Programming of neuroendocrine self in the thymus and its defect in the development of neuroendocrine autoimmunity.

For centuries after its first description by Galen, the thymus was considered as only a vestigial endocrine organ until the discovery in 1961 by Jacques FAP Miller of its essential role in the development of T (thymo-dependent) lymphocytes. A unique thymus first appeared in cartilaginous fishes some 500 million years ago, at the same time or shortly after the emergence of the adaptive (acquired) immune system. The thymus may be compared to a small brain or a computer highly specialized in the orchestration of central immunological self-tolerance. This was a necessity for the survival of species, given the potent evolutionary pressure imposed by the high risk of autotoxicity inherent in the stochastic generation of the diversity of immune cell receptors that characterize the adaptive immune response. A new paradigm of "neuroendocrine self-peptides" has been proposed, together with the definition of "neuroendocrine self." Neuroendocrine self-peptides are secreted by thymic epithelial cells (TECs) not according to the classic model of neuroendocrine signaling, but are processed for presentation by, or in association with, the thymic major histocompatibility complex (MHC) proteins. The autoimmune regulator (AIRE) gene/protein controls the transcription of neuroendocrine genes in TECs. The presentation of self-peptides in the thymus is responsible for the clonal deletion of self-reactive T cells, which emerge during the random recombination of gene segments that encode variable parts of the T cell receptor for the antigen (TCR). At the same time, self-antigen presentation in the thymus generates regulatory T (Treg) cells that can inhibit, in the periphery, those self-reactive T cells that escaped negative selection in the thymus. Several arguments indicate that the origin of autoimmunity directed against neuroendocrine glands results primarily from a defect in the intrathymic programming of self-tolerance to neuroendocrine functions. This defect may be genetic or acquired, for example during an enteroviral infection. This novel knowledge of normal and pathologic functions of the thymus constitutes a solid basis for the development of a novel type of tolerogenic/negative self-vaccination against type 1 diabetes (T1D).

Persistent infection of thymic epithelial cells with coxsackievirus B4 results in decreased expression of type 2 insulin-like growth factor.

It has been hypothesized that a disturbance of central self-tolerance to islet ß cells may play a role in the enteroviral pathogenesis of type 1 diabetes. Whether enteroviruses can induce an impaired expression of ß-cell self-antigens in thymic epithelial cells has been investigated in a murine thymic epithelial (MTE) cell line. This cell line was permissive to the diabetogenic group B4 coxsackievirus (CV-B4) strain CV-B4 E2 and spontaneously expressed type 2 insulin-like growth factor (Igf2), the dominant self-antigen of the insulin family. In this model, a persistent replication of CV-B4 E2 was obtained, as attested to by the prolonged detection of intracellular positive- and negative-strand viral RNA by reverse transcription-PCR (RT-PCR) and capsid protein VP1 by immunofluorescent staining and by the release of infectious particles in culture supernatants. The chronic stage of the infection was characterized by a low proportion of VP1-positive cells (1 to 2%), whereas many cells harbored enteroviral RNA, as displayed by RT-PCR without extraction applied directly to a few cells. Igf2 mRNA and IGF-2 protein were dramatically decreased in CV-B4 E2-infected MTE cell cultures compared with mock-infected cultures, whereas housekeeping and interleukin-6 (Il6) gene expression was maintained and Igf1 mRNA was decreased, but to a lower extent. Inoculation of CV-B3, CV-B4 JVB, or echovirus 1 resulted in a low level of IGF-2 in culture supernatants as well, whereas herpes simplex virus 1 stimulated the production of the protein. Thus, a persistent infection of a thymic epithelial cell line with enteroviruses like CV-B4 E2 can result in a disturbed production of IGF-2, a protein involved in central self-tolerance toward islet ß cells.

Expression of the growth hormone/insulin-like growth factor axis during Balb/c thymus ontogeny and effects of growth hormone upon ex vivo T cell differentiation.

AIMS: We address the question of the expression and the role of the growth hormone/insulin-like growth factor (GH/IGF) axis in the thymus. METHODS: Using RT-qPCR, the expression profile of various components of the somatotrope GH/IGF axis was measured in different thymic cell types and during thymus embryogenesis in Balb/c mice. The effect of GH on T cell differentiation was explored via thymic organotypic culture. RESULTS: Transcription of Gh, Igf1, Igf2 and their related receptors predominantly occurred in thymic epithelial cells (TEC), while a low level of Gh and Igf1r transcription was also evidenced in thymic T cells (thymocytes). Gh, Ghr, Ins2, Igf1, Igf2, and Igfr1 displayed distinct expression profiles depending on the developmental stage. The protein concentrations of IGF-1 and IGF-2 were in accordance with the profile of their gene expression. In fetal thymus organ cultures (FTOC) derived from Balb/c mice, treatment with exogenous GH resulted in a significant increase of double negative CD4-CD8- T cells and CD4+ T cells, together with a decrease in double positive CD4+CD8+ T cells. These changes were inhibited by concomitant treatment with GH and the GH receptor (GHR) antagonist pegvisomant. However, GH treatment also induced a significant decrease in FTOC Gh, Ghr and Igf1 expression. CONCLUSION: These data show that the thymotropic properties of the somatotrope GH/IGF-1 axis involve an interaction between exogenous GH and GHR expressed by TEC. Since thymic IGF-1 is not increased by GH treatment, the effects of GH upon T cell differentiation could implicate a different local growth factor or cytokine.

Thymic self-antigens for the design of a negative/tolerogenic self-vaccination against type 1 diabetes.

Before being able to react against infectious nonself-antigens, the immune system has to be educated in the recognition and tolerance of neuroendocrine proteins and this critical process takes place only in the thymus. The development of the autoimmune diabetogenic response results from a thymus dysfunction in programing central self-tolerance to pancreatic insulin-secreting islet beta cells, leading to the breakdown of immune homeostasis with an enrichment of islet beta-cell reactive effector T cells and a deficiency of beta-cell specific natural regulatory T cells (nTregs) in the peripheral T-lymphocyte repertoire. Insulin-like growth factor 2 (IGF-2) is the dominant member of the insulin family expressed during fetal life by the thymic epithelium under the control of the autoimmune regulator (AIRE) gene/protein. The very low degree of insulin gene transcription in normal murine and human thymus explains why the insulin protein is poorly tolerogenic as demonstrated in many studies, including the failure of all clinical trials that have attempted immune tolerance to islet beta cells via various methods of insulin administration. On the basis of the close homology and crosstolerance between insulin, the primary T1D autoantigen, and IGF-2, the dominant self-antigen of the insulin family, a novel type of vaccination, so-called 'negative/tolerogenic self-vaccination', is currently being developed for the prevention and cure of T1D. If this approach were found to be effective for reprograming immunological tolerance in T1D, it could pave the way for the design of other self-vaccines against autoimmune endocrine diseases, as well as other organ-specific autoimmune diseases.

Chondrocyte-specific modulation of Cyp27b1 expression supports a role for local synthesis of 1,25-dihydroxyvitamin D3 in growth plate development.

The Cyp27b1 enzyme (25-hydroxyvitamin D-1alpha-hydroxylase) that converts 25-hydroxyvitamin D into the active metabolite, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], is expressed in kidney but also in other cell types such as chondrocytes. This suggests that local production of 1,25(OH)(2)D(3) could play an important role in the differentiation of these cells. To test this hypothesis, we engineered mutant mice that do not express the Cyp27b1 gene in chondrocytes. Inactivation of both alleles of the Cyp27b1 gene led to decreased RANKL expression and reduced osteoclastogenesis, increased width of the hypertrophic zone of the growth plate at embryonic d 15.5, increased bone volume in neonatal long bones, and increased expression of the chondrocytic differentiation markers Indian Hedgehog and PTH/PTHrP receptor. The expression of the angiogenic marker VEGF was decreased, accompanied by decreased platelet/endothelial cell adhesion molecule-1 staining in the neonatal growth plate, suggesting a delay in vascularization. In parallel, we engineered strains of mice overexpressing a Cyp27b1 transgene in chondrocytes by coupling the Cyp27b1 cDNA to the collagen alpha(1)(II) promoter. The transgenic mice showed a mirror image phenotype when compared with the tissue-specific inactivation, i.e. a reduction in the width of the hypertrophic zone of the embryonic growth plate, decreased bone volume in neonatal long bones, and inverse expression patterns of chondrocytic differentiation markers. These results support an intracrine role of 1,25(OH)(2)D(3) in endochondral ossification and chondrocyte development in vivo.

Rescue of the phenotype of CYP27B1 (1alpha-hydroxylase)-deficient mice.

The treatment of choice for pseudo Vitamin D deficiency rickets (PDDR), caused by mutations in the 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1; 1alpha-OHase) gene, is replacement therapy with 1,25(OH)(2)D(3). We have previously engineered an animal model of PDDR by targeted inactivation of the 1alpha-OHase gene in mice (Endocrinology 142 (2001) 3135). Replacement therapy was performed in this model, and compared to feeding with a high calcium diet containing 2% calcium, 1.25% phosphorus, 20% lactose (rescue diet). Blood biochemistry analysis revealed that both rescue treatments corrected the hypocalcemia and secondary hyperparathyroidism. Bone histology and histomorphometry confirmed that the rickets and osteomalacia were cured by both rescue protocols. However, despite the restoration of normocalcemia, the rescue diet did not entirely correct bone growth as femur size remained significantly smaller than control in 1alpha-OHase(-/-) mice fed the rescue diet. These results demonstrate that correction of the abnormal mineral ion homeostasis by feeding with a high calcium rescue diet is effective to rescue the PDDR phenotype of 1alpha-OHase mutant mice. This treatment, however, does not appear as effective as 1,25(OH)(2)D(3) replacement therapy since bone growth remained impaired.

1,25-Dihydroxyvitamin D3 alters the profile of bone marrow-derived dendritic cells of NOD mice.

1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] prevents autoimmune diabetes in nonobese diabetic (NOD) mice. A major target for 1,25(OH)(2)D(3) in the immune system is the dendritic cell (DC). Since important DC abnormalities have been described in NOD mice, we investigated the effects of 1,25(OH)(2)D(3) on the yield and phenotype of DCs generated from bone marrow of NOD mice compared to control congenic nonobese diabetes-resistant (NOR) mice. In both mouse strains, exposure of the bone marrow-derived cells to 1,25(OH)(2)D(3) increased the proportion of CD11c(+) DCs after culture. Surface expression of MHC II, CD86, and CD54 on NOR-derived DCs was decreased after 1,25(OH)(2)D(3) treatment, while CD40 remained unchanged. On NOD-derived DCs, 1,25(OH)(2)D(3) only inhibited the expression of MHC II and CD86. 1,25(OH)(2)D(3) inhibited IL-12 and IL-10 secretion after IFNgamma and LPS stimulation. In vitro treatment with 1,25(OH)(2)D(3) alters DC yield from bone marrow cultures and alters the phenotype of the cells in NOD as well as in NOR mice. NOD-derived DCs were more resistant to the 1,25(OH)(2)D(3) effects than were NOR-derived DCs.

Redefining the role of psr in beta-lactam resistance and cell autolysis of Enterococcus hirae.

The contribution of penicillin-binding protein 5 (PBP5) and the PBP5 synthesis repressor (Psr) to the beta-lactam resistance, growth, and cell autolysis of wild-type strain ATCC 9790 and resistant strain R40 of Enterococcus hirae was investigated by disruption or substitution of the corresponding pbp5 and psr genes by Campbell-type recombination. The resulting modifications were confirmed by hybridization and PCR. The low susceptibility of E. hirae to beta-lactams was confirmed to be largely dependent on the presence of PBP5. However, against all expectations, inactivation of psr in ATCC 9790 or complementation of R40 cells with psr did not modify the susceptibility to benzylpenicillin or the growth and cell autolysis rates. These results indicated that the psr gene does not seem to be involved in the regulation of PBP5 synthesis and consequently in beta-lactam resistance or in the regulation of cell autolysis in E. hirae.

Rescue of the pseudo-vitamin D deficiency rickets phenotype of CYP27B1-deficient mice by treatment with 1,25-dihydroxyvitamin D3: biochemical, histomorphometric, and biomechanical analyses.

The treatment of choice for pseudo-vitamin D deficiency rickets (PDDR), caused by mutations in the 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1; 1alpha-OHase) gene, is replacement therapy with 1,25(OH)2D3. We have previously engineered an animal model of PDDR by targeted inactivation of the 1alpha-OHase gene in mice. Replacement therapy was performed in this model. The 1alpha-OHase-/- mice and heterozygote controls were treated with 500 pg of 1,25(OH)2D/g body weight/day for 2 weeks, followed by 100 pg of 1,25(OH)2D3/g body weight/day for an additional 3 weeks before death at 8 weeks of age. Blood biochemistry analysis revealed that the rescue treatment corrected the hypocalcemia and secondary hyperparathyroidism. The daily injections of 1,25(OH)2D3 induced strong expression of CYP24, the 25-hydroxyvitamin D 24-hydroxylase gene. Bone histology and histomorphometry confirmed that the rickets and osteomalacia were cured. The rescue regimen also restored the biomechanical properties of the bone tissue within normal parameters. These results show that chronic treatment with the active 1,25(OH)2D3 metabolite is effective to rescue the PDDR phenotype of 1alpha-OHase mutant mice.

Conventional and tissue-specific inactivation of the 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1).

Mutations in the human 25-hydroxyvitamin-D(3)-1alpha-hydroxylase (CYP27B1) gene cause pseudo vitamin D deficiency rickets (PDDR). The kidney is the main site of expression of the CYP27B1 gene, but expression has been documented in other cell types, including chondrocytes. We engineered a tissue-specific and a conventional knockout of CYP27B1 in mice. The conventional knockout strain reproduced the PDDR phenotype. Homozygote mutant animals were treated with 1,25(OH)(2)D(3) or fed a high-calcium diet (2% calcium, 1.25% phosphate, 20% lactose) for 5 weeks post-weaning. Blood biochemistry revealed that both rescue treatments corrected the hypocalcemia and secondary hyperparathyroidism. Bone histomorphometry confirmed that rickets were cured. The rescue regimen restored the biomechanical properties of the bone tissue. Mice carrying the loxP-bearing allele were bred to transgenic animals expressing the Cre recombinase in chondrocytes under the control of the collagen type II promoter. Genotyping confirmed excision of exon 8 in chondrocytes. Serum biochemistry revealed that mineral ion homeostasis is normal in mutant animals. Preliminary observation of bone tissue from mutant mice did not reveal major changes to the growth plate. Precise histomorphometric analysis will be required to assess the impact of chondrocyte-specific inactivation of CYP27B1 on the maturation and function of growth plate cells in vivo.

Modulation of renal Ca2+ transport protein genes by dietary Ca2+ and 1,25-dihydroxyvitamin D3 in 25-hydroxyvitamin D3-1alpha-hydroxylase knockout mice.

Pseudovitamin D-deficiency rickets (PDDR) is an autosomal disease characterized by hyperparathyroidism, rickets, and undetectable levels of 1,25-dihydroxyvitaminD3 (1,25(OH)2D3). Mice in which the 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-OHase) gene was inactivated presented the same clinical phenotype as patients with PDDR and were used to study renal expression of the epithelial Ca2+ channel (ECaC1), the calbindins, Na+/Ca2+ exchanger (NCX1), and Ca2+-ATPase (PMCA1b). Serum Ca2+ (1.20+/-0.05 mM) and mRNA/protein expression of ECaC1 (41+/-3%), calbindin-D28K (31+/-2%), calbindin-D9K (58+/-7%), NCX1 (10+/-2%), PMCA1b (96+/-4%) were decreased in 1alpha-OHase-/- mice compared with 1alpha-OHase+/- littermates. Feeding these mice a Ca2+-enriched diet normalized serum Ca2+ levels and expression of Ca2+ proteins except for calbindin-D9K expression. 1,25(OH)2D3 repletion resulted in increased expression of Ca2+ transport proteins and normalization of serum Ca2+ levels. Localization of Ca2+ transport proteins was clearly polarized in which ECaC1 was localized along the apical membrane, calbindin-D28K in the cytoplasm, and calbindin-D9K along the apical and basolateral membranes, resulting in a comprehensive mechanism facilitating renal transcellular Ca2+ transport. This study demonstrated that high dietary Ca2+ intake is an important regulator of the renal Ca2+ transport proteins in 1,25(OH)2D3-deficient status and thus contributes to the normalization of blood Ca2+ levels.

1,25-dihydroxyvitamin D(3)-independent stimulatory effect of estrogen on the expression of ECaC1 in the kidney.

Estrogen deficiency results in a negative Ca(2+) balance and bone loss in postmenopausal women. In addition to bone, the intestine and kidney are potential sites for estrogen action and are involved in Ca(2+) handling and regulation. The epithelial Ca(2+) channel ECaC1 (or TRPV5) is the entry channel involved in active Ca(2+) transport. Ca(2+) entry is followed by cytosolic diffusion, facilitated by calbindin-D(28K) and/or calbindin-D(9k), and active extrusion across the basolateral membrane by the Na(+)/Ca(2+)-exchanger (NCX1) and plasma membrane Ca(2+)-ATPase (PMCA1b). In this transcellular Ca(2+) transport, ECaC1 probably represents the final regulatory target for hormonal control. The aim of this study was to determine whether 17beta-estradiol (17beta-E(2)) is involved in Ca(2+) reabsorption via regulation of the expression of ECaC1. The ovariectomized rat model was used to investigate the regulation of ECaC1, at the mRNA and protein levels, by 17beta-E(2) replacement therapy. Using real-time quantitative PCR and immunohistochemical analyses, this study demonstrated that 17beta-E(2) treatment at pharmacologic doses increased renal mRNA levels of ECaC1, calbindin-D(28K), NCX1, and PMCA1b and increased the protein abundance of ECaC1. Furthermore, the involvement of 1,25-dihydroxyvitamin D(3) in the effects of 17beta-E(2) was examined in 25-hydroxyvitamin D(3)-1alpha-hydroxylase-knockout mice. Renal mRNA expression of calbindin-D(9K), calbindin-D(28K), NCX1, and PMCA1b was not significantly altered after 17beta-E(2) treatment. In contrast, ECaC1 mRNA and protein levels were both significantly upregulated. Moreover, 17beta-E(2) treatment partially restored serum Ca(2+) levels, from 1.63 +/- 0.06 to 2.03 +/- 0.12 mM. In conclusion, this study suggests that 17beta-E(2) is positively involved in renal Ca(2+) reabsorption via the upregulation of ECaC1, an effect independent of 1,25-dihydroxyvitamin D(3).