Cholecystokinin elevates mouse plasma lipids

Multi-organ Coordination of Lipoprotein Secretion by Hormones, Nutrients and Neural Networks

Plasma triglyceride-rich lipoproteins (TRL), particularly atherogenic remnant lipoproteins, contribute to atherosclerotic cardiovascular disease. Hypertriglyceridemia may arise in part from hypersecretion of TRLs by the liver and intestine. Here we focus on the complex network of hormonal, nutritional, and neuronal interorgan communication that regulates secretion of TRLs and provide our perspective on the relative importance of these factors. Hormones and peptides originating from the pancreas (insulin, glucagon), gut [glucagon-like peptide 1 (GLP-1) and 2 (GLP-2), ghrelin, cholecystokinin (CCK), peptide YY], adipose tissue (leptin, adiponectin) and brain (GLP-1) modulate TRL secretion by receptor-mediated responses and indirectly via neural networks. In addition, the gut microbiome and bile acids influence lipoprotein secretion in humans and animal models. Several nutritional factors modulate hepatic lipoprotein secretion through effects on the central nervous system. Vagal afferent signaling from the gut to the brain and efferent signals from the brain to the liver and gut are modulated by hormonal and nutritional factors to influence TRL secretion. Some of these factors have been extensively studied and shown to have robust regulatory effects whereas others are "emerging" regulators, whose significance remains to be determined. The quantitative importance of these factors relative to one another and relative to the key regulatory role of lipid availability remains largely unknown. Our understanding of the complex interorgan regulation of TRL secretion is rapidly evolving to appreciate the extensive hormonal, nutritional, and neural signals emanating not only from gut and liver but also from the brain, pancreas, and adipose tissue.

Serum DJ-1 level is positively associated with improvements in some aspects of metabolic syndrome in Japanese women through lifestyle intervention

DJ-1 is a protein that is associated with Parkinson disease and cancer, and the reduction of DJ-1 function and expression is also thought to be a cause of diabetes and hypertension. However, little is known about the association between the plasma concentration of DJ-1 and risk of metabolic syndrome. We hypothesized that a lifestyle intervention would increase serum DJ-1 and that up-regulated DJ-1 functions will result in the prevention of metabolic syndrome. The objective of our study is to examine whether the level of serum DJ-1 is associated with the risk of metabolic syndrome. Therefore, to reveal the association between DJ-1 and metabolic syndrome, this study investigated lifestyle intervention in a control group (n = 37) and intervention group (n = 45). The results showed that body mass index, body fat ratio, waist-hip ratio, waist circumference, blood pressure, and plasma glucose level were improved in the intervention group, as compared with those in the control group. Furthermore, serum levels of DJ-1 were increased in the intervention group, when compared with those in the control group. These results suggest that serum DJ-1 is increased by lifestyle intervention and that increased serum DJ-1 prevents metabolic syndrome. Thus, the level of serum DJ-1 will become one of the indexes for the risk of metabolic syndrome.

Up-regulation of cholesterol absorption is a mechanism for cholecystokinin-induced hypercholesterolemia

Excessive absorption of intestinal cholesterol is a risk factor for atherosclerosis. This report examines the effect of cholecystokinin (CCK) on plasma cholesterol level and intestinal cholesterol absorption using the in vivo models of C57BL/6 wild-type and low density lipoprotein receptor knock-out (LDLR(-/-)) mice. These data were supported by in vitro studies involving mouse primary intestinal epithelial cells and human Caco-2 cells; both express CCK receptor 1 and 2 (CCK1R and CCK2R). We found that intravenous injection of [Thr(28),Nle(31)]CCK increased plasma cholesterol levels and intestinal cholesterol absorption in both wild-type and LDLR(-/-) mice. Treatment of mouse primary intestinal epithelial cells with [Thr(28),Nle(31)]CCK increased cholesterol absorption, whereas selective inhibition of CCK1R and CCK2R with antagonists attenuated CCK-induced cholesterol absorption. In Caco-2 cells, CCK enhanced CCK1R/CCK2R heterodimerization. Knockdown of both CCK1R and CCK2 or either one of them diminished CCK-induced cholesterol absorption to the same extent. CCK also increased cell surface-associated NPC1L1 (Niemann-Pick C1-like 1) transporters but did not alter their total protein expression. Inhibition or knockdown of NPC1L1 attenuated CCK-induced cholesterol absorption. CCK enhanced phosphatidylinositide 3-kinase (PI3K) and Akt phosphorylation and augmented the interaction between NPC1L1 and Rab11a (Rab-GTPase-11a), whereas knockdown of CCK receptors or inhibition of G protein βγ dimer (Gβγ) diminished CCK-induced PI3K and Akt phosphorylation. Inhibition of PI3K and Akt or knockdown of PI3K diminished CCK-induced NPC1L1-Rab11a interaction and cholesterol absorption. Knockdown of Rab11a suppressed CCK-induced NPC1L1 translocation and cholesterol absorption. These data imply that CCK enhances cholesterol absorption by activation of a pathway involving CCK1R/CCK2R, Gβγ, PI3K, Akt, Rab11a, and NPC1L.

Inhibition of endoplasmic reticulum stress and atherosclerosis by 2-aminopurine in apolipoprotein e-deficient mice

We previously reported that the apolipoprotein (apo) B48-carrying lipoproteins obtained from apoE knockout (apoE^−/−) mice, so called E⁻/B48 lipoproteins, transformed mouse macrophages into foam cells and enhanced the phosphorylation of eukaryotic translation initiation factor 2α (eIF-2α). Furthermore, the eIF-2α phosphorylation inhibitor, 2-aminopurine (2-AP), attenuated E⁻/B48 lipoprotein-induced foam cell formation. The present report studied the effect of 2-AP on atherosclerosis in apoE^−/− mice. Our results showed that the level of food intake, bodyweight, plasma cholesterol, and triglycerides was comparable in apoE^−/− mice treated with or without 2-AP. However, the mean size of atherosclerotic lesions in the aorta sinus as well as the surface area of the entire aorta of 2-AP-treated apoE^−/− mice were reduced by about 55% and 39%, respectively, compared to samples from untreated control apoE^−/− mice. In addition, the 2-AP-treated apoE^−/− mice showed a significant decrease in glucose-regulated protein 78 (GRP78) and phosphorylated eIF-2α in their aortic samples as compared to levels in untreated control apoE^−/− mice. These observations suggest that endoplasmic reticulum stress is a causal mechanism for the development of atherosclerosis in apoE^−/− mice and that therapeutic strategies can be developed for using eIF-2α phosphorylation inhibitors, such as 2-AP, to prevent or treat atherosclerosis.