Heart failure is characterized by metabolic derangements such as altered substrate metabolism and mitochondrial dysfunction. Mitochondrial supercomplexes, which are higher-order molecular structures comprised of multisubunit complexes of the electron transport chain, are decreased in heart failure. To investigate the supercomplex proteome composition in heart failure, we used an in vivo myocardial infarction (MI) model in which mice exhibited reduced cardiac function, confirmed by two-dimensional echocardiography at 4 wk postinfarction. To assess proteins within supercomplexes, we used an emerging technique known as complexome profiling. This technique involved separating out mitochondrial protein complexes using Blue-Native PAGE combined with mass spectrometry to identify proteins within supercomplex gel bands. We identified band-dependent decreases or increases in the relative abundance of subunits of the electron transport chain between MI and sham mice. Decreased abundance of proteins involved in α-ketoglutarate dehydrogenase metabolism, including dihydrolipoamide S-succinyltransferase (DLST), was also identified in the supercomplex bands of MI mice compared with sham mice. In addition, decreased abundance of redox-related proteins such as superoxide dismutase 2 (SOD2) and changes in ribosome protein subunits were identified in the MI mitochondria. In conclusion, we identified changes in the mitochondrial supercomplex proteome in a murine model of heart failure, providing insight and novel mechanisms that may be contributing to the metabolic dysfunction in heart failure.NEW & NOTEWORTHY This study identified novel changes in the proteome of mitochondrial supercomplexes in a murine model of heart failure, including alterations in the relative abundance of metabolic protein complexes, redox proteins, and ribosomal proteins. These findings provide new insights into potential mechanisms that may contribute to metabolic dysfunction in heart failure.

Treatment responses to behavioral, surgical, and pharmacological approaches in obesity are highly variable in quantity and quality. Here we refer to high-quality weight loss as a high proportion of fat to skeletal muscle mass lost. Given the role of skeletal muscle in energy expenditure, glucose homeostasis, metabolic flexibility, mobility, and strength, excessive loss of skeletal muscle during weight loss is a concern for overall health. Challenges in accurately measuring body composition, especially skeletal muscle, limit our understanding of muscle loss during obesity treatment. Recent incretin-related pharmacotherapies improve muscle metabolic health by enhancing glucose uptake and reducing muscle lipids but, like other weight loss interventions, are associated with muscle loss. Newer pharmacological interventions are being developed to minimize muscle loss, but many questions remain. This article examines the metabolic importance of skeletal muscle and its measurement clinically, as well as key genetic and metabolic factors influencing skeletal muscle and the quality of weight loss. Genetics can affect muscle composition (e.g., fiber types) and function. Together with metabolic factors, including neurohormonal responses and skeletal muscle metabolic efficiency and adaptation, there is variability in weight loss outcomes. In future research investigators should continue to focus on factors affecting skeletal muscle and on personalized strategies to optimize weight loss quality preserving the physical and metabolic functions of skeletal muscle. ARTICLE HIGHLIGHTS:High-quality weight loss, i.e., a high proportion of fat to skeletal muscle lost during the treatment of obesity, is advantageous for metabolic and physical health. Precise and accurate determinations of skeletal muscle mass in clinical settings are often challenging. In prevention of excessive loss of skeletal muscle during weight loss, advantages include minimization of metabolic adaptation that makes it difficult to sustain weight loss, improved glucose homeostasis and metabolic flexibility, and better mobility and strength. Effective approaches to preserving skeletal muscle include sufficient dietary protein and inclusion of exercise (especially resistance exercise) during weight loss; new pharmacological approaches are under development.

Muscle satellite cell (MuSC) proliferation is tightly regulated by redox homeostasis and nutrient availability, which are often disrupted in muscular pathologies. Beyond its role in maintaining cellular redox homeostasis, this study identified a key metabolic role for cystine/glutamate antiporter xCT in proliferating MuSCs. We investigated the impact of impaired xCT-mediated cystine import in Slc7a11sut/sut MuSCs isolated from mice that harbor a mutation in the SLC7A11 gene, which encodes xCT. We used complementary approaches to study how disrupted cystine import affects glutathione (GSH) redox, cellular bioenergetics, mitochondrial dynamics, and metabolism. Oxygen consumption rates of Slc7a11sut/sut MuSCs were lower, indicative of compromised mitochondrial oxidative capacity. This was accompanied by a fragmented mitochondrial network associated with OPA1 cleavage and redox-sensitive DRP1 oligomerization. Metabolomic profiling revealed a distinct metabolic signature in Slc7a11sut/sut MuSCs, manifested by major differences in BCAAs, pyrimidines, cysteine, methionine, and GSH. Despite lower overall bioenergetic flux, stable-isotope tracing analyses (SITA) showed that xCT deficiency increased glucose uptake, channeling glucose-derived carbons into de novo serine biosynthesis to fuel cysteine production via the transsulfuration pathway, partially compensating for disrupted GSH redox. Furthermore, xCT deficiency triggered upregulated pyrroline-5-carboxylate synthase (P5CS)-mediated proline reductive biosynthesis. By directing glutamate into proline synthesis, MuSCs apparently downregulate oxidative phosphorylation (OXPHOS) and regulate intracellular glutamate levels in response to impaired cystine/glutamate antiporter function. Our findings highlight the roles of xCT in regulating redox balance and metabolic reprogramming in proliferating MuSCs, providing insights that may inform therapeutic strategies for muscular and redox-related pathologies.

BACKGROUND:Alterations of metabolism, including changes in mitochondrial metabolism as well as glutathione (GSH) metabolism are a well appreciated hallmark of many cancers. Mitochondrial GSH (mGSH) transport is a poorly characterized aspect of GSH metabolism, which we investigate in the context of cancer. Existing functional annotation approaches from machine (ML) or deep learning (DL) models based only on protein sequences, were unable to annotate functions in biological contexts. RESULTS:We develop a flexible ML framework for functional annotation from diverse feature data. This hybrid ML framework leverages cancer cell line multi-omics data and other biological knowledge data as features, to uncover potential genes involved in mGSH metabolism and membrane transport in cancers. This framework achieves strong performance across functional annotation tasks and several cell line and primary tumor cancer samples. For our application, classification models predict the known mGSH transporter SLC25A39 but not SLC25A40 as being highly probably related to mGSH metabolism in cancers. SLC25A10, SLC25A50, and orphan SLC25A24, SLC25A43 are predicted to be associated with mGSH metabolism in multiple biological contexts and structural analysis of these proteins reveal similarities in potential substrate binding regions to the binding residues of SLC25A39. CONCLUSION:These findings have implications for a better understanding of cancer cell metabolism and novel therapeutic targets with respect to GSH metabolism through potential novel functional annotations of genes. The hybrid ML framework proposed here can be applied to other biological function classifications or multi-omics datasets to generate hypotheses in various biological contexts. Code and a tutorial for generating models and predictions in this framework are available at: https://github.com/lkenn012/mGSH_cancerClassifiers .

Early cerebrovascular alterations affect brain maturation by impacting trophic support and energy supply. Recent evidence in a 16p11.2 deletion mouse model of autism spectrum disorder (ASD) revealed brain endothelial abnormalities postnatally. Yet, the endothelial alterations eliciting these changes remain unknown. Isolation of brain endothelial cells (ECs) from 14-day old male 16p11.2-deficient and wild-type mice revealed that 16p11.2 deletion-induced endothelial dysfunction is linked to a bioenergetic failure, with reduced intracellular ATP. Intra- or extra-cellular ATP supplementation rescued the function of 16p11.2-deficient ECs in vitro via P2 purinergic receptor activation, specifically P2Y2 receptors. Activating P2Y2 receptors restored cerebrovascular reactivity in 16p11.2-deficient parenchymal arterioles ex vivo and rescued 16p11.2 deletion-associated mouse behaviors. Taken together, this study demonstrates that metabolic reprogramming of brain ECs via purinergic receptor engagement represents a possible therapeutic avenue for ASD. ### Competing Interest Statement The authors have declared no competing interest. Canadian Institutes of Health Research, 388805, 506513

Background and aimsDysregulated cholesterol metabolism is a hallmark of atherosclerotic cardiovascular diseases, yet our understanding of how endogenous cholesterol synthesis affects atherosclerosis is not clear. The energy sensor AMP-activated protein kinase (AMPK) phosphorylates and inhibits the rate-limiting enzyme in the mevalonate pathway HMG-CoA reductase (HMGCR). Recent work demonstrated that when AMPK-HMGCR signaling was compromised in an Apoe-/- model of hypercholesterolemia, atherosclerosis was exacerbated due to elevated hematopoietic stem and progenitor cell mobilization and myelopoiesis. We sought to validate the significance of the AMPK-HMGCR signaling axis in atherosclerosis using a non-germline hypercholesterolemia model with functional ApoE.MethodsMale and female HMGCR S871A knock-in (KI) mice and wild-type (WT) littermate controls were made atherosclerotic by intravenous injection of a gain-of-function Pcsk9D374Y-adeno-associated virus followed by high-fat and high-cholesterol atherogenic western diet feeding for 16 weeks.ResultsAMPK activation suppressed endogenous cholesterol synthesis in primary bone marrow-derived macrophages from WT but not HMGCR KI mice, without changing other parameters of cholesterol regulation. Atherosclerotic plaque area was unchanged between WT and HMGCR KI mice, independent of sex. Correspondingly, there were no phenotypic differences observed in hematopoietic progenitors or differentiated immune cells in the bone marrow, blood, or spleen, and no significant changes in systemic markers of inflammation. When lethally irradiated female mice were transplanted with KI bone marrow, there was similar plaque content relative to WT.ConclusionsGiven previous work, our study demonstrates the importance of preclinical atherosclerosis model comparison and brings into question the importance of AMPK-mediated control of cholesterol synthesis in atherosclerosis.

Cysteine, the rate-controlling amino acid in cellular glutathione synthesis is imported as cystine, by the cystine/glutamate antiporter, xCT, and subsequently reduced to cysteine. As glutathione redox is important in muscle regeneration in aging, we hypothesized that xCT exerts upstream control over skeletal muscle glutathione redox, metabolism and regeneration. Bioinformatic analyses of publicly available datasets revealed that expression levels of xCT and GSH-related genes are inversely correlated with myogenic differentiation genes. Muscle satellite cells (MuSCs) isolated from Slc7a11sut/sut mice, which harbour a mutation in the Slc7a11 gene encoding xCT, required media supplementation with 2-mercaptoethanol to support cell proliferation but not myotube differentiation, despite persistently lower GSH. Slc7a11sut/sut primary myotubes were larger compared to WT myotubes, and also exhibited higher glucose uptake and cellular oxidative capacities. Immunostaining of myogenic markers (Pax7, MyoD, and myogenin) in cardiotoxin-damaged tibialis anterior muscle fibres revealed greater MuSC activation and commitment to differentiation in Slc7a11sut/sut muscle compared to WT mice, culminating in larger myofiber cross-sectional areas at 21 days post-injury. Slc7a11sut/sut mice subjected to a 5-week exercise training protocol demonstrated enhanced insulin tolerance compared to WT mice, but blunted muscle mitochondrial biogenesis and respiration in response to exercise training. Our results demonstrate that the absence of xCT inhibits cell proliferation but promotes myotube differentiation by regulating cellular metabolism and glutathione redox. Altogether, these results support the notion that myogenesis is a redox-regulated process and may help inform novel therapeutic approaches for muscle wasting and dysfunction in aging and disease.

Mitochondrial electron transport chain complexes organize into supramolecular structures called respiratory supercomplexes (SCs). The role of respiratory SCs remains largely unconfirmed despite evidence supporting their necessity for mitochondrial respiratory function. The mechanisms underlying the formation of the I1III2IV1 "respirasome" SC are also not fully understood, further limiting insights into these processes in physiology and diseases, including neurodegeneration and metabolic syndromes. NDUFB4 is a complex I accessory subunit that contains residues that interact with the subunit UQCRC1 from complex III, suggesting that NDUFB4 is integral for I1III2IV1 respirasome integrity. Here, we introduced specific point mutations to Asn24 (N24) and Arg30 (R30) residues on NDUFB4 to decipher the role of I1III2-containing respiratory SCs in cellular metabolism while minimizing the functional consequences to complex I assembly. Our results demonstrate that NDUFB4 point mutations N24A and R30A impair I1III2IV1 respirasome assembly and reduce mitochondrial respiratory flux. Steady-state metabolomics also revealed a global decrease in citric acid cycle metabolites, affecting NADH-generating substrates. Taken together, our findings highlight an integral role of NDUFB4 in respirasome assembly and demonstrate the functional significance of SCs in regulating mammalian cell bioenergetics.

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.

OPA1 is an inner mitochondrial membrane protein that mediates diverse signaling processes. OPA1 is important for cardiac function and protects against cardiac insults such as ischemia reperfusion injury. We sought to further assess OPA1 in human and mouse cardiac pathologies, hypothesizing that OPA1 may also function in a protective manner in chronic heart failure. Bioinformatic analyses of histological and transcript data from the GTEx database indicated that OPA1 expression levels vary in the human heart, where elevated OPA1 transcript levels were correlated with fatty acid, branch chain amino acid and contractile gene signatures. To experimentally assess these correlations, mice with a 1.5-fold whole body OPA1 overexpression (OPA1-OE) were subjected to transverse aortic constriction surgery and displayed improved 2D and 4D cardiac functional parameters compared to WT mice. OPA1-OE mice had no induction of fibrotic transcript markers and displayed sustained transcript levels of fatty acid, branch chain amino acid and contractile markers. Maximal oxidative capacity was sustained in both WT and OPA1-OE cardiac myofibers post-TAC. These results further demonstrate the important role of OPA1 in mediating cardiac function and highlight protective signaling pathways. ### Competing Interest Statement CJG is a paid consultant of FUJIFILM VisualSonics Inc.

While conventional wisdom initially postulated that PD-L1 serves as the inert ligand for PD-1, an emerging body of literature suggests that PD-L1 has cell-intrinsic functions in immune and cancer cells. In line with these studies, here we show that engagement of PD-L1 via cellular ligands or agonistic antibodies, including those used in the clinic, potently inhibits the type I interferon pathway in cancer cells. Hampered type I interferon responses in PD-L1-expressing cancer cells resulted in enhanced efficacy of oncolytic viruses in vitro and in vivo. Consistently, PD-L1 expression marked tumor explants from cancer patients that were best infected by oncolytic viruses. Mechanistically, PD-L1 promoted a metabolic shift characterized by enhanced glycolysis rate that resulted in increased lactate production. In turn, lactate inhibited type I IFN responses. In addition to adding mechanistic insight into PD-L1 intrinsic function, our results will also help guide the numerous ongoing efforts to combine PD-L1 antibodies with oncolytic virotherapy in clinical trials.

Natural killer (NK) cells are predominant innate lymphocytes that initiate the early immune response during infection. NK cells undergo a metabolic switch to fuel augmented proliferation and activation following infection. Tumor necrosis factor-alpha (TNFα) is a well-known inflammatory cytokine that enhances NK cell function; however, the mechanism underlying NK cell proliferation in response to TNFα is not well established. Here, we demonstrated that upon infection/inflammation, NK cells upregulate the expression of TNF receptor 2 (TNFR2), which is associated with increased proliferation, metabolic activity, and effector function. Notably, IL-18 can induce TNFR2 expression in NK cells, augmenting their sensitivity toward TNFα. Mechanistically, TNFα-TNFR2 signaling upregulates the expression of CD25 (IL-2Rα) and nutrient transporters in NK cells, leading to a metabolic switch toward aerobic glycolysis. Transcriptomic analysis revealed significantly reduced expression levels of genes involved in cellular metabolism and proliferation in NK cells from TNFR2 KO mice. Accordingly, our data affirmed that genetic ablation of TNFR2 curtails CD25 upregulation and TNFα-induced glycolysis, leading to impaired NK cell proliferation and antiviral function during MCMV infection in vivo. Collectively, our results delineate the crucial role of the TNFα-TNFR2 axis in NK cell proliferation, glycolysis, and effector function.

Whether impaired mitochondrial capacity contributes to skeletal muscle insulin resistance is debated. Our multifactorial analysis shows no differences in skeletal muscle mitochondrial content, mitochondrial capacity, and mitochondrial molecular profiles between obese individuals with and without T2D that had comparable levels of confounding factors (BMI, age, aerobic capacity). We highlight that lean, active individuals have enhanced skeletal muscle mitochondrial capacity that is also reflected at the level of DNA methylation and gene transcription.

Background and ObjectivesCoenzyme Q(10) (CoQ(10)) is an important electron carrier and antioxidant. The COQ7 enzyme catalyzes the hydroxylation of 5-demethoxyubiquinone-10 (DMQ(10)), the second-to-last step in the CoQ(10) biosynthesis pathway. We report a consanguineous family presenting with a hereditary motor neuropathy associated with a homozygous c.1A > G p.? variant of COQ7 with abnormal CoQ(10) biosynthesis.MethodsAffected family members underwent clinical assessments that included nerve conduction testing, histologic analysis, and MRI. Pathogenicity of the COQ7 variant was assessed in cultured fibroblasts and skeletal muscle using a combination of immunoblots, respirometry, and quinone analysis.ResultsThree affected siblings, ranging from 12 to 24 years of age, presented with a severe length-dependent motor neuropathy with marked symmetric distal weakness and atrophy with normal sensation. Muscle biopsy of the quadriceps revealed chronic denervation pattern. An MRI examination identified moderate to severe fat infiltration in distal muscles. Exome sequencing demonstrated the homozygous COQ7 c.1A > G p.? variant that is expected to bypass the first 38 amino acid residues at the n-terminus, initiating instead with methionine at position 39. This is predicted to cause the loss of the cleavable mitochondrial targeting sequence and 2 additional amino acids, thereby preventing the incorporation and subsequent folding of COQ7 into the inner mitochondrial membrane. Pathogenicity of the COQ7 variant was demonstrated by diminished COQ7 and CoQ(10) levels in muscle and fibroblast samples of affected siblings but not in the father, unaffected sibling, or unrelated controls. In addition, fibroblasts from affected siblings had substantial accumulation of DMQ(10), and maximal mitochondrial respiration was impaired in both fibroblasts and muscle.DiscussionThis report describes a new neurologic phenotype of COQ7-related primary CoQ(10) deficiency. Novel aspects of the phenotype presented by this family include pure distal motor neuropathy involvement, as well as the lack of upper motor neuron features, cognitive delay, or sensory involvement in comparison with cases of COQ7-related CoQ(10) deficiency previously reported in the literature.

This file contains the full descriptive legends for Supplementary Figures S1-S7.

<p>This file provides supplementary data pertaining to TSC2 mutation and protein expression analysis in human fibroblast cell lines (Figure S1); as well as Karyotypes (Figure S2), in vitro and in vivo pluripotency and differentiation potential (Figure S3), and genotyping mutation analysis (Figure S4) of human iPSC lines used in this study. Supplementary data regarding human-derived SMC lines, with and without TSC2 mRNA knock-down, specifically cell size analysis (Figure S5), gp100 and ER- expression (Figure S6) and cell death analysis (Figure S7), is also shown.</p>