A role of CD9 in pain pathway of spinal dorsal horn

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Tetraspanin CD9 acts as molecular scavenger, which collects signaling molecules and help to organize the specific site for effective signal transduction in the cells. Previously, we found that CD9 was concentrated in the superficial layers (I and II) of the dorsal horn of mouse spinal cord and the spinal trigeminal nucleus, both of which are main pain pathways, The purpose of this study was to clarify the cellular localization of CD9 and the relationship with other pain-related molecules. This following results were obtained.1) CD9 often forms functional complex with other tetraspanins, especially with CD81 and CD151, however, both proteins did not show any specific distributions in the dorsal horn. 2) The similar distribution pattern of CD9 was observed in human spinal cord (collaboration with Dr. Takahashi, Niigata Univ., Brain Res. Inst.), suggesting that this protein may be involved in pain signaling in human as well. 3) Using spinal cord sections, in which green fluorescence prote … More in was specifically expressed in astrocytes under the control of glial fibrillary acidic protein (GFAP) promoter, and dorsal ganglion cell culture, cellular distribution of CD9 was examined. Similar to TRPV1 and other pain-related molecules, CD9 was present in axon terminals of DRG neurons of dorsal horn layers I and II. 4) CD9 is known to bind to Gq protein and PKC in an extracellular signal-dependent manner. Interestingly, Gq and a subtype of PKC were also concentrated in dorsal horn, however, direct evidences of specific binding of CD9 with these molecules have not obtained by immunoprecipitaion method at present. The relationship between these signaling molecules and CD9 in pain pathway is still underway. In addition, we found that CD9 was expressed in DRG neuron from relatively early stage of development and the shapes and cell arrangements of DRG were abnormal in some (but not all) of CD9 knockout mice, suggesting that this molecule may be involved in the formation of sensory pathway during development as well. The manuscripts related to this study are now in preparation. Less