P.19.9 Gαi2 signaling is required for skeletal muscle regeneration and for satellite cell differentiation

Armani

J cachexia sarcopenia muscle

et al. 2018

Background Perilipin2 (Plin2) belongs to a family of five highly conserved proteins, known for their role in lipid storage. Recent data indicate that Plin2 has an important function in cell metabolism and is involved in several human pathologies, including liver steatosis and Type II diabetes. An association between Plin2 and lower muscle mass and strength has been found in elderly and inactive people, but its function in skeletal muscle is still unclear. Here, we addressed the role of Plin2 in adult muscle by gain and loss of function experiments. Methods By mean of in vivo Plin2 down‐regulation (shPlin2) and overexpression (overPlin2) in murine tibialis anterior muscle, we analysed the effects of Plin2 genetic manipulations on myofiber size and lipid composition. An analysis of skeletal muscle lipid composition was also performed in vastus lateralis samples from young and old patients undergoing hip surgery. Results We found that Plin2 down‐regulation was sufficient to induce a 30% increase of myofiber cross‐sectional area, independently of mTOR pathway. Alterations of lipid content and modulation of genes involved in lipid synthesis occurred in hypertrophic muscles. In particular, we showed a decrease of triglycerides, ceramides, and phosphatidylcoline:phosphatidylethanolamine ratio, a condition known to impact negatively on muscle function. Plin2 overexpression did not change fibre size; however, lipid composition was strongly affected in a way that is similar to that observed in human samples from old patients. Conclusions Altogether these data indicate that Plin2 is a critical mediator for the control of muscle mass, likely, but maybe not exclusively, through its critical role in the regulation of intracellular lipid content and composition.

Section: Discussionsupporting

confidence: 90%

Muscle‐specific Perilipin2 down‐regulation affects lipid metabolism and induces myofiber hypertrophy

Armani

J cachexia sarcopenia muscle

et al. 2018

“…PKCα levels have been shown to increase with increasing levels of hsa-miR-328 in A549 cells (Arora et al 2011). PKCα has been reported to up-regulate hsa-miR-1 (Minetti et al 2014), hsa-miR-101 (Chiang et al 2010), and hsa-miR-15a (von Brandenstein et al 2011). Our results show that three of the miRNAs that target PKCα are expressed at higher levels during hypothermia, which may contribute to unanticipated consequences of hypothermia exposure.…”

Section: Figure 5 Functional Analysis Of the Pkcαmentioning

confidence: 57%

Shifts in temperature within the physiologic range modify strand-specific expression of select human microRNAs

Potla

Singh

Atamas

et al. 2015

RNA

Previous studies have revealed that clinically relevant changes in temperature modify clinically relevant gene expression profiles through transcriptional regulation. Temperature dependence of post-transcriptional regulation, specifically, through expression of miRNAs has been less studied. We comprehensively analyzed the effect of 24 h exposure to 32°C or 39.5°C on miRNA expression profile in primary cultured human small airway epithelial cells (hSAECs) and its impact on expression of a targeted protein, protein kinase C α (PKCα). Using microarray, and solution hybridization-based nCounter assays, with confirmation by quantitative RT-PCR, we found significant temperature-dependent changes in expression level of only five mature human miRNAs, representing only 1% of detected miRNAs. Four of these five miRNAs are the less abundant passenger (star) strands. They exhibited a similar pattern of increased expression at 32°C and reduced expression at 39.5°C relative to 37°C. As PKCα mRNA has multiple potential binding sites for three of these miRNAs, we analyzed PKCα protein expression in HEK 293T cells and hSAECs. PKCα protein levels were lowest at 32°C and highest at 39.5°C and specific miRNA inhibitors reduced these effects. Finally, we analyzed cell-cycle progression in hSAECs and found 32°C cells exhibited the greatest G1 to S transition, a process known to be inhibited by PKCα, and the effect was mitigated by specific miRNA inhibitors. These results demonstrate that exposure to clinically relevant hypothermia or hyperthermia modifies expression of a narrow subset of miRNAs and impacts expression of at least one signaling protein involved in multiple important cellular processes.

“…Many signaling cascades have been identified that promote muscle adaptation, among the most studied are the IGF1/PI3K/AKT hypertrophy signaling pathways and AMPK/PGC-1α metabolic signaling pathways. More recently, G protein coupled receptors (GPCRs) and specific G proteins have emerged as mechanisms regulating muscle adaptation (7)(8)(9)(10). We aimed to determine if the molecular mechanisms regulating muscle response to lifelong running would differ with and without satellite cell participation, enabling the identification of satellite cell-dependent processes in muscle response to physical activity.…”

Section: Introductionmentioning

confidence: 99%

Depletion of resident muscle stem cells inhibits muscle fiber hypertrophy induced by lifelong physical activity

Murach

et al. 2019

Preprint

Background: A reduction in skeletal muscle stem cell (satellite cell) content with advancing age is thought to directly contribute to the progressive loss of skeletal muscle mass and function with aging (sarcopenia). However, we reported that the depletion of satellite cells throughout adulthood did not affect the onset or degree of sarcopenia observed in sedentary old mice. The current study was designed to determine if lifelong physical activity would alter the requirements for satellite cells during aging. Methods:We administered vehicle or tamoxifen to adult (5 months old) female Pax7-DTA mice for 5 consecutive days to effectively deplete satellite cells. Following a 2month washout period, mice were assigned to physically active (free access to a running wheel) or sedentary (locked running wheel) conditions. Thirteen months later, at a mean age of 20 months, mice were sacrificed for subsequent analysis.Results: Satellite cell depletion throughout adulthood negatively impacted physical function and limited muscle fiber hypertrophy in response to lifelong physical activity. To further interrogate these findings, we performed transcriptome-wide analyses on the hind limb muscles that experienced hypertrophic growth (plantaris and soleus) in response to lifelong physical activity. Our findings demonstrate that satellite cell function is muscle type-specific; fusion with fibers is apparent in oxidative muscles, while initiation of Gα i2 signaling appears to require satellite cells in glycolytic muscles to induce muscle growth. . Conclusions: These findings suggest that satellite cells, or their secretory products, are viable therapeutic targets to preserve physical function with aging and promote muscle growth in older adults who regularly engage in physical activity.