Comprehensive Gene Expression Profiling in the Prefrontal Cortex Links Immune Activation and Neutrophil Infiltration to Antinociception

Abstract

Functional neuroimaging studies have implicated the prefrontal cortex (PFCTX) in descending modulation of pain and the placebo effect. This study was performed to elucidate comprehensive PFCTX gene expression in an animal model of persistent trigeminal pain. Adult male C57BL/6J mice received facial carrageenan injection and showed sustained increase in nociceptive responses. Microarray analyses of differentially expressed genes in the PFCTX at 3 d after injection showed "immune system process" as the dominant ontology term and increased mRNA expression of S100a8, S100a9, Lcn2, Il2rg, Fcgr1, Fcgr2b, C1qb, Ptprc, Ccl12, and Cd52 were verified by RT-PCR. Upregulation of S100A8, S100A9, and lipocalin 2 (LCN2) were confirmed by Western blots, and cells in the PFCTX were double immunolabeled with MPO, indicating they were neutrophils. Analyses of blood of facial carrageenan-injected mice also showed increased mRNA expression of these markers, suggesting transmigration of activated neutrophils into the brain. Other immune-related genes, Il2rg, Fcgr2b, C1qb, Ptprc, and Ccl12 were upregulated in the PFCTX but not blood. Approximately 70% of S100A9-positive cells in the PFCTX of carrageenan-injected mice were located in capillaries adherent to endothelial cells, whereas 30% were within the brain parenchyma. Carrageenan-injected mice showed significantly reduced nociceptive responses after injection of C terminus of murine S100A9 protein in the lateral ventricles and PFCTX but not somatosensory barrel cortex. Together, these findings demonstrate activation of immunerelated genes in the PFCTX during inflammatory pain and highlight an exciting role of neutrophils in linking peripheral inflammation with immune activation of the PFCTX and antinociception.

Social stress increases expression of hemoglobin genes in mouse prefrontal cortex

“…Opposite changes in hippocampus and amygdala expression of hemoglobin alpha and beta ( Hba-a2 and Hbb ) were found in rats subjected to chronic restraint stress [ 46 ]. However, changes in expression of hemoglobin were not reported in other models of stress, such as repeated forced swimming [ 47 ], unavoidable electric shocks [ 48 , 49 ], sub-chronic restraint [ 50 ], and chronic inflammatory pain [ 51 ]. Relatively low reproducibility of results is not surprising considering recent meta-analysis of microarray experiments investigating pain-induced changes in brain transcriptome [ 14 ].…”

From the periphery to the brain: Lipocalin-2, a friend or foe?

“…A first report described its up-regulation in whole brain homogenates in response to peripheral turpentine-induced inflammation (Liu and Nilsen-Hamilton, 1995). Later descriptions demonstrated LCN2 up-regulation in the brain upon a peripheral inflammatory stimulus (with LPS) (Marques et al, 2008) and in animal models of CNS diseases such as experimental autoimmune encephalomyelitis (EAE) (Marques et al, 2012), AD (Naude et al, 2012) and in spinal cord injury (Poh et al, 2012;Rathore et al, 2011). In this context, LCN2 is likely to be engaged in identical mechanisms as those described in the periphery such as in the modulation of the innate immune response (through siderophore binding and iron homeostasis), in the balance between pro-and anti-inflammatory responses, in cellular activation and cellular migration, and, eventually, also in mechanisms still undetermined or not clearly identified (Lee et al, 2011;Lee et al, 2009).…”

Systems biology approaches to finding novel pain mediators

“…Within an injured nerve, Schwann cells de‐differentiate and increase expression of cytokines and growth factors 32. In addition, there is marked immune cell recruitment and ‘activation’ within injured nerves, DRG, dorsal horn of the spinal cord and even within the brainstem, thalamus, and cortex 15,33,34. Injured sensory neurons acquire altered connectivity to peripheral and central targets and sympathetic neurons sprout around DRG cell bodies 35.…”