Photobiomodulation Increases M2-Type Polarization of Macrophages by Inhibiting Versican Production After Spinal Cord Injury.

Spinal cord injury (SCI) is a catastrophic accidence with little effective treatment, and inflammation played an important role in that. Previous studies showed photobiomodulation (PBM) could effectively downregulate the process of inflammation with modification of macrophage polarization after SCI; however, the potential mechanism behind that is still unclear. In the presented study, we aimed to investigate the effect of PBM on the expression level of versican, a matrix molecular believed to be associated with inflammation, and tried to find the mechanism on how that could regulate the inflammation process. Using immunofluorescence technique and western blot, we found the expression level of versican is increased after injury and markedly downregulated by irradiation treatment. Using virus intrathecal injection, we found the knock-down of versican could produce the effect similar to that of PBM and might have an effect on inflammation and macrophage polarization after SCI. To further verify the deduction, we peptide the supernatant of astrocytes to induce M0, M1, and M2 macrophages. We found that the versican produced by astrocytes might have a role on the promotion of M2 macrophages to inflammatory polarization. Finally, we investigated the potential pathway in the regulation of M2 polarization with the induction of versican. This study tried to give an interpretation on the mechanism of inflammation inhibition for PBM in the perspective of matrix regulation. Our results might provide light on the inflammation regulation after SCI.

Photobiomodulation provides neuroprotection through regulating mitochondrial fission imbalance in the subacute phase of spinal cord injury.

Increasing evidence indicates that mitochondrial fission imbalance plays an important role in delayed neuronal cell death. Our previous study found that photobiomodulation improved the motor function of rats with spinal cord injury. However, the precise mechanism remains unclear. To investigate the effect of photobiomodulation on mitochondrial fission imbalance after spinal cord injury, in this study, we treated rat models of spinal cord injury with 60-minute photobiomodulation (810 nm, 150 mW) every day for 14 consecutive days. Transmission electron microscopy results confirmed the swollen and fragmented alterations of mitochondrial morphology in neurons in acute (1 day) and subacute (7 and 14 days) phases. Photobiomodulation alleviated mitochondrial fission imbalance in spinal cord tissue in the subacute phase, reduced neuronal cell death, and improved rat posterior limb motor function in a time-dependent manner. These findings suggest that photobiomodulation targets neuronal mitochondria, alleviates mitochondrial fission imbalance-induced neuronal apoptosis, and thereby promotes the motor function recovery of rats with spinal cord injury.

Potential targets and mechanisms of photobiomodulation for spinal cord injury.

As a classic noninvasive physiotherapy, photobiomodulation, also known as low-level laser therapy, is widely used for the treatment of many diseases and has anti-inflammatory and tissue repair effects. Photobiomodulation has been shown to promote spinal cord injury repair. In our previous study, we found that 810 nm low-level laser therapy reduced the M1 polarization of macrophages and promoted motor function recovery. However, the mechanism underlying this inhibitory effect is not clear. In recent years, transcriptome sequencing analysis has played a critical role in elucidating the progression of diseases. Therefore, in this study, we performed M1 polarization on induced mouse bone marrow macrophages and applied low-level laser therapy. Our sequencing results showed the differential gene expression profile of photobiomodulation regulating macrophage polarization. We analyzed these genes using gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. Networks of protein-protein interactions and competing RNA endogenous networks were constructed. We found that photobiomodulation inhibited STAT3 expression through increasing the expression of miR-330-5p, and that miR-330-5p binding to STAT3 inhibited STAT3 expression. Inducible nitric oxide synthase showed trends in changes similar to the changes in STAT3 expression. Finally, we treated a mouse model of spinal cord injury using photobiomodulation and confirmed that photobiomodulation reduced inducible nitric oxide synthase and STAT3 expression and promoted motor function recovery in spinal cord injury mice. These findings suggest that STAT3 may be a potential target of photobiomodulation, and the miR-330-5p/STAT3 pathway is a possible mechanism by which photobiomodulation has its biological effects.