Podocyte injury is the major cause of proteinuria in primary glomerular diseases. Oxidative stress has long been thought to play a role in triggering podocyte damage; however, the underlying mechanism remains poorly understood. Here we show that the Wnt/b-catenin pathway is involved in mediating oxidative stress-induced podocyte dysfunction. Advanced oxidation protein products, a marker and trigger of oxidative stress, were increased in the serum of patients with chronic kidney disease and correlated with impaired glomerular filtration, proteinuria, and circulating level of Wnt1. Both serum from patients with chronic kidney disease and exogenous advanced oxidation protein products induced Wnt1 and Wnt7a expression, activated b-catenin, and reduced expression of podocyte-specific markers in vitro and in vivo. Blockade of Wnt signaling by Klotho or knockdown of b-catenin by shRNA in podocytes abolished b-catenin activation and the upregulation of fibronectin, desmin, matrix metalloproteinase-9, and Snail1 triggered by advanced oxidation protein products. Furthermore, conditional knockout mice with podocyte-specific ablation of b-catenin were protected against podocyte injury and albuminuria after treatment with advanced oxidation protein products. The action of Wnt/b-catenin was dependent on the receptor of advanced glycation end products (RAGE)mediated NADPH oxidase induction, reactive oxygen species generation, and nuclear factor-kB activation. These studies uncover a novel mechanistic linkage of oxidative stress, Wnt/b-catenin activation, and podocyte dysfunction.

The morbidity of CKD is in highly increasing rate and compels nephrologists to face the great difficulties for blankness of effective therapeutic strategies (Isakova et al., 2020; Legrand et al., 2020). Although a series of drugs such as angiotensin receptor blocker and calcium channel blocker (Woo et al., 2013) or the new drug FG-4592, an oral hypoxia-inducible factor prolyl hydroxylase inhibitor (Provenzano et al., 2016), show the therapeutic potential in the progression of CKD, however, there is still a high incidence of end-stage renal disease (ESRD) in the coming

The endocannabinoid system has multiple effects. Through interacting with cannabinoid receptor type 1 and type 2, this system can greatly affect disease progression. Previously, we showed that activated cannabinoid receptor type 2 (CB2) mediated kidney fibrosis. However, the underlying mechanisms remain underdetermined. Here, we report that CB2 was upregulated predominantly in kidney tubular epithelial cells in unilateral urinary obstruction and ischemia-reperfusion injury models in mice, and in patients with a variety of kidney diseases. CB2 expression was closely correlated with the progression of kidney fibrosis and accompanied by the activation of b-catenin. Furthermore, CB2 induced the formation of a b-arrestin 1/ Src/b-catenin complex, which further triggered the nuclear translocation of b-catenin and caused fibrotic injury. Incubation with XL-001, an inverse agonist to CB2, or knockdown of b-arrestin 1 inhibited CB2-triggered activation of b-catenin and fibrotic injury. Notably, CB2 potentiated Wnt1-induced b-arrestin 1/b-catenin activation and augmented the pathogenesis of kidney fibrosis in mice with unilateral ischemia-reperfusion injury or folic acidinduced nephropathy. Knockdown of b-arrestin 1 inhibited the CB2 agonist AM1241-induced b-catenin activation and kidney fibrosis. By promoter sequence analysis, putative transcription factor binding sites for T-cell factor/lymphoid enhancer factor were found in the promoter regions of the CB2 gene regardless of the species. Overexpression of bcatenin induced the binding of T-cell factor/lymphoid enhancer factor-1 to these sites, promoted the expression of CB2, b-arrestin 1, and the proto-oncogene Src, and triggered their accumulation. Thus, the CB2/b-catenin pathway appears to create a reciprocal activation feedback loop that plays a central role in the pathogenesis of kidney fibrosis.