TREM-1 as a potential gatekeeper of neuroinflammatory responses: therapeutic validation and mechanistic insights in experimental traumatic brain injury.

Background: Traumatic brain injury (TBI) triggers a cascade of neuroinflammatory responses mediated by microglial activation, which significantly contributes to secondary brain damage. While triggering receptor expressed on myeloid cells-1 (TREM-1) is a key inflammatory amplifier, its mechanistic role and therapeutic potential in TBI remain elusive. Thus, this study endeavored to elucidate the exact role of TREM-1 in experimental TBI. Methods: A controlled cortical impact (CCI) model was established in male C57BL/6 mice to induce TBI. The temporal expression profile of TREM-1 was assessed using RNA sequencing and Western blot (WB). The TREM-1 inhibitory peptide LP17 was administered intranasally at 2 hours post-injury (hpi). Neurobehavioral assessments, histological analyses, immunofluorescence (IF), brain water content (BWC) measurement, Evans blue (EB) assays and laser speckle contrast imaging (LSCI) were performed in this study. Results: TBI significantly upregulated TREM-1 expression in microglia, peaking at 3 days post-injury (dpi). Intranasal administration of the TREM-1 antagonist LP17 treatment attenuated neuroinflammation, reduced blood-brain barrier disruption, ameliorated cerebral blood flow decrease, promoted synaptic remodeling, and improved functional outcomes. Mechanistically, through its interaction with SYK, TREM-1 triggered the CARD9/NF-κB signaling and induced pyroptosis. SYK inhibition reversed these effects, confirming the necessity of the TREM-1/SYK axis in neuroinflammatory signaling. Conclusion: Our finding demonstrates that TREM-1 critically mediates neuroinflammation and synaptic dysfunction after TBI. Pharmacological targeting of TREM-1 attenuates neuroinflammation, reduces cerebral edema, preserves blood-brain barrier integrity, and improves functional recovery. These effects are mediated through suppression of TREM-1-dependent NF-κB signaling and pyroptosis. These results highlight TREM-1 as a promising therapeutic target for TBI.