Skeletal Muscle Mitochondrial Function Research Articles

The Impact of SRT2104 on Skeletal Muscle Mitochondrial Function, Redox Biology, and Loss of Muscle Mass in Hindlimb Unloaded Rats.

Mechanical unloading during microgravity causes skeletal muscle atrophy and impairs mitochondrial energetics. The elevated production of reactive oxygen species (ROS) by mitochondria and Nox2, coupled with impairment of stress protection (e.g., SIRT1, antioxidant enzymes), contribute to atrophy. We tested the hypothesis that the SIRT1 activator, SRT2104 would rescue unloading-induced mitochondrial dysfunction. Mitochondrial function in rat gastrocnemius and soleus muscles were evaluated under three conditions (10 days): ambulatory control (CON), hindlimb unloaded (HU), and hindlimb-unloaded-treated with SRT2104 (SIRT). Oxidative phosphorylation, electron transfer capacities, H2O2 production, and oxidative and antioxidant enzymes were quantified using high-resolution respirometry and colorimetry. In the gastrocnemius, (1) integrative (per mg tissue) proton LEAK was lesser in SIRT than in HU or CON; (2) intrinsic (relative to citrate synthase) maximal noncoupled electron transfer capacity (ECI+II) was lesser, while complex I-supported oxidative phosphorylation to ECI+II was greater in HU than CON; (3) the contribution of LEAK to ECI+II was greatest, but cytochrome c oxidase activity was lowest in HU. In both muscles, H2O2 production and concentration was greatest in SIRT, as was gastrocnemius superoxide dismutase activity. In the soleus, H2O2 concentration was greater in HU compared to CON. These results indicate that SRT2104 preserves mitochondrial function in unloaded skeletal muscle, suggesting its potential to support healthy muscle cells in microgravity by promoting necessary energy production in mitochondria.

305-OR: Short-Term Hyperglycemia Impacts Mouse Skeletal Muscle in a Sex-Specific Manner

Cardiorespiratory Fitness (CRF) a universal predictor of cardiovascular and all-cause mortality, is lower in people with diabetes. Skeletal muscle is a key determinant of CRF, in particular mitochondrial content, function and oxygen extraction. Hyperglycemia is implicated in the dysfunction of microvascular blood flow. Our previous work demonstrated lower mitochondrial density/fiber and capillary mean flow velocity (MFV) with 4 weeks of hyperglycemia in males and females. Treadmill running resulted in greater capillary MFV and mitochondrial density in only hyperglycemic females. We hypothesize that along with alterations in mitochondrial density and blood flow, there is a disruption in skeletal muscle mitochondrial function with hyperglycemia, and that these parameters will respond to nitrite (NO2-) treatment in a sex-specific manner. We used a model of short-term hyperglycemia with tamoxifen inducible β-cell deletion of glucokinase. Two weeks after induction, blood flow in the gastrocnemius (gastroc) was measured using intravital microscopy, and the gastroc was collected from male (M) and female (F) mice with blood glucose >400mg/dl (HG) and euglycemic controls (EG). A subset of mice received NO2- treatment for 1-2 weeks prior to gastroc measurements. Immunofluorescence imaging of gastroc were analyzed for expression of COX1 (mitochondrial marker), Dystrophin (muscle fiber sarcolemma boundary), and CD31 (capillary marker). Mitochondrial respiration was measured in gastroc fibers using Oroboros O2k. Mitochondrial respiration was lower in HG compared to EG (p<0.0009), but only respiration in M appeared to respond to NO2- treatment (p=0.0252). No difference was observed in mitochondrial density in EG versus HG. Capillary MFV was greater with HG and mitigated by NO2-treatment. NO2- targets mitochondrial function by improving capillary blood flow, but only in males. Our combined data sets suggest HG-associated mitochondrial defects need to be treated in a sex-specific manner. Disclosure N.A.Hulett: None. L.Knaub: None. G.Pott: None. D.Ramirez: None. A.Johnston: None. R.L.Scalzo: None. J.E.B.Reusch: Advisory Panel; Medtronic. Funding U.S. Department of Veterans Affairs (BX002046, CX001532); National Institutes of Health (P30DK116073, 5T32AG000279-20)

265-LB: Human Skeletal Muscle Mitochondrial Dynamics across the Insulin-Sensitivity Spectrum

Introduction: There is immense dispute as to whether perturbations in skeletal muscle mitochondrial function contribute to the onset and progression of type 2 diabetes (T2D). The purpose of this study was to examine differences in mitochondrial dynamics, structure, and energetic function in humans across the spectrum of insulin sensitivity. Methods: 58 sedentary adults (37±12 years) were enrolled into one of three groups based upon the following criteria: (1) healthy weight without T2D (HW; BMI: 22.6±1.8 kg/m2 and HbA1c: 5.0±1.1 %); (2) overweight/obesity without T2D (Ov/Ob; BMI: 32.6±3.3 kg/m2 and HbA1c: 5.6±0.4 %); or (3) overweight/obesity with T2D (T2D; BMI: 36.1±6.5 kg/m2 and HbA1c: 6.9±0.9 %). Participants underwent a 3-day inpatient stay consisting of body composition (DXA), aerobic capacity (VO2MAX), and insulin sensitivity (hyperinsulinemic euglycemic clamp). Prior to insulin sensitivity testing, a skeletal muscle biopsy was obtained for determination of mitochondrial dynamics (Western blot), DNA content (qPCR), ultrastructure (electron microscopy), and respiratory capacity (respirometry). Comparisons were made using a one-way ANOVA with contrasts. Results: Insulin sensitivity and aerobic capacity were lower in Ov/Ob and T2D compared to HW. Markers of mitochondrial fission were higher in T2D (Drp1Ser616, MiD49), and fusion lower in T2D and Ov/Ob (Mfn2). The mitophagy marker Parkin was higher in T2D only while Pink1 was lower in T2D relative to Ov/Ob but not HW. The autophagy marker LC3II was higher in Ov/Ob. Mitochondrial content was lower in Ov/Ob and T2D relative to HW. Mitochondrial respiratory capacity was similar between groups. Conclusions: T2D is associated with heightened expression of proteins required for mitochondrial quality control and reduced mitochondrial volume despite intact respiratory function. These data support the notion that mitochondria adapt to progressive insulin resistance by increasing fragmentation to maintain bioenergetic capacity. Disclosure C. L. Axelrod: None. C. Fealy: Employee; Mission Therapeutics. C. L. Hoppel: None. J. P. Kirwan: None. W. S. Dantas: None. E. R. M. Zunica: None. K. Belmont: None. E. C. Heintz: None. G. Davuluri: None. J. T. Mey: None. M. Erickson: None. H. Fujioka: None. Funding National Institutes of Health (DK108089, GM104940)

Improving Mitochondrial Function in Skeletal Muscle Contributes to the Amelioration of Insulin Resistance by Nicotinamide Riboside.

High-fat diet (HFD)-induced insulin resistance (IR) in skeletal muscle is often accompanied by mitochondrial dysfunction and oxidative stress. Boosting nicotinamide adenine dinucleotide (NAD) using nicotinamide riboside (NR) can effectively decrease oxidative stress and increase mitochondrial function. However, whether NR can ameliorate IR in skeletal muscle is still inconclusive. We fed male C57BL/6J mice with an HFD (60% fat) ± 400 mg/kg·bw NR for 24 weeks. C2C12 myotube cells were treated with 0.25 mM palmitic acid (PA) ± 0.5 mM NR for 24 h. Indicators for IR and mitochondrial dysfunction were analyzed. NR treatment alleviated IR in HFD-fed mice with regard to improved glucose tolerance and a remarkable decrease in the levels of fasting blood glucose, fasting insulin and HOMA-IR index. NR-treated HFD-fed mice also showed improved metabolic status regarding a significant reduction in body weight and lipid contents in serum and the liver. NR activated AMPK in the skeletal muscle of HFD-fed mice and PA-treated C2C12 myotube cells and upregulated the expression of mitochondria-related transcriptional factors and coactivators, thereby improving mitochondrial function and alleviating oxidative stress. Upon inhibiting AMPK using Compound C, NR lost its ability in enhancing mitochondrial function and protection against IR induced by PA. In summary, improving mitochondrial function through the activation of AMPK pathway in skeletal muscle may play an important role in the amelioration of IR using NR.

Invasive and noninvasive markers of human skeletal muscle mitochondrial function.

Mitochondria are organelles that fuel cellular energy requirements by ATP formation via aerobic metabolism. Given the wide variety of methods to assess skeletal muscle mitochondrial capacity, we tested how well different invasive and noninvasive markers of skeletal muscle mitochondrial capacity reflect mitochondrial respiration in permeabilized muscle fibers. Nineteen young men (mean age: 24 ± 4 years) were recruited, and a muscle biopsy was collected to determine mitochondrial respiration from permeabilized muscle fibers and to quantify markers of mitochondrial capacity, content such as citrate synthase (CS) activity, mitochondrial DNA copy number, TOMM20, VDAC, and protein content for complex I-V of the oxidative phosphorylation (OXPHOS) system. Additionally, all participants underwent noninvasive assessments of mitochondrial capacity: PCr recovery postexercise (by 31 P-MRS), maximal aerobic capacity, and gross exercise efficiency by cycling exercise. From the invasive markers, Complex V protein content and CS activity showed the strongest concordance (Rc = 0.50 to 0.72) with ADP-stimulated coupled mitochondrial respiration, fueled by various substrates. Complex V protein content showed the strongest concordance (Rc = 0.72) with maximally uncoupled mitochondrial respiration. From the noninvasive markers, gross exercise efficiency, VO2max , and PCr recovery exhibited concordance values between 0.50 and 0.77 with ADP-stimulated coupled mitochondrial respiration. Gross exercise efficiency showed the strongest concordance with maximally uncoupled mitochondrial respiration (Rc = 0.67). From the invasive markers, Complex V protein content and CS activity are surrogates that best reflect skeletal muscle mitochondrial respiratory capacity. From the noninvasive markers, exercise efficiency and PCr recovery postexercise most closely reflect skeletal muscle mitochondrial respiratory capacity.

Skeletal Muscle Mitochondrial Respiration and Exercise Intolerance in Patients With Heart Failure With Preserved Ejection Fraction

The pathophysiology of exercise intolerance in patients with heart failure with preserved ejection fraction (HFpEF) remains incompletely understood. Multiple lines of evidence suggest that abnormal skeletal muscle metabolism is a key contributor, but the mechanisms underlying metabolic dysfunction remain unresolved. To evaluate the associations of skeletal muscle mitochondrial function using respirometric analysis of biopsied muscle fiber bundles from patients with HFpEF with exercise performance. In this cross-sectional study, muscle fiber bundles prepared from fresh vastus lateralis biopsies were analyzed by high-resolution respirometry to provide detailed analyses of mitochondrial oxidative phosphorylation, including maximal capacity and the individual contributions of complex I-linked and complex II-linked respiration. These bioenergetic data were compared between patients with stable chronic HFpEF older than 60 years and age-matched healthy control (HC) participants and analyzed for intergroup differences and associations with exercise performance. All participants were treated at a university referral center, were clinically stable, and were not undergoing regular exercise or diet programs. Data were collected from March 2016 to December 2017, and data were analyzed from November 2020 to May 2021. Skeletal muscle mitochondrial function, including maximal capacity and respiration linked to complex I and complex II. Exercise performance was assessed by peak exercise oxygen consumption, 6-minute walk distance, and the Short Physical Performance Battery. Of 72 included patients, 50 (69%) were women, and the mean (SD) age was 69.6 (6.1) years. Skeletal muscle mitochondrial function measures were all markedly lower in skeletal muscle fibers obtained from patients with HFpEF compared with HCs, even when adjusting for age, sex, and body mass index. Maximal capacity was strongly and significantly correlated with peak exercise oxygen consumption (R = 0.69; P < .001), 6-minute walk distance (R = 0.70; P < .001), and Short Physical Performance Battery score (R = 0.46; P < .001). In this study, patients with HFpEF had marked abnormalities in skeletal muscle mitochondrial function. Severely reduced maximal capacity and complex I-linked and complex II-linked respiration were associated with exercise intolerance and represent promising therapeutic targets.

O008 The impact of home-based exercise prehabilitation on skeletal muscle mitochondrial function in patients awaiting curative surgery for cancer

Abstract Introduction Cancer cachexia is associated with poor surgical outcomes, including increased length of stay, morbidity and mortality. Cachexia is a complex multi-faceted pathological process consistently associated with energy imbalance via hypermetabolism. Beyond this, pre-clinical animal models suggest mitochondrial dysfunction to be an important component of cachexia, although this is unconfirmed in humans. This study aimed to investigate the mitochondrial function of pre-surgical cancer patients, and the impact of exercise prehabilitation on this. Methods This study was approved by an NHS research ethics committee (IRAS: 275264). Male patients awaiting surgery with curative intent for colorectal and prostate cancer were eligible, with healthy volunteers recruited for comparison. Muscle biopsies of vastus lateralis were taken before and after 4-weeks home-based exercise (3x/wk). Mitochondrial oxidative phosphorylation (OXPHOS) was analysed using high-resolution respirometry (Oroboros Instruments). Results Eleven cancer patients and 6 healthy volunteers were recruited. Cancer patients had significantly lower maximal coupled (44.49pmol/(s*mg) vs. 74.81pmol/(s*mg), p=0.004) and uncoupled (55.82pmol/(s*mg) vs. 100.00pmol/(s*mg), p&amp;lt;0.001) OXPHOS capacity compared to healthy controls. Exercise training significantly increased maximal coupled (44.10pmol/(s*mg) vs. 54.64pmol/(s*mg), p=0.045) and uncoupled (56.20pmol/(s*mg) vs. 71.96pmol/(s*mg), p=0.001) OXPHOS capacity in this cancer cohort. Conclusion Declines in mitochondrial function appear to play a role in cancer cachexia. Short-term exercise training, in keeping with target timeframes for surgery (i.e., &amp;lt;31-days from decision-to-treat), appears to attenuate these declines. Further work is needed to determine if declines in mitochondrial function are causative or reactive, and to identify optimal exercise regimes to mitigate these declines.

Can exercise prevent the age‐related decline in adaptive homeostasis? Evidence across organisms and tissues

Can exercise prevent the age‐related decline in adaptive homeostasis? Evidence across organisms and tissues

Two Weeks of Nrf2 Activation Improves Maximal Mitochondrial Respiration in Older Adults with Lower Starting Values

Background: The impact of aging on skeletal muscle mitochondrial function, as assessed by maximal mitochondrial respiration (OXPHOS), is a developing field of research with no clear consensus. Older individuals often display a greater range of OXPHOS, compared to younger individuals, possibly reflecting heterogeneity in the aging process. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a transcription factor that plays a role in the transcription of genes involved in many pathways including the regulation of metabolism, inflammation, oxidative stress, and mitochondrial physiology. Since Nrf2 is downregulated with aging and significantly inactivated with sedentary behaviors, we hypothesized that activating this pathway with the nutraceutical PB125 would improve OXPHOS in older individuals with lower OXPHOS starting values. Methods: OXPHOS (CI&amp;II, State 3) was assessed in permeabilized muscle fibers via high-resolution respirometry (Oroboros, O2k) on samples biopsied from the vastus lateralis in 19 young (26 ± 5 years; 13 female) and 18 older (67 ± 7 years; 11 female) volunteers. Sixteen of the older individuals were then randomized to receive a two-week supplementation of either PB125 (n = 10) or Placebo (n = 6) and OXPHOS was reassessed post-supplementation. Results: Baseline OXPHOS was not different between the young (32 ± 8 pmol/s/mg; Range: 18-44) and old (35 ± 12 pmol/s/mg; Range: 14-60; P = 0.49). The supplement-induced change in OXPHOS was not different between the older groups (PB125: 3 ± 9 vs Placebo: -0 ± 10 pmol/s/mg; P = 0.56) and neither was different from baseline (both, P &gt; 0.05). However, a “threshold-like” relationship between the baseline OXPHOS and the PB125-induced change was identified within the PB125-treated group, whereby older individuals with a relatively lower baseline OXPHOS (&lt;25 pmol/s/mg) had a significant improvement (11 ± 7 pmol/s/mg, n = 4; P = 0.03) compared to baseline, while individuals with a normal baseline OXPHOS had no significant change (-2 ± 2 pmol/s/mg, n = 6; P &gt; 0.05). Conclusion: These findings support previous reports that mitochondrial function, as measured by OXPHOS, is not impaired in older individuals compared to their younger counterparts. However, older individuals with low mitochondrial function exhibited improved OXPHOS following Nrf2 activation via PB125 supplementation. These findings highlight the importance of heterogeneity in aging and provide novel evidence that activating Nrf2 may prove beneficial to improve maximal mitochondrial respiration. NIH: T32HL007576, T32HL139451, R01HL142603; VA: I01CX001999 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.

Skeletal muscle microcirculatory and mitochondrial function in patients with claudication and critical limb ischemia

Introduction: Peripheral artery disease (PAD) is an atherosclerotic progressive disorder that impairs blood flow to the lower extremities. Early-stage patients often present with intermittent claudication (leg pain during walking, CLD), but as the disease progresses, patients can experience pain at rest and tissue death (critical limb ischemia, CLI). We recently reported that skeletal muscle microvascular endothelial dysfunction presented in claudicating patients with PAD. However, it is unknown if this microvascular dysfunction continues to progress with disease severity. Objective: To compare a direct investigation of the skeletal muscle microcirculation and the mitochondrial respiratory environment in patients with claudication and patients with CLI. Hypothesis: We hypothesize that (1) CLI will have greater attenuation in microcirculatory endothelial-dependent and endothelial-independent vasodilatory function (smooth muscle function) than CLD and (2) impairments in skeletal muscle microcirculatory vasodilatory function will contribute to attenuated mitochondrial respiratory function in CLD and CLI. Methods: Medial gastrocnemius muscles were harvested from PAD patients with CLD ( n = 5), CLI ( n = 6), and age-matched controls ( n = 6) by both muscle biopsies and open incisions. Arterioles were isolated to assess endothelium-dependent and independent vasodilatory responses to flow (30 mL·min -1 ), acetylcholine (ACh), and sodium nitroprusside (SNP). Skeletal muscle mitochondrial respiratory function was determined by high-resolution respirometry. Results: Endothelium-dependent vasodilation was attenuated ( P &lt; 0.05) in response to flow (CON: 53.6 ± 23%, PAD: 26.7 ± 10.4%, CLI: 20.1 ± 14.5%) and ACh (10 -3 M, CON: 64 ± 6.9%, PAD: 39.1 ± 6.7%, CLI: 20.1 ± 14.5%) in both PAD and CLI compared to CON. However, endothelium-independent vasodilation with SNP was not different in any condition ( P &gt; 0.05). Complex I+II state 3 mitochondrial respiration was blunted in both CLD and CLI compared to CON ( P &lt; 0.05). However, state 4 respiration in CON was greater than CLI ( P &lt; 0.05) but lower than CLD. Additionally, complex I+II state 3 respiration was positively associated with both flow ( r = 0.5, P = 0.01) and ACh mediated vasodilation ( r = 0.6, P = 0.009). No differences were found between CLD and CLI conditions. Conclusions: This was the first the first study to directly examine and compare skeletal muscle microvascular function in PAD patients with CLD and CLI. Our initial data indicate that functional characteristics of the skeletal muscle microvasculature and mitochondria are altered in PAD and deteriorate with disease progression. There is a correlation between alterations in the endothelium-dependent microvessel function and the dysfunction of mitochondria in the ischemic muscle raising the possibility that the microvascular dysfunction in PAD is produced by defects in the mitochondria of the microvascular endothelium. National Institutes of Health (R01 AG034995, R01 AG049868) NIH National Institute of General Medical Sciences, which funds the Great Plains IdeA-CTR Network (U54 GM115458) 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.

30 Intrinsic skeletal muscle mitochondrial function decreases while mitochondrial volume density increases from 6 months to 3-years-old in Thoroughbreds

As the primary source of cellular energy, mitochondria are critical for athletic performance, and the intricacies of mitochondrial electron transfer may be related to Thoroughbred race performance. However, little is known about specific mitochondrial adaptations to growth in the equine athlete. To test the hypothesis that mitochondrial metrics would increase with age, gluteus medius samples were collected from the same Thoroughbred horses as weanlings (4 colts, 9 fillies; mean ± SD, 6 ± 1mo), yearlings (4 colts, 10 fillies; 20 ± 1mo), 2-year-olds (2yo; 3 geldings, 10 mares; 32 ± 1mo), and 3yo (2 geldings, 3 mares; 44 ± 1mo) from the same Kentucky farm over 4 years. Thoroughbreds were broke to ride in August of their yearling year then began race training. Mitochondrial oxidative phosphorylation (P) and electron transfer (E) capacities were determined via high-resolution respirometry. Citrate synthase (CS) and cytochrome c oxidase (CCO) activities were quantified as measures of mitochondrial volume density and function, respectively. Data were analyzed using PROC MIXED in SASv9.4 with age and sex as fixed effects, sire and dam as random effects, and age as a repeated effect with horse as the subject. Intrinsic (relative to CS activity) CCO activity, P supported by complex I (PCI), maximal P (PCI+II), and maximal E (ECI+II) weregreatest in weanlings compared with all other ages (P ≤ 0.003) and greater in yearlings than 2yo (P ≤ 0.05). Intrinsic E supported by complex II only (ECII) was greater in weanlings than 2 or 3yo (P ≤ 0.01) and greater in yearlings than 2yo (P ≤ 0.04). Weanlings also had a greater contribution of PCI+II to ECI+II than yearlings, 2yo, or 3yo (P ≤ 0.05). However, CS activity was greatest in 3yo (P ≤ 0.03) and lowest in weanlings (P ≤ 0.0001) with yearlings and 2yo intermediate, indicating expansion of the mitochondrial network with age and training. Additionally, 3yo had the greatest integrative (per mg tissue) PCI of all ages (P ≤ 0.005). Two and 3yo had greater integrative PCI+II, ECI+II, and ECII capacities than weanlings (P ≤ 0.05). Overall, weanlings had the greatest intrinsic mitochondrial capacities and function but 2 and 3yo Thoroughbreds had greater mitochondrial volume density resulting in greater integrative capacities. Skeletal muscle mitochondria of young Thoroughbreds appear to adapt to meet energetic demands of growth and race training by increasing volume density rather than intrinsic capacity, but further research is warranted to characterize the impacts of various training programs on mitochondrial metrics.

Effects of short-term endurance and strength exercise in the molecular regulation of skeletal muscle in hyperinsulinemic and hyperglycemic Slc2a4+/- mice.

Intriguingly, hyperinsulinemia, and hyperglycemia can predispose insulin resistance, obesity, and type 2 diabetes, leading to metabolic disturbances. Conversely, physical exercise stimulates skeletal muscle glucose uptake, improving whole-body glucose homeostasis. Therefore, we investigated the impact of short-term physical activity in a mouse model (Slc2a4+/-) that spontaneously develops hyperinsulinemia and hyperglycemia even when fed on a chow diet. Slc2a4+/- mice were used, that performed 5days of endurance or strength exercise training. Further analysis included physiological tests (GTT and ITT), skeletal muscle glucose uptake, skeletal muscle RNA-sequencing, mitochondrial function, and experiments with C2C12 cell line. When Slc2a4+/- mice were submitted to the endurance or strength training protocol, improvements were observed in the skeletal muscle glucose uptake and glucose metabolism, associated with broad transcriptomic modulation, that was, in part, related to mitochondrial adaptations. The endurance training, but not the strength protocol, was effective in improving skeletal muscle mitochondrial activity and unfolded protein response markers (UPRmt). Moreover, experiments with C2C12 cells indicated that insulin or glucose levels could contribute to these mitochondrial adaptations in skeletal muscle. Both short-term exercise protocols were efficient in whole-body glucose homeostasis and insulin resistance. While endurance exercise plays an important role in transcriptome and mitochondrial activity, strength exercise mostly affects post-translational mechanisms and protein synthesis in skeletal muscle. Thus, the performance of both types of physical exercise proved to be a very effective way to mitigate the impacts of hyperglycemia and hyperinsulinemia in the Slc2a4+/- mouse model.

The Effect of High-Intensity Interval Training on Apoptotic-Related Genes in Skeletal Muscle and Serumic TNF-Alpha of Diabetic Rats

Objective: Diabetes is characterized by a comprehensive increase in apoptosis, mitochondrial dysfunction, and inflammation in skeletal muscle. Impaired mitochondrial function in skeletal muscle leads to an increase in Cytochrome C and Caspase-9, and muscle performance is reduced consequently. Exercise training through decreasing inflammatory factors and increasing anti-inflammatory elements prevents apoptosis pathways.&#x0D; Materials and Methods: Forty male Wistar rats (150±10 g, 8 weeks age) were assigned to 4 groups: control (C), diabetes (D), high-intensity interval training (HIIT), and diabetes high-intensity interval training (DHIIT). Diabetes was induced with intraperitoneal injections of Streptozotocin (STZ) and blood sugar higher than 250 was considered diabetic. The effects of six weeks of HIIT on soleus muscles, Cytochrome C, and Caspase-9 gene expression, as well as evaluation of tumor necrosis factor-alpha (TNF-α ) in serum were evaluated using Real-Time PCR and ELISA techniques respectively.&#x0D; Results: In comparison with C group Diabetes has significantly increased the Cytochrome C (P= 0.001) and caspase-9 (P= 0.003). However, HIIT training in diabetic rats significantly decreased the Cytochrome C (P= 0.001) and caspase-9 (P= 0.008) in comparison of D group. Also, TNFα (P= 0.01) increased in the D group in comparison with C and DHIIT group (P= 0.001). In comparison between DHIIT groups in HIIT groups, has a significant increase in time to exhaustion post test than pretest (P= 0.001).&#x0D; Conclusion: It seems that HIIT training decreases intrinsic factors of the apoptosis pathway by decreasing inflammatory factors which leads to significant improvement in skeletal muscle function and overall health in diabetic rats.

Indirect regulation of HIPPO pathway by miRNA mediates high-intensity intermittent exercise to ameliorate aging skeletal muscle function.

Exercise-induced microRNA (miRNA) and HIPPO pathways participate in the regulation of skeletal muscle plasticity but their underlying mechanisms remain unclear. We aimed to investigate the effect of high-intensity interval training (HIIT) on miRNA expression and the HIPPO pathway in the skeletal muscle of aging rats to determine its role in the amelioration of muscle aging. Thirty-six 18-month-old female rats were randomly divided into sedentary control (SED, n=12), moderate-intensity continuous training (MICT, n=12), and HIIT (n=12) groups, with continuous exercise for 8 months. Quantitative reverse transcription-polymerase chain reaction, immunoblotting, KEGG enrichment, and dual-luciferase assays were performed on the target skeletal muscle. Compared with the SED group, the MICT and HIIT groups showed a significant trend of improvement in Lee's index and grip strength and a marked increase in skeletal muscle mitochondrial function, apoptosis, antioxidant, and lipolysis-related protein expression. They also exhibited PI3K/AKT pathway activation and a decrease in expression of HIPPO pathway-related proteins; 20 miRNAs were differentially expressed and enriched in the exercise group compared with the SED group, including the HIPPO pathway and metabolic pathways. Further analysis of L6 cells confirmed that miR-182 may target PTEN, which indirectly regulates HIPPO signaling, but not Mob1. the combined application of HIIT and MICT increased the antioxidant and lipolytic capacities of skeletal muscle and improved atrophy of aging skeletal muscle; HIIT was more effective than MICT. This may be related to HIIT-mediated AKT pathway activation and HIPPO pathway inhibition by miRNAs (miR-486 and miR-182).

ATP and NAD+ Deficiency in Parkinson’s Disease

The goal of this study is to identify a signature of bioenergetic and functional markers in the muscles of individuals with Parkinson's disease (PD). Quantitative physiological properties of in vivo hand muscle (FDI, first dorsal interosseus) and leg muscle (TA, Tibialis Anterior) of older individuals with PD were compared to historical age/gender-matched controls (N = 30). Magnetic resonance spectroscopy and imaging (MRS) were used to assess in vivo mitochondrial and cell energetic dysfunction, including maximum mitochondrial ATP production (ATPmax), NAD concentrations linked to energy/stress pathways, and muscle size. Muscle function was measured via a single muscle fatigue test. TA ATPmax and NAD levels were significantly lower in the PD cohort compared to controls (ATPmax: 0.66 mM/s ± 0.03 vs. 0.76 ± 0.02; NAD: 0.75 mM ± 0.05 vs. 0.91 ± 0.04). Muscle endurance and specific force were also lower in both hand and leg muscles in the PD subjects. Exploratory analyses of mitochondrial markers and individual symptoms suggested that higher ATPmax was associated with a greater sense of motivation and engagement and less REM sleep behavior disorder (RBD). ATPmax was not associated with clinical severity or individual symptom(s), years since diagnosis, or quality of life. Results from this pilot study contribute to a growing body of evidence that PD is not a brain disease, but a systemic metabolic syndrome with disrupted cellular energetics and function in peripheral tissues. The significant impairment of both mitochondrial ATP production and resting metabolite levels in the TA muscles of the PD patients suggests that skeletal muscle mitochondrial function may be an important tool for mechanistic understanding and clinical application in PD patients. This study looked at individuals with mid-stage PD; future research should evaluate whether the observed metabolic perturbations in muscle dysfunction occur in the early stages of the disease and whether they have value as theragnostic biomarkers.

Adult skeletal muscle peroxisome proliferator-activated receptor γ -related coactivator 1 is involved in maintaining mitochondrial content.

The peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) family of transcriptional coactivators are regulators of mitochondrial oxidative capacity and content in skeletal muscle. Many of these conclusions are based primarily on gain-of-function studies using muscle-specific overexpression of PGC1s. We have previously reported that genetic deletion of both PGC-1α and PGC-1β in adult skeletal muscle resulted in a significant reduction in oxidative capacity with no effect on mitochondrial content. However, the contribution of PGC-1-related coactivator (PRC), the third PGC-1 family member, in regulating skeletal muscle mitochondria is unknown. Therefore, we generated an inducible skeletal muscle-specific PRC knockout mouse (iMS-PRC-KO) to assess the contribution of PRC in skeletal muscle mitochondrial function. We measured mRNA expression of electron transport chain (ETC) subunits as well as markers of mitochondrial content in the iMS-PRC-KO animals and observed an increase in ETC gene expression and mitochondrial content. Furthermore, the increase in ETC gene expression and mitochondrial content was associated with increased expression of PGC-1α and PGC-1β. We therefore generated an adult-inducible PGC-1 knockout mouse in which all PGC-1 family members are deleted (iMS-PGC-1TKO). The iMS-PGC-1TKO animals exhibited a reduction in ETC mRNA expression and mitochondrial content. These data suggest that in the absence of PRC alone, compensation occurs by increasing PGC-1α and PGC-1β to maintain mitochondrial content. Moreover, the removal of all three PGC-1s in skeletal muscle results in a reduction in both ETC mRNA expression and mitochondrial content. Taken together, these results suggest that PRC plays a role in maintaining baseline mitochondrial content in skeletal muscle.

Melatonin supplementation promotes muscle fiber hypertrophy and regulates lipid metabolism of skeletal muscle in weaned piglets.

Melatonin has been reported to play crucial roles in regulating meat quality, improving reproductive properties, and maintaining intestinal health in animal production, but whether it regulates skeletal muscle development in weaned piglet is rarely studied. This study was conducted to investigate the effects of melatonin on growth performance, skeletal muscle development, and lipid metabolism in animals by intragastric administration of melatonin solution. Twelve 28-d-old DLY (Duroc × Landrace × Yorkshire) weaned piglets with similar body weight were randomly divided into two groups: control group and melatonin group. The results showed that melatonin supplementation for 23 d had no effect on growth performance, but significantly reduced serum glucose content (P < 0.05). Remarkably, melatonin increased longissimus dorsi muscle (LDM) weight, eye muscle area and decreased the liver weight in weaned piglets (P < 0.05). In addition, the cross-sectional area of muscle fibers was increased (P < 0.05), while triglyceride levels were decreased in LDM and psoas major muscle by melatonin treatment (P < 0.05). Transcriptome sequencing showed melatonin induced the expression of genes related to skeletal muscle hypertrophy and fatty acid oxidation. Enrichment analysis indicated that melatonin regulated cholesterol metabolism, protein digestion and absorption, and mitophagy signaling pathways in muscle. Gene set enrichment analysis also confirmed the effects of melatonin on skeletal muscle development and mitochondrial structure and function. Moreover, quantitative real-time polymerase chain reaction analysis revealed that melatonin supplementation elevated the gene expression of cell differentiation and muscle fiber development, including paired box 7 (PAX7), myogenin (MYOG), myosin heavy chain (MYHC) IIA and MYHC IIB (P < 0.05), which was accompanied by increased insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein 5 (IGFBP5) expression in LDM (P < 0.05). Additionally, melatonin regulated lipid metabolism and activated mitochondrial function in muscle by increasing the mRNA abundance of cytochrome c oxidase subunit 6A (COX6A), COX5B, and carnitine palmitoyltransferase 2 (CPT2) and decreasing the mRNA expression of peroxisome proliferator-activated receptor gamma (PPARG), acetyl-CoA carboxylase (ACC) and fatty acid-binding protein 4 (FABP4) (P < 0.05). Together, our results suggest that melatonin could promote skeletal muscle growth and muscle fiber hypertrophy, improve mitochondrial function and decrease fat deposition in muscle.

Revisiting Skeletal Muscle Dysfunction and Exercise in Chronic Obstructive Pulmonary Disease: Emerging Significance of Myokines.

Skeletal muscle dysfunction (SMD) is the most significant extrapulmonary complication and an independent prognostic indicator in patients with chronic obstructive pulmonary disease (COPD). Myokines, such as interleukin (IL)-6, IL-15, myostatin, irisin, and insulin-like growth factor (IGF)-1, play important roles in skeletal muscle mitochondrial function, protein synthesis and breakdown balance, and regeneration of skeletal muscles in COPD. As the main component of pulmonary rehabilitation, exercise can improve muscle strength, muscle endurance, and exercise capacity in patients with COPD, as well as improve the prognosis of SMD and COPD by regulating the expression levels of myokines. The mechanisms by which exercise regulates myokine levels are related to microRNAs. IGF-1 expression is upregulated by decreasing the expression of miR-1 or miR-29b. Myostatin downregulation and irisin upregulation are associated with increased miR-27a expression and decreased miR-696 expression, respectively. These findings suggest that myokines are potential targets for the prevention and treatment of SMD in COPD. A comprehensive analysis of the role and regulatory mechanisms of myokines can facilitate the development of new exercise-based therapeutic approaches for patients with COPD.

Skeletal muscle insulin resistance and adipose tissue hypertrophy persist beyond the reshaping of gut microbiota in young rats fed a fructose-rich diet

To investigate whether short term fructose-rich diet induces changes in the gut microbiota as well as in skeletal muscle and adipose tissue physiology and verify whether they persist even after fructose withdrawal, young rats of 30 d of age were fed for 3 weeks a fructose-rich or control diet. At the end of the 3-weeks period, half of the rats from each group were maintained for further 3 weeks on a control diet. Metagenomic analysis of gut microbiota and short chain fatty acids levels (faeces and plasma) were investigated. Insulin response was evaluated at the whole-body level and both in skeletal muscle and epididymal adipose tissue, together with skeletal muscle mitochondrial function, oxidative stress, and lipid composition. In parallel, morphology and physiological status of epididymal adipose tissue was also evaluated. Reshaping of gut microbiota and increased content of short chain fatty acids was elicited by the fructose diet and abolished by switching back to control diet. On the other hand, most metabolic changes elicited by fructose-rich diet in skeletal muscle and epididymal adipose tissue persisted after switching to control diet. Increased dietary fructose intake even on a short-time basis elicits persistent changes in the physiology of metabolically relevant tissues, such as adipose tissue and skeletal muscle, through mechanisms that go well beyond the reshaping of gut microbiota. This picture delineates a harmful situation, in particular for the young populations, posed at risk of metabolic modifications that may persist in their adulthood.

Oral combined contraceptives induce liver mitochondrial reactive oxygen species and whole-body metabolic adaptations in female mice.

Compared to age-matched men, pre-menopausal women show greater resilience against cardiovascular disease (CVD), hepatic steatosis, diabetes and obesity - findings that are widely attributed to oestrogen. However, meta-analysis data suggest that current use of oral combined contraceptives (OC) is a risk factor for myocardial infarction, and OC use further compounds with metabolic disease risk factors to increase CVD susceptibility. While mitochondrial function in tissues such as the liver and skeletal muscle is an emerging mechanism by which oestrogen may confer its protection, effects of OC use on mitochondria and metabolism in the context of disease risk remain unexplored. To answer this question, female C57Bl/6J mice were fed a high fat diet and treated with vehicle or OCs for 3, 12 or 20weeks (n=6 to 12 per group) at a dose and ratio that mimic the human condition of cycle cessation in the low oestrogen, high progesterone stage. Liver and skeletal muscle mitochondrial function (respiratory capacity, H2 O2 , coupling) was measured along with clinical outcomes of cardiometabolic disease such as obesity, glucose tolerance, hepatic steatosis and aortic atherosclerosis. The main findings indicate that regardless of treatment duration, OCs robustly increase hepatic mitochondrial H2 O2 levels, likely due to diminished antioxidant capacity, but have no impact on muscle mitochondrial H2 O2 . Furthermore, OC-treated mice had lower adiposity and hepatic triglyceride content compared to control mice despite reduced wheel running, spontaneous physical activity and total energy expenditure. Together, these studies describe tissue-specific effects of OC use on mitochondria as well as variable impacts on markers of metabolic disease susceptibility. KEY POINTS: Oestrogen loss in women increases risk for cardiometabolic diseases, a link that has been partially attributed to negative impacts on mitochondria and energy metabolism. To study the effect of oral combined contraceptives (OCs) on hepatic and skeletal muscle mitochondria and whole-body energy metabolism, we used an animal model of OCs which mimics the human condition of cessation of hormonal cycling in the low oestrogen, high progesterone state. OC-treated mice have increased hepatic mitochondrial oxidative stress and decreased physical activity and energy expenditure, despite displaying lower adiposity and liver fat at this time point. These pre-clinical data reveal tissue-specific effects of OCs that likely underlie the clinical findings of increased cardiometabolic disease in women who use OCs compared to non-users, when matched for obesity.