ANGPTL8 promotes the ability of ANGPTL3 to bind and inhibit lipoprotein lipase

Angiopoietin-like protein inhibitors: Promising agents for the treatment of familial hypercholesterolemia and atherogenic dyslipidemia

BACKGROUND AND AIMS

This review examines the physiological functions of Angiopoietin-like proteins (ANGPTLs) in lipid metabolism and the epidemiology of atherosclerotic cardiovascular disease (ASCVD), while discussing their potential as therapies for dyslipidemias.

METHODS

A review of contemporary literature on ANGPTLs was conducted.

RESULTS

ANGPTLs comprise eight secreted proteins that share structural similarities with the angiopoietin family and serve as key regulators of various physiological and biochemical functions. Notably, ANGPTL3, ANGPTL4, and ANGPTL8 act as physiological inhibitors of lipoprotein lipase (LPL), playing a crucial role in lipoprotein and triglyceride metabolism in response to the body's nutritional status. A deficiency in these proteins is linked to hypolipidemia, characterized by a decrease in all lipid fractions, and genetic studies indicate a reduced risk of ASCVD in individuals with loss-of-function variants in ANGPTL3 and ANGPTL4. Conversely, elevated levels of ANGPTL3, ANGPTL4, and ANGPTL8 seem to increase the risk of cardiovascular disease. The role of ANGPTLs in regulating lipid metabolism underscores their potential in targeted therapies for managing dyslipidemias and lowering ASCVD risk, particularly in patients with difficult-to-control dyslipidemia phenotypes, such as homozygous Familial Hypercholesterolemia and mixed dyslipidemia.

CONCLUSIONS

The development of ANGPTL inhibitors could provide an effective strategy for preventing ASCVD.

Bridging systemic metabolic dysfunction and Alzheimer's disease: the liver interface

Alzheimer's disease (AD) is increasingly recognized as a systemic disorder with a substantial metabolic disorder component, where the liver significantly impacts the brain via the liver-brain axis. Key mechanisms include the liver's role in clearing peripheral β-amyloid (Aβ), the influence of hepatic enzymes and metabolites on cognitive decline, and the systemic effects of metabolic disorders on AD progression. Hepatokines, liver-secreted proteins including fibroblast growth factor (FGF)-21, selenoprotein P (SELENOP), Fetuin-A, Midbrain astrocyte-derived neurotrophic factor (MANF), apolipoprotein J (ApoJ), sex hormone-binding globulin (SHBG), Adropin and Angiopoietin-like protein 3 (ANGPTL3), could regulate insulin sensitivity, lipid metabolism, oxidative stress, immune responses, and neurotrophic support. These pathways are closely linked to core AD pathologies, including Aβ aggregation, tau hyperphosphorylation, neuroinflammation, oxidative stress and mitochondrial dysfunction. Lifestyle interventions, including exercise and dietary modifications, that regulate hepatokines expression may offer novel preventive and therapeutic strategies for AD. This review synthesizes current knowledge on the liver-brain crosstalk in AD, emphasizing the mechanistic role of liver in bridging metabolic dysfunction with neurodegeneration and underscores the diagnostic and therapeutic potential of hepatokines in addressing AD's complex pathology.

Genetics of remnant cholesterol

PURPOSE OF REVIEW

Remnant cholesterol is receiving increasing attention as a target to reduce residual atherosclerotic cardiovascular disease (ASCVD) risk in individuals already treated with statins. New therapeutic options as antisense oligonucleotides, small interfering RNA, and monoclonal antibodies allow specific targeting of genes and proteins to counter pathological pathways promoted by these genes. Identifying genetic determinants of remnant cholesterol and relating these to risk of ASCVD is thus an appealing path to identifying and evaluating new and existing drug targets.

RECENT FINDINGS

Human genetic epidemiology has identified several genetic variants in genes involved in lipoprotein metabolism with effect on plasma concentrations of remnant cholesterol. Lipoprotein lipase (LPL) is central to the metabolism of remnant lipoproteins and plasma concentrations of remnant cholesterol, and several genes, including APOC3, ANGPTL3 and ANGPTL4, whose gene products regulate activity of LPL, are important determinants of remnant cholesterol.

SUMMARY

Current opinion is that remnant cholesterol is a likely causal factor in the development of ASCVD. Human genetic studies have identified several genes, many involved in LPL function, affecting remnant cholesterol concentrations, some of which are already used as therapeutic targets, and others which are subject to investigation of their remnant cholesterol and triglyceride-lowering effect in clinical trials.

The vicious circle of chronic kidney disease and hypertriglyceridemia: What is first, the hen or the egg?

Chronic kidney disease (CKD) is documented to cause alterations in lipid metabolism, and this was considered a potent driver of increased cardiovascular risk. Among the diverse alteration of lipid traits in CKD, research endeavours have predominantly concentrated on low-density lipoproteins (LDL) in view of the potent pro-atherogenic role of these lipoprotein particles and the demonstration of protective cardiovascular effect of reducing LDL. However, few studies have focused on the metabolism of triglyceride-rich lipoproteins and even fewer on their role in causing kidney damage. Therefore, the comprehensive description of the impact of hypertriglyceridemia (HTG) in CKD pathophysiology remains largely undetermined. This reflects the difficulty of disentangling the independent role of triglycerides (TG) in the complex, bidirectional relationship between TG and kidney disease. Abnormal neutral lipid accumulation in the intrarenal vasculature and renal cells eventually due to HTG may also promote glomerular injury, throughout mechanisms including oxidative stress, mitochondrial dysfunction and proinflammatory responses. While epidemiological and experimental evidence suggests a potential role of TG in kidney damage, the causal mechanisms and their clinical relevance remain unclear, representing a significant area for future investigation. This review aims to highlight the intricate interplay between TG metabolism and kidney disease, shedding light on the mechanisms through which HTG may influence kidney functionality.

ANGPTL3/8 is an atypical unfoldase that regulates intravascular lipolysis by catalyzing unfolding of lipoprotein lipase

Lipoprotein lipase (LPL) carries out the lipolytic processing of triglyceride-rich lipoproteins (TRL) along the luminal surface of capillaries. LPL activity is regulated by the angiopoietin-like proteins (ANGPTL3, ANGPTL4, ANGPTL8), which control the delivery of TRL-derived lipid nutrients to tissues in a temporal and spatial fashion. This regulation of LPL mediates the partitioning of lipid delivery to adipose tissue and striated muscle according to nutritional status. A complex between ANGPTL3 and ANGPTL8 (ANGPTL3/8) inhibits LPL activity in oxidative tissues, but its mode of action has remained unknown. Here, we used biophysical techniques to define how ANGPTL3/8 and ANGPTL3 interact with LPL and how they drive LPL inactivation. We demonstrate, by mass photometry, that ANGPTL3/8 is a heterotrimer with a 2:1 ANGPTL3:ANGPTL8 stoichiometry and that ANGPTL3 is a homotrimer. Hydrogen-deuterium exchange mass spectrometry (HDX-MS) studies revealed that ANGPTL3/8 and ANGPTL3 use the proximal portion of their N-terminal α-helices to interact with sequences surrounding the catalytic pocket in LPL. That binding event triggers unfolding of LPL's α/β-hydrolase domain and irreversible loss of LPL catalytic activity. The binding of LPL to its endothelial transporter protein (GPIHBP1) or to heparan-sulfate proteoglycans protects LPL from unfolding and inactivation, particularly against the unfolding triggered by ANGPTL3. Pulse-labeling HDX-MS studies revealed that ANGPTL3/8 and ANGPTL3 catalyze LPL unfolding in an ATP-independent fashion, which categorizes these LPL inhibitors as atypical unfoldases. The catalytic nature of LPL unfolding by ANGPTL3/8 explains why low plasma concentrations of ANGPTL3/8 are effective in inhibiting a molar excess of LPL in capillaries.

Circulating ANGPTL3/8 Concentrations Are Associated With an Atherogenic Lipoprotein Profile and Increased CHD Risk in Swedish Population-Based Studies

BACKGROUND

Binding of ANGPTL (angiopoietin-like protein)-3 to ANGPTL8 generates a protein complex (ANGPTL3/8) that strongly inhibits LPL (lipoprotein lipase) activity, as compared with ANGPTL3 alone, suggesting that ANGPTL3/8 concentrations are critical for the regulation of circulation lipoprotein concentrations and subsequent increased coronary heart disease (CHD) risk. To test this hypothesis in humans, we evaluated the associations of circulating free ANGPTL3 and ANGPTL3/8 complex concentrations with lipoprotein concentrations and CHD risk in 2 prospective cohort studies.

METHODS

Fasting blood samples were obtained in conjunction with the baseline evaluation of 9479 subjects from 2 population-based Swedish cohorts of middle-aged men and women. Standard biochemical blood analyses, including all lipid/lipoprotein measurements, were performed in these samples at baseline. Additional serum samples were stored at -80 °C and used at a later stage for ANGPTL3 and ANGPTL3/8 concentration measurements. Information about incident CHD was obtained for both cohorts by matching to the Swedish National Patient Register and the Cause of Death Register.

RESULTS

ANGPTL3 concentrations showed modest, positive associations with all lipoprotein concentrations but were not associated with CHD risk. In contrast, ANGPTL3/8 concentrations were associated in both cohorts with an atherogenic lipoprotein profile (characterized by increased triglyceride and LDL [low-density lipoprotein] concentrations and reduced HDL [high-density lipoprotein] concentrations). In the combined cohort, ANGPTL3/8 was associated with increased CHD risk. Hazard ratio per 1 SD increase was 1.10 (95% CI, 1.03-1.17) after adjustment for age, sex, cohort, smoking, and hypertension.

CONCLUSIONS

Elevated concentrations of ANGPTL3/8, but not ANGPTL3, are associated with an atherogenic lipoprotein profile and increased CHD risk in humans.

Lipoprotein Lipase: Structure, Function, and Genetic Variation

Biallelic rare pathogenic loss-of-function (LOF) variants in lipoprotein lipase (LPL) cause familial chylomicronemia syndrome (FCS). Heterozygosity for these same variants is associated with a highly variable plasma triglyceride (TG) phenotype ranging from normal to severe hypertriglyceridemia (HTG), with longitudinal variation in phenotype severity seen often in a given carrier. Here, we provide an updated overview of genetic variation in LPL in the context of HTG, with a focus on disease-causing and/or disease-associated variants. We provide a curated list of 300 disease-causing variants discovered in LPL, as well as an exon-by-exon breakdown of the LPL gene and protein, highlighting the impact of variants and the various functional residues of domains of the LPL protein. We also provide a curated list of variants of unknown or uncertain significance, many of which may be upgraded to pathogenic/likely pathogenic classification should an additional case and/or segregation data be reported. Finally, we also review the association between benign/likely benign variants in LPL, many of which are common polymorphisms, and the TG phenotype.

Adipocyte Angptl8 deletion improves glucose and energy metabolism and obesity associated inflammation in mice

Angiopoietin-like protein 8 (Angptl8), expressed in the liver and adipocytes, forms a complex with Angptl3 or Angptl4, which regulates lipoprotein lipase and triglyceride metabolism. However, the precise functions of adipocyte Angptl8 remain elusive. Here we report that adipocyte-specific inducible Angptl8-knockout (AT-A8-KO) male mice on normal diet showed minor phenotypic changes, but after a high-fat high fructose (HFHF) diet, exhibited decreased body weight gain and glycemia, elevated rectal temperature and early dark phase energy expenditure compared to the Cre controls. AT-A8-KO mice also displayed improved glucose tolerance, a trend for better insulin sensitivity, improved insulin-stimulated glucose uptake in adipose tissues, and reduced visceral adipose tissue crown-like structures, plasma MCP-1 and leptin levels. The results indicate the importance of adipose Angptl8 in the context of nutri-stress and obesity, as its deletion in mice promotes a metabolically healthy obese phenotype by slightly ameliorating obesity, improving glucose and energy homeostasis, and mitigating inflammation.

Postprandial exercise regulates tissue-specific triglyceride uptake through angiopoietin-like proteins

Fuel substrate switching between carbohydrates and fat is essential for maintaining metabolic homeostasis. During aerobic exercise, the predominant energy source gradually shifts from carbohydrates to fat. While it is well known that exercise mobilizes fat storage from adipose tissues, it remains largely obscure how circulating lipids are distributed tissue-specifically according to distinct energy requirements. Here, we demonstrate that aerobic exercise is linked to nutrient availability to regulate tissue-specific activities of lipoprotein lipase (LPL), the key enzyme catabolizing circulating triglyceride (TG) for tissue uptake, through the differential actions of angiopoietin-like (ANGPTL) proteins. Exercise reduced the tissue binding of ANGPTL3 protein, increasing LPL activity and TG uptake in the heart and skeletal muscle in the postprandial state specifically. Mechanistically, exercise suppressed insulin secretion, attenuating hepatic Angptl8 transcription through the PI3K/mTOR/CEBPα pathway, which is imperative for the tissue binding of its partner ANGPTL3. Constitutive expression of ANGPTL8 hampered lipid utilization and resulted in cardiac dysfunction in response to exercise. Conversely, exercise promoted the expression of ANGPTL4 in white adipose tissues, overriding the regulatory actions of ANGPTL8/ANGPTL3 in suppressing adipose LPL activity, thereby diverting circulating TG away from storage. Collectively, our findings show an overlooked bifurcated ANGPTL-LPL network that orchestrates fuel switching in response to aerobic exercise.

The minor allele of ANGPTL8 rs2278426 has a protective effect against CAD in T2DM patients

BACKGROUND

Coronary artery disease (CAD) is the leading cause of death worldwide despite advanced treatment and diagnosis strategies. Angiopoietin-like protein 8 (ANGPTL8) mainly functions in the lipid mechanism, which is a dysregulated mechanism during CAD pathogenesis. In this study, we aimed to determine the associations between an ANGPTL8 polymorphism rs2278426 and the severity, presence, and risk factors of CAD.

METHODS

A total of 1367 unrelated Turkish individuals who underwent coronary angiography were recruited for the study and grouped as CAD (n = 736, ≥50 stenosis) and non-CAD (n = 549, ≤30 stenosis). Also, subjects were further divided into groups regarding type 2 diabetes mellitus (T2DM) status. Subjects were genotyped for rs2278426 (C/T) by quantitative real-time PCR. Secondary structure analyses of protein interactions were revealed using I-TASSER and PyMOL.

RESULTS

Among CAD patients, T allele carriage frequency was lower in the T2DM group (p = 0.046). Moreover, in male non-CAD group, T allele carriage was more prevalent among T2DM patients than non-T2DM (p = 0.033). In logistic regression analysis adjusted for obesity, T allele carrier males had an increased risk for T2DM in non-CAD group (OR = 2.244, 95 % CI: 1.057-4.761, p = 0.035). Also, in T2DM group, stenosis (p = 0.002) and SYNTAX score (p = 0.040) were lower in T allele carrier males than in non-carriers. Analyzes of secondary structure showed that ANGPTL8 could not directly form complexes with ANGPTL3 or ANGPTL4.

CONCLUSION

In conclusion, T allele carriage of ANGPTL8 rs2278426 has a protective effect on CAD in T2DM patients. Further research should be conducted to explore the association between ANGPTL8 polymorphism (rs2778426) and CAD.

APOA5 deficiency causes hypertriglyceridemia by reducing amounts of lipoprotein lipase in capillaries

Apolipoprotein AV (APOA5) deficiency causes hypertriglyceridemia in mice and humans. For years, the cause remained a mystery, but the mechanisms have now come into focus. Here, we review progress in defining APOA5's function in plasma triglyceride metabolism. Biochemical studies revealed that APOA5 binds to the angiopoietin-like protein 3/8 complex (ANGPTL3/8) and suppresses its ability to inhibit the activity of lipoprotein lipase (LPL). Thus, APOA5 deficiency is accompanied by increased ANGPTL3/8 activity and lower levels of LPL activity. APOA5 deficiency also reduces amounts of LPL in capillaries of oxidative tissues (e.g., heart, brown adipose tissue). Cell culture experiments revealed the likely explanation: ANGPTL3/8 detaches LPL from its binding sites on the surface of cells, and that effect is blocked by APOA5. Both the low intracapillary LPL levels and the high plasma triglyceride levels in Apoa5-/- mice are normalized by recombinant APOA5. Carboxyl-terminal sequences in APOA5 are crucial for its function; a mutant APOA5 lacking 40-carboxyl-terminal residues cannot bind to ANGPTL3/8 and lacks the ability to change intracapillary LPL levels or plasma triglyceride levels in Apoa5-/- mice. Also, an antibody against the last 26 amino acids of APOA5 reduces intracapillary LPL levels and increases plasma triglyceride levels in wild-type mice. An inhibitory ANGPTL3/8-specific antibody functions as an APOA5-mimetic reagent, increasing intracapillary LPL levels and lowering plasma triglyceride levels in both Apoa5-/- and wild-type mice. That antibody is a potentially attractive strategy for treating elevated plasma lipid levels in human patients.

A unified model for regulating lipoprotein lipase activity

The regulation of triglyceride (TG) tissue distribution, storage, and utilization, a fundamental process of energy homeostasis, critically depends on lipoprotein lipase (LPL). We review the intricate mechanisms by which LPL activity is regulated by angiopoietin-like proteins (ANGPTL3, 4, 8), apolipoproteins (APOA5, APOC3, APOC2), and the cAMP-responsive element-binding protein H (CREBH). ANGPTL8 functions as a molecular switch, through complex formation, activating ANGPTL3 while deactivating ANGPTL4 in their LPL inhibition. The ANGPTL3-4-8 model integrates the roles of the aforementioned proteins in TG partitioning between white adipose tissue (WAT) and oxidative tissues (heart and skeletal muscles) during the feed/fast cycle. This model offers a unified perspective on LPL regulation, providing insights into TG metabolism, metabolic diseases, and therapeutics.

Xanthohumol, a prenylated chalcone, regulates lipid metabolism by modulating the LXRα/RXR-ANGPTL3-LPL axis in hepatic cell lines and high-fat diet-fed zebrafish models

Angiopoietin-like 3 (ANGPTL3) acts as an inhibitor of lipoprotein lipase (LPL), impeding the breakdown of triglyceride-rich lipoproteins (TGRLs) in circulation. Targeting ANGPTL3 is considered a novel strategy for improving dyslipidemia and atherosclerotic cardiovascular diseases (ASCVD). Hops (Humulus lupulus L.) contain several bioactive prenylflavonoids, including xanthohumol (Xan), isoxanthohumol (Isoxan), 6-prenylnaringenin (6-PN), and 8-prenylnaringenin (8-PN), with the potential to manage lipid metabolism. The aim of this study was to investigate the lipid-lowering effects of Xan, the effective prenylated chalcone in attenuating ANGPTL3 transcriptional activity, both in vitro using hepatic cells and in vivo using zebrafish models, along with exploring the underlying mechanisms. Xan (10 and 20 μM) significantly reduced ANGPTL3 mRNA and protein expression in HepG2 and Huh7 cells, leading to a marked decrease in secreted ANGPTL3 proteins via hepatic cells. In animal studies, orally administered Xan significantly alleviated plasma triglyceride (TG) and cholesterol levels in zebrafish fed a high-fat diet. Furthermore, it reduced hepatic ANGPTL3 protein levels and increased LPL activity in zebrafish models, indicating its potential to modulate lipid profiles in circulation. Furthermore, molecular docking results predicted that Xan exhibits a higher binding affinity to interact with liver X receptor α (LXRα) and retinoic acid X receptor (RXR) than their respective agonists, T0901317 and 9-Cis-retinoic acid (9-Cis-RA). We observed that Xan suppressed hepatic ANGPTL3 expression by antagonizing the LXRα/RXR-mediated transcription. These findings suggest that Xan ameliorates dyslipidemia by modulating the LXRα/RXR-ANGPTL3-LPL axis. Xan represents a novel potential inhibitor of ANGPTL3 for the prevention or treatment of ASCVD.

ANGPTL3 inhibition, dyslipidemia, and cardiovascular diseases

Optimal management of low-density lipoprotein cholesterol (LDL-C) is a central tenet in the primary and secondary prevention of atherosclerotic cardiovascular disease (ASCVD). However, significant residual cardiovascular risk remains despite achieving guideline-directed LDL-C levels, in part due to mixed hyperlipidemia with elevated fasting and non-fasting triglyceride-rich lipoprotein levels. Advances in human genetics have identified angiopoietin-like 3 (ANGPTL3) as a promising therapeutic target to lower cardiovascular risk. Evidence accrued from genetic epidemiological studies demonstrate that ANGPTL3 loss of function is strongly associated with lowering of circulating LDL-C, triglyceride-rich lipoproteins and concurrent risk reduction in development of coronary artery disease. Pharmacological inhibition of ANGPTL3 with monoclonal antibodies, antisense oligonucleotides and gene editing are in development with early studies showing their safety and efficacy in lowering in both, LDL-C and TGs, circumventing a key limitation of previous therapies. Monoclonal antibodies targeting ANGPTL3 are approved for clinical use in homozygous familial hypercholesteremia in USA and Europe. Although promising, future studies focusing on long-term beneficial effect in reducing cardiovascular events with inhibition of ANGPTL3 are warranted.

Angiopoietin-like protein 8: a multifaceted protein instrumental in regulating triglyceride metabolism

PURPOSE OF REVIEW

The angiopoietin-like (ANGPTL) proteins ANGPTL3 and ANGPTL4 are critical lipoprotein lipase (LPL) inhibitors. This review discusses the unique ability of the insulin-responsive protein ANGPTL8 to regulate triglyceride (TG) metabolism by forming ANGPTL3/8 and ANGPTL4/8 complexes that control tissue-specific LPL activities.

RECENT FINDINGS

After feeding, ANGPTL4/8 acts locally in adipose tissue, has decreased LPL-inhibitory activity compared to ANGPTL4, and binds tissue plasminogen activator (tPA) and plasminogen to generate plasmin, which cleaves ANGPTL4/8 and other LPL inhibitors. This enables LPL to be fully active postprandially to promote efficient fatty acid (FA) uptake and minimize ectopic fat deposition. In contrast, liver-derived ANGPTL3/8 acts in an endocrine manner, has markedly increased LPL-inhibitory activity compared to ANGPTL3, and potently inhibits LPL in oxidative tissues to direct TG toward adipose tissue for storage. Circulating ANGPTL3/8 levels are strongly correlated with serum TG, and the ANGPTL3/8 LPL-inhibitory epitope is blocked by the TG-lowering protein apolipoprotein A5 (ApoA5).

SUMMARY

ANGPTL8 plays a crucial role in TG metabolism by forming ANGPTL3/8 and ANGPTL4/8 complexes that differentially modulate LPL activities in oxidative and adipose tissues respectively. Selective ANGPTL8 inhibition in the context of the ANGPTL3/8 complex has the potential to be a promising strategy for treating dyslipidemia.

Silencing ANGPTL8 reduces mouse preadipocyte differentiation and insulin signaling

ANGPTL8, expressed mainly in the liver and adipose tissue, regulates the activity of lipoprotein lipase (LPL) present in the extracellular space and triglyceride (TG) metabolism through its interaction with ANGPTL3 and ANGPTL4. Whether intracellular ANGPTL8 can also exert effects in tissues where it is expressed is uncertain. ANGPTL8 expression was low in preadipocytes and much increased during differentiation. To better understand the role of intracellular ANGPTL8 in adipocytes and assess whether it may play a role in adipocyte differentiation, we knocked down its expression in normal mouse subcutaneous preadipocytes. ANGPTL8 knockdown reduced adipocyte differentiation, cellular TG accumulation and also isoproterenol-stimulated lipolysis at day 7 of differentiation. RNA-Seq analysis of ANGPTL8 siRNA or control siRNA transfected SC preadipocytes on days 0, 2, 4 and 7 of differentiation showed that ANGPTL8 knockdown impeded the early (day 2) expression of adipogenic and insulin signaling genes, PPARγ, as well as genes related to extracellular matrix and NF-κB signaling. Insulin mediated Akt phosphorylation was reduced at an early stage during adipocyte differentiation. This study based on normal primary cells shows that ANGPTL8 has intracellular actions in addition to effects in the extracellular space, like modulating LPL activity. Preadipocyte ANGPTL8 expression modulates their differentiation possibly via changes in insulin signaling gene expression.

Genetic variation in apolipoprotein A-V in hypertriglyceridemia

PURPOSE OF REVIEW

While biallelic rare APOA5 pathogenic loss-of-function (LOF) variants cause familial chylomicronemia syndrome, heterozygosity for such variants is associated with highly variable triglyceride phenotypes ranging from normal to severe hypertriglyceridemia, often in the same individual at different time points. Here we provide an updated overview of rare APOA5 variants in hypertriglyceridemia.

RECENT FINDINGS

Currently, most variants in APOA5 that are considered to be pathogenic according to guidelines of the American College of Medical Genetics and Genomics are those resulting in premature termination codons. There are minimal high quality functional data on the impact of most rare APOA5 missense variants; many are considered as variants of unknown or uncertain significance. Furthermore, particular common polymorphisms of APOA5 , such as p.Ser19Trp and p.Gly185Cys in Caucasian and Asian populations, respectively, are statistically overrepresented in hypertriglyceridemia cohorts and are sometimes misattributed as being causal for chylomicronemia, when they are merely risk alleles for hypertriglyceridemia.

SUMMARY

Both biallelic and monoallelic LOF variants in APOA5 are associated with severe hypertriglyceridemia, although the biochemical phenotype in the monoallelic state is highly variable and is often exacerbated by secondary factors. Currently, with few exceptions, the principal definitive mechanism for APOA5 pathogenicity is through premature truncation. The pathogenic mechanisms of most missense variants in APOA5 remain unclear and require additional functional experiments or family studies.

Zinc finger protein ZNF638 regulates triglyceride metabolism via ANGPTL8 in an estrogen dependent manner

BACKGROUND AND AIM

Triglyceride (TG) levels are closely related to obesity, fatty liver and cardiovascular diseases, while the regulatory factors and mechanism for triglyceride homeostasis are still largely unknown. Zinc Finger Protein 638 (ZNF638) is a newly discovered member of zinc finger protein family for adipocyte function in vitro. The aim of the present work was to investigate the role of ZNF638 in regulating triglyceride metabolism in mice.

METHODS

We generated ZNF638 adipose tissue specific knockout mice (ZNF638 FKO) by cross-breeding ZNF638 flox to Adiponectin-Cre mice and achieved adipose tissue ZNF638 overexpression via adenoviral mediated ZNF638 delivery in inguinal adipose tissue (iWAT) to examined the role and mechanisms of ZNF638 in fat biology and whole-body TG homeostasis.

RESULTS

Although ZNF638 FKO mice showed similar body weights, body composition, glucose metabolism and serum parameters compared to wild-type mice under chow diet, serum TG levels in ZNF638 FKO mice were increased dramatically after refeeding compared to wild-type mice, accompanied with decreased endothelial lipoprotein lipase (LPL) activity and increased lipid absorption of the small intestine. Conversely, ZNF638 overexpression in iWAT reduced serum TG levels while enhanced LPL activity after refeeding in female C57BL/6J mice and obese ob/ob mice. Specifically, only female mice exhibited altered TG metabolism upon ZNF638 expression changes in fat. Mechanistically, RNA-sequencing analysis revealed that the TG regulator angiopoietin-like protein 8 (Angptl8) was highly expressed in iWAT of female ZNF638 FKO mice. Neutralizing circulating ANGPTL8 in female ZNF638 FKO mice abolished refeeding-induced TG elevation. Furthermore, we demonstrated that ZNF638 functions as a transcriptional repressor by recruiting HDAC1 for histone deacetylation and broad lipid metabolic gene suppression, including Angptl8 transcription inhibition. Moreover, we showed that the sexual dimorphism is possibly due to estrogen dependent regulation on ZNF638-ANGPTL8 axis.

CONCLUSION

We revealed a role of ZNF638 in the regulation of triglyceride metabolism by affecting Angptl8 transcriptional level in adipose tissue with sexual dimorphism.

Eight weeks of daily cottonseed oil intake attenuates postprandial angiopoietin-like proteins 3 and 4 responses compared to olive oil in adults with hypercholesterolemia: A secondary analysis of a randomized clinical trial

Angiopoietin-like proteins (ANGPTLs) -3, -4, and -8 are regulators of lipid metabolism and have been shown to respond to changes in dietary fats. It is unknown how ANGPTLs respond to cottonseed oil (CSO) and olive oil (OO) consumption in a population with hypercholesterolemia. The purpose of this study was to determine the impact of CSO vs. OO consumption on fasting and postprandial ANGPTL responses in adults with hypercholesterolemia. We hypothesized that CSO would have lower fasting and postprandial ANGPTL responses compared with OO. Forty-two adults with high cholesterol completed a single-blind, randomized trial comparing CSO (n = 21) vs. OO (n = 21) diet enrichment. An 8-week partial outpatient feeding intervention provided ∼60% of the volunteers' total energy expenditure (∼30% of total energy expenditure as CSO or OO). The remaining 40% was not controlled. Fasting blood draws were taken at pre-, mid-, and postintervention visits. Volunteers consumed a high saturated fat meal followed by 5 hours of blood draws pre- and postvisits. Fasting ANGPTL3 had a marginally significant treatment by visit interaction (P = .06) showing an increase from pre- to postintervention in CSO vs. OO (CSO: 385.1 ± 27.7 to 440.3 ± 33.9 ng/mL; OO: 468.2 ± 38.3 to 449.2 ± 49.5 ng/mL). Both postprandial ANGPTL3 (P = .02) and ANGPTL4 (P < .01) had treatment by visit interactions suggesting increases from pre- to postintervention in OO vs. CSO with no differences between groups in ANGPTL8. These data show a worsening (increase) of postprandial ANGPTLs after the OO, but not CSO, intervention. This aligns with previously reported data in which postprandial triglycerides were protected from increases compared with OO. ANGPTLs may mediate protective effects of CSO consumption on lipid control. This trial was registered at clinicaltrials.gov (NCT04397055).

Endothelial lipase variant T111I does not alter inhibition by angiopoietin-like proteins

High levels of HDL-C are correlated with a decreased risk of cardiovascular disease. HDL-C levels are modulated in part by the secreted phospholipase, endothelial lipase (EL), which hydrolyzes the phospholipids of HDL and decreases circulating HDL-C concentrations. A 584C/T polymorphism in LIPG, the gene which encodes EL, was first identified in individuals with increased HDL levels. This polymorphism results in a T111I point mutation the EL protein. The association between this variant, HDL levels, and the risk of coronary artery disease (CAD) in humans has been extensively studied, but the findings have been inconsistent. In this study, we took a biochemical approach, investigating how the T111I variant affected EL activity, structure, and stability. Moreover, we tested whether the T111I variant altered the inhibition of phospholipase activity by angiopoietin-like 3 (ANGPTL3) and angiopoietin-like 4 (ANGPTL4), two known EL inhibitors. We found that neither the stability nor enzymatic activity of EL was altered by the T111I variant. Moreover, we found no difference between wild-type and T111I EL in their ability to be inhibited by ANGPTL proteins. These data suggest that any effect this variant may have on HDL-C levels or cardiovascular disease are not mediated through alterations in these functions.

Effects of exercise training on ANGPTL3/8 and ANGPTL4/8 and their associations with cardiometabolic traits

Angiopoietin-like protein (ANGPTL) complexes 3/8 and 4/8 are established inhibitors of LPL and novel therapeutic targets for dyslipidemia. However, the effects of regular exercise on ANGPTL3/8 and ANGPTL4/8 are unknown. We characterized ANGPTL3/8 and ANGPTL4/8 and their relationship with in vivo measurements of lipase activities and cardiometabolic traits before and after a 5-month endurance exercise training intervention in 642 adults from the HERITAGE (HEalth, RIsk factors, exercise Training And GEnetics) Family Study. At baseline, higher levels of both ANGPTL3/8 and ANGPTL4/8 were associated with a worse lipid, lipoprotein, and cardiometabolic profile, with only ANGPTL3/8 associated with postheparin LPL and HL activities. ANGPTL3/8 significantly decreased with exercise training, which corresponded with increases in LPL activity and decreases in HL activity, plasma triglycerides, apoB, visceral fat, and fasting insulin (all P < 5.1 × 10-4). Exercise-induced changes in ANGPTL4/8 were directly correlated to concomitant changes in total cholesterol, LDL-C, apoB, and HDL-triglycerides and inversely related to change in insulin sensitivity index (all P < 7.0 × 10-4). In conclusion, exercise-induced decreases in ANGPTL3/8 and ANGPTL4/8 were related to concomitant improvements in lipase activity, lipid profile, and cardiometabolic risk factors. These findings reveal the ANGPTL3-4-8 model as a potential molecular mechanism contributing to adaptations in lipid metabolism in response to exercise training.

Macromolecular Interactions of Lipoprotein Lipase (LPL)

Lipoprotein lipase (LPL) is a critical enzyme in humans that provides fuel to peripheral tissues. LPL hydrolyzes triglycerides from the cores of lipoproteins that are circulating in plasma and interacts with receptors to mediate lipoprotein uptake, thus directing lipid distribution via catalytic and non-catalytic functions. Functional losses in LPL or any of its myriad of regulators alter lipid homeostasis and potentially affect the risk of developing cardiovascular disease-either increasing or decreasing the risk depending on the mutated protein. The extensive LPL regulatory network tunes LPL activity to allocate fatty acids according to the energetic needs of the organism and thus is nutritionally responsive and tissue dependent. Multiple pharmaceuticals in development manipulate or mimic these regulators, demonstrating their translational importance. Another facet of LPL biology is that the oligomeric state of the enzyme is also central to its regulation. Recent structural studies have solidified the idea that LPL is regulated not only by interactions with other binding partners but also by self-associations. Here, we review the complexities of the protein-protein and protein-lipid interactions that govern LPL structure and function.

Circumventing Cardiovascular Calamities: The Dawn of ANGPTL3 Blockade in Severe Dyslipidemia Management

The landscape of severe dyslipidemia treatment is undergoing a remarkable transformation with the advent of angiopoietin-like 3 (ANGPTL3) inhibitors. ANGPTL3, a pivotal regulator of lipoprotein lipase and endothelial lipase, orchestrates the catabolism of triglyceride-rich and high-density lipoproteins, thus playing a critical role in lipid homeostasis. This review article examines the therapeutic potential of ANGPTL3 blockade and its implications for patients with severe dyslipidemias, particularly those unresponsive to traditional lipid-lowering regimens. We delve into the molecular mechanisms by which ANGPTL3 influences lipid metabolism and appraise the clinical utility of emerging therapeutics, such as monoclonal antibodies and antisense oligonucleotides. Moreover, we discuss the impact of ANGPTL3 inhibition on cardiovascular risk factors and project its promising role in reducing cardiovascular morbidity and mortality. The narrative synthesizes data from recent clinical trials, including the efficacy and safety profiles of ANGPTL3 inhibitors, and forecasts the potential of these agents to revolutionize the management of dyslipidemic conditions. The advent of ANGPTL3-targeted therapies signifies a potential breakthrough in the therapeutic armamentarium against complex lipid disorders, heralding a new era of precision medicine in cardiovascular risk mitigation.

The GPIHBP1-LPL complex and its role in plasma triglyceride metabolism: Insights into chylomicronemia

GPIHBP1 is a protein found in the endothelial cells of capillaries that is anchored by glycosylphosphatidylinositol and binds to high-density lipoproteins. GPIHBP1 attaches to lipoprotein lipase (LPL), subsequently carrying the enzyme and anchoring it to the capillary lumen. Enabling lipid metabolism is essential for the marginalization of lipoproteins alongside capillaries. Studies underscore the significance of GPIHBP1 in transporting, stabilizing, and aiding in the marginalization of LPL. The intricate interplay between GPIHBP1 and LPL has provided novel insights into chylomicronemia in recent years. Mutations hindering the formation or reducing the efficiency of the GPIHBP1-LPL complex are central to the onset of chylomicronemia. This review delves into the structural nuances of the GPIHBP1-LPL interaction, the consequences of mutations in the complex leading to chylomicronemia, and cutting-edge advancements in chylomicronemia treatment.

Chromatin regulator SMARCAL1 modulates cellular lipid metabolism

Biallelic mutations of the chromatin regulator SMARCAL1 cause Schimke Immunoosseous Dysplasia (SIOD), characterized by severe growth defects and premature mortality. Atherosclerosis and hyperlipidemia are common among SIOD patients, yet their onset and progression are poorly understood. Using an integrative approach involving proteomics, mouse models, and population genetics, we investigated SMARCAL1's role. We found that SmarcAL1 interacts with angiopoietin-like 3 (Angptl3), a key regulator of lipoprotein metabolism. In vitro and in vivo analyses demonstrate SmarcAL1's vital role in maintaining cellular lipid homeostasis. The observed translocation of SmarcAL1 to cytoplasmic peroxisomes suggests a potential regulatory role in lipid metabolism through gene expression. SmarcAL1 gene inactivation reduces the expression of key genes in cellular lipid catabolism. Population genetics investigations highlight significant associations between SMARCAL1 genetic variations and body mass index, along with lipid-related traits. This study underscores SMARCAL1's pivotal role in cellular lipid metabolism, likely contributing to the observed lipid phenotypes in SIOD patients.

Hypertriglyceridemia in Apoa5-/- mice results from reduced amounts of lipoprotein lipase in the capillary lumen

Why apolipoprotein AV (APOA5) deficiency causes hypertriglyceridemia has remained unclear, but we have suspected that the underlying cause is reduced amounts of lipoprotein lipase (LPL) in capillaries. By routine immunohistochemistry, we observed reduced LPL staining of heart and brown adipose tissue (BAT) capillaries in Apoa5-/- mice. Also, after an intravenous injection of LPL-, CD31-, and GPIHBP1-specific mAbs, the binding of LPL Abs to heart and BAT capillaries (relative to CD31 or GPIHBP1 Abs) was reduced in Apoa5-/- mice. LPL levels in the postheparin plasma were also lower in Apoa5-/- mice. We suspected that a recent biochemical observation - that APOA5 binds to the ANGPTL3/8 complex and suppresses its capacity to inhibit LPL catalytic activity - could be related to the low intracapillary LPL levels in Apoa5-/- mice. We showed that an ANGPTL3/8-specific mAb (IBA490) and APOA5 normalized plasma triglyceride (TG) levels and intracapillary LPL levels in Apoa5-/- mice. We also showed that ANGPTL3/8 detached LPL from heparan sulfate proteoglycans and GPIHBP1 on the surface of cells and that the LPL detachment was blocked by IBA490 and APOA5. Our studies explain the hypertriglyceridemia in Apoa5-/- mice and further illuminate the molecular mechanisms that regulate plasma TG metabolism.

Gender-Dependent Associations between Serum Betatrophin Levels and Lipoprotein Subfractions in Diabetic and Nondiabetic Obese Patients

Betatrophin, also known as angiopoietin-like protein 8 (ANGPTL8), mainly plays a role in lipid metabolism. To date, associations between betatrophin and lipoprotein subfractions are poorly investigated. For this study, 50 obese patients with type 2 diabetes (T2D) and 70 nondiabetic obese (NDO) subjects matched in gender, age, and body mass index (BMI) as well as 49 gender- and age-matched healthy, normal-weight controls were enrolled. Serum betatrophin levels were measured with ELISA, and lipoprotein subfractions were analyzed using Lipoprint gel electrophoresis. Betatrophin concentrations were found to be significantly higher in the T2D and NDO groups compared to the controls in all subjects and in females, but not in males. We found significant positive correlations between triglyceride, very low density lipoprotein (VLDL), large LDL (low density lipoprotein), small LDL, high density lipoprotein (HDL) -6-10 subfractions, and betatrophin, while negative correlations were detected between betatrophin and IDL, mean LDL size, and HDL-1-5. Proportion of small HDL was the best predictor of betatrophin in all subjects. Small LDL and large HDL subfractions were found to be the best predictors in females, while in males, VLDL was found to be the best predictor of betatrophin. Our results underline the significance of serum betatrophin measurement in the cardiovascular risk assessment of obese patients with and without T2D, but gender differences might be taken into consideration.

Phylogenetic and expression analysis of the angiopoietin-like gene family and their role in lipid metabolism in pigs

OBJECTIVE

The objective of this study was to investigate the phylogenetic and expression analysis of the angiopoietin-like (ANGPTL) gene family and their role in lipid metabolism in pigs.

METHODS

In this study, the amino acid sequence analysis, phylogenetic analysis, and chromosome adjacent gene analysis were performed to identify the ANGPTL gene family in pigs. According to the body weight data from 60 Jinhua pigs, different tissues of 6 pigs with average body weight were used to determine the expression profile of ANGPTL1-8. The ileum, subcutaneous fat, and liver of 8 pigs with distinct fatness were selected to analyze the gene expression of ANGPTL3, ANGPTL4, and ANGPTL8.

RESULTS

The sequence length of ANGPTLs in pigs was between 1,186 and 1,991 bp, and the pig ANGPTL family members shared common features with human homologous genes, including the high similarity of the amino acid sequence and chromosome flanking genes. Amino acid sequence analysis showed that ANGPTL1-7 had a highly conserved domain except for ANGPTL8. Phylogenetic analysis showed that each ANGPTL homologous gene shared a common origin. Quantitative reverse-transcription polymerase chain reaction analysis showed that ANGPTL family members had different expression patterns in different tissues. ANGPTL3 and ANGPTL8 were mainly expressed in the liver, while ANGPTL4 was expressed in many other tissues, such as the intestine and subcutaneous fat. The expression levels of ANGPTL3 in the liver and ANGPTL4 in the liver, intestine and subcutaneous fat of Jinhua pigs with low propensity for adipogenesis were significantly higher than those of high propensity for adipogenesis.

CONCLUSION

These results increase our knowledge about the biological role of the ANGPTL family in this important economic species, it will also help to better understand the role of ANGPTL3, ANGPTL4, and ANGPTL8 in lipid metabolism of pigs, and provide innovative ideas for developing strategies to improve meat quality of pigs.

Decoding the role of angiopoietin-like protein 4/8 complex-mediated plasmin generation in the regulation of LPL activity

After feeding, adipose tissue lipoprotein lipase (LPL) activity should be maximized, therefore the potent LPL-inhibitory activity of angiopoietin-like protein 4 (ANGPTL4) must be blocked by ANGPTL8 through formation of ANGPTL4/8 complexes. ANGPTL4/8 tightly binds and protects LPL but also partially inhibits its activity. Recently, we demonstrated ANGPTL4/8 also binds tissue plasminogen activator (tPA) and plasminogen to generate plasmin that cleaves ANGPTL4/8 to restore LPL activity. Although fully active LPL in the fat postprandially is desirable, ANGPTL4/8 removal could subject LPL to profound inhibition by ANGPTL3/8 (the most potent circulating LPL inhibitor), inhibition by other LPL inhibitors like ANGPTL4, ANGPTL3, and ApoC3 or interfere with ApoC2-mediated LPL activation. To understand better these potential paradoxes, we examined LPL inhibition by ANGPTL3/8, ANGPTL4, ANGPTL3, and ApoC3 and LPL stimulation by ApoC2 in the presence of ANGPTL4/8 + tPA + plasminogen. Remarkably, ANGPTL3/8-mediated LPL inhibition was almost completely blocked, with the mechanism being cleavage of fibrinogen-like domain-containing ANGPTL3 present in the ANGPTL3/8 complex. The LPL-inhibitory effects of ANGPTL4, ANGPTL3, and ApoC3 were also largely reduced in the presence of ANGPTL4/8 + tPA + plasminogen. In contrast, the ability of ApoC2 to stimulate LPL activity was unaffected by ANGPTL4/8-mediated plasmin generation. Together, these results explain how plasmin generated by increased postprandial ANGPTL4/8 levels in adipose tissue enables maximal LPL activity by preventing ANGPTL3/8, ANGPTL4, ANGPTL3, and ApoC3 from inhibiting LPL, while permitting ApoC2-mediated LPL activation to occur.

Novel and future lipid-modulating therapies for the prevention of cardiovascular disease

Lowering the levels of LDL cholesterol in the plasma has been shown to reduce the risk of atherosclerotic cardiovascular disease (ASCVD). Several other lipoproteins, such as triglyceride-rich lipoproteins, HDL and lipoprotein(a) are associated with atherosclerosis and ASCVD, with strong evidence supporting causality for some. In this Review, we discuss novel and upcoming therapeutic strategies targeting different pathways in lipid metabolism to potentially attenuate the risk of cardiovascular events. Key proteins involved in lipoprotein metabolism, such as PCSK9, angiopoietin-related protein 3, cholesteryl ester transfer protein and apolipoprotein(a), have been identified as viable targets for therapeutic intervention through observational and genetic studies. These proteins can be targeted using a variety of approaches, such as protein inhibition or interference, inhibition of translation at the mRNA level (with the use of antisense oligonucleotides or small interfering RNA), and the introduction of loss-of-function mutations through base editing. These novel and upcoming strategies are complementary to and could work synergistically with existing therapies, or in some cases could potentially replace therapies, offering unprecedented opportunities to prevent ASCVD. Moreover, a major challenge in the prevention and treatment of non-communicable diseases is how to achieve safe, long-lasting reductions in causal exposures. This challenge might be overcome with approaches such as small interfering RNAs or genome editing, which shows how far the field has advanced from when the burden of achieving this goal was placed upon patients through rigorous adherence to daily small-molecule drug regimens.

Plasma insulin is required for the increase in plasma angiopoietin-like protein 8 in response to nutrient ingestion

BACKGROUND

Plasma levels of angiopoietin-like protein 8 (ANGPTL8) are regulated by feeding and they increase following glucose ingestion. Because both plasma glucose and insulin increase following food ingestion, we aimed to determine whether the increase in plasma insulin and glucose or both are responsible for the increase in ANGPTL8 levels.

METHODS

ANGPTL8 levels were measured in 30 subjects, 14 with impaired fasting glucose (IFG), and 16 with normal fasting glucose (NFG); the subjects received 75g glucose oral Glucose tolerance test (OGTT), multistep euglycaemic hyperinsulinemic clamp and hyperglycaemic clamp with pancreatic clamp.

RESULTS

Subjects with IFG had significantly higher ANGPTL8 than NGT subjects during the fasting state (p < 0.05). During the OGTT, plasma ANGPTL8 concentration increased by 62% above the fasting level (p < 0.0001), and the increase above fasting in ANGPTL8 levels was similar in NFG and IFG individuals. During the multistep insulin clamp, there was a dose-dependent increase in plasma ANGPTL8 concentration. During the 2-step hyperglycaemic clamp, the rise in plasma glucose concentration failed to cause any change in the plasma ANGPTL8 concentration from baseline.

CONCLUSIONS

In response to nutrient ingestion, ANGPTL8 level increased due to increased plasma insulin concentration, not to the rise in plasma glucose. The incremental increase above baseline in plasma ANGLPTL8 during OGTT was comparable between people with normal glucose tolerance and IFG.

Endothelial Lipase Variant, T111I, Does Not Alter Inhibition by Angiopoietin-like Proteins

High levels of HDL-C are correlated with a decreased risk of cardiovascular disease. HDL-C levels are modulated in part by the secreted phospholipase, endothelial lipase (EL), which hydrolyzes the phospholipids of HDL and decreases circulating HDL-C concentrations. A 584C/T polymorphism in LIPG, the gene which encodes EL, was first identified in individuals with increased HDL levels. This polymorphism results in a T111I point mutation the EL protein. The association between this variant, HDL levels, and the risk of coronary artery disease (CAD) in humans has been extensively studied, but the findings have been inconsistent. In this study, we took a biochemical approach, investigating how the T111I variant affected EL activity, structure, and stability. Moreover, we tested whether the T111I variant altered the inhibition of phospholipase activity by angiopoietin-like 3 (ANGPTL3) and angiopoietin-like 4 (ANGPTL4), two known EL inhibitors. We found that neither the stability nor enzymatic activity of EL was altered by the T111I variant. Moreover, we found no difference between wild-type and T111I EL in their ability to be inhibited by ANGPTL proteins. These data suggest that any effect this variant may have on HDL-C levels or cardiovascular disease are not mediated through alterations in these functions.

Plasma ANGPTL8 Levels and Risk for Secondary Cardiovascular Events in Japanese Patients With Stable Coronary Artery Disease Receiving Statin Therapy

BACKGROUND

The ability to predict secondary cardiovascular events could improve health of patients undergoing statin treatment. Circulating ANGPTL8 (angiopoietin-like protein 8) levels, which positively correlate with proatherosclerotic lipid profiles, activate the pivotal proatherosclerotic factor ANGPTL3. Here, we assessed potential association between circulating ANGPTL8 levels and risk of secondary cardiovascular events in statin-treated patients.

METHODS

We conducted a biomarker study with a case-cohort design, using samples from a 2018 randomized control trial known as randomized evaluation of high-dose (4 mg/day) or low-dose (1 mg/day) lipid-lowering therapy with pitavastatin in coronary artery disease (REAL-CAD [Randomized Evaluation of Aggressive or Moderate Lipid-Lowering Therapy With Pitavastatin in Coronary Artery Disease])." From that study's full analysis set (n=12 413), we selected 2250 patients with stable coronary artery disease (582 with the primary outcome, 1745 randomly chosen, and 77 overlapping subjects). A composite end point including cardiovascular-related death, nonfatal myocardial infarction, nonfatal ischemic stroke, or unstable angina requiring emergent admission was set as a primary end point. Circulating ANGPTL8 levels were measured at baseline and 6 months after randomization.

RESULTS

Over a 6-month period, ANGPTL8 level changes significantly decreased in the high-dose pitavastatin group, which showed 19% risk reduction of secondary cardiovascular events compared with the low-dose group in the REAL-CAD [Randomized Evaluation of Aggressive or Moderate Lipid-Lowering Therapy With Pitavastatin in Coronary Artery Disease] study. In the highest quartiles, relative increases in ANGPTL8 levels were significantly associated with increased risk for secondary cardiovascular events, after adjustment for several cardiovascular disease risk factors and pitavastatin treatment (hazard ratio in Q4, 1.67 [95% CI, 1.17-2.39). Subgroup analyses showed relatively strong relationships between relative ANGPTL8 increases and secondary cardiovascular events in the high-dose pitavastatin group (hazard ratio in Q4, 2.07 [95% CI, 1.21-3.55]) and in the low ANGPTL8 group at baseline (166

CONCLUSIONS

Monitoring ANGPTL8 levels over time might be useful to assess residual risk of cardiovascular secondary events in patients with cardiovascular disease undergoing statin therapy.

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Key Words

• coronary artery disease
• dyslipidemias
• hydroxymethylglutaryl-CoA reductase inhibitors
• risk factors

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MESH Headings

• Humans
• Angiopoietin-Like Protein 3
• Angiopoietin-Like Protein 8
• Cardiovascular Diseases/blood
• Cardiovascular Diseases/chemically induced
• Cardiovascular Diseases/diagnosis
• Cardiovascular Diseases/epidemiology
• Coronary Artery Disease/blood
• Coronary Artery Disease/drug therapy
• Coronary Artery Disease/epidemiology
• East Asian People
• Hydroxymethylglutaryl-CoA Reductase Inhibitors/adverse effects
• Hydroxymethylglutaryl-CoA Reductase Inhibitors/therapeutic use
• Lipids
• Myocardial Infarction/drug therapy
• Peptide Hormones
• Treatment Outcome

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Affiliation(s)

Jun Morinaga Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan Department of Nephrology (J.M., A.K., E.M., H.F., M.M.), Graduate School of Medical Sciences, Kumamoto University, Japan Department of Clinical Investigation, Kumamoto University Hospital, Japan (J.M.)
Kosuke Kashiwabara Data Science Office, Clinical Research Promotion Center, The University of Tokyo Hospital, Japan (K.K.)
Daisuke Torigoe Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan
Yusuke Okadome Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan
Kenichi Aizawa Division of Clinical Pharmacology, Department of Pharmacology, Jichi Medical University, Tochigi, Japan (K.A.)
Kohei Uemura Department of Biostatistics and Bioinformatics, Interfaculty Initiative in Information Studies (K.U.), The University of Tokyo, Japan
Ai Kurashima Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan Department of Nephrology (J.M., A.K., E.M., H.F., M.M.), Graduate School of Medical Sciences, Kumamoto University, Japan
Eiji Matsunaga Department of Nephrology (J.M., A.K., E.M., H.F., M.M.), Graduate School of Medical Sciences, Kumamoto University, Japan
Hirotaka Fukami Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan Department of Nephrology (J.M., A.K., E.M., H.F., M.M.), Graduate School of Medical Sciences, Kumamoto University, Japan
Haruki Horiguchi Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan
Michio Sato Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan
Taichi Sugizaki Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan
Keishi Miyata Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan
Tsuyoshi Kadomatsu Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan
Masashi Mukoyama Department of Nephrology (J.M., A.K., E.M., H.F., M.M.), Graduate School of Medical Sciences, Kumamoto University, Japan
Katsumi Miyauchi Department of Cardiovascular Medicine, Juntendo University Graduate School of Medicine, Tokyo, Japan (K.M., H.I., H.D.)
Seiji Hokimoto Kumamoto Municipal Ueki Hospital, Japan (S.H.)
Yoshihiro Fukumoto Division of Cardiovascular Medicine, Department of Internal Medicine, Kurume University School of Medicine, Japan (Y.F.)
Takafumi Hiro Division of Cardiology, Department of Medicine, Nihon University School of Medicine, Tokyo, Japan (T.H.)
Kiyoshi Hibi Division of Cardiology, Yokohama City University Medical Center, Japan (K.H.)
Yoshihisa Nakagawa Department of Cardiovascular Medicine, Shiga University of Medical Science, Otsu, Japan (Y.N.)
Ichiro Sakuma Caress Sapporo Hokko Memorial Clinic, Japan (I.S.)
Yukio Ozaki Department of Cardiology, Fujita Health University School of Medicine, Toyoake, Japan (Y.O.)
Hiroshi Iwata Department of Cardiovascular Medicine, Juntendo University Graduate School of Medicine, Tokyo, Japan (K.M., H.I., H.D.)
Satoshi Iimuro Innovation and Research Support Center, International University of Health and Welfare, Tokyo, Japan (S.I.)
Hiroyuki Daida Department of Cardiovascular Medicine, Juntendo University Graduate School of Medicine, Tokyo, Japan (K.M., H.I., H.D.)
Hiroaki Shimokawa Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan (H.S.) International University of Health and Welfare, Narita, Japan (H.S.)
Takeshi Kimura Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Japan (T.K.)
Masunori Matsuzaki St. Hill Hospital, Ube, Japan (M.M.)
Yasushi Saito Chiba University, Japan (Y.S.)
Yutaka Matsuyama Department of Biostatistics, School of Public Health, Graduate School of Medicine (Y.M.), The University of Tokyo, Japan
Ryozo Nagai Jichi Medical University, Shimotsuke, Japan (R.N.)
Yuichi Oike Department of Molecular Genetics (J.M., D.T., Y. Okadome., A.K., E.M., H.F., H.H., M.S., T.S., K.M., T.K. Y. Oike),, Graduate School of Medical Sciences, Kumamoto University, Japan

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Hepatokines, bile acids and ketone bodies are novel Hormones regulating energy homeostasis

Current views show that an impaired balance partly explains the fat accumulation leading to obesity. Fetal malnutrition and early exposure to endocrine-disrupting compounds also contribute to obesity and impaired insulin secretion and/or sensitivity. The liver plays a major role in systemic glucose homeostasis through hepatokines secreted by hepatocytes. Hepatokines influence metabolism through autocrine, paracrine, and endocrine signaling and mediate the crosstalk between the liver, non-hepatic target tissues, and the brain. The liver also synthetizes bile acids (BAs) from cholesterol and secretes them into the bile. After food consumption, BAs mediate the digestion and absorption of fat-soluble vitamins and lipids in the duodenum. In recent studies, BAs act not simply as fat emulsifiers but represent endocrine molecules regulating key metabolic pathways. The liver is also the main site of the production of ketone bodies (KBs). In prolonged fasting, the brain utilizes KBs as an alternative to CHO. In the last few years, the ketogenic diet (KD) became a promising dietary intervention. Studies on subjects undergoing KD show that KBs are important mediators of inflammation and oxidative stress. The present review will focus on the role played by hepatokines, BAs, and KBs in obesity, and diabetes prevention and management and analyze the positive effects of BAs, KD, and hepatokine receptor analogs, which might justify their use as new therapeutic approaches for metabolic and aging-related diseases.

Angiopoietin-like 3: An important protein in regulating lipoprotein levels

ANGPTL3 has emerged as a therapeutic target whose inhibition results in profound reductions of plasma lipids, including atherogenic triglyceride-rich lipoproteins and low-density lipoprotein cholesterol. The identification of ANGPTL3 deficiency as a cause of familial combined hypolipidemia in humans hastened the development of anti-ANGPTL3 therapeutic agents, including evinacumab (a monoclonal antibody inhibiting circulating ANGPTL3), vupanorsen (an antisense oligonucleotide [ASO] targeting hepatic ANGPTL3 mRNA for degradation), and others. Advances have also been made in ANGPTL3 vaccination and gene editing strategies, with the former still in preclinical phases and the latter in preparation for Phase 1 trials. Here, we review the discovery of ANGPTL3 as an important regulator of lipoprotein metabolism, molecular characteristics of the protein, mechanisms by which it regulates plasma lipids, and the clinical development of anti-ANGPTL3 agents. The clinical success of therapies inhibiting ANGPTL3 highlights the importance of this target as a novel approach in treating refractory hypertriglyceridemia and hypercholesterolemia.

Integrated Control of Fatty Acid Metabolism in Heart Failure

Disrupted fatty acid metabolism is one of the most important metabolic features in heart failure. The heart obtains energy from fatty acids via oxidation. However, heart failure results in markedly decreased fatty acid oxidation and is accompanied by the accumulation of excess lipid moieties that lead to cardiac lipotoxicity. Herein, we summarized and discussed the current understanding of the integrated regulation of fatty acid metabolism (including fatty acid uptake, lipogenesis, lipolysis, and fatty acid oxidation) in the pathogenesis of heart failure. The functions of many enzymes and regulatory factors in fatty acid homeostasis were characterized. We reviewed their contributions to the development of heart failure and highlighted potential targets that may serve as promising new therapeutic strategies.

Combined action of albumin and heparin regulates lipoprotein lipase oligomerization, stability, and ligand interactions

Lipoprotein lipase (LPL), a crucial enzyme in the intravascular hydrolysis of triglyceride-rich lipoproteins, is a potential drug target for the treatment of hypertriglyceridemia. The activity and stability of LPL are influenced by a complex ligand network. Previous studies performed in dilute solutions suggest that LPL can appear in various oligomeric states. However, it was not known how the physiological environment, that is blood plasma, affects the action of LPL. In the current study, we demonstrate that albumin, the major protein component in blood plasma, has a significant impact on LPL stability, oligomerization, and ligand interactions. The effects induced by albumin could not solely be reproduced by the macromolecular crowding effect. Stabilization, isothermal titration calorimetry, and surface plasmon resonance studies revealed that albumin binds to LPL with affinity sufficient to form a complex in both the interstitial space and the capillaries. Negative stain transmission electron microscopy and raster image correlation spectroscopy showed that albumin, like heparin, induced reversible oligomerization of LPL. However, the albumin induced oligomers were structurally different from heparin-induced filament-like LPL oligomers. An intriguing observation was that no oligomers of either type were formed in the simultaneous presence of albumin and heparin. Our data also suggested that the oligomer formation protected LPL from the inactivation by its physiological regulator angiopoietin-like protein 4. The concentration of LPL and its environment could influence whether LPL follows irreversible inactivation and aggregation or reversible LPL oligomer formation, which might affect interactions with various ligands and drugs. In conclusion, the interplay between albumin and heparin could provide a mechanism for ensuring the dissociation of heparan sulfate-bound LPL oligomers into active LPL upon secretion into the interstitial space.

Genetically determined deficiency of ANGPTL3 does not alter HDL ability to preserve endothelial homeostasis

Individuals with loss-of-function mutations in the ANGPTL3 gene express a rare lipid phenotype called Familial Combined Hypolipidemia (FHBL2). FHBL2 individuals show reduced plasma concentrations of total cholesterol and triglycerides as well as of lipoprotein particles, including HDL. This feature is particularly remarkable in homozygotes in whom ANGPTL3 in blood is completely absent. ANGPTL3 acts as a circulating inhibitor of LPL and EL and it is thought that EL hyperactivity is the cause of plasma HDL reduction in FHBL2. Nevertheless, the consequences of ANGTPL3 deficiency on HDL functionality have been poorly explored. In this report, HDL isolated from homozygous and heterozygous FHBL2 individuals were evaluated for their ability to preserve endothelial homeostasis as compared to control HDL. It was found that only the complete absence of ANGPTL3 alters HDL subclass distribution, as homozygous, but not heterozygous, carriers have reduced content of large and increased content of small HDL with no alterations in HDL2 and HDL3 size. The plasma content of preβ-HDL was reduced in carriers and showed a positive correlation with plasma ANGPTL3 levels. Changes in composition did not however alter the functionality of FHBL2 HDL, as particles isolated from carriers retained their capacity to promote NO production and to inhibit VCAM-1 expression in endothelial cells. Furthermore, no significant changes in circulating levels of soluble ICAM-1 and E-selectin were detected in carriers. These results indicate that changes in HDL composition associated with the partial or complete absence of ANGPTL3 did not alter some of the potentially anti-atherogenic functions of these lipoproteins.

Molecular characterization and immune functions of lipasin in Nile tilapia (Oreochromis niloticus): Involvement in the regulation of tumor necrosis factor-α secretion

Lipasin, the product of the angiopoietin-like 8 (angptl8) gene, is known as a critical regulator of plasma lipid metabolism. However, its immune function in vertebrates is currently poorly understood. By 5'/3'-rapid amplification of cDNA ends (RACE), we established the structural identity of Nile tilapia (Oreochromis niloticus) angptl8. The transcripts of tilapia angptl8 were widely expressed in various tissues, with the highest levels in the liver. Following lipopolysaccharide in vivo challenges, time-dependent angptl8 gene expression was observed in the head kidney and liver. On the basis of the sequence obtained, we produced recombinant lipasin that inhibited lipoprotein lipase activity. Treatment of head kidney leukocytes with lipasin stimulated tumor necrosis factor-α (TNF-α) secretion and gene expression. In addition, lipasin-induced TNF-α secretion could be prevented by inhibiting the nuclear factor-kappa B (NF-κB) signaling pathway. Furthermore, lipasin enhanced the phosphorylation and degradation of IκBα and promoted translocation of the p65 subunit of NF-κB to the nucleus. Collectively, the current findings suggested that lipasin was involved in the immune response of Nile tilapia and stimulated TNF-α secretion by activating the NF-κB pathway in tilapia head kidney leukocytes.

A hepatokine derived from the ER protein CREBH promotes triglyceride metabolism by stimulating lipoprotein lipase activity

The endoplasmic reticulum (ER)-tethered, liver-enriched stress sensor CREBH is processed in response to increased energy demands or hepatic stress to release an amino-terminal fragment that functions as a transcription factor for hepatic genes encoding lipid and glucose metabolic factors. Here, we discovered that the carboxyl-terminal fragment of CREBH (CREBH-C) derived from membrane-bound, full-length CREBH was secreted as a hepatokine in response to fasting or hepatic stress. Phosphorylation of CREBH-C mediated by the kinase CaMKII was required for efficient secretion of CREBH-C through exocytosis. Lipoprotein lipase (LPL) mediates the lipolysis of circulating triglycerides for tissue uptake and is inhibited by a complex consisting of angiopoietin-like (ANGPTL) 3 and ANGPTL8. Secreted CREBH-C blocked the formation of ANGPTL3-ANGPTL8 complexes, leading to increased LPL activity in plasma and metabolic tissues in mice. CREBH-C administration promoted plasma triglyceride clearance and partitioning into peripheral tissues and mitigated hypertriglyceridemia and hepatic steatosis in mice fed a high-fat diet. Individuals with obesity had higher circulating amounts of CREBH-C than control individuals, and human CREBH loss-of-function variants were associated with dysregulated plasma triglycerides. These results identify a stress-induced, secreted protein fragment derived from CREBH that functions as a hepatokine to stimulate LPL activity and triglyceride homeostasis.

Physiological roles and regulation of hepatic angiopoietin-like protein 3 in Japanese Black cattle (Bos taurus) during the fattening period

Angiopoietin-like protein 3 (ANGPTL3) is expressed predominantly in the liver and plays a major role in regulating the circulating triglyceride and lipoprotein fraction concentrations by inhibiting lipoprotein lipase (LPL) activity. Given these physiological roles, ANGPTL3 may play an important role in metabolic changes related to fat accumulation during the fattening period in Japanese Black. This study aimed to reveal the physiological roles of hepatic ANGPTL3 in Japanese Black steers (Bos taurus) during the fattening period and investigate the regulatory effects of hepatic ANGPTL3. To investigate the gene expression and protein localization of ANGPTL3, 18 tissue samples were collected from tree male Holstein bull calves aged 7 wk. Biopsied liver tissues and blood samples were collected from 21 Japanese Black steers during the early (T1; 13 mo of age), middle (T2; 20 mo), and late fattening phases (T3; 28 mo). Relative mRNA expression, blood metabolite concentrations, hormone concentrations, growth, and carcass traits were analyzed. To identify the regulatory factors of hepatic ANGPTL3, primary bovine hepatocytes collected by two Holstein calves aged 7 wk were incubated with insulin, palmitate, oleate, propionate, acetate, or beta-hydroxybutyric acid (BHBA). The ANGPTL3 gene was most highly expressed in the liver, with minor expression in the renal cortex, lungs, reticulum, and jejunum in Holstein bull calves. In Japanese Black steers, relative ANGPTL3 mRNA expressions were less as fattening progressed, and blood triglyceride, total cholesterol, and nonesterified fatty acid (NEFA) concentrations increased. Relative ANGPTL8 and Liver X receptor alpha (LXRα) mRNA expressions decreased in late and middle fattening phases, respectively. Furthermore, relative ANGTPL3 mRNA expression was positively correlated with ANGPTL8 (r = 0.650; P < 0.01) and ANGPTL4 (r = 0.540; P < 0.05) in T3 and T1, respectively, and LXRα showed no correlation with ANGPTL3. Relative ANGTPL3 mRNA expression was negatively correlated with total cholesterol (r = -0.434; P < 0.05) and triglyceride (r = -0.645; P < 0.01) concentrations in T3 and T1, respectively; There was no significant correlation between ANGTPL3 and carcass traits. Relative ANGTPL3 mRNA expression in cultured bovine hepatocytes was downregulated in oleate treatment. Together, these findings suggest that ANGPTL3 downregulation in late fattening phases is associated with the changes in lipid metabolism.

New Therapeutic Approaches to the Treatment of Dyslipidemia 1: ApoC-III and ANGPTL3

Low-density lipoprotein cholesterol (LDL-C)-lowering therapy that increases LDL receptor expression in several ways robustly reduces the risk of atherosclerotic cardiovascular disease (CVD). However, a substantial risk of CVD still remains after intensive LDL-C reduction, which requires new treatment modalities for dyslipidemia and cardiovascular risk management. Triglycerides (TGs) and triglyceride-rich lipoproteins (TRLs) have received attention as indicators of residual cardiovascular risk and as direct causal factors for atherosclerosis and CVDs. Advances in understanding TG and TRL metabolism and their association with clinically evident CVDs have led to the development of novel therapeutic targets, including apolipoprotein C-III (apoC-III) and angiopoietin-like protein 3 (ANGPTL3). Genetic association studies have indicated that both apoC-III and ANGPTL3 play a causal role in the development of atherosclerotic CVD. Both molecules contribute to lipid dysregulation and atherosclerosis primarily by inhibiting lipoprotein lipase; however, recent evidence has shown that novel pathways exist in relation to their lipid-modifying activities. Notably, recent progress in therapeutic approaches, such as monoclonal antibodies or antisense oligonucleotides, has led to several novel therapeutics targeting apoC-III and ANGPTL3. This review summarized the recent updates and discussions related to apoC-III and ANGPTL3 expression.

Genetic Mimicry Analysis Reveals the Specific Lipases Targeted by the ANGPTL3-ANGPTL8 Complex and ANGPTL4

Angiopoietin-like proteins, ANGPTL3, ANGPTL4, and ANGPTL8, are involved in regulating plasma lipids. In vitro and animal-based studies point to LPL and endothelial lipase (EL, LIPG) as key targets of ANGPTLs. To examine the ANGPTL mechanisms for plasma lipid modulation in humans, we pursued a genetic mimicry analysis of enhancing or suppressing variants in the LPL, LIPG, lipase C hepatic type (LIPC), ANGPTL3, ANGPTL4, and ANGPTL8 genes using data on 248 metabolic parameters derived from over 110,000 nonfasted individuals in the UK Biobank and validated in over 13,000 overnight fasted individuals from 11 other European populations. ANGPTL4 suppression was highly concordant with LPL enhancement but not HL or EL, suggesting ANGPTL4 impacts plasma metabolic parameters exclusively via LPL. The LPL-independent effects of ANGPTL3 suppression on plasma metabolic parameters showed a striking inverse resemblance with EL suppression, suggesting ANGPTL3 not only targets LPL but also targets EL. Investigation of the impact of the ANGPTL3-ANGPTL8 complex on plasma metabolite traits via the ANGPTL8 R59W substitution as an instrumental variable showed a much higher concordance between R59W and EL activity than between R59W and LPL activity, suggesting the R59W substitution more strongly affects EL inhibition than LPL inhibition. Meanwhile, when using a rare and deleterious protein-truncating ANGPTL8 variant as an instrumental variable, the ANGPTL3-ANGPTL8 complex was very LPL specific. In conclusion, our analysis provides strong human genetic evidence that the ANGPTL3-ANGPTL8 complex regulates plasma metabolic parameters, which is achieved by impacting LPL and EL. By contrast, ANGPTL4 influences plasma metabolic parameters exclusively via LPL.

The Regulation of Triacylglycerol Metabolism and Lipoprotein Lipase Activity

Triacylglycerol (TG) metabolism is tightly regulated to maintain a pool of TG within circulating lipoproteins that can be hydrolyzed in a tissue-specific manner by lipoprotein lipase (LPL) to enable the delivery of fatty acids to adipose or oxidative tissues as needed. Elevated serum TG concentrations, which result from a deficiency of LPL activity or, more commonly, an imbalance in the regulation of tissue-specific LPL activities, have been associated with an increased risk of atherosclerotic cardiovascular disease through multiple studies. Among the most critical LPL regulators are the angiopoietin-like (ANGPTL) proteins ANGPTL3, ANGPTL4, and ANGPTL8, and a number of different apolipoproteins including apolipoprotein A5 (ApoA5), apolipoprotein C2 (ApoC2), and apolipoprotein C3 (ApoC3). These ANGPTLs and apolipoproteins work together to orchestrate LPL activity and therefore play pivotal roles in TG partitioning, hydrolysis, and utilization. This review summarizes the mechanisms of action, epidemiological findings, and genetic data most relevant to these ANGPTLs and apolipoproteins. The interplay between these important regulators of TG metabolism in both fasted and fed states is highlighted with a holistic view toward understanding key concepts and interactions. Strategies for developing safe and effective therapeutics to reduce circulating TG by selectively targeting these ANGPTLs and apolipoproteins are also discussed.

ANGPTL8 accelerates liver fibrosis mediated by HFD-induced inflammatory activity via LILRB2/ERK signaling pathways

INTRODUCTION

High calorie intake is known to induce nonalcoholic fatty liver disease (NAFLD) by promoting chronic inflammation. However, the mechanisms are poorly understood.

OBJECTIVES

This study examined the roles of ANGPTL8 in the regulation of NAFLD-associated liver fibrosis progression induced by high fat diet (HFD)-mediated inflammation.

METHODS

The ANGPTL8 concentration was measured in serum samples from liver cancer and liver cirrhosis patients. ANGPTL8 knockout mice were used to induce disease models (HFD, HFHC and CCL4) followed by pathological staining, western blot and immunohistochemistry. Hydrodynamic injection of an adeno-associated virus 8 (AAV8) was used to establish a model for restoring ANGPTL8 expression specifically in ANGPTL8 KO mice livers. RNA-sequencing, protein array, Co-IP, etc. were used to study ANGPTL8's mechanisms in regulating liver fibrosis progression, and drug screening was used to identify an effective inhibitor of ANGPTL8 expression.

RESULTS

ANGPTL8 level is associated with liver fibrogenesis in both cirrhosis and hepatocellular carcinoma patients. Mouse studies demonstrated that ANGPTL8 deficiency suppresses HFD-stimulated inflammatory activity, hepatic steatosis and liver fibrosis. The AAV-mediated restoration of liver ANGPTL8 expression indicated that liver-derived ANGPTL8 accelerates HFD-induced liver fibrosis. Liver-derived ANGPTL8, as a proinflammatory factor, activates HSCs (hepatic stellate cells) by interacting with the LILRB2 receptor to induce ERK signaling and increase the expression of genes that promote liver fibrosis. The FDA-approved drug metformin, an ANGPTL8 inhibitor, inhibited HFD-induced liver fibrosis in vivo.

CONCLUSIONS

Our data support that ANGPTL8 is a proinflammatory factor that accelerates NAFLD-associated liver fibrosis induced by HFD. The serum ANGPTL8 level may be a potential and specific diagnostic marker for liver fibrosis, and targeting ANGPTL8 holds great promise for developing innovative therapies to treat NAFLD-associated liver fibrosis.

Angiopoietin-Like Protein 3 (ANGPTL3) Inhibitors in the Management of Refractory Hypercholesterolemia

Cardiovascular disease (CVD) is the most common cause of death in a global scale and significantly depends on the elevated plasma levels of low-density lipoprotein cholesterol (LDL-C) and the subsequent formation of atherosclerotic plaques. While physicians have several LDL-C-lowering agents with diverse mechanisms of action, including statins, ezetimibe, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors and inclisiran, angiopoietin-like protein 3 (ANGPTL3) inhibitors have recently emerged as a powerful addition in the armamentarium of lipid-lowering strategies, especially for patients with refractory hypercholesterolemia, as in the case of patients with homozygous familial hypercholesterolemia (HoFH). ANGPTL3 protein is a glycoprotein secreted by liver cells that is implicated in the metabolism of lipids along with other ANGPTL proteins. These proteins inhibit lipoprotein lipase (LPL) and endothelial lipase (EL) in tissues. Loss-of-function mutations affecting the gene encoding ANGPTL3 are linked with lower total cholesterol, LDL-C, and triglyceride (TG) levels. Evinacumab is a monoclonal antibody that targets, binds to, and pharmacologically inhibits ANGPTL3, which was recently approved by the United States Food and Drug Administration (FDA) as a complementary agent to other LDL-C lowering regimens for patients aged 12 or older with HoFH, based on clinical trial evidence that confirmed its safety and efficacy in those patients. Antisense oligonucleotides (ASOs) also represent an interesting class of agents that target and inhibit the mRNA derived from the transcription of ANGPTL3 gene. This review aims to present and discuss the current clinical and scientific data pertaining to the role of ANGPTL3 inhibitors, a novel lipid-modifying class of agents capable of reducing LDL-C levels via a mechanism independent of LDL receptors.

Serum ANGPTL8 and ANGPTL3 as Predictors of Triglyceride Elevation in Adult Women

Angiopoietin-like proteins ANGPTL3 and ANGPTL8 have been shown to inhibit lipoprotein lipase, and thus regulate triglyceride level in the circulation. Whether the regulation of lipid metabolism by ANGPTLs is affected by the menopausal status remains unclear. We aimed to assess the relationships between serum ANGPTL3 and ANGPTL8 and atherogenic biomarkers in presumably healthy women during ageing. The study group included 94 women of whom 31 were premenopausal (PRE ≤ 40 years) and 37 were postmenopausal (POST ≥ 52 years). Atherogenic lipid and non-lipid biomarkers and ANGPTLs (ANGPTL3, ANGPTL8) were assayed in serum samples. TG/HDL-C index, non-HDL-cholesterol, remnant cholesterol concentrations, and BMI were calculated. Median levels of ANGPTL3 and concentrations of lipid biomarkers were significantly higher in POST comparing to PRE but ANGPTL8 levels were not different. In PRE, ANGPTL8 levels correlated significantly with TG and TG/HDL-C index while there were no correlations between ANGPTL3 and these biomarkers. In POST both ANGPTLs correlated with TG, sdLDL-C, and TG/HDL-C. ANGPTL8 and sd-LDL-C were the most significant predictors of early triglyceride elevation > 100 mg/dL (1.13 mmol/L) in the whole group and POST whereas the prediction power of ANGPTL3 was negligible in the whole group and non-significant in the subgroups. We demonstrated a significant positive correlation of ANGPTL3 with age category which predisposes to postmenopause. Despite the increase in ANGPTL3 level with ageing the ANGPTL3/ANGPL8 ratio was maintained. In conclusion, ANGPTL8 predicts the early triglyceride elevation better than ANGPTL3, especially in postmenopausal women. The association of ANGPTL3 with triglyceride levels is weaker than ANGPTL8 and depends on menopausal status. We suggest that the choice for the best efficient treatment of dyslipidemia with new inhibitors of angiopoietin-like proteins may depend on the menopausal status.

The Fibrinogen-like Domain of ANGPTL3 Facilitates Lipolysis in 3T3-L1 Cells by Activating the Intracellular Erk Pathway

Background: ANGPTL3 stimulates lipolysis in adipocytes, but the underlying molecular mechanism is yet unknown. The C-terminal fibrinogen-like domain of ANGPTL3 (ANGPTL3-Fld) activates the AKT pathway in endothelial cells. Hence, we evaluated whether ANGPTL3-Fld stimulates lipolysis in adipocytes through the MAPK kinase pathway. Materials and Methods: 3T3-L1 adipocytes were treated with isoproterenol (ISO), ANGPTL3-Fld, or both. Lipolysis was evaluated through the release of free fatty acids (FFAs) in the culture medium. The activation status of intracellular kinases was evaluated with and without the inhibition of the BRAF–ERK arm of the MAPK pathway. Results: ANGPTL3-Fld alone was not able to activate lipolysis, while the combination of ANGPTL3-Fld and ISO determined a 10-fold enrichment of the FFA concentration in the culture medium with an incremental effect (twofold) when compared with ISO alone. ANGPTL3-Fld alone inhibited hormone-sensitive lipase (HSL), whereas the treatment with ISO induced the activation of HSL. The net balance of ANGPTL3-Fld and ISO cotreatment resulted in HSL activation. The results indicate that ANGPTL3-Fld generated an intracellular activation signal involving the MAPK–ERK pathway, possibly through the PDGFRβ—PLCγ-AMPK axis. Conclusion: ANGPTL3-Fld appears to act as a facilitator of lipolysis in adipocytes, and this effect was driven by a signal mediated by a pathway that is different from the canonical β-adrenergic stimulus.

ANGPTL4: a new mode in the regulation of intravascular lipolysis

PURPOSE OF REVIEW

Lipoprotein lipase (LPL) is the rate-limiting enzyme for intravascular processing of circulating triglyceride-rich lipoproteins (TRLs). One emerging strategy for therapeutic lowering of plasma triglyceride levels aims at increasing the longevity of LPL activity by attenuating its inhibition from angiopoietin-like proteins (ANGPTL) 3, 4 and 8. This mini-review focuses on recent insights into the molecular mechanisms underpinning the regulation of LPL activity in the intravascular unit by ANGPTLs with special emphasis on ANGPTL4.

RECENT FINDINGS

Our knowledge on the molecular interplays between LPL, its endothelial transporter GPIHBP1, and its inhibitor(s) ANGPTL4, ANGPTL3 and ANGPTL8 have advanced considerably in the last 2 years and provides an outlined on how these proteins regulate the activity and compartmentalization of LPL. A decisive determinant instigating this control is the inherent protein instability of LPL at normal body temperature, a property that is reciprocally impacted by the binding of GPIHBP1 and ANGPTLs. Additional layers in this complex LPL regulation is provided by the different modulation of ANGPTL4 and ANGPTL3 activities by ANGPTL8 and the inhibition of ANGPTL3/8 complexes by apolipoprotein A5 (APOA5).

SUMMARY

Posttranslational regulation of LPL activity in the intravascular space is essential for the differential partitioning of TRLs across tissues and their lipolytic processing in response to nutritional cues.