DDAH1 deficiency promotes intracellular oxidative stress and cell apoptosis via a miR-21-dependent pathway in mouse embryonic fibroblasts.

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, is degraded by dimethylarginine dimethylaminohydrolase 1 (DDAH1). Emerging evidence suggests that plasma ADMA accumulation, DDAH1 activity/expression reduction, and microRNA-21 (miR-21) upregulation are linked to disease pathology, but the mechanisms remain largely unknown. In the present study, we assessed the potential role of the ADMA-DDAH1-miR-21 pathway in the regulation of the cellular redox state and apoptosis using wild-type (WT) and DDAH1-knockout (KO) immortalized mouse embryonic fibroblasts (MEFs). DDAH1 deficiency significantly increased ADMA levels, enhanced cellular oxidative stress, and rendered cells more vulnerable to apoptosis induced by tert-butyl hydroperoxide (tBHP) or A23187. However, treatment with exogenous ADMA (1-80μM) for 24h or for a prolonged period (10μM, 10 passages) in WT MEFs had no marked effect on intracellular reactive oxygen species and apoptosis sensitivity. Interestingly, miR-21 expression was significantly increased, by 4 fold, in DDAH1(-/-) MEFs, and the induction of miR-21 by DDAH1 deficiency was dependent on oxidative stress and NF-κB activation. Inhibition of DDAH1 activity by PD 404182 also increased miR-21 expression. Furthermore, inhibition of miR-21 with a lentiviral vector in DDAH1(-/-) MEFs significantly upregulated SOD2 expression and the attenuated oxidative stress and apoptosis induced by tBHP or A23187. Taken together, our results suggest that DDAH1 not only acts as an enzyme degrading ADMA but also controls cellular oxidative stress and apoptosis via a miR-21-dependent pathway.

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