The Role of the p38 MAPK Signaling Pathway in High Glucose-Induced Epithelial-Mesenchymal Transition of Cultured Human Renal Tubular Epithelial Cells

Abstract

BackgroundEpithelial-mesenchymal transition of tubular epithelial cells, which is characterized by a loss of epithelial cell characteristics and a gain of ECM-producing myofibroblast characteristics, is an essential mechanism that is involved in tubulointerstitial fibrosis, an important component of the renal injury that is associated with diabetic nephropathy. Under diabetic conditions, p38 MAPK activation has been reported in glomeruli and mesangial cells; however, studies on p38 MAPK in TECs are lacking. In this study, the role of p38 MAPK in AP-1 activation and in the EMT in the human proximal tubular epithelial cell line (HK-2) under high glucose concentration conditions is investigated.Methodology/Principal FindingsA vector for small interfering RNA that targets p38 MAPK was constructed; the cells were then either transfected with p38 siRNA or pretreated with a chemical inhibitor of AP-1 and incubated with low glucose plus TGF-β1 or high glucose for 48 h. Cells that were not transfected or pretreated and were exposed to low glucose with or without TGF-β1 or high glucose for 48 h were considered to be the controls. We found that high glucose induced an increase in TGF-β1. And high glucose-induced p38 MAPK activation was inhibited by p38 siRNA (P<0.05). A significant decline in E-cadherin and CK expression and a notable increase in vimentin and α-SMA were detected when exposed to low glucose with TGF-β1 or high glucose, and a significant raise of secreted fibronectin were detected when exposed to high glucose; whereas these changes were reversed when the cells were treated with p38 siRNA or AP-1 inhibitor (P<0.05). AP-1 activity levels and Snail expression were up-regulated under high glucose conditions but were markedly down-regulated through knockdown of p38 MAPK with p38 siRNA or pretreatment with AP-1 inhibitor (P<0.05).ConclusionThis study suggests that p38 MAPK may play an important role in the high glucose-induced EMT by activating AP-1 in tubular epithelial cells.

FAK contributes to proteinuria in hypercholesterolaemic rats and modulates podocyte F‐actin re‐organization via activating p38 in response to ox‐LDL

“…P38 MAPK (p38) is a member of the MAPK family and is in close association with a variety of renal diseases 20, 21, 22. We found hyper‐activity of p38 was driven by ox‐LDL, compared with the controls ( P < 0.05; Fig.…”

Fasudil Inhibits Epithelial-Myofibroblast Transdifferentiation of Human Renal Tubular Epithelial HK-2 Cells Induced by High Glucose

“…14) TGF-β 1 and CTGF have been found to be up-regulated in both experimental and human DN, and to be associated with EMT, 7,10,11,[15][16][17][18][19][20][21] supporting a key role for these signaling molecules. A previous study in diabetic rats showed that using fasudil as a treatment also decreased EMT.…”

“…[5][6][7][8][9][10][11] Overaccumulation of ECM in the tubulointerstitium is known to lead to tubulointerstitial fibrosis, and this is thought to be an important contributor to DN pathogenesis. 36) There are emerging evidences that a large proportion of the myofibroblasts that secrete ECM are derived from EMT of tubular epithelial cells.…”

“…9) This transition is associated with a reduction in the expression of the epithelial marker, E-cadherin, and an increase in the expression of mesenchymal markers, such as vimentin and α-smooth muscle actin (α-SMA). 10,11) Transforming growth factor (TGF)-β 1 is an important fibrogenic growth factor known to play an important role in EMT development. 12,13) Although TGF-β 1 is thought to act via a number of cellular signaling pathways, connective tissue growth factor (CTGF) is a downstream target responsible for many of the pro-fibrotic effects of TGF-β 1 .…”

Thioredoxin-interacting Protein Mediates High Glucose-induced Reactive Oxygen Species Generation by Mitochondria and the NADPH Oxidase, Nox4, in Mesangial Cells

“…Under basal conditions, Trx in mitochondria binds and inhibits ASK (apoptosis signalregulating kinase)-1, an upstream MKK3/6 and p38 MAPK activator (61)(62)(63). TxNIP up-regulation has been proposed to bind Trx and release ASK-1 to activate p38 (64 -66), which in turn would stimulate AP-1 (67,68). In support of this possibility, TxNIP has recently been reported to translocate to the mitochondria in the presence of ROS in pancreatic ␤-cells (65).…”