TRIM21-mediated ubiquitination of PLIN2 regulates neuronal lipid droplet accumulation after acute spinal cord injury

Abstract

To investigate the changes in neuronal lipid droplet (LD) accumulation and lipid metabolism after acute spinal cord injury (SCI), we established a rat model of compressive SCI. Oil Red O staining, BODIPY 493/503 staining, and 4-hydroxynonenal immunofluorescence staining were performed to determine overall LD accumulation, neuronal LD accumulation, and lipid peroxidation. Lipidomics was conducted to identify the lipid components in the local SCI microenvironment. We focused on the expression and regulation of perilipin 2 (PLIN2) and knocked down PLIN2 in vivo by intrathecal injection of adeno-associated virus 9–synapsin–short-hairpin RNA-PLIN2 (AAV9-SYN-shPlin2). Motor function was assessed using the Basso–Beattie–Bresnahan score. Proteins that interacted with PLIN2 were screened by immunoprecipitation (IP) and qualitative shotgun proteomics, and confirmed by co-IP. A ubiquitination assay was performed to validate whether ubiquitination was involved in PLIN2 degradation. Oil Red O staining indicated that LDs steadily accumulated after SCI. Fluorescent staining indicated the accumulation of LDs in neurons with increased lipid peroxidation. Lipidomics revealed significant changes in lipid components after SCI. PLIN2 expression significantly increased following SCI, and knockdown of PLIN2 using AAV9-SYN-Plin2 reduced neuronal LD accumulation. This intervention improved the neuronal survival and motor function of injured rats. IP and qualitative shotgun proteomics identified tripartite motif-containing protein 21 (TRIM21) as a direct binding protein of PLIN2, and this interaction was confirmed by co-IP in vitro and immunofluorescence staining in vivo. By manipulating TRIM21 expression, we found it was negatively correlated with PLIN2 expression. In conclusion, PLIN2 is involved in neuronal LD accumulation following SCI. TRIM21 mediated the ubiquitination and degradation of PLIN2 in neurons. Inhibition of PLIN2 enhanced the recovery of motor function after SCI.