Tie Ke

Mutation in Nuclear Pore Component NUP155 Leads to Atrial Fibrillation and Early Sudden Cardiac Death

Atrial fibrillation (AF) is the most common form of sustained clinical arrhythmia. We previously mapped an AF locus to chromosome 5p13 in an AF family with sudden death in early childhood. Here we show that the specific AF gene underlying this linkage is NUP155, which encodes a member of the nucleoporins, the components of the nuclear pore complex (NPC). We have identified a homozygous mutation, R391H, in NUP155 that cosegregates with AF, affects nuclear localization of NUP155, and reduces nuclear envelope permeability. Homozygous NUP155(-/-) knockout mice die before E8.5, but heterozygous NUP155(+/-) mice show the AF phenotype. The R391H mutation and reduction of NUP155 are associated with inhibition of both export of Hsp70 mRNA and nuclear import of Hsp70 protein. These human and mouse studies indicate that loss of NUP155 function causes AF by altering mRNA and protein transport and link the NPC to cardiovascular disease.

Genome-wide association identifies a susceptibility locus for coronary artery disease in the Chinese Han population

Coronary artery disease (CAD) causes more than 700,000 deaths each year in China. Previous genome-wide association studies (GWAS) in populations of European ancestry identified several genetic loci for CAD, but no such study has yet been reported in the Chinese population. Here we report a three-stage GWAS in the Chinese Han population. We identified a new association between rs6903956 in a putative gene denoted as C6orf105 on chromosome 6p24.1 and CAD (P = 5.00 × 10−3, stage 2 validation; P = 3.00 × 10−3, P = 1.19 × 10−8 and P = 4.00 × 10−3 in three independent stage 3 replication populations; P = 4.87 × 10−12, odds ratio = 1.51 in the combined population). The minor risk allele A of rs6903956 is associated with decreased C6orf105 mRNA expression. We report the first GWAS for CAD in the Chinese Han population and identify a SNP, rs6903956, in C6orf105 associated with susceptibility to CAD in this population.

Novel CACNA1S mutation causes autosomal dominant hypokalemic periodic paralysis in a Chinese family

Hypokalemic periodic paralysis (HypoPP) is an autosomal dominant disorder which is characterized by periodic attacks of muscle weakness associated with a decrease in the serum potassium level. The skeletal muscle calcium channel α-subunit gene CACNA1S is a major disease-causing gene for HypoPP, however, only three specific HypoPP-causing mutations, Arg528His, Arg1,239His and Arg1,239Gly, have been identified in CACNA1S to date. In this study, we studied a four-generation Chinese family with HypoPP with 43 living members and 19 affected individuals. Linkage analysis showed that the causative mutation in the family is linked to the CACNA1S gene with a LOD score of 6.7. DNA sequence analysis revealed a heterozygous C to G transition at nucleotide 1,582, resulting in a novel 1,582C→G (Arg528Gly) mutation. The Arg528Gly mutation co-segregated with all affected individuals in the family, and was not present in 200 matched normal controls. The penetrance of the Arg528Gly mutation was complete in male mutation carriers, however, a reduced penetrance of 83% (10/12) was observed in female carriers. No differences were detected for age-at-onset and severity of the disease (frequency of symptomatic attacks per year) between male and female patients. Oral intake of KCl is effective in blocking the symptomatic attacks. This study identifies a novel Arg528Gly mutation in the CACNA1S gene that causes HypoPP in a Chinese family, expands the spectrum of mutations causing HypoPP, and demonstrates a gender difference in the penetrance of the disease.

Regulation of CARD8 Expression by ANRIL and Association of CARD8 Single Nucleotide Polymorphism rs2043211 (p.C10X) With Ischemic Stroke

Background and Purpose— ANRIL has long been considered as the strongest candidate gene at the 9p21 locus, robustly associated with stroke and coronary artery disease. However, the underlying molecular mechanism remains unknown. The present study works to elucidate such a mechanism. Methods— Using expression quantitative loci analysis, we identified potential genes whose expression may be influenced by genetic variation in ANRIL. To verify the identified gene(s), knockdown and overexpression of ANRIL were evaluated in human umbilical vein endothelial cells and HepG2 cells. Ischemic stroke and coronary artery disease risk were then evaluated in the gene(s) demonstrated to be mediated by ANRIL in 3 populations of Chinese Han ancestry: 2 ischemic stroke populations consisting of the Central China cohort (903 cases and 873 controls) and the Northern China cohort (816 cases and 879 controls) and 1 coronary artery disease cohort consisting of 772 patients and 873 controls. Results— Expression quantitative loci analysis identified CARD8 among others, with knockdown of ANRIL expression decreasing CARD8 expression and overexpression of ANRIL increasing CARD8 expression. The minor T allele of a previously identified CARD8 variant (rs2043211) was found to be significantly associated with a protective effect of ischemic stroke under the recessive model in 2 independent stroke cohorts. No significant association was found between rs2043211 and coronary artery disease. Conclusions— CARD8 is a downstream target gene regulated by ANRIL. Single nucleotide polymorphism rs2043211 in CARD8 is significantly associated with ischemic stroke. ANRIL may increase the risk of ischemic stroke through regulation of the CARD8 pathway.

Novel Roles of GATA1 in Regulation of Angiogenic Factor AGGF1 and Endothelial Cell Function

AGGF1 is an angiogenic factor, and its deregulation is associated with a vascular malformation consistent with Klippel-Trenaunay syndrome (KTS). This study defines the molecular mechanism for transcriptional regulation of AGGF1 expression. Transcription of AGGF1 starts at two nearby sites, −367 and −364 bp upstream of the translation start site. Analyses of 5′- and 3′-serial promoter deletions defined the core promoter/regulatory elements, including two repressor sites (from −1971 to −3990 and from −7521 to −8391, respectively) and two activator sites (a GATA1 consensus binding site from −295 to −300 and a second activator site from −129 to −159). Both the GATA1 site and the second activator site are essential for AGGF1 expression. A similar expression profile was found for GATA1 and AGGF1 in cells (including various endothelial cells) and tissues. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays demonstrated that GATA1 was able to bind to the AGGF1 DNA in vitro and in vivo. Overexpression of GATA1 increased expression of AGGF1. We identified one rare polymorphism −294C>T in a sporadic KTS patient, which is located in the GATA1 site, disrupts binding of GATA1 to DNA, and abolishes the GATA1 stimulatory effect on transcription of AGGF1. Knockdown of GATA1 expression by siRNA reduced expression of AGGF1, and resulted in endothelial cell apoptosis and inhibition of endothelial capillary vessel formation and cell migration, which was rescued by purified recombinant human AGGF1 protein. These results demonstrate that GATA1 regulates expression of AGGF1 and reveal a novel role for GATA1 in endothelial cell biology and angiogenesis.

HSF4 regulates DLAD expression and promotes lens de-nucleation

HSF4 mutations lead to both congenital and age-related cataract. The purpose of this study was to explore the mechanism of cataract formation caused by HSF4 mutations. The degradation of nuclear DNA is essential for the lens fiber differentiation. DNase 2β (DLAD) is highly expressed in lens cells, and mice with deficiencies in the DLAD gene develop nuclear cataracts. In this study, we found that HSF4 promoted the expression and DNase activity of DLAD by directly binding to the DLAD promoter. In contrast, HSF4 cataract causative mutations failed to bind to the DLAD promoter, abrogating the expression and DNase activity of DLAD. These results were confirmed by HSF4 knockdown in zebrafish, which led to incomplete de-nucleation of the lens and decreased expression and activity of DLAD. Together, our results suggest that HSF4 exerts its function on lens differentiation via positive regulation of DLAD expression and activity, thus facilitating de-nucleation of lens fiber cells. Our demonstration that HSF4 cataract causative mutations abrogate the induction of DLAD expression reveals a novel molecular mechanism regarding how HSF4 mutations cause cataractogenesis.

A novel de novo frame-shift mutation of the EDA gene in a Chinese Han family with hypohidrotic ectodermal dysplasia

AbstractHypohidrotic ectodermal dysplasia (HED) is characterized by severe hypohidrosis, hypotrichosis, and hypodontia. It can be inherited in autosomal dominant, autosomal recessive, or X-linked patterns. Mutations in the EDA gene, which encodes ectodysplasin-A, are responsible for X-linked HED (XLHED). In the present study, we identified a Chinese Han family with XLHED. Direct DNA sequence analysis of the entire coding region and exon-intron boundaries of EDA identified a novel de novo mutation, c.573_574insT, in two affected males and one carrier female. Restriction fragment length polymorphism (RFLP) analysis showed that the mutation was not present in 200 controls. The 1-bp insertion mutation resulted in a frameshift, which causes premature termination of EDA polypeptide and truncation of the EDA protein. These results suggest that the c.573_574insT mutation of the EDA gene is a cause for XLHED in the family. To the best of our knowledge, this is the first de novo insertion mutation of EDA described for XLHED.

Molecular Basis of Gene-Gene Interaction: Cyclic Cross-Regulation of Gene Expression and Post-GWAS Gene-Gene Interaction Involved in Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia at the clinic. Recent GWAS identified several variants associated with AF, but they account for <10% of heritability. Gene-gene interaction is assumed to account for a significant portion of missing heritability. Among GWAS loci for AF, only three were replicated in the Chinese Han population, including SNP rs2106261 (G/A substitution) in ZFHX3, rs2200733 (C/T substitution) near PITX2c, and rs3807989 (A/G substitution) in CAV1. Thus, we analyzed the interaction among these three AF loci. We demonstrated significant interaction between rs2106261 and rs2200733 in three independent populations and combined population with 2,020 cases/5,315 controls. Compared to non-risk genotype GGCC, two-locus risk genotype AATT showed the highest odds ratio in three independent populations and the combined population (OR=5.36 (95% CI 3.87-7.43), P=8.00×10-24). The OR of 5.36 for AATT was significantly higher than the combined OR of 3.31 for both GGTT and AACC, suggesting a synergistic interaction between rs2106261 and rs2200733. Relative excess risk due to interaction (RERI) analysis also revealed significant interaction between rs2106261 and rs2200733 when exposed two copies of risk alleles (RERI=2.87, P<1.00×10-4) or exposed to one additional copy of risk allele (RERI=1.29, P<1.00×10-4). The INTERSNP program identified significant genotypic interaction between rs2106261 and rs2200733 under an additive by additive model (OR=0.85, 95% CI: 0.74-0.97, P=0.02). Mechanistically, PITX2c negatively regulates expression of miR-1, which negatively regulates expression of ZFHX3, resulting in a positive regulation of ZFHX3 by PITX2c; ZFHX3 positively regulates expression of PITX2C, resulting in a cyclic loop of cross-regulation between ZFHX3 and PITX2c. Both ZFHX3 and PITX2c regulate expression of NPPA, TBX5 and NKX2.5. These results suggest that cyclic cross-regulation of gene expression is a molecular basis for gene-gene interactions involved in genetics of complex disease traits.

Novel CACNA1S mutation causes autosomal dominant hypokalemic periodic paralysis in a South American family

Hypokalaemic periodic paralysis (HypoPP) is an autosomal dominant disorder, which is characterized by periodic attacks of muscle weakness associated with a decrease in the serum potassium level. A major disease-causing gene for HypoPP has been identified as CACNA1S, which encodes the skeletal muscle calcium channel α-subunit with four transmembrane domains (I–IV), each with six transmembrane segments (S1–S6). To date, all CACNA1S mutations identified in HypoPP patients are located within the voltage-sensor S4 segment. In this study we report a novel CACNA1S mutation in a new region of the protein, the S3 segment of domain III. We characterized a four-generation South American family with HypoPP. Genetic analysis identified a novel V876E mutation in all HypoPP patients in the family, but not in normal family members or 160 control people. Clinical analysis indicates that mutation V876E is associated with a severe outcome as characterized by a very early age of onset, complete penetrance and a severe prognosis including death. These results identify a new mutation in CACNA1S and expand the spectrum of CACNA1S mutations associated with HypoPP.

Cataract mutation P20S of αB-crystallin impairs chaperone activity of αA-crystallin and induces apoptosis of human lens epithelial cells

Cataract is a common cause of childhood blindness worldwide. alpha-crystallin, which is comprised of two homologous subunits, alphaA- and alphaB-crystallin, plays a key role in the maintenance of lens transparency. Recently, we have identified a missense mutation in alphaB-crystallin that changes the proline residue at codon 20 to a serine residue (P20S) in a large Chinese family with autosomal dominant posterior polar congenital cataract. To explore the molecular mechanism by which the P20S mutation causes cataract, we examined the quaternary structure, subunit exchange and chaperone activity of the reconstituted heteroaggregates of alpha-crystallins containing wild type (WT) alphaA in combination with either WT-alphaB- or mutant alphaB-crystallin, respectively. Compared with heteroaggregates of WT-alphaA and WT-alphaB, heteroaggregates containing WT-alphaA and mutant alphaB showed nearly the same molecular mass, but the subunit-exchange rate and chaperone activity were decreased markedly. In human lens epithelial cells, unlike WT-alphaB-crystallin, the P20S mutant protein showed abnormal nuclear localization, and unusual ability to trigger apoptosis. These results suggest that the changes in the structure and function of the alpha-crystallin complex and cytotoxicity are vital factors in the pathogenesis of congenital cataract linked to the P20S mutation in the alphaB-crystallin.