Molecular mechanisms of morning onset of myocardial infarction

CircRNA MFACR Is Upregulated in Myocardial Infarction and Downregulates miR-125b to Promote Cardiomyocyte Apoptosis Induced by Hypoxia

ABSTRACT

Circular RNA (circRNA) MFACR promotes cardiomyocyte death that leads to myocardial infarction (MI). This study aimed to explore the role of MFACR in MI. T-qPCRs were performed to measure the expression levels of MFACR and miR-125b in plasma samples from both MI patients (n = 61) and healthy controls (n = 61). MFACR or miR-125b was overexpressed in AC16 cells (cardiomyocytes) to explore the interaction between them. Methylation of miR-125b gene in cells with the overexpression of MFACR was detected by methylation-specific PCR. Cell apoptosis after transfections was detected by cell apoptosis assay. MI model was constructed to further demonstrate the effect of MFACR in vivo. We found that MFACR was upregulated in MI and inversely correlated with miR-125b. In AC16 cells, hypoxia treatment increased the expression levels of MFACR and decreased the expression levels of miR-125b. In AC16 cells, overexpression of MFACR decreased the expression levels of miR-125b and increased the methylation of miR-125b gene. Under hypoxia treatment, overexpression of MFACR increased AC16 cell apoptosis, and overexpression of miR-125b decreased cell apoptosis. In addition, overexpression of miR-125b reversed the effects of overexpression of MFACR on cell apoptosis both in vivo and in vitro.

A Timely Call to Arms: COVID-19, the Circadian Clock, and Critical Care

We currently find ourselves in the midst of a global coronavirus disease 2019 (COVID-19) pandemic, caused by the highly infectious novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we discuss aspects of SARS-CoV-2 biology and pathology and how these might interact with the circadian clock of the host. We further focus on the severe manifestation of the illness, leading to hospitalization in an intensive care unit. The most common severe complications of COVID-19 relate to clock-regulated human physiology. We speculate on how the pandemic might be used to gain insights on the circadian clock but, more importantly, on how knowledge of the circadian clock might be used to mitigate the disease expression and the clinical course of COVID-19.

BMAL1 regulates mitochondrial fission and mitophagy through mitochondrial protein BNIP3 and is critical in the development of dilated cardiomyopathy

Dysregulation of circadian rhythms associates with cardiovascular disorders. It is known that deletion of the core circadian gene Bmal1 in mice causes dilated cardiomyopathy. However, the biological rhythm regulation system in mouse is very different from that of humans. Whether BMAL1 plays a role in regulating human heart function remains unclear. Here we generated a BMAL1 knockout human embryonic stem cell (hESC) model and further derived human BMAL1 deficient cardiomyocytes. We show that BMAL1 deficient hESC-derived cardiomyocytes exhibited typical phenotypes of dilated cardiomyopathy including attenuated contractility, calcium dysregulation, and disorganized myofilaments. In addition, mitochondrial fission and mitophagy were suppressed in BMAL1 deficient hESC-cardiomyocytes, which resulted in significantly attenuated mitochondrial oxidative phosphorylation and compromised cardiomyocyte function. We also found that BMAL1 binds to the E-box element in the promoter region of BNIP3 gene and specifically controls BNIP3 protein expression. BMAL1 knockout directly reduced BNIP3 protein level, causing compromised mitophagy and mitochondria dysfunction and thereby leading to compromised cardiomyocyte function. Our data indicated that the core circadian gene BMAL1 is critical for normal mitochondria activities and cardiac function. Circadian rhythm disruption may directly link to compromised heart function and dilated cardiomyopathy in humans.

Comparison of clinical outcomes in STEMI patients treated with primary PCI according to day-time of medical attention and its relationship with circadian pattern

OBJECTIVE

Relationship between STEMI time of presentation, its circadian pattern and cardiovascular outcomes is unclear. Our objective is to analyze clinical outcomes of STEMI according to time of presentation and circadian pattern.

METHODS

We analyzed data from patients treated within the regional STEMI Network from January 2010 to December 2015. On-hour group included patients treated between 8:00 h and 19:59 h on weekdays, the rest were catalogued as off-hour group. The primary endpoint was 1-year all-cause mortality. Secondary endpoints were 30-day all-cause mortality and in-hospital complications.

RESULTS

A total of 8608 patients were included, 44.1% in the on-hour group and 55.9% in the off-hour group. We observed a shorter patient delay and longer system delay in the off-hour group compared to on-hour group with no difference in total ischemic time. At 30-day and 1-year follow-up there were no differences in adjusted all-cause mortality between groups [OR 0.91 (CI95%: 0.73-1.12; p = 0.35) and OR 0.99 (CI95%: 0.83-1.17; p = 0.87), respectively]. A circadian pattern was observed between 9:00 am and 12:30 pm, with no differences in 30-day and 1-year mortality between patients included in this time interval [OR 1.02 (IC95%: 0.81-1.30; p = 0.85) and OR 1.12 (IC95%: 0.92-1.36; p = 0.25) respectively].

CONCLUSIONS

Off-hour STEMI presentation was associated with a shorter patient delay and longer system delay without an increase in total ischemic time. The off-hour presentation was not related to an increase in 1-year all-cause mortality when compared to on-hour. A circadian pattern was found, without differences in 30-day and 1-year mortality.

ASSOCIATION OF CIRCADIAN RHYTHM WITH MYOCARDIAL INFARCTION

- Cardiovascular diseases are the world's leading cause of death. Human physiologic activities and state during illness are under the control of circadian rhythm. The aim of the study was to determine the potential association of chronotype and daytime sleepiness with susceptibility to myocardial infarction. We conducted a case-control study on 200 patients hospitalized due to myocardial infarction and 200 healthy controls. Systematic information on the past and present medical history was obtained from all participants. Chronotype was assessed using the Morningness-Eveningness Questionnaire (MEQ), and daytime sleepiness was assessed by the Epworth Sleepiness Scale (ESS). The mean age of the study population was 64±13 years, and 54.5% were male. There was no significant difference in MEQ (58.88±6.52 vs. 58.46±7.78, p=0.601) or ESS (5 (interquartile range, IQR 4-7.5) vs. 6 (IQR 3-8), p=0.912) score between patients and controls. Nevertheless, we found statistically significant differences related to risk factors for cardiovascular diseases, such as hypertension, dyslipidemia, and diabetes mellitus. However, there was no association of MEQ and ESS score with myocardial infarction in the study population.

An overview of the emerging interface between cardiac metabolism, redox biology and the circadian clock

At various biological levels, mammals must integrate with 24-hr rhythms in their environment. Daily fluctuations in stimuli/stressors of cardiac metabolism and oxidation-reduction (redox) status have been reported over the course of the day. It is therefore not surprising that the heart exhibits dramatic oscillations in various cellular processes over the course of the day, including transcription, translation, ion homeostasis, metabolism, and redox signaling. This temporal partitioning of cardiac processes is governed by a complex interplay between intracellular (e.g., circadian clocks) and extracellular (e.g., neurohumoral factors) influences, thus ensuring appropriate responses to daily stimuli/stresses. The purpose of the current article is to review knowledge regarding control of metabolism and redox biology in the heart over the course of the day, and to highlight whether disruption of these daily rhythms contribute towards cardiac dysfunction observed in various disease states.

Circadian clock and the onset of cardiovascular events

The onset of cardiovascular diseases often shows time-of-day variation. Acute myocardial infarction or ventricular arrhythmia such as ventricular tachycardia occurs mainly in the early morning. Multiple biochemical and physiological parameters show circadian rhythm, which may account for the diurnal variation of cardiovascular events. These include the variations in blood pressure, activity of the autonomic nervous system and renin-angiotensin axis, coagulation cascade, vascular tone and the intracellular metabolism of cardiomyocytes. Importantly, the molecular clock system seems to underlie the circadian variation of these parameters. The center of the biological clock, also known as the central clock, exists in the suprachiasmatic nucleus. In contrast, the molecular clock system is also activated in each cell of the peripheral organs and constitute the peripheral clock. The biological clock system is currently considered to have a beneficial role in maintaining the homeostasis of each organ. Discoordination, however, between the peripheral clock and external environment could potentially underlie the development of cardiovascular events. Therefore, understanding the molecular and cellular pathways by which cardiovascular events occur in a diurnal oscillatory pattern will help the establishment of a novel therapeutic approach to the management of cardiovascular disorders.

The role of clock genes and circadian rhythm in the development of cardiovascular diseases

The time of onset of cardiovascular disorders such as myocardial infarctions or ventricular arrhythmias exhibits a circadian rhythm. Diurnal variations in autonomic nervous activity, plasma cortisol level or renin-angiotensin activity underlie the pathogenesis of cardiovascular diseases. Transcriptional-translational feedback loop of the clock genes constitute a molecular clock system. In addition to the central clock in the suprachiasmatic nucleus, clock genes are also expressed in a circadian fashion in each organ to make up the peripheral clock. The peripheral clock seems to be beneficial for anticipating external stimuli and thus contributes to the maintenance of organ homeostasis. Loss of synchronization between the central and peripheral clocks also augments disease progression. Moreover, accumulating evidence shows that clock genes affect inflammatory and intracellular metabolic signaling. Elucidating the roles of the molecular clock in cardiovascular pathology through the identification of clock controlled genes will help to establish a novel therapeutic approach for cardiovascular disorders.

Circadian Clocks in the Hematologic System

The hematologic system performs a number of essential functions, including oxygen transport, the execution of the immune response against tumor cells and invading pathogens, and hemostasis (blood clotting). These roles are performed by erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets), respectively. Critically, circadian rhythms are evident in the function of all 3 cell types. In this review, we describe these oscillations, explore their mechanistic bases, and highlight their key implications. Since erythrocytes are anucleate, circadian rhythms in these cells testify to the existence of a nontranscriptional circadian clock. From a clinical perspective, leukocyte rhythms could underlie daily variation in the severity of allergic reactions, the symptoms of chronic inflammatory diseases, and the body’s response to infection, while the rhythmic properties of thrombocytes may explain daily fluctuations in the incidence of heart attack and stroke. Consequently, the efficacy of treatments for these conditions is likely to depend on the timing of their administration. Last, we outline preliminary evidence that circadian disruption in the hematologic system could contribute to the deleterious effects of poor diet, shift work, and alcohol abuse on human health.

Large multiethnic Candidate Gene Study for C-reactive protein levels: identification of a novel association at CD36 in African Americans

C-reactive protein (CRP) is a heritable biomarker of systemic inflammation and a predictor of cardiovascular disease (CVD). Large-scale genetic association studies for CRP have largely focused on individuals of European descent. We sought to uncover novel genetic variants for CRP in a multiethnic sample using the ITMAT Broad-CARe (IBC) array, a custom 50,000 SNP gene-centric array having dense coverage of over 2,000 candidate CVD genes. We performed analyses on 7,570 African Americans (AA) from the Candidate gene Association Resource (CARe) study and race-combined meta-analyses that included 29,939 additional individuals of European descent from CARe, the Women's Health Initiative (WHI) and KORA studies. We observed array-wide significance (p < 2.2 × 10(-6)) for four loci in AA, three of which have been reported previously in individuals of European descent (IL6R, p = 2.0 × 10(-6); CRP, p = 4.2 × 10(-71); APOE, p = 1.6 × 10(-6)). The fourth significant locus, CD36 (p = 1.6 × 10(-6)), was observed at a functional variant (rs3211938) that is extremely rare in individuals of European descent. We replicated the CD36 finding (p = 1.8 × 10(-5)) in an independent sample of 8,041 AA women from WHI; a meta-analysis combining the CARe and WHI AA results at rs3211938 reached genome-wide significance (p = 1.5 × 10(-10)). In the race-combined meta-analyses, 13 loci reached significance, including ten (CRP, TOMM40/APOE/APOC1, HNF1A, LEPR, GCKR, IL6R, IL1RN, NLRP3, HNF4A and BAZ1B/BCL7B) previously associated with CRP, and one (ARNTL) previously reported to be nominally associated with CRP. Two novel loci were also detected (RPS6KB1, p = 2.0 × 10(-6); CD36, p = 1.4 × 10(-6)). These results highlight both shared and unique genetic risk factors for CRP in AA compared to populations of European descent.

Circadian rhythms in patients with ST-elevation myocardial infarction

BACKGROUND

Circadian rhythms with regard to time of symptom onset for patients with acute myocardial infarction have been observed, although their relationship to outcomes has been debated. We evaluated these rhythms in patients with ST-elevation myocardial infarction as a function of the 24-hour circadian cycle.

METHODS AND RESULTS

The relationship between onset of symptoms during the 24-hour circadian cycle and prehospital delays from symptom onset to hospital arrival, timeliness of reperfusion, and in-hospital death was assessed in 2143 patients with ST-elevation myocardial infarction presenting from 2004-2008 at 1 of 3 tertiary-care healthcare ST-elevation myocardial infarction systems. There was a significant association between time of onset and the circadian cycle, with the greatest percentage (39%) of patients experiencing onset between 8 AM and 3 PM (P<0.001). Time of onset was associated with prehospital delay and timeliness of reperfusion. Patients with onset from 12 AM to 5:59 AM had median prehospital delays of 121 minutes versus 70 minutes from 12 PM to 5:59 PM (P<0.001). Patients with onset time from 12 AM to 5:59 AM had median door-to-balloon times of 75 minutes versus 60 minutes from 6 AM to 11:59 AM (P<0.001). Using multivariable modeling to control for baseline patient characteristics, prehospital delay, and timeliness of reperfusion, there was no significant association between time of symptom onset with in-hospital death.

CONCLUSIONS

Patients with ST-elevation myocardial infarction exhibit significant circadian patterns in symptom onset, prehospital delay, and timeliness of reperfusion. Patients who develop symptoms from 12 AM to 5:59 AM present with longer prehospital delays and have longer door-to-balloon times. After multivariable adjustment, there was no significant association between circadian patterns of time of onset and in-hospital death.

Thrombomodulin is a clock-controlled gene in vascular endothelial cells

Cardiovascular diseases are closely related to circadian rhythm, which is under the control of an internal biological clock mechanism. Although a biological clock exists not only in the hypothalamus but also in each peripheral tissue, the biological relevance of the peripheral clock remains to be elucidated. In this study we searched for clock-controlled genes in vascular endothelial cells using microarray technology. The expression of a total of 229 genes was up-regulated by CLOCK/BMAL2. Among the genes that we identified, we examined the thrombomodulin (TM) gene further, because TM is an integral membrane glycoprotein that is expressed primarily in vascular endothelial cells and plays a major role in the regulation of intravascular coagulation. TM mRNA and protein expression showed a clear circadian oscillation in the mouse lung and heart. Reporter analyses, gel shift assays, and chromatin immunoprecipitation analyses using the TM promoter revealed that a heterodimer of CLOCK and BMAL2 binds directly to the E-box of the TM promoter, resulting in TM promoter transactivation. Indeed, the oscillation of TM gene expression was abolished in clock mutant mice, suggesting that TM expression is regulated by the clock gene in vivo. Finally, the phase of circadian oscillation of TM mRNA expression was altered by temporal feeding restriction, suggesting TM gene expression is regulated by the peripheral clock system. In conclusion, these data suggest that the peripheral clock in vascular endothelial cells regulates TM gene expression and that the oscillation of TM expression may contribute to the circadian variation of cardiovascular events.

Rapid attenuation of circadian clock gene oscillations in the rat heart following ischemia-reperfusion

The intracellular circadian clock consists of a series of transcriptional modulators that together allow the cell to perceive the time of day. Circadian clocks have been identified within various components of the cardiovascular system (e.g. cardiomyocytes, vascular smooth muscle cells) and possess the potential to regulate numerous aspects of cardiovascular physiology and pathophysiology. The present study tested the hypothesis that ischemia/reperfusion (I/R; 30 min occlusion of the rat left main coronary artery in vivo) alters the circadian clock within the ischemic, versus non-ischemic, region of the heart. Left ventricular anterior (ischemic) and posterior (non-ischemic) regions were isolated from I/R, sham-operated, and naïve rats over a 24-h period, after which mRNAs encoding for both circadian clock components and known clock-controlled genes were quantified. Circadian clock gene oscillations (i.e. peak-to-trough fold differences) were rapidly attenuated in the I/R, versus the non-ischemic, region. Consistent with decreased circadian clock output, we observe a rapid induction of E4BP4 in the ischemic region of the heart at both the mRNA and protein levels. In contrast with I/R, chronic (1 week) hypobaric chamber-induced hypoxia did not attenuate oscillations in circadian clock genes in either the left or right ventricle of the rat heart. In conclusion, these data show that in a rodent model of myocardial I/R, circadian clocks within the ischemic region become rapidly impaired, through a mechanism that appears to be independent of hypoxia.

Aryl hydrocarbon receptor nuclear translocator-like (BMAL1) is associated with susceptibility to hypertension and type 2 diabetes

Many aspects of physiology and behavior follow a circadian rhythm. Brain and muscle Arnt-like protein-1 (BMAL1) is a key component of the mammalian molecular clock, which controls circadian oscillations. In the rat, the gene encoding Bmal1 is located within hypertension susceptibility loci. We analyzed the SNP distribution pattern in a congenic interval associated with hypertension in the spontaneously hypertensive rat (SHR), and we show that Bmal1 maps close to a region genetically divergent between SHR and its normotensive (Wistar-Kyoto) counterpart. Bmal1 sequencing in rat strains identified 19 polymorphisms, including an SHR promoter variant that significantly affects Gata-4 activation of transcription in transient transfection experiments. A genetic association study designed to test the relevance of these findings in 1,304 individuals from 424 families primarily selected for type 2 diabetes showed that two BMAL1 haplotypes are associated with type 2 diabetes and hypertension. This comparative genetics finding translated from mouse and rat models to human provides evidence of a causative role of Bmal1 variants in pathological components of the metabolic syndrome.

Potential role for peripheral circadian clock dyssynchrony in the pathogenesis of cardiovascular dysfunction

Circadian clocks are intracellular molecular mechanisms designed to allow the cell, organ, and organism to prepare for an anticipated stimulus prior to its onset. In order for circadian clocks to maintain their selective advantage, they must be entrained to the environment. Light, sound, temperature, physical activity (including sleep/wake transitions), and food intake are among the strongest environmental factors influencing mammalian circadian clocks. Normal circadian rhythmicities in these environmental factors have become severely disrupted in our modern day society, concomitant with increased incidence of type 2 diabetes mellitus, obesity, and cardiovascular disease. Here, we review our current knowledge regarding the roles of peripheral circadian clocks, concentrating on those found within tissues directly involved in metabolic homeostasis and cardiovascular function. We propose that both inter- and intra-organ dyssynchronization, through alteration/impairment of peripheral circadian clocks, accelerates the development of cardiovascular disease risk factors associated with cardiometabolic syndrome.

Circadian Rhythms in the CNS and Peripheral Clock Disorders: Role of the Biological Clock in Cardiovascular Diseases

The cardiovascular diseases are closely related to circadian rhythm, which is under the control of the biological clock. Clock genes show circadian oscillation not only in the suprachiasmatic nucleus but also in peripheral tissues, suggesting the existence of the peripheral clock. We previously demonstrated that plasminogen activator inhibitor-1 (PAI-1) might be an output gene of the peripheral clock. To further elucidate the functional relevance of the peripheral clock in the cardiovascular system, we screened target genes of the peripheral clock by cDNA microarray analysis. A total of 29 genes including transcription factor, growth factors, and membrane receptors were upregulated by CLOCK/BMAL and showed circadian oscillation. These results suggest that cardiovascular systems have their own peripheral clocks, and at least in part, they may regulate the circadian oscillation of cardiovascular function directly. These results potentially provide a molecular basis for the circadian variation of cardiovascular function and novel strategies for the prevention and treatment of cardiovascular diseases.

Adrenal gland-dependent augmentation of plasminogen activator inhibitor-1 expression in streptozotocin-induced diabetic mice

BACKGROUND

Diabetes is associated with an excess risk of cardiac events, and one risk factor for infarction is an elevated level of plasminogen activator inhibitor-1 (PAI-1).

OBJECTIVES AND METHODS

To evaluate whether the glucocorticoid hormones are involved in the diabetes-induced PAI-1 production, we examined expression profiles of PAI-1 mRNA in adrenalectomized (ADX) mice with streptozotocin (STZ)-induced diabetes.

RESULTS

The diabetes-induced augmentation of plasma PAI-1 levels and PAI-1 mRNA expression in the heart and lungs was completely normalized in diabetic ADX mice. The glucocorticoid receptor antagonist RU486 significantly, but only partly suppressed PAI-1 induction in STZ-induced diabetic mice, suggesting that factors other than glucocorticoids are also involved in PAI-1 induction provoked by diabetes.

CONCLUSION

Our results suggested that the adrenal gland plays a critical role in the progression of thrombosis in diabetic patients by inducing expression of the PAI-1 gene.

The circadian clock within the heart: potential influence on myocardial gene expression, metabolism, and function

It is becoming increasingly clear that the intrinsic properties of both the heart and vasculature exhibit dramatic oscillations over the course of the day. Diurnal variations in the responsiveness of the cardiovascular system to environmental stimuli are mediated by a complex interplay between extracellular (i.e., neurohumoral factors) and intracellular (i.e., circadian clock) influences. The intracellular circadian clock is composed of a series of transcriptional modulators that together allow the cell to perceive the time of day, thereby enabling preparation for an anticipated stimulus. These molecular timepieces have been characterized recently within both vascular smooth muscle cells and cardiomyocytes, giving rise to a multitude of hypotheses relating to the potential role(s) of the circadian clock as a modulator of physiological and pathophysiological cardiovascular events. For example, evidence strongly supports the hypothesis that the circadian clock within the heart modulates myocardial metabolism, which in turn facilitates anticipation of diurnal variations in workload, substrate availability, and/or the energy supply-to-demand ratio. The purpose of this review is therefore to summarize our current understanding of the molecular events governing diurnal variations in the intrinsic properties of the heart, with special emphasis on the intramyocardial circadian clock. Whether impairment of this molecular mechanism contributes toward cardiovascular disease associated with hypertension, diabetes mellitus, shift work, sleep apnea, and/or obesity will be discussed.

New insights into the mechanisms of temporal variation in the incidence of acute coronary syndromes

Over the last few years, patterns have emerged regarding the daily (circadian), weekly (circaseptan), and yearly (circannual) variation in the incidence of acute coronary syndromes (ACS). Peaks of incidence occur in the morning, on Mondays, and in winter. There is a difference in the pattern of incidence in different subgroups such as diabetics and smokers, which, along with the incidence alteration seen with aspirin and beta blockers, gives us some potential understanding of underlying mechanisms. Recent advances in the study of endothelial function, cytokine biology, and adhesion molecules have led to new insights into the way that natural fluctuations in these systems may affect ACS incidence. It is hoped that understanding these developments will lead to therapeutic advances in ACS prevention.

Circadian rhythms in cardiac gene expression

Circadian rhythms in blood pressure, heart rate, and cardiac output have been intensely studied, largely due to the well-documented phenomenon of increased cardiovascular death in the early hours of the morning. Circadian rhythmicity in both cardiovascular physiology and pathophysiology has been attributed primarily to diurnal variations in neurohumoral factors, such as sympathetic activity. It has become increasingly apparent that the intrinsic properties of the heart (seen at the level of gene and protein expression, energy metabolism, and contractile function) show significant fluctuations during the course of the day. These changes might be due to extracardiac (eg, neurohumoral factors) and/or intracardiac (eg, circadian clocks) influences. Circadian clocks are transcriptionally based, molecular mechanisms that enable the cell to anticipate diurnal variations in environmental stimuli. The cardiac circadian clock synchronizes responsiveness of the heart to diurnal variations in its environment, and impairment of this mechanism might contribute to the pathogenesis of cardiovascular disease.