Faculty Bibliography

BACKGROUND & AIM/UNASSIGNED:Metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing health issue. Identifying factors that prevent hepatic lipid accumulation could inform new MASLD prevention or treatment strategies. We previously demonstrated that adipocyte microsomal triglyceride transfer protein (MTP) regulates intracellular lipolysis by inhibiting adipose triglyceride lipase activity. The aim of this study was to investigate the impact of adipose MTP deficiency on MASLD. METHODS/UNASSIGNED: RESULTS/UNASSIGNED: CONCLUSION/UNASSIGNED:These findings highlight the importance of regulated FA flux from adipose tissue to the liver and the liver's adaptive capacity to utilize adipose-derived FAs in maintaining hepatic health. Modulation of adipocyte FA release may represent a therapeutic strategy to reduce hepatic steatosis. IMPACT AND IMPLICATIONS/UNASSIGNED:This study provides significant insights into the role of adipose-specific microsomal triglyceride transfer protein in regulating hepatic lipid metabolism and its potential implications for treating metabolic dysfunction-associated steatotic liver disease. By demonstrating that microsomal triglyceride transfer protein deficiency in adipose tissue leads to increased fatty acid oxidation and reduced hepatic steatosis through enhanced PPARα activation, the research underscores the importance of adipose-liver crosstalk in maintaining liver health. These findings suggest that targeting adipocyte fatty acid release could be a promising therapeutic strategy to mitigate hepatic lipid accumulation and combat metabolic dysfunction-associated steatotic liver disease, offering a novel approach to addressing this growing health issue.

Insulin resistance impairs benefits of lipid-lowering treatment as evidenced by higher cardiovascular risk in individuals with type 2 diabetes versus those without. Because platelet activity is higher in insulin-resistant patients and promotes atherosclerosis progression, we questioned whether platelets impair inflammation resolution in plaques during lipid-lowering. In mice with obesity and insulin resistance, we induced advanced plaques, then implemented lipid-lowering to promote atherosclerotic plaque inflammation-resolution. Concurrently, mice were treated with either platelet-depleting or control antibodies for 3 weeks. Platelet activation and insulin resistance were unaffected by lipid-lowering. Both antibody-treated groups showed reduced plaque macrophages, but plaque cellular and structural composition differed. In platelet-depleted mice, scRNA seq revealed dampened inflammatory gene expression in plaque macrophages and an expansion of a subset of Fcgr4+ macrophages having features of inflammation-resolving, phagocytic cells. Necrotic core size was smaller and collagen content greater, resembling stable human plaques. Consistent with the mouse results, clinical data showed that patients with lower platelet counts had decreased pro-inflammatory signaling pathways in circulating non-classical monocytes after lipid-lowering. These findings highlight that platelets hinder inflammation-resolution in atherosclerosis during lipid-lowering treatment. Identifying novel platelet-targeted therapies following lipid-lowering treatment in individuals with insulin resistance may be a promising therapeutic approach to promote atherosclerotic plaque inflammation-resolution.

PURPOSE OF REVIEW/OBJECTIVE:Cardiovascular diseases (CVDs) are a leading cause of death worldwide. While it is well known that obesity, dyslipidemia and diabetes are major risk factors of CVD, observational clinical studies have shown that variability in body weight, circulating LDL-cholesterol (LDL-C) or glucose levels further increase this risk. The underlying mechanisms, however, leading to increased risk of CVD due to metabolic cycling are not well understood. RECENT FINDINGS/RESULTS:Recent studies have shown that metabolic cycling can cause reprogramming of immune cells and their progenitors. Weight, LDL-C, or glucose cycling induced myelopoiesis, monocytosis and/or altered immune cell functions. This resulted in a heightened immune response, ultimately worsening atherosclerosis. SUMMARY/CONCLUSIONS:Even though there are differences in how metabolic cycling is measured in clinical and basic research studies, the conclusion remains the same: metabolic cycling increases CVD severity. Some studies have highlighted the role of reprogramming of myeloid cells and their progenitors in progression of atherosclerosis due to metabolic cycling, but further research is required to better understand the mechanisms behind it.

PURPOSE/OBJECTIVE:Lipoproteins are endogenous nanoparticles with essential roles in lipid transport and inflammation. Lipoproteins are also valuable in diagnosing and treating disease. For instance, certain lipoproteins are overexpressed in patients with atherosclerotic cardiovascular disease, and reconstituted lipoproteins have been extensively used for drug delivery. Radiolabeling has proven an especially powerful approach for studying and therapeutically exploiting lipoproteins. This review details how radiochemistry and nuclear imaging can facilitate the study of lipoproteins in health and disease. Among other topics, we discuss approaches for radiolabeling lipoproteins and detail how these have helped advance our understanding of lipoprotein biology and the diagnosis and treatment of diseases, including atherosclerosis, cancer, and hypercholesteremia. METHODS:We performed an extensive literature search on all peer-reviewed studies involving radiolabeled lipoproteins and selected representative examples to provide a high-level overview of the most important discoveries and technological advancements. RESULTS:More than 200 peer-reviewed papers involved radiolabeled lipoproteins, spanning mechanistic, diagnostic, and therapeutic studies across a wide range of diseases. CONCLUSION/CONCLUSIONS:Radiolabeling has been critical in advancing our understanding of lipoprotein biology and leveraging these nanomaterials for diagnosing and treating disease.

While weight loss is highly recommended for those with obesity, >60% will regain their lost weight. This weight cycling is associated with elevated risk of cardiovascular disease, relative to never having lost weight. How weight loss/regain directly influence atherosclerotic inflammation is unknown. Thus, we studied short-term caloric restriction (stCR) in obese hypercholesterolemic mice, without confounding effects from changes in diet composition. Weight loss was found to promote atherosclerosis resolution independent of plasma cholesterol. From single-cell RNA-sequencing and subsequent mechanistic studies, this can be partly attributed to a unique subset of macrophages accumulating with stCR in epididymal white adipose tissue (eWAT) and atherosclerotic plaques. These macrophages, distinguished by high expression of Fcgr4, help to clear necrotic cores in atherosclerotic plaques. Conversely, weight regain (WR) following stCR accelerated atherosclerosis progression with disappearance of Fcgr4+ macrophages from eWAT and plaques. Furthermore, WR caused reprogramming of immune progenitors, sustaining hyper-inflammatory responsiveness. In summary, we have developed a model to investigate the inflammatory effects of weight cycling on atherosclerosis and the interplay between adipose tissue, bone marrow, and plaques. The findings suggest potential approaches to promote atherosclerosis resolution in obesity and weight cycling through induction of Fcgr4+ macrophages and inhibition of immune progenitor reprogramming.

The current generation of highly successful atherosclerosis treatments, such as low-density lipoprotein (LDL)-cholesterol reduction, blood pressure management, and smoking cessation, has largely focused on ameliorating factors perceived to drive incident disease and its complications. The adverse contributions of these factors have typically been identified through epidemiological studies. The therapeutic strategies that arose in response focused on risk factors for disease development and tended to overlook the fact that patients already have established disease, by the time of presentation. However, by capitalizing on contemporary biological knowledge and technologies, it is becoming increasingly possible to shift from a model based on population-derived risk factor management to next-generation treatments (including monoclonal antibodies, small interfering RNA [siRNA], mRNA, epigenetic reprogramming, and gene editing) for atherosclerosis that are tailored to patient-level disease processes, informed by mechanistic characterization, offer potential to reverse or regress disease, and incorporate systems-level interventions that extend beyond the atherosclerotic plaque.

Atherosclerotic cardiovascular diseases (ASCVD) remain the leading cause of death globally. Animal and human studies link psychological stress-related disorders to ASCVD. Despite this accumulating evidence linking stress to increased cardiovascular disease (CVD) risk, it remains unclear whether stress impairs the benefits of standard risk-reduction therapies, of which lipid-lowering remains the most common, or whether this increased risk is driven by systemic inflammatory states. We tested the hypothesis that psychological stress limits the benefits of lipid lowering on resolving inflammation in atherosclerotic plaques by combining two established mouse models, namely one in which levels of atherogenic LDL cholesterol (LDL-C) can be lowered after plaques develop, and the other a model of chronic social defeat stress (CSDS). Here we show that mice susceptible to CSDS ("SUS") had attenuated benefits of LDL-C lowering compared to control (CON) or resilient (RES) mice. Moreover, in SUS mice (vs. CON or RES) there was heightened inflammation in the plaque macrophages, with evidence that this was a result of re-programming in the bone marrow (BM) of the precursors of macrophages, namely monocytes. Remarkably, these observations aligned with human imaging studies, in which LDL-C lowering therapy was not as effective in reducing either systemic or arterial inflammation in subjects with higher (vs. lower) neural imaging measures of psychological stress. In summary, the integration of the mouse model and human data provides important mechanistic and clinical insights into the crucial role of chronic stress in ASCVD, highlighting that this common risk factor impairs the anti-atherosclerotic benefits of lipid-lowering medications and may represent an important determinant of residual ASCVD risk.

Angiopoietin-like 3 (ANGPTL3) inhibits lipases that hydrolyze triglycerides (TGs) in TG-rich lipoproteins (TRLs). We evaluated TRL-TGs, TRL particle (apolipoprotein B), palmitate, and glucose kinetics during a mixed-meal test that included intravenous and oral tracer administrations in people with extremely rare compound heterozygous ANGTPL3 loss-of-function mutations (ANGPTL3^-/- group, n = 3) and matched control participants (n = 7). Multi-organ (liver, muscle, and adipose tissue) insulin sensitivity was evaluated with a two-step hyperinsulinemic-euglycemic clamp procedure and glucose and palmitate tracer infusions. We find that plasma TG and TRL particle concentrations are more than 10-fold lower in the ANGPTL3^-/- than in the control group due to both markedly reduced liver-derived TRL particle and TG secretion rates combined with increased plasma clearance of both liver- and gut-derived TRLs. Palmitate and glucose kinetics during the meal test are not different between the groups. We conclude that the biological function of ANGPTL3 reaches beyond inhibiting intravascular lipase activity.

BACKGROUND/UNASSIGNED:Cholesterol efflux capacity (CEC) of HDL (high-density lipoprotein) is inversely associated with incident cardiovascular events, independent of HDL cholesterol. Obesity is characterized by low HDL cholesterol and impaired HDL function, such as CEC. Bariatric surgery, including Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), broadly leads to improved cardiovascular outcomes, but impacts on risk factors differ by procedure, with greater improvements in weight loss, blood pressure, and glycemic control after RYGB, but greater improvements in HDL cholesterol and CEC levels after SG. This study sought to determine effects of RYGB and SG on HDL protein and lipid cargo and investigate associations with CEC changes. METHODS/UNASSIGNED:We prospectively studied nondiabetic, premenopausal Hispanic women with severe obesity not using lipid medications undergoing RYGB (n=31) or SG (n=36). Anthropometric measurements and blood sampling were obtained before and at 6 and 12 months after surgery. HDL was isolated from plasma, and quantitative proteomic and lipidomic assessments were performed with LC-MS/MS (liquid chromatography with tandem mass spectrometry). CEC was assessed ex vivo using apoB-depleted serum. RESULTS/UNASSIGNED:Participants experienced similar, significant weight loss over 12 months following bariatric surgery (38.0±10.4 kg) regardless of the procedure. Relative quantities of 47 proteins (34 increased, 13 decreased) and 150 lipids (71 increased, 79 decreased) carried on HDL were significantly altered following either surgical procedure. Proteins with similar aggregate response patterns were clustered into 15 groups (5 increased, 5 decreased, 5 minimal change) and lipids with similar aggregate responses into 25 groups (7 increased, 11 decreased, 7 minimal change). Network mediation analyses suggested that changes in 4 protein and 2 lipid clusters mediated changes in ABCA1 (ATP-binding cassette transporter A1) CEC and that 1 lipid cluster mediated changes in non-ABCA1 CEC. The protein and lipid clusters that mediated changes in CEC were distinct between SG and RYGB. CONCLUSIONS/UNASSIGNED:Bariatric surgery produces substantial changes in HDL lipid and protein cargo, and specific changes may mediate changes in HDL function in CEC. Further study of these mechanisms may lead to improved interventions to reduce cardiovascular risk in patients with obesity.