Molecular phenotyping for analyzing subtle genetic effects in mice: Application to an angiotensinogen gene titration

The angiotensinogen M235T polymorphism in humans is linked to differential expression of the human angiotensinogen gene (AGT) gene and hypertension, but the homeostatic responses resulting from this polymorphism are not known. We therefore investigated how mice respond to five genetically determined levels of mouse angiotensinogen gene (Agt) expression covering the range associated with the M235T variants. By using high-throughput molecular phenotyping, tissue RNAs were assayed for expression of 10 genes important in hypertension. Significant positive and negative responses occurred in both sexes as Agt expression increased twofold, including a three-fold increase in aldosterone synthase expression in adrenal gland, and a two-fold decrease in renin expression in kidney. In males, cardiac expression of the precursor of atrial natriuretic peptide B and of adrenomedullin also increased approximately twofold. The relative expression of all genes studied except Agt differed significantly in the two sexes, and several unexpected relationships were encountered. A highly significant correlation between renal expression of the angiotensin type 1a receptor and kallikrein, independent of Agt genotype, is present in females (P < 0.0001) but not males (P = 0.4). The correlation between blood pressure (BP) and liver Agt expression within the five Agt genotypes is significant in females (P = 0.0005) but not in males (P = 0.2), whereas correlation of BP with differences between the genotypes is less in females (P = 0.06) than in males (P = 0.001). The marked gender differences in gene expression in wild-type mice and the changes induced by moderate alterations in Agt expression and BP emphasize the need to look for similar differences in humans.

人类血管紧张素原M235T多态性（angiotensinogen M235T polymorphism）与人类血管紧张素原基因（AGT）的差异表达以及高血压的发生密切相关，但该多态性所引发的机体稳态应答目前仍未明确。为此，本研究探究了小鼠对五种由遗传调控的小鼠血管紧张素原基因（Agt）表达水平的应答情况，这些表达水平覆盖了与M235T变异体相关的表达区间。本研究采用高通量分子表型分析技术（high-throughput molecular phenotyping），对各组织RNA中10个与高血压密切相关的基因的表达水平进行了检测。当Agt表达水平升高两倍时，雌雄小鼠均出现了显著的上调与下调应答：肾上腺组织中醛固酮合酶（aldosterone synthase）的表达上调三倍，肾脏组织中肾素（renin）的表达下调两倍。在雄性小鼠中，心房利钠肽B前体（precursor of atrial natriuretic peptide B）以及肾上腺髓质素（adrenomedullin）的心脏组织表达水平也上调了约两倍。除Agt外，本研究检测的所有基因的相对表达水平在雌雄小鼠间均存在显著差异，同时还发现了若干意料之外的关联。在不考虑Agt基因型的情况下，雌性小鼠肾脏组织中血管紧张素1a型受体（angiotensin type 1a receptor）与激肽释放酶（kallikrein）的表达水平存在极强的相关性（P < 0.0001），但该相关性在雄性小鼠中并不显著（P = 0.4）。在五种Agt基因型小鼠中，雌性小鼠的血压（BP）与肝脏Agt表达水平之间存在显著相关性（P = 0.0005），但雄性小鼠中该相关性并不显著（P = 0.2）；而血压与基因型间差异的相关性在雌性小鼠中（P = 0.06）弱于雄性小鼠（P = 0.001）。野生型小鼠基因表达中存在的显著性别差异，以及Agt表达水平和血压适度改变所引发的表达变化，均提示我们有必要在人类群体中探寻类似的差异。