4β-Hydroxycholesterol is a prolipogenic factor that promotes SREBP1c expression and activity through the liver X receptor

Liver X Receptor Agonist 4β-Hydroxycholesterol as a Prognostic Factor in Coronary Artery Disease

BACKGROUND

Regardless of progress in treatment of coronary artery disease (CAD), there is still a significant residual risk of death in patients with CAD, highlighting the need for additional risk stratification markers. Our previous study provided evidence for a novel blood pressure-regulating mechanism involving 4β-hydroxycholesterol (4βHC), an agonist for liver X receptors, as a hypotensive factor. The aim was to determine the role of 4βHC as a prognostic factor in CAD.

METHODS AND RESULTS

The ARTEMIS (Innovation to Reduce Cardiovascular Complications of Diabetes at the Intersection) cohort consists of 1946 patients with CAD. Men and women were analyzed separately in quartiles according to plasma 4βHC. Basic characteristics, medications, ECG, and echocardiography parameters as well as mortality rate were analyzed. At baseline, subjects with a beneficial cardiovascular profile, as assessed with traditional markers such as body mass index, exercise capacity, prevalence of diabetes, and use of antihypertensives, had the highest plasma 4βHC concentrations. However, in men, high plasma 4βHC was associated with all-cause death, cardiac death, and especially sudden cardiac death (SCD) in a median follow-up of 8.8 years. Univariate and comprehensively adjusted hazard ratios for SCD in the highest quartile were 3.76 (95% CI, 1.6-8.7; P=0.002) and 4.18 (95% CI, 1.5-11.4; P=0.005), respectively. In contrast, the association of cardiac death and SCD in women showed the lowest risk in the highest 4βHC quartile.

CONCLUSIONS

High plasma 4βHC concentration was associated with death and especially SCD in men, while an inverse association was detected in women. Our results suggest 4βHC as a novel sex-specific risk marker of cardiac death and especially SCD in chronic CAD.

REGISTRATION INFORMATION

clinicaltrials.gov. Identifier NCT01426685.

Flindissone, a Limonoid Isolated from Trichilia prieuriana, Is an LXR Agonist

In this study, the ability of six limonoids from Trichilia prieuriana (Meliaceae) to activate the liver X receptor (LXR) was assessed. One of these limonoids, flindissone, was shown to activate LXR by reporter-gene assays. Flindissone is a ring-intact limonoid, structurally similar to sterol-like LXR ligands. In endogenous cellular settings, flindissone showed an activity profile that is characteristic of LXR agonists. It induced cholesterol efflux in THP-1 macrophages by increasing the cholesterol transporter ABCA1 and ABCG1 gene expression. In HepG2 cells, flindissone induced the expression of IDOL, an LXR-target gene that is associated with the downregulation of the LDL receptor. However, unlike synthetic and similarly to sterol-based LXR agonists, flindissone did not induce the expression of the SREBP1c gene, a major transcription factor regulating de novo lipogenesis. Additionally, flindissone also appeared to be able to inhibit post-translational activation of SREBP1c. The results presented here reveal a natural product as a new LXR agonist and point to an additional property of T. prieuriana and other plant extracts containing flindissone.

The role of TLR2 in exercise-induced immunomodulation in normal weight individuals

Toll-like receptors (TLRs) have been targeted for therapeutic drug development for several disorders, including cardiovascular diseases (CVD), and diabetes mellitus. Daily levels physical activity (PA) has been purported to influence the systemic circulation of cytokines, affecting the overall activation of TLRs and influencing the inflammatory milieu. Objective and self-reported daily PA was tracked in 69 normal-weight adults. Freedson's cut-offs categorized daily PA intensity into the 25th lowest, medium, and top percentiles. Monocytic TLR2 expression was quantified by flow cytometry in fresh whole blood. Cross-sectional associations between flow cytometry measured TLR2⁺ subsets and clinical biomarkers were evaluated. PA increased circulation of TLR2⁺ monocytes. TLR2 expression was adversely corelated with reduced diastolic blood pressure (DBP), triglyceride (TG), and matrix metallopeptidase 9 (MMP9) levels. However, regression analysis indicated that only TG levels were independently linked with TLR2⁺ subsets in circulation in active participants. Higher daily levels of physical activity are associated with improved cardiovascular blood markers and elevated circulatory monocytic TLR2⁺ subsets. These findings suggest that TLR2 may play a role in modulating CVD risk factors in individuals leading physically active lifestyles.

Targeting Liver X Receptors for the Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) refers to a range of conditions in which excess lipids accumulate in the liver, possibly leading to serious hepatic manifestations such as steatohepatitis, fibrosis/cirrhosis and cancer. Despite its increasing prevalence and significant impact on liver disease-associated mortality worldwide, no medication has been approved for the treatment of NAFLD yet. Liver X receptors α/β (LXRα and LXRβ) are lipid-activated nuclear receptors that serve as master regulators of lipid homeostasis and play pivotal roles in controlling various metabolic processes, including lipid metabolism, inflammation and immune response. Of note, NAFLD progression is characterized by increased accumulation of triglycerides and cholesterol, hepatic de novo lipogenesis, mitochondrial dysfunction and augmented inflammation, all of which are highly attributed to dysregulated LXR signaling. Thus, targeting LXRs may provide promising strategies for the treatment of NAFLD. However, emerging evidence has revealed that modulating the activity of LXRs has various metabolic consequences, as the main functions of LXRs can distinctively vary in a cell type-dependent manner. Therefore, understanding how LXRs in the liver integrate various signaling pathways and regulate metabolic homeostasis from a cellular perspective using recent advances in research may provide new insights into therapeutic strategies for NAFLD and associated metabolic diseases.

Thermal Proteome Profiling Reveals Distinct Target Selectivity for Differentially Oxidized Oxysterols

Oxysterols are produced physiologically by many species; however, their distinct roles in regulating human physiology have not been studied systematically. The role of differing oxidation states and sites in mediating their biological functions is also unclear. As oxysterols have been associated with atherosclerosis, neurodegeneration, and cancer, a better understanding of their protein targets is desirable. To address this, we mapped the oxysterol interactome with three A- and B-ring oxidized sterols as well as 25-hydroxy cholesterol using thermal proteome profiling, validating selected targets with the cellular thermal shift assay and isothermal dose response fingerprinting. This revealed that the site of oxidation has a profound impact on target selectivity, with each oxysterol possessing an almost unique set of target proteins. Overall, targets clustered in pathways relating to vesicular transport and phosphoinositide metabolism, suggesting that while individual oxysterols bind to a unique set of proteins, the processes they modulate are highly interconnected.

Association of demographic and health characteristics with circulating oxysterol concentrations

BACKGOUND

Circulating oxysterols, cholesterol metabolites with important signaling functions, are increasingly being recognized as candidate biomarkers for several diseases, but associations with demographic and health characteristics remain poorly described.

OBJECTIVE

This study aims to characterize associations of major circulating oxysterols with sex, age, race/ethnicity, body mass index (BMI), lifestyle factors, and use of common medications.

METHODS

We measured plasma concentrations of 27-hydroxycholesterol (27-OHC), 25-hydroxycholesterol (25-OHC), 24(S)-hydroxycholesterol (24(S)-OHC), 7ɑ-hydroxycholesterol (7ɑ-OHC), and 4β-hydroxycholesterol (4β-OHC) from 1,440 participants of a completed clinical trial for the chemoprevention of colorectal adenomas. Adjusted percent difference in means were calculated using linear regression.

RESULTS

Women had 18% (95% CI, 14%, 22%) lower 27-OHC and 21% (15%, 27%) higher 4β-OHC than men. Blacks had 15% (7%, 23%) higher 4β-OHC than Non-Hispanic Whites, and Asian or Pacific Islanders had 19% (2%, 35%) higher 7ɑ-OHC than Non-Hispanic Whites. Individuals of BMI ≥35 kg/m2 had 33% (25%, 41%) lower 4β-OHC than those <25 kg/m2. Current smokers had 15% (5%, 24%) higher 7ɑ-OHC than never smokers, and daily alcohol drinkers had 17% (10%, 24%) higher 7ɑ-OHC than never drinkers. Statin use was associated with lower concentrations of all 5 oxysterols. Differences in mean <15% were found for characteristics such as age, total dietary energy intake, physical activity, diabetes, and anti-inflammatory drug use.

CONCLUSION

Circulating oxysterols are uniquely associated with multiple demographic and health characteristics.

Pregnane X Receptor‒4β-Hydroxycholesterol Axis in the Regulation of Overweight- and Obesity-Induced Hypertension

Background Mechanisms mediating hypertensive effects of overweight and obesity have not been fully elucidated. We showed previously that activation of pregnane X receptor (PXR) by rifampicin elevates 24-hour blood pressure (BP) and plasma 4β-hydroxycholesterol (4βHC), agonist for liver X receptor (LXR). Methods and Results In combined "PXR activation data set" (n=62) of 4 clinical trials, 1 week rifampicin dosing increased office systolic BP (SBP) by 3.1 mm Hg, DBP 1.8 mm Hg, and mean arterial pressure 2.2 mm Hg in comparison with placebo (P<0.01). Plasma 4βHC had negative correlation with SBP both in rifampicin (r=-0.46, P=0.0002) and placebo (r=-0.45, P=0.0003) arms, although 4βHC was elevated >3-fold by rifampicin. In "non-intervention data set" (n=102) of patients with obesity and healthy volunteers (body mass index, 19.2-55.2 kg/m²), 4βHC had negative correlations (P<0.00001) with office SBP (r=-0.51), diastolic BP (r=-0.50), and mean arterial pressure (r=-0.54). Lean women had higher 4βHC than men, with increasing weight repressing 4βHC (r=-0.62, P<0.00001) in both sexes. In multiple linear regression analysis, the only statistically significant predictor for SBP was 4βHC. Six-day PXR agonist dosing elevated SBP in rats (n=7-8/group). PXR activation elevated 4βHC and after PXR agonist was withdrawn and elevated 4βHC was left to act alone, SBP was reduced on days 7 to 14 in comparison with control rats. Conclusions PXR activation elevates SBP. Elevated circulating 4βHC lowers SBP in rats, and higher 4βHC is an independent predictor of lower SBP in humans. PXR-4βHC-LXR is novel BP-regulating pathway deregulated in overweight and obesity by repressed 4βHC, with implications for sex-specific BP regulation. Registration URL: https://www.clinicaltrials.gov; Unique identifiers: NCT00985270, NCT01293422, NCT01690104, NCT02329405, and NCT01330251.

Integrative analysis reveals multiple modes of LXR transcriptional regulation in liver

The nuclear receptors liver X receptor (LXR) α and β play crucial roles in hepatic metabolism. Many genes induced in response to pharmacologic LXR agonism have been defined; however, the transcriptional consequences of loss of LXR binding to its genomic targets are less well characterized. Here, we addressed how deletion of both LXRα and LXRβ from mouse liver (LXR double knockout [DKO]) affects the transcriptional regulatory landscape by integrating changes in LXR binding, chromatin accessibility, and gene expression. Many genes involved in fatty acid metabolism showed reduced expression and chromatin accessibility at their intergenic and intronic regions in LXRDKO livers. Genes that were up-regulated with LXR deletion had increased chromatin accessibility at their promoter regions and were enriched for functions not linked to lipid metabolism. Loss of LXR binding in liver reduced the activity of a broad set of hepatic transcription factors, inferred through changes in motif accessibility. By contrast, accessibility at promoter nuclear factor Y (NF-Y) motifs was increased in the absence of LXR. Unexpectedly, we also defined a small set of LXR targets for direct ligand-dependent repression. These genes have LXR-binding sites but showed increased expression in LXRDKO liver and reduced expression in response to the LXR agonist. In summary, the binding of LXRs to the hepatic genome has broad effects on the transcriptional landscape that extend beyond its canonical function as an activator of lipid metabolic genes.

Ablation of fatty acid desaturase 2 (FADS2) exacerbates hepatic triacylglycerol and cholesterol accumulation in polyunsaturated fatty acid-depleted mice

Deficiency of polyunsaturated fatty acids (PUFAs) is known to induce hepatic steatosis. However, it is not clearly understood which type of PUFA is responsible for the worsening of steatosis. This study observed a marked accumulation of hepatic triacylglycerol and cholesterol in fatty acid desaturase 2 knockout (FADS2^-/- ) mice lacking both C18 and ≥ C20 PUFAs that were fed a PUFA-depleted diet. Hepatic triacylglycerol accumulation was associated with enhanced sterol regulatory element-binding protein (SREBP)-1-dependent lipogenesis and decreased triacylglycerol secretion into the plasma via very-low-density lipoprotein (VLDL). Furthermore, upregulation of cholesterol synthesis contributed to increased hepatic cholesterol content in FADS2^-/- mice. These results suggest that ≥ C20 PUFAs synthesized by FADS2 are important in regulating hepatic triacylglycerol and cholesterol accumulation during PUFA deficiency.