Osteopontin neutralisation abrogates the liver progenitor cell response and fibrogenesis in mice

Abstract

Background Chronic liver injury triggers a progenitor-cell repair-response, and liver fibrosis occurs when repair becomes de-regulated. Previously, we reported that reactivation of the Hedgehog (Hh) pathway promotes fibrogenic liver-repair. Osteopontin (OPN) is a Hh-target, and a cytokine that is highly upregulated in fibrotic tissues, and regulates stem-cell fate. Thus, we hypothesized that OPN may modulate liver progenitor-cell response, and thereby, modulate fibrotic outcomes. We further evaluated the impact of OPN-neutralization on murine liver fibrosis. Methods Liver progenitors (603B and BMOL) were treated with OPN-neutralizing aptamers in the presence or absence of TGF–β, to determine if (and how) OPN modulates liver progenitor function. Effects of OPN-neutralization (using OPN-aptamers or OPN-neutralizing antibodies) on liver progenitor-cell response and fibrogenesis were assessed in three models of liver fibrosis (carbon tetrachloride, methionine-choline deficient diet, 3, 5,-diethoxycarbonyl-1,4-dihydrocollidine diet) by qRTPCR, Sirius-Red staining, hydroxyproline assay, and semi-quantitative double-immunohistochemistry. Finally, OPN expression and liver progenitor response were corroborated in liver tissues obtained from patients with chronic liver disease. Results OPN is over-expressed by liver progenitors in humans and mice. In cultured progenitors, OPN enhances viability and wound-healing by modulating TGF-β signaling. In vivo, OPN-neutralization attenuates the liver progenitor-cell response, reverses epithelial-mesenchymal-transition in Sox9+ cells, and abrogates liver fibrogenesis. Conclusions OPN upregulation during liver injury is a conserved repair-response, and influences liver progenitor-cell function. OPN-neutralization abrogates the liver progenitor-cell response and fibrogenesis in mouse models of liver fibrosis.

Hepatic Progenitor Cells and Cells Resistant to Apoptosis in Chronic HCV

“…The results suggest that interferon may exert direct effects on hepatic progenitor cells, reducing their rate of cell growth as well as stimulating them to undergo apoptosis [33]. This is in accordance with the observed effects of interferon on human HCCderived cell lines, in which interferon alpha caused delayed S-phase progression through inhibition of cyclin-dependent kinases [34] and induced caspase-dependent apoptosis [35]. Hh signal released by dying hepatocyte could activate the compensatory outgrowth of hepatic progenitors, which are involved in liver regeneration [35].…”

“…Hh signal released by dying hepatocyte could activate the compensatory outgrowth of hepatic progenitors, which are involved in liver regeneration [35]. As a Hh target, osteopontin is highly expressed in fibrotic liver tissue and influences the function of hepatic progenitors (34). HOWEVER, neutralization of osteopontin could suppress progenitor cell response and attenuate liver fibrosis in CCl4, methionine-choline-deficient diet (MCD) and 3,5-diethoxycarbonyl-1,4-dihydrocollidine diet (DDC) mice.…”

Phenotypic Changes in Hepatic Stellate Cells in Response to Toxic Liver Injury

“…In addition, treatment of these mice chronically with carbon tetrachloride resulted in enhanced liver fibrosis, which may have resulted from increased liver injury in these mice [50]. In a separate study, inhibition of osteopontin in mice with a neutralizing antibody decreased fibrosis in mice fed a methionine/choline-deficient diet and in mice treated chronically with carbon tetrachloride [51]. It is not completely clear why these studies are conflicting, although the difference may have resulted from the method of osteopontin inhibition (i.e., knockout mouse vs. neutralization).…”

Differential osteopontin functions: The role of osteopontin isoforms

“…As both iOPN and sOPN are generated from the same messenger RNA, selective silencing of either of these isoforms is not possible: Spp1-/-mice will be deficient for both of these isoforms, while the administration of OPN neutralizing antibodies or aptamers will selectively deplete only sOPN. 7 Therefore, if sOPN were to "promote" and iOPN to "protect" disease, then selective depletion of sOPN (rather than genetic silencing) will be more appropriate. Indeed, our cell culture data show that the loss of iOPN (and sOPN) (with RNAi) leads to nonidentical outcomes when compared with loss of sOPN alone (OPN-aptamer).…”

“…The administration of anti-OPN once ASH/AH has developed is also likely to be more clinically useful. 7 JASON D. COOMBES, PH.D. 1 WING-KIN SYN, M.D. [1][2][3] The authors appreciate the comments submitted by Drs.…”