Angiotensinogen promoter B-haplotype associated with cerebral small vessel disease enhances basal transcriptional activity.
OBJECTIVE
Previously, we described the presence of 5 haplotypes (A to E) at the angiotensinogen (AGT) promoter and reported a significant association between the B-haplotype (nucleotide substitutions -6:G-->A and -20:A-->C compared with the wild-type A-haplotype) and magnetic resonance imaging correlates of cerebral small vessel disease (cSVD). The association was independent of hypertension, suggesting a brain-specific effect of this haplotype. In the current study, we investigated transcriptional activities of the 5 promoter haplotypes in astrocytes, the main source of cerebral AGT, and in hepatocytes, the main source of systemic AGT, as well as determined the evolutionary relatedness of the promoter haplotypes.


METHODS
Transcriptional activity depending on the haplotypes and the -6:A and -20:C substitutions was measured in transiently transfected A172 and HepG2 cells. We genotyped 5 new single nucleotide polymorphisms (SNPs) at the AGT gene and measured linkage disequilibrium (LD) among SNPs and the promoter haplotypes. An evolution-based haplotype tree was constructed.


RESULTS
The B-haplotype increased transcriptional activity in both cell types. Its effect was stronger in astrocytes than in hepatocytes (2.4+/-0.09-fold, P<0.001 versus 1.6+/-0.06-fold, P=0.014). Importantly, in astrocytes the combination of the -6:A and the -20:C was mandatory for increased activity, whereas in hepatocytes the -20:C on its own was sufficient. Strong LD between the 5 new SNPs and the promoter haplotypes allowed the reconstruction of 9 haplotypes over the AGT gene. Cladistic analyses suggest that the B-haplotype represents an ancient promoter variant.


CONCLUSIONS
Combination of the -6:A and -20:C substitutions in the B-haplotype may promote the development of cSVD by enhancing cerebral angiotensinogen expression.
Institute of Medical Molecular Biology and Biochemistry, Medical University of Graz, Harrachgasse 21, 8010 Graz, Austria. helena.schmidt@uni-graz.at
Helena
H
Schmidt
Yurii S
YS
Aulchenko
Natascha
N
Schweighofer
Reinhold
R
Schmidt
Sasa
S
Frank
Gerhard M
GM
Kostner
Erwin
E
Ott
Cornelia
C
van Duijn
D000808:Angiotensinogen / Q000235:genetics* / Q000378:metabolism; D001253:Astrocytes / Q000502:physiology; D002460:Cell Line; D002561:Cerebrovascular Disorders / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006239:Haplotypes; D022781:Hepatocytes / Q000502:physiology; D006801:Humans; D015810:Linkage Disequilibrium; D008297:Male; D008875:Middle Aged; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D014162:Transfection
D000808:Angiotensinogen