p107 mediated mitochondrial function controls muscle stem cell proliferative fates

Mitochondrial-cytochrome c oxidase II promotes glutaminolysis to sustain tumor cell survival upon glucose deprivation

Glucose deprivation, a hallmark of the tumor microenvironment, compels tumor cells to seek alternative energy sources for survival and growth. Here, we show that glucose deprivation upregulates the expression of mitochondrial-cytochrome c oxidase II (MT-CO2), a subunit essential for the respiratory chain complex IV, in facilitating glutaminolysis and sustaining tumor cell survival. Mechanistically, glucose deprivation activates Ras signaling to enhance MT-CO2 transcription and inhibits IGF2BP3, an RNA-binding protein, to stabilize MT-CO2 mRNA. Elevated MT-CO2 increases flavin adenosine dinucleotide (FAD) levels in activating lysine-specific demethylase 1 (LSD1) to epigenetically upregulate JUN transcription, consequently promoting glutaminase-1 (GLS1) and glutaminolysis for tumor cell survival. Furthermore, MT-CO2 is indispensable for oncogenic Ras-induced glutaminolysis and tumor growth, and elevated expression of MT-CO2 is associated with poor prognosis in lung cancer patients. Together, these findings reveal a role for MT-CO2 in adapting to metabolic stress and highlight MT-CO2 as a putative therapeutic target for Ras-driven cancers.

Sulforaphane, Urolithin A, and ZLN005 induce time-dependent alterations in antioxidant capacity, mitophagy, and mitochondrial biogenesis in muscle cells

Efficient signal transduction that mediates mitochondrial turnover is a strong determinant of metabolic health in skeletal muscle. Of these pathways, our focus was aimed towards the enhancement of antioxidant capacity, mitophagy, and mitochondrial biogenesis. While physical activity is an excellent inducer of mitochondrial turnover, its ability to ubiquitously activate and enhance mitochondrial turnover prevents definitive differentiation of the contribution made by each pathway. Therefore, we employed three agents, Sulforaphane (SFN), Urolithin A (UroA), and ZLN005 (ZLN), which are activators of important biological markers involved in antioxidant signaling, mitophagy, and biogenesis, respectively. We investigated the time-dependent changes in proteins related to each mechanism in C2C12 myotubes. SFN treatment resulted in increased nuclear localization of the transcription factor Nuclear factor (erythroid-derived 2)-like 2 (Nrf-2) after 4 ​hour (h), with subsequent 2-fold increases in the antioxidant enzymes Nicotinamide Quinone Oxidoreductase 1 (NQO1) and Heme-Oxygenase-1 (HO-1) by 24 ​h and 48 ​h. Mitochondrial respiration and ATP production were significantly increased by both 24 h and 48 ​h. UroA showed a 2-fold increase in AMP-activated Protein Kinase (AMPK) after 4 ​h, which led to a modest 30% increase in whole cell mitophagy markers p62 and LC3, after 48 ​h. This was accompanied by a reduction in cellular Reactive Oxygen Species (ROS), detected with the CellROX Green reagent. Mitophagy flux measurements showed mitophagy activation as both LC3-II and p62 flux increased with UroA at 24-h and 48-h time points, respectively. Finally, AMPK activation was observed by 4 ​h, in addition to a 2-fold increase in Mitochondrial Transcription Factor A (TFAM) promoter activity by 24 ​h of ZLN treatment following transient transfection of a TFAM promoter-luciferase construct. Mitochondrial respiration and ATP production were enhanced by 24 ​h. Our results suggest that early time points of treatment increase upstream pathway activity, whereas later time points represent the increased phenotypic expression of related downstream markers. Our findings suggest that the spatiotemporal progression of these mechanisms following drug treatment is another important factor to consider when examining subcellular changes towards mitochondrial turnover in muscle.

Inhibition of SIRT1 relieves hepatocarcinogenesis via alleviating autophagy and inflammation

Imbalanced Sirtuin 1 (SIRT1) levels may lead to liver diseases through abnormal regulation of autophagy, but the roles of SIRT1-regulated autophagy in hepatocellular carcinoma are still controversial. In this study, we found that SIRT1 mRNA and protein levels were upregulated in hepatocellular carcinoma, and high SIRT1 expression hinted an advanced stage and a poor prognosis. The differentially expressed proteins were significantly elevated in autophagy, cellular response to stress, and immune signaling pathways. In a thioacetamide-induced hepatocellular carcinoma mouse model, we found that SIRT1 expression was highly increased with increased autophagy and excessive macrophage inflammatory response. Next, we established a Hepa 1-6 cells and macrophage co-culture system in vitro to model the alteration of tumor microenvironment, and found that the medium from CCl4-treated or SIRT1-overexpressing Hepa 1-6 cells triggered the polarization of macrophage M1, and the culture medium derived from M1 macrophage promoted Hepa 1-6 cells growth and intracellular oxidative stress. The progression of liver fibrosis in the CCl4-induced liver fibrosis mouse model showed that inhibition of SIRT1 alleviated inflammatory response and ameliorated liver fibrosis. These findings suggest that SIRT1-regulated autophagy and inflammation are oncogenic in hepatocarcinogenesis.

Low-Se Diet Increased Mitochondrial ROS to Suppress Myoblasts Proliferation and Promote Apoptosis in Broilers via miR-365-3p/SelT Signaling Axis

microRNA (miRNA) controls the post-transcriptional translation of mRNA to affect the expression of many genes participating in functional interaction pathways. Selenoproteins are characterized by their antioxidant activity, wherein selenoprotein T (SelT) is an essential membrane-bound selenoprotein serving as a guardian of intracellular homeostasis. During muscle development and regeneration, myoblasts enter the cell cycle and rapidly proliferate. However, the role of SelT in muscle development and selenium (Se) deficiency-induced muscle damage remains poorly investigated. This study established Se deficient broiler models, chicken embryos models, and cultured chicken primary myoblasts in vitro. We showed that Se deficiency induced skeletal muscle damage in broilers, promoted miR-365-3p expression, and downregulated the level of SelT, significantly. The absence of SelT led to the accumulation of mitochondrial superoxide and downregulated mitochondrial dynamics gene expression, which, in turn, induced the disruption of mitochondria potential and blocked the oxidative phosphorylation (OXPHOS) process. Limited ATP production rate caused by mitochondrial ROS overproduction went along with cell cycle arrest, cell proliferation slowness, and myocyte apoptosis increase. Using Mito-TEMPO for mitochondrial ROS elimination could effectively mitigate the above adverse reactions and significantly restore the proliferation potential of myoblasts. Moreover, we identified miR-365-3p, a miRNA that targeted SelT mRNA to inhibit myoblast proliferation by disrupting intracellular redox balance. The omics analysis results showed that Se deficiency led to the significant enrichment of "cell cycle", "oxidative stress response", and "oxidative phosphorylation" pathway genes. Finally, we proved that the effect of the miR-365-3p/SelT signaling axis on muscle development did exist in the chicken embryo stage. In summary, our findings revealed that miR-365-3p was involved in broiler skeletal muscle damage in Se deficiency by targeting SelT, and SelT, serving as an intracellular homeostasis guardian, resisted mitochondrial oxidative stress, and protected ATP generation, promoting myoblast proliferation and inhibiting apoptosis. This study provides an attractive target for the cultivated meat industry and regenerative medicine.

NAD+: An Old but Promising Therapeutic Agent for Skeletal Muscle Ageing

More than a century after the discovery of nicotinamide adenine dinucleotide (NAD+), our understanding of the molecule's role in the biology of ageing continues to evolve. As a coenzyme or substrate for many enzymes, NAD+ governs a wide range of biological processes, including energy metabolism, genomic stability, signal transduction, and cell fate. NAD+ deficiency has been recognised as a bona fide hallmark of tissue degeneration, and restoring NAD+ homeostasis helps to rejuvenate multiple mechanisms associated with tissue ageing. The progressive loss of skeletal muscle homeostasis with age is directly associated with high morbidity, disability and mortality. The aetiology of skeletal muscle ageing is complex, involving mitochondrial dysfunction, senescence and stem cell depletion, autophagy defects, chronic cellular stress, intracellular ion overload, immune cell dysfunction, circadian clock disruption, microcirculation disorders, persistent denervation, and gut microbiota dysbiosis. This review focuses on the therapeutic potential of NAD+ restoration to alleviate the above pathological factors and discusses the effects of in vivo administration of different NAD+ boosting strategies on skeletal muscle homeostasis, aiming to provide a reference for combating skeletal muscle ageing.

The role of metabolism in cellular quiescence

Cellular quiescence is a dormant, non-dividing cell state characterized by significant shifts in physiology and metabolism. Quiescence plays essential roles in a wide variety of biological processes, ranging from microbial sporulation to human reproduction and wound repair. Moreover, when the regulation of quiescence is disrupted, it can drive cancer growth and compromise tissue regeneration after injury. In this Review, we examine the dynamic changes in metabolism that drive and support dormant and transiently quiescent cells, including spores, oocytes and adult stem cells. We begin by defining quiescent cells and discussing their roles in key biological processes. We then examine metabolic factors that influence cellular quiescence in both healthy and disease contexts, and how these could be leveraged in the treatment of cancer.

Restoration of CPEB4 prevents muscle stem cell senescence during aging

Age-associated impairments in adult stem cell functions correlate with a decline in somatic tissue regeneration capacity. However, the mechanisms underlying the molecular regulation of adult stem cell aging remain elusive. Here, we provide a proteomic analysis of physiologically aged murine muscle stem cells (MuSCs), illustrating a pre-senescent proteomic signature. During aging, the mitochondrial proteome and activity are impaired in MuSCs. In addition, the inhibition of mitochondrial function results in cellular senescence. We identified an RNA-binding protein, CPEB4, downregulated in various aged tissues, which is required for MuSC functions. CPEB4 regulates the mitochondrial proteome and activity through mitochondrial translational control. MuSCs devoid of CPEB4 induced cellular senescence. Importantly, restoring CPEB4 expression rescued impaired mitochondrial metabolism, improved geriatric MuSC functions, and prevented cellular senescence in various human cell lines. Our findings provide the basis for the possibility that CPEB4 regulates mitochondrial metabolism to govern cellular senescence, with an implication of therapeutic intervention for age-related senescence.

Mitochondrial remodelling is essential for female germ cell differentiation and survival

Stem cells often possess immature mitochondria with few inner membrane invaginations, which increase as stem cells differentiate. Despite this being a conserved feature across many stem cell types in numerous organisms, how and why mitochondria undergo such remodelling during stem cell differentiation has remained unclear. Here, using Drosophila germline stem cells (GSCs), we show that Complex V drives mitochondrial remodelling during the early stages of GSC differentiation, prior to terminal differentiation. This endows germline mitochondria with the capacity to generate large amounts of ATP required for later egg growth and development. Interestingly, impairing mitochondrial remodelling prior to terminal differentiation results in endoplasmic reticulum (ER) lipid bilayer stress, Protein kinase R-like ER kinase (PERK)-mediated activation of the Integrated Stress Response (ISR) and germ cell death. Taken together, our data suggest that mitochondrial remodelling is an essential and tightly integrated aspect of stem cell differentiation. This work sheds light on the potential impact of mitochondrial dysfunction on stem and germ cell function, highlighting ER lipid bilayer stress as a potential major driver of phenotypes caused by mitochondrial dysfunction.