Human IL-17A protein production is controlled through a PIP5K1α-dependent translational checkpoint.

The cytokine interleukin-17 (IL-17) is secreted by T helper 17 (TH17) cells and is beneficial for microbial control; however, it also causes inflammation and pathological tissue remodeling in autoimmunity. Hence, TH17 cell differentiation and IL-17 production must be tightly regulated, but, to date, this has been defined only in terms of transcriptional control. Phosphatidylinositols are second messengers produced during T cell activation that transduce signals from the T cell receptor (TCR) and costimulatory receptors at the plasma membrane. Here, we found that phosphatidylinositol 4,5-bisphosphate (PIP2) was enriched in the nuclei of human TH17 cells, which depended on the kinase PIP5K1α, and that inhibition of PIP5K1α impaired IL-17A production. In contrast, nuclear PIP2 enrichment was not observed in TH1 or TH2 cells, and these cells did not require PIP5K1α for cytokine production. In T cells from people with multiple sclerosis, IL-17 production elicited by myelin basic protein was blocked by PIP5K1α inhibition. IL-17 protein was affected without altering either the abundance or stability of IL17A mRNA in TH17 cells. Instead, analysis of PIP5K1α-associating proteins revealed that PIP5K1α interacted with ARS2, a nuclear cap-binding complex scaffold protein, to facilitate its binding to IL17A mRNA and subsequent IL-17A protein production. These findings highlight a transcription-independent, translation-dependent mechanism for regulating IL-17A protein production that might be relevant to other cytokines.

IL-17-dependent fibroblastic reticular cell training boosts tissue protective mucosal immunity through IL-10-producing B cells.

Prior experience of pathogen-associated stimuli reduces morbidity and mortality to newly encountered infections through innate immune training, which can be enhanced by childhood vaccination. Fibroblastic reticular cells (FRCs) are stromal cells in lymphoid organs that support lymphocyte localization and survival and modulate adaptive immune responses. IL-17 signaling is important for FRC metabolism and proliferation during inflammatory responses. Here, we show that FRC-intrinsic IL-17 signaling was required for protective antibody-mediated immunity to the gut bacterial pathogen Citrobacter rodentium. We asked whether prior activation of FRC through nonspecific inflammatory "training" of the gut would alter subsequent immune response to C. rodentium. Inflammatory training increased the number of activated FRC in mesenteric LN (MLN) and enhanced the antibody response to C. rodentium in an IL-17­dependent manner. FRC demonstrated cardinal features of innate immune training, including increased epigenetic markers of activation and increased metabolic response to infection. Enhanced responses were still evident 6 weeks after training. The kinetics of bacterial infection were not changed by inflammatory training, but colon inflammation was paradoxically reduced. Mechanistically, IL-10 production by activated B cells was required for colon protective effects of inflammatory training. Enhancing tissue protective B cell responses thus led to increased production of antibody and IL-10, allowing clearance of infection with reduced tissue inflammation. These data identify a new mode of immune training through FRC to modulate future adaptive responses and better preserve host health.

Noncanonical STAT3 activity sustains pathogenic Th17 proliferation and cytokine response to antigen.

The STAT3 signaling pathway is required for early Th17 cell development, and therapies targeting this pathway are used for autoimmune disease. However, the role of STAT3 in maintaining inflammatory effector Th17 cell function has been unexplored. Th17ΔSTAT3 mice, which delete STAT3 in effector Th17 cells, were resistant to experimental autoimmune encephalomyelitis (EAE), a murine model of MS. Th17 cell numbers declined after STAT3 deletion, corresponding to reduced cell cycle. Th17ΔSTAT3 cells had increased IL-6-mediated phosphorylation of STAT1, known to have antiproliferative functions. Th17ΔSTAT3 cells also had reduced mitochondrial membrane potential, which can regulate intracellular Ca2+. Accordingly, Th17ΔSTAT3 cells had reduced production of proinflammatory cytokines when stimulated with myelin antigen but normal production of cytokines when TCR-induced Ca2+ flux was bypassed with ionomycin. Thus, early transcriptional roles of STAT3 in developing Th17 cells are later complimented by noncanonical STAT3 functions that sustain pathogenic Th17 cell proliferation and cytokine production.

The Alzheimer's Disease-Associated Protein BACE1 Modulates T Cell Activation and Th17 Function.

ß-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is best known for its role in Alzheimer's disease amyloid plaque formation but also contributes to neurodegenerative processes triggered by CNS injury. In this article, we report that BACE1 is expressed in murine CD4+ T cells and regulates signaling through the TCR. BACE1-deficient T cells have reduced IL-17A expression under Th17 conditions and reduced CD73 expression in Th17 and inducible T regulatory cells. However, induction of the Th17 and T regulatory transcription factors RORγt and Foxp3 was unaffected. BACE1-deficient T cells showed impaired pathogenic function in experimental autoimmune encephalomyelitis. These data identify BACE1 as a novel regulator of T cell signaling pathways that impact autoimmune inflammatory T cell function.

IL-17 metabolically reprograms activated fibroblastic reticular cells for proliferation and survival.

Lymph-node (LN) stromal cell populations expand during the inflammation that accompanies T cell activation. Interleukin-17 (IL-17)-producing helper T cells (TH17 cells) promote inflammation through the induction of cytokines and chemokines in peripheral tissues. We demonstrate a critical requirement for IL-17 in the proliferation of LN and splenic stromal cells, particularly fibroblastic reticular cells (FRCs), during experimental autoimmune encephalomyelitis and colitis. Without signaling via the IL-17 receptor, activated FRCs underwent cell cycle arrest and apoptosis, accompanied by signs of nutrient stress in vivo. IL-17 signaling in FRCs was not required for the development of TH17 cells, but failed FRC proliferation impaired germinal center formation and antigen-specific antibody production. Induction of the transcriptional co-activator IκBζ via IL-17 signaling mediated increased glucose uptake and expression of the gene Cpt1a, encoding CPT1A, a rate-limiting enzyme of mitochondrial fatty acid oxidation. Hence, IL-17 produced by locally differentiating TH17 cells is an important driver of the activation of inflamed LN stromal cells, through metabolic reprogramming required to support proliferation and survival.

IL-23 and IL-1ß Drive Human Th17 Cell Differentiation and Metabolic Reprogramming in Absence of CD28 Costimulation.

Th17 cells drive autoimmune disease but also control commensal microbes. A common link among antigens from self-proteins or commensal microbiota is relatively low activation of T cell receptor (TCR) and costimulation signaling. Indeed, strong TCR/CD28 stimulation suppressed Th17 cell differentiation from human naive T cells, but not effector/memory cells. CD28 suppressed the classical Th17 transcriptional program, while inducing known Th17 regulators, and acted through an Akt-dependent mechanism. Th17 cells differentiated without CD28 were not anergic: they showed robust proliferation and maintained Th17 cytokine production following restimulation. Interleukin (IL)-23 and IL-1ß promoted glucose uptake and increased glycolysis. Although modestly increased compared to CD28 costimulation, glycolysis was necessary to support Th17 differentiation, indicating that cytokine-mediated metabolic shifts were sufficient to obviate the classical requirement for CD28 in Th17 differentiation. Together, these data propose that, in humans, strength of TCR/CD28/Akt activation serves as a rheostat tuning the magnitude of Th17 development driven by IL-23 and IL-1ß.

Role of estrogen related receptor beta (ESRRB) in DFN35B hearing impairment and dental decay.

BACKGROUND: Congenital forms of hearing impairment can be caused by mutations in the estrogen related receptor beta (ESRRB) gene. Our initial linkage studies suggested the ESRRB locus is linked to high caries experience in humans. METHODS: We tested for association between the ESRRB locus and dental caries in 1,731 subjects, if ESRRB was expressed in whole saliva, if ESRRB was associated with the microhardness of the dental enamel, and if ESRRB was expressed during enamel development of mice. RESULTS: Two families with recessive ESRRB mutations and DFNB35 hearing impairment showed more extensive dental destruction by caries. Expression levels of ESRRB in whole saliva samples showed differences depending on sex and dental caries experience. CONCLUSIONS: The common etiology of dental caries and hearing impairment provides a venue to assist in the identification of individuals at risk to either condition and provides options for the development of new caries prevention strategies, if the associated ESRRB genetic variants are correlated with efficacy.

Synovial membrane immunohistology in early-untreated rheumatoid arthritis reveals high expression of catabolic bone markers that is modulated by methotrexate.

INTRODUCTION: We aimed to investigate the expression and therapeutic modulation of the receptor activator of the NF-κB ligand (RANKL) system in early-untreated rheumatoid arthritis (RA). METHODS: In this study, 15 patients with newly diagnosed RA (median symptom duration 7 months) were started on methotrexate (MTX) 20 mg weekly. Synovial biopsies were obtained by needle arthroscopy at baseline and 8 weeks after initiation of therapy. X-rays of the hands and feet were obtained at baseline and 1 year after diagnosis. Immunohistochemistry was performed to detect RANKL, receptor activator of nuclear factor-κB (RANK) and osteoprotegerin (OPG) in the synovial biopsies. The in vitro effect of MTX was tested on RA-derived primary fibroblasts and the osteoblasts-like osteosarcoma cell line (rtPCR, Western blot and ELISA) and in osteoclasts (tartrate-resistant acid phosphatase staining and dentine pit formation assay). RESULTS: MTX decreased synovial cellularity as well as RANK expression and the RANKL/OPG ratio. We confirmed this effect by a decrease of the mRNA and protein RANKL/OPG ratio in synovial-derived fibroblasts and osteoblasts-like tumoral cells exposed in vitro to methotrexate. Supernatants from MTX treated osteoblasts-like tumoral cells prevented pre-osteoclast formation in the absence of exogenous RANKL. Furthermore, MTX blocked osteoclastogenesis from peripheral blood mononuclear cells despite the presence of macrophage colony stimulating factor and RANKL, which indicates that MTX directly inhibits osteoclastogenesis. CONCLUSIONS: The synovial membrane of early-untreated RA is characterized by a high RANKL/OPG ratio that can be reversed by methotrexate.

Local administration of glucocorticoids decreases synovial citrullination in rheumatoid arthritis.

INTRODUCTION: Protein citrullination is present in the rheumatoid synovium, presumably contributing to the perpetuation of chronic inflammation, in the presence of specific autoimmunity. As a result, the present study examined the possibility that effective antirheumatic treatment will decrease the level of synovial citrullination. METHODS: Synovial biopsies were obtained from 11 rheumatoid arthritis (RA) patients before and after 8 weeks of treatment with 20 mg methotrexate weekly, 15 RA patients before and 2 weeks after an intraarticular glucocorticoid injection, and eight healthy volunteers. Synovial inflammation was assessed with double-blind semiquantitative analysis of lining thickness, cell infiltration, and vascularity by using a 4-point scale. Expression of citrullinated proteins (CPs) with the monoclonal antibody F95 and peptidylarginine deiminase (PAD) 2 and 4 was assessed immunohistochemically with double-blind semiquantitative analysis. In vitro synovial fluid (SF), peripheral blood (PB), mononuclear cells (MCs), and synovial explants obtained from RA patients were incubated with dexamethasone and analyzed with immunohistochemistry for expression of CP as well as PAD2 and PAD4 enzymes. RESULTS: The presence of synovial CP was almost exclusive in RA compared with healthy synovium and correlated with the degree of local inflammation. Treatment with glucocorticoids but not methotrexate alters expression of synovial CP and PAD enzymes, in parallel with a decrease of synovial inflammation. Ex vivo and in vitro studies suggest also a direct effect of glucocorticoids on citrullination, as demonstrated by the decrease in the level of citrullination and PAD expression after incubation of SFMC and synovial explants with dexamethasone. CONCLUSION: Synovial citrullination and PAD expression are dependent on local inflammation and targeted by glucocorticoids.

Monocytes are essential for inhibition of synovial T-cell glucocorticoid-mediated apoptosis in rheumatoid arthritis.

INTRODUCTION: Rheumatoid arthritis (RA) is characterized by synovial inflammation with local accumulation of mononuclear cells such as macrophages and lymphocytes. We previously demonstrated that intra-articular glucocorticoids decrease the synovial tissue (ST) T-cell population and therefore aimed to investigate whether this is mediated through modulation of apoptosis. METHODS: Apoptosis and cell phenotype were evaluated by immunohistochemistry and dual-immunofluorescence in synovial biopsy sections from 12 RA patients before and after a mean of 11 days of an intra-articular triamcinolone knee injection. In vitro, RA synovial fluid (SF)-derived T cells were evaluated for Annexin V expression by multicolor flow cytometry after 24-hour exposure to dexamethasone, methylprednisolone, or triamcinolone. We also tested induction of apoptosis by dexamethasone on psoriatic arthritis SF-derived T cells using the same method. RESULTS: Intra-articular glucocorticoids reduced ST T cells but not macrophage number. ST apoptosis levels were unchanged following treatment, virtually absent from lymphoid aggregates, and minimal in CD3+ cells both before and after treatment. RA SF T cells were resistant to glucocorticoid-induced apoptosis when cultured in the presence of monocytes but were rendered sensitive to all three tested compounds upon SF isolation. Furthermore, transwell coculture of monocytes and T cells demonstrated that soluble factor(s) and not cellular contact are essential for T-cell resistance to glucocorticoid-mediated apoptosis. This feature is RA-specific as far as dexamethasone-induced apoptosis in nonisolated SF T cells obtained from psoriatic arthritis patients is concerned. CONCLUSIONS: We demonstrate that monocytes rescue synovial T cells from glucocorticoid-induced apoptosis, a feature that is specific for RA. To overcome this, we propose the use of monocyte-targeted therapies rather than T-cell apoptosis-inducing therapies.