IDENTIFICATION OF CONNECTIVE-TISSUE GENE TRANSCRIPTS IN FRESHLY ISOLATED PARENCHYMAL, ENDOTHELIAL, KUPFFER AND FAT-STORING CELLS BY NORTHERN HYBRIDIZATION ANALYSIS

The aim of the present study was to identify the cell types that express collagen alpha1(I), alpha1(III) and alpha1(IV), fibronectin and laminin B1 genes in normal rat liver. Parenchymal, sinusoidal endothelial, Kupffer and fat-storing (Ito) cells were isolated and purified. Total RNA of the freshly isolated cells was subjected to Northern hybridization analysis. We also compared the steady state levels of specific mRNAs in freshly isolated fat-storing cells to the levels in myofibroblast-like cells obtained from purified fat-storing cells cultured for two passages. The average purity of each cell preparation, and the percentage of contaminating cells, were determined by transmission electron microscopy and by examining the presence of vitamin A-autofluorescent cells. Fibronectin and collagen alpha1(III) mRNAs were detected in total RNA of purified parenchymal cells. In poly(A)+ enriched RNA, small amounts of collagen alpha1(I) mRNA were also present. In total RNA of freshly isolated fat-storing cells, collagen alpha1(III), alpha1(IV), and laminin B1 transcripts were found, whereas collagen alpha1(I) and fibronectin mRNAs were not detected. Cultured fat-storing cells, however, did contain high levels of collagen alpha1(I) and fibronectin mRNAs. The molecular size of the latter transcript was larger than the fibronectin transcript found in parenchymal cells and the whole liver. Endothelial cells contained small amounts of alpha1(IV) mRNA. Kupffer cells,did not contain the investigated transcripts. We conclude that normal parenchymal, fat-storing and endothelial cells each express a typical pattern of connective tissue molecules. When fat-storing cells are allowed to differentiate into myofibroblast-like cells, they express high levels of collagen alpha1(I) and fibronectin mRNAs, in addition to collagen alpha1(III) and alpha1(IV), and laminin B1 chain mRNAs.