Hippocampal astrocyte St6galnac5 silencing improves spatial memory and preserves synaptic integrity in an AD mouse model.

Cognitive resilience in Alzheimer's disease (AD) requires the maintenance of synaptic integrity despite progressive pathological insults. Reactive astrocytes can switch between neuroprotective and neurotoxic states, and their maladaptive transition significantly accelerates neurodegeneration, yet the molecular drivers of this shift remain elusive. Here, using published single-nucleus transcriptomic data, we identified the sialyltransferase St6galnac5 as a candidate regulator associated with reactive, pro-inflammatory astrocyte states. We further show that astrocyte-specific, AAV-mediated knockdown of St6galnac5 in female 3xTg-AD mice improves spatial learning, memory and anxiety-like behaviors. Neuropathological assessment revealed that this functional recovery was underpinned by a marked reduction in amyloid-β and tau pathologies, alongside the preservation of synaptic integrity. Consistent with a shift toward a less inflammatory astrocyte state, St6galnac5 knockdown decreased A1-associated markers and increased A2-associated markers in vitro and alleviated neurite outgrowth deficits in neuron-astrocyte co-culture. Together, our findings identify St6galnac5 as a critical molecular switch driving astrocytic dysfunction in AD, and further propose that targeted inhibition of this sialylation pathway represents a viable strategy to bolster astrocytic resilience and slow disease progression.