Epidemiology, risk factors, and the promotion of pancreatic cancer: role of the stellate cell

Abstract

There are approximately 277,000 new cases of pancreatic cancer and 266,000 deaths from pancreatic cancer annually, indicating a mortality rate of 96% of the cases diagnosed. Because of the ineffectiveness of therapies, a major emphasis needs to be placed on prevention. This paper reviews the epidemiology and risk factors for pancreatic cancer, and uses this information to propose plausible research directions for determining the biological mechanisms mediating the effects of risk factors on the promotion of pancreatic cancer, with a focus on the pancreatic stellate cell.

Figure 1

Age and environmental risk factors for pancreatic cancer. Greatest risk factor for pancreatic cancer is age. Risk further increases with smoking and alcohol abuse, the metabolic syndrome, and solar radiation/vitamin D system.

Figure 2

Components of desmoplasia in pancreatic cancer. Pancreatic cancer cells and pancreatic stellate cells (PaSC) promote each others’ growth and proliferation, and together regulate processes of extracellular matrix proteins deposition, angiogenesis, and disordered immune surveillance. FGF, fibroblast growth factor; PDGF, platelet-derived growth factor; TGF-β, transforming growth factor-β.

Figure 3

Mechanisms of regulation of pancreatic stellate cells (PaSC) and pancreatic carcinogenesis by environmental risk factors. Potential pathways emanating from the environmental risk factors that regulate the activation state of PaSC and emphasizes the emerging role of PaSC in pancreatic carcinogenesis are shown. LPS, lipopolysaccharide; TNF-α, tumor necrosis factor-α.

Figure 4

Mice with pancreas-specific overexpression of Kras (Kras^G120) display abundant desmoplasia surrounding pancreatic intra-epithelial neoplasias (PanIN). Representative images show Sirius red (a) and a-smooth muscle actin (α-SMA) staining (b) in serial sections of pancreas from 8-month-old, conditional Kras^G120 mice. As illustrated in (a), tumor cells are surrounded by abundant collagen fibers (red staining). Moreover, α-SMA staining (brown staining), representing active pancreatic stellate cells, is abundant in areas with marked accumulation of collagen fibers.

Figure 5

High-fat diets promote desmopla-sia in mice with pancreas-specific overexpression of Kras (Kras^G120). Conditional Kras^G120 mice were fed either a standard diet (a) or a high-fat, high-calorie (HFCD) diet (b) for 3 months. Mice also received a daily injection of cerulein to promote pancreatic inflammation. Five-month-old mice fed the HFCD diet displayed a greater number of active pancreatic stellate cells (α-smooth muscle actin marker, red staining), and deposition of extracellular matrix proteins (fibronectin, green staining) than mice fed the standard diet. Blue staining represents DAPI-positive nuclei.

Figure 6

Conditioned medium from pancreatic intra-epithelial neopla-sias (PanIN) cells stimulates pancreatic stellate cell (PaSC) activation. Mouse PanIN cells were cultured for 2 days in 10% fetal bovine serum medium, and subsequently, aliquots of conditioned medium were transferred onto freshly isolated mouse PaSC. PaSC were cultured for 3 days in 1% serum medium in the presence of PanIN-conditioned media (up to 60% of the total culture medium) or equal volume of cell-free 10% media as the control. PaSC activation was evaluated by measuring (a) cell proliferation (total cell number) and (b) protein expression levels of fibronectin, α-smooth muscle actin (α-SMA), and metalloproteinase-13 (MMP-13) (proform) in cell lysates (Western blot analysis). ERK, extracellular signal-regulated kinase.

Figure 7

Combination of ethanol and leptin treatment increases extracellular matrix deposition via the PI3K/AKT/mTOR signaling in cultured activated mouse pancreatic stellate cells (PaSC). (a) PaSC cultured in 1% fetal bovine serum medium were either untreated or treated with leptin (0.5 mg/mL) and/or ethanol (50 mmol/mL) for 24 h. Immunoblots show cellular levels of fibronectin and α-smooth muscle actin (α-SMA). (b) Immunoblots show levels of phosphorylated p70S6K, an mTOR substrate, p-Akt, and extracellular signal-regulated kinase-1/2 in activated PaSC untreated or treated for 30 min with leptin (0.5 mg/mL) alone or in combination with ethanol (50 mmol/mL). GAPDH was used as loading control. Pretreatment with rapamycin (Ra) or LY294002 (Ly) (data not shown) inhibited p70S6K phosphorylation. (c) Graphs show fibronectin levels in PaSC treated for 24 h with 0.5 mg/mL leptin and 50 mmol/mL ethanol in the presence or absence of Ra or Ly.