Skeletal Muscle Bioenergetics Research Articles

Associations between regional adipose tissue distribution and skeletal muscle bioenergetics in older men and women.

The aim of this study was to examine associations of ectopic adipose tissue (AT) with skeletal muscle (SM) mitochondrial bioenergetics in older adults. Cross-sectional data from 829 adults ≥70 years of age were used. Abdominal, subcutaneous, and visceral AT and thigh muscle fat infiltration (MFI) were quantified by magnetic resonance imaging. SM mitochondrial energetics were characterized in vivo (31P-magnetic resonance spectroscopy; ATPmax) and ex vivo (high-resolution respirometry maximal oxidative phosphorylation [OXPHOS]). ActivPal was used to measure physical activity ([PA]; step count). Linear regression adjusted for covariates was applied, with sequential adjustment for BMI and PA. Independent of BMI, total abdominal AT (standardized [Std.] β = -0.21; R2 = 0.09) and visceral AT (Std. β = -0.16; R2 = 0.09) were associated with ATPmax (p < 0.01; n = 770) but not following adjustment for PA (p ≥ 0.05; n = 658). Visceral AT (Std. β = -0.16; R2 = 0.25) and thigh MFI (Std. β = -0.11; R2 = 0.24) were associated with carbohydrate-supported maximal OXPHOS independent of BMI and PA (p < 0.05; n = 609). Total abdominal AT (Std. β = -0.19; R2 = 0.24) and visceral AT (Std. β = -0.17; R2 = 0.24) were associated with fatty acid-supported maximal OXPHOS independent of BMI and PA (p < 0.05; n = 447). Skeletal MFI and abdominal visceral, but not subcutaneous, AT are inversely associated with SM mitochondrial bioenergetics in older adults independent of BMI. Associations between ectopic AT and in vivo mitochondrial bioenergetics are attenuated by PA.

Preliminary analysis of the THRIVE clinical trial on the effect of resistance exercise on skeletal muscle bioenergetics, strength and body composition in breast cancer survivors

Objective: Breast cancer survivors (BCS) are at high risk for loss in skeletal muscle mass, which can be exacerbated by cancer treatment and tumor related factors. While resistance exercise has been shown to be effective in improving strength and physical function in BCS, little is known as to how exercise modulates skeletal muscle bioenergetics in oncology populations. Uncovering these factors are critical for explaining adaptations to exercise among cancer survivors. Therefore, the objective of the THRIVE clinical trial is to determine the effects of resistance exercise training on modulating skeletal muscle bioenergetics in BCS. Hypothesis: We hypothesized that 12 weeks of resistance exercise would improve skeletal muscle bioenergetics, strength and body composition in BCS. Methodology: Preliminary analysis was performed on BCS (n=10; 45.7 ± 11.5 yr) who had completed chemotherapy within the previous 6 months and were recruited to complete 12 weeks of progressive, home-based resistance exercise program (3 supervised training bouts per week). Baseline and 12 weeks strength was assessed with isometric dynamometry and 1 rep max (RM) testing, body composition was measured with DEXA, and physical function was assessed with a 6 minute walk test. Changes in muscle bioenergetics, specifically changes in resting phosphorus metabolites, were assessed using 31-phosphorus magnetic resonance spectroscopy. In the original study design, participants were randomized to either receive creatinine supplement + exercise (n=5) or exercise alone (n=5); however, there were no significant differences between the interventions on the primary outcomes reported here, so the intervention groups were collapsed. Data: Handgrip strength, 1 RM chest press, 1 RM bicep curl, 1 RM leg press and 1 RM leg extension significantly increased (p&lt;0.05) following 12 weeks of training in breast cancer survivors. Twelve weeks of resistance exercise training also significantly increased skeletal muscle phosphodiester (PDE) content and tended to increase total phosphocreatine and gammaATP. There were no significant changes in isometric knee strength, fat mass, lean mass, 6 minute walk testing distance or skeletal muscle inorganic phosphorous. Summary: This preliminary analysis indicates changes in strength and skeletal muscle bioenergetics occur in BCS following a 12-week home-based resistance exercise intervention. Further research is needed to validate these results. The ThriveWell Foundation, NIH (P30 CA054174 and P30 AG044271). 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.

Mitochondrial Transplantation's Role in Rodent Skeletal Muscle Bioenergetics: Recharging the Engine of Aging.

Mitochondria are the 'powerhouses of cells' and progressive mitochondrial dysfunction is a hallmark of aging in skeletal muscle. Although different forms of exercise modality appear to be beneficial to attenuate aging-induced mitochondrial dysfunction, it presupposes that the individual has a requisite level of mobility. Moreover, non-exercise alternatives (i.e., nutraceuticals or pharmacological agents) to improve skeletal muscle bioenergetics require time to be effective in the target tissue and have another limitation in that they act systemically and not locally where needed. Mitochondrial transplantation represents a novel directed therapy designed to enhance energy production of tissues impacted by defective mitochondria. To date, no studies have used mitochondrial transplantation as an intervention to attenuate aging-induced skeletal muscle mitochondrial dysfunction. The purpose of this investigation, therefore, was to determine whether mitochondrial transplantation can enhance skeletal muscle bioenergetics in an aging rodent model. We hypothesized that mitochondrial transplantation would result in sustained skeletal muscle bioenergetics leading to improved functional capacity. Fifteen female mice (24 months old) were randomized into two groups (placebo or mitochondrial transplantation). Isolated mitochondria from a donor mouse of the same sex and age were transplanted into the hindlimb muscles of recipient mice (quadriceps femoris, tibialis anterior, and gastrocnemius complex). The results indicated significant increases (ranging between ~36% and ~65%) in basal cytochrome c oxidase and citrate synthase activity as well as ATP levels in mice receiving mitochondrial transplantation relative to the placebo. Moreover, there were significant increases (approx. two-fold) in protein expression of mitochondrial markers in both glycolytic and oxidative muscles. These enhancements in the muscle translated to significant improvements in exercise tolerance. This study provides initial evidence showing how mitochondrial transplantation can promote skeletal muscle bioenergetics in an aging rodent model.

The Effect of L-Carnitine Supplementation on Sportive Performance

L-carnitine is a derivative of two essential amino acids synthesized in the liver and kidneys that our body needs for energy. In the bioenergetics of skeletal muscle, carnitine plays crucial roles. A severe reduction in muscular activity is associated with skeletal muscle carnitine insufficiency. Since L-carnitine supplement is known as a fat burner, its use among athletes has become more common in recent years. This review's objective is to assess the potential mechanistic effects of L-carnitine supplementation on athletic performance. In this context, the literature in the SportDiscus, EMBASE, PubMed and Google Scholar databases was scanned during a 15-year period to gather the data from the publications screened within the scope of SCI, SCI-Expanded, and ESCI. Consequently, it may be argued that taking carnitine supplementation improves athletic performance through a number of processes; including the maintenance of glycogen.

FRI607 SGLT2 Inhibition Improves Muscle Oxidative Capacity And Its Relationship With Cardiac Performance In Patients With T2D And Heart Failure

Abstract Disclosure: Y. Qin: None. N.D. Sanchez: None. A.J. Moody: None. F.M. Acosta: None. S. Neppala: None. M. Brown: None. H. Honka: None. B. Todd: None. L.A. Cruz Moreno: None. A.R. Stepanenko: None. S.E. Espinoza: None. N. Musi: None. C. Triplitt: None. G. Clarke: None. E. Cersosimo: None. R.A. DeFronzo: None. C. Solis-Herrera: None. Cardioprotective benefits of SGLT2 inhibitors (SGLT2i) have been largely thought to be coupled to a physiologic increase in plasma ketones, with much interest in the role of adaptive changes in cardiac fuel source in subjects with T2D and HF. Given the changes in the global dynamics of bioenergetics with SGLT2i, and the proven pleiotropic effects of ketone bodies, suggest that, in addition to their cardioprotective function, SGLT2i may influence other organ systems. In particular, how skeletal muscle (SkM), or cardiopulmonary function, respond to these global bioenergetics changes remains largely unknown. A pilot randomized-controlled clinical study was designed to examine the effects of SGLT2i on SkM bioenergetics (31P MRS), &amp; cardiopulmonary function (CPET), and its association with left ventricular cardiac function (MRI). Six subjects (Age=59±2.6, BMI=33.3±1.1, A1c=7.1±0.3) with T2D and HF (&amp;lt;50%) were randomized empagliflozin 25mg/day (SGLT2i) vs. placebo (control) in a 2:1 fashion for 12 weeks. Imaging and clinical evaluations were performed pre- and post-intervention. The SGLT2i group improved EF (28.7 vs. 38.8, p=0.1). SkM 31P MRS at rest, measuring the relative intracellular concentrations of high-energy metabolites of phospholipid breakdown, reduced with SGLT2i, suggesting better energy utilization by the SkM. 31P MRS-after exercise, showed significant improvements in SkM oxidative capacity (KPCR*[PCr], 0.6 to 0.8, p=0.03), with SGLT2i.During CPET testing, the ventilatory anaerobic threshold (VT), with SGLT2i, showed a significant (p=0.05) increase in VT time, suggesting an increase in the time in aerobiosis in these subjects. The minute ventilation-to-carbon dioxide output slope (a strong predictor of cardiopulmonary complications/death) was improved in the SGLT2i group vs. placebo, which could be associated with the CV benefit observed with these agents. Additionally, patient self-reported outcomes (Promis) showed a trend of improvement in the SGLT2i group. In summary, we demonstrate novel and exciting preliminary findings that in patients with T2D &amp; HF, SGLT2i-associated benefits are not isolated to the heart and may also expand to the SkM, including improved oxidative capacity, energy utilization, and SkM recovery post-exercise. With improvements in HF prognostic markers and patient self-reported outcomes. These original findings may represent novel mechanisms contributing to the cardiac benefits of SGLT2i. Presentation: Friday, June 16, 2023

98-LB: Effects of SGLT2 Inhibition on Skeletal Muscle Bioenergetics and Myocellular Lipids in Patients with T2D and HFrEF

Background: The CV benefits of SGLT2i are well established. However, how skeletal muscle (SkM) bioenergetics respond to SGLT2i in T2D and HFrEF remains largely unknown. Objective: To explore the effects of empagliflozin on SkM bioenergetics (phosphorus metabolites &amp; myocellular lipid content) at rest and post-exercise (31P &amp; 1H MRS) and cardiac function (MRI). Methods: Subjects with T2D &amp; HFrEF (&amp;lt;40%) (n=6) were randomized 2:1 to empagliflozin 25mg (SGLT2i) or placebo for 12 wks (Age=59±2.6, BMI=33.3±1.1, A1c=7.1±0.3, EF 28±4%). A cardiac MRI, &amp; static/dynamic 31P &amp; 1H SkM by MRS, were performed before &amp; after treatment. Results: In the empagliflozin group, SkM 31P MRS at rest, showed decrease in phosphodiesterase [PDE]. 31P MRS post-exercise, showed significant improvement in Phosphocreatinine (PCr) recovery, expressed by the K value. 1H MRS showed a reduction of saturated intramyocellular lipids (IMCL-CH2:CH3 ratio). Conclusion: Empagliflozin in subjects with T2D and HFrEF had beneficial effects in SkM energy utilization and muscle recovery post-exercise as determined by a decrease in PDE and increase in K value. Additionally, empagliflozin decreased saturated IMCL, which could be expected to improve mitochondrial function and energy utilization. If similar findings were to occur in cardiac muscle, this could provide a novel mechanism for the beneficial CV effects of SGLT2i. Disclosure Y. Qin: None. N. D. Sanchez: None. A. Moody: None. F. M. Acosta: None. S. Neppala: None. M. Brown: None. H. Honka: None. L. A. Cruz Moreno: None. C. L. Triplitt: Speaker's Bureau; Novo Nordisk. G. D. Clarke: None. E. Cersosimo: None. R. A. DeFronzo: Speaker's Bureau; AstraZeneca. Advisory Panel; AstraZeneca, Bayer Inc., Boehringer-Ingelheim, Novo Nordisk. Research Support; AstraZeneca, Boehringer-Ingelheim, Merck &amp; Co., Inc. C. Solis-Herrera: None. Funding Doris Duke Charitable Foundation; Voelcker Foundation; National Institutes of Health

Combined effect of high-fat, high-sugar diet and volumetric muscle loss injury on skeletal muscle bioenergetics, pyruvate dehydrogenase activity and post-translational regulation

INTRODUCTION: Volumetric muscle loss (VML) injury due to trauma or surgery cannot fully rejuvenate muscle mass and function, resulting in pathologic comorbidities, including alteration in whole-body metabolism, and long-term disability. Western diets (WD), i.e., high-fat, high-sugar diets, are associated with metabolic stress in the skeletal muscle because of the excessive fuel supplies regardless of energy demand. The objective of this study was to determine the extent to which WD affects metabolic function following a VML injury, and to interrogate enzyme kinetics as potential mechanistic contributors if metabolic dysfunction is present. METHODS: Male C57BL/6 mice (N=35) were randomized into four groups: Normal Chow (NC), WD, VML, and VML+WD. At age 12 weeks, VML groups underwent unilateral VML surgery to the plantar flexors (gastrocnemius, plantaris, soleus). WD groups received a 60% high-fat diet plus 11% high-fructose corn syrup for 8 weeks ad libitum, and diet was started at age 12 weeks also. Mitochondrial function was assessed by oxygen consumption rate and electron conductance (efficiency of electron flow) in permeabilized gastrocnemius muscle fibers using carbohydrate substrate glutamate/malate; enzyme kinetic function included citrate synthase (CS) and pyruvate dehydrogenase (PDH); PDH post-translational regulation included immunoblots for PDH kinase 4 (PDK4), PDH phosphatase (PDP), total PDH, phospho-PDHser293. Two-way ANOVA was used to detect significant interaction effects between diet and injury, or in the absence of a significant interaction, the main effects of diet or injury. RESULTS: Mice on WD had 51% greater body mass compared to mice on NC (p&lt;0.001), independent of injury and worse blood glucose regulation (ipGTT 83% higher in WD groups compared to NC groups, irrespective of injury, p&lt;0.001). There were significant interaction effects between diet and injury for permeabilized muscle fiber maximal JO2 (p=0.014) and conductance (p=0.027). Especially, the VML+WD group had 48% lower maximal JO2, and 47% reduced conductance compared to the VML group. PDH enzyme activity was 20% less in WD groups, independent of injury (p&lt;0.001), and 24% lower in VML-injured groups, independent of diets (p&lt;0.001). CS activity was 23% greater in WD groups compared to NC groups, regardless of injury (p=0.005). WD had 48% greater phospho-to-total PDH at the inhibitor site ser293 compared to NC groups, irrespective of injury (p=0.041). CONCLUSIONS: PDH plays an important role in glucose-dependent NADH-linked mitochondrial function as it converts glycolysis end-product pyruvate into acetyl-CoA for Krebs cycle entry. This study demonstrates WD exacerbates carbohydrate-supported mitochondrial function after VML injury. PDH regulation and enzymatic function may influence this phenomenon and future research is required to further define the cellular mechanisms. W81XWH-20-1-0885 to JAC and SMG, R01-AR078903 to JAC and SMG This is the full abstract presented at the American Physiology Summit 2023 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.

Bisphenol S reduces locomotor performance and modifies muscle protein levels but not mitochondrial bioenergetics in adult zebrafish

Human activity has now introduced novel chemicals into most aquatic ecosystems. Endocrine-disrupting compounds originating from plastic pollution and manufacture can have pronounced biological effects by disrupting hormone-mediated processes. Bisphenol A (BPA) is one of the most commonly produced endocrine-disrupting compounds, which interferes with signalling by a broad range of hormones. In recognition of its potentially harmful effects, BPA is being replaced by substitutes such as bisphenol S (BPS). However, toxicological studies revealed that BPS too can bind to hormone receptors and disrupt signalling, particularly of thyroid hormone. The aim of this study was to test whether BPS exposure impacts locomotor performance and muscle function in zebrafish (Danio rerio). Locomotor performance depends on thyroid hormone signalling, and it is closely related to fitness so that its disruption can have negative ecological and evolutionary consequences. BPS exposure of 15 μg l−1 [∼60 nM] and 30 μg l−1 (but not 60 μg l−1) decreased sustained swimming performance (Ucrit), but not sprint speed. In a fully factorial design, we show that living in flowing water increased Ucrit compared to a still water control, and that BPS reduced Ucrit under both conditions but did not eliminate the training effect. In a second factorial experiment, we show that BPS did not affect mitochondrial bioenergetics in skeletal muscle (state 3 and 4 rates, respiratory control ratios, ROS production), but that induced hypothyroidism decreased state 3 and 4 rates of respiration. However, both hypothyroidism and BPS exposure decreased activity of AMP-activated protein kinase (pAMPK:total AMPK) but increased protein levels of myocyte enhancer factor 2, and slow and fast myosin heavy chains. Our data indicate that BPS is not a safe alternative for BPA and that exposure to BPS can have ecological consequences, which are likely to be at least partly mediated via thyroid hormone disruption.

Effects of hydroxyurea on skeletal muscle energetics and force production in a sickle cell disease murine model.

Hydroxyurea (HU) is commonly used as a treatment for patients with sickle cell disease (SCD) to enhance fetal hemoglobin production. This increased production is expected to reduce anemia (which depresses oxygen transport) and abnormal Hb content alleviating clinical symptoms such as vaso-occlusive crisis and acute chest syndrome. The effects of HU on skeletal muscle bioenergetics in vivo are still unknown. Due to the beneficial effects of HU upon oxygen delivery, improved skeletal muscle energetics and function in response to a HU treatment have been hypothesized. Muscle energetics and function were analyzed during a standardized rest-exercise-recovery protocol, using 31P-magnetic resonance spectroscopy in Townes SCD mice. Measurements were performed in three groups of mice: one group of 2-mo-old mice (SCD2m, n = 8), another one of 4-mo-old mice (SCD4m, n = 8), and a last group of 4-mo-old mice that have been treated from 2 mo of age with HU at 50 mg/kg/day (SCD4m-HU, n = 8). As compared with SCD2m mice, SCD4m mice were heavier and displayed a lower acidosis. As lower specific forces were developed by SCD4m compared with SCD2m, greater force-normalized phosphocreatine consumption and oxidative and nonoxidative costs of contraction were also reported. HU-treated mice (SCD4m-HU) displayed a significantly higher specific force production as compared with untreated mice (SCD4m), whereas muscle energetics was unchanged. Overall, our results support a beneficial effect of HU on muscle function.NEW & NOTEWORTHY Our results highlighted that force production decreases between 2 and 4 mo of age in SCD mice thereby indicating a decrease of muscle function during this period. Of interest, HU treatment seemed to blunt the observed age effect given that SCD4m-HU mice displayed a higher specific force production as compared with SCD4m mice. In that respect, HU treatment would help to maintain a higher capacity of force production during aging in SCD.

Resistin impairs mitochondrial homeostasis via cyclase-associated protein 1-mediated fission, leading to obesity-induced metabolic diseases

ObjectiveOne of the suggested mechanisms of obesity-induced insulin resistance is mitochondrial dysfunction in target tissues such as skeletal muscle. In our study, we examined whether resistin, an adipokine associated with obesity-mediated insulin resistance, induced metabolic disorders by impairing mitochondrial homeostasis. MethodsThe morphology and function of mitochondria of skeletal muscle were examined in resistin-knockout and humanized resistin mice that were subjected to high-fat diet for 3 months. Morphology was examined by transmission electron microscopy. Mitochondria bioenergetics of skeletal muscle were evaluated using a Seahorse XF96 analyzer. Human skeletal myoblasts were used for in vitro studies on signaling mechanisms in responses to resistin. ResultsA high-fat diet in humanized resistin mice increased fragmented and shorter mitochondria in the skeletal muscle, whereas resistin-knockout mice had healthy normal mitochondria. In vitro studies showed that human resistin treatment impaired mitochondrial homeostasis by inducing mitochondrial fission, leading to a decrease in ATP production and mitochondrial dysfunction. Induction of mitochondrial fission by resistin was accompanied by increased formation of mitochondria-associated ER membranes (MAM). At the same time, resistin induced up-regulation of the protein kinase A (PKA) pathway. This activation of PKA induced phosphorylation of Drp1 at serine 616, leading to Drp1 activation and subsequent induction of mitochondrial fission. The key molecule that mediated human resistin-induced mitochondrial fission was adenylyl cyclase-associated protein 1 (CAP1), which was reported as a bona fide receptor for human resistin. Moreover, our newly developed biomimetic selective blocking peptide could repress human resistin-mediated mitochondrial dysfunction. High-fat diet-fed mice showed lower exercise capacity and higher insulin resistance, which was prevented by a novel peptide to block the binding of resistin to CAP1 or in the CAP1-knockdown mice. ConclusionsOur study demonstrated that human resistin induces mitochondrial dysfunction by inducing abnormal mitochondrial fission. This result suggests that the resistin-CAP1 complex could be a potential therapeutic target for the treatment of obesity-related metabolic diseases such as diabetes and cardiometabolic diseases.

Direct Effects of Vitamin D Supplementation on Ultramarathon-Induced Changes in Kynurenine Metabolism.

In humans, most free tryptophan is degraded via kynurenine pathways into kynurenines. Kynurenines modulate the immune system, central nervous system, and skeletal muscle bioenergetics. Consequently, kynurenine pathway metabolites (KPMs) have been studied in the context of exercise. However, the effect of vitamin D supplementation on exercise-induced changes in KPMs has not been investigated. Here, we analyzed the effect of a single high-dose vitamin D supplementation on KPMs and tryptophan levels in runners after an ultramarathon. In the study, 35 amateur runners were assigned into two groups: vitamin D supplementation group, administered 150,000 IU vitamin D in vegetable oil 24 h before the run (n = 16); and control (placebo) group (n = 19). Blood was collected for analysis 24 h before, immediately after, and 24 h after the run. Kynurenic, xanthurenic, quinolinic, and picolinic acids levels were significantly increased after the run in the control group, but the effect was blunted by vitamin D supplementation. Conversely, the decrease in serum tryptophan, tyrosine, and phenylalanine levels immediately after the run was more pronounced in the supplemented group than in the control. The 3-hydroxy-l-kynurenine levels were significantly increased in both groups after the run. We conclude that vitamin D supplementation affects ultramarathon-induced changes in tryptophan metabolism.

Calorie Restriction Rescues Mitochondrial Dysfunction in Adck2-Deficient Skeletal Muscle.

ADCK2 haploinsufficiency-mediated mitochondrial coenzyme Q deficiency in skeletal muscle causes mitochondrial myopathy associated with defects in beta-oxidation of fatty acids, aged-matched metabolic reprogramming, and defective physical performance. Calorie restriction has proven to increase lifespan and delay the onset of chronic diseases associated to aging. To study the possible treatment by food deprivation, heterozygous Adck2 knockout mice were fed under 40% calorie restriction (CR) and the phenotype was followed for 7 months. The overall glucose and fatty acids metabolism in muscle was restored in mutant mice to WT levels after CR. CR modulated the skeletal muscle metabolic profile of mutant mice, partially rescuing the profile of WT animals. The analysis of mitochondria isolated from skeletal muscle demonstrated that CR increased both CoQ levels and oxygen consumption rate (OCR) based on both glucose and fatty acids substrates, along with mitochondrial mass. The elevated aerobic metabolism fits with an increase of type IIa fibers, and a reduction of type IIx in mutant muscles, reaching WT levels. To further explore the effect of CR over muscle stem cells, satellite cells were isolated and induced to differentiate in culture media containing serum from animals in either ad libitum or CR diets for 72 h. Mutant cells showed slower differentiation alongside with decreased oxygen consumption. In vitro differentiation of mutant cells was increased under CR serum reaching levels of WT isolated cells, recovering respiration measured by OCR and partially beta-oxidation of fatty acids. The overall increase of skeletal muscle bioenergetics following CR intervention is paralleled with a physical activity improvement, with some increases in two and four limbs strength tests, and weights strength test. Running wheel activity was also partially improved in mutant mice under CR. These results demonstrate that CR intervention, which has been shown to improve age-associated physical and metabolic decline in WT mice, also recovers the defective aerobic metabolism and differentiation of skeletal muscle in mice caused by ADCK2 haploinsufficiency.

D-galactose-induced aging in rats - The effect of metformin on bioenergetics of brain, skeletal muscle and liver.

Chronic D-galactose administration induces accelerated aging in rodents. The aim of the study was to find by in vivo31P MRS suitable markers of early stages of brain degeneration on this metabolic model in rats. Additionally, we studied the therapeutic effect of antidiabetic drug metformin. The study has been extended by in vitro determination of mitochondrial function in brain, skeletal muscle and liver mitochondria, oxidative stress parameter thiobarbituric acid reactive substances (TBARS), and lipophilic antioxidants levels. In vivo31P MRS revealed lower intracellular pH (pHi) and lower inorganic phosphate to ATP ratio (Pi/ATP), with higher index of oxidative phosphorylation - phosphocreatine (PCr) to Pi ratio - in brain of rats chronically administered with D-galactose. The function of brain mitochondria was not affected. Administration of metformin diminished changes in brain pHi and plasma TBARS. The function of skeletal muscle mitochondria and their coenzyme Q (CoQ) content were considerably reduced after D-galactose administration. Metformin administered simultaneously with D-galactose did not prevent these changes. The results of in vivo31P MRS revealed evidence of early stage of neurodegeneration that may indicate pre-inflammation. Our data show different susceptibility of brain, skeletal muscle, and liver to the chronic exposure to D-galactose and metformin. The D-galactose model presented in the literature as a model for "age-related dementia" had much more devastating effects on skeletal muscle than on the brain.

1369-P: The Differential Effects of Estrogen on Determinants of Skeletal Muscle Bioenergetics with a High-Fat, High-Sucrose Diet in Rats

Estrogen is a powerful, beneficial regulator of skeletal muscle mitochondria. Premenopausal women with type 2 diabetes (T2D) have relatively greater complications associated with their T2D compared with the effect of the disease in men. We hypothesize that this impact of T2D in women is in part due to the impairment of estrogen-mediated regulation of skeletal muscle mitochondrial content and function. To explore the interaction between estrogen, diabetes and mitochondrial biogenesis in a rat model, 4-week-old, female Wistar Rats were fed a chow or a high fat/high sugar diet (HFHS) . At 8 weeks all mice underwent an ovariectomy (OVX) and randomized to estradiol (E2) replacement or none. One week prior to sacrifice, deuterium oxide was administered to determine skeletal muscle mitochondrial biogenesis. OVX +/- E2, animals were sacrificed 6 weeks post-randomization. Endpoints: body weight, gonadal fat mass, blood glucose and insulin levels, and gastrocnemius (mitochondrial biogenesis and function) . OVX+E2 rats had lower body mass compared with OVX (P = 0.0028) . HFHS fed rats had greater relative fat mass independent of E2 status (P = 0.0007) , and the OVX+E2 fed the HFHS diet were hyperglycemic (P = 0.00for the diet x E2 interaction) . State 3 mitochondrial respiration with carbohydrate-linked substrates was elevated in chow fed animals with E2, and this response was absent in HFHS animals (P = 0.0138 for the diet x E2 interaction) . Contrary to our hypothesis, there was no effect of diet or E2 on mitochondrial biogenesis measured with deuterium oxide (P &amp;gt; 0.4) . These data support the hypothesis that, in the context of a HFHS diet, the beneficial effect of E2 on skeletal muscle mitochondrial function is impaired. However, mitochondrial biogenesis does not appear to mediate this interaction of diet and E2. Future studies will focus on the E2-mediated regulation of mitochondrial quality to determine their role in the impairment of mitochondrial function. Disclosure N.A.Hulett: None. S.Hull: None. L.Knaub: None. G.Pott: None. B.F.Miller: None. J.Reusch: Advisory Panel; Medtronic. R.L.Scalzo: None. Funding Veterans Affairs (BX004533)

Skeletal Muscle Deoxygenation Amplitude, Rather Than Splenic Emptying Contributes to Higher V̇O2max. During Supine Cycling in Healthy Active Men

The aim of the present study was to investigate whether greater splenic emptying or higher skeletal muscle deoxygenation amplitude (determined by near‐infrared spectroscopy, NIRS) contributes to higher V̇O2 max. during supine cycling. We hypothesized that the reduction in splenic volume, and subsequent manipulations of O2 delivery by blood ejected from the spleen, would not contribute to higher V̇O2max. during supine cycling, because this transient increase in circulating red blood cells (RBC’s) would be insufficient to increase the O2 storage capacity in the blood. Rather, O2 uptake during supine cycling in healthy subjects is expected to be limited, at least in part, by skeletal muscle bioenergetics. Here, fourteen healthy young individuals completed all study procedures. On three separate days they underwent a medical examination, supine V̇O2 max. test, and three step‐transitions from 20 W to a moderate‐intensity power output equivalent to V̇O2 uptake at 90% gas exchange threshold. During these step‐transitions, pulmonary V̇O2, NIRS of the vastus lateralis (VL), and cardiovascular responses (via Finapres) were measured continuously. In parallel, minute‐by‐minute ultrasound measurements of the spleen were performed. Blood samples were taken before and immediately after the step‐transition cycling. Mean V̇O2 max. was 46.5±6.5 mL·kg·min‐1. In response to supine step‐transition cycling, spleen volume was significantly reduced (by ~38%, p=.001). Both hematocrit and hemoglobin concentration increased by ~4%, after exercise cessation. There was no correlation between: i)spleen volume at rest, ii) changes in spleen volume (%), iii) hematocrit at rest and V̇O2 max. However, a linear, near‐significant correlation was observed between VL deoxygenation amplitude and V̇O2 max. Apparently, individuals with a higher V̇O2 max. are capable of greater O2 extraction from the superficial knee extensors, whereas in parallel, greater splenic emptying does not correlate with higher V̇O2 max, regardless of the subsequent release of erythrocytes. Therefore, it is reasonable to suggest that maximal O2 utilization during supine cycling in healthy young men is limited, in part, by skeletal muscle bioenergetics.ReferencesHolmström, PK, Karlsson Ö, Lindblom H, McGawley K, &amp; Schagatay, EK. (2021). Enhanced splenic volume and contraction in elite endurance athletes. J Appl Physiol, 131(2), 474‐486, DOI: 10.1152/japplphysiol.01066.2020;Zubac, D, Obad, A, Bosnjak, A, Zec, M, Ivancev, V, Valic, Z. (2021). Spleen emptying does not correlate with faster oxygen kinetics during a step‐transition supine cycling. Appl Physiol Nutr Metab. Accepted for publication in Jun 24. doi: 10.1139/apnm‐2021‐0294.2021.

Exercise and Creatine Supplementation to Augment the Adaptation of Exercise Training Among Breast Cancer Survivors Completing Chemotherapy: Protocol for an Open-label Randomized Controlled Trial (the THRIVE Study).

BackgroundIn breast cancer survivors, chemotherapy-induced muscle loss has been shown to be attenuated with structured resistance exercise. Creatine supplementation can increase bioenergetics in skeletal muscle, which helps to improve overall strength and endurance and reduce muscular fatigue. Therefore, we hypothesize that adding creatinine supplementation to exercise training will accelerate improvements in strength, endurance, and bioenergetics in breast cancer survivors.ObjectiveThe primary objective is to determine the effects of combining creatine supplementation with exercise on modulating strength and physical function in breast cancer survivors by comparing these effects to those of exercise alone. The secondary objectives are to determine if creatine supplementation and exercise can increase the intramuscular storage of creatine and improve body composition by comparing this intervention to exercise alone.MethodsWe aim to test our hypothesis by conducting an open-label randomized controlled trial of 30 breast cancer survivors who have completed chemotherapy within 6 months of enrollment. Eligible participants will be equally randomized (1:1) to either a creatine and exercise group or an exercise-only group for this 12-week intervention. Individuals who are randomized to receive creatine will be initially dosed at 20 g per day for 7 days to boost the availability of creatine systemically. Thereafter, the dose will be reduced to 5 g per day for maintenance throughout the duration of the 12-week protocol. All participants will engage in 3 center-based exercise sessions, which will involve completing 3 sets of 8 to 12 repetitions on chest press, leg press, seated row, shoulder press, leg extension, and leg curl machines. The primary outcomes will include changes in strength, body composition, and physical function in breast cancer survivors. The secondary outcomes will be intramuscular concentrations of creatine and adenosine triphosphate in the vastus lateralis, midthigh cross-sectional area, and quality of life.ResultsAs of October 2021, a total of 9 patients have been enrolled into the study. No unexpected adverse events have been reported.ConclusionsCreatine is being studied as a potential agent for improving strength, endurance, and bioenergetics in breast cancer survivors following chemotherapy. The findings from our trial may have future implications for supporting breast cancer survivors in reversing the muscle loss experienced during chemotherapy and improving their physical function and quality of life.Trial RegistrationClinicalTrials.gov NCT04207359; https://clinicaltrials.gov/ct2/show/NCT04207359International Registered Report Identifier (IRRID)PRR1-10.2196/26827

Passing on the exercise baton: What can endocrine patients learn from elite athletes?

As elite athletes demonstrate through the Olympic motto ‘Citius, Altius, Fortius‐ Communiter’, new performance records are driven forward by favourable skeletal muscle bioenergetics, cardiorespiratory, and endocrine system adaptations. At a recreational level, regular physical activity is an effective nonpharmacological therapy in the treatment of many endocrine conditions. However, the impact of physical exercise on endocrine function and how best to incorporate exercise therapy into clinical care are not well understood. Beyond the pursuit of an Olympic medal, elite athletes may therefore serve as role models for showcasing how exercise can help in the management of endocrine disorders and improve metabolic dysfunction. This review summarizes research evidence for clinicians who wish to understand endocrine changes in athletes who already perform high levels of activity as well as to encourage patients to exercise more safely. Herein, we detail the upper limits of athleticism to showcase the adaptability of human endocrine‐metabolic‐physiological systems. Then, we describe the growing research base that advocates the importance of understanding maladaptation to physical training and nutrition in males and females; especially the young. Finally, we explore the impact of physical activity in improving some endocrine disorders with guidance on how lessons can be taken from athletes training and incorporated into strategies to move more people more often.

Microproteins in skeletal muscle: hidden keys in muscle physiology.

Recent advances in the transcriptomics, translatomics, and proteomics have led us to the exciting new world of functional endogenous microproteins. These microproteins have a small size and are derived from small open reading frames (smORFs) of RNAs previously annotated as non‐coding (e.g. lncRNAs and circRNAs) as well as from untranslated regions and canonical mRNAs. The presence of these microproteins reveals a much larger translatable portion of the genome, shifting previously defined dogmas and paradigms. These findings affect our view of organisms as a whole, including skeletal muscle tissue. Emerging evidence demonstrates that several smORF‐derived microproteins play crucial roles during muscle development (myogenesis), maintenance, and regeneration, as well as lipid and glucose metabolism and skeletal muscle bioenergetics. These microproteins are also involved in processes including physical activity capacity, cellular stress, and muscular‐related diseases (i.e. myopathy, cachexia, atrophy, and muscle wasting). Given the role of these small proteins as important key regulators of several skeletal muscle processes, there are rich prospects for the discovery of new microproteins and possible therapies using synthetic microproteins.

1189-P: Ankyrin-B Modulates the Integrity and Bioenergetic Capacity of Skeletal Muscle Fibers

Ankyrin-B (AnkB) is a cytoskeletal protein that positions and stabilizes specialized membrane-associated protein complexes. AnkB also associates with organelles and facilitates their dynamics across cell types. AnkB variants have been linked to higher risk for obesity and type 2 diabetes (T2D) in humans and mice. In skeletal muscle (SKM), AnkB localizes to costameres and acts as a scaffold to β-dystroglycan/dystrophin complexes. This protein complex has been demonstrated to be essential for SKM integrity and exercise injury protection. However, besides this structural role, our findings suggest that AnkB associates with mitochondria in SKM and likely plays important roles in SKM bioenergetics. We found that non-obese young mice lacking AnkB solely in SKM (SKM-AnkB KO) develop early signs of myofibrillar disorganization and fibrosis and display reduced physical activity without changes in body weight, fasting glucose levels, or peripheral insulin response. In contrast, SKM-AnkB KO mice are more susceptible to the metabolic effects of a HFD, manifested as lower insulin sensitivity and further reductions in physical activity. Our findings suggest that loss of myofibril organization synergizes with changes in mitochondrial function to worsen SKM bioenergetics and insulin action. These physiological alterations are in agreement with our RNA-seq and proteomics studies, which implicate AnkB in the regulation of SKM oxidative capacity, protein translation, and cellular responses to stress and nutrient availability. We will discuss our ongoing efforts to uncover the mechanistic basis of these metabolic impairments cause by AnkB deficits. Disclosure K. Voos: None. J. Tzeng: None. D. Lorenzo: None. Funding American Diabetes Association (1-19-JDF-081 to D.L.)

Contextualizing the biological relevance of standardized high-resolution respirometry to assess mitochondrial function in permeabilized human skeletal muscle.

AimThis study sought to provide a statistically robust reference for measures of mitochondrial function from standardized high‐resolution respirometry with permeabilized human skeletal muscle (ex vivo), compare analogous values obtained via indirect calorimetry, arterial‐venous O2 differences and 31P magnetic resonance spectroscopy (in vivo) and attempt to resolve differences across complementary methodologies as necessary.MethodsData derived from 831 study participants across research published throughout March 2009 to November 2019 were amassed to examine the biological relevance of ex vivo assessments under standard conditions, ie physiological temperatures of 37°C and respiratory chamber oxygen concentrations of ~250 to 500 μmol/L.ResultsStandard ex vivo‐derived measures are lower (Z ≥ 3.01, P ≤ .0258) en masse than corresponding in vivo‐derived values. Correcting respiratory values to account for mitochondrial temperatures 10°C higher than skeletal muscle temperatures at maximal exercise (~50°C): (i) transforms data to resemble (Z ≤ 0.8, P > .9999) analogous yet context‐specific in vivo measures, eg data collected during maximal 1‐leg knee extension exercise; and (ii) supports the position that maximal skeletal muscle respiratory rates exceed (Z ≥ 13.2, P < .0001) those achieved during maximal whole‐body exercise, e.g. maximal cycling efforts.ConclusionThis study outlines and demonstrates necessary considerations when actualizing the biological relevance of human skeletal muscle respiratory control, metabolic flexibility and bioenergetics from standard ex vivo‐derived assessments using permeabilized human muscle. These findings detail how cross‐procedural comparisons of human skeletal muscle mitochondrial function may be collectively scrutinized in their relationship to human health and lifespan.