Preferential increase of extracellular matrix expression relative to transforming growth factor beta1 in the pancreas during the early stage of acute hemorrhagic pancreatitis in rats.

OBJECTIVES: To elucidate the role of transforming growth factor (TGF) beta1 and extracellular matrix (ECM) after acute necrotizing pancreatitis, we studied the regulation of TGF-beta1 and ECM after induction of pancreatitis. METHODS: We examined the serial changes of levels of plasma TGF-beta1 by enzyme-linked immunoassay and expression of TGF-beta1 and ECM by Northern and Western blot analyses, respectively, in the pancreas after induction of sodium taurocholate-induced acute pancreatitis. RESULTS: Plasma total (active and inactive) TGF-beta1 levels at 3 hours after induction of pancreatitis were significantly increased compared with baseline values. The levels of TGF-beta1 messenger RNA (mRNA) were unaltered by day 2. Levels of fibronectin mRNA at 3 hours after induction of pancreatitis were already higher than the baseline values. Latency-associated peptide-TGF-beta1 showed a peak on day 7. Thus, the expression of ECM mRNA increased earlier than that of TGF-beta1 mRNA. CONCLUSIONS: These results suggest that the increase in plasma TGF-beta1 concentration probably results from the elevated secretion of TGF-beta1 from several cells and/or the redistribution of TGF-beta1 protein and that the increase in expression of ECM probably is associated with the activation of TGF-beta1. It is conceivable that both increased plasma concentration and focal activation of TGF-beta1 play an important role in ECM production during the early stage of acute pancreatitis.

High glucose activates rat pancreatic stellate cells through protein kinase C and p38 mitogen-activated protein kinase pathway.

OBJECTIVE: Hyperglycemia is implicated in fibrosis in many organs. Exocrine and endocrine pancreas are closely linked both anatomically and physiologically, and pathological conditions in the exocrine gland can cause impairment of endocrine function and vice versa. Chronic pancreatitis causes pancreatic fibrosis and sometimes results in diabetes mellitus. Pancreatic stellate cells (PSCs) play a pivotal role in pancreatic fibrogenesis. However, the effects of high glucose concentrations on PSC activation have not been fully elucidated. METHODS: Cultured PSCs were incubated in the presence of various concentrations of glucose. Pancreatic stellate cell proliferation, alpha-smooth muscle actin (alpha-SMA) expression, and collagen production were determined by colorimetric conversion assay, Western blot analysis, and Sirius red dye binding assay, respectively. RESULTS: High glucose concentrations significantly increased PSC proliferation, alpha-SMA expression, and collagen type I production in PSCs. High glucose concentrations activated protein kinase C (PKC) in PSCs, and PKC inhibitor GF109203X inhibited glucose-stimulated PSC proliferation, alpha-SMA expression, and collagen secretion. High glucose also activated p38 mitogen-activated protein kinase (MAPK) in PSCs, and p38 MAPK inhibitor SB203580 inhibited glucose-stimulated collagen secretion. CONCLUSIONS: Our results indicate that high glucose concentrations stimulate PSC activation via PKC-p38 MAP kinase pathway and suggest that high glucose may aggravate pancreatic fibrosis.

Pressure activates rat pancreatic stellate cells.

Pancreatic stellate cells (PSCs) play a central role in development of pancreatic fibrosis. In chronic pancreatitis, pancreatic tissue pressure is higher than that of the normal pancreas. We here evaluate the effects of pressure on the activation of rat PSCs. PSCs were isolated from the pancreas of Wistar rat using collagenase digestion and centrifugation with Nycodenz gradient. Pressure was applied to cultured rat PSCs by adding compressed helium gas into the pressure-loading apparatus to raise the internal pressure. Cell proliferation rate was assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation. MAPK protein levels and alpha-smooth muscle actin (alpha-SMA) expression were evaluated by Western blot analysis. Concentration of activated transforming growth factor-beta1 (TGF-beta1) secreted from PSCs into culture medium was determined by ELISA. Collagen type I mRNA expression and collagen secretion were assessed by quantitative PCR and Sirius red dye binding assay, respectively. Application of pressure significantly increased BrdU incorporation and alpha-SMA expression. In addition, pressure rapidly increased the phosphorylation of p44/42 and p38 MAPK. Treatment of PSCs with an MEK inhibitor and p38 MAPK inhibitor suppressed pressure-induced cell proliferation and alpha-SMA expression, respectively. Moreover, pressure significantly promoted activated TGF-beta1 secretion, collagen type I mRNA expression, and collagen secretion. Our results demonstrate that pressure itself activates rat PSCs and suggest that increased pancreatic tissue pressure may accelerate the development of pancreatic fibrosis in chronic pancreatitis.

Angiotensin II type 1 receptor interaction is an important regulator for the development of pancreatic fibrosis in mice.

The renin-angiotensin system (RAS) plays important roles in various pathophysiological processes. However, the role of the RAS in pancreatic fibrosis has not been established. We investigated the role of angiotensin II (ANG II)-ANG II type 1 (AT(1)) receptor pathway in the development of pancreatic fibrosis with AT(1a) receptor-deficient [AT(1a)(-/-)] mice. To induce pancreatic fibrosis, AT(1a)(-/-) and wild-type (WT) mice were submitted to three episodes of acute pancreatitis induced by six intraperitoneal injections of 50 microg/kg body wt cerulein at hourly intervals, per week, for four consecutive weeks. Pancreatic fibrosis was assessed by histology and hydroxyproline content. Pancreatic stellate cell (PSC) activation and the localization of AT(1) receptors were assessed by Western blot analysis for alpha-smooth muscle actin and immunostaining. Transforming growth factor-beta(1) (TGF-beta(1)) mRNA expression in the pancreas was assessed by RT-PCR. Six intraperitoneal injections of cerulein induced acute pancreatitis in both AT(1a)(-/-) and WT mice. There were no significant differences between two groups with regard to serum amylase and histological changes. Pancreatic fibrosis induced by repeated episodes of acute pancreatitis was significantly attenuated in AT(1a)(-/-) mice compared with that in WT mice. This finding was accompanied by a reduction of activated PSCs. Dual-immunofluorescence staining in WT mice revealed that activated PSCs express AT(1) receptors. The level of TGF-beta(1) mRNA was lower in AT(1a)(-/-) mice than in WT mice. Our results demonstrate that the ANG II-AT(1) receptor pathway is not essential for the local pancreatic injury in acute pancreatitis but plays an important role in the development of pancreatic fibrosis through PSC activation and proliferation.