Involvement of AP-1 proteins in pancreatic stellate cell activation in vitro

Pancreatic stellate cells (PSCs) play a key role in the development of pancreatic fibrosis. The molecular mechanisms underlying their activation in response to profibrogenic mediators, however, are largely unknown. Extending previous studies on the transcriptional regulation of PSC activation, we have now focused on the involvement of activator protein (AP)-1.

Using cultured rat PSCs, phenotypic transition of PSCs towards activated myofibroblasts was monitored by an immunoblot analysis of alpha-smooth muscle actin (alpha-SMA) expression. Transcription factor activation profiles were studied by electrophoretic mobility shift assays. DNA synthesis in PSCs was assessed through the quantification of 5-bromo-2'-deoxyuridine incorporation.

Activated AP-1 complexes were detectable already before high levels of alpha-SMA were expressed. Maximal DNA binding activity of AP-1, as well as of NF-kappaB, was observed early in the course of PSC culture, while the strongest activation of STAT3 was observed much later. A detailed analysis of AP-1 complex composition revealed that phenotypic transition of PSCs towards myofibroblasts was accompanied by an increase of the JunD content relative to the one of JunB. Studies on the role of JunB and JunD in PSC activation indicated an inhibition of platelet-derived growth factor-induced DNA synthesis by antisense oligonucleotides to JunB but not JunD.

The results of this study implicate AP-1 in PSC activation and suggest distinct roles of individual Jun proteins in the regulation of PSC function. In further studies, it should be analyzed whether signaling pathways involved in PSC activation might be suitable targets for antifibrotic therapies.