Secretory leukocyte protease inhibitor (SLPI) attenuates TLR4/NF-κB-mediated neuroinflammation in amyotrophic lateral sclerosis: a candidate molecule associated with neuro-pathology

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disorder driven by neuroinflammation involving activated microglia and astrocytes, which accelerates the loss of motor neurons. While Secretory leukocyte protease inhibitor (SLPI) is known for its immunomodulatory properties, its specific role in ALS pathogenesis has not been fully established. This study aimed to characterize the expression patterns and functional significance of SLPI in ALS models. METHODS: mice to analyze the spatiotemporal dynamics of SLPI expression in the gastrocnemius muscle, lumbar spinal cord, and serum across different disease stages. In vitro functional assays were conducted using siRNA-mediated knockdown of SLPI in BV2 (microglia), MA (astrocytes), and NSC-34 (motor neurons) cell lines. Additionally, recombinant SLPI protein was applied to LPS-stimulated BV2 cells to investigate its effect on the TLR4/ NF-κB signaling pathway. RESULTS: mice, SLPI was significantly upregulated in the gastrocnemius muscle from the pre-symptomatic stage (60 days) through the late stage (130 days). In the lumbar spinal cord, SLPI showed a transient initial increase but declined sharply by the end-stage; a similar significant reduction was observed in late-stage serum levels. In vitro, SLPI knockdown exacerbated pro-inflammatory cytokine production in all three cell types and impaired the antioxidant capacity of NSC-34 motor neurons. Mechanistically, recombinant SLPI attenuated inflammation in BV2 cells by modulating the TLR4/NF-κB pathway. CONCLUSIONS: The dynamic changes in SLPI levels suggest its potential relevance as a candidate molecule for disease staging. Meanwhile, its protective effects in regulating inflammation suggest that it could be a promising therapeutic candidate for mitigating ALS-associated neuroinflammation.