New Strategies to Promote Macrophage Cholesterol Efflux

The capacity of macrophages to dispose of cholesterol deposited in the atherosclerotic plaque depends on their ability to activate cholesterol efflux pathways. To develop athero-protective therapies aimed at promoting macrophage cholesterol efflux, cholesterol metabolism in THP-1 monocyte-derived macrophages has been extensively studied, but the intrinsic sensitivity of monocytes and the lack of a standardized procedure to differentiate THP-1 monocytes into macrophages have made it difficult to utilize THP-1 macrophages in the same or similar degree of differentiation across studies. The variability has resulted in lack of understanding of how the differentiation affects cholesterol metabolism, and here we review and investigate the effects of THP-1 differentiation on cholesterol efflux. The degree of THP-1 differentiation was inversely associated with ATP binding cassette A1 (ABCA1) transporter-mediated cholesterol efflux. The differentiation-associated decrease in ABCA1-mediated cholesterol efflux occurred despite an increase in ABCA1 expression. In contrast, DSC1 expression decreased during the differentiation. DSC1 is a negative regulator of the ABCA1-mediated efflux pathway and a DSC1-targeting agent, docetaxel showed high potency and efficacy in promoting ABCA1-mediated cholesterol efflux in THP-1 macrophages. These data suggest that pharmacological targeting of DSC1 may be more effective than increasing ABCA1 expression in promoting macrophage cholesterol efflux. In summary, the comparison of THP-1 macrophage subtypes in varying degrees of differentiation provided new insights into cholesterol metabolism in macrophages and allowed us to identify a viable target DSC1 for the promotion of cholesterol efflux in differentiated macrophages. Docetaxel and other pharmacological strategies targeting DSC1 may hold significant potential for reducing atherogenic cholesterol deposition.

Relationship of Para and Perirenal Fat and High-Density Lipoprotein and Its Function in Patients with Type 2 Diabetes Mellitus

Background. Para and perirenal fat is a fat pad surrounding the kidneys. Recent studies showed the association between para and perirenal fat and cardiovascular diseases including atherosclerosis and hypertension. We aimed to assess the relationship between para-perirenal ultrasonographic fat thickness and serum high-density lipoprotein (HDL) level and cholesterol efflux capacity of HDL in patients with type 2 diabetes mellitus (T2DM). Methods. We recruited 58 subjects with T2DM and collected anthropometric indices including height, weight, waist circumference, and other clinical data. Para-perirenal ultrasonographic fat thickness (PUFT) was measured via ultrasound. Serum lipid profile and other metabolic indices were determined as well. Correlation analysis and regression analysis were performed to analyze the relationship between PUFT and HDL level and cholesterol efflux capacity in all patients and subgroups. Results. Patients with higher PUFT have lower serum HDL level but increased cholesterol efflux capacity. Further analysis showed that PUFT negatively correlated with the serum HDL level in all patients, with no difference in groups divided by body mass index (BMI). In addition, PUFT was positively correlated with cholesterol efflux capacity in all patients. Multiple stepwise regression analysis showed an independent association of PUFT and serum HDL level and cholesterol efflux capacity. Conclusions. PUFT is closely correlated with the serum HDL level and cholesterol efflux capacity in patients with T2DM.

Reduced Levels of ABCA1 Transporter Are Responsible for the Cholesterol Efflux Impairment in β-Amyloid-Induced Reactive Astrocytes: Potential Rescue from Biomimetic HDLs

The cerebral synthesis of cholesterol is mainly handled by astrocytes, which are also responsible for apoproteins’ synthesis and lipoproteins’ assembly required for the cholesterol transport in the brain parenchyma. In Alzheimer disease (AD), these processes are impaired, likely because of the astrogliosis, a process characterized by morphological and functional changes in astrocytes. Several ATP-binding cassette transporters expressed by brain cells are involved in the formation of nascent discoidal lipoproteins, but the effect of beta-amyloid (Aβ) assemblies on this process is not fully understood. In this study, we investigated how of Aβ1-42-induced astrogliosis affects the metabolism of cholesterol in vitro. We detected an impairment in the cholesterol efflux of reactive astrocytes attributable to reduced levels of ABCA1 transporters that could explain the decreased lipoproteins’ levels detected in AD patients. To approach this issue, we designed biomimetic HDLs and evaluated their performance as cholesterol acceptors. The results demonstrated the ability of apoA-I nanodiscs to cross the blood–brain barrier in vitro and to promote the cholesterol efflux from astrocytes, making them suitable as a potential supportive treatment for AD to compensate the depletion of cerebral HDLs.

Cyclophilin A Impairs Efferocytosis and Accelerates Atherosclerosis by Overexpressing CD 47 and Down-Regulating Calreticulin

Impairment of efferocytosis in apoptotic macrophages is a known determinant of the severity of atherosclerosis and the vulnerability of plaques to rupture. The precise mechanisms involved in impaired efferocytosis are unclear. Given the well-recognized role of the inflammatory cytokine cyclophilin A (Cyp A) in modulating several atherogenic mechanisms in high-glucose primed monocytes, we investigated the role of Cyp A in macrophage efferocytosis. The efficiency of efferocytosis in RAW 264.7 macrophages grown in vitro and primed with cyclophilin A was assessed using flow cytometry and confocal assays. Cholesterol content in cells was measured using cell-based cholesterol efflux assay. Proteomic analysis and bioinformatics tools were employed to decipher the link between cyclophilin A and the known ligand receptors involved in efferocytosis. Cyclophilin A was found to impair efferocytosis in apoptotic macrophages by reducing ABCA1-mediated cholesterol efflux in foam cells derived from macrophages. Cyclophilin A-primed macrophages showed an increase in expression of the don’t-eat-me signal CD 47 and a decrease in the expression of the eat-me signal, calreticulin. Phagocytosis was restored upon silencing of cyclophilin A. New Zealand white rabbits were fed a high-fat diet, and lesions in their aortae were analyzed histologically for evidence of atherosclerosis and the expression of Cyp A, CD 47 and calreticulin, the ligand receptor involved in efferocytosis. Gene and protein expressions in aortae and macrophages were analyzed by real-time PCR and Western blotting. Cyclophilin A, via its effects on the expression of CD 47 and calreticulin, impairs efferocytosis in apoptotic macrophages. Together with its impact on cholesterol efflux from macrophages, these effects can amplify other mechanisms of Cyp A in accelerating the progression of atherosclerosis.

Cholesterol Efflux Capacity and Its Association With Adverse Cardiovascular Events: A Systematic Review and Meta-Analysis

Background: Serum high-density lipoprotein cholesterol (HDL-C) levels are inversely associated with cardiovascular disease events. Yet, emerging evidence suggests that it is the functional properties of HDL, in particular, reverse cholesterol transport, which is a key protective mechanism mediating cholesterol removal from macrophage cells and reducing plaque lipid content. Cholesterol efflux capacity (CEC) measures the capacity of HDL to perform this function. A systematic review and meta-analysis were conducted to explore the association of CEC and adverse cardiovascular events.Methods: A comprehensive literature review of Embase, PubMed, and Web of Science Core Collection from inception to September 2019 was performed for all studies that examined the association between CEC and cardiovascular outcomes. The primary outcome was adverse cardiovascular events, which were inclusive of atherosclerotic cardiovascular disease (ASCVD) or mortality.Results: A total of 20 trials were included. Compared with low CEC levels, high CEC levels were associated with a 37% lower risk of adverse cardiovascular events (crude RR = 0.63; 95% CI, 0.52–0.76; P < 0.00001). Every SD increase of CEC was associated with a 20% lower risk of adverse cardiovascular events (HR = 0.80; 95% CI, 0.66–0.97; P = 0.02). The association remained significant after adjusting for cardiovascular risk factors, medications, and HDL-C levels (HR = 0.76; 95% CI, 0.63–0.91; P = 0.004). A significant CEC-endpoint relationship was observed (P = 0.024) such that for every 0.1 unit increase in CEC, there was a 5% reduced risk for adverse cardiovascular events (RR = 0.95; 95% CI, 0.91–0.99).Conclusions: Higher CEC is associated with lower adverse cardiovascular outcomes. These findings warrant further research on whether CEC is merely a biomarker or a mechanism that could be targeted as a pharmacologic intervention for improving clinical outcomes.PROSPERO Registration Number: CRD42020146681; https://www.crd.york.ac.uk/prospero/.

Macrophage-Specific IGF-1 Overexpression Reduces CXCL12 Chemokine Levels and Suppresses Atherosclerotic Burden in Apoe-Deficient Mice

Objective: IGF-1 (insulin-like growth factor 1) exerts pleiotropic effects including promotion of cellular growth, differentiation, survival, and anabolism. We have shown that systemic IGF-1 administration reduced atherosclerosis in Apoe −/ − (apolipoprotein E deficient) mice, and this effect was associated with a reduction in lesional macrophages and a decreased number of foam cells in the plaque. Almost all cell types secrete IGF-1, but the effect of macrophage-derived IGF-1 on the pathogenesis of atherosclerosis is poorly understood. We hypothesized that macrophage-derived IGF-1 will reduce atherosclerosis. Approach and Results: We created macrophage-specific IGF-1 overexpressing mice on an Apoe − / − background. Macrophage-specific IGF-1 overexpression reduced plaque macrophages, foam cells, and atherosclerotic burden and promoted features of stable atherosclerotic plaque. Macrophage-specific IGF1 mice had a reduction in monocyte infiltration into plaque, decreased expression of CXCL12 (CXC chemokine ligand 12), and upregulation of ABCA1 (ATP-binding cassette transporter 1), a cholesterol efflux regulator, in atherosclerotic plaque and in peritoneal macrophages. IGF-1 prevented oxidized lipid-induced CXCL12 upregulation and foam cell formation in cultured THP-1 macrophages and increased lipid efflux. We also found an increase in cholesterol efflux in macrophage-specific IGF1–derived peritoneal macrophages. Conclusions: Macrophage IGF-1 overexpression reduced atherosclerotic burden and increased features of plaque stability, likely via a reduction in CXCL12-mediated monocyte recruitment and an increase in ABCA1-dependent macrophage lipid efflux.

Histone deacetylase 3 represses cholesterol efflux during CD4+ T-cell activation

After antigenic activation, quiescent naive CD4+ T cells alter their metabolism to proliferate. This metabolic shift increases production of nucleotides, amino acids, fatty acids, and sterols. Here, we show that histone deacetylase 3 (HDAC3) is critical for activation of murine peripheral CD4+ T cells. HDAC3-deficient CD4+ T cells failed to proliferate and blast after in vitro TCR/CD28 stimulation. Upon T-cell activation, genes involved in cholesterol biosynthesis are upregulated while genes that promote cholesterol efflux are repressed. HDAC3-deficient CD4+ T cells had reduced levels of cellular cholesterol both before and after activation. HDAC3-deficient cells upregulate cholesterol synthesis appropriately after activation, but fail to repress cholesterol efflux; notably, they overexpress cholesterol efflux transporters ABCA1 and ABCG1. Repression of these genes is the primary function for HDAC3 in peripheral CD4+ T cells, as addition of exogenous cholesterol restored proliferative capacity. Collectively, these findings demonstrate HDAC3 is essential during CD4+ T-cell activation to repress cholesterol efflux.