Aim: Tumour necrosis factor-α (TNF-α) is one of the major inflammatory cytokines involved in the pathogenesis of various vitreoretinal diseases. The authors investigated the effect of hypoxia, TNF-α and dexamethasone on vascular endothelial growth factor (VEGF) expression by cultured hyalocytes.
Methods: Hyalocytes were isolated from bovine vitreous. Hypoxic and TNF-α-dependent effects on cultured hyalocytes were investigated using several assays to determine VEGF protein expression, hypoxia-inducible factor (HIF)-1α protein levels, HIF-1α-DNA-binding ability and VEGF mRNA stability. The effects of dexamethasone on VEGF expression and its intracellular signalling under hypoxic or TNF-α stimulated conditions were also examined.
Results: Hypoxic conditions and TNF-α stimulation induce VEGF expression in hyalocytes. These stimuli also stabilise HIF-1α protein and increase its DNA-binding ability. Dexamethasone significantly inhibits both HIF-1α protein levels and HIF-1α-DNA-binding activity, and also decreases the hypoxic- and TNF-α -dependent induction of VEGF expression in hyalocyte. However, dexamethasone has no significant effect on the stability of VEGF mRNA.
Conclusions: Hyalocytes may be involved in various vitreoretinal diseases by increasing HIF-1α protein stability and HIF-1α-DNA binding, and thus increasing VEGF production under pathological conditions. Dexamethasone seems to be capable of inhibiting hypoxic and TNF-α dependent VEGF production, presumably via its inhibitory effects on HIF-1α protein levels and its DNA-binding activity.
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Funding: The study was supported in part by grants from the Ministry of Education, Science, Sports and Culture, Japan (Grant-in-Aid for Scientific Research #19592026).
Competing interests: None.
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