Abstract 631 ADAM12 Is An Important Regulator Of Myocyte Apoptosis Induced By β-adrenergic Receptor Stimulation
ADAM (A Disintegrin And Metalloprotease)12 is a member of a family of cell surface proteins with protease and cell-binding activities. Recent work showed ADAM12 up-regulation in human heart failure. However, the activation mechanisms of ADAM12 in the heart are obscure. We hypothesized that β-adrenergic receptors (AR) stimulation regulates ADAM12 activation in neonatal rat ventricular myocytes (NRVMs) in-vitro and after injection of isoproterenol (ISO) in-vivo. Wistar rats received a single injection of ISO (5 mg/kg) and were sacrificed 6, 24 and 72 hrs later. In comparison with controls, left ventricular function was impaired in rats 24 hrs after ISO injection and started to improve at 72 hrs. The fraction of myocytes undergoing apoptosis peaked 24 hrs after ISO injection and declined thereafter. ADAM12 protein was reduced in hearts from ISO treated animals at 6 hrs, pointing to a possible increase in ADAM12 proteolytic activity. However, both ADAM12 expression and activation were significantly up-regulated at 24 and 72 hrs after ISO injection. We therefore assessed whether ADAM12 activation was involved in myocyte apoptosis secondary to excess exposure of catecholamine. Acute stimulation with ISO (10 μM, 30 min to 3 hrs) induced accumulation of ADAM12 N-terminal cleavage product in conditioned medium, demonstrating activation of the ADAM metalloprotease activity. However, chronic stimulation with ISO for 24 hrs and 48 hrs significantly increased both ADAM12 expression and secretion. This ISO-induced ADAM12 expression/activation was mediated through β1-AR stimulation and was dependent on intracellular calcium elevation and protein kinase C activation. Adenoviral expression of an ADAM12 protease-deficient mutant (ADAM12DeltaMP) blocks β-AR-induced myocyte apoptosis, while transduction of NRVMs with adenovirus harboring ADAM12 significantly increased myocyte apoptosis. These data suggest that ADAM12 is a regulator of myocyte apoptosis induced by β-AR in NRVMs and may play an important autocrine role in mediating the effects of β-AR on myocardial remodeling.