Kidney fibrosis is characterized by the continuous mesenchymal accumulation of matrix components, leading to progressive decline in kidney function in chronic kidney diseases (CKD). Transforming growth factor beta (TGF-β) is the key driver in kidney fibrosis. However, there is no effective way to target TGF-β to prevent fibrosis, because inhibition of TGF-β also abolishes its protective anti-inflammatory and wound healing effects. Therefore, aimed to dissociate TGF-β’s profibrotic (unwanted) effects from anti-inflammatory and wound healing (wanted) effects. Hence, targeting β-catenin/Foxo not only protects against TGF-β’s profibrotic effects but also enhances its wound healing and anti-inflammatory effects.
In chapter two, examined the interactions of β-catenin with TCF1 and Foxo1 in human kidney biopsies, in mouse proximal tubular epithelial cells (C1.1) and in the kidney fibrosis model unilateral ureteral obstruction (UUO). The results demonstrated that in human kidney biopsies, β-catenin/Foxo1 interactions were negatively correlated while β-catenin/TCF1 interactions were positively correlated with kidney fibrosis. By using CRISPR/Cas9 knockout of Foxo1 or TCF1 gene, as well as β-catenin/TCF inhibitors and β-catenin degradation in C1.1 cells, found that β-catenin/Foxo1 is protective against rhTGF-β1-induced profibrotic changes. In UUO, combined treatment of rhTGF-β and ICG-001 protected against kidney fibrosis via ICG-001 inhibition of β-catenin/TCF and consequent enhancement of β-catenin/Foxo1. These results suggest β-catenin/Foxo1 interaction protects against TGF-β–mediated kidney fibrosis.
In chapter three, examined the wound healing effects of TGF-β1. Co-administration of rhTGF-β with either ICG-001 or iCRT3 in an in vitro scratch assay and in an in vivo unilateral renal ischemia reperfusion (UIR) increased β-catenin/Foxo1 interaction and resulted in repair of kidney ischemia reperfusion injury with less kidney fibrosis. In a collagen contraction assay, co-administration of rhTGF-β with either ICG-001 or iCRT3 reduced TGF-β–induced fibroblast contraction. These results suggest that β-catenin/Foxo1 interaction promotes fibrosis-free healing in TGF-β–mediated kidney fibrosis.
In chapter four, examined the anti-inflammatory effects of TGF-β1. Co-administration of rhTGF-β and ICG-001 increased Foxp3 expression, and β-catenin which was positively correlated with Foxo transcriptional activity in EL4 T cells. In both UUO and UIR mouse models, co-administration of rhTGF-β and ICG-001 increased the number of regulatory T cells (Tregs) and reduced inflammation and kidney fibrosis. These results suggest that inhibition of β-catenin/TCF1 increases β-catenin/Foxo1–mediated anti-inflammatory effects of TGF-β via upregulation of Tregs.
This thesis showed that redirection of β-catenin binding from TCF to Foxo through ICG-001 or iCRT3 inhibits TGF-β–induced β-catenin/TCF–mediated profibrotic effects while increasing the β-catenin/Foxo–mediated wound healing and anti-inflammatory effects. In conclusion, targeting β-catenin/Foxo may serve as a novel therapeutic strategy in the treatment of kidney fibrosis in chronic kidney diseases.