Rhythm changes of clock genes, apoptosis-related genes and atherosclerosis-related genes in apolipoprotein E knockout mice

Acrolein, an environmental toxicant and its applications to in vivo and in vitro atherosclerosis models: An update

Cardiovascular disease, the foremost cause of death worldwide, is an overarching disease term that encompasses a number of disorders involving the heart and circulatory system, including atherosclerosis. Atherosclerosis is a primary cause of cardiovascular diseases and is caused by buildup of plaque and narrowing of blood vessels. Epidemiological studies have suggested that environmental pollutants are implicated in atherosclerosis disease progression. Among many environmental pollutants, acrolein (Acr) is an abundant reactive aldehyde and is ubiquitously present in cigarette smoke as well as food products (e.g., overheated oils and wine). Despite its ubiquitous presence and potential impact on the etiology of cardiovascular disease, a limited consensus has been made in regard to Acr exposure conditions to induce atherosclerosis in vivo. This mini-review summarizes in vivo atherosclerosis models using Acr to investigate biochemical and phenotypic changes related to atherosclerosis and in vitro mechanistic studies involving Acr and atherosclerosis.

Nuclear Receptors and Clock Components in Cardiovascular Diseases

Cardiovascular diseases (CVD) are still the first cause of death worldwide. Their main origin is the development of atherosclerotic plaque, which consists in the accumulation of lipids and inflammatory leucocytes within the vascular wall of large vessels. Beyond dyslipidemia, diabetes, obesity, hypertension and smoking, the alteration of circadian rhythms, in shift workers for instance, has recently been recognized as an additional risk factor. Accordingly, targeting a pro-atherogenic pathway at the right time window, namely chronotherapy, has proven its efficiency in reducing plaque progression without affecting healthy tissues in mice, thus providing the rationale of such an approach to treat CVD and to reduce drug side effects. Nuclear receptors are transcriptional factors involved in the control of many physiological processes. Among them, Rev-erbs and RORs control metabolic homeostasis, inflammatory processes and the biological clock. In this review, we discuss the opportunity to dampen atherosclerosis progression by targeting such ligand-activated core clock components in a (chrono-)therapeutic approach in order to treat CVD.

MicroRNA-21 Controls Circadian Regulation of Apoptosis in Atherosclerotic Lesions

Background: The necrotic core partly formed by ineffective efferocytosis increases the risk of an atherosclerotic plaque rupture. microRNAs contribute to necrotic core formation by regulating efferocytosis and macrophage apoptosis. Atherosclerotic plaque rupture occurs at increased frequency in the early morning, indicating diurnal changes in plaque vulnerability. Although circadian rhythms play a role in atherosclerosis, the molecular clock output pathways that control plaque composition and rupture susceptibility are unclear. Methods: Circadian gene expression, necrotic core size, and apoptosis and efferocytosis in aortic lesions were investigated at different times of the day in Apoe^-/-Mir21^+/+ mice and Apoe^-/- Mir21^-/- mice after consumption of a high-fat diet for 12 weeks feeding. Genome-wide gene expression and lesion formation were analyzed in bone marrow (BM)-transplanted mice. Diurnal changes in apoptosis and clock gene expression were determined in human atherosclerotic lesions. Results: The expression of molecular clock genes, lesional apoptosis, and necrotic core size were diurnally regulated in Apoe^-/- mice. Efferocytosis did not match the diurnal increase in apoptosis at the beginning of the active phase. However, in parallel with apoptosis, expression levels of oscillating Mir21 strands decreased in the mouse atherosclerotic aorta. Mir21 knockout abolished circadian regulation of apoptosis and reduced necrotic core size, but did not affect core clock gene expression. Further, Mir21 knockout upregulated expression of pro-apoptotic XIAP associated factor 1 (Xaf1) in the atherosclerotic aorta, which abolished circadian expression of Xaf1. The anti-apoptotic effect of Mir21 was mediated by non-canonical targeting of Xaf1 through both Mir21 strands. Mir21 knockout in BM cells also reduced atherosclerosis and necrotic core size. Circadian regulation of clock gene expression was confirmed in human atherosclerotic lesions. Apoptosis oscillated diurnally in phase with XAF1 expression, demonstrating an early morning peak anti-phase to that of the Mir21 strands. Conclusions: Our findings suggest that the molecular clock in atherosclerotic lesions induces a diurnal rhythm of apoptosis regulated by circadian Mir21 expression in macrophages that is not matched by efferocytosis, thus increasing the size of the necrotic core.

Circadian Rhythm: Potential Therapeutic Target for Atherosclerosis and Thrombosis

Every organism has an intrinsic biological rhythm that orchestrates biological processes in adjusting to daily environmental changes. Circadian rhythms are maintained by networks of molecular clocks throughout the core and peripheral tissues, including immune cells, blood vessels, and perivascular adipose tissues. Recent findings have suggested strong correlations between the circadian clock and cardiovascular diseases. Desynchronization between the circadian rhythm and body metabolism contributes to the development of cardiovascular diseases including arteriosclerosis and thrombosis. Circadian rhythms are involved in controlling inflammatory processes and metabolisms, which can influence the pathology of arteriosclerosis and thrombosis. Circadian clock genes are critical in maintaining the robust relationship between diurnal variation and the cardiovascular system. The circadian machinery in the vascular system may be a novel therapeutic target for the prevention and treatment of cardiovascular diseases. The research on circadian rhythms in cardiovascular diseases is still progressing. In this review, we briefly summarize recent studies on circadian rhythms and cardiovascular homeostasis, focusing on the circadian control of inflammatory processes and metabolisms. Based on the recent findings, we discuss the potential target molecules for future therapeutic strategies against cardiovascular diseases by targeting the circadian clock.

Acrolein-induced apoptosis of smooth muscle cells through NEAT1-Bmal1/Clock pathway and a protection from asparagus extract

Apoptosis of vascular smooth muscle cells (VSMCs) accelerates manifestation of plaque vulnerability in atherosclerosis. Long noncoding RNA NEAT1 participates in the proliferation and apoptosis of cells. In addition, circadian clock genes play a significant role in cell apoptosis. However, whether acrolein, an environmental pollutant, affects the apoptosis of VSMCs by regulating NEAT1 and clock genes is still elusive. We established VSMCs as an atherosclerotic cell model in vitro. Acrolein exposure reduced survival rate of VSMCs, and raised apoptosis percentage through upregulating the expression of Bax, Cytochrome c and Cleaved caspase-3 and downregulating Bcl-2. Asparagus extract (AE), as a dietary supplementation, was able to protect VSMCs against acrolein-induced apoptosis. Expression of NEAT1, Bmal1 and Clock was decreased by acrolein, while was ameliorated by AE. Knockdown of NEAT1, Bmal1 or Clock promoted VSMCs apoptosis by regulating Bax, Bcl-2, Cytochrome c and Caspase-3 levels. Correspondingly, overexpression of NEAT1 inhibited the apoptosis. We also observed that silence of NEAT1 repressed the expression of Bmal1/Clock and vice versa. In this study, we demonstrated that VSMCs apoptosis induced by acrolein was associated with downregulation of NEAT1 and Bmal1/Clock. AE alleviated the effects of proapoptotic response and circadian disorders caused by acrolein, which shed a new light on cardiovascular protection.

Transcriptomic regulation of seasonal coat color change in hares

Color molts from summer brown to winter white coats have evolved in several species to maintain camouflage year-round in environments with seasonal snow. Despite the eco-evolutionary relevance of this key phenological adaptation, its molecular regulation has only recently begun to be addressed. Here, we analyze skin transcription changes during the autumn molt of the mountain hare (Lepus timidus) and integrate the results with an established model of gene regulation across the spring molt of the closely related snowshoe hare (L. americanus). We quantified differences in gene expression among three stages of molt progression-"brown" (early molt), "intermediate," and "white" (late molt). We found 632 differentially expressed genes, with a major pulse of expression early in the molt, followed by a milder one in late molt. The functional makeup of differentially expressed genes anchored the sampled molt stages to the developmental timeline of the hair growth cycle, associating anagen to early molt and the transition to catagen to late molt. The progression of color change was characterized by differential expression of genes involved in pigmentation, circadian, and behavioral regulation. We found significant overlap between differentially expressed genes across the seasonal molts of mountain and snowshoe hares, particularly at molt onset, suggesting conservatism of gene regulation across species and seasons. However, some discrepancies suggest seasonal differences in melanocyte differentiation and the integration of nutritional cues. Our established regulatory model of seasonal coat color molt provides an important mechanistic context to study the functional architecture and evolution of this crucial seasonal adaptation.

Circadian locomotor output cycles kaput accelerates atherosclerotic plaque formation by upregulating plasminogen activator inhibitor-1 expression

To explore the association between clock circadian regulator circadian locomotor output cycles kaput gene (CLOCK) and the forming of atherosclerotic plaques and its underlying mechanisms, mouse aortic endothelial cells (MAECs) and atherosclerosis (AS) mouse model were recruited for our study. The apoE gene knockout mouse was used as the model of AS and we accelerated the formation of unstable plaques through the combination of carotid artery ligation and high-fat (HF) diet administration (0.2% cholesterol, 20% fat). The mRNA and protein expressions of CLOCK in peripheral blood monouclear cells of acute coronary syndrome (ACS) patients or mouse AS model were detected by qPCR, western blot analysis and immunohistochemical staining. The number of adherent cells and atherosclerotic plaques was counted to assess the effects of CLOCK on the progression of ACS, and adherence-associated genes, such as vascular cell adhesion molecule (VCAM)-1, C-C motif chemokine ligand 2 (CCL-2), and CCL-5. The results showed that CLOCK expression was significantly increased in both ACS patients and AS mouse model. The levels of CLOCK, leukemia inhibitory factor (LIF), intercellular adhesion molecule 1 (ICAM-1), perilipin 2 (ADFP), nuclear factor kappa B (NF-κB), and plasminogen activator inhibitor-1 (PAI-1), as well as the number of atherosclerotic plaques were elevated in the AS mouse model, as compared with the control group. Chromatin immunoprecipitation assay showed that CLOCK bound directly to the promoter of PAI-1 gene and CLOCK could positively regulate the expressions of LIF, ICAM-1, ADFP, NF-κB, and PAI-1. Reduction of CLOCK expression would decrease the expressions of VCAM-1, CCL-2, and CCL-5, and the number of adherent cells and atherosclerotic plaques, but these effects were neutralized when PAI-1 was simultaneously overexpressed in either mouse model or MAECs. Our results demonstrate that CLOCK overexpression triggers the formation of atherosclerotic plaques by directly upregulating PAI-1 expression.

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

Background

The clock genes are involved in regulating cardiovascular functions, and their expression disorders would lead to circadian rhythm disruptions of clock-controlled genes (CCGs), resulting in atherosclerotic plaque formation and rupture. Our previous study revealed the rhythmic expression of clock genes were attenuated in human plaque-derived vascular smooth muscle cells (PVSMCs), but failed to detect the downstream CCGs expressions and the underlying molecular mechanism. In this study, we examined the difference of CCGs rhythmic expression between human normal carotid VSMCs (NVSMCs) and PVSMCs. Furthermore, we compared the cholesterol and triglycerides levels between two groups and the link to clock genes and CCGs expressions.

Methods

Seven health donors’ normal carotids and 19 carotid plaques yielded viable cultured NVSMCs and PVSMCs. The expression levels of target genes were measured by quantitative real-time PCR and Western-blot. The intracellular cholesterol and triglycerides levels were measured by kits.

Result

The circadian expressions of apoptosis-related genes and fibrinolytic-related genes were disordered. Besides, the cholesterol levels were significant higher in PVSMCs. After treated with cholesterol or oxidized low density lipoprotein (ox-LDL), the expressions of clock genes were inhibited; and the rhythmic expressions of clock genes, apoptosis-related genes and fibrinolytic-related genes were disturbed in NVSMCs, which were similar to PVSMCs.

Conclusion

The results suggested that intracellular high cholesterol content of PVSMCs would lead to the disorders of clock genes and CCGs rhythmic expressions. And further studies should be conducted to demonstrate the specific molecular mechanisms involved.

Circadian Control of Inflammatory Processes in Atherosclerosis and Its Complications

Physiological cardiovascular functions show daily diurnal variations, which are synchronized by intrinsic molecular clocks and environment-driven cues. The clinical manifestation of cardiovascular disease also exhibits diurnal variation, with an increased incidence in the early morning. This coincides with circadian oscillations of circulating parameters, such as hormones and leukocyte counts. We are just at the beginning of understanding how circadian rhythms of immune functions are related to cardiovascular disease progression and outcome after an acute ischemic event. Here, we briefly summarize clinical data on oscillations of circulating inflammatory parameters, as well as experimental evidences for the role of circadian clocks in atherosclerosis, postmyocardial infarction inflammatory responses, and cardiac healing.

hCLOCK induction by hypoxia promotes inflammatory responses by activating the NF‑κB pathway

The expression and secretion of infla-mmation‑associated cytokines are induced by hypoxia. Circadian locomotor output cycles protein kaput (CLOCK) has previously been shown to activate the nuclear factor‑κB (NF‑κB) pathway, which is a key transcription factor during hypoxia. The present study evaluated the role of the NF‑κB pathway in the CLOCK‑induced inflammatory response. Under hypoxic conditions, the expression levels of NF‑κB and proinflammatory cytokines, including interleukin (IL)‑1, IL‑1β, IL‑6, intercellular adhesion molecule 1, cyclooxygenase 2 and tumor necrosis factor alpha, were significantly increased compared with under control conditions. Conversely, human umbilical vein endothelial cells (HUVECs) that were transfected with small hairpin RNA against human CLOCK exhibited reversed effects. Furthermore, inhibition of NF‑κB with pyrrolidine dithiocarbamate (PDTC) reduced the expression of proinflammatory cytokines in HUVECs treated under hypoxic conditions. In addition, the CLOCK‑induced inflammatory response was abolished with PDTC treatment. These findings suggest that the mechanism by which CLOCK induces inflammation mainly involves activation of the NF‑κB signaling pathway.

Degeneration and energy shortage in the suprachiasmatic nucleus underlies the circadian rhythm disturbance in ApoE-/- mice: implications for Alzheimer's disease

Alzheimer's disease (AD) patients suffer sleep disorders and circadian rhythm disturbances (CRDs). The underlying mechanisms are incompletely understood, and treatments are lacking. In this study, we characterized the locomotor activity, clock gene expression, morphological degeneration and energy metabolism of suprachiasmatic nucleus (SCN), together with retinal light sensing, in ApoE^-/- mice, a model for AD. Compared with the control C57BL/6J mice, ApoE^-/- mice exhibited disordered circadian locomotor activity under dim light and constant darkness, with impaired re-entrainment to phase change schedules. Decreased retinal melanopsin expression, together with amyloidosis and tau deposition, was evident in ApoE^-/- mice. Mitochondrial and synaptic deterioration, altered SIRT1-mediated energy metabolism and clock gene expression were also observed in ApoE^-/- SCN. Supplementation with fat or ketone bodies but not glucose, or intraperitoneal administration of nicotinamide, restored the locomotor rhythmicity and circadian expression of SIRT1 and clock genes, as well as reducing neurodegeneration. Taken together, ApoE deficiency induced degeneration and a significant disturbance in the SCN rhythmicity. Decline of retinal light sensing and SCN structural and metabolic deteriorations represented the major pathologies accounting for the CRDs in ApoE^-/- mice. Our curative experiments may help develop future therapies to treat the CRDs and sleep disorders in AD patients.

Altered Clock and Lipid Metabolism-Related Genes in Atherosclerotic Mice Kept with Abnormal Lighting Condition

Background. The risk of atherosclerosis is elevated in abnormal lipid metabolism and circadian rhythm disorder. We investigated whether abnormal lighting condition would have influenced the circadian expression of clock genes and clock-controlled lipid metabolism-related genes in ApoE-KO mice. Methods. A mouse model of atherosclerosis with circadian clock genes expression disorder was established using ApoE-KO mice (ApoE-KO LD/DL mice) by altering exposure to light. C57 BL/6J mice (C57 mice) and ApoE-KO mice (ApoE-KO mice) exposed to normal day and night and normal diet served as control mice. According to zeitgeber time samples were acquired, to test atheromatous plaque formation, serum lipids levels and rhythmicity, clock genes, and lipid metabolism-related genes along with Sirtuin 1 (Sirt1) levels and rhythmicity. Results. Atherosclerosis plaques were formed in the aortic arch of ApoE-KO LD/DL mice. The serum lipids levels and oscillations in ApoE-KO LD/DL mice were altered, along with the levels and diurnal oscillations of circadian genes, lipid metabolism-associated genes, and Sirt1 compared with the control mice. Conclusions. Abnormal exposure to light aggravated plaque formation and exacerbated disorders of serum lipids and clock genes, lipid metabolism genes and Sirt1 levels, and circadian oscillation.

Endotoxin Disrupts Circadian Rhythms in Macrophages via Reactive Oxygen Species

The circadian clock is a transcriptional network that functions to regulate the expression of genes important in the anticipation of changes in cellular and organ function. Recent studies have revealed that the recognition of pathogens and subsequent initiation of inflammatory responses are strongly regulated by a macrophage-intrinsic circadian clock. We hypothesized that the circadian pattern of gene expression might be influenced by inflammatory stimuli and that loss of circadian function in immune cells can promote pro-inflammatory behavior. To investigate circadian rhythms in inflammatory cells, peritoneal macrophages were isolated from mPer2^luciferase transgenic mice and circadian oscillations were studied in response to stimuli. Using Cosinor analysis, we found that LPS significantly altered the circadian period in peritoneal macrophages from mPer2^luciferase mice while qPCR data suggested that the pattern of expression of the core circadian gene (Bmal1) was disrupted. Inhibition of TLR4 offered protection from the LPS-induced impairment in rhythm, suggesting a role for toll-like receptor signaling. To explore the mechanisms involved, we inhibited LPS-stimulated NO and superoxide. Inhibition of NO synthesis with L-NAME had no effect on circadian rhythms. In contrast, inhibition of superoxide with Tempol or PEG-SOD ameliorated the LPS-induced changes in circadian periodicity. In gain of function experiments, we found that overexpression of NOX5, a source of ROS, could significantly disrupt circadian function in a circadian reporter cell line (U2OS) whereas iNOS overexpression, a source of NO, was ineffective. To assess whether alteration of circadian rhythms influences macrophage function, peritoneal macrophages were isolated from Bmal1-KO and Per-TKO mice. Compared to WT macrophages, macrophages from circadian knockout mice exhibited altered balance between NO and ROS release, increased uptake of oxLDL and increased adhesion and migration. These results suggest that pro-inflammatory stimuli can disrupt circadian rhythms in macrophages and that impaired circadian rhythms may contribute to cardiovascular diseases by altering macrophage behavior.

Hepatocyte growth factor regulates neovascularization in developing fat pads

In this study, we used lentiviral-delivered shRNA to generate a clonal line of 3T3-F442A preadipocytes with stable silencing of hepatocyte growth factor (HGF) expression and examined the long-term consequence of this modification on fat pad development. HGF mRNA expression was reduced 94%, and HGF secretion 79% (P < 0.01), compared with preadipocytes treated with nontargeting shRNA. Fat pads derived from HGF knockdown preadipocytes were significantly smaller (P < 0.01) than control pads beginning at 3 days postinjection (0.022 ± 0.003 vs. 0.037 ± 0.004 g), and further decreased in size at day 7 (0.015 ± 0.004 vs. 0.037 ± 0.003 g) and day 14 (0.008 ± 0.002 vs. 0.045 ± 0.007 g). Expression of the endothelial cell genes TIE1 and PECAM1 increased over time in control fat pads (1.6 ± 0.4 vs. 11.4 ± 1.7 relative units at day 3 and 14, respectively; P < 0.05) but not in HGF knockdown fat pads (1.1 ± 0.5 vs. 5.9 ± 2.2 relative units at day 3 and 14). Contiguous vascular structures were observed in control fat pads but were much less developed in HGF knockdown fat pads. Differentiation of preadipocytes to mature adipocytes was significantly attenuated in HGF knockdown fat pads. Fat pads derived from preadipocytes with knockdown of the HGF receptor c-MET were smaller than control pads at day 3 postinjection (0.034 ± 0.002 vs. 0.049 ± 0.004 g; P < 0.05), and remained the same size through day 14. c-MET knockdown fat pads developed a robust vasculature, and preadipocytes differentiated to mature adipocytes. Overall these data suggest that preadipocyte-secreted HGF is an important regulator of neovascularization in developing fat pads.

The rhythmic expression of clock genes attenuated in human plaque-derived vascular smooth muscle cells

BACKGROUND

Acute myocardial infarction and stroke are more likely to occur in the early morning. Circadian pacemakers are considered to be involved in the process. Many peripheral tissues and cells also contain clock systems. In this study, we examined whether the primary cultured human plaque-derived vascular smooth muscle cells (VSMCs) process circadian rhythmicity; furthermore, we investigated the expression difference of clock genes between normal human carotid VSMCs and human plaque-derived VSMCs.

METHODS

Fifty-six human carotid plaques provided the atherosclerotic tissue, and 21 samples yielded viable cultured primary VSMCs. The normal carotid VSMCs were cultured from donors' normal carotids. The mRNA levels of the target genes were measured by Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR).

RESULTS

After serum shock, both types of cells showed clear circadian expressions of Bmal1, Cry1, Cry2, Per1, Per2, Per3 and Rev-erbα mRNA; meanwhile the Clock mRNA show a rhythmic expression in plaque-derived SMCs but not in normal carotid VSMCs. The expression levels of these main clock genes were significantly attenuated in human plaque-derived VSMCs compared with normal human carotid VSMCs. The rhythm of Bmal1 mRNA in plaque-derived VSMCs was changed.

CONCLUSION

The present results demonstrate that the human plaque-derived VSMCs possess different circadian rhythmicity from that of normal carotid VSMCs. The rhythm changes of clock genes in plaque-derived VSMCs may be involved in the process of atherosclerosis and finally promote the rupture of plaque.

Clock upregulates intercellular adhesion molecule-1 expression and promotes mononuclear cells adhesion to endothelial cells

Clock is a basic helix-loop-helix (bHLH) transcription factor that plays important role in circadian rhythms of various physiological functions. Previous study showed that the expression of intercellular adhesion molecule-1 (ICAM-1) was reduced in the liver tissues of Clock mutant mice. However, how Clock regulates ICAM-1 expression and whether Clock affects cell adhesion function remain unknown. In the present study, we found that exogenous expression of Clock upregulated the gene expressions of ICAM-1 and other adhesion-related genes including VCAM1 and CCL-2, and increased the transcriptional activity of ICAM-1 in mouse brain microvascular endothelial cell lines. In contrast, loss of Clock decreased these gene expressions and ICAM-1 transcriptional activity. Chromatin immunoprecipitation (ChIP) assay revealed that Clock binds to the E-box-like enhancer of ICAM-1 gene. ICAM-1 gene showed rhythmic expression in endothelial cells after serum shock in vitro, suggesting ICAM-1 may be a Clock-controlled gene. Clock regulates the adhesion of mononuclear cells to endothelial cells via ICAM-1. Together, our findings show that Clock is a positive regulator of ICAM-1, and promotes the adhesion of mononuclear cells to endothelial cells.

Effect of hyperlipidemia on the expression of circadian genes in apolipoprotein E knock-out atherosclerotic mice

Background

Circadian patterns of cardiovascular vulnerability were well characterized, with a peak incidence of acute myocardial infarction and stroke secondary to atherosclerosis in the morning, which showed the circadian clock may take part in the pathological process of atherosclerosis induced by hyperlipidemia. Hence, the effect of hyperlipidemia on the expression of circadian genes was investigated in atherosclerotic mouse model.

Results

In apoE-/-mice on regular chow or high-fat diet, an atherosclerotic mouse model induced by heperlipidemia, we found that the peak concentration of serum lipids was showed four or eight hours later in apoE-/- mice, compared to C57BL/6J mice. During the artificial light period, a reduce in circulating level of serum lipids corresponded with the observed increase of the expression levels of some the transcription factors involved in lipid metabolism, such as PPARα and RXRα. Meanwhile, the expression of circadian genes was changed following with amplitude reduced or the peak mRNA level delayed.

Conclusions

Our studies indicated that heperlipidemia altered both the rhythmicity and expression of circadian genes. Diet-induced circadian disruption may affect the process of atherosclerosis and some acute cardiovascular disease.