V1a AVP receptor is required for neurohypophyseal hormonedependent differentiation in C2C12 cells

Vasopressin (AVP), oxytocin (OT) and related peptides induce differentiation and hypertrophy\r\nin myogenic cells expressing the V1a-vasopressin receptor (V1aR) or the oxytocin receptor\r\n(OTR). Either receptor can transduce both ligand signals. Binding of AVP and OT to the V1aR\r\nthe target cells activates phosphatidylinositol hydrolysis, which in turn releases Ca2+ from\r\ninternal stores. The AVP-dependent increase in cytosolic Ca2+ induces the activation of\r\ncalcium/calmodulin-dependent kinase (CaMK) and calcineurin signaling, two pathways\r\nrequired for the full expression of the differentiated phenotype. Here we investigate the role of\r\nV1aR in myogenesis and hypertrophy by ectopically restoring V1aR expression and function\r\nusing the C2C12 cell line, which is an experimental model of satellite cells that do not respond\r\nto AVP treatment. Our results show that AVP treatment enhances myogenic differentiation in\r\nV1aR-transfected C2C12 cultures alone. Moreover, calcium imaging analyses performed in\r\nindividual control and V1aR-transfected C2C12 cells demonstrated that the presence of V1aR\r\nis sufficient to make C2C12 cells responsive to neurohypophyseal hormones stimulation, as\r\ndemonstrated by the rapid and sustained release of calcium from internal stores observed in\r\nV1aR-transfected cells. These data demonstrate that, despite the high levels of OTR expressed\r\nby C2C12 cells, both AVP and OT failed to stimulate the differentiation program, thereby\r\nindicating that the presence of V1aR is essential to mediate the effects of neurohypophyseal\r\nhormones on myogenic differentiation in C2C12 cells.