MHC-I promotes apoptosis of GABAergic interneurons in the spinal dorsal horn and contributes to cancer induced bone pain

Cancer induced bone pain (CIBP) remains one of the most intractable clinical problems due to poor understanding of its underlying mechanisms. Recent studies demonstrate the decline of inhibitory interneurons, especially GABAergic interneurons in the spinal cord, can evoke generation of chronic pain. It has also been reported that neuronal MHC-I expression renders neurons vulnerable to cytotoxic CD8+ T cells and finally lead to neurons apoptosis in a variety neurological disorders. However, whether MHC-I could induce the apoptosis of GABAergic interneurons in spinal cord and contribute to the development of CIBP remains unknown. In this study, we investigated roles of MHC-I and underlying mechanisms in CIBP on a rat model. Our results showed that increased MHC-I expression on GABAergic interneurons could deplete GABAergic interneurons by inducing their apoptosis in the spinal dorsal horn of tumor-bearing rats. Pretreatment of MHC-I RNAi-lentivirus could prevent the apoptosis of GABAergic interneurons and therefore alleviated mechanical allodynia induced by tumor cells intratibial injection. Additionally, we also found that CD8+ T cells were colocalized with MHC-I and GABAergic neurons and presented a significant and persistent increase in the spinal cord of tumor-bearing rats. Taken together, these findings indicated that MHC-I could evoke CIBP by promoting apoptosis of GABAergic interneurons in the dorsal horn, and this apoptosis was closely related to local CD8+ T cells.