Acute biliary obstruction leads to periductal myofibroblasts and fibrosis, the origin of which is uncertain. Our study provides new information on this question in mice and humans. We show that bile duct obstruction induces a striking increase in cholangiocyte ␣v␤6 integrin and that expression of this integrin is directly linked to fibrogenesis through activation of transforming growth factor beta (TGF-␤). Administration of blocking antibody to ␣v␤6 significantly reduces the extent of acute fibrosis after bile duct ligation. Moreover, in ␤6-null mice subjected to the injury, fibrosis is reduced by 50% relative to that seen in wild-type mice, whereas inflammation occurs to the same extent. The data indicate that ␣v␤6, rather than inflammation, is linked to fibrogenesis. It is known that ␣v␤6 binds latent TGF-␤ and that binding results in release of active TGF␤. Consistent with this, intracellular signaling from the TGF␤ receptor is increased after bile duct ligation in wild-type mice but not in ␤6 ؊/؊ mice, and a competitive inhibitor of the TGF␤ receptor type II blocks fibrosis to the same extent as antibody to ␣v␤6. In a survey of human liver disease, expression of ␣v␤6 is increased in acute, but not chronic, biliary injury and is localized to cholangiocyte-like cells. Conclusion: Cholangiocytes respond to acute bile duct obstruction with markedly increased expression of ␣v␤6 integrin, which is closely linked to periductal fibrogenesis. The findings provide a rationale for the use of inhibitors of ␣v␤6 integrin or TGF␤ for down-regulating fibrosis in the setting of acute or ongoing biliary injury. (HEPATOLOGY 2007;46:1404-1412

The transforming growth factor (TGF)-␤-inducible integrin ␣v␤6 is preferentially expressed at sites of epithelial remodeling and has been shown to bind and activate latent precursor TGF-␤. Herein , we show that ␣v␤6 is overexpressed in human kidney epithelium in membranous glomerulonephritis , diabetes mellitus , IgA nephropathy , Goodpasture's syndrome , and Alport syndrome renal epithelium. To assess the potential regulatory role of ␣v␤6 in renal disease , we studied the effects of functionblocking ␣v␤6 monoclonal antibodies (mAbs) and genetic ablation of the ␤6 subunit on kidney fibrosis in Col4A3 ؊/؊ mice , a mouse model of Alport syndrome. Expression of ␣v␤6 in Alport mouse kidneys was observed primarily in cortical tubular epithelial cells and in correlation with the progression of fibrosis. Treatment with ␣v␤6-blocking mAbs inhibited accumulation of activated fibroblasts and deposition of interstitial collagen matrix. Similar inhibition of renal fibrosis was observed in ␤6-deficient Alport mice. Transcript profiling of kidney tissues showed that ␣v␤6-blocking mAbs significantly inhibited disease-associated changes in expression of fibrotic and inflammatory mediators. Similar patterns of transcript modulation were produced with recombinant soluble TGF-␤ RII treatment , suggesting shared regulatory functions of ␣v␤6 and TGF-␤. These findings demonstrate that ␣v␤6 can contribute to the regulation of renal fibrosis and suggest this integrin as a potential therapeutic target.

Invest. 1994. 93:776-787.)

Integrin alpha4beta1 mediates leukocyte recruitment, activation, mediator release, and apoptosis inhibition, and it plays a central role in inflammatory pathophysiology. High-affinity, selective inhibitors of alpha4beta1, based on the Leu-Asp-Val (LDV) sequence from the alternatively spliced connecting segment-1 (CS-1) peptide of cellular fibronectin, are described that employ a novel N-terminal peptide "cap" strategy. One inhibitor, BIO-1211, was approximately 10(6)-fold more potent than the starting peptide and exhibited tight-binding properties (koff = 1.4 x 10(-4) s-1, KD = 70 pM), a remarkable finding for a noncovalent, small-molecule inhibitor of a protein receptor. BIO-1211 was also 200-fold selective for the activated form of alpha4beta1, and it stimulated expression of ligand-induced epitopes on the integrin beta1 subunit, a property consistent with occupancy of the receptor's ligand-binding site. Pretreatment of allergic sheep with a 3-mg nebulized dose of BIO-1211 inhibited early and late airway responses following antigen challenge and prevented development of nonspecific airway hyperresponsiveness to carbachol. These results show that highly selective and potent small-molecule antagonists can be identified to integrins with primary specificity for peptide domains other than Arg-Gly-Asp (RGD); they confirm the generality of integrins as small molecule targets; and they validate alpha4beta1 as a therapeutic target for asthma.