Increased expression of ryanodine receptor type-2 during atrial fibrillation by miR-106-25 cluster independent mechanism

MEF2C Directly Interacts with Pre-miRNAs and Distinct RNPs to Post-Transcriptionally Regulate miR-23a-miR-27a-miR-24-2 microRNA Cluster Member Expression

Transcriptional regulation constitutes a key step in gene expression regulation. Myocyte enhancer factor 2C (MEF2C) is a transcription factor of the MADS box family involved in the early development of several cell types, including muscle cells. Over the last decade, a novel layer of complexity modulating gene regulation has emerged as non-coding RNAs have been identified, impacting both transcriptional and post-transcriptional regulation. microRNAs represent the most studied and abundantly expressed subtype of small non-coding RNAs, and their functional roles have been widely documented. On the other hand, our knowledge of the transcriptional and post-transcriptional regulatory mechanisms that drive microRNA expression is still incipient. We recently demonstrated that MEF2C is able to transactivate the long, but not short, regulatory element upstream of the miR-23a-miR-27a-miR-24-2 transcriptional start site. However, MEF2C over-expression and silencing, respectively, displayed distinct effects on each of the miR-23a-miR-27a-miR-24-2 mature cluster members without affecting pri-miRNA expression levels, thus supporting additional MEF2C-driven regulatory mechanisms. Within this study, we demonstrated a complex post-transcriptional regulatory mechanism directed by MEF2C in the regulation of miR-23a-miR-27a-miR-24-2 cluster members, distinctly involving different domains of the MEF2C transcription factor and the physical interaction with pre-miRNAs and Ksrp, HnRNPa3 and Ddx17 transcripts.

Progress of circRNA/lncRNA-miRNA-mRNA axis in atrial fibrillation

Atrial fibrillation (AF) is a prevalent arrhythmia that requires effective biomarkers and therapeutic targets for clinical management. In recent years, non-coding RNAs (ncRNAs) have emerged as key players in the pathogenesis of AF, particularly through the ceRNA (competitive endogenous RNA) mechanism. By acting as ceRNAs, ncRNAs can competitively bind to miRNAs and modulate the expression of target mRNAs, thereby influencing the biological behavior of AF. The ceRNA axis has shown promise as a diagnostic and prognostic biomarker for AF. This review provides a comprehensive overview of the roles of ncRNAs in the development and progression of AF, highlighting the intricate crosstalk between different ncRNAs in AF pathophysiology. Furthermore, we discuss the potential implications of targeting the circRNA/lncRNA-miRNA-mRNA axis for the diagnosis, prognosis, and therapeutic intervention of AF.

Research progress of non-coding RNA in atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia in clinic, and its incidence is increasing year by year. In today's increasingly prevalent society, ageing poses a huge challenge to global healthcare systems. AF not only affects patients' quality of life, but also causes thrombosis, heart failure and other complications in severe cases. Although there are some measures for the diagnosis and treatment of AF, specific serum markers and targeted therapy are still lacking. In recent years, ncRNAs have become a hot topic in cardiovascular disease research. These ncRNAs are not only involved in the occurrence and development of AF, but also in pathophysiological processes such as myocardial infarction and atherosclerosis, and are potential biomarkers of cardiovascular diseases. We believe that the understanding of the pathophysiological mechanism of AF and the study of diagnosis and treatment targets can form a more systematic diagnosis and treatment framework of AF and provide convenience for individuals with AF and the society.

Non-Coding RNAs in the Cardiac Action Potential and Their Impact on Arrhythmogenic Cardiac Diseases

Cardiac arrhythmias are prevalent among humans across all age ranges, affecting millions of people worldwide. While cardiac arrhythmias vary widely in their clinical presentation, they possess shared complex electrophysiologic properties at cellular level that have not been fully studied. Over the last decade, our current understanding of the functional roles of non-coding RNAs have progressively increased. microRNAs represent the most studied type of small ncRNAs and it has been demonstrated that miRNAs play essential roles in multiple biological contexts, including normal development and diseases. In this review, we provide a comprehensive analysis of the functional contribution of non-coding RNAs, primarily microRNAs, to the normal configuration of the cardiac action potential, as well as their association to distinct types of arrhythmogenic cardiac diseases.

Cardiomyocyte calcium handling in health and disease: Insights from in vitro and in silico studies

Calcium (Ca²⁺) plays a central role in cardiomyocyte excitation-contraction coupling. To ensure an optimal electrical impulse propagation and cardiac contraction, Ca²⁺ levels are regulated by a variety of Ca²⁺-handling proteins. In turn, Ca²⁺ modulates numerous electrophysiological processes. Accordingly, Ca²⁺-handling abnormalities can promote cardiac arrhythmias via various mechanisms, including the promotion of afterdepolarizations, ion-channel modulation and structural remodeling. In the last 30 years, significant improvements have been made in the computational modeling of cardiomyocyte Ca²⁺ handling under physiological and pathological conditions. However, numerous questions involving the Ca²⁺-dependent regulation of different macromolecular complexes, cross-talk between Ca²⁺-dependent regulatory pathways operating over a wide range of time scales, and bidirectional interactions between electrophysiology and mechanics remain to be addressed by in vitro and in silico studies. A better understanding of disease-specific Ca²⁺-dependent proarrhythmic mechanisms may facilitate the development of improved therapeutic strategies. In this review, we describe the fundamental mechanisms of cardiomyocyte Ca²⁺ handling in health and disease, and provide an overview of currently available computational models for cardiomyocyte Ca²⁺ handling. Finally, we discuss important uncertainties and open questions about cardiomyocyte Ca²⁺ handling and highlight how synergy between in vitro and in silico studies may help to answer several of these issues.

Crosstalk between PKC and MAPK pathway activation in cardiac fibroblasts in a rat model of atrial fibrillation

OBJECTIVE

Atrial fibrillation (AF) is the most frequent form of cardiac arrhythmia and major cause of cardiac ischemia. Defective calcium homeostasis due to anomalous expression of ryanodine receptor type 2 (RyR2) or its hyperactivation by phosphorylation by serine threonine kinases has been implicated as a central mechanism of AF pathogenesis. Given the role of protein kinase C (PKC) isoforms in cardiac function we investigated role of PKC in AF using a rat model.

RESULTS

PMA induced global increase in protein synthesis in cardiac fibroblasts isolated from AF rats, but not healthy controls, and the increase was inhibited by PKC inhibition. PMA mediated activation of both PKC and ERK and either inhibition of PKC by Go6983 or ERK by the MEK inhibitor Trametinib attenuated both P-ERK and P-PKC in both cardiac fibroblasts isolated from AF rats or from healthy rats but transduced with PKC-delta. The PKC and ERK mediated induction of global protein synthesis was found to be mediated by increased phosphorylation of the ribosomal protein S6.

CONCLUSION

Our findings provide a foundation for future testing of PKC and MEK inhibitors to treat AF in pre-clinical models. It also needs to be determined if PKC and MAPK pathway activation is functioning via RyR2 or some yet undefined substrates.