Relationship between the development of autoimmunity and sensorimotor gating in MRL-lpr mice with reduced IL-2 production

The contribution of interleukin-2 to effective wound healing

Ineffective skin wound healing is a significant source of morbidity and mortality. Roughly 6.5 million Americans experience chronically open wounds and the cost of treating these wounds numbers in the billions of dollars annually. In contrast, robust wound healing can lead to the development of either hypertrophic scarring or keloidosis, both of which can cause discomfort and can be cosmetically undesirable. Appropriate wound healing requires the interplay of a variety of factors, including the skin, the local microenvironment, the immune system, and the external environment. When these interactions are perturbed, wounds can be a nidus for infection, which can cause them to remain open an extended period of time, or can scar excessively. Interleukin-2, a cytokine that directs T-cell expansion and phenotypic development, appears to play an important role in wound healing. The best-studied role for Interleukin-2 is in influencing T-cell development. However, other cell types, including fibroblasts, the skin cells responsible for closing wounds, express the Interleukin-2 receptor, and therefore may respond to Interleukin-2. Studies have shown that treatment with Interleukin-2 can improve the strength of healed skin, which implicates Interleukin-2 in the wound healing process. Furthermore, diseases that involve impaired wound healing, such as diabetes and systemic lupus erythematosus, have been linked to deficiencies in Interleukin-2 or defects Interleukin-2-receptor signaling. The focus of this review is to summarize the current understanding of the role of Interleukin-2 in wound healing, to highlight diseases in which Interleukin-2 and its receptor may contribute to impaired wound healing, and to assess Interleukin-2-modulating approaches as potential therapies to improve wound healing.

Cognitive deterioration among bipolar disorder patients infected by Toxoplasma gondii is correlated to interleukin 6 levels

BACKGROUND

Cognitive deficits are present in a large majority of Bipolar Disorder (BD) patients and known to be a marker of bad prognosis. Because, these deficits encompass several domains and no specific medical treatment seems to be effective, it is important to better understand the mechanisms underlying cognitive deterioration. As Toxoplasma gondii is known to induce the synthesis of pro-inflammatory cytokines such as IL-6, we will explore here the possible role of T. gondii in the cognitive decline observed in BD.

METHODS

42 euthymic BD patients and 36 controls were assessed for episodic verbal memory using the CVLT and for working memory and verbal ability using the WAIS III. Patients and controls were also screened for seropositivity to T. gondii and evaluated for the levels of IL-6 transcripts.

RESULTS

The seropositivity for T. gondii was significantly higher in BD patients as compared to controls (p=0.005). The cognitive deterioration index (DI) was higher in BD patients (p=5.10(-6)) and correlated to high IL-6 mRNA expression only among those infected by T. gondii (rho=0.43, p=0.01). Among deteriorated patients (defined by scores above 0.10 according to Weschler׳s definition), the IL-6 mRNA expression was twice greater (p=0.01).

LIMITATIONS

Our results are to be interpreted with caution because of our small sample size and the cross-sectional design.

CONCLUSIONS

A long-term exposure to inflammation, measured here with IL-6 mRNA expression in T. gondii infected BD may alter cognitive functioning. IL-6 could thus be a useful predictive marker of cognitive deterioration in BD and may help to design personalized treatment.

Selective Neuronal and Brain Regional Expession of IL-2 in IL2P 8-GFP Transgenic Mice: Relation to Sensorimotor Gating

Brain-derived interleukin-2 (IL-2) has been implicated in diseases processes that arise during CNS development (e.g., autism) to neurodegenerative alterations involving neuroinflammation (e.g., Alzheimer’s disease). Progress has been limited, however, because the vast majority of current knowledge of IL-2’s actions on brain function and behavior is based on the use exogenously administered IL-2 to make inferences about the function of the endogenous cytokine. Thus, to identify the cell-type(s) and regional circuitry that express brain-derived IL-2, we used B6.Cg-Tg/ IL2-EGFP17Evr (IL2p8-GFP) transgenic mice, which express green fluorescent protein (GFP) in peripheral immune cells known to produce IL-2. We found that the IL2-GFP transgene was localized almost exclusively to NeuN-positive cells, indicating that the IL-2 is produced primarily by neurons. The IL2-GFP transgene was expressed in discrete nuclei throughout the rostral-caudal extent of the brain and brainstem, with the highest levels found in the cingulate, dorsal endopiriform nucleus, lateral septum, nucleus of the solitary tract, magnocellular/gigantocellular reticular formation, red nucleus, entorhinal cortex, mammilary bodies, cerebellar fastigial nucleus, and posterior interposed nucleus. Having identified IL-2 gene expression in brain regions associated with the regulation of sensorimotor gating (e.g., lateral septum, dorsal endopiriform nucleus, entorhinal cortex, striatum), we compared prepulse inhibition (PPI) of the acoustic startle response in congenic mice bred in our lab that have selective loss of the IL-2 gene in the brain versus the peripheral immune system, to test the hypothesis that brain-derived IL-2 plays a role in modulating PPI. We found that congenic mice devoid of IL-2 gene expression in both the brain and the peripheral immune system, exhibited a modest alteration of PPI. These finding suggest that IL2p8-GFP transgenic mice may be a useful tool to elucidate further the role of brain-derived IL-2 in normal CNS function and disease.

Dissecting the effects of endogenous brain IL-2 and normal versus autoreactive T lymphocytes on microglial responsiveness and T cell trafficking in response to axonal injury

IL-2 is essential for T-helper regulatory (Treg) cell function and self-tolerance, and dysregulation of both endogenous brain and peripheral IL-2 gene expression may have important implications for neuronal injury and repair. We used an experimental approach combining mouse congenic breeding and immune reconstitution to test the hypothesis that the response of motoneurons to injury is modulated by the combined effects of IL2-mediated processes in the brain that modulate its endogenous neuroimmunological milieu, and IL2-mediated processes in the peripheral immune system that regulate T cell function (i.e., normal versus autoreactive Treg-deficient T cells). This experimental strategy enabled us to test our hypothesis by disentangling the effect of normal versus autoreactive T lymphocytes from the effect of endogenous brain IL-2 on microglial responsiveness (microglial phagocytic clusters normally associated with dead motoneurons and MHC2(+) activated microglia) and T cell trafficking, using the facial nerve axotomy model of injury. The results demonstrate that the loss of both brain and peripheral IL-2 had an additive effect on numbers of microglial phagocytic clusters at day 14 following injury, whereas the autoreactive status of peripheral T cells was the primary factor that determined the degree to which T cells entered the injured brain and contributed to increased microglial phagocytic clusters. Changes in activated MHC2(+) microglial in the injured FMN were associated with loss of endogenous brain IL-2 and/or peripheral IL-2. This model may provide greater understanding of the mechanisms involved in determining if T cells entering the injured central nervous system (CNS) have damaging or proregenerative effects.

Loss of CNS IL-2 gene expression modifies brain T lymphocyte trafficking: response of normal versus autoreactive Treg-deficient T cells

Emerging data from our lab and others suggested that dysregulation of the brain's endogenous neuroimmunological milieu may occur with the loss of brain IL-2 gene expression and be involved in initiating processes that lead to CNS autoimmunity. We sought to test our working hypothesis that IL-2 deficiency induces endogenous changes in the CNS that play a key role in eliciting T cell homing into the brain. To accomplish this goal, we used an experimental approach that combined mouse congenic breeding and immune reconstitution. In congenic mice without brain IL-2 (two IL-2 KO alleles) that were reconstituted with a normal wild-type immune system, the loss of brain IL-2 doubled the number of T cells that trafficked into the brain in all regions quantified (hippocampus, septum, and cerebellum) compared to mice with two wild-type brain IL-2 alleles and a wild-type peripheral immune system. Congenic mice with normal brain IL-2 (two wild-type IL-2 alleles) that were immune reconstituted with autoreactive Treg-deficient T cells from IL-2 KO mice developed the expected peripheral autoimmunity (splenomegaly) and had a comparable doubling of T cell trafficking into the hippocampus and septum, whereas they exhibited an additional twofold proclivity for the cerebellum over the septohippocampal regions. Unlike brain trafficking of wild-type T cells, the increased homing of IL-2 KO T cells to the cerebellum was independent of brain IL-2 gene expression. These findings demonstrate that brain IL-2 deficiency induces endogenous CNS changes that may lead to the development of brain autoimmunity, and that autoreactive Treg-deficient IL-2 KO T cells trafficking to the brain could have a proclivity to induce cerebellar neuropathology.

The MRL/lpr mouse strain as a model for neuropsychiatric systemic lupus erythematosus

To date, CNS disease and neuropsychiatric symptoms of systemic lupus erythematosus (NP-SLE) have been understudied compared to end-organ failure and peripheral pathology. In this review, we focus on a specific mouse model of lupus and the ways in which this model reflects some of the most common manifestations and potential mechanisms of human NP-SLE. The mouse MRL lymphoproliferation strain (a.k.a. MRL/lpr) spontaneously develops the hallmark serological markers and peripheral pathologies typifying lupus in addition to displaying the cognitive and affective dysfunction characteristic of NP-SLE, which may be among the earliest symptoms of lupus. We suggest that although NP-SLE may share common mechanisms with peripheral organ pathology in lupus, especially in the latter stages of the disease, the immunologically privileged nature of the CNS indicates that early manifestations of particularly mood disorders maybe derived from some unique mechanisms. These include altered cytokine profiles that can activate astrocytes, microglia, and alter neuronal function before dysregulation of the blood-brain barrier and development of clinical autoantibody titres.

Interleukin-2 deficiency-induced T cell autoimmunity in the mouse brain

Interleukin-2 (IL-2) has been implicated in the pathogenesis of neurodevelopmental and neurodegenerative disorders. Studies from our lab have shown that adult IL-2 knockout (KO) mice exhibit septohippocampal pathology and related behavioral deficits. Compared to IL-2 wild-type (WT) mice, IL-2 KO mice have a marked and selective loss of septal cholinergic neurons that occurs between the third postnatal week and adulthood. Given that the development of septal neurons is completed by embryonic day 17 and that IL-2 KO mice exhibit peripheral autoimmunity that develops progressively post-weaning, our data and others led us to postulate that the loss of septal neurons in adult IL-2 KO mice is due to selective autoimmune neurodegeneration that coincides with increasing levels of peripheral autoimmunity. Thus, the present study tested the hypotheses: (1) that T cells selectively target the septum, and; (2) that T lymphocyte infiltration to the septum would correlate with peripheral autoimmune disease. We quantified CD3(+) T cells in the septum, hippocampus, and cerebellum of IL-2 KO and IL-2 WT mice at ages ranging from 2 to 14 weeks. T cells infiltrated the brains of IL-2 deficient mice, but were not selective for the septum. Brain T lymphocyte levels in IL-2 KO mice correlated positively with the degree of peripheral autoimmunity. We did not detect CD19(+) B lymphocytes, IgG-positive lymphocytes or IgG deposition indicative of autoantibodies in the brains of IL-2 KO mice. Further study is needed to understand how IL-2 deficiency-induced autoimmune T lymphocytes interact with endogenous brain cells to alter function and promote disease.

Proclivity to self-injurious behavior in MRL-lpr mice: implications for autoimmunity-induced damage in the dopaminergic system

Systemic lupus erythematosus is frequently accompanied by psychiatric manifestations of unknown origin. Although damage of central neurons had been documented, little is known about neurotransmitter systems affected by the autoimmune/inflammatory process. Recent studies on lupus-prone MRL-lpr mice point to imbalanced dopamine function and neurodegeneration in dopamine-rich brain regions. We follow up on anecdotal observations of singly housed mice developing chest wounds. Compulsive grooming and/or skin biting accounted for open lesions, lending itself to the operational term 'self-injurious behavior' (SIB). Low incidence of spontaneous SIB increased significantly after repeated injections of dopamine-2/3 receptor (D2/D3R) agonist quinpirole (QNP). To further probe the dopaminergic circuitry and examine whether SIB is associated with development of lupus-like disease, we compared behavioral responses among cohorts that differed in the immune status. Two-week treatment with QNP (intraperitoneal, 0.5 mg kg(-1) body weight per day) induced SIB in 60% of diseased MRL-lpr mice, and exacerbated their splenomegaly. Although increased grooming and stereotypy were observed in less symptomatic MRL+/+ controls, only one mouse (10%) developed SIB. Similarly, SIB was not seen in young, asymptomatic groups despite dissimilar ambulatory responses to QNP. In situ hybridization revealed treatment-independent upregulation of D2R mRNA in substantia nigra of diseased MRL-lpr mice. The above results suggest that development of systemic autoimmunity alters sensitivity of the dopaminergic system and renders MRL-lpr mice prone to SIB. Although pathogenic factors were not examined, we hypothesize that immune and endocrine mechanisms jointly contribute to early neuronal damage, which underlies behavioral deficiency in the adulthood.

Realistic expectations of prepulse inhibition in translational models for schizophrenia research

INTRODUCTION

Under specific conditions, a weak lead stimulus, or "prepulse", can inhibit the startling effects of a subsequent intense abrupt stimulus. This startle-inhibiting effect of the prepulse, termed "prepulse inhibition" (PPI), is widely used in translational models to understand the biology of brainbased inhibitory mechanisms and their deficiency in neuropsychiatric disorders. In 1981, four published reports with "prepulse inhibition" as an index term were listed on Medline; over the past 5 years, new published Medline reports with "prepulse inhibition" as an index term have appeared at a rate exceeding once every 2.7 days (n=678). Most of these reports focus on the use of PPI in translational models of impaired sensorimotor gating in schizophrenia. This rapid expansion and broad application of PPI as a tool for understanding schizophrenia has, at times, outpaced critical thinking and falsifiable hypotheses about the relative strengths vs. limitations of this measure.

OBJECTIVES

This review enumerates the realistic expectations for PPI in translational models for schizophrenia research, and provides cautionary notes for the future applications of this important research tool.

CONCLUSION

In humans, PPI is not "diagnostic"; levels of PPI do not predict clinical course, specific symptoms, or individual medication responses. In preclinical studies, PPI is valuable for evaluating models or model organisms relevant to schizophrenia, "mapping" neural substrates of deficient PPI in schizophrenia, and advancing the discovery and development of novel therapeutics. Across species, PPI is a reliable, robust quantitative phenotype that is useful for probing the neurobiology and genetics of gating deficits in schizophrenia.

Regulation of dopaminergic loss by Fas in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease

Accumulating evidence suggests that apoptotic and inflammatory factors contribute to the demise of dopaminergic neurons. In this respect, Fas, a member of the tumor necrosis factor receptor family with proapoptotic and inflammatory functions, was reported to be elevated within the striatum and substantia nigra pars compacta (SNc) of Parkinson's disease (PD) patients. Accordingly, the present investigation evaluated the function of Fas in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. Injection of MPTP increased nigral Fas expression, and mice lacking Fas displayed attenuated MPTP-induced SNc dopaminergic loss and microglial activation. In addition, Fas induction was blocked by expression of a dominant-negative c-Jun adenovirus that also protected dopamine neurons from MPTP-induced damage. Together, these data suggest the critical nature of the c-Jun-Fas signaling pathway in MPTP-induced neuronal loss. Although critical for degeneration of the soma, Fas deficiency did not significantly prevent the reduction of dopaminergic terminal fibers within the striatum or normalize the activation of striatal microglia and elevation of the postsynaptic activity marker DeltaFosB induced by denervation. Interestingly, Fas-deficient mice displayed a pre-existing reduction in striatal dopamine levels and locomotor behavior when compared with wild-type mice. Despite the reduced terminals, dopamine levels were not further suppressed by MPTP treatment in mutant mice, raising the possibility of a compensatory response in basal ganglia function in Fas-deficient mice.