Near-Infrared Imaging of Senescence-Associated β-Galactosidase Enables Discovery of a Glycerol-3-Phosphate Dehydrogenase 2-Regulated Neuroprotective Pathway in Alzheimer’s Disease

Neuronal senescence is increasingly recognized as a contributor to Alzheimer's disease (AD), yet the molecular mechanisms underlying its progression remain incompletely understood. Herein, we introduce XCH-sen, a β-galactosidase (β-Gal)-responsive near-infrared fluorescent probe designed for imaging senescence-associated β-Gal activity in living cells and animals. Utilizing XCH-sen, we identified glycerol-3-phosphate dehydrogenase 2 (GPD2) as a previously unrecognized regulator of neuronal senescence. The deficiency of GPD2 significantly increased β-Gal activity and accelerated neuronal senescence, which was consistent with the results of SA-β-Gal staining. Mechanistically, loss of GPD2 disrupts mitochondrial redox homeostasis, leading to oxidative stress, mitochondrial dysfunction, impaired autophagic flux, and inflammatory activation, which collectively drive activation of the P16/P21/P53 pathway and cell-cycle arrest. In vivo, GPD2 deficiency exacerbates cognitive impairment, neuroinflammation, Aβ accumulation, and neuronal damage in AD models. Together, this work identifies GPD2 as a metabolic regulator of neuronal senescence and demonstrates the utility of molecular imaging in uncovering mechanisms underlying the progression of neurodegenerative diseases.