Ketone flux through BDH1 supports metabolic remodeling of skeletal and cardiac muscles in response to intermittent time-restricted feeding.

Time-restricted feeding (TRF) has gained attention as a dietary regimen that promotes metabolic health. This study questioned if the health benefits of an intermittent TRF (iTRF) schedule require ketone flux specifically in skeletal and cardiac muscles. Notably, we found that the ketolytic enzyme beta-hydroxybutyrate dehydrogenase 1 (BDH1) is uniquely enriched in isolated mitochondria derived from heart and red/oxidative skeletal muscles, which also have high capacity for fatty acid oxidation (FAO). Using mice with BDH1 deficiency in striated muscles, we discover that this enzyme optimizes FAO efficiency and exercise tolerance during acute fasting. Additionally, iTRF leads to robust molecular remodeling of muscle tissues, and muscle BDH1 flux does indeed play an essential role in conferring the full adaptive benefits of this regimen, including increased lean mass, mitochondrial hormesis, and metabolic rerouting of pyruvate. In sum, ketone flux enhances mitochondrial bioenergetics and supports iTRF-induced remodeling of skeletal muscle and heart.

Acetyl-CoA carboxylase 1 is a suppressor of the adipocyte thermogenic program.

Disruption of adipocyte de novo lipogenesis (DNL) by deletion of fatty acid synthase (FASN) in mice induces browning in inguinal white adipose tissue (iWAT). However, adipocyte FASN knockout (KO) increases acetyl-coenzyme A (CoA) and malonyl-CoA in addition to depletion of palmitate. We explore which of these metabolite changes triggers adipose browning by generating eight adipose-selective KO mouse models with loss of ATP-citrate lyase (ACLY), acetyl-CoA carboxylase 1 (ACC1), ACC2, malonyl-CoA decarboxylase (MCD) or FASN, or dual KOs ACLY/FASN, ACC1/FASN, and ACC2/FASN. Preventing elevation of acetyl-CoA and malonyl-CoA by depletion of adipocyte ACLY or ACC1 in combination with FASN KO does not block the browning of iWAT. Conversely, elevating malonyl-CoA levels in MCD KO mice does not induce browning. Strikingly, adipose ACC1 KO induces a strong iWAT thermogenic response similar to FASN KO while also blocking malonyl-CoA and palmitate synthesis. Thus, ACC1 and FASN are strong suppressors of adipocyte thermogenesis through promoting lipid synthesis rather than modulating the DNL intermediates acetyl-CoA or malonyl-CoA.

Pyruvate-supported flux through medium-chain ketothiolase promotes mitochondrial lipid tolerance in cardiac and skeletal muscles.

Even-chain acylcarnitine (AC) metabolites, most of which are generated as byproducts of incomplete fatty acid oxidation (FAO), are viewed as biomarkers of mitochondrial lipid stress attributable to one or more metabolic bottlenecks in the ß-oxidation pathway. The origins and functional implications of FAO bottlenecks remain poorly understood. Here, we combined a sophisticated mitochondrial phenotyping platform with state-of-the-art molecular profiling tools and multiple two-state mouse models of respiratory function to uncover a mechanism that connects AC accumulation to lipid intolerance, metabolic inflexibility, and respiratory inefficiency in skeletal muscle mitochondria. These studies also identified a short-chain carbon circuit at the C4 node of FAO wherein reverse flux of glucose-derived acetyl CoA through medium-chain ketothiolase enhances lipid tolerance and redox stability in heart mitochondria by regenerating free CoA and NAD+. The findings help to explain why diminished FAO capacity, AC accumulation, and metabolic inflexibility are tightly linked to poor health outcomes.

RIP140 deficiency enhances cardiac fuel metabolism and protects mice from heart failure.

During the development of heart failure (HF), the capacity for cardiomyocyte (CM) fatty acid oxidation (FAO) and ATP production is progressively diminished, contributing to pathologic cardiac hypertrophy and contractile dysfunction. Receptor-interacting protein 140 (RIP140, encoded by Nrip1) has been shown to function as a transcriptional corepressor of oxidative metabolism. We found that mice with striated muscle deficiency of RIP140 (strNrip1-/-) exhibited increased expression of a broad array of genes involved in mitochondrial energy metabolism and contractile function in heart and skeletal muscle. strNrip1-/- mice were resistant to the development of pressure overload-induced cardiac hypertrophy, and CM-specific RIP140-deficient (csNrip1-/-) mice were protected against the development of HF caused by pressure overload combined with myocardial infarction. Genomic enhancers activated by RIP140 deficiency in CMs were enriched in binding motifs for transcriptional regulators of mitochondrial function (estrogen-related receptor) and cardiac contractile proteins (myocyte enhancer factor 2). Consistent with a role in the control of cardiac fatty acid oxidation, loss of RIP140 in heart resulted in augmented triacylglyceride turnover and fatty acid utilization. We conclude that RIP140 functions as a suppressor of a transcriptional regulatory network that controls cardiac fuel metabolism and contractile function, representing a potential therapeutic target for the treatment of HF.

Effects of SGLT2 inhibitor dapagliflozin in patients with type 2 diabetes on skeletal muscle cellular metabolism.

OBJECTIVE: SGLT2 inhibitors increase urinary glucose excretion and have beneficial effects on cardiovascular and renal outcomes; the underlying mechanism may be metabolic adaptations due to urinary glucose loss. Here, we investigated the cellular and molecular effects of 5 weeks of dapagliflozin treatment on skeletal muscle metabolism in type 2 diabetes patients. METHODS: Twenty-six type 2 diabetes mellitus patients were randomized to a 5-week double-blind, cross-over study with 6-8-week wash-out. Skeletal muscle acetylcarnitine levels, intramyocellular lipid (IMCL) content and phosphocreatine (PCr) recovery rate were measured by magnetic resonance spectroscopy (MRS). Ex vivo mitochondrial respiration was measured in skeletal muscle fibers using high resolution respirometry. Intramyocellular lipid droplet and mitochondrial network dynamics were investigated using confocal microscopy. Skeletal muscle levels of acylcarnitines, amino acids and TCA cycle intermediates were measured. Expression of genes involved in fatty acid metabolism were investigated. RESULTS: Mitochondrial function, mitochondrial network integrity and citrate synthase and carnitine acetyltransferase activities in skeletal muscle were unaltered after dapagliflozin treatment. Dapagliflozin treatment increased intramyocellular lipid content (0.060 (0.011, 0.110) %, p = 0.019). Myocellular lipid droplets increased in size (0.03 µm2 (0.01-0.06), p < 0.05) and number (0.003 µm-2 (-0.001-0.007), p = 0.09) upon dapagliflozin treatment. CPT1A, CPT1B and malonyl CoA-decarboxylase mRNA expression was increased by dapagliflozin. Fasting acylcarnitine species and C4-OH carnitine levels (0.4704 (0.1246, 0.8162) pmoles∗mg tissue-1, p < 0.001) in skeletal muscle were higher after dapagliflozin treatment, while acetylcarnitine levels were lower (-40.0774 (-64.4766, -15.6782) pmoles∗mg tissue-1, p < 0.001). Fasting levels of several amino acids, succinate, alpha-ketoglutarate and lactate in skeletal muscle were significantly lower after dapagliflozin treatment. CONCLUSION: Dapagliflozin treatment for 5 weeks leads to adaptive changes in skeletal muscle substrate metabolism favoring metabolism of fatty acid and ketone bodies and reduced glycolytic flux. The trial is registered with ClinicalTrials.gov, number NCT03338855.

Chemotherapeutic drug screening in 3D-Bioengineered human myobundles provides insight into taxane-induced myotoxicities.

Two prominent frontline breast cancer (BC) chemotherapies commonly used in combination, doxorubicin (DOX) and docetaxel (TAX), are associated with long-lasting cardiometabolic and musculoskeletal side effects. Whereas DOX has been linked to mitochondrial dysfunction, mechanisms underlying TAX-induced myotoxicities remain uncertain. Here, the metabolic and functional consequences of TAX ± DOX were investigated using a 3D-bioengineered model of adult human muscle and a drug dosing regimen designed to resemble in vivo pharmacokinetics. DOX potently reduced mitochondrial respiratory capacity, 3D-myobundle size, and contractile force, whereas TAX-induced acetylation and remodeling of the microtubule network led to perturbations in glucose uptake, mitochondrial respiratory sensitivity, and kinetics of fatigue, without compromising tetanic force generation. These findings suggest TAX-induced remodeling of the microtubule network disrupts glucose transport and respiratory control in skeletal muscle and thereby have important clinical implications related to the cardiometabolic health and quality of life of BC patients and survivors.

Rheumatoid arthritis T cell and muscle oxidative metabolism associate with exercise-induced changes in cardiorespiratory fitness.

Rheumatoid arthritis (RA) T cells drive autoimmune features via metabolic reprogramming that reduces oxidative metabolism. Exercise training improves cardiorespiratory fitness (i.e., systemic oxidative metabolism) and thus may impact RA T cell oxidative metabolic function. In this pilot study of RA participants, we took advantage of heterogeneous responses to a high-intensity interval training (HIIT) exercise program to identify relationships between improvements in cardiorespiratory fitness with changes in peripheral T cell and skeletal muscle oxidative metabolism. In 12 previously sedentary persons with seropositive RA, maximal cardiopulmonary exercise tests, fasting blood, and vastus lateralis biopsies were obtained before and after 10 weeks of HIIT. Following HIIT, improvements in RA cardiorespiratory fitness were associated with changes in RA CD4 + T cell basal and maximal respiration and skeletal muscle carnitine acetyltransferase (CrAT) enzyme activity. Further, changes in CD4 + T cell respiration were associated with changes in naïve CD4 + CCR7 + CD45RA + T cells, muscle CrAT, and muscle medium-chain acylcarnitines and fat oxidation gene expression profiles. In summary, modulation of cardiorespiratory fitness and molecular markers of skeletal muscle oxidative metabolism during exercise training paralleled changes in T cell metabolism. Exercise training that improves RA cardiorespiratory fitness may therefore be valuable in managing pathologically related immune and muscle dysfunction.Trial registration: ClinicalTrials.gov, NCT02528344. Registered on 19 August 2015.

Nicotinamide riboside supplementation confers marginal metabolic benefits in obese mice without remodeling the muscle acetyl-proteome.

Nicotinamide riboside supplements (NRS) have been touted as a nutraceutical that promotes cardiometabolic and musculoskeletal health by enhancing nicotinamide adenine dinucleotide (NAD+) biosynthesis, mitochondrial function, and/or the activities of NAD-dependent sirtuin deacetylase enzymes. This investigation examined the impact of NRS on whole body energy homeostasis, skeletal muscle mitochondrial function, and corresponding shifts in the acetyl-lysine proteome, in the context of diet-induced obesity using C57BL/6NJ mice. The study also included a genetically modified mouse model that imposes greater demand on sirtuin flux and associated NAD+ consumption, specifically within muscle tissues. In general, whole body glucose control was marginally improved by NRS when administered at the midpoint of a chronic high-fat diet, but not when given as a preventative therapy upon initiation of the diet. Contrary to anticipated outcomes, the study produced little evidence that NRS increases tissue NAD+ levels, augments mitochondrial function, and/or mitigates diet-induced hyperacetylation of the skeletal muscle proteome.

Disruption of STIM1-mediated Ca2+ sensing and energy metabolism in adult skeletal muscle compromises exercise tolerance, proteostasis, and lean mass.

OBJECTIVE: Stromal interaction molecule 1 (STIM1) is a single-pass transmembrane endoplasmic/sarcoplasmic reticulum (E/SR) protein recognized for its role in a store operated Ca2+ entry (SOCE), an ancient and ubiquitous signaling pathway. Whereas STIM1 is known to be indispensable during development, its biological and metabolic functions in mature muscles remain unclear. METHODS: Conditional and tamoxifen inducible muscle STIM1 knock-out mouse models were coupled with multi-omics tools and comprehensive physiology to understand the role of STIM1 in regulating SOCE, mitochondrial quality and bioenergetics, and whole-body energy homeostasis. RESULTS: This study shows that STIM1 is abundant in adult skeletal muscle, upregulated by exercise, and is present at SR-mitochondria interfaces. Inducible tissue-specific deletion of STIM1 (iSTIM1 KO) in adult muscle led to diminished lean mass, reduced exercise capacity, and perturbed fuel selection in the settings of energetic stress, without affecting whole-body glucose tolerance. Proteomics and phospho-proteomics analyses of iSTIM1 KO muscles revealed molecular signatures of low-grade E/SR stress and broad activation of processes and signaling networks involved in proteostasis. CONCLUSION: These results show that STIM1 regulates cellular and mitochondrial Ca2+ dynamics, energy metabolism and proteostasis in adult skeletal muscles. Furthermore, these findings provide insight into the pathophysiology of muscle diseases linked to disturbances in STIM1-dependent Ca2+ handling.

Myocardial Lipin 1 knockout in mice approximates cardiac effects of human LPIN1 mutations.

Lipin 1 is a bifunctional protein that is a transcriptional regulator and has phosphatidic acid (PA) phosphohydrolase activity, which dephosphorylates PA to generate diacylglycerol. Human lipin 1 mutations lead to episodic rhabdomyolysis, and some affected patients exhibit cardiac abnormalities, including exercise-induced cardiac dysfunction and cardiac triglyceride accumulation. Furthermore, lipin 1 expression is deactivated in failing heart, but the effects of lipin 1 deactivation in myocardium are incompletely understood. We generated mice with cardiac-specific lipin 1 KO (cs-Lpin1-/-) to examine the intrinsic effects of lipin 1 in the myocardium. Cs-Lpin1-/- mice had normal systolic cardiac function but mild cardiac hypertrophy. Compared with littermate control mice, PA content was higher in cs-Lpin1-/- hearts, which also had an unexpected increase in diacylglycerol and triglyceride content. Cs-Lpin1-/- mice exhibited diminished cardiac cardiolipin content and impaired mitochondrial respiration rates when provided with pyruvate or succinate as metabolic substrates. After transverse aortic constriction-induced pressure overload, loss of lipin 1 did not exacerbate cardiac hypertrophy or dysfunction. However, loss of lipin 1 dampened the cardiac ionotropic response to dobutamine and exercise endurance in association with reduced protein kinase A signaling. These data suggest that loss of lipin 1 impairs cardiac functional reserve, likely due to effects on glycerolipid homeostasis, mitochondrial function, and protein kinase A signaling.

Muscle-Liver Trafficking of BCAA-Derived Nitrogen Underlies Obesity-Related Glycine Depletion.

Glycine levels are inversely associated with branched-chain amino acids (BCAAs) and cardiometabolic disease phenotypes, but biochemical mechanisms that explain these relationships remain uncharted. Metabolites and genes related to BCAA metabolism and nitrogen handling were strongly associated with glycine in correlation analyses. Stable isotope labeling in Zucker fatty rats (ZFRs) shows that glycine acts as a carbon donor for the pyruvate-alanine cycle in a BCAA-regulated manner. Inhibition of the BCAA transaminase (BCAT) enzymes depletes plasma pools of alanine and raises glycine levels. In high-fat-fed ZFRs, dietary glycine supplementation raises urinary acyl-glycine content and lowers circulating triglycerides but also results in accumulation of long-chain acyl-coenzyme As (acyl-CoAs), lower 5' adenosine monophosphate-activated protein kinase (AMPK) phosphorylation in muscle, and no improvement in glucose tolerance. Collectively, these studies frame a mechanism for explaining obesity-related glycine depletion and also provide insight into the impact of glycine supplementation on systemic glucose, lipid, and amino acid metabolism.

Nutritional modulation of heart failure in mitochondrial pyruvate carrier-deficient mice.

The myocardium is metabolically flexible; however, impaired flexibility is associated with cardiac dysfunction in conditions including diabetes and heart failure. The mitochondrial pyruvate carrier (MPC) complex, composed of MPC1 and MPC2, is required for pyruvate import into the mitochondria. Here we show that MPC1 and MPC2 expression is downregulated in failing human and mouse hearts. Mice with cardiac-specific deletion of Mpc2 (CS-MPC2-/-) exhibited normal cardiac size and function at 6 weeks old, but progressively developed cardiac dilation and contractile dysfunction, which was completely reversed by a high-fat, low-carbohydrate ketogenic diet. Diets with higher fat content, but enough carbohydrate to limit ketosis, also improved heart failure, while direct ketone body provisioning provided only minor improvements in cardiac remodelling in CS-MPC2-/- mice. An acute fast also improved cardiac remodelling. Together, our results reveal a critical role for mitochondrial pyruvate use in cardiac function, and highlight the potential of dietary interventions to enhance cardiac fat metabolism to prevent or reverse cardiac dysfunction and remodelling in the setting of MPC deficiency.

Extreme Acetylation of the Cardiac Mitochondrial Proteome Does Not Promote Heart Failure.

RATIONALE: Circumstantial evidence links the development of heart failure to posttranslational modifications of mitochondrial proteins, including lysine acetylation (Kac). Nonetheless, direct evidence that Kac compromises mitochondrial performance remains sparse. OBJECTIVE: This study sought to explore the premise that mitochondrial Kac contributes to heart failure by disrupting oxidative metabolism. METHODS AND RESULTS: A DKO (dual knockout) mouse line with deficiencies in CrAT (carnitine acetyltransferase) and Sirt3 (sirtuin 3)-enzymes that oppose Kac by buffering the acetyl group pool and catalyzing lysine deacetylation, respectively-was developed to model extreme mitochondrial Kac in cardiac muscle, as confirmed by quantitative acetyl-proteomics. The resulting impact on mitochondrial bioenergetics was evaluated using a respiratory diagnostics platform that permits comprehensive assessment of mitochondrial function and energy transduction. Susceptibility of DKO mice to heart failure was investigated using transaortic constriction as a model of cardiac pressure overload. The mitochondrial acetyl-lysine landscape of DKO hearts was elevated well beyond that observed in response to pressure overload or Sirt3 deficiency alone. Relative changes in the abundance of specific acetylated lysine peptides measured in DKO versus Sirt3 KO hearts were strongly correlated. A proteomics comparison across multiple settings of hyperacetylation revealed ≈86% overlap between the populations of Kac peptides affected by the DKO manipulation as compared with experimental heart failure. Despite the severity of cardiac Kac in DKO mice relative to other conditions, deep phenotyping of mitochondrial function revealed a surprisingly normal bioenergetics profile. Thus, of the >120 mitochondrial energy fluxes evaluated, including substrate-specific dehydrogenase activities, respiratory responses, redox charge, mitochondrial membrane potential, and electron leak, we found minimal evidence of oxidative insufficiencies. Similarly, DKO hearts were not more vulnerable to dysfunction caused by transaortic constriction-induced pressure overload. CONCLUSIONS: The findings challenge the premise that hyperacetylation per se threatens metabolic resilience in the myocardium by causing broad-ranging disruption to mitochondrial oxidative machinery.

Rejuvenation of Neutrophil Functions in Association With Reduced Diabetes Risk Following Ten Weeks of Low-Volume High Intensity Interval Walking in Older Adults With Prediabetes - A Pilot Study.

Neutrophil dysfunction is a common feature of aging, and is associated with the pathogenesis of many age-related diseases, including type 2 diabetes mellitus (T2DM). Although exercise training improves metabolic health, decreases risk of T2DM, and is associated with improving neutrophil functions, involvement in regular physical activity declines with age. The aim of this study was to determine if neutrophil functions could be improved in association with changes in fitness and metabolic parameters in older adults at risk for T2DM using 10-weeks of low volume high-intensity interval exercise training (HIIT). Ten older (71 ± 5 years) sedentary adults with prediabetes (HbA1c: 6.1 ± 0.3%) completed 10 weeks of a supervised HIIT program. Three 30 min sessions/week consisted of ten 60 s intervals of low intensity [50-60% heart rate reserve (HRR)] separated with similar durations of high intensity intervals (80-90% HRR). Before and after training, glucose and insulin sensitivity, neutrophil chemotaxis, bacterial phagocytosis, reactive oxygen species (ROS) production, and mitochondrial functions were assessed. Exercise-mediated changes in cardiorespiratory fitness (VO2peak) and neutrophil functions were compared to six young (23 ± 1 years) healthy adults. Following training, significant reductions in fasting glucose and insulin were accompanied by improved glucose control and insulin sensitivity (all p < 0.05). Before exercise training, VO2peak in the old participants was significantly less than that of the young controls (p < 0.001), but increased by 16 ± 11% following training (p = 0.002) resulting in a 6% improvement of the deficit. Neutrophil chemotaxis, phagocytosis and stimulated ROS production were significantly less than that of the young controls, while basal ROS were higher before training (all p < 0.05). Following training, chemotaxis, phagocytosis and stimulated ROS increased while basal ROS decreased, similar to levels observed in the young controls (all p < 0.05) and reducing the deficit of the young controls between 2 and 154%. In five of the adults with prediabetes, neutrophil mitochondrial functions were significantly poorer than the six young controls before training. Following training, mitochondrial functions improved toward those observed in young controls (all p < 0.05), reducing the deficit of the young controls between 14.3 and 451%. Ten weeks of HIIT in older adults at risk for T2DM reduced disease risk accompanied by improved primary and bioenergetic neutrophil functions. Our results are consistent with a reduced risk of infections mediated by relationships in exercise induced systemic and cellular metabolic features. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT02441205, registered on May 12th, 2015.

Disruption of Acetyl-Lysine Turnover in Muscle Mitochondria Promotes Insulin Resistance and Redox Stress without Overt Respiratory Dysfunction.

This study sought to examine the functional significance of mitochondrial protein acetylation using a double knockout (DKO) mouse model harboring muscle-specific deficits in acetyl-CoA buffering and lysine deacetylation, due to genetic ablation of carnitine acetyltransferase and Sirtuin 3, respectively. DKO mice are highly susceptible to extreme hyperacetylation of the mitochondrial proteome and develop a more severe form of diet-induced insulin resistance than either single KO mouse line. However, the functional phenotype of hyperacetylated DKO mitochondria is largely normal. Of the >120 measures of respiratory function assayed, the most consistently observed traits of a markedly heightened acetyl-lysine landscape are enhanced oxygen flux in the context of fatty acid fuel and elevated rates of electron leak. In sum, the findings challenge the notion that lysine acetylation causes broad-ranging damage to mitochondrial quality and performance and raise the possibility that acetyl-lysine turnover, rather than acetyl-lysine stoichiometry, modulates redox balance and carbon flux.

Plasma MicroRNAs in Established Rheumatoid Arthritis Relate to Adiposity and Altered Plasma and Skeletal Muscle Cytokine and Metabolic Profiles.

Background: MicroRNAs have been implicated in the pathogenesis of rheumatoid arthritis (RA), obesity, and altered metabolism. Although RA is associated with both obesity and altered metabolism, expression of RA-related microRNA in the setting of these cardiometabolic comorbidities is unclear. Our objective was to determine relationships between six RA-related microRNAs and RA disease activity, inflammation, body composition, and metabolic function. Methods: Expression of plasma miR-21, miR-23b, miR-27a, miR-143, miR-146a, and miR-223 was measured in 48 persons with seropositive and/or erosive RA (mean DAS-28-ESR 3.0, SD 1.4) and 23 age-, sex-, and BMI-matched healthy controls. Disease activity in RA was assessed by DAS-28-ESR. Plasma cytokine concentrations were determined by ELISA. Body composition was assessed using CT scan to determine central and muscle adipose and thigh muscle tissue size and tissue density. Plasma and skeletal muscle acylcarnitine, amino acid, and organic acid metabolites were measured via mass-spectroscopy. Plasma lipoproteins were measured via nuclear magnetic resonance (NMR) spectroscopy. Spearman correlations were used to assess relationships for microRNA with inflammation and cardiometabolic measures. RA and control associations were compared using Fisher transformations. Results: Among RA subjects, plasma miR-143 was associated with plasma IL-6 and IL-8. No other RA microRNA was positively associated with disease activity or inflammatory markers. In RA, microRNA expression was associated with adiposity, both visceral adiposity (miR-146a, miR-21, miR-23b, and miR-27a) and thigh intra-muscular adiposity (miR-146a and miR-223). RA miR-146a was associated with greater concentrations of cardiometabolic risk markers (plasma short-chain dicarboxyl/hydroxyl acylcarnitines, triglycerides, large VLDL particles, and small HDL particles) and lower concentrations of muscle energy substrates (long-chain acylcarnitines and pyruvate). Despite RA and controls having similar microRNA levels, RA, and controls differed in magnitude and direction for several associations with cytokines and plasma and skeletal muscle metabolic intermediates. Conclusion: Most microRNAs thought to be associated with RA disease activity and inflammation were more reflective of RA adiposity and impaired metabolism. These associations show that microRNAs in RA may serve as an epigenetic link between RA inflammation and cardiometabolic comorbidities.

Respiratory Phenomics across Multiple Models of Protein Hyperacylation in Cardiac Mitochondria Reveals a Marginal Impact on Bioenergetics.

Acyl CoA metabolites derived from the catabolism of carbon fuels can react with lysine residues of mitochondrial proteins, giving rise to a large family of post-translational modifications (PTMs). Mass spectrometry-based detection of thousands of acyl-PTMs scattered throughout the proteome has established a strong link between mitochondrial hyperacylation and cardiometabolic diseases; however, the functional consequences of these modifications remain uncertain. Here, we use a comprehensive respiratory diagnostics platform to evaluate three disparate models of mitochondrial hyperacylation in the mouse heart caused by genetic deletion of malonyl CoA decarboxylase (MCD), SIRT5 demalonylase and desuccinylase, or SIRT3 deacetylase. In each case, elevated acylation is accompanied by marginal respiratory phenotypes. Of the >60 mitochondrial energy fluxes evaluated, the only outcome consistently observed across models is a ∼15% decrease in ATP synthase activity. In sum, the findings suggest that the vast majority of mitochondrial acyl PTMs occur as stochastic events that minimally affect mitochondrial bioenergetics.

A Mitochondrial Progesterone Receptor Increases Cardiac Beta-Oxidation and Remodeling.

Progesterone is primarily a pregnancy-related hormone, produced in substantial quantities after ovulation and during gestation. Traditionally known to function via nuclear receptors for transcriptional regulation, there is also evidence of nonnuclear action. A previously identified mitochondrial progesterone receptor (PR-M) increases cellular respiration in cell models. In these studies, we demonstrated that expression of PR-M in rat H9c2 cardiomyocytes resulted in a ligand-dependent increase in oxidative cellular respiration and beta-oxidation. Cardiac expression in a TET-On transgenic mouse resulted in gene expression of myofibril proteins for remodeling and proteins involved in oxidative phosphorylation and fatty acid metabolism. In a model of increased afterload from constant transverse aortic constriction, mice expressing PR-M showed a ligand-dependent preservation of cardiac function. From these observations, we propose that PR-M is responsible for progesterone-induced increases in cellular energy production and cardiac remodeling to meet the physiological demands of pregnancy.

Systematic Dissection of the Metabolic-Apoptotic Interface in AML Reveals Heme Biosynthesis to Be a Regulator of Drug Sensitivity.

Crosstalk between metabolic and survival pathways is critical for cellular homeostasis, but the connectivity between these processes remains poorly defined. We used loss-of-function CRISPR/Cas9 knockout screening to identify metabolic genes capable of influencing cellular commitment to apoptosis, using sensitization to the BCL-2 inhibitor ABT-199 in BCL-2-dependent acute myeloid leukemia (AML) cell lines as a proxy for apoptotic disposition. This analysis revealed metabolic pathways that specifically cooperate with BCL-2 to sustain survival. In particular, our analysis singled out heme biosynthesis as an unappreciated apoptosis-modifying pathway. Although heme is broadly incorporated into the proteome, reduction of heme biosynthesis potentiates apoptosis through the loss of ETC activity, resulting in baseline depolarization of the mitochondrial membrane and an increased propensity to undergo apoptosis. Collectively, our findings chart the first apoptotic map of metabolism, motivating the design of metabolically engaged combination chemotherapies and nominating heme biosynthesis as an apoptotic modulator in AML.

Electrical stimulation increases hypertrophy and metabolic flux in tissue-engineered human skeletal muscle.

In vitro models of contractile human skeletal muscle hold promise for use in disease modeling and drug development, but exhibit immature properties compared to native adult muscle. To address this limitation, 3D tissue-engineered human muscles (myobundles) were electrically stimulated using intermittent stimulation regimes at 1 Hz and 10 Hz. Dystrophin in myotubes exhibited mature membrane localization suggesting a relatively advanced starting developmental maturation. One-week stimulation significantly increased myobundle size, sarcomeric protein abundance, calcium transient amplitude (∼2-fold), and tetanic force (∼3-fold) resulting in the highest specific force generation (19.3mN/mm2) reported for engineered human muscles to date. Compared to 1 Hz electrical stimulation, the 10 Hz stimulation protocol resulted in greater myotube hypertrophy and upregulated mTORC1 and ERK1/2 activity. Electrically stimulated myobundles also showed a decrease in fatigue resistance compared to control myobundles without changes in glycolytic or mitochondrial protein levels. Greater glucose consumption and decreased abundance of acetylcarnitine in stimulated myobundles indicated increased glycolytic and fatty acid metabolic flux. Moreover, electrical stimulation of myobundles resulted in a metabolic shift towards longer-chain fatty acid oxidation as evident from increased abundances of medium- and long-chain acylcarnitines. Taken together, our study provides an advanced in vitro model of human skeletal muscle with improved structure, function, maturation, and metabolic flux.