Aims: Low-density lipoprotein receptor-related protein 5 (LRP5) is known as a co-receptor of canonical Wnt signaling. This study aimed to investigate LRP5’s role in chronic kidney diseases including diabetic and obstructive nephropathies, and its new role in regulating TGF-β-Smad2/3 signaling in renal fibrogenesis.
Methods: The expression of LRP5 was examined in the kidneys of Akita mice, db/db mice and mice with obstructive nephropathy. The regulation of TGF-β signaling by LRP5 was determined in both obstructed kidneys and in human proximal tubule epithelial cells exposed to TGF-β1. Interaction of LRP5 with TGF-β receptors was evaluated by Co-IP assays, immunostainings and cell fractionation.
Results: We found that LRP5 levels were substantially up-regulated in the renal tubules of diabetic mice and mice with obstructive nephropathy. In the obstructed kidneys, Lrp5 knockout significantly ameliorated tubulointerstitial fibrosis and attenuated the increases of TGF-β1 and TGF-β receptors (TβRI and TβRII), without affecting canonical Wnt signaling. Utilizing SBE-Luc reporter mice and immunostaining assays, LRP5 depletion was demonstrated to attenuate the activation and nuclear translocation of Smad2/3, whereas LRP5 overexpression enhanced TGF-β-Smad2/3 signaling in tubule epithelial cells. Obstruction-induced LRP5 and TβRI were co-localized in the injured tubules, and furthermore, LRP5 was co-precipitated with TβRI and TβRII. The extracellular domain of LRP5 was essential for its association with TGF-β receptors and profibrotic activity. In addition, LRP5 stabilized TGF-β receptors, 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.
Conclusion: These findings reveal a novel profibrotic activity of LRP5 by interacting with TGF-β receptors, independent of canonical Wnt signaling.
X. He: None. R. Cheng: None. C. Huang: None. Y. Chen: None. J. Ma: None.