Objectives Adult myocyte dedifferentiation/re-differentiation (AMDR) occurs during both acute and chronic cardiac diseases. AMDR-based regenerative circuits have been considered as conduits through which this mechanism achieves cardiac repair. However, the mechanism is not clear. We hypothesise that calcium signalling propagating from neighbouring myocytes via gap junction plays an important role in the AMDR process.
Methods We co-cultured adult cardiac myocytes (ACMs) from α-actin-GFP transgenic mice with neonatal rat ventricular myocytes (NRVMs) for up to 7 days. ACMs were demonstrated to have the potential of dedifferentiation and re-differentiation in the co-culture system. ACM dedifferentiation was identified by the embryonic myocyte marker α-smooth muscle-actin (α-SMA) and stem cell marker c-kit via immunocytochemistry.
Results Re-differentiation was characterised by organised sarcomere & α-actinin+ and spontaneous cellular beating. Conditioned medium of NRVM or transwell co-cultured with NRVMs promoted ACM dedifferentiation but was not able to induce re-differentiation, indicating the importance of direct cell-to-cell contact. This was further confirmed when ACM re-differentiation was inhibited by the gap junction uncoupler heptanol. Similar to NRVM, contracting substrates of fetal cardiac myocyte (fCM) potently induced ACM re-differentiation. However, mouse embryonic fibroblast (MEF) minimally induced ACM re-differentiation. The Ca2+ chelator BAPTA and SERCA inhibitor thapsigargin abrogated the pro-re-differentiation effect of NRVMs. Ca2+ handling in NRVMs was manipulated by overexpressing SERCA or NCX. SERCA overexpression in NRVMs induced a higher rate while NCX overexpression induced a lower rate of re-differentiation.
Conclusions This study suggests that Ca2+ signal transmission from NRVMs to ACMs via the gap junctions regulates NRVM co-culture induced ACM AMDR. This process may contribute to cardiac regeneration in conditions when Ca2+ handling of surviving myocytes are altered, and may suggest a novel therapeutic target for numerous cardiovascular diseases.