Proximal Tubular Epithelial Cell Integrins Respond to High Glucose by Altered Cell-Matrix Interactions and Differentially Regulate Matrixin Expression

Abstract

SUMMARY:Thickening of the tubular basement membrane (TBM) occurs in diabetic nephropathy, but the effects of high glucose on the functional aspects of proximal tubular epithelial cells are not clearly understood. In the present study, we examined the effects of elevated glucose concentrations on (a) integrin expression by human proximal tubular epithelial cells (HK-2) and integrin-mediated interactions with type IV collagen (colIV) and laminin, major components of TBM; (b) the expression of matrixins/matrix metalloproteinases (MMPs), which is regulated by integrins; and (c) the expression of tissue inhibitors of metalloproteinases (TIMPs). HK-2 cells cultured in 25 mM glucose underwent a reduction of the expression of ␣3, ␤1, ␣v␤3, and ␣5 integrin subunits, with a concomitant increase of the ␣2 subunit, compared with cells grown in 5 mM glucose. Adhesion experiments demonstrated that high glucose led to increased cell adhesion on either colIV or laminin. Experiments of competition of adhesion using anti-integrin antibodies indicated that HK-2 cells in 5 mM glucose used mainly ␣v␤3 and ␣5␤1 integrins to adhere to colIV, whereas in 25 mM glucose they additionally used ␣2␤1. In the case of laminin, a ␤1-mediated adhesion was observed when HK-2 cells were in 5 mM glucose, whereas in 25 mM glucose, ␣2␤1 and ␣v␤3 were also involved. Elevated glucose concentrations resulted in decreased expression of MMP-9 and MMP-2, whereas an increase in TIMP-1 and a decrease in TIMP-2 expression were observed. We also examined which integrins mediated the expression and secretion of matrixins MMP-2 and MMP-9. Ligation of ␣3␤1 with mAbs resulted in induction of MMP-2 expression and secretion, whereas antibody ligation of ␣v␤3 led to down-regulation of MMP-9. The above data implicate integrins of proximal tubular epithelial cells in the regulation of MMPs and in the development of TBM thickening in diabetic nephropathy. (Lab Invest 2002, 82:1081-1093.

Enhanced podocalyxin expression alters the structure of podocyte basal surface

“…Cells were cultured on several substrates including EHS-derived intact laminin (corresponding to laminin 1), intact collagen IV (composed of (α1)2(α2) chains) or intact human GBM. It was previously reported that these substrates promote cell adhesion, differentiation, or gene expression in cultured podocytes Krishnamurti et al, 1997;Krishnamurti et al, 2001;Kobayashi et al, 2001;Kitsiou et al, 2003) and other epithelial cells of the kidney Karamessinis et al, 2002). We showed that EHS-derived laminin (laminin 1), up-regulated the expression of PC by HGEC.…”

Microvascular basement membranes in diabetes mellitus

“…These results suggest that expression and/or activity of collagenolytic enzymes, in association with hyperglycaemia-induced modulation of integrin expression, may be at least partly responsible for Microvascular basement membranes in diabetes 539 GBM accumulation. Similar alterations were found in the expression of integrins in tubular epithelial cells, and in their interaction with basement membrane components [18].…”

“…This activity was accompanied by increased metalloproteinase (MMP-2 and 9) production [54]. Proximal tubular cells cultured in the presence of high glucose concentration changed their pattern of integrin expression, as did glomerular epithelial [18] and mesangial cells [55]. It should be noted that in different renal cell types the changes in patterns of integrin expression are different.…”

Cyclic stretch-induced TGF-β1 and fibronectin expression is mediated by β1-integrin through c-Src- and STAT3-dependent pathways in renal epithelial cells

“…While not possessing kinase domains, integrin receptors can transduce information from the ECM to the cell to activate various intracellular signaling pathways, thereby regulating cellular processes as diverse as cytoskeletal organization, proliferation, differentiation, apoptosis, and cell migration (8,30,47,62,65). Numerous studies have linked integrins in the pathogenesis of renal fibrosis.…”