Expression of variant fibronectins in wound healing: cellular source and biological activity of the EIIIA segment in rat hepatic fibrogenesis.

Abstract

Abstract. We have examined the cell-specific expression of two fibronectin isoforms, EIIIA and EIHB, during experimental hepatic fibrosis induced by ligation of the biliary duct. At the mRNA level, EIIIA and EIIIB were undetectable in normal liver but expressed early in injury, preceding fibrosis. The cellular sources of these changes were determined by fractionating the liver at various time points after bile duct ligation into its constituent cell populations and extracting RNA from the fresh isolates. EIllA-containing fibronectin mRNA was undetectable in normal sinusoidal endothelial cells but increased rapidly within 12 h of injury. By contrast, the EIIIB form was restricted to hepatic lipocytes (Ito or fat-storing cells) and appeared only after a lag of 12-24 h: it was minimal in sinusoidal endothelial cells. Both forms were minimal in hepatocytes. At the protein level, EIIIA-containing fibronectin was markedly increased within two days of injury and exhibited a sinusoidal distribution. Secretion of this form by endothelial cells was confirmed in primary culture. Matrices deposited in situ by endothelial cells from injured liver accelerated the conversion ("activation") of normal lipocytes to myofibroblast-like cells, and pretreatment of matrices with monoclonal antibody to the EIIIA segment blocked this response. Finally, recombinant fibronectin peptide containing the EIIIA segment was stimulatory to lipocytes in culture. We conclude that expression of EIIIA fibronectin by sinusoidal endothelial cells is a critical early event in the liver's response to injury and that the EIIIA segment is biologically active, mediating the conversion of lipocytes to myofibroblasts.

Platelet-derived growth factor isoform expression in carbon tetrachloride-induced chronic liver injury

“…Fibronectin has been shown to stimulate the conversion of resting stellate cells to myofibroblast-like cells, consistent with the role of fibronectin in fibrogenesis and wound repair initiation. 14 Collagen type I and a-smooth muscle actin (a-SMA) were upregulated and levels sustained throughout CCl 4 administration, with the exception of a few animals that showed a decline of a-SMA, in correspondence with a lesser degree of fibrosis, confirmed by immunohistochemistry (Supplementary Figure 5). As expected, representative liver sections taken from animals that received long-term CCl 4 exposure showed reactive chromatin condensation of hepatocyte nuclei (Supplementary Figure 6).…”

Hepatocyte transplantation activates hepatic stellate cells with beneficial modulation of cell engraftment in the rat

“…1,5 Endothelial injury stimulates conversion of latent TGF-␤ to its active form via plasmin, 15 and release of fibronectin isoforms may activate HSC. 23 Among HSC-related genes expressed after cell transplantation, VEGF activates HSC and induces HSC proliferation. 24,25 Our observation of VEGF mRNA expression here was in agreement with that of previous immunostaining studies showing VEGF expression within a few hours after cell transplantation.…”

Stimulation of inducible nitric oxide synthase in rat liver by hyaluronan fragments

“…16,35 Radiolabeled cRNA was generated by transcription with T7 polymerase using [␣-32 P] CTP. 36 The specific activity of all radiolabeled transcripts was approximately 0.5 ϫ 10 9 cpm per microgram.…”