Submitted on November 2, 2007
Accepted on July 7, 2008
Inhibition of Vascular Smooth Muscle Cell Proliferation by Chronic Hemin Treatment
Tuanjie Chang1, Lingyun Wu2, and Rui Wang3*
1 Pharmacology, Unviersity of saskatchewan, Sakatoon, Canada; , Canada
2 Saskatoon, Canada
3 Office of VP Research, Lakehead University, Thunder Bay, Canada; , Canada
* To whom correspondence should be addressed. E-mail: rwang{at}lakeheadu.ca.
Hemin, an oxidized form of heme, is an essential regulator of gene expression and cell cycle progression. We previously reported that chronic hemin treatment of spontaneously hypertensive rats reversed the eutrophic inward remodeling of small peripheral arteries. Whether long-term treatment of cultured vascular smooth muscle cells (VSMCs) with hemin alters the proliferation status of these cells has been unknown. In the present study, hemin treatment at 5 µM for 4, 7, 14, and 21 days significantly inhibited the proliferation of cultured rat aortic VSMCs (A-10 cells) by arresting cells at G0/G1 phases so to decelerate cell cycle progression. Heme oxygenase (HO) activity and inducible HO-1 protein expression were significantly increased by hemin treatment. HO inhibitor SnPP abolished the effects of hemin on cell proliferation and HO activity. Interestingly, hemin-induced HO-1 expression was further increased in the presence of SnPP. Hemin treatment had no significant effect on the expression of constitutive HO-2. Expression of p21 protein and the level of reactive oxygen species (ROS) were decreased by hemin treatment, which was reversed by application of SnPP. After removal of hemin from culture medium, inhibited cell proliferation and increased HO-1 expression in VSMCs were returned to control level within 1 week. Transfection with HO-1 siRNA significantly knocked down HO-1 expression and decreased HO activity, but had no effect on HO-2 expression, in cells treated with or without hemin for 7 days. The inhibitory effect of hemin on cell proliferation was abolished in HO-1 silenced cells. It is concluded that induction of HO-1 and consequently increased HO activity are responsible for the chronic inhibitory effect of hemin on VSMCs proliferation. Changes in the levels of p21 and ROS might also participate in the cellular effects of hemin.
