Snapin mediates neuronal PANoptosis after mild traumatic brain injury via H2S-dependent S-sulfhydration of CTSD

Abstract

Introduction

Traumatic brain injury (TBI) induces complex secondary neuronal death, yet no specific therapeutic strategies are available to ameliorate post-traumatic neurological dysfunction. PANoptosis is a coordinated cell death pathway involving apoptosis, pyroptosis, and necroptosis; however, it remains unknown whether PANoptosis contributes to mild TBI (mTBI)-induced neuronal death and what precise mechanisms govern this process.

Objective

This study aimed to investigate whether Snapin regulates neuronal PANoptosis following mTBI and to elucidate its functional mechanism through the hydrogen sulfide (H₂S)/ cathepsin D (CTSD) pathway.

Methods

We utilized a controlled cortical impact (CCI) protocol to create a model of mTBI. Neuronal Snapin was conditionally knocked down via AAV-shSnapin. PANoptosis-related proteins were evaluated using immunofluorescence staining and Western blot. Endogenous H₂S levels were measured with a sulfide ion-selective electrode. The interaction between Snapin and cystathionine β-synthase (CBS) was examined by molecular docking and co-immunoprecipitation, while S-sulfhydration of CTSD was detected using a modified biotin switch assay. Therapeutic effects were assessed through behavioral tests including the wire-grip test, open field test, beam balanced walk, novel object recognition, and Morris water maze.

Results

Snapin was significantly upregulated in cortical and hippocampal neurons after mTBI. Knockdown of Snapin attenuated neurodegeneration, reduced PANoptosis-related proteins, and improved neurofunctional recovery. Mechanistically, Snapin bound to CBS, disrupting H₂S metabolic homeostasis and reducing endogenous H₂S levels. The decrease in H₂S limited S-sulfhydration of pro-CTSD, promoting its maturation into active CTSD and ultimately inducing PANoptosis. Both pepstatin A and NaHS treatment conferred neuroprotection, reducing neuronal death and neuroinflammation.

Conclusion

Snapin promotes mTBI-induced neuronal PANoptosis by disrupting the H₂S/CTSD pathway through specific binding with CBS. Therapeutic strategies targeting Snapin, restoring H₂S homeostasis, or inhibiting CTSD activation may significantly alleviate neurological impairment and neuroinflammation post-mTBI, highlighting novel therapeutic avenues for mTBI treatment.