-mediated accumulation of lipid peroxides, provides a novel avenue for delving into the intersection of cellular metabolism, oxidative stress, and disease pathology. We have witnessed a mounting fascination with ferroptosis, attributed to its pivotal roles across diverse physiological and pathological conditions including developmental processes, metabolic dynamics, oncogenic pathways, neurodegenerative cascades, and traumatic tissue injuries. By unraveling the intricate underpinnings of the molecular machinery, pivotal contributors, intricate signaling conduits, and regulatory networks governing ferroptosis, researchers aim to bridge the gap between the intricacies of this unique mode of cellular death and its multifaceted implications for health and disease. In light of the rapidly advancing landscape of ferroptosis research, we present a comprehensive review aiming at the extensive implications of ferroptosis in the origins and progress of human diseases. This review concludes with a careful analysis of potential treatment approaches carefully designed to either inhibit or promote ferroptosis. Additionally, we have succinctly summarized the potential therapeutic targets and compounds that hold promise in targeting ferroptosis within various diseases. This pivotal facet underscores the burgeoning possibilities for manipulating ferroptosis as a therapeutic strategy. In summary, this review enriched the insights of both investigators and practitioners, while fostering an elevated comprehension of ferroptosis and its latent translational utilities. By revealing the basic processes and investigating treatment possibilities, this review provides a crucial resource for scientists and medical practitioners, aiding in a deep understanding of ferroptosis and its effects in various disease situations.

FAM210A is essential for cold-induced mitochondrial remodeling in brown adipocytes

Cold stimulation dynamically remodels mitochondria in brown adipose tissue (BAT) to facilitate non-shivering thermogenesis in mammals, but what regulates mitochondrial plasticity is poorly understood. Comparing mitochondrial proteomes in response to cold revealed FAM210A as a cold-inducible mitochondrial inner membrane protein. An adipocyte-specific constitutive knockout of Fam210a (Fam210aAKO) disrupts mitochondrial cristae structure and diminishes the thermogenic activity of BAT, rendering the Fam210aAKO mice vulnerable to lethal hypothermia under acute cold exposure. Induced knockout of Fam210a in adult adipocytes (Fam210aiAKO) does not affect steady-state mitochondrial structure under thermoneutrality, but impairs cold-induced mitochondrial remodeling, leading to progressive loss of cristae and reduction of mitochondrial density. Proteomics reveals an association between FAM210A and OPA1, whose cleavage governs cristae dynamics and mitochondrial remodeling. Mechanistically, FAM210A interacts with mitochondrial protease YME1L and modulates its activity toward OMA1 and OPA1 cleavage. These data establish FAM210A as a key regulator of mitochondrial cristae remodeling in BAT and shed light on the mechanism underlying mitochondrial plasticity in response to cold.

Use of Deep-Learning Assisted Assessment of Cardiac Parameters in Zebrafish to Discover Cyanidin Chloride as a Novel Keap1 Inhibitor Against Doxorubicin-Induced Cardiotoxicity

Doxorubicin-induced cardiomyopathy (DIC) brings tough clinical challenges as well as continued demand in developing agents for adjuvant cardioprotective therapies. Here, a zebrafish phenotypic screening with deep-learning assisted multiplex cardiac functional analysis using motion videos of larval hearts is established. Through training the model on a dataset of 2125 labeled ventricular images, ZVSegNet and HRNet exhibit superior performance over previous methods. As a result of high-content phenotypic screening, cyanidin chloride (CyCl) is identified as a potent suppressor of DIC. CyCl effectively rescues cardiac cell death and improves heart function in both in vitro and in vivo models of Doxorubicin (Dox) exposure. CyCl shows strong inhibitory effects on lipid peroxidation and mitochondrial damage and prevents ferroptosis and apoptosis-related cell death. Molecular docking and thermal shift assay further suggest a direct binding between CyCl and Keap1, which may compete for the Keap1-Nrf2 interaction, promote nuclear accumulation of Nrf2, and subsequentially transactivate Gpx4 and other antioxidant factors. Site-specific mutation of R415A in Keap1 significantly attenuates the protective effects of CyCl against Dox-induced cardiotoxicity. Taken together, the capability of deep-learning-assisted phenotypic screening in identifying promising lead compounds against DIC is exhibited, and new perspectives into drug discovery in the era of artificial intelligence are provided.

Temporal landscape of mitochondrial proteostasis governed by the UPRmt

Breakdown of mitochondrial proteostasis activates quality control pathways including the mitochondrial unfolded protein response (UPRmt) and PINK1/Parkin mitophagy. However, beyond the up-regulation of chaperones and proteases, we have a limited understanding of how the UPRmt remodels and restores damaged mitochondrial proteomes. Here, we have developed a functional proteomics framework, termed MitoPQ (Mitochondrial Proteostasis Quantification), to dissect the UPRmt's role in maintaining proteostasis during stress. We find essential roles for the UPRmt in both protecting and repairing proteostasis, with oxidative phosphorylation metabolism being a central target of the UPRmt. Transcriptome analyses together with MitoPQ reveal that UPRmt transcription factors drive independent signaling arms that act in concert to maintain proteostasis. Unidirectional interplay between the UPRmt and PINK1/Parkin mitophagy was found to promote oxidative phosphorylation recovery when the UPRmt failed. Collectively, this study defines the network of proteostasis mediated by the UPRmt and highlights the value of functional proteomics in decoding stressed proteomes.

DELE1 oligomerization promotes integrated stress response activation

Mitochondria are dynamic organelles that continually respond to cellular stress. Recent studies have demonstrated that mitochondrial stress is relayed from mitochondria to the cytosol by the release of a proteolytic fragment of DELE1 that binds to the eIF2α kinase HRI to initiate integrated stress response (ISR) signaling. We report the cryo-electron microscopy structure of the C-terminal cleavage product of human DELE1, which assembles into a high-order oligomer. The oligomer consists of eight DELE1 monomers that assemble with D4 symmetry via two sets of hydrophobic inter-subunit interactions. We identified the key residues involved in DELE1 oligomerization, and confirmed their role in stabilizing the octamer in vitro and in cells using mutagenesis. We further show that assembly-impaired DELE1 mutants are compromised in their ability to induce HRI-dependent ISR activation in cell culture models. Together, our findings provide molecular insights into the activity of DELE1 and how it signals to promote ISR activity following mitochondrial insult.

The in vivo drug delivery pattern of the organelle-targeting small molecules

Eukaryotic cell organelles sustain the life of cells. Their structural changes and dysfunctions can cause abnormal physiological activities and lead to various diseases. Molecular imaging technology enables the visualization of subcellular structures, cells, organs, and the whole living body's structure and metabolism dynamic changes. This could help to reveal the pharmacology mechanisms and drug delivery pathway in vivo. This article discusses the relationship between organelles and human disease, reviews recent probes targeting organelles and their behavior in vivo. We found that mitochondria-targeting probes prefer accumulation in the intestine, heart, and tumor. The lysosome-targeting probe accumulates in the intestine and tumor. Few studies on endoplasmic reticulum- or Golgi apparatus-targeting probes have been reported for in vivo imaging. We hope this review could provide new insights for developing and applying organelle-targeting probes.

Disease models of mitochondrial aminoacyl-tRNA synthetase defects

Mitochondrial aminoacyl-tRNA synthetases (mtARS) are enzymes critical for the first step of mitochondrial protein synthesis by charging mitochondrial tRNAs with their cognate amino acids. Pathogenic variants in all 19 nuclear mtARS genes are now recognized as causing recessive mitochondrial diseases. Most mtARS disorders affect the nervous system, but the phenotypes range from multisystem diseases to tissue-specific manifestations. However, the mechanisms behind the tissue specificities are poorly understood, and challenges remain in obtaining accurate disease models for developing and testing treatments. Here, some of the currently existing disease models that have increased our understanding of mtARS defects are discussed.

Mitochondrial integrated stress response controls lung epithelial cell fate

Alveolar epithelial type 1 (AT1) cells are necessary to transfer oxygen and carbon dioxide between the blood and air. Alveolar epithelial type 2 (AT2) cells serve as a partially committed stem cell population, producing AT1 cells during postnatal alveolar development and repair after influenza A and SARS-CoV-2 pneumonia1-6. Little is known about the metabolic regulation of the fate of lung epithelial cells. Here we report that deleting the mitochondrial electron transport chain complex I subunit Ndufs2 in lung epithelial cells during mouse gestation led to death during postnatal alveolar development. Affected mice displayed hypertrophic cells with AT2 and AT1 cell features, known as transitional cells. Mammalian mitochondrial complex I, comprising 45 subunits, regenerates NAD+ and pumps protons. Conditional expression of yeast NADH dehydrogenase (NDI1) protein that regenerates NAD+ without proton pumping7,8 was sufficient to correct abnormal alveolar development and avert lethality. Single-cell RNA sequencing revealed enrichment of integrated stress response (ISR) genes in transitional cells. Administering an ISR inhibitor9,10 or NAD+ precursor reduced ISR gene signatures in epithelial cells and partially rescued lethality in the absence of mitochondrial complex I function. Notably, lung epithelial-specific loss of mitochondrial electron transport chain complex II subunit Sdhd, which maintains NAD+ regeneration, did not trigger high ISR activation or lethality. These findings highlight an unanticipated requirement for mitochondrial complex I-dependent NAD+ regeneration in directing cell fate during postnatal alveolar development by preventing pathological ISR induction.

An integrated view of lipid metabolism in ferroptosis revisited via lipidomic analysis

Ferroptosis is a form of regulated cell death characterized by iron-dependent lipid peroxidation. This process contributes to cellular and tissue damage in various human diseases, such as cardiovascular diseases, neurodegeneration, liver disease, and cancer. Although polyunsaturated fatty acids (PUFAs) in membrane phospholipids are preferentially oxidized, saturated/monounsaturated fatty acids (SFAs/MUFAs) also influence lipid peroxidation and ferroptosis. In this review, we first explain how cells differentially synthesize SFA/MUFAs and PUFAs and how they control fatty acid pools via fatty acid uptake and β-oxidation, impacting ferroptosis. Furthermore, we discuss how fatty acids are stored in different lipids, such as diacyl or ether phospholipids with different head groups; triglycerides; and cholesterols. Moreover, we explain how these fatty acids are released from these molecules. In summary, we provide an integrated view of the diverse and dynamic metabolic processes in the context of ferroptosis by revisiting lipidomic studies. Thus, this review contributes to the development of therapeutic strategies for ferroptosis-related diseases.