Background During the Pathogenesis of rheumatoid arthritis (RA), the chronic inflammatory process in the arthritic joint leads to degradation of articular cartilage and subchondral bone. Local hypoxic regions result from massive infiltration and proliferation of immune cells, leading to angiogenesis which facilitates cell survival and progressive chronicity. A key regulator of the hypoxia induced cell adaption processes is the transcription factor HIF (hypoxia-inducible factor). HIF consists of a β-subunit, which needs to heterodimerize with the oxygen sensitive HIF-1α or HIF-2α subunit in order to be transcriptionally active.

Objectives However, the distinct functions of HIF-1α and HIF-2α in the hypoxia induced endothelial cell adaption processes are unknown.

Methods For this purpose we investigated the adaption of Human Microvascular Endothelial Cell (HMEC)-1 to hypoxic conditions by angiogenesis and the bioenergetic switch to glycolysis with regard to 2D angiogenesis, ATP/ADP-ratio gene and protein expression. We further established specific knockdown cells for HIF-1α, HIF-2α, and the HIF-1α/HIF-2α in order to identify distinct functions of both transcription factors.

Results We showed that HMEC-1 cells are suitable for our study aim and that HIF-1α and HIF-2α knockdown resulted in impaired angiogenesis. Transcriptome analysis and evaluation of pro-angiogenic factors indicated major impact on angiogenesis by HIF-2α. Overlapping functions of both transcription factors were found regarding bioenergetics adaption with priority for HIF-1α. However, a respectful amount of solely regulated HIF-1α genes were identified and indicate a distinct function of HIF-1α in the bioenergetic adaption process. Data were supported by the results of HIF-1α/HIF-2α combined knockdown.

Conclusions Our results indicate distinct functions of HIF-1α and HIF-2α and demonstrate a major impact of HIF-2α on angiogenesis. This is of high interest regarding intervention of the chronicity of the inflammatory process in RA and opens new possibilities for therapeutic approaches by targeting the specific hypoxia induced transcription factors.

Disclosure of Interest None declared