Mitohormesis linking metabolic dysfunction and neurodegeneration: implications for dementia and therapeutic strategies.

Mitochondria are central regulators of cellular metabolism, redox homeostasis, and stress adaptation. Mitohormesis refers to an adaptive response in which mild or transient mitochondrial perturbation activates stress-response pathways that subsequently enhance mitochondrial or cellular resilience; however, persistent or excessive stress can overwhelm adaptive capacity and promote mitochondrial dysfunction and tissue injury. Metabolic diseases, including obesity and type 2 diabetes mellitus, are major risk factors for cognitive decline and dementia, and clinical studies have demonstrated associations between metabolic dysfunction, structural brain abnormalities, accelerated brain aging, and impaired cognitive function. However, direct evidence linking mitochondrial dysfunction to neurodegeneration in humans remains limited, with most mechanistic insights derived from experimental animal models and cultured neuronal systems. Experimental evidence indicates that chronic metabolic stress can disrupt mitochondrial quality control and proteostasis, increase mitochondrial reactive oxygen species production, and promote neuroinflammation and neuronal dysfunction. Conversely, adaptive mitochondrial stress responses can preserve mitochondrial integrity and cellular resilience through coordinated regulation of the integrated stress response, mitochondrial quality-control mechanisms, lysosomal-mitochondrial crosstalk, extracellular vesicle-mediated communication, and inter-organ signaling. In Alzheimer's disease, mitochondrial dysfunction and amyloid-β/tau pathology may interact bidirectionally, potentially generating self-reinforcing cycles of neuronal injury. Lifestyle and pharmacological interventions-including exercise; caloric restriction; nutritional ketosis; and the use of metformin, sodium-glucose cotransporter 2 inhibitors, and glucagon-like peptide-1 receptor agonists-have been associated with adaptive mitochondrial and metabolic responses involving AMP-activated protein kinase, nuclear factor erythroid 2-related factor 2, mitochondrial biogenesis, mitophagy, and redox signaling. However, evidence that mitohormesis directly mediates their beneficial effects varies substantially across interventions and remains predominantly indirect or hypothesized in humans. Moreover, the discrepancy between encouraging preclinical findings and clinical outcomes highlights important translational barriers, including the lack of validated biomarkers, uncertainty regarding optimal stress intensity and timing, and tissue- and disease-specific differences in adaptive capacity. Collectively, current evidence supports mitohormesis as a conceptual framework for integrating mitochondrial stress adaptation, metabolic dysfunction, and neuronal resilience rather than as an established unifying mechanism underlying neurodegeneration. Defining the conditions under which mitochondrial stress is adaptive, identifying reliable biomarkers of mitohormesis, and determining whether these responses can be safely and effectively modulated in humans will be essential for establishing its therapeutic relevance in metabolic and neurodegenerative diseases.