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The characterization of ₅-integrin expression on tubular epithelium during renal injury

¹Division of Nephrology, Department of Medicine and ²Department of Pathology University of Calgary, Calgary, Alberta, Canada

Submitted 12 June 2006 ; accepted in final form 26 September 2006

The hallmark of progressive chronic kidney disease is the deposition of extracellular matrix proteins and tubulointerstitial fibrosis. Integrins mediate cell-extracellular matrix interaction and may play a role tubular epithelial injury. Murine primary tubular epithelial cells (TECs) express ₅-integrin, a fibroblast marker and the natural receptor for fibronectin. Microscopy localized ₅-integrin on E-cadherin-positive cells, confirming epithelial expression. The expression of ₅-integrin increased in TECs grown on fibronectin and occurred in parallel with an upregulation of -smooth muscle actin (SMA), a marker of epithelial-mesenchymal transition (EMT). Exposure of TECs to transforming growth factor (TGF)- also increased TEC ₅-integrin expression in association with SMA and EMT. Knock-down of 5-integrin expression with short interfering RNA attenuated the TGF- induction of SMA but did not alter morphologic EMT. Rather, 5-integrin was necessary for epithelial cell migration on fibronectin but not type IV collagen during cell spreading and epithelial wound healing in vitro. Immunohistochemistry revealed basolateral tubular epithelial ₅-integrin expression in mouse kidneys after unilateral ureteric obstruction but not in contralateral control kidneys. In patient biopsies of nondiabetic kidney disease, ₅-integrin expression was increased significantly in the renal interstitium. Focal basolateral staining was also detected in injured, but not in normal, tubular epithelium. In summary, these data show that TECs are induced to express ₅-integrin during EMT and tubular epithelial injury in vitro and in vivo. These results increase our understanding of the biology of integrins during EMT and tubular injury in chronic kidney disease.

chronic kidney disease; epithelial mesenchymal transition

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