D2 dopamine receptor antagonist raclopride induces non-canonical autophagy in cardiac myocytes.

Cell death by autophagy is an important means of maintaining cellular homeostasis in adult cardiac myocytes. Autophagy was previously shown to exert a cardioprotective effect, suggesting that modulation of autophagy pathways is a potential therapeutic strategy in the treatment of heart disease. Although dopamine is known to induce autophagy in neuroblastoma cells, the underlying mechanism and the types of dopamine receptors involved in this process remain unclear. In this study, we used various dopamine receptor antagonists and agonists to identify the specific dopamine receptor that mediates induction of autophagy. We evaluated autophagy induction by the expression of autophagy markers in neonatal rat ventricular cardiac myocytes. We evaluated intracellular calcium levels using Fluo-3/AM and demonstrated autophagy-induced morphological changes in cardiac myocytes using electron microscopy. We also examined the pathway for dopamine-induced autophagy using RNAi-mediated gene knockdown. Raclopride, the well-documented D2 receptor antagonist, significantly upregulated autophagy in cardiac myocytes via an mTOR-independent pathway. There was no difference in intracellular calcium levels between raclopride-treated cells and untreated cells. siRNA-mediated knockdown of Rab9 resulted in decreased expression of autophagy markers in raclopride-treated cells. Interestingly, siRNA-mediated knockdown of Atg7 resulted in a significant increase in Rab9 levels in raclopride-treated cells, suggesting that blocking the classical autophagy pathway results in activation of an alternative pathway. Our study suggests that (1) the D2 dopamine receptor plays a role in autophagy and (2) raclopride mediated a non-canonical autophagy pathway in cardiac myocytes via Rab9.