Hyaluronan-induced VEGF-C promotes fibrosis-induced lymphangiogenesis via Toll-like receptor 4-dependent signal pathway.

Hyaluronan (HA), a component of the extracellular matrix, modulates cellular behavior including angiogenesis. However, little is known about the effect of HA on lymphangiogenesisin fibrosis model. In this study, we investigated the roles of HA in lymphangiogenesisof unilateral ureteral obstruction (UUO). We found that HA cooperated synergistically with vascular endothelial cell growthfactor-C to stimulate capillary-like tube formation and increase migration of cells in a haptotaxisassay. Accumulation of HA in the cortical interstitial spacewas positively correlated with the number of lymphatic vesselsafter UUO. Depletion of macrophages with clodronate decreased UUO-induced HA accumulation and lymphangiogenesis. Additionally, hyaluronan synthase(HAS) mRNA expression and HA production were increased in bone marrow-derived macrophagesupon stimulation with TGF-β1. Transfer of mHAS2 and mHAS3 knock-down CD11b-positive macrophages to SCID mice resulted in a partial decrease in UUO-induced lymphangiogenesis. HA increased expression of vascular endothelial cell growthfactor-C in macrophages. Vascular endothelial cell growthfactor-C expression and LYVE-1-positive lymphatic area was significantly lower in the UUO-kidney from TLR4null mice than that from TLR4wild-type mice. Collectively, these results suggest that HA increases lymphangiogenesisin renal fibrosis model and also stimulates vascular endothelial cell growthfactor-C production from macrophages through Toll-like receptor 4-dependent signal pathway.