Bradykinin B2 Receptor Contributes to Inflammatory Responses in Human Endothelial Cells by the Transactivation of the Fibroblast Growth Factor Receptor FGFR-1.

Elevated levels of bradykinin (BK) and fibroblast growth factor-2 (FGF-2) have been implicated in the pathogenesis of inflammatory and angiogenic disorders. In angiogenesis, both stimuli induce a pro-inflammatory signature in endothelial cells, activating an autocrine/paracrine amplification loop that sustains the neovascularization process. Here we investigated the contribution of the FGF-2 pathway in the BK-mediated human endothelial cell permeability and migration, and the role of the B2 receptor (B2R) of BK in this cross-talk. BK (1 µM) upregulated the FGF-2 expression and promoted the FGF-2 signaling, both in human umbilical vein endothelial cells (HUVEC) and in retinal capillary endothelial cells (HREC) by the activation of Fibroblast growth factor receptor-1 (FGFR-1) and its downstream signaling (fibroblast growth factor receptor substrate: FRSα, extracellular signal⁻regulated kinases1/2: ERK1/2, and signal transducer and activator of transcription 3: STAT3 phosphorylation). FGFR-1 phosphorylation triggered by BK was c-Src mediated and independent from FGF-2 upregulation. Either HUVEC and HREC exposed to BK showed increased permeability, disassembly of adherens and tight-junction, and increased cell migration. B2R blockade by the selective antagonist, fasitibant, significantly inhibited FGF-2/FGFR-1 signaling, and in turn, BK-mediated endothelial cell permeability and migration. Similarly, the FGFR-1 inhibitor, SU5402, and the knock-down of the receptor prevented the BK/B2R inflammatory response in endothelial cells. In conclusion, this work demonstrates the existence of a BK/B2R/FGFR-1/FGF-2 axis in endothelial cells that might be implicated in propagation of angiogenic/inflammatory responses. A B2R blockade, by abolishing the initial BK stimulus, strongly attenuated FGFR-1-driven cell permeability and migration.