Stimulated Muscle Contractions Regulate Membrane-Bound and Soluble TLR4 to Prevent LPS-Induced Signaling and Myotube Atrophy in Skeletal Muscle Cells

Toll-like receptor 4 (TLR4) activation by lipopolysaccharides (LPS) contributes to chronic inflammation and causes upregulation of muscle atrophy signaling pathways. Exercise can suppress LPS/TLR4 axis activation by reducing the expression of TLR4 on immune cells. It is unknown how this regulation occurs, and it is not clear how exercise affects TLR4 on skeletal muscle. PURPOSE: To uncover the nature and mechanisms by which exercise affects TLR4 expression and intracellular signaling using cell culture models and human experiments. METHODS: C2C12 myotubes were subjected to electrical pulse stimulation (EPS) with and without subsequent treatment with 500 ng/mL lipopolysaccharide (LPS) along with corresponding control conditions. To investigate the effect of muscle contraction on the regulation of TLR4 in-vivo, we analyzed PBMC and serum samples from eight recreationally active men that completed 60-minutes of cycling at a moderate intensity (65% of VO2max). RESULTS: In-vitro, LPS decreased membrane-bound TLR4, increased TLR4 signaling (decreased inhibitor of κBα), and induced myotube atrophy. However, stimulated muscle contractions decreased membrane-bound TLR4, increased soluble TLR4 (sTLR4), and prevented LPS-induced signaling and myotube atrophy. In human participants, a single bout of moderate-intensity exercise decreased membrane-bound TLR4 on PBMCs and increased serum-borne sTLR4. CONCLUSION: These experiments support exercise may exert a novel anti-catabolic/ anti-inflammatory effect by increasing sTLR4 and decreasing TLR4 expressed on the muscle membrane. These results could help improve interventions for conditions associated with TLR4-mediated inflammation and muscle atrophy, such as diabetes, sarcopenia, and cancer cachexia

Physiological and Biomechanical Differences Between Seated and Standing Uphill Cycling

International Journal of Exercise Science 13(2): 996-1011, 2020. Despite differences in economy, cyclists climb in seated and standing positions. Prompted by gaps in research, we compared VO2 and heart rate (HR) (Study 1), muscle activation (Study 2) and breathing and pedaling entrainment (Study 3). METHODS: Subjects rode their bicycles on a treadmill in seated and standing positions. In Study 1, VO2 and HR of four male cyclists (21.3 ± 1.7 yrs; 69.1 ± 6 ml/kg/min) were collected, alternating positions every 5 minutes for 20 minutes (8 mph, 8% grade). In Study 2, muscle activations of eight male cyclists (24 ± 5 yrs, 67.6 ± 5.5 ml/kg/min) were collected on Rectus Femoris (RF), Biceps Femoris, Vastus Medialis (VM) and Gastrocnemius alternating positions every minute (8 mph, 8% grade). In Study 3, flow rate and entrainment of nine male cyclists (28 ± 7 yrs, 62.7 ± 7.7 ml/kg/min) were collected in 2-minute stages at 6, 8 and 10 mph, (8% grade) alternating positions every minute. RESULTS: VO2 and HR increased standing (3.17± 0.43 L/min, 175 ± 4 bpm) compared to seated (3.06 ± 0.37 L/min, 166 ± 5 bpm) (p \u3c 0.05). Normalized EMG for RF and VM increased standing (47 ± 5%, 57 ± 15%) compared to seated (34 ± 3%, 36 ± 8%) (p \u3c 0.05). Peak Inspiratory and Expiratory Flow increased standing (3.44±0.07 and 2.45±0.05 L/sec) compared to seated (3.09 ±0.06 and 2.21±0.04 L/sec) (p \u3c 0.05). CONCLUSION: Uphill cycling while standing results in decreased cycling economy due to physiological and biomechanical variations compared to riding seated

Effect of Moderate Intensity Cycle Ergometer Exercise in Normoxia and Hypobaric Hypoxia on Markers Related to Autophagy – A Pilot Study

Autophagy is a process by which damaged and dysfunctional cellular components are transported to and decomposed in the lysosome, which is integral for maintenance of healthy cellular function and homeostasis. Among many health benefits, exercise is shown to catalyze autophagy. However, limited research exists on the effect of high-altitude exercise (\u3e2500m) on autophagy in humans. PURPOSE: To determine the effect of exercise in hypoxia (HYP) on autophagic markers compared to intensity-matched exercise in normoxia (NORM). METHODS: 8 healthy and active males (23.3 ± 2.4 yrs, 75.2 ± 10.7 kg, 49.6 ± 6.5 ml/kg/min) completed 1hr of moderate intensity cycling (65% normoxic VO2max) in normoxia (1600m) and hypobaric hypoxia (4300m), in a randomized counterbalanced crossover design, separated by two weeks. Venous blood samples were collected pre and post exercise, from which peripheral blood mononuclear cells (PBMCs) were isolated and analyzed for expression of a regulatory autophagic protein (p62) and an upstream contributor to hypoxia-inducible factor 1α (HIF1α) mediated autophagy (PHD2). Comparisons between conditions were made using paired t-tests. RESULTS: Post exercise decreases in protein expression were similar between HYP and NORM for p62 (0.50 ± 0.2 vs 0.70 ± 0.5 Fold Change) and PHD2 (0.15 ± 0.17 vs 0.21 ± 0.16 Fold Change), respectively (p\u3e0.05). CONCLUSION: Decreased expression of p62 following exercise is suggestive of upregulation in autophagy regardless of exercise condition. Further, inhibition of PHD2 in immune cells post exercise may be due to exercise induced hypoxemia, and activation of autophagy via the HIF1α/BNIP3 pathway. These data suggest that oxygen sensing occurs in PBMCs as a result of physiological stressors such as altitude and exercise which increase autophagic processes. Autophagic flux may occur similarly following exercise in hypoxic and normoxic environments, however more comprehensive analyses of multiple autophagic markers measured in heterogenous participant sample sizes are warranted