Spinal microglia contribute to cancer-induced pain through system xC_-mediated glutamate release

Authors
T Miladinovic, G Singh

Lab
Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada

Journal
Pain Reports

Abstract
Introduction:ÊMicroglial cells, the resident macrophages of the central nervous system, are a key contributor to the generation and maintenance of cancer-induced pain (CIP). In healthy organisms, activated microglia promote recovery through the release of trophic and anti-inflammatory factors to clear toxins and pathogens and support neuronal survival. Chronically activated microglia, however, release toxic substances, including excess glutamate, causing cytotoxicity. Accordingly, rising attention is given to microglia for their role in abnormal physiology and in mediating neurotoxicity.
Objectives:ÊTo examine the nociceptive relationship between peripherally-released glutamate and microglial xCT.
Methods:ÊA validated murine model of 4T1 carcinoma cellÐinduced nociception was used to assess the effect of peripheral tumour on spinal microglial activation and xCT expression. Coculture systems were then used to investigate the direct effect of glutamate released by wildtype and xCT knockdown MDA-MB-231 carcinoma cells on microglial activation, functional system xC_ activity, and protein levels of interferon regulatory factor 8 (IRF8), a transcription factor implicated in microglia-mediated nociception.
Results:ÊBlockade of system xC_ with sulfasalazine (SSZ) in vivo attenuated nociception in a 4T1 murine model of CIP and attenuates tumour-induced microglial activation in the dorsal horn of the spinal cord. Furthermore, knockdown of xCT in MDA-MB-231 cells mitigated tumour cellÐinduced microglial activation and functional system xC_ activity in vitro.
Conclusions:ÊThese data collectively demonstrate that the system xCT antiporter is functionally implicated in CIP and may be particularly relevant to pain progression through microglia. Upregulated xCT in chronically activated spinal microglia may be one pathway to central glutamate cytotoxicity. Microglial xCT may therefore be a valuable target for mitigating CIP.

BIOSEB Instruments Used:
Dynamic Weight Bearing 2.0 (BIO-DWB-DUAL)