Photobiomodulation regulates inflammation and autophagy in spinal cord injury through NLRP3/Caspase-1/IL-1β pathway by targeting TLR2

After spinal cord injury (SCI), peripherally derived macrophages infiltrated the injury area to exert inflammatory effects, causing barriers to the repair of spinal cord injury. Our previous study confirmed that photobiomodulation (PBM) could promote the motor function recovery and inhibit the secretion of inflammatory cytokines after SCI, moreover, PBM also has a role in promoting Autophagy, but the mechanism is not clear. Therefore, we aimed to investigate whether PBM promotes Autophagy by regulating the inflammatory response of macrophages, which in turn regulates functional repair after SCI. Male C57/BL6 mice were used to prepare a model of clamped spinal cord injury, and PBM irradiation was performed for 28 consecutive days, which showed that motor function of the mice was improved. We observed that Autophagy proteins (LC3, Beclin-1 and p62) were inhibited and inflammasome-related proteins (NLRP3, Caspase-1 and IL-1β) expression was significantly enhanced in SCI mice. We analyzed the RNA Sequencing (RNA-seq) of SCI, SCI+PBM treated mice in combination with Autophagy database. The results showed 25 differentially expressed genes (DEGs). Protein-protein interaction (PPI) network and Hub gene analysis revealed TLR2 as a key molecule in the regulation of Autophagy levels by PBM after SCI. We performed preliminary analysis in macrophages cultured in vitro and observed that PBM suppressed the expression of TLR2 and inflammasome-related proteins in M1-type macrophages and promoted the expression of Autophagy proteins. Subsequently, we used an agonist of TLR2 (CU-T12-9) to up regulate TLR2 expression and observed that macrophage Autophagy was inhibited and inflammatory response was enhanced. After PBM irradiation, the effect of CU-T12-9 was counteracted. Taken together, PBM promotes Autophagy and attenuates the inflammatory response by regulating TLR2, a key molecule of Autophagy in spinal cord injury.

Autophagy; Inflammation; Photobiomodulation; Spinal cord injury; TLR2.