Hypoxia inducible factor (HIF)-2α is required for the development of the catecholaminergic phenotype of sympathoadrenal cells

The basic helix-loop-helix transcription factor, hypoxia inducible factor (HIF)-2α has been implicated in the development of the catecholaminergic phenotype in cells of the sympathoadrenal (SA) lineage; however, the underlying mechanisms and HIF-2α targets remain unclear. Using an immortalized rat adrenomedullary chromaffin cell line (MAH cells) derived from a fetal SA progenitor, we examined the role of HIF-2α in catecholamine biosynthesis. Chronic hypoxia (2% O₂, 24 h) induced HIF-2α in MAH cells but expression of the rate-limiting enzyme, tyrosine hydroxylase (TH) and catecholamine levels were unaltered. Interestingly, HIF-2α depleted MAH cells showed dramatically lower (5-12 times) levels of dopamine and noradrenaline compared with wild-type and scrambled controls, even in normoxia (21% O₂). This was correlated with a marked reduction in the expression of DOPA decarboxylase (DDC) and dopamine β hydroxylase (DβH) but not TH. Chromatin immunoprecipitation assays revealed that HIF-2α was bound to the DDC gene promoter which contains two putative hypoxia response elements. These data suggest that a basal level of HIF-2α function is required for the normal developmental expression of DDC and DβH in SA progenitor cells, and that loss of this function leads to impaired catecholamine biosynthesis.