Identification of multiple, oxygen-stable HIF1 alpha isoforms, and augmented expression of adrenomedullin in rheumatoid arthritis.

OBJECTIVES: To identify and quantitate hypoxia inducible factor 1 alpha (HIF1 α) isoforms in circulating peripheral blood mononuclear cells (PBMCs), and to assess their effects on target gene expression in rheumatoid arthritis (RA) patients. METHODS: PBMCs from healthy controls and from RA patients were analysed ex-vivo for expression of HIF isoforms, and target genes were assessed by RT-PCR. RESULTS: Transcripts of multiple HIF1α isoforms exist in circulating PBMCs. Expression of all these isoforms is dramatically, and maximally, augmented by foreign surface recognition. However, HIF1α protein stabilisation requires additional cell activation with phorbol ester. No difference in the expression or regulation of the HIF1α isoforms was seen between patients with active RA and healthy controls. However, analysis of a panel of HIF1α target genes revealed increased basal expression of the adrenomedullin gene in RA PBMCs, with resulting loss of further induction upon cell activation. CONCLUSIONS: Even in normoxia PBMCs express stable HIF1α protein on cell activation. Whilst multiple HIF1α isoforms exist in PBMCs no differences in expression were seen in RA compared with healthy controls. RA causes constitutive adrenomedullin expression in PBMCs that is not explicable by altered HIF expression, or stabilisation. Adrenomedullin has a variety of potential biological roles in RA, including regulation of angiogenesis, and aberrant gene regulation may be relevant in RA pathogenesis.