Enhanced secretion of promyogenic exosomes by quiescent muscle cells.

Signaling interactions are important during skeletal muscle regeneration, where muscle cells in distinct states (quiescent, reactivated, proliferating and differentiated) must coordinate their response to injury. Here, we probed the role of secreted small extracellular vesicles (sEV/exosomes) using a culture model of physiologically relevant cell states seen in muscle regeneration. Unexpectedly, G0 myoblasts exhibited enhanced secretion of sEV (∼150 nm) displaying exosome markers (Alix, TSG101, flotillin-1, and CD9), and increased expression of Kibra, a regulator of exosome biogenesis. Perturbation of Kibra levels confirmed a role in controlling sEV secretion rates. Purified sEVs displayed a common exosome marker-enriched proteome in all muscle cell states, as well as state-specific proteins. Exosomes derived from G0 cells showed an antioxidant signature, and were most strongly internalized by differentiated myotubes. Functionally, donor exosomes from all muscle cell states could activate an integrated Wnt reporter in target cells, but only G0-derived exosomes could induce myogenic differentiation in proliferating cells. Taken together, we provide evidence that quiescence in muscle cells is accompanied by enhanced secretion of exosomes with distinct uptake, cargo and signal activating features. Our study suggests the novel possibility that quiescent muscle stem cells in vivo may play a previously under-appreciated signaling role during muscle homeostasis.

Immunomodulation exhibited by piperinic acid through suppression of proinflammatory cytokines.

Piper longum (PL) has been reported for its varied pharmacological activities including bio-enhancer and anti-inflammatory activities in traditional medicine. Here the premise of the study was to investigate the immunoregulatory potential of PL and piperinic acid, one of its active constituent, in Balb/C mice (in vivo) and human PBMCs (in vitro) models. Piperinic acid moderated the proinflammatory mediators and cytokines in our experiments. At doses of 10, 20, 40 and 80 mg/kg p.o. PL showed a dose dependent decrease of lymphocytes (CD4+ and CD8+ T cells) and cytokine levels in sensitized Balb/C mice with a marked inhibition at 40 mg/kg. At an in vitro dose of 20 mug/ml of PL and 5 mug/ml of piperinic acid, there was a significant inhibition of mitogen induced human PBMC proliferation, mRNA transcripts of IL-2 (ConA) and TNFalpha, IL-1beta and iNOS (LPS) respectively under stimulated conditions in time dependent (6 h, 12 h and 24 h respectively) expression studies. In parallel, induced nitric oxide production was also reduced by stimulated macrophages. Our observations rationalize the traditional use of PL and also validate the immunoregulatory potential of piperinic acid.