Peroxisome proliferator-activated receptor-gamma agonists prevent experimental autoimmune encephalomyelitis

Defining a vitamin A5/X specific deficiency - vitamin A5/X as a critical dietary factor for mental health

A healthy and balanced diet is an important factor to assure a good functioning of the central and peripheral nervous system. Retinoid X receptor (RXR)-mediated signaling was identified as an important mechanism of transmitting major diet-dependent physiological and nutritional signaling such as the control of myelination and dopamine signalling. Recently, vitamin A5/X, mainly present in vegetables as provitamin A5/X, was identified as a new concept of a vitamin which functions as the nutritional precursor for enabling RXR-mediated signaling. The active form of vitamin A5/X, 9-cis-13,14-dehydroretinoic acid (9CDHRA), induces RXR-activation, thereby acting as the central switch for enabling various heterodimer-RXR-signaling cascades involving various partner heterodimers like the fatty acid and eicosanoid receptors/peroxisome proliferator-activated receptors (PPARs), the cholesterol receptors/liver X receptors (LXRs), the vitamin D receptor (VDR), and the vitamin A(1) receptors/retinoic acid receptors (RARs). Thus, nutritional supply of vitamin A5/X might be a general nutritional-dependent switch for enabling this large cascade of hormonal signaling pathways and thus appears important to guarantee an overall organism homeostasis. RXR-mediated signaling was shown to be dependent on vitamin A5/X with direct effects for beneficial physiological and neuro-protective functions mediated systemically or directly in the brain. In summary, through control of dopamine signaling, amyloid β-clearance, neuro-protection and neuro-inflammation, the vitamin A5/X - RXR - RAR - vitamin A(1)-signaling might be "one of" or even "the" critical factor(s) necessary for good mental health, healthy brain aging, as well as for preventing drug addiction and prevention of a large array of nervous system diseases. Likewise, vitamin A5/X - RXR - non-RAR-dependent signaling relevant for myelination/re-myelination and phagocytosis/brain cleanup will contribute to such regulations too. In this review we discuss the basic scientific background, logical connections and nutritional/pharmacological expert recommendations for the nervous system especially considering the ageing brain.

Smouldering Lesion in MS: Microglia, Lymphocytes and Pathobiochemical Mechanisms

Multiple sclerosis (MS) is an immune-mediated, chronic inflammatory, demyelinating, and neurodegenerative disease of the central nervous system (CNS). Immune cell infiltration can lead to permanent activation of macrophages and microglia in the parenchyma, resulting in demyelination and neurodegeneration. Thus, neurodegeneration that begins with acute lymphocytic inflammation may progress to chronic inflammation. This chronic inflammation is thought to underlie the development of so-called smouldering lesions. These lesions evolve from acute inflammatory lesions and are associated with continuous low-grade demyelination and neurodegeneration over many years. Their presence is associated with poor disease prognosis and promotes the transition to progressive MS, which may later manifest clinically as progressive MS when neurodegeneration exceeds the upper limit of functional compensation. In smouldering lesions, in the presence of only moderate inflammatory activity, a toxic environment is clearly identifiable and contributes to the progressive degeneration of neurons, axons, and oligodendrocytes and, thus, to clinical disease progression. In addition to the cells of the immune system, the development of oxidative stress in MS lesions, mitochondrial damage, and hypoxia caused by the resulting energy deficit and iron accumulation are thought to play a role in this process. In addition to classical immune mediators, this chronic toxic environment contains high concentrations of oxidants and iron ions, as well as the excitatory neurotransmitter glutamate. In this review, we will discuss how these pathobiochemical markers and mechanisms, alone or in combination, lead to neuronal, axonal, and glial cell death and ultimately to the process of neuroinflammation and neurodegeneration, and then discuss the concepts and conclusions that emerge from these findings. Understanding the role of these pathobiochemical markers would be important to gain a better insight into the relationship between the clinical classification and the pathomechanism of MS.

Nuclear hormone receptors in demyelinating diseases

Demyelination results from the pathological loss of myelin and is a hallmark of many neurodegenerative diseases. Despite the prevalence of demyelinating diseases, there are no disease modifying therapies that prevent the loss of myelin or promote remyelination. This review aims to summarize studies in the field that highlight the importance of nuclear hormone receptors in the promotion and maintenance of myelination and the relevance of nuclear hormone receptors as potential therapeutic targets for demyelinating diseases. These nuclear hormone receptors include the estrogen receptor, progesterone receptor, androgen receptor, vitamin D receptor, thyroid hormone receptor, peroxisome proliferator-activated receptor, liver X receptor, and retinoid X receptor. Pre-clinical studies in well-established animal models of demyelination have shown a prominent role of these nuclear hormone receptors in myelination through their promotion of oligodendrocyte maturation and development. The activation of the nuclear hormone receptors by their ligands also promotes the synthesis of myelin proteins and lipids in mouse models of demyelination. There are limited clinical studies that focus on how the activation of these nuclear hormone receptors could alleviate demyelination in patients with diseases such as multiple sclerosis (MS). However, the completed clinical trials have reported improved clinical outcome in MS patients treated with the ligands of some of these nuclear hormone receptors. Together, the positive results from both clinical and pre-clinical studies point to nuclear hormone receptors as promising therapeutic targets to counter demyelination.

A Narrative Review on Axonal Neuroprotection in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) resulting in demyelination and neurodegeneration. The therapeutic strategy is now largely based on reducing inflammation with immunosuppressive drugs. Unfortunately, when disease progression is observed, no drug offers neuroprotection apart from its anti-inflammatory effect. In this review, we explore current knowledge on the assessment of neurodegeneration in MS and look at putative targets that might prove useful in protecting the axon from degeneration. Among them, Bruton's tyrosine kinase inhibitors, anti-apoptotic and antioxidant agents, sex hormones, statins, channel blockers, growth factors, and molecules preventing glutamate excitotoxicity have already been studied. Some of them have reached phase III clinical trials and carry a great message of hope for our patients with MS.

Pioglitazone rescues high-fat diet-induced depression-like phenotypes and hippocampal astrocytic deficits in mice

The prevalence of diabetes is rapidly increasing worldwide and is highly associated with the incidence of depression. Pioglitazone, a Peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist, is widely used for treating patients with type 2 diabetes. However, whether pioglitazone alleviates metabolic disorder-related depression and astrocytic deficits remains unclear. Here we showed that 12 weeks of high-fat diet (HFD) feeding (from 8- to 20-week-old) induced not only obesity and insulin resistance, but also depression-like behaviors in mice. Astrocytic activation, a sign closely associated with depression, was also evident in the ventral hippocampus. Four weeks of pioglitazone (10 or 20 mg/kg, daily, from 20- to 24-week-old) treatment alleviated the HFD-induced glucose-metabolic dysfunctions, upregulation of ventral hippocampal GFAP, reduction of the total process lengths and the number of branch points of the ventral hippocampal CA1 GFAP-immunoreactive astrocytes and depressive phenotypes but had no effect on anxiety-like behaviors or hippocampus-related learning and memory in mice. These findings suggest that pioglitazone could be a potential therapeutic agent for metabolic disorders and associated depression.

Cross-Linking Cellular Prion Protein Induces Neuronal Type 2-Like Hypersensitivity

Background

Previous reports identified proteins associated with ‘apoptosis’ following cross-linking PrP^C with motif-specific anti-PrP antibodies in vivo and in vitro. The molecular mechanisms underlying this IgG-mediated neurotoxicity and the role of the activated proteins in the apoptotic pathways leading to neuronal death has not been properly defined. Previous reports implicated a number of proteins, including apolipoprotein E, cytoplasmic phospholipase A2, prostaglandin and calpain with anti-PrP antibody-mediated ‘apoptosis’, however, these proteins are also known to play an important role in allergy. In this study, we investigated whether cross-linking PrP^C with anti-PrP antibodies stimulates a neuronal allergenic response.

Methods

Initially, we predicted the allergenicity of the epitope sequences associated with ‘neurotoxic’ anti-PrP antibodies using allergenicity prediction servers. We then investigated whether anti-PrP antibody treatment of mouse primary neurons (MPN), neuroblastoma cells (N2a) and microglia (N11) cell lines lead to a neuronal allergenic response.

Results

In-Silico studies showed that both tail- and globular-epitopes were allergenic. Specifically, binding regions that contain epitopes for previously reported ‘neurotoxic’ antibodies such as ICSM18 (146-159), ICSM35 (91-110), POM 1 (138-147) and POM 3 (95-100) lead to activation of allergenic related proteins. Following direct application of anti-PrP^C antibodies on N2a cells, we identified 4 neuronal allergenic-related proteins when compared with untreated cells. Furthermore, we identified 8 neuronal allergenic-related proteins following treatment of N11 cells with anti-PrP^C antibodies prior to co-culture with N2a cells when compared with untreated cells. Antibody treatment of MPN or MPN co-cultured with antibody-treated N11 led to identifying 10 and 7 allergenic-related proteins when compared with untreated cells. However, comparison with 3F4 antibody treatment revealed 5 and 4 allergenic-related proteins respectively. Of importance, we showed that the allergenic effects triggered by the anti-PrP antibodies were more potent when antibody-treated microglia were co-cultured with the neuroblastoma cell line. Finally, co-culture of N2a or MPN with N11-treated with anti-PrP antibodies resulted in significant accumulation of NO and IL6 but not TNF-α in the cell culture media supernatant.

Conclusions

This study showed for the first time that anti-PrP antibody binding to PrP^C triggers a neuronal hypersensitivity response and highlights the important role of microglia in triggering an IgG-mediated neuronal hypersensitivity response. Moreover, this study provides an important impetus for including allergenic assessment of therapeutic antibodies for neurodegenerative disorders to derive safe and targeted biotherapeutics.

Targeting Nuclear Receptors in Neurodegeneration and Neuroinflammation

Nuclear receptors, also known as ligand-activated transcription factors, regulate gene expression upon ligand signals and present as attractive therapeutic targets especially in chronic diseases. Despite the therapeutic relevance of some nuclear receptors in various pathologies, their potential in neurodegeneration and neuroinflammation is insufficiently established. This perspective gathers preclinical and clinical data for a potential role of individual nuclear receptors as future targets in Alzheimer's disease, Parkinson's disease, and multiple sclerosis, and concomitantly evaluates the level of medicinal chemistry targeting these proteins. Considerable evidence suggests the high promise of ligand-activated transcription factors to counteract neurodegenerative diseases with a particularly high potential of several orphan nuclear receptors. However, potent tools are lacking for orphan receptors, and limited central nervous system exposure or insufficient selectivity also compromises the suitability of well-studied nuclear receptor ligands for functional studies. Medicinal chemistry efforts are needed to develop dedicated high-quality tool compounds for the therapeutic validation of nuclear receptors in neurodegenerative pathologies.

The brain penetrant PPARγ agonist leriglitazone restores multiple altered pathways in models of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD), a potentially fatal neurometabolic disorder with no effective pharmacological treatment, is characterized by clinical manifestations ranging from progressive spinal cord axonopathy [adrenomyeloneuropathy (AMN)] to severe demyelination and neuroinflammation (cerebral ALD-cALD), for which molecular mechanisms are not well known. Leriglitazone is a recently developed brain penetrant full PPARγ agonist that could modulate multiple biological pathways relevant for neuroinflammatory and neurodegenerative diseases, and particularly for X-ALD. We found that leriglitazone decreased oxidative stress, increased adenosine 5'-triphosphate concentration, and exerted neuroprotective effects in primary rodent neurons and astrocytes after very long chain fatty acid-induced toxicity simulating X-ALD. In addition, leriglitazone improved motor function; restored markers of oxidative stress, mitochondrial function, and inflammation in spinal cord tissues from AMN mouse models; and decreased the neurological disability in the EAE neuroinflammatory mouse model. X-ALD monocyte-derived patient macrophages treated with leriglitazone were less skewed toward an inflammatory phenotype, and the adhesion of human X-ALD monocytes to brain endothelial cells decreased after treatment, suggesting the potential of leriglitazone to prevent the progression to pathologically disrupted blood-brain barrier. Leriglitazone increased myelin debris clearance in vitro and increased myelination and oligodendrocyte survival in demyelination-remyelination in vivo models, thus promoting remyelination. Last, leriglitazone was clinically tested in a phase 1 study showing central nervous system target engagement (adiponectin increase) and changes on inflammatory biomarkers in plasma and cerebrospinal fluid. The results of our study support the use of leriglitazone in X-ALD and, more generally, in other neuroinflammatory and neurodegenerative conditions.

Neurodegeneration in Multiple Sclerosis: Symptoms of Silent Progression, Biomarkers and Neuroprotective Therapy-Kynurenines Are Important Players

Neurodegeneration is one of the driving forces behind the pathogenesis of multiple sclerosis (MS). Progression without activity, pathopsychological disturbances (cognitive impairment, depression, fatigue) and even optic neuropathy seems to be mainly routed in this mechanism. In this article, we aim to give a comprehensive review of the clinical aspects and symptomology, radiological and molecular markers and potential therapeutic targets of neurodegeneration in connection with MS. As the kynurenine pathway (KP) was evidenced to play an important role in the pathogenesis of other neurodegenerative conditions (even implied to have a causative role in some of these diseases) and more and more recent evidence suggest the same central role in the neurodegenerative processes of MS as well, we pay special attention to the KP. Metabolites of the pathway are researched as biomarkers of the disease and new, promising data arising from clinical evaluations show the possible therapeutic capability of KP metabolites as neuroprotective drugs in MS. Our conclusion is that the kynurenine pathway is a highly important route of research both for diagnostic and for therapeutic values and is expected to yield concrete results for everyday medicine in the future.

Guggulsterone ameliorates ethidium bromide-induced experimental model of multiple sclerosis via restoration of behavioral, molecular, neurochemical and morphological alterations in rat brain

Multiple Sclerosis (MS) is a progressive neurodegenerative disease with clinical signs of neuroinflammation and the central nervous system's demyelination. Numerous studies have identified the role of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) overexpression and the low level of peroxisome proliferator-activated receptor-gamma (PPAR-γ) in MS pathogenesis. Guggulsterone (GST), an active component derived from 'Commiphora Mukul,' has been used to treat various diseases. Traditional uses indicate that GST is a suitable agent for anti-inflammatory action. Therefore, we assessed the therapeutic potential of GST (30 and 60 mg/kg) in ethidium bromide (EB) induced demyelination in experimental rats and investigated the molecular mechanism by modulating the JAK/STAT and PPAR-γ receptor signaling. Wistar rats were randomly divided into six groups (n = 6). EB (0.1%/10 μl) was injected selectively in the intracerebropeduncle (ICP) region for seven days to cause MS-like manifestations. The present study reveals that long-term administration of GST for 28 days has a neuroprotective effect by improving behavioral deficits (spatial cognition memory, grip, and motor coordination) associated with lower STAT-3 levels. While elevating PPAR-γ and myelin basic protein levels in rat brains are consistent with the functioning of both signaling pathways. Also, GST modulates the neurotransmitter level by increasing Ach, dopamine, serotonin and by reducing glutamate. Moreover, GST ameliorates inflammatory cytokines (TNF, IL-1β), and oxidative stress markers (AchE, SOD, catalase, MDA, GSH, nitrite). In addition, GST prevented apoptosis, as demonstrated by the reduction of caspase-3 and Bax. Simultaneously, Bcl-2 elevation and the restoration of gross morphology alterations are also recovered by long-term GST treatment. Therefore, it can be concluded that GST may be a potential alternative drug candidate for MS-related motor neuron dysfunctions.

Regulation of Proinflammatory Enzymes by Peroxisome Proliferator-Activated Receptor Gamma in Astroglia Infected with Toxoplasma gondii

Peroxisome proliferator-activated receptor gamma (PPARγ) regulates neuroinflammation, and its agonists act as neuroprotective agents. This study aims to investigate the correlation between PPARγ and proinflammatory enzyme expression in astroglia infected with Toxoplasma gondii tachyzoite in vitro. Our results showed that matrix metalloprotease (MMP)-2, MMP-9, cyclooxygenase-2 (COX-2), prostaglandin (PGE)-2, inducible nitric-oxide synthase (iNOS), and nitric oxide (NO) were significantly increased in T. gondii-infected astroglia. Furthermore, the expression levels of MMP-2, MMP-9, COX-2, PGE-2, iNOS, and NO were significantly decreased by rosiglitazone-a PPARγ agonist. By contrast, the treatment with GW9662, a PPARγ antagonist, efficiently increased the expression levels of MMP-2, MMP-9, COX-2, PGE-2, iNOS, and NO. These results suggested that the treatment with rosiglitazone offers a potential strategy for controlling the inflammatory factors in T. gondii infection.

Regulation of the germinal center response by nuclear receptors and implications for autoimmune diseases

The immune system plays an essential role in protecting the host from infectious diseases and cancer. Notably, B and T lymphocytes from the adaptive arm of the immune system can co-operate to form long-lived antibody responses and are therefore the main target in vaccination approaches. Nevertheless, protective immune responses must be tightly regulated to avoid hyper-responsiveness and responses against self that can result in autoimmunity. Nuclear receptors (NRs) are perfectly adapted to rapidly alter transcriptional cellular responses to altered environmental settings. Their functional role is associated with both immune deficiencies and autoimmunity. Despite extensive linking of nuclear receptor function with specific CD4 T helper subsets, research on the functional roles and mechanisms of specific NRs in CD4 follicular T helper cells (Tfh) and germinal center (GC) B cells during the germinal center reaction is just emerging. We review recent advances in our understanding of NR regulation in specific cell types of the GC response and discuss their implications for autoimmune diseases such as systemic lupus erythematosus (SLE).

Pioglitazone-Mediated Peroxisome Proliferator-Activated Receptor γ Activation Aggravates Murine Immune-Mediated Hepatitis

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) regulates target gene expression upon ligand binding. Apart from its effects on metabolism, PPARγ activity can inhibit the production of pro-inflammatory cytokines by several immune cells, including dendritic cells and macrophages. In chronic inflammatory disease models, PPARγ activation delays the onset and ameliorates disease severity. Here, we investigated the effect of PPARγ activation by the agonist Pioglitazone on the function of hepatic immune cells and its effect in a murine model of immune-mediated hepatitis. Cytokine production by both liver sinusoidal endothelial cells (IL-6) and in T cells ex vivo (IFNγ) was decreased in cells from Pioglitazone-treated mice. However, PPARγ activation did not decrease pro-inflammatory tumor necrosis factor alpha TNFα production by Kupffer cells after Toll-like receptor (TLR) stimulation ex vivo. Most interestingly, although PPARγ activation was shown to ameliorate chronic inflammatory diseases, it did not improve hepatic injury in a model of immune-mediated hepatitis. In contrast, Pioglitazone-induced PPARγ activation exacerbated D-galactosamine (GalN)/lipopolysaccharide (LPS) hepatitis associated with an increased production of TNFα by Kupffer cells and increased sensitivity of hepatocytes towards TNFα after in vivo Pioglitazone administration. These results unravel liver-specific effects of Pioglitazone that fail to attenuate liver inflammation but rather exacerbate liver injury in an experimental hepatitis model.

Peroxisome proliferator-activated receptor gamma participates in the acquisition of brain ischemic tolerance induced by ischemic preconditioning via glial glutamate transporter 1 in vivo and in vitro

Glial glutamate transporter 1 (GLT-1) plays a vital role in the induction of brain ischemic tolerance (BIT) by ischemic preconditioning (IPC). However, the mechanism still needs to be further explained. The aim of this study was to investigate whether peroxisome proliferator-activated receptor gamma (PPARγ) participates in regulating GLT-1 during the acquisition of BIT induced by IPC. Initially, cerebral IPC induced BIT and enhanced PPARγ and GLT-1 expression in the CA1 hippocampus in rats. The ratio of nuclear/cytoplasmic PPARγ was also increased. At the same time, the up-regulation of PPARγ expression in astrocytes in the CA1 hippocampus was revealed by double immunofluorescence for PPARγ and glial fibrillary acidic protein. Then, the mechanism by which PPARγ regulates GLT-1 was studied in rat cortical astrocyte-neuron cocultures. We found that IPC [45 min of oxygen glucose deprivation (OGD)] protected neuronal survival after lethal OGD (4 h of OGD), which usually leads to neuronal death. The activation of PPARγ occurred earlier than the up-regulation of GLT-1 in astrocytes after IPC, as determined by western blot and immunofluorescence. Moreover, the preadministration of the PPARγ antagonist T0070907 or PPARγ siRNA significantly attenuated GLT-1 up-regulation and the neuroprotective effects induced by IPC in vitro. Finally, the effect of the PPARγ antagonist on GLT-1 expression and BIT was verified in vivo. We observed that the preadministration of T0070907 by intracerebroventricular injection dose-dependently attenuated the up-regulation of GLT-1 and BIT induced by cerebral IPC in rats. In conclusion, PPARγ participates in regulating GLT-1 during the acquisition of BIT induced by IPC. Cover Image for this issue: doi: 10.1111/jnc.14532. Open Science: This manuscript was awarded with the Open Materials Badge For more information see: https://cos.io/our-services/open-science-badges/.

Deciphering targets of Th17 cells fate: From metabolism to nuclear receptors

Evidence indicates that reprogramming of metabolism is critically important for the differentiation of CD4 + T lymphocytes, and the manipulation of metabolic pathways in these cells may shape their fate and function. Distinct subgroups from T lymphocytes, such as Th17, adopt specific metabolic programmes to support their needs. Some important metabolic reactions, such as glycolysis, oxidative phosphorylation, are considered important for the differentiation of these lymphocytes. Since their discovery nearly a decade ago, Th17 lymphocytes have received significant attention because of their role in the pathology of several immune-mediated inflammatory diseases such as multiple sclerosis. In this review, it will be discussed as the involvement of T cell metabolism and as metabolic reprogramming in activated T cells dictates fate decisions to Th17. The involvement of nuclear receptors such as RORyt e PPARs in the induction of Th17 cells was also discussed. Understanding the metabolic pathways involved in the differentiation of the distinct subgroups of T lymphocytes helps in the design of promising therapeutic proposals.

Simvastatin exerts antidepressant-like activity in mouse forced swimming test: Role of NO-cGMP-KATP channels pathway and PPAR-gamma receptors

Simvastatin, one of the lipophilic statins, has been shown to be effective in reducing depression in rodents. The present study aimed to investigate the potential antidepressant-like activity of simvastatin and the possible involvement of NO-cGMP-K_ATP channels pathway and PPARγ using forced swimming test (FST) in mice. In addition, the interaction between simvastatin and fluoxetine as a reference drug was examined. After assessment of locomotor behavior in the open-field test (OFT), FST was applied for evaluation of depressive behavior in mice. Simvastatin at doses (20, 30, and 40 mg/kg, i.p.) was administrated 30 min before the OFT or FST. To evaluate the involvement of NO-cGMP-K_ATP channels pathway, mice were pre-treated intraperitoneally with l-arginine (a nitric oxide precursor, 750 mg/kg), L-NAME (a NOS inhibitor, 10 mg/kg), methylene blue (guanylyl cyclase inhibitor, 20 mg/kg), sildenafil (a PDE-5 inhibitor, 5 mg/kg), glibenclamide (ATP-sensitive K⁺ channel blocker, 1 mg/kg), and diazoxide (K⁺ channels opener, 10 mg/kg). Moreover, to clarify the probable involvement of PPARγ receptors, pioglitazone, a PPARγ agonist (5 mg/kg, i.p.), and GW9662, a PPARγ antagonist (2 mg/kg, i.p.), were pre-treated with simvastatin. Immobility time was significantly decreased after simvastatin injection. Administration of L-NAME, methylene blue, glibenclamide and pioglitazone in combination with the sub-effective dose of simvastatin (20 mg/kg, i.p.) reduced the immobility time in the FST compared to drugs alone, while co-administration of effective doses of simvastatin (30 mg/kg, i.p.) with l-arginine, sildenafil, diazoxide, and GW9662 prevented the antidepressant-like effect of simvastatin. In addition, simvastatin (20 mg/kg) potentiated the antidepressant-like effect of fluoxetine through the NO pathway. None of the drugs produced any significant alterations in locomotor activity using OFT. These results demonstrated that NO-cGMP-K_ATP channels pathway and PPARγ receptors may be involved in the antidepressant-like effect of simvastatin.

Molecular Control of Oligodendrocyte Development

Myelin is a multilayer lipid membrane structure that wraps and insulates axons, allowing for the efficient propagation of action potentials. During developmental myelination of the central nervous system (CNS), oligodendrocyte progenitor cells (OPCs) proliferate and migrate to their final destination, where they terminally differentiate into mature oligodendrocytes and myelinate axons. Lineage progression and terminal differentiation of oligodendrocyte lineage cells are under tight transcriptional and post-transcriptional control. The characterization of several recently identified regulatory factors that govern these processes, which are the focus of this review, has greatly increased our understanding of oligodendrocyte development and function. These insights are critical to facilitate efforts to enhance OPC differentiation in neurological disorders that disrupt CNS myelin.

Exploiting the Therapeutic Potential of Endogenous Immunomodulatory Systems in Multiple Sclerosis-Special Focus on the Peroxisome Proliferator-Activated Receptors (PPARs) and the Kynurenines

Multiple sclerosis (MS) is a progressive neurodegenerative disease, characterized by autoimmune central nervous system (CNS) demyelination attributable to a disturbed balance between encephalitic T helper 1 (Th1) and T helper 17 (Th17) and immunomodulatory regulatory T cell (Treg) and T helper 2 (Th2) cells, and an alternatively activated macrophage (M2) excess. Endogenous molecular systems regulating these inflammatory processes have recently been investigated to identify molecules that can potentially influence the course of the disease. These include the peroxisome proliferator-activated receptors (PPARs), PPARγ coactivator-1alpha (PGC-1α), and kynurenine pathway metabolites. Although all PPARs ameliorate experimental autoimmune encephalomyelitis (EAE), recent evidence suggests that PPARα, PPARβ/δ agonists have less pronounced immunomodulatory effects and, along with PGC-1α, are not biomarkers of neuroinflammation in contrast to PPARγ. Small clinical trials with PPARγ agonists have been published with positive results. Proposed as immunomodulatory and neuroprotective, the therapeutic use of PGC-1α activation needs to be assessed in EAE/MS. The activation of indolamine 2,3-dioxygenase (IDO), the rate-limiting step of the kynurenine pathway of tryptophan (Trp) metabolism, plays crucial immunomodulatory roles. Indeed, Trp metabolites have therapeutic relevance in EAE and drugs with structural analogy to kynurenines, such as teriflunomide, are already approved for MS. Further studies are required to gain deeper knowledge of such endogenous immunomodulatory pathways with potential therapeutic implications in MS.

Bisphenol A induces Pomc gene expression through neuroinflammatory and PPARγ nuclear receptor-mediated mechanisms in POMC-expressing hypothalamic neuronal models

Endocrine disrupting chemicals, such as bisphenol A (BPA), have been linked to obesity. However, the direct effect of BPA on the hypothalamic pro-opiomelanocortin (POMC) neurons, which regulate energy homeostasis, remains unexplored. We define the effect of BPA on functionally characterized, POMC-expressing cell models, mHypoA-POMC/GFP-2 and mHypoE-43/5. Exposure to BPA significantly induced the mRNA levels of Pomc in both primary culture and the cell lines. Neuroinflammatory and steroid receptor mRNA levels were assessed to delineate the potential mechanisms, including inflammatory markers Nfκb, Il6 and Iκba, and steroid receptors Esr1, Esr2, Gpr30, Esrrg, and Pparg. Pre-treatment with anti-inflammatory compounds gonadotropin-releasing hormone, and PS1145, an IκB kinase inhibitor, abrogated the BPA-mediated Pomc induction. Furthermore, T0070907, a PPARγ antagonist, abolished Pomc induction, while the GPR30 antagonist G15 had no effect. These findings indicate that BPA may have direct effects on POMC neurons in the hypothalamus, utilizing neuroinflammatory mechanisms and through PPARγ nuclear receptors.

Current Progress on Peroxisome Proliferator-activated Receptor Gamma Agonist as an Emerging Therapeutic Approach for the Treatment of Alzheimer's Disease: An Update

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder, characterized by the deposition of amyloid-β within the brain parenchyma resulting in a significant decline in cognitive functions. The pathophysiological conditions of the disease are recognized by the perturbation of synaptic function, energy and lipid metabolism. In Addition deposition of amyloid plaques also triggers inflammation upon the induction of microglia. Peroxisome proliferatoractivated receptors (PPARs) are ligand-activated transcription factors known to play important role in the regulation of glucose absorption, homeostasis of lipid metabolism and are further known to involved in repressing the expression of genes related to inflammation. Therefore, agonists of this receptor represent an attractive therapeutic target for AD. Recently, both clinical and preclinical studies showed that use of Peroxisome proliferator-activated receptor gamma (PPARγ) agonist improves both learning and memory along with other AD related pathology. Thus, PPARγ signifies a significant new therapeutic target in treating AD. In this review, we have shed some light on the recent progress of how, PPARγ agonist selectively modulated different cellular targets in AD and its amazing potential in the treatment of AD.

Crosstalk between PPARγ Ligands and Inflammatory-Related Pathways in Natural T-Regulatory Cells from Type 1 Diabetes Mouse Model

Immunomodulation, as a means of immunotherapy, has been studied in major research and clinical laboratories for many years. T-Regulatory (Treg) cell therapy is one of the modulators used in immunotherapy approaches. Similarly, nuclear receptor peroxisome proliferator activated receptor gamma (PPARγ) has extensively been shown to play a role as an immuno-modulator during inflammation. Given their mutual roles in downregulating the immune response, current study examined the influence of PPARγ ligands i.e., thiazolidinedione (TZD) class of drugs on Forkhead Box P3 (Foxp3) expression and possible crosstalk between PPARγ and nTreg cells of Non-Obese Diabetes (NOD) and Non-Obese Diabetes Resistant (NOR) mice. Results showed that TZD drug, ciglitazone and natural ligand of PPARγ 15d-prostaglandin downregulated Foxp3 expression in activated nTreg cells from both NOD and NOR mice. Interestingly, addition of the PPARγ inhibitor, GW9662 further downregulated Foxp3 expression in these cells from both mice. We also found that PPARγ ligands negatively regulate Foxp3 expression in activated nTreg cells via PPARγ-independent mechanism(s). These results demonstrate that both natural and synthetic PPARγ ligands capable of suppressing Foxp3 expression in activated nTreg cells of NOD and NOR mice. This may suggest that the effect of PPARγ ligands in modulating Foxp3 expression in activated nTreg cells is different from their reported effects on effector T cells. Given the capability to suppress Foxp3 gene, it is possible to be tested as immunomodulators in cancer-related studies. The co-lateral use of PPARγ ligands in nTreg cells in inducing tolerance towards pseudo-self antigens as in tumor microenvironment may uphold beneficial outcomes.

Pioglitazone Represents an Effective Therapeutic Target in Preventing Oxidative/Inflammatory Cochlear Damage Induced by Noise Exposure

Recent progress in hearing loss research has provided strong evidence for the imbalance of cellular redox status and inflammation as common predominant mechanisms of damage affecting the organ of Corti including noise induced hearing loss. The discovery of a protective molecule acting on both mechanisms is challenging. The thiazolidinediones, a class of antidiabetic drugs including pioglitazone and rosiglitazone, have demonstrated diverse pleiotrophic effects in many tissues where they exhibit anti-inflammatory, anti-proliferative, tissue protective effects and regulators of redox balance acting as agonist of peroxisome proliferator-activated receptors (PPARs). They are members of the family of ligand regulated nuclear hormone receptors that are also expressed in several cochlear cell types, including the outer hair cells. In this study, we investigated the protective capacity of pioglitazone in a model of noise-induced hearing loss in Wistar rats and the molecular mechanisms underlying this protective effects. Specifically, we employed a formulation of pioglitazone in a biocompatible thermogel providing rapid, uniform and sustained inner ear drug delivery via transtympanic injection. Following noise exposure (120 dB, 10 kHz, 1 h), different time schedules of treatment were employed: we explored the efficacy of pioglitazone given immediately (1 h) or at delayed time points (24 and 48 h) after noise exposure and the time course and extent of hearing recovery were assessed. We found that pioglitazone was able to protect auditory function at the mid-high frequencies and to limit cell death in the cochlear basal/middle turn, damaged by noise exposure. Immunofluorescence and western blot analysis provided evidence that pioglitazone mediates both anti-inflammatory and anti-oxidant effects by decreasing NF-κB and IL-1β expression in the cochlea and opposing the oxidative damage induced by noise insult. These results suggest that intratympanic pioglitazone can be considered a valid therapeutic strategy for attenuating noise-induced hearing loss and cochlear damage, reducing inflammatory signaling and restoring cochlear redox balance.

How to reprogram microglia toward beneficial functions

Microglia, brain cells of nonneural origin, orchestrate the inflammatory response to diverse insults, including hypoxia/ischemia or maternal/fetal infection in the perinatal brain. Experimental studies have demonstrated the capacity of microglia to recognize pathogens or damaged cells activating a cytotoxic response that can exacerbate brain damage. However, microglia display an enormous plasticity in their responses to injury and may also promote resolution stages of inflammation and tissue regeneration. Despite the critical role of microglia in brain pathologies, the cellular mechanisms that govern the diverse phenotypes of microglia are just beginning to be defined. Here we review emerging strategies to drive microglia toward beneficial functions, selectively reporting the studies which provide insights into molecular mechanisms underlying the phenotypic switch. A variety of approaches have been proposed which rely on microglia treatment with pharmacological agents, cytokines, lipid messengers, or microRNAs, as well on nutritional approaches or therapies with immunomodulatory cells. Analysis of the molecular mechanisms relevant for microglia reprogramming toward pro‐regenerative functions points to a central role of energy metabolism in shaping microglial functions. Manipulation of metabolic pathways may thus provide new therapeutic opportunities to prevent the deleterious effects of inflammatory microglia and to control excessive inflammation in brain disorders.

Pioglitazone is superior to quetiapine, clozapine and tamoxifen at alleviating experimental autoimmune encephalomyelitis in mice

Recent evidence suggests that clozapine and quetiapine (atypical antipsychotics), tamoxifen (selective-estrogen receptor modulator) and pioglitazone (PPARγ agonist) may improve functional recovery in multiple sclerosis (MS). We have compared the effectiveness of oral administration of these drugs, beginning at peak disease, at reducing ascending paralysis, motor deficits and demyelination in mice subjected to experimental autoimmune encephalomyelitis (EAE). Mice were immunized with an immunogenic peptide corresponding to amino acids 35-55 of the myelin oligodendrocyte glycoprotein (MOG_35-55) in complete Freund's adjuvant and injected with pertussis toxin to induce EAE. Unlike clozapine, quetiapine and tamoxifen, administration of pioglitazone beginning at peak disease decreased both clinical scores and lumbar white matter loss in EAE mice. Using kinematic gait analysis, we found that pioglitazone also maintained normal movement of the hip, knee and ankle joints for at least 44 days after MOG_35-55 immunization. This long-lasting preservation of hindleg joint movements was accompanied by reduced white matter loss, microglial and macrophage activation and the expression of pro-inflammatory genes in the lumbar spinal cords of EAE mice. These results support clinical findings that suggest pioglitazone may reduce the progressive loss of motor function in MS by decreasing inflammation and myelin damage.

Demyelination in Multiple Sclerosis: Reprogramming Energy Metabolism and Potential PPARγ Agonist Treatment Approaches

Demyelination in multiple sclerosis (MS) cells is the site of several energy metabolic abnormalities driven by dysregulation between the opposed interplay of peroxisome proliferator-activated receptor γ (PPARγ) and WNT/β-catenin pathways. We focus our review on the opposing interactions observed in demyelinating processes in MS between the canonical WNT/β-catenin pathway and PPARγ and their reprogramming energy metabolism implications. Demyelination in MS is associated with chronic inflammation, which is itself associated with the release of cytokines by CD4⁺ Th17 cells, and downregulation of PPARγ expression leading to the upregulation of the WNT/β-catenin pathway. Upregulation of WNT/β-catenin signaling induces activation of glycolytic enzymes that modify their energy metabolic behavior. Then, in MS cells, a large portion of cytosolic pyruvate is converted into lactate. This phenomenon is called the Warburg effect, despite the availability of oxygen. The Warburg effect is the shift of an energy transfer production from mitochondrial oxidative phosphorylation to aerobic glycolysis. Lactate production is correlated with increased WNT/β-catenin signaling and demyelinating processes by inducing dysfunction of CD4⁺ T cells leading to axonal and neuronal damage. In MS, downregulation of PPARγ decreases insulin sensitivity and increases neuroinflammation. PPARγ agonists inhibit Th17 differentiation in CD4⁺ T cells and then diminish release of cytokines. In MS, abnormalities in the regulation of circadian rhythms stimulate the WNT pathway to initiate the demyelination process. Moreover, PPARγ contributes to the regulation of some key circadian genes. Thus, PPARγ agonists interfere with reprogramming energy metabolism by directly inhibiting the WNT/β-catenin pathway and circadian rhythms and could appear as promising treatments in MS due to these interactions.

Role of catalpol in ameliorating the pathogenesis of experimental autoimmune encephalomyelitis by increasing the level of noradrenaline in the locus coeruleus

The endogenous neurotransmitter, noradrenaline, exerts anti-inflammatory and neuroprotective effects in vivo and in vitro. Reduced noradrenaline levels results in increased inflammation and neuronal damage. The primary source of noradrenaline in the central nervous system is tyrosine hydroxylase (TH)-positive neurons, located in the locus coeruleus (LC). TH is the rate-limiting enzyme for noradrenaline synthesis; therefore, regulation of TH protein expression and intrinsic enzyme activity represents the central means for controlling the synthesis of noradrenaline. Catalpol is an iridoid glycoside purified from Rehmannia glutinosa Libosch, which exerts a neuroprotective effect in multiple sclerosis (MS). The present study used an experimental mouse model of autoimmune encephalomyelitis to verify the neuroprotective effects of catalpol. Significant improvements in the clinical scores were observed in catalpol-treated mice. Furthermore, catalpol increased TH expression and increased noradrenaline levels in the spinal cord. In primary cultures, catalpol exerted a neuroprotective effect in rat LC neurons by increasing the noradrenaline output. These results suggested that drugs targeting LC survival and function, including catalpol, may be able to benefit patients with MS.

Oxidative stress and mitochondrial dynamics malfunction are linked in Pelizaeus-Merzbacher disease

Pelizaeus‐Merzbacher disease (PMD) is a fatal hypomyelinating disorder characterized by early impairment of motor development, nystagmus, choreoathetotic movements, ataxia and progressive spasticity. PMD is caused by variations in the proteolipid protein gene PLP1, which encodes the two major myelin proteins of the central nervous system, PLP and its spliced isoform DM20, in oligodendrocytes. Large duplications including the entire PLP1 gene are the most frequent causative mutation leading to the classical form of PMD. The Plp1 overexpressing mouse model (PLP‐tg^66/66) develops a phenotype very similar to human PMD, with early and severe motor dysfunction and a dramatic decrease in lifespan. The sequence of cellular events that cause neurodegeneration and ultimately death is poorly understood. In this work, we analyzed patient‐derived fibroblasts and spinal cords of the PLP‐tg^66/66 mouse model, and identified redox imbalance, with altered antioxidant defense and oxidative damage to several enzymes involved in ATP production, such as glycolytic enzymes, creatine kinase and mitochondrial proteins from the Krebs cycle and oxidative phosphorylation. We also evidenced malfunction of the mitochondria compartment with increased ROS production and depolarization in PMD patient's fibroblasts, which was prevented by the antioxidant N‐acetyl‐cysteine. Finally, we uncovered an impairment of mitochondrial dynamics in patient's fibroblasts which may help explain the ultrastructural abnormalities of mitochondria morphology detected in spinal cords from PLP‐tg^66/66 mice. Altogether, these results underscore the link between redox and metabolic homeostasis in myelin diseases, provide insight into the pathophysiology of PMD, and may bear implications for tailored pharmacological intervention.

Immunometabolic profiling of T cells from patients with relapsing-remitting multiple sclerosis reveals an impairment in glycolysis and mitochondrial respiration

BACKGROUND

Metabolic reprogramming is shaped to support specific cell functions since cellular metabolism controls the final outcome of immune response. Multiple sclerosis (MS) is an autoimmune disease resulting from loss of immune tolerance against central nervous system (CNS) myelin. Metabolic alterations of T cells occurring during MS are not yet well understood and their studies could have relevance in the comprehension of the pathogenetic events leading to loss of immune tolerance to self and to develop novel therapeutic strategies aimed at limiting MS progression.

METHODS AND RESULTS

In this report, we observed that extracellular acidification rate (ECAR) and oxygen consumption rate (OCR), indicators of glycolysis and oxidative phosphorylation, respectively, were impaired during T cell activation in naïve-to-treatment relapsing remitting (RR)MS patients when compared with healthy controls. These results were also corroborated at biochemical level by a reduced expression of the glycolitic enzymes aldolase, enolase 1, hexokinase I, and by reduction of Krebs cycle enzymes dihydrolipoamide-S-acetyl transferase (DLAT) and dihydrolipoamide-S-succinyl transferase (DLST). Treatment of RRMS patients with interferon beta-1a (IFN beta-1a) was able to restore T cell glycolysis and mitochondrial respiration as well as the amount of the metabolic enzymes to a level comparable to that of healthy controls. These changes associated with an up-regulation of the glucose transporter-1 (GLUT-1), a key element in intracellular transport of glucose.

CONCLUSIONS

Our data suggest that T cells from RRMS patients display a reduced engagement of glycolysis and mitochondrial respiration, reversible upon IFN beta-1a treatment, thus suggesting an involvement of an altered metabolism in the pathogenesis of MS.

Molecular Mechanisms Modulating the Phenotype of Macrophages and Microglia

Macrophages and microglia play crucial roles during central nervous system development, homeostasis and acute events such as infection or injury. The diverse functions of tissue macrophages and microglia are mirrored by equally diverse phenotypes. A model of inflammatory/M1 versus a resolution phase/M2 macrophages has been widely used. However, the complexity of macrophage function can only be achieved by the existence of varied, plastic and tridimensional macrophage phenotypes. Understanding how tissue macrophages integrate environmental signals via molecular programs to define pathogen/injury inflammatory responses provides an opportunity to better understand the multilayered nature of macrophages, as well as target and modulate cellular programs to control excessive inflammation. This is particularly important in MS and other neuroinflammatory diseases, where chronic inflammatory macrophage and microglial responses may contribute to pathology. Here, we perform a comprehensive review of our current understanding of how molecular pathways modulate tissue macrophage phenotype, covering both classic pathways and the emerging role of microRNAs, receptor-tyrosine kinases and metabolism in macrophage phenotype. In addition, we discuss pathway parallels in microglia, novel markers helpful in the identification of peripheral macrophages versus microglia and markers linked to their phenotype.

Peroxisome proliferator-activated receptor γ (PPARγ): A master gatekeeper in CNS injury and repair

Peroxisome proliferator-activated receptor γ (PPARγ) is a widely expressed ligand-modulated transcription factor that governs the expression of genes involved in inflammation, redox equilibrium, trophic factor production, insulin sensitivity, and the metabolism of lipids and glucose. Synthetic PPARγ agonists (e.g. thiazolidinediones) are used to treat Type II diabetes and have the potential to limit the risk of developing brain injuries such as stroke by mitigating the influence of comorbidities. If brain injury develops, PPARγ serves as a master gatekeeper of cytoprotective stress responses, improving the chances of cellular survival and recovery of homeostatic equilibrium. In the acute injury phase, PPARγ directly restricts tissue damage by inhibiting the NFκB pathway to mitigate inflammation and stimulating the Nrf2/ARE axis to neutralize oxidative stress. During the chronic phase of acute brain injuries, PPARγ activation in injured cells culminates in the repair of gray and white matter, preservation of the blood-brain barrier, reconstruction of the neurovascular unit, resolution of inflammation, and long-term functional recovery. Thus, PPARγ lies at the apex of cell fate decisions and exerts profound effects on the chronic progression of acute injury conditions. Here, we review the therapeutic potential of PPARγ in stroke and brain trauma and highlight the novel role of PPARγ in long-term tissue repair. We describe its structure and function and identify the genes that it targets. PPARγ regulation of inflammation, metabolism, cell fate (proliferation/differentiation/maturation/survival), and many other processes also has relevance to other neurological diseases. Therefore, PPARγ is an attractive target for therapies against a number of progressive neurological disorders.

PPAR-α Modulates the Anti-Inflammatory Effect of Melatonin in the Secondary Events of Spinal Cord Injury

Melatonin is the principal secretory product of the pineal gland, and its role as an immunomodulator is well established. Recent evidence shows that melatonin is a scavenger of oxyradicals and peroxynitrite and reduces the development of inflammation and tissue injury events associated with spinal cord trauma. Previous results suggest that peroxisome proliferator-activated receptor α (PPAR-α), a nuclear receptor protein that functions as a transcription factor activated by fatty acids, plays a role in control of secondary inflammatory process associated with spinal cord injury (SCI).With the aim to characterize the role of PPAR-α in melatonin-mediated anti-inflammatory activity, we tested the efficacy of melatonin (30 mg/kg) in an experimental model of spinal cord trauma, induced in mice, by the application of vascular clips (force of 24 g) to the dura via a four-level T5-T8 laminectomy, and comparing mice lacking PPAR-α (PPAR-α KO) with wild-type (WT) mice.The results obtained indicate that melatonin-mediated anti-inflammatory activity is weakened in PPAR-α KO mice, as compared to WT controls. In particular, melatonin was less effective in PPAR-α KO, compared to WT mice, as evaluated by inhibition of the degree of spinal cord inflammation and tissue injury, neutrophil infiltration, pro-inflammatory cytokine expression, nuclear factor κB (NF-κB) activation, and inducible nitric oxide synthase (iNOS) expression. This study indicates that PPAR-α can contribute to the anti-inflammatory activity of melatonin in SCI.

PPAR-gamma agonist pioglitazone modifies craving intensity and brain white matter integrity in patients with primary cocaine use disorder: a double-blind randomized controlled pilot trial

BACKGROUND AND AIMS

Pioglitazone (PIO), a potent agonist of PPAR-gamma, is a promising candidate treatment for cocaine use disorder (CUD). We tested the effects of PIO on targeted mechanisms relevant to CUD: cocaine craving and brain white matter (WM) integrity. Feasibility, medication compliance and tolerability were evaluated.

DESIGN

Two-arm double-blind randomized controlled proof-of-concept pilot trial of PIO or placebo (PLC).

SETTING

Single-site out-patient treatment research clinic in Houston, TX, USA.

PARTICIPANTS

Thirty treatment-seeking adults, 18 to 60 years old, with CUD. Eighteen participants (8 = PIO; 10 = PLC) completed diffusion tensor imaging (DTI) of WM integrity at pre-/post-treatment.

INTERVENTION

Study medication was dispensed at thrice weekly visits along with once-weekly cognitive behavioral therapy for 12 weeks.

MEASUREMENTS

Measures of target engagement mechanisms of interest included cocaine craving assessed by the Brief Substance Craving Scale (BSCS), the Obsessive Compulsive Drug Use Scale (OCDUS), a visual analog scale (VAS) and change in WM integrity. Feasibility measures included number completing treatment, medication compliance (riboflavin detection) and tolerability (side effects, serious adverse events).

FINDINGS

Target engagement change in mechanisms of interest, defined as a ≥ 0.75 Bayesian posterior probability of an interaction existing favoring PIO over PLC, was demonstrated on measures of craving (BSCS, VAS) and WM integrity indexed by fractional anisotropy (FA) values. Outcomes indicated greater decrease in craving and greater increase in FA values in the PIO group. Feasibility was demonstrated by high completion rates among those starting treatment (21/26 = 80%) and medication compliance (≥ 80%). There were no reported serious adverse events for PIO.

CONCLUSIONS

Compared with placebo, patients receiving pioglitazone show a higher likelihood of reduced cocaine craving and improved brain white matter integrity as a function of time in treatment. Pioglitazone shows good feasibility as a treatment for cocaine use disorder.

Unlike PPARgamma, neither other PPARs nor PGC-1alpha is elevated in the cerebrospinal fluid of patients with multiple sclerosis

Corroborating with prior experimental findings, we recently reported the pronounced elevation of peroxisome proliferator-activated receptor gamma (PPARγ) protein concentration in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS), in association with neuroinflammatory markers and clinical severity. Based on subsequent reports on the possible involvement of other PPARs and PPARγ coactivator-1alpha (PGC-1α) in neuroinflammation in MS, we analyzed the protein levels of PPARα, PPARβ/δ, and PGC-1α in a subset of CSF samples from the same cohort of relapsing-remitting MS patients. Unlike PPARγ, none of these proteins were found elevated in MS patients (n=25) compared to non-inflammatory controls (n=16), with the levels of PPARα and PPARβ/δ found generally below the limit of detection, and that of PGC-1α being detectable but comparable in both groups. The clinical and laboratory associations previously reported with PPARγ were however significant even in this smaller subset. The potential underlying causes of these differential alterations are discussed. The findings suggest that despite their proposed involvement in the regulation of inflammatory processes in MS, PPARα, PPARβ/δ, and PGC-1α proteins are not potential biomarkers of neuroinflammation in MS, and indicate a preferential role of PPARγ in the endogenous regulation of autoimmune response in the human CNS within its receptor family.

Apoptosis Induced by the UV Filter Benzophenone-3 in Mouse Neuronal Cells Is Mediated via Attenuation of Erα/Pparγ and Stimulation of Erβ/Gpr30 Signaling

Although benzophenone-3 (BP-3) has frequently been reported to play a role in endocrine disruption, there is insufficient data regarding the impact of BP-3 on the nervous system, including its possible adverse effects on the developing brain. Our study demonstrated that BP-3 caused neurotoxicity and activated apoptosis via an intrinsic pathway involving the loss of mitochondrial membrane potential and the activation of caspases-9 and -3 and kinases p38/MAPK and Gsk3β. These biochemical alterations were accompanied by ROS production, increased apoptotic body formation and impaired cell survival, and by an upregulation of the genes involved in apoptosis. The BP-3-induced effects were tissue-specific and age-dependent with the most pronounced effects observed in neocortical cells at 7 days in vitro. BP-3 changed the messenger RNA (mRNA) expression levels of Erα, Erβ, Gpr30, and Pparγ in a time-dependent manner. At 3 h of exposure, BP-3 downregulated estrogen receptor mRNAs but upregulated Pparγ mRNA. After prolonged exposures, BP-3 downregulated the receptor mRNAs except for Erβ mRNA that was upregulated. The BP-3-induced patterns of mRNA expression measured at 6 and 24 h of exposure reflected alterations in the protein levels of the receptors and paralleled their immunofluorescent labeling. Erα and Pparγ agonists diminished, but Erβ and Gpr30 agonists stimulated the BP-3-induced apoptotic and neurotoxic effects. Receptor antagonists caused the opposite effects, except for ICI 182,780. This is in line with a substantial reduction in the effects of BP-3 in cells with siRNA-silenced Erβ/Gpr30 and the maintenance of BP-3 effects in Erα- and Pparγ siRNA-transfected cells. We showed for the first time that BP-3-affected mRNA and protein expression levels of Erα, Erβ, Gpr30, and Pparγ, paralleled BP-3-induced apoptosis and neurotoxicity. Therefore, we suggest that BP-3-evoked apoptosis of neuronal cells is mediated via attenuation of Erα/Pparγ and stimulation of Erβ/Gpr30 signaling.

PPARγ as a therapeutic target to rescue mitochondrial function in neurological disease

There is increasing evidence for the involvement of mitochondrial dysfunction and oxidative stress in the pathogenesis of many of the major neurodegenerative and neuroinflammatory diseases, suggesting that mitochondrial and antioxidant pathways may represent potential novel therapeutic targets. Recent years have seen a rapidly growing interest in the use of therapeutic strategies that can limit the defects in, or even to restore, mitochondrial function while reducing free radical generation. The peroxisome proliferation-activated receptor gamma (PPARγ), a ligand-activated transcription factor, has a wide spectrum of biological functions, regulating mitochondrial function, mitochondrial turnover, energy metabolism, antioxidant defence and redox balance, immune responses and fatty acid oxidation. In this review, we explore the evidence for potential beneficial effects of PPARγ agonists in a number of neurological disorders, including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis and Huntington's disease, ischaemia, autoimmune encephalomyelitis and neuropathic pain. We discuss the mechanisms underlying those beneficial effects in particular in relation to mitochondrial function, antioxidant defence, cell death and inflammation, and suggest that the PPARγ agonists show significant promise as therapeutic agents in otherwise intractable neurological disease.

Development of a high throughput drug screening assay to identify compounds that protect oligodendrocyte viability and differentiation under inflammatory conditions

Background

Newly proliferated oligodendrocyte precursor cells (OPCs) migrate and surround lesions of patients with multiple sclerosis (MS) and other demyelinating diseases, but fail to differentiate into oligodendrocytes (OLs) and remyelinate remaining viable axons. The abundance of secreted inflammatory factors within and surrounding these lesions likely plays a major inhibitory role, promoting cell death and preventing OL differentiation and axon remyelination. To identify clinical candidate compounds that may protect existing and differentiating OLs in patients, we have developed a high throughput screening (HTS) assay that utilizes purified rat OPCs.

Results

Using a fluorescent indicator of cell viability coupled with image quantification, we developed an assay to allow the identification of compounds that promote OL viability and differentiation in the presence of the synergistic inflammatory cytokines, tumor necrosis factor α and interferon-γ. We have utilized this assay to screen the NIH clinical collection library and identify compounds that protect OLs and promote OL differentiation in the presence of these inflammatory cytokines.

Conclusion

This primary OL-based cytokine protection assay is adaptable for HTS and may be easily modified for profiling of compounds in the presence of other potentially inhibitory molecules found in MS lesions. This assay should be of use to those interested in identifying drugs for the treatment of MS and other demyelinating diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2219-8) contains supplementary material, which is available to authorized users.

Sex-Based Selectivity of PPARγ Regulation in Th1, Th2, and Th17 Differentiation

Peroxisome proliferator-activated receptor gamma (PPARγ) has recently been recognized to regulate adaptive immunity through Th17 differentiation, Treg functions, and T_FH responses. However, its role in adaptive immunity and autoimmune disease is still not clear, possibly due to sexual differences. Here, we investigated in vitro treatment study with the PPARγ agonist pioglitazone to compare Th1, Th2, and Th17 differentiation in male and female mouse splenic T cells. Pioglitazone treatment significantly inhibited various effector T cell differentiations including Th1, Th2, and Th17 cells from female naïve T cells, but it selectively reduced IL-17 production in male Th17 differentiation. Interestingly, pioglitazone and estradiol (E2) co-treatment of T cells in males inhibited differentiation of Th1, Th2, and Th17 cells, suggesting a mechanism for the greater sensitivity of PPARγ to ligand treatment in the regulation of effector T cell differentiation in females. Collectively, these results demonstrate that PPARγ selectively inhibits Th17 differentiation only in male T cells and modulates Th1, Th2, and Th17 differentiation in female T cells based on different level of estrogen exposure. Accordingly, PPARγ could be an important immune regulator of sexual differences in adaptive immunity.

Dual Peroxisome Proliferator-Activated Receptor-alpha/gamma Agonists : In the Treatment of Type 2 Diabetes Mellitus and the Metabolic Syndrome

The metabolic syndrome consists of a combination of cardiovascular risk factors that include hyperglycemia with or without type 2 diabetes mellitus, visceral obesity, elevated blood pressure, and atherogenic dyslipidemia. These interrelated disorders and their associated lipotoxicity, oxidative stress, and inflammatory state predispose to a constellation of cardiovascular conditions leading to high risk of heart attack, stroke, renal failure, blindness, and lower extremity amputation. Visceral obesity, a prime risk factor for type 2 diabetes and a major component of the metabolic syndrome, potentiates atherogenesis, atherosclerosis, organ lipotoxicity, and oxidative tissue damage.Peroxisome proliferator-activated receptors (PPARs) are relatively recently discovered nuclear transcription factors that are modulated by dietary fatty acids, including the essential polyunsaturated fatty acids, arachidonic acid and its metabolites, and are essential to the control of energy metabolism. Of the three PPAR isoforms (alpha, gamma, and delta), synthetic pharmaceutical ligands that activate PPARalpha (the antidyslipidemic fibric acid derivatives ['fibrates']) and PPARgamma (the antidiabetic thiazolidinediones) have been studied extensively. Recently developed dual PPARalpha/gamma agonists may combine the therapeutic effects of these drugs, creating the expectation of greater efficacy, and perhaps other advantages in the treatment of type 2 diabetes and the metabolic syndrome. However, thiazolidinediones are hampered by adverse effects related to increased weight gain and fluid overload. It remains to be seen whether the dual PPARalpha/gamma agonists currently under development have similar limitations. Nevertheless, existing clinical data imply that the combined effects of thiazolidinediones and fibrates are likely to be emulated by dual PPARalpha/gamma agonists, providing superior efficacy to these classes for the treatment of type 2 diabetes, the metabolic syndrome, and their cardiovascular and other end-organ complications.

Obeticholic acid, a synthetic bile acid agonist of the farnesoid X receptor, attenuates experimental autoimmune encephalomyelitis

Bile acids are ligands for the nuclear hormone receptor, farnesoid X receptor (FXR). The bile acid-FXR interaction regulates bile acid synthesis, transport, and cholesterol metabolism. Recently, bile acid-FXR regulation has been reported to play an integral role in both hepatic and intestinal inflammation, and in atherosclerosis. In this study, we found that FXR knockout mice had more disease severity in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Obeticholic acid (6α-ethyl-chenodeoxycholic acid, 6-ECDCA), a synthetic FXR agonist, is an orally available drug that is currently in clinical trials for the treatment of inflammatory diseases such as alcoholic hepatitis, nonalcoholic steatohepatitis, and primary biliary cirrhosis. When we treated mice exhibiting established EAE with 6-ECDCA, or the natural FXR ligand chenodeoxycholic acid (CDCA), clinical disease was ameliorated by (i) suppressing lymphocyte activation and proinflammatory cytokine production; (ii) reducing CD4(+) T cells and CD19(+) B cell populations and their expression of negative checkpoint regulators programmed cell death protein 1 (PD1), programmed death-ligand 1 (PD-L1), and B and T lymphocyte attenuator (BTLA); (iii) increasing CD8(+) T cells and PD1, PDl-1, and BTLA expression; and (iv) reducing VLA-4 expression in both the T- and B-cell populations. Moreover, adoptive transfer of 6-ECDCA- or CDCA-treated donor cells failed to transfer disease in naive recipients. Thus, we show that FXR functions as a negative regulator in neuroinflammation and we highlight that FXR agonists represent a potential previously unidentified therapy for MS.

Changing paradigm to target microglia in neurodegenerative diseases: from anti-inflammatory strategy to active immunomodulation

INTRODUCTION

The importance of microglia in most neurodegenerative pathologies, from Parkinson's disease to amyotrophic lateral sclerosis and Alzheimer's disease, is increasingly recognized. Until few years ago, microglial activation in pathological conditions was considered dangerous to neurons due to its causing inflammation. Today we know that these glial cells also play a crucial physiological and neuroprotective role, which is altered in neurodegenerative conditions.

AREAS COVERED

The neuroinflammatory hypothesis for neurodegenerative diseases has led to the trial of anti-inflammatory agents as therapeutics with largely disappointing results. New information about the physiopathological role of microglia has highlighted the importance of immunomodulation as a potential new therapeutic approach. This review summarizes knowledge on microglia as a potential therapeutic target in the most common neurodegenerative diseases, with focus on compounds directed toward the modulation of microglial immune response through specific molecular pathways.

EXPERT OPINION

Here we support the innovative concept of targeting microglial cells by modulating their activity, rather than simply trying to counteract their inflammatory neurotoxicity, as a potential therapeutic approach for neurodegenerative diseases. The advantage of this therapeutic approach could be to reduce neuroinflammation and toxicity, while at the same time strengthening intrinsic neuroprotective properties of microglia and promoting neuroregeneration.

Importance of Apolipoprotein A-I in Multiple Sclerosis

Jean-Martin Charcot has first described multiple sclerosis (MS) as a disease of the central nervous system (CNS) over a century ago. MS remains incurable today, and treatment options are limited to disease modifying drugs. Over the years, significant advances in understanding disease pathology have been made in autoimmune and neurodegenerative components. Despite the fact that brain is the most lipid rich organ in human body, the importance of lipid metabolism has not been extensively studied in this disorder. In MS, the CNS is under attack by a person's own immune system. Autoantigens and autoantibodies are known to cause devastation of myelin through up regulation of T-cells and cytokines, which penetrate through the blood-brain barrier to cause inflammation and myelin destruction. The anti-inflammatory role of high-density lipoproteins (HDLs) has been implicated in a plethora of biological processes: vasodilation, immunity to infection, oxidation, inflammation, and apoptosis. However, it is not known what role HDL plays in neurological function and myelin repair in MS. Understanding of lipid metabolism in the CNS and in the periphery might unveil new therapeutic targets and explain the partial success of some existing MS therapies.

A single dose of PPARγ agonist pioglitazone reduces cortical oxidative damage and microglial reaction following lateral fluid percussion brain injury in rats

Neuroprotective actions of the peroxisome proliferator-activated receptor-γ (PPARγ) agonists have been observed in various animal models of the brain injuries. In this study we examined the effects of a single dose of pioglitazone on oxidative and inflammatory parameters as well as on neurodegeneration and the edema formation in the rat parietal cortex following traumatic brain injury (TBI) induced by the lateral fluid percussion injury (LFPI) method. Pioglitazone was administered in a dose of 1mg/kg at 10min after the brain trauma. The animals of the control group were sham-operated and injected by vehicle. The rats were decapitated 24h after LFPI and their parietal cortices were analyzed by biochemical and histological methods. Cortical edema was evaluated in rats sacrificed 48h following TBI. Brain trauma caused statistically significant oxidative damage of lipids and proteins, an increase of glutathione peroxidase (GSH-Px) activity, the cyclooxygenase-2 (COX-2) overexpression, reactive astrocytosis, the microglia activation, neurodegeneration, and edema, but it did not influence the superoxide dismutase activity and the expressions of interleukin-1 beta, interleukin-6 and tumor necrosis factor-alpha in the rat parietal cortex. Pioglitazone significantly decreased the cortical lipid and protein oxidative damage, increased the GSH-Px activity and reduced microglial reaction. Although a certain degree of the TBI-induced COX-2 overexpression, neurodegeneration and edema decrease was detected in pioglitazone treated rats, it was not significant. In the injured animals, cortical reactive astrocytosis was unchanged by the tested PPARγ agonist. These findings demonstrate that pioglitazone, administered only in a single dose, early following LFPI, reduced cortical oxidative damage, increased antioxidant defense and had limited anti-inflammatory effect, suggesting the need for further studies of this drug in the treatment of TBI.