Fundamental Differences in Cell Survival and Molecular Stress Response in Embryonic Compared to Adult Cardiomyocytes Subjected to Mitochondrial Dysfunction

Background: Mitochondria are essential eukaryotic cell organelles, involved in cellular stress response and cell death. Mitochondrial dysfunction results in ATP deficiency, disruption of calcium homeostasis, and increased formation of reactive oxygen species. In cardiomyocytes, this can lead to contractile dysfunction and apoptotic or necrotic cell death. Such cell loss is associated with the development of cardiovascular diseases including ischemia/reperfusion injury and cardiotoxicity of certain drugs. Thus, important therapeutic concepts aim to increase the tolerance of cells to stress and prevent cell death.

Method: To characterize the molecular mechanisms in response to stress, we isolated and cultured adult and embryonic primary mouse cardiomyocytes. The cells were treated with antimycin A (AMA), an inhibitor of complex III of the mitochondrial respiratory chain, and cell morphology, death, contractility, and molecular stress responses were examined.

Results: Despite a significant increase in reactive oxygen species during treatment with AMA, embryonic cardiomyocytes were shown to be almost resistant to the inhibitor. Phase contrast microscopy showed confluent and contractile cell layers in both DMSO and AMA treated wells over 24 hours. Cell counting revealed a proportion of cardiomyocytes of 60 to 80% among all cultured cells which did not change over 24 hours AMA treatment indicating no major cell loss. Cell cycle activity investigated by Ki67 immunofluorescence was not different in AMA versus DMSO treated embryonic cardiomyocytes after 24 hours. In contrast, adult cardiomyocytes showed morphological changes and cell death within 30 minutes after onset of AMA treatment. Mitochondrial dysfunction activates a series of stress responses in embryonic cardiomyocytes known to maintain protein homeostasis and cellular integrity. As such, the mitochondrial unfolded protein response, the integrated stress response, and mechanisms of antioxidant protection were significantly induced by AMA. In contrast, AMA treated adult cardiomyocytes revealed substantial deficits in the activity of crucial components of stress-induced signaling pathways.

Conclusion: The results show remarkable differences in the molecular stress response and survival of adult versus embryonic cardiomyocytes when exposed to mitochondrial dysfunction. Improving stress tolerance of adult cardiomyocytes by understanding embryonic survival mechanisms could potentially attenuate the course of cardiovascular disease.

Publication History

Article published online:
12 February 2022