Neuropilin 1 Promotes Unilateral Ureteral Obstruction-Induced Renal Fibrosis via RACK1 in Renal Tubular Epithelial Cells

Neuropilin 1 (NRP1) is a single-channel transmembrane glycoprotein whose role and mechanism in renal fibrosis remain incompletely elucidated. Therefore, we investigated the effect of NRP1 on renal fibrosis and its potential mechanism. NRP1 expression in the renal sections from chronic kidney disease (CKD) patients and a unilateral ureteral obstruction (UUO) mouse model was detected. Nrp1 overexpression or knockdown plasmid was transfected into mice, TKPTS mouse kidney proximal tubular epithelial cells (TECs), and rat kidney fibroblasts, after which pathological injury evaluation and fibrosis marker detection were conducted. The direct interaction of the receptor of activated protein C kinase 1 (RACK1) with NRP1 was validated by immunoprecipitation and Western blotting. We found that the upregulated renal NRP1 expression in CKD patients was located in proximal TECs, consistent with the degree of interstitial fibrosis. In the UUO mouse model, NRP1 expression was upregulated in the kidney, and overexpression of Nrp1 increased the mRNA and protein expression of fibronectin (Fn) and α-smooth muscle actin (α-SMA), whereas Nrp1 knockdown significantly reduced Fn and α-SMA expression and downregulated the inflammatory response. NRP1 promoted transforming growth factor beta 1 (TGF-β1)-induced pro-fibrotic responses in the TKPTS cells and fibroblasts, and Nrp1 knockdown partially reversed these responses. Immunoprecipitation combined with liquid chromatography-tandem mass spectrometry verified that NRP1 can directly bind to RACK1, and Rack1 knockdown reversed the NRP1-induced fibrotic response. In summary, NRP1 may enhance the TGF-β1 pathway by binding to RACK1, thus promoting renal fibrosis.

Chronic kidney disease; Neuropilin 1; Receptor for activated C kinase 1; Renal fibrosis.