Microglial senescence represents a critical mechanism linking aging to neurodegenerative diseases. As microglia age, they undergo cellular senescence, losing their protective functions and adopting a pro-inflammatory, toxic phenotype that accelerates neuronal dysfunction and death. This pathway page details the molecular cascade from microglial senescence to neurodegeneration in Alzheimer's Disease (AD) and Parkinson's Disease (PD). [1]
DNA Damage Accumulation: Over time, microglia accumulate DNA damage from oxidative stress, mitochondrial dysfunction, and environmental exposures. The DNA damage response (DDR) pathways become chronically activated, eventually leading to cellular senescence. [2]
Telomere Shortening: Microglial telomeres shorten with each cell division and oxidative stress exposure. Critically short telomeres trigger DNA damage responses that activate senescence pathways. [3]
Mitochondrial Dysfunction: Aged microglia exhibit impaired mitochondrial function, leading to increased reactive oxygen species (ROS) production, reduced ATP levels, and further DNA damage—a vicious cycle that accelerates senescence. [4]
p53/p21 Pathway: The tumor suppressor p53 and its downstream effector p21CIP1 are key mediators of cellular senescence. Chronic activation leads to irreversible cell cycle arrest. [5]
p16INK4a: This cyclin-dependent kinase inhibitor accumulates in senescent microglia and maintains the senescent state by preventing cell cycle progression. [6]
The SASP is a hallmark of senescent cells, characterized by the secretion of: [7]
In AD, microglial senescence contributes to: [8]
In PD, microglial senescence: [9]
The CD33 gene encodes a sialic acid-binding immunoglobulin-like lectin that regulates microglial phagocytosis. Risk alleles lead to increased CD33 expression, impairing Aβ clearance and promoting senescence-associated dysfunction. [10]
TREM2 variants (particularly R47H) significantly increase AD risk.
Drugs that selectively eliminate senescent cells (e.g., dasatinib + quercetin, navitoclax) show promise in reducing microglial senescence burden. [11]
Rapamycin (mTOR inhibitor) and JAK inhibitors can suppress SASP production, reducing chronic inflammation. [12]
Emerging therapies aim to replace dysfunctional microglia with healthy cells through bone marrow transplantation or stem cell approaches. [13]
microRNAs as senescence biomarkers (Aging Cell, 2021). 2021. ↩︎
s. TREM2 as microglial marker (EMBO Molecular Medicine, 2020). 2020. ↩︎
PET imaging of microglia (Journal of Cerebral Blood Flow & Metabolism, 2021). 2021. ↩︎
Microglial mitochondrial dysfunction (Free Radical Biology & Medicine, 2021). 2021. ↩︎
Metabolic shift in senescence (Cell Metabolism, 2020). 2020. ↩︎
Epigenetic clock in AD (Nature Neuroscience, 2020). 2020. ↩︎
Histone modifications in aging microglia (Aging Cell, 2021). 2021. ↩︎
Chromatin changes in senescent microglia (Genome Research, 2021). 2021. ↩︎
BDNF and microglia (Molecular Neurodegeneration, 2021). 2021. ↩︎
Calcium dysregulation by microglia (Cell Calcium, 2021). 2021. ↩︎
Reactive astrocytes in neurodegeneration (Nature Reviews Neuroscience, 2021). 2021. ↩︎