Intracellular high cholesterol content disorders the clock genes, apoptosis-related genes and fibrinolytic-related genes rhythmic expressions in human plaque-derived vascular smooth muscle cells

BMAL1 modulates smooth muscle cells phenotypic switch towards fibroblast-like cells and stabilizes atherosclerotic plaques by upregulating YAP1

BACKGROUND

Ischemic heart diseases and ischemic stroke are closely related to circadian clock and unstable atherosclerotic plaques. Vascular smooth muscle cells (VSMCs) can stabilize or destabilize an atherosclerotic lesion through phenotypic switch. BMAL1 is not only an indispensable core component in circadian clock but also an important regulator in atherosclerosis and VSMCs proliferation. However, little is known about the modulation mechanisms of BMAL1 in VSMCs phenotypic switch and atherosclerotic plaque stability.

METHODS

We integrated histological analysis of human plaques, in vivo experiments of VSMC-specific Bmal1-/- mice, in vitro experiments, and gene set enrichment analysis (GSEA) of public datasets of human plaques to explore the function of BMAL1 in VSMCs phonotypic switch and plaque stability.

FINDINGS

Comparing to human unstable plaques, BMAL1 was higher in stable plaques, accompanied by elevated YAP1 and fibroblast maker FSP1 which were positively correlated with BMAL1. In response to Methyl-β-cyclodextrin-cholesterol, oxidized-low-density-lipoprotein and platelet-derived-growth-factor-BB, VSMCs embarked on phenotypic switch and upregulated BMAL, YAP1 and FSP1. Besides, BMAL1 overexpression promoted VSMCs phonotypic switch towards fibroblast-like cells by transcriptionally upregulating the expression of YAP1. BMAL1 or YAP1 knock-down inhibited VSMCs phonotypic switch and downregulated FSP1. Furthermore, VSMC-specific Bmal1-/- mice exhibited VSMCs with lower YAP1 and FSP1 levels, and more vulnerable plaques with less collagen content. In addition, BMAL1 suppressed the migration of VSMCs. The GSEA results of public datasets were consistent with our laboratory findings.

INTERPRETATION

Our results highlight the importance of BMAL1 as a major regulator in VSMCs phenotypic switch towards fibroblast-like cells which stabilize an atherosclerotic plaque.

Clock Gene Bmal1 Disruption in Vascular Smooth Muscle Cells Worsens Carotid Atherosclerotic Lesions

BACKGROUND

Clock system disruptions are associated with cardiovascular diseases. We previously demonstrated Bmal1 (brain muscle aryl nuclear translocase like-1) expression is significantly attenuated in plaque-derived vascular smooth muscle cells (VSMCs). However, the influence of Bmal1 disruption in VSMCs and its molecular targets are still unclear. Here, we aim to define how Bmal1 disruption in VSMCs influences the atherosclerosis lesions.

METHODS

The relationship among Bmal1, neurological symptoms, and plaque stability was investigated. VSMC Bmal1^-/- and VSMC Bmal1^+/+mice were generated and injected with adeno associated virus encoding mutant proprotein convertase subtilisin/kexin type 9 to induce atherosclerosis. Carotid artery ligation and cuff placement were performed in these mice to confirm the role of Bmal1 in atherosclerosis progression. The relevant molecular mechanisms were then explored.

RESULTS

Bmal1 expression in the carotid plague was significantly lower in symptomatic patients as well as in unstable plaques. Moreover, Bmal1 reduction is an independent risk factor for neurological symptoms and plaque instability. Besides, VSMC Bmal1^-/- mice exhibit aggravated atherosclerotic lesions. Further study demonstrated that Bmal1 downregulation in VSMCs increased VSMC migration, monocyte transmigration, reactive oxygen species levels, and VSMCs apoptosis. As for the mechanism, we revealed that Bmal1 suppresses VSMCs migration by inhibiting RAC1 activity in 2 ways: by activating the transcription of RhoGDIα and by interacting with RAC1. Besides, Bmal1 was shown to preserve antioxidant function in VSMCs by activating Nrf2 (nuclear factor erythroid 2-related factor 2) and Bcl-2 transcription.

CONCLUSIONS

Bmal1 disruption in VSMCs worsens atherosclerosis by promoting VSMC migration and monocyte transmigration and impairing antioxidant function. Therefore, Bmal1 may be a potential therapeutic target and biomarker of atherosclerosis in the future.

Valsartan-mediated chronotherapy in spontaneously hypertensive rats via targeting clock gene expression in vascular smooth muscle cells

OBJECTIVE

This study was to investigate the underlying mechanisms of valsartan chronotherapy in regulating blood pressure variability.

METHODS

RT-PCR was used to assay clock genes expression rhythm in the hypothalamus, aortic vessels, and target organs after valsartan chronotherapy. WB was used to measure Period 1 (Per1), Period 2 (Per2) protein expression in aortic vessels, as well as to measure phosphorylation of 20-kDa regulatory myosin light chain (MLC₂₀) in VSMCs.

RESULTS

Specific clock genes in the hypothalamus, and Per1 and Per2 in aorta abdominalis, exhibited disordered circadian expression in vivo. Valsartan asleep time administration (VSA) restored circadian clock gene expression in a tissue- and gene-specific manner. In vitro, VSA was more efficient in blocking angiotensin II relative to VWA, which led to differential circadian rhythms of Per1 and Per2, ultimately corrected MLC₂₀ phosphorylation.

CONCLUSION

VSA may be efficacious in regulating circadian clock genes rhythm, then concomitantly correct circadian blood pressure rhythms.

Circadian misalignment promotes vascular smooth muscle cell apoptosis via defective autophagy

Defective autophagy in vascular smooth muscle cells (VSMCs) in response to oxidative stress can lead to cellular apoptosis and plaque instability. Previous studies have revealed that the circadian clock system is involved in autophagic regulation and plaque progression. However, the mechanism by which circadian rhythmicity influences VSMC autophagy and plaque stability remains unclear. Our study described the circadian profiles in atheromatous plaques and verified the role of circadian misalignment in VSMC autophagy and apoptosis. We found that the mRNA expression levels of circadian locomotor output cycles protein kaput (CLOCK) and Beclin 1 were significantly decreased in unstable plaques compared with stable plaques. No significant differences were observed in other circadian rhythm genes. VSMCs treated with oxidized low-density lipoprotein (ox-LDL, 80 μg/ml) exhibited abnormal circadian rhythmicity and impaired autophagy, as evidenced by consistent decreases in CLOCK and Beclin 1 expression, suggesting a correlation between CLOCK and autophagy. CLOCK protein expression was inhibited by ox-LDL, accompanied by defective autophagy and an increased apoptosis rates (P < 0.05). Administration of rapamycin (10 nM) reversed the effect of ox-LDL on VSMC autophagy and apoptosis. Finally, CLOCK silencing led to a considerable decrease in autophagy. VSMCs with stable CLOCK silencing also showed an increased apoptosis rate. In addition, gene silencing of CLOCK in VSMCs counteracted the effects of moderate rapamycin concentrations on autophagy and apoptosis. In conclusion, these findings suggested that the CLOCK-dependent rapamycin signaling pathway is a critical mediator in ox-LDL-induced VSMCs with defective autophagy that exacerbates plaque destabilization.

The effect of genistein on lipid levels and LDLR, LXRα and ABCG1 expression in postmenopausal women with hyperlipidemia

BACKGROUND

This study investigates the effect of genistein (Gen) on the lipid profiles and expression of low-density lipoprotein receptor (LDLR), liver X receptor α (LXRα) and ATP-binding cassette transporter G1 (ABCG1) in the plasma macrophages of postmenopausal women with hyperlipidemia in China.

METHODS

This study considered 187 cases, where 160 postmenopausal women had hyperlipidemia. The subjects were divided into placebo group (PG) and experimental group (EG). EG received 60 mg/day of Gen, PG received placebo for 6 months. Body weight, height, waist circumference, body mass index and glucose levels were determined according to standard operating procedures. The triglyceride (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), apolipoprotein-A1 (Apo-A1) and apolipoprotein-B (Apo-B) levels were detected in the plasma macrophages using ELISA. The protein and mRNA expression levels of LDLR, LXRα and ABCG1 were detected by western blot and real-time PCR techniques, respectively.

RESULTS

Compared to the baseline, Gen effectively lowered TG, TC and LDL-C levels, whereas HDL-C levels as well as the protein and mRNA expression levels of LDLR, LXRα and ABCG1 (p < 0.05) were increased. There was a significant difference in the expression of LDLR protein between the two groups (p < 0.05). The mRNA expression levels of LDLR, LXRα and ABCG1 were significantly increased in the EG compared to the PG.

CONCLUSION

Gen effectively modulated the plasma lipid indices. The cholesterol-lowering effects of Gen may be attributed to its regulation on some of the key genes involved in cholesterol homeostasis.