α1-Antitrypsin attenuates microglial NLR family pyrin domain containing 3 inflammasome activation via cannabinoid receptor 2 signaling to ameliorate α-synucleinopathy-related behavioral deficits.

α-Synucleinopathies are marked by persistent neuroinflammation and disabling non-motor symptoms involving nucleus accumbens (NAc) dysfunction, yet the neuroimmune mechanisms linking microglial activation to accumbal synaptic pathology remain poorly understood. Here, we identify α1-antitrypsin (AAT) as a previously unrecognized modulator of cannabinoid receptor 2 (CB2R)-associated signaling in α-syn pathology. An acute transcriptomic screen revealed prominent induction of the Serpina1 gene family, while primary-microglial and chronic AAV-α-syn experiments showed that Cnr2 deficiency amplified Serpina1/AAT responses, consistent with an insufficient compensatory reaction to persistent inflammation. Molecular docking, reciprocal co-immunoprecipitation, and surface plasmon resonance provided complementary evidence supporting an AAT-CB2R association under the respective assay conditions. Functionally, AAT reduced the α-syn-associated elevation of intracellular cAMP in an AM630-sensitive manner and attenuated ATP-evoked Ca2⁺ responses, calpain-1 activity, GSK-3β N-terminal cleavage, and NLRP3/caspase-1-related cytokine production; these effects were substantially diminished in Cnr2-deficient microglia. Calpeptin reproduced key molecular effects, implicating calpain-related proteolysis in this neuroimmune response. In vivo, intracerebroventricular AAT preserved NAc synaptic ultrastructure, ameliorated excitatory synaptic abnormalities in dopamine D2 receptor-expressing medium spiny neurons, and improved fear-memory retrieval, spontaneous alternation, and anxiety-like behavior, without affecting novel object recognition or motor performance. Several effects were attenuated under Cnr2-deficient conditions, although selected electrophysiological responses persisted. Our findings identify AAT-CB2R-linked signaling as a modulator of microglial inflammatory homeostasis and support the therapeutic potential of AAT for NLRP3-associated neuroinflammation and non-motor dysfunction in α-synucleinopathies.