The Regenerative Potential of Female Skeletal Muscle upon Hypobaric Hypoxic Exposure

Ganoderma lucidum Induces Myogenesis Markers to Avert Damage to Skeletal Muscles in Rats Exposed to Hypobaric Hypoxia

Jatwani, Arti, and Rajkumar Tulsawani. Ganoderma lucidum induces myogenesis markers to avert damage to skeletal muscles in rats exposed to hypobaric hypoxia. High Alt Med Biol. 24:287-295, 2023. Background: Hypobaric hypoxia (HH) has been reported to induce skeletal muscle loss and impair myogenesis. Aqueous extract of G. lucidum (AqGL) contains bioactive metabolites attributed to various pharmacological effects. In this study, protective effect of AqGL in ameliorating muscle mass loss following acute HH has been reported. Materials and Methods: Male Sprague-Dawley rats were divided into following five groups of six rats in each group: unexposed control (Group 1), 6 hours of HH exposure (Group 2), 6 hours of HH exposure+AqGL extract 50 mg/kg body weight (BW) (Group 3), 6 hours of HH exposure+AqGL extract 100 mg/kg BW (Group 4), and 6 hours of HH exposure+AqGL extract 200 mg/kg BW (Group 5). Experimental animals from all groups, except Group, 1 were exposed to HH, simulated altitude of 25,000 ft for 6 hours. After exposure period, gastrocnemius muscle was collected, weighed, and morphological, biochemical, and molecular markers were analyzed. Results: HH-exposed rat muscle showed significant (p < 0.05) increase in oxidative stress markers (reactive oxygen species & malondialdehyde), which was concomitant with decrease in its mass compared to controls. AqGL treatment significantly (p < 0.05) prevented muscle oxidative stress, restored reduced glutathione content, reduced protein carbonyl content and advanced oxidation protein product, and restored muscle mass loss at effective dose of 100 mg/kg BW. Furthermore, AqGL supplementation enhanced Myf5 (p < 0.01), MyoD (p < 0.01), MyoG (p < 0.05), and Mrf4 (nonsignificantly), brain-derived neurotrophic factor (p < 0.01), and interleukin 6 (p < 0.01) expression along with restoration of tumor necrosis factor alpha (p < 0.001) and myostatin (p < 0.05) in hypoxia-exposed muscle, evidencing induction of myogenesis markers. Moreover, histological analysis showed increased myocyte number; nuclei shifted toward the periphery in the treatment group supporting muscle regeneration. Conclusion: AqGL supplementation attenuates muscle mass loss by preventing oxidative stress and inducing modulation in myogenesis markers under HH environment.

Acute hypoxia attenuates resistance exercise-induced ribosome signaling but does not impact satellite cell pool expansion in human skeletal muscle

Cumulative evidence supports the hypothesis that hypoxia acts as a regulator of muscle mass. However, the underlying molecular mechanisms remain incompletely understood, particularly in human muscle. Here we examined the effect of hypoxia on signaling pathways related to ribosome biogenesis and myogenic activity following an acute bout of resistance exercise. We also investigated whether hypoxia influenced the satellite cell response to resistance exercise. Employing a randomized, crossover design, eight men performed resistance exercise in normoxia (FiO₂ 21%) or normobaric hypoxia (FiO₂ 12%). Muscle biopsies were collected in a time-course manner (before, 0, 90, 180 min and 24 h after exercise) and were analyzed with respect to cell signaling, gene expression and satellite cell content using immunoblotting, RT-qPCR and immunofluorescence, respectively. In normoxia, resistance exercise increased the phosphorylation of RPS6, TIF-1A and UBF above resting levels. Hypoxia reduced the phosphorylation of these targets by ~37%, ~43% and ~ 67% throughout the recovery period, respectively (p < .05 vs. normoxia). Resistance exercise also increased 45 S pre-rRNA expression and mRNA expression of c-Myc, Pol I and TAF-1A above resting levels, but no differences were observed between conditions. Similarly, resistance exercise increased mRNA expression of myogenic regulatory factors throughout the recovery period and Pax7⁺ cells were elevated 24 h following exercise in mixed and type II muscle fibers, with no differences observed between normoxia and hypoxia. In conclusion, acute hypoxia attenuates ribosome signaling, but does not impact satellite cell pool expansion and myogenic gene expression following a bout of resistance exercise in human skeletal muscle.

Neuropsychological and Neuroimaging Correlates of High-Altitude Hypoxia Trekking During the "Gokyo Khumbu/Ama Dablam" Expedition

Committeri Giorgia, Danilo Bondi, Carlo Sestieri, Ginevra Di Matteo, Claudia Piervincenzi, Christian Doria, Roberto Ruffini, Antonello Baldassarre, Tiziana Pietrangelo, Rosamaria Sepe, Riccardo Navarra, Piero Chiacchiaretta, Antonio Ferretti, and Vittore Verratti. Neuropsychological and neuroimaging correlates of high-altitude hypoxia trekking during the "Gokyo Khumbu/Ama Dablam" expedition. High Alt Med Biol 00:000-000, 2021. Background: Altitude hypoxia exposure may produce cognitive detrimental adaptations and damage to the brain. We aimed at investigating the effects of trekking and hypoxia on neuropsychological and neuroimaging measures. Methods: We recruited two balanced groups of healthy adults, trekkers (n = 12, 6 F and 6 M, trekking in altitude hypoxia) and controls (gender- and age-matched), who were tested before (baseline), during (5,000 m, after 9 days of trekking), and after the expedition for state anxiety, depression, verbal fluency, verbal short-term memory, and working memory. Personality and trait anxiety were also assessed at a baseline level. Neuroimaging measures of cerebral perfusion (arterial spin labeling), white-matter microstructural integrity (diffusion tensor imaging), and resting-state functional connectivity (functional magnetic resonance imaging) were assessed before and after the expedition in the group of trekkers. Results: At baseline, the trekkers showed lower trait anxiety (p = 0.003) and conscientiousness (p = 0.03) than the control group. State anxiety was lower in the trekkers throughout the study (p < 0.001), and state anxiety and depression decreased at the end of the study in both groups (p = 0.043 and p = 0.007, respectively). Verbal fluency increased at the end of the study in both groups (p < 0.001), whereas verbal short-term memory and working memory performance did not change. No significant differences between before and after the expedition were found for neuroimaging measures. Conclusions: We argue that the observed differences in the neuropsychological measures mainly reflect aspecific familiarity and learning effects due to the repeated execution of the same questionnaires and task. The present results thus suggest that detrimental effects on neuropsychological and neuroimaging measures do not necessarily occur as a consequence of short-term exposure to altitude hypoxia up to 5,000 m, especially in the absence of altitude sickness.

Regulation of satellite cells by exercise in hypoxic conditions: a narrative review

PURPOSE

To investigate in vivo the adaptations of satellite cell induced by exercise performed in acute or chronic hypoxic conditions and their contribution to muscle remodeling and hypertrophy.

METHODS

Search terms related to exercise, hypoxia and satellite cells were entered on Embase, PubMed and Scopus. Studies were selected for their relevance in terms of regulation of satellite cells by in vivo exercise and muscle contraction in hypoxic conditions.

RESULTS

Satellite cell activation and proliferation seem to be enabled after acute hypoxic exercise via regulations induced by myogenic regulatory factors. Several studies reported also a role of the inflammatory pathway nuclear factor-kappa B and angiogenic factors such as vascular endothelial growth factor, both known to upregulate myogenesis. By stimulating angiogenesis, repeated exercise performed in acute hypoxia might contribute to satellite cell activation. Contrary to such exercise conditions, chronic exposure to hypoxia downregulates myogenesis despite the maintenance of physical activity. This impaired myogenesis might be induced by excessive oxidative stress and proteolysis.

CONCLUSION

In vivo studies suggest that, in comparison to exercise or hypoxia alone, exercise performed in a hypoxic environment, may improve or impair muscle remodeling induced by contractile activity depending upon the duration of hypoxia. Satellite cells seem to be major actors in these dichotomous adaptations. Further research on the role of angiogenesis, types of contraction and autophagy is needed for a better understanding of their respective role in hypoxic exercise-induced modulations of satellite cell activity in human.

Serum ferritin and vitamin D evaluation in response to high altitude comparing Italians trekkers vs Nepalese porters

Altitude hypoxia induces changes in iron homeostasis with serum ferritin (sFER) response being recently linked to erythropoiesis. The main aim of this study was to investigate sFER and Vitamin D (Vit D) response to hypobaric hypoxia, taking into account factors including nutrition and ethnic origin. As part of a "Kanchenjunga Exploration & Physiology" project, 6 Italian trekkers and 6 Nepalese porters took part in a 19-days long altitude trek in the Himalayas self-recording daily food consumption. Blood samples were collected and analyzed before and after the trek for sFER and Vit D. A web-based system calculated the dietary intake, generating reports that were used for later statistical analyses. sFER decreased after the trek (on average by 26% p = 0.013, partial η² = 0.479) in both groups, whereas Vit D did not change in both groups. Nepalese tended to have lower sFER, but this difference was reduced when corrected for the dietary intake. Mean Cell Volume (MCV) and Hematocrit (HCT), in respect to baseline, remained higher 10 days after the trek (respectively, 87.37-88.85 fL with p = 0.044, and 43.05-44.63% with p = 0.065) in Italian trekkers. The observed reduction of sFER levels was related to altitude per se as inflammation or anemia were medically excluded. sFER, therefore, may act as a primary factor in the examination of hypobaric hypoxia in field studies. The results of this study open a new door into the mechanisms of iron homeostasis in specific tissues related to hypoxia adaptations, taking into account dietary intake and ethnic origin.

Body Composition and Endocrine Adaptations to High-Altitude Trekking in the Himalayas

Long-term exposure to high altitude causes adaptive changes in several blood biochemical markers along with a marked body mass reduction involving both the lean and fat components. The aim of this study was to evaluate the impact of extended physical strain, due to extensive trekking at high altitude, on body composition, selected biomarkers in the blood, and the protective role of a high-protein diet in muscle dysfunction. We found that physical strain at high altitude caused a significant reduction in body mass and body fat, with a concomitant increase in the cross-sectional area of thigh muscles and an unchanged total lean body mass. Further, we found reductions in plasma leptin and homocysteine, while myoglobin, insulin, and C-reactive protein significantly increased. Creatine kinase, lactate dehydrogenase, and leptin normalized per body fat were unchanged. These findings demonstrate that high-altitude hypoxia, involving extended physical effort, has an impact on muscle function and body composition, facilitating sarcopenia and affecting body mass and fat distribution. It also activates pro-inflammatory metabolic pathways in response to muscular distress. These changes can be mitigated by a provision of a high-protein diet.

Physiological effects of high-altitude trekking on gonadal, thyroid hormones and macrophage migration inhibitory factor (MIF) responses in young lowlander women

Altitude hypoxia is often associated with impairment of human reproduction. In this study, hormones and macrophage migration inhibitory factor (MIF, a proinflammatory cytokine with key roles in human reproduction) were determined in seven regularly menstruating, lowlander native women living at sea level participating in 14 days of trekking at moderate and high altitude. Blood and saliva samples were collected from each subject at high altitude (5050 m a.s.l. [above sea level]), and at sea level before and after the expedition. Testosterone level was lowered by high altitude and was restored after the end of the expedition, while progesterone decreased significantly in all participants at the end of the expedition, although most of the participants were in the luteal phase. The salivary concentration of MIF decreased greatly at altitude, but its levels were completely restored after the return to sea level. Our findings showed high sensitivity and rapid changes in the determined parameters in response to the high‐altitude hypoxic environment, particularly MIF.

Extracellular Guanosine 5'-Triphosphate Induces Human Muscle Satellite Cells to Release Exosomes Stuffed With Guanosine

The extracellular guanosine 5'-triphosphate, GTP, has been demonstrated to be an enhancer of myogenic cell differentiation in a murine cell line, not yet in human muscle cells. Our hypothesis was that GTP could influence also human skeletal muscle regeneration, specifically in the first phases. We tested GTP stimulus on human muscle precursor cells established in culture by human satellite cells derived from Vastus Lateralis of three young male. Our data show that extracellular GTP (a) up-regulated miRNA (specifically miR133a and miR133b) and myogenic regulator factor and (b) induces human myogenic precursor cells to release exosomes stuffed with guanosine based molecules (mainly guanosine) in the extracellular milieu. We think that probably these exosomes could be addressed to influence by means of their content (mainly guanosine) in paracrine or autocrine manner the surrounding cells and/or at distance other muscles or tissues.

Neuromuscular electrical stimulation improves skeletal muscle regeneration through satellite cell fusion with myofibers in healthy elderly subjects

The aim of this study was to determine whether neuromuscular electrical stimulation (NMES) affects skeletal muscle regeneration through a reduction of oxidative status in satellite cells of healthy elderly subjects. Satellite cells from the vastus lateralis skeletal muscle of 12 healthy elderly subjects before and after 8 wk of NMES were allowed to proliferate to provide myogenic populations of adult stem cells [myogenic precursor cells (MPCs)]. These MPCs were then investigated in terms of their proliferation, their basal cytoplasmic free Ca2+concentrations, and their expression of myogenic regulatory factors ( PAX3, PAX7, MYF5, MYOD, and MYOG) and micro-RNAs (miR-1, miR-133a/b, and miR-206). The oxidative status of these MPCs was evaluated through superoxide anion production and superoxide dismutase and glutathione peroxidase activities. On dissected single skeletal myofibers, the nuclei were counted to determine the myonuclear density, the fiber phenotype, cross-sectional area, and tension developed. The MPCs obtained after NMES showed increased proliferation rates along with increased cytoplasmic free Ca2+concentrations and gene expression of MYOD and MYOG on MPCs. Muscle-specific miR-1, miR-133a/b, and miR-206 were upregulated. This NMES significantly reduced superoxide anion production, along with a trend to reduction of superoxide dismutase activity. The NMES-dependent stimulation of muscle regeneration enhanced satellite cell fusion with mature skeletal fibers. NMES improved the regenerative capacity of skeletal muscle in elderly subjects. Accordingly, the skeletal muscle strength and mobility of NMES-stimulated elderly subjects significantly improved. NMES may thus be further considered for clinical or ageing populations.

NEW & NOTEWORTHY The neuromuscular electrical stimulation (NMES) effect on skeletal muscle regeneration was assessed in healthy elderly subjects for the first time. NMES improved the regenerative capacity of skeletal muscle through increased myogenic precursor cell proliferation and fusion with mature myofibers. The increased cytoplasmic free Ca2+concentration along with MYOD, MYOG, and micro-RNA upregulation could be related to reduced O2·−production, which, in turn, favors myogenic regeneration. Accordingly, the skeletal muscle strength of NMES-stimulated lower limbs of healthy elderly subjects improved along with their mobility.