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 patients with chronic kidney disease (CKD) and a unilateral ureteral obstruction (UUO) mouse model was detected. 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 blot analysis. We found that the upregulated renal NRP1 expression in patients with CKD 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 knockdown significantly reduced Fn and α-SMA expression and downregulated the inflammatory response. NRP1 promoted transforming growth factor β1 (TGF-β1)-induced profibrotic responses in the TKPTS cells and fibroblasts, and knockdown partially reversed these responses. Immunoprecipitation combined with liquid chromatography-tandem mass spectrometry verified that NRP1 can directly bind to RACK1, and knockdown reversed the NRP1-induced fibrotic response. In summary, NRP1 may enhance the TGF-β1 pathway by binding to RACK1, thus promoting renal fibrosis. Although a few studies have confirmed the correlation between neuropilin 1 (NRP1) and renal diseases, the mechanism of NRP1 in renal fibrosis remains unclear. Here, we investigated the effects of NRP1 on renal fibrosis through in vitro and in vivo experiments and explored the possible downstream mechanisms. We found that NRP1 can stimulate the TGF-β1 signaling pathway, possibly by binding to RACK1, thereby promoting renal fibrosis.