Mitochondrial Maintenance Research Articles

#489 UCP1 regulates cardiolipin metabolism and mediates mitochondrial homeostasis maintenance of ANXA1 in diabetic nephropathy

Abstract Background and Aims Diabetic nephropathy (DN) is accounted for a large proportion of chronic kidney disease (CKD) and is the leading cause of end-stage renal disease (ESRD) nowadays. The complex pathogenesis of DN has hindered the development of a single effective medicine, so it is of great significance to seek new therapeutic targets. Uncoupling of mitochondrial respiration by chemical uncouplers has proven effective in ameliorating obesity, insulin resistance, and hyperglycemia, which were risk factors for DN. Recently, we found that ANXA1 could improve mitochondrial function to mitigate DN progression. However, the underlying mechanism is not fully clear yet. Method We used kidney samples from patients in our hospital. ANXA1-KO mice with local renal overexpression of UCP1 were constructed, UCP1-KO mice were constructed for STZ/HFD modeling, and db/db mice were treated with CL316243. UCP1-KO mice with renal overexpression of CRLS1 were constructed. Mice with PTECs-specific deletion of ANXA1 were constructed. Cell lines with UCP1/ANXA1/GATA3 knockdown and UCP1/ANXA1/GATA3 overexpression were constructed, and cell reversal tests were performed using Ac2-26, CL316243 and siRNA targeting the above genes. Results Here, we identified uncoupling protein 1 (UCP1), an inner membrane protein of mitochondria, as a key to mitochondrial homeostasis improved by ANXA1. Specifically, ANXA1 attenuated mitochondrial dysfunction via appropriately upregulating UCP1 by stabilizing its transcription factor GATA binding protein 3 (GATA3) through combining with thioredoxin. Moreover, specific overexpression of UCP1 in renal cortex rescued renal injuries in diabetic Anxa1-KO mice. UCP1 deletion aggravated renal injuries in HFD/STZ-induced diabetic mice. Mechanistically, UCP1 reduced mitochondrial fission through the aristaless-related homeobox (ARX)/cardiolipin synthase 1 (CRLS1) pathway. Therapeutically, CL316243, a UCP1 agonist, could attenuate established DN in db/db mice. Conclusion Thus, our data unraveled specific mechanism by which UCP1 mediated mitochondrial homeostasis maintenance via the ANXA1-GATA3-UCP1-ARX-CRLS1 signaling pathway. This work established a novel principle to harness the power of uncouplers for the treatment of DN.

Mitochondrial Protein TAMM41 Modulates Depressive-like Behaviors.

Several lines of evidence have highlighted the crucial role of mitochondria-based therapy in depression. However, there are still less mitochondrial targets for the depression treatment. TAM41 mitochondrial translocator assembly and maintenance homolog (TAMM41) is a mitochondrial inner membrane protein for maintaining mitochondrial function, which is tightly related to many brain diseases including Alzheimer's diseases and epilepsy. Here, we investigated whether TAMM41 would be a potential target to treat depression. We found that the expression of TAMM41 was markedly lower in corticosterone-induced depression, lipopolysaccharide-induced depression, and depressed patients. Meanwhile, loss of TAMM41 resulted in increased immobility in the forced swim test (FST), tail suspension test (TST), and center time in open field test (OFT), suggesting depressive-like behaviors in mice. Moreover, genetic overexpression of TAMM41 obviously exerted antidepressant-like activities. Mechanistically, proteomics revealed that pacsin1 might be the underlying target of TAMM41. Further data supported that TAMM41 regulated the expression of pacsin1, and its antidepressant-like effect at least partially was attributed to pacsin1. In addition, exosomes containing TAMM41 was sufficient to exhibit antidepressant-like effect, suggesting an alternative strategy to exert the effect of TAMM41. Taken together, the present study demonstrates the antidepressant-like effect of TAMM41 and sheds light on its molecular mechanism. These finding provide new insights into a therapeutic strategy targeting mitochondria in the development of novel antidepressants.

Transcriptomic analysis reveals extensive modulation of mitochondrial gene expressions after volumetric muscle loss injury

Volumetric muscle loss (VML) is characterized by the unrecoverable loss of muscle tissue and function. Therapeutic modalities remain elusive in part because the etiology of the pathology remains unclear. Past RNA-sequencing analyses shed light on transcriptional regulation, but differential gene expression and gene set enrichment analysis (GSEA) results are often dominated by the robust inflammatory and fibrotic response to the injury. The primary objective of this study was to leverage past datasets and interrogate transcriptional regulation of cellular metabolism because our group has previously reported that VML injury disrupts mitochondrial function in the remaining muscle after VML injury. We hypothesized that a metabolic GSEA analysis will identify several differentially expressed mitochondrial gene sets. Utilizing a publicly-available rat species RNAseq dataset, we transformed that data from transcripts per million (TPM) to a Z-score with respect to the uninjured group. Since TPM is not compatible with cross-sample comparisons, we opted for a single-sample GSEA that permits phenotype comparisons. Visualizing the normalized enrichment scores (NES) into heatmaps allowed us to select the top-25 enriched gene sets. The majority of the top-25 could be split into three groups: electron transport chain (ETC, n=8), substrate metabolism (SM, n=5), and mitochondrial maintenance (MM, n=2). The NES at each day post-VML injury (dpi) was compared to its respective uninjured group using a two-tailed t-test. We found that all ETC-related pathways were significantly enriched and downregulated at 7-, 14-, and 28-dpi (p ≤ 0.039). For example, the percent change in NES of ‘complex 1’ was- 436%, -419%, and -816%, respectively (p≤0.002). SM-related pathways followed a similar downward trend (p≤0.044). For example, ‘TCA’ -149%, -303%, and -697%, respectively (p≤0.028). Interestingly, within the MM-related gene sets, mitochondrial ‘fusion’ was significant down at 7- and 28-dpi (-319%, -414%, p≤0.009) while ‘fission’ was significantly down at 3-, 7-, and 14-dpi (-157%, -319%, and -797%, p≤0.030). We next analyzed a publicly-available mouse species scRNAseq data set. To examine the muscle-specific transcriptional response we combined the counts for myonuclei and satellite cells. GSEA revealed six significantly enriched gene sets, notably ‘all metabolism genes’ (NES = 1.33, FDR q = 0.050), and the remaining four were related to the ETC (NES ≥ 1.81, FDR q ≤ 0.050). This retrospective, comprehensive analysis confirms dynamic changes in the expression of mitochondrial-related genes in response to VML injury in both rats and mice. The modulation of genes related to the electron transport chain, mitochondrial maintenance, and substrate metabolism agree with physiological outcomes of impaired mitochondrial carbohydrate metabolism, hyperpolarized mitochondria, and slowed electron conductance from previous mouse studies. R01AR078903 to SG and JC. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Regulation of the mitochondrial integrated stress response and ATF4 by acute contractile activity in mouse muscle

In the context of energetically demanding conditions, such as exercise, skeletal muscle relies on mitochondria to support its metabolic requirements. Maintenance of mitochondria and their bioenergetic availability is thus critical to sustain the metabolic flexibility of muscle. The quality of the organelle network is highly regulated by the coordination of mitochondrial quality control (MQC) processes. One MQC pathway that has garnered recent interest is the integrated stress response (ISR), which is activated in response to a variety of stimuli. The transcription factor ATF4, denoted as the main effector of this response pathway, serves to ameliorate cellular stress by upregulating a plethora of cytoprotective genes, such as CHOP and ATF5. Current literature has shown that the ISR is activated upon mitochondrial stress/perturbations to restore optimal organelle function and health. However, the precise mechanism that constitutes the activation of ISR and thus the response of ATF4 following acute exercise-induced stress is unknown. Therefore, our objective is to determine the extent of ISR/ATF4 induction in vivo and to test whether this pathway is required for the maintenance of muscle function. To investigate this, a mouse in situ hindlimb protocol was utilized to acutely stimulate muscles at 0.25-1 tetani/per second for 9 mins, followed by a 1-hour recovery period. The kinases, CAMKIIα and JNK2, were robustly phosphorylated/activated 6-fold immediately following the protocol. The initial stage of ISR activation, reflected in the ratio of phosphorylated to total-eIF2α protein levels, was also increased in response to acute contractile activity, evident in the recovery phase. Downstream of ISR activation, the total protein expression of ATF4 remained unchanged, however, contractile activity induced an increase in the localization of ATF4 to the nucleus. Robust 2-fold increases in the mRNA expression of ATF4 and CHOP were also observed and enhanced following the recovery period. Changes in ATF4 mRNA appeared to be independent of transcriptional activation, as assessed using an ATF4 promoter-reporter plasmid. An in vitro cell free mRNA decay assay revealed an increase in ATF4 mRNA stability post-stimulation, possibly as a result of cellular compartmental changes in the RNA binding proteins, HuR and CUGBP1. RNA sequencing analyses also confirmed the observed increase in related ISR genes following an exhaustive bout of exercise. These data suggest that acute contractile activity is indeed suffcient to induce mitochondrial stress and activate the ISR, corresponding to the induction of ATF4. Future work will reveal the underlying mitochondrial signal responsible for activating this pathway, as well as the downstream consequences for the regulation of MQC processes in maintaining mitochondrial homeostasis. This work was supported by funds from the Canadian Institutes for Health Research (CIHR). Victoria C. Sanfrancesco is the recipient of the CIHR Frederick Banting and Charles Best Canada Graduate Scholarship-Master's (CGS-M). David A. Hood is the holder of a Canadian Research Chair in Cell Physiology. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

SIRT6 in Regulation of Mitochondrial Damage and Associated Cardiac Dysfunctions: A Possible Therapeutic Target for CVDs.

Cardiovascular diseases (CVDs) can be described as a global health emergency imploring possible prevention strategies. Although the pathogenesis of CVDs has been extensively studied, the role of mitochondrial dysfunction in CVD development has yet to be investigated. Diabetic cardiomyopathy, ischemic-reperfusion injury, and heart failure are some of the CVDs resulting from mitochondrial dysfunction Recent evidence from the research states that any dysfunction of mitochondria has an impact on metabolic alteration, eventually causes the death of a healthy cell and therefore, progressively directing to the predisposition of disease. Cardiovascular research investigating the targets that both protect and treat mitochondrial damage will help reduce the risk and increase the quality of life of patients suffering from various CVDs. One such target, i.e., nuclear sirtuin SIRT6 is strongly associated with cardiac function. However, the link between mitochondrial dysfunction and SIRT6 concerning cardiovascular pathologies remains poorly understood. Although the Role of SIRT6 in skeletal muscles and cardiomyocytes through mitochondrial regulation has been well understood, its specific role in mitochondrial maintenance in cardiomyocytes is poorly determined. The review aims to explore the domain-specific function of SIRT6 in cardiomyocytes and is an effort to know how SIRT6, mitochondria, and CVDs are related.

Zebrafish polg2 knock-out recapitulates human POLG-disorders; implications for drug treatment.

The human mitochondrial DNA polymerase gamma is a holoenzyme, involved in mitochondrial DNA (mtDNA) replication and maintenance, composed of a catalytic subunit (POLG) and a dimeric accessory subunit (POLG2) conferring processivity. Mutations in POLG or POLG2 cause POLG-related diseases in humans, leading to a subset of Mendelian-inherited mitochondrial disorders characterized by mtDNA depletion (MDD) or accumulation of multiple deletions, presenting multi-organ defects and often leading to premature death at a young age. Considering the paucity of POLG2 models, we have generated a stable zebrafish polg2 mutant line (polg2ia304) by CRISPR/Cas9 technology, carrying a 10-nucleotide deletion with frameshift mutation and premature stop codon. Zebrafish polg2 homozygous mutants present slower development and decreased viability compared to wild type siblings, dying before the juvenile stage. Mutants display a set of POLG-related phenotypes comparable to the symptoms of human patients affected by POLG-related diseases, including remarkable MDD, altered mitochondrial network and dynamics, and reduced mitochondrial respiration. Histological analyses detected morphological alterations in high-energy demanding tissues, along with a significant disorganization of skeletal muscle fibres. Consistent with the last finding, locomotor assays highlighted a decreased larval motility. Of note, treatment with the Clofilium tosylate drug, previously shown to be effective in POLG models, could partially rescue MDD in Polg2 mutant animals. Altogether, our results point at zebrafish as an effective model to study the etiopathology of human POLG-related disorders linked to POLG2, and a suitable platform to screen the efficacy of POLG-directed drugs in POLG2-associated forms.

AAV-mediated upregulation of VDAC1 rescues the mitochondrial respiration and sirtuins expression in a SOD1 mouse model of inherited ALS.

Mitochondrial dysfunction represents one of the most common molecular hallmarks of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder caused by the selective degeneration and death of motor neurons. The accumulation of misfolded proteins on and within mitochondria, as observed for SOD1 G93A mutant, correlates with a drastic reduction of mitochondrial respiration and the inhibition of metabolites exchanges, including ADP/ATP and NAD+/NADH, across the Voltage-Dependent Anion-selective Channel 1 (VDAC1), the most abundant channel protein of the outer mitochondrial membrane. Here, we show that the AAV-mediated upregulation of VDAC1 in the spinal cord of transgenic mice expressing SOD1 G93A completely rescues the mitochondrial respiratory profile. This correlates with the increased activity and levels of key regulators of mitochondrial functions and maintenance, namely the respiratory chain Complex I and the sirtuins (Sirt), especially Sirt3. Furthermore, the selective increase of these mitochondrial proteins is associated with an increase in Tom20 levels, the receptor subunit of the TOM complex. Overall, our results indicate that the overexpression of VDAC1 has beneficial effects on ALS-affected tissue by stabilizing the Complex I-Sirt3 axis.

Clinical and Genetic Analysis of Patients With TK2 Deficiency

Clinical and Genetic Analysis of Patients With TK2 Deficiency

Abstract 4012: SOT302: Dual expression of exogenous glutamine oxaloacetate transaminase (GOT2) and TP53-induced glycolysis and apoptosis regulator (TIGAR) enhance CAR T cell activity in preclinical solid tumor models

Abstract Background: Despite success in hematological malignancies, CAR T therapy has had limited efficacy against solid tumors. The suppressive tumor microenvironment limits CAR T activity through various mechanisms including competition for available nutrients and chronic stimulation resulting in reduced effector functions or T cell exhaustion. CAR T cells with enhanced metabolic fitness or more durable memory phenotype could potentially improve the clinical outcome in solid tumors. GOT2 plays an important role in mitochondrial function and maintenance of redox homeostasis. We have previously demonstrated enhancement of CAR T cells overexpressing GOT2. TIGAR is an enzyme known to promote antioxidative activites and reduce reactive oxygen species and has a role in protecting against apoptosis. Here we tested SOT302 CAR T cells expressing both GOT2 and TIGAR in preclinical solid tumor models. Results: Expression of GOT2 and TIGAR transgenes were confirmed by qRT-PCR and western blot. Activity of GOT2 and TIGAR were confirmed by measuring aminotransferase activity (AST) and glutathione production, respectively. Compared to control CAR T cells, SOT302 is enriched for CD8+ Tscm cells and has a higher percentage functional, non-senescent (CD28+CD57-) cells. SOT302 has similar cytokine expression and cytotoxicity in standard co-culture assays compared to controls. SOT302 cells were chronically stimulated with plate-bound antigen every 3-4 days for 4 rounds. SOT302 had greater expansion of cells and were less exhausted and had better cytolytic capacity compared to controls. SOT302 cells were then evaluated in tumor xenograft mouse models. Consistent with our previous findings, CAR T cells expressing the single GOT2 transgene were more efficacious compared to CAR T cells alone. Expression of the single TIGAR transgene had no apparent benefit over CAR alone, however SOT302 cells expressing both GOT2 and TIGAR had superior anti-tumor activity compared to CAR alone and CAR+GOT2. No overt toxicity or significant body weight loss was observed. Ex vivo analyses to measure peripheral expansion, tumor infiltration and exhaustion were also performed. Preliminary findings indicate that SOT302 has better peripheral expansion compared to CAR alone and similar expansion compared to CAR+GOT2 controls. SOT302 cells had better tumor infiltration compared to both the CAR alone and CAR+GOT2 cells. Tumor infiltrating SOT302 cells also exhibited lower levels of exhaustion compared to CAR alone or CAR+GOT2 controls. Summary: SOT302 cells express exogenous GOT2 and TIGAR transgenes and have superior anti-tumor activity in preclinical solid tumor models. These data suggest that SOT302 may be a promising candidate for patients with solid tumor cancers. Citation Format: Emily Kuiper, Samyabrata Bhaduri, Daniel Garafola, Kshitij Sharma, Jennifer Coccia, Kathleen Whiteman, Amy Jensen-Smith. SOT302: Dual expression of exogenous glutamine oxaloacetate transaminase (GOT2) and TP53-induced glycolysis and apoptosis regulator (TIGAR) enhance CAR T cell activity in preclinical solid tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4012.

Abstract 7055: Elucidation of the interplay between phospholipid byosynthesis and oxidative stress in the pathogenesis of renal cell carcinoma

Abstract Introduction: Renal cell carcinoma (RCC) is a primary malignant kidney tumor. We reported on the critical role of Protein of Relevant Evolutionary and Lymphoid Interest Domain 2 (PRELID2) in cell proliferation, emphasizing its regulatory function on mitochondrial ROS and maintenance of mitochondrial spare respiratory capacity. Recent studies have begun to clarify the molecular mechanism of phospholipid biosynthesis by PRELID1 and PRELID3 under oxidative stress conditions. Inspired by this evidence, we analyzed the relationship between PRELID2 and phospholipid biosynthesis, aiming to elucidate the molecular mechanism of PRELID2 related to the control of mitochondrial ROS. Methods: To analyze the dynamics of phospholipids and related mitochondrial molecules induced by oxidative stress, we examined the expression of YME1L and its substrates (OPA1, PRELID1) using Western blotting, which has been shown to be related to the turnover of other PRELI family proteins. Lipidomic analysis was performed using LC-MS on samples from HEK293 cells with stable expression of PRELID2 and control cells, as well as renal carcinoma cell lines with suppressed PRELID2 expression using siRNA and control cells. Additionally, we analyzed the expression of mitochondrial respiratory chain complexes Cytochrome C and COX4 and their relationship with PRELID2 expression via Western blotting. Results: Oxidative stress led to a noticeable decline in YME1L expression, which was correlated with decreased OPA1 and PRELID1 levels in control cells. Conversely, PRELID2-overexpressing cells retained stable expression of OPA1 and PRELID1. Furthermore, these cells exhibited a significant reduction in phosphatidyl glycerol (PG) levels. Suppressing PRELID2 expression in 786-O cells using siRNA resulted in significantly higher PG levels. When analyzing the molecules of the mitochondrial respiratory chain during oxidative stress induction, we observed that although oxidative stress induced a decline in cytochrome C expression in control cells, it remained consistent in PRELID2-expressing cells. However, PRELID2 expression did not affect COX4 levels. Conclusions: Our findings underscore the pivotal role of PRELIDs in maintaining mitochondrial homeostasis, proving instrumental in the oxidative stress-driven progression of renal cancer. Citation Format: Renpei Kato, Daiki Ikarashi, Shigekatsu Maekawa, Mitsugu Kanehira, Ryo Takata, Yosuke Matsushita, Tetsuro Yoshimaru, Tomoya Fukawa, Toyomasa Katagiri, Wataru Obrara. Elucidation of the interplay between phospholipid byosynthesis and oxidative stress in the pathogenesis of renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7055.

Abstract 659: TR-107 and erastin produce synergistic inhibition of colorectal cancer cell viability in vitro

Abstract Introduction: Ferroptosis is an emerging potential target for the treatment of colorectal cancer (CRC) and has been shown to sensitize cancer cells to combinatory chemotherapy. Our studies show that the TR-107 compound, an agonist of ClpP - the proteolytic subunit of mitochondrial maintenance complex - can synergize with Erastin, an inducer of ferroptosis cell death. TR-107 potently disrupts mitochondrial proteostasis and attenuates oxidative phosphorylation, resulting in excessive oxidative stress. Here, we show that Erastin synergizes with TR-107 activity by downregulating the cofactor of GPX4, a major intracellular antioxidant defense resulting in CRC cell apoptosis. Methods: We first evaluated the efficacy of TR-107 against eight CRC cell lines belonging to four established consensus molecular subtypes. Cells were treated with control (DMSO) or TR-107 (10 nM, 50 nM, 1 µM) for 24, 48, and 72 hours. We determined IC50 values with Cell Titer-Glo, cell proliferation with the Beckman Coulter cell counter, cell cycle with flow cytometry, OXPHOS activity with Seahorse Real-Time ATP Rate assay, mitochondrial protein levels with western blot and proteomics, and differential gene expression using RNA sequencing and RT-PCR. Subsequently, we assessed the efficacy of TR-107 and Erastin co-treatment. Cells were treated with DMSO, TR-107 (10, 50 nM), Erastin (1, 10 µM), or combinations of the abovementioned concentrations. Cell viability was measured 72 hours post-treatment with Cell Titer-Glo. Synergy scores (HSA) were calculated with Synergyfinder on RStudio. Ferroptosis-related protein expression 24 hours after co-treatment was assessed with western blot and densitometry. Results: TR-107 IC50 values ranged from 2-70 nM, producing a dose- and time-dependent inhibitory effect in cell proliferation. Western blot showed that 50 nM TR-107 abolished the expression of critical mitochondrial proteins ClpX, TFAM, and TUFM. Seahorse data showed a significant reduction in OXPHOS activity. Multi-omics revealed downregulation of respiratory chain complex subunits, mtDNA transcription/translation factors, and upregulation of mitophagy and ferroptosis-related pathways in treated cells. Co-treatment with Erastin produced synergistic HSA scores in 63% (5/8) of assessed CRC cell lines. RKO and NCI-H508 were highly sensitive to Erastin treatment, suggesting that lower Erastin concentrations may synergize with TR-107 and thus reduce dose toxicity. Western blot analysis 24 hours post-treatment showed a loss of GPX4 protein levels in co-treated cells compared to 50 nM TR-107 treatment. This suggests a rapid downregulation of intracellular antioxidant defense that may induce ferroptosis sooner and more effectively than single-agent treatment. Conclusion: In vitro results suggest that co-treating with TR-107 and Erastin produces a significant, synergistic reduction in CRC cell viability. Citation Format: Michael Giarrizzo, Joseph F. LaComb, Hetvi R. Patel, Agnieszka B. Bialkowska, Rohan Reddy, Lee M. Graves, Edwin J. Iwanowicz. TR-107 and erastin produce synergistic inhibition of colorectal cancer cell viability in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 659.

A stagewise response to mitochondrial dysfunction in mitochondrial DNA maintenance disorders

Mitochondrial DNA (mtDNA) deletions which clonally expand in skeletal muscle of patients with mtDNA maintenance disorders, impair mitochondrial oxidative phosphorylation dysfunction. Previously we have shown that these mtDNA deletions arise and accumulate in perinuclear mitochondria causing localised mitochondrial dysfunction before spreading through the muscle fibre. We believe that mito-nuclear signalling is a key contributor in the accumulation and spread of mtDNA deletions, and that knowledge of how muscle fibres respond to mitochondrial dysfunction is key to our understanding of disease mechanisms.To understand the contribution of mito-nuclear signalling to the spread of mitochondrial dysfunction, we use imaging mass cytometry. We characterise the levels of mitochondrial Oxidative Phosphorylation proteins alongside a mitochondrial mass marker, in a cohort of patients with mtDNA maintenance disorders. Our expanded panel included protein markers of key signalling pathways, allowing us to investigate cellular responses to different combinations of oxidative phosphorylation dysfunction and ragged red fibres.We find combined Complex I and IV deficiency to be most common. Interestingly, in fibres deficient for one or more complexes, the remaining complexes are often upregulated beyond the increase of mitochondrial mass typically observed in ragged red fibres. We further find that oxidative phosphorylation deficient fibres exhibit an increase in the abundance of proteins involved in proteostasis, e.g. HSP60 and LONP1, and regulation of mitochondrial metabolism (including oxidative phosphorylation and proteolysis, e.g. PHB1). Our analysis suggests that the cellular response to mitochondrial dysfunction changes depending on the combination of deficient oxidative phosphorylation complexes in each fibre.

Luteolin rescues postmenopausal osteoporosis elicited by OVX through alleviating osteoblast pyroptosis via activating PI3K-AKT signaling

BackgroundRecently, osteoblast pyroptosis has been proposed as a potential pathogenic mechanism underlying osteoporosis, although this remains to be confirmed. Luteolin (Lut), a flavonoid phytochemical, plays a critical role in the anti-osteoporosis effects of many traditional Chinese medicine prescriptions. However, its protective impact on osteoblasts in postmenopausal osteoporosis (PMOP) has not been elucidated. PurposeThis research aimed to determine the effect of Lut in ameliorating PMOP by alleviating osteoblast pyroptosis and sustaining osteogenesis. Study designThis research was designed to investigate the novel mechanism of Lut in alleviating PMOP both in cell and animal models. MethodsOvariectomy-induced PMOP models were established in mice with/without daily gavaged of 10 or 20 mg/kg body weight Lut. The impact of Lut on bone microstructure, metabolism and oxidative stress was evaluated with 0.104 mg/kg body weight Estradiol Valerate Tablets daily gavaged as positive control. Network pharmacological analysis and molecular docking were employed to investigate the mechanisms of Lut in PMOP treatment. Subsequently, the impacts of Lut on the PI3K/AKT axis, oxidative stress, mitochondria, and osteoblast pyroptosis were assessed. In vitro, cultured MC3T3-E1(14) cells were exposed to H2O2 with/without Lut to examine its effects on the PI3K/AKT signaling pathway, osteogenic differentiation, mitochondrial function, and osteoblast pyroptosis. ResultsOur findings demonstrated that 20 mg/kg Lut, similar to the positive control drug, effectively reduced systemic bone loss and oxidative stress, and enhanced bone metabolism induced by ovariectomy. Network pharmacological analysis and molecular docking indicated that the PI3K/AKT axis was a potential target, with oxidative stress response and nuclear membrane function being key mechanisms. Consequently, the effects of Lut on the PI3K/AKT axis and pyroptosis were investigated. In vivo data revealed that the PI3K/AKT axis was deactivated following ovariectomy, and Lut restored the phosphorylation of key proteins, thereby reactivating the axis. Additionally, Lut alleviated osteoblast pyroptosis and mitochondrial abnormalities induced by ovariectomy. In vitro, Lut intervention mitigated the inhibition of the PI3K/AKT axis and osteogenesis, as well as H2O2-induced pyroptosis. Furthermore, Lut attenuated ROS accumulation and mitochondrial dysfunction. The effects of Lut, including osteogenesis restoration, anti-pyroptosis, and mitochondrial maintenance, were all reversed with LY294002 (a PI3K/AKT pathway inhibitor). ConclusionIn summary, Lut could improve mitochondrial dysfunction, alleviate GSDME-mediated pyroptosis and maintain osteogenesis via activating the PI3K/AKT axis, offering a new therapeutic strategy for PMOP.

Structural basis of how MGME1 processes DNA 5' ends to maintain mitochondrial genome integrity.

Mitochondrial genome maintenance exonuclease 1 (MGME1) helps to ensure mitochondrial DNA (mtDNA) integrity by serving as an ancillary 5'-exonuclease for DNA polymerase γ. Curiously, MGME1 exhibits unique bidirectionality in vitro, being capable of degrading DNA from either the 5' or 3' end. The structural basis of this bidirectionally and, particularly, how it processes DNA from the 5' end to assist in mtDNA maintenance remain unclear. Here, we present a crystal structure of human MGME1 in complex with a 5'-overhang DNA, revealing that MGME1 functions as a rigid DNA clamp equipped with a single-strand (ss)-selective arch, allowing it to slide on single-stranded DNA in either the 5'-to-3' or 3'-to-5' direction. Using a nuclease activity assay, we have dissected the structural basis of MGME1-derived DNA cleavage patterns in which the arch serves as a ruler to determine the cleavage site. We also reveal that MGME1 displays partial DNA-unwinding ability that helps it to better resolve 5'-DNA flaps, providing insights into MGME1-mediated 5'-end processing of nascent mtDNA. Our study builds on previously solved MGME1-DNA complex structures, finally providing the comprehensive functional mechanism of this bidirectional, ss-specific exonuclease.

Shared and more specific genetic determinants and pathways underlying yeast tolerance to acetic, butyric, and octanoic acids

BackgroundThe improvement of yeast tolerance to acetic, butyric, and octanoic acids is an important step for the implementation of economically and technologically sustainable bioprocesses for the bioconversion of renewable biomass resources and wastes. To guide genome engineering of promising yeast cell factories toward highly robust superior strains, it is instrumental to identify molecular targets and understand the mechanisms underlying tolerance to those monocarboxylic fatty acids. A chemogenomic analysis was performed, complemented with physiological studies, to unveil genetic tolerance determinants in the model yeast and cell factory Saccharomyces cerevisiae exposed to equivalent moderate inhibitory concentrations of acetic, butyric, or octanoic acids.ResultsResults indicate the existence of multiple shared genetic determinants and pathways underlying tolerance to these short- and medium-chain fatty acids, such as vacuolar acidification, intracellular trafficking, autophagy, and protein synthesis. The number of tolerance genes identified increased with the linear chain length and the datasets for butyric and octanoic acids include the highest number of genes in common suggesting the existence of more similar toxicity and tolerance mechanisms. Results of this analysis, at the systems level, point to a more marked deleterious effect of an equivalent inhibitory concentration of the more lipophilic octanoic acid, followed by butyric acid, on the cell envelope and on cellular membranes function and lipid remodeling. The importance of mitochondrial genome maintenance and functional mitochondria to obtain ATP for energy-dependent detoxification processes also emerged from this chemogenomic analysis, especially for octanoic acid.ConclusionsThis study provides new biological knowledge of interest to gain further mechanistic insights into toxicity and tolerance to linear-chain monocarboxylic acids of increasing liposolubility and reports the first lists of tolerance genes, at the genome scale, for butyric and octanoic acids. These genes and biological functions are potential targets for synthetic biology approaches applied to promising yeast cell factories, toward more robust superior strains, a highly desirable phenotype to increase the economic viability of bioprocesses based on mixtures of volatiles/medium-chain fatty acids derived from low-cost biodegradable substrates or lignocellulose hydrolysates.

Analysis of the Mouse Hepatic Peroxisome Proteome-Identification of Novel Protein Constituents Using a Semi-Quantitative SWATH-MS Approach.

Ongoing technical and bioinformatics improvements in mass spectrometry (MS) allow for the identifying and quantifying of the enrichment of increasingly less-abundant proteins in individual fractions. Accordingly, this study reassessed the proteome of mouse liver peroxisomes by the parallel isolation of peroxisomes from a mitochondria- and a microsome-enriched prefraction, combining density-gradient centrifugation with a semi-quantitative SWATH-MS proteomics approach to unveil novel peroxisomal or peroxisome-associated proteins. In total, 1071 proteins were identified using MS and assessed in terms of their distribution in either high-density peroxisomal or low-density gradient fractions, containing the bulk of organelle material. Combining the data from both fractionation approaches allowed for the identification of specific protein profiles characteristic of mitochondria, the ER and peroxisomes. Among the proteins significantly enriched in the peroxisomal cluster were several novel peroxisomal candidates. Five of those were validated by colocalization in peroxisomes, using confocal microscopy. The peroxisomal import of HTATIP2 and PAFAH2, which contain a peroxisome-targeting sequence 1 (PTS1), could be confirmed by overexpression in HepG2 cells. The candidates SAR1B and PDCD6, which are known ER-exit-site proteins, did not directly colocalize with peroxisomes, but resided at ER sites, which frequently surrounded peroxisomes. Hence, both proteins might concentrate at presumably co-purified peroxisome-ER membrane contacts. Intriguingly, the fifth candidate, OCIA domain-containing protein 1, was previously described as decreasing mitochondrial network formation. In this work, we confirmed its peroxisomal localization and further observed a reduction in peroxisome numbers in response to OCIAD1 overexpression. Hence, OCIAD1 appears to be a novel protein, which has an impact on both mitochondrial and peroxisomal maintenance.

Mitochondrial Outer Membrane Translocase MoTom20 Modulates Mitochondrial Morphology and Is Important for Infectious Growth of the Rice Blast Fungus Magnaporthe oryzae.

Mitochondria are highly dynamic organelles that constantly change their morphology to adapt to the cellular environment through fission and fusion, which is critical for a cell to maintain normal cellular functions. Despite the significance of this process in the development and pathogenicity of the rice blast fungus Magnaporthe oryzae, the underlying mechanism remains largely elusive. Here, we identified and characterized a mitochondrial outer membrane translocase, MoTom20, in M. oryzae. Targeted gene deletion revealed that MoTom20 plays an important role in vegetative growth, conidiogenesis, penetration, and infectious growth of M. oryzae. The growth rate, conidial production, appressorium turgor, and pathogenicity are decreased in the ΔMotom20 mutant compared with the wild-type and complemented strains. Further analysis revealed that MoTom20 localizes in mitochondrion and plays a key role in regulating mitochondrial fission and fusion balance, which is critical for infectious growth. Finally, we found that MoTom20 is involved in fatty-acid utilization, and its yeast homolog ScTom20 is able to rescue the defects of ΔMotom20 in mitochondrial morphology and pathogenicity. Overall, our data demonstrate that MoTom20 is a key regulator for mitochondrial morphology maintenance, which is important for infectious growth of the rice blast fungus M. oryzae. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The role of TFE3 in mediating skeletal muscle mitochondrial adaptations to exercise training.

Transcription factor E3 (TFE3) is a transcription factor that activates the expression of lysosomal genes involved in the clearance of dysfunctional mitochondria, termed mitophagy. With exercise, TFE3 is presumed to optimize the mitochondrial pool through the removal of organelles via lysosomes. However, the molecular mechanisms of the involved pathways remain unknown. Wild-type (WT) and TFE3 knockout (KO) mice were subjected to 6 wk of voluntary wheel running as an endurance training regimen. This was followed by a 45-min bout of in situ stimulation of the sciatic nerve innervating hindlimb muscles to evaluate muscle fatigue and contractile properties. A subset of animals was treated with colchicine to measure autophagy and mitophagy flux. Fatigability during stimulation was reduced with training in WT animals, as seen by a 13% increase in the percentage of maximum force at 5 min of stimulation, and a 30% increase at 30 minutes. Permeabilized fiber oxygen consumption was also improved with training. Concurrent with improved muscle and mitochondrial function, cytochrome c oxidase (COX) activity and COX I protein expression were increased in trained WT animals compared to untrained animals, signifying an increase in mitochondrial content. These training adaptations were abolished with the loss of TFE3. Surprisingly, the absence of TFE3 did not affect lysosomal content nor did it blunt the induction of mitophagy flux with contractile activity compared to WT mice. Our results suggest that the loss of TFE3 compromises beneficial training adaptations that lead to improved muscle endurance and mitochondrial function.NEW & NOTEWORTHY Our understanding of the role of transcription factor E3 (TFE3) in skeletal muscle is very limited. This research shows that TFE3 plays a direct role in skeletal muscle mitochondrial enhancement with exercise training, thereby introducing a paradigm shift in our perception of the function of TFE3 in mitochondrial maintenance, beyond mitophagy. This research serves to introduce TFE3 as a protein that holds promise as a future therapeutic target for metabolic diseases and skeletal muscle dysfunction.

4-amino-2-trifluoromethyl-phenyl retinate alleviates lipopolysaccharide-induced acute myocardial injury through activation of the KLF4/p62 axis

Ferroptosis plays a pivotal role in the pathological process of sepsis-induced cardiomyopathy (SIC). All-trans retinoic acid (ATRA) enhances the host immune response to lipopolysaccharides (LPS). This study investigated the role of 4-amino-2-trifluoromethyl-phenyl retinate (ATPR), a derivative of ATRA, in myocardial injury caused by sepsis. Male C57BL/6 mice were intraperitoneally injected with LPS to establish a sepsis model. H9c2 cells were stimulated by LPS to establish an injury model. We observed that ATPR improved myocardial injury in mice, which was presented in terms of an increased glutathione (GSH) level and reduced production of malondialdehyde (MDA), as well as an increased number of mitochondrial cristae and maintenance of the mitochondrial membrane integrity. ATPR improved cardiac function in the LPS-injured mice. It inhibited the inflammatory response as evidenced by the decreasing mRNA levels of TNF-α and IL-6. The elevated protein expression levels of Nrf2, SLC7A11, GPX4, and FTH1 in mice and H9c2 cells showed that ATPR inhibited ferroptosis. Immunoprecipitation of LPS-stimulated H9c2 cells demonstrated that ATPR increased the interaction between p62 and Keap1. ATPR upregulated the KLF4 and p62 protein expression. However, the inhibition of Nrf2 by ML385 reduced the protective effect of ATPR in LPS-treated H9c2 cells. Furthermore, we used siRNA to knock down KLF4 in H9c2 cells and found that the KLF4 knockdown eliminated the inhibition of ferroptosis by ATPR in H9c2 cells. Therefore, ATPR alleviates LPS-induced myocardial injury by inhibiting ferroptosis via the KLF4/p62 axis.

Abstract 14975: SIRT1 Ameliorates Cardiac Dysfunction Caused by Lamin A/C Deficiency via Mitochondrial Bioenergetics Improvement

Background: The LMNA gene encodes lamin A/C and is the second most frequently mutated gene associated with dilated cardiomyopathy (DCM) but lacks effective therapeutic options. Recent transcriptomic studies have shown that mutation of LMNA leads to abnormal expression of genes related to mitochondrial function, however, the mechanisms have not been investigated further. Hypothesis: LMNA protects against cardiac dysfunction via mitochondrial bioenergetics maintenance. Aims To decipher the mechanism by which LMNA mediates mitochondrial bioenergetics and DCM phenotype. Methods: Proteomics was performed to decipher the pathogenesis of DCM in Lmna -/- mice. Neonatal rat ventricular myocytes (NRVMs) were used to dissect molecular mechanisms. Adenovirus and adeno-associated virus (AAV) were constructed to overexpress SIRT1 in vitro and in vivo , respectively. Results: Lmna -/- mice at 1 month of age showed obvious cardiac dysfunction, while 2-week-old Lmna -/- mice showed no obvious cardiac phenotype. Proteomics revealed downregulated mitochondrial function-related pathways in Lmna -/- hearts. Early injured mitochondria with decreased cristae density were detected and the only reduced mitochondrial biogenesis regulator SIRT1 was found in 2 week-old Lmna -/- hearts. Overexpression of SIRT1 in lamin A/C knockdown NRVMs effectively improved mitochondrial oxidative respiration capacity. AAV-SIRT1 injection significantly alleviated mitochondrial injury, DCM phenotype of Lmna -/- mice, and prolonged lifespan (Figure 1). Mechanistically, LMNA maintains mitochondrial bioenergetics through SIRT1-PARKIN axis. Conclusions: Lamin A/C deficiency leads to mitochondrial damage in cardiomyocytes and promotes the development of DCM through SIRT1 downregulation. Targeting SIRT1 ameliorates mitochondrial injury and DCM phenotype in Lmna -/- mice, which may provide a novel therapeutic strategy for LMNA mutation-associated DCM.