The role of the cardiomyocyte circadian clocks in ion channel regulation and cardiac electrophysiology

Circadian (Diurnal/Nocturnal) Pattern of Cardiac Arrhythmias

Circadian rhythms follow 24-hour biological-cycle patterns controlled by internal biological or circadian clocks that optimize organismal homeostasis according to predictable environmental changes. These clocks are found in virtually all cells in the body, including cardiomyocytes. Triggers for and/or the occurrence of sudden cardiac death (SCD), and cardiac arrhythmias seem to follow such daily patterns. This review highlights data from studies exploring the role of day/night rhythms in the timing of arrhythmic events, studies describing the enviromental, behavioral and circadian mechanisms regulating cardiac electrophysiology focusing on the circadian pattern of arrhythmias and SCD. Mechanisms involved relate to circadian control of electrophysiological properties, vagal tone, and sleep disorders, as well as the potential interaction and synergism among these factors. By studying the diurnal variations of arrhythmias, therapy can be improved by optimally timing it to their circadian pattern and a person's internal body clock-time. Potential treatment targets for arrhythmias with nocturnal onset may include upstream therapy for underlying comorbidities, type and timing of drug intake, pulmonary vein isolation, ablation of the ganglionated plexus, and autonomic nervous system control. Thus, specific history taking, screening and diagnostic workup are recommended to identify and characterize comorbidities and potential contributors to nocturnal arrhythmias, such as obesity, advanced age, diabetes, hypertension and heart failure. In this direction, symptoms of sleep apnea may comprise snoring and excessive daytime sleepiness. Risk factors include obesity, decreased upper airway dimensions, and heart failure. Thus, one should have a low threshold for sleep testing to assess for sleep apnea. Sleep apnea treatment decreases ventricular arrhythmias and ameliorates some severe bradycardic episodes often obviating the need for pacemaker implantation. Importantly, comorbidity treatment and lifestyle optimization remain crucial.

Feeding behavior modifies the circadian variation in RR and QT intervals by distinct mechanisms in mice

Rhythmic feeding behavior is critical for regulating phase and amplitude in the ≈24-h variation of heart rate (RR intervals), ventricular repolarization (QT intervals), and core body temperature in mice. We hypothesized changes in cardiac electrophysiology associated with feeding behavior were secondary to changes in core body temperature. Telemetry was used to record electrocardiograms and core body temperature in mice during ad libitum-fed conditions and after inverting normal feeding behavior by restricting food access to the light cycle. Light cycle-restricted feeding modified the phase and amplitude of 24-h rhythms in RR and QT intervals, and core body temperature to realign with the new feeding time. Changes in core body temperature alone could not account for changes in phase and amplitude in the ≈24-h variation of the RR intervals. Heart rate variability analysis and inhibiting β-adrenergic and muscarinic receptors suggested that changes in the phase and amplitude of 24-h rhythms in RR intervals were secondary to changes in autonomic signaling. In contrast, changes in QT intervals closely mirrored changes in core body temperature. Studies at thermoneutrality confirmed that the daily variation in QT interval, but not RR interval, primarily reflected daily changes in core body temperature (even in ad libitum-fed conditions). Correcting the QT interval for differences in core body temperature helped unmask QT interval prolongation after starting light cycle-restricted feeding and in a mouse model of long QT syndrome. We conclude feeding behavior alters autonomic signaling and core body temperature to regulate phase and amplitude in RR and QT intervals, respectively.NEW & NOTEWORTHY We used time-restricted feeding and thermoneutrality to demonstrate that different mechanisms regulate the 24-h rhythms in heart rate and ventricular repolarization. The daily rhythm in heart rate reflects changes in autonomic input, whereas daily rhythms in ventricular repolarization reflect changes in core body temperature. This novel finding has major implications for understanding 24-h rhythms in mouse cardiac electrophysiology, arrhythmia susceptibility in transgenic mouse models, and interpretability of cardiac electrophysiological data acquired in thermoneutrality.

Feeding Behavior Modifies the Circadian Variation in RR and QT intervals by Distinct Mechanisms in Mice

Rhythmic feeding behavior is critical for regulating the phase and amplitude in the ≍24-hour variation of the heart rate (RR intervals), ventricular repolarization (QT intervals), and core body temperature in mice. We hypothesized the changes in cardiac electrophysiology associated with feeding behavior were secondary to changes in core body temperature. Telemetry was used to record electrocardiograms and core body temperature in mice during ad libitum-fed conditions and after inverting normal feeding behavior by restricting food access to the light cycle. Light cycle-restricted feeding quickly modified the phase and amplitude of the 24-hour rhythms in RR intervals, QT intervals, and core body temperature to realign with the new feeding time. Heart rate variability analysis and inhibiting β-adrenergic and muscarinic receptors suggested that the changes in the phase and amplitude of the 24-hour rhythms in RR intervals were secondary to changes in autonomic signaling. In contrast, the changes in the QT intervals closely mirrored changes in core body temperature. Studies at thermoneutrality confirmed the daily variation in the QT interval, but not the RR interval, and reflected daily changes in core body temperature (even in ad libitum-fed conditions). Correcting the QT interval for differences in core body temperature helped to unmask QT interval prolongation after starting light cycle-restricted feeding and in a mouse model of long QT syndrome. We conclude feeding behavior alters autonomic signaling and core body temperature to regulate the phase and amplitude in RR and QT intervals, respectively.

Hapln1 promotes dedifferentiation and proliferation of iPSC-derived cardiomyocytes by promoting versican-based GDF11 trapping

Hyaluronan and proteoglycan link protein 1 (Hapln1) supports active cardiomyogenesis in zebrafish hearts, but its regulation in mammal cardiomyocytes is unclear. This study aimed to explore the potential regulation of Hapln1 in the dedifferentiation and proliferation of cardiomyocytes and its therapeutic value in myocardial infarction with human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs) and an adult mouse model of myocardial infarction. HiPSC-CMs and adult mice with myocardial infarction were used as in vitro and in vivo models, respectively. Previous single-cell RNA sequencing data were retrieved for bioinformatic exploration. The results showed that recombinant human Hapln1 (rhHapln1) promotes the proliferation of hiPSC-CMs in a dose-dependent manner. As a physical binding protein of Hapln1, versican interacted with Nodal growth differentiation factor (NODAL) and growth differentiation factor 11 (GDF11). GDF11, but not NODAL, was expressed by hiPSC-CMs. GDF11 expression was unaffected by rhHapln1 treatment. However, this molecule was required for rhHapln1-mediated activation of the transforming growth factor (TGF)-β/Drosophila mothers against decapentaplegic protein (SMAD)2/3 signaling in hiPSC-CMs, which stimulates cell dedifferentiation and proliferation. Recombinant mouse Hapln1 (rmHapln1) could induce cardiac regeneration in the adult mouse model of myocardial infarction. In addition, rmHapln1 induced hiPSC-CM proliferation. In conclusion, Hapln1 can stimulate the dedifferentiation and proliferation of iPSC-derived cardiomyocytes by promoting versican-based GDF11 trapping and subsequent activation of the TGF-β/SMAD2/3 signaling pathway. Hapln1 might be an effective hiPSC-CM dedifferentiation and proliferation agent and a potential reagent for repairing damaged hearts.

Circadian regulation of sinoatrial nodal cell pacemaking function: Dissecting the roles of autonomic control, body temperature, and local circadian rhythmicity

Strong circadian (~24h) rhythms in heart rate (HR) are critical for flexible regulation of cardiac pacemaking function throughout the day. While this circadian flexibility in HR is sustained in diverse conditions, it declines with age, accompanied by reduced maximal HR performance. The intricate regulation of circadian HR involves the orchestration of the autonomic nervous system (ANS), circadian rhythms of body temperature (CRBT), and local circadian rhythmicity (LCR), which has not been fully understood. Here, we developed a mathematical model describing ANS, CRBT, and LCR in sinoatrial nodal cells (SANC) that accurately captures distinct circadian patterns in adult and aged mice. Our model underscores how the alliance among ANS, CRBT, and LCR achieves circadian flexibility to cover a wide range of firing rates in SANC, performance to achieve maximal firing rates, while preserving robustness to generate rhythmic firing patterns irrespective of external conditions. Specifically, while ANS dominates in promoting SANC flexibility and performance, CRBT and LCR act as primary and secondary boosters, respectively, to further enhance SANC flexibility and performance. Disruption of this alliance with age results in impaired SANC flexibility and performance, but not robustness. This unexpected outcome is primarily attributed to the age-related reduction in parasympathetic activities, which maintains SANC robustness while compromising flexibility. Our work sheds light on the critical alliance of ANS, CRBT, and LCR in regulating time-of-day cardiac pacemaking function and dysfunction, offering insights into novel therapeutic targets for the prevention and treatment of cardiac arrhythmias.

Detection of genetic variation in bovine CRY1 gene and its associations with carcass traits

The biological clock (also known as circadian clock) is closely related to growth and development, metabolism, and diseases in animals. As a part of the circadian clock, the cryptochrome circadian regulator 1 (CRY1) gene is involved in the regulation of biological processes such as osteogenesis, energy metabolism and cell proliferation, however, few studies have been reported on the relationship between this gene and animal carcass traits. Herein, a total of four insertion/deletion (InDel) loci within the CRY1 gene were detected in Shandong Black Cattle Genetic Resource (SDBCGR) population (n = 433). Among them, the P1-6-bp-del locus was polymorphic in population of interest. Moreover, the P1-6-bp-del locus showed two genotypes, with a higher insertion/insertion (II) genotype frequency (0.751) than insertion/deletion (ID) genotype frequency (0.249). Correlation analysis showed that the P1-6-bp-del locus polymorphisms were significantly associated with twenty carcass traits (e.g., slaughter weight, limb weight, and belly meat weight). Individuals with II genotype were significantly better than those with ID genotype for eighteen carcass traits. Therefore, the P1-6-bp-del locus of the CRY1 gene can be used as a molecular marker for beef cattle breeding.

Targeting mitochondrial circadian rhythms: The potential intervention strategies of Traditional Chinese medicine for myocardial ischaemia‒reperfusion injury

Coronary artery disease has one of the highest mortality rates in the country, and methods such as thrombolysis and percutaneous coronary intervention (PCI) can effectively improve symptoms and reduce mortality, but most patients still experience symptoms such as chest pain after PCI, which seriously affects their quality of life and increases the incidence of adverse cardiovascular events (myocardial ischaemiareperfusion injury, MIRI). MIRI has been shown to be closely associated with circadian rhythm disorders and mitochondrial dysfunction. Mitochondria are a key component in the maintenance of normal cardiac function, and new research shows that mitochondria have circadian properties. Traditional Chinese medicine (TCM), as a traditional therapeutic approach characterised by a holistic concept and evidence-based treatment, has significant advantages in the treatment of MIRI, and there is an interaction between the yin-yang theory of TCM and the circadian rhythm of Western medicine at various levels. This paper reviews the clinical evidence for the treatment of MIRI in TCM, basic experimental studies on the alleviation of MIRI by TCM through the regulation of mitochondria, the important role of circadian rhythms in the pathophysiology of MIRI, and the potential mechanisms by which TCM regulates mitochondrial circadian rhythms to alleviate MIRI through the regulation of the biological clock transcription factor. It is hoped that this review will provide new insights into the clinical management, basic research and development of drugs to treat MIRI.

The Circadian Biology of Heart Failure

Driven by autonomous molecular clocks that are synchronized by a master pacemaker in the suprachiasmatic nucleus, cardiac physiology fluctuates in diurnal rhythms that can be partly or entirely circadian. Cardiac contractility, metabolism, and electrophysiology, all have diurnal rhythms, as does the neurohumoral control of cardiac and kidney function. In this review, we discuss the evidence that circadian biology regulates cardiac function, how molecular clocks may relate to the pathogenesis of heart failure, and how chronotherapeutics might be applied in heart failure. Disrupting molecular clocks can lead to heart failure in animal models, and the myocardial response to injury seems to be conditioned by the time of day. Human studies are consistent with these findings, and they implicate the clock and circadian rhythms in the pathogenesis of heart failure. Certain circadian rhythms are maintained in patients with heart failure, a factor that can guide optimal timing of therapy. Pharmacologic and nonpharmacologic manipulation of circadian rhythms and molecular clocks show promise in the prevention and treatment of heart failure.

Diversification of Potassium Currents in Excitable Cells via Kvβ Proteins

Excitable cells of the nervous and cardiovascular systems depend on an assortment of plasmalemmal potassium channels to control diverse cellular functions. Voltage-gated potassium (Kv) channels are central to the feedback control of membrane excitability in these processes due to their activation by depolarized membrane potentials permitting K⁺ efflux. Accordingly, Kv currents are differentially controlled not only by numerous cellular signaling paradigms that influence channel abundance and shape voltage sensitivity, but also by heteromeric configurations of channel complexes. In this context, we discuss the current knowledge related to how intracellular Kvβ proteins interacting with pore complexes of Shaker-related Kv1 channels may establish a modifiable link between excitability and metabolic state. Past studies in heterologous systems have indicated roles for Kvβ proteins in regulating channel stability, trafficking, subcellular targeting, and gating. More recent works identifying potential in vivo physiologic roles are considered in light of these earlier studies and key gaps in knowledge to be addressed by future research are described.

Re-evaluating methods reporting practices to improve reproducibility: an analysis of methodological rigor for the Langendorff whole-heart technique

In recent decades, the scientific community has seen an increased interest in rigor and reproducibility. In 2017, concerns of methodological thoroughness and reporting practices were implicated as significant barriers to reproducibility within the preclinical cardiovascular literature, particularly in studies employing animal research. The Langendorff, whole-heart technique has proven to be an invaluable research tool, being modified in a myriad of ways to probe questions across the spectrum of physio- and pathophysiologic function of the heart. As a result, significant variability in the application of the Langendorff technique exists. This literature review quantifies the different methods employed in the implementation of the Langendorff technique and provides brief examples of how individual parametric differences can impact the outcomes and interpretation of studies. From 2017-2020, significant variability of animal models, anesthesia, cannulation time, and perfusate composition, pH, and temperature demonstrate that the technique has diversified to meet new challenges and answer different scientific questions. The review also reveals which individual methods are most frequently reported, even if there is no explicit agreement upon which parameters should be reported. The analysis of methods related to the Langendorff technique suggests a framework for considering methodological approach when interpreting seemingly contradictory results, rather than concluding that results are irreproducible.