Consequences of receptor cross talk on inflammation and algesia

点击翻译按钮获取中文摘要

We established that neurons present in dorsal root ganglia (DRG), similar to leukocytes, express a wide variety of receptors for cytokines, chemokines, opioids, anandamide and other neuropeptides. We previously showed that prior exposure to chemokines such as MIP1-alpha results in PKC mediated desensitization of the chemotactic response to opioids by opioid receptors, and thus potentially enhances pain. This decrease in the analgesic effect of opioids was evident from the enhanced tail flick assay of rats administered MIP-alpha or RANTES prior to an analgesic opioid into the PAG of the CNS. We then extended these earlier studies by showing that prior administration of chemokines sensitized and primed the calcium flux of capsaicin or anandamide stimulated vanilloid (TRPV1) algesic receptor on DRG neurons. This response also increased pain as shown by the enhancement of paw withdrawal in response to the intrathecal administration of the chemokine prior to capsaicin in vivo. This sensitization of the vanilloid receptor was also PKC dependent. Consequently, proinflammatory chemokines can increase pain both by suppressing opioid and enhancing vanilloid receptor responses. Our current project focuses on neuroimmune interactions contributing to pain sensation in cancer patients previously funded by an INIP postdoctoral IRA financial grant from NIAID and NCI. As previously shown, chemokine receptor cross-talk suppresses analgesic opioid receptors, but enhances algesic transient receptor potential channel (TRP) receptors, thus resulting in painful inflammation. a) In collaboration with Dr. Jeffrey Cohen, NIAID we have investigated this in a cotton rat herpes virus infection model for chemotherapy induced Herpes Zoster. Herpes infection of dorsal root ganglia results in extremely painful inflammatory responses along nerve tracts. It has been reported that VZV infection produces TLR ligands and we have found that peripheral neurons present in dorsal root ganglia express TLR3, 7 and 9 which when stimulated express mRNA for many cytokines and chemokines. In addition, TLR ligand stimulation of neurons upregulate the expression of TLRs and transactivate TRPV1. Furthermore, preincubation of neurons for 16 hours with the TLR ligands, enhances the calcium flux induced by capsaicin stimulation of TRPV1. Consequently, products of the herpes virus interacting with these TLR's can either directly or indirectly, by inducing chemokines, enhance the response of TRPV1 pain receptors, providing one possible basis for herpes Zoster neuralgesia in immunosuppressed cancer patients. Furthermore, in a mouse tumor model administration of suppressive oligonucleotides that block TLR9 were found to inhibit enhanced sensitivity to heat, which is considered to be mediated by TRPV1. This provides additional evidence for the cross-talk between immune and pain sensing receptors. These studies in a pain model suggest that the peripheral pain reported by many cancer patients may be addressed by effective regulation of neuroimmune molecules.