Emelyanova, Larisa

Background Age‐related heart diseases are significant contributors to increased morbidity and mortality. Emerging evidence indicates that mitochondria within cardiomyocytes contribute to age‐related increased reactive oxygen species (ROS) generation that plays an essential role in aging‐associated cardiac diseases. Methods and Results The present study investigated differences between ROS production in cardiomyocytes isolated from adult (6 months) and aged (24 months) Fischer 344 rats, and in cardiac tissue of adult (18–65 years) and elderly (>65 years) patients with preserved cardiac function. Superoxide dismutase inhibitable ferricytochrome c reduction assay (1.32±0.63 versus 0.76±0.31 nMol/mg per minute; P =0.001) superoxide and H 2 O 2 production, measured as dichlorofluorescein diacetate fluorescence (1646±428 versus 699±329, P =0.04), were significantly higher in the aged versus adult cardiomyocytes. Similarity in age‐related alteration between rats and humans was identified in mitochondrial‐electron transport chain‐complex‐I‐associated increased oxidative‐stress by MitoSOX fluorescence (53.66±18.58 versus 22.81±12.60; P =0.03) and in 4‐HNE adduct levels (187.54±54.8 versus 47.83±16.7 ng/mg protein, P =0.0063), indicative of increased peroxidation in the elderly. These differences correlated with changes in functional enrichment of genes regulating ROS homeostasis pathways in aged human and rat hearts. Functional merged collective network and pathway enrichment analysis revealed common genes prioritized in human and rat aging‐associated networks that underlay enriched functional terms of mitochondrial complex I and common pathways in the aging human and rat heart. Conclusions Aging sensitizes mitochondrial and extramitochondrial mechanisms of ROS buildup within the heart. Network analysis of the transcriptome highlights the critical elements involved with aging‐related ROS homeostasis pathways common in rat and human hearts as targets.

Introduction: Although alterations in mitochondrial function have been observed in senescent hearts, the molecular basis for aging-associated decline in energy metabolism in the human heart is not fully understood. Objective: To determine aging-related changes in functional activity and protein expression level of mitochondrial oxidative phosphorylation (OXPHOS) complexes and expression of genes regulating mitochondrial energetics in the human heart. Methods: Right atrial appendages from well-matched adult (29-57 y.o., n=19) and aged (65-85 y.o., n=22) patients undergoing elective CABG surgery were used. Functional activity of OXPHOS complexes was measured spectrophotometrically. Protein expression level of corresponding OXPHOS protein subunits was determined by Western blot. Gene expression profiling was performed using Affymetrix Human Genome U133 Plus 2.0 microarrays. Results: Mitochondria from senescent hearts demonstrated a significant decrease in complex I and V functional activity without significant changes in the rest of the complexes (Fig. A). At the protein expression level, there was reduction in complex I, III, and IV (Fig. B). This was associated with downregulation of the majority (86%, 90 of 105) of genes coding mitochondrial proteins (Fig. C). Forty-six percent (41 of 90) of the downregulated genes were confined to pathways regulating mitochondrial energetics. Conclusion: With aging, the functional activity of OXPHOS is reduced due to supression of protein expression and downregulation of genes regulating mitochondrial energetics. This provides a substrate for reduced energetic efficiency associated with senescence in the human atria.