Involvement of hepatic stellate cell cytoglobin in acute hepatocyte damage through the regulation of CYP2E1-mediated xenobiotic metabolism.

Oxygen (O2) is required for cytochrome P450 (CYP)-dependent drug metabolism. Cytoglobin (CYGB) is a unique globin expressed exclusively in hepatic stellate cells (HSCs). However, its role in O2-dependent metabolism in neighboring hepatocytes remains unknown. This study provides evidence that CYGB in HSCs is involved in acetaminophen (N-acetyl-p-aminophenol; APAP)-induced hepatotoxicity. Serum alanine aminotransferase levels were higher in wild-type mice than in Cygb-null mice. Wild-type mice exhibited more severe hepatocyte necrosis around the central vein area compared with Cygb-null mice, thus indicating that CYGB deficiency protects against APAP-induced liver damage. Although no difference in the hepatic expression of CYP2E1, a key enzyme involved in APAP toxicity, was observed between wild-type and Cygb-null mice, the serum levels of the APAP metabolites cysteinyl-APAP and N-acetyl-cysteinyl-APAP were decreased in Cygb-null mice, suggesting reduced APAP metabolism in the livers of Cygb-null mice. In primary cultures, APAP-induced hepatocyte damage was increased by co-culturing with wild-type HSCs but not with Cygb-null HSCs. In addition, cell damage was markedly alleviated under low O2 condition (5% O2), suggesting the requirement of O2 for APAP toxicity. Carbon tetrachloride-induced liver injury (CYP2E1-dependent), but not lipopolysaccharide/D-galactosamine-induced injury (CYP2E1-independent), was similarly alleviated in Cygb-null mice. Considering the function of CYGB as O2 carrier, these results strongly support the hypothesis that HSCs are involved in the CYP2E1-mediated xenobiotic activation by augmenting O2 supply to hepatocytes. In conclusion, CYGB in HSCs contributes to the CYP-mediated metabolism of xenobiotics in hepatocytes by supplying O2 for enzymatic oxidation.

Developmental pathway for biofilm formation in curli-producing Escherichia coli strains: role of flagella, curli and colanic acid.

This work was performed to establish a model describing bacterial surface structures involved in biofilm development, in curli-overproducing Escherichia coli K-12 strains, at 30 degrees C, and in minimal growth medium. Using a genetic approach, in association with observations of sessile communities by light and electron microscopic techniques, the role of protein surface structures, such as flagella and curli, and saccharidic surface components, such as the E. coli exopolysaccharide, colanic acid, was determined. We show that, in the context of adherent ompR234 strains, (i) flagellar motility is not required for initial adhesion and biofilm development; (ii) both primary adhesion to inert surfaces and development of multilayered cell clusters require curli synthesis; (iii) curli display direct interactions with the substratum and form interbacterial bundles, allowing a cohesive and stable association of cells; and (iv) colanic acid does not appear critical for bacterial adhesion and further biofilm development but contributes to the biofilm architecture and allows for the formation of voluminous biofilms.