Microbiota derived D-malate inhibits skeletal muscle growth and angiogenesis during aging via acetylation of Cyclin A

Metabolites derived from the intestinal microbiota play an important role in maintaining skeletal muscle growth, function, and metabolism. Here, we found that D-malate (DMA) is produced by mouse intestinal microorganisms and its levels increase during aging. Moreover, we observed that dietary supplementation of 2% DMA inhibits metabolism in mice, resulting in reduced muscle mass, strength, and the number of blood vessels, as well as the skeletal muscle fiber type I/IIb ratio. In vitro assays demonstrate that DMA decreases the proliferation of vascular endothelial cells and suppresses the formation of blood vessels. In vivo, we further demonstrated that boosting angiogenesis by muscular VEGFB injection rescues the inhibitory effects of D-malate on muscle mass and fiber area. By transcriptomics analysis, we identified that the mechanism underlying the effects of DMA depends on the elevated intracellular acetyl-CoA content and increased Cyclin A acetylation rather than redox balance. This study reveals a novel mechanism by which gut microbes impair muscle angiogenesis and may provide a therapeutic target for skeletal muscle dysfunction in cancer or aging.

One-Step Bioprinting of Multi-Channel Hydrogel Filaments Using Chaotic Advection: Fabrication of Pre-Vascularized Muscle-Like Tissues

The biofabrication of living constructs containing hollow channels is critical for manufacturing thick tissues. However, current technologies are limited in their effectiveness in the fabrication of channels with diameters smaller than hundreds of micrometers. It is demonstrated that the co-extrusion of cell-laden hydrogels and sacrificial materials through printheads containing Kenics static mixing elements enables the continuous and one-step fabrication of thin hydrogel filaments (1 mm in diameter) containing dozens of hollow microchannels with widths as small as a single cell. Pre-vascularized skeletal muscle-like filaments are bioprinted by loading murine myoblasts (C2C12 cells) in gelatin methacryloyl - alginate hydrogels and using hydroxyethyl cellulose as a sacrificial material. Higher viability and metabolic activity are observed in filaments with hollow multi-channels than in solid constructs. The presence of hollow channels promotes the expression of Ki67 (a proliferation biomarker), mitigates the expression of hypoxia-inducible factor 1-alpha , and markedly enhances cell alignment (i.e., 82% of muscle myofibrils aligned (in ±10°) to the main direction of the microchannels after seven days of culture). The emergence of sarcomeric α-actin is verified through immunofluorescence and gene expression. Overall, this work presents an effective and practical tool for the fabrication of pre-vascularized engineered tissues.

Low-Load Resistance Exercise with Blood Flow Restriction Increases Hypoxia-Induced Angiogenic Genes Expression

The aim of the study was to determine whether low-load exercise (LL) with blood flow restriction (LL-BFR) would induce similar changes in expression of genes involved in hypoxia and angiogenesis compared to LL and high-load exercise (HL). Twenty-four males (age: 21.3 ± 1.9 years, body height: 1.74 ± 0.8 m, body mass: 73 ± 1.8 kg) were allocated into three groups: low-load exercise (LL), low-load exercise with blood-flow restriction (LL-BFR), and high-load exercise (HL). For the LL-BFR group a pneumatic cuff was inflated at 80% of the arterial occlusion pressure. All participants performed bilateral knee extension exercise, twice a week, for 8 weeks. LL and LL-BFR groups performed 3-4 sets of 15 reps at 20% 1RM, whilst the HL group performed 3-4 sets of 8-10 reps at 80% 1RM with a 60-s rest interval between sets. The hypoxia-inducible factor-1 alpha (HIF-1α) and beta (HIF-1β), vascular endothelial growth factor (VEGF), neuronal (nNOS), and inducible nitric oxide synthase (iNOS) genes expression were assessed before and after training. HIF-1α and HIF-1β mRNA levels significantly increased in the LL-BFR group and exceeded those elicited by HL and LL groups (p < .0001). VEGF gene expression was increased in both LL-BFR and HL groups, however, LL-BFR elicited a greater increase than LL (p < .0001). nNOS and iNOS genes expression significantly increased in all groups with greatest increases being observed in the LL-BFR group (p < .0001). The findings suggest that LL-BFR induces greater increases in genes expression related to hypoxia and angiogenesis than traditional resistance training.

The Importance of Muscle Capillarization for Optimizing Satellite Cell Plasticity

Satellite cells are essential for skeletal muscle regeneration, repair, and adaptation. The activity of satellite cells is influenced by their interactions with muscle-resident endothelial cells. We postulate that the microvascular network between muscle fibers plays a critical role in satellite cell function. Exercise-induced angiogenesis can mitigate the decline in satellite cell function with age.

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.

Sleep deprivation and endothelial function: reconciling seminal evidence with recent perspectives

Sleep is critical for the maintenance of physiological homeostasis and, as such, inadequate sleep beckons a myriad of pathologies. Sleep deprivation is a growing health concern in contemporary society since short sleep durations are associated with increased cardiovascular disease risk and atherosclerotic plaque development. Vascular endothelial dysfunction is an antecedent to atherosclerosis and cardiovascular disease. Herein, we review seminal literature indicating that short sleep durations attenuate endothelial function and explore more recent evidence indicating that sleep deprivation perturbs autonomic balance and the circadian rhythmicity of peripheral vascular clock components. We further examine literature that indicates a mechanistic link between short sleep duration and endothelial dysfunction and subsequent morbidity. Understanding the mechanisms that regulate endothelial function in the context of sleep deprivation facilitates the development and optimization of interventions, such as exercise, that mitigate the ramifications of inadequate sleep on vascular function and cardiovascular health.Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/sleep-deprivation-and-endothelial-function/.

August Krogh's theory of muscle microvascular control and oxygen delivery: a paradigm shift based on new data

August Krogh twice won the prestigious international Steegen Prize, for nitrogen metabolism (1906) and overturning the concept of active transport of gases across the pulmonary epithelium (1910). Despite this, at the beginning of 1920, the consummate experimentalist was relatively unknown worldwide and even among his own University of Copenhagen faculty. But, in early 1919, he had submitted three papers to Dr Langley, then editor of The Journal of Physiology in England. These papers coalesced anatomical observations of skeletal muscle capillary numbers with O₂ diffusion theory to propose a novel active role for capillaries that explained the prodigious increase in blood-muscle O₂ flux from rest to exercise. Despite his own appraisal of the first two papers as "rather dull" to his friend, the eminent Cambridge respiratory physiologist, Joseph Barcroft, Krogh believed that the third one, dealing with O₂ supply and capillary regulation, was"interesting". These papers, which won Krogh an unopposed Nobel Prize for Physiology or Medicine in 1920, form the foundation for this review. They single-handedly transformed the role of capillaries from passive conduit and exchange vessels, functioning at the mercy of their upstream arterioles, into independent contractile units that were predominantly closed at rest and opened actively during muscle contractions in a process he termed 'capillary recruitment'. Herein we examine Krogh's findings and some of the experimental difficulties he faced. In particular, the boundary conditions selected for his model (e.g. heavily anaesthetized animals, negligible intramyocyte O₂ partial pressure, binary open-closed capillary function) have not withstood the test of time. Subsequently, we update the reader with intervening discoveries that underpin our current understanding of muscle microcirculatory control and place a retrospectroscope on Krogh's discoveries. The perspective is presented that the imprimatur of the Nobel Prize, in this instance, may have led scientists to discount compelling evidence. Much as he and Marie Krogh demonstrated that active transport of gases across the blood-gas barrier was unnecessary in the lung, capillaries in skeletal muscle do not open and close spontaneously or actively, nor is this necessary to account for the increase in blood-muscle O₂ flux during exercise. Thus, a contemporary model of capillary function features most muscle capillaries supporting blood flow at rest, and, rather than capillaries actively vasodilating from rest to exercise, increased blood-myocyte O₂ flux occurs predominantly via elevating red blood cell and plasma flux in already flowing capillaries. Krogh is lauded for his brilliance as an experimentalist and for raising scientific questions that led to fertile avenues of investigation, including the study of microvascular function.