Expression of myeloid differentiation factor 88 in neurons is not requisite for the induction of sickness behavior by interleukin-1β
© Braun et al.; licensee BioMed Central Ltd. 2012
Received: 23 April 2012
Accepted: 25 September 2012
Published: 3 October 2012
Animals respond to inflammation by suppressing normal high-energy activities, including feeding and locomotion, in favor of diverting resources to the immune response. The cytokine interleukin-1 beta (IL-1β) inhibits normal feeding and locomotor activity (LMA) via its actions in the central nervous system (CNS). Behavioral changes in response to IL-1β are mediated by myeloid differentiation factor 88 (MyD88) in non-hematopoietic cells. It is unknown whether IL-1β acts directly on neurons or requires transduction by non-neuronal cells.
The Nestin-cre mouse was crossed with MyD88lox mice to delete MyD88 from neurons and glia in the CNS (MyD88ΔCNS). These mice were compared to total body MyD88KO and wild type (WT) mice. Mice had cannulae stereotactically placed in the lateral ventricle and telemetry transponders implanted into the peritoneum. Mice were treated with either intracerebroventricular (i.c.v.) IL-1β (10 ng) or vehicle. Food intake, body weight and LMA were continuously monitored for 24 h after treatment. I.c.v. tumor necrosis factor (TNF), a MyD88-independent cytokine, was used to control for normal immune development. Peripheral inflammation was modeled using intraperitoneal lipopolysaccharide (LPS). Groups were compared using two-way ANOVA with Bonferroni post-test. Efficacy of recombination was evaluated using tdTomato reporter mice crossed with the Nestin-cre mouse. MyD88 deletion was confirmed by Western blot.
I.c.v. IL-1β treatment caused a significant reduction in feeding, body weight and LMA in WT mice. MyD88KO mice were protected from these changes in response to i.c.v. IL-1β despite having intact behavioral responses to TNF. Cre-mediated recombination was observed in neurons and astrocytes, but not microglia or endothelial cells. In contrast to MyD88KO mice, the behavioral responses of MyD88ΔCNS mice to i.c.v. IL-1β or intraperitoneal (i.p.) LPS were indistinguishable from those of WT mice.
Sickness behavior is mediated by MyD88 and is dependent on the activity of cytokines within the brain. Our results demonstrate that MyD88 is not required in neurons or astrocytes to induce this behavioral response to IL-1β or LPS. This suggests that a non-Nestin expressing cell population responds to IL-1β in the CNS and transduces the signal to neurons controlling feeding and activity.
KeywordsSickness behavior MyD88 Cytokines Inflammation Hypothalamus IL-1β Cachexia Lethargy
Systemic inflammation elicits an evolutionarily conserved behavioral response, including anorexia, lethargy, anhedonia and hyperalgesia . Collectively known as sickness behavior, this response is likely adaptive in the acute setting in that it reduces energy expenditure associated with foraging, but becomes pathological when present in a chronic state. Individuals suffering from chronic inflammatory illnesses, such as cancer, chronic renal failure, congestive heart failure and many others, exhibit decreased appetite and decreased energy to complete activities in the course of daily living . Decreased nutritional intake consequent to decreased appetite contributes to ongoing weight loss in such individuals. Both weight loss and decreased activity not only negatively impact quality of life, but also are tightly correlated with mortality [3, 4]. Despite this, there are currently no effective therapeutic interventions that alter the impact of the behavioral response to disease.
Sickness behavior is associated with increases in inflammatory cytokines, both circulating and in the central nervous system (CNS) . Administration of inflammatory cytokines recapitulates the behavioral features of sickness, whereas cytokine antagonism has some efficacy in reversing these behaviors [6, 7]. However, the mechanism by which inflammatory cytokines mediate behavioral changes remains incompletely described. Myeloid differentiation factor 88 (MyD88) is a signaling protein downstream from Toll-like receptors (TLRs) and the type I interleukin 1 receptor (IL-1RI). Sickness behavior in response to the inflammatory cytokine interleukin-1β (IL-1β) or the bacterial cell wall product LPS requires intact MyD88 signaling . A series of bone marrow transplant experiments between WT and MyD88KO mice localized this requirement for MyD88 to a non-transplantable (that is, non-hematopoeitic) cell population . Direct administration of IL-1β into the brain potently suppresses feeding and locomotor activity (LMA) indicating that cytokines act within the CNS to derive their behavioral effect . Cytokine receptors are expressed on neurons known to regulate feeding and other behavioral responses, and neuron-specific disruption of these signaling pathways alters the behavioral responses to cytokine administration [11–13]. However, others provide evidence that cerebrovascular endothelial cells and perivascular macrophages are the targets of inflammatory cytokines in mediating sickness behavior [14–16].
To explore these distinct mechanisms of cytokine action and to establish the necessity of CNS MyD88 expression, we performed intracerebroventricular (i.c.v.) injections of IL-1β in MyD88 knockout mice (MyD88KO) and mice with a targeted deletion of MyD88 in the CNS only (MyD88ΔCNS). Our work here describes the feeding and locomotor responses to CNS inflammation, and the role of neuronal and astrocytic MyD88 in mediating this response.
Male C57BL/6 J wild type and MyD88KO (Stock# 009088) mice were purchased from The Jackson Labs (Bar Harbor, ME, USA). Nestin-cre mice (Stock# 003771) and MyD88 Flox mice (Stock# 008888) were obtained from The Jackson Labs, and crossed to obtained Nes-cre+/#8722;/MyD88 Flox+/+ mice. These mice were then crossed back to the original MyD88 Flox+/+ line to obtain MyD88ΔCNS and MyD88Flox littermate controls. Nestin-cre mice were also bred to mice harboring a Flox-Stop-Flox tdTomato behind a CAG promoter knocked into the ROSA locus (The Jackson Labs, Stock# 007908) or nuclear-localized green fluorescent protein/beta-galactosidase fusion protein (GNZ) (The Jackson Labs, Stock# 008606) to examine the cellular specificity of cre-mediated recombination. All mice were genotyped using standard protocols from The Jackson Labs. All animals were maintained on a normal 12:12 hr light/dark cycle and provided ad libitum access to water and food (Purina rodent diet 5001; Purina Mills, St. Louis, MO, USA). Mice were used for experiments at between 6 and 10 weeks of age. Experiments were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and approved by the Animal Care and Use Committee of Oregon Health and Science University.
26-gauge lateral ventricle cannulas were placed (PlasticsOne, Roanoke, VA, USA) under isofluorane anesthesia, using a stereotactic alignment instrument (Kopf, Tujunga, CA, USA) at the following coordinates relative to bregma: -1.0 mm X, -0.5 mm Y and −2.25 mm Z. Ten ng mouse IL-1β or 500 ng mouse tumor necrosis factor (TNF, R&D, Minneapolis, MN, USA) injections were given in 1 μL total volume. IL-1β and TNF were dissolved in artificial cerebrospinal fluid (aCSF, 150 mM NaCl, 3 mM KCl, 1.4 mM CaCl2, 0.8 mM MgCl2, 1.0 mM NaPO4) with 0.1% endotoxin free BSA.
LPS (Sigma, St. Louis, MO, USA) was dissolved at 62.5 μg/mL in 0.9% saline/0.5% endotoxin free BSA, and injected intraperitoneally at 4 μL/g body weight (250 μg/kg).
Locomotor activity measurement
Voluntary home cage LMA was measured using implantable telemetric transponders (MiniMitter, Bend, OR, USA). Animals were anesthetized using 2% isoflurane, a small midline incision was made in the abdominal wall, and transponders were implanted adjacent to the abdominal aorta in the retroperitoneal space. Transponders were implanted during the lateral ventricle cannulation surgery. Mice were individually housed and allowed to acclimate for at least five days before temperature and net movement in x-, y- and z-axes was recorded in one minute intervals (Vital View, MiniMitter).
Overnight feeding studies
Animals were transferred to clean cages and injected with i.c.v. IL-1β (10 ng), i.c.v. TNF (500 ng) or i.p. LPS (250 μg) 1 h prior to lights off. At 2, 6, 13, 24, 37 and 48 h after the onset of the dark cycle, food was weighed and returned to the cage. Body weight was recorded at 13, 24 and 48 h.
Fast-refeed feeding studies
At lights out, food was removed from the cages and animals were fasted for 12 h. At the start of the light cycle, animals were injected i.c.v with IL-1β (10 ng) and food was returned to the cages 15 minutes later. Food intake was measured at 1, 2, 5, 8, 12 and 24 h after the return of food to the cages.
For histology experiments, mice were deeply anesthetized using a ketamine cocktail and sacrificed by transcardial perfusion fixation with 15 mL ice cold 0.01 M PBS + heparin sodium (15,000 U/L) followed by 25 mL 4% paraformadehyde (PFA) in 0.01 M PBS. Brains were post-fixed in 4% PFA overnight at 4°C and cryoprotected in 20% sucrose for 24 h at 4°C before being stored at −80°C until used for immunohistochemistry (IHC). Dual-immunofluorescence histochemistry was performed as described below. Free-floating sections were cut at 30 μm from perfused brains using a sliding microtome (Leica SM2000R, Leica Microsystems, Bannockburn, IL, USA). Hypothalamic sections were collected from the division of the optic chiasm (bregma −1.0 mm) caudally through the mammillary bodies (bregma −3.0 mm). The sections were incubated for 1 h at room temperature in blocking reagent (5% normal donkey serum in 0.01 M PBS and 0.1% Triton X-100). After the initial blocking step, the sections were incubated in mouse anti-NeuN (1:1,000, Millipore, Billerica, MA, USA), rabbit anti-GFAP (1:500, DAKO, Carpinteria, CA, USA), rabbit anti-IbaI (1:500, DAKO), rat anti-CD31 (1:100, BD Pharmingen, Sparks, MD, USA) in blocking reagent for 72 h at 4°C, followed by incubation in donkey anti-rabbit Alexa 488 (1:500), donkey anti-mouse Alexa 488 or 647 (1:500), goat anti-rat Alexa 488 or 633 (1:500, Invitrogen) for 2 h at room temperature. Between each stage, the sections were washed thoroughly with 0.01 M PBS. Incubating the sections in the absence of primary antisera was used to ensure specificity of the secondary antibodies. Sections were mounted onto gelatin-coated slides, coverslipped using Vectashield mounting media (Vector Laboratories, Burlingame, CA, USA), and viewed on a Nikon A1 inverted laser-scanning confocal microscope (Nikon Instruments, Melville, NY, USA). Sections from Nestin-cre x GNZ animals were cut at 75 μm on a vibratome (Leica Microsystems, Buffalo Grove, IL, USA). Sections were incubated for 30 minutes in 98°C pH 6 sodium citrate buffer, then blocked as above. Sections were then incubated overnight at 4°C in 1:500 chicken anti-GFP antibody (Aves, Tigard, OR, USA). Sections were then washed as above, and incubated for 1 h in goat anti-chicken Alexa 568 and 647. Images were obtained as above, and both red and far red channels superimposed to generate higher anti-GFP signal.
Embryonic Day 14.5 (E14.5) timed pregnant female Nestin-cre/tdTomato mice were sacrificed by cervical dislocation and embryos were collected in cold complete HBSS. Heads were removed and cortices and hypothalami dissected and collected in cold complete HBSS. Tails were collected to confirm genotyping. Cortical and hypothalamic neurons were dissociated and were cultured for five days on Poly-D-Lysine-Laminin-coated glass coverslips in serum-free Gibco Neurobasal Medium containing Invitrogen penicillin-streptomycin and Invitrogen B-27 Supplement. Neurons were fixed in 4% paraformaldehyde in 1X PBS for 20 minutes at room temperature, then blocked and immunostained in a 1% BSA, 0.1% cold fish skin gelatin, 0.5% Triton-X 100, 10 mM TBS solution (blocking buffer). Neurons were immunostained overnight for MAP2 (1:1,000, Aves), Tau (1:10,000, Chemicon, Billerica, MA), NeuN (1:1,000, Chemicon) and βIII Tubulin (1:1,000, Chemicon) to confirm polarity and neuronal identity, respectively. Primary antibodies were applied overnight at 4°C and were washed off the next day 3x with 1XPBS. Hoechst and Alexa-Fluor secondary antibodies were used at 1:1,000 for one hour at room temperature in blocking buffer. Coverslips were mounted on slides and imaged on a Nikon A1 inverted laser-scanning confocal microscope. Neurons were scored for the presence of TdTomato using ImageJ software is open source free software from the National Institutes of Health. It is available at http://rsbweb.nih.gov/ij/download.html to determine efficiency of recombination.
Muscles were homogenized in cell lysis buffer (Cell Signaling, Danvers, MA, USA): 20 mM Tris pH 7.5, 150 mM NaCl, 1 mM EDTA, 1 mM EGTA 1% Triton X, 2.5 mM sodium pyrophosphate, 1 mM beta-glycerophosphate, 1 mM sodium orthovanadate, 1 ug/mL leupeptin, and supplemented with Complete protease inhibitors (Roche, Indianapolis, IN, USA), 1 mM PMSF (Sigma), and 5 μL/mL phosphatase inibitor cocktail II (Sigma). Samples were homogenized for 30 s using a Polytron homogenizer (Kinematica, Bohemia, NY, USA), then were sonicated 2 x 10s. Samples were then centrifuged at 13,000 RPM for 10 minutes at 4°C. For Western blots, 100 ug of total protein per lane was run on Criterion 4 to 15% gradient polyacrylamide gels (Biorad, Hercules, CA, USA), and transferred to Immobilon PVDF membranes (Millipore. Proteins were detected using a Lumi-Imager (Roche) and SuperSignal West Pico Chemiluminescent Substrate (Thermo, Rockford, IL, USA). The following antibodies were used: rabbit anti-MyD88 (Cell Signaling) and an anti-rabbit HRP conjugate (Promega, Madison, WI, USA).
To validate that MyD88KO mice are capable of displaying sickness behavior in response to a MyD88-independent inflammatory stimulus, we performed i.c.v. injections of the MyD88 independent cytokine TNF (500 ng) in MyD88KO mice. As TNF is a far less potent inducer of sickness behavior than IL-1β, and the purpose of this experiment was not to model physiologic inflammation, but to rule out developmental limitations, a relatively high dose of the cytokine was used. Anorexia, weight loss and decreased LMA were all present in MyD88KO mice treated with TNF during the first six hours after treatment (Figure 1e-h). During the second half of the dark phase, TNF-treated MyD88KO mice consumed more food than veh-treated controls such that no differences in cumulative food intake were apparent 13 h after treatment. Thus, MyD88KO mice display normal sickness behavior at early time points in response to an inflammatory challenge that does not require MyD88. The limited duration of this effect demonstrates that MyD88 is important for the propagation of sickness behavior beyond the acute period irrespective of the inciting inflammatory stimulus.
Nes-cre mice exhibit cre-mediated recombination in neurons
To further confirm recombination in neurons, we isolated and cultured hypothalamic and cortical neurons from Nestin-cre/tdTomato reporter mice and costained them with antibodies against neuronal markers NeuN, Map2, Tau and β3 Tubulin. We did not observe any cultured cells with neuronal phenotype that did not express tdTomato fluorescence (Figures 2c, d). As a control, neurons from tdTomato reporter mice lacking cre-7expression were harvested, stained and visualized using identical microscope settings. We observed no red fluorescence in any control mice, verifying the specificity of the Nestin-cre recombination (Figure 2e). Because tdTomato is only expressed in the cytoplasm, we wanted to verify that the diffuse tdTomato fluorescence accurately represented pan-neuronal recombination. To do so we crossed the Nes-cre mouse with the GNZ reporter mouse, in which nuclear-localized GFP is conditionally expressed in cells expressing cre-recombinase. We observed densely labeled nuclei in all brain regions, including the hypothalamus, with absence of staining in the cytoplasm, consistent with pan-neuronal recombination (Figure 2f).
Nes-cre mice exhibit cre-mediated recombination in astrocytes, but not microglia or cerebrovascular endothelial cells
Brain MyD88 expression is significantly reduced in MyD88ΔCNS mice
Deletion of MyD88 from neurons and astrocytes does not alter sickness behavior in response to IL-1Î² or LPS
MyD88 is not required in neurons or astrocytes for LPS-induced sickness behavior
Sickness behavior is an integral component of the adaptive metabolic response to infection. In chronically ill patients this response becomes maladaptive, significantly worsening quality of life and potentially contributing to mortality. Despite numerous mechanistic inroads into the pathogenesis of sickness behavior, the precise cell type upon which IL-1β acts to produce sickness behavior has remained elusive. In this work, we demonstrate a requirement for MyD88 in transducing IL-1β within the brain into sickness behavior. Although MyD88 expression in neurons has been suggested to play a critical role in the behavioral response to inflammation, we find that IL-1β induced anorexia and lethargy is not contingent upon MyD88-expression in both neurons and astrocytes.
The receptor for IL-1β is expressed in multiple locations within the CNS, many of which are known to regulate food intake. In particular, IL-1R1) is expressed in the arcuate nucleus of the hypothalamus (ARC) on anorectic proopiomelanocortin (POMC) and orexigenic Agouti Related Peptide (AgRP) neurons. IL-1β increases the firing of POMC neurons, and increases the release of alpha-melanocyte stimulating hormone (α-MSH), the natural ligand of the type-4 melanocortin receptor (MC4R), from hypothalamic explants . IL-1β simultaneously decreases the release of AgRP, the endogenous antagonist of the MC4R . Consistent with this, mice lacking the MC4R resist IL-1β induced anorexia, demonstrating that alterations in melanocortin signaling underlie changes in feeding in response to IL-1β .
Despite clear recombination in the ARC in the tdTomato reporter mouse, MyD88ΔCNS mice respond normally to IL-1β. There are several possible explanations to resolve these apparently conflicting results. Cre mediated recombination of the MyD88 allele may be incomplete, with a sufficient number of neurons remaining responsive to IL-1β in the MyD88ΔCNS mouse to engender a normal anorectic response. If the results of our tissue and cell culture IHC are representative, less than 1% of neurons are sufficient to mediate these behaviors. Alternatively, it is possible that IL-1β produces anorexia in an IL-1RI mediated, MyD88-independent manner. There is some precedence for this, as it has been proposed that IL-1β signals via a PI3K dependent mechanism in neurons, similar to the mechanism by which leptin mediates electrophysiologic changes in neurons . A third possibility is that cytokine signaling has an obligate amplification step in a cell type that does not undergo recombination in the MyD88ΔCNS mouse, leading to the paracrine release of a second messenger that then conveys the anorectic signal to neurons.
The identity of this second messenger remains in question. Some propose that prostaglandins convey the inflammatory signal to neurons [15, 16, 24]. Whereas this is clearly the case for fever , cyclooxygenase inhibition fails to alter the changes in volitional activity observed after i.p. LPS injection , and decreases, but does not block, the anorectic response to peripheral and central inflammatory challenges [11, 26, 27]. Therefore, while prostaglandins mediate some of the behavioral response to systemic inflammation, other second messengers must also relay inflammatory signals to the neurons regulating behavior.
IL-1β itself may be the ultimate mediator of inflammation-induced anorexia. Previous work by Konsman et al. demonstrates that i.c.v. administration of IL-1β to rats diffuses throughout the parenchyma, eliciting neuronal activation . These cellular responses may be secondary to direct activation of the IL-1RI on neurons by IL-1β that has diffused from the ventricles. It is also possible that IL-1β, at the doses given in the present study, does not reach sufficient concentration after i.c.v. injection to engage the IL-1RI on feeding center neurons, yet is amplified locally by a non-neuronal cell. There is some experimental evidence to support this mechanism. First, i.c.v. IL-1β exhibits preferential perivascular diffusion, suggesting a role for perivascular or endothelial amplification in its acute effects . Second, IL-1β mRNA increases specifically in the parenchyma of the ARC following i.c.v. IL-1β or i.p. LPS administration . When IL-1 receptor antagonist (IL-1Ra) is administered at a high dose during peripheral endotoxemia, anorexia is prevented, demonstrating that endogenous brain IL-1 signaling is integral to the anorectic response . Endogenous IL-1 signaling also plays a role in mediating protein catabolism, as i.c.v. infusion of IL-1Ra attenuates the loss of muscle mass in experimental sepsis models . However, in order for this mechanism to be consistent with the presented data, the induction of hypothalamic IL-1β would have to be dependent on MyD88, yet its ultimate action on neurons is independent from MyD88. As evidence exists from other cell types that cytokine production is dependent on MyD88 , and IL-1β signaling on neurons is MyD88 independent , this remains a plausible explanation for the data presented here.
Logical targets for IL-1β signaling in the context of these findings are cerebrovascular endothelial cells. Endothelial knockdown of the IL-1RI blocks the suppression of home cage LMA after i.c.v. IL-1β injection and prevents the activation of neurons in the paraventricular nucleus (PVN) of the hypothalamus, which is associated with hypothalamic-pituitary-adrenal, sympathetic nervous system and anorectic responses to inflammation . Furthermore, brain endothelial specific knockout of transforming growth factor β-activated kinase attenuates the depression in LMA seen after IL-1β administration . Perivascular macrophages have also been implicated as key intermediaries in the central response to inflammation. Selective depletion of perivascular macrophages decreases the activation PVN neurons in response to peripheral IL-1β but does not alter the depression of LMA . Neither endothelium nor microglia show cre-mediated recombination in the Nestin-cre mice. Therefore, endothelium and perivascular macrophages likely represent a component of the cell population in which MyD88 is required for sickness behavior.
In summary, our results demonstrate that MyD88 is not required in neurons or astrocytes to induce the behavioral response to i.c.v. IL-1β. This suggests that a non-nestin expressing cell population in the CNS responds to IL-1β and transduces the signal to neurons controlling feeding and activity. We posit that cerebrovascular cells or perivascular macrophages/microglia are the most likely targets for IL-1β signaling in the brain, implying that systemic therapy addressing anorexia and fatigue need not penetrate the blood brain barrier.
Alpha-melanocyte stimulating hormone
Artificial cerebrospinal fluid
Arcuate nucleus of the hypothalamus
Bovine serum albumin
Cluster of differentiation 31
Central nervous system
Glial fibrillary acidic protein
Ionized calcium binding adaptor molecule 1
IL-1 receptor antagonist
Interleukin-1 receptor I
Microtubule associated protein-2
Type-4 melanocortin receptor
Myeloid differentiation factor 88
- MyD88ΔCNS :
CNS-specific MyD88 knockout mouse
Myeloid differentiation factor 88 knockout mouse
Neuronal nuclear antigen
Paraventricular nucleus of the hypothalamus
Tumor necrosis factor
Funding was provided by NIH DK 70333 (DLM), NIH DK 084646 (TPB), DK 084711 (AJG), Canadian Institutes of Health Research 200948 (DLM), and the Portland Chapter of Achievement Rewards for College Scientists (TPB and AJG).
- Dantzer R, Bluthé RM, Layé S, Bret-Dibat JL, Parnet P, Kelley KW: Cytokines and sickness behavior. Ann N Y Acad Sci 1998, 840:586–590.View ArticlePubMedGoogle Scholar
- Morley JE, Thomas DR, Wilson M-MG: Cachexia: pathophysiology and clinical relevance. Am J Clin Nutr 2006, 83:735–743.PubMedGoogle Scholar
- Ross PJ, Ashley S, Norton A, Priest K, Waters JS, Eisen T, Smith IE, O’Brien ME: Do patients with weight loss have a worse outcome when undergoing chemotherapy for lung cancers? Br J Cancer 2004, 90:1905–1911.View ArticlePubMedPubMed CentralGoogle Scholar
- Zhou X, Wang JL, Lu J, Song Y, Kwak KS, Jiao Q, Rosenfeld R, Chen Q, Boone T, Simonet WS, Lacey DL, Goldberg AL, Han HQ: Reversal of cancer cachexia and muscle wasting by ActRIIB antagonism leads to prolonged survival. Cell 2010, 142:531–543.View ArticlePubMedGoogle Scholar
- Lampa J, Westman M, Kadetoff D, Agréus AN, Le Maître E, Gillis-Haegerstrand C, Andersson M, Khademi M, Corr M, Christianson CA, Delaney A, Yaksh TL, Kosek E, Svensson CI: Peripheral inflammatory disease associated with centrally activated IL-1 system in humans and mice. Proc Natl Acad Sci U S A 2012, 109:12728–12733.View ArticlePubMedPubMed CentralGoogle Scholar
- Plata-Salamán CR, Sonti G, Borkoski JP, Wilson CD, French-Mullen JM: Anorexia induced by chronic central administration of cytokines at estimated pathophysiological concentrations. Physiol Behav 1996, 60:867–875.View ArticlePubMedGoogle Scholar
- Layé S, Gheusi G, Cremona S, Combe C, Kelley K, Dantzer R, Parnet P: Endogenous brain IL-1 mediates LPS-induced anorexia and hypothalamic cytokine expression. Am J Physiol Regul Integr Comp Physiol 2000, 279:R93-R98.PubMedGoogle Scholar
- Ogimoto K, Harris MK Jr, Wisse BE: MyD88 is a key mediator of anorexia, but not weight loss, induced by lipopolysaccharide and interleukin-1 beta. Endocrinology 2006, 147:4445–4453.View ArticlePubMedGoogle Scholar
- Wisse BE, Ogimoto K, Tang J, Harris MK Jr, Raines EW, Schwartz MW: Evidence that lipopolysaccharide-induced anorexia depends upon central, rather than peripheral, inflammatory signals. Endocrinology 2007, 148:5230–5237.View ArticlePubMedGoogle Scholar
- Grossberg AJ, Zhu X, Leinninger GM, Levasseur PR, Braun TP, Myers MG, Marks DL: Inflammation-induced lethargy is mediated by suppression of orexin neuron activity. J Neurosci 2011, 31:11376–11386.View ArticlePubMedPubMed CentralGoogle Scholar
- Grossberg AJ, Scarlett JM, Zhu X, Bowe DD, Batra AK, Braun TP, Marks DL: Arcuate nucleus proopiomelanocortin neurons mediate the acute anorectic actions of leukemia inhibitory factor via gp130. Endocrinology 2010, 151:606–616.View ArticlePubMedGoogle Scholar
- Scarlett JM, Jobst EE, Enriori PJ, Bowe DD, Batra AK, Grant WF, Cowley MA, Marks DL: Regulation of central melanocortin signaling by interleukin-1 beta. Endocrinology 2007, 148:4217–4225.View ArticlePubMedGoogle Scholar
- Scarlett JM, Zhu X, Enriori PJ, Bowe DD, Batra AK, Levasseur PR, Grant WF, Meguid MM, Cowley MA, Marks DL: Regulation of agouti-related protein messenger ribonucleic acid transcription and peptide secretion by acute and chronic inflammation. Endocrinology 2008, 149:4837–4845.View ArticlePubMedPubMed CentralGoogle Scholar
- Serrats J, Schiltz JC, García-Bueno B, van Rooijen N, Reyes TM, Sawchenko PE: Dual roles for perivascular macrophages in immune-to-brain signaling. Neuron 2010, 65:94–106.View ArticlePubMedPubMed CentralGoogle Scholar
- Ching S, Zhang H, Belevych N, He L, Lai W, Pu X-a, Jaeger LB, Chen Q, Quan N: Endothelial-specific knockdown of interleukin-1 (IL-1) type 1 receptor differentially alters CNS responses to IL-1 depending on its route of administration. J Neurosci 2007, 27:10476–10486.View ArticlePubMedGoogle Scholar
- Ridder DA, Lang M-F, Salinin S, Röderer J-P, Struss M, Maser-Gluth C, Schwaninger M: TAK1 in brain endothelial cells mediates fever and lethargy. J Exp Med 2011, 208:2615–2623.View ArticlePubMedPubMed CentralGoogle Scholar
- Davis CN, Mann E, Behrens MM, Gaidarova S, Rebek M, Rebek J, Bartfai T: MyD88-dependent and -independent signaling by IL-1 in neurons probed by bifunctional Toll/IL-1 receptor domain/BB-loop mimetics. Proc Natl Acad Sci USA 2006, 103:2953–2958.View ArticlePubMedPubMed CentralGoogle Scholar
- Kleinridders A, Schenten D, Könner AC, Belgardt BF, Mauer J, Okamura T, Wunderlich FT, Medzhitov R, Brüning JC: MyD88 signaling in the CNS is required for development of fatty acid-induced leptin resistance and diet-induced obesity. Cell Metab 2009, 10:249–259.View ArticlePubMedPubMed CentralGoogle Scholar
- Leinninger GM, Jo Y-H, Leshan RL, Louis GW, Yang H, Barrera JG, Wilson H, Opland DM, Faouzi MA, Gong Y, Jones JC, Rhodes CJ, Chua S Jr, Diano S, Horvath TL, Seeley RJ, Becker JB, Münzberg H, Myers MG Jr: Leptin acts via leptin receptor-expressing lateral hypothalamic neurons to modulate the mesolimbic dopamine system and suppress feeding. Cell Metab 2009, 10:89–98.View ArticlePubMedPubMed CentralGoogle Scholar
- Kawai T, Adachi O, Ogawa T, Takeda K, Akira S: Unresponsiveness of MyD88-deficient mice to endotoxin. Immunity 1999, 11:115–122.View ArticlePubMedGoogle Scholar
- Lau LT, Yu AC: Astrocytes produce and release interleukin-1, interleukin-6, tumor necrosis factor alpha and interferon-gamma following traumatic and metabolic injury. J Neurotrauma 2001, 18:351–359.View ArticlePubMedGoogle Scholar
- Breder CD, Dinarello CA, Saper CB: Interleukin-1 immunoreactive innervation of the human hypothalamus. Science 1988, 240:321–324.View ArticlePubMedGoogle Scholar
- Marks DL, Ling N, Cone RD: Role of the central melanocortin system in cachexia. Cancer Res 2001, 61:1432–1438.PubMedGoogle Scholar
- Ericsson A, Arias C, Sawchenko PE: Evidence for an intramedullary prostaglandin-dependent mechanism in the activation of stress-related neuroendocrine circuitry by intravenous interleukin-1. J Neurosci 1997, 17:7166–7179.PubMedGoogle Scholar
- Lazarus M, Yoshida K, Coppari R, Bass CE, Mochizuki T, Lowell BB, Saper CB: EP3 prostaglandin receptors in the median preoptic nucleus are critical for fever responses. Nat Neuroscie 2007, 10:1131–1133.View ArticleGoogle Scholar
- Shimomura Y, Inukai T, Kuwabara S, Shimizu H, Takahashi M, Sato N, Uehara Y, Tanaka Y, Kobayashi I: Both cyclooxygenase and lipoxygenase inhibitor partially restore the anorexia by interleukin-1 beta. Life Sci 1992, 51:1419–1426.View ArticlePubMedGoogle Scholar
- Johnson PM, Vogt SK, Burney MW, Muglia LJ: COX-2 inhibition attenuates anorexia during systemic inflammation without impairing cytokine production. Am JPhysiol Endocrinol Metab 2002, 282:E650-E656.View ArticleGoogle Scholar
- Konsman JP, Tridon V, Dantzer R: Diffusion and action of intracerebroventricularly injected interleukin-1 in the CNS. Neuroscience 2000, 101:957–967.View ArticlePubMedGoogle Scholar
- Braun TP, Zhu X, Szumowski M, Scott GD, Grossberg AJ, Levasseur PR, Graham K, Khan S, Damaraju S, Colmers WF, Baracos VE, Marks DL: Central nervous system inflammation induces muscle atrophy via activation of the hypothalamic-pituitary-adrenal axis. J Exp Med 2011, 208:2449–2463.View ArticlePubMedPubMed CentralGoogle Scholar
- Lloyd CE, Palopoli M, Vary TC: Effect of central administration of interleukin-1 receptor antagonist on protein synthesis in skeletal muscle, kidney, and liver during sepsis. Metabolism 2003, 52:1218–1225.View ArticlePubMedGoogle Scholar
- Adachi O, Kawai T, Takeda K, Matsumoto M, Tsutsui H, Sakagami M, Nakanishi K, Akira S: Targeted disruption of the MyD88 gene results in loss of IL-1-and IL-18-mediated function. Immunity 1998, 9:143–150.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.