Agrin requires specific proteins to selectively activate γ-aminobutyric acid neurons for pain suppression

Agrin, a heparan sulfate proteoglycan functioning as a neuro-muscular junction inducer, has been shown to inhibit neuropathic pain in sciatic nerve injury rat models, via phosphorylation of N-Methyl-d-aspartate receptor NR1 subunits in gamma-aminobutyric acid neurons. However, its effects on spinal cord injury-induced neuropathic pain, a debilitating syndrome frequently encountered after various spine traumas, are unknown. In the present investigation, we studied the 50kDa agrin isoform effects in a quisqualic acid dorsal horn injection rat model mimicking spinal cord injury-induced neuropathic pain. Our results indicate that 50kDa agrin decreased only in the dorsal horn of neuropathic animals and increased 50kDa agrin expression in the dorsal horn, via intra-spinal injection of adeno-associated virus serum type two, suppressed spinal cord injury-induced neuropathic pain. Also, the reason why 50kDa agrin only activates the N-Methyl-d-aspartate receptor NR1 subunits in the GABA neurons, but not in sensory neurons, is unknown. Using immunoprecipitation and Western-blot analysis, two dimensional gel separation, and mass spectrometry, we identified several specific proteins in the reaction protein complex, such as neurofilament 200 and mitofusin 2, that are required for the activation of the NR1 subunits of gamma-aminobutyric acid inhibitory neurons by 50kDa agrin. These findings indicate that 50kDa agrin is a promising agent for neuropathic pain treatment.