Z Gastroenterol 2006; 44 - P137
DOI: 10.1055/s-2006-950724

Characterization of TGF-β pathways and regulation of nerve growth factor (NGF) expression in pancreatic stellate cells

SL Haas 1, R Jaster 2, MJ Löhr 1, MV Singer 1, S Dooley 1, K Breitkopf 1
  • 1Dept. of Medicine II, University Hospital at Mannheim, University of Heidelberg, Germany., Molecular Alcohol Research in Gastroenterology, Mannheim, Germany
  • 2Department of Medicine, Division of Gastroenterology, Medical Faculty, University of Rostock, Rostock, Germany

Purpose: In chronic pancreatitis (cP), which is characterized by intermittent bouts of inflammation in conjunction with severe abdominal pain a proliferation of intrapancreatic nerves was described histologically. Nerve growth factor (NGF), a member of the neurotrophin family, promotes neurite outgrowth and is involved in the development of pain. Two receptors for NGF have been described: the low-affinity NGF receptor p75 and the high-affinity tyrosine kinase receptor TrkA. The role of NGF expresssion in pancreatic stellate cells (PSC) is up to now not well defined and so are the effects of the pro-fibrogenic cytokine transforming growth factor (TGF)-β.

Methods: NGF, p75 and TrkA expression was studied by RT-PCR, Western blot and immunofluorescence in a recently characterized immortalized human PSC cell line (ihPSC) and in primary rat PSC (prPSC). Time and dose-dependent regulation of expression was examined after TGF-β1 stimulation. Activation of the TGF-β induced Smad signaling pathways was investigated by Western blot measuring Smad phosphorylation and in reporter gene assays.

Results: While TGF-β stimulation led to activation of Smad2 in ihPSC as well as prPSC, only in prPSC parallel activation of Smad1 and expression of the TGF-β receptor ALK1 was detected. NGF itself did not activate the TGF-β/Smad pathway. NGF, p75 and TrkA were all expressed and induced by TGF-β in ihPSC while this was only true for NGF and TrkA in prPSC. The TGF-β mediated induction of NGF secretion was blocked by inhibiting the ALK5/Smad1/5/8 pathway using a chemical compound drug that blocks ALK5 (SB431542).

Summary and Conclusions: Like hepatic stellate cells, primary PSC respond to TGF-β treatment by activation of two parallel Smad signaling cascades, initiated by binding of TGF-β either to ALK1 or to ALK5 and the ALK5 pathway leads to increased expression and secretion of NGF.

By secretion of NGF PSC might have a modulatory role in the development of pain and intrapancreatic nerve proliferation in chronic pancreatitis. Upregulated expression by TGF-β which is known to be an important mediator of fibrotic processes and wound healing underlines the potential biological significance of our findings.