Adipose-derived stem cells overexpressing SK4 calcium-activated potassium channel generate biological pacemakers

Recent studies have suggested that calcium-activated potassium channel (K(Ca)) agonists increase the proportion of mouse embryonic stem cell-derived cardiomyocytes and promote the differentiation of pacemaker cells. In the present study, it was hypothesized that adipose-derived stem cells (ADSCs) can differentiate into pacemaker-like cells via over-expression of the SK4 gene. ADSCs were transduced with a recombinant adenovirus vector carrying the mouse SK4 gene, whereas the control group was transduced with GFP vector. ADSCs transduced with SK4 vector were implanted into the rat left ventricular free wall. Complete atrioventricular block (AVB) was established in isolated perfused rat hearts after 2 weeks. SK4 was successfully and stably expressed in ADSCs following transduction. The mRNA levels of the pluripotent markers Oct-4 and Sox-2 declined and that of the transcription factor Shox2 was upregulated following SK4 transduction. The expression of α-actinin and hyperpolarization-activated cyclic nucleotide-gated potassium channel 4 (HCN4) increased in the SK4 group. The hyperpolarizing activated pacemaker current I(f) (8/20 cells) was detected in ADSCs transduced with SK4, but not in the GFP group. Furthermore, SK4 transduction induced the expression of p-ERK1/2 and p-p38 MAPK. In the ex vivo experiments, the heart rate of the SK4 group following AVB establishment was significantly higher compared with that in the GFP group. Immunofluorescence revealed that the transduced ADSCs were successfully implanted and expressed HCN4 in the SK4 group. In conclusion, SK4 induced ADSCs to differentiate into cardiomyocyte-like and pacemaker-like cells via activation of the extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase pathways. Therefore, ADSCs transduced with SK4 may be used to generate biological pacemakers in ex vivo rat hearts.