A Profibrotic Role of LRP5 in Chronic Kidney Diseases Through Interactions with TGF-β Receptors

Background: Low-density lipoprotein receptor-related protein 5 (LRP5) is a co-receptor of Wnt signaling and has been shown to regulate TGF-β1 levels through activation of the Wnt pathway in idiopathic pulmonary fibrosis. This study aimed to investigate a novel and Wnt pathway-independent profibrotic activity of LRP5 through direct interactions with TGF-β receptors. Method: Renal tubulointerstitial fibrosis was evaluated in Lrp5 knockout mice with obstructive nephropathy. The effects of LRP5 on TGF-β receptors and TGF-β-Smad2/3 signaling were determined by cell fractionation, immunostaining and immunoprecipitation. Finding: LRP5 levels were up-regulated in the renal tubules of both type 1 and type 2 diabetic models and obstructive nephropathy models. In the obstructed kidneys, Lrp5 knockout significantly ameliorated tubulointerstitial fibrosis and attenuated the increases of TGF-β1 and TGF-β receptors (TβR), without affecting canonical Wnt signaling. Utilizing SBE-Luc reporter mice and immunostaining, we showed that LRP5 depletion attenuated the activation and nuclear translocation of Smad2/3, whereas LRP5 overexpression enhanced TGF-β-Smad2/3 signaling in tubule epithelial cells. Furthermore, LRP5 was co-immuoprecipitated with TβRI and TβRII, and the extracellular domain of LRP5 was essential for its interactions with TβR and profibrotic activity. In addition, LRP5 stabilized TβR, increased their membrane presentation in the absence of TGF-β1, and promoted the TGF-β1-induced formation of TβRI/TβRII heterodimers and internalization of these receptors. Interestingly, LRP5 was also internalized by TGF-β1 stimulation. Interpretation: LRP5 interacts with TβR to enhance TGF-β-Smad2/3 signaling, driving renal fibrosis in chronic kidney diseases. Funding Statement: This study was supported by a grant from Oklahoma Center for the Advancement of Science and Technology (HR16-041) and NIH grants EY012231, EY018659, EY028949, EY019309 and GM122744. Declaration of Interests: The authors have declared that no conflict of interest exists. Ethics Approval Statement: All the procedures on mice were approved by the Institutional Animal Care and Use Committee at the University of Oklahoma Health Sciences Center.