Loss of tumour suppressor PTEN expression in renal injury initiates SMAD3‐ and p53‐dependent fibrotic responses

Abstract

Deregulation of the tumour suppressor PTEN occurs in lung and skin fibrosis, diabetic and ischaemic renal injury. However, the potential role of PTEN and associated mechanisms in the progression of kidney fibrosis is unknown. Tubular and interstitial PTEN expression was dramatically decreased in several models of renal injury including aristolochic acid nephropathy (AAN), streptozotocin (STZ)-mediated injury and ureteral unilateral obstruction (UUO), correlating with Akt, p53 and SMAD3 activation and fibrosis. Stable silencing of PTEN in HK-2 human tubular epithelial cells induced dedifferentiation and CTGF, PAI-1, vimentin, α-SMA and fibronectin expression compared to HK-2 cells expressing control shRNA. Furthermore, PTEN knockdown stimulated Akt, SMAD3 and p53Ser15 phosphorylation with an accompanying decrease in population density and an increase in epithelial G1 cell cycle arrest. SMAD3 or p53 gene silencing or pharmacological blockade partially suppressed fibrotic gene expression and relieved growth inhibition orchestrated by deficiency or inhibition of PTEN. Similarly, shRNA suppression of PAI-1 rescued the PTEN loss-associated epithelial proliferative arrest. Moreover, TGF-β1-initiated fibrotic gene expression is further enhanced by PTEN depletion. Combined TGF-β1 treatment and PTEN silencing potentiated epithelial cell death via p53 dependent pathways. Thus, PTEN loss initiates tubular dysfunction via SMAD3- and p53-mediated fibrotic gene induction with accompanying PAI-1 dependent proliferative arrest, and cooperates with TGF-β1 to induce the expression of profibrotic genes and tubular apoptosis.

Inhibition of PTEN Activity Aggravates Post Renal Fibrosis in Mice with Ischemia Reperfusion-Induced Acute Kidney Injury

“…Previous research demonstrated that activation of proinflammatory cytokines contributed substantially to the development of renal interstitial fibrosis [13, 14]. Moreover, mounting evidence in vivo and in vitro has indicated that PTEN mediates multiple signal pathways involved in the pathophysiologic process of fibrosis in the kidney such as SMAD3, p53, and JNK[15, 16]. Here, we investigated the inhibition of PTEN activity by bisperoxovanadium (bpV) in post renal fibrosis induced by AKI with ischemia reperfusion (IR) models in mice.…”

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

“…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.…”

“…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). 45,46 Relatively, little is known about PPM1A regulation in general or in the context of tissue injury. PTEN, however, interacts with PPM1A in scleroderma 65 and PTEN silencing in macrophages increased LPS-induced expression of TNF-a, IL-1b, IL-6, IL-8, and IL-10.…”

“…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.…”