Cycloastragenol reduces microglial NLRP3 inflammasome activation in Parkinson's disease models by promoting autophagy and reducing Scrib-driven ROS

Background: In Parkinson's disease (PD), microglial autophagy is crucial for the maintenance of cellular redox homeostasis. Meanwhile, cycloastragenol (CAG), a triterpenoid saponin and the principal active component of Astragalus, reduces the activation of NLRP3 inflammasomes. Nevertheless, the specific molecular mechanisms underlying the CAG-mitigated microglial neuroinflammation remains obscure in PD. Purpose: This study explored the role of CAG in the activation of microglial NLRP3 inflammasome and the mechanisms underlying its therapeutic potential for PD treatment. Study design: The effect of CAG was assessed in alpha-Syn-induced primary microglia and PD models. Methods: AAV1/2-hsyn-SNCA (A53T) was stereo-injected into the striatum of mice to induce PD models and CAG was orally administered. The mice underwent quantitative 4D proteomics analysis and behavioral assessments. The primary microglia and neuron cultures were analyzed by western blotting, immunofluorescence, transmission electron microscopy, etc. Results: CAG reduced phagocytosis-induced reactive oxygen species (ROS) by suppressing the microglial Scribble (Scrib) and p22 phox expression. Concurrently, CAG enhanced autophagy, promoted alpha-Syn clearance, and reduced mitochondrial damage. These synergistic effects downregulated NLRP3 inflammasome activation, in turn reducing gasdermin D cleavage, caspase-1 activation, and the release of interleukin-1 beta and interleukin-18. Further investigation revealed that CAG shielded neurons from alpha-Syn toxicity, thus attenuating behavioral impairments observed in the mouse PD model. Conclusion: CAG mitigates neuroinflammation by inhibiting ROS-induced NLRP3 inflammasome activation in microglia via promoting microglial autophagy and reducing the activity of Scrib-associated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, which signifies a promising alternative approach to PD management.