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

Cholesterol uptake in the intestine is regulated by the LASP1-AKT-NPC1L1 signaling pathway

Cholesterol is essential for the stability and architecture of the plasma membrane and a precursor of bile acids and steroid hormones in mammals. Excess dietary cholesterol uptake leads to hypercholesterolemia and atherosclerosis and plays a role in cancer development. The role of actin-binding scaffolding protein LIM and SH3 protein 1 (LASP1) in cholesterol trafficking has not been investigated previously. Cholesterol levels, its uptake, and excretion were studied in mice deficient for low-density lipoprotein receptor and Lasp1 (Ldlr-/-Lasp1-/- mice) upon feeding a high-fat diet, and in LASP1-knockdown, differentiated human intestinal epithelial CaCo-2 cells. When compared with diet-fed Ldlr-/- control mice, Ldlr-/-Lasp1-/- mice displayed a reduction in serum cholesterol levels. Mechanistically, we identified a new role of LASP1 in controlling the translocation of the intestinal cholesterol transporter Niemann-Pick C1-like 1 (NPC1L1) to the apical cell surface, which was limited in LASP1-knockdown human CaCo-2 enterocytes and in the intestine of Ldlr-/- Lasp1-/- compared with Ldlr-/- mice, linked to LASP1-pAKT signaling but not CDC42 activation. In line, a reduction in cholesterol reabsorption was noted in LASP1-knockdown CaCo-2 cells in vitro, and an enhanced cholesterol excretion via the feces was observed in Ldlr-/- Lasp1-/- mice. These data uncover a novel function of Lasp1 in cholesterol trafficking, promoting cholesterol reabsorption in the intestine. Targeting LASP1 locally could thus represent a novel targeting strategy to ameliorate hypercholesterolemia and associated diseases.NEW & NOTEWORTHY We here uncovered LASP1 as a novel regulator of the shuttling of the sterol transporter NPC1L1 to the cell surface in enterocytes to control cholesterol absorption. Accordingly, LASP1-deficient mice displayed lowered serum cholesterol levels under dietary cholesterol supplementation.

Genomic divergence during artificial selection by feed conversion ratio in Pekin ducks

Pekin ducks are world-famous for its fast growth and have become the majority of breeds rearing in duck industry. Feed conversion ratio (FCR) is an important trait in Pekin ducks breeding and production, and the underlying biological processes are complex. To gain an insight to the possible biological mechanism underlying the FCR in Pekin ducks, an artificial selection population (S) and a natural population (Z7) were used in this study. The FCR of S line decreased from 2.184 ± 0.057 in the first generation to 1.886 ± 0.063 in the eighth generation, which displays significantly low FCR (p = 0.0032) than that of the Z7 line (2.23 ± 0.046). Then, 9 samples from eighth generation of S line and 10 samples from Z7 were used for whole-genome resequencing. Analyses of F_ST, θπ and XP-EHH revealed 450, 479 and 356 candidate genes, which involved in 1,955, 1,933 and 1,964 candidate divergent regions (CDRs), respectively. And the integration of three approaches resulted in 30 overlapping genes. Functional analysis of 30 candidate genes revealed that variants of KCNQ1 and ADCY7, which were involved in the pancreatic secretion signal pathway, could be important molecular markers for high feed conversion efficiency in S line breeding.

Does eating eggs matter?

Dietary cholesterol is absorbed in proportion to the amount ingested, blocking its hepatic synthesis, increasing its biliary excretion, only slightly increasing production of bile acids while potentially raising the serum concentration of the atherogenic low-density lipoprotein. Humans lie midway between rats and rabbits that respond to dietary cholesterol, respectively, with high and low capacity to produce bile acids, and low or high capacity to raise blood cholesterol. There are regular studies exonerating as well as blaming dietary cholesterol as a cardiovascular risk factor, particularly in genetic hypercholesterolemic individuals. We then resorted at reviewing all meta-analyses on the subject but failed to reach at a clear conclusion useful in medical practice. Nevertheless, ingestion of the same amount of cholesterol results in wide variation in the amounts absorbed and in plasma lipoprotein profiles depending on poorly understood genetic factors. Several genetic conditions are capable of interfering with the absorption and synthesis of cholesterol. Hyperabsorption of dietary cholesterol elicits the accumulation of cholesterol in the liver and in plasma. In this regard, most cases of familial hypercholesterolemia that have a case of intestinal hyperabsorption of cholesterol also demonstrate the same defect. A practical useful suggestion is to measure for a few weeks the total serum cholesterol and its fractions at least three times before and during the intake of eggs that the candidate wishes to maintain in his usual dietary practice as an efficient procedure to identify those who respond with undesirable increases in serum cholesterol.

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.

Mechanisms of Carotenoid Intestinal Absorption: Where Do We Stand?

A growing literature is dedicated to the understanding of carotenoid beneficial health effects. However, the absorption process of this broad family of molecules is still poorly understood. These highly lipophilic plant metabolites are usually weakly absorbed. It was long believed that β-carotene absorption (the principal provitamin A carotenoid in the human diet), and thus all other carotenoid absorption, was driven by passive diffusion through the brush border of the enterocytes. The identification of transporters able to facilitate carotenoid uptake by the enterocytes has challenged established statements. After a brief overview of carotenoid metabolism in the human upper gastrointestinal tract, a focus will be put on the identified proteins participating in the transport and the metabolism of carotenoids in intestinal cells and the regulation of these processes. Further progress in the understanding of the molecular mechanisms regulating carotenoid intestinal absorption is still required to optimize their bioavailability and, thus, their health effects.

Vitamin E intestinal absorption: Regulation of membrane transport across the enterocyte

Vitamin E is an essential molecule for our development and health. It has long been thought that it was absorbed and transported through cellular membranes by a passive diffusion process. However, data obtained during the past 15 years showed that its absorption is actually mediated, at least in part, by cholesterol membrane transporters including the scavenger receptor class B type I (SR-BI), CD36 molecule (CD36), NPC1-like transporter 1 (NPC1L1), and ATP-binding cassettes A1 and G1 (ABCA1 and ABCG1). This review focuses on the absorption process of vitamin E across the enterocyte. A special attention is given to the regulation of this process, including the possible competition with other fat-soluble micronutrients, and the modulation of transporter expressions. Overall, recent results noticeably increased the comprehension of vitamin E intestinal transport, but additional investigations are still required to fully appreciate the mechanisms governing vitamin E bioavailability. © 2018 IUBMB Life, 71(4):416-423, 2019.

Long-Chain Free Fatty Acid Receptor GPR120 Mediates Oil-Induced GIP Secretion Through CCK in Male Mice

Free fatty acid receptors GPR120 and GPR40 are involved in the secretion of gut hormones. GPR120 and GPR40 are expressed in enteroendocrine K cells, and their activation induces the secretion of the incretin glucose-dependent insulinotropic polypeptide (GIP). However, the role of these receptors in fat-induced GIP secretion in vivo and the associated mechanisms are unclear. In this study, we investigated corn oil-induced GIP secretion in GPR120-knockout (GPR120-/-) and GPR40-knockout (GPR40-/-) mice. Oil-induced GIP secretion was reduced by 50% and 80% in GPR120-/- and GPR40-/- mice, respectively, compared with wild-type mice. This was not associated with a significant difference in K-cell number or GIP content in K cells, nor messenger RNA levels of the lipid receptor GPR119, nor bile acid receptors TGR5 and farnesoid X receptor. GPR120-/- and GPR40-/- mice also exhibited substantially decreased levels of cholecystokinin (CCK), a hormone from I cells that promotes bile and pancreatic lipase secretion, and this decrease was associated with impaired gallbladder contraction. Notably, treatment with a CCK analog resulted in recovery of oil-induced GIP secretion in GPR120-/- mice but not in GPR40-/- mice. These results indicate that corn oil-induced GIP secretion from K cells involves both GPR120 and GPR40 signaling pathways, and GPR120-induced GIP secretion is indirectly mediated by CCK.

Dyslipidaemia of diabetes and the intestine

Atherosclerosis is the major complication of diabetes and has become a major issue in the provision of medical care. In particular the economic burden is growing at an alarming rate in parallel with the increasing world-wide prevalence of diabetes. The major disturbance of lipid metabolism in diabetes relates to the effect of insulin on fat metabolism. Raised triglycerides being the hallmark of uncontrolled diabetes, i.e., in the presence of hyperglycaemia. The explosion of type 2 diabetes has generated increasing interest on the aetiology of atherosclerosis in diabetic patients. The importance of the atherogenic properties of triglyceride rich lipoproteins has only recently been recognised by the majority of diabetologists and cardiologists even though experimental evidence has been strong for many years. In the post-prandial phase 50% of triglyceride rich lipoproteins come from chylomicrons produced in the intestine. Recent evidence has secured the chylomicron as a major player in the atherogenic process. In diabetes chylomicron production is increased through disturbance in cholesterol absorption, in particular Neimann Pick C1-like1 activity is increased as is intestinal synthesis of cholesterol through 3-hydroxy-3-methyl glutaryl co enzyme A reductase. ATP binding cassette proteins G5 and G8 which regulate cholesterol in the intestine is reduced leading to chylomicronaemia. The chylomicron particle itself is atherogenic but the increase in the triglyceride-rich lipoproteins lead to an atherogenic low density lipoprotein and low high density lipoprotein. The various steps in the absorption process and the disturbance in chylomicron synthesis are discussed.

Melatonin-mediated inhibition of Purkinje neuron P-type Ca²⁺ channels in vitro induces neuronal hyperexcitability through the phosphatidylinositol 3-kinase-dependent protein kinase C delta pathway

Although melatonin receptors are widely expressed in the mammalian central nervous system and peripheral tissues, there are limited data regarding the functions of melatonin in cerebellar Purkinje cells. Here, we identified a novel functional role of melatonin in modulating P-type Ca(2+) channels and action-potential firing in rat Purkinje neurons. Melatonin at 0.1 μm reversibly decreased peak currents (I(Ba)) by 32.9%. This effect was melatonin receptor 1 (MT(R1)) dependent and was associated with a hyperpolarizing shift in the voltage dependence of inactivation. Pertussis toxin pretreatment, intracellular application of QEHA peptide, and a selective antibody raised against the Gβ subunit prevented the inhibitory effects of melatonin. Pretreatment with phosphatidylinositol 3-kinase (PI3K) inhibitors abolished the melatonin-induced decrease in I(Ba). Surprisingly, melatonin responses were not regulated by Akt, a common downstream target of PI3K. Melatonin treatment significantly increased protein kinase C (PKC) activity 2.1-fold. Antagonists of PKC, but not of protein kinase A, abolished the melatonin-induced decrease in I(Ba). Melatonin application increased the membrane abundance of PKCδ, and PKCδ inhibition (either pharmacologically or genetically) abolished the melatonin-induced IBa response. Functionally, melatonin increased spontaneous action-potential firing by 53.0%; knockdown of MT(R1) and blockade of P-type channels abolished this effect. Thus, our results suggest that melatonin inhibits P-type channels through MT(R1) activation, which is coupled sequentially to the βγ subunits of G(i/o)-protein and to downstream PI3K-dependent PKCδ signaling. This likely contributes to its physiological functions, including spontaneous firing of cerebellar Purkinje neurons.