Coexpressed Nitric Oxide Synthase and Apical β1Integrins Influence Tubule Cell Adhesion after Cytokine-Induced Injury

Abstract

Abstract. In sepsis-induced acute renal failure, actin cytoskeletal alterations result in shedding of proximal tubule epithelial cells (PTEC) and tubular obstruction. This study examined the hypothesis that inflammatory cytokines, released early in sepsis, cause PTEC cytoskeletal damage and alter integrin-dependent cell-matrix adhesion. The question of whether the intermediate nitric oxide (NO) modulates these cytokine effects was also examined. After exposure of human PTEC to tumor necrosis factor-α, interleukin-1α, and interferon-γ, the actin cytoskeleton was disrupted and cells became elongated, with extension of long filopodial processes. Cytokines induced shedding of viable, apoptotic, and necrotic PTEC, which was dependent on NO synthesized by inducible NO synthase (iNOS) produced as a result of cytokine actions on PTEC. Basolateral exposure of polarized PTEC monolayers to cytokines induced maximal NO-dependent cell shedding, mediated in part through NO effects on cGMP. Cell shedding was accompanied by dispersal of basolateral β1integrins and E-cadherin, with corresponding upregulation of integrin expression in clusters of cells elevated above the epithelial monolayer. These cells demonstrated coexpression of iNOS and apically redistributed β1integrins. Attachment studies demonstrated that the major ligand involved in cell anchorage was laminin, probably through interactions with the integrin α3β1. This interaction was downregulated by cytokines but was not dependent on NO. These studies provide a mechanism by which inflammatory cytokines induce PTEC damage in sepsis, in the absence of hypotension and ischemia. Future therapeutic strategies aimed at specific iNOS inhibition might inhibit PTEC shedding after cytokine-induced injury and delay the onset of acute renal failure in sepsis.