Circadian misalignment promotes vascular smooth muscle cell apoptosis via defective autophagy

Autophagy, Clock Genes, and Cardiovascular Disease

Circadian rhythms are 24-hour cycles that regulate physical, mental, and behavioural changes of most living organisms. In the heart, circadian rhythms regulate processes such as heart rate, blood pressure, blood coagulability, and vascular tone. However, in addition to regulating physiologic processes, circadian rhythms regulate pathophysiologic processes in the heart. In this regard, circadian rhythms regulate the onset, severity, and outcome of many cardiovascular diseases (CVDs), including myocardial infarction, diabetic cardiomyopathy, doxorubicin (Dox)-induced cardiotoxicity, and heart failure. Notably, the underlying mechanism of many of these diseases is linked to impaired cellular quality control processes, such as autophagy. Autophagy is a homeostatic cellular process that regulates the removal of damaged cellular components, allowing their degradation and recycling into their basic constituents for production of cellular energy. Many studies from recent years point to a regulatory link between autophagy and circadian machinery in the control of CVDs. In this review, we highlight the recent discoveries in the field of circadian-induced autophagy in the heart and provide the molecular mechanisms and signalling pathways that underlie the crosstalk between autophagy and clock gene control in response to cardiac injury. Understanding the mechanisms that underlie circadian-induced autophagy in response to cardiac stress may prove to be beneficial in developing novel therapeutic approaches to treat cardiac disease.

Circadian gene CLOCK accelerates atherosclerosis by promoting endothelial autophagy

Atherosclerosis (AS) is a chronic inflammatory disease which gives rise to life-threatening complications like ischemic stroke. Rupture of carotid atherosclerotic plaque is the main cause of ischemic stroke. Emerging evidence has demonstrated that disturbed circadian rhythms could accelerate the progression of atherosclerosis by regulating endothelial function. Moreover, our previous study implicated the circadian gene circadian locomotor output cycles kaput (CLOCK) in the pathogenesis of unstable plaques. In this study, we explored the underlying mechanism that CLOCK mediates endothelial cell autophagy involved in the progression of AS. Circadian and autophagy gene expression was analyzed in the GSE41571 dataset and human carotid atherosclerotic plaque samples. Then we used ox-LDL to treat HUVECs, and analyzed CLOCK and autophagy gene in endothelial cells. Besides that, we comprehensively analyzed in vivo experiments to explore the function of CLOCK in autophagy and atherosclerosis using different staining including HE, MT and IF staining. In the dataset and patient samples, CLOCK expression and autophagy were decreased in the unstable plaque group compared with the stable group. Decreased Beclin1, ATG5, LC3, and CLOCK were also observed in HUVECs under oxidative stress condition which also enhances cell proliferation. In vivo, we also found decreasing level of CLOCK, Beclin1, LC3 and ATG5 in ApoE^-/- mice compared with WT mice. Silencing of CLOCK in ApoE^-/- mice may further aggravate atherosclerosis including decreased cap thickness and collagens. Our findings implicated that downregulation CLOCK would impair endothelial cell autophagy and accelerate atherosclerotic plaque, which provides a novel strategy for treatment of progression in AS.

Biomechanical stretch-induced CLOCK upregulation in venous smooth muscle cells promotes phenotypic and functional transformation

BACKGROUND

A chronic change in hemodynamic forces might activate the pathophysiological process of maladaptive venous remodeling. Biomechanical stretching stimulates venous smooth muscle cells (SMCs) in the media, and biomechanical loads exceeding physiological levels affect the intrinsic circadian rhythm and cellular phenotype. This study aimed to investigate the changes in the expression patterns of circadian clock genes under biomechanical stretching and their role in the regulation of the SMC phenotype.

METHODS

Circadian genes were detected in venous specimens and venous SMCs from patients with varicose veins (VVs) and patients with autologous vein grafts (normal veins). Molecular mechanism studies of SMC phenotypic switching under biomechanical stretching were performed in human umbilical venous SMCs (HUVSMCs).

RESULTS

CLOCK upregulation was observed in VVs. The circadian rhythm was disrupted in venous SMCs derived from VVs. In addition, CLOCK expression and cell proliferation and migration were increased in HUVSMCs exposed to biomechanical stretch. CLOCK overexpression activated NF-κB signaling and phenotypic transformation in HUVSMCs, whereas CLOCK depletion had inhibitory effects on these pathways. Further experiments revealed that the CLOCK protein regulates phenotypic and functional transformation via the RHOA/ROCK1 pathway.

CONCLUSIONS

Our results demonstrate that CLOCK is a crucial regulator of the SMC phenotype under mechanical stretch. The CLOCK/RHOA/ROCK1 pathway is important in phenotypic adaptation, and targeting RHOA/ROCK1 could potentially reverse stretch-induced phenotypic switching.

Senescence in Vascular Smooth Muscle Cells and Atherosclerosis

Vascular smooth muscle cells (VSMCs) are the primary cell type involved in the atherosclerosis process; senescent VSMCs are observed in both aged vessels and atherosclerotic plaques. Factors associated with the atherosclerotic process, including oxidative stress, inflammation, and calcium-regulating factors, are closely linked to senescence in VSMCs. A number of experimental studies using traditional cellular aging markers have suggested that anti-aging biochemical agents could be used to treat atherosclerosis. However, doubt has recently been cast on such potential due to the increasingly apparent complexity of VSMCs status and an incomplete understanding of the role that these cells play in the atherosclerosis process, as well as a lack of specific or spectrum-limited cellular aging markers. The utility of anti-aging drugs in atherosclerosis treatment should be reevaluated. Promotion of a healthy lifestyle, exploring in depth the characteristics of each cell type associated with atherosclerosis, including VSMCs, and development of targeted drug delivery systems will ensure efficacy whilst evaluation of the safety and tolerability of drug use should be key aims of future anti-atherosclerosis research. This review summarizes the characteristics of VSMC senescence during the atherosclerosis process, the factors regulating this process, as well as an overview of progress toward the development and application of anti-aging drugs.

A wrinkle in time: circadian biology in pulmonary vascular health and disease

An often overlooked element of pulmonary vascular disease is time. Cellular responses to time, which are regulated directly by the core circadian clock, have only recently been elucidated. Despite an extensive collection of data regarding the role of rhythmic contribution to disease pathogenesis (such as systemic hypertension, coronary artery, and renal disease), the roles of key circadian transcription factors in pulmonary hypertension remain understudied. This is despite a large degree of overlap in the pulmonary hypertension and circadian rhythm fields, not only including shared signaling pathways, but also cell-specific effects of the core clock that are known to result in both protective and adverse lung vessel changes. Therefore, the goal of this review is to summarize the current dialogue regarding common pathways in circadian biology, with a specific emphasis on its implications in the progression of pulmonary hypertension. In this work, we emphasize specific proteins involved in the regulation of the core molecular clock while noting the circadian cell-specific changes relevant to vascular remodeling. Finally, we apply this knowledge to the optimization of medical therapy, with a focus on sleep hygiene and the role of chronopharmacology in patients with this disease. In dissecting the unique relationship between time and cellular biology, we aim to provide valuable insight into the practical implications of considering time as a therapeutic variable. Armed with this information, physicians will be positioned to more efficiently use the full four dimensions of patient care, resulting in improved morbidity and mortality of pulmonary hypertension patients.