Fibroblasts stimulate acinar cell proliferation through IGF-I during regeneration from acute pancreatitis

Mesenchyme-derived IGF2 is a major paracrine regulator of pancreatic growth and function

The genetic mechanisms that determine the size of the adult pancreas are poorly understood. Imprinted genes, which are expressed in a parent-of-origin-specific manner, are known to have important roles in development, growth and metabolism. However, our knowledge regarding their roles in the control of pancreatic growth and function remains limited. Here we show that many imprinted genes are highly expressed in pancreatic mesenchyme-derived cells and explore the role of the paternally-expressed insulin-like growth factor 2 (Igf2) gene in mesenchymal and epithelial pancreatic lineages using a newly developed conditional Igf2 mouse model. Mesenchyme-specific Igf2 deletion results in acinar and beta-cell hypoplasia, postnatal whole-body growth restriction and maternal glucose intolerance during pregnancy, suggesting that the mesenchyme is a developmental reservoir of IGF2 used for paracrine signalling. The unique actions of mesenchymal IGF2 are demonstrated by the absence of any discernible growth or functional phenotypes upon Igf2 deletion in the developing pancreatic epithelium. Additionally, increased IGF2 levels specifically in the mesenchyme, through conditional Igf2 loss-of-imprinting or Igf2r deletion, leads to pancreatic acinar overgrowth. Furthermore, ex-vivo exposure of primary acinar cells to exogenous IGF2 activates AKT, a key signalling node, and increases their number and amylase production. Based on these findings, we propose that mesenchymal Igf2, and perhaps other imprinted genes, are key developmental regulators of adult pancreas size and function.

Fibroblast Growth Factor (FGF) Signaling Protects Against Acute Pancreatitis-Induced Damage by Modulating Inflammatory Responses

BACKGROUND Acute pancreatitis (AP) is a symptom of sudden pancreas inflammation, which causes patients severe suffering. In general, fibroblast growth factor (FGF) levels are increased and amylase and lipase activities are elevated during AP pathogenesis, but protein concentration are low. However, the mechanism through which FGF signaling regulates AP pathogenesis remains elusive. MATERIAL AND METHODS The concentrations of PGE2, TNF-alpha, sCRP, FGF1, and FGF2 in the serum samples of the AP group and healthy control group were detected by enzyme-linked immunosorbent assay. In addition, IkappaBalpha and p-IkappaBalpha levels were analyzed in the serum samples. Subsequently, the AP rat model was established, and FGF1, FGF2, anti-FGF1, and anti-FGF2 antibodies and Bay11-7082 were injected into AP rats. TNF-alpha, PAI-1 JNK, p-JNK, IkappaBalpha, and p-IkappaBalpha levels were also examined. RESULTS Results showed that levels of PGE2, TNF-alpha, sCRP, p-IkappaBalpha, FGF1, and FGF2, as well as amylase and lipase activity were increased in patients with AP compared with those in healthy people. In addition, protein concentrations were lower in patients with AP than in the healthy group. Activation of FGF signaling by injecting FGF1 or FGF2 also inhibited AP-induced inflammation response in the pancreas and increased amylase and lipase activities, as well as protein concentration. However, the injection of FGF1 and FGF2 antibodies accelerated AP-mediated inflammation responses in the serum. In addition, Bay11-7082 injection inhibited AP activation of inflammation response and amylase and lipase activities. Protein concentration were also increased in AP rats. CONCLUSIONS FGF signaling protects against AP-mediated damage by inhibition of AP-activating inflammatory responses.

Insulin/IGF-driven cancer cell-stroma crosstalk as a novel therapeutic target in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is unrivalled the deadliest gastrointestinal cancer in the western world. There is substantial evidence implying that insulin and insulin-like growth factor (IGF) signaling axis prompt PDAC into an advanced stage by enhancing tumor growth, metastasis and by driving therapy resistance. Numerous efforts have been made to block Insulin/IGF signaling pathway in cancer therapy. However, therapies that target the IGF1 receptor (IGF-1R) and IGF subtypes (IGF-1 and IGF-2) have been repeatedly unsuccessful. This failure may not only be due to the complexity and homology that is shared by Insulin and IGF receptors, but also due to the complex stroma-cancer interactions in the pancreas. Shedding light on the interactions between the endocrine/exocrine pancreas and the stroma in PDAC is likely to steer us toward the development of novel treatments. In this review, we highlight the stroma-derived IGF signaling and IGF-binding proteins as potential novel therapeutic targets in PDAC.

Expression of insulin-like growth factor binding protein-4 (IGFBP-4) in acute pancreatitis induced by L-arginine in mice

The mechanisms of injury and regeneration after acute pancreatitis are still incompletely understood. Insulin-like growth factor binding proteins (IGFBPs) have been reported to play roles in various pancreatic diseases, but the involvement of insulin-like growth factor binding protein-4 (IGFBP-4) in acute pancreatitis is unknown. The aim of the study was to examine the expression of IGFBP-4 in mice with acute pancreatitis induced by two doses of L-arginine. IGFBP-4 expression was assayed by microarray test, real-time RT-PCR, Western blotting, ELISA and by an immunohistochemical assay. Microarray test of pancreatic mRNA showed that IGFBP-4 mRNA increased significantly after L-arginine treatment and the increase was confirmed by real-time RT-PCR. Western blotting and ELISA assay showed similar patterns of increase of IGFBP-4 in pancreatic tissues and serum. In the control pancreas, IGFBP-4 was mainly immunolocalized in the pancreatic islets. In the pancreatic tissues of mice with pancreatitis induced by L-arginine, the immunolocalization of IGFBP-4 was detected in both acinar cells and pancreatic islets. In conclusion, our results suggest that IGFBP-4 may play a potential role in pancreatic injury and regeneration in a murine model of acute pancreatitis induced by L-arginine.

c-Jun/AP-1 is required for CCK-induced pancreatic acinar cell dedifferentiation and DNA synthesis in vitro

Endogenous CCK plays an important role in pancreatic regeneration after pancreatitis. We used primary culture of mouse pancreatic acinar cells to evaluate the effect of CCK on acinar cell morphology and gene expression and to determine signaling pathways required for proliferation of acinar cells in vitro. Over 4 days in culture, cells grew out from acini and formed patches of monolayer, which displayed a reduced expression of acinar cell markers including digestive enzymes and Mist1 and an increased expression of ductal and embryonic markers, including cytokeratin 7, β-catenin, E-cadherin, pdx-1, and nestin. There was no appearance of stellate cell markers. CCK enhanced cellular spreading, DNA synthesis, and cyclin D1 expression. When signaling pathways were evaluated, CCK stimulation increased c-Jun expression, JNK and ERK activity, and AP-1 activation. Chemical inhibitors of JNK and ERK pathways, dominant-negative JNK and c-Jun, and c-Jun shRNA significantly inhibited CCK-induced DNA synthesis, CCK-induced AP-1 activation, and cyclin D1 expression. Furthermore, dominant-negative c-Jun reduced the increased expression of β-catenin and the decreased expression of amylase during culture. These results show that MAPK/c-Jun/AP-1 pathway plays an important role in pancreatic acinar cell dedifferentiation and proliferation in culture. Monolayer culture can serve as a model to study acinar cell proliferation similar to regeneration after pancreatitis in vivo.

Age-dependent reduction of the PI3K regulatory subunit p85α suppresses pancreatic acinar cell proliferation

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is important for tissue proliferation. Previously, we found that tissue regeneration after partial pancreatic resection was markedly attenuated in aged mice as compared to young mice and that this attenuation was because of an age-dependent reduction of PI3K/Akt signaling in the pancreatic acini; however, the mechanisms for the age-associated decline of pancreatic PI3K/Akt signaling remained unknown. To better delineate the mechanisms for the decreased PI3K/Akt activation with aging, age-associated changes in cell proliferation and PI3K/Akt signaling were investigated in the present study using in vitro primary pancreatic acinar cell cultures derived from young and aged mice. In response to treatment with insulin-like growth factor 1 (IGF-1), acinar cells from young but not aged mice showed increased activation of PI3K/Akt signaling and cell proliferation, indicating that intrinsic cellular mechanisms cause the age-associated changes in pancreatic acinar cells. We also found that the expression of PI3K p85α subunit, but not IGF-1 receptor or other PI3K subunits, was significantly reduced in pancreatic acinar cells from aged mice; this age-associated reduction of p85α was confirmed in both mouse and human pancreatic tissues. Finally, small interfering RNA (siRNA)-mediated knockdown of p85α expression in acinar cells from young mice resulted in markedly attenuated activation of PI3K/Akt downstream signaling in response to IGF-1. From these results, we conclude that exocrine pancreatic expression of PI3K p85α subunit is attenuated by aging, which is likely responsible for the age-associated decrease in activation of pancreatic PI3K signaling and acinar cell proliferation in response to growth-promoting stimuli.

Rosiglitazone promotes pancreatic regeneration in experimental model of acute pancreatitis

Acute pancreatitis is an inflammatory disease of the pancreas caused by release of activated digestive enzymes in the pancreas. A number of therapeutic options have been explored for acute pancreatitis, but none has been unambiguously proven to be effective. Rosiglitazone has been shown to be efficacious in acute pancreatitis; thus, the present study was planned to evaluate the effect of rosiglitazone on pancreatic regeneration. Pancreatitis was induced by l-arginine in rats which were divided into three groups: cholecystokinin (CCK-8), rosiglitazone and vehicle. Rats were sacrificed at four time points after induction of pancreatitis i.e. 24h, day 3, day 14 and day 28 for determination of biochemical parameters and histological examination. Rate of DNA synthesis, immunohistochemistry and RT-PCR were performed at day 3 and day 7. Drug administration was started 2h after last L-arginine injection and continued till the day of sacrifice. The lower levels of enzyme in rosiglitazone-treated group compared to vehicle group proved the efficacy of rosiglitazone treatment in reducing severity of acute pancreatitis. The nucleic acid content and rate of DNA synthesis were significantly higher in rosiglitazone group indicating promotion of pancreatic regeneration. The histopathological score were lower in rosiglitazone group. Rosiglitazone treatment promoted pancreatic regeneration after acute injury. Currently, only symptomatic treatment is available, regeneration of pancreatic tissue can be a future strategy in the management of acute pancreatitis. Further studies are required to support the findings of the present study.

Growth factor mediated signaling in pancreatic pathogenesis

Functionally, the pancreas consists of two types of tissues: exocrine and endocrine. Exocrine pancreatic disorders mainly involve acute and chronic pancreatitis. Acute pancreatitis typically is benign, while chronic pancreatitis is considered a risk factor for developing pancreatic cancer. Pancreatic carcinoma is the fourth leading cause of cancer related deaths worldwide. Most pancreatic cancers develop in the exocrine tissues. Endocrine pancreatic tumors are more uncommon, and typically are less aggressive than exocrine tumors. However, the endocrine pancreatic disorder, diabetes, is a dominant cause of morbidity and mortality. Importantly, different growth factors and their receptors play critical roles in pancreatic pathogenesis. Hence, an improved understanding of how various growth factors affect pancreatitis and pancreatic carcinoma is necessary to determine appropriate treatment. This chapter describes the role of different growth factors such as vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF), platelet derived growth factor (PDGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), and transforming growth factor (TGF) in various pancreatic pathophysiologies. Finally, the crosstalk between different growth factor axes and their respective signaling mechanisms, which are involved in pancreatitis and pancreatic carcinoma, are also discussed.

Characterization of proliferative effects of insulin, insulin analogues and insulin-like growth factor-1 (IGF-1) in human lung fibroblasts

Insulin has been approved for inhaled application, but safety concerns remain, because of un-physiologically high insulin concentrations in the lung. Since insulin may act as growth factor, possible proliferative effects of insulin, insulin analogues and insulin-like growth factor-1 (IGF-1) on human lung fibroblasts were studied. As measure of proliferation [(3)H]-thymidine incorporation was studied in HEL-299, MRC-5, IMR-90 and primary human lung fibroblasts. In all cells, mRNA encoding IGF-1 receptors and two variants of insulin receptors was detected. Insulin and IGF-1 stimulated [(3)H]-thymidine incorporation in all cells. Comparison of the concentration-dependent effects in HEL-299 cells showed that IGF-1 and insulin glargine were more potent (EC(50), 3 and 6 nM) and more effective (maximum increase, by 135-150%) than insulin and insulin detemir (EC(50), 22 and 110 nM; maximum increase: by 80%). Proliferative effects of IGF-1 and insulin were inhibited to the same extent by an antibody (1H7) directed against the IGF-1 receptor α-subunit. Insulin-induced stimulation of [(3)H]-thymidine incorporation was reduced by 83% after siRNA-mediated down-regulation of IGF-1 receptor by about 75%, but not affected by a similar down-regulation of the insulin receptor. Insulin and IGF-1 caused rapid up-regulation of the early genes FOS, EGR-1 and EGR-2 as well as of the gene coding for IGF-1. In conclusion, in human lung fibroblasts insulin exerts marked proliferative effects and the pharmacological profile of this response as well as specific receptor knock-down experiments suggest mediation via IGF-1 receptors. The risk of unwanted structural lung alterations by long-term inhalative application of insulin should be considered.

Connective tissue growth factor is involved in pancreatic repair and tissue remodeling in human and rat acute necrotizing pancreatitis

OBJECTIVE

To analyze the involvement of connective tissue growth factor (CTGF) in the transforming growth factor-beta (TGF-beta) pathway during acute necrotizing pancreatitis (ANP) in humans and rats.

SUMMARY BACKGROUND DATA

Connective tissue growth factor is involved in several fibrotic diseases and has a critical role in fibrogenesis and tissue remodeling after injury.

METHODS

Normal human pancreas tissue samples were obtained through an organ donor program from five individuals without a history of pancreatic disease. Human ANP tissues were obtained from eight persons undergoing surgery for this disease. In rats, ANP was induced by intraductal infusion of taurocholate. The expression of CTGF was studied by Northern blot analysis, in situ hybridization, and immunohistochemistry in both human and rat pancreatic tissue samples.

RESULTS

Northern blot analysis revealed enhanced CTGF mRNA expression in human ANP tissue samples compared with normal controls. In addition, a concomitant increase in TGF-beta1 was present. By in situ hybridization, CTGF mRNA was localized in the remaining acinar and ductal cells and in fibroblasts. In regions of intense damage adjacent to areas of necrosis, CTGF mRNA signals were most intense. Inflammatory cells were devoid of any CTGF mRNA signals. By immunohistochemistry, CTGF protein was localized at high levels in the same cell types as CTGF mRNA. In ANP in rats, concomitantly enhanced mRNA levels of CTGF, TGF-beta1, and collagen type 1 were present, with a biphasic peak pattern on days 2 to 3 and day 7 after induction of ANP.

CONCLUSIONS

These data indicate that CTGF participates in tissue remodeling in ANP. The expression of CTGF predominantly in the remaining acinar and ductal cells indicates that extracellular matrix synthesis after necrosis is at least partly regulated by the remaining pancreatic parenchyma and only to a minor extent by inflammatory cells. Blockage of CTGF, a downstream mediator of TGF-beta in fibrogenesis, might be useful as a target to influence and reduce fibrogenesis in this disorder.

Fibroblast biology. Signals targeting the synovial fibroblast in arthritis

Fibroblast-like cells in the synovial lining (type B lining cells), stroma and pannus tissue are targeted by many signals, such as the following: ligands binding to cell surface receptors; lipid soluble, small molecular weight mediators (eg nitric oxide [NO], prostaglandins, carbon monoxide); extracellular matrix (ECM)-cell interactions; and direct cell-cell contacts, including gap junctional intercellular communication. Joints are subjected to cyclic mechanical loading and shear forces. Adherence and mechanical forces affect fibroblasts via the ECM (including the hyaluronan fluid phase matrix) and the pericellular matrix (eg extracellular matrix metalloproteinase inducer [EMMPRIN]) matrices, thus modulating fibroblast migration, adherence, proliferation, programmed cell death (including anoikis), synthesis or degradation of ECM, and production of various cytokines and other mediators [1]. Aggressive, transformed or transfected mesenchymal cells containing proto-oncogenes can act in the absence of lymphocytes, but whether these cells represent regressed fibroblasts, chondrocytes or bone marrow stem cells is unclear.