Interleukin-1 receptor antagonist exerts agonist activity in the hippocampus independent of the interleukin-1 type I receptor

Acrylamide inhibits long-term potentiation and learning involving microglia and pro-inflammatory signaling

Acrylamide is a chemical used in various industries and a product following high-temperature cooking of vegetables containing asparagine. Environmental or dietary exposure to acrylamide could impair cognitive function because of its neurotoxicity. Using rat hippocampal slices, we tested whether acrylamide alters induction of long-term potentiation (LTP), a cellular model of learning and memory. We hypothesized that acrylamide impairs cognitive function via activation of pro-inflammatory cytokines because robust upregulation of NLRP3 inflammasome has been reported. Although acrylamide up to 3 mM did not alter basal synaptic transmission, incubation with 10 μM or acute administration of 100 μM acrylamide inhibited induction of LTP. Inhibitors of toll-like receptor 4 (TLR4), and minocycline, an inhibitor of microglial activation, overcame the effects of acrylamide on LTP induction. Furthermore, we observed that acrylamide failed to inhibit LTP after administration of MCC950, an inhibitor of NLRP3, or in the presence of Interleukin-1 receptor antagonist (IL-1Ra). We also found that in vivo acrylamide injection transiently impaired body weight gain and impaired one-trial inhibitory avoidance learning. This learning deficit was overcome by MCC950. These results indicate that cognitive impairment by acrylamide is mediated by mechanisms involving microglia and release of cytokines via NLRP3 activation.

Osteoblastic Swedish mutant APP expedites brain deficits by inducing endoplasmic reticulum stress-driven senescence

Patients with Alzheimer’s disease (AD) often have osteoporosis or osteopenia. However, their direct link and relationship remain largely unclear. Previous studies have detected osteoporotic deficits in young adult Tg2576 and TgAPP_swe^OCN mice, which express APP_swe (Swedish mutant) ubiquitously and selectively in osteoblast (OB)-lineage cells. This raises the question, whether osteoblastic APP_swe contributes to AD development. Here, we provide evidence that TgAPP_swe^OCN mice also exhibit AD-relevant brain pathologies and behavior phenotypes. Some brain pathologies include age-dependent and regional-selective increases in glial activation and pro-inflammatory cytokines, which are accompanied by behavioral phenotypes such as anxiety, depression, and altered learning and memory. Further cellular studies suggest that APP_swe, but not APP_wt or APP_lon (London mutant), in OB-lineage cells induces endoplasmic reticulum-stress driven senescence, driving systemic and cortex inflammation as well as behavioral changes in 6-month-old TgAPP_swe^OCN mice. These results therefore reveal an unrecognized function of osteoblastic APP_swe to brain axis in AD development.

Jin-Xiu Pan et al. report that an osteoblast-specific expression of Swedish mutant amyloid precursor protein (APPswe) induces ER stress-driven senescence, leading to systemic inflammation and inflammation in the cortex that drives behavioral changes. The results demonstrate a previously unrecognized function of osteoblastic APPswe to brain axis in AD development.

Modulation of Neural Networks by Interleukin-1

Interleukin-1 (IL-1) is an inflammatory cytokine that has been shown to modulate neuronal signaling in homeostasis and diseases. In homeostasis, IL-1 regulates sleep and memory formation, whereas in diseases, IL-1 impairs memory and alters affect. Interestingly, IL-1 can cause long-lasting changes in behavior, suggesting IL-1 can alter neuroplasticity. The neuroplastic effects of IL-1 are mediated via its cognate receptor, Interleukin-1 Type 1 Receptor (IL-1R1), and are dependent on the distribution and cell type(s) of IL-1R1 expression. Recent reports found that IL-1R1 expression is restricted to discrete subpopulations of neurons, astrocytes, and endothelial cells and suggest IL-1 can influence neural circuits directly through neuronal IL-1R1 or indirectly via non-neuronal IL-1R1. In this review, we analyzed multiple mechanisms by which IL-1/IL-1R1 signaling might impact neuroplasticity based upon the most up-to-date literature and provided potential explanations to clarify discrepant and confusing findings reported in the past.

Neuroimmune Mechanisms as Novel Treatment Targets for Substance Use Disorders and Associated Comorbidities

Recent studies examining the neurobiology of substance abuse have revealed a significant role of neuroimmune signaling as a mechanism through which drugs of abuse induce aberrant changes in synaptic plasticity and contribute to substance abuse-related behaviors. Immune signaling within the brain and the periphery critically regulates homeostasis of the nervous system. Perturbations in immune signaling can induce neuroinflammation or immunosuppression, which dysregulate nervous system function including neural processes associated with substance use disorders (SUDs). In this review, we discuss the literature that demonstrates a role of neuroimmune signaling in regulating learning, memory, and synaptic plasticity, emphasizing specific cytokine signaling within the central nervous system. We then highlight recent preclinical studies, within the last 5 years when possible, that have identified immune mechanisms within the brain and the periphery associated with addiction-related behaviors. Findings thus far underscore the need for future investigations into the clinical potential of immunopharmacology as a novel approach toward treating SUDs. Considering the high prevalence rate of comorbidities among those with SUDs, we also discuss neuroimmune mechanisms of common comorbidities associated with SUDs and highlight potentially novel treatment targets for these comorbid conditions. We argue that immunopharmacology represents a novel frontier in the development of new pharmacotherapies that promote long-term abstinence from drug use and minimize the detrimental impact of SUD comorbidities on patient health and treatment outcomes.

Neuroinflammatory inhibition of synaptic long-term potentiation requires immunometabolic reprogramming of microglia

Immunometabolism refers to the rearrangement of metabolic pathways in response to immune stimulation, and the ability of these metabolic pathways themselves to control immune functions. Many aspects of immunometabolism have been revealed through studies of peripheral immune cells. However, immunometabolic reprogramming of microglia, the resident immune cell of the central nervous system, and the consequential outcome on neuronal activity have remained difficult to unravel. Microglia are highly sensitive to subtle changes in their environment, limiting the techniques available to study their metabolic and inflammatory profiles. Here, using fluorescence lifetime imaging of endogenous NAD(P)H, we measure the metabolic activity of individual microglia within acute hippocampal slices. We observed an LPS-induced increase in aerobic glycolysis, which was blocked by the addition of 5 mM 2-deoxyglucose (2DG). This LPS-induced glycolysis in microglia was necessary for the stabilization of hypoxia inducible factor-1α (HIF-1α) and production of the proinflammatory cytokine, interleukin-1β (IL-1β). Upon release, IL-1β acted via the neuronal interleukin-1 receptor to inhibit the formation of synaptic long-term potentiation (LTP) following high frequency stimulation. Remarkably, the addition of 2DG to blunt the microglial glycolytic increase also inhibited HIF-1α accumulation and IL-1β production, and therefore rescued LTP in LPS-stimulated slices. Overall, these data reveal the importance of metabolic reprogramming in regulating microglial immune functions, with appreciable outcomes on cytokine release and neuronal activity.

IL-1 receptor blockade skews inflammation towards Th2 in a mouse model of systemic sclerosis

The interleukin (IL)-1 family of cytokines is strongly associated with systemic sclerosis (SSc) and pulmonary involvement, but the molecular mechanisms are poorly understood. The aim of this study was to assess the role of IL-1α and IL-1β in pulmonary vascular and interstitial remodelling in a mouse model of SSc.IL-1α and IL-1β were localised in lungs of SSc patients and in the fos-related antigen-2 (Fra-2) transgenic (TG) mouse model of SSc. Lung function, haemodynamic parameters and pulmonary inflammation were measured in Fra-2 TG mice with or without 8 weeks of treatment with the IL-1 receptor antagonist anakinra (25 mg·kg-1·day-1). Direct effects of IL-1 on pulmonary arterial smooth muscle cells (PASMCs) and parenchymal fibroblasts were investigated in vitroFra-2 TG mice exhibited increased collagen deposition in the lung, restrictive lung function and enhanced muscularisation of the vasculature with concomitant pulmonary hypertension reminiscent of the changes in SSc patients. Immunoreactivity of IL-1α and IL-1β was increased in Fra-2 TG mice and in patients with SSc. IL-1 stimulation reduced collagen expression in PASMCs and parenchymal fibroblasts via distinct signalling pathways. Blocking IL-1 signalling in Fra-2 TG worsened pulmonary fibrosis and restriction, enhanced T-helper cell type 2 (Th2) inflammation, and increased the number of pro-fibrotic, alternatively activated macrophages.Our data suggest that blocking IL-1 signalling as currently investigated in several clinical studies might aggravate pulmonary fibrosis in specific patient subsets due to Th2 skewing of immune responses and formation of alternatively activated pro-fibrogenic macrophages.

No requirement of interlukine-1 for long-term potentiation in the anterior cingulate cortex of adult mice

Background

The enhanced expression of cytokines in the pathological states suggests that they have important roles in the initiation or maintenance of disease states.

Findings: To determine the involvement of cytokines in chronic neuropathic pain, the expression of cytokines in the anterior cingulate cortex neurons in the ligation of the common peroneal nerve mice was investigated. We utilized a cytokine enzyme-linked immunosorbent assay plate array to detect 23 cytokines in total eight mice including a female, and no significant differences were found in those cytokines between the common peroneal nerve model and sham surgery mice. Quantification of TNF-α at protein level revealed the unvaried expression in the anterior cingulate cortex in both neuropathic pain and visceral pain, but enhanced expression in the insular cortex in the visceral pain. Furthermore, we found that the IL-Ira, a kind of IL-1 receptor antagonist, had no effect on the theta burst stimulation-induced long-term potentiation in the anterior cingulate cortex.

Conclusions

Cytokines are not involved in chronic neuropathic pain induced by nerve injury in the anterior cingulate cortex. Our findings suggested that cytokines may not be a viable drug target to treat chronic neuropathic pain in the anterior cingulate cortex.

The family of the interleukin-1 receptors

The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.

Dynamic cross-talk between microglia and peripheral monocytes underlies stress-induced neuroinflammation and behavioral consequences

Psychological stress promotes the development and recurrence of anxiety and depressive behavioral symptoms. Basic and clinical research indicates that stress exposure can influence the neurobiology of mental health disorders through dysregulation of neuroimmune systems. Consistent with this idea several studies show that repeated stress exposure causes microglia activation and recruitment of peripheral monocytes to the brain contributing to development of anxiety- and depressive-like behavior. Further studies show that stress-induced re-distribution of peripheral monocytes leads to stress-sensitized neuroimmune responses and recurrent anxiety-like behavior. These stress-associated immune changes are important because brain resident and peripheral immune cells contribute to physiological processes that support neuroplasticity. Thus, perturbations in neuroimmune function can lead to impaired neuronal responses and synaptic plasticity deficits that underlie behavioral symptoms of mental health disorders. In this review we discuss recent advances in neuroimmune regulation of behavior and summarize studies showing that stress-induced microglia activation and monocyte trafficking in the brain contribute to the neurobiology of mental health disorders.

Targeting innate immunity for neurodegenerative disorders of the central nervous system

Neuroinflammation is critically involved in numerous neurodegenerative diseases, and key signaling steps of innate immune activation hence represent promising therapeutic targets. This mini review series originated from the 4th Venusberg Meeting on Neuroinflammation held in Bonn, Germany, 7-9th May 2015, presenting updates on innate immunity in acute brain injury and chronic neurodegenerative disorders, such as traumatic brain injury and Alzheimer disease, on the role of astrocytes and microglia, as well as technical developments that may help elucidate neuroinflammatory mechanisms and establish clinical relevance. In this meeting report, a brief overview of physiological and pathological microglia morphology is followed by a synopsis on PGE2 receptors, insights into the role of arginine metabolism and further relevant aspects of neuroinflammation in various clinical settings, and concluded by a presentation of technical challenges and solutions when working with microglia and astrocyte cultures. Microglial ontogeny and induced pluripotent stem cell-derived microglia, advances of TREM2 signaling, and the cytokine paradox in Alzheimer's disease are further contributions to this article. Neuroinflammation is critically involved in numerous neurodegenerative diseases, and key signaling steps of innate immune activation hence represent promising therapeutic targets. This mini review series originated from the 4th Venusberg Meeting on Neuroinflammation held in Bonn, Germany, 7-9th May 2015, presenting updates on innate immunity in acute brain injury and chronic neurodegenerative disorders, such as traumatic brain injury and Alzheimer's disease, on the role of astrocytes and microglia, as well as technical developments that may help elucidate neuroinflammatory mechanisms and establish clinical relevance. In this meeting report, a brief overview on physiological and pathological microglia morphology is followed by a synopsis on PGE2 receptors, insights into the role of arginine metabolism and further relevant aspects of neuroinflammation in various clinical settings, and concluded by a presentation of technical challenges and solutions when working with microglia cultures. Microglial ontogeny and induced pluripotent stem cell-derived microglia, advances of TREM2 signaling, and the cytokine paradox in Alzheimer's disease are further contributions to this article.

Microglia Function in the Normal Brain

The activation of microglia has been recognized for over a century by their morphological changes. Long slender microglia acquire a short sturdy ramified shape when activated. During the past 20 years, microglia have been accepted as an essential cellular component for understanding the pathogenic mechanism of many brain diseases, including neurodegenerative diseases. More recently, functional studies and imaging in mouse models indicate that microglia are active in the healthy central nervous system. It has become evident that microglia release several signal molecules that play key roles in the crosstalk among brain cells, i.e., astrocytes and oligodendrocytes with neurons, as well as with regulatory immune cells. Recent studies also reveal the heterogeneous nature of microglia diverse functions depending on development, previous exposure to stimulation events, brain region of residence, or pathological state. Subjects to approach by future research are still the unresolved questions regarding the conditions and mechanisms that render microglia protective, capable of preventing or reducing damage, or deleterious, capable of inducing or facilitating the progression of neuropathological diseases. This novel knowledge will certainly change our view on microglia as therapeutic target, shifting our goal from their general silencing to the generation of treatments able to change their activation pattern.

Microglia in neuronal plasticity: Influence of stress

The central nervous system (CNS) has previously been regarded as an immune-privileged site with the absence of immune cell responses but this dogma was not entirely true. Microglia are the brain innate immune cells and recent findings indicate that they participate both in CNS disease and infection as well as facilitate normal CNS function. Microglia are highly plastic and play integral roles in sculpting the structure of the CNS, refining neuronal circuitry and connectivity, and contribute actively to neuronal plasticity in the healthy brain. Interestingly, psychological stress can perturb the function of microglia in association with an impaired neuronal plasticity and the development of emotional behavior alterations. As a result it seemed important to describe in this review some findings indicating that the stress-induced microglia dysfunction may underlie neuroplasticity deficits associated to many mood disorders. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Biphasic effects of luteolin on interleukin-1β-induced cyclooxygenase-2 expression in glioblastoma cells

Success in developing therapeutic approaches to target brain tumor-associated inflammation in patients has been limited. Given that the inflammatory microenvironment is a hallmark signature of solid tumor development, anti-inflammatory targeting strategies have been envisioned as preventing glioblastoma initiation or progression. Consumption of foods from plant origin is associated with reduced risk of developing cancers, a chemopreventive effect that is, in part, attributed to their high content of phytochemicals with potent anti-inflammatory properties. We explored whether luteolin, a common flavonoid in many types of plants, may inhibit interleukin (IL)-1β function induction of the inflammation biomarker cyclooxygenase (COX)-2. We found that IL-1β triggered COX-2 expression in U-87 glioblastoma cells and synergized with luteolin to potentiate or inhibit that induction in a biphasic manner. Luteolin pretreatment of cells inhibited IL-1β-mediated phosphorylation of inhibitor of κB, nuclear transcription factor-κB (NF-κB) p65, extracellular signal-regulated kinase-1/2, and c-Jun amino-terminal kinase in a concentration-dependent manner. Luteolin also inhibited AKT phosphorylation and survivin expression, while it triggered both caspase-3 cleavage and expression of glucose-regulated protein 78. These effects were all potentiated by IL-1β, in part through increased nuclear translocation of NF-κB p65. Finally, luteolin was able to reduce IL-1 receptor gene expression, and treatment with IL-1 receptor antagonist or gene silencing of IL-1 receptor prevented IL-1β/luteolin-induced COX-2 expression. Our results document a novel adaptive cellular response to luteolin, which triggers anti-survival and anti-inflammatory mechanisms that contribute to the chemopreventive properties of this diet-derived molecule.

Prion infection of mouse brain reveals multiple new upregulated genes involved in neuroinflammation or signal transduction

Gliosis is often a preclinical pathological finding in neurodegenerative diseases, including prion diseases, but the mechanisms facilitating gliosis and neuronal damage in these diseases are not understood. To expand our knowledge of the neuroinflammatory response in prion diseases, we assessed the expression of key genes and proteins involved in the inflammatory response and signal transduction in mouse brain at various times after scrapie infection. In brains of scrapie-infected mice at pre- and postclinical stages, we identified 15 previously unreported differentially expressed genes related to inflammation or activation of the STAT signal transduction pathway. Levels for the majority of differentially expressed genes increased with time postinfection. In quantitative immunoblotting experiments of STAT proteins, STAT1α, phosphorylated-STAT1α (pSTAT1α), and pSTAT3 were increased between 94 and 131 days postinfection (p.i.) in brains of mice infected with strain 22L. Furthermore, a select group of STAT-associated genes was increased preclinically during scrapie infection, suggesting early activation of the STAT signal transduction pathway. Comparison of inflammatory markers between mice infected with scrapie strains 22L and RML indicated that the inflammatory responses and gene expression profiles in the brains were strikingly similar, even though these scrapie strains infect different brain regions. The endogenous interleukin-1 receptor antagonist (IL-1Ra), an inflammatory marker, was newly identified as increasing preclinically in our model and therefore might influence scrapie pathogenesis in vivo. However, in IL-1Ra-deficient or overexpressor transgenic mice inoculated with scrapie, neither loss nor overexpression of IL-1Ra demonstrated any observable effect on gliosis, protease-resistant prion protein (PrPres) formation, disease tempo, pathology, or expression of the inflammatory genes analyzed.

IMPORTANCE

Prion infection leads to PrPres deposition, gliosis, and neuroinflammation in the central nervous system before signs of clinical illness. Using a scrapie mouse model of prion disease to assess various time points postinoculation, we identified 15 unreported genes that were increased in the brains of scrapie-infected mice and were associated with inflammation and/or JAK-STAT activation. Comparison of mice infected with two scrapie strains (22L and RML), which have dissimilar neuropathologies, indicated that the inflammatory responses and gene expression profiles in the brains were similar. Genes that increased prior to clinical signs might be involved in controlling scrapie infection or in facilitating damage to host tissues. We tested the possible role of the endogenous IL-1Ra, which was increased at 70 days p.i. In scrapie-infected mice deficient in or overexpressing IL-1Ra, there was no observable effect on gliosis, PrPres formation, disease tempo, pathology, or expression of inflammatory genes analyzed.

Neuromodulatory properties of inflammatory cytokines and their impact on neuronal excitability

Increasing evidence underlines that prototypical inflammatory cytokines (IL-1β, TNF-α and IL-6) either synthesized in the central (CNS) or peripheral nervous system (PNS) by resident cells, or imported by immune blood cells, are involved in several pathophysiological functions, including an unexpected impact on synaptic transmission and neuronal excitability. This review describes these unconventional neuromodulatory properties of cytokines, that are distinct from their classical action as effector molecules of the immune system. In addition to the role of cytokines in brain physiology, we report evidence that dysregulation of their biosynthesis and cellular release, or alterations in receptor-mediated intracellular pathways in target cells, leads to neuronal cell dysfunction and modifications in neuronal network excitability. As a consequence, targeting of these cytokines, and related signalling molecules, is considered a novel option for the development of therapies in various CNS or PNS disorders associated with an inflammatory component. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Modulation of learning and memory by cytokines: signaling mechanisms and long term consequences

This review describes the role of cytokines and their downstream signaling cascades on the modulation of learning and memory. Immune proteins are required for many key neural processes and dysregulation of these functions by systemic inflammation can result in impairments of memory that persist long after the resolution of inflammation. Recent research has demonstrated that manipulations of individual cytokines can modulate learning, memory, and synaptic plasticity. The many conflicting findings, however, have prevented a clear understanding of the precise role of cytokines in memory. Given the complexity of inflammatory signaling, understanding its modulatory role requires a shift in focus from single cytokines to a network of cytokine interactions and elucidation of the cytokine-dependent intracellular signaling cascades. Finally, we propose that whereas signal transduction and transcription may mediate short-term modulation of memory, long-lasting cellular and molecular mechanisms such as epigenetic modifications and altered neurogenesis may be required for the long lasting impact of inflammation on memory and cognition.

IL-1β increases necrotic neuronal cell death in the developing rat hippocampus after status epilepticus by activating type I IL-1 receptor (IL-1RI)

Interleukin-1β (IL-1β) is associated with seizure-induced neuronal cell death in the adult brain. The contribution of IL-1β to neuronal injury induced by status epilepticus (SE) in the immature brain remains unclear. In the present study, we investigated the effects of IL-1β administration on hippocampal neuronal cell death associated with SE in the immature brain, and the role of the type I receptor of IL-1β (IL-1RI). SE was induced with lithium-pilocarpine in 14-days-old (P14) rat pups. Six hours after SE onset, pups were i.c.v. injected in the right ventricle with IL-1β (0, 0.3, 3, 30, or 300 ng), 30 ng of IL-1RI antagonist (IL-1Ra) alone, or 30 ng of IL-1Ra plus 3ng of IL-1β. As control groups, pups without seizures were injected with 3 ng of IL-1β or vehicle. Twenty-four hours after SE onset, neuronal cell death in the CA1 field of dorsal hippocampus was assessed by hematoxylin-eosin, Fluoro-Jade B and in vivo propidium iodide (PI) staining; expression of active caspase-3 (aCas-3) was also determined, using immunohistochemistry. The concentration-response curve of IL-1β showed a bell-shape. Only pups injected with 3 ng of IL-1β after SE showed a significant increase in the number of cells with eosinophilic cytoplasm and pyknotic nuclei, as well as F-JB positive cells with respect to the vehicle group. This effect was prevented when IL-1β was injected with IL-1Ra. Injection of 3 ng of IL-1β increased the number of PI-positive cells in CA1 area after SE. Injection of 3 ng of IL-1β did not produce hippocampal cell death in rats without seizures. Active caspase-3 expression was not observed after treatments in hippocampus. The activation of the IL-1β/IL-1RI system increases necrotic neuronal cell death caused by SE in rat pups.

Knock-down of IL-1Ra in obese mice decreases liver inflammation and improves insulin sensitivity

Interleukin 1 Receptor antagonist (IL-1Ra) is highly elevated in obesity and is widely recognized as an anti-inflammatory cytokine. While the anti-inflammatory role of IL-1Ra in the pancreas is well established, the role of IL-1Ra in other insulin target tissues and the contribution of systemic IL-1Ra levels to the development of insulin resistance remains to be defined. Using antisense knock down of IL-1Ra in vivo, we show that normalization of IL-1Ra improved insulin sensitivity due to decreased inflammation in the liver and improved hepatic insulin sensitivity and these effects were independent of changes in body weight. A similar effect was observed in IL1-R1 KO mice, suggesting that at high concentrations of IL-1Ra typically observed in obesity, IL-1Ra can contribute to the development of insulin resistance in a mechanism independent of IL-1Ra binding to IL-1R1. These results demonstrate that normalization of plasma IL-1Ra concentration improves insulin sensitivity in diet- induced obese mice.

Neuroinflammatory changes negatively impact on LTP: A focus on IL-1β

In recent years it has become clear that neuroinflammatory changes develop in the brain with age and that similar, though more profound changes, occur in neurodegenerative conditions and in animal models of neurodegeneration. These changes are linked with deterioration in plasticity and the evidence suggests that a key causative factor is microglial activation and the associated increase in production and release of inflammatory cytokines. Several groups have reported that interleukin (IL)-1β negatively impacts on hippocampal-dependent learning and has an inhibitory effect on LTP although this is concentration-dependent. Similarly other inflammatory cytokines, which are also produced by microglia similarly decrease LTP. The evidence supporting these findings will be reviewed here and will be discussed in the context of considering mechanisms by which the negative impact of neuroinflammation can be ameliorated. This article is part of a Special Issue entitled SI: Brain and Memory.

Activation of gastrin-releasing peptide receptors at the infralimbic cortex elicits gastrin-releasing peptide release at the basolateral amygdala: implications for conditioned fear

The basolateral amygdala (BLA) and infralimbic (IL) cortex share strong reciprocal interconnections and are key structures in conditioned fear circuitry. Gastrin-releasing peptide (GRP) or its receptor antagonists can modulate the conditioned fear response when exogenously administered at either of these sites, and increased release of GRP at the BLA occurs in response to conditioned fear recall. The present study sought to determine whether a functional pathway utilizing GRP exists between the IL cortex and BLA and whether this pathway is also influenced by amygdala corticotropin-releasing factor (CRF) release. To this end, we assessed the effects of intra-IL cortex injection of GRP or GRP co-administered with a receptor antagonist, RC-3095, on the downstream release of GRP and/or CRF at the BLA. Results showed that microinjection of GRP at the IL cortex increased the release of GRP, but not CRF, at the BLA, an effect blocked by co-administration of RC-3095. Administration of RC-3095 into the IL cortex on its own, however, also elicited the release of GRP (but not CRF) at the BLA. These findings suggest that a functional pathway utilizing GRP (among other factors) exists between the IL cortex and BLA that may be relevant to conditioned fear, but that GRP and CRF do not interact within this circuitry. Moreover, the finding that the release profile of GRP was similar following administration of either GRP or its receptor antagonist, lends support to the view that RC-3095 has partial agonist properties. Together these findings provide further evidence for the involvement of GRP in fear and anxiety-related disorders.

The role of markers of inflammation in traumatic brain injury

Within minutes of a traumatic impact, a robust inflammatory response is elicited in the injured brain. The complexity of this post-traumatic squeal involves a cellular component, comprising the activation of resident glial cells, microglia, and astrocytes, and the infiltration of blood leukocytes. The second component regards the secretion immune mediators, which can be divided into the following sub-groups: the archetypal pro-inflammatory cytokines (Interleukin-1, Tumor Necrosis Factor, Interleukin-6), the anti-inflammatory cytokines (IL-4, Interleukin-10, and TGF-beta), and the chemotactic cytokines or chemokines, which specifically drive the accumulation of parenchymal and peripheral immune cells in the injured brain region. Such mechanisms have been demonstrated in animal models, mostly in rodents, as well as in human brain. Whilst the humoral immune response is particularly pronounced in the acute phase following Traumatic brain injury (TBI), the activation of glial cells seems to be a rather prolonged effect lasting for several months. The complex interaction of cytokines and cell types installs a network of events, which subsequently intersect with adjacent pathological cascades including oxidative stress, excitotoxicity, or reparative events including angiogenesis, scarring, and neurogenesis. It is well accepted that neuroinflammation is responsible of beneficial and detrimental effects, contributing to secondary brain damage but also facilitating neurorepair. Although such mediators are clear markers of immune activation, to what extent cytokines can be defined as diagnostic factors reflecting brain injury or as predictors of long term outcome needs to be further substantiated. In clinical studies some groups reported a proportional cytokine production in either the cerebrospinal fluid or intraparenchymal tissue with initial brain damage, mortality, or poor outcome scores. However, the validity of cytokines as biomarkers is not broadly accepted. This review article will discuss the evidence from both clinical and laboratory studies exploring the validity of immune markers as a correlate to classification and outcome following TBI.

The role of markers of inflammation in traumatic brain injury

Within minutes of a traumatic impact, a robust inflammatory response is elicited in the injured brain. The complexity of this post-traumatic squeal involves a cellular component, comprising the activation of resident glial cells, microglia, and astrocytes, and the infiltration of blood leukocytes. The second component regards the secretion immune mediators, which can be divided into the following sub-groups: the archetypal pro-inflammatory cytokines (Interleukin-1, Tumor Necrosis Factor, Interleukin-6), the anti-inflammatory cytokines (IL-4, Interleukin-10, and TGF-beta), and the chemotactic cytokines or chemokines, which specifically drive the accumulation of parenchymal and peripheral immune cells in the injured brain region. Such mechanisms have been demonstrated in animal models, mostly in rodents, as well as in human brain. Whilst the humoral immune response is particularly pronounced in the acute phase following Traumatic brain injury (TBI), the activation of glial cells seems to be a rather prolonged effect lasting for several months. The complex interaction of cytokines and cell types installs a network of events, which subsequently intersect with adjacent pathological cascades including oxidative stress, excitotoxicity, or reparative events including angiogenesis, scarring, and neurogenesis. It is well accepted that neuroinflammation is responsible of beneficial and detrimental effects, contributing to secondary brain damage but also facilitating neurorepair. Although such mediators are clear markers of immune activation, to what extent cytokines can be defined as diagnostic factors reflecting brain injury or as predictors of long term outcome needs to be further substantiated. In clinical studies some groups reported a proportional cytokine production in either the cerebrospinal fluid or intraparenchymal tissue with initial brain damage, mortality, or poor outcome scores. However, the validity of cytokines as biomarkers is not broadly accepted. This review article will discuss the evidence from both clinical and laboratory studies exploring the validity of immune markers as a correlate to classification and outcome following TBI.

Neuroplastic changes in depression: a role for the immune system

Accumulating evidence suggests that there is a rich cross-talk between the neuroimmune system and neuroplasticity mechanisms under both physiological conditions and pathophysiological conditions in depression. Anti-neuroplastic changes which occur in depression include a decrease in proliferation of neural stem cells (NSCs), decreased survival of neuroblasts and immature neurons, impaired neurocircuitry (cortical-striatal-limbic circuits), reduced levels of neurotrophins, reduced spine density and dendritic retraction. Since both humoral and cellular immune factors have been implicated in neuroplastic processes, in this review we present a model suggesting that neuroplastic processes in depression are mediated through various neuroimmune mechanisms. The review puts forward a model in that both humoral and cellular neuroimmune factors are involved with impairing neuroplasticity under pathophysiological conditions such as depression. Specifically, neuroimmune factors including interleukin (IL)-1, IL-6, tumour necrosis factor (TNF)-α, CD4⁺CD25⁺T regulatory cells (T reg), self-specific CD4⁺T cells, monocyte-derived macrophages, microglia and astrocytes are shown to be vital to processes of neuroplasticity such as long-term potentiation (LTP), NSC survival, synaptic branching, neurotrophin regulation and neurogenesis. In rodent models of depression, IL-1, IL-6 and TNF are associated with reduced hippocampal neurogenesis; mechanisms which are associated with this include the stress-activated protein kinase (SAPK)/Janus Kinase (JNK) pathway, hypoxia-inducible factors (HIF)-1α, JAK-Signal Transducer and Activator of Transcription (STAT) pathway, mitogen-activated protein kinase (MAPK)/cAMP responsive element binding protein (CREB) pathway, Ras-MAPK, PI-3 kinase, IKK/nuclear factor (NF)-κB and TGFβ activated kinase-1 (TAK-1). Neuroimmunological mechanisms have an active role in the neuroplastic changes associated with depression. Since therapies in depression, including antidepressants (AD), omega-3 polyunsaturated fatty acids (PUFAs) and physical activity exert neuroplasticity-enhancing effects potentially mediated by neuroimmune mechanisms, the immune system might serve as a promising target for interventions in depression.

Interleukin-1R3 mediates interleukin-1-induced potassium current increase through fast activation of Akt kinase

Inflammatory cytokine interleukin-1 (IL-1) performs multiple functions in the central nervous system. The type 1 IL-1 receptor (IL-1R1) and the IL-1 receptor accessory protein (IL-1RAcP) form a functional IL-1 receptor complex that is thought to mediate most, if not all, IL-1-induced effects. Several recent studies, however, suggest the existence of a heretofore-unidentified receptor for IL-1. In this study, we report that the IL-1R1 gene contains an internal promoter that drives the transcription of a shortened IL-1R1 mRNA. This mRNA is the template for a unique IL-1R protein that is identical to IL-1R1 at the C terminus, but with a shorter extracellular domain at the N terminus. We have termed this molecule IL-1R3. The mRNA and protein for IL-1R3 are expressed in normal and two strains of commercially available IL-1R1 knockout mice. Western blot analysis shows IL-1R3 is preferentially expressed in neural tissues. Furthermore, IL-1β binds specifically to IL-1R3 when it is complexed with the newly discovered alternative IL-1 receptor accessory protein, IL-1RAcPb. Stimulation of neurons expressing both IL-1R3 and IL-1RAcPb with IL-1β causes fast activation of the Akt kinase, which leads to an increase in voltage-gated potassium current. These results demonstrate that IL-1R3/IL-1RAcPb complex mediates a unique subset of IL-1 activity that accounts for many previously unexplained IL-1 effects in the central nervous system.

Interleukin-1alpha and HMGB1 mediate hippocampal dysfunction in SIGIRR-deficient mice

Single-Ig-interleukin-1 related receptor (SIGIRR) is a member of the interleukin (IL)-1/Toll-like receptor (TLR) family. It negatively regulates inflammation, rendering SIGIRR(-/-) mice more susceptible to inflammatory challenge. This susceptibility extends to the brain, where increased responsiveness to lipopolysaccharide has been observed in SIGIRR-deficient mice. While this is likely due to enhanced TLR4-mediated signaling, the functional consequences of these changes have not yet been described. In the current study, we have investigated the impact of SIGIRR deficiency on hippocampal function, and show that novel object recognition, spatial reference memory, and long-term potentiation (LTP) were impaired in SIGIRR(-/-) mice. These changes were accompanied by increased expression of IL-1RI and TLR4, and upregulation of their downstream signaling events, namely IRAK1 (IL-1R-associated kinase 1), c-Jun N-terminal protein kinase (JNK), and nuclear factor κB (NF-κB). The deficit in LTP was attenuated by the endogenous IL-1 receptor antagonist (IL-1ra) and an anti-TLR4 antibody, and also by inhibition of JNK and NF-κB. We propose that IL-1RI is activated by IL-1α and TLR4 is activated by the endogenous agonist, high mobility group box 1 (HMGB1), as we identified enhanced expression of both cytokines in the hippocampus of SIGIRR(-/-) mice. Additionally, application of HMGB1 increased the activation of JNK and NF-κB and was found to be detrimental to LTP in a TLR4-dependent manner. These findings highlight the functional role of SIGIRR in regulating inflammatory-mediated synaptic and cognitive decline, and describe evidence of the key role of HMGB1 in this process.

Age-related neuroinflammatory changes negatively impact on neuronal function

Neuroinflammatory changes, characterized by an increase in microglial activation and often accompanied by upregulation of inflammatory cytokines like interleukin-1β (IL-1β), are common to many, if not all, neurodegenerative diseases. Similar, though less dramatic neuroinflammatory changes, are also known to occur with age. Among the consequences of these changes is an impairment in synaptic function and the evidence suggests that inflammatory cytokines may be the primary contributory factor responsible for the deficits in synaptic plasticity which have been identified in aged rodents. Specifically a decrease in the ability of aged rats to sustain long-term potentiation (LTP) in perforant path-granule cells of the hippocampus is associated with increased microglial activation. This review considers the evidence which suggests a causal relationship between these changes and the factors which contribute to the age-related microglial activation, and reflects on data which demonstrate that agents which inhibit microglial activation also improve ability of rats to sustain LTP.

Successful inhibition of excitotoxic neuronal damage and microglial activation after delayed application of interleukin-1 receptor antagonist

Interleukin (IL)-1 is an important mediator of neuronal demise and glial activation after acute central nervous system lesions and is antagonized by IL-1 receptor antagonist (IL-1RA). Here we determined the time window in which IL-1RA elicits neuroprotective effects in rat organotypic hippocampal slice cultures (OHSC). OHSC were lesioned with N-methyl-D-aspartate (NMDA) and treated with IL-1RA (100 ng/ml) at different time points postinjury or were left untreated. Damaged neurons, microglial cells, and astrocytes were labelled with NeuN, propidium iodide, isolectin B(4), or glial fibrillary acidic protein (GFAP), respectively, and were analyzed by confocal laser scanning microscopy. In lesioned OHSC, the most dramatic increase in microglial cell number occurred between 8 and 16 hr postinjury, and the maximal neuronal demise was found between 16 and 24 hr postinjury. The cellular source of IL-1beta was investigated by immunohistochemistry, and IL-1beta immunoreactivity was found in few microglial cells at 4 hr postinjury and in numerous microglial cells and astrocytes at 16 hr postinjury. In both glial populations, IL-1beta immunoreactivity peaked at 24 hr postinjury. IL-1RA treatment potently suppressed neuronal damage by 55% when initiated within the first 16 hr postinjury (P < 0.05), and IL-1RA treatment initiated at 24 hr postinjury resulted in weaker but still significant neuroprotection. IL-1RA treatment also reduced the number of microglial cells significantly when initiated within 36 hr postinjury (P < 0.05). In conclusion, IL-1RA exhibits significant neuroprotective effects in this in vitro model of excitotoxic injury even after delayed application.

Interleukin-1 (IL-1): a central regulator of stress responses

Ample evidence demonstrates that the pro-inflammatory cytokine interleukin-1 (IL-1), produced following exposure to immunological and psychological challenges, plays an important role in the neuroendocrine and behavioral stress responses. Specifically, production of brain IL-1 is an important link in stress-induced activation of the hypothalamus-pituitary-adrenal axis and secretion of glucocorticoids, which mediate the effects of stress on memory functioning and neural plasticity, exerting beneficial effects at low levels and detrimental effects at high levels. Furthermore, IL-1 signaling and the resultant glucocorticoid secretion mediate the development of depressive symptoms associated with exposure to acute and chronic stressors, at least partly via suppression of hippocampal neurogenesis. These findings indicate that whereas under some physiological conditions low levels of IL-1 promote the adaptive stress responses necessary for efficient coping, under severe and chronic stress conditions blockade of IL-1 signaling can be used as a preventive and therapeutic procedure for alleviating stress-associated neuropathology and psychopathology.

IL-1F5 mediates anti-inflammatory activity in the brain through induction of IL-4 following interaction with SIGIRR/TIR8

Similarity in structure and sequence homology has led to the identification of new members of the interleukin-1 (IL-1) ligand and receptor superfamilies. IL-1F6, IL-1F8 and IL-1F9 have been shown to signal through IL-1R-related protein 2 and IL-1 receptor accessory protein leading to activation of NFkappaB, while IL-1F7 and IL-1F10 interact with the IL-18 receptor and the soluble IL-1 receptor type I respectively. In contrast, identification of a biological role for IL-1F5 has remained elusive, with conflicting data relating to its possible ability to antagonize IL-1F9-stimulated activation of NFkappaB in Jurkat cells transfected with IL-1R-related protein 2. In this study, we set out to investigate a possible role for IL-1F5 in the brain and report that it antagonizes the inflammatory effects of IL-1beta and lipopolysaccharide (LPS) in vivo and in vitro including the inhibitory effect on long-term potentiation (LTP) in rat hippocampus. We demonstrate that IL-1F5 induces IL-4 mRNA and protein expression in glia in vitro and enhances hippocampal expression of IL-4 following intracerebroventricular (i.c.v.) injection. The inhibitory effect of IL-1F5 on LPS-induced IL-1beta is attenuated in cells from IL-4-defective (IL-4-/- mice). Our findings suggest that IL-1F5 mediates anti-inflammatory effects through its ability to induce IL-4 production and that this is a consequence of its interaction with the orphan receptor, single Ig IL-1R-related molecule (SIGIRR)/TIR8, as the effects were not observed in SIGIRR-/- mice. In contrast to its effects in brain tissue, IL-1F5 did not attenuate LPS-induced changes, or up-regulated IL-4 in macrophages or dendritic cells, suggesting that the effect is confined to the brain.

Immunosuppression after traumatic or ischemic CNS damage: it is neuroprotective and illuminates the role of microglial cells

Acute traumatic and ischemic events in the central nervous system (CNS) invariably result in activation of microglial cells as local representatives of the immune system. It is still under debate whether activated microglia promote neuronal survival, or whether they exacerbate the original extent of neuronal damage. Protagonists of the view that microglial cells cause secondary damage have proposed that inhibition of microglial activation by immunosuppression is beneficial after acute CNS damage. It is the aim of this review to analyse the effects of immunosuppressants on isolated microglial cells and neurons, and to scrutinize the effects of immunosuppression in different in vivo models of acute CNS trauma or ischemia. It is found that the immunosuppressants cytosine-arabinoside, different steroids, cyclosporin A, FK506, rapamycin, mycophenolate mofetil, and minocycline all have direct inhibitory effects on microglial cells. These effects are mainly exerted by inhibiting microglial proliferation or microglial secretion of neurotoxic substances such as proinflammatory cytokines and nitric oxide. Furthermore, immunosuppression after acute CNS trauma or ischemia results in improved structure preservation and, mostly, in enhanced function. However, all investigated immunosuppressants also have direct effects on neurons, and some immunosuppressants affect other glial cells such as astrocytes. In summary, it is safe to conclude that immunosuppression after acute CNS trauma or ischemia is neuroprotective. Furthermore, circumferential evidence indicates that microglial activation after traumatic or ischemic CNS damage is not beneficial to adjacent neurons in the immediate aftermath of such acute lesions. Further experiments with more specific agents or genetic approaches that specifically inhibit microglial cells are needed in order to fully answer the question of whether microglial activation is "good or bad".

Studies on brain volume, Alzheimer-related proteins and cytokines in mice with chronic overexpression of IL-1 receptor antagonist

Inflammation is associated with both acute and chronic neurological disorders, including stroke and Alzheimer's disease (AD). Cytokines such as interleukin (IL)-1 have several activities in the brain both under physiological and pathophysiological conditions. The objective of this study was to evaluate consequences of the central blockade of IL-1 transmission in a previously developed transgenic mouse strain with brain-directed overexpression of human soluble IL-1 receptor antagonist (Tg hsIL-1ra). Effects on brain morphology and brain levels of the AD-related proteins beta-amyloid precursor protein (APP) and presenilin 1(PS1), as well as the levels of IL-1beta, IL-6 and tumour necrosis factor-alpha (TNF-alpha) were analysed in homozygotic and heterozygotic mice and wild type (WT) controls, of both genders and of young (30-40 days) and adult (13-14 months) age. A marked reduction in brain volume was observed in transgenic mice as determined by volumetry. Western blot analysis showed higher levels of APP, but lower levels of PS1, in adult animals than in young ones. In the cerebellum, heterozygotic (Tg hsIL-1ra(+/-)) mice had lower levels of APP and PS1 than WT mice. With one exception, there were no genotypic differences in the levels of IL-1beta, IL-6 and TNF-alpha. The cytokine levels were generally higher in adult than in young mice. In conclusion, the chronic blockade of IL-1 signalling in the brain was associated with an atrophic phenotype of the brain, and with modified levels of APP and PS1. Brain-directed overexpression of hsIL-1ra was not followed by major compensatory changes in the levels of pro-inflammatory cytokines.

Pro-inflammatory cytokines modify neuronal nicotinic acetylcholine receptor assembly

We have examined the impact of the inflammatory cytokines interleukin-1 beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) on assembly of nAChRs from subunit mixtures of nAChRalpha4, beta2 and beta4 transiently transfected into 293 cells. In control transfections approximately 55% of alpha4 associated preferentially with beta4, but less than 15% complexed with beta2 and the remainder was associated with both beta subunits. These relative ratios were modified by pro-inflammatory cytokines. IL-1beta strongly enhanced alpha4/beta2 association and decreased alpha4/beta4, whereas TNFalpha promoted mixed alpha4/beta2/beta4 interactions. These results show that the emerging rules governing assembly of nAChRs are subject to modification by the pro-inflammatory cytokine environment.

Interleukin-1 and neuronal injury

Interleukin-1 is a pro-inflammatory cytokine that has numerous biological effects, including activation of many inflammatory processes (through activation of T cells, for example), induction of expression of acute-phase proteins, an important function in neuroimmune responses and direct effects on the brain itself. There is now extensive evidence to support the direct involvement of interleukin-1 in the neuronal injury that occurs in both acute and chronic neurodegenerative disorders. This article discusses the key evidence of a role for interleukin-1 in acute neurodegeneration - for example, stroke and brain trauma - and provides a rationale for targeting the interleukin-1 system as a therapeutic strategy.

Impaired long-term potentiation in c-Jun N-terminal kinase 2-deficient mice

c-Jun N-terminal kinases (JNKs) are thought to be involved in regulating synaptic plasticity. We therefore investigated the specific role of JNK2 in modulating long-term potentiation (LTP) in hippocampus during development, using JNK2-deficient mice. The morphological structure and the numbers of both NeuN, a specific neuronal marker, and GABA-positive neurons in the hippocampal areas were similar in wild-type and Jnk2(-/-) mice. Western blot analysis revealed that JNK2 expression was higher and stable at 1 and 3 months of age, but JNK1 levels were lower at 1 month of age and almost undetectable in 3-month-old wild-type mice. In contrast to wild-type mice, there was a significant increase in JNK1 expression in JNK2 mutant mice, especially at 1 month of age. Electrophysiological studies demonstrated that LTP was impaired in both the CA1 and CA3 regions in 1-month-old, but not in adult, Jnk2(-/-) mice, probably owing to decreased presynaptic neurotransmitter release. Moreover, late-phase LTP, but not early-phase LTP, was impaired in the Jnk2(-/-) adult mice, suggesting that JNK2 plays a role in transforming early LTP to late LTP. Together, the data highlight the specific role of JNK2 in hippocampal synaptic plasticity during development.

The effects of endogenous interleukin-1 bioactivity on locus coeruleus neurons in response to bacterial and viral substances

In a previous study, we found that microinjection of the cytokine interleukin-1 (IL-1) into the locus coeruleus (LC) increased the electrophysiological activity of LC neurons. To determine if endogenous IL-1 similarly affects the LC, brain IL-1 was induced with lipopolysaccharide (LPS), a substance derived from Gram-negative bacteria. LPS microinjected directly into the LC increased the activity of LC neurons in anesthetized rats, and this effect was blocked by microinfusion of the IL-1 receptor antagonist (IL-1RA) protein into the LC indicating the involvement of IL-1 receptors. Similarly, intraperitoneal (i.p.) LPS injection increased the activity of LC neurons in a dose- and time-related manner that was sensitive to IL-1RA. The change in the activity of LC neurons caused by a single i.p. injection of LPS was surprisingly long-lasting, and evolved over a period of at least 3 weeks. Other microbial substances-namely, peptidoglycan from Gram-positive bacteria and poly-inosine/poly-cytosine (poly(I)/(C)), which resembles RNA viruses-were used to determine the generality of the findings with LPS. Both i.p. peptidoglycan and poly(I)/(C) increased LC activity but with lesser efficacy than LPS. IL-1RA reversed the increase in the activity of LC neurons caused by i.p. peptidoglycan treatment; however, that caused by i.p. Poly(I)/(C) was not diminished by IL-1RA. Thus, the increased activity of LC neurons caused by LPS and peptidoglycan requires IL-1 receptor binding, suggesting the involvement of endogenously-produced IL-1. In contrast, poly(I)/(C) increased the activity of LC neurons but this did not critically involve IL-1 receptors in the LC.

A dual role for interleukin-1 in LTP in mouse hippocampal slices

Interleukin-1 (IL-1) exerts numerous effects in the central nervous system and has been implicated in synaptic plasticity. The objective of this study was to investigate the role of endogenous as well as exogenous IL-1 on long-term potentiation (LTP). Hippocampal slices incubated at 34-36 degrees C show enhanced levels of IL-1alpha and IL-1beta compared to slices incubated at 21-24 degrees C. IL-1 inhibits LTP induced by theta-burst stimulation (TBS) at either temperature. IL-1 receptor antagonist (IL-1ra) had no effect on LTP at 21-24 degrees C, but displayed a concentration-dependent inhibition of LTP at 34-36 degrees C. Under control conditions, the magnitude of LTP was not temperature dependent. These data suggest that IL-1 is required for LTP under physiological conditions but at higher doses, as encountered in pathological conditions, IL-1 inhibits LTP.