Deficiency of CXXC finger protein 1 leads to small changes in heart rate but moderate epigenetic alterations and significant protein downregulation of hyperpolarization-activated cyclic nucleotide-gated 4 (HCN4) ion channels in mice

BACKGROUND The normal cardiac rhythm is generated in the sino-atrial node (SAN). Changes in ionic currents of the SAN may cause sinus arrhythmia. CXXC finger protein 1 (Cfp1) is an epigenetic regulator that is involved in transcriptional regulation of multiple genes. OBJECTIVE The purpose of this study was to explore whether Cfp1 controls SAN function through regulation of ion channel-related genes. METHODS Electrophysiological study, patch clamp recording, reverse transcriptase polymerase chain reaction, optical mapping, chromatin immunoprecipitation, and immunofluorescence staining were performed to evaluate the function of SAN and underlying mechanism on Cfp1 heterozygous knockout (Cfp1(+/-)) mice. RESULTS Heart rate was slower slightly and SAN recovery time was longer in Cfp1(+/-) mice than controls. Whole-cell patch-clamp recording showed that the firing rate of action potentials was reduced in Cfp1(+/-) mice. The density of If current was reduced by 66% in SAN cells of Cfp1(+/-) mice but the densities of ICa, ICa-L, and ICa-T were not changed. The hyperpolarization-activated cyclic nucleotide-gated 4 (HCN4) mRNA level in SAN tissue of Cfp1(+/-) mice was reduced. The HCN4 protein was significantly decreased in SAN cells and tissues after heterozygous deletion of Cfp1. Chro-matin immunoprecipitation assay on cultured HL-1 cells demonstrated that Cfp1 was enriched in the promoter regions of HCN4. Knockdown of Cfp1 reduced H3K4 trimethylation, H3K9 acetylation, and H3K27 acetylation of HCN4 promoter region. CONCLUSION Deficiency of Cfp1 leads to small changes in heart rate by moderate epigenetic modification alterations and significant protein downregulation of HCN4 ion channels in mice.