Urokinase-type plasminogen activator supports liver repair independent of its cellular receptor

BACKGROUND: The urokinase-type (uPA) and tissue-type (tPA) plasminogen activators regulate liver matrix remodelling through the conversion of plasminogen (Plg) to the active protease plasmin. Based on the efficient activation of plasminogen when uPA is bound to its receptor (uPAR) and on the role of uPA in plasmin-mediated liver repair, we hypothesized that uPA requires uPAR for efficient liver repair. METHODS: To test this hypothesis, we administered one dose of carbon tetrachloride (CCl(4)) to mice with single or combined deficiencies of uPA, uPAR and tPA, and examined hepatic morphology, cellular proliferation, fibrin clearance, and hepatic proteolysis 2–14 days later. RESULTS: Absence of uPAR alone or the combined absence of uPAR and tPA had no impact on the resolution of centrilobular injury, but the loss of receptor-free uPA significantly impaired the clearance of necrotic hepatocytes up to 14 days after CCl(4). In response to the injury, hepatocyte proliferation was normal in mice of all genotypes, except for uPAR-deficient (uPAR°) mice, which had a reproducible but mild decrease by 33% at day 2, with an appropriate restoration of liver mass by 7 days similar to experimental controls. Immunostaining and zymographic analysis demonstrated that uPA alone promoted fibrin clearance from centrilobular regions and efficiently activated plasminogen. CONCLUSION: uPA activates plasminogen and promotes liver matrix proteolysis during repair via a process that neither requires its receptor uPAR nor requires a contribution from its functional counterpart tPA

Loss of interleukin-12 modifies the pro-inflammatory response but does not prevent duct obstruction in experimental biliary atresia

BACKGROUND: Livers of infants with biliary atresia and of neonatal mice infected with rotavirus (RRV) have increased expression of interferon-gamma (IFNγ) and interleukin (IL)-12. While the expression of IFNγ regulates the obstruction of extrahepatic bile ducts by lymphocytes, the role of IL-12 in the pathogenesis of biliary obstruction is unknown. Based on the role of IL-12 as a key proinflammatory cytokine, we hypothesized that loss of IL-12 prevents the obstruction of extrahepatic bile ducts. METHODS: IL12-knockout (IL-12KO) and wild type mice were injected with RRV or saline at day 1 of age and monitored for the development of symptoms. The cellular and molecular phenotypes were determined at days 3, 7, and 14 by real-time PCR and flow cytometry. RESULTS: RRV infection of IL-12KO mice resulted in growth failure, jaundice/acholic stools, and decreased survival similar to wild-type mice. IL-12KO mice had a remarkable neutrophil-rich portal inflammation and epithelial sloughing of extrahepatic bile ducts. Loss of IL-12 decreased but did not abolish the hepatic expression of IFNγ, displayed a remarkable increase in expression of TNFα, IFNα, IFNβ and decreased expression of IL-4 and IL-5. CONCLUSION: Loss of IL-12 did not modify the progression of bile duct obstruction in experimental biliary atresia. However, the inflammatory response was predominantly neutrophil-based and displayed a Th1 response in the absence of IL-12

Urokinase-type plasminogen activator supports liver repair independent of its cellular receptor

Abstract Background The urokinase-type (uPA) and tissue-type (tPA) plasminogen activators regulate liver matrix remodelling through the conversion of plasminogen (Plg) to the active protease plasmin. Based on the efficient activation of plasminogen when uPA is bound to its receptor (uPAR) and on the role of uPA in plasmin-mediated liver repair, we hypothesized that uPA requires uPAR for efficient liver repair. Methods To test this hypothesis, we administered one dose of carbon tetrachloride (CCl4) to mice with single or combined deficiencies of uPA, uPAR and tPA, and examined hepatic morphology, cellular proliferation, fibrin clearance, and hepatic proteolysis 2–14 days later. Results Absence of uPAR alone or the combined absence of uPAR and tPA had no impact on the resolution of centrilobular injury, but the loss of receptor-free uPA significantly impaired the clearance of necrotic hepatocytes up to 14 days after CCl4. In response to the injury, hepatocyte proliferation was normal in mice of all genotypes, except for uPAR-deficient (uPAR°) mice, which had a reproducible but mild decrease by 33% at day 2, with an appropriate restoration of liver mass by 7 days similar to experimental controls. Immunostaining and zymographic analysis demonstrated that uPA alone promoted fibrin clearance from centrilobular regions and efficiently activated plasminogen. Conclusion uPA activates plasminogen and promotes liver matrix proteolysis during repair via a process that neither requires its receptor uPAR nor requires a contribution from its functional counterpart tPA.</p

A proinflammatory program of perinatal plasmacytoid dendritic cells activate natural killer (NK) cells to damage the bile duct epithelium in experimental biliary atresia (43.2)

Abstract Biliary atresia results from an NK cell-mediated inflammatory injury of the bile duct epithelium with onset in the early postnatal period. Based on key immunoregulatory roles of dendritic cells (DC), we hypothesized that early neonatal DC activation triggers an effector immune response that results in biliary atresia. We tested this hypothesis in a mouse model of rotavirus-induced biliary atresia. Following rotavirus challenge on day 1 of life, viral immunogenic protein NSP3 was detected in hepatic PDCA-1+ plasmacytoid DC (pDC) but not CD11c+ conventional DC (cDC) within 3 days of infection. Hepatic pDC increased 3 fold, while non-pDC (CD11b+CD11c+ cells) decreased 2.5 fold. Rotavirus-naïve perinatal hepatic pDC and cDC spontaneously expressed B7.1/2 (2-3 fold higher than adults), with a much higher increased expression in B7.1/2, IFNγ, and IL-12p40 by pDC after rotavirus challenge. IL-15 was spontaneously expressed by naïve perinatal pDC and increased dramatically after rotavirus infection, but in vitro activation of NK cells required co-culture with both pDC and cDC. Most notably, ablation of pDC decreased the liver population of NK cells and prevented the mucosa injury and obstruction of neonatal bile ducts, leading to improved symptoms and long-term survival. Thus early activation of pDC due upon viral exposure regulates neonatal duct injury and obstruction in biliary atresia.</jats:p