Shannon E. Dunn

Isoprenoids determine Th1/Th2 fate in pathogenic T cells, providing a mechanism of modulation of autoimmunity by atorvastatin

3-hydroxy-3-methylglutaryl–coenzyme A (HMG-CoA) reductase is a critical enzyme in the mevalonate pathway that regulates the biosynthesis of cholesterol as well as isoprenoids that mediate the membrane association of certain GTPases. Blockade of this enzyme by atorvastatin (AT) inhibits the destructive proinflammatory T helper cell (Th)1 response during experimental autoimmune encephalomyelitis and may be beneficial in the treatment of multiple sclerosis and other Th1-mediated autoimmune diseases. Here we present evidence linking specific isoprenoid intermediates of the mevalonate pathway to signaling pathways that regulate T cell autoimmunity. We demonstrate that the isoprenoid geranylgeranyl-pyrophosphate (GGPP) mediates proliferation, whereas both GGPP and its precursor, farnesyl-PP, regulate the Th1 differentiation of myelin-reactive T cells. Depletion of these isoprenoid intermediates in vivo via oral AT administration hindered these T cell responses by decreasing geranylgeranylated RhoA and farnesylated Ras at the plasma membrane. This was associated with reduced extracellular signal–regulated kinase (ERK) and p38 phosphorylation and DNA binding of their cotarget c-fos in response to T cell receptor activation. Inhibition of ERK and p38 mimicked the effects of AT and induced a Th2 cytokine shift. Thus, by connecting isoprenoid availability to regulation of Th1/Th2 fate, we have elucidated a mechanism by which AT may suppress Th1-mediated central nervous system autoimmune disease.

Peroxisome proliferator–activated receptor (PPAR)α expression in T cells mediates gender differences in development of T cell–mediated autoimmunity.

Peroxisome proliferator–activated receptor (PPAR)α is a nuclear receptor that mediates gender differences in lipid metabolism. PPARα also functions to control inflammatory responses by repressing the activity of nuclear factor κB (NF-κB) and c-jun in immune cells. Because PPARα is situated at the crossroads of gender and immune regulation, we hypothesized that this gene may mediate sex differences in the development of T cell–mediated autoimmune disease. We show that PPARα is more abundant in male as compared with female CD4+ cells and that its expression is sensitive to androgen levels. Genetic ablation of this gene selectively removed the brake on NF-κB and c-jun activity in male T lymphocytes, resulting in higher production of interferon γ and tumor necrosis factor (but not interleukin 17), and lower production of T helper (Th)2 cytokines. Upon induction of experimental autoimmune encephalomyelitis, male but not female PPARα−/− mice developed more severe clinical signs that were restricted to the acute phase of disease. These results suggest that males are less prone to develop Th1-mediated autoimmunity because they have higher T cell expression of PPARα.

Anti-NMDA receptor encephalitis. The disorder, the diagnosis and the immunobiology.

Anti-NMDAR encephalitis is a newly characterized syndrome with a progressive, predictable clinical course and the possibility of effective treatment. Accurate and timely diagnosis is critical to selection and implementation of treatments, and optimal patient outcomes. Outcomes are improved with early diagnosis via indirect immunofluorescence or cell-based assays, and the rapid and appropriate administration of immunosuppressant and anti-psychotic therapies. Three possible scenarios accounting for the immunopathogenesis of anti-NMDAR encephalitis are presented, with the most probable one being that of paraneoplastic autoimmunity. Future efforts in this disorder should focus on elucidating the mechanisms that contribute to initiation of this antibody response, as well as exploring the role of tumors, infectious triggers and immune-reactivation. Finally, accessible tools need to be developed that allow for reliable identification of specific antibody markers against synaptic proteins.

Regulation of obesity-related insulin resistance with gut anti-inflammatory agents.

Obesity has reached epidemic proportions, but little is known about its influence on the intestinal immune system. Here we show that the gut immune system is altered during high-fat diet (HFD) feeding and is a functional regulator of obesity-related insulin resistance (IR) that can be exploited therapeutically. Obesity induces a chronic phenotypic pro-inflammatory shift in bowel lamina propria immune cell populations. Reduction of the gut immune system, using beta7 integrin-deficient mice (Beta7(null)), decreases HFD-induced IR. Treatment of wild-type HFD C57BL/6 mice with the local gut anti-inflammatory, 5-aminosalicyclic acid (5-ASA), reverses bowel inflammation and improves metabolic parameters. These beneficial effects are dependent on adaptive and gut immunity and are associated with reduced gut permeability and endotoxemia, decreased visceral adipose tissue inflammation, and improved antigen-specific tolerance to luminal antigens. Thus, the mucosal immune system affects multiple pathways associated with systemic IR and represents a novel therapeutic target in this disease.

Peroxisome proliferator-activated receptor (PPAR)α and -γ regulate IFNγ and IL-17A production by human T cells in a sex-specific way

Women develop certain autoimmune diseases more often than men. It has been hypothesized that this may relate to the development of more robust T-helper (Th)1 responses in women. To test whether women exhibit a Th1 bias, we isolated naïve cluster of differentiation (CD)4+ T cells from peripheral blood of healthy women and men and measured the proliferation and cytokine production by these cells in response to submaximal amounts of anti-CD3 and anti-CD28. We observed that CD4+ T cells from women produced higher levels of IFNγ as well as tended to proliferate more than male CD4+ T cells. Intriguingly, male CD4+ T cells instead had a predilection toward IL-17A production. This sex dichotomy in Th cytokine production was found to be even more striking in the Swiss/Jackson Laboratory (SJL) mouse. Studies in mice and humans indicated that the sexual dimorphism in Th1 and Th17 cytokine production was dependent on the androgen status and the T-cell expression of peroxisome proliferator activated receptor (PPAR)α and PPARγ. Androgens increased PPARα and decreased PPARγ expression by human CD4+ T cells. PPARα siRNA-mediated knockdown had the effect of increasing IFNγ by male CD4+ T cells, while transfection of CD4+ T cells with PPARγ siRNAs increased IL-17A production uniquely by female T cells. Together, our observations indicate that human T cells exhibit a sex difference in the production of IFNγ and IL-17A that may be driven by expressions of PPARα and PPARγ.

Peroxisome proliferator–activated receptor δ limits the expansion of pathogenic Th cells during central nervous system autoimmunity

Peroxisome proliferator–activated receptors (PPARs; PPAR-α, PPAR-δ, and PPAR-γ) comprise a family of nuclear receptors that sense fatty acid levels and translate this information into altered gene transcription. Previously, it was reported that treatment of mice with a synthetic ligand activator of PPAR-δ, GW0742, ameliorates experimental autoimmune encephalomyelitis (EAE), indicating a possible role for this nuclear receptor in the control of central nervous system (CNS) autoimmune inflammation. We show that mice deficient in PPAR-δ (PPAR-δ−/−) develop a severe inflammatory response during EAE characterized by a striking accumulation of IFN-γ+IL-17A− and IFN-γ+IL-17A+ CD4+ cells in the spinal cord. The preferential expansion of these T helper subsets in the CNS of PPAR-δ−/− mice occurred as a result of a constellation of immune system aberrations that included higher CD4+ cell proliferation, cytokine production, and T-bet expression and enhanced expression of IL-12 family cytokines by myeloid cells. We also show that the effect of PPAR-δ in inhibiting the production of IFN-γ and IL-12 family cytokines is ligand dependent and is observed in both mouse and human immune cells. Collectively, these findings suggest that PPAR-δ serves as an important molecular brake for the control of autoimmune inflammation.

Puberty in females enhances the risk of an outcome of multiple sclerosis in children and the development of central nervous system autoimmunity in mice.

Background: For reasons that remain unclear, three times more women develop multiple sclerosis (MS) than men. This preponderance among women is evident only after 12 years of age, implicating pubertal factors in the risk of MS. Objective: To investigate the influence of female puberty on central nervous system (CNS) autoimmunity. Methods: We examined the relationship between age of menarche on MS outcomes in 116 female children (< 16 years old) whom presented with incident ‘acquired demyelinating syndromes’ (ADS) and were followed prospectively in the national Canadian Pediatric Demyelinating Disease Study, from 2004–2013. Furthermore, we directly investigated the effects of puberty on susceptibility to experimental autoimmune encephalomyelitis (EAE) in two groups of female mice that differed only in their pubertal status. Results: In the ADS children, a later age of menarche was associated with a decreased risk of subsequent MS diagnosis. This relationship persisted, after accounting for patient age at ADS presentation and the presence of ≥1 T2 lesions on brain magnetic resonance imaging (MRI), with a hazard ratio (HR) of 0.64; and additional factors that associate with MS outcomes in ADS children, including low vitamin D levels. Furthermore, we found female mice that had transitioned through puberty were more susceptible to EAE than age-matched, pre-pubertal mice. Conclusion: Puberty in females enhances CNS autoimmune mechanisms that lead to MS in humans and EAE in mice.

Sex-Based Differences in Multiple Sclerosis (Part I): Biology of Disease Incidence.

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease that leads to neuron damage and progressive disability. One major feature of multiple sclerosis (MS) is that it affects women three times more often than men. In this chapter, we overview the evidence that the autoimmune component of MS, which predominates in the early stages of this disease, is more robust in women than in men and undergoes a sharp increase with the onset of puberty. In addition, we discuss the common rodent models of MS that have been used to study the sex-based differences in the development of central nervous system (CNS) autoimmunity. We then address the biological underpinnings of this enhanced MS risk in women by first reviewing the autoimmune mechanisms that are thought to lead to the initiation of this disease and then honing in on how these mechanisms differ between the sexes. Finally, we review what is known about the hormonal and genetic basis of these sex differences in CNS autoimmunity.

Sex-Based Differences in Multiple Sclerosis (MS): Part II: Rising Incidence of Multiple Sclerosis in Women and the Vulnerability of Men to Progression of this Disease

It is well known that a number of autoimmune diseases including multiple sclerosis (MS) predominantly affect women and there has been much attention directed toward understanding why this is the case. Past research has revealed a number of sex differences in autoimmune responses that can account for the female bias in MS. However, much less is known about why the incidence of MS has increased exclusively in women over the past half century. The recency of this increase suggests that changing environmental or lifestyle factors are interacting with biological sex to increase MS risk predominantly in females. Indeed, a number of recent studies have identified sex-specific differences in the effect of environmental factors on MS incidence. The first part of this chapter will overview this evidence and will discuss the possible scenarios of how the environment may be interacting with autoimmune mechanisms to contribute to the preferential rise in MS incidence in women. Despite the strong female bias in MS incidence, culminating evidence from natural history studies, and imaging and pathology studies suggests that males who develop MS may exhibit a more rapid decline in disability and cognitive functioning than women. Very little is known about the biological basis of this more rapid deterioration, but some insights have been provided by studies in rodent models of demyelination/remyelination. The second part of this chapter will overview the evidence that males with relapsing-onset MS undergo a more rapid progression of disease than females and will discuss potential biological mechanisms that account for this sex difference.

The Gender Gap in Multiple Sclerosis: Intersection of Science and Society

M O R E T H A N 3 t imes more women than men have multiple sclerosis (MS). Over the past 50 years, this ratio has been steadily increasing. The burdens to those who battle this disease, as well as the costs for society in dealing with MS, are substantial, and deciphering this 50-year-old trend in female preponderance in this disease is critical. In attempting to understand this growing imbalance, a number of intriguing discoveries have been made. These discoveries illuminate the pathogenesis of MS, with applications and benefits for both men and women. These breakthroughs potentially allow for the repurposing of certain approved drugs for potential use as treatments of MS. One obvious hypothesis about the rapid increase in the incidence of MS in the past 50 years is that it is likely due to “something” in the environment, rather than simply a “genetic” factor. That makes sense because women could not have undergone genetic changes in this short a time frame. One of the most striking changes in women is the decreasing number of pregnancies, a major protective factor against relapses in MS. The age for parturition is also increasing in women. Another striking nominee for an environmental factor that affects the incidence of MS is the level of vitamin D3 and the associated amount of sunlight exposure. Vitamin D3, a sterol, is a negative regulator of Tcell–mediated inflammation and acts as a transcriptional regulator of an important cytokine known as IL17. IL-17 and associated cytokines mark 1 of 2 major inflammatory Tcell pathways involved in the pathogenesis of MS, known as the T helper 17 (TH17) pathway. Vitamin D through the vitamin D receptor upregulates the expression of the major MS-associated risk allele, HLADRB*1501. A higher expression of HLA-DRB*1501 in the thymus could prevent MS by inducing the deletion of highly autoreactive myelinreactive T-cell clones. The other major inflammatory pathway in MS is known as TH1, and its main mediator is IFN. Many T cells in humans have the characteristics of both TH1 and TH17. Surprisingly, vitamin D3 has a greater modulatory effect in women with MS than in men with MS, where it inhibits both TH1 and TH17 pathways to a greater extent. This may be due in part to a deficiency in females of the inactivating enzyme, CYP24A1 for vitamin D3, leading to accumulation of more vitamin D3 in target cells. Interestingly, in the animal model of MS, known as experimental autoimmune encephalomyelitis, vitamin D3 inhibits paralysis in females, again to a much greater extent than in males. Estradiol is another molecule that has a large effect on the immune system and, of course, is produced to a much greater extent in women. Bodhankar and colleagues have shown that 17 -estradiol protects against experimental autoimmune encephalomyelitis and that this protection is mediated mainly through the estrogen receptor and the membrane receptor G protein– coupled receptor 30. This effect is mediated by B cells, a major target of interest in MS therapy. Voskuhl and colleagues are taking estriol forward into phase 2 clinical trials in patients with MS, with the goal of preserving cognition. One of the most stunning discoveries in the past few years is that male and female immune systems are tuned very differently. Females have a much stronger TH1 immune reAndrogens PPARα