Background and Aims

Background: Hypertriglyceridemia has emerged as an important coronary artery disease (CAD) risk factor. Rare loss of function (LOF) variants in apolipoprotein CIII have been reported to reduce triglycerides (TG) and decrease the risk of CAD in American Indians and Europeans. However, there is a paucity of data on whether these variants are cardioprotective in other European and non-European populations. Also, whether genetically increased TG due to ApoCIII is causally associated with increased CAD risk is still unclear and inconsistent.

Objective: The goal of this study was to evaluate the causal association of genetically raised TG for increasing the risk for CAD and type 2 diabetes (T2D) using a Mendelian randomization approach.

Methods

Methods: Using genome-wide genotypes and sequencing data of ten independent multiethnic cohorts comprising up to 397,460 individuals, we have evaluated the role of genetic variation in APOCIII for affecting circulating TG and the risk for developing CAD and T2D.

Results

Results: Two common variants (rs5128 and rs734104) in the APOCIII were robustly associated with elevated TG across all cohorts showing an allelic risk-score p-value of 1.74x10^-674 in joint meta-analysis. A per risk allele-associated increase of TG of 12mmol/L ± SE 0.02mmol/L was predicted to enhance CAD risk by 5% 95%CI (3% to 6%; p=2.01x10^-05). On the contrary, the same TG raising variants reveal marginal protection from T2D (OR 0.99 95%CI 0.98-1.00; p=0.02).

Conclusions

Conclusions: Our Mendelian randomization study suggests that the genetically regulated HTG via APOCIII may be causally associated with the increased risk for CAD.

Background and Aims

Apolipoprotein C-III (apoC-III) is a key regulator in triglyceride metabolism and correlates positively with hypertriglyceridemia and incidences of CVD. Recent studies also identified apoC-III as an inducer of sterile inflammation by activating the inflammasome, another CVD risk factor. It remains unclear if therapeutic apoC-III lowering can reduce CVD risk, nor is it clear if this is depended on lipid-lowering or anti-inflammatory properties or both.

Methods

In this study, we determined the impact of interventional apoC-III lowering on atherogenesis using an apoC-III antisense oligonucleotides (ASOs) in hypertriglyceridemic mouse models where the intervention results in triglyceride-lowering (Apoe^-/-Ndst1^f/fAlb-Cre⁺, Ldlr^-/-Ndst1^f/fAlb-Cre⁺) or not (Ldlr^-/-Lrp1^f/fAlb-Cre⁺).

Results

ApoC-III ASO treatment did not alter atherosclerotic lesion volume in the murine models mice simultaneously fed a Western diet. However, when triglyceride-lowering was obtained, apoC-III ASO treatment significantly attenuated advanced and unstable plaque development. In contrast, no improvement in lesion composition and hyperlipidemia was observed in apoC-III ASO-treated Ldlr^-/-Lrp1^f/fAlb-Cre⁺ mice. To mimic an intreventional setting we tested the impact of therapeutic apoC-III lowering in combination with a switch to a lipid-poor chow diet intervention after 12-week Western diet feeding. We observed that apoC-III ASO treatment significantly reduced atherosclerotic lesion size progression when an additive triglyceride-lowering was achieved. No differences in lesion development were observed in similarly treated Ldlr^-/-Lrp1^f/fAlb-Cre⁺ mice wherein no additive triglyceride-lowering was achieved by apoC-III ASO intervention.

Conclusions

Our data highlight that the impact of apoC-III on atherogenesis depends on its lipid-modifying properties. Hence, our findings suggest that interventional apoC-III lowering in hypertriglyceridemia patients can prevent plaques rupture and reduce CVD-associated mortality.

Background and Aims

Compromised secretion of very low-density lipoprotein (VLDL) can result in hepatic lipid accumulation, a risk factor for non-alcoholic fatty liver disease (NAFLD). Basic knowledge of VLDL assembly and the secretion pathway may help to find solutions for NAFLD. Here, we present a novel gene, SMLR1, identified through contextual co-expression analysis with APOC3 as anchor. SMLR1 expression is strictly confined to liver and small intestine. Here, we present a first study on the role of SMLR1 in hepatic and plasma lipid metabolism.

Methods

Using somatic CRISPR/Cas9 gene editing, we downregulated Smlr1 expression in livers of wild-type male and female mice, fed a chow diet. Liver lipids were extracted, and VLDL secretion rate was assessed after poloxamer injection. Lipoprotein profiling was conducted by FPLC. Immortalized human hepatoma cells where used for localization studies.

Results

Downregulation of Smlr1 at the mRNA level (80%) and protein level (67%), resulted in 50% reduction of plasma cholesterol and triglycerides (p<0.001 for both), and increased hepatic lipid levels (>2.9fold, p<0.001). In line, VLDL secretion rate was reduced by 45% (Fig1A). Both LDL and HDL cholesterol were reduced (Fig1B). SMLR1 was found to be localized in the endoplasmic reticulum (ER) and Golgi complex.

Conclusions

Smlr1 is a key gene in the regulation of plasma and hepatic lipid metabolism. It is noteworthy that, until now, the phenotype resembles a phenocopy of the liver-specific MTTP-/- mice. SMLR1 is localized in the ER and Golgi complex and anticipated to play a role in the trafficking of lipoproteins.

Background and Aims

Tirzepatide, a dual GIP/GLP-1 receptor agonist, was recently shown to cause robust weight loss in patients with Type II Diabetes (Frias et al. 2018). Since GIPR agonism stimulates lipolysis in white adipose tissue and GLP1R agonism promotes brown adipose tissue (BAT) thermogenesis, we hypothesized that combining GIPR and GLP1R agonism enhances the fatty acid (FA) flux to BAT to facilitate thermogenesis, thereby alleviating dyslipidemia and atherosclerosis development.

Methods

Dyslipidemic Western-type diet fed female APOE*3-Leiden.CETP mice were subcutaneously injected with either vehicle, a GIPR agonist (GIPFA-085; 300 nmol/kg/day), a GLP1R agonist (GLP-140; 30 nmol/kg/day) or both agonists for up to 10 weeks. Plasma triglyceride (TG) levels were measured, and TG-rich lipoprotein (TRL) metabolism was assessed using injection of glycerol tri[³H]oleate and [¹⁴C]cholesteryl oleate-labeled TRL-like particles. In the aortic valve region, atherosclerotic lesions were scored.

Results

GLP1R agonism lowered body weight (-2.0 g) and increased the uptake of VLDL-TG-derived FA by BAT (+157%) compared to vehicle. On these parameters concomitant GIPR and GLP1R agonism outperformed GLP1R agonism alone (body weight -2.8 g; VLDL-TG derived FA uptake by BAT +191%). Concomitant GIPR and GLP1R agonism, but not GLP1R agonism or GIPR agonism alone, tended to lower plasma TG levels (-46%) and markedly increased hepatic TRL-remnant uptake (+67%). Importantly, concomitant GIPR and GLP1R agonism decreased atherosclerotic lesion progression (-35% severe lesions).

Conclusions

Concomitant GIPR and GLP1R agonism stimulates TRL lipolysis and clearance more than the individual agonists and correspondingly attenuates atherosclerosis development. Current studies evaluate the effects of co-treatment on atherosclerosis in an obese setting.

Background and Aims

Homozygosity for loss-of-function mutations in the ANGPTL3 gene leads to a rare phenotype called familial combined hypolipidemia (FHBL2), characterized by a comprehensive reduction of circulating lipoproteins (VLDL, LDL and HDL) and reduced risk of atherosclerosis. Regulatory T-cells (Treg) play a role as inflammation modulators in the atherosclerotic plaque environment and are highly sensitive to metabolic changes. Indeed, recent evidence has highlighted the central role of cholesterol and the mevalonate pathway in Treg functionality.

The aim of this study was to investigate the possible effect of hypolipidemia due to ANGPTL3 deficiency in modulating Treg distribution and characteristics.

Methods

Peripheral blood mononuclear cells (PBMCs) isolated from 5 FHBL2 subjects and 5 healthy sex and age -matched control subjects were analyzed by flow cytometry (FC). Tregs were gated as CD4⁺/CD127^low/FOXP3⁺ cells. HELIOS staining was used as a stability marker, whereas CD45RA^- was used as a marker of Treg cell activation. Cellular lipid content was analyzed through Bodipy staining.

Results

FHBL2 subjects showed an increased Treg fraction (7.80±1.61% vs 4.52±1.05 %, P<0.01), with a stable effector phenotype. Percentages of circulating Tregs were inversely related to plasma levels of total (r=-0.7212; P=0.023) and LDL cholesterol (r= -0.7818; p=0.0105). Bodipy staining highlighted a significantly lower lipid content in activated Tregs of FHBL2 subjects when compared to healthy controls (2613 average gMFI vs. 2033 average gMFI, P<0.05).

Conclusions

The expansion of Treg population characterized by with reduced lipid content in FHBL2 subjects might potentially contribute to the atheroprotective role of ANGPTL3 deficiency throughout the induction of a regulatory immune profile.