The Autoimmunity-Associated Gene CLEC16A Modulates Thymic Epithelial Cell Autophagy and Alters T Cell Selection.

CLEC16A variation has been associated with multiple immune-mediated diseases, including type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, celiac disease, Crohn's disease, Addison's disease, primary biliary cirrhosis, rheumatoid arthritis, juvenile idiopathic arthritis, and alopecia areata. Despite strong genetic evidence implicating CLEC16A in autoimmunity, this gene's broad association with disease remains unexplained. We generated Clec16a knock-down (KD) mice in the nonobese diabetic (NOD) model for type 1 diabetes and found that Clec16a silencing protected against autoimmunity. Disease protection was attributable to T cell hyporeactivity, which was secondary to changes in thymic epithelial cell (TEC) stimuli that drive thymocyte selection. Our data indicate that T cell selection and reactivity were impacted by Clec16a variation in thymic epithelium owing to Clec16a's role in TEC autophagy. These findings provide a functional link between human CLEC16A variation and the immune dysregulation that underlies the risk of autoimmunity.

The type 1 diabetes candidate gene Dexi does not affect disease risk in the nonobese diabetic mouse model.

Genome-wide association studies have implicated more than 50 genomic regions in type 1 diabetes (T1D). A T1D region at chromosome 16p13.13 includes the candidate genes CLEC16A and DEXI. Conclusive evidence as to which gene is causal for the disease association of this region is missing. We previously reported that Clec16a deficiency modified immune reactivity and protected against autoimmunity in the nonobese diabetic (NOD) mouse model for T1D. However, the diabetes-associated SNPs at 16p13.13 were described to also impact on DEXI expression and others have argued that DEXI is the causal gene in this disease locus. To help resolve whether DEXI affects disease, we generated Dexi knockout (KO) NOD mice. We found that Dexi deficiency had no effect on the frequency of diabetes. To test for possible interactions between Dexi and Clec16a, we intercrossed Dexi KO and Clec16a knockdown (KD) NOD mice. Dexi KO did not modify the disease protection afforded by Clec16a KD. We conclude that Dexi plays no role in autoimmune diabetes in the NOD model. Our data provide strongly suggestive evidence that CLEC16A, not DEXI, is causal for the T1D association of variants in the 16p13.13 region.

Anti-CD3 Antibody for the Prevention of Type 1 Diabetes: A Story of Perseverance.

Type 1 diabetes (T1D) is an autoimmune disease characterized by an insulin deficiency. Ever since the discovery of insulin almost 100 years ago, patients with T1D have relied on multiple daily insulin injections to survive an otherwise deadly disease. Despite decades of research and clinical trials, no treatment exists yet to prevent or cure T1D. A recent prevention trial using the anti-CD3 antibody teplizumab in individuals at a high risk of developing T1D has provided the first piece of evidence that a safe and transient intervention may be able to delay disease. In this Perspective, we review the 40-year long history of anti-CD3 and discuss how this antibody became a candidate for the treatment of autoimmune diabetes. The path that leads to its use in this latest clinical trial for T1D has been winding and strewn with setbacks. The molecular actions of the anti-CD3 antibody that target T lymphocytes are well-understood, but its systemic effect on immune function has proven more difficult to unravel. Moreover, preclinical data suggested that the utility of anti-CD3 for the prevention of T1D may be limited. However, the latest clinical data are encouraging and exemplify how a basic discovery can, decades later and with much perseverance, become a promising therapeutic candidate.

Peripherally induced regulatory T cells contribute to the control of autoimmune diabetes in the NOD mouse model.

Type 1 diabetes (T1D) results from the autoimmune destruction of pancreatic beta cells and is partly caused by deficiencies in the Foxp3+ regulatory T-cell (Treg) compartment. Conversely, therapies that increase Treg function can prevent autoimmune diabetes in animal models. The majority of Tregs develop in the thymus (tTregs), but a proportion of Foxp3+ Tregs is generated in the periphery (pTregs) from Foxp3- CD4+ T-cell precursors. Whether pTregs play a distinct role in T1D has not yet been explored. We report here that pTregs are a key modifier of disease in the nonobese diabetic (NOD) mouse model for T1D. We generated NOD mice deficient for the Foxp3 enhancer CNS1 involved in pTreg induction. We show that CNS1 knockout decreased the frequency of pTregs and increased the risk of diabetes. Our results show that pTregs fulfill an important non-redundant function in the prevention of beta cell autoimmunity that causes T1D.

Ptpn22 Modifies Regulatory T Cell Homeostasis via GITR Upregulation.

PTPN22 gene variation associates with multiple autoimmune diseases, including type 1 diabetes and rheumatoid arthritis. Loss of function studies have demonstrated that PTPN22 impinges on the homeostatic behavior of regulatory T (Treg) cells, a lineage critical for immune tolerance. The frequency and absolute number of Treg cells is increased in Ptpn22-deficient mice, but the mechanism driving this increase is unknown. In this study, we show that Ptpn22 knockdown (KD) promoted the expansion of the Treg cell compartment by upregulating the glucocorticoid-induced TNFR family-related protein (GITR) and increasing GITR signaling. Ptpn22 KD did not accelerate cell division but instead prolonged Treg cell survival, as measured by a decrease in the frequency of apoptotic Treg cells. Loss of Ptpn22 caused a concomitant increase in the proportion of CD44(hi)CD62L(lo) effector Treg cells, at the expense of CD44(lo)CD62L(hi) central Treg cells. The increase in Treg cell numbers, but not their differentiation toward an effector phenotype, was dependent on GITR signaling, because blockade of GITR ligand prevented Treg cell expansion caused by Ptpn22 KD. These findings indicate that GITR plays a key role in regulating the overall size of the Treg cell pool. Our results suggest that the size and composition of the Treg cell compartment are independently controlled and have implications for the design of immunotherapies that seek to improve Treg cell function.

Deficiency of HIF1α in Antigen-Presenting Cells Aggravates Atherosclerosis and Type 1 T-Helper Cell Responses in Mice.

OBJECTIVE: Although immune responses drive the pathogenesis of atherosclerosis, mechanisms that control antigen-presenting cell (APC)-mediated immune activation in atherosclerosis remain elusive. We here investigated the function of hypoxia-inducible factor (HIF)-1α in APCs in atherosclerosis. APPROACH AND RESULTS: We found upregulated HIF1α expression in CD11c(+) APCs within atherosclerotic plaques of low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice. Conditional deletion of Hif1a in CD11c(+) APCs in high-fat diet-fed Ldlr(-/-) mice accelerated atherosclerotic plaque formation and increased lesional T-cell infiltrates, revealing a protective role of this transcription factor. HIF1α directly controls Signal Transducers and Activators of Transcription 3 (Stat3), and a reduced STAT3 expression was found in HIF1α-deficient APCs and aortic tissue, together with an upregulated interleukin-12 expression and expansion of type 1 T-helper (Th1) cells. Overexpression of STAT3 in Hif1a-deficient APCs in bone marrow reversed enhanced atherosclerotic lesion formation and reduced Th1 cell expansion in chimeric Ldlr(-/-) mice. Notably, deletion of Hif1a in LysM(+) bone marrow cells in Ldlr(-/-) mice did not affect lesion formation or T-cell activation. In human atherosclerotic lesions, HIF1α, STAT3, and interleukin-12 protein were found to colocalize with APCs. CONCLUSIONS: Our findings identify HIF1α to antagonize APC activation and Th1 T cell polarization during atherogenesis in Ldlr(-/-) mice and to attenuate the progression of atherosclerosis. These data substantiate the critical role of APCs in controlling immune mechanisms that drive atherosclerotic lesion development.

In vivo RNA interference demonstrates a role for Nramp1 in modifying susceptibility to type 1 diabetes.

Type 1 diabetes is an autoimmune disease influenced by multiple genetic loci. Although more than 20 insulin-dependent diabetes (Idd) loci have been implicated in the nonobese diabetic (NOD) mouse model, few causal gene variants have been identified. Here we show that RNA interference (RNAi) can be used to probe candidate genes in this disease model. Slc11a1 encodes a phagosomal ion transporter, Nramp1, that affects resistance to intracellular pathogens and influences antigen presentation. This gene is the strongest candidate among the 42 genes in the Idd5.2 region; a naturally occurring mutation in the protective Idd5.2 haplotype results in loss of function of the Nramp1 protein. Using lentiviral transgenesis, we generated NOD mice in which Slc11a1 is silenced by RNAi. Silencing reduced the frequency of type 1 diabetes, mimicking the protective Idd5.2 region. Our results demonstrate a role for Slc11a1 in modifying susceptibility to type 1 diabetes and illustrate that RNAi can be used to study causal genes in a mammalian model organism.

IL-17 silencing does not protect nonobese diabetic mice from autoimmune diabetes.

The long-held view that many autoimmune disorders are primarily driven by a Th1 response has been challenged by the discovery of Th17 cells. Since the identification of this distinct T cell subset, Th17 cells have been implicated in the pathogenesis of several autoimmune diseases, including multiple sclerosis and rheumatoid arthritis. Type 1 diabetes has also long been considered a Th1-dependent disease. In light of the emerging role for Th17 cells in autoimmunity, several recent studies investigated the potential of this subset to initiate autoimmune diabetes. However, direct evidence supporting the involvement of Th17 cells in actual pathogenesis, particularly during spontaneous onset, is lacking. In this study, we sought to directly address the role of IL-17, the cytokine by which Th17 cells are primarily characterized, in the pathogenesis of autoimmune diabetes. We used lentiviral transgenesis to generate NOD mice in which IL-17 is silenced by RNA interference. The loss of IL-17 had no effect on the frequency of spontaneous or cyclophosphamide-induced diabetes. In contrast, IL-17 silencing in transgenic NOD mice was sufficient to reduce the severity of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis, consistent with reports that IL-17 deficiency is protective in this experimental model of multiple sclerosis. We concluded that IL-17 is dispensable, at least in large part, in the pathogenesis of autoimmune diabetes.

MicroRNA-21 contributes to myocardial disease by stimulating MAP kinase signalling in fibroblasts.

MicroRNAs comprise a broad class of small non-coding RNAs that control expression of complementary target messenger RNAs. Dysregulation of microRNAs by several mechanisms has been described in various disease states including cardiac disease. Whereas previous studies of cardiac disease have focused on microRNAs that are primarily expressed in cardiomyocytes, the role of microRNAs expressed in other cell types of the heart is unclear. Here we show that microRNA-21 (miR-21, also known as Mirn21) regulates the ERK-MAP kinase signalling pathway in cardiac fibroblasts, which has impacts on global cardiac structure and function. miR-21 levels are increased selectively in fibroblasts of the failing heart, augmenting ERK-MAP kinase activity through inhibition of sprouty homologue 1 (Spry1). This mechanism regulates fibroblast survival and growth factor secretion, apparently controlling the extent of interstitial fibrosis and cardiac hypertrophy. In vivo silencing of miR-21 by a specific antagomir in a mouse pressure-overload-induced disease model reduces cardiac ERK-MAP kinase activity, inhibits interstitial fibrosis and attenuates cardiac dysfunction. These findings reveal that microRNAs can contribute to myocardial disease by an effect in cardiac fibroblasts. Our results validate miR-21 as a disease target in heart failure and establish the therapeutic efficacy of microRNA therapeutic intervention in a cardiovascular disease setting.

Beta Cells Deficient for Renalase Counteract Autoimmunity by Shaping Natural Killer Cell Activity.

Type 1 diabetes (T1D) arises from autoimmune-mediated destruction of insulin-producing pancreatic beta cells. Recent advancements in the technology of generating pancreatic beta cells from human pluripotent stem cells (SC-beta cells) have facilitated the exploration of cell replacement therapies for treating T1D. However, the persistent threat of autoimmunity poses a significant challenge to the survival of transplanted SC-beta cells. Genetic engineering is a promising approach to enhance immune resistance of beta cells as we previously showed by inactivating of the Renalase (Rnls) gene. Here we demonstrate that Rnls loss-of-function in beta cells shape autoimmunity by mediating a regulatory Natural Killer (NK) cell phenotype important for the induction of tolerogenic antigen presenting cells. Rnls-deficient beta cells mediate cell-cell-contact-independent induction of hallmark anti-inflammatory cytokine Tgfß1 in NK cells. In addition, surface expression of key regulatory NK immune checkpoints CD47 and Ceacam1 are markedly elevated on beta cells deficient for Rnls. Enhanced glucose metabolism in Rnls mutant beta cells is responsible for upregulation of CD47 surface expression. These findings are crucial to a better understand how genetically engineered beta cells shape autoimmunity giving valuable insights for future therapeutic advancements to treat and cure T1D.

Renalase inhibition regulates ß cell metabolism to defend against acute and chronic stress.

Renalase (Rnls), annotated as an oxidase enzyme, is a GWAS gene associated with Type 1 Diabetes (T1D) risk. We previously discovered that Rnls inhibition delays diabetes onset in mouse models of T1D in vivo , and protects pancreatic ß cells against autoimmune killing, ER and oxidative stress in vitro . The molecular biochemistry and functions of Rnls are entirely uncharted. Here we find that Rnls inhibition defends against loss of ß cell mass and islet dysfunction in chronically stressed Akita mice in vivo . We used RNA sequencing, untargeted and targeted metabolomics and metabolic function experiments in mouse and human ß cells and discovered a robust and conserved metabolic shift towards glycolysis, amino acid abundance and GSH synthesis to counter protein misfolding stress, in vitro . Our work illustrates a function for Rnls in mammalian cells, and suggests an axis by which manipulating intrinsic properties of ß cells can rewire metabolism to protect against diabetogenic stress.

Gata3 is detrimental to regulatory T cell function in autoimmune diabetes.

Regulatory T cells (Tregs) protect against autoimmunity. In type 1 diabetes (T1D), Tregs slow the progression of beta cell autoimmunity within pancreatic islets. Increasing the potency or frequency of Tregs can prevent diabetes, as evidenced by studies in the nonobese diabetic (NOD) mouse model for T1D. We report herein that a significant proportion of islets Tregs in NOD mice express Gata3. The expression of Gata3 was correlated with the presence of IL-33, a cytokine known to induce and expand Gata3+ Tregs. Despite significantly increasing the frequency of Tregs in the pancreas, exogenous IL-33 was not protective. Based on these data, we hypothesized that Gata3 is deleterious to Treg function in autoimmune diabetes. To test this notion, we generated NOD mice with a Treg-specific deletion of Gata3. We found that deleting Gata3 in Tregs strongly protected against diabetes. Disease protection was associated with a shift of islet Tregs toward a suppressive CXCR3+Foxp3+ population. Our results suggest that islet Gata3+ Tregs are maladaptive and that this Treg subpopulation compromises the regulation of islet autoimmunity, contributing to diabetes onset.

Protective Renalase Deficiency in ß-Cells Shapes Immune Metabolism and Function in Autoimmune Diabetes.

Type 1 diabetes (T1D) is caused by the immune-mediated loss of pancreatic ß-cells that produce insulin. The latest advances in stem cell (SC) ß-cell differentiation methods have made a cell replacement therapy for T1D feasible. However, recurring autoimmunity would rapidly destroy transplanted SC ß-cells. A promising strategy to overcome immune rejection is to genetically engineer SC ß-cells. We previously identified Renalase (Rnls) as a novel target for ß-cell protection. Here we show that Rnls deletion endows ß-cells with the capacity to modulate the metabolism and function of immune cells within the local graft microenvironment. We used flow cytometry and single-cell RNA sequencing to characterize ß-cell graft-infiltrating immune cells in a mouse model for T1D. Loss of Rnls within transplanted ß-cells affected both the composition and the transcriptional profile of infiltrating immune cells in favor of an anti-inflammatory profile with decreased antigen-presenting capacity. We propose that changes in ß-cell metabolism mediate local immune regulation and that this feature could be exploited for therapeutic goals. ARTICLE HIGHLIGHTS: Protective Renalase (Rnls) deficiency impacts ß-cell metabolism. Rnls-deficient ß-cell grafts do not exclude immune infiltration. Rnls deficiency in transplanted ß-cells broadly modifies local immune function. Immune cell in Rnls mutant ß-cell grafts adopt a noninflammatory phenotype.

Genetic Modifiers of Thymic Selection and Central Tolerance in Type 1 Diabetes.

Type 1 diabetes (T1D) is caused by the T cell-driven autoimmune destruction of insulin-producing cells in the pancreas. T1D served as the prototypical autoimmune disease for genome wide association studies (GWAS) after having already been the subject of many linkage and association studies prior to the development of GWAS technology. Of the many T1D-associated gene variants, a minority appear disease-specific, while most are shared with one or more other autoimmune condition. Shared disease variants suggest defects in fundamental aspects of immune tolerance. The first layer of protective tolerance induction is known as central tolerance and takes place during the thymic selection of T cells. In this article, we will review candidate genes for type 1 diabetes whose function implicates them in central tolerance. We will describe examples of gene variants that modify the function of T cells intrinsically and others that indirectly affect thymic selection. Overall, these insights will show that a significant component of the genetic risk for T1D - and autoimmunity in general - pertains to the earliest stages of tolerance induction, at a time when protective intervention may not be feasible.

Bioluminescent Monitoring of Graft Survival in an Adoptive Transfer Model of Autoimmune Diabetes in Mice.

Type 1 diabetes is characterized by the autoimmune destruction of the insulin-producing beta cells of the pancreas. A promising treatment for this disease is the transplantation of stem cell-derived beta cells. Genetic modifications, however, may be necessary to protect the transplanted cells from persistent autoimmunity. Diabetic mouse models are a useful tool for the preliminary evaluation of strategies to protect transplanted cells from autoimmune attack. Described here is a minimally invasive method for transplanting and imaging cell grafts in an adoptive transfer model of diabetes in mice. In this protocol, cells from the murine pancreatic beta cell line NIT-1 expressing the firefly luciferase transgene luc2 are transplanted subcutaneously into immunodeficient non-obese diabetic (NOD)-severe combined immunodeficient (scid) mice. These mice are simultaneously injected intravenously with splenocytes from spontaneously diabetic NOD mice to transfer autoimmunity. The grafts are imaged at regular intervals via non-invasive bioluminescent imaging to monitor the cell survival. The survival of mutant cells is compared to that of control cells transplanted into the same mouse.

CD5 Controls Gut Immunity by Shaping the Cytokine Profile of Intestinal T Cells.

CD5 is constitutively expressed on all T cells and is a negative regulator of lymphocyte function. However, the full extent of CD5 function in immunity remains unclear. CD5 deficiency impacts thymic selection and extra-thymic regulatory T cell generation, yet CD5 knockout was reported to cause no immune pathology. Here we show that CD5 is a key modulator of gut immunity. We generated mice with inducible CD5 knockdown (KD) in the autoimmune-prone nonobese diabetic (NOD) background. CD5 deficiency caused T cell-dependent wasting disease driven by chronic gut immune dysregulation. CD5 inhibition also exacerbated acute experimental colitis. Mechanistically, loss of CD5 increased phospho-Stat3 levels, leading to elevated IL-17A secretion. Our data reveal a new facet of CD5 function in shaping the T cell cytokine profile.

STIM1-independent T cell development and effector function in vivo.

Store-operated Ca(2+) entry (SOCE) is believed to be of pivotal importance in T cell physiology. To test this hypothesis, we generated mice constitutively lacking the SOCE-regulating Ca(2+) sensor stromal interaction molecule 1 (STIM1). In vitro analyses showed that SOCE and Ag receptor complex-triggered Ca(2+) flux into STIM1-deficient T cells is virtually abolished. In vivo, STIM1-deficient mice developed a lymphoproliferative disease despite normal thymic T cell maturation and normal frequencies of CD4(+)Foxp3(+) regulatory T cells. Unexpectedly, STIM1-deficient bone marrow chimeric mice mounted humoral immune responses after vaccination and STIM1-deficient T cells were capable of inducing acute graft-versus-host disease following adoptive transfer into allogeneic hosts. These results demonstrate that STIM1-dependent SOCE is crucial for homeostatic T cell proliferation, but of much lesser importance for thymic T cell differentiation or T cell effector functions.

T cell costimulation through CD28 depends on induction of the Bcl-xgamma isoform: analysis of Bcl-xgamma-deficient mice.

The molecular basis of CD28-dependent costimulation of T cells is poorly understood. Bcl-xgamma is a member of the Bcl-x family whose expression is restricted to activated T cells and requires CD28-dependent ligation for full expression. We report that Bcl-xgamma-deficient (Bcl-xgamma-/-) T cells display defective proliferative and cytokine responses to CD28-dependent costimulatory signals, impaired memory responses to proteolipid protein peptide (PLP), and do not develop PLP-induced experimental autoimmune encephalomyelitis (EAE). In contrast, enforced expression of Bcl-xgamma largely replaces the requirement for B7-dependent ligation of CD28. These findings identify the Bcl-xgamma cytosolic protein as an essential downstream link in the CD28-dependent signaling pathway that underlies T cell costimulation.

Regulation of B cell homeostasis by Ptpn22 contributes to type 1 diabetes in NOD mice.

PURPOSE: A coding variant in PTPN22 (C1858T) is one of the most important genetic risk factors in type 1 diabetes (T1D). The role of the PTPN22 risk allele in B cells is still incompletely understood and has not been investigated directly in T1D. This study aimed to explore the role of PTPN22 in the homeostasis of B cells and its influence in T1D. METHODS: Wild-type (WT) and Ptpn22 inducible knockdown (KD) NOD mice were treated with 200 µg/ml doxycycline at the age of 10 weeks for 1-2 months. B cell compositions in the bone marrow, peritoneal cavity and spleen were examined. The pathogenicity of Ptpn22 KD B cells was explored by adoptive cell transfer. RESULTS: Ptpn22 silencing increased the frequency of recirculating mature B cells in the bone marrow, decreased the frequency of B-1a cells in the peritoneal cavity and suppressed the formation of marginal zone B cells and plasma cells in the spleen. Changes in the composition of the peripheral B cell compartment caused by altered cell proliferation while rates of apoptosis were not affected. Significantly, co-transfer of Ptpn22 KD B cells with NY8.3 diabetogenic T cells diminished the frequency of diabetes in recipient NOD.scid mice compared with co-transfer of WT B cells. CONCLUSIONS: Our study constitutes the first functional study of Ptpn22 in B cells in NOD mice. Our findings suggest that Ptpn22 variation contributes to T1D by modifying the B cell compartment and support a gain-of-function for the PTPN22 disease variant.