Regulating Plasma Lipid Research Articles

Comparative genomics reveals convergent adaptations in lipid metabolism and low genetic diversity in carnivorous bats

AbstractDietary specialization stands as a major factor in the study of adaptive evolution and the field of conservation biology among animals. Although bats show unparalleled dietary diversification among mammals, specialized carnivory remains relatively rare within this group. Consequently, our comprehension of the genetic and conservation aspects associated with this specific dietary niche in bats has largely remained uncharted. To investigate molecular adaptations and conservation genetics in carnivorous bats, we produced a new draft genome assembly for the carnivorous bat Vampyrum spectrum. Furthermore, we utilized this genome alongside another distantly related carnivorous bat Megaderma lyra, to conduct genome‐wide comparative analyses with other bat species. Our findings unveil that genes linked to lipid metabolism exhibit signatures of positive selection and convergent molecular adaptation in the two divergent lineages of carnivorous bats. Intriguingly, we have uncovered that the evolution of dietary specialization in carnivorous bats is accompanied by molecular adaptations acting on genes in the peroxisome proliferator‐activated receptors pathways, which are crucial in regulating plasma lipid metabolism and sustaining lipid homeostasis. Additionally, our genomic analyses also reveal low genetic diversity in both carnivorous bat species. This pattern is attributed to their continuously declining population sizes and low levels of heterozygosity, signaling their vulnerability and emphasizing the pressing need for conservation efforts. These genomic discoveries advance our understanding of genetic underpinnings of carnivory in bats and underscore substantial conservation concerns associated with carnivorous bat species.

Deficiency of the lipid flippase ATP10A causes diet-induced dyslipidemia in female mice

Genetic association studies have linked ATP10A and closely related type IV P-type ATPases (P4-ATPases) to insulin resistance and vascular complications, such as atherosclerosis. ATP10A translocates phosphatidylcholine and glucosylceramide across cell membranes, and these lipids or their metabolites play important roles in signal transduction pathways regulating metabolism. However, the influence of ATP10A on lipid metabolism in mice has not been explored. Here, we generated gene-specific Atp10A knockout mice and show that Atp10A−/− mice fed a high-fat diet did not gain excess weight relative to wild-type littermates. However, Atp10A−/− mice displayed female-specific dyslipidemia characterized by elevated plasma triglycerides, free fatty acids and cholesterol, as well as altered VLDL and HDL properties. We also observed increased circulating levels of several sphingolipid species along with reduced levels of eicosanoids and bile acids. The Atp10A−/− mice also displayed hepatic insulin resistance without perturbations to whole-body glucose homeostasis. Thus, ATP10A has a sex-specific role in regulating plasma lipid composition and maintaining hepatic liver insulin sensitivity in mice.

Integration of network pharmacology, lipidomics, and transcriptomics analysis to reveal the mechanisms underlying the amelioration of AKT-induced nonalcoholic fatty liver disease by total flavonoids in vine tea.

Nonalcoholic fatty liver disease (NAFLD) is the main reason for chronic liver diseases and malignancies. Currently, there is a lack of approved drugs for the prevention or treatment of NAFLD. Vine tea (Ampelopsis grossedentata) has been used as a traditional Chinese beverage for centuries. Vine tea carries out several biological activities including the regulation of plasma lipids and blood glucose, hepato-protective function, and anti-tumor activity and contains the highest content of flavonoids. However, the underlying mechanisms of total flavonoids from vine tea (TF) in the attenuation of NAFLD remain unclear. Therefore, we investigated the interventions and mechanisms of TF in mice with NAFLD using an integrated analysis of network pharmacology, lipidomics, and transcriptomics. Staining and biochemical tests revealed a significant increase in AKT-overexpression-induced (abbreviated as AKT-induced) NAFLD in mice. Lipid accumulation in hepatic intracellular vacuoles was alleviated after TF treatment. In addition, TF reduced the hepatic and serum triglyceride levels in mice with AKT-induced NAFLD. Lipidomics results showed 32 differential lipids in the liver, mainly including triglycerides (TG), diglycerides (DG), phosphatidylcholine (PC), and phosphatidylethanolamine (PE). Transcriptomic analysis revealed that 314 differentially expressed genes were commonly upregulated in the AKT group and downregulated in the TF group. The differential regulation of lipids by the genes Pparg, Scd1, Chpt1, Dgkz, and Pla2g12b was further revealed by network enrichment analysis and confirmed by RT-qPCR. Furthermore, we used immunohistochemistry (IHC) to detect changes in the protein levels of the key proteins PPARγ and SCD1. In summary, TF can improve hepatic steatosis by targeting the PPAR signaling pathway, thereby reducing de novo fatty acid synthesis and modulating the glycerophospholipid metabolism.

Gene network based analysis identifies a coexpression module involved in regulating plasma lipids with high-fat diet response

Plasma lipids are modulated by gene variants and many environmental factors, including diet-associated weight gain. However, understanding how these factors jointly interact to influence molecular networks that regulate plasma lipid levels is limited. Here, we took advantage of the BXD recombinant inbred family of mice to query weight gain as an environmental stressor on plasma lipids. Coexpression networks were examined in both nonobese and obese livers, and a network was identified that specifically responded to the obesogenic diet. This obesity-associated module was significantly associated with plasma lipid levels and enriched with genes known to have functions related to inflammation and lipid homeostasis. We identified key drivers of the module, including Cidec, Cidea, Pparg, Cd36, and Apoa4. The Pparg emerged as a potential master regulator of the module as it can directly target 19 of the top 30 hub genes. Importantly, activation of this module is causally linked to lipid metabolism in humans, as illustrated by correlation analysis and inverse-variance weighed Mendelian randomization. Our findings provide novel insights into gene-by-environment interactions for plasma lipid metabolism that may ultimately contribute to new biomarkers, better diagnostics, and improved approaches to prevent or treat dyslipidemia in patients.

Plasma concentrations of apolipoproteins C3 and C2 do not explain differences in insulin-stimulated endothelial-bound lipoprotein lipase activity in insulin resistant humans

Elevated circulating triglycerides (i.e., dyslipidemia) is a hallmark of insulin resistance and is generally caused by decrease in lipoprotein lipase (LPL) activity. LPL hydrolyzes triglycerides (TG) into free fatty acids in plasma for use and/or storage in tissues (i.e., adipose, skeletal muscle). Plasma apolipoproteins (Apos) C3 and C2 interact with LPL to modulate its function by activating or inhibiting LPL. Previous research shows, in the metabolic environment of insulin resistance, the concentration of ApoC3 is increased in plasma while that of ApoC2 is decreased. Thus, Apos are considered key factors in regulating plasma lipid metabolism via modulation of LPL function. The purpose of this study was to investigate the concentrations of ApoC3 and ApoC2 in plasma and along endothelial-bound LPL activity in insulin resistant and healthy/non-insulin resistant individuals. We evaluated insulin resistance (IR)/insulin sensitivity (IS) using an oral glucose tolerance test (i.e., Matsuda index calculation) in subjects between ages 19 and 45 years old. Subjects were placed in the following two groups: 1) IR, if Matsuda index <4.0 (N=6; 4 males, 2 females; BMI: 23-45 kg/m2), or 2) IS, if Matsuda index >7.0 (N=11, 9 males, 2 females; BMI: 18-26 kg/m2). Subjects received an intravenous insulin infusion (0.5 mU/kg/min) for 30 minutes to resemble increased postprandial plasma insulin response. To release whole-body endothelial-bound LPL, subjects received an injection of intravenous heparin (75 UI/kg). Plasma samples were collected 10 minutes after the heparin infusion and analyzed for LPL concentration and activity, and ApoC3 and ApoC2 concentrations using ELISA. Differences between IS and IR subjects were determined using a t-test, and the P value was set at P < 0.05. Plasma LPL concentrations were not different between groups (IR = 457 ± 17 ng/ml, IS = 453 ± 27 ng/ml, P > 0.05), but plasma LPL activity was higher in the IR subjects (IR = 665 ± 113 nmol/min/ml, IS = 365 ± 59 nmol/min/ml, P = 0.02). IR subjects had higher concentrations of plasma ApoC3 (IR = 3.6 ± 0.5 mg/dl, IS = 2.7 ± 0.2 mg/dl, P=0.03) but ApoC2 was not different between groups (IR = 0.15 ± 0.03 mg/dl, IS = 0.11 ± 0.01 mg/dl, P = 0.11). The ratio of circulating LPL to circulating ApoC3 (IR = 145 ± 22, IS = 176 ± 15) or circulating ApocC2 (IR = 4104 ± 844, IS = 4391 ± 483) were not different between groups (P > 0.05). We conclude that interactions of LPL with APOC3 and ApoC2 may not be main determinants regulating differential whole-body plasma LPL activity under plasma insulin-stimulated conditions in insulin resistant humans. American Diabetes Association Grant #7-12-CT-40 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Uncovering the complex genetic architecture of human plasma lipidome using machine learning methods

Genetic architecture of plasma lipidome provides insights into regulation of lipid metabolism and related diseases. We applied an unsupervised machine learning method, PGMRA, to discover phenotype-genotype many-to-many relations between genotype and plasma lipidome (phenotype) in order to identify the genetic architecture of plasma lipidome profiled from 1,426 Finnish individuals aged 30–45 years. PGMRA involves biclustering genotype and lipidome data independently followed by their inter-domain integration based on hypergeometric tests of the number of shared individuals. Pathway enrichment analysis was performed on the SNP sets to identify their associated biological processes. We identified 93 statistically significant (hypergeometric p-value < 0.01) lipidome-genotype relations. Genotype biclusters in these 93 relations contained 5977 SNPs across 3164 genes. Twenty nine of the 93 relations contained genotype biclusters with more than 50% unique SNPs and participants, thus representing most distinct subgroups. We identified 30 significantly enriched biological processes among the SNPs involved in 21 of these 29 most distinct genotype-lipidome subgroups through which the identified genetic variants can influence and regulate plasma lipid related metabolism and profiles. This study identified 29 distinct genotype-lipidome subgroups in the studied Finnish population that may have distinct disease trajectories and therefore could be useful in precision medicine research.

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.

Abstract 425: Genetic Inhibition Of Hepatic Dolichol Biosynthesis Results In Hypolipidemia

Dolichol is a nonsterol isoprenoid derived from the mevalonate pathway. Dehydrodolichyl diphosphate synthase subunit (DHDDS) is a branch point enzyme that - in complex with Nogo-B receptor (NgBR) - catalyzes the first committed step of dolichol biosynthesis. Next, dolichol is phosphorylated, and used as carrier for oligosaccharides, which are transferred to nascent proteins in the N-linked glycosylation pathway. A growing body of evidence highlights the importance of N-linked glycosylation in regulating plasma lipid levels in humans. However, the underlying molecular mechanisms are largely unexplored. Therefore, the goal of this project is to define the role of dolichol biosynthesis in lipid metabolism in the liver, the major organ for the biosynthesis and clearance of lipoproteins. We used Adeno-Associated Virus (AAV)-mediated delivery of CRISPR/Cas9 (AAV-CRISPR) to delete Dhdds in mouse liver, to inhibit the hepatic biosynthesis of dolichol. Mice were injected with AAV-CRISPR or saline as control, and fed a high-fat diet for 4 to 12 weeks. Surprisingly, Dhdds liver-specific knockout (LSKO) mice gained less weight compared to control mice. Plasma total cholesterol and triglyceride levels were also reduced over time in Dhdds LSKO mice. Moreover, we observed less cholesterol content in the high-density lipoprotein (HDL) fractions as well as less triglycerides in very-low-density lipoproteins (VLDL). At the cellular level, Dhdds LSKO mice showed hepatic endoplasmic reticulum (ER) stress and decreased N-linked glycosylation. In addition, we observed significant downregulation of Sterol Regulatory Element-Binding Protein 1c ( Srebp-1c ) - a key regulator of de novo lipogenesis (DNL) - and downstream-regulated genes in the DNL pathway. Conversely, the expression of genes regulating cholesterol biosynthesis was unaffected. Taken together, our data show an important role for hepatic dolichol biosynthesis in regulating plasma lipids, potentially through modulation of Srebp-1c expression and DNL.

Adipocyte-specific tribbles pseudokinase 1 regulates plasma adiponectin and plasma lipids in mice

ObjectiveMultiple genome-wide association studies (GWAS) have identified SNPs in the 8q24 locus near TRIB1 that are significantly associated with plasma lipids and other markers of cardiometabolic health, and prior studies have revealed the roles of hepatic and myeloid Trib1 in plasma lipid regulation and atherosclerosis. The same 8q24 SNPs are additionally associated with plasma adiponectin levels in humans, implicating TRIB1 in adipocyte biology. Here, we hypothesize that TRIB1 in adipose tissue regulates plasma adiponectin, lipids, and metabolic health. MethodsWe investigate the metabolic phenotype of adipocyte-specific Trib1 knockout mice (Trib1_ASKO) fed on chow and high-fat diet (HFD). Through secretomics of adipose tissue explants and RNA-seq of adipocytes and livers from these mice, we further investigate the mechanism of TRIB1 in adipose tissue. ResultsTrib1_ASKO mice have an improved metabolic phenotype with increased plasma adiponectin levels, improved glucose tolerance, and decreased plasma lipids. Trib1_ASKO adipocytes have increased adiponectin production and secretion independent of the known TRIB1 function of regulating proteasomal degradation. RNA-seq analysis of adipocytes and livers from Trib1_ASKO mice indicates that alterations in adipocyte function underlie the observed plasma lipid changes. Adipose tissue explant secretomics further reveals that Trib1_ASKO adipose tissue has decreased ANGPTL4 production, and we demonstrate an accompanying increase in the lipoprotein lipase (LPL) activity that likely underlies the triglyceride phenotype. ConclusionsThis study shows that adipocyte Trib1 regulates multiple aspects of metabolic health, confirming previously observed genetic associations in humans and shedding light on the further mechanisms by which TRIB1 regulates plasma lipids and metabolic health.

Abstract 10706: Alpha Aminoadipic Acid Down-Regulates Sr-bi Abca1 and Abcg1 Expression and May Regulate Plasma Lipid Profiles, Cellular Cholesterol Efflux, and Efferocytosis

Introduction: The metabolite α-aminoadipic acid (2-AAA) has been identified as a predictor of diabetes and atherosclerosis in large human prospective studies. However, the mechanisms linking this metabolite to disease pathophysiology remain unknown. Efferocytosis, a macrophage-mediated process for clearance of apoptotic cells (ACs), is critical in preventing necrosis of dead cells and triggers anti-inflammatory and pro-resolving responses in phagocytes. Cholesterol efflux from peripheral cells in atherosclerotic plaque is a critical step in Reverse Cholesterol Transport (RCT). We hypothesized that the 2-AAA pathway relates to atherosclerosis through modulation of plasma lipid profiles, cholesterol efflux, and macrophage efferocytosis. Results: We found a significant negative correlation between plasma 2-AAA and HDL cholesterol (r=-0.53, P&lt;0.0001), and a significant positive correlation with triglycerides (r=0.35, P=0.006), in two separate samples of individuals with and without cardiometabolic disease (N=98), suggesting a relationship between 2-AAA and cardiovascular risk. We investigated the consequences of 2-AAA stimulation in several primary cells and cell lines. We found that 2-AAA stimulation downregulates three key genes (SR-BI (up to 86% reduction, P=0.005), ABCA1 (up to 92% reduction, P=0.007), ABCG1 (up to 94% reduction, P=0.008)) that directly relate to cholesterol efflux in THP-1 macropohages, suggesting an important role of 2-AAA in cholesterol efflux. Next, we found that treatment with 2-AAA at physiologically-relevant doses (30μM and 100μM) for times ranging from 30 minutes to 6 hours led to consistent reductions of efferocytosis of up to 60% (P&lt;0.001) in mouse macrophages, J774 cells and Raw 264.7 cells, suggesting a pivotal role of 2-AAA in efferocytosis. Conclusions: Our data suggest 2-AAA is associated with plasma lipid profiles (HDL, triglycerides), cholesterol efflux, and macrophage efferocytosis. These novel data could provide a new target for the treatment of atherosclerosis.

A cargo-specific role for hepatocyte retriever in lipoprotein receptor recycling

Background and Aims: We recently demonstrated that the CCC (CCDC22/CCDC93/COMMDs) complex is required for the endosomal recycling of the lipoprotein receptors LDLR, LRP1 and SR-BI. Hepatic loss of CCC causes hypercholesterolemia in mice and humans. Retriever, a multiprotein complex consisting of VPS29, VPS26C and VPS35L, shares the subunit VPS35L with the CCC complex but its contribution to lipoprotein receptor recycling and plasma lipid regulation remains unclear. This study aimed to assess the contribution of retriever to the regulation of plasma lipids.

Diet-induced differential effects on plasma lipids secretion by the inositol-requiring transmembrane kinase/endoribonuclease 1α.

Intestinal and hepatic lipid metabolism plays an essential role in regulating plasma lipid levels. These lipids are mobilized on apolipoprotein B (apoB)-containing lipoproteins and their plasma homeostasis is maintained by balancing production and catabolism. Microsomal triglyceride transfer protein (MTP) which is expressed mainly in the intestine and liver plays an essential role in regulating the assembly and secretion of apoB-lipoproteins. Any imbalance in the production or clearance of lipoproteins leads to hyperlipidemia which is a major risk factor for atherosclerosis, obesity, diabetes, and metabolic syndrome. Here, we identify a new role of inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α) in the regulation of plasma lipids. We generated intestine specific IRE1α knockout mice to study whether intestinal IRE1α regulates plasma lipids by modulating intestinal lipid absorption. Intestine specific deletion of Ire1a gene in mice fed chow diet, significantly reduced plasma cholesterol and triglycerides by 29% and 43% in Ire1a-⁣/- mice (P < 0.01 & P < 0.001, respectively). These changes were not associated with any alteration of MTP activity nor its mRNA expression. On the other hand, Western diet increased plasma triglyceride by 37% (P < 0.01) without affecting total plasma cholesterol in Ire1a-⁣/- mice. Interestingly, this effect was associated with a significant increase in the intestinal MTP activity and its mRNA expression (25%, P < 0.01 and 70%, P < 0.05, respectively). Collectively, our findings reveal key role of intestinal IRE1α in the regulation of plasma lipids that may provide a therapeutic target for disorders of lipid metabolism.

Gene networks and pathways for plasma lipid traits via multitissue multiomics systems analysis

Genome-wide association studies (GWASs) have implicated ∼380 genetic loci for plasma lipid regulation. However, these loci only explain 17–27% of the trait variance, and a comprehensive understanding of the molecular mechanisms has not been achieved. In this study, we utilized an integrative genomics approach leveraging diverse genomic data from human populations to investigate whether genetic variants associated with various plasma lipid traits, namely, total cholesterol, high and low density lipoprotein cholesterol (HDL and LDL), and triglycerides, from GWASs were concentrated on specific parts of tissue-specific gene regulatory networks. In addition to the expected lipid metabolism pathways, gene subnetworks involved in “interferon signaling,” “autoimmune/immune activation,” “visual transduction,” and “protein catabolism” were significantly associated with all lipid traits. In addition, we detected trait-specific subnetworks, including cadherin-associated subnetworks for LDL; glutathione metabolism for HDL; valine, leucine, and isoleucine biosynthesis for total cholesterol; and insulin signaling and complement pathways for triglyceride. Finally, by using gene-gene relations revealed by tissue-specific gene regulatory networks, we detected both known (e.g., APOH, APOA4, and ABCA1) and novel (e.g., F2 in adipose tissue) key regulator genes in these lipid-associated subnetworks. Knockdown of the F2 gene (coagulation factor II, thrombin) in 3T3-L1 and C3H10T1/2 adipocytes altered gene expression of Abcb11, Apoa5, Apof, Fabp1, Lipc, and Cd36; reduced intracellular adipocyte lipid content; and increased extracellular lipid content, supporting a link between adipose thrombin and lipid regulation. Our results shed light on the complex mechanisms underlying lipid metabolism and highlight potential novel targets for lipid regulation and lipid-associated diseases.

LDL Cholesterol and Dysglycemia: an Intriguing Physiological Relationship

It is an unexpected but pleasant surprise when new clinical relationships are identified, and one of the most interesting is the inverse association between LDL cholesterol (LDLc) and type 2 diabetes (T2D) risk. Evidence from both randomized clinical trials and genetic studies indicates that regulation of plasma lipids and glycemic control is more closely linked than previously assumed, yet in a counterintuitive, one could even say paradoxical, manner. Meta-analyses of randomized clinical trials have found that drugs designed to reduce LDLc, in addition to their hypolipidemic and cardioprotective effects, appear to also modestly increase T2D risk (1,2). Furthermore, naturally occurring genetic variation in molecular targets of LDLc-lowering therapy, such as genetic variants in or near HMGCR , NCP1L1 , and PCSK9 genes, have been found to be associated with impaired insulin sensitivity and new-onset T2D, particularly among people with impaired fasting glucose levels (3–6). Further supporting that this is a fundamental biologic relationship, individuals with familial hypercholesterolemia, a dominantly inherited disease characterized by high plasma levels of LDLc due to genetic mutations in LDLR or APOB genes, appear to have a lower prevalence of diabetes than unaffected relatives (7). However, not all genetic variants that raise LDLc have similar effects on glycemic control (8). This suggests that the mechanism by which LDLc is reduced might have relevant implications for glycemic deterioration and reveal potential important mechanisms for diabetogenesis in general. As reported in this issue of Diabetes , Klimentidis et al. (9) conducted a study to examine the phenotypic and genotypic relationships between LDLc …

Fatty Acids of the Liver and the Blood Plasma During the Hibernation of the Yakutian Ground Squirrel Spermophilus undulatus

Abstract—We investigated the effect of hibernation on the levels of fatty acids and monoglycerides in the liver tissue and in the blood plasma of the Yakut ground squirrel Spermophilus undulatus. In the liver tissue of dormant animals (the hibernation bout) the level of fatty acids (μg of fatty acids/mg of protein) increases by 5 times compared to the summer period. In ground squirrels that are active in the winter (a hibernation interbout), the level of fatty acids was halved compared to dormant ones. The level of monoglycerides in the liver of hibernating animals was halved compared to summer animals. The protein level (mg/g of tissue) in the liver did not change during hibernation. The level of fatty acids decreased by half in the blood plasma of animals during the hibernation and returned to summer level in active winter animals. The level of monoglycerides in the blood plasma did not change. The protein concentration in the blood plasma during hibernation is increased by 20% compared with the summer period. Changes in the level of fatty acids in the liver and blood plasma indicate the adaptive role of fatty acids in the hibernation of the ground squirrel S. undulatus. A high fat level is maintained in the liver of hibernating animals with a reduced level of fatty acid in the blood plasma during torpor. Fatty acids of the liver play a role in the return of the fatty acid plasma level to the summer level during the hibernation interbout. The analysis of our results demonstrated that the liver plays a role in the regulation of plasma lipids, acting as a depot for fatty acids with an adaptive decrease in their concentration in the blood plasma during the hibernation season. A high level of liver fatty acids can cause adaptive changes in the lipid composition of the intracellular organelles of the liver tissue during the hibernation of the ground squirrel S. undulatus.

Rosa rugosa flavonoids exhibited PPARα agonist-like effects on genetic severe hypertriglyceridemia of mice

Ethnopharmacological relevanceRosa rugosa Thunb. is a traditional Chinese medicine that was used in the treatment of cardiovascular diseases and relative risk factors such as diabetes, hyperlipidemia, hypertension, and inflammation. Rosa rugosa flavonoids (RRFs) are the main components in Rosa rugosa Thunb. Several studies have demonstrated that RRFs can regulate plasma lipid contents, but the related mechanism of which has not yet been elucidated clearly. Aim of the studyThe goal of this study was to clarify the effects of RRFs on triglyceride metabolism and its related mechanisms. Materials and methodsRRFs were obtained by ethanol extraction from Rosa rugosa Thunb.. Transgenic mice expressing human Apolipoprotein C3 (ApoC3) were used as a mouse model of hypertriglyceridemia. Fenofibrate (FNB), a PPARα agonist, was used as a positive control drug of decreasing high triglyceride. FNB (100 mg/kg) or RRFs (300 mg/kg) were given to the mice by gavage daily. Two weeks later, the changes of plasma lipid levels in the mice were measured by commercial kits, the clearance of triglyceride was evaluated by oral fat load test, and expression of the genes related to lipid β-oxidation and synthesis was detected in the mice livers by real time PCR. ResultsRRFs, as well as FNB, were found to significantly reduce plasma triglyceride (TG) levels in ApoC3 transgenic mice after administration of the drug for two weeks. Plasma lipid clearance rate was increased and lipid content in the mice livers was reduced after administration of RRF. Treatment with RRFs up-regulated mRNA expression of PPARα and its downstream gene of ACOX, while down-regulated mRNA expression of the genes related to fatty acid synthesis (FASN, SREBP-1c, and ACC1). The expression of LPL was raised, while the expression of ApoC3 was decreased, and Foxo1 was inhibited by RRFs in the mice livers. ConclusionRRFs can reduce plasma TG levels by repressing the expression of ApoC3 and inducing the expression of LPL in liver. RRFs could also reduce triglyceride in hepatocytes through increasing β-oxidation and decreasing synthesis of the lipids. These findings show the potency of further clinical application of RRFs as a hypolipidemic drug for treatment of cardiovascular diseases.

FADS and PPARG2 Single Nucleotide Polymorphisms are Associated with Plasma Lipids in 9-Mo-Old Infants

Dietary intake of polyunsaturated fatty acids (PUFAs), e.g., linoleic acid and n-3 (ω-3) long-chain PUFAs, has been shown in adults to affect plasma cholesterol and triglycerides (TGs), respectively. Little is known about the effects of PUFAs on plasma lipids in early life. The aim of this study was to explore the associations between plasma concentrations of total, LDL, and HDL cholesterol and TGs in infants and 2 single nucleotide polymorphisms (SNPs) in the fatty acid desaturase genes (FADS) oppositely associated with docosahexaenoic acid (rs1535 and rs174448) and potential effect modification by a functional peroxisome proliferator-activated receptor-γ2 gene variant (PPARG2 Pro12Ala). In 9-mo-old infants (n=561) from 3 Danish cohorts, we analyzed associations between plasma lipids, erythrocyte PUFAs, and FADS SNPs, and interactions with PPARG2 Pro12Ala genotype, by multiple linear regression. We also examined potential effect modification by breastfeeding, as 46% of the infants were still being breastfed. Minor allele carriage of rs174448 was associated with lower total cholesterol (difference: -0.22 mmol/L; 95% CI: -0.37, -0.06 mmol/L; P=0.006) and LDL cholesterol (difference: -0.15 mmol/L; 95% CI: -0.29, -0.01 mmol/L; P=0.035), but no associations were observed with TGs or for rs1535. Minor allele carriage of both FADS SNPs was associated with 1 SD lower HDL cholesterol, but only in currently breastfed infants (rs174448×breastfeeding, P=0.080; rs1535×breastfeeding, P=0.030) and PPARG2 minor allele carriers (rs174448×PPARG2, P=0.001; rs1535×PPARG2, P=0.004). Erythrocyte arachidonic acid and eicosapentaenoic acid were inversely associated with LDL cholesterol [estimated effect (β): -0.3 mmol/L; 95% CI: -0.06, -0.00 mmol/L per percentage of fatty acids (FA%); P=0.035] and TGs (β: -0.23 mmol/L; 95% CI: -0.41, -0.05 mmol/L per FA%; P=0.015), respectively. The observed associations with FADS variants indicate that PUFAs are involved in plasma lipid regulation in 9-mo-old infants. Observed FADS SNP differences and interactions with breastfeeding and PPARG2 warrant additional studies to explore the effects of individual FADS SNPs on PUFA status and potential genetic modification of dietary PUFA effects.

Regulation of PCSK9 Levels by the Ubiquitin‐Binding Domain of Histone Deacetylase 6

Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) regulates plasma lipid homeostasis by altering the abundance of low‐density lipoprotein(LDL)‐receptors in the liver. Therefore, this critical role in lipid homeostasis makes PCSK9 an attractive target for the therapeutic management of familial hypercholesterolemia as well as other refractory dyslipidemias. Recently, monoclonal antibodies that bind circulating PCSK9 were approved for therapeutic use to reduce LDL‐C levels to control hypercholesterolemia. However, other strategies to inhibit PCSK9 have not as yet been explored. We have recently demonstrated that HDAC6, a class IIB deacetylase, is a potent regulator of PCSK9 levels. Our data show that co‐expression of PCSK9 with full length HDAC6 in 293A cells results in marked upregulation of PCSK9, while gene silencing of endogenous HDAC6 leads to reduction in PCSK9. Interestingly, this effect was found to be independent of the deacetylase activity of HDAC6 and dependent upon the unique ubiquitin‐binding (BUZ) domain located at the C‐terminal tail of HDAC6. Small molecule inhibition of HDAC6 activity by Tubacin in vivo in hypercholesterolemic ApoE knockout mice had no effect on liver PCSK9 and LDL receptor levels. Further, co‐expression of the catalytic deficient mutant of HDAC6 (H216/611A) with PCSK9 did not modulate the high PCSK9 levels. The effect of HDAC6 on PCSK9 abundance was abolished when PCSK9 was co‐expressed with a BUZ domain deletion mutant of HDAC6. Our co‐immunoprecipitation data further suggest that HDAC6 binds to the polyubiquitin chain of PCSK9, recruits the deubiquitinating enzyme USP7 and protects PCSK9 from degradation. These signaling events lead to augmented PCSK9, followed by reduction of LDLr in liver, and eventually to hyperlipidemia.Our data indicate that the HDAC6 BUZ domain regulates PCSK9 levels via post‐translational modification by deubiquitinase USP7, and this may represent a novel target for hyperlipidemia.Support or Funding InformationAmerican Heart Association Scientist Development Grant (16SDG27340010) Gilead Sciences Pulmonary Arterial Hypertension Research Scholar AwardThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Trimethylamine N-Oxide: A Link among Diet, Gut Microbiota, Gene Regulation of Liver and Intestine Cholesterol Homeostasis and HDL Function.

Recent evidence, including massive gene-expression analysis and a wide-variety of other multi-omics approaches, demonstrates an interplay between gut microbiota and the regulation of plasma lipids. Gut microbial metabolism of choline and l-carnitine results in the formation of trimethylamine (TMA) and concomitant conversion into trimethylamine-N-oxide (TMAO) by liver flavin monooxygenase 3 (FMO3). The plasma level of TMAO is determined by the genetic variation, diet and composition of gut microbiota. Multiple studies have demonstrated an association between TMAO plasma levels and the risk of atherothrombotic cardiovascular disease (CVD). We aimed to review the molecular pathways by which TMAO production and FMO3 exert their proatherogenic effects. TMAO may promote foam cell formation by upregulating macrophage scavenger receptors, deregulating enterohepatic cholesterol and bile acid metabolism and impairing macrophage reverse cholesterol transport (RCT). Furthermore, FMO3 may promote dyslipidemia by regulating multiple genes involved in hepatic lipogenesis and gluconeogenesis. FMO3 also impairs multiple aspects of cholesterol homeostasis, including transintestinal cholesterol export and macrophage-specific RCT. At least part of these FMO3-mediated effects on lipid metabolism and atherogenesis seem to be independent of the TMA/TMAO formation. Overall, these findings have the potential to open a new era for the therapeutic manipulation of the gut microbiota to improve CVD risk.

A Diurnal Rhythm in Brown Adipose Tissue Causes Rapid Clearance and Combustion of Plasma Lipids at Wakening

Many favorable metabolic effects have been attributed to thermogenic activity of brown adipose tissue (BAT). Yet, time of day has rarely been considered in this field of research. Here, we show that a diurnal rhythm in BAT activity regulates plasma lipid metabolism. We observed a high-amplitude rhythm in fatty acid uptake by BAT that synchronized with the light/dark cycle. Highest uptake was found at the onset ofthe active period, which coincided with high lipoprotein lipase expression and low angiopoietin-like 4 expression by BAT. Diurnal rhythmicity in BAT activity determined the rate at which lipids were cleared from the circulation, thereby imposing the daily rhythm in plasma lipid concentrations. In mice as well as humans, postprandial lipid excursions were nearly absent at waking. We anticipate that diurnal BAT activity is an important factor to consider when studying the therapeutic potential of promoting BAT activity.