Impaired proteolysis of collagen I inhibits proliferation of hepatic stellate cells: implications for regulation of liver fibrosis.
Myofibroblastic-activated hepatic stellate cells are the major source of the collagen I-rich extracellular matrix in liver fibrosis but also produce matrix metalloproteinases, which remodel this protein. We have investigated the role of collagen I proteolysis in both regulating proliferation and maintaining the activated myofibroblastic phenotype of stellate cells in vitro. Compared with stellate cells plated on normal collagen I, those plated on a collagenase-resistant form of collagen I (r/r collagen) had reduced thymidine incorporation and proliferating cell nuclear antigen expression but increased p21 expression. Collagen I was shown to be rendered resistant to matrix metalloproteinases by artificial cross-linking in vitro using tissue transglutaminase exerted similar antiproliferative effects on stellate cells to r/r collagen. Of the stellate cell activation markers examined (tissue inhibitor of metalloproteinases-1, alpha-smooth muscle actin, matrix metalloproteinases-2 and -9, and procollagen I) only the last was decreased by culture on r/r collagen relative to normal collagen I. Antagonists of integrin alphavbeta3, an integrin reported to stimulate stellate cell proliferation, significantly inhibited adhesion, proliferation, and procollagen I synthesis of stellate cells plated on normal collagen I but had reduced effectiveness on these parameters in cells on r/r collagen. We conclude that proliferation of stellate cells is promoted by pericellular collagen I proteolysis acting via alphavbeta3 integrin. Cross-linking of collagen I by tissue transglutaminase, a process known to occur in chronic liver fibrosis, might not only increase its resistance to matrix metalloproteinases thereby inhibiting resolution of fibrosis but also functions to constrain the fibroproliferative process.
Zhou
Xiaoying
X
Liver Group, University Division of Infection, Inflammation and Repair, Southampton General Hospital, Southampton, Hants, SO16 6YD, United Kingdom.
Jamil
Aqeel
A
Nash
Andrew
A
Chan
James
J
Trim
Nathan
N
Iredale
John P
JP
Benyon
R Christopher
RC
D000818:Animals; D002251:Carbon Tetrachloride / Q000633:toxicity; D049109:Cell Proliferation; D002478:Cells, Cultured; D024042:Collagen Type I / Q000235:genetics / Q000378:metabolism*; D003432:Cross-Linking Reagents; D006131:Growth Inhibitors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008099:Liver / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology*; D008103:Liver Cirrhosis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D020782:Matrix Metalloproteinases / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010447:Peptide Hydrolases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011503:Transglutaminases / Q000378:metabolism
D024042:Collagen Type I; D003432:Cross-Linking Reagents; D006131:Growth Inhibitors; D002251:Carbon Tetrachloride; D011503:Transglutaminases; D010447:Peptide Hydrolases; D020782:Matrix Metalloproteinases