Targeting Astrocytic Stat3 Reveals Context-Dependent Modulation of Prion Disease

Reactive astrogliosis is a prominent feature of prion diseases, yet the molecular mechanisms regulating astrocyte activation and their contribution to disease progression remain poorly understood. Signal transducer and activator of transcription 3 (Stat3) is a master regulator of reactive astrocytes in numerous neurological disorders, but its role in prion disease has not been established. Here, we investigated the contribution of astrocytic Stat3 signaling to prion pathogenesis using an inducible astrocyte-specific Stat3 knockout mouse model. Stat3 expression was elevated across multiple neuroinflammatory conditions but was most strongly induced during prion disease. Among four mouse-adapted prion strains (ME7, RML, 22L, and SSLOW), the magnitude of Stat3 activation closely paralleled the severity of neuroinflammation. Astrocyte-specific Stat3 deletion was evaluated in mice infected with either the highly inflammatory SSLOW strain or the less inflammatory 22L strain. Stat3 deletion had no detectable effect on disease progression in SSLOW-infected mice but modestly delayed disease onset and behavioral decline in male mice infected with the 22L strain, particularly when knockout was induced before prion inoculation. Despite its limited effect on survival, astrocyte-specific Stat3 deletion consistently attenuated astrocyte reactivity, as evidenced by reduced vimentin expression, delayed cortical GFAP induction, and lower GFAP expression in recombined astrocytes at the single-cell level, demonstrating a cell-autonomous role for Stat3 in promoting reactive astrogliosis. In contrast, PrPSc accumulation and overall microglial activation remained unchanged, indicating that astrocytic Stat3 signaling is dispensable for prion replication and does not substantially influence the global microglial response. Tamoxifen-induced recombination occurred in only 40-70% of astrocytes, resulting in partial and region-dependent Stat3 deletion that likely underestimated the impact of astrocytic Stat3 loss. Together, these findings identify Stat3 as an important regulator of astrocyte reactivity during prion disease but demonstrate that its contribution to disease progression is limited and highly context-dependent, varying with the inflammatory milieu, timing of pathway inhibition, and biological sex. Our results highlight the redundancy of inflammatory signaling networks driving chronic prion neurodegeneration and suggest that targeting astrocytic Stat3 alone is unlikely to substantially alter disease progression.