Mitochondria at the heart of aging: structure, function, and failure

Abstract

Mitochondria are critical for cellular metabolism, signaling, and health throughout life. Evidence increasingly links age-related mitochondrial dysfunction to a progressive decline in tissue homeostasis. Mitochondrial dysfunction is caused by various mitochondrial DNA (mtDNA) structural and genetic alterations, impaired oxidative phosphorylation, and increased reactive oxygen species (ROS) production. Advances in high-resolution sequencing have revealed vulnerabilities and mutation signatures in tissues previously unknown, reinforcing the precarious balance between mitochondrial damage and injury compensatory response. Age-related changes in mitochondrial dynamics, including fission, fusion, and cristae remodeling, are closely related to declining bioenergetic efficiency and cell survival. Disruption of crucial mediators (Drp1, MFN1/2, OPA1) drives cristae degeneration, mimicking pathogenic changes seen in human mitochondrial disorders. Additionally, nutrient and stress sensing pathways, including PGC-1α, AMPK, sirtuins, and mTOR, coordinate mitochondrial biogenesis and metabolic flexibility, linking the energetic status of the organism to the maintenance of organelles. Mitophagy is an important quality-control mechanism that removes damaged mitochondria through the PINK1-Parkin pathway and receptor-mediated pathways involving BNIP3, NIX, and FUNDC1. With aging, this waste-management system deteriorates, compounded by increased ROS and decreased NAD+. Dysregulation of NAD+ metabolism alters the coordination between mitochondrial bioenergetics and signaling. Age-related NAD+ depletion is associated with mitochondrial decline, and preclinical and clinical studies have shown varying, yet moderate medical promise of NAD⁺ precursors including NMN and NR. Several intervention options have emerged, including mitochondria-targeted antioxidants (e.g., MitoQ), mitophagy-activating compounds (e.g., urolithin A), NAD⁺ precursors, senolytics, and gene-based strategies. Despite some progress, challenges remain in establishing reliable biomarkers, developing targeted delivery, and assessing long-term safety. Combating the hindrance of mitochondrial clearance and restorative pathways appears paramount for reinstating organelle function. Interconnected deficits in genomic stability, dynamics, metabolism, and quality-control systems ultimately cause age-related mitochondrial degeneration. A better understanding of how these approaches into sustained clinical outcomes will require rigorous diagnostic tools and testing interventions. Combining pathways for mitochondrial clearance, degradation, and restoration appears highly promising for countering the effects of aging.