Genetic regulation of T regulatory, CD4, and CD8 cell numbers by the arthritis severity loci Cia5a, Cia5d, and the MHC/Cia1 in the rat

Integrative analysis of genome-wide association study and expression quantitative trait loci datasets identified various immune cell-related pathways for rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune chronic disorder manifesting as warm, swollen, and painful joints. Multiple immune cells are implicated in the development of RA. Previous studies demonstrated that integrating the genetic information of genome-wide association studies (GWAS) and expression quantitative trait loci (eQTLs) is capable of identifying new disease-risk loci and providing novel insights into the etiology of complex human disease. In this study, we conducted an integrative pathway association analysis of RA by using GWAS summary data and five immune cell types related to eQTL datasets of RA. After combining the cell-specific eQTLs and GWAS summary of RA and performing a pathway-enrichment analysis, we detected a group of RA-associated pathways with common or cell-specific enriched in the five immune cell types. 41 pathways for B cells, 33 pathways for CD4⁺ T cells, 27 pathways for CD8⁺ T cells, 39 pathways for monocyte, and 25 pathways for natural killer cells are significant in RA, among which 48% are common pathways and 32% are cell-specific pathways. We detected a group of RA-associated eQTL pathways related to five different immune cell types. Our findings may provide novel insights into the pathogenesis of RA.

Combined sequence-based and genetic mapping analysis of complex traits in outbred rats

Genetic mapping on fully sequenced individuals is transforming understanding of the relationship between molecular variation and variation in complex traits. Here we report a combined sequence and genetic mapping analysis in outbred rats that maps 355 quantitative trait loci for 122 phenotypes. We identify 35 causal genes involved in 31 phenotypes, implicating new genes in models of anxiety, heart disease and multiple sclerosis. The relationship between sequence and genetic variation is unexpectedly complex: at approximately 40% of quantitative trait loci, a single sequence variant cannot account for the phenotypic effect. Using comparable sequence and mapping data from mice, we show that the extent and spatial pattern of variation in inbred rats differ substantially from those of inbred mice and that the genetic variants in orthologous genes rarely contribute to the same phenotype in both species.

Whole-genome sequences of DA and F344 rats with different susceptibilities to arthritis, autoimmunity, inflammation and cancer

DA (D-blood group of Palm and Agouti, also known as Dark Agouti) and F344 (Fischer) are two inbred rat strains with differences in several phenotypes, including susceptibility to autoimmune disease models and inflammatory responses. While these strains have been extensively studied, little information is available about the DA and F344 genomes, as only the Brown Norway (BN) and spontaneously hypertensive rat strains have been sequenced to date. Here we report the sequencing of the DA and F344 genomes using next-generation Illumina paired-end read technology and the first de novo assembly of a rat genome. DA and F344 were sequenced with an average depth of 32-fold, covered 98.9% of the BN reference genome, and included 97.97% of known rat ESTs. New sequences could be assigned to 59 million positions with previously unknown data in the BN reference genome. Differences between DA, F344, and BN included 19 million positions in novel scaffolds, 4.09 million single nucleotide polymorphisms (SNPs) (including 1.37 million new SNPs), 458,224 short insertions and deletions, and 58,174 structural variants. Genetic differences between DA, F344, and BN, including high-impact SNPs and short insertions and deletions affecting >2500 genes, are likely to account for most of the phenotypic variation between these strains. The new DA and F344 genome sequencing data should facilitate gene discovery efforts in rat models of human disease.

Investigate pathogenic mechanism of TXNDC5 in rheumatoid arthritis

Hypoxia stimulates synovial hypoperfusion in rheumatoid arthritis (RA). TXNDC5 stimulates cellular proliferation in hypoxic conditions. We previously detected increased TXNDC5 expression in synovial tissues and blood from RA patients and demonstrated that the gene encoding TXNDC5 increased RA risk. The present study investigated the pathogenic roles of TXNDC5 in RA. Transgenic mice that over-expressed TXNDC5 (TXNDC5-Tg) were generated using C57BL/6J mice and treated with bovine collagen II to induce arthritis (CIA). Synovial fibroblasts from RA patients (RASFs) were cultured and incubated with TXNDC5-siRNA or CoCl(2), a chemical that induces hypoxia. CIA was observed in 80% of the TXNDC5-Tg, but only 20% of the wild-type mice (WT) developed CIA. The clinical arthritis scores reached 5 in the TXNDC5-Tg, but this index only reached 2 in the control mice. CIA TXNDC5-Tg exhibited clear pannus proliferation and bone erosion in joint tissues. A significant increase in CD4 T cells was observed in the thymus and spleen of TXNDC5-Tg during CIA. Serum levels of anti-collagen II IgG, IgG1 and IgG2a antibodies were significantly elevated in the mice. Increased cell proliferation, cell migration and TXNDC5 expression were observed in RASFs following incubation with 1 µM CoCl(2). However, this effect was diminished when TXNDC5 expression was inhibited with 100 nM siRNA. TNF-alpha, IL-1α, IL-1β and IL-17 levels were significantly increased in the blood of TXNDC5-Tg mice, but the levels of these cytokines declined in the supernatant of RASFs that were treated with TXNDC5 siRNA. The expression of adiponectin, a cytokine-like mediator, decreased significantly in RASFs following TXNDC5 siRNA treatment. These results suggest that TXNDC5-over-expressing mice were susceptible to CIA. This study also suggests that hypoxia induced TXCNDC5 expression, which contributed to adiponectin expression, cytokine production and the cellular proliferation and migration of fibroblasts in RA.

Combined use of etanercept and MTX restores CD4⁺/CD8⁺ ratio and Tregs in spleen and thymus in collagen-induced arthritis

OBJECTIVE

To further explore the mechanism of etanercept (ENT, rhTNFR:Fc) and methotrexate (MTX) in the combined treatment of rheumatoid arthritis (RA), we investigated whether thymic and splenic T-cell subsets and their related cytokines imbalance could be restored by ETN/MTX treatment.

METHODS

The effect of ETN/MTX on collagen-induced arthritis (CIA) was evaluated by arthritis scores, joint and spleen histopathology, as well as indices of thymus and spleen. T lymphocytes proliferation was determined by [(3)H]-TdR incorporation. Levels of TNF-α, LT-α, IL-1β, RANKL, IL-10, IL-17, IFN-γ and IL-6 were detected by enzyme linked immunosorbent assay. The subsets of T lymphocytes including CD4(+), CD8(+), CD3(+)CD4(+), CD4(+)CD25(+), CD4(+)CD62L(+) and CD4(+)CD25(+)Foxp3(+) cells were quantified using flow cytometry.

RESULTS

Combined administration of ETN/MTX significantly inhibited the proliferation of T lymphocytes, decreased serum IL-6, TNF-α, IL-1β, RANKL and macrophage supernatant IL-17, LT-α, increased serum IFN-γ and macrophage supernatant IL-10. Moreover, the combined administration could restore CD4(+)/CD8(+) ratio and Treg cells of CIA thymus and spleen.

CONCLUSION

Taken together, our findings suggest that ENT/MTX may modify the abnormal T lymphocytes balance from central to peripheral lymphoid organs, which may partially, explained the mechanism of the combined administration.

Impact of MHC class II polymorphism on blood counts of CD4+ T lymphocytes in macaque

While the number of peripheral blood T lymphocytes and of their two main subsets (CD4+CD8- and CD4-CD8+) varies little in a given healthy individual, substantial variation is observed between individuals. It was proposed that these counts could be influenced by MHC polymorphisms because of the well-established role of MHC molecules in thymic T lymphocyte maturation and presentation of antigenic peptides to peripheral T lymphocytes. To test this hypothesis, we have chosen the crab-eating macaque (Macaca fascicularis), an animal model phylogenetically close to man. We selected the Philippine macaque population because of a restriction of the MHC polymorphism in this islander population. Peripheral blood lymphocytes were counted with an automated analyzer and T lymphocyte subsets were assessed by immunolabeling and flow cytometry. The MHC polymorphism was investigated in 200 unrelated subjects using 14 microsatellites markers distributed across the MHC and the DRB locus that was genotyped by denaturing gradient gel electrophoresis and sequencing. All markers were in Hardy-Weinberg equilibrium. Allelic associations were tested with the UNPHASED software. We revealed a significant influence of the MHC class II region on CD4+ T lymphocyte blood count with the largest effect associated with a two-locus haplotypes combining the DRACA allele 274 and the DRB haplotype #8a (p < 8 × 10(-7)). Our data should stimulate a similar association study of the CD4+ T cell counts in humans.

Dietary strategies of immunomodulation in infants at risk for celiac disease

Celiac disease is an inflammatory disorder of the small intestine, triggered by the ingestion of gluten proteins contained in wheat, barley or rye, in genetically susceptible individuals. This disorder is considered to be mainly mediated by cellular immunity and restricted to the human leucocyte antigen-DQ presentation of gluten-derived toxic peptides to T-cells. Moreover, the involvement of innate immunity has been recently demonstrated to be necessary also for the development of intestinal tissue damage. Genetic susceptibility accounts for an uncertain proportion of the disease risk and gluten introduction works as the precipitating factor. However, currently, the research interest is also focused on environmental factors and gene–environment interactions, especially during the first months of life, which might help explain the onset of the disease. Infectious and dietary factors that could modulate the immune response orientating it either towards tolerance or intolerance/autoimmunity are the focus of primary attention. A significant number of studies have looked into the protective effect of breast-feeding against the disease. It is generally accepted that breast-feeding during the introduction of dietary gluten and increasing the duration of breast-feeding are associated with reduced risk of developing celiac disease. However, it is still not fully established whether breast-feeding truly protects with permanent tolerance acquisition or only reduces the symptoms and delays the diagnosis. Moreover, the timing and dose of gluten introduction also seem to be relevant and long-term prospective cohort studies are being carried out in order to elucidate its role in celiac disease development.

Contribution of genetic studies in rodent models of autoimmune arthritis to understanding and treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic and potentially debilitating autoimmune disease. While novel therapies have emerged in recent years, disease remission is rarely achieved. RA is a complex trait, and the identifying of its susceptibility and severity genes has been anticipated to generate new targets for therapeutic intervention. However, finding those genes and understanding their function has been a challenging task. Studies in rodent intercrosses and congenics generated from inbred strains have been an important complementary strategy to identify arthritis genes, and understand how they operate to regulate disease. Furthermore, these new rodent arthritis genes will be new targets for therapeutic interventions, and will identify new candidate genes or candidate pathways for association studies in RA. In this review-opinion article I discuss RA genetics, difficulties involved in gene identification, and how rodent models can facilitate (1) the discovery of both arthritis susceptibility and severity genes, (2) studies of gene-environment interactions, (3) studies of gene-gender interactions, (4) epistasis, (5) functional characterization of the specific genes, (6) development of novel therapies and (7) how the information generated from rodent studies will be useful to understanding and potentially treating RA.