HIF-1-Dependent Induction of β3 Adrenoceptor: Evidence from the Mouse Retina

A major player in the homeostatic response to hypoxia is the hypoxia-inducible factor (HIF)-1 that transactivates a number of genes involved in neovessel proliferation in response to low oxygen tension. In the retina, hypoxia overstimulates beta-adrenoceptors (beta-ARs) which play a key role in the formation of pathogenic blood vessels. Among beta-ARs, beta 3-AR expression is increased in proliferating vessels in concomitance with increased levels of HIF-1 alpha and vascular endothelial growth factor (VEGF). Whether, similarly to VEGF, hypoxia-induced beta 3-AR upregulation is driven by HIF-1 is still unknown. We used the mouse model of oxygen-induced retinopathy (OIR), an acknowledged model of retinal angiogenesis, to verify the hypothesis of beta 3-AR transcriptional regulation by HIF-1. Investigation of beta 3-AR regulation over OIR progression revealed that the expression profile of beta 3-AR depends on oxygen tension, similar to VEGF. The additional evidence that HIF-1 alpha stabilization decouples beta 3-AR expression from oxygen levels further indicates that HIF-1 regulates the expression of the beta 3-AR gene in the retina. Bioinformatics predicted the presence of six HIF-1 binding sites (HBS #1-6) upstream and inside the mouse beta 3-AR gene. Among these, HBS #1 has been identified as the most suitable HBS for HIF-1 binding. Chromatin immunoprecipitation-qPCR demonstrated an effective binding of HIF-1 to HBS #1 indicating the existence of a physical interaction between HIF-1 and the beta 3-AR gene. The additional finding that beta 3-AR gene expression is concomitantly activated indicates the possibility that HIF-1 transactivates the beta 3-AR gene. Our results are indicative of beta 3-AR involvement in HIF-1-mediated response to hypoxia.

Automated summary

The hypoxia-inducible factor (HIF)-1 plays a major role in the homeostatic response to hypoxia by activating genes involved in neovessel proliferation. In the retina, hypoxia leads to overstimulation of beta-adrenoceptors (beta-ARs) and the formation of pathogenic blood vessels. This study demonstrates that HIF-1 regulates the expression of the beta 3-AR gene in the retina, and its involvement in the hypoxia response.