Thus, the overall aim of this work was to address these questions, identify the mechanism for the OPN-driven Collagen-I up-regulation in HSCs, and determine the functional role of OPN

in the pathogenesis of liver fibrosis. The idea that OPN mediates liver fibrosis is relevant for several reasons. First, because the observation that OPN is up-regulated in HSCs during hepatic injury provides an excellent conceptual advance in our understanding of liver fibrogenesis, as it appears that OPN up-regulates HSC Collagen-I protein both in an autocrine and paracrine fashion. Second,

it supports the clinicopathological finding that injury occurring in the central region is accompanied by fibrosis. Third, it opens the possibility of linking a soluble cytokine/matricellular PS-341 cell line protein with fibrogenesis. Last, the identification of the mechanism and mediators involved in the profibrogenic actions of OPN could help in devising strategies for therapeutic targeting. Our in vitro experiments validated the hypothesis of the profibrogenic and proinvasive actions of OPN in HSCs. Mechanistic studies identified the HSC membrane proteins engaged by OPN and the proximal signaling molecules/oxidant stress-sensitive kinases activated upon OPN binding that trigger the fibrogenic cascade. The experimental data selleck inhibitor identified integrin αvβ3 as an efficient conveyor of the OPN-mediated profibrogenic actions in HSCs and pointed at PI3K-pAkt activation and the NFκB-signaling pathway as highly O-methylated flavonoid involved in this process. Because OPN signals via integrins and CD44, it is feasible that following liver injury, a ligand for αvβ3 integrin, such as OPN, accumulates in the space

of Disse and acts in a αvβ3 integrin-dependent manner to maintain Collagen-I induction, HSC activation, invasion and migration. Because OPN binds ECM proteins,35, 36 this binding ability may enhance HSC activation, migration and invasion—key HSC features for the development of fibrosis. The finding that blocking CD44 did not prevent the effect of rOPN on Collagen-I may be related to the ability of hyaluronic acid—a glycosaminglycan synthesized during HSC activation24, 37—to bind CD44; thus, competitive inhibition between hyaluronic acid and rOPN for CD44 binding could occur in HSCs, although this possibility needs further investigation.