Loss of expression of protein phosphatase magnesium‐dependent 1A during kidney injury promotes fibrotic maladaptive repair

Abstract

Protein phosphatase magnesium-dependent-1A (PPM1A) dephosphorylates SMAD2/3, which suppresses TGF-β signaling in keratinocytes and during Xenopus development; however, potential involvement of PPM1A in chronic kidney disease is unknown. PPM1A expression was dramatically decreased in the tubulointerstitium in obstructive and aristolochic acid nephropathy, which correlates with progression of fibrotic disease. Stable silencing of PPM1A in human kidney-2 human renal epithelial cells increased SMAD3 phosphorylation, stimulated expression of fibrotic genes, induced dedifferentiation, and orchestrated epithelial cell-cycle arrest via SMAD3-mediated connective tissue growth factor and plasminogen activator inhibitor-1 up-regulation. PPM1A stable suppression in normal rat kidney-49 renal fibroblasts, in contrast, promoted a SMAD3-dependent connective tissue growth factor and plasminogen activator inhibitor-1-induced proliferative response. Paracrine factors secreted by PPM1A-depleted epithelial cells augmented fibroblast proliferation (>50%) compared with controls. PPM1A suppression in renal cells further enhanced TGF-β1-induced SMAD3 phosphorylation and fibrotic gene expression, whereas PPM1A overexpression inhibited both responses. Moreover, phosphate tensin homolog on chromosome 10 depletion in human kidney-2 cells resulted in loss of expression and decreased nuclear levels of PPM1A, which enhanced SMAD3-mediated fibrotic gene induction and growth arrest that were reversed by ectopic PPM1A expression. Thus, phosphate tensin homolog on chromosome 10 is an upstream regulator of renal PPM1A deregulation. These findings establish PPM1A as a novel repressor of the SMAD3 pathway in renal fibrosis and as a new therapeutic target in patients with chronic kidney disease.-Samarakoon, R., Rehfuss, A., Khakoo, N. S., Falke, L. L., Dobberfuhl, A. D., Helo, S., Overstreet, J. M., Goldschmeding, R., Higgins, P. J. Loss of expression of protein phosphatase magnesium-dependent 1A during kidney injury promotes fibrotic maladaptive repair.

Integration of Canonical and Noncanonical Pathways in TLR4 Signaling: Complex Regulation of the Wound Repair Program

“…PTEN expression is lost in several models of injury-induced fibrosis, and targeted PTEN depletion reduces PPM1A levels while promoting SMAD3 phosphorylation as well as SMAD3 nuclear translocalization. 43,46 PPM1A suppression further enhanced TGF-b1-induced SMAD3 phosphorylation and fibrotic gene expression, while PPM1A overexpression inhibited both responses. 45,46 Thus, these findings implicate PTEN as an upstream regulator of PPM1A function in dysfunctional tissue repair and establish PPM1A as a novel repressor of the SMAD3 fibrotic pathway.…”

“…43,46 PPM1A suppression further enhanced TGF-b1-induced SMAD3 phosphorylation and fibrotic gene expression, while PPM1A overexpression inhibited both responses. 45,46 Thus, these findings implicate PTEN as an upstream regulator of PPM1A function in dysfunctional tissue repair and establish PPM1A as a novel repressor of the SMAD3 fibrotic pathway. Stable silencing of PTEN, moreover, induced many of the same fibrotic genes as LPS or TGF-b1 (e.g., CTGF, PAI-1, vimentin, a-SMA, and fibronectin).…”

“…63 PTEN silencing induces dedifferentiation and cell cycle arrest, both biomarkers of maladaptive repair, and cooperates with TGF-b1 to further stimulate expression of the fibrotic signature genes CTGF, PAI-1, vimentin, a-SMA, and EDA-fibronectin. 45,46 The mechanism of PTEN downregulation in the context of fibrosis is not known but is likely the result of increased TGF-b1 levels in the injury microenvironment. TGF-b1 reduces, moreover, the levels of the C-terminal SMAD2/3 protein phosphatase PPM1A, a terminator of TGF-b1 signaling.…”

“…64 While the specific molecular events are unknown, persistent TGF-b1 stimulation reduces PPM1A levels via the Rho/rhoassociated, coiled-coil-containing protein kinase (ROCK) pathway enhancing and maintaining, thereby, SMAD3-dependent transcription of this profibrotic signature. 43,46,57 Rho-ROCK signaling leads to inhibition of PTEN-PPM1A activity in TGF-b1-stimulated cells resulting in a reduction of nuclear PPM1A, maintaining pSMAD2/3 levels required for profibrotic gene expression. 57 Similar to their involvement in EGFR and TGF-b1 signaling, Src kinases are key intermediates in the Rho/ ROCK pathway leading to the expression of the profibrotic genes PAI-1 and CTGF.…”

“…40 The mechanism appears to involve downregulation of the TGF-b1 inhibitory receptor BAMBI (through a TLR4/MyD88/NF-jB pathway) that, in turn, may sensitize cells to the relatively abundant levels of TGF-b1 at the wound site. 41,42 A specific TGF-b1 gene signature that includes the potent profibrotic serine protease inhibitor plasminogen activator inhibitor-1 (PAI-1; SERPINE1), connective tissue growth factor (CTGF, CCN2), EDA-fibronectin, collagen I, TGF-b1, vimentin, p53, p21, miR-21, miR-29, and a-smooth muscle actin (a-SMA) [43][44][45][46] is consistently associated with fibrosis in human cells and mouse models. Several of these genes are upregulated in the cutaneous tissue of systemic sclerosis patients as well as in the LPS-treated mouse skin, via a TLR4 pathway and downstream MyD88 signaling, and attenuated by TGF-b1 neutralizing antibodies.…”