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Titered FOXO overexpression maintains cardiac proteostasis and ameliorates age-associated functional decline

ABSTRACT: Heart performance declines with age. Reduced protein quality control (PQC) due to decreased function of the ubiquitin/proteasome system (UPS), autophagy, and/or chaperone-mediated protein refolding is a likely contributor to age-associated cardiac performance decline. The transcription factor FOXO participates in the regulation of genes involved PQC and a host of other processes. Here, the effect of cardiac-restricted dFOXO overexpression was investigated in Drosophila, a genetically pliable and rapidly aging model. Modest dFOXO overexpression in the heart was protective, ameliorating functional decline with age. Increased expression of genes associated predominantly with UPS relative to other PQC components accompanied dFOXO-mediated cardioprotection, which was corroborated by a significant decrease in ubiquitinated myocardial proteins. In agreement, knockdown of upregulated UPS components seemingly induced premature aging. Despite these findings, excessive dFOXO overexpression or knockdown proved detrimental to heart function and overall organismal development. This study highlights Drosophila as a model of cardiac aging and FOXO as a tightly-regulated mediator of proteostasis and heart performance over time.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE73205 | GEO | 2016/07/01

SECONDARY ACCESSION(S): PRJNA296368

REPOSITORIES: GEO

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Project description:To identify in vivo new cardiac SRF target genes and to study the response of these novel genes to SRF overexpression, we employed a cardiac-specific, transgenic mouse model that has a phenotype in young adulthood which resembles that of the typically aged heart. Using this “cardiac aging” model, we identified 207 genes that are important to cardiac function that were differentially expressed in vivo. Among them, 192 genes had SRF binding motifs (56 with CArG and 136 with CArG-like elements) in their promoter region. Fifty-one of 56 genes with classic CArG elements were not previously reported. These SRF target genes were grouped into 12 categories based on their function. It was observed that genes associated with cardiac energy metabolism shifted toward that of carbohydrate metabolism and away from that of fatty acid metabolism. The expression of genes that are involved in transcription and ion regulation were decreased, but expression of cytoskeletal genes were significantly increased. Using public databases of mouse models of stress, we also found that altered expression of the SRF target genes occurred in these hearts as well. Thus, SRF target genes are actively regulated under various physiological and pathological conditions, including hemodynamic stress. The mild elevation of SRF protein in the rodent heart that is observed during typical adult aging may have a major impact on many SRF target genes, thereby affecting cardiac structure and performance. In addition, these results could help to enhance our understanding of SRF regulation of cellular processes, including metabolic and cytoskeletal function. The generation and characterization of transgenic mice with mild cardiac-specific overexpression of SRF was previously reported (Zhang et al., 2003). At 6 months of age, the transgenic mice manifested cardiac changes suggestive of an “aged heart” (Zhang et al., 2003). Therefore, 6-month-old transgenic and non-transgenic mice were used in this study. Cardiac gene expression in SRF Tg heart was compared to that of wild-type mice.

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Titered FOXO overexpression maintains cardiac proteostasis and ameliorates age-associated functional decline

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