The role of AMPKα in high-glucose-induced dysfunction of cultured rat mesangial cells.

AIM: Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) is known as a mammalian cell energy sensor, which could regulate cellular energy metabolism via sensing the alterations of energy balance, such as oversupply or lack of glucose and fatty acid. Recent studies have suggested that AMPK could also regulate many other biological processes, including cell cycling, inflammation, protein synthesis, and so on. In this study, AMPK signaling in high-glucose-induced dysfunction of mesangial cells (MCs) was investigated. METHODS: Established rat glomerular MCs were treated under normal glucose (5.6 mM glucose) or high-glucose conditions (30 mM glucose). mRNA levels of AMPK subunits were detected by reverse transcriptase-polymerase chain reaction. Expressions of AMPKα, phosphorylated AMPKα (p-AMPKα), phosphorylated acetyl-CoA carboxylase (p-ACC), and collagen IV were measured by Western blot. RESULTS: Under high-glucose conditions, AMPKα protein expression and mRNA levels were significantly decreased. High-glucose treatment also induced a notable decrease in p-AMPKα and p-ACC expression. AMPKα activation by 5-aminoimidazole-4-carboxamide-1-ß-d-ribofuranoside (AICAR) effectively ameliorated high-glucose-induced dysfunction of MCs, including cell proliferation, cell-cycle progression, and collagen IV production. CONCLUSION: High glucose impaired AMPKα in its expression and activity; AICAR significantly ameliorated high-glucose-induced proliferation of MCs and collagen IV production, indicating a role of AMPKα in high-glucose-induced dysfunction of MCs.

The role of the p38 MAPK signaling pathway in high glucose-induced epithelial-mesenchymal transition of cultured human renal tubular epithelial cells.

BACKGROUND: Epithelial-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 FINDINGS: A 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-ß1 or high glucose for 48 h. Cells that were not transfected or pretreated and were exposed to low glucose with or without TGF-ß1 or high glucose for 48 h were considered to be the controls. We found that high glucose induced an increase in TGF-ß1. 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-ß1 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). CONCLUSION: This study suggests that p38 MAPK may play an important role in the high glucose-induced EMT by activating AP-1 in tubular epithelial cells.