BACKGROUND:Indolepropionic acid has been shown to reduce diabetes-induced central nervous system inflammation.However,there is a lack of research on whether to inhibit microglia M1 polarization for the treatment of spinal cord injury. OBJECTIVE:To investigate the mechanism of indolepropionic acid inhibition of microglial cell M1 polarization for the treatment of spinal cord injury through cell and animal experiments. METHODS:(1)In vitro experiments:BV2 cell viability was assessed using the CCK-8 assay to determine optimal concentrations of indolepropionic acid.Subsequently,BV2 cells were categorized into control group,administration group(50 μmol/L indolepropionic acid),lipopolysaccharide group(100 ng/mL lipopolysaccharide),and treatment group(100 ng/mL lipopolysaccharide + 50 μmol/L indolepropionic acid).Nitric oxide content was quantified using the Griess method.Real-time quantitative PCR and western blot assay were employed to measure mRNA and protein levels of pro-inflammatory factors.Cell immunofluorescence staining was conducted to assess inducible nitric oxide synthase expression.The Seahorse assay was employed to assess glycolytic stress levels in BV2 cells.(2)In vivo experiments:30 SD rats were randomly divided into three groups:sham surgery group,spinal cord injury group,and indolepropionic acid group.Motor function recovery in rats after spinal cord injury was assessed using BBB scoring and the inclined plane test.Immunofluorescence staining of spinal cord tissue was conducted to evaluate the expression of inducible nitric oxide synthase in microglial cells.ELISA was employed to measure protein expression levels of the pro-inflammatory cytokines interleukin-1β and tumor necrosis factor-α in spinal cord tissue. RESULTS AND CONCLUSION:(1)In vitro experiments:Indolepropionic acid exhibited significant suppression of BV2 cell viability when its concentration exceeded 50 μmol/L.Indolepropionic acid achieved this by inhibiting the activation of the nuclear factor κB signaling pathway,thereby suppressing the mRNA and protein expression levels of pro-inflammatory cytokines(interleukin-1β and tumor necrosis factor-α),as well as the M1 polarization marker,inducible nitric oxide synthase,in BV2 cells.Additionally,indolepropionic acid notably reduced the glycolytic level in BV2 cells induced by lipopolysaccharides.(2)In vivo experiments:Following indolepropionic acid intervention in spinal cord injury rats,there was a noticeable increase in BBB scores and the inclined plane test angle.There was also a significant decrease in the number of M1-polarized microglial cells in spinal cord tissue,accompanied by a marked reduction in the protein expression levels of pro-inflammatory cytokines(interleukin-1β and tumor necrosis factor-α).(3)These results conclude that indolepropionic acid promotes functional recovery after spinal cord injury by improving the inflammatory microenvironment through inhibition of microglia M1 polarization.

Spinal cord injury (SCI) causes motor, sensory, and autonomic dysfunctions. The gut microbiome has an important role in SCI, while short-chain fatty acids (SCFAs) are one of the main bioactive mediators of microbiota. In the present study, we explored the effects of oral administration of exogenous SCFAs on the recovery of locomotor function and tissue repair in SCI. Allen's method was utilized to establish an SCI model in Sprague-Dawley (SD) rats. The animals received water containing a mixture of 150 mmol/L SCFAs after SCI. After 21 d of treatment, the Basso, Beattie, and Bresnahan (BBB) score increased, the regularity index improved, and the base of support (BOS) value declined. Spinal cord tissue inflammatory infiltration was alleviated, the spinal cord necrosis cavity was reduced, and the numbers of motor neurons and Nissl bodies were elevated. Enzyme-linked immunosorbent assay (ELISA), real-time quantitative polymerase chain reaction (qPCR), and immunohistochemistry assay revealed that the expression of interleukin (IL)‍-10 increased and that of IL-17 decreased in the spinal cord. SCFAs promoted gut homeostasis, induced intestinal T cells to shift toward an anti-inflammatory phenotype, and promoted regulatory T (Treg) cells to secrete IL-10, affecting Treg cells and IL-17⁺ γδ T cells in the spinal cord. Furthermore, we observed that Treg cells migrated from the gut to the spinal cord region after SCI. The above findings confirm that SCFAs can regulate Treg cells in the gut and affect the balance of Treg and IL-17⁺ γδ T cells in the spinal cord, which inhibits the inflammatory response and promotes the motor function in SCI rats. Our findings suggest that there is a relationship among gut, spinal cord, and immune cells, and the "gut-spinal cord-immune" axis may be one of the mechanisms regulating neural repair after SCI.
Animals ; Rats ; Interleukin-17 ; Rats, Sprague-Dawley ; Recovery of Function ; Spinal Cord Injuries/drug therapy* ; T-Lymphocytes, Regulatory ; Receptors, Antigen, T-Cell, gamma-delta/immunology*