Graded attenuation of TCR signaling elicits distinct autoimmune diseases by altering thymic T cell selection and regulatory T cell function.

Mice with a mutation of the zeta-associated protein of 70 kDa gene (skg mutation) are genetically prone to develop autoimmune arthritis, depending on the environment. In a set of mice with the mutation, the amount of zeta-associated protein of 70 kDa protein as well as its tyrosine phosphorylation upon TCR stimulation decreased from +/+, skg/+, skg/skg, to skg/- mice in a stepwise manner. The reduction resulted in graded alterations of thymic positive and negative selection of self-reactive T cells and Foxp3(+) natural regulatory T cells (Tregs) and their respective functions. Consequently, skg/- mice spontaneously developed autoimmune arthritis even in a microbially clean environment, whereas skg/skg mice required stimulation through innate immunity for disease manifestation. After Treg depletion, organ-specific autoimmune diseases, especially autoimmune gastritis, predominantly developed in +/+, at a lesser incidence in skg/+, but not in skg/skg BALB/c mice, which suffered from other autoimmune diseases, especially autoimmune arthritis. In correlation with this change, gastritis-mediating TCR transgenic T cells were positively selected in +/+, less in skg/+, but not in skg/skg BALB/c mice. Similarly, on the genetic background of diabetes-prone NOD mice, diabetes spontaneously developed in +/+, at a lesser incidence in skg/+, but not in skg/skg mice, which instead succumbed to arthritis. Thus, the graded attenuation of TCR signaling alters the repertoire and the function of autoimmune T cells and natural Tregs in a progressive manner. It also changes the dependency of disease development on environmental stimuli. These findings collectively provide a model of how genetic anomaly of T cell signaling contributes to the development of autoimmune disease.

Complement drives Th17 cell differentiation and triggers autoimmune arthritis.

Activation of serum complement triggers Th17 cell-dependent spontaneous autoimmune disease in an animal model. In genetically autoimmune-prone SKG mice, administration of mannan or beta-glucan, both of which activate serum complement, evoked Th17 cell-mediated chronic autoimmune arthritis. C5a, a chief component of complement activation produced via all three complement pathways (i.e., lectin, classical, and alternative), stimulated tissue-resident macrophages, but not dendritic cells, to produce inflammatory cytokines including IL-6, in synergy with Toll-like receptor signaling or, notably, granulocyte/macrophage colony-stimulating factor (GM-CSF). GM-CSF secreted by activated T cells indeed enhanced in vitro IL-6 production by C5a-stimulated macrophages. In vivo, C5a receptor (C5aR) deficiency in SKG mice inhibited the differentiation/expansion of Th17 cells after mannan or beta-glucan treatment, and consequently suppressed the development of arthritis. Transfer of SKG T cells induced Th17 cell differentiation/expansion and produced arthritis in C5aR-sufficient recombination activating gene (RAG)-/- mice but not in C5aR-deficient RAG-/- recipients. In vivo macrophage depletion also inhibited disease development in SKG mice. Collectively, the data suggest that complement activation by exogenous or endogenous stimulation can initiate Th17 cell differentiation and expansion in certain autoimmune diseases and presumably in microbial infections. Blockade of C5aR may thus be beneficial for controlling Th17-mediated inflammation and autoimmune disease.

Preferential recruitment of CCR6-expressing Th17 cells to inflamed joints via CCL20 in rheumatoid arthritis and its animal model.

This report shows that interleukin (IL) 17-producing T helper type 17 (Th17) cells predominantly express CC chemokine receptor (CCR) 6 in an animal model of rheumatoid arthritis (RA). Th17 cells induced in vivo in normal mice via homeostatic proliferation similarly express CCR6, whereas those inducible in vitro by transforming growth factor beta and IL-6 additionally need IL-1 and neutralization of interferon (IFN) gamma and IL-4 for CCR6 expression. Forced expression of RORgamma t, a key transcription factor for Th17 cell differentiation, induces not only IL-17 but also CCR6 in naive T cells. Furthermore, Th17 cells produce CCL20, the known ligand for CCR6. Synoviocytes from arthritic joints of mice and humans also produce a large amount of CCL20, with a significant correlation (P = 0.014) between the amounts of IL-17 and CCL20 in RA joints. The CCL20 production by synoviocytes is augmented in vitro by IL-1beta, IL-17, or tumor necrosis factor alpha, and is suppressed by IFN-gamma or IL-4. Administration of blocking anti-CCR6 monoclonal antibody substantially inhibits mouse arthritis. Thus, the joint cytokine milieu formed by T cells and synovial cells controls the production of CCL20 and, consequently, the recruitment of CCR6+ arthritogenic Th17 cells to the inflamed joints. These results indicate that CCR6 expression contributes to Th17 cell function in autoimmune disease, especially in autoimmune arthritis such as RA.

The HND mouse, a nonobese model of type 2 diabetes mellitus with impaired insulin secretion.

OBJECTIVES: This study aimed to develop a novel type 2 diabetes model designated the HND (Horio-Niki diabetic) mouse, by transferring diabetogenic genes from wild castaneus mice (Mus musculus castaneus) captured in the Philippines into laboratory mice (C57BL/6J:B6). METHODS: Offspring from the cross between a wild male and a B6 female were backcrossed to the sire. One male backcross which exhibited fasting hyperglycemia was crossed with a B6 female to comprise the fundamental stock (F0). Thereafter, full-sib mating was performed, and mice with impaired glucose tolerance were selected and bred from the F2 generation. Characterization of the phenotype of HND mice and insulin release from their islets was evaluated with F12 generation males. RESULTS: The male HND mice were lean, and spontaneously exhibited impaired glucose tolerance at a high incidence rate at 6 weeks of age. Their serum insulin levels in response to intraperitoneal glucose were markedly attenuated. However, glucose-induced insulin release from isolated HND islets was not affected. Notably, inhibition of glucose-induced insulin release by epinephrine was more pronounced in HND islets than in B6 islets. Moreover, in vivo treatment of HND mice with the alpha2-adrenergic receptor agonist clonidine resulted in marked hypoinsulinemic hyperglycemia. CONCLUSIONS: We suggest the HND mouse may be a distinctive and useful model for type 2 diabetes with impaired neural control of insulin secretion.

Calmodulin overexpression causes Ca(2+)-dependent apoptosis of pancreatic beta cells, which can be prevented by inhibition of nitric oxide synthase.

We investigated the mechanism of beta-cell loss in transgenic mice with elevated levels of beta cell calmodulin. The transgenic mice experienced a sudden rise in blood glucose levels between 21 and 28 days of age. This change was associated with development of severe hypoinsulinemia and loss of beta cells from the islets. Ultrastructural analysis revealed that compromised granule formation and apoptotic changes in the transgenic beta cells preceded the onset of hyperglycemia. Intraperitoneal injection of tolbutamide, an antidiabetic sulfonylurea, decreased blood glucose levels but increased the number of apoptotic beta cells. Finally, injection of transgenic mice with N(omega)-nitro-L-arginine methyl ester, which inhibits nitric oxide synthase activity, prevented hyperglycemia and lessened the changes in number and size of beta cells. Because immunofluorescent staining revealed preferential distribution of neural nitric oxide synthase in pancreatic beta cells, we speculate that overexpression of calmodulin sensitizes the beta cells to Ca(2+)-dependent activation of neural nitric oxide synthase, which mediates apoptosis.

Radical scavenging activities of niacin-related compounds.

We investigated whether niacin-related compounds had radical-scavenging activity by electron spin resonance methods. Many compounds, but not trigonelline, had radical-scavenging activity against hydroxyl radicals. However, for the nitric oxide radical and 1,1-diphenyl-2-picrylhydrazyl radical, only nicotinic acid hydrazide and isonicotinic acid hydrazide had scavenging activities. These results suggest that the moiety of hydrazide might have an important role in scavenging abilities of various radicals.