HIF-2
haploinsufficient mice have blunted retinal neovascularization due to impaired expression of a proangiogenic gene battery
Elhadji M. Dioum 1,
Stephen L. Clarke 2,
Kan Ding 1,
Joyce J. Repa 1,
and
Joseph A. Garcia 1*
1 Internal Medicine, UT Southwestern Medical Center at Dallas, Dallas, Texas, United States
2 Department of Nutritional Sciences, Oklahoma State University, Stillwater, Oklahoma, United States
* To whom correspondence should be addressed. E-mail: joseph.garcia{at}utsouthwestern.edu.
 |
Abstract |
|---|
Purpose: To characterize the effect of HIF-2
haploinsufficiency upon retinal neovascularization and angiogenic signaling in neonatal mice.
Methods: Retinal samples were obtained from HIF-2 haploinsufficient (Epas1+/-) and wildtype (Epas1+/+) neonatal mice exposed to an oxygen-induced retinopathy (OIR) protocol. Histological and molecular studies were performed immediately, twelve hours, or five days after initiation of the hypoxic phase of the OIR protocol. Molecular profiling was performed in mouse brain endothelial cells maintained under normoxia or hypoxia. Transfection studies assessed the response of isolated promoter regions from proangiogenic genes to HIF-1 or HIF-2 over-expression.
Results: Epas1+/- mice exhibited no significant differences in retinal vasculature during normal development, but had reduced neovascularization in an OIR protocol. Multiple proangiogenic factors were induced during the hypoxic phase in Epas1+/+ OIR retinal samples whereas Epas1+/- OIR retinal samples had absent or blunted induction of these same factors. Several, but not all, proangiogenic factors were induced in mouse brain endothelial cells after hypoxia exposure. In transfection assays, the majority of proangiogenic promoter regions were preferentially activated by HIF-2 relative to HIF-1.
Conclusions: HIF-2 deficiency results in reduced neovascularization and blunted inducibility of proangiogenic factors in the retinas from mice with OIR. We propose HIF-2 is a master regulator of proangiogenic factors in retinal vascular endothelial cells, the predominant cell type of the retina in which HIF-2 is expressed. Future studies will address whether the molecular and functional roles for HIF-2 identified from these studies can be generalized to other pathophysiological states involving neovascularization.
Key Words:
neovascularization, hypoxia, transcription factors, retinopathy of prematurity, oxygen-induced retinopathy, HIF
