👤 M Groenendijk

The zinc finger protein Znf202 is a transcriptional suppressor of lipid related genes and has been linked to hypoalphalipoproteinemia. A functional role of Znf202 in lipid metabolism in vivo still remains to be established. We generated mouse Znf202 expression vectors, the functionality of which was established in several in vitro systems. Next, effects of adenoviral znf202 overexpression in vivo were determined in normo- as well as hyperlipidemic mouse models. Znf202 overexpression in mouse hepatoma cells mhAT3F2 resulted in downregulation of members of the Apoe/c1/c2 and Apoa1/c3/a4 gene cluster. The repressive activity of Znf202 was firmly confirmed in an apoE reporter assay and Znf202 responsive elements within the ApoE promoter were identified. Adenoviral Znf202 transfer to Ldlr-/- mice resulted in downregulation of apoe, apoc1, apoa1, and apoc3 within 24 h after gene transfer. Interestingly, key genes in bile flux (abcg5/8 and bsep) and in bile acid synthesis (cyp7a1) were also downregulated. At 5 days post-infection, the expression of the aforementioned genes was normalized, but mice had developed severe hepatosteatosis accompanied by hypercholesterolemia and hypoalphalipoproteinemia. A much milder phenotype was observed in wildtype mice after 5 days of hepatic Znf202 overexpression. Interestingly and similar to Ldl-/- mice, HDL-cholesterol levels in wildtype mice were lowered after hepatic Znf202 overexpression. Znf202 overexpression in vivo reveals an important role of this transcriptional regulator in liver lipid homeostasis, while firmly establishing the proposed key role in the control of HDL levels. Show less

The APOLIPOPROTEIN (APO)A1/C3/A4/A5 gene cluster on chromosome 11 has been hypothesized to be a modifier of plasma triglycerides in FCH. In the present study, we extended previous association analyses of the gene cluster to include APOA5, a newly discovered member of the cluster. Eight SNPs across the APOA1/C3/A4/A5 gene region were analyzed in 78 FCH probands and their normolipidemic spouses as well as in 27 Dutch FCH families. Of the individual SNPs tested in the case-control panel, the strongest evidence of association was obtained with SNPs in APOA1 (P=0.001) and APOA5 (P=0.001). A single haplotype defined by a missense mutation in APOA5 was enriched 3-fold in FCH probands when compared with the normolipidemic spouses (P=0.001) and a second haplotype was significantly enriched in the spouses (P=0.001). Family-based tests also indicated significant association of triglyceride levels and LDL particle size with the investigated SNPs of APOC3 and APOA5. These findings suggest that genetic variation in the APOA1/C3/A4/A5 gene cluster acts as a modifier of plasma triglyceride levels and LDL particle size within FCH families and furthermore indicate that a number of haplotypes may contribute to FCH. Show less

Linkage and association of the apo AI-CIII-IV gene region to familial combined hyperlipidemia (FCHL) was reported previously, based on the presence of genetic variants in the apo CIII and apo AI gene. No data were available yet on the contribution of the apo A-IV locus. Two DNA variants in exon 3 of the apo A-IV gene, A (Thr)(347)T (Ser) and [CTGT](3-4) were characterized by sequencing the coding region of the apo A-IV gene and were analyzed in our Dutch FCHL cohort (30 probands, 159 affected relative, 317 unaffected relatives and 218 spouses). The genotype frequency of the A(347)T variant was different in probands and spouses. In probands no 2/2 carriers were found, resulting in a significant decreased frequency of the 2-allele (P<0.05). This was suggestive for a protective role of the presence of the serine (T) allele on the prevalence of FCHL. No difference in frequency distribution was found for the [CTGT](3-4) variant between the groups. Homozygous 4/4 carriers in spouses had a more favorable lipid profile (LDL-cholesterol and apo B, P<0.05). The absence of linkage disequilibrium of the A(347)T with other markers in the gene cluster, and the absence of linkage disequilibrium with [CTGT](3-4) marker and the MspI-AI marker in the apo A-I promoter showed that these two apo A-IV variants reside on different haplotypes from the apo A-I and apo C-III markers. This was illustrated by extensive haplotype analysis. The present data on the contribution of DNA variants in the apo A-IV gene support our previous observations that the apo AI-CIII-AIV gene cluster has a complex genetic contribution to FCHL both by conferring susceptibility and protection. Show less

The apoAI-CIII-AIV gene cluster, located on chromosome 11, contributes to the phenotype of familial combined hyperlipidemia (FCH), but this contribution is genetically complex. Combinations of haplotypes, based on three restriction enzyme polymorphisms: XmnI and MspI sites, 5' of the start site of the apoA-I gene and SstI polymorphism in the 3' untranslated region of exon 4 of the apoC-III gene, were analyzed to characterize their effect on the expression of severe hyperlipidemia. An epistatic interaction was demonstrated: the S2 allele on one haplotype was synergistic in its hyperlipidemic effect to the X2M2 allele on the other haplotype (Dallinga-Thie, G. M. et al. J. Clin. Invest. 1997. 99: 953-961). In the present study two additional polymorphic sites in the insulin response element (IRE) of the apoC-III gene promoter, T-455C: FokI restriction site, C-482T: MspI restriction site, were studied in 34 FCH pedigrees including 34 probands, 220 hyperlipidemic relatives, 300 normolipidemic relatives, and 236 spouses. In contrast to the earlier data for the other polymorphisms in this gene cluster (XmnI, MspI/AI, and SstI), there were no differences in frequency distributions of the T-455C and the C-482T variants between probands, hyperlipidemic and normolipidemic relatives and spouses. No significant associations between plasma lipid traits and DNA variants in the IRE were observed. Analysis of combinations of haplotypes based on the five polymorphisms in the gene cluster provided further evidence for a dominant role of the SstI polymorphism as a major susceptibility locus in FCH. The inclusion of the IRE markers did not improve genetic informativeness, nor our understanding of the observed synergistic relationship associated with the high risk combination of haplotypes in FCH families. Show less