Histological Validation of Heart Slices as a Model in Cardiac Research

Recently vibratome-cut heart slices has been proposed as a new model in cardiac research, particularly in studying functional integration of transplanted donor stem cells into the host myocardium. This emerging model has, over co-culture models, a theoretical advantage in maintaining the 3-dimensional cardiac structure and physiological cell-cell connections; however, further validation is needed for this to be an established model. Particularly, the ability of cardiomyocytes in heart slices to connect with administered donor cells remains uncertain. Heart slices of 300 μm thickness were cut from adult and embryonic rat hearts using a vibratome and cultured. Adult heart slices maintained localized contraction for up to 3 days. Various histological studies demonstrated that the myocardial morphology was well preserved with necrotic cells being restricted to the edges of slices, but the number of apoptotic cells in the slices increased with culture periods (16.0 ± 3.2% at day 2 and 59.1 ± 8.3% at day 6). Importantly, immunohistolabeling and western blotting showed that connexin43 expression, which is a prerequisite for gap junction formation between donor-derived and host cardiomyocytes, was markedly diminished by 1 day in culture, suggesting rapid functional deterioration of adult heart slices. In contrast, embryonic heart slices remained contracting at least for 35 days with myocardial morphology and connexin43-involved gap junctions remaining intact, though in the embryonic, immature pattern. Collectively, both adult and embryonic rodent heart slices, in the current style, have critical limitations to assess integration between donor-derived and host cardiomyocytes. Further study to improve the quality of heart slices is warranted.