Inhibiting LXRα phosphorylation in hematopoietic cells reduces inflammation and attenuates atherosclerosis and obesity in mice

Atherosclerosis and obesity share pathological features including inflammation mediated by innate and adaptive immune cells. LXRα plays a central role in the transcription of inflammatory and metabolic genes. LXRα is modulated by phosphorylation at serine 196 (LXRα pS196), however, the consequences of LXRα pS196 in hematopoietic cell precursors in atherosclerosis and obesity have not been investigated. To assess the importance of LXRα phosphorylation, bone marrow from LXRα WT and S196A mice was transplanted into Ldlr^−/− mice, which were fed a western diet prior to evaluation of atherosclerosis and obesity. Plaques from S196A mice showed reduced inflammatory monocyte recruitment, lipid accumulation, and macrophage proliferation. Expression profiling of CD68⁺ and T cells from S196A mouse plaques revealed downregulation of pro-inflammatory genes and in the case of CD68⁺ upregulation of mitochondrial genes characteristic of anti-inflammatory macrophages. Furthermore, S196A mice had lower body weight and less visceral adipose tissue; this was associated with transcriptional reprograming of the adipose tissue macrophages and T cells, and resolution of inflammation resulting in less fat accumulation within adipocytes. Thus, reducing LXRα pS196 in hematopoietic cells attenuates atherosclerosis and obesity by reprogramming the transcriptional activity of LXRα in macrophages and T cells to promote an anti-inflammatory phenotype.

Voisin et al. show that reducing phosphorylation at serine 196 of LXRα (LXRα pS196) in hematopoietic cells attenuates atherosclerosis and obesity of mice fed a high-fat diet. They find that the transcriptional activity of LXRα is reprogrammed in macrophages and T cells to promote an anti-inflammatory phenotype, thus identifying a functional role of LXRα pS196 in immune cells.

Atherosclerosis Regression and Cholesterol Efflux in Hypertriglyceridemic Mice

[Figure: see text].

The Long Non-coding Road to Atherosclerosis

Purpose of Review

To summarize recent insights into long non-coding RNAs (lncRNAs) involved in atherosclerosis. Because atherosclerosis is the main underlying pathology of cardiovascular diseases (CVD), the world’s deadliest disease, finding novel therapeutic strategies is of high interest.

Recent Findings

LncRNAs can bind to proteins, DNA, and RNA regulating disease initiation and plaque growth as well as plaque stability in different cell types such as endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and macrophages. A number of lncRNAs have been implicated in cholesterol homeostasis and foam cell formation such as LASER, LeXis, and CHROME. Among others, MANTIS, lncRNA-CCL2, and MALAT1 were shown to be involved in vascular inflammation. Further regulations include, but are not limited to, DNA damage response in ECs, phenotypic switch of VSMCs, and various cell death mechanisms. Interestingly, some lncRNAs are closely correlated with response to statin treatment, such as NEXN-AS1 or LASER. Additionally, some lncRNAs may serve as CVD biomarkers.

Summary

LncRNAs are a potential novel therapeutic target to treat CVD, but research of lncRNA in atherosclerosis is still in its infancy. With increasing knowledge of the complex and diverse regulations of lncRNAs in the heterogeneous environment of atherosclerotic plaques, lncRNAs hold promise for their clinical translation in the near future.

Neutrophil extracellular traps promote macrophage inflammation and impair atherosclerosis resolution in diabetic mice

Neutrophil extracellular traps (NETs) promote inflammation and atherosclerosis progression. NETs are increased in diabetes and impair the resolution of inflammation during wound healing. Atherosclerosis resolution, a process resembling wound healing, is also impaired in diabetes. Thus, we hypothesized that NETs impede atherosclerosis resolution in diabetes by increasing plaque inflammation. Indeed, transcriptomic profiling of plaque macrophages from NET+ and NET- areas in low-density lipoprotein receptor-deficient (Ldlr-/-) mice revealed inflammasome and glycolysis pathway upregulation, indicating a heightened inflammatory phenotype. We found that NETs declined during atherosclerosis resolution, which was induced by reducing hyperlipidemia in nondiabetic mice, but they persisted in diabetes, exacerbating macrophage inflammation and impairing resolution. In diabetic mice, deoxyribonuclease 1 treatment reduced plaque NET content and macrophage inflammation, promoting atherosclerosis resolution after lipid lowering. Given that humans with diabetes also exhibit impaired atherosclerosis resolution with lipid lowering, these data suggest that NETs contribute to the increased cardiovascular disease risk in this population and are a potential therapeutic target.

Role of LpL (Lipoprotein Lipase) in Macrophage Polarization In Vitro and In Vivo

OBJECTIVE

Fatty acid uptake and oxidation characterize the metabolism of alternatively activated macrophage polarization in vitro, but the in vivo biology is less clear. We assessed the roles of LpL (lipoprotein lipase)-mediated lipid uptake in macrophage polarization in vitro and in several important tissues in vivo. Approach and Results: We created mice with both global and myeloid-cell specific LpL deficiency. LpL deficiency in the presence of VLDL (very low-density lipoproteins) altered gene expression of bone marrow-derived macrophages and led to reduced lipid uptake but an increase in some anti- and some proinflammatory markers. However, LpL deficiency did not alter lipid accumulation or gene expression in circulating monocytes nor did it change the ratio of Ly6C^high/Ly6C^low. In adipose tissue, less macrophage lipid accumulation was found with global but not myeloid-specific LpL deficiency. Neither deletion affected the expression of inflammatory genes. Global LpL deficiency also reduced the numbers of elicited peritoneal macrophages. Finally, we assessed gene expression in macrophages from atherosclerotic lesions during regression; LpL deficiency did not affect the polarity of plaque macrophages.

CONCLUSIONS

The phenotypic changes observed in macrophages upon deletion of Lpl in vitro is not mimicked in tissue macrophages.

Adipose tissue macrophages induce hepatic neutrophil recruitment and macrophage accumulation in mice

OBJECTIVE

Obesity is a risk factor for non-alcoholic steatohepatitis (NASH). This risk has been attributed to visceral adipose tissue (vAT) expansion associated with increased proinflammatory mediators. Accumulation of CD11c⁺ proinflammatory adipose tissue macrophages (ATM) is an important driver of vAT inflammation. We investigated the role of ATMs in hepatic inflammation during NASH development.

DESIGN

vAT isolated from lean, obese or ATM-depleted (using clodronate liposomes) obese mice was transplanted to lean ldlr^-/- acceptor mice. Systemic and hepatic inflammation was assessed either after 2 weeks on standard chow or after 8 weeks on high cholesterol diet (HCD) to induce NASH.

RESULTS

Transplanting donor vAT from obese mice increased HCD-induced hepatic macrophage content compared with lean-transplanted mice, worsening liver damage. ATM depletion prior to vAT transplantation reduced this increased hepatic macrophage accumulation. On chow, vAT transplantation induced a more pronounced increase in circulating and hepatic neutrophil numbers in obese-transplanted than lean-transplanted mice, while ATM depletion prior to vAT transplantation reversed this effect. Microarray analysis of fluorescence-activated cell sorting of CD11c⁺ and CD11c^- macrophages isolated from donor adipose tissue showed that obesity resulted in enhanced expression of neutrophil chemotaxis genes specifically in CD11c⁺ ATMs. Involvement of the neutrophil chemotaxis proteins, CXCL14 and CXCL16, was confirmed by culturing vAT. In humans, CD11c expression in vAT of obese individuals correlated with vAT expression of neutrophil chemotactic genes and with hepatic expression of neutrophil and macrophage marker genes.

CONCLUSION

ATMs from obese vAT induce hepatic macrophage accumulation during NASH development, possibly by enhancing neutrophil recruitment.

Abstract 388: High-density Lipoprotein Cholesterol Efflux Capacity is not associated with Atherosclerosis and Cardiovascular Events: the CODAM Study

Cholesterol Efflux Capacity (CEC) is considered to be a key atheroprotective property of high-density lipoproteins (HDL). However, its role in atherosclerosis risk is still controversial. In this study, we have analyzed the relationship between HDL CEC and atherosclerosis surrogates (carotid intima media thickness (cIMT), endothelial dysfunction (EnD); Z-Scores) in a well-characterized clinical population in the Cohort of Diabetes and Atherosclerosis Maastricht (CODAM) study, which consists of 574 individuals (age 59.6±0.3yrs, 61.3% men, 24.4% T2DM). Multiple linear regression analyses were performed to identify the associations in baseline data between HDL CEC (%), plasma HDL cholesterol (HDL-C, mmol/L), HDL size (nm), apoprotein A1 (ApoA1, g/L), and HDL Particle Concentration (HDL-P, nmol/L (LN), by NMR) with cIMT and EnD. Logistic regression analyses were done to identify the association of the above-mentioned HDL characteristics and CV events (CVE; N=499, 80 CVE cases). Analyses were adjusted for lifestyle, medication and metabolic confounders.

The results show that HDL-C (ß=-0.65, 95%CI -0.91; -0.42), HDL size (ß=-0.57, 95%CI -0.98; -0.15), apoA1 (ß=-0.65, 96%CI -1.01; -0.29), and HDL-P (ß=-0.77, 95%CI -1.47; -0.11) were inversely associated with EnD (N=532), whereas HDL CEC was not (ß=-0.03, 95%CI=-0.24;0.24). Interestingly, preliminary analyses show that these associations are lost in diabetic subjects (N=131), but not in non-diabetics (N=401). An inverse association also exists between HDL-C, HDL size, apoA1, and HDL-P with cIMT (N=494), which was not statistically significant likely due to variability and relative insensitivity of cIMT measurements. Further, a 1 unit increase of HDL-C was associated with ~4fold lower prevalence of CVE (OR=0.25, 95%CI 0.08;0.83), and for HDL-P, with ~20fold less CVE (OR=0.05, 95%CI 0.00;0.70), but no association was found between HDL CEC and CVE (OR=1.26, 95%CI 0.41;3.84).

Our results show that certain HDL-related parameters have atheroprotective associations, but HDL-CEC is not one of them. This result agrees with, but differs from, some other studies, and might reflect population differences in the relationships between measurements of HDL lipids/particle number, and HDL CEC.