No abstract

Interaction of the neuropeptide substance P (SP) and its neurokinin-1 receptor (NK-1R) plays an important role in the pathophysiology of intestinal inflammation. SP is known to stimulate production of interleukin (IL)-6 and IL-8 in the U-373-MG human astrocytoma cell line via activation of p38 MAPK (mitogen-activated protein kinase) and nuclear factor (NF)-kappaB, respectively. However, the signalling mechanisms by which SP-NK-1R interaction induces NF-kappaB activation and IL-8 expression are still not clear. In this study we demonstrate that SP stimulates IL-8 secretion and IL-8 promoter activity in the NCM460 non-transformed human colonic epithelial cell line transfected with NK-1R cDNA. Our results indicate that inhibition of endogenous Rho family proteins (RhoA, Rac1 and Cdc42) by their respective dominant negative mutants significantly decreases SP-induced IL-8 secretion and IL-8 promoter activity. We also demonstrate that SP rapidly activates RhoA, Rac1 and Cdc42 and that co-expression of the dominant negative mutants of RhoA, Rac1 and Cdc42 in NK-1R cDNA-transfected NCM460 cells significantly inhibits SP-induced NF-kappaB-dependent gene expression. These results demonstrate that Rho family small GTPases RhoA, Rac1 and Cdc42 are novel signal transducers for SP-stimulated IL-8 expression.

Background Non-alcoholic fatty liver disease (NAFLD) results from over-consumption and is a significant and increasing cause of liver failure. The type of diet that is conducive to the development of this disease has not been established and evidence-based treatment options are currently lacking. We hypothesized that the onset of hepatic steatosis is linked to the consumption of a diet with a high fat content, rather than related to excess caloric intake. In addition, we also hypothesized that fully manifested hepatic steatosis could be reversed by reducing the fat percentage in the diet of obese mice. Methods C57Bl/6J male mice were either fed a purified rodent diet containing 10% fat or a diet with 60% of calories derived from fat. A pair-feeding design was used to distinguish the effects of dietary fat content and caloric intake on dietary-induced hepatic lipid accumulation and associated injury. Livers were analyzed by quantitative RT-PCR for lipid metabolism-related gene expression. Results After 9 weeks, mice on the 60% fat diet exhibited more weight gain, insulin resistance and hepatic steatosis, compared to mice on a 10% fat diet with equal caloric intake. Furthermore, mice with established metabolic syndrome at 9 weeks showed reversal of hepatic steatosis, insulin resistance and obesity when switched to a 10% fat diet for an additional 9 weeks, independent of caloric intake. Quantitative RT-PCR revealed that transcripts related to both de novo lipogenesis and increased uptake of free fatty acids were significantly upregulated in mice pair-fed a 60% fat diet, compared to 10% fat-fed animals. Conclusion Dietary fat content, independent from caloric intake, is a crucial factor in the development of hepatic steatosis, obesity and insulin resistance in the C57Bl/6J diet-induced obesity model caused by increased uptake of free fatty acids and de novo lipogenesis. In addition, once established, all these features of the metabolic syndrome can be successfully reversed after switching obese mice to a diet low in fat. Low fat diets deserve attention in the investigation of a potential treatment of patients with NAFLD.