Lipopolysaccharide from Escherichia coli induces the expression of vascular endothelial growth factor via toll-like receptor 4 in human limbal fibroblasts

Corneal neovascularization can be induced by a severe ocular infection, injury or immunological diseases. The vascular endothelial growth factor (VEGF) is the main cytokine involved in this phenomenon, inducing angiogenesis from the vascularized ocular tissues. As the limbal tissue is located between conjunctival and corneal tissues, we suggest that the limbal cells are participating in the production of VEGF induced by bacterial components as LPS. In this work, RT-PCRs and immunoblots were used to investigate the expression of VEGF and other pro-angiogenic genes in primary cultures of human limbal fibroblasts (PCHLF) treated with lipopolysaccharide (LPS) from Escherichia coli. We found that the expression of VEGF was initiated at 6 h and reaches its highest expression at 72 h after stimulation with LPS. Up-regulation of toll-like receptor 4 (TLR4) after 3 h of treatment was also observed. LPS-induced the expression of VEGF in a dose-dependent manner, and the blocking of TLR4 with an anti-TLR4 antibody prevented VEGF expression. We also analyzed the molecules that modulate VEGF expression. LPS did not induce the up-regulation of LL-37 nor the hypoxia induced factor 1 alpha (HIF-1α) mRNA expression, however, an up-regulation of interleukin 13 receptor alpha 1 (IL-13Rα1) and interleukin 4 receptor alpha (IL-4Rα) were observed after 3 and 12 h of stimulation, respectively. The expression of interleukin 13 did not change throughout the treatment. These results suggest that TLR4, IL-13Rα1 and IL-4Rα induced by LPS in PCHLF could be playing an important role in the corneal neovascularization.