Identification of the transcription factor ARNTL2 as a candidate gene for the type 1 diabetes locus Idd6

Deletion of the Clock Gene Bmal2 Leads to Alterations in Hypothalamic Clocks, Circadian Regulation of Feeding, and Energy Balance

BMAL2 (ARNTL2) is a paralog of BMAL1 that can form heterodimers with the other circadian factors CLOCK and NPAS2 to activate transcription of clock and clock-controlled genes. To assess a possible role of Bmal2 in the circadian regulation of metabolism, we investigated daily variations of energy metabolism, feeding behavior, and locomotor behavior, as well as ability to anticipate restricted food access in male mice knock-out for Bmal2 (B2KO). While their amount of food intake and locomotor activity were normal compared with wild-type mice, B2KO mice displayed increased adiposity (1.5-fold higher) and fasted hyperinsulinemia (fourfold higher) and tended to have lower energy expenditure at night. Impairment of the master clock in the suprachiasmatic nuclei was evidenced by the shorter free-running period (-14 min/cycle) of B2KO mice compared with wild-type controls and by a loss of daily rhythmicity in expression of intracellular metabolic regulators (e.g., Lipoprotein lipase and Uncoupling protein 2). The circadian window of eating was longer in B2KO mice. The circadian patterns of food intake and meal numbers were bimodal in control mice but not in B2KO mice. In response to restricted feeding, food-anticipatory activity was almost prevented in B2KO mice, suggesting altered food clock that controls anticipation of food availability. In the mediobasal hypothalamus of B2KO mice, expression of genes coding orexigenic neuropeptides (including Neuropeptide y and Agouti-Related Peptide) was downregulated, while Lipoprotein lipase expression lost its rhythmicity. Together, these data highlight that BMAL2 has major impacts on brain regulation of metabolic rhythms, sleep-wake cycle, and food anticipation.

Mapping the daily rhythmic transcriptome in the diabetic retina

Retinal function changes dramatically from day to night, yet clinical diagnosis, treatments, and experimental sampling occur during the day. To begin to address this gap in our understanding of disease pathobiology, this study investigates whether diabetes affects the retina's daily rhythm of gene expression. Diabetic, Ins2Akita/J mice, and non-diabetic littermates were kept under a 12 h:12 h light/dark cycle until 4 months of age. mRNA sequencing was conducted in retinas collected every 4 h throughout the 24 hr light/dark cycle. Computational approaches were used to detect rhythmicity, predict acrophase, identify differential rhythmic patterns, analyze phase set enrichment, and predict upstream regulators. The retinal transcriptome exhibited a tightly regulated rhythmic expression with a clear 12-hr transcriptional axis. Day-peaking genes were enriched for DNA repair, RNA splicing, and ribosomal protein synthesis, night-peaking genes for metabolic processes and growth factor signaling. Although the 12-hr transcriptional axis is retained in the diabetic retina, it is phase advanced for some genes. Upstream regulator analysis for the phase-shifted genes identified oxygen-sensing mechanisms and HIF1alpha, but not the circadian clock, which remained in phase with the light/dark cycle. We propose a model in which, early in diabetes, the retina is subjected to an internal desynchrony with the circadian clock and its outputs are still light-entrained whereas metabolic pathways related to neuronal dysfunction and hypoxia are phase advanced. Further studies are now required to evaluate the chronic implications of such desynchronization on the development of diabetic retinopathy.

A seven-transmembrane protein-TM7SF3, resides in nuclear speckles and regulates alternative splicing

The seven-transmembrane superfamily member 3 protein (TM7SF3) is a p53-regulated homeostatic factor that attenuates cellular stress and the unfolded protein response. Here we show that TM7SF3 localizes to nuclear speckles; eukaryotic nuclear bodies enriched in splicing factors. This unexpected location for a trans -membranal protein enables formation of stable complexes between TM7SF3 and pre-mRNA splicing factors including DHX15, LARP7, HNRNPU, RBM14, and HNRNPK. Indeed, TM7SF3 regulates alternative splicing of >330 genes, mainly at the 3'end of introns by directly modulating the activity of splicing factors such as HNRNPK. These effects are observed both in cell lines and primary human pancreatic islets. Accordingly, silencing of TM7SF3 results in differential expression of 1465 genes (about 7% of the human genome); with 844 and 621 genes being up- or down-regulated, respectively. Our findings implicate TM7SF3, as a resident protein of nuclear speckles and suggest a role for seven-transmembrane proteins as regulators of alternative splicing.

ITGB1-DT/ARNTL2 axis may be a novel biomarker in lung adenocarcinoma: a bioinformatics analysis and experimental validation

BACKGROUND

Lung cancer is one of the most lethal malignant tumors that endangers human health. Lung adenocarcinoma (LUAD) has increased dramatically in recent decades, accounting for nearly 40% of all lung cancer cases. Increasing evidence points to the importance of the competitive endogenous RNA (ceRNA) intrinsic mechanism in various human cancers. However, behavioral characteristics of the ceRNA network in lung adenocarcinoma need further study.

METHODS

Groups based on SLC2A1 expression were used in this study to identify associated ceRNA networks and potential prognostic markers in lung adenocarcinoma. The Cancer Genome Atlas (TCGA) database was used to obtain the patients' lncRNA, miRNA, and mRNA expression profiles, as well as clinical data. Informatics techniques were used to investigate the effect of hub genes on prognosis. The Cox regression analyses were performed to evaluate the prognostic effect of hub genes. The methylation, GSEA, and immune infiltration analyses were utilized to explore the potential mechanisms of the hub gene. The CCK-8, transwell, and colony formation assays were performed to detect the proliferation and invasion of lung cancer cells.

RESULTS

We eventually identified the ITGB1-DT/ARNTL2 axis as an independent fact may promote lung adenocarcinoma progression. Furthermore, methylation analysis revealed that hypo-methylation may cause the dysregulated ITGB1-DT/ARNTL2 axis, and immune infiltration analysis revealed that the ITGB1-DT/ARNTL2 axis may affect the immune microenvironment and the progression of lung adenocarcinoma. The CCK-8, transwell, and colonu formation assays suggested that ITGB1-DT/ARNTL2 promotes the progression of lung adenocarcinoma. And hsa-miR-30b-3p reversed the ITGB1/ARNTL2-mediated oncogenic processes.

CONCLUSION

Our study identified the ITGB1-DT/ARNTL2 axis as a novel prognostic biomarker affects the prognosis of lung adenocarcinoma.

Circadian clock genes as promising therapeutic targets for autoimmune diseases

Circadian rhythm is a natural, endogenous process whose physiological functions are controlled by a set of clock genes. Disturbance of the clock genes have detrimental effects on both innate and adaptive immunity, which significantly enhance pro-inflammatory responses and susceptibility to autoimmune diseases via strictly controlling the individual cellular components of the immune system that initiate and perpetuate the inflammation pathways. Autoimmune diseases, especially rheumatoid arthritis (RA), often exhibit substantial circadian oscillations, and circadian rhythm is involved in the onset and progression of autoimmune diseases. Mounting evidence indicate that the synthetic ligands of circadian clock genes have the property of reducing the susceptibility and clinical severity of subjects. This review supplies an overview of the roles of circadian clock genes in the pathology of autoimmune diseases, including BMAL1, CLOCK, PER, CRY, REV-ERBα, and ROR. Furthermore, summarized some circadian clock genes as candidate genes for autoimmune diseases and current advancement on therapy of autoimmune diseases with synthetic ligands of circadian clock genes. The existing body of knowledge demonstrates that circadian clock genes are inextricably linked to autoimmune diseases. Future research should pay attention to improve the quality of life of patients with autoimmune diseases and reduce the effects of drug preparation on the normal circadian rhythms.

Clock genes alterations and endocrine disorders

BACKGROUND

Various endocrine signals oscillate over the 24-hour period and so does the responsiveness of target tissues. These daily oscillations do not occur solely in response to external stimuli but are also under the control of an intrinsic circadian clock.

DESIGN

We searched the PubMed database to identify studies describing the associations of clock genes with endocrine diseases.

RESULTS

Various human single nucleotide polymorphisms of brain and muscle ARNT-like 1 (BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK) genes exhibited significant associations with type 2 diabetes mellitus. ARNTL2 gene expression and upregulation of BMAL1 and PER1 were associated with the development of type 1 diabetes mellitus. Thyroid hormones modulated PER2 expression in a tissue-specific way, whereas BMAL1 regulated the expression of type 2 iodothyronine deiodinase in specific tissues. Adrenal gland and adrenal adenoma expressed PER1, PER2, CRY2, CLOCK and BMAL1 genes. Adrenal sensitivity to adrenocorticotrophin was also affected by circadian oscillations. A significant correlation between the expression of propio-melanocorticotrophin and PER 2, as well as between prolactin and CLOCK, was found in corticotroph and lactosomatotroph cells, respectively, in the pituitary. Clock genes and especially BMAL1 showed an important role in fertility, whereas oestradiol and androgens exhibited tissue-specific effects on clock gene expression. Metabolic disorders were also associated with circadian dysregulation according to studies in shift workers.

CONCLUSIONS

Clock genes are associated with various endocrine disorders through complex mechanisms. However, data on humans are scarce. Moreover, clock genes exhibit a tissue-specific expression representing an additional level of regulation. Their specific role in endocrine disorders and their potential implications remain to be further clarified.

Altered expression of circadian clock genes in polyglandular autoimmune syndrome type III

PURPOSE

Circadian timing system is a highly conserved, ubiquitous molecular "clock" which creates internal circadian rhythmicity. Dysregulation of clock genes expression is associated with various diseases including immune dysregulation. In this study we investigated the circadian pattern of Clock-related genes in patients with polyglandular autoimmune syndrome type III (PAS type III).

METHODS

Nineteen patients diagnosed with PAS type III and 12 healthy controls were enrolled. mRNA and protein expression of Clock-related genes (CLOCK, BMAL1, ROR and Per-1,-2,-3), as well as the GR-a and the GILZ genes were determined by real-time quantitative PCR and western blot analysis from blood samples drawn at 8 pm and 8am. Serum cortisol and TSH, as well as plasma ACTH, were measured by chemiluminescence.

RESULTS

There were no statistical significant differences in the metabolic profile, cortisol, ACTH and TSH levels between patients and controls. Patients with PAS type III expressed higher transcript levels of CLOCK, BMAL1 and Per-1 in the evening than in the morning (p = 0.03, p = 0.029, p = 0.013, respectively), while the ratios (R_pm/am) of GR-a, CLOCK, BMAL1, and Per-3 mRNA levels were statistically different between patients and controls. Cortisol circadian variation (F_pm/am) was positively correlated with GILZ mRNA circadian pattern (R_pm/am) in the patient group and with the GR-a mRNA (R_pm/am) in the control group.

CONCLUCIONS

Our findings suggest that there is an aberrant circadian rhythm of Clock-related genes in patients with PAS type III. The disruption of the expression of 4 circadian Clock-related genes could indicate a possible association with the pathogenesis of the disease.

Sleeping Beauty Transposon Mutagenesis as a Tool for Gene Discovery in the NOD Mouse Model of Type 1 Diabetes

A number of different strategies have been used to identify genes for which genetic variation contributes to type 1 diabetes (T1D) pathogenesis. Genetic studies in humans have identified >40 loci that affect the risk for developing T1D, but the underlying causative alleles are often difficult to pinpoint or have subtle biological effects. A complementary strategy to identifying "natural" alleles in the human population is to engineer "artificial" alleles within inbred mouse strains and determine their effect on T1D incidence. We describe the use of the Sleeping Beauty (SB) transposon mutagenesis system in the nonobese diabetic (NOD) mouse strain, which harbors a genetic background predisposed to developing T1D. Mutagenesis in this system is random, but a green fluorescent protein (GFP)-polyA gene trap within the SB transposon enables early detection of mice harboring transposon-disrupted genes. The SB transposon also acts as a molecular tag to, without additional breeding, efficiently identify mutated genes and prioritize mutant mice for further characterization. We show here that the SB transposon is functional in NOD mice and can produce a null allele in a novel candidate gene that increases diabetes incidence. We propose that SB transposon mutagenesis could be used as a complementary strategy to traditional methods to help identify genes that, when disrupted, affect T1D pathogenesis.

Circadian rhythm-related genes: implication in autoimmunity and type 1 diabetes

Recent gene association and functional studies have proven the implication of several circadian rhythm-related genes in diabetes. Diabetes has been related to variation in central circadian regulation and peripheral oscillation. Different transcriptional regulators have been identified. Circadian genes are clearly implicated in metabolic pathways, pancreatic function and in type 2 diabetes. Much less evidence has been shown for the link between circadian regulation and type 1 diabetes. The hypothesis that circadian genes are involved in type 1 diabetes is reinforced by findings that the immune system undergoes circadian variation and that several autoimmune diseases are associated with circadian genes. Recent findings in the non-obese diabetic mouse model pinpoint to specific mechanisms controlling type 1 diabetes by the clock-related gene Arntl2 in the immune system.

Linking the circadian rhythm gene Arntl2 to interleukin 21 expression in type 1 diabetes

The circadian rhythm-related aryl hydrocarbon receptor nuclear translocator-like 2 (Arntl2) gene has been identified as a candidate gene for the murine type 1 diabetes locus Idd6.3. Previous studies suggested a role in expansion of CD4(+)CD25(-) T cells, and this then creates an imbalance in the ratio between T-effector and CD4(+)CD25(+) T-regulator cells. Our transcriptome analyses identify the interleukin 21 (IL21) gene (Il21) as a direct target of ARNTL2. ARNTL2 binds in an allele-specific manner to the RNA polymerase binding site of the Il21 promoter and inhibits its expression in NOD.C3H congenic mice carrying C3H alleles at Idd6.3. IL21 is known to promote T-cell expansion, and in agreement with these findings, mice with C3H alleles at Idd6.3 produce lower numbers of CD4(+)IL21(+) and CD4(+) and CD8(+) T cells compared with mice with NOD alleles at Idd6.3. Our results describe a novel and rather unexpected role for Arntl2 in the immune system that lies outside of its predicted function in circadian rhythm regulation.

Increased sensitivity of the circadian system to temporal changes in the feeding regime of spontaneously hypertensive rats - a potential role for Bmal2 in the liver

The mammalian timekeeping system generates circadian oscillations that rhythmically drive various functions in the body, including metabolic processes. In the liver, circadian clocks may respond both to actual feeding conditions and to the metabolic state. The temporal restriction of food availability to improper times of day (restricted feeding, RF) leads to the development of food anticipatory activity (FAA) and resets the hepatic clock accordingly. The aim of this study was to assess this response in a rat strain exhibiting complex pathophysiological symptoms involving spontaneous hypertension, an abnormal metabolic state and changes in the circadian system, i.e., in spontaneously hypertensive rats (SHR). The results revealed that SHR were more sensitive to RF compared with control rats, developing earlier and more pronounced FAA. Whereas in control rats, the RF only redistributed the activity profiles into two bouts (one corresponding to FAA and the other corresponding to the dark phase), in SHR the RF completely phase-advanced the locomotor activity according to the time of food presentation. The higher behavioral sensitivity to RF was correlated with larger phase advances of the hepatic clock in response to RF in SHR. Moreover, in contrast to the controls, RF did not suppress the amplitude of the hepatic clock oscillation in SHR. In the colon, no significant differences in response to RF between the two rat strains were detected. The results suggested the possible involvement of the Bmal2 gene in the higher sensitivity of the hepatic clock to RF in SHR because, in contrast to the Wistar rats, the rhythm of Bmal2 expression was advanced similarly to that of Bmal1 under RF. Altogether, the data demonstrate a higher behavioral and circadian responsiveness to RF in the rat strain with a cardiovascular and metabolic pathology and suggest a likely functional role for the Bmal2 gene within the circadian clock.

Comparative genetics: synergizing human and NOD mouse studies for identifying genetic causation of type 1 diabetes

Although once widely anticipated to unlock how human type 1 diabetes (T1D) develops, extensive study of the nonobese diabetic (NOD) mouse has failed to yield effective treatments for patients with the disease. This has led many to question the usefulness of this animal model. While criticism about the differences between NOD and human T1D is legitimate, in many cases disease in both species results from perturbations modulated by the same genes or different genes that function within the same biological pathways. Like in humans, unusual polymorphisms within an MHC class II molecule contributes the most T1D risk in NOD mice. This insight supports the validity of this model and suggests the NOD has been improperly utilized to study how to cure or prevent disease in patients. Indeed, clinical trials are far from administering T1D therapeutics to humans at the same concentration ranges and pathological states that inhibit disease in NOD mice. Until these obstacles are overcome it is premature to label the NOD mouse a poor surrogate to test agents that cure or prevent T1D. An additional criticism of the NOD mouse is the past difficulty in identifying genes underlying T1D using conventional mapping studies. However, most of the few diabetogenic alleles identified to date appear relevant to the human disorder. This suggests that rather than abandoning genetic studies in NOD mice, future efforts should focus on improving the efficiency with which diabetes susceptibility genes are detected. The current review highlights why the NOD mouse remains a relevant and valuable tool to understand the genes and their interactions that promote autoimmune diabetes and therapeutics that inhibit this disease. It also describes a new range of technologies that will likely transform how the NOD mouse is used to uncover the genetic causes of T1D for years to come.

An siRNA screen identifies transmembrane 7 superfamily member 3 (TM7SF3), a seven transmembrane orphan receptor, as an inhibitor of cytokine-induced death of pancreatic beta cells

AIMS/HYPOTHESIS

Pro-inflammatory cytokines induce death of pancreatic beta cells, leading to the development of type 1 diabetes. We sought to identify novel players and the underlying mechanisms involved in this process.

METHODS

A high-throughput screen of 3,850 mouse small interfering RNAs (siRNAs) was performed in cytokine-treated MIN6 beta cells. Cells were transfected with the different siRNAs and then treated with a combination of TNFα, IL-1β and IFNγ. Cellular apoptosis (caspase-3/7 activity), and changes in cellular reducing power and cell morphology were monitored. The resulting data were analysed and the corresponding z scores calculated.

RESULTS

Several gene families were identified as promoting cytokine-induced beta cell apoptosis, the most prominent being those encoding ubiquitin ligases and serine/threonine kinases. Conversely, deubiquitinating enzymes appeared to reduce apoptosis, while protein phosphatases were mainly associated with lowering cellular reducing power. The screen suggested with high confidence the involvement of several novel genes in cytokine-induced beta cell death, including Camkk2, Epn3, Foxp3 and Tm7sf3, which encodes an orphan seven transmembrane receptor. siRNAs to Tm7sf3 promoted cytokine-induced death of MIN6 cells and human pancreatic islets, and abrogated insulin secretion in these cells. These findings implicate transmembrane 7 superfamily member 3 as a potential new player in the inhibition of cytokine-induced death and in the promotion of insulin secretion from pancreatic beta cells.

CONCLUSIONS/INTERPRETATION

The signalling pathways and novel genes that we identified in this screen and that mediate beta cell death offer new possible targets for therapeutic intervention in diabetes and its adverse complications.

Decreased expression of Bmal2 in patients with Parkinson's disease

Bmal1 is one of the central regulators of the clock machinery. Recently, we examined the expression profile of Bmal1 in total leukocytes for a 12h duration during the evening, overnight, and the morning, in subjects with Parkinson's disease (PD) and healthy controls. The results indicate that the expression of Bmal1 is significantly lower in PD patients versus control subjects. However, it is still unclear whether other key regulators of the clock machinery, especially Bmal2, the paralog of Bmal1, are also expressed differently in PD. To address this issue, the expression profiles of Bmal2, Clock, and Dec1 were examined in the same samples using real-time RT-PCR assay. The results show a difference in the expression pattern of Bmal2, but not Clock and Dec1. The expression of Bmal2 is significantly lower in PD at 21:00 h (p=0.005) and 00:00 h (p=0.025). These results together with our previous findings suggest that the molecular clock in total leukocytes is disturbed in PD patients.

Genetic and Molecular Basis of QTL of Diabetes in Mouse: Genes and Polymorphisms

A systematic study has been conducted of all available reports in PubMed and OMIM (Online Mendelian Inheritance in Man) to examine the genetic and molecular basis of quantitative genetic loci (QTL) of diabetes with the main focus on genes and polymorphisms. The major question is, What can the QTL tell us? Specifically, we want to know whether those genome regions differ from other regions in terms of genes relevant to diabetes. Which genes are within those QTL regions, and, among them, which genes have already been linked to diabetes? whether more polymorphisms have been associated with diabetes in the QTL regions than in the non-QTL regions.

Our search revealed a total of 9038 genes from 26 type 1 diabetes QTL, which cover 667,096,006 bp of the mouse genomic sequence. On one hand, a large number of candidate genes are in each of these QTL; on the other hand, we found that some obvious candidate genes of QTL have not yet been investigated. Thus, the comprehensive search of candidate genes for known QTL may provide unexpected benefit for identifying QTL genes for diabetes.

Downregulation of the circadian rhythm related gene Arntl2 suppresses diabetes protection in Idd6 NOD.C3H congenic mice

1. Our previous studies of the murine genetic locus Idd6 revealed the aryl hydrocarbon receptor nuclear translocator-like protein 2 (Arntl2) as a candidate gene for type 1 diabetes; and in Idd6 NOD.C3H congenic mice, Arntl2 upregulation is linked to decreased diabetes development. 2. In the present study, shRNA plasmids capable of suppressing Arntl2 expression were developed and given to diabetes resistant NOD.C3H congenic mice by hydrodynamic tail vein injection. The effects of Arntl2 suppression on diabetes incidence and immune cell numbers were investigated. 3. Diabetes incidence was increased by Arntl2 mRNA interference in the congenic strain and this was associated with an increase in CD4(+) T cells and a decrease in regulatory T cells in the peripheral immune system. 4. These results provide additional support for the protective role of the Arntl2 gene located in locus Idd6 in diabetes progression in NOD.C3H congenic mice.

A recombination hotspot leads to sequence variability within a novel gene (AK005651) and contributes to type 1 diabetes susceptibility

More than 25 loci have been linked to type 1 diabetes (T1D) in the nonobese diabetic (NOD) mouse, but identification of the underlying genes remains challenging. We describe here the positional cloning of a T1D susceptibility locus, Idd11, located on mouse chromosome 4. Sequence analysis of a series of congenic NOD mouse strains over a critical 6.9-kb interval in these mice and in 25 inbred strains identified several haplotypes, including a unique NOD haplotype, associated with varying levels of T1D susceptibility. Haplotype diversity within this interval between congenic NOD mouse strains was due to a recombination hotspot that generated four crossover breakpoints, including one with a complex conversion tract. The Idd11 haplotype and recombination hotspot are located within a predicted gene of unknown function, which exhibits decreased expression in relevant tissues of NOD mice. Notably, it was the recombination hotspot that aided our mapping of Idd11 and confirms that recombination hotspots can create genetic variation affecting a common polygenic disease. This finding has implications for human genetic association studies, which may be affected by the approximately 33,000 estimated hotspots in the genome.

Use of nonobese diabetic mice to understand human type 1 diabetes

In 1922, Leonard Thompson received the first injections of insulin prepared from the pancreas of canine test subjects. From pancreatectomized dogs to the more recent development of animal models that spontaneously develop autoimmune syndromes, animal models have played a meaningful role in furthering diabetes research. Of these animals, the nonobese diabetic (NOD) mouse is the most widely used for research in type 1 diabetes (T1D) because the NOD shares several genetic and immunologic traits with the human form of the disease. In this article, the authors discuss the similarities and differences in NOD and human T1D and the potential role of NOD mice in future preclinical studies, aiming to provide a better understanding of the genetic and immune defects that lead to T1D.

Hypoxia-inducible factor (HIF) and HIF-stabilizing agents in neonatal care

Oxygen is essential for multicellular existence. Its reduction to water by the mitochondrial electron transport chain forms the cornerstone of aerobic metabolism. Conditions in which oxygen is limiting for electron transport result in bioenergetic collapse in metazoans. However, compared with postnatal existence, all of mammalian development occurs in a hypoxic environment in utero. Not just an epiphenomenon, this 'physiological hypoxia' is required for the activation of a transcriptional response mediated by the hypoxia-inducible factor (HIF) family of transcriptional regulators that coordinates the expression of hundreds of genes, many with developmentally critical functions. Oxygen tension, therefore, is a morphogen. Understanding the physiological significance of hypoxia responses during human development and the role of the HIF family of transcriptional regulators will have important consequences for the care of preterm neonates. Defining clinical care guidelines for the proper oxygenation of critically ill neonates that take account of these observations is therefore of paramount importance. The pharmacological stabilization of HIF family members may therefore have clinical utility in premature infants in whom this important morphogen has been inactivated by exposure to supraphysiological oxygen levels.

Inhibition of type 1 diabetes by upregulation of the circadian rhythm-related aryl hydrocarbon receptor nuclear translocator-like 2

The genetic locus Idd6 is involved in type 1 diabetes development in the non-obese diabetic (NOD) mouse through its effect on the immune system and in particular, on T cell activities. Analysis of congenic strains for Idd6 has established the Aryl hydrocarbon receptor nuclear translocator-like 2 (Arntl2) as a likely candidate gene. In this study we investigate the role of Arntl2 in the autoimmune disease and T cell activation. An Arntl2 expressing plasmid was transfected into CD4(+) T cells by nucleofection. Expression levels of cytokines and CD4(+) T cell activation markers, cell death, apoptosis, and cell proliferation rates were characterized in ex vivo experiments whilst in vivo the transfected cells were transferred into NOD.SCID mice to monitor diabetes development. The results demonstrate that Arntl2 overexpression leads to inhibition of CD4(+) T cell proliferation and decreases in their diabetogenic activity without influence on the expression levels of cytokines, CD4(+) T cell activation markers, cell death, and apoptosis. Our findings suggest that Arntl2 at the Idd6 locus may act via the inhibition of CD4(+) T cell proliferation and the reduction in the diabetogenic activity of CD4(+) T cells to protect against autoimmune type 1 diabetes in the NOD mice.

Sweetness and light: perspectives for rodent models of type 1 diabetes

Type 1 diabetes (T1D) is a major disease affecting primarily young children with an incidence in Western societies of around 0.3% by 20 years of age. Although both genetic and environmental factors contribute to the disease aetiology, the precise nature of both the genetic and environmental contribution to human disease onset and progression remains poorly defined. Despite showing some differences from human T1D, rodent models for T1D (Leiter and von Herrath, 2004; von Herrath and Nepom, 2009) and, in particular the nonobese diabetic (NOD) mouse (Atkinson and Leiter, 1999; Kikutani and Makino, 1992), have provided important insights into the disease process, even if they have not yet allowed definitive identification of many of the genetic factors involved in the process. The recent isolation of germline-competent embryonic stem (ES) cells from the NOD mouse strain, and from the rat, will greatly facilitate the functional analysis of T1D in the mouse, and open up the possibility of improved exploitation of rat T1D models. This important technological breakthrough has the potential to remove bottlenecks from the identification of T1D genes, allowing the underlying metabolic pathways to be established and facilitating evaluation of the eventual role of the human homologues in the disease process. The current status and perspectives for an improved mechanistic understanding of the disease process will be addressed.

Circadian clock gene Bmal1 is not essential; functional replacement with its paralog, Bmal2

Most of the central circadian clock genes in the mouse exist as paralog pairs (Per1 and Per2, Cry1 and Cry2, Clock and Npas2) in which each gene of the pair must be knocked out to confer arrhythmicity. The only exception to this pattern is Bmal1 (also known as Mop3), the single knockout of which confers arrhythmicity, despite the presence of its paralog, Bmal2 (also known as Mop9). The knockout of Bmal1 also has significant effects on longevity, metabolism, etc. These results have led to the conclusion that Bmal1 is a singularly essential clock gene and that Bmal2 has a minimal role in the clock system. In contrast, we find that expression of Bmal2 from a constitutively expressed promoter can rescue the clock and metabolic phenotypes of Bmal1-knockout mice, including rhythmic locomotor activity, rhythmic metabolism, low body weight, and enhanced fat deposition. Combined with the data of Bunger and colleagues, who reported that knockout of Bmal1 downregulates Bmal2, we conclude that Bmal1 and Bmal2 form a circadian paralog pair that is functionally redundant and that, in the mouse, Bmal2 is regulated by Bmal1 such that knockout of Bmal1 alone results in a functionally double Bmal1 and Bmal2 knockout. Therefore, the role(s) of Bmal2 may be more important than has been appreciated heretofore.

An NZW-derived interval on chromosome 7 moderates sialadenitis, but not insulitis in congenic nonobese diabetic mice

Autoimmune lymphocytic infiltration of the salivary glands, termed sialadenitis, is a pathologic feature of Sjögren's syndrome (SjS) that is also prominent in nonobese diabetic (NOD) mice. Genetic factors regulate sialadenitis, and a previous (NOD x NZW)F2 study detected linkage to murine chromosome (Chr) 7. The locus, subsequently annotated as Ssial3, maps to the distal end of Chr7 and overlaps a region associated with type 1 diabetes susceptibility in NOD mice. To examine whether Ssial3 could contribute to both diseases, or was specific for SjS, we generated a congenic mouse strain that harbored an NZW-derived Chr7 interval on the NOD genetic background. This congenic strain exhibited reduced sialadenitis compared with NOD mice and confirmed Ssial3. This reduction, however, did not ameliorate saliva abnormalities associated with SjS-like disease in NOD mice, nor were congenic mice protected against insulitis (lymphocytic infiltration of the pancreatic islets) or diabetes onset. Thus, the Ssial3 locus appears to have a tissue-specific effect for which the NZW allele is unable to prevent other autoimmune traits in the NOD mouse. Anomalous increases for antinuclear Ab production and frequency of marginal-zone B cells were also identified in congenic mice, indicating that the NZW-derived Chr7 interval has a complex effect on the NOD immune system.

Gene-gene interactions in the NOD mouse model of type 1 diabetes

Human genome wide association studies (GWAS) have recently identified at least four new, non-MHC-linked candidate genes or gene regions causing type one diabetes (T1D), highlighting the need for functional models to investigate how susceptibility alleles at multiple common genes interact to mediate disease. Progress in localizing genes in congenic strains of the nonobese diabetic (NOD) mouse has allowed the reproducible testing of gene functions and gene-gene interactions that can be reflected biologically as intrapathway interactions, for example, IL-2 and its receptor CD25, pathway-pathway interactions such as two signaling pathways within a cell, or cell-cell interactions. Recent studies have identified likely causal genes in two congenic intervals associated with T1D, Idd3, and Idd5, and have documented the occurrence of gene-gene interactions, including "genetic masking", involving the genes encoding the critical immune molecules IL-2 and CTLA-4. The demonstration of gene-gene interactions in congenic mouse models of T1D has major implications for the understanding of human T1D since such biological interactions are highly likely to exist for human T1D genes. Although it is difficult to detect most gene-gene interactions in a population in which susceptibility and protective alleles at many loci are randomly segregating, their existence as revealed in congenic mice reinforces the hypothesis that T1D alleles can have strong biological effects and that such genes highlight pathways to consider as targets for immune intervention.

Influence of a non-NK complex region of chromosome 6 on CD4+ invariant NK T cell homeostasis

The number and function of immunoregulatory invariant NKT (iNKT) cells are genetically controlled. A defect of iNKT cell ontogeny and function has been implicated as one causal factor of NOD mouse susceptibility to type 1 diabetes. Other factors of diabetes susceptibility, such as a decrease of regulatory T cell function or an increase in TLR1 expression, are corrected in diabetes-resistant Idd6 NOD.C3H 6.VIII congenic mice. Thus, we surmised that the iNKT cell defects found in NOD mice may also be rescued in congenic mice. Unexpectedly, we found, in both the thymus and the periphery, a 50% reduction in iNKT cell number in NOD.C3H 6.VIII mice as compared with NOD mice. This reduction only affected CD4(+) iNKT cells, and left the double negative iNKT cells unchanged. In parallel, the production of IL-4 and IFN-gamma following alpha-GalCer stimulation was proportionally reduced. Using three subcongenic strains, we have narrowed down the region controlling iNKT development within Idd6 (5.8 Mb) to Idd6.2 region (2.5 Mb). Idd6 region had no effect on NK cell number and in vivo cytotoxic activity. These results indicate that the role of iNKT cells in diabetes development is equivocal and more complex than initially considered. In addition, they bring strong evidence that the regulation of CD4(+) iNKT cell production is independent from that of DN iNKT cells, and involves genes of the Idd6 locus.

Glucose and endoplasmic reticulum calcium channels regulate HIF-1beta via presenilin in pancreatic beta-cells

Pancreatic beta-cell death is a critical event in type 1 diabetes, type 2 diabetes, and clinical islet transplantation. We have previously shown that prolonged block of ryanodine receptor (RyR)-gated release from intracellular Ca(2+) stores activates calpain-10-dependent apoptosis in beta-cells. In the present study, we further characterized intracellular Ca(2+) channel expression and function in human islets and the MIN6 beta-cell line. All three RyR isoforms were identified in human islets and MIN6 cells, and these endoplasmic reticulum channels were observed in close proximity to mitochondria. Blocking RyR channels, but not sarco/endoplasmic reticulum ATPase (SERCA) pumps, reduced the ATP/ADP ratio. Blocking Ca(2+) flux through RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of hypoxia-inducible factor (HIF-1beta). Moreover, inhibition of RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of presenilin-1. Both HIF-1beta and presenilin-1 expression were also induced by low glucose. Overexpression of presenilin-1 increased HIF-1beta, suggesting that HIF is downstream of presenilin. Our results provide the first evidence of a presenilin-HIF signaling network in beta-cells. We demonstrate that this pathway is controlled by Ca(2+) flux through intracellular channels, likely via changes in mitochondrial metabolism and ATP. These findings provide a mechanistic understanding of the signaling pathways activated when intracellular Ca(2+) homeostasis and metabolic activity are suppressed in diabetes and islet transplantation.

The type 1 diabetes locus Idd6 controls TLR1 expression

The Idd6 locus on mouse chromosome 6, which controls the development of type 1 diabetes in the NOD mouse, affects proliferation rates of T cells and the activity of regulatory CD4+CD25+ T cells. Using a transcriptional profiling approach, we show that splenocytes and thymocytes from diabetes-resistant Idd6 NOD.C3H-congenic mouse strains exhibit a constitutive and specific down-regulation of Toll-like receptor 1 (Tlr1) gene expression compared with diabetes prone NOD mice. This phenotype correlates with a diminished proliferation capacity of both CD4+CD25- effector and CD4+CD25+ regulatory T cells upon in vitro stimulation of the TLR1/TLR2 pathway by the ligand palmitoyl-3-cysteine-serine-lysine 4, and with the constitutive down-regulation of Tnf-alpha and IL-6 in macrophages of Idd6- congenic mice. These data suggest that TLR1 is involved in the regulation of mechanisms that impinge on diabetes development in the NOD mouse.

The Idd6.2 diabetes susceptibility region controls defective expression of the Lrmp gene in nonobese diabetic (NOD) mice

The identification of genes mediating susceptibility to type 1 diabetes (T1D) remains a challenging task. Using a positional cloning approach based on the analysis of nonobese diabetic (NOD) mice congenic over the Idd6 diabetes susceptibility region, we found that the NOD allele at this locus mediates lower mRNA expression levels of the lymphoid restricted membrane protein gene (Lrmp/Jaw1). Analysis of thymic populations indicates that Lrmp is expressed mainly in immature thymocytes. The Lrmp gene encodes a type 1 transmembrane protein that localizes to the ER membrane and has homology to the inositol 1,4,5-triphosphate receptor-associated cGMP kinase substrate gene, which negatively regulates intracellular calcium levels. We hypothesize that the observed decrease in expression of the Lrmp gene in NOD mice may constitute a T1D susceptibility factor in the Idd6 region.