Differential effects of Th1 versus Th2 cytokines in combination with hypoxia on HIFs and angiogenesis in RA Full Text
Arthritis Research & Therapy, 08/08/2012
Larsen H et al. – The present work demonstrates that T helper cell 1 (Th1) cytokines in combination with hypoxia are not sufficient to induce angiogenic activity by rheumatoid arthritis (RA) fibroblast–like synoviocytes despite hypoxia inducible transcription factor (HIF)–1 activation and vascular endothelial growth factor production. In contrast, Th2 cytokines induce angiogenic activity in normoxia and hypoxia, despite their inability to activate HIFs, highlighting the complex relationships between hypoxia, angiogenesis and inflammation in RA.
Methods- Human Angiogenesis PCR Arrays were used to screen cDNA from RA FLS exposed to hypoxia (1% O2) or dimethyloxalylglycine (DMOG), which stabilises HIFs.
- The involvement of HIF isoforms in generating the angiogenic signature of RA FLS stimulated with hypoxia and/or cytokines was investigated using a DNA-binding assay and RNA interference.
- The angiogenic potential of conditioned media from hypoxia- and/or cytokine-treated RA FLS was measured using an in vitro endothelial-based assay.
- Expression of 12 angiogenic genes were significantly altered in RA FLS exposed to hypoxia, and of these 7 were changed by DMOG, including ephrin A3 (EFNA3), vascular endothelial growth factor (VEGF), adipokines angiopoietin-like (ANGPTL)-4 and leptin.
- These 4 pro-angiogenic genes were dependent on HIF-1 in hypoxia to various degrees: ephrin A3>ANGPTL-4>VEGF>leptin.
- Th1 cytokines tumour necrosis factor alpha (TNFalpha and interleukin 1 beta (IL-1beta induced HIF-1but not HIF-2 transcription as well as activity, and this effect was additive with hypoxia.
- In contrast, Th2 cytokines had no effect on HIFs.
- IL-1beta synergised with hypoxia to upregulate EFNA3 and VEGF in a HIF-1-dependent fashion but despite strongly inducing HIF-1, TNFalpha suppressed adipokine expression and had minimal effect on EFNA3.
- Supernatants from RA FLS subjected to hypoxia and TNFalpha induced fewer endothelial tubules than those from FLS subjected to TNFalpha or hypoxia alone, despite high VEGF protein levels.
- The Th2 cytokine IL-4 strongly induced ANGPTL-4 and angiogenesis by normoxic FLS and synergised with hypoxia to induce further pro-angiogenic activity.
