Abnormal Circadian Rhythms Exacerbate Dilated Cardiomyopathy by Reducing the Ventricular Mechanical Strength

Cardiovascular System Medicine
dilated cardiomyopathy circadian rhythm sleep apnea transcriptome cytoskeleton fibrosis

Dilated Cardiomyopathy (DCM) is a cardiac disease characterized by ventricular dilation and systolic dysfunction, and it is one of the primary indications for heart transplantation worldwide. The etiology of DCM is complex, including genetic factors, infections, drugs, toxins, and endocrine disturbances. Due to the heterogeneity of its causes, early and precise intervention becomes extremely challenging. The circadian rhythm is an internal physiological rhythm in organisms that regulates cardiac contraction, metabolism, electrophysiology, and neurohumoral control. Abnormal Circadian Rhythm (ACR) has been proven to be a risk factor for Heart Failure (HF) and arrhythmias. However, the specific role of ACR in the development of DCM has not been thoroughly explored in clinical samples.

Sleep Apnea (SA) is the most common disease associated with ACR. SA patients often experience nocturnal hypoxia and reduced sleep quality, which may lead to circadian rhythm disturbances. Although SA has been shown to be associated with arrhythmias and hypertension, its specific impact on DCM has not been fully studied. Therefore, this study aims to explore the effects of SA-related ACR on DCM and its underlying cellular biological mechanisms through clinical samples and single-cell sequencing technology.

Source of the Paper

This paper was authored by Hao Jia, Hao Cui, and others from the Department of Cardiac Surgery at Fuwai Hospital, Chinese Academy of Medical Sciences. It was published online on September 13, 2024, in the journal Cardiovascular Research. The study was funded by the National Natural Science Foundation of China.

Research Process and Results

1. Study Design and Sample Collection

This study included a derivation cohort (n=105) and a validation cohort (n=65). All patients were DCM patients who underwent heart transplantation. Based on the diagnostic criteria for SA, patients were divided into SA and non-SA groups. Additionally, six healthy heart samples were included as baseline controls.

2. Circadian Rhythm Gene Expression Analysis

Using RT-qPCR technology, the researchers detected the expression levels of four key circadian rhythm genes (NR1D1, NR1D2, ARNTL, and CLOCK) in heart samples from DCM patients. The results showed that the amplitude of circadian rhythm gene expression was significantly reduced in the SA group, especially in the morning. Furthermore, the expression of NR1D1 and ARNTL genes in the SA group exhibited a phase shift.

3. Single-Nucleus RNA Sequencing (snRNA-seq)

The researchers performed single-nucleus RNA sequencing on heart samples from 16 DCM patients to explore the impact of ACR on the cardiac transcriptome. Through unbiased clustering and UMAP analysis, 167,708 nuclei were divided into 10 main cell populations, including cardiomyocytes (CM), fibroblasts (Fib), endothelial cells (Endo), and pericytes (Peri). The results showed that heart cells in the ACR group lost the morning-specific transcriptional pattern, particularly in CM and Fib cells.

4. Phenotypic Changes in Cardiomyocytes

By analyzing 44,386 CM cells, the researchers found that actin cytoskeleton organization in CM cells of the ACR group was disrupted, leading to aggravated cell hypertrophy. Additionally, fatty acid metabolism activity in CM cells of the ACR group was reduced, which is closely related to the pathological progression of DCM.

5. Phenotypic Changes in Fibroblasts

By analyzing 36,985 Fib cells, the researchers found that the proportion of activated fibroblasts (Activated Fib) in the ACR group was significantly reduced, leading to decreased cardiac fibrosis. Fibrosis is an important component of cardiac remodeling, and its reduction may result in decreased structural strength of the left ventricular wall.

6. Pathological Staining and Mechanical Experiments

Through immunofluorescence staining and atomic force microscopy (AFM) experiments, the researchers further validated the snRNA-seq results. The results showed that actin cytoskeleton organization in CM cells of the ACR group was disordered, and the mechanical strength of the cells was significantly reduced. Additionally, the degree of cardiac fibrosis in the SA group was significantly lower than in the non-SA group.

7. REV-ERBα/β Knockout Mouse Analysis

By analyzing RNA-seq data from REV-ERBα/β knockout mice, the researchers found that the expression of genes related to actin cytoskeleton organization and fibrosis was significantly reduced in the heart tissues of these mice, further supporting the findings in human samples.

Conclusions and Significance

This study found that SA-related ACR exacerbates the pathological progression of DCM by disrupting actin cytoskeleton organization in cardiomyocytes and reducing the activation of fibroblasts, leading to decreased structural strength of the left ventricular wall. This discovery provides new insights into the etiology of DCM and offers potential targets for precise treatment.

Research Highlights

  1. First Confirmation of the Impact of SA-Related ACR on DCM in Clinical Samples: Using RT-qPCR and single-cell sequencing, the researchers first confirmed the association between SA-related ACR and cardiac structural remodeling in DCM patients.
  2. Revealed the Cellular Biological Mechanisms of ACR’s Impact on DCM: The study found that ACR reduces the structural strength of the left ventricular wall by disrupting actin cytoskeleton organization in cardiomyocytes and reducing fibroblast activation.
  3. Provided New Insights for Precision Treatment of DCM: The study suggests treating ACR-related DCM by restoring circadian rhythm gene expression patterns or enhancing the mechanical strength of the left ventricular wall.

Future Prospects

Although this study revealed the impact of ACR on DCM and its potential cellular biological mechanisms, some questions remain to be further explored. For example, future research could investigate whether left ventricular dilation in DCM patients is inhibited after correcting SA and ACR. Additionally, the researchers plan to construct prospective studies to observe the clinical outcomes of long-term continuous positive airway pressure ventilation in DCM patients.

This report details the study published in Cardiovascular Research on how abnormal circadian rhythms exacerbate dilated cardiomyopathy. Through clinical samples and single-cell sequencing technology, the researchers revealed the impact of SA-related ACR on DCM and its underlying cellular biological mechanisms, providing new insights for the precision treatment of DCM.