The role of alpha1beta1 integrin in wound contraction. A quantitative analysis of liver myofibroblasts in vivo and in primary culture.

An unresolved question in wound contraction concerns the identity of integrins mediating the attachment of tissue myofibroblasts to matrix in the injury site. Previous studies with cell lines have focussed on alpha1beta1 and alpha2beta1, the principal collagen-binding integrins, but have yielded conflicting data. We have examined this issue in wound healing in the liver, isolating the myofibroblast population (activated stellate cells) and quantitating expression of the alpha1 and alpha2 integrin subunits during the in vivo injury. Normal stellate cells displayed alpha1 but no detectable alpha2. During injury, alpha1 expression was maintained; alpha2 became detectable at the mRNA level but at all times was <8% of alpha1 mRNA. Contraction of collagen lattices, studied with 24-h cultured cells and initiated by endothelin 1, was blocked 70% by anti-alpha1 and 30% by anti-alpha2 (both significant, p < 0.05). The inhibition by anti-alpha2, which was unexpected, was attributable to culture-induced change in integrin expression; both the mRNA and protein for alpha2 increased strikingly within 24 h of plating stellate cells on a collagen gel. We conclude that alpha1beta1 is the sole integrin utilized by contracting myofibroblasts in vivo. Although alpha2beta1 is capable of mediating contraction, its expression by myofibroblasts occurs largely, if not exclusively, in response to culture.

The metabolic organization of the adult human liver: a comparative study of normal, fibrotic, and cirrhotic liver tissue.

Little is known about the alterations of metabolic organization of the human liver tissue in chronic liver diseases. We therefore compared the distribution of the following zonal metabolic markers in 10 samples of normal liver tissue, 10 samples of fibrotic tissue, and 22 samples of cirrhotic tissue: (a) the enzymatic activities of glucose-6-phosphatase (G6P), lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), nicotinamide-adenine-dinucleotide-phosphate [NAPH] dehydrogenase (ND), beta-hydroxybutyrate dehydrogenase (HBDH), and glutamate dehydrogenase (GDH); (b) the protein glutamine synthetase (GLS); and (c) albumin messenger RNA (mRNA). The normal human hepatic lobule was characterized by the periportal predominance of G6P and SDH enzymatic activities and albumin mRNAs, the perivenous predominance of ND and GDH, the restriction of GLS to a small perivenous compartment, and the predominanc of beta-HBDH at the contact of both portal tracts and centrilobular veins. In fibrosis, the overall metabolic organization of the normal liver tissue was retained. The expression of periportal markers predominated around enlarged portal tracts and that of perivenous markers around residual centrilobular veins. GLS was constantly detected at the contact of centrilobular veins. In cirrhotic nodules, no zonation was observed for most enzymatic activities or for albumin. Only G6P usually predominated at the periphery of the nodules. GLS was constantly undetectable. No difference accordingly to the etiology of the underlying disease was observed. In conclusion, the normal human hepatic lobule presents a marked metabolic zonation, preserved in fibrotic lesions, but lost in cirrhotic nodules. The alterations of the metabolic organization observed in cirrhosis might contribute to the pathogenesis of some of the metabolic disorders associated with advanced liver disease.

Coexpression of periportal and perivenous enzymes in rat hepatocytes after experimental bile duct ligation: comparison with intrasplenically transplanted hepatocytes.

The coexpression of normally periportal and perivenous markers has been described in heterotopically transplanted hepatocytes. To determine whether such a coexpression might also occur in hepatocytes retaining their original intrahepatic location, we compared in bile-duct-ligated livers and intrasplenically transplanted hepatocytes, the expression and distribution of the predominantly periportal glucose-phosphatase, succinate dehydrogenase, and lactate dehydrogenase, the predominantly perivenous glutamate dehydrogenase, NADPH-dehydrogenase, and beta-hydroxybutyrate dehydrogenase, and the strictly perivenous glutamine synthetase. The coexpression of high levels of the two periportal markers glucose-6-phosphatase and lactate dehydrogenase and of the perivenous marker NADPH dehydrogenase was observed in two situations: in clusters of hepatocytes isolated within the ductular proliferation in bile-duct-ligated livers and the majority of intrasplenically transplanted hepatocytes. The expression of glutamine synthetase was different according to the site. The protein was observed in certain intrasplenically transplanted hepatocytes bordering the splenic vessels but was never detected in hepatocyte clusters found in bile-duct-ligated livers. Our study therefore suggests that the coexpression of periportal and perivenous markers in the same hepatocytes is likely to be a non-specific consequence of the loss of the normal connections of hepatocytes with the normal liver microcirculation.