Abstract
Background Inflammation and oxidative stress play a key role in vascular injury in atherogenesis. Heme-oxygenase 1 (HO-1) is the rate limiting enzyme in the conversion of heme to carbon monoxide, biliverdin and iron and exerts anti-inflammatory and anti-oxidant effects in VSMC. However, the mechanisms underlying HO-1 activation in response to these atherogenic stimuli are not known. Recent evidence from our work suggests that HO-1-mediated cytoprotection is dependent on Akt activity. Objective We investigated the role of Akt in transcriptional regulation of HO-1 in response to oxidative stress. Methods Human aortic smooth muscle cells (HASMC) were transduced with a retroviral vector (MSCV) expressing Akt, rendered quiescent and exposed to 300 μM of H2O2. HO-1 mRNA was quantified 6 hr after exposure to H2O2 using RT-PCR. HO-1 promoter activity was assessed in COS-7 cells using a pGL3-luc reporter construct containing the full length human HO-1 promoter. Results H2O2 increase HO-1 mRNA and protein levels in a time-dependent fashion. Akt overexpression potentiated H2O2 induced HO-1 mRNA synthesis and increased protein expression. The effect of H2O2 on HO-1 transcription was abrogated by knockdown of Akt using siRNA. In parallel with induction of HO-1 message, H2O2 increased HO-1 promoter activity several fold in COS-7 cells. Akt siRNA significantly reduced H2O2 induced HO-1 promoter activity. Conclusion Akt upregulates oxidative stress-induced HO-1 activity at the transcriptional level. This mechanism of HO-1 induction may underlie the dependence of HO-1 on Akt for protection against oxidative stress-induced injury in VSMC. Supported by grants from CIHR and HSFC to L.G. Melo
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