Role of Hedgehog signalling at the transition from double-positive to single-positive thymocyte

Staphylococcal enterotoxin B exposed to pregnant rats inhibits the hedgehog signaling pathway in thymic T lymphocytes of the offspring

The Hedgehog (Hh) signaling pathway is involved in T cell differentiation and development and plays a major regulatory part in different stages of T cell development. A previous study by us suggested that prenatal exposure to staphylococcal enterotoxin B (SEB) changed the percentages of T cell subpopulation in the offspring thymus. However, it is unclear whether prenatal SEB exposure impacts the Hh signaling pathway in thymic T cells. In the present study, pregnant rats at gestational day 16 were intravenously injected once with 15 μg SEB, and the thymi of both neonatal and adult offspring rats were aseptically acquired to scrutinize the effects of SEB on the Hh signaling pathway. It firstly found that prenatal SEB exposure clearly caused the increased expression of Shh and Dhh ligands of the Hh signaling pathway in thymus tissue of both neonatal and adult offspring rats, but significantly decreased the expression levels of membrane receptors of Ptch1 and Smo, transcription factor Gli1, as well as target genes of CyclinD1, C-myc, and N-myc in Hh signaling pathway of thymic T cells. These data suggest that prenatal SEB exposure inhibits the Hh signaling pathway in thymic T lymphocytes of the neonatal offspring, and this effect can be maintained in adult offspring via the imprinting effect.

The emerging role of the hedgehog signaling pathway in immunity response and autoimmune diseases

The Hedgehog (Hh) family is a prototypical morphogen involved in embryonic patterning, multi-lineage differentiation, self-renewal, morphogenesis, and regeneration. There are studies that have demonstrated that the Hh signaling pathway differentiates developing T cells into MHC-restricted self-antigen tolerant T cells in a concentration-dependent manner in the thymus. Whereas Hh signaling pathway is not required in the differentiation of B cells but is indispensable in maintaining the regeneration of hematopoietic stem cells (HSCs) and the viability of germinal centers (GCs) B cells. The Hh signaling pathway exerts both positive and negative effects on immune responses, which involves activating human peripheral CD4+ T cells, regulating the accumulation of natural killer T (NKT) cells, recruiting and activating macrophages, increasing CD4+Foxp3+ regulatory T cells in the inflammation sites to sustain homeostasis. Hedgehog signaling is involved in the patterning of the embryo, as well as homeostasis of adult tissues. Therefore, this review aims to highlight evidence for Hh signaling in the differentiation, function of immune cells and autoimmune disease. Targeting Hh signaling promises to be a novel, alternative or adjunct approach to treating tumors and autoimmune diseases.

Understanding the Roles of the Hedgehog Signaling Pathway during T-Cell Lymphopoiesis and in T-Cell Acute Lymphoblastic Leukemia (T-ALL)

The Hedgehog (HH) signaling network is one of the main regulators of invertebrate and vertebrate embryonic development. Along with other networks, such as NOTCH and WNT, HH signaling specifies both the early patterning and the polarity events as well as the subsequent organ formation via the temporal and spatial regulation of cell proliferation and differentiation. However, aberrant activation of HH signaling has been identified in a broad range of malignant disorders, where it positively influences proliferation, survival, and therapeutic resistance of neoplastic cells. Inhibitors targeting the HH pathway have been tested in preclinical cancer models. The HH pathway is also overactive in other blood malignancies, including T-cell acute lymphoblastic leukemia (T-ALL). This review is intended to summarize our knowledge of the biological roles and pathophysiology of the HH pathway during normal T-cell lymphopoiesis and in T-ALL. In addition, we will discuss potential therapeutic strategies that might expand the clinical usefulness of drugs targeting the HH pathway in T-ALL.

Sonic Hedgehog signalling in the regulation of barrier tissue homeostasis and inflammation

Epithelial barrier tissues such as the skin and airway form an essential interface between the mammalian host and its external environment. These physical barriers are crucial to prevent damage and disease from environmental insults and allergens. Failure to maintain barrier function against such risks can lead to severe inflammatory disorders, including atopic dermatitis and asthma. Here, we discuss the role of the morphogen Sonic Hedgehog in postnatal skin and lung and the impact of Shh signalling on repair, inflammation, and atopic disease in these tissues.

The Pioneer Transcription Factor Foxa2 Modulates T Helper Differentiation to Reduce Mouse Allergic Airway Disease

Foxa2, a member of the Forkhead box (Fox) family of transcription factors, plays an important role in the regulation of lung function and lung tissue homeostasis. FOXA2 expression is reduced in the lung and airways epithelium of asthmatic patients and in mice absence of Foxa2 from the lung epithelium contributes to airway inflammation and goblet cell hyperplasia. Here we demonstrate a novel role for Foxa2 in the regulation of T helper differentiation and investigate its impact on lung inflammation. Conditional deletion of Foxa2 from T-cells led to increased Th2 cytokine secretion and differentiation, but decreased Th1 differentiation and IFN-γ expression in vitro. Induction of mouse allergic airway inflammation resulted in more severe disease in the conditional Foxa2 knockout than in control mice, with increased cellular infiltration to the lung, characterized by the recruitment of eosinophils and basophils, increased mucus production and increased production of Th2 cytokines and serum IgE. Thus, these experiments suggest that Foxa2 expression in T-cells is required to protect against the Th2 inflammatory response in allergic airway inflammation and that Foxa2 is important in T-cells to maintain the balance of effector cell differentiation and function in the lung.

The pioneer transcription factors Foxa1 and Foxa2 regulate alternative RNA splicing during thymocyte positive selection

During positive selection at the transition from CD4+CD8+ double-positive (DP) to single-positive (SP) thymocyte, TCR signalling results in appropriate MHC restriction and signals for survival and progression. We show that the pioneer transcription factors Foxa1 and Foxa2 are required to regulate RNA splicing during positive selection of mouse T cells and that Foxa1 and Foxa2 have overlapping/compensatory roles. Conditional deletion of both Foxa1 and Foxa2 from DP thymocytes reduced positive selection and development of CD4SP, CD8SP and peripheral naïve CD4+ T cells. Foxa1 and Foxa2 regulated the expression of many genes encoding splicing factors and regulators, including Mbnl1, H1f0, Sf3b1, Hnrnpa1, Rnpc3, Prpf4b, Prpf40b and Snrpd3. Within the positively selecting CD69+DP cells, alternative RNA splicing was dysregulated in the double Foxa1/Foxa2 conditional knockout, leading to >850 differentially used exons. Many genes important for this stage of T-cell development (Ikzf1-3, Ptprc, Stat5a, Stat5b, Cd28, Tcf7) and splicing factors (Hnrnpab, Hnrnpa2b1, Hnrnpu, Hnrnpul1, Prpf8) showed multiple differentially used exons. Thus, Foxa1 and Foxa2 are required during positive selection to regulate alternative splicing of genes essential for T-cell development, and, by also regulating splicing of splicing factors, they exert widespread control of alternative splicing.

The hedgehog pathway suppresses neuropathogenesis in CD4 T cell-driven inflammation

The concerted actions of the CNS and the immune system are essential to coordinating the outcome of neuroinflammatory responses. Yet, the precise mechanisms involved in this crosstalk and their contribution to the pathophysiology of neuroinflammatory diseases largely elude us. Here, we show that the CNS-endogenous hedgehog pathway, a signal triggered as part of the host response during the inflammatory phase of multiple sclerosis and experimental autoimmune encephalomyelitis, attenuates the pathogenicity of human and mouse effector CD4 T cells by regulating their production of inflammatory cytokines. Using a murine genetic model, in which the hedgehog signalling is compromised in CD4 T cells, we show that the hedgehog pathway acts on CD4 T cells to suppress the pathogenic hallmarks of autoimmune neuroinflammation, including demyelination and axonal damage, and thus mitigates the development of experimental autoimmune encephalomyelitis. Impairment of hedgehog signalling in CD4 T cells exacerbates brain-brainstem-cerebellum inflammation and leads to the development of atypical disease. Moreover, we present evidence that hedgehog signalling regulates the pathogenic profile of CD4 T cells by limiting their production of the inflammatory cytokines granulocyte-macrophage colony-stimulating factor and interferon-γ and by antagonizing their inflammatory program at the transcriptome level. Likewise, hedgehog signalling attenuates the inflammatory phenotype of human CD4 memory T cells. From a therapeutic point of view, our study underlines the potential of harnessing the hedgehog pathway to counteract ongoing excessive CNS inflammation, as systemic administration of a hedgehog agonist after disease onset effectively halts disease progression and significantly reduces neuroinflammation and the underlying neuropathology. We thus unveil a previously unrecognized role for the hedgehog pathway in regulating pathogenic inflammation within the CNS and propose to exploit its ability to modulate this neuroimmune network as a strategy to limit the progression of ongoing neuroinflammation.

Sonic Hedgehog Is a Determinant of γδ T-Cell Differentiation in the Thymus

Here we investigate the function of Hedgehog (Hh) signaling in thymic γδ T-cell maturation and subset differentiation. Analysis of Hh mutants showed that Hh signaling promotes γδ T-cell development in the thymus and influences γδ T-cell effector subset distribution. Hh-mediated transcription in thymic γδ cells increased γδ T-cell number, and promoted their maturation and increased the γδNKT subset, whereas inhibition of Hh-mediated transcription reduced the thymic γδ T-cell population and increased expression of many genes that are normally down-regulated during γδ T-cell maturation. These changes were also evident in spleen, where increased Hh signaling increased γδNKT cells, but reduced CD27-CD44+ and Vγ2+ populations. Systemic in vivo pharmacological Smoothened-inhibition reduced γδ T-cell and γδNKT cells in the thymus, and also reduced splenic γδ T-cell and γδNKT populations, indicating that Hh signaling also influences homeostasis of peripheral γδ T-cell populations. Taken together our data indicate that Sonic Hedgehog is an important determinant of γδ T-cell effector subset differentiation.

Hedgehog pathway mutations drive oncogenic transformation in high-risk T-cell acute lymphoblastic leukemia

The role of Hedgehog signaling in normal and malignant T-cell development is controversial. Recently, Hedgehog pathway mutations have been described in T-ALL, but whether mutational activation of Hedgehog signaling drives T-cell transformation is unknown, hindering the rationale for therapeutic intervention. Here, we show that Hedgehog pathway mutations predict chemotherapy resistance in human T-ALL, and drive oncogenic transformation in a zebrafish model of the disease. We found Hedgehog pathway mutations in 16% of 109 childhood T-ALL cases, most commonly affecting its negative regulator PTCH1. Hedgehog mutations were associated with resistance to induction chemotherapy (P = 0.009). Transduction of wild-type PTCH1 into PTCH1-mutant T-ALL cells induced apoptosis (P = 0.005), a phenotype that was reversed by downstream Hedgehog pathway activation (P = 0.007). Transduction of most mutant PTCH1, SUFU, and GLI alleles into mammalian cells induced aberrant regulation of Hedgehog signaling, indicating that these mutations are pathogenic. Using a CRISPR/Cas9 system for lineage-restricted gene disruption in transgenic zebrafish, we found that ptch1 mutations accelerated the onset of notch1-induced T-ALL (P = 0.0001), and pharmacologic Hedgehog pathway inhibition had therapeutic activity. Thus, Hedgehog-activating mutations are driver oncogenic alterations in high-risk T-ALL, providing a molecular rationale for targeted therapy in this disease.

Foxa1 and Foxa2 in thymic epithelial cells (TEC) regulate medullary TEC and regulatory T-cell maturation

The Foxa1 and Foxa2 transcription factors are essential for mouse development. Here we show that they are expressed in thymic epithelial cells (TEC) where they regulate TEC development and function, with important consequences for T-cell development. TEC are essential for T-cell differentiation, lineage decisions and repertoire selection. Conditional deletion of Foxa1 and Foxa2 from murine TEC led to a smaller thymus with a greater proportion of TEC and a greater ratio of medullary to cortical TEC. Cell-surface MHCI expression was increased on cortical TEC in the conditional Foxa1Foxa2 knockout thymus, and MHCII expression was reduced on both cortical and medullary TEC populations. These changes in TEC differentiation and MHC expression led to a significant reduction in thymocyte numbers, reduced positive selection of CD4+CD8+ cells to the CD4 lineage, and increased CD8 cell differentiation. Conditional deletion of Foxa1 and Foxa2 from TEC also caused an increase in the medullary TEC population, and increased expression of Aire, but lower cell surface MHCII expression on Aire-expressing mTEC, and increased production of regulatory T-cells. Thus, Foxa1 and Foxa2 in TEC promote positive selection of CD4SP T-cells and modulate regulatory T-cell production and activity, of importance to autoimmunity.

The kinesin motor protein Kif7 is required for T-cell development and normal MHC expression on thymic epithelial cells (TEC) in the thymus

Kif7 is a ciliary kinesin motor protein that regulates mammalian Hedgehog pathway activation through influencing structure of the primary cilium. Here we show that Kif7 is required for normal T-cell development, despite the fact that T-cells lack primary cilia. Analysis of Kif7-deficient thymus showed that Kif7-deficiency increases the early CD44+CD25+CD4-CD8- thymocyte progenitor population but reduces differentiation to CD4+CD8+ double positive (DP) cell. At the transition from DP to mature T-cell, Kif7-deficiency selectively delayed maturation to the CD8 lineage. Expression of CD5, which correlates with TCR signal strength, was reduced on DP and mature CD4 and CD8 cells, as a result of thymocyte-intrinsic Kif7-deficiency, and Kif7-deficient T-cells from radiation chimeras activated less efficiently when stimulated with anti-CD3 and anti-CD28 in vitro. Kif7-deficient thymocytes showed higher expression of the Hedgehog target gene Ptch1 than WT, but were less sensitive to treatment with recombinant Shh, and Kif7-deficient T-cell development was refractory to neutralisation of endogenous Hh proteins, indicating that Kif7-deficient thymocytes were unable to interpret changes in the Hedgehog signal. In addition, Kif7-deficiency reduced cell-surface MHCII expression on thymic epithelial cells.

Gli3 in fetal thymic epithelial cells promotes thymocyte positive selection and differentiation by repression of Shh

Gli3 is a Hedgehog (Hh)-responsive transcription factor that can function as a transcriptional repressor or activator. We show that Gli3 activity in mouse thymic epithelial cells (TECs) promotes positive selection and differentiation from CD4⁺ CD8⁺ to CD4⁺ CD8^- single-positive (SP4) cells in the fetal thymus and that Gli3 represses Shh Constitutive deletion of Gli3, and conditional deletion of Gli3 from TECs, reduced differentiation to SP4, whereas conditional deletion of Gli3 from thymocytes did not. Conditional deletion of Shh from TECs increased differentiation to SP4, and expression of Shh was upregulated in the Gli3-deficient thymus. Use of a transgenic Hh reporter showed that the Hh pathway was active in thymocytes, and increased in the Gli3-deficient fetal thymus. Neutralisation of endogenous Hh proteins in the Gli3^-/- thymus restored SP4 differentiation, indicating that Gli3 in TECs promotes SP4 differentiation by repression of Shh Transcriptome analysis showed that Hh-mediated transcription was increased whereas TCR-mediated transcription was decreased in Gli3^-/- thymocytes compared with wild type.

The transcription factor Gli3 promotes B cell development in fetal liver through repression of Shh

Solanki et al. show that stromal activity of the transcription factor Gli3 is required for B cell development in the fetal liver. Gli3 functions to repress Shh expression, and Shh signals to developing B cells to regulate their development at multiple developmental stages.

Before birth, B cells develop in the fetal liver (FL). In this study, we show that Gli3 activity in the FL stroma is required for B cell development. In the Gli3-deficient FL, B cell development was reduced at multiple stages, whereas the Sonic hedgehog (Hh [Shh])–deficient FL showed increased B cell development, and Gli3 functioned to repress Shh transcription. Use of a transgenic Hh-reporter mouse showed that Shh signals directly to developing B cells and that Hh pathway activation was increased in developing B cells from Gli3-deficient FLs. RNA sequencing confirmed that Hh-mediated transcription is increased in B-lineage cells from Gli3-deficient FL and showed that these cells expressed reduced levels of B-lineage transcription factors and B cell receptor (BCR)/pre-BCR–signaling genes. Expression of the master regulators of B cell development Ebf1 and Pax5 was reduced in developing B cells from Gli3-deficient FL but increased in Shh-deficient FL, and in vitro Shh treatment or neutralization reduced or increased their expression, respectively.

GATA binding protein 3 is correlated with leptin regulation of PPARγ1 in hepatic stellate cells

Accumulating evidence reveals that hormone leptin, mainly produced by adipocyte, plays a unique role in promotion of liver fibrosis. Hepatic stellate cell (HSC) activation is a key step in liver fibrosis and peroxisome‐proliferator activated receptor γ (PPARγ) exerts a crucial role in inhibition of HSC activation. Our previous researches demonstrated that leptin reduced PPARγ1 (a major subtype of PPARγ in HSCs) expression through GATA binding protein 2 (GATA2) binding to a site around −2323 in PPARγ1 promoter. The present researches aimed to examine the effect of GATA3 on leptin‐induced inhibition of PPARγ1 and elucidate the relationship between GATA3 and GATA2. Gene expressions were analysed by real‐time PCR, western blot, luciferase assay and immunostaining. C57BL/6J ob/ob mouse model of thioacetamide‐induced liver injury was used in vivo. Results demonstrate that leptin significantly induces GATA3 expression in HSCs by multiple signalling pathways including NADPH oxidase pathway. There exist crosstalks between NADPH oxidase pathway and the other pathways. GATA3 can bind to GATA2‐binding site in PPARγ1 promoter and interacts with GATA2, contributing to leptin inhibition of PPARγ1 expression in HSCs. These data demonstrated novel molecular events for leptin inhibition of PPARγ1 expression in HSCs and thus might have potential implications for clarifying the detailed mechanisms underlying liver fibrosis in diseases in which circulating leptin levels are elevated such as non‐alcoholic steatohepatitis in obese patients.

Hedgehog Signalling in the Embryonic Mouse Thymus

T cells develop in the thymus, which provides an essential environment for T cell fate specification, and for the differentiation of multipotent progenitor cells into major histocompatibility complex (MHC)-restricted, non-autoreactive T cells. Here we review the role of the Hedgehog signalling pathway in T cell development, thymic epithelial cell (TEC) development, and thymocyte-TEC cross-talk in the embryonic mouse thymus during the last week of gestation.

Ptch2 loss drives myeloproliferation and myeloproliferative neoplasm progression

Klein et al. show that Ptch2 loss in either the niche or in hematopoietic cells drives myeloproliferation and accelerates JAK2V617F-driven pathogenesis, causing transformation of nonlethal chronic MPNs into aggressive lethal leukemias.

JAK2V617F⁺ myeloproliferative neoplasms (MPNs) frequently progress into leukemias, but the factors driving this process are not understood. Here, we find excess Hedgehog (HH) ligand secretion and loss of PTCH2 in myeloproliferative disease, which drives canonical and noncanonical HH-signaling. Interestingly, Ptch2^−/− mice mimic dual pathway activation and develop a MPN-phenotype with leukocytosis (neutrophils and monocytes), strong progenitor and LKS mobilization, splenomegaly, anemia, and loss of lymphoid lineages. HSCs exhibit increased cell cycling with improved stress hematopoiesis after 5-FU treatment, and this results in HSC exhaustion over time. Cytopenias, LKS loss, and mobilization are all caused by loss of Ptch2 in the niche, whereas hematopoietic loss of Ptch2 drives leukocytosis and promotes LKS maintenance and replating capacity in vitro. Ptch2^−/− niche cells show hyperactive noncanonical HH signaling, resulting in reduced production of essential HSC regulators (Scf, Cxcl12, and Jag1) and depletion of osteoblasts. Interestingly, Ptch2 loss in either the niche or in hematopoietic cells dramatically accelerated human JAK2V617F-driven pathogenesis, causing transformation of nonlethal chronic MPNs into aggressive lethal leukemias with >30% blasts in the peripheral blood. Our findings suggest HH ligand inhibitors as possible drug candidates that act on hematopoiesis and the niche to prevent transformation of MPNs into leukemias.

Sonic Hedgehog regulates thymic epithelial cell differentiation

Sonic Hedgehog (Shh) is expressed in the thymus, where it regulates T cell development. Here we investigated the influence of Shh on thymic epithelial cell (TEC) development. Components of the Hedgehog (Hh) signalling pathway were expressed by TEC, and use of a Gli Binding Site-green fluorescence protein (GFP) transgenic reporter mouse demonstrated active Hh-dependent transcription in TEC in the foetal and adult thymus. Analysis of Shh-deficient foetal thymus organ cultures (FTOC) showed that Shh is required for normal TEC differentiation. Shh-deficient foetal thymus contained fewer TEC than wild type (WT), the proportion of medullary TEC was reduced relative to cortical TEC, and cell surface expression of MHC Class II molecules was increased on both cortical and medullary TEC populations. In contrast, the Gli3-deficient thymus, which shows increased Hh-dependent transcription in thymic stroma, had increased numbers of TEC, but decreased cell surface expression of MHC Class II molecules on both cortical and medullary TEC. Neutralisation of endogenous Hh proteins in WT FTOC led to a reduction in TEC numbers, and in the proportion of mature Aire-expressing medullary TEC, but an increase in cell surface expression of MHC Class II molecules on medullary TEC. Likewise, conditional deletion of Shh from TEC in the adult thymus resulted in alterations in TEC differentiation and consequent changes in T cell development. TEC numbers, and the proportion of mature Aire-expressing medullary TEC were reduced, and cell surface expression of MHC Class II molecules on medullary TEC was increased. Differentiation of mature CD4 and CD8 single positive thymocytes was increased, demonstrating the regulatory role of Shh production by TEC on T cell development. Treatment of human thymus explants with recombinant Shh or neutralising anti-Shh antibody indicated that the Hedgehog pathway is also involved in regulation of differentiation from DP to mature SP T cells in the human thymus.

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TEC express components of the Hedgehog signalling pathway and transduce it's signals.

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Sonic hedgehog (Shh) is required for normal TEC development.

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Sonic hedgehog particularly influences differentiation to the medullary TEC lineage.

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Shh regulates cell surface MHCII expression on both cortical and medullary TEC.

The transcriptional activator Gli2 modulates T-cell receptor signalling through attenuation of AP-1 and NFκB activity

Different tissues contain diverse and dynamic cellular niches, providing distinct signals to tissue-resident or migratory infiltrating immune cells. Hedgehog (Hh) proteins are secreted inter-cellular signalling molecules, which are essential during development and are important in cancer, post-natal tissue homeostasis and repair. Hh signalling mediated by the Hh-responsive transcription factor Gli2 also has multiple roles in T-lymphocyte development and differentiation. Here, we investigate the function of Gli2 in T-cell signalling and activation. Gene transcription driven by the Gli2 transcriptional activator isoform (Gli2A) attenuated T-cell activation and proliferation following T-cell receptor (TCR) stimulation. Expression of Gli2A in T-cells altered gene expression profiles, impaired the TCR-induced Ca²⁺ flux and nuclear expression of NFAT2, suppressed upregulation of molecules essential for activation, and attenuated signalling pathways upstream of the AP-1 and NFκB complexes, leading to reduced activation of these important transcription factors. Inhibition of physiological Hh-dependent transcription increased NFκB activity upon TCR ligation. These data are important for understanding the molecular mechanisms of immunomodulation, particularly in tissues where Hh proteins or other Gli-activating ligands such as TGFβ are upregulated, including during inflammation, tissue damage and repair, and in tumour microenvironments.

An overview of the intrathymic intricacies of T cell development

The generation of a functional and diverse repertoire of T cells occurs in the thymus from precursors arriving from the bone marrow. In this article, we introduce the various stages of mouse thymocyte development and highlight recent work using various in vivo, and, where appropriate, in vitro models of T cell development that led to discoveries in the regulation afforded by transcription factors and receptor-ligand signaling pathways in specifying, maintaining, and promoting the T cell lineage and the production of T cells. This review also discusses the role of the thymic microenvironment in providing a niche for the successful development of T cells. In particular, we focus on advances in Notch signaling and developments in Notch ligand interactions in this process.

The hedgehog receptor patched1 in T cells is dispensable for adaptive immunity in mice

Hedgehog (Hh) signaling modulates T cell development and function but its exact role remains a matter of debate. To further address this issue we made use of conditional knock-out mice in which the Hh receptor Patched1 (Ptch) is inactivated in the T cell lineage. Thymocyte development was moderately compromised by the deletion of Ptch as characterized by reduced numbers of CD4 and CD8 single-positive cells. In contrast, peripheral T cells were not affected. Proliferation and IFNγ secretion by Ptch-deficient T cells were indistinguishable from controls irrespectively of whether we used strong or suboptimal conditions for stimulation. Analysis of CTL and T_reg cell functions did not reveal any differences between both genotypes, and T cell apoptosis induced by glucocorticoids or γ-irradiation was also similar. Surprisingly, absence of Ptch did not lead to an activation of canonic Hh signaling in peripheral T cells as indicated by unaltered expression levels of Gli1 and Gli2. To test whether we could uncover any role of Ptch in T cells in vivo we subjected the mutant mice to three different disease models, namely allogeneic bone marrow transplantation mimicking graft-versus-host disease, allergic airway inflammation as a model of asthma and growth of adoptively transferred melanoma cells as a means to test tumor surveillance by the immune system. Nonetheless, we were neither able to demonstrate any difference in the disease courses nor in any pathogenic parameter in these three models of adaptive immunity. We therefore conclude that the Hh receptor Ptch is dispensable for T cell function in vitro as well as in vivo.

Tissue-derived hedgehog proteins modulate Th differentiation and disease

Genome-wide association studies of complex immune-mediated diseases have indicated that many genetic factors, each with individual low risk, contribute to overall disease. It is therefore timely and important to characterize how immune responses may be subtly modified by tissue context. In this article, we explore the role of tissue-derived molecules in influencing the function of T cells, which, owing to their migratory nature, come into contact with many different microenvironments through their lifespan. Hedgehog (Hh) proteins act as secreted morphogens, providing concentration-dependent positional and temporal cell-fate specification in solid tissues. Hh signaling is required for embryogenesis and is important in postnatal tissue renewal and in malignancy. However, the function of Hh in dynamic, fluid systems, such as in mammalian immunity, is largely unknown. In this article, we show that Hh-dependent transcription in T cells promoted Th2 transcriptional programs and differentiation, exacerbating allergic disease. Of interest, expression of Sonic Hh increased in lung epithelial cells following the induction of allergic disease, and lung T cells upregulated Hh target gene expression, indicating that T cells respond to locally secreted Hh ligands in vivo. We show that Il4, the key Th2 cytokine, is a novel transcriptional target of Hh signals in T cells, providing one mechanism for the role of Hh in Th differentiation. We propose that Hh, secreted from inflamed, remodeling, or malignant tissue, can modulate local T cell function. Our data present an unexpected and novel role for tissue-derived morphogens in the regulation of fluid immune responses, with implications for allergy and tumor responses, suggesting new uses for anti-Hh therapeutics.