Differential and synergistic effects of platelet-derived growth factor-BB and transforming growth factor-β1 on activated pancreatic stellate cells

Objective: The cytokines platelet-derived growth factor (PDGF) and transforming growth factor ( TGF)-beta 1 are major factors influencing the transformation from the quiescent to the activated phenotype of pancreatic stellate cells (PSC), a process involved in the pathogenesis of chronic pancreatitis. Albeit much effort has been made to study the effects of PDGF and TGF-beta 1 on PSCs, their interaction is still unclear, because these cytokines show both differential and synergistic effects as outlined by this study. Methods: Culture-activated PSCs of rats were treated with PDGF-BB and TGF-beta 1. Subsequent changes of cell proliferation and migration were determined by cell counting, (+)- bromo-2'- deoxyuridine enzyme-linked immunosarbant assay ( ELISA), and migration assay. Gene expression, synthesis of proteins, and activation of kinases were further studied by reverse transcription-polymerase chain reaction, real-time polymerase chain reaction, ELISA, and Western blot. Results: PDGF-BB increased PSC proliferation and migration, accompanied by elevated expression of matrix metalloproteinases (MMP)13 and MMP-3. The mRNA amount of procollagen alpha 2( I), alpha-smooth muscle actin (alpha-SMA), tissue inhibitor of metalloproteinase ( TIMP)- 1, and TGF-beta 1 was also increased by PDGF-BB. In contrast, PDGF-BB reduced collagen type I in culture medium and synthesis of alpha-SMA. Treatment of PSC with TGF-beta 1 decreased proliferation, had no significant effect on migration and MMP expression, but increased expression and synthesis of procollagen alpha 2( I) and alpha-SMA. Both cytokines induced phosphorylation of extracellular signal regulated kinase (ERK)-1/2 and p38(MAPK), but only PDGF-BB activated the protein kinase B signaling pathway. Conclusion: PDGF-BB augments effects of TGF-beta 1 on the mRNA level presumably because of up-regulation of TGF-beta 1 synthesis and common signaling pathways of the 2 cytokines. However, at the protein level, PDGF-BB impairs typical TGF-beta 1 effects such as increased synthesis of collagen ( type I) and alpha-SMA. Moreover, PDGF-BB facilitates degradation of extracellular matrix proteins by enhancement of MMP synthesis, but MMP activity was probably limited because of elevated tissue inhibitor of metalloproteinase 1 expression.