Establishment of a mouse model with mutagenesis induced hyperaldosteronism

According to recent epidemiological studies, primary aldosteronism
is considered to be responsible for almost 10-15% of all cases of
arterial hypertension. The genetic background of this common
disease, however, has been elucidated only for the rare familial
types whereas in the large majority of sporadic cases genetic
causes or modifiers still remain unclear. In an attempt to define
novel genetic mechanisms of hyperaldosteronism we utilized a random
mutagenesis screen after treatment with the alkylating agent
N-ethylnitrosourea (ENU) and phenotypically characterized affected
mice for their blood aldosterone levels. As the detection method we
used a time resolved fluorescent immunoassay which allows the
measurement of aldosterone in very small murine plasma volumes.
Using this assay we determined the normal aldosterone values for
C3HeB/FeJ wild type mice under baseline conditions and following
specific stimulation and suppression tests. We could demonstrate
the expected increase in aldosterone response upon ACTH
stimulation, a high potassium diet and an angiotensin II injection,
as well as the decrease after a dexamethasone suppression test, a
normal saline load test and a fludrocortisone suppression test. On
the molecular level, the expression of aldosterone synthase showed
a similar pattern with a fast response to the investigated stimuli.
These tests should later be applied to the mouse lines derived from
the ENU screen, in order to investigate potential abnormal response
to these stimuli in comparison to wild type animals. Furthermore,
aldosterone measurement was carried out in more than 2000 F1
offspring (of both genders) of chemically mutated inbred C3HeB/FeJ
mice. From these tested F1 offspring, aldosterone levels were
consistently elevated (defined as levels above 3 SD over the mean
of untreated animals)upon repeated measurement in 9 animals (8
females and 1 male). Further breeding of affected female animals
gave rise to F2 pedigrees from which four established lines
displayed high aldosterone values. These animals served for a
detailed phenotypic characterization and showed an increased
aldosterone to renin ratio, low potassium values and normal renal
function in line with the presence of primary aldosteronism. In
addition, the investigation of their cardiac phenotype showed
increased collagen deposits and subsequently cardiac fibrosis, as
also observed in patients suffering from primary aldosteronism. In
the future, genetic SNP analysis can be performed to identify
underlying genetic loci, responsible for this trait. Taken
together, these data demonstrate the feasibility of a
phenotype-driven mutagenesis screen to detect and establish mutant
mouse lines with a high aldosterone phenotype.