Papers of the Week

Bone Morphogenetic Protein-2/4 (BMP2/4) have been recognized as promoters of astrocyte activity. Substantial evidence suggests BMP2/4 may be elevated and play a critical role in astrocyte activation upon spinal cord injury. Although neuropathic pain (NP) is similarly associated with astrocyte activation, the participation of BMP2/4 in this regard still remains unclear. A rat model of NP achieved by spinal nerve ligation (SNL) at L5 was used to evaluate the expression of glial fibrillary acidic protein (GFAP) and BMP2/4 in the spinal cord in days 1, 4, 7, 10 and 14. Next, normal rats received intrathecal exogenous BMP2/4 and the antagonist Noggin to assess the effect of BMP2/4 on astrocyte activation. In both experiments, von Frey filaments were used to evaluate changes in paw withdrawal threshold (PWT). In addition, Western blotting and immunofluorescence were performed to assess the expression of glial fibrillary acidic protein (GFAP), BMP2/4, p-Smad 1/5/8, p-STAT3 in the spinal cord. Firstly, SNL caused a significant increase in the expression of BMP4, while BMP2 levels remained unchanged. Secondly, exogenous BMP4 but not BMP2 induced a significant decrease in PWT, along with upregulation of GFAP. Moreover, exogenous BMP4 stimulated both p-Smad 1/5/8 and p-STAT3, while BMP2 only upregulated p-Smad 1/5/8. Finally, exogenous Noggin alleviated the decrease in PWT induced by BMP4, and reduced astrocyte activation, as well as p-STAT3 upregulation. Our results indicate only BMP4-and not BMP2-intervened in allodynia in rats by eliciting glial activation, probably through both p-Smad 1/5/8 andp-STAT3 signaling.