Implication of satellite cell behaviors in capillary growth via VEGF expression-independent mechanism in response to mechanical loading in HeyL-null mice

Time-series transcriptomics reveals distinctive mRNA expression dynamics associated with gene ontology specificity and protein expression in skeletal muscle after electrical stimulation-induced resistance exercise

Resistance exercise upregulates and downregulates the expression of a wide range of genes in skeletal muscle. However, detailed analysis of mRNA dynamics such as response rates and temporal patterns of the transcriptome after resistance exercise has not been performed. We aimed to clarify the dynamics of time-series transcriptomics after resistance exercise. We used electrical stimulation-induced muscle contraction as a resistance exercise model (5 sets × 10 times of 3 s of 100-Hz electrical stimulation) on the tibialis anterior muscle of rats and measured the transcriptome in the muscle before and at 0, 1, 3, 6, and 12 h after muscle contractions by RNA sequencing. We also examined the relationship between the parameters of mRNA dynamics and the increase in protein expression at 12 h after muscle contractions. We found that the function of the upregulated genes differed after muscle contractions depending on their response rate. Genes related to muscle differentiation and response to mechanical stimulus were enriched in the sustainedly upregulated genes. Furthermore, there was a positive correlation between the magnitude of upregulated mRNA expression and the corresponding protein expression level at 12 h after muscle contractions. Although it has been theoretically suggested, this study experimentally demonstrated that the magnitude of the mRNA response after electrical stimulation-induced resistance exercise contributes to skeletal muscle adaptation via increases in protein expression. These findings suggest that mRNA expression dynamics such as response rate, a sustained upregulated expression pattern, and the magnitude of the response contribute to mechanisms underlying adaptation to resistance exercise.

Leg immobilization and subsequent recovery resistance training affect skeletal muscle angiogenesis related markers in young healthy adults regardless of prior resistance training experience

We recently reported that resistance trained (T, n=10) and untrained (UT, n=11) young adults experience vastus lateralis (VL) muscle atrophy following two weeks of disuse, and 8 weeks of recovery resistance training (RT) promotes VL hypertrophy in both participant cohorts. However, angiogenesis targets and muscle capillary number were not examined and currently no human studies that have sought to determine if disuse followed by recovery RT affects these outcomes. Thus, we examined whether disuse and/or recovery RT affected these outcomes. All participants underwent two weeks of left leg immobilization using locking leg braces and crutches followed by eight weeks (3d/week) of knee extensor focused progressive RT. VL biopsies were obtained at baseline (PRE), immediately after disuse (MID), and after RT (POST). Western blotting was used to assay angiogenesis markers and immunohistochemistry was performed in 16/21 participants to determine type I and II muscle fiber capillary number. Significant main effects of time (p<0.05) were observed for protein levels of VEGF (MID0.100). Although disuse and recovery RT affect skeletal muscle angiogenesis-related protein targets, prior training history does not differentially affect these outcomes.

NEW AND NOTEWORTHY

This is the first study to examine how limb immobilization and recovery resistance training affect molecular outcomes related to angiogenesis in younger adults with or without a prior training history. Regardless of resistance training history, the molecular responses are largely similar between participant cohorts and is suggestive of a reduced (pre-mid) and increased (mid-post) angiogenic response, with disuse and subsequent recovery resistance training.

Decreased number of satellite cells-derived myonuclei in both fast- and slow-twitch muscles in HeyL-KO mice during voluntary running exercise

BACKGROUND

Skeletal muscles possess unique abilities known as adaptation or plasticity. When exposed to external stimuli, such as mechanical loading, both myofiber size and myonuclear number increase. Muscle stem cells, also known as muscle satellite cells (MuSCs), play vital roles in these changes. HeyL, a direct target of Notch signaling, is crucial for efficient muscle hypertrophy because it ensures MuSC proliferation in surgically overloaded muscles by inhibiting the premature differentiation. However, it remains unclear whether HeyL is essential for MuSC expansion in physiologically exercised muscles. Additionally, the influence of myofiber type on the requirement for HeyL in MuSCs within exercised muscles remains unclear.

METHODS

We used a voluntary wheel running model and HeyL-knockout mice to investigate the impact of HeyL deficiency on MuSC-derived myonuclei, MuSC behavior, muscle weight, myofiber size, and myofiber type in the running mice.

RESULTS

The number of new MuSC-derived myonuclei was significantly lower in both slow-twitch soleus and fast-twitch plantaris muscles from exercised HeyL-knockout mice than in control mice. However, expect for the frequency of Type IIb myofiber in plantaris muscle, exercised HeyL-knockout mice exhibited similar responses to control mice regarding myofiber size and type.

CONCLUSIONS

HeyL expression is crucial for MuSC expansion during physiological exercise in both slow and fast muscles. The frequency of Type IIb myofiber in plantaris muscle of HeyL-knockout mice was not significantly reduced compared to that of control mice. However, the absence of HeyL did not affect the increased size and frequency of Type IIa myofiber in plantaris muscles. In this model, no detectable changes in myofiber size or type were observed in the soleus muscles of either control or HeyL-knockout mice. These findings imply that the requirement for MuSCs in the wheel-running model is difficult to observe due to the relatively low degree of hypertrophy compared to surgically overloaded models.

Exercise Training Attenuates the Muscle Mitochondria Genomic Response to Bed Rest

PURPOSE

Exercise training during the National Aeronautics and Space Administration 70-d bed rest study effectively counteracted the decline in aerobic capacity, muscle mass, strength, and endurance. We aimed to characterize the genomic response of the participants' vastus lateralis on day 64 of bed rest with and without exercise countermeasures.

METHODS

Twenty-two healthy young males were randomized into three groups: 1) bed rest only ( n = 7), 2) bed rest + aerobic (6 d·wk -1 ) and resistance training (3 d·wk -1 ) on standard equipment ( n = 7), and 3) bed rest + aerobic and resistance training using a flywheel device ( n = 8). The vastus lateralis gene and microRNA microarrays were analyzed using GeneSpring GX 14.9.1 (Agilent Technologies, Palo Alto, CA).

RESULTS

Bed rest significantly altered the expression of 2113 annotated genes in at least one out of the three study groups (fold change (FC) > 1.2; P < 0.05). Interaction analysis revealed that exercise attenuated the bed rest effect of 511 annotated genes (FC = 1.2, P < 0.05). In the bed rest only group, a predominant downregulation of genes was observed, whereas in the two exercise groups, there was a notable attenuation or reversal of this effect, with no significant differences between the two exercise modalities. Enrichment analysis identified functional categories and gene pathways, many of them related to the mitochondria. In addition, bed rest significantly altered the expression of 35 microRNAs (FC > 1.2, P < 0.05) with no difference between the three groups. Twelve are known to regulate some of the mitochondrial-related genes that were altered following bed rest.

CONCLUSIONS

Mitochondrial gene expression was a significant component of the molecular response to long-term bed rest. Although exercise attenuated the FC in the downregulation of many genes, it did not completely counteract all the molecular consequences.

Mechanisms of mechanical overload-induced skeletal muscle hypertrophy: current understanding and future directions

Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill trained. Much of the preclinical rodent and human resistance training research to date supports that involved mechanisms include enhanced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, an expansion in translational capacity through ribosome biogenesis, increased satellite cell abundance and myonuclear accretion, and postexercise elevations in muscle protein synthesis rates. However, several lines of past and emerging evidence suggest that additional mechanisms that feed into or are independent of these processes are also involved. This review first provides a historical account of how mechanistic research into skeletal muscle hypertrophy has progressed. A comprehensive list of mechanisms associated with skeletal muscle hypertrophy is then outlined, and areas of disagreement involving these mechanisms are presented. Finally, future research directions involving many of the discussed mechanisms are proposed.

TBX3 regulates the transcription of VEGFA to promote osteoblasts proliferation and microvascular regeneration

Objective

Osteochondral decellularization can promote local vascular regeneration, but the exact mechanism is unknown. The aim of this study is to study osteogenic microvascular regeneration in single cells.

Methods

The scRNA-seq dataset of human periosteal-derived cells (hPDCs) were analyzed by pySCENIC. To examine the role of TBX3 in osteogenesis and vascularization, cell transfection, qRT-PCR, western blot, and CCK-8 cell proliferation assays were performed.

Results

TCF7L2, TBX3, FLI1, NFKB2, and EZH2 were found to be transcription factors (TFs) most closely associated with corresponding cells. The regulatory network of these TFs was then visualized. Our study knocked down the expression of TBX3 in human osteoblast cell lines. In the TBX3 knockdown group, we observed decreased expression of VEGFA, VEGFB, and VEGFC. Moreover, Western blot analysis showed that downregulating TBX3 resulted in a reduction of VEGFA expression. And TBX3 stimulated osteoblast proliferation in CCK-8 assays.

Conclusion

TBX3 regulates VEGFA expression and promotes osteoblast proliferation in skeletal microvasculature formation. The findings provide a theoretical basis for investigating the role of TBX3 in promoting local vascular regeneration.

Muscle-Specific Cellular and Molecular Adaptations to Late-Life Voluntary Concurrent Exercise

Murine exercise models can provide information on factors that influence muscle adaptability with aging, but few translatable solutions exist. Progressive weighted wheel running (PoWeR) is a simple, voluntary, low-cost, high-volume endurance/resistance exercise approach for training young mice. In the current investigation, aged mice (22-mo-old) underwent a modified version of PoWeR for 8 wk. Muscle functional, cellular, biochemical, transcriptional, and myonuclear DNA methylation analyses provide an encompassing picture of how muscle from aged mice responds to high-volume combined training. Mice run 6-8 km/d, and relative to sedentary mice, PoWeR increases plantarflexor muscle strength. The oxidative soleus of aged mice responds to PoWeR similarly to young mice in every parameter measured in previous work; this includes muscle mass, glycolytic-to-oxidative fiber type transitioning, fiber size, satellite cell frequency, and myonuclear number. The oxidative/glycolytic plantaris adapts according to fiber type, but with modest overall changes in muscle mass. Capillarity increases markedly with PoWeR in both muscles, which may be permissive for adaptability in advanced age. Comparison to published PoWeR RNA-sequencing data in young mice identified conserved regulators of adaptability across age and muscles; this includes Aldh1l1 which associates with muscle vasculature. Agrn and Samd1 gene expression is upregulated after PoWeR simultaneous with a hypomethylated promoter CpG in myonuclear DNA, which could have implications for innervation and capillarization. A promoter CpG in Rbm10 is hypomethylated by late-life exercise in myonuclei, consistent with findings in muscle tissue. PoWeR and the data herein are a resource for uncovering cellular and molecular regulators of muscle adaptation with aging.