Primate Neurons Flex Their Musclin

Myokine Musclin Is Critical for Exercise-Induced Cardiac Conditioning

This study investigates the role and mechanisms by which the myokine musclin promotes exercise-induced cardiac conditioning. Exercise is one of the most powerful triggers of cardiac conditioning with proven benefits for healthy and diseased hearts. There is an emerging understanding that muscles produce and secrete myokines, which mediate local and systemic "crosstalk" to promote exercise tolerance and overall health, including cardiac conditioning. The myokine musclin, highly conserved across animal species, has been shown to be upregulated in response to physical activity. However, musclin effects on exercise-induced cardiac conditioning are not established. Following completion of a treadmill exercise protocol, wild type (WT) mice and mice with disruption of the musclin-encoding gene, Ostn, had their hearts extracted and exposed to an ex vivo ischemia-reperfusion protocol or biochemical studies. Disruption of musclin signaling abolished the ability of exercise to mitigate cardiac ischemic injury. This impaired cardioprotection was associated with reduced mitochondrial content and function linked to blunted cyclic guanosine monophosphate (cGMP) signaling. Genetic deletion of musclin reduced the nuclear abundance of protein kinase G (PKGI) and cyclic adenosine monophosphate (cAMP) response element binding (CREB), resulting in suppression of the master regulator of mitochondrial biogenesis, peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α), and its downstream targets in response to physical activity. Synthetic musclin peptide pharmacokinetic parameters were defined and used to calculate the infusion rate necessary to maintain its plasma level comparable to that observed after exercise. This infusion was found to reproduce the cardioprotective benefits of exercise in sedentary WT and Ostn-KO mice. Musclin is essential for exercise-induced cardiac protection. Boosting musclin signaling might serve as a novel therapeutic strategy for cardioprotection.

Serum Level of Musclin Is Elevated Following Severe Burn

Muscle wasting induced by severe burn worsens clinical outcomes is associated with hyperglycemia. A novel muscle-specific secretory factor, musclin, was reported to regulate glucose metabolism with a homologous sequence of natriuretic peptides. The purpose of the study was to investigate musclin expression in response to burn injury in both human and animal models. Serum was collected from 13 adult burn patients and circulating levels of musclin protein were measured via elisa. The cytokine profile was measured by Bio-Plex multiple immunoassay. Following the clinical study, we used a burn rat model with 40% TBSA to study the time course of musclin expression till day 14. Rat serum and muscle tissue sample were harvested. Finally, an in vitro study was applied to investigate whether the muscle cell C2C12 myoblast expressed musclin under 10% burn serum stimulation. Pearson analysis showed that there was a significant positive correlation of musclin expression to total body surface area of burn in patients (P &= .038). Musclin expression was significantly positively correlated with IL-4, IL-7, IL-12, and IL-13 in burn patients’ serum (P < .05). In the animal study, we found that the musclin level evaluated at 6 hours and 1 day in burn rat serum (P < .05). In vitro, musclin mRNA expression significantly increased with burn serum stimulation at 24 hours (P < .05). In conclusion, serum level of musclin elevated both in human patients and burn animals; musclin was correlated with the severity of burn injury as well as with an elevated cytokine profile in patients; burn serum-stimulated musclin expression in vitro further identified the resource of musclin expression after burn.