CD36 deficiency impairs intestinal lipid secretion and clearance of chylomicrons from the blood

scProAtlas: an atlas of multiplexed single-cell spatial proteomics imaging in human tissues

Spatial proteomics can visualize and quantify protein expression profiles within tissues at single-cell resolution. Although spatial proteomics can only detect a limited number of proteins compared to spatial transcriptomics, it provides comprehensive spatial information with single-cell resolution. By studying the spatial distribution of cells, we can clearly obtain the spatial context within tissues at multiple scales. Spatial context includes the spatial composition of cell types, the distribution of functional structures, and the spatial communication between functional regions, all of which are crucial for the patterns of cellular distribution. Here, we constructed a comprehensive spatial proteomics functional annotation knowledgebase, scProAtlas (https://relab.xidian.edu.cn/scProAtlas/#/), which is designed to help users comprehensively understand the spatial context within different tissue types at single-cell resolution and across multiple scales. scProAtlas contains multiple modules, including neighborhood analysis, proximity analysis and neighborhood network, to comprehensively construct spatial cell maps of tissues and multi-modal integration, spatial gene identification, cell-cell interaction and spatial pathway analysis to display spatial variable genes. scProAtlas includes data from eight spatial protein imaging techniques across 15 tissues and provides detailed functional annotation information for 17 468 394 cells from 945 region of interests. The aim of scProAtlas is to offer a new insight into the spatial structure of various tissues and provides detailed spatial functional annotation.

Traditional Chinese medicine and plant-derived natural products in regulating triglyceride metabolism: Mechanisms and therapeutic potential

The incidence of cardiometabolic disease is increasing globally, with a trend toward younger age of onset. Among these, atherosclerotic cardiovascular disease is a leading cause of mortality worldwide. Despite the efficacy of traditional lipid-lowering drugs, such as statins, in reducing low-density lipoprotein cholesterol levels, a significant residual risk of cardiovascular events remains, which is closely related to unmet triglyceride (TG) targets. The clinical application of current TG-lowering Western medicines has certain limitations, necessitating alternative or complementary therapeutic strategies. Traditional Chinese medicine (TCM) and plant-derived natural products, known for their safety owing to their natural origins and diverse biological activities, offer promising avenues for TG regulation with potentially fewer side effects. This review systematically summarises the mechanisms of TG metabolism and subsequently reviews the regulatory effects of TCM and plant-derived natural products on TG metabolism, including the inhibition of TG synthesis (via endogenous and exogenous pathways), promotion of TG catabolism, regulation of fatty acid absorption and transport, enhancement of lipophagy, modulation of the gut microbiota, and other mechanisms. In conclusion, through a comprehensive analysis of recent studies, this review consolidates the multifaceted regulatory roles of TCM and plant-derived natural products in TG metabolism and elucidates their potential as safer, multi-target therapeutic agents in managing hypertriglyceridemia and mitigating cardiovascular risk, thereby providing a basis for new drug development.

Dietary lipid sensing through fatty acid oxidation and chylomicron formation in the gastrointestinal tract of rainbow trout

In mammals, physiological processes related to lipid metabolism, such as chylomicron synthesis or fatty acid oxidation (FAO), modulate eating, highlighting the importance of energostatic mechanisms in feeding control. This study, using rainbow trout (Oncorhynchus mykiss) as model, aimed to characterize the role of FAO and chylomicron formation as peripheral lipid sensors potentially able to modulate feeding in fish. Fish fed with either a normal- (24%) or high- (32%) fat diet were intraperitoneally injected with water alone or containing etomoxir (inhibitor of FAO rate-limiting enzyme carnitine palmitoyl-transferase 1). First, feed intake levels were recorded. We observed an etomoxir-derived decrease in feeding at short times, but a significant increase at 48 h after treatment in fish fed normal-fat diet. Then, we evaluated putative etomoxir effects on the mRNA abundance of genes related to lipid metabolism, chylomicron synthesis and appetite-regulating peptides. Etomoxir treatment upregulated mRNA levels of genes related to chylomicron assembly in proximal intestine, while opposite effects occurred in distal intestine, indicating a clear regionalization in response. Etomoxir also modulated gastrointestinal hormone mRNAs in proximal intestine, upregulating ghrl in fish fed normal-fat diet and pyy and gcg in fish fed high-fat diet. These results provide evidence for an energostatic control of feeding related to FAO and chylomicron formation at the peripheral level in fish.

Mechanical regulation of lipid and sugar absorption by Piezo1 in enterocytes

Obesity is primarily caused by excessive intake as well as absorption of sugar and lipid. Postprandial surge in distention pressure and intestinal motility accelerates the absorption of nutrients. The response of intestinal epithelial cells to mechanical stimulation is not fully understood. Piezo1, a mechanosensitive ion channel, is widely expressed throughout the digestive tract. However, its function in intestinal nutrient absorption is not yet clear. In our study, excessive lipid deposition was observed in the duodenum of obese patients, while duodenal Piezo1-CaMKK2-AMPKα was decreased when compared to normal-weight individuals. Under high-fat diet condition, the Piezo1 iKO mice exhibited abnormally elevated sugar and lipid absorption as well as severe lipid deposition in the duodenum and liver. These phenotypes were mainly caused by the inhibition of duodenal CaMKK2-AMPKα and the upregulation of SGLT1 and DGAT2. In contrast, Yoda1, a Piezo1 agonist, was found to reduce intestinal lipid absorption in diet induced obese mice. Overexpression of Piezo1, stretch and Yoda1 inhibited lipid accumulation and the expression of DGAT2 and SGLT1, whereas knockdown of Piezo1 stimulated lipid accumulation and DGAT2 in Caco-2 cells. Our study reveals a previously unexplored mechanical regulation of nutrient absorption in intestinal epithelial cells, which may shed new light on the therapy of obesity.

Cluster of Differentiation 36 (CD36) Preferentially Mediates Intestinal Absorption of Dietary Z-Astaxanthin and Especially 9-Z-Isomer via Higher Binding Affinity

Variances in the biological functions of astaxanthin geometric isomers (i.e., all-E, Z) are related to their intestinal absorption, but the mechanism of isomer absorption mediated by transporters remains unclear. Here, models of in vitro cell overexpression, in situ intestinal perfusion, and in vivo mouse inhibition were employed to investigate the impact of cluster of differentiation 36 (CD36) on the absorption of astaxanthin isomers. Cells overexpressing CD36 notably enhanced the uptake of Z-astaxanthin, particularly the 9-Z-isomer (47.76%). The absorption rate and permeability of Z-astaxanthin surpassed that of the all-E-isomer by the in situ model. Furthermore, the addition of the CD36-specific inhibitor sulfo-N-succinimidyl oleate significantly reduced the absorption of Z-astaxanthin in the mouse duodenum and jejunum, especially the 9-Z-isomer (57.66%). Molecular docking and surface plasmon resonance techniques further validated that 9-Z-astaxanthin binds to more amino acids of CD36 with higher affinity and in a fast-binding, fast-dissociating mode, thus favoring transport. Our findings elucidate, for the first time, the mechanism of the CD36-mediated transmembrane transport of astaxanthin geometric isomers.

Whole-body deletion of Endospanin 1 protects from obesity-associated deleterious metabolic alterations

The importance of the proper localization of most receptors at the cell surface is often underestimated, although this feature is essential for optimal receptor response. Endospanin 1 (Endo1) (also known as OBRGRP or LEPROT) is a protein generated from the same gene as the human leptin receptor and regulates the trafficking of proteins to the surface, including the leptin receptor. The systemic role of Endo1 on whole-body metabolism has not been studied so far. Here, we report that general Endo1-KO mice fed a high-fat diet develop metabolically healthy obesity with lipid repartitioning in organs and preferential accumulation of fat in adipose tissue, limited systematic inflammation, and better controlled glucose homeostasis. Mechanistically, Endo1 interacts with the lipid translocase CD36, thus regulating its surface abundance and lipid uptake in adipocytes. In humans, the level of Endo1 transcripts is increased in the adipose tissue of patients with obesity, but low levels rather correlate with a profile of metabolically healthy obesity. We suggest here that Endo1, most likely by controlling CD36 cell surface abundance and lipid uptake in adipocytes, dissociates obesity from diabetes and that its absence participates in metabolically healthy obesity.

Diarrhea induced by insufficient fat absorption in weaned piglets: Causes and nutrition regulation

Fat is one of the three macronutrients and a significant energy source for piglets. It plays a positive role in maintaining intestinal health and improving production performance. During the weaning period, physiological, stress and diet-related factors influence the absorption of fat in piglets, leading to damage to the intestinal barrier, diarrhea and even death. Signaling pathways, such as fatty acid translocase (CD36), pregnane X receptor (PXR), and AMP-dependent protein kinase (AMPK), are responsible for regulating intestinal fat uptake and maintaining intestinal barrier function. Therefore, this review mainly elaborates on the reasons for diarrhea induced by insufficient fat absorption and related signaling pathways in weaned-piglets, with an emphasis on the intestinal fat absorption disorder. Moreover, we focus on introducing nutritional strategies that can promote intestinal fat absorption in piglets with insufficient fat absorption-related diarrhea, such as lipase, amino acids, and probiotics.

Deciphering scavenger receptors reveals key regulators in the intestine that function in carotenoid coloration of leopard coral groupers (Plectropomus leopardus)

Carotenoid based body coloration are common features in fish, which depends on the diet derived carotenoids pigments deposition, employing a bunch of carotenoid uptake, absorption and processing related genes. Scavenger receptors are a large family of cell surface receptors with complex structure and diverse functions. However, the SRs genes have been insufficiently explored concerning their role in fish carotenoid coloration. Here, we systemically identified 19 SRs family genes and investigated their expression patterns of in various tissues of P. leopardus. Expression analysis unveiled the diverse involvements of SRs in the intestine of P. leopardus with different body colors and the responses to exogenous carotenoids. Notably, cd36, emerged as a pivotal factor in intestinal functions predominantly localized in the intestinal epithelial and goblet cells. Knockdown of cd36 led to the reduction in skin brightness and carotenoid levels in both intestine and skin, while overexpressing cd36 increased the carotenoids uptake of cells in vitro. Additionally, our investigations revealed that cd36 exerts regulation on genes associated with carotenoid uptake, transport, and processing. To sum up, our results provide a comprehensive view on SRs functions in carotenoid coloration of P. leopardus and will facilitate the understanding on the mechanism of carotenoids coloration of vertebrates.

Targeting host-specific metabolic pathways-opportunities and challenges for anti-infective therapy

Microorganisms can takeover critical metabolic pathways in host cells to fuel their replication. This interaction provides an opportunity to target host metabolic pathways, in addition to the pathogen-specific ones, in the development of antimicrobials. Host-directed therapy (HDT) is an emerging strategy of anti-infective therapy, which targets host cell metabolism utilized by facultative and obligate intracellular pathogens for entry, replication, egress or persistence of infected host cells. This review provides an overview of the host lipid metabolism and links it to the challenges in the development of HDTs for viral and bacterial infections, where pathogens are using important for the host lipid enzymes, or producing their own analogous of lecithin-cholesterol acyltransferase (LCAT) and lipoprotein lipase (LPL) thus interfering with the human host's lipid metabolism.

Mechanisms and functions of intestinal vascular specialization

The intestinal vasculature has been studied for the last 100 years, and its essential role in absorbing and distributing ingested nutrients is well known. Recently, fascinating new insights into the organization, molecular mechanisms, and functions of intestinal vessels have emerged. These include maintenance of intestinal epithelial cell function, coping with microbiota-induced inflammatory pressure, recruiting gut-specific immune cells, and crosstalk with other organs. Intestinal function is also regulated at the systemic and cellular levels, such that the postprandial hyperemic response can direct up to 30% of systemic blood to gut vessels, while micron-sized endothelial cell fenestrations are necessary for nutrient uptake. In this review, we will highlight past discoveries made about intestinal vasculature in the context of new findings of molecular mechanisms underpinning gut function. Such comprehensive understanding of the system will pave the way to breakthroughs in nutrient uptake optimization, drug delivery efficiency, and treatment of human diseases.

Si-Ni-San reverses dietary fat absorption defects in a murine model of depression

Depression is often associated with fatigue/energy loss. However, we lack a detailed understanding of the factors explaining this association. In this study, we uncovered that depressed mice have a defect in fat absorption, resulting in weight loss and reduced circulating lipid levels. Si-Ni-San (SNS), a basic formula of traditional Chinese medicine (TCM) for the treatment of depression, was found to not only alleviate depression-like behaviors, but also reverse the weight loss and dietary fat absorption of depressed mice. We found that SNS improved body weight and circulating lipid levels of depressed mice by up-regulating proteins [such as FFA uptake protein (CD36), TAG synthesis proteins (GPAT3, MOGAT2, DGAT1 and DGAT2) and chylomicron packaging proteins (MTP and APOB)] in the fat absorption pathway. Furthermore, cell-based results conducted with LPS-stimulated mouse MODE-K and human Caco-2 cells support that SNS, as well as Sinensetin (SIN) and Nobiletin (NOB), the two active components of the formula, have a role in regulating lipid absorption. Mechanistic studies revealed that SNS reverses body weight and fat absorption defects of depressed mice in part through the NR1D1/BMAL1/DGAT2 axis. These findings advance our understanding of the crosstalk between depression and energy loss, highlight the importance of gut function in disease management, and provide a basis for the application of SNS in the clinical treatment of depression and related disorders.

Cluster-determinant 36 (CD36) mediates intestinal absorption of dietary astaxanthin and affects its secretion

The functional activity of dietary astaxanthin is closely related to its absorption, and the absorption of dietary carotenoids mainly mediated by transmembrane transport protein (TTP) has become the mainstream research direction in recent years. However, the main TTP mediating astaxanthin absorption and its potential mechanisms are still unclear. Hence, based on the preliminary screening results, this study aims to elucidate the role of cluster-determinant 36 (CD36) mediating astaxanthin absorption from the perspective of expression levels through in vitro cell model, in situ single-pass intestinal perfusion model and in vivo mice model. The results showed that astaxanthin uptake was significantly increased by 45.13% in CD36 overexpressing cells and decreased by 20.92% in the case of sulfo-N-succinimidyl oleate (SSO) inhibition. A similar trend also appeared in the duodenum and jejunum by in situ model. Moreover, astaxanthin uptake in the small intestine of CD36 knockout mice was significantly reduced by 88.22%. Furthermore, the inhibition or knockout of CD36 suppressed the expression of other transporters (SR-BI and NPC1L1). Interestingly, CD36 was also involved in the downstream secretion pathway, which is manifested by interfering with the expression of related proteins (ERK1/2, MTP, ApoB48, and ApoAI). Therefore, these results indicate the important role of CD36 in astaxanthin transmembrane transport for the first time, providing vital exploration way for the absorption of dietary fat-soluble substances.

Intestinal Knockout of Peroxisome Proliferator-Activated Receptor-Alpha Affects Structural Adaptation but not Liver Injury Following Massive Enterectomy

BACKGROUND

Resection-associated liver steatosis, injury, and fibrosis is a devastating complication associated with massive small bowel resection (SBR). Peroxisome proliferator-activated receptor-alpha (PPARα) is a key regulator of intestinal lipid transport and metabolism whose expression is selectively increased after SBR. Here we asked if attenuating intestinal PPARα signaling would prevent steatosis and liver injury after SBR.

METHODS

Pparα was deleted selectively in adult mouse intestine using a tamoxifen-inducible Cre-LoxP breeding schema. Mice underwent 50% SBR. At 10 weeks post-operatively, metabolic phenotyping, body composition analysis, in vivo assessment of lipid absorption and intestinal permeability, and assessment of adaptation and liver injury was completed.

RESULTS

Pparα intestinal knockout and littermate control mice were phenotypically similar in terms of weight trends and body composition after SBR. All mice demonstrated intestinal adaptation with increased villus height and crypt depth; however, Pparα intestinal knockout mice exhibited decreased villus growth at 10 weeks compared to littermate controls. Liver injury and fibrosis were similar between groups as assessed by serum AST and ALT levels, Sirius Red staining, and hepatic expression of Col1a1 and Acta2.

CONCLUSIONS

Inducible intestinal deletion of Pparα influences structural adaptation but does not mitigate liver injury after SBR. These findings suggest that enterocyte PPARα signaling in adult mice is dispensable for resection-induced liver injury. The results are critical for understanding the contribution of intestinal lipid metabolic signaling pathways to the pathogenesis of hepatic injury associated with short bowel syndrome.

Intestinal SEC16B modulates obesity by regulating chylomicron metabolism

OBJECTIVE

Genome-wide association studies (GWAS) have identified genetic variants in SEC16 homolog B (SEC16B) locus to be associated with obesity and body mass index (BMI) in various populations. SEC16B encodes a scaffold protein located at endoplasmic reticulum (ER) exit sites that is implicated to participate in the trafficking of COPII vesicles in mammalian cells. However, the function of SEC16B in vivo, especially in lipid metabolism, has not been investigated.

METHODS

We generated Sec16b intestinal knockout (IKO) mice and assessed the impact of its deficiency on high-fat diet (HFD) induced obesity and lipid absorption in both male and female mice. We examined lipid absorption in vivo by acute oil challenge and fasting/HFD refeeding. Biochemical analyses and imaging studies were performed to understand the underlying mechanisms.

RESULTS

Our results showed that Sec16b intestinal knockout (IKO) mice, especially female mice, were protected from HFD-induced obesity. Loss of Sec16b in intestine dramatically reduced postprandial serum triglyceride output upon intragastric lipid load or during overnight fasting and HFD refeeding. Further studies showed that intestinal Sec16b deficiency impaired apoB lipidation and chylomicron secretion.

CONCLUSIONS

Our studies demonstrated that intestinal SEC16B is required for dietary lipid absorption in mice. These results revealed that SEC16B plays important roles in chylomicron metabolism, which may shed light on the association between variants in SEC16B and obesity in human.

Fatty Acid Transport and Signaling: Mechanisms and Physiological Implications

Long-chain fatty acids (FAs) are components of plasma membranes and an efficient fuel source and also serve as metabolic regulators through FA signaling mediated by membrane FA receptors. Impaired tissue FA uptake has been linked to major complications of obesity, including insulin resistance, cardiovascular disease, and type 2 diabetes. Fatty acid interactions with a membrane receptor and the initiation of signaling can modify pathways related to nutrient uptake and processing, cell proliferation or differentiation, and secretion of bioactive factors. Here, we review the major membrane receptors involved in FA uptake and FA signaling. We focus on two types of membrane receptors for long-chain FAs: CD36 and the G protein-coupled FA receptors FFAR1 and FFAR4. We describe key signaling pathways and metabolic outcomes for CD36, FFAR1, and FFAR4 and highlight the parallels that provide insight into FA regulation of cell function.

New insights into the role of dietary triglyceride absorption in obesity and metabolic diseases

The incidence of obesity and associated metabolic diseases is increasing globally, adversely affecting human health. Dietary fats, especially triglycerides, are an important source of energy for the body, and the intestine absorbs lipids through a series of orderly and complex steps. A long-term high-fat diet leads to intestinal dysfunction, inducing obesity and metabolic disorders. Therefore, regulating dietary triglycerides absorption is a promising therapeutic strategy. In this review, we will discuss diverse aspects of the dietary triglycerides hydrolysis, fatty acid uptake, triglycerides resynthesis, chylomicron assembly, trafficking, and secretion processes in intestinal epithelial cells, as well as potential targets in this process that may influence dietary fat-induced obesity and metabolic diseases. We also mention the possible shortcomings and deficiencies in modulating dietary lipid absorption targets to provide a better understanding of their administrability as drugs in obesity and related metabolic disorders.

Diet-induced gut dysbiosis and inflammation: Key drivers of obesity-driven NASH

Sucrose, the primary circulating sugar in plants, contains equal amounts of fructose and glucose. The latter is the predominant circulating sugar in animals and thus the primary fuel source for various tissue and cell types in the body. Chronic excessive energy intake has, however, emerged as a major driver of obesity and associated pathologies including nonalcoholic fatty liver diseases (NAFLD) and the more severe nonalcoholic steatohepatitis (NASH). Consumption of a high-caloric, western-style diet induces gut dysbiosis and inflammation resulting in leaky gut. Translocation of gut-derived bacterial content promotes hepatic inflammation and ER stress, and when either or both of these are combined with steatosis, it can cause NASH. Here, we review the metabolic links between diet-induced changes in the gut and NASH. Furthermore, therapeutic interventions for the treatment of obesity and liver metabolic diseases are also discussed with a focus on restoring the gut-liver axis.

Lysolecithin Improves Broiler Growth Performance through Upregulating Growth-Related Genes and Nutrient Transporter Genes Expression Independent of Experimental Diet Nutrition Level

We investigated the effect and interaction of lysolecithin (LPL) and nutrition level on growth performance, nutrient ileal digestibility, expression of growth-related genes and nutrient transporter genes in broilers. A total of 1280 one day old Ross 308 mixed sex chicks with an average body weight 42.23 ± 2.4 g were randomly allotted into 2 × 2 factorial arrangement (20 replicates per treatment and 16 chickens per replicate) with two types of diet (Normal nutrition treatments starter, grower and finisher diets with ME of 3000 kcal/kg, 3100 kcal/kg and 3200 kcal/kg, respectively, and CP level of 22%, 21%, and 20%, respectively; high nutrition treatments diets with 50 kcal/kg ME and 0.5% CP higher than normal nutrition treatment at each stage). Two levels of LPL supplementation (0 and 500 mg/kg) were also employed. From day 21 to day 35 and full stage of the experiment, the birds fed a high nutrition (HN) diet had a greater body weight gain (BWG) and lower feed conversion ratio (FCR) than those fed a normal nutrition (NN) diet (p < 0.05). Besides, lysolecithin increased BWG significantly (p < 0.05). The birds fed a diet with LPL revealed increasing fat digestibility compared to birds fed the basal diet (p < 0.05). LPL significantly increased the ileal digestibility of amino acids, including Ile, Thr, Phe, His, Arg, Tyr, Glu, Pro, Gly, Ala (p < 0.05). No interaction was found between LPL and nutrition level in BWG, FCR and nutrient digestibility. In HN diet, the genes expression of myogenic differentiation 1 (MYOD1), myogenin (MYOG), cluster of differentiation 36 (CD36), fatty acid-binding protein (FABP1), cationic amino acid transporter 1 (CAT1) and Y + L amino acid transporter 1 (y+, LAT1) were significantly elevated via LPL supplementation (p < 0.05). In NN diet, LPL significantly increased the genes expression of growth hormone (GH), insulin-like growth factor 1 (IGF1), MYOD1 and y+, LAT1 (p < 0.05). In conclusion, upregulating the nutrients transporter gene and growth-related gene expression of the host, independent of nutrition level changes, may be the action mechanism of lysolecithin on growth promotion in animals.

Vascular and lymphatic regulation of gastrointestinal function and disease risk

The vascular and lymphatic systems in the gut regulate lipid transport while restricting transfer of commensal gut microbiota and directing immune cell trafficking. Increased permeability of the endothelial systems in the intestine associates with passage of antigens and microbiota from the gut into the bloodstream leading to tissue inflammation, the release of pro-inflammatory mediators and ultimately to abnormalities of systemic metabolism. Recent studies show that lipid metabolism maintains homeostasis and function of intestinal blood and lymphatic endothelial cells, BECs and LECs, respectively. This review highlights recent progress in this area, and information related to the contribution of the lipid transporter CD36, abundant in BECs and LECs, to gastrointestinal barrier integrity, inflammation, and to gut regulation of whole body metabolism. The potential role of endothelial lipid delivery in epithelial tissue renewal after injury and consequently in the risk of gastric and intestinal diseases is also discussed.

A nexus of lipid and O-Glcnac metabolism in physiology and disease

Although traditionally considered a glucose metabolism-associated modification, the O-linked β-N-Acetylglucosamine (O-GlcNAc) regulatory system interacts extensively with lipids and is required to maintain lipid homeostasis. The enzymes of O-GlcNAc cycling have molecular properties consistent with those expected of broad-spectrum environmental sensors. By direct protein-protein interactions and catalytic modification, O-GlcNAc cycling enzymes may provide both acute and long-term adaptation to stress and other environmental stimuli such as nutrient availability. Depending on the cell type, hyperlipidemia potentiates or depresses O-GlcNAc levels, sometimes biphasically, through a diversity of unique mechanisms that target UDP-GlcNAc synthesis and the availability, activity and substrate selectivity of the glycosylation enzymes, O-GlcNAc Transferase (OGT) and O-GlcNAcase (OGA). At the same time, OGT activity in multiple tissues has been implicated in the homeostatic regulation of systemic lipid uptake, storage and release. Hyperlipidemic patterns of O-GlcNAcylation in these cells are consistent with both transient physiological adaptation and feedback uninhibited obesogenic and metabolic dysregulation. In this review, we summarize the numerous interconnections between lipid and O-GlcNAc metabolism. These links provide insights into how the O-GlcNAc regulatory system may contribute to lipid-associated diseases including obesity and metabolic syndrome.

Adaptation to short-term extreme fat consumption alters intestinal lipid handling in male and female mice

The small intestine is a highly adaptable organ serving as both a barrier to the external environment and a conduit for nutrient absorption. Enterocytes package dietary triglycerides (TG) into chylomicrons for transport into circulation; the remaining TGs are stored in cytosolic lipid droplets (CLDs). The current study aimed to characterize the impact of diet composition on intestinal lipid handling in male and female wild-type mice. Mice were continued on their grain-based diet (GBD) and switched to a high-fat, high cholesterol Western-style diet (WD) or a ketogenic diet (KD) for 3 or 5 weeks. KD-fed mice displayed significantly higher plasma TG levels in response to an olive oil gavage than WD- and GBD-fed mice; TG levels were ~2-fold higher in male KD-fed mice than female KD-fed mice. Poloxamer-407 experiments revealed enhanced intestinal-TG secretion rates in male mice fed a KD upon olive oil gavage, whereas secretion rates were unchanged in female mice. Surprisingly, jejunal CLD size and TG mass after oil gavage were similar among the groups. At fasting, TG mass was significantly higher in the jejunum of male KD-fed mice and the duodenum of female KD-fed mice, providing increased substrate for chylomicron formation. In addition to greater fasting intestinal TG stores, KD-fed male mice displayed longer small intestinal lengths, while female mice displayed markedly longer jejunal villi lengths. After 5 week of diet, 12 h fasting-2 h refeeding experiments revealed jejunal TG levels were similar between diet groups in male mice; however, in female mice, jejunal TG mass was significantly higher in KD-fed mice compared to GBD- and WD-fed mice. These experiments reveal that KD feeding promotes distinct morphological and functional changes to the small intestine compared to the WD diet. Moreover, changes to intestinal lipid handling in response to carbohydrate and protein restriction manifest differently in male and female mice.

Idol Depletion Protects against Spontaneous Atherosclerosis in a Hamster Model of Familial Hypercholesterolemia

Inducible degrader of low-density lipoprotein (LDL) receptor (Idol) is an E3 ubiquitin ligase coded by Idol, the target gene of liver X receptor (LXR), which primarily mediates the ubiquitination and lysosomal degradation of low-density lipoprotein receptor (LDLR). Previous studies from independent groups have shown that plasma cholesterol regulation by the LXR-Idol-LDLR axis is tissue- and species-specific, indicating that the precise molecular mechanism by which Idol modulates lipid metabolism has not been completely understood and needs to be further validated in other species. Hamster, a small rodent animal model expressing endogenous cholesterol ester transfer protein (CETP), possesses many metabolic characteristics that are different from mouse but similar to human. In this study, an Idol knockout (Idol^−/−) hamster model was developed using CRISPR/Cas9 gene editing system to investigate the effect of Idol depletion on plasma lipid metabolism and atherosclerosis. Our results showed that there were no significant differences in hepatic LDLR protein and plasma cholesterol levels in Idol^−/− hamsters compared with wild-type (WT) controls, which was consistent with the observation that LXR agonist treatment increased the expression of Idol mRNA in the small intestine but not in the liver of WT hamsters. However, we found that plasma triglyceride (TG) levels were significantly reduced in Idol^−/− hamsters due to an enhancement of TG clearance. In addition, the morphological data demonstrated that inactivation of Idol significantly lowered plasma total cholesterol and TG levels and protected against spontaneous atherosclerotic lesions in aged LDLR knockout hamsters on a chow diet but had no effect on diet-induced atherosclerosis in hamsters lacking one copy of the Ldlr gene. In conclusion, our findings suggest that Idol can regulate plasma lipid metabolism and atherosclerosis independent of LDLR function.

When fat meets the gut-focus on intestinal lipid handling in metabolic health and disease

The regular overconsumption of energy‐dense foods (rich in lipids and sugars) results in elevated intestinal nutrient absorption and consequently excessive accumulation of lipids in the liver, adipose tissue, skeletal muscles, and other organs. This can eventually lead to obesity and obesity‐associated diseases such as type 2 diabetes (T2D), non‐alcoholic fatty liver disease (NAFLD), cardiovascular disease, and certain types of cancer, as well as aggravate inflammatory bowel disease (IBD). Therefore, targeting the pathways that regulate intestinal nutrient absorption holds significant therapeutic potential. In this review, we discuss the molecular and cellular mechanisms controlling intestinal lipid handling, their relevance to the development of metabolic diseases, and emerging therapeutic strategies.

Amentoflavone-Enriched Selaginella rossii Warb. Suppresses Body Weight and Hyperglycemia by Inhibiting Intestinal Lipid Absorption in Mice Fed a High-Fat Diet

Many Selaginellaceae species are used as traditional medicines in Asia. This study is the first to investigate the anti-obesity and anti-diabetic effects of Selaginella rossii (SR) in high-fat diet (HFD)–fed C57BL/6J mice. Seven-day oral administration of ethanol extract (100 mg/kg/day) or ethyl acetate (EtOAc) extract (50 mg/kg/day) from SR improved oral fat tolerance by inhibiting intestinal lipid absorption; 10-week long-term administration of the EtOAc extract markedly reduced HFD-induced body weight gain and hyperglycemia by reducing adipocyte hypertrophy, glucose levels, HbA1c, and plasma insulin levels. Treatment with SR extracts reduced the expression of intestinal lipid absorption-related genes, including Cd36, fatty acid-binding protein 6, ATP-binding cassette subfamily G member 8, NPC1 like intracellular cholesterol transporter 1, and ATP-binding cassette subfamily A member 1. In addition, the EtOAc extract increased the expression of protein absorption–related solute carrier family genes, including Slc15a1, Slc8a2, and Slc6a9. SR extracts reduced HFD-induced hepatic steatosis by suppressing fatty acid transport to hepatocytes and hepatic lipid accumulation. Furthermore, amentoflavone (AMF), the primary compound in SR extracts, reduced intestinal lipid absorption by inhibiting fatty acid transport in HFD-fed mice. AMF-enriched SR extracts effectively protected against HFD-induced body weight gain and hyperglycemia by inhibiting intestinal lipid absorption.

Dietary supplementation with Korean pine nut oil decreases body fat accumulation and dysregulation of the appetite-suppressing pathway in the hypothalamus of high-fat diet-induced obese mice

BACKGROUND/OBJECTIVES

Korean pine nut oil (PNO) has been reported to suppress appetite by increasing satiety hormone release. However, previous studies have rendered inconsistent results and there is lack of information on whether dietary Korean PNO affects the expression of satiety hormone receptors and hypothalamic neuropeptides. Therefore, our study sought to evaluate the chronic effects of Korean PNO on the long-term regulation of energy balance.

MATERIALS/METHODS

Five-week-old male C57BL/6 mice were fed with control diets containing 10% kcal fat from Korean PNO or soybean oil (SBO) (PC or SC) or high-fat diets (HFDs) containing 35% kcal fat from lard and 10% kcal fat from Korean PNO or SBO (PHFD or SHFD) for 12 weeks. The expression of gastrointestinal satiety hormone receptors, hypothalamic neuropeptides, and genes related to intestinal lipid absorption and adipose lipid metabolism was then measured.

RESULTS

There was no difference in the daily food intake between PNO- and SBO-fed mice; however, the PC and PHFD groups accumulated 30% and 18% less fat compared to SC and SHFD, respectively. Korean PNO-fed mice exhibited higher messenger RNA (mRNA) expression of Ghsr (ghrelin receptor) and Agrp (agouti-related peptide) (P < 0.05), which are expressed when energy consumption is low to induce appetite as well as the appetite-suppressing neuropeptides Pomc and Cartpt (P = 0.079 and 0.056, respectively). Korean PNO downregulated jejunal Cd36 and epididymal Lpl mRNA expressions, which could suppress intestinal fatty acid absorption and fat storage in white adipose tissue. Consistent with these findings, Korean PNO-fed mice had higher levels of fecal non-esterified fatty acid excretion. Korean PNO also tended to downregulate jejunal Apoa4 and upregulate epididymal Adrb3 mRNA levels, suggesting that PNO may decrease chylomicron synthesis and induce lipolysis.

CONCLUSIONS

In summary, Korean PNO attenuated body fat accumulation, and appeared to prevent HFD-induced dysregulation of the hypothalamic appetite-suppressing pathway.

Identification of core gene in obese type 2 diabetes patients using bioinformatics analysis

Objectives Adipocytes and adipocyte lipid metabolism are closely related with obesity and type 2 diabetes, but the molecular mechanism still needs further investigation. The aim of this study is to discover the adipocyte genes and pathways involved in obesity and type 2 diabetes using bioinformatics analysis.

Methods The GSE27951 gene expression profile was obtained. Software and online tools (STRING, Cytoscape, BioGPS, CTD, and FunRich) were used to identify core genes.21 human subcutaneous adipose samples, with 10 from type 2 diabetic patients and 11 from normal controls, were included in these analyses.

Results 184 differentially expressed genes (DEGs) including 42 up-regulated genes and 142 down-regulated genes were found to be enriched in metabolism, receptor activity, collagen type IV and glutamine biosynthesis I pathway by using the enrichment analysis. Seven hub genes were identified from the PPI network using various software (Cytoscape, STRING, BioGPS, and CTD). Four core genes (COL4A2, ACACB, GLUL, and CD36) were found to be highly expressed in subcutaneous adipose tissue of obese patients accompanying type 2 diabetes.

Conclusion COL4A2, ACACB, GLUL and CD36 might be the core molecular biomarkers of obesity in patients with or without type 2 diabetes.

The Roles of Cytoplasmic Lipid Droplets in Modulating Intestinal Uptake of Dietary Fat

Dietary fat absorption is required for health but also contributes to hyperlipidemia and metabolic disease when dysregulated. One step in the process of dietary fat absorption is the formation of cytoplasmic lipid droplets (CLDs) in small intestinal enterocytes; these CLDs serve as dynamic triacylglycerol storage organelles that influence the rate at which dietary fat is absorbed. Recent studies have uncovered novel factors regulating enterocyte CLD metabolism that in turn influence the absorption of dietary fat. These include peroxisome proliferator-activated receptor α activation, compartmentalization of different lipid pools, the gut microbiome, liver X receptor and farnesoid X receptor activation, obesity, and physiological factors stimulating CLD mobilization. Understanding how enterocyte CLD metabolism is regulated is key in modulating the absorption of dietary fat in the prevention of hyperlipidemia and its associated metabolic disorders. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The mechanism of increased intestinal palmitic acid absorption and its impact on hepatic stellate cell activation in nonalcoholic steatohepatitis

Dietary palmitic acid (PA) promotes liver fibrosis in patients with nonalcoholic steatohepatitis (NASH). Herein, we clarified the intestinal absorption kinetics of dietary PA and effect of trans-portal PA on the activation of hepatic stellate cells (HSCs) involved in liver fibrosis in NASH. Blood PA levels after meals were significantly increased in patients with NASH compared to those in the control. Expression of genes associated with fat absorption and chylomicron formation, such as CD36 and MTP, was significantly increased in the intestine of NASH model rats compared with that in the controls. Plasma levels of glucagon-like peptide-2, involved in the upregulation of CD36 expression, were elevated in NASH rats compared with those in the controls. Furthermore, portal PA levels after meals in NASH rats were significantly higher than those in control and nonalcoholic fatty liver rats. Moreover, PA injection into the portal vein to the liver in control rats increased the mRNA levels associated with the activation of HSCs. Increased intestinal absorption of diet-derived PA was observed in NASH. Thus, the rapid increase in PA levels via the portal vein to the liver may activate HSCs and affect the development of liver fibrosis in NASH.

Intestinal GLUT5 and FAT/CD36 transporters and blood glucose are reduced by a carotenoid/MUFA-rich oil in high-fat fed mice

AIMS

Intestinal nutrient absorption plays a vital role in developing obesity, and nutrient transporters expressed in the enterocytes facilitate this process. Moreover, previous studies have shown that specific foods and diets can affect their cell levels. Herein, we investigated the effects of pequi oil (PO), which is high in several bioactive compounds, on intestinal nutrient transporter levels as well as on intestinal morphology and metabolic biomarkers.

MAIN METHODS

Groups of male C57BL/6 mice were fed either a standard (C) or a high-fat diet (HFD) and pequi oil (CP and HFDP with PO by gavage at 150 mg/day) for eight weeks. Food intake and body weight were monitored, serum metabolic biomarkers, intestinal transporter levels and histological analyses were performed.

KEY FINDINGS

PO increased caloric intake without increasing body or fat mass regardless of diet. The HFD group treated with PO reduced fasting blood glucose and villus width. PO did not affect GLUT2, L-FABP, FATP4, NPC1L1, NHE3 or PEPT1 content in CP or HFDP groups. GLUT5 and FAT/CD36 levels were reduced in both CP and HFDP.

SIGNIFICANCE

Our data suggest that PO attenuated monosaccharide and fatty acid absorption, contributing to lower fasting glycemia and higher food intake without affecting body weight or visceral fat of high-fat feed mice.

Visceral obesity and insulin resistance associate with CD36 deletion in lymphatic endothelial cells

Disruption of lymphatic lipid transport is linked to obesity and type 2 diabetes (T2D), but regulation of lymphatic vessel function and its link to disease remain unclear. Here we show that intestinal lymphatic endothelial cells (LECs) have an increasing CD36 expression from lymphatic capillaries (lacteals) to collecting vessels, and that LEC CD36 regulates lymphatic integrity and optimizes lipid transport. Inducible deletion of CD36 in LECs in adult mice (Cd36^ΔLEC) increases discontinuity of LEC VE-cadherin junctions in lacteals and collecting vessels. Cd36^ΔLEC mice display slower transport of absorbed lipid, more permeable mesenteric lymphatics, accumulation of inflamed visceral fat and impaired glucose disposal. CD36 silencing in cultured LECs suppresses cell respiration, reduces VEGF-C-mediated VEGFR2/AKT phosphorylation and destabilizes VE-cadherin junctions. Thus, LEC CD36 optimizes lymphatic junctions and integrity of lymphatic lipid transport, and its loss in mice causes lymph leakage, visceral adiposity and glucose intolerance, phenotypes that increase risk of T2D.

Genetic variants in CD36 have been associated with metabolic syndrome. Here, the authors found that lymphatic vessel integrity and lipid transport are influenced by CD36 expression, and lymphatic endothelial cell CD36 deficiency causes visceral obesity and insulin resistance, which are risk factors for metabolic syndrome and diabetes.

CD36 Senses Dietary Lipids and Regulates Lipids Homeostasis in the Intestine

Dietary lipids absorbed in the intestine are closely related to the development of metabolic syndrome. CD36 is a multi-functional scavenger receptor with multiple ligands, which plays important roles in developing hyperlipidemia, insulin resistance, and metabolic syndrome. In the intestine, CD36 is abundant on the brush border membrane of the enterocytes mainly localized in proximal intestine. This review recapitulates the update and current advances on the importance of intestinal CD36 in sensing dietary lipids and regulating intestinal lipids uptake, synthesis and transport, and regulating intestinal hormones secretion. However, further studies are still needed to demonstrate the complex interactions between intestinal CD36 and dietary lipids, as well as its importance in diet associated metabolic syndrome.

Altered intestinal epithelial nutrient transport: an underappreciated factor in obesity modulated by diet and microbiota

Dietary nutrients absorbed in the proximal small intestine and assimilated in different tissues have a profound effect on overall energy homeostasis, determined by a balance between body's energy intake and expenditure. In obesity, altered intestinal absorption and consequently tissue assimilation of nutrients may disturb the energy balance leading to metabolic abnormalities at the cellular level. The absorption of nutrients such as sugars, amino acids and fatty acids released from food digestion require high-capacity transporter proteins expressed in the intestinal epithelial absorptive cells. Furthermore, nutrient sensing by specific transporters/receptors expressed in the epithelial enteroendocrine cells triggers release of gut hormones involved in regulating energy homeostasis via their effects on appetite and food intake. Therefore, the intestinal epithelial cells play a pivotal role in the pathophysiology of obesity and associated complications. Over the past decade, gut microbiota has emerged as a key factor contributing to obesity via its effects on digestion and absorption of nutrients in the small intestine, and energy harvest from dietary fiber, undigested component of food, in the large intestine. Various mechanisms of microbiota effects on obesity have been implicated. However, the impact of obesity-associated microbiota on the intestinal nutrient transporters needs extensive investigation. This review marshals the limited studies addressing the altered structure and function of the gut epithelium in obesity with special emphasis on nutrient transporters and role of diet and microbiota. The review also discusses the thoughts and controversies and research gaps in this field.

Human microsporidian pathogen Encephalitozoon intestinalis impinges on enterocyte membrane trafficking and signaling

Microsporidia are a large phylum of obligate intracellular parasites. Approximately a dozen species of microsporidia infect humans, where they are responsible for a variety of diseases and occasionally death, especially in immunocompromised individuals. To better understand the impact of microsporidia on human cells, we infected human colonic Caco2 cells with Encephalitozoon intestinalis, and showed that these enterocyte cultures can be used to recapitulate the life cycle of the parasite, including the spread of infection with infective spores. Using transmission electron microscopy, we describe this lifecycle and demonstrate nuclear, mitochondrial and microvillar alterations by this pathogen. We also analyzed the transcriptome of infected cells to reveal host cell signaling alterations upon infection. These high-resolution imaging and transcriptional profiling analysis shed light on the impact of the microsporidial infection on its primary human target cell type.This article has an associated First Person interview with the first authors of the paper.

From Congenital Disorders of Fat Malabsorption to Understanding Intra-Enterocyte Mechanisms Behind Chylomicron Assembly and Secretion

During the last two decades, a large body of information on the events responsible for intestinal fat digestion and absorption has been accumulated. In particular, many groups have extensively focused on the absorptive phase in order to highlight the critical "players" and the main mechanisms orchestrating the assembly and secretion of chylomicrons (CM) as essential vehicles of alimentary lipids. The major aim of this article is to review understanding derived from basic science and clinical conditions associated with impaired packaging and export of CM. We have particularly insisted on inborn metabolic pathways in humans as well as on genetically modified animal models (recapitulating pathological features). The ultimate goal of this approach is that "experiments of nature" and in vivo model strategy collectively allow gaining novel mechanistic insight and filling the gap between the underlying genetic defect and the apparent clinical phenotype. Thus, uncovering the cause of disease contributes not only to understanding normal physiologic pathway, but also to capturing disorder onset, progression, treatment and prognosis.

NT-PGC-1α deficiency attenuates high-fat diet-induced obesity by modulating food intake, fecal fat excretion and intestinal fat absorption

Transcriptional coactivator PGC-1α and its splice variant NT-PGC-1α regulate metabolic adaptation by modulating many gene programs. Selective ablation of PGC-1α attenuates diet-induced obesity through enhancing fatty acid oxidation and thermogenesis by upregulation of NT-PGC-1α in brown adipose tissue (BAT). Recently, we have shown that selective ablation of NT-PGC-1α reduces fatty acid oxidation in BAT. Thus, the objective of this study was to test our hypothesis that NT-PGC-1α^−/− mice would be more prone to diet-induced obesity. Male and female NT-PGC-1α^+/+ (WT) and NT-PGC-1α^−/− mice were fed a regular chow or 60% high-fat (HF) diet for 16 weeks. Contrary to our expectations, both male and female NT-PGC-1α^−/− mice fed HFD were protected from diet-induced obesity, with more pronounced effects in females. This lean phenotype was primarily driven by reduced dietary fat intake. Intriguingly, HFD-fed female, but not male, NT-PGC-1α^−/− mice further exhibited decreased feed efficiency, which was closely associated with increased fecal fat excretion and decreased uptake of fatty acids by the intestinal enterocytes and adipocytes with a concomitant decrease in fatty acid transporter gene expression. Collectively, our results highlight the role for NT-PGC-1α in regulating whole body lipid homeostasis under HFD conditions.

Absence of CD36 alters systemic vitamin A homeostasis

Fatty acid translocase (CD36) is a scavenger receptor with multiple ligands and diverse physiological actions. We recently reported that alcohol-induced hepatic retinoid mobilization is impaired in Cd36-/- mice, leading us to hypothesize that CD36 has a novel role in hepatic vitamin A mobilization. Given the central role of the liver in systemic vitamin A homeostasis we also postulated that absence of CD36 would affect whole-body vitamin A homeostasis. We tested this hypothesis in aging wild type and Cd36-/- mice, as well as mice fed a vitamin A-deficient diet. In agreement with our hypothesis, Cd36-/- mice accumulated hepatic retinyl ester stores with age to a greater extent than wild type mice. However, contrary to expectations, Cd36-/- mice consuming a vitamin A-deficient diet mobilized hepatic retinoid similar to wild type mice. Interestingly, we observed that Cd36-/- mice had significantly reduced white adipose tissue retinoid levels compared to wild type mice. In conclusion, we demonstrate that the absence of CD36 alters whole-body vitamin A homeostasis and suggest that this phenotype is secondary to the impaired chylomicron metabolism previously reported in these mice.

Advances in fatty acids nutrition in dairy cows: from gut to cells and effects on performance

High producing dairy cows generally receive in the diet up to 5-6% of fat. This is a relatively low amount of fat in the diet compared to diets in monogastrics; however, dietary fat is important for dairy cows as demonstrated by the benefits of supplementing cows with various fatty acids (FA). Several FA are highly bioactive, especially by affecting the transcriptome; thus, they have nutrigenomic effects. In the present review, we provide an up-to-date understanding of the utilization of FA by dairy cows including the main processes affecting FA in the rumen, molecular aspects of the absorption of FA by the gut, synthesis, secretion, and utilization of chylomicrons; uptake and metabolism of FA by peripheral tissues, with a main emphasis on the liver, and main transcription factors regulated by FA. Most of the advances in FA utilization by rumen microorganisms and intestinal absorption of FA in dairy cows were made before the end of the last century with little information generated afterwards. However, large advances on the molecular aspects of intestinal absorption and cellular uptake of FA were made on monogastric species in the last 20 years. We provide a model of FA utilization in dairy cows by using information generated in monogastrics and enriching it with data produced in dairy cows. We also reviewed the latest studies on the effects of dietary FA on milk yield, milk fatty acid composition, reproduction, and health in dairy cows. The reviewed data revealed a complex picture with the FA being active in each step of the way, starting from influencing rumen microbiota, regulating intestinal absorption, and affecting cellular uptake and utilization by peripheral tissues, making prediction on in vivo nutrigenomic effects of FA challenging.

Requirement for the intestinal epithelial insulin-like growth factor-1 receptor in the intestinal responses to glucagon-like peptide-2 and dietary fat

The intestinal hormone, glucagon-like peptide-2 (GLP-2), enhances the enterocyte chylomicron production. However, GLP-2 is known to require the intestinal-epithelial insulin-like growth factor-1 receptor (IE-IGF-1R) for its other actions to increase intestinal growth and barrier function. The role of the IE-IGF-1R in enterocyte lipid handling was thus tested in the GLP-2 signaling pathway, as well as in response to a Western diet (WD). IE-IGF-1R knockout (KO) and control mice were treated for 11 days with h(GLY² )GLP-2 or fed a WD for 18 weeks followed by a duodenal fat tolerance test with C¹⁴ -labeled triolein. Human Caco-2BBE cells were treated with an IGF-1R antagonist or signaling inhibitors to determine triglyceride-associated protein expression. The IE-IGF-1R was required for GLP-2-induced increases in CD36 and FATP-4 in chow-fed mice, and for expression in vitro; FATP-4 also required PI3K/Akt. Although WD-fed IE-IGF-1R KO mice demonstrated normal CD36 expression, the protein was incorrectly localized 2h post-duodenal fat administration. IE-IGF-1R KO also prevented the WD-induced increase in MTP and decrease in APOC3, increased jejunal mucosal C¹⁴ -fat accumulation, and elevated plasma triglyceride and C¹⁴ -fat levels. Collectively, these studies elucidate new roles for the IE-IGF-1R in enterocyte lipid handling, under basal conditions and in response to GLP-2 and WD-feeding.

Regulation of intestinal lipid metabolism: current concepts and relevance to disease

Lipids entering the gastrointestinal tract include dietary lipids (triacylglycerols, cholesteryl esters and phospholipids) and endogenous lipids from bile (phospholipids and cholesterol) and from shed intestinal epithelial cells (enterocytes). Here, we comprehensively review the digestion, uptake and intracellular re-synthesis of intestinal lipids as well as their packaging into pre-chylomicrons in the endoplasmic reticulum, their modification in the Golgi apparatus and the exocytosis of the chylomicrons into the lamina propria and subsequently to lymph. We also discuss other fates of intestinal lipids, including intestinal HDL and VLDL secretion, cytosolic lipid droplets and fatty acid oxidation. In addition, we highlight the applicability of these findings to human disease and the development of therapeutics targeting lipid metabolism. Finally, we explore the emerging role of the gut microbiota in modulating intestinal lipid metabolism and outline key questions for future research.

Development of a novel murine model of lymphatic metastasis

Current laboratory models of lymphatic metastasis generally require either genetically modified animals or are technically challenging. Herein, we have developed a robust protocol for the induction of intralymphatic metastasis in wild-type mice with reproducible outcomes. To determine an optimal injection quantity and timeline for tumorigenesis, C57Bl/6 mice were injected directly into the mesenteric lymph duct (MLD) with varying numbers of syngeneic murine colon cancer cells (MC38) or gastric cancer cells (YTN16) expressing GFP/luciferase and monitored over 2-4 weeks. Tumor growth was tracked via whole-animal in vivo bioluminescence imaging (IVIS). Our data indicate that the injection of tumor cells into the MLD is a viable model for lymphatic metastasis as necropsies revealed large tumor burdens and metastasis in regional lymph nodes. This protocol enables a closer study of the role of lymphatics in cancer metastasis and opens a window for the development of novel approaches for treatment of metastatic diseases.

Why Do Men Accumulate Abdominal Visceral Fat?

Men have a higher tendency to accumulate abdominal visceral fat compared to pre-menopausal women. The accumulation of abdominal visceral fat in men, which is a strong independent predictor of mortality, is mainly due to the higher dietary fat uptake by their abdominal visceral fat. Since dietary fat is absorbed by the enterocytes and transported to the circulation in the forms of chylomicrons and very low density lipoproteins (VLDLs), it is crucial to understand how these lipoproteins are different between men and women. The chylomicrons in men are generally bigger in size and more in quantity than those in women. During the postprandial state, these chylomicrons congest the lamina propria and the low-pressure lymphatics. In this paper, we propose that this congestion predisposes the chylomicron triglycerides to hydrolysis by lipoprotein lipase (LPL). The liberated fatty acids are then stored by the nearby abdominal visceral adipocytes, leading to the accumulation of abdominal visceral fat. These mechanisms perhaps explain why men, through their bigger and higher production of chylomicrons, are more likely to accumulate abdominal visceral fat than pre-menopausal women. This accumulation eventually leads to belly enlargement, which confers men their apple-shaped body.

Metabolic control via nutrient-sensing mechanisms: role of taste receptors and the gut-brain neuroendocrine axis

Nutrient sensing plays an important role in ensuring that appropriate digestive or hormonal responses are elicited following the ingestion of fuel substrates. Mechanisms of nutrient sensing in the oral cavity have been fairly well characterized and involve lingual taste receptors. These include heterodimers of G protein-coupled receptors (GPCRs) of the taste receptor type 1 (T1R) family for sensing sweet (T1R2-T1R3) and umami (T1R1-T1R3) stimuli, the T2R family for sensing bitter stimuli, and ion channels for conferring sour and salty tastes. In recent years, several studies have revealed the existence of additional nutrient-sensing mechanisms along the gastrointestinal tract. Glucose sensing is achieved by the T1R2-T1R3 heterodimer on enteroendocrine cells, which plays a role in triggering the secretion of incretin hormones for improved glycemic and lipemic control. Protein hydrolysates are detected by Ca²⁺-sensing receptor, the T1R1-T1R3 heterodimer, and G protein-coupled receptor 92/93 (GPR92/93), which leads to the release of the gut-derived satiety factor cholecystokinin. Furthermore, several GPCRs have been implicated in fatty acid sensing: GPR40 and GPR120 respond to medium- and long-chain fatty acids, GPR41 and GPR43 to short-chain fatty acids, and GPR119 to endogenous lipid derivatives. Aside from the recognition of fuel substrates, both the oral cavity and the gastrointestinal tract also possess T2R-mediated mechanisms of recognizing nonnutrients such as environmental contaminants, bacterial toxins, and secondary plant metabolites that evoke a bitter taste. These gastrointestinal sensing mechanisms result in the transmission of neuronal signals to the brain through the release of gastrointestinal hormones that act on vagal and enteric afferents to modulate the physiological response to nutrients, particularly satiety and energy homeostasis. Modulating these orally accessible nutrient-sensing pathways using particular foods, dietary supplements, or pharmaceutical compounds may have therapeutic potential for treating obesity and metabolic diseases.

Roux-en-Y gastric bypass surgery reprograms enterocyte triglyceride metabolism and postprandial secretion in rats

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) surgery produces rapid and persistent reductions in plasma triglyceride (TG) levels associated with fewer cardiovascular events. The mechanisms of the reduction in systemic TG levels remain unclear. We hypothesized that RYGB reduces intestinal TG secretion via altered enterocyte lipid handling.

METHODS

RYGB or Sham surgery was performed in diet-induced obese, insulin-resistant male Sprague-Dawley rats. First, we tested whether RYGB reduced test meal-induced TG levels in the intestinal lymph, a direct readout of enterocyte lipid secretion. Second, we examined whether RYGB modified TG enterocyte secretion at the single lipid level and in comparison to other lipid subclasses, applying mass spectrometry lipidomics to the intestinal lymph of RYGB and Sham rats (0-21 days after surgery). Third, we explored whether RYGB modulated the metabolic characteristics of primary enterocytes using transcriptional and functional assays relevant to TG absorption, reesterification, storage in lipid droplets, and oxidation.

RESULTS

RYGB reduced overall postprandial TG concentrations compared to Sham surgery in plasma and intestinal lymph similarly. RYGB reduced lymphatic TG concentrations more than other lipid subclasses, and shifted the remaining TG pool towards long-chain, unsaturated species. In enterocytes of fasted RYGB rats, lipid uptake was transcriptionally (Fatp4, Fabp2, Cd36) and functionally reduced compared to Sham, whereas TG reesterification genes were upregulated.

CONCLUSION

Our results show that RYGB substantially reduces intestinal TG secretion and modifies enterocyte lipid absorption and handling in rats. These changes likely contribute to the improvements in the plasma TG profile observed after RYGB in humans.

Chronic exposure to a pollutant mixture at low doses led to tissue-specific metabolic alterations in male mice fed standard and high-fat high-sucrose diet

Excessive consumption of industrialized food and beverages is a major etiologic factor in the epidemics of obesity and associated metabolic diseases because these products are rich in fat and sugar. In addition, they contain food contact materials and environmental pollutants identified as metabolism disrupting chemicals. To evaluate the metabolic impact of these dietary threats (individually or combined), we used a male mouse model of chronic exposure to a mixture of low-dose archetypal food-contaminating chemicals that was added in standard or high-fat, high-sucrose (HFHS) diet. Specifically, the mixture contained bisphenol A, diethylhexylphthalate, 2,3,7,8-tetrachlorodibenzo-p-dioxine and polychlorinated biphenyl 153. Exposure lasted from 5 to 20 weeks of age. Metabolic exploration was conducted setting the basis of candidate gene expression mRNA analyses in liver, jejunum and adipose tissue depots from 20 week-old mice. Strong metabolic deleterious effects of the HFHS diet were demonstrated in line with obesity-associated metabolic features and insulin resistance. Pollutant exposure resulted in significant changes on plasma triglyceride levels and on the expression levels of genes mainly encoding xenobiotic processing in jejunum; estrogen receptors, regulators of lipoprotein lipase and inflammatory markers in jejunum and adipose tissues as well as adipogenesis markers. Importantly, the impact of pollutants was principally evidenced under standard diet. In addition, depending on nutritional conditions and on the metabolic tissue considered, the impact of pollutants could mimic or oppose the HFHS effects. Collectively, the present study extends the cocktail effect concept of a low-dosed pollutant mixture and originally points to tissue-specificity responsiveness especially in jejunum and adipose tissues.

Dietary sn-2 palmitic triacylglycerols reduced faecal lipids, calcium contents and altered lipid metabolism in Sprague-Dawley rats

In this study, the impact of dietary sn-2 palmitic triacylglycerol (sn-2 PTAG) on faecal lipids, calcium excretion and lipid metabolic alternation was investigated in Sprague-Dawley (SD) rats fed with high-fat diet containing either palm olein (PO, sn-2 palmitic acid (PA) of 14.8%), sn-2 PTAG50 (sn-2 PA of 56.4%) or sn-2 PTAG70 (sn-2 PA of 72.4%), respectively. After 4-week feeding period, SD rats fed with sn-2 PTAGs showed reduced faecal soap fatty acids, neutral lipid and calcium excretion compared to those of PO-fed rats, whereas a significant difference was only observed for the sn-2 PTAG70-fed rats (p < .05). Moreover, dietary sn-2 PTAG70 also showed a significant effect on decreasing serum triacylglycerol (TAG) level, reducing perirenal adipocyte size and regulating lipid metabolism in small intestine and perirenal adipose tissue of SD rats. Significantly increased mRNA levels of genes involved in intestinal lipid anabolism as well as lipid catabolism were both observed in the sn-2 PTAG70-fed rats (p < .05). Meanwhile, dietary sn-2 PTAG70 also significantly up-regulated lipolysis, mitochondrial fatty acid oxidation and thermogenesis-related gene and protein levels in perirenal adipose tissue, which might be correlated with the reduced perirenal adipocyte size. Taken together, our findings indicated that sn-2 PTAG70 may have some beneficial effects on intestinal lipid utilisation and lipid metabolic activity for energy supply in visceral adipose tissue.

Mettl3 Deficiency Sustains Long-Chain Fatty Acid Absorption through Suppressing Traf6-Dependent Inflammation Response

A better understanding of the molecular mechanism of intestinal fatty acid absorption could lead to novel approaches to treatment and prevention of fatty acid-related metabolic diseases. Although it is confirmed that absorption of long-chain fatty acids (LCFAs) decreases during the pathological processes, the genetic basis and molecular mechanisms remain largely unknown. N ⁶-methyladenosine (m⁶A) is the most prevalent internal modification on eukaryotic mRNA. Recently, m⁶A has been found to play important roles in inflammation and antiviral responses. In this study, we show that deficiency of Mettl3, the core methyltransferase of m⁶A, exerts antimalabsorption of LCFA activity in vitro through inhibiting the inflammation response mediated by LPS. To substantiate this finding further, we found the levels of triglycerides were also sustained in cells with depleted Mettl3, which were cultured in Transwell to polarize with villus formation to simulate the situation in vivo. Mechanistically, depletion of Mettl3 decreases the m⁶A level of Traf6 mRNA, thereby its transcripts are entrapped in the nucleus, followed by the decreased expression of Traf6, leading to the suppression of NF-κB and MAPK signaling pathway. Thus, the inflammation response was suppressed, resulting in the sustained absorption of LCFA. Moreover, we found that ectopic expression of Traf6 largely abolishes the sustained absorption LCFA in Mettl3 depletion cells. Collectively, silencing Mettl3 could sustain LCFA absorption through blocking the TRAF6-dependent inflammation response. Our work uncovers a critical function of m⁶A methylation and provides insight into critical roles of Mettl3 in LCFA absorption and inflammatory disease.

The Intestinal Lymphatic System: Functions and Metabolic Implications

The lymphatic system of the gut plays important roles in the transport of dietary lipids, as well as in immunosurveillance and removal of interstitial fluid. Historically, despite its crucial functions in intestinal homeostasis, the lymphatic system has been poorly studied. In the last 2 decades, identification of specific molecular mediators of lymphatic endothelial cells (LECs) growth together with novel genetic approaches and intravital imaging techniques, have advanced our understanding of the mechanisms regulating intestinal lymphatic physiology in health and disease. As its metabolic implications are gaining recognition, intestinal lymphatic biology is currently experiencing a surge in interest. This review describes current knowledge related to molecular control of intestinal lymphatic vessel structure and function. We discuss regulation of chylomicron entry into lymphatic vessels by vascular endothelial growth factors (VEGFs), hormones, transcription factors and the specific signaling pathways involved. The information covered supports the emerging role of intestinal lymphatics in etiology of the metabolic syndrome and their potential as a therapeutic target.