Keith W. Kelley

Interferon-γ and Tumor Necrosis Factor-α Mediate the Upregulation of Indoleamine 2,3-Dioxygenase and the Induction of Depressive-Like Behavior in Mice in Response to Bacillus Calmette-Guérin

Although the tryptophan-degrading enzyme, indoleamine 2,3-dioxygenase (IDO), is a pivotal mediator of inflammation-induced depression, its mechanism of regulation has not yet been investigated in this context. Here, we demonstrate an essential role for interferon (IFN)γ and tumor necrosis factor (TNF)α in the induction of IDO and depressive-like behaviors in response to chronic immune activation. Wild-type (WT) control mice and IFNγR−− mice were inoculated with an attenuated form of Mycobacterium bovis, bacille Calmette-Guérin (BCG). Infection with BCG induced an acute episode of sickness that was similar in WT and IFNγR−− mice. Increased immobility during the forced swim and tail suspension tests occurred in WT mice 7 d after BCG inoculation but was entirely absent in IFNγR−− mice. In WT mice, these indices of depressive-like behavior were associated with chronic upregulation of IFNγ, interleukin(IL)-1β, TNFα, and IDO. Proinflammatory cytokine expression was elevated in BCG-infected IFNγR−− mice as well, but upregulation of lung and brain IDO mRNA was completely abolished. This was accompanied by an attenuation of BCG-induced TNFα mRNA and the lack of an increase in plasma kynurenine/tryptophan ratio in the BCG-inoculated IFNγR−− mice compared with WT controls. Pretreatment of mice with the TNFα antagonist, etanercept, partially blunted BCG-induced IDO activation and depressive-like behavior. In accordance with these in vivo data, IFNγ and TNFα synergized to induce IDO in primary microglia. Together, these data demonstrate that IFNγ, with TNFα, is necessary for induction of IDO and depressive-like behavior in mice after BCG infection.

Induction of IDO by Bacille Calmette-Guérin Is Responsible for Development of Murine Depressive-Like Behavior

Chronic inflammation activates the tryptophan-degrading enzyme IDO, which is well known to impair T cell proliferation. We have previously established that bacille Calmette-Guérin (BCG), an attenuated form of Mycobacterium bovis, is associated with persistent activation of IDO in the brain and chronic depressive-like behavior, but a causative role has not been established. In these experiments we used both pharmacologic and genetic approaches to test the hypothesis that IDO activation is responsible for the development of chronic depression that follows BCG infection. BCG induced TNF-α, IFN-γ, and IDO mRNA steady-state transcripts in the brain as well as the enzyme 3-hydroxyanthranilic acid oxygenase (3-HAO) that lies downstream of IDO and generates the neuroactive metabolite, quinolinic acid. Behaviors characteristic of depression were apparent 1 wk after BCG infection. Pretreatment with the competitive IDO inhibitor 1-methyltryptophan fully blocked BCG-induced depressive-like behaviors. Importantly, IDO-deficient mice were completely resistant to BCG-induced depressive-like behavior but responded normally to BCG induction of proinflammatory cytokines. These results are the first to prove that the BCG-induced persistent activation of IDO is accompanied by the induction of 3-hydroxyanthranilic acid oxygenase and that IDO is required as an initial step for the subsequent development of chronic depressive-like behavior.

Inoculation of Bacillus Calmette-Guerin to mice induces an acute episode of sickness behavior followed by chronic depressive-like behavior

Although cytokine-induced sickness behavior is now well-established, the mechanisms by which chronic inflammation and depression are linked still remain elusive. Therefore this study aimed to develop a suitable model to identify the neurobiological basis of depressive-like behavior induced by chronic inflammation, independently of sickness behavior. We chose to measure the behavioral consequences of chronic inoculation of mice with Bacillus Calmette-Guerin (BCG), which has been shown to chronically activate both lung and brain indoleamine 2,3-dioxygenase (IDO), a tryptophan-catabolizing enzyme that mediates the occurrence of depressive-like behavior following acute innate immune system activation. BCG inoculation induced an acute episode of sickness (approximately 5 days) that was followed by development of delayed depressive-like behaviors lasting over several weeks. Transient body weight loss, reduction of motor activity and the febrile response to BCG were dissociated temporarily from a sustained increase in the duration of immobility in both forced swim and tail suspension tests, reduced voluntary wheel running and decreased preference for sucrose (a test of anhedonia). Moreover, we show that a distinct pattern of cytokine production and IDO activation parallels the transition from sickness to depression. Protracted depressive-like behavior, but not sickness behavior, was associated with sustained increase in plasma interferon-gamma and TNF-alpha concentrations and peripheral IDO activation. Together, these promising new data establish BCG inoculation of mice as a reliable rodent model of chronic inflammation-induced depressive-like behaviors that recapitulate many clinical observations and provide important clues about the neurobiological basis through which cytokines may have an impact on affective behaviors.

Microglial/macrophage GRK2 determines duration of peripheral IL-1β-induced hyperalgesia: Contribution of spinal cord CX3CR1, p38 and IL-1 signaling

&NA; Chronic pain associated with inflammation is a major clinical problem, but the underlying mechanisms are incompletely understood. Recently, we reported that GRK2+/− mice with a ˜50% reduction of GRK2 develop prolonged hyperalgesia following a single intraplantar injection of the pro‐inflammatory cytokine interleukin‐1&bgr; (IL‐1&bgr;). Here we show that spinal microglia/macrophage GRK2 is reduced during chronic inflammation‐induced hyperalgesia. Next, we applied CRE‐Lox technology to create mice with low GRK2 in microglia/macrophages/granulocytes (LysM‐GRK2f/+), or sensory neurons or astrocytes. Only mice deficient in microglial/macrophage/granulocyte GRK2 display prolonged IL‐1&bgr;‐induced hyperalgesia that lasts up to 8 days. Two days after intraplantar IL‐1&bgr;, increased microglial/macrophage activity occurs in the lumbar but not thoracic spinal cord of GRK2‐deficient mice. Intrathecal pre‐treatment with minocycline, an inhibitor of microglia/macrophage activation, accelerates resolution of hyperalgesia independent of genotype and prevents transition to chronic hyperalgesia in GRK2+/− mice. Ongoing hyperalgesia in GRK2+/− mice is reversed by minocycline administration at days 1 and 2 after IL‐1&bgr; injection. Similarly, IL‐1&bgr;‐induced hyperalgesia in LysM‐GRK2f/+ mice is attenuated by intrathecal administration of anti‐CX3CR1 to abrogate fractalkine signaling, the p38 inhibitor SB239063 and the IL‐1 antagonist IL‐1ra. These data establish that chronic inflammatory hyperalgesia is associated with reduced GRK2 in microglia/macrophages and that low GRK2 in these cells is sufficient to markedly prolong hyperalgesia after a single intraplantar injection of IL‐1&bgr;. Ongoing hyperalgesia is maintained by spinal microglial/macrophage activity, fractalkine signaling, p38 activation and IL‐1 signaling. We propose that chronic inflammation decreases spinal microglial/macrophage GRK2, which prevents silencing of microglia/macrophage activity and thereby contributes to prolonged hyperalgesia.

Low Nociceptor GRK2 Prolongs Prostaglandin E2 Hyperalgesia via Biased cAMP Signaling to Epac/Rap1, Protein Kinase Cε, and MEK/ERK

Hyperexcitability of peripheral nociceptive pathways is often associated with inflammation and is an important mechanism underlying inflammatory pain. Here we describe a completely novel mechanism via which nociceptor G-protein-coupled receptor kinase 2 (GRK2) contributes to regulation of inflammatory hyperalgesia. We show that nociceptor GRK2 is downregulated during inflammation. In addition, we show for the first time that prostaglandin E2 (PGE2)-induced hyperalgesia is prolonged from <6 h in wild-type (WT) mice to 3 d in mice with low GRK2 in Nav1.8+ nociceptors (SNS–GRK2 +/− mice). This prolongation of PGE2 hyperalgesia in SNS–GRK2 +/− mice does not depend on changes in the sensitivity of the prostaglandin receptors because prolonged hyperalgesia also developed in response to 8-Br-cAMP. PGE2 or cAMP-induced hyperalgesia in WT mice is PKA dependent. However, PKA activity is not required for hyperalgesia in SNS–GRK2 +/− mice. SNS–GRK2 +/− mice developed prolonged hyperalgesia in response to the Exchange proteins directly activated by cAMP (Epac) activator 8-pCPT-2′-O-Me-cAMP (8-pCPT). Coimmunoprecipitation experiments showed that GRK2 binds to Epac1. In vitro, GRK2 deficiency increased 8-pCPT-induced activation of the downstream effector of Epac, Rap1, and extracellular signal-regulated kinase (ERK). In vivo, inhibition of MEK1 or PKCε prevented prolonged PGE2, 8-Br-cAMP, and 8-pCPT hyperalgesia in SNS–GRK2 +/− mice. In conclusion, we discovered GRK2 as a novel Epac1-interacting protein. A reduction in the cellular level of GRK2 enhances activation of the Epac–Rap1 pathway. In vivo, low nociceptor GRK2 leads to prolonged inflammatory hyperalgesia via biased cAMP signaling from PKA to Epac–Rap1, ERK/PKCε pathways.

GRK2 in sensory neurons regulates epinephrine-induced signalling and duration of mechanical hyperalgesia

&NA; Epinephrine (EPI) contributes to hyperalgesia in inflammatory and stress conditions. EPI signals via adrenoceptors, which are regulated by G protein‐coupled receptor kinase 2 (GRK2). We previously reported that GRK2 is decreased in nociceptors during chronic inflammation. Herein, we investigated whether GRK2 modulates EPI‐induced mechanical and thermal hyperalgesia by using GRK2+/− mice, which express 50% of the GRK2 protein. We demonstrate for the first time that EPI‐induced mechanical as well as thermal hyperalgesia is prolonged to approximately 21 days in GRK2+/− mice, whereas it lasts only 3 to 4 days in wild‐type mice. Using cell‐ specific GRK2‐deficient mice, we further show that a low level of GRK2 in primary sensory neurons is critical for this prolongation of EPI‐induced hyperalgesia. Low GRK2 in microglia had only a small effect on EPI‐induced hyperalgesia. Low GRK2 in astrocytes did not alter EPI‐induced hyperalgesia. EPI‐induced hyperalgesia was prolonged similarly in mice with tamoxifen‐induced homozygous or heterozygous deletion of GRK2. In terms of EPI signalling pathways, the protein kinase A (PKA) inhibitor H‐89 inhibited EPI‐induced mechanical hyperalgesia in wild‐type mice, whereas H‐89 had no effect in mice with low GRK2 in sensory neurons (SNS‐GRK2+/− mice). Conversely, intraplantar injection of the protein kinase Cε PKCε inhibitor TAT‐PKCεv1‐2 inhibited hyperalgesia in sensory neuron specific (SNS)‐GRK2+/− mice and not in wild‐type mice. These results indicate that low GRK2 in primary sensory neurons switches EPI‐induced signalling from a protein kinase A‐dependent toward a PKCε‐dependent pathway that ultimately mediates prolonged EPI‐induced hyperalgesia. G protein‐coupled receptor kinase 2 (GRK2) is a crucial regulator of hyperalgesia. Low GRK2 in sensory neurons markedly prolongs epinephrine (EPI)‐induced hyperalgesia, by switching EPI signalling from protein kinase A‐dependent toward PKCε‐dependent pathways.

Ten years of Nature Reviews Neuroscience: Insights from the highly cited

To celebrate the first 10 years of Nature Reviews Neuroscience, we invited the authors of the most cited article of each year to look back on the state of their field of research at the time of publication and the impact their article has had, and to discuss the questions that might be answered in the next 10 years. This selection of highly cited articles provides interesting snapshots of the progress that has been made in diverse areas of neuroscience. They show the enormous influence of neuroimaging techniques and highlight concepts that have generated substantial interest in the past decade, such as neuroimmunology, social neuroscience and the network approach to brain function. These advancements will pave the way for further exciting discoveries that lie ahead.

Practice of traditional Chinese medicine for psycho-behavioral intervention improves quality of life in cancer patients: A systematic review and meta-analysis

Background Cancer patients suffer from diverse symptoms, including depression, anxiety, pain, and fatigue and lower quality of life (QoL) during disease progression. This study aimed to evaluate the benefits of Traditional Chinese Medicine psycho-behavioral interventions (TCM PBIs) on improving QoL by meta-analysis. Methods Electronic literature databases (PubMed, CNKI, VIP, and Wanfang) were searched for randomized, controlled trials conducted in China. The primary intervention was TCM PBIs. The main outcome was health-related QoL (HR QoL) post-treatment. We applied standard meta analytic techniques to analyze data from papers that reached acceptable criteria. Results The six TCM PBIs analyzed were acupuncture, Chinese massage, Traditional Chinese Medicine five elements musical intervention (TCM FEMI), Traditional Chinese Medicine dietary supplement (TCM DS), Qigong and Tai Chi. Although both TCM PBIs and non-TCM PBIs reduced functional impairments in cancer patients and led to pain relief, depression remission, reduced time to flatulence following surgery and sleep improvement, TCM PBIs showed more beneficial effects as assessed by reducing both fatigue and gastrointestinal distress. In particular, acupuncture relieved fatigue, reduced diarrhea and decreased time to flatulence after surgery in cancer patients, while therapeutic Chinese massage reduced time to flatulence and time to peristaltic sound. Conclusion These findings demonstrate the efficacy of TCM PBIs in improving QoL in cancer patients and establish that TCM PBIs represent beneficial adjunctive therapies for cancer patients.

G protein-coupled receptor kinase 6 acts as a critical regulator of cytokine-induced hyperalgesia by promoting phosphatidylinositol 3-kinase and inhibiting p38 signaling

The molecular mechanisms determining magnitude and duration of inflammatory pain are still unclear. We assessed the contribution of G protein-coupled receptor kinase (GRK)-6 to inflammatory hyperalgesia in mice. We showed that GRK6 is a critical regulator of severity and duration of cytokine-induced hyperalgesia. In GRK6−/− mice, a significantly lower dose (100 times lower) of intraplantar interleukin (IL)-1β was sufficient to induce hyperalgesia compared with wild-type (WT) mice. In addition, IL-1β hyperalgesia lasted much longer in GRK6−/− mice than in WT mice (8 d in GRK6−/− versus 6 h in WT mice). Tumor necrosis factor (TNF)-α-induced hyperalgesia was also enhanced and prolonged in GRK6−/− mice. In vitro, IL-1β-induced p38 phosphorylation in GRK6−/− dorsal root ganglion (DRG) neurons was increased compared with WT neurons. In contrast, IL-1β only induced activation of the phosphatidylinositol (PI) 3-kinase/Akt pathway in WT neurons, but not in GRK6−/− neurons. In vivo, p38 inhibition attenuated IL-1β- and TNF-α-induced hyperalgesia in both genotypes. Notably, however, whereas PI 3-kinase inhibition enhanced and prolonged hyperalgesia in WT mice, it did not have any effect in GRK6-deficient mice. The capacity of GRK6 to regulate pain responses was also apparent in carrageenan-induced hyperalgesia, since thermal and mechanical hypersensitivity was significantly prolonged in GRK6−/− mice. Finally, GRK6 expression was reduced in DRGs of mice with chronic neuropathic or inflammatory pain. Collectively, these findings underline the potential role of GRK6 in pathological pain. We propose the novel concept that GRK6 acts as a kinase that constrains neuronal responsiveness to IL-1β and TNF-α and cytokine-induced hyperalgesia via biased cytokine-induced p38 and PI 3-kinase/Akt activation.

Recurrent ECSIT mutation encoding V140A triggers hyperinflammation and promotes hemophagocytic syndrome in extranodal NK/T cell lymphoma

Hemophagocytic syndrome (HPS) is a fatal hyperinflammatory disease with a poorly understood mechanism that occurs most frequently in extranodal natural killer/T cell lymphoma (ENKTL). Through exome sequencing of ENKTL tumor–normal samples, we have identified a hotspot mutation (c.419T>C) in the evolutionarily conserved signaling intermediate in Toll pathway (ECSIT) gene, encoding a V140A variant of ECSIT. ECSIT-V140A activated NF-κB more potently than the wild-type protein owing to its increased affinity for the S100A8 and S100A9 heterodimer, which promotes NADPH oxidase activity. ECSIT-T419C knock-in mice showed higher peritoneal NADPH oxidase activity than mice with wild-type ECSIT in response to LPS. ECSIT-T419C-transfected ENKTL cell lines produced tumor necrosis factor (TNF)-α and interferon (IFN)-γ, which induced macrophage activation and massive cytokine secretion in cell culture and mouse xenografts. In individuals with ENKTL, ECSIT-V140A was associated with activation of NF-κB, higher HPS incidence, and poor prognosis. The immunosuppressive drug thalidomide prevented NF-κB from binding to the promoters of its target genes (including TNF and IFNG), and combination treatment with thalidomide and dexamethasone extended survival of mice engrafted with ECSIT-T419C-transfected ENKTL cells. We added thalidomide to the conventional dexamethasone-containing therapy regimen for two patients with HPS who expressed ECSIT-V140A, and we observed reversal of their HPS and disease-free survival for longer than 3 years. These findings provide mechanistic insights and a potential therapeutic strategy for ENKTL-associated HPS.