RNA-Binding Profiles of CKAP4 as an RNA-Binding Protein in Myocardial Tissues

Background: Pathological tissue remodeling such as fibrosis is developed in various cardiac diseases. As one of cardiac activated-myofibroblast protein markers, CKAP4 may be involved in this process and the mechanisms have not been explored.Methods: We assumed that CKAP4 held a role in the regulation of cardiac fibrotic remodeling as an RNA-binding protein. Using improved RNA immunoprecipitation and sequencing (iRIP-seq), we sought to analyze the RNAs bound by CKAP4 in normal atrial muscle (IP1 group) and remodeling fibrotic atrial muscle (IP2 group) from patients with cardiac valvular disease. Quantitative PCR and Western blotting were applied to identify CKAP4 mRNA and protein expression levels in human right atrium samples.Results: iRIP-seq was successfully performed, CKAP4-bound RNAs were characterized. By statistically analyzing the distribution of binding peaks in various regions on the reference human genome, we found that the reads of IP samples were mainly distributed in the intergenic and intron regions implying that CKAP4 is more inclined to combine non-coding RNAs. There were 913 overlapping binding peaks between the IP1 and IP2 groups. The top five binding motifs were obtained by HOMER, in which GGGAU was the binding sequence that appeared simultaneously in both IP groups. Binding peak-related gene cluster enrichment analysis demonstrated these genes were mainly involved in biological processes such as signal transduction, protein phosphorylation, axonal guidance, and cell connection. The signal pathways ranking most varied in the IP2 group compared to the IP1 group were relating to mitotic cell cycle, protein ubiquitination and nerve growth factor receptors. More impressively, peak analysis revealed the lncRNA-binding features of CKAP4 in both IP groups. Furthermore, qPCR verified CKAP4 differentially bound lncRNAs including LINC00504, FLJ22447, RP11-326N17.2, and HELLPAR in remodeling myocardial tissues when compared with normal myocardial tissues. Finally, the expression of CKAP4 is down-regulated in human remodeling fibrotic atrium.Conclusions: We reveal certain RNA-binding features of CKAP4 suggesting a relevant role as an unconventional RNA-binding protein in cardiac remodeling process. Deeper structural and functional analysis will be helpful to enrich the regulatory network of cardiac remodeling and to identify potential therapeutic targets.

Huge Left Atrial Aneurysm: First Case Report in Bangladesh

The left atrial aneurysm (LAA) is an extremely rare congenital malformation of the heart. It can be caused by congenital dysplasia of atrial muscle. It may result secondarily from severe mitral valvular disease. This is the first ever case of left atrial aneurysm in an 8 months old child of Bangladesh who was treated successfully and now leading a normal life after surgical resection. Cardiovasc j 2021; 14(1): 70-72

Identification of Key Small Non‐Coding MicroRNAs Controlling Pacemaker Mechanisms in the Human Sinus Node

Background The sinus node (SN) is the primary pacemaker of the heart. SN myocytes possess distinctive action potential morphology with spontaneous diastolic depolarization because of a unique expression of ion channels and Ca 2+ ‐handling proteins. MicroRNAs (miRs) inhibit gene expression. The role of miRs in controlling the expression of genes responsible for human SN pacemaking and conduction has not been explored. The aim of this study was to determine miR expression profile of the human SN as compared with that of non‐pacemaker atrial muscle. Methods and Results SN and atrial muscle biopsies were obtained from donor or post‐mortem hearts (n=10), histology/immunolabeling were used to characterize the tissues, TaqMan Human MicroRNA Arrays were used to measure 754 miRs, Ingenuity Pathway Analysis was used to identify miRs controlling SN pacemaker gene expression. Eighteen miRs were significantly more and 48 significantly less abundant in the SN than atrial muscle. The most interesting miR was miR‐486‐3p predicted to inhibit expression of pacemaking channels: HCN1 (hyperpolarization‐activated cyclic nucleotide‐gated 1), HCN4, voltage‐gated calcium channel (Ca v )1.3, and Ca v 3.1. A luciferase reporter gene assay confirmed that miR‐486‐3p can control HCN4 expression via its 3′ untranslated region. In ex vivo SN preparations, transfection with miR‐486‐3p reduced the beating rate by ≈35±5% ( P <0.05) and HCN4 expression ( P <0.05). Conclusions The human SN possesses a unique pattern of expression of miRs predicted to target functionally important genes. miR‐486‐3p has an important role in SN pacemaker activity by targeting HCN4, making it a potential target for therapeutic treatment of SN disease such as sinus tachycardia.