Overexpression of Foxo in the Heart Ameliorates Performance Decline through Enhanced UPS Processing in Aging Drosophila

Heart performance declines with age. A likely contributor to age-associated cardiac dysfunction is reduced protein quality control due to decreased function of the ubiquitin/proteasome system (UPS) and the autophagy lysosomal pathway (ALP). The transcription factor, FOXO, has been shown to be involved in the regulation of genes related to both of these interrelated pathways as well as a host of other cellular processes. Here, we investigated the effects of cardiac-restricted overexpression of dFOXO in Drosophila melanogaster, an ideal model for aging studies, exploiting the tissue-specific UAS-GAL4 expression system. Using high-speed video microscopy and motion analysis and atomic force microscopy, we showed that with age, mild heart-specific overexpression of dFOXO significantly attenuated senescence-associated cardiac functional decline and stiffening, respectively. We also determined that differing amounts of heart-specific dFOXO overexpression elicited disparate effects, the strongest driver proving fatal. Overexpression of dFOXO in all Drosophila muscle has been shown to increase lifespan, likely owing to systemic expression of autophagy related proteins and reduced ubiquitin content. Similarly, we found that dFOXO-mediated improvement in heart function with age was also accompanied by a significant decrease in ubiquitinated myocardial proteins as determined by quantitative western blot analysis. However, microarray data suggested that this reduction was caused by increased expression of genes associated with the UPS rather than autophagy, indicating that FOXO may perform its function differently in the heart than in other striated muscles. Because FOXO transcriptionally regulates genes associated with many facets of cellular life, we have established a list of specific targets that dFOXO may affect when its expression is increased to attenuate cardiac dysfunction with age. We will systematically investigate these candidates to pinpoint how mild FOXO overexpression ameliorates the natural decline in heart performance in Drosophila.