STING-Mediated NLRP3 Inflammasome Priming in ALS Microglia

This hypothesis proposes that cytoplasmic mtDNA released from TDP-43-damaged mitochondria in ALS activates the cGAS-STING pathway in microglia, which subsequently primes and hyperactivates the NLRP3 inflammasome through IRF3-mediated transcriptional upregulation and direct STING-NLRP3 protein interactions. The molecular mechanism begins with TDP-43 aggregation disrupting mitochondrial homeostasis, leading to mtDNA leakage into the cytoplasm where it binds cGAS. Activated cGAS synthesizes cGAMP, which binds STING and triggers its oligomerization and translocation from the ER to perinuclear puncta. STING activation then occurs through two convergent pathways: (1) canonical IRF3/NF-κB signaling that transcriptionally upregulates NLRP3, pro-IL-1β, and pro-IL-18 expression (priming signal), and (2) direct STING-NLRP3 physical interaction at ER-mitochondrial contact sites that facilitates NLRP3 oligomerization and inflammasome assembly (activation signal). This dual STING-mediated mechanism amplifies microglial NLRP3 inflammasome activity, resulting in excessive caspase-1 activation and IL-1β/IL-18 secretion that drives chronic neuroinflammation and motor neuron death. The hypothesis predicts that pharmacological STING antagonists will simultaneously block both NLRP3 priming and direct inflammasome activation, breaking the self-perpetuating cycle of mitochondrial damage and inflammatory escalation. This can be tested by treating ALS mouse models with STING inhibitors and measuring microglial NLRP3 expression, inflammasome assembly, cytokine secretion, and motor neuron survival, while confirming STING-NLRP3 co-localization through proximity ligation assays in human ALS microglia.