The Role of Thrombocytes in Liver Fibrogenesis: Effects of Platelet Lysate and Thrombocyte-Derived Growth Factors on the Mitogenic Activity and Glycosaminoglycan Synthesis of Cultured Rat Liver Fat Storing Cells

Abstract

A central problem in the study of the pathogenesis of liver fibrosis (fibrogenesis) is the identification of the cellular sources of the extracellular matrix and the dissection of the molecular mediators stimulating connective tissue synthesis in certain hepatic target cells. In the present study the role of platelets and of some platelet-derived polypeptide growth factors in the proliferation and proteoglycan synthesis of rat liver fat storing cells in culture (the principle connective tissue-producing cell type in liver) was determined. Fat storing cell proliferation was determined by measurement of the DNA-content, and [ 3 H]thymidine-and bromodeoxyuridine-incorporation. Glycosaminoglycan synthesis was determined by the measurement of [ 35 S]sulphate incorporation. Human platelet lysate (0.3 to 2.6 g protein per litre medium) stimulated, in a dose-dependent manner, both the proliferation and glycosaminoglycan synthesis of rat liver fat storing cells kept äs a primary culture in Dulbecco's modificätion of Eagle's medium in the absence of foetal calf serum. More than 70% of the newly synthesized glycosaminoglycans were found in the medium. Among the various thrombocyte-derived polypeptides tested äs candidate mediators of the platelet-derived fibrogenic activity, platelet derived growth factor was not effective in enhancing glycosaminoglycan synthesis, and it stimulated the proliferation of fat storing .cells only about 2 fold. On the other hand, epidermal growth factor proved to be a Stimulus of both processes. Transforming growth factor (> 10 pmol/1) inhibited foetal calf serum (Dulbecco's modificätion of Eagle's medium with a fraction of foetal calf serum of 0.1) and epidermal growth factor stimulated proliferation but enhanced the synthesis of sulphated glycosaminoglycans about 2-fold. These results suggest the possible role of transforming growth factor äs a negative modulator for fat storing cells proliferation but a positive modulator for fat storing cell transformation and extracellular glycosaminoglycan matrix synthesis. Furthermore, our results indicate a cpoperation between different hepatic and extrahepatic cell types by paracrine Stimulation of fat storing cells. Transfonning growth factor in combination with epidermal growth factor appear to be candidate mediators of the platelet-derived fibrogenic activity, which stimulates fat storing cells in culture, and might also be effective in vivo during hepatic repair processes following liver injury.

Activation of rat liver perisinusoidal lipocytes by transforming growth factors derived from myofibroblastlike cells. A potential mechanism of self perpetuation in liver fibrogenesis.

“…Studies from others and our laboratory have shown recently that secretions of activated Kupffer cells and platelets stimulate proliferation of PL in culture (10)(11)(12)(13) and also the synthesis ofcollagens ( 13), proteoglycans ( 14), and hyaluronan (15) by these cells. Potential candidates ofthe Kupffer cell and platelet-derived fibrogenic activity seem to be transforming growth factor a/epidermal growth factor (TGFa/EGF) and TGF3 (7,(16)(17)(18).…”

“…Detailed procedures of the isolation and culture of PL from rats have been published previously by this laboratory (10,12,14,15,26). The purity of the PL preparations attained > 80% (nonvital hepatocytes, Kupffer cells, and endothelial cells represented the remaining 20%) as assessed by light microscopy using the presence of perinuclear lipid droplets and the typical cell shape as a marker.…”

Increased Release of Platelet-Derived Growth Factor from Platelets in Chronic Liver Disease

“…Several types of in vivo studies have demonstrated that fat-storing cells play a central role in liver fibrogenesis (11 -13). Recent studies have also shown that platelet-derived growth factor stimülates proliferation of cultured fafcstoring cells and synthesis of mätrix components by fat-storirig cells (14)(15)(16)(17). However, the source of platelet-derived growth factor in liver fibrogenesis is unceftain.…”

“…Therefore, human platelet-derived growth factor is platelet-derived growth factor and thrombocyte lysate thought to participate in wound healing and the develop-promote proliferation of cultured fat-storing cells and ment of arteriosclerosis in vivo (9). On the other hand, stimulate synthesis of extracellular matrix, suggesting chronic liver diseases, including chronic hepatitis and the participation of platelet-derived growth factor in filiver cirrhosis, are characterized by destruction and de-brosis of the liver (14)(15)(16)(17). Thrombocytopenia, which is frequently seen in chronic liver diseases, has been attributed to hypersplenism (10).…”

Review article: the prevention and reversal of hepatic fibrosis in autoimmune hepatitis

“…Cytokines, including transforming growth factor-beta 1 (TGFb1), platelet-derived growth factor (PDGF) and endothelial growth factor (EGF) induce the activated hepatic stellate cells to transform into myofibroblasts, [112][113][114][115] and interventions that inhibit the production of these cytokines may limit this transformation and reduce collagen production. Similarly, angiotensin II is secreted by hepatic stellate cells, and it induces their proliferation and the production of extracellular matrix.…”