Pleiotropy and heterogeneity in the expression of atherogenic lipoproteins: the IRAS Family Study

OBJECTIVE: Dyslipidemia is an important determinant of coronary disease. Phenotypic correlations between atherogenic lipids are well established, but the contribution of common genetic influences is less clear. METHODS: This study investigates the pair-wise genetic (rhog) and environmental (rhoe) correlations between apoB, LDL-C, HDL-C, and triglyceride (Tg) from Hispanic and African American families of the IRAS Family Study. RESULTS: Heritability estimates (?2) indicate significant genetic effects on apoB (?2=0.46+/-0.05), LDL-C (?2=0.40+/-0.05), HDL-C (?2=0.47+/-0.05), and Tg (?2=0.35+/-0.05) (all p<0.001). Genetic and environmental correlations were strong for apoB-LDL-C (rhog=0.87, rhoe=0.84), apoB-Tg (rhog=0.38, rhoe=0.65), and HDL-C-Tg (rhog=-0.42, rhoe=-0.46). Environmental correlations were strong for apoB-HDL-C (rhoe=-0.40), LDL-C-HDL-C (rhoe=-0.24), and Tg-LDL-C (rhoe=0.33) with weak genetic correlations for these pairs (rhog=-0.09, 0.10, 0.09 respectively). CONCLUSIONS: These results suggest multiple pathways leading to atherogenic dyslipidemia. There are common genetic and environmental influences contributing to variations in apoB and LDL-C as well as apoB and Tg. In addition, the inverse relation between Tg and HDL-C appears to have both genetic and environmental basis. Identifying genes involved in atherogenic dyslipidemia will require careful dissection of the genetic architecture of these pathways.     

Genetics of Coronary Artery Disease in Taiwan: A Cardiometabochip Study by the Taichi Consortium

By means of a combination of genome-wide and follow-up studies, recent large-scale association studies of populations of European descent have now identified over 46 loci associated with coronary artery disease (CAD). As part of the TAICHI Consortium, we have collected and genotyped 8556 subjects from Taiwan, comprising 5423 controls and 3133 cases with coronary artery disease, for 9087 CAD SNPs using the CardioMetaboChip. We applied penalized logistic regression to ascertain the top SNPs that contribute together to CAD susceptibility in Taiwan. We observed that the 9p21 locus contributes to CAD at the level of genome-wide significance (rs1537372, with the presence of C, the major allele, the effect estimate is -0.216, standard error 0.033, p value 5.8x10^-10). In contrast to a previous report, we propose that the 9p21 locus is a single genetic contribution to CAD in Taiwan because: 1) the penalized logistic regression and the follow-up conditional analysis suggested that rs1537372 accounts for all of the CAD association in 9p21, and 2) the high linkage disequilibrium observed for all associated SNPs in 9p21. We also observed evidence for the following loci at a false discovery rate >5%: SH2B3, ADAMTS7, PHACTR1, GGCX, HTRA1, COL4A1, and LARP6-LRRC49. We also took advantage of the fact that penalized methods are an efficient approach to search for gene-by-gene interactions, and observed that two-way interactions between the PHACTR1 and ADAMTS7 loci and between the SH2B3 and COL4A1 loci contribute to CAD risk. Both the similarities and differences between the significance of these loci when compared with significance of loci in studies of populations of European descent underscore the fact that further genetic association of studies in additional populations will provide clues to identify the genetic architecture of CAD across all populations worldwide.     

Emergence of Distinct Genotypes of Cryptosporidium parvum in Structured Host Populations

Cryptosporidium parvum is an apicomplexan parasite that infects humans and ruminants. C. parvum isolated from cattle in northeastern Turkey and in Israel was genotyped using multiple polymorphic genetic markers, and the two populations were compared to assess the effect of cattle husbandry on the parasite's population structure. Dairy herds in Israel are permanently confined with essentially no opportunity for direct herd-to-herd transmission, whereas in Turkey there are more opportunities for transmission as animals range over wider areas and are frequently traded. A total of 76 C. parvum isolates from 16 locations in Israel and seven farms in the Kars region in northeastern Turkey were genotyped using 16 mini- and microsatellite markers. Significantly, in both countries distinct multilocus genotypes confined to individual farms were detected. The number of genotypes per farm was higher and mixed isolates were more frequent in Turkey than in Israel. As expected from the presence of distinct multilocus genotypes in individual herds, linkage disequilibrium among loci was detected in Israel. Together, these observations show that genetically distinct populations of C. parvum can emerge within a group of hosts in a relatively short time. This may explain the frequent detection of host-specific genotypes with unknown taxonomic status in surface water and the existence of geographically restricted C. hominis genotypes in humans.     

Variation in antigenic determinants of p53 transformation-related protein obtained from various species

p53 is a cellular-encoded transformation-related protein. It is synthesized at elevated levels in tumor cells but has also been detected at low concentrations in several types of nontransformed cells. The p53 of tumor cells is immunogenic and elicits specific antibody production. The antigenic determinants of the p53 protein were studied by specific binding to anti-p53 monoclonal antibodies obtained from the RA3-2C2, PAb122, and PAb421 established hybridoma cell lines, and their conservation was followed in various animal species. We found that whereas mouse p53 efficiently immunoprecipitated with all three anti-p53 monoclonal antibodies, human and rat p53 bound PAb122 and PAb421 but lacked a determinant binding RA3-2C2. The hamster p53 molecule represented a third category, which immunoprecipitated with polyclonal anti-p53 antibodies but failed to bind all three monoclonal antibodies analyzed here. Using these monoclonal antibodies, we detected no variations between p53 found in transformed and p53 found in nontransformed cells, within a given species. The results also showed that RA3-2C2, which recognizes a mouse-specific determinant, binds a site located at a proteolytic digestion fragment of the p53 molecule that differs from that containing PAb122 and PAb421 recognition site(s). p53 is a single protein that can be immunoprecipitated through different antigenic determinants that vary between species.     

Ca-mediated regulation of VDAC1 expression levels is associated with cell death induction

VDAC1, an outer mitochondrial membrane (OMM) protein, is crucial for regulating mitochondrial metabolic and energetic functions and acts as a convergence point for various cell survival and death signals. VDAC1 is also a key player in apoptosis, involved in cytochrome c (Cyto c) release and interactions with anti-apoptotic proteins. Recently, we demonstrated that various pro-apoptotic agents induce VDAC1 oligomerization and proposed that a channel formed by VDAC1 oligomers mediates cytochrome c release. As VDAC1 transports Ca^2 + across the OMM and because Ca^2 + has been implicated in apoptosis induction, we addressed the relationship between cytosolic Ca^2 + levels ([Ca^2 +]i), VDAC1 oligomerization and apoptosis induction. We demonstrate that different apoptosis inducers elevate cytosolic Ca^2 + and induce VDAC1 over-expression. Direct elevation of [Ca^2 +]i by the Ca^2 +-mobilizing agents A23187, ionomycin and thapsigargin also resulted in VDAC1 over-expression, VDAC1 oligomerization and apoptosis. In contrast, decreasing [Ca^2 +]i using the cell-permeable Ca^2 +-chelating reagent BAPTA-AM inhibited VDAC1 over-expression, VDAC1 oligomerization and apoptosis. Correlation between the increase in VDAC1 levels and oligomerization, [Ca^2 +]i levels and apoptosis induction, as induced by H₂O₂ or As₂O₃, was also obtained. On the other hand, cells transfected to overexpress VDAC1 presented Ca^2 +-independent VDAC1 oligomerization, cytochrome c release and apoptosis, suggesting that [Ca^2 +]i elevation is not a pre-requisite for apoptosis induction when VDAC1 is over-expressed. The results suggest that Ca^2 + promotes VDAC1 over-expression by an as yet unknown signaling pathway, leading to VDAC1 oligomerization, ultimately resulting in apoptosis. These findings provide a new insight into the mechanism of action of existing anti-cancer drugs involving induction of VDAC1 over-expression as a mechanism for inducing apoptosis. This article is part of a Special Issue entitled: Calcium Signaling in Health and Disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau     

The gene for familial Mediterranean fever in both Armenians and non-Ashkenazi Jews is linked to the alpha-globin complex on 16p: evidence for locus homogeneity.

Familial Mediterranean fever (FMF) is a recurrent inflammatory disorder characterized by short episodes of fever, peritonitis, pleuritis, and arthritis. While FMF has been shown to be inherited in an autosomal recessive fashion in both non-Ashkenazi Jews and Armenian families, clinical differences have raised the possibility of genetic heterogeneity. As its pathogenesis is unknown, mapping of the gene for FMF may provide the first objective method for early and accurate diagnosis of this disease. After excluding 45% of the entire human genome, we studied 14 Armenian and 9 non-Ashkenazi Jewish families with FMF and tested linkage with the alpha-globin locus on chromosome 16. Analysis of the PvuII length polymorphism of the 3' HVR (hypervariable region) probe showed significant linkage with the FMF gene (maximum lod score [lodmax] = 9.76 at maximum recombination fraction [theta] = .076). In the Armenians, the lodmax = 3.61 at theta = .10; and for the non-Ashkenazi Jews, lodmax = 6.28 at theta = .06. There was no evidence for genetic heterogeneity between the Armenians and the non-Ashkenazi Jews (chi 2 = 1.28; P = .26) or within either ethnic group (chi 2 = .00; P = .50). Thus, the gene for FMF is linked to the alpha-globin complex on chromosome 16p in both non-Ashkenazi Jews and Armenians.     

IBD-Associated TL1A Gene (TNFSF15) Haplotypes Determine Increased Expression of TL1A Protein

Background

The recently identified member of the TNF superfamily TL1A (TNFSF15) increases IFN-γ production by T cells in peripheral and mucosal CCR9+ T cells. TL1A and its receptor DR3 are up-regulated during chronic intestinal inflammation in ulcerative colitis and Crohn''s disease (CD). TL1A gene haplotypes increase CD susceptibility in Japanese, European, and US cohorts.

Methodology and Principal Findings

Here we report that the presence of TL1A gene haplotype B increases risk in Jewish CD patients with antibody titers for the E. coli outer membrane porin C (OmpC+) (Haplotype B frequency in Jewish CD patients: 24.9% for OmpC negative and 41.9% for OmpC positive patients, respectively, P≤0.001). CD14+ monocytes isolated from Jewish OmpC+ patients homozygous for TL1A gene haplotype B express higher levels of TL1A in response to FcγR stimulation, a known inducing pathway of TL1A, as measured by ELISA. Furthermore, the membrane expression of TL1A is increased on peripheral monocytes from Jewish but not non-Jewish CD patients with the risk haplotype.

Conclusions and Significance

These findings suggest that TL1A gene variation exacerbates induction of TL1A in response to FcγR stimulation in Jewish CD patients and this may lead to chronic intestinal inflammation via overwhelming T cell responses. Thus, TL1A may provide an important target for therapeutic intervention in this subgroup of IBD patients.