Genetic progress towards the molecular basis of autoimmunity

The past few years have seen the identification of PTPN22 and the confirmation of CTLA-4 as common autoimmune disease genes. Together with MHC and INS, these developments have increased the collection of confirmed susceptibility loci for autoimmunity. In this article, the latest developments related to these genes and to other recently studied candidate autoimmune susceptibility loci (PDCD1, FCRL3, SUMO4, CD25, PADI4 and SLC22A4) are reviewed. Collectively, these genes strongly indicate that aberrant inhibition of the signalling cascade initiated by activation of the T-cell receptor is involved in the aetiology of autoimmune disease. However, much basic genetic, molecular and clinical research is still needed to help us fully understand the underlying mechanisms of autoimmunity and how these translate into prognosis or therapy.     

Polymorphisms in the organic cation transporter genes SLC22A4 and SLC22A5 and Crohn's disease in a New Zealand Caucasian cohort

Polymorphisms in the organic cation transporter (OCTN) genes SLC22A4 (OCTN1; polymorphism 1672C/T) and SLC22A5 (OCTN2; polymorphism -207G/C) at the inflammatory bowel disease (IBD) 5 locus comprise a two-allele haplotype (SLC22A-TC) associated with increased risk for Crohn's disease (CD). In this study, we examined the contribution of the disease susceptibility haplotype SLC22A-TC to CD in a New Zealand Caucasian population. The frequencies of the gene polymorphisms 1672C/T and -207G/C were examined in 182 patients with CD and 188 ethnically matched controls by PCR-RFLP analysis. There was a significant difference in the allele frequency (0.444 vs 0.519; P = 0.041) of the 1672T polymorphism in the SLC22A4 gene between controls and patients with CD. In contrast, there was no significant difference (0.497 vs 0.552; P = 0.135) for the -207C polymorphism in the SLC22A5 gene. The homozygote SLC22A-TC diplotype was significantly associated with an increased risk for CD (odds ratio 2.19), and the SLC22A-TC haplotype was associated with increased risk (P = 0.0007) of ileocolonic involvement. The population-attributable risk for the SLC22A-TC haplotype is 15.1%. Thus, SLC22A-TC is associated with an increased risk of CD and disease phenotype in our New Zealand CD cohort.     

Loss of GGN Leads to Pre-Implantation Embryonic Lethality and Compromised Male Meiotic DNA Double Strand Break Repair in the Mouse

The integrity of male germ cell genome is critical for the correct progression of spermatogenesis, successful fertilization, and proper development of the offspring. Several DNA repair pathways exist in male germ cells. However, unlike somatic cells, key components of such pathways remain largely unidentified. Gametogenetin (GGN) is a testis-enriched protein that has been shown to bind to the DNA repair protein FANCL via yeast-two-hybrid assays. This finding and its testis-enriched expression pattern raise the possibility that GGN plays a role in DNA repair during spermatogenesis. Herein we demonstrated that the largest isoform GGN1 interacted with components of DNA repair machinery in the mouse testis. In addition to FANCL, GGN1 interacted with the critical component of the Fanconi Anemia (FA) pathway FANCD2 and a downstream component of the BRCA pathway, BRCC36. To define the physiological function of GGN, we generated a Ggn null mouse line. A complete loss of GGN resulted in embryonic lethality at the very earliest period of pre-implantation development, with no viable blastocysts observed. This finding was consistent with the observation that Ggn mRNA was also expressed in lower levels in the oocyte and pre-implantation embryos. Moreover, pachytene spermatocytes of the Ggn heterozygous knockout mice showed an increased incidence of unrepaired DNA double strand breaks (DSBs). Together, our results suggest that GGN plays a role in male meiotic DSB repair and is absolutely required for the survival of pre-implantation embryos.     

Association of CD247 Polymorphisms with Rheumatoid Arthritis: A Replication Study and a Meta-Analysis

Given the role of CD247 in the response of the T cells, its entailment in autoimmune diseases and in order to better clarify the role of this gene in RA susceptibility, we aimed to analyze CD247 gene variants previously associated with other autoimmune diseases (rs1052237, rs2056626 and rs864537) in a large independent European Caucasian population. However, no evidence of association was found for the analyzed CD247 single-nucleotide polymorphisms (SNPs) with RA and with the presence/absence of anti-cyclic citrullinated polypeptide. We performed a meta-analysis including previously published GWAS data from the rs864537 variant, revealing an overall genome-wide significant association between this CD247 SNP and RA with anti-CCP (OR = 0.90, CI 95% = 0.87–0.93, P_overall = 2.1×10⁻¹⁰). Our results show for first time a GWAS-level association between this CD247 polymorphism and RA risk.     

A test for enhancement of cytotype regulation in Drosophila melanogaster by the transposase-encoding P Element ∆2-3

Transposable P elements are regulated in the germ line by piRNAs, which are small RNAs that associate with the Piwi class of proteins. This regulation, called the P cytotype, is enhanced by genetic interactions between P elements that are primary sources of these RNAs and other P elements. The enhanced regulation is thought to reflect amplification of the primary piRNAs by cleavage of mRNAs derived from the other P elements through a mechanism called the ping-pong cycle. We tested the transposase-encoding P element known as ?2-3 for its ability to enhance cytotype regulation anchored in P elements inserted at the telomere of the left arm of the X chromosome (TP elements). The ?2-3 P element lacks the intron between exons 2 and 3 in the structurally complete P element (CP). Unlike the CP element, it does not markedly enhance cytotype regulation anchored in TP elements, nor does it transmit transposase activity through the egg cytoplasm. However, mRNAs from both the CP and ?2-3 elements are maternally deposited in embryos. These observations suggest that maternally transmitted CP mRNA enhances cytotype regulation by participating in the ping-pong cycle and that it encodes the P transposase in the embryonic germ line, whereas maternally transmitted ?2-3 mRNA does not, possibly because it is not efficiently directed into the primordial embryonic germ line. Strong transposon regulation may, therefore, require ping-pong cycling with maternally inherited mRNAs in the embryo.     

Association of Body Composition with Outcome of Docetaxel Chemotherapy in Metastatic Prostate Cancer: A Retrospective Review

Background

Docetaxel, a lipophilic drug, is indicated for castration-resistant metastatic prostate cancer. Most men with such disease would have had androgen-deprivation therapy, which decreases muscle and increases body fat. Obesity and body composition changes may influence the outcomes of docetaxel therapy.

Methods

We conducted a retrospective review of 333 patients with metastatic prostate cancer treated with docetaxel at a comprehensive cancer center between October 7, 2004 and December 31, 2012. Body composition parameters were measured based on the areas of muscle and adipose tissues in the visceral and subcutaneous compartments on CT images at L3-4 levels. Dose calculations, toxicity and adverse reaction profiles, and overall survival were analyzed.

Results

Obese patients were younger at the diagnosis of prostate cancer and had a shorter duration from diagnosis to docetaxel therapy. Analysis of body composition found that a high visceral fat-to-subcutaneous fat area ratio (VSR) was associated with poor prognosis but a high visceral fat-to-muscle area ratio (VMR) and high body mass index were associated with increased duration from starting docetaxel to death, allowing such men to catch up with patients with normal body mass index in overall survival from cancer diagnosis to death. Cox proportional hazard regression showed that age ≥65 years, high VSR, abnormal serum alkaline phosphatase, and >10% reduction of initial dosage were significant predictors of shorter time between starting docetaxel and death, and that high VMR, obesity, and weekly regimens were significant predictors of longer survival after docetaxel.

Conclusion

Obese and overweight patients may benefit more from weekly docetaxel regimens using the reference dosage of 35 mg/m² without empirical dosage reduction.     

A novel core genome-encoded superantigen contributes to lethality of community-associated MRSA necrotizing pneumonia

Bacterial superantigens (SAg) stimulate T-cell hyper-activation resulting in immune modulation and severe systemic illnesses such as Staphylococcus aureus toxic shock syndrome. However, all known S. aureus SAgs are encoded by mobile genetic elements and are made by only a proportion of strains. Here, we report the discovery of a novel SAg staphylococcal enterotoxin-like toxin X (SElX) encoded in the core genome of 95% of phylogenetically diverse S. aureus strains from human and animal infections, including the epidemic community-associated methicillin-resistant S. aureus (CA-MRSA) USA300 clone. SElX has a unique predicted structure characterized by a truncated SAg B-domain, but exhibits the characteristic biological activities of a SAg including Vβ-specific T-cell mitogenicity, pyrogenicity and endotoxin enhancement. In addition, SElX is expressed by clinical isolates in vitro, and during human, bovine, and ovine infections, consistent with a broad role in S. aureus infections of multiple host species. Phylogenetic analysis suggests that the selx gene was acquired horizontally by a progenitor of the S. aureus species, followed by allelic diversification by point mutation and assortative recombination resulting in at least 17 different alleles among the major pathogenic clones. Of note, SElX variants made by human- or ruminant-specific S. aureus clones demonstrated overlapping but distinct Vβ activation profiles for human and bovine lymphocytes, indicating functional diversification of SElX in different host species. Importantly, SElX made by CA-MRSA USA300 contributed to lethality in a rabbit model of necrotizing pneumonia revealing a novel virulence determinant of CA-MRSA disease pathogenesis. Taken together, we report the discovery and characterization of a unique core genome-encoded superantigen, providing new insights into the evolution of pathogenic S. aureus and the molecular basis for severe infections caused by the CA-MRSA USA300 epidemic clone.