Astrocyte Senescence Impairs Synaptogenesis due to Thrombospondin‐1 Loss

ABSTRACT Cellular senescence is an irreversible state linked to aging that involves molecular and functional alterations. The mammalian hippocampus, a key brain region for learning and memory, is highly vulnerable to damage in age‐related neurodegenerative diseases, yet the role of cellular senescence in hippocampal aging remains underexplored. Here, we report an early onset of senescence signatures in hippocampal astrocytes of the accelerated aging and frailty mouse model SAMP8. We examine how astrocyte senescence affects excitatory synapse formation, focusing on soluble signals released by astrocytes. Astrocytes isolated from SAMP8 brain and those differentiated from SAMP8 neural stem cells show senescence hallmarks (SA‐β‐gal, p16 INK4a , Lamin B1 loss), alongside a significant reduction in synaptogenic function. While astrocyte‐conditioned medium (ACM) from control mice promotes excitatory synaptogenesis through thrombospondin‐1/α2δ‐1 neuronal receptor signaling, ACM from senescent SAMP8 astrocytes lacks this capacity. Supplementing senescent ACM with thrombospondin‐1 protein or overexpressing thrombospondin‐1 gene in senescent astrocytes reinstates synaptogenesis. At the hippocampal level, thrombospondin‐1 and synaptic puncta are reduced in SAMP8 mice. Our findings reveal that senescent astrocytes exhibit reduced synaptogenic capacity due to thrombospondin‐1 loss, highlighting their contribution to synaptic dysfunction during aging. Preventing senescence in hippocampal astrocytes may thus restore astrocyte‐mediated synaptogenesis in the aged brain.