Absence of NC14A Domain of COLXVII/BP180 in Mice Results in IL-17‒Associated Skin Inflammation.

The deletion of exon 18 from Col17a1 in transgenic ΔNC14A mice results in the absence of the NC14A domain. NC14A corresponds to the human NC16A domain, the immunodominant epitope in bullous pemphigoid. Before the age of 1 year, 84% of ΔNC14A mice have developed severe itch and skin erosion. Further characterization of mice with mutated CoLXVII (Bp180) revealed acanthosis; subepidermal blistering; and inflammatory cell infiltrates, especially neutrophils, eosinophils, and mast cells in the lesional skin. Direct immunofluorescence analysis detected linear complement C3, IgG, and/or IgA deposition in the dermo‒epidermal junction of symptomatic ΔNC14A mice. Elevated gene expression of IL-17‒associated cytokines was detected in the lesional skin. An increased proportion of dendritic cells, myeloid-derived suppressor cells, and NK cells and a decrease of T cells were found in both the spleen and lymph nodes of symptomatic ΔNC14A mice. The proportions of B cells and regulatory T cells were increased in lymph nodes. An 8-week treatment with an anti‒IL-17A decreased the expression of Il6, Il23a, and Cxcl1 in the nonlesional skin. Our results suggest that the absence of the NC14A domain of CoLXVII in mice causes an autoimmune response against the cutaneous basement membrane and manifests as an IL-17‒associated inflammation in the skin.

The effects of post-translational modifications on Th17/Treg cell differentiation.

Regulatory T (Treg) cells and Th17 cells are subsets of CD4+ T cells which play an essential role in immune homeostasis and infection. Dysregulation of the Th17/Treg cell balance was shown to be implicated in the development and progression of several disorders such as autoimmune disease, inflammatory disease, and cancer. Multiple factors, including T cell receptor (TCR) signals, cytokines, metabolic and epigenetic regulators can influence the differentiation of Th17 and Treg cells and affect their balance. Accumulating evidence indicates that the activity of key molecules such as forkhead box P3 (Foxp3), the retinoic acid-related orphan receptor gamma t (RORγt), and signal transducer and activator of transcription (STAT)s are modulated by the number of post-translational modifications (PTMs) such as phosphorylation, methylation, nitrosylation, acetylation, glycosylation, lipidation, ubiquitination, and SUMOylation. PTMs might affect the protein folding efficiency and protein conformational stability, and consequently determine protein structure, localization, and function. Here, we review the recent progress in our understanding of how PTMs modify the key molecules involved in the Th17/Treg cell differentiation, regulate the Th17/Treg balance, and initiate autoimmune diseases caused by dysregulation of the Th17/Treg balance. A better understanding of Th17/Treg regulation may help to develop novel potential therapeutics to treat immune-related diseases.

Gene Doping with Peroxisome-Proliferator-Activated Receptor Beta/Delta Agonists Alters Immunity but Exercise Training Mitigates the Detection of Effects in Blood Samples.

Synthetic ligands of peroxisome-proliferator-activated receptor beta/delta (PPARß/δ) are being used as performance-enhancing drugs by athletes. Since we previously showed that PPARß/δ activation affects T cell biology, we wanted to investigate whether a specific blood T cell signature could be employed as a method to detect the use of PPARß/δ agonists. We analyzed in primary human T cells the in vitro effect of PPARß/δ activation on fatty acid oxidation (FAO) and on their differentiation into regulatory T cells (Tregs). Furthermore, we conducted studies in mice assigned to groups according to an 8-week exercise training program and/or a 6-week treatment with 3 mg/kg/day of GW0742, a PPARß/δ agonist, in order to (1) determine the immune impact of the treatment on secondary lymphoid organs and to (2) validate a blood signature. Our results show that PPARß/δ activation increases FAO potential in human and mouse T cells and mouse secondary lymphoid organs. This was accompanied by increased Treg polarization of human primary T cells. Moreover, Treg prevalence in mouse lymph nodes was increased when PPARß/δ activation was combined with exercise training. Lastly, PPARß/δ activation increased FAO potential in mouse blood T cells. Unfortunately, this signature was masked by training in mice. In conclusion, beyond the fact that it is unlikely that this signature could be used as a doping-control strategy, our results suggest that the use of PPARß/δ agonists could have potential detrimental immune effects that may not be detectable in blood samples.

Invalidation of the Transcriptional Modulator of Lipid Metabolism PPARß/δ in T Cells Prevents Age-Related Alteration of Body Composition and Loss of Endurance Capacity.

Anti-inflammatory regulatory T cells (Tregs) are the most metabolically flexible CD4+ T cells by using both glycolysis and fatty acid oxidation (FAO) which allow them to migrate in tissues. With aging, Tregs accumulate in secondary lymphoid organs and are involved in impairment of skeletal muscle (SKM) regeneration and mass maintenance. In this study, we showed that a deletion of a FAO modulator, peroxisome proliferator-activated receptor beta/delta (PPARß/δ), specifically in T cells (KO-T PPARß/δ), increased the number of CD4+ T cells at day 2 following a cardiotoxin-induced SKM regeneration. Older KO-T PPARß/δ mice maintained a Tregs prevalence in lymph nodes similar to young mice. Surprisingly, KO-T PPARß/δ mice were protected from the effects of age on lean and fat mass and endurance capacity. Our results lead us to propose an original potential role of T cell metabolism in the effects of aging on the maintenance of body composition and endurance capacity.

Complementary Immunometabolic Effects of Exercise and PPARß/δ Agonist in the Context of Diet-Induced Weight Loss in Obese Female Mice.

Regular aerobic exercise, independently of weight loss, improves metabolic and anti-inflammatory states, and can be regarded as beneficial in counteracting obesity-induced low-grade inflammation. However, it is still unknown how exercise alters immunometabolism in a context of dietary changes. Agonists of the Peroxisome Proliferator Activated-Receptor beta/delta (PPARß/δ) have been studied this last decade as "exercise-mimetics", which are potential therapies for metabolic diseases. In this study, we address the question of whether PPARß/δ agonist treatment would improve the immunometabolic changes induced by exercise in diet-induced obese female mice, having switched from a high fat diet to a normal diet. 24 mice were assigned to groups according to an 8-week exercise training program and/or an 8-week treatment with 3 mg/kg/day of GW0742, a PPARß/δ agonist. Our results show metabolic changes of peripheral lymphoid tissues with PPARß/δ agonist (increase in fatty acid oxidation gene expression) or exercise (increase in AMPK activity) and a potentiating effect of the combination of both on the percentage of anti-inflammatory Foxp3+ T cells. Those effects are associated with a decreased visceral adipose tissue mass and skeletal muscle inflammation (TNF-α, Il-6, Il-1ß mRNA level), an increase in skeletal muscle oxidative capacities (citrate synthase activity, endurance capacity), and insulin sensitivity. We conclude that a therapeutic approach targeting the PPARß/δ pathway would improve obesity treatment.

Decrease in αß/γδ T-cell ratio is accompanied by a reduction in high-fat diet-induced weight gain, insulin resistance, and inflammation.

The implication of αß and γδ T cells in obesity-associated inflammation and insulin resistance (IR) remains uncertain. Mice lacking γδ T cells show either no difference or a decrease in high-fat diet (HFD)-induced IR, whereas partial depletion in γδ T cells does not protect from HFD-induced IR. αß T-cell deficiency leads to a decrease in white adipose tissue (WAT) inflammation and IR without weight change, but partial depletion of these cells has not been studied. We previously described a mouse model overexpressing peroxisome proliferator-activated receptor ß (PPAR-ß) specifically in T cells [transgenic (Tg) T-PPAR-ß] that exhibits a partial depletion in αß T cells and no change in γδ T-cell number. This results in a decreased αß/γδ T-cell ratio in lymphoid organs. We now show that Tg T-PPAR-ß mice are partially protected against HFD-induced weight gain and exhibit decreased IR and liver steatosis independently of animal weight. These mice display an alteration of WAT-depots distribution with an increased epididymal-WAT mass and a decreased subcutaneous WAT mass. Immune cell number is decreased in both WAT-depots, except for γδ T cells, which are increased in epididymal-WAT. Overall, we show that decreasing αß/γδ T-cell ratio in WAT-depots alters their inflammatory state and mass repartition, which might be involved in improvement of insulin sensitivity.-Le Menn, G., Sibille, B., Murdaca, J., Rousseau, A.-S., Squillace, R., Vergoni, B., Cormont, M., Niot, I., Grimaldi, P. A., Mothe-Satney, I., Neels, J. G. Decrease in αß/γδ T-cell ratio is accompanied by a reduction in high-fat diet-induced weight gain, insulin resistance, and inflammation.

Developmental Requirement of Homeoprotein Otx2 for Specific Habenulo-Interpeduncular Subcircuits.

The habenulo-interpeduncular system (HIPS) is now recognized as a critical circuit modulating aversion, reward, and social behavior. There is evidence that dysfunction of this circuit leads to psychiatric disorders. Because psychiatric diseases may originate in developmental abnormalities, it is crucial to investigate the developmental mechanisms controlling the formation of the HIPS. Thus far, this issue has been the focus of limited studies. Here, we explored the developmental processes underlying the formation of the medial habenula (MHb) and its unique output, the interpeduncular nucleus (IPN), in mice independently of their gender. We report that the Otx2 homeobox gene is essential for the proper development of both structures. We show that MHb and IPN neurons require Otx2 at different developmental stages and, in both cases, Otx2 deletion leads to disruption of HIPS subcircuits. Finally, we show that Otx2+ neurons tend to be preferentially interconnected. This study reveals that synaptically connected components of the HIPS, despite radically different developmental strategies, share high sensitivity to Otx2 expression.SIGNIFICANCE STATEMENT Brain reward circuits are highly complex and still poorly understood. In particular, it is important to understand how these circuits form as many psychiatric diseases may arise from their abnormal development. This work shows that Otx2, a critical evolutionary conserved gene implicated in brain development and a predisposing factor for psychiatric diseases, is required for the formation of the habenulo-interpeduncular system (HIPS), an important component of the reward circuit. Otx2 deletion affects multiple processes such as proliferation and migration of HIPS neurons. Furthermore, neurons expressing Otx2 are preferentially interconnected. Therefore, Otx2 expression may represent a code that specifies the connectivity of functional subunits of the HIPS. Importantly, the Otx2 conditional knock-out animals used in this study might represent a new genetic model of psychiatric diseases.

Regulation of Immune Cell Function by PPARs and the Connection with Metabolic and Neurodegenerative Diseases.

Increasing evidence points towards the existence of a bidirectional interconnection between metabolic disease and neurodegenerative disorders, in which inflammation is linking both together. Activation of members of the peroxisome proliferator-activated receptor (PPAR) family has been shown to have beneficial effects in these interlinked pathologies, and these improvements are often attributed to anti-inflammatory effects of PPAR activation. In this review, we summarize the role of PPARs in immune cell function, with a focus on macrophages and T cells, and how this was shown to contribute to obesity-associated inflammation and insulin resistance, atherosclerosis, and neurodegenerative disorders. We address gender differences as a potential explanation in observed contradictory results, and we highlight PPAR-induced metabolic changes as a potential mechanism of regulation of immune cell function through these nuclear receptors. Together, immune cell-specific activation of PPARs present a promising therapeutic approach to treat both metabolic and neurodegenerative diseases.

A role for Peroxisome Proliferator-Activated Receptor Beta in T cell development.

Metabolism plays an important role in T cell biology and changes in metabolism drive T cell differentiation and fate. Most research on the role of metabolism in T lymphocytes focuses on mature T cells while only few studies have investigated the role of metabolism in T cell development. In this study, we report that activation or overexpression of the transcription factor Peroxisome Proliferator-Activated Receptor ß (PPARß) increases fatty acid oxidation in T cells. Furthermore, using both in vivo and in vitro models, we demonstrate that PPARß activation/overexpression inhibits thymic T cell development by decreasing proliferation of CD4-CD8- double-negative stage 4 (DN4) thymocytes. These results support a model where PPARß activation/overexpression favours fatty acid- instead of glucose-oxidation in developing T cells, thereby hampering the proliferative burst normally occurring at the DN4 stage of T cell development. As a consequence, the αß T cells that are derived from DN4 thymocytes are dramatically decreased in peripheral lymphoid tissues, while the γδ T cell population remains untouched. This is the first report of a direct role for a member of the PPAR family of nuclear receptors in the development of T cells.