Oxidized protein aggregate lipofuscin impairs cardiomyocyte contractility via late-stage autophagy inhibition.

Aging of the heart is accompanied by impairment of cardiac structure and function. At molecular level, autophagy plays a crucial role in preserving cardiac health. Autophagy maintains cellular homeostasis by facilitating balanced degradation of cytoplasmic components including organelles and misfolded or aggregated proteins. The age-related decline in autophagy favors an accumulation of protein aggregates such as lipofuscin particularly in the heart, which is composed primarily of non-proliferating cells. Therefore, this study investigates whether lipofuscin accumulation contributes to age-related functional decline of primary adult cardiomyocytes isolated from C57BL/6J mice and examines the role of autophagic flux in mediating these effects. Results showed an age-associated reduction in cardiomyocyte contraction amplitude and an increase in autofluorescence, indicating the accumulation of lipofuscin with age. In vitro treatment of adult primary cardiomyocytes with artificial lipofuscin increased autofluorescence and decreased both contraction amplitude and cellular autophagic flux. Induction of autophagy with rapamycin mitigated contractile dysfunction in lipofuscin-treated cardiomyocytes, whereas inhibition of autophagic flux revealed stage-dependent effects. Late-stage autophagy inhibition using chloroquine or concanamycin A reduced cardiomyocyte contraction amplitude, whereas early-stage autophagy inhibition via 3-methyladenine did not affect contraction within 24 h. In conclusion, our results indicate that lipofuscin directly impairs cardiomyocyte function by diminishing late-stage autophagic flux. These findings highlight the essential role of the autophagy-lysosomal system in preserving age-related loss of cardiomyocyte function caused by accumulating protein aggregates.