Treadmill training improves respiratory function in rats after spinal cord injury by inhibiting the HMGB1/TLR-4/NF-κB signaling pathway.

Objective: To investigate the effects of treadmill training on lung injury and HMGB1/TLR4/NF-κB after spinal cord injury (SCI) in rats.

Methods: A total of 108 female SD rats were randomly divided into three groups: sham operation group, SCI brake group, and SCI exercise group. The rats in the SCI exercise group began treadmill training on the 3rd day after the operation. The rats in the SCI brake group underwent braking treatment. The lung tissues were obtained on the 3rd, 7th, and 14th days after exercise. Locomotor functional recovery was determined using the BBB scores and inclined plane test. Respiratory function was determined via abdominal aortic blood gas analysis. HE staining was used to detect pathological changes in rat lung tissue. RNA sequencing was used to identify differentially expressed genes at different phases in each group of lung tissues. HMGB1, TLR4, and NF-κB in lung tissue were detected using immunohistochemistry and immunofluorescence. Detection of HMGB1 levels in serum, spinal cord tissues and lung tissues by ELISA. HMGB1, TLR4, NF-κB, IL-1β, IL-6, TNF-α mRNA, and protein expression levels were detected via qRT PCR and western blot.

Results: Motor and respiratory functions significantly decreased after SCI (P < 0.05). However, locomotion and respiratory functions were significantly improved after treadmill training intervention (P < 0.05). HE staining showed that interstitial thickening, inflammatory cells, and erythrocyte infiltration occurred in lung tissue of rats after SCI (P < 0.05). Moreover, inflammatory reaction in lung tissue was significantly reduced after treadmill training intervention (P < 0.05). A total of 428 differentially expressed mRNAs [(|log2(FC)| > 2, P < 0.05)] were identified in the intersection of the three groups. KEGG analysis identified five enriched signal pathways, including NF-kappa B. ELISA results showed that treadmill training could significantly reduce the levels of HMGB1 in serum, spinal cord tissue and lung tissue that were elevated after SCI (P < 0.05). Immunohistochemistry, immunofluorescence, qRT PCR, and Western blot showed that HMGB1, TLR4, IL-1β, IL-6, TNF-α, and NF-κB expressions were significantly up-regulated at the 3rd, 7th and 14th days after SCI, compared with the sham group. Besides, inflammatory cytokines were significantly lower in the SCI exercise group than in the SCI brake group at all time points after intervention (P < 0.05).

Conclusion: Treadmill training alleviates lung tissue inflammation and promotes recovery of motor and respiratory functions by inhibiting the HMGB1/TLR4/NF-κB signaling pathway after SCI in rats.