Th17 cell-mediated neuroinflammation is involved in neurodegeneration of aβ1-42-induced Alzheimer's disease model rats

Adaptive Immunity in Schizophrenia: Functional Implications of T Cells in the Etiology, Course and Treatment

Schizophrenia is a severe and highly complex neurodevelopmental disorder with an unknown etiopathology. Recently, immunopathogenesis has emerged as one of the most compelling etiological models of schizophrenia. Over the past few years considerable research has been devoted to the role of innate immune responses in schizophrenia. The findings of such studies have helped to conceptualize schizophrenia as a chronic low-grade inflammatory disorder. Although the contribution of adaptive immune responses has also been emphasized, however, the precise role of T cells in the underlying neurobiological pathways of schizophrenia is yet to be ascertained comprehensively. T cells have the ability to infiltrate brain and mediate neuro-immune cross-talk. Conversely, the central nervous system and the neurotransmitters are capable of regulating the immune system. Neurotransmitter like dopamine, implicated widely in schizophrenia risk and progression can modulate the proliferation, trafficking and functions of T cells. Within brain, T cells activate microglia, induce production of pro-inflammatory cytokines as well as reactive oxygen species and subsequently lead to neuroinflammation. Importantly, such processes contribute to neuronal injury/death and are gradually being implicated as mediators of neuroprogressive changes in schizophrenia. Antipsychotic drugs, commonly used to treat schizophrenia are also known to affect adaptive immune system; interfere with the differentiation and functions of T cells. This understanding suggests a pivotal role of T cells in the etiology, course and treatment of schizophrenia and forms the basis of this review.

Deleterious versus protective autoimmunity in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disorder of central nervous system, in which myelin specific CD4(+) T cells have a central role in orchestrating pathological events involved in disease pathogenesis. There is compelling evidence that Th1, Th9 and Th17 cells, separately or in cooperation, could mediate deleterious autoimmune response in MS. However, the phenotype differences between Th cell subpopulations initially employed in MS pathogenesis are mainly reflected in the different patterns of inflammation introduction, which results in the development of characteristic pathological features (blood-brain barrier disruption, demyelination and neurodegeneration), clinically presented with MS symptoms. Although, autoimmunity was traditionally seen as deleterious, some studies indicated that autoimmunity mediated by Th2 cells and T regulatory cells could be protective by nature. The concept of protective autoimmunity in MS pathogenesis is still poorly understood, but could be of great importance in better understanding of MS immunology and therefore, creating better therapeutic strategies.

Microbial Sources of Amyloid and Relevance to Amyloidogenesis and Alzheimer's Disease (AD)

Since the inception of the human microbiome project (HMP) by the US National Institutes of Health (NIH) in 2007 there has been a keen resurgence in our recognition of the human microbiome and its contribution to development, immunity, neurophysiology, metabolic and nutritive support to central nervous system (CNS) health and disease. What is not generally appreciated is that (i) the ~1014 microbial cells that comprise the human microbiome outnumber human host cells by approximately one hundred-to-one; (ii) together the microbial genes of the microbiome outnumber human host genes by about one hundred-and-fifty to one; (iii) collectively these microbes constitute the largest 'diffuse organ system' in the human body, more metabolically active than the liver; strongly influencing host nutritive-, innate-immune, neuroinflammatory-, neuromodulatory- and neurotransmission-functions; and (iv) that these microbes actively secrete highly complex, immunogenic mixtures of lipopolysaccharide (LPS) and amyloid from their outer membranes into their immediate environment. While secreted LPS and amyloids are generally quite soluble as monomers over time they form into highly insoluble fibrous protein aggregates that are implicated in the progressive degenerative neuropathology of several common, age-related disorders of the human CNS including Alzheimer's disease (AD). This general commentary-perspective paper will highlight some recent findings on microbial-derived secreted LPS and amyloids and the potential contribution of these neurotoxic and proinflammatory microbial exudates to age-related inflammatory amyloidogenesis and neurodegeneration, with specific reference to AD wherever possible.

Protection of TGF-β1 against neuroinflammation and neurodegeneration in Aβ1-42-induced Alzheimer's disease model rats

Neuroinflammation has been reported to be associated with Alzheimer’s disease (AD) pathogenesis. Neuroinflammation is generally considered as an outcome of glial activation; however, we recently demonstrated that T helper (Th)17 cells, a subpopulation of proinflammatory CD4+ T cells, are also involved in AD pathogenesis. Transforming growth factor (TGF)-β1, a cytokine that can be expressed in the brain, can be immunosuppressive, but its effects on lymphocyte-mediated neuroinflammation in AD pathogenesis have not been well addressed. In the current study we administered TGF-β1 via intracerebroventricle (ICV) and intranasal (IN) routes in AD model rats to investigate its antiinflammatory and neuroprotective effects. The AD rat model was prepared by bilateral hippocampal injection of amyloid-β (Aβ)_1–42. TGF-β1 was administered via ICV one hour prior to Aβ_1–42 injection or via both nares seven days after Aβ_1–42 injection. ICV administration of TGF-β1 before Aβ_1–42 injection remarkably ameliorated Aβ_1–42-induced neurodegeneration and prevented Aβ_1–42-induced increases in glia-derived proinflammatory mediators (TNF-α, IL-1β and iNOS), as well as T cell-derived proinflammatory cytokines (IFN-γ, IL-2, IL-17 and IL-22), in the hypothalamus, serum or cerebrospinal fluid (CSF) in a concentration-dependent manner. TGF-β1 pretreatment also prevented Aβ_1–42-induced decreases in the neurotrophic factors, IGF-1, GDNF and BDNF, and in the antiinflammatory cytokine, IL-10. Similarly, IN administration of TGF-β1 after Aβ_1–42 injection reduced neurodegeneration, elevation of proinflammatory mediators and cytokines, and reduction of neurotrophic and antiinflammatory factors, in the hypothalamus, serum or CSF. These findings suggest that TGF-β1 suppresses glial and T cell-mediated neuroinflammation and thereby alleviates AD-related neurodegeneration. The effectiveness of IN administered TGF-β1 in reducing Aβ_1–42 neurotoxicity suggests a possible therapeutic approach in patients with AD.

T-cell-mediated regulation of neuroinflammation involved in neurodegenerative diseases

Neuroinflammation is involved in several neurodegenerative disorders and emerging evidence indicates that it constitutes a critical process that is required for the progression of neurodegeneration. Microglial activation constitutes a central event in neuroinflammation. Furthermore, microglia can not only be activated with an inflammatory and neurotoxic phenotype (M1-like phenotype), but they also can acquire a neurosupportive functional phenotype (M2-like phenotype) characterised by the production of anti-inflammatory mediators and neurotrophic factors. Importantly, during the past decade, several studies have shown that CD4⁺ T-cells infiltrate the central nervous system (CNS) in many neurodegenerative disorders, in which their participation has a critical influence on the outcome of microglial activation and consequent neurodegeneration. In this review, we focus on the analysis of the interplay of the different sub-populations of CD4⁺ T-cells infiltrating the CNS and how they participate in regulating the outcome of neuroinflammation and neurodegeneration in the context of Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis and multiple sclerosis. In this regard, encephalitogenic inflammatory CD4⁺ T-cells, such as Th1, Th17, GM-CSF-producer CD4⁺ T-cells and γδT-cells, strongly contribute to chronic neuroinflammation, thus perpetuating neurodegenerative processes. In contrast, encephalitogenic or meningeal Tregs and Th2 cells decrease inflammatory functions in microglial cells and promote a neurosupportive microenvironment. Moreover, whereas some neurodegenerative disorders such as multiple sclerosis, Parkinson’s disease and Alzheimer’s disease involve the participation of inflammatory CD4⁺ T-cells 'naturally', the physiopathology of other neurodegenerative diseases, such as amyotrophic lateral sclerosis, is associated with the participation of anti-inflammatory CD4⁺ T-cells that delay the neurodegenerative process. Thus, current evidence supports the hypothesis that the involvement of CD4⁺ T-cells against CNS antigens constitutes a key component in regulating the progression of the neurodegenerative process.

TGF-β1 protection against Aβ1-42-induced neuroinflammation and neurodegeneration in rats

Transforming growth factor (TGF)-β1, a cytokine that can be expressed in the brain, is a key regulator of the brain's responses to injury and inflammation. Alzheimer's disease (AD), the most common neurodegenerative disorder, involves inflammatory processes in the brain in addition to the hallmarks, amyloid-β (Aβ) plaques and neurofibrillary tangles. Recently, we have shown that T-helper (Th) 17 cells, a subpopulation of CD4+ T-cells with high proinflammation, also participate in the brain inflammatory process of AD. However, it is poorly known whether TGF-β1 ameliorates the lymphocyte-mediated neuroinflammation and, thereby, alleviates neurodegeneration in AD. Herein, we administered TGF-β1 via the intracerebroventricle (ICV) in AD model rats, by Aβ1-42 injection in both sides of the hippocampus, to show the neuroprotection of TGF-β1. The TGF-β1 administration after the Aβ1-42 injection ameliorated cognitive deficit and neuronal loss and apoptosis, reduced amyloid precursor protein (APP) expression, elevated protein phosphatase (PP)2A expression, attenuated glial activation and alleviated the imbalance of the pro-inflammatory/anti-inflammatory responses of T-lymphocytes, compared to the Aβ1-42 injection alone. These findings demonstrate that TGF-β1 provides protection against AD neurodegeneration and suggest that the TGF-β1 neuroprotection is implemented by the alleviation of glial and T-cell-mediated neuroinflammation.

Dual destructive and protective roles of adaptive immunity in neurodegenerative disorders

Inappropriate T cell responses in the central nervous system (CNS) affect the pathogenesis of a broad range of neuroinflammatory and neurodegenerative disorders that include, but are not limited to, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. On the one hand immune responses can exacerbate neurotoxic responses; while on the other hand, they can lead to neuroprotective outcomes. The temporal and spatial mechanisms by which these immune responses occur and are regulated in the setting of active disease have gained significant recent attention. Spatially, immune responses that affect neurodegeneration may occur within or outside the CNS. Migration of antigen-specific CD4+ T cells from the periphery to the CNS and consequent immune cell interactions with resident glial cells affect neuroinflammation and neuronal survival. The destructive or protective mechanisms of these interactions are linked to the relative numerical and functional dominance of effector or regulatory T cells. Temporally, immune responses at disease onset or during progression may exhibit a differential balance of immune responses in the periphery and within the CNS. Immune responses with predominate T cell subtypes may differentially manifest migratory, regulatory and effector functions when triggered by endogenous misfolded and aggregated proteins and cell-specific stimuli. The final result is altered glial and neuronal behaviors that influence the disease course. Thus, discovery of neurodestructive and neuroprotective immune mechanisms will permit potential new therapeutic pathways that affect neuronal survival and slow disease progression.

Th17 pathway-mediated immunopathogenesis of schizophrenia: mechanisms and implications

Schizophrenia is a highly complex and severe neuropsychiatric disorder with an unknown etiopathology. Evidence for a dysregulated immune system in both the risk for and progression of schizophrenia has recently been overwhelming. Importantly, chronic low-grade inflammation both in the periphery and central nervous system has been shown to contribute predominantly to the pathogenesis of schizophrenia in a subset of individuals. Inflammation in the central nervous system is mediated by a range of proinflammatory cytokines, resident immune cells such as microglia, and brain infiltrating peripheral immunocompetent cells, such as T lymphocytes. Recently, Th17 cells, a subset of T helper cells have emerged as crucial players in mucosal defense against infections. It is linked to atopic, inflammatory, and autoimmune disorders. The risk factors/mechanisms leading to low-grade inflammation in schizophrenia are diverse and include infectious agents, stress, trauma, environmental toxins, genetic vulnerability, physical inactivity, obesity, poor diet, and sleep disruption. Herein, we propose that fetal programming of cellular immune components driven by intrauterine adversity can lead to the generation of long-lasting effector/memory Th17 cells. Th17 cells can disrupt the blood-brain barrier, infiltrate the central nervous system, and, along with other cytokines and microglia, lead to neuroprogression through neuroinflammation in schizophrenia.

Temporal gene profiling of the 5XFAD transgenic mouse model highlights the importance of microglial activation in Alzheimer's disease

BACKGROUND

The 5XFAD early onset mouse model of Alzheimer's disease (AD) is gaining momentum. Behavioral, electrophysiological and anatomical studies have identified age-dependent alterations that can be reminiscent of human AD. However, transcriptional changes during disease progression have not yet been investigated. To this end, we carried out a transcriptomic analysis on RNAs from the neocortex and the hippocampus of 5XFAD female mice at the ages of one, four, six and nine months (M1, M4, M6, M9).

RESULTS

Our results show a clear shift in gene expression patterns between M1 and M4. At M1, 5XFAD animals exhibit region-specific variations in gene expression patterns whereas M4 to M9 mice share a larger proportion of differentially expressed genes (DEGs) that are common to both regions. Analysis of DEGs from M4 to M9 underlines the predominance of inflammatory and immune processes in this AD mouse model. The rise in inflammation, sustained by the overexpression of genes from the complement and integrin families, is accompanied by an increased expression of transcripts involved in the NADPH oxidase complex, phagocytic processes and IFN-γ related pathways.

CONCLUSIONS

Overall, our data suggest that, from M4 to M9, sustained microglial activation becomes the predominant feature and point out that both detrimental and neuroprotective mechanisms appear to be at play in this model. Furthermore, our study identifies a number of genes already known to be altered in human AD, thus confirming the use of the 5XFAD strain as a valid model for understanding AD pathogenesis and for screening potential therapeutic molecules.

Inflammation in neurodegenerative diseases--an update

Neurodegeneration, the progressive dysfunction and loss of neurons in the central nervous system (CNS), is the major cause of cognitive and motor dysfunction. While neuronal degeneration is well-known in Alzheimer's and Parkinson's diseases, it is also observed in neurotrophic infections, traumatic brain and spinal cord injury, stroke, neoplastic disorders, prion diseases, multiple sclerosis and amyotrophic lateral sclerosis, as well as neuropsychiatric disorders and genetic disorders. A common link between these diseases is chronic activation of innate immune responses including those mediated by microglia, the resident CNS macrophages. Such activation can trigger neurotoxic pathways leading to progressive degeneration. Yet, microglia are also crucial for controlling inflammatory processes, and repair and regeneration. The adaptive immune response is implicated in neurodegenerative diseases contributing to tissue damage, but also plays important roles in resolving inflammation and mediating neuroprotection and repair. The growing awareness that the immune system is inextricably involved in mediating damage as well as regeneration and repair in neurodegenerative disorders, has prompted novel approaches to modulate the immune system, although it remains whether these approaches can be used in humans. Additional factors in humans include ageing and exposure to environmental factors such as systemic infections that provide additional clues that may be human specific and therefore difficult to translate from animal models. Nevertheless, a better understanding of how immune responses are involved in neuronal damage and regeneration, as reviewed here, will be essential to develop effective therapies to improve quality of life, and mitigate the personal, economic and social impact of these diseases.

Neuroantibody biomarkers: links and challenges in environmental neurodegeneration and autoimmunity

The majority of neurodegenerative (ND) and autoimmune diseases (AID) remain idiopathic. The contribution of environmental chemicals to the development of these disorders has become of great interest in recent years. A convergence of mechanism between of ND and AID development has also emerged. In the case of ND, including neurotoxicity, the focus of this review, work over the last two decade in the realm of biomarker development, indicates that the immune response provides a venue whereby humoral immunity, in the form of autoantibodies to nervous system specific proteins, or neuroantibodies (NAb), may provide, once validated, a sensitive high throughput surrogate biomarker of effect with the potential of predicting outcome in absence of overt neurotoxicity/neurodegeneration. In addition, NAb may prove to be a contributor to the progression of the nervous system pathology, as well as biomarker of stage and therapeutic efficacy. There is a compelling need for biomarkers of effect in light of the introduction of new chemicals, such as nanoengineered material, where potential neurotoxicity remains to be defined. Furthermore, the convergence of mechanisms associated with ND and AID draws attention to the neglected arena of angiogenesis in defining the link between environment, ND, and AID.

Glia maturation factor deficiency suppresses 1-methyl-4-phenylpyridinium-induced oxidative stress in astrocytes

Inflammation is closely intertwined with pathogenesis of Parkinson's disease (PD). Increasing evidence suggests that inhibition of glia-mediated inflammation might represent a promising therapeutic target for PD. Glia maturation factor (GMF), an inflammatory protein, predominantly localized in astrocytes is previously isolated, sequenced and cloned in our laboratory. In the present investigation, we demonstrate that GMF-deficiency in astrocytes upregulates the antioxidant status and limit the extent of lipid peroxidation and production of reactive oxygen species (ROS) along with diminished nuclear factor-κB-mediated inflammatory responses in 1-methyl-4-phenylpyridinium (MPP(+))-induced toxicity. Primary astrocytes obtained from wild-type (Wt) and GMF-deficient (GMF-KO) mice were treated with 5, 10, and 20 μM MPP(+) for 24, 48, and 72 h in vitro. Our results show decreased release of ROS and increased level of glutathione in astrocytes obtained from GMF-KO mice when compared to astrocytes derived from Wt mice following MPP(+) treatment. Additionally, we found decreased activity of NF-κB, and reduced levels of proinflammatory tumor necrosis factor- α, interleukin-1β (IL-1β), IL-17, IL-33, and chemokine (C-C motif) ligand 2 (CCL2) in GMF-KO astrocytes when compared to Wt astrocytes. Our overall results suggest that GMF-KO astrocytes are significantly resistant to MPP(+) toxicity when compared to Wt astrocytes.