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SUMMARY:At present, the cell-cell interactions and molecular mechanisms of pancreas fibrogenesis are largely unknown. The purpose of this study was to investigate paracrine stimulatory loops between platelets and pancreatic stellate cells (PSC). Human PSC were obtained by outgrowth from fibrotic human pancreas. Native platelet lysate (nPL) and transiently acidified platelet lysate (aPL) were added to cultured PSC (passage 4 to 7) in the absence of serum. The synthesis of collagen types I and III and c-fibronectin (cFN) was demonstrated on protein (immunofluorescence and quantitative immunoassay) and mRNA (Northern blot) level. Using sections of human pancreas with acute pancreatitis, platelet aggregates in capillaries were demonstrated by transmission electron microscopy. nPL, and to an even greater extent aPL, significantly increased the synthesis of collagen types I and III and of c-FN (120 l/ml aPL increased collagen type I concentration in PSC supernatants by 1.99 Ϯ 0.17 times and c-FN of 2.49 Ϯ 0.28 times, mean Ϯ SD, n ϭ 3). nPL and aPL also significantly stimulated cell proliferation (increased bromodeoxyuridine (BrdU) incorporation by 6.4 Ϯ 0.78 times and 10 Ϯ 0.29 times, respectively). By preincubating aPL with transforming growth factor ␤ (TGF␤)-and platelet-derived growth factor (PDGF)-neutralizing antibodies and the TGF␤-latency associated peptide, respectively, TGF␤1 was identified as the main mediator stimulating matrix synthesis and PDGF as the responsible mitogen. Our data demonstrate that platelets contain fibrogenic mediators that stimulate proliferation (PDGF) and matrix synthesis (TGF␤1) of cultured PSC. We suggest that platelets and PSC cooperate in the development of pancreas fibrosis. (Lab Invest 2000, 80:47-55).

Through complex interactions between stellate cells and carcinoma cells, tumor progression and cancer cell invasion are accelerated. As we gain better understanding of these mechanisms, adequate therapies to reduce tumor cell invasion and cancer progression might be developed.

The effect of the characteristic desmoplastic reaction of pancreatic cancer on tumor progression is largely unknown. We investigated whether pancreatic stellate cells, which are responsible for the desmoplastic reaction, support tumor progression. Immunohistology revealed that