Cellular Senescence and Its Contribution to Alzheimer’s Disease

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Introduction

Aging is a major risk factor for a wide range of diseases, including cardiovascular disease, cancer, diabetes, osteoporosis, and neurodegenerative disorders. Alzheimer’s disease (AD) is no exception, as advancing age represents the most significant risk factor for late-onset AD, which accounts for over 95% of cases. Another hallmark of aging is the progressive accumulation of senescent cells across multiple tissues. Increasing evidence suggests that cellular senescence is not merely a byproduct of aging, but an active driver of age-related pathologies, including AD.

Senescent cells undergo irreversible cell cycle arrest while remaining metabolically active. They resist apoptosis and secrete a range of proinflammatory and tissue-remodeling factors, collectively termed the senescence-associated secretory phenotype (SASP). This phenotype promotes chronic inflammation and tissue dysfunction, which are highly relevant to AD pathogenesis. Stressors such as DNA damage, mitochondrial impairment, oncogenic activation, and the accumulation of pathogenic proteins including amyloid-beta (Aβ) and tau can initiate senescence across various brain cell populations.

Senescence in the Alzheimer’s Brain

Extracellular deposition of Aβ plaques and intracellular aggregation of hyperphosphorylated tau are defining features of AD. Microglia and astrocytes are frequently observed clustering around Aβ plaques. While these glial cells normally support neuronal health, in the diseased brain they often adopt a proinflammatory phenotype, contributing to chronic neuroinflammation. Importantly, astrocytes and microglia at sites of Aβ pathology have been shown to exhibit molecular and functional hallmarks of senescence. Tau accumulation has also been implicated as a potent inducer of senescence in these glial populations.

Senescence is not restricted to microglia and astrocytes. Oligodendrocyte progenitor cells (OPCs), which give rise to mature oligodendrocytes, are also vulnerable. OPCs are essential for remyelination and neuronal repair; however, exposure to Aβ has been shown to drive OPC senescence. This process likely contributes to white matter damage and impaired neural connectivity, both of which are strongly linked to AD progression.

Therapeutic Targeting of Senescent Cells

Recent preclinical studies have demonstrated that clearance of senescent cells can mitigate AD pathology. Removal of senescent glial and astrocytic cells in transgenic mouse models reduced tau tangle formation and improved cognitive performance. Biomarkers such as elevated p16^Ink4a expression have been identified as indicators of senescence, and notably, increased p16^Ink4a activity has been observed in AD models prior to tau pathology development.

Senolytic therapies—agents designed to selectively eliminate senescent cells—are under investigation as potential disease-modifying strategies. In mouse models, senolytics reduced senescent cell burden, decreased tau aggregation, and enhanced neuronal survival. These findings support senolytics as a promising intervention for slowing or reversing AD progression.

Senolytic Compounds Under Investigation

Several pharmacological approaches are being explored:

• Dasatinib and Quercetin (D+Q): This drug combination has been shown to clear senescent OPCs, reduce inflammation associated with Aβ plaques, and improve cognitive performance in mouse models of AD. Early clinical data suggest that D+Q is safe, tolerable, and effective in lowering senescent cell burden.
• Rapamycin: Already FDA-approved for other indications, rapamycin has demonstrated efficacy in reducing Aβ and tau pathology in preclinical models. It also improves cerebral blood flow and cognitive performance.

These agents highlight the translational potential of senolytics, several of which are advancing through early-phase human trials for AD.

Genetic Contributions to Senescence in AD

Genetic susceptibility further strengthens the link between senescence and AD. Variants in genes such as ADAMTS4, associated with SASP activity, and BIN1, a stress-responsive gene, have been implicated in increasing vulnerability to AD. These findings suggest that both genetic predisposition and cellular senescence converge to amplify disease risk and progression.

Conclusion

Cellular senescence plays a pivotal role in the pathophysiology of Alzheimer’s disease. By promoting chronic inflammation, impairing neural repair mechanisms, and exacerbating protein aggregation, senescent cells contribute to both disease onset and progression. Mounting evidence supports the therapeutic potential of senolytic strategies, which are now entering clinical trials. Further exploration of senescence-targeted interventions may provide new opportunities to delay or modify the course of AD.

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