Fibrosis in chronic rejection of human liver allografts: expression patterns of transforming growth factor-TGFbeta1 and TGF-beta3.
Activation and transformation of lipocytes (Ito cells, stellate cells) into alpha-actin-positive myofibroblast-like cells is an essential step in the initiation of liver fibrosis. Transforming growth factor-beta (TGF-beta) is considered an important mediator of this process. In order to determine mechanisms of fibrotic deposition in a hepatic transplant setting, we analyzed 10 chronically rejected human liver allografts for the expression of extracellular matrix (ECM) molecules, myofibroblast-like cells (alpha-actin), macrophages, and TGF-beta1 and -beta3. Using single- and double-immunohistochemical staining techniques, all specimens investigated showed increased deposition of the ECM proteins fibronectin, tenascin, undulin, and collagen VI with a characteristic densification especially in pericentral areas. Likewise, strong accumulation of alpha-actin-positive cells and TGF-beta1-expressing macrophages was observed in the same fields, supporting the concept of lipocyte activation/transformation and subsequent ECM production fostered by macrophage-derived TGF-beta1. In contrast, TGF-beta3 was found to be mainly expressed by a markedly increased number of lipocytes. Interestingly, distribution of TGF-beta3 corresponded to that of tenascin, an ECM molecule known to be involved in early matrix organization, suggesting that TGF-beta3 may likewise act mainly in early stages of fibrogenesis. Furthermore, TGF-beta3 restriction to high numbers of a single cell type (i.e., lipocytes) implied a possible role in cell proliferation through autocrine loops. In conclusion, fibrosis in chronic rejection seems to follow similar mechanisms as in non-transplanted livers but additionally suggests differential temporal and functional roles for the TGF-beta isoforms 1 and 3 in the course of a multistep process leading to lipocyte transformation and ECM production.
Demirci
G
G
Klinik für Abdominal- und Transplantationschirurgie, Medizinische Hochschule Hannover, Germany.
Nashan
B
B
Pichlmayr
R
R
D000199:Actins / Q000032:analysis; D002452:Cell Count; D004730:Endothelium, Vascular / Q000737:chemistry; D005109:Extracellular Matrix / Q000473:pathology; D006084:Graft Rejection / Q000150:complications / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008103:Liver Cirrhosis / Q000209:etiology*; D016031:Liver Transplantation / Q000276:immunology*; D008264:Macrophages / Q000166:cytology; D009130:Muscle, Smooth / Q000737:chemistry; D016212:Transforming Growth Factor beta / Q000096:biosynthesis
D000199:Actins; D016212:Transforming Growth Factor beta