Submitted on July 23, 2008
Revised on March 9, 2009
Accepted on March 19, 2009
Prolyl hydroxylase 2 deficiency limits proliferation of vascular smooth muscle cells by HIF-1
-dependent mechanisms
Kelly Schultz1, Vanishree Murthy1, Jeffrey B. Tatro1, and Debbie Beasley1*
1 Tufts Medical Center
* To whom correspondence should be addressed. E-mail: dbeasley{at}tuftsmedicalcenter.org.
Arterial O2 levels are thought to modulate vascular smooth muscle cell (VSMC) proliferation and vascular remodeling, but the mechanisms involved are poorly understood. Here we tested the hypothesis that PHD2, a prolyl hydroxylase domain (PHD)-containing O2 sensor, modulates growth factor-induced proliferative responses of human pulmonary artery SMC (HPASMC). We found that both PHD1 and PHD2 were robustly expressed by HPASMC, and inhibiting prolyl hydroxylase activity pharmacologically by using the nonselective dioxygenase inhibitor dimethoxalylglycine (DMOG) inhibited proliferation and cyclin A expression induced by platelet-derived growth factor (PDGF)-AB or fibroblast growth factor (FGF)-2. Specific knockdown of PHD2 using small interfering RNAs had similar effects. The inhibitory effects of DMOG and PHD2 knockdown on proliferation and cyclin A expression were seen under both normoxic (20% O2) and moderately hypoxic (5% O2) conditions, and PHD2 expression was not affected by O2 level nor by stimulation with PDGF or FGF-2, indicating that the pro-proliferative influence of PHD2 does not involve alterations of its expression. Knockdown of PHD2 increased HIF-1
expression, as expected, but we also found that HIF-1 knockdown abolished the inhibitory effect of PHD2 knockdown on PDGF-induced cyclin A expression. Therefore, we conclude that PHD2 promotes growth factor-induced responses of human VSMC, acting by HIF-1-dependent mechanisms. Given the role of PHD2 as an oxygen sensor in mammalian cells, these results raise the possibility that PHD2 links VSMC proliferation to O2 availability.
