Genetic characterization of a mouse line with primary aldosteronism

In an attempt to define novel genetic loci involved in the pathophysiology of primary aldosteronism, a mutagenesis screen after treatment with the alkylating agent N-ethyl-N-nitrosourea was established for the parameter aldosterone. One of the generated mouse lines with hyperaldosteronism was phenotypically and genetically characterized. This mouse line had high aldosterone levels but normal creatinine and urea values. The steroidogenic enzyme expression levels in the adrenal gland did not differ significantly among phenotypically affected and unaffected mice. Upon exome sequencing, point mutations were identified in seven candidate genes (Sspo, Dguok, Hoxaas2, Clstn3, Atm, Tipin and Mapk6). Subsequently, animals were stratified into wild-type and mutated groups according to their genotype for each of these candidate genes. A correlation of their genotypes with the respective aldosterone, aldosterone-to-renin ratio (ARR), urea and creatinine values as well as steroidogenic enzyme expression levels was performed. Aldosterone values were significantly higher in animals carrying mutations in four different genes (Sspo, Dguok, Hoxaas2 and Clstn3) and associated statistically significant adrenal Cyp11b2 overexpression as well as increased ARR was present only in mice with Sspo mutation. In contrast, mutations of the remaining candidate genes (Atm, Tipin and Mapk6) were associated with lower aldosterone values and lower Hsd3b6 expression levels. In summary, these data demonstrate association between the genes Sspo, Dguok, Hoxaas2 and Clstn3 and hyperaldosteronism. Final proofs for the causative nature of the mutations have to come from knock-out and knock-in experiments.

Enhanced oxidative stress and endocrine pancreas alterations are linked to a novel glucokinase missense mutation in ENU-derived Munich Gck(D217V) mutants

In the large-scale Munich N-ethyl-N-nitrosourea (ENU) mouse mutagenesis project murine models recapitulating human diseases were generated. In one strain, a novel missense mutation (D217V) in the glucokinase (Gck) gene was identified, resulting in decreased glucokinase activity. Heterozygous mutants display mild hyperglycaemia, disturbed glucose tolerance, and decreased glucose-induced insulin secretion. In contrast, homozygous mutants exhibit severe but not survival affecting hyperglycaemia, mild growth retardation, diminished oxidative capacity, and increased abundance of CHOP protein in the islets. Furthermore, the total islet and β-cell volumes and the total volume of isolated β-cells are significantly decreased in adult homozygous mutants, whereas in neonatal mice, β-cell mass is not yet significantly decreased and islet neogenesis is unaltered. Therefore, reduced total islet and β-cell volumes of adult homozygous mutants might predominantly emerge from disturbed postnatal islet neogenesis. Thus, we identified a novel Gck mutation in mice, with relevance in humans, leading to glycaemic disease.