Abstract
Macrophages and resident microglia play an import role in the secondary neuroinflammation response following spinal cord injury. Reprogramming of macrophage/microglia polarization is an import strategy for spinal cord injury restoration. Low-level laser therapy (LLLT) is a noninvasive treatment that has been widely used in neurotrauma and neurodegenerative diseases. However, the influence of low-level laser on polarization of macrophage/microglia following spinal cord injury remains unknown. The present study applied low-level laser therapy on a crush spinal cord injury rat model. Using immunofluorescence, flow cytometry, RT-qPCR, and western blot assays, we found that low-level laser therapy altered the polarization state to a M2 tendency. A greater number of neurons survived in the pare injury site, which was accompanied by higher BBB scores in the LLLT group. Furthermore, low-level laser therapy elevated expression of interleukin 4 (IL-4) and interleukin 13 (IL-13). Results from this study show that low-level laser therapy has the potential for reducing inflammation, regulating macrophage/microglia polarization, and promoting neuronal survival. These beneficial effects demonstrate that low-level laser therapy may be an effective candidate for clinical treatment of spinal cord injury.
Highlights
The secondary neuroinflammation response is a key event after spinal cord injury (SCI)[1]
Results from the present study demonstrated that level laser therapy (LLLT) had a moderate influence on macrophage/microglia polarization
Haematogenous macrophages migrate to the lesion site because of several pairs of chemokines and their ligands[33]
Summary
LLLT significantly increased expression of the M2 marker IL-10 (at 3 dpi) and Arg[1] (at 3 and 7 dpi) (Fig. 4) These results suggested that the lesion site was mainly occupied by iNOS+CD11b+ cells, LLLT partly reversed the M1 predominant state and drove polarization to a relatively M2 elevated state at 7 dpi. The total number of surviving neurons in the R1 (500 μm rostral to the epicentre) and C1 (500 μm rostral to the epicentre) region was significantly greater in the LLLT group at 3, 7, and 14 dpi (Fig. 7D) These results indicated that LLLT has a beneficial neuroprotective effect in the SCI environment. BBB scores in the LLLT group were significantly greater at 7 and 14 dpi compared with the control group (Fig. 9) These results suggested that rats achieved better locomotor function recovery following laser therapy
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