Microglial cell-derived interleukin-6 influences behavior and inflammatory response in the brain following traumatic brain injury.

Traumatic brain injury (TBI) is a major health problem with high rates of mortality and morbidity worldwide. The response of the brain to TBI is orchestrated by a number of cytokines, including interleukin-6 (IL-6). IL-6 is a major cytokine in the central nervous system and it is produced by different cells, such as neurons, glial cells, and endothelial cells. Since glial cells are one of the most important sources and targets of IL-6, we have examined the role of microglia-derived IL-6 in normal conditions and following a model of TBI, cryolesion of the somatosensorial cortex. To this end, tamoxifen-inducible microglial IL-6-deficient (Il6ΔMic , using Cx3cr1 CreER model) mice and control (Il6lox/lox ) mice were used. In normal conditions, microglial IL-6 deficiency reduced deambulation and exploratory behavior and decreased anxiety in a sex-dependent manner. The transcriptome profile following cryolesion was dramatically altered 1 day post-lesion in Il6ΔMic compared with Il6lox/lox mice. However, the phenotype of Il6ΔMic mice was less compromised in the following days, suggesting that compensatory mechanisms are at play.

A new mouse model to study restoration of interleukin-6 (IL-6) expression in a Cre-dependent manner: microglial IL-6 regulation of experimental autoimmune encephalomyelitis.

BACKGROUND: Interleukin-6 (IL-6) is a pleiotropic cytokine that controls numerous physiological processes both in basal and neuroinflammatory conditions, including the inflammatory response to experimental autoimmune encephalomyelitis (EAE). IL-6 is produced by multiple peripheral and central cells, and until now, the putative roles of IL-6 from different cell types have been evaluated through conditional cell-specific IL-6 knockout mice. Nevertheless, these mice probably undergo compensatory responses of IL-6 from other cells, which makes it difficult to assess the role of each source of IL-6. METHODS: To give some insight into this problem, we have produced a novel mouse model: a conditional reversible IL-6 KO mouse (IL6-DIO-KO). By using double-inverted, open-reading-frame (DIO) technology, we created a mouse line with the loss of Il6 expression in all cells that can be restored by the action of Cre recombinase. Since microglia are one of the most important sources and targets of IL-6 into the central nervous system, we have recovered microglial Il6 expression in IL6-DIO-KO mice through breeding to Cx3cr1-CreER mice and subsequent injection of tamoxifen (TAM) when mice were 10-16 weeks old. Then, they were immunized with myelin oligodendrocyte glycoprotein 35-55 peptide (MOG35-55) 7 weeks after TAM treatment to induce EAE. Clinical symptoms and demyelination, CD3 infiltration, and gliosis in the spinal cord were evaluated. RESULTS: IL6-DIO-KO mice were resistant to EAE, validating the new model. Restoration of microglial Il6 was sufficient to develop a mild version of EAE-related clinical symptoms and neuropathology. CONCLUSIONS: IL6-DIO-KO mouse is an excellent model to understand in detail the role of specific cellular sources of IL-6 within a recovery-of-function paradigm in EAE.

IL-6 trans-signaling in the brain influences the behavioral and physio-pathological phenotype of the Tg2576 and 3xTgAD mouse models of Alzheimer's disease.

Alzheimer's disease (AD) is the most commonly diagnosed dementia but its underlying pathological mechanisms still unclear. Neuroinflammation and secretion of cytokines such as interleukin-6 (IL-6) accompany the main hallmarks of the disease: amyloid plaques and neurofibrillary tangles. In this study, we analyzed the role of IL-6 trans-signaling in two mouse models of AD, Tg2576 and 3xTg-AD mice. The inhibition of IL-6 trans-signaling partially rescued the AD-induced mortality in females of both models. Before amyloid plaques deposition, it reversed AD-induced changes in exploration and anxiety (but did not affect locomotion) in Tg2576 female mice. However, after plaque deposition the only behavioral trait affected by the inhibition of IL-6 trans-signaling was locomotion. Results in the Morris water maze suggest that cognitive flexibility was reduced by the blocking of the IL-6 trans-signaling in young and old Tg2576 female mice. The inhibition of IL-6 trans-signaling also decreased amyloid plaque burden in cortex and hippocampus, and Aß40 and Aß42 levels in the cortex, of Tg2576 female mice. The aforementioned changes might be correlated with changes in blood vessels and matrix structure and organization rather than changes in neuroinflammation. 3xTgAD mice showed a very mild phenotype regarding amyloid cascade, but results were in accordance with those of Tg2576 mice. These results strongly suggest that the inhibition of the IL-6 trans-signaling could represent a powerful therapeutic target in AD.

Influence of Transgenic Metallothionein-1 on Gliosis, CA1 Neuronal Loss, and Brain Metal Levels of the Tg2576 Mouse Model of Alzheimer's Disease.

The mouse model of Alzheimer's disease (AD), Tg2576 mice (APP), has provided valuable information, such as the role of the metallothionein (MT) family in their behavioral and amyloidosis phenotypes. In this study, we further characterize the role of MT-1 by crossing Mt1-overexpressing mice with Tg2576 mice (APPTgMT). In 14-month-old mice, MT-1(/2) protein levels were dramatically increased by Mt1 overexpression throughout the cortex (Cx), which showed a prominent caudal-rostral gradient, and the hippocampus (HC). There was a trend for MT-1(/2) immunostaining to be increased in the areas surrounding the amyloid plaques in control male mice but not in Mt1-overexpressing mice. Gliosis was elicited by the amyloid plaques, but the effects of Mt1 overexpression were modest. However, in hippocampal western blots the microglial marker Iba-1 was increased in old male APPTgMT mice compared to APP-wild type (APPWT) mice, and the opposite was observed in young mice. Hippocampal CA1 neuronal loss was observed in Tg2576 mice, but was unaffected by Mt1 overexpression. Aging increased Zn and Cu levels differently depending on brain area, sex, and genotype. Thus, the effects of Mt1 overexpression on the phenotype of Tg2576 mice here studied are modest.

Interleukin-6 Derived from the Central Nervous System May Influence the Pathogenesis of Experimental Autoimmune Encephalomyelitis in a Cell-Dependent Manner.

BACKGROUND: Interleukin-6 (IL-6) is a pleiotropic and multifunctional cytokine that plays a critical role in induction of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis (MS). Although EAE has always been considered a peripherally elicited disease, Il6 expression exclusively within central nervous system is sufficient to induce EAE development. Neurons, astrocytes, and microglia can secrete and respond to IL-6. METHODS: To dissect the relevance of each cell source for establishing EAE, we generated and immunized conditional Il6 knockout mice for each of these cell types with myelin oligodendrocyte glycoprotein 35-55 (MOG35-55) peptide dissolved in complete Freund's adjuvant (CFA) and supplemented with Mycobacterium tuberculosis. RESULTS AND CONCLUSIONS: The combined results reveal a minor role for Il6 expression in both astrocytes and microglia for symptomatology and neuropathology of EAE, whereas neuronal Il6 expression was not relevant for the variables analyzed.

IL-6 Trans-Signaling in the Brain Influences the Metabolic Phenotype of the 3xTg-AD Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder that causes the most prevalent dementia in the elderly people. Obesity and insulin resistance, which may cause major health problems per se, are risk factors for AD, and cytokines such as interleukin-6 (IL-6) have a role in these conditions. IL-6 can signal either through a membrane receptor or by trans-signaling, which can be inhibited by the soluble form of the co-receptor gp130 (sgp130). We have addressed the possibility that blocking IL-6 trans-signaling in the brain could have an effect in the triple transgenic 3xTg-AD mouse model of AD and/or in obesity progression, by crossing 3xTg-AD mice with GFAP-sgp130Fc mice. To serve as control groups, GFAP-sgp130Fc mice were also crossed with C57BL/6JOlaHsd mice. Seventeen-month-old mice were fed a control diet (18% kcal from fat) and a high-fat diet (HFD; 58.4% kcal from fat). In our experimental conditions, the 3xTg-AD model showed a mild amyloid phenotype, which nevertheless altered the control of body weight and related endocrine and metabolic factors, suggestive of a hypermetabolic state. The inhibition of IL-6 trans-signaling modulated some of these traits in both 3xTg-AD and control mice, particularly during HFD, and in a sex-dependent manner. These experiments provide evidence of IL-6 trans-signaling playing a role in the CNS of a mouse model of AD.