Drosophila nociceptive sensitization requires BMP signaling via the canonical SMAD pathway

Nociceptive sensitization is a common feature in chronic pain, but its basic cellular mechanisms are only partially understood. The present study used the Drosophila melanogaster model system and a candidate gene approach to identify novel components required for modulation of an injury-induced nociceptive sensitization pathway presumably downstream of Hedgehog. This study demonstrates that RNAi silencing of a member of the Bone Morphogenetic Protein (BMP) signaling pathway, Decapentaplegic (Dpp), specifically in the Class IV multidendritic nociceptive neuron, significantly attenuated ultraviolet injury-induced sensitization. Furthermore, overexpression of Dpp in Class IV neurons was sufficient to induce thermal hypersensitivity in the absence of injury. The requirement of various BMP receptors and members of the SMAD signal transduction pathway in nociceptive sensitization was also demonstrated. The effects of BMP signaling were shown to be largely specific to the sensitization pathway and not associated with changes in nociception in the absence of injury or with changes in dendritic morphology. Thus, the results demonstrate that Dpp and its pathway play a crucial and novel role in nociceptive sensitization. Because the BMP family is so strongly conserved between vertebrates and invertebrates, it seems likely that the components analyzed in this study represent potential therapeutic targets for the treatment of chronic pain in humans.