Gap junctional coupling is important for functional integration of transplanted cells with host myocardium. However, the role of gap junctions in cardiomyogenic differentiation of transplanted cells has not been directly investigated. In this study, the role of connexin43 (Cx43) expression in cardiomyogenic differentiation of human mesenchymal stem cells (hMSCs) was investigated.Methods
Knockdown of Cx43 gene expression was established in naturally Cx43-rich fetal amniotic membrane hMSCs (Cx43↓ fetal AM hMSCs), while Cx43 was overexpressed in inherently Cx43-poor adult adipose tissue hMSCs (Cx43↑ adult AT hMSCs). The hMSCs were exposed to cardiomyogenic stimuli by co-incubation with neonatal rat cardiomyocytes (nrCMCs) for 10 days. Differentiation was assessed by immunostaining and whole-cell current-clamping. To establish whether the effects of Cx43 knockdown could be rescued Cx45 was overexpressed in Cx43↓ fetal AM hMSCs.Results
Ten days after co-incubation not a single Cx43↓ fetal AM hMSC or adult AT MsC expressed α-actinin, while control fetal AM hMSCs did (2.18 ± 0.4%, n=5,000). Moreover, functional cardiomyogenic differentiation, based on action potential recordings, occurred only in control fetal AM hMSCs. Of interest, Cx45 overexpression in Cx43↓ fetal AM hMSCs restored their ability to undergo cardiomyogenesis (1.57 ± 0.4%, n=2,500) in co-culture with nrCMCs.Conclusion
Gap junctional coupling is required for differentiation of fetal AM hMSCs into functional cardiomyocytes after co-incubation with nrCMCs. Heterocellular gap junctional coupling thus plays an important role in the transfer of cardiomyogenic signals from nrCMCs to fetal hMSCs but is not sufficient to induce cardiomyogenic differentiation in adult AT hMSCs.