Faculty Bibliography

The positive relationship between increased levels of circulating triglycerides and cardiovascular events has been observed for decades. Driven by genetic cohort studies, inhibitors of APOC3 (apolipoprotein C3) and ANGPTL (angiopoietin-like protein) 3 that reduce circulating triglycerides are poised to enter clinical practice. We will review the biology of how inhibition of these 2 proteins affects circulating lipoproteins as well as the current state of clinical development of monoclonal antibodies, antisense oligonucleotides, and silencing RNAs targeting APOC3 and ANGPTL3.

As the worldwide prevalence of overweight and obesity continues to rise, so too does the urgency to fully understand mediating mechanisms, to discover new targets for safe and effective therapeutic intervention, and to identify biomarkers to track obesity and the success of weight loss interventions. In 2016, the American Heart Association sought applications for a Strategically Focused Research Network (SFRN) on Obesity. In 2017, 4 centers were named, including Johns Hopkins University School of Medicine, New York University Grossman School of Medicine, University of Alabama at Birmingham, and Vanderbilt University Medical Center. These 4 centers were convened to study mechanisms and therapeutic targets in obesity, to train a talented cadre of American Heart Association SFRN-designated fellows, and to initiate and sustain effective and enduring collaborations within the individual centers and throughout the SFRN networks. This review summarizes the central themes, major findings, successful training of highly motivated and productive fellows, and the innovative collaborations and studies forged through this SFRN on Obesity. Leveraging expertise in in vitro and cellular model assays, animal models, and humans, the work of these 4 centers has made a significant impact in the field of obesity, opening doors to important discoveries, and the identification of a future generation of obesity-focused investigators and next-step clinical trials. The creation of the SFRN on Obesity for these 4 centers is but the beginning of innovative science and, importantly, the birth of new collaborations and research partnerships to propel the field forward.

Lipid accumulation in non-adipose tissues can cause lipotoxicity, leading to cell death and severe organ dysfunction. Adipose triglyceride lipase (ATGL) deficiency causes human Neutral Lipid Storage Disease and leads to cardiomyopathy; ATGL deficiency has no current treatment. One possible approach to alleviate this disorder has been to alter the diet and reduce the supply of dietary lipids and, hence, myocardial lipid uptake. However, in this study, when we supplied cardiac Atgl knockout mice a low- or high-fat diet, we found heart lipid accumulation, heart dysfunction, and death were not altered. We next deleted lipid uptake pathways in the ATGL-deficient mice through the generation of double knockout mice also deficient in either cardiac lipoprotein lipase (LpL) or cluster of differentiation (CD) 36, which is involved in an LpL-independent pathway for fatty acid uptake in the heart. We show neither deletion ameliorated ATGL-deficient heart dysfunction. Similarly, we determined non-lipid-containing media did not prevent lipid accumulation by cultured myocytes; rather, the cells switched to increased de novo fatty acid synthesis. Thus, we conclude pathological storage of lipids in ATGL deficiency cannot be corrected by reducing heart lipid uptake.

Benefits of omega 3 fatty acids for cardiovascular and other diseases have been touted for more than 50 years. The one clear clinical benefit of these lipids is the reduction of circulating levels of triglycerides, making them a useful approach for the prevention of pancreatitis in severely hypertriglyceridemic patients. After a series of spectacularly failed clinical trials that were criticized for the choice of subjects and doses of omega 3 fatty acids used, Reduction of Cardiovascular Events with Icosapent Ethyl-Intervention Trial (REDUCE-IT) using a high dose of icosapent ethyl (IPE) reported a reduction in cardiovascular disease (CVD) events. However, this trial has generated controversy due to the use of mineral oil in the control group and the associated side effects of the IPA. This review will focus on the following topics: What are the epidemiologic data suggesting a benefit of omega 3 fatty acids? What might be the mechanisms for these benefits? Why have the clinical trials failed to resolve whether these fatty acids provide benefit? What choices should a clinician consider?

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.

During obesity, tissue macrophages increase in number and become pro-inflammatory, thereby contributing to metabolic dysfunction. Lipoprotein lipase (LPL), which hydrolyzes triglyceride (TG) in lipoproteins, is secreted by macrophages. However, the role of macrophage-derived LPL in adipose tissue remodeling and lipoprotein metabolism is largely unknown. To clarify these issues, we crossed leptin-deficient Lep^ob/ob mice with mice lacking the Lpl gene in myeloid cells (Lpl^m-/m-) to generate Lpl^m-/m-;Lep^ob/ob mice. We found the weight of perigonadal white adipose tissue (WAT) was increased in Lpl^m-/m-;Lep^ob/ob mice compared with Lep^ob/ob mice due to substantial accumulation of both adipose tissue macrophages (ATMs) and collagen that surrounded necrotic adipocytes. In the fibrotic epidydimal WAT of Lpl^m-/m-;Lep^ob/ob mice, we observed an increase in collagen VI and high mobility group box 1 (HMGB1), while α-smooth muscle cell actin, a marker of myofibroblasts, was almost undetectable, suggesting that the adipocytes were the major source of the collagens. Furthermore the ATMs from Lpl^m-/m-;Lep^ob/ob mice showed increased expression of genes related to fibrosis and inflammation. In addition, we determined Lpl^m-/m-;Lep^ob/ob mice were more hypertriglyceridemic than Lep^ob/ob mice. Lpl^m-/m-;Lep^ob/ob mice also showed slower weight gain than Lep^ob/ob mice, which was primarily due to reduced food intake. In conclusion, we discovered that the loss of myeloid Lpl led to extensive fibrosis of perigonadal WAT and hypertriglyceridemia. In addition to illustrating an important role of macrophage LPL in regulation of circulating TG levels, these data show that macrophage LPL protects against fibrosis in obese adipose tissues.

Prediabetes affects at least 1 in 3 adults in the U.S. and 1 in 5 in Europe. Although guidelines advocate aggressive management of lipid parameters in diabetes, most guidelines do not address treatment of dyslipidemia in prediabetes despite the increased atherosclerotic cardiovascular disease (ASCVD) risk. Several criteria are used to diagnose prediabetes: impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and HbA1c of 5.7-6.4%. Individuals with prediabetes have a greater risk of diabetes, a higher prevalence of dyslipidemia with a more atherogenic lipid profile and an increased risk of ASCVD. In addition to calculating ASCVD risk using traditional methods, an OGTT may further stratify risk. Those with 1-hour plasma glucose ≥8.6 mmol/L (155 mg/dL) and/or 2-hour ≥7.8 mmol/L (140 mg/dL) (IGT) have a greater risk of ASCVD. Diet and lifestyle modification are fundamental in prediabetes. Statins, ezetimibe and PCSK9 inhibitors are recommended in people requiring pharmacotherapy. Although high-intensity statins may increase risk of diabetes, this is acceptable because of the greater reduction of ASCVD. The LDL-C goal in prediabetes should be individualized. In those with IGT and/or elevated 1-hour plasma glucose, the same intensive approach to dyslipidemia as recommended for diabetes should be considered, particularly if other ASCVD risk factors are present.

The LDL receptor related protein 1 (LRP1) partakes in metabolic and signaling events regulated in a tissue-specific manner. The function of LRP1 in airways has not been studied. We aimed to study the function of LRP1 in smoke-induced disease. We found that bronchial epithelium of patients with chronic obstructive pulmonary disease (COPD) and airway epithelium of mice exposed to smoke had increased LRP1 expression. We then knocked out LRP1 in human bronchial epithelial cells in vitro and in airway epithelial club cells in mice. In vitro, LRP1 knockdown decreased cell migration and increased TGFβ activation. Tamoxifen-inducible airway-specific LRP1 knockout mice (club Lrp1^-/-) induced after complete lung development had increased inflammation in the bronchoalveolar space and lung parenchyma at baseline. After 6 months of smoke exposure, club Lrp1^-/- mice showed a combined restrictive and obstructive phenotype, with lower compliance, inspiratory capacity, and FEV0.05/FVC than WT smoke-exposed mice. This was associated with increased values of Ashcroft fibrotic index. Proteomic analysis of room air exposed-club Lrp1^-/- mice showed significantly decreased levels of proteins involved in cytoskeleton signaling and xenobiotic detoxification, as well as decreased levels of glutathione. The proteome fingerprint created by smoke eclipsed many of the original differences, but club Lrp1^-/- mice continued to have decreased lung glutathione levels and increased protein oxidative damage and airway cell proliferation. Therefore, LRP1 deficiency leads to greater lung inflammation and damage and exacerbates smoke-induced lung disease.

Despite the success of LDL-lowering drugs in reducing cardiovascular disease (CVD), there remains a large burden of residual disease due in part to persistent dyslipidemia characterized by elevated levels of triglyceride-rich lipoproteins (TRLs) and reduced levels of HDL. This form of dyslipidemia is increasing globally as a result of the rising prevalence of obesity and metabolic syndrome. Accumulating evidence suggests that impaired hepatic clearance of cholesterol-rich TRL remnants leads to their accumulation in arteries, promoting foam cell formation and inflammation. Low levels of HDL may associate with reduced cholesterol efflux from foam cells, aggravating atherosclerosis. While fibrates and fish oils reduce TRL, they have not been uniformly successful in reducing CVD, and there is a large unmet need for new approaches to reduce remnants and CVD. Rare genetic variants that lower triglyceride levels via activation of lipolysis and associate with reduced CVD suggest new approaches to treating dyslipidemia. Apolipoprotein C3 (APOC3) and angiopoietin-like 3 (ANGPTL3) have emerged as targets for inhibition by antibody, antisense, or RNAi approaches. Inhibition of either molecule lowers TRL but respectively raises or lowers HDL levels. Large clinical trials of such agents in patients with high CVD risk and elevated levels of TRL will be required to demonstrate efficacy of these approaches.