Intestine-specific DGAT1 deficiency improves atherosclerosis in apolipoprotein E knockout mice by reducing systemic cholesterol burden

Modeling the cell biology of monogenetic intestinal epithelial disorders

Monogenetic variants are responsible for a range of congenital human diseases. Variants in genes that are important for intestinal epithelial function cause a group of disorders characterized by severe diarrhea and loss of nutrient absorption called congenital diarrheas and enteropathies (CODEs). CODE-causing genes include nutrient transporters, enzymes, structural proteins, and vesicular trafficking proteins in intestinal epithelial cells. Several severe CODE disorders result from the loss-of-function in key regulators of polarized endocytic trafficking such as the motor protein, Myosin VB (MYO5B), as well as STX3, STXBP2, and UNC45A. Investigations of the cell biology and pathophysiology following loss-of-function in these genes have led to an increased understanding of both homeostatic and pathological vesicular trafficking in intestinal epithelial cells. Modeling different CODEs through investigation of changes in patient tissues, coupled with the development of animal models and patient-derived enteroids, has provided critical insights into the enterocyte differentiation and function. Linking basic knowledge of cell biology with the phenotype of specific patient variants is a key step in developing effective treatments for rare monogenetic diseases. This knowledge can also be applied more broadly to our understanding of common epithelial disorders.

Amelioration of Atherosclerosis by lycopene is linked to the modulation of gut microbiota dysbiosis and related gut-heart axis activation in high-fat diet-fed ApoE-/- mice

BACKGROUND

Interplay between gut microbiota and heart, termed "gut-heart" axis, has a crucial role in the pathogenesis of atherosclerosis. Our previous study showed that lycopene possesses anti-inflammatory and anti-atherosclerotic effects, but its link to the gut microbiota is poorly understood. Herein, we surmised that lycopene could regulate the gut microbiota, exert anti-atherosclerotic effect by regulating the "gut-heart" axis.

METHODS

Male ApoE-/- mice were fed a high-fat diet (HFD) with or without lycopene (0.1% w/w) for 19 weeks. Gut microbiota was analyzed by 16 S rRNA sequencing, the protein levels of zonula occludens-1 (ZO-1), occludin, toll-like receptor 4 (TLR4) and phospho-nuclear factor-κB (NF-κB) p65 were measured by Western blotting, the levels of serum inflammatory factors including monocyte chemotactic protein 1 (MCP-1), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 were assayed using ELISA kits. Also, the concentrations of serum lipopolysaccharide (LPS), D-lactic acid (D-LA) and diamine peroxidase (DAO) were measured through ELISA method.

RESULTS

The aortic sinus sections revealed that lycopene supplementation significantly reduced the extent of atherosclerotic lesions and inhibited atherosclerosis development caused by HFD. The analysis of gut microbiota showed that lycopene reduced the ratio of Firmicutes/Bacteroides and increased the relative abundance of Verrucomicrobia, Akkermansia and Alloprevotella, which were related to elevated intestinal barrier function and reduced inflammation. Moreover, lycopene up-regulated the expression of intestinal ZO-1 and occludin and decreased serum LPS, D-LA and DAO levels. In addition, lycopene inhibited the expression of TLR4 and phospho-NF-κB p65 in aortic sinus plaque, serum MCP-1, TNF-α, IL-1β, and IL-6 levels were also lowered by lycopene treatment.

CONCLUSIONS

Our results indicated the protective effect of lycopene against atherosclerosis induced by HFD and further revealed that its mechanism might be its prebiotic effect on maintaining gut microbiota homeostasis and improving intestinal barrier function, consequently reducing serum LPS-triggered inflammatory response in the heart.

A look into DGAT1 through the EM lenses

With the advent of modern detectors and robust structure solution pipeline, cryogenic electron microscopy has recently proved to be game changer in structural biology. Membrane proteins are challenging targets for structural biologists. This minireview focuses a membrane embedded triglyceride synthesizing machine, DGAT1. Decades of research had built the foundational knowledge on this enzyme's activity. However, recently solved cryo-EM structures of this enzyme, in apo and bound form, has provided critical mechanistic insights. The flipping of the catalytic histidine is critical of enzyme catalysis. The structures explain why the enzyme has preference to long fatty acyl chains over the short forms.

Recent advances in cytoplasmic lipid droplet metabolism in intestinal enterocyte

Processing of dietary fats in the intestine is a highly regulated process that influences whole-body energy homeostasis and multiple physiological functions. Dysregulated lipid handling in the intestine leads to dyslipidemia and atherosclerotic cardiovascular disease. In intestinal enterocytes, lipids are incorporated into lipoproteins and cytoplasmic lipid droplets (CLDs). Lipoprotein synthesis and CLD metabolism are inter-connected pathways with multiple points of regulation. This review aims to highlight recent advances in the regulatory mechanisms of lipid processing in the enterocyte, with particular focus on CLDs. In-depth understanding of the regulation of lipid metabolism in the enterocyte may help identify therapeutic targets for the treatment and prevention of metabolic disorders.

SCD1 is nutritionally and spatially regulated in the intestine and influences systemic postprandial lipid homeostasis and gut-liver crosstalk

Stearoyl-CoA desaturase-1 is an endoplasmic reticulum (ER)-membrane resident protein that inserts a double bond into saturated fatty acids, converting them into their monounsaturated counterparts. Previous studies have demonstrated an important role for SCD1 in modulating tissue and systemic health. Specifically, lack of hepatic or cutaneous SCD1 results in significant reductions in tissue esterified lipids. While the intestine is an important site of lipid esterification and assimilation into the body, the regulation of intestinal SCD1 or its impact on lipid composition in the intestine and other tissues has not been investigated. Here we report that unlike other lipogenic enzymes, SCD1 is enriched in the distal small intestine and in the colon of chow-fed mice and is robustly upregulated by acute refeeding of a high-sucrose diet. We generated a mouse model lacking SCD1 specifically in the intestine (iKO mice). These mice have significant reductions not only in intestinal lipids, but also in plasma triacylglycerols, diacylglycerols, cholesterol esters, and free cholesterol. Additionally, hepatic accumulation of diacylglycerols is significantly reduced in iKO mice. Comprehensive targeted lipidomic profiling revealed a consistent reduction in the myristoleic (14:1) to myristic (14:0) acid ratios in intestine, liver, and plasma of iKO mice. Consistent with the reduction of the monounsaturated fatty acid myristoleic acid in hepatic lipids of chow fed iKO mice, hepatic expression of Pgc-1α, Sirt1, and related fatty acid oxidation genes were reduced in chow-fed iKO mice. Further, lack of intestinal SCD1 reduced expression of de novo lipogenic genes in distal intestine of chow-fed mice and in the livers of mice fed a lipogenic high-sucrose diet. Taken together, these studies reveal a novel pattern of expression of SCD1 in the intestine. They also demonstrate that intestinal SCD1 modulates lipid content and composition of not only intestinal tissues, but also that of plasma and liver. Further, these data point to intestinal SCD1 as a modulator of gut-liver crosstalk, potentially through the production of novel signaling lipids such as myristoleic acid. These data have important implications to understanding how intestinal SCD1 may modulate risk for post-prandial lipemia, hepatic steatosis, and related pathologies.

Mechanisms of intestinal triacylglycerol synthesis

Triacylglycerols are a major source of stored energy that are obtained either from the diet or can be synthesized to some extent by most tissues. Alterations in pathways of triacylglycerol metabolism can result in their excessive accumulation leading to obesity, insulin resistance, cardiovascular disease and nonalcoholic fatty liver disease. Most tissues in mammals synthesize triacylglycerols via the glycerol 3-phosphate pathway. However, in the small intestine the monoacylglycerol acyltransferase pathway is the predominant pathway for triacylglycerol biosynthesis where it participates in the absorption of dietary triacylglycerol. In this review, the enzymes that are part of both the glycerol 3-phosphate and monoacylglycerol acyltransferase pathways and their contributions to intestinal triacylglycerol metabolism are reviewed. The potential of some of the enzymes involved in triacylglycerol synthesis in the small intestine as possible therapeutic targets for treating metabolic disorders associated with elevated triacylglycerol is briefly discussed.

Lycopene Reduces Cholesterol Absorption and Prevents Atherosclerosis in ApoE-/- Mice by Downregulating HNF-1α and NPC1L1 Expression

Our previous study showed that lycopene reduced the absorption of cholesterol in Caco-2 cells through inhibiting Niemann-Pick C1-Like 1 (NPC1L1) expression. Herein, we aimed to explore whether lycopene supplementation can decrease cholesterol absorption in the intestine and prevent atherosclerosis progression in high-fat diet (HFD)-fed apolipoprotein E knockout (ApoE^-/-) mice. Male ApoE^-/- mice were fed a high-fat diet with or without lycopene for 19 weeks. Supplementation of lycopene markedly lowered serum total cholesterol and low-density lipoprotein cholesterol (LDL-C) levels. Additionally, serum high-density lipoprotein cholesterol (HDL-C) levels were increased after lycopene administration. Lycopene also downregulated the expression of NPC1L1 and hepatocyte nuclear factor-1α (HNF-1α) in the small intestine. Furthermore, the Oil Red O staining of the aorta and aortic sinus showed that lycopene supplementation remarkably reduced atherosclerotic lesions. These results indicated that lycopene inhibited intestinal cholesterol absorption and protected against HFD-induced atherosclerosis through inhibiting HNF-1α and NPC1L1 expression. Lycopene exhibits a potential antiatherosclerotic effect through suppressing intestinal cholesterol absorption.