TSPO-mediated mitochondrial retrograde signaling primes the microglial NLRP3 inflammasome.

Uncontrolled microglial activation is a central driver of neuroinflammatory brain diseases. The mitochondrial translocator protein (TSPO) is a well-established molecular signature of brain inflammation and serves as a diagnostic marker. However, despite this strong association, it remains unclear whether TSPO acts as a positive or negative regulator of microglial function and how it influences the inflammatory and healing responses that follow brain injury. Moreover, recent evidence of species-specific differences in TSPO expression underscores the need to better define its biology in brain-resident macrophages. Here, using a murine microglial model, we demonstrate that TSPO is required for the mitochondrial priming of inflammation and acts as a conduit for its amplification. This function relies on the engagement of multiple intracellular pathways and can be effectively counteracted by the tricyclic indole compound GE-180. Specifically, in response to inflammatory stimuli, TSPO (i) stabilizes on the mitochondrial membrane where it binds and sequesters NOD-like receptor (NLR) proteins, (ii) represses PARK2-mediated mitophagy, and (iii) promotes nuclear retrograde signaling through NF-κB accumulation, thereby enhancing the expression of pro-inflammatory genes. Sustained TSPO-dependent inflammation further drives cellular demise and excitotoxicity. Collectively, these findings advance our understanding of TSPO's molecular physiology in microglia, highlight its pivotal role in mitochondrial control of inflammation, and identify TSPO as a promising target for the pharmacological modulation of neuroinflammatory responses.