Distribution and characteristics of telocytes as nurse cells in the architectural organization of engineered heart tissues.

Interstitial Cajal-like cells are a distinct type of interstitial cell with a wide distribution in mammalian organs and tissues, and have been given the name "telocytes". Recent studies have demonstrated the potential roles of telocytes in heart development, renewal, and repair. However, further research on the functions of telocytes is limited by the complicated in vivo environment. This study was designed to construct engineered heart tissue (EHT) as a three-dimensional model in vitro to better understand the role of telocytes in the architectural organization of the myocardium. EHTs were constructed by seeding neonatal cardiomyocytes in collagen/Matrigel scaffolds followed by culture under persistent static stretch. Telocytes in EHTs were identified by histology, toluidine blue staining, immunofluorescence, and transmission electron microscopy. The results from histology and toluidine blue staining demonstrated widespread putative telocytes with compact toluidine blue-stained nuclei, which were located around cardiomyocytes. Prolongations from the cell bodies showed a characteristic dichotomous branching pattern and formed networks in EHTs. Immunofluorescence revealed positive staining of telocytes for CD34 and vimentin with typical moniliform prolongations. A series of electron microscopy images further showed that typical telocytes embraced the cardiomyocytes with their long prolongations and exhibited a marked appearance of nursing cardiomyocytes during the construction of EHTs. This finding highlights the great importance of telocytes in the architectural organization of EHTs. It also suggests that EHT is an appropriate physical and pathological model system in vitro to study the roles of telocytes during heart development and regeneration.