Attenuation of renal fibrosis in mice due to lack of bombesin receptor-activated protein homologue

Bombesin receptor-activated protein (BRAP), encoded by the C6orf89 gene in humans, is expressed in various cells with undefined functions. BC004004, the mouse homologue of C6orf89, has been shown to play a role in bleomycin-induced pulmonary fibrosis through the use of a BC004004 gene knockout mouse (BC004004^−/−). In this study, we investigated the potential involvement of BRAP in renal fibrosis using two mouse models: unilateral ureteral obstruction (UUO) and type 2 diabetes mellitus induced by combination of a high-fat diet (HFD) and streptozocin (STZ). BRAP or its homologue was expressed in tubular epithelial cells (TECs) in the kidneys of patients with chronic kidney disease (CKD) and in BC004004^+/+ mice. Compared to control mice, BC004004^−/− mice exhibited attenuated renal injury and renal fibrosis after UUO or after HFD/STZ treatment. Immunohistochemistry and immunoblot analyses of the kidneys of BC004004^+/+ mice after UUO surgery showed a more significant decrease in E-cadherin expression and a more significant increase in both α smooth muscle actin (α-SMA) and vimentin expression compared to BC004004^−/− mice. Additionally, stimulation with transforming growth factor-β1 (TGF-β1) led to a more significant decrease in E-cadherin expression and a more significant increase in α-SMA and vimentin expression in isolated TECs from BC004004^+/+ than in those from BC004004^−/− mice. These results suggest that an enhanced epithelial-mesenchymal transition (EMT) process occurred in TECs in BC004004^+/+ mice during renal injury, which might contribute to renal fibrosis. The loss of the BRAP homologue in BC004004^−/− mice suppressed EMT activation in kidneys and contributed to the suppression of fibrosis during renal injury.