AI Summary
This article examines the role of Toll-like receptor 4 (TLR4) in chronic spinal cord injury (SCI). The study found that TLR4 deletion led to improved secondary damage and functional recovery in mice with SCI. Lack of TLR4 signaling resulted in reduced neuronal and myelin loss, decreased inflammation, and reduced expression of inflammatory cytokines and cell death pathways. TLR4 null mice also showed a decrease in scar-related extracellular matrix (ECM) molecules and an increase in ECM molecules associated with perineuronal nets. This was accompanied by increased axonal sprouting and improved locomotor recovery. The findings suggest that targeting TLR4 as a potential therapy for chronic SCI may be beneficial.
Toll-like receptors (TLRs) play an important role in the innate immune response after CNS injury. Although TLR4 is one of the best characterized, its role in chronic stages after spinal cord injury (SCI) is not well understood. We examined the role of TLR4 signaling in injury-induced responses at 1 d, 7 d, and 8 weeks after spinal cord contusion injury in adult female TLR4 null and wild-type mice. Analyses include secondary damage, a range of transcriptome and protein analyses of inflammatory, cell death, and extracellular matrix (ECM) molecules, as well as immune cell infiltration and changes in axonal sprouting and locomotor recovery. Lack of TLR4 signaling results in reduced neuronal and myelin loss, reduced activation of NFB, and decreased expression of inflammatory cytokines and necroptotic cell death pathway at a late time point (8 weeks) after injury. TLR4 null mice also showed reduction of scar-related ECM molecules at 8 weeks after SCI, accompanied by increase in ECM molecules associated with perineuronal nets, increased sprouting of serotonergic fibers, and improved locomotor recovery. These findings reveal novel effects of TLR4 signaling in chronic SCI. We show that TLR4 influences inflammation, cell death, and ECM deposition at late-stage post-injury when secondary injury processes are normally considered to be over. This highlights the potential for late-stage targeting of TLR4 as a potential therapy for chronic SCI.