Spinal cord Toll like receptor 4 and its co-stimulatory molecule heat shock protein 90 may parti-cipate in electroacupuncture analgesia in rats with chronic neuropathic pain

Abstract

To observe the effect of electroacupuncture (EA) on the expression of Toll like receptor 4(TLR4)and heat shock protein 90(HSP90) in the spinal cord of rats with chronic constriction injury (CCI) of sciatic nerve, so as to explore the mechanism of spinal cord TLR4 and HSP90 in alleviating chronic neuropathic pain by EA. Male Wistar rats were randomized into control, model, EA, HSP90 inhibitor (inhibitor) and EA+ inhibitor groups (n=10 in each group). The neuropathic pain model was established by ligature of the right sciatic nerve to induce CCI. EA (1 mA，2 Hz/15 Hz)was applied at bilateral "Zusanli"(ST36) and "Yanglingquan"(GB34) for 30 min, once daily for 5 days. Rats of the inhibitor and EA+inhibitor groups were given a subcutaneous injection of HSP90 inhibitor geldanamycin (50 μg/kg) at the neck before daily EA. The paw withdrawal latency (PWL) of the bilateral hind-limbs was detected by using an algesia-detector. The contents of interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) in the lumbar spinal cord (L2-L4) tissue were detected by enzyme-linked immunosorbent assay. The relative expression levels of HSP90 and TLR4 proteins in the lumbar spinal cord (L2-L4) were detected using Western blot and immunofluorescence double labeling, respectively. Following CCI, a strong thermal hyperalgesia, an apparent up-regulation of expression of HSP90 and TLR4 proteins and TLR4 in microglia, and increasing levels of IL-1β and TNF-α in the spinal cord were induced in the model group relevant to the control group (P<0.01，P<0.05). Five sessions of EA intervention or inhibitor injection significantly attenuated hyperalgesia, reversed the increase of IL-1β and TNF-α, and down-regulated the expression of TLR4 in microglia (P<0.05). Compared with the model group, the expression of HSP90 was further increased (P<0.05), and those of TLR4 in microglia and neurons were significantly decreased and increased, respectively in the EA group (P<0.05). Compared with the EA group, the levels of PWLD,TLR4 and HSP90 expression, and the proportions of neuronal nuclei antigen（NeuN） and TLR4, and ionized calcium binding adapter molecule （Iba1） and TLR4 co-expressed cells were significantly decreased in the inhibitor group and EA+inhibitor group (P<0.05). The proportion of NeuN and TLR4 co-expression cells in the EA+inhibitor group was significantly higher than that of the inhibitor group (P<0.05). EA stimulation of ST36 and GB34 can alleviate thermal hyperalgesia in CCI rats, which is closely associated with its effect in regulating the expression of TLR4 in the spinal cord neurons and microglia. HSP90 in the spinal cord may be a co-stimulatory molecule for EA induced relief of neuropathic pain by regulating TLR4.