Collagen XVIII is localized in sinusoids and basement membrane zones and expressed by hepatocytes and activated stellate cells in fibrotic human liver

Abstract

Type XVIII collagen is a recently discovered nonfibrillar collagen associated with basement membranes in mice and expressed at high levels in human liver. We studied the origin, distribution, and RNA levels of type XVIII collagen in normal and fibrotic human livers by in situ hybridization, immunohistochemistry, and Northern and dot blots and compared procollagen ␣1(XVIII) RNA levels with those of procollagen ␣1(IV) and laminin ␥1, the two major components of liver basement membranes. In normal liver, type XVIII collagen was heavily deposited in perisinusoidal spaces and basement membrane zones. The major source of type XVIII collagen was hepatocytes and, to a lesser extent, endothelial, biliary epithelial, and vascular smooth muscle cells and peripheral nerves. In cirrhosis, type XVIII collagen formed a thick deposit along capillarized sinusoids. Grain counts after in situ hybridization showed myofibroblasts to increase their expression 13-fold in active and twofold in quiescent fibrosis, whereas hepatocytes increased their expression only twofold in both active and quiescent fibrosis. Activated stellate cells in vitro expressed type XVIII collagen at high levels. These data indicate that type XVIII collagen is a component of the perisinusoidal space and is associated with basement membrane remodeling. Hepatocytes and activated stellate cells are important sources of type XVIII collagen in normal and fibrotic liver respectively, which suggests tissue-specific regulation of its expression. (HEPATOLOGY 1998;28:98-107.)The collagen superfamily comprises at least 19 molecules that share repeating -Gly-X-Y-sequences and fold into triplehelical structures. 1,2 Specific collagen types arrange within extracellular matrices in precise aggregates, maintaining a delicate equilibrium in specialized tissues. 1,3,4 In the liver, collagen breakdown and deposition occur in fibrosis and cirrhosis as a result of the cooperation of injured or regenerating hepatocytes with stellate cells. Activated stellate cells are a major source of extracellular matrix proteins in fibrotic liver. 5-10 Indeed, upon activation during liver injury, stellate cells undergo phenotypic changes characteristic of myofibroblasts, express ␣-smooth muscle actin (␣-SMA), and produce extracellular matrix components at high levels. 11,12 The newly discovered type XVIII collagen [13][14][15] belongs to the nonfibrilar collagens, with frequent interruptions in the triple-helical structure, which possibly confer flexibility to the molecules. Type XVIII collagen is present in highly vascularized organs such as the liver, lung, kidney, and placenta. [16][17][18] Muragaki et al. 17 detected type XVIII collagen in vascular basement membrane zones in mice, and it has been hypothesized that this collagen type could be a new component of basement membranes, 19 the highly specialized extracellular matrices underlying epithelial or endothelial cells and surrounding muscle cells, fat, and peripheral nerve cells. Three variant N-terminal ends for mouse procollagen ␣1(XVIII...

Tumor hepatocytes and basement membrane–Producing cells specifically express two different forms of the endostatin precursor, collagen XVIII, in human liver cancers

“…We have shown that hepatocytes express high and stable levels of collagen XVIII in normal liver, active and quiescent fibrosis, 6 and small hepatocellular carcinomas, 11 whereas liver myofibroblasts increase their collagen XVIII expression by 13-fold in active liver fibrogenesis. 6 We thus hypothesized that hepatocytes and activated stellate cells may express different collagen XVIII forms and that one of these variants could be specifically involved in extracellular matrix remodeling in liver cancers.In the present study, we analyzed the expression of both LONG and SHORT collagen XVIII forms in 53 human liver biopsies, including primary and metastatic liver cancers and in primary liver cell cultures. The LONG form appears to be exclusively expressed by normal and tumor hepatocytes and is a plasma protein.…”

“…1,2 It is a component of most epithelial and vascular basement membranes [3][4][5] and is expressed at high levels by human hepatocytes in normal and fibrotic livers. 6 In normal human tissues, 2 forms of collagen XVIII, respectively designated the SHORT and LONG variants, are differentially expressed: the SHORT form is ubiquitously found in basement membranes 3 ; the LONG form is almost exclusively found in the liver, expressed at remarkably high levels by normal human hepatocytes, 6,7 and regulated by liver-enriched transcription factors in similarity with other liver-specific genes. 8 The SHORT and LONG forms of collagen XVIII originate from 2 alternate promoters and have amino-terminal noncollagenous domains of 303 and 493 amino acids (Fig.…”

“…We have shown that hepatocytes express high and stable levels of collagen XVIII in normal liver, active and quiescent fibrosis, 6 and small hepatocellular carcinomas, 11 whereas liver myofibroblasts increase their collagen XVIII expression by 13-fold in active liver fibrogenesis. 6 We thus hypothesized that hepatocytes and activated stellate cells may express different collagen XVIII forms and that one of these variants could be specifically involved in extracellular matrix remodeling in liver cancers.…”

“…3,7 The probes for albumin, collagen IV, laminin ␥1, ␣-smooth muscle actin (␣-SMA), matrix metalloproteinase-2, and 18S ribosomal RNA have been described. 6,13 Anti-a-SMA 14 16 Specimens were routinely processed for histology, i.e., hematoxylin-eosin-saffran and Sirius red staining.…”

“…As described, 6,11,[16][17][18] after macroscopic examination by a pathologist, representative samples were fixed in formalin and embedded in paraffin for histopathologic routine diagnosis and analyzed independently; a part of the fresh material was frozen in liquid nitrogen and stored at Ϫ80°C until use. Before RNA extraction, 5-m frozen serial sections were stained with methylene blue and observed under light microscopy.…”