Protein phosphatase Mg ²⁺ /Mn ²⁺ dependent‐1A and PTEN deregulation in renal fibrosis: Novel mechanisms and co‐dependency of expression

Abstract

PPM1A and PTEN emerged as novel suppressors of chronic kidney disease (CKD).Since loss of PPM1A and PTEN in the tubulointerstitium promotes fibrogenesis, defining molecular events underlying PPM1A/PTEN deregulation is necessary to develop expression rescue as novel therapeutic strategies. Here we identify TGF-β1 as a principle repressor of PPM1A, as conditional renal tubular-specific induction of TGF-β1 in mice dramatically downregulates kidney PPM1A expression. TGF-β1 similarly attenuates PPM1A and PTEN expression in human renal epithelial cells and fibroblasts, via a protein degradation mechanism by promoting their ubiquitination. A proteasome inhibitor MG132 rescues PPM1A and PTEN expression, even in the presence of TGF-β1, along with decreased fibrogenesis. Restoration of PPM1A or PTEN similarly limits SMAD3 phosphorylation and the activation of TGF-β1induced fibrotic genes. Concurrent loss of PPM1A and PTEN levels in aristolochic acid nephropathy further suggests crosstalk between these repressors. PPM1A silencing in renal fibroblasts, moreover, results in PTEN loss, while PTEN stable depletion decreases PPM1A expression with acquisition of a fibroproliferative phenotype in each case. Transient PPM1A expression, conversely, elevates cellular PTEN levels while lentiviral PTEN introduction increases PPM1A expression. PPM1A and PTEN, therefore, co-regulate each other's relative abundance, identifying a previously unknown pathological link between TGF-β1 repressors, contributing to CKD.

The Genomic Response to TGF-β1 Dictates Failed Repair and Progression of Fibrotic Disease in the Obstructed Kidney

“…Extensive or recurring sublethal epithelial trauma, usually in the context of persistent transforming growth factor-β1 (TGF-β1) pathway activation, initiates and sustains a program of maladaptive repair that facilitates the progression of AKI to CKD (Friedman et al, 2013;Emlet et al, 2015;Ferenbach and Bonventre, 2015;Venkatachalam et al, 2015;Basile et al, 2016;Takaori et al, 2016;Chang-Panesso and Humphreys, 2017;Schnaper, 2017;Chung et al, 2018;Qi and Yang, 2018;Gewin, 2019;Tang et al, 2020; Figure 2). The major source of TGF-β1, as well as other proinflammatory cytokines, in the kidney is the injured epithelium although both resident and infiltrative macrophages are also major contributors (Bonventre and Yang, 2011;Liu et al, 2018;Black et al, 2019;Zhang et al, 2020).…”

“…The contribution of TGF-β1 to the fibrotic response, importantly, was confirmed using genetic approaches. Conditional overexpression of TGF-β1 in the tubular epithelium of Pax8-rtTA-tet-o-TGF-β1 double transgenic mice induces extensive peritubular fibrosis, focal nephron degeneration (Traykova-Brauch et al, 2008;Koesters et al, 2010) and TGF-β1-dependent loss of the SMAD phosphatase PPM1A (Tang et al, 2020). Similarly, Pax8 promoter-driven expression of a ligand-independent constitutively-active TGF-β type I receptor results in the acquisition of features typical of AKI (e.g., epithelial apoptosis, necrosis and dedifferentiation; renal inflammation) (Gentle et al, 2013).…”

“…Recent studies, furthermore, link tubular epithelial dysfunction in response to both acute (e.g., ischemiareperfusion, nephrotoxins) and more protracted (UUO) injury to the progression of renal fibrosis via the p53 and JNK pathways with the retention of TGF-β signaling . p53 is activated in the injured renal epithelium initiating cell cycle arrest at the G 1 and G 2 /M checkpoints depending on the participating effectors (e.g., ATM, ATR, CK1, CK2, p21, TGF-β1) and extent of tissue hypoxia (Thomasova and Anders, 2015;Tang et al, 2018Tang et al, , 2019Tang et al, , 2020Liu et al, 2019). TGF-β1 signaling in the damaged kidney increases p53 levels and phosphorylation, particularly at p53 S9/15 , promoting p53 stabilization and triggering p53-SMAD2/3 interactions resulting in transcription of the growth inhibitor p21 and subsequent p21-dependent G 1 arrest (Higgins et al, 2019).…”

Poricoic acid A suppresses TGF‑β1‑induced renal fibrosis and proliferation via the PDGF‑C, Smad3 and MAPK pathways

“…However, previous studies have shown that even if these factors are controlled effectively, including blood pressure, blood glucose and drug damage, the process of renal fibrosis remains difficult to prevent (6). Therefore, investigating the molecular mechanism underlying the occurrence and development of fibrosis, identifying therapeutic agents and target genes that can directly interfere with the fibrotic process has become an important topic of study in recent years (7)(8)(9).…”

Upregulation of miR-382 contributes to renal fibrosis secondary to aristolochic acid-induced kidney injury via PTEN signaling pathway

“…Phosphatase and tensin homologs deleted on chromosome 10 (PTEN)/protein kinase B(AKT) pathway has been reported in tumors as a tumor suppressor 16,17 . In addition, depletion of PTEN was characteristic of renal fibrosis and overexpression of PTEN expression attenuated tubulointerstitial fibrosis [18][19][20][21][22] , inhibited macrophage polarization from M1 to M2 23,24 and suppressed inflammation responses 25,26 . Given that PTEN has been identified as a target of miR-382 in liver generation, acute promyelocytic leukemia, and tumor angiogenesis as well as oxidative stress of the tubular epithelium [27][28][29][30] , which remains unclear in kidney fibrosis.…”