TLR4-MyD88 signaling is involved in the spinal neurons during the full length of recovery from transection of the motor branch of the femoral nerve in mice

Abstract

This study was designed to see the expression of toll-like receptor 4 (TLR4) and downstream molecules including myeloid differentiation factor 88 (MyD88) and interleukin 1-β (IL-1β) in the spinal cord as peripheral nerve injury recovered in mice. We established a model of femoral nerve injury (FNI) in C57BL/6 mice by transection of the motor branch of the femoral nerve, followed by retrograde labeling to show the according motor neurons in the anterior horn of the spinal cord pars lumbar. We observed the motor function recovery of the injured hind limbs using behavioral tests. The expression of TLR4, MyD88, and IL-1β was examined by immunofluorescent staining and western blot. According to the behavior test, the FNI animals fully recovered within 6-8 weeks. TLR4, MyD88, and IL-1β were expressed in the ventral horn of the spinal cord both at 72 h till 6 weeks after the femoral nerve transection surgery, and these proteins were mostly co-localized with neurons. IL-1β also tended to rise in the same surgery groups, but more intimate with microglia surrounding nearby retrograde labeled neurons. And western blot results were consistent with histological findings. The results indicate that peripheral nerve injury may induce innate immune reactions of the central neurons and critical signaling like TLR4/MyD88 in the spinal cord may reflect the recovery of the injury. These findings suggest that peripheral nerve injury triggered the TLR4/MyD88 signal in the soma of spinal neurons may be involved in function and nerve restoration through neuron-glia crosstalk.