Introduction Pancreatic stellate cells (PSC) are exposed to supranormal concentrations of insulin via the islet–acinar portal system. We initially hypothesised that this might influence PSC numbers by effects on proliferation or apoptosis. This effect could be mediated via insulin receptors or via receptors for insulin-like growth factor (IGF-1). In this context, we examined the role of IGF-1 and insulin in the prevention of pancreatic stellate cell apoptosis. Following initial experiments, it became apparent that PSC can synthesise IGF-1, we therefore examined whether IGF-1 might be an autocrine growth factor in cultured stellate cells. The aims were to determine (1) the expression of IGF-1 and insulin receptor by PSC; (2) the secretion of IGF-1 by pancreatic stellate cells; (3) the effects of IGF-1 on PSC proliferation and apoptosis.
Methods Culture-activated rat PSCs were used between passages 1 and 4 and serum deprived prior to all experiments. PSC proliferation was determined by [3H]-thymidine incorporation. Apoptosis was determined with acridine orange counting of apoptotic bodies and caspase 3 activity assays. Western blotting and immunocytochemistry were used to demonstrate the presence of IGF-1 and insulin receptors. Real-time quantitative PCR was used to detect receptor mRNA. A sandwich ELISA was used to determine the secretion of IGF-1, and real-time quantitative PCR use to confirm mRNA expression.
Results Activated PSC express protein and mRNA for IGF-1 and insulin receptors. IGF-1 secretion is upregulated 2.40-fold following serum withdrawal compared with 16% FCS (see Abstract 001). This upregulation is also seen at the level of mRNA in response to serum withdrawal. Exogenous IGF-1 (100 ng/ml) and insulin (10 000 ng/ml) prevented cycloheximide-induced PSC apoptosis in a concentration-dependent manner, 63% at 24 h, and 71% at 24 h, respectively. There was moderate effect on PSC proliferation following exposure to IGF-1 but not with insulin.
Conclusion These data suggest that IGF-1 has an autocrine role in reducing PSC apoptosis on serum withdrawal. Inhibiting IGF-1 expression or blocking the IGF-1 receptor may increase susceptibility to apoptosis. This represents a potential therapeutic target for prevention or treatment of pancreatic fibrosis.
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