All-Trans Retinoic Acid Inhibits Cobalt Chloride-Induced Apoptosis in PC12 Cells: Role of the Dimethylarginine Dimethylaminohydrolase/Asymmetric Dimethylarginine Pathway

Previous studies have shown that the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and its specific hydrolase dimethylarginine dimethylaminohydrolase (DDAH) are involved in the regulation of apoptosis in different cell types. In the present study, we investigated the role of the DDAH/ADMA pathway in cobalt chloride (CoCl2)-induced apoptosis and the antiapoptotic effect of all-trans retinoic acid (atRA) in undifferentiated pheochromocytorna (PC12) cells. Treatment Of CoCl2 (125 mu M) for 48 hr significantly induced the apoptosis of PC12 cells, concomitantly with increased intracellular reactive oxygen species (ROS) production and caspase-3 activity. CoCl2 treatment also decreased the activity of DDAH and the expression of DDAH2 (mRNA and protein), resulting in an increased level of ADMA. All these alterations induced by CoCl2 were attenuated by atRA (0.1, 1, or 10 mu M). Interestingly, the antiapoptotic effects of atRA were inhibited by DDAH2 small RNA interference. In contrast, DDAH2 overexpression inhibited the proapoptotic effects Of CoCl2. We also found that treatment of exogenous ADMA (3, 10, or 30 mu M) induced the apoptosis of PC12 cells in a concentration- and time-dependent manner, which was inhibited by the antioxidant or the caspase-3 inhibitor. These findings suggest that the modulation of the DDAH/ADMA/ROS pathway plays an important role in CoCl2-induced apoptosis and the antiapoptotic effects of atRA in undifferentiated PC12 cells. (C) 2009 Wiley-Liss, Inc.