Abstract 10461: Single-Cell Transcriptional Analysis of Altered Cardiomyocyte Pdk4 as Indicator of Ischemic Stress Vulnerability in Aging

Introduction: The mechanisms by which aging increases vulnerability to ischemic insult are not well understood. Single-Cell RNA sequencing (scRNA seq) was employed to characterize transcriptional differences in various cell types between aged and young mice which may contribute to aged-related vulnerability to ischemic insult. Pyruvate Dehydrogenase Kinase 4 (Pdk4) has been shown to impact capacity for fatty-acid oxidation (FAO) and consequently adaption to metabolic alterations of ischemic insult. Hypothesis: Alteration of Pdk4 expression levels is an adaptive response transcriptionally under pathological stress to maintain metabolic homeostasis during ischemia and reperfusion (I/R). Methods: Young (3-5 months) and aged (24-26 months) C57BL/6J mice were subjected to in vivo regional 45 min of ischemia and 24 hr of reperfusion (I/R) or sham operations. Bioinformatic analysis was done using Seurat integration vignettes allowing for cell type identification and differential expression testing. Observing genetic expression profiles by cell types. Substrate metabolism was determined with working heart system and Seahorse XF Analyzer. Results: Pdk4 was profoundly found in cardiomyocytes versus fibroblasts, endothelial cells and macrophages of both young and aged hearts. Interestingly, I/R stress triggered Pdk4 mRNA expression of young but not aged cardiomyocytes. Moreover, there is a relative higher Pdk4 level in aged versus young cardiomyocytes under sham operations, indicating Pdk4 mRNA respond to pathological stress. The ex vivo working heart perfusion data showed that young versus aged hearts exhibited higher FAO in response to I/R. Moreover, Seahorse XF Analyzer showed a higher glycolysis rate in young versus aged cardiomyocytes during I/R. It suggests that an impaired cardiomyocyte Pdk4 mRNA response occurred in aging under I/R stress conditions, this could result in cardiac maladaptive metabolic alterations in aging during pathological stress. Conclusions: Alterations in Pdk4 levels of cardiomyocytes regulates cardiac adaptive metabolism in response to pathological stress. This adaptive regulation of cardiomyocyte Pdk4 is impaired in aging that leads to more vulnerability of aged versus young hearts to ischemic insult.