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Mice deficient in cystathionine beta-synthase: animal models for mild and severe homocyst(e)inemia
M Watanabe1, J Osada, Y Aratani
1Department of Pathology, University of North Carolina, Chapel Hill 27599-7525.
Insights
Researchers created mice lacking cystathionine beta-synthase to study high homocysteine. Severe deficiency caused early death, while moderate deficiency offers a model for cardiovascular disease research.
Area of Science:
- Genetics and Molecular Biology
- Cardiovascular Research
- Metabolic Disorders
Background:
- Elevated plasma homocysteine is linked to occlusive vascular diseases.
- The direct causative role of homocysteine in cardiovascular disease remains unclear.
- Understanding homocysteine's role requires suitable animal models.
Purpose of the Study:
- To generate and characterize mouse models of homocyst(e)inemia.
- To investigate the in vivo effects of cystathionine beta-synthase deficiency.
- To establish models for studying the etiology of cardiovascular diseases.
Main Methods:
- Homologous recombination in mouse embryonic stem cells to inactivate the cystathionine beta-synthase gene.
- Generation of homozygous and heterozygous mutant mice.
- Biochemical and histological analysis of mutant mice and plasma homocysteine levels.
Main Results:
- Homozygous mutants lacking cystathionine beta-synthase exhibited severe growth retardation and mortality within 5 weeks.
- Histological analysis revealed enlarged, multinucleated hepatocytes with lipid droplets in homozygotes.
- Homozygous mutants displayed approximately 40-fold elevated plasma homocysteine levels.
- Heterozygous mutants showed a 50% reduction in enzyme activity and doubled plasma homocysteine levels.
Conclusions:
- Complete cystathionine beta-synthase deficiency leads to severe homocyst(e)inemia and associated pathologies.
- The generated mouse models are valuable for studying the impact of homocyst(e)inemia on cardiovascular health.
- Heterozygous mutants provide a promising model for investigating the role of moderately elevated homocysteine in cardiovascular disease etiology.
Abstract:
Studies by various investigators have indicated that elevated levels of plasma homocyst(e)ine are strongly associated with the occurrence of occlusive vascular diseases. With the eventual aim of determining whether or not elevated plasma homocyst(e)ine concentrations are directly causative of cardiovascular diseases, we have generated mice that are moderately and severely homocyst(e)inemic. Homologous recombination in mouse embryonic stem cells was used to inactivate the cystathionine beta-synthase [L-serine hydrolyase (adding homocysteine), EC 4.2.1.22] gene. Homozygous mutants completely lacking cystathionine beta-synthase were born at the expected frequency from matings of heterozygotes, but they suffered from severe growth retardation and a majority of them died within 5 weeks after birth. Histological examination showed that the hepatocytes of homozygotes were enlarged, multinucleated, and filled with microvesicular lipid droplets. Plasma homocyst(e)ine levels of the homozygotes were approximately 40 times normal. These mice, therefore, represent a model for severe homocyst(e)inemia resulting from the complete lack of cystathionine beta-synthase. Heterozygous mutants have approximately 50% reduction in cystathionine beta-synthase mRNA and enzyme activity in the liver and have twice normal plasma homocyst(e)ine levels. Thus, the heterozygous mutants are promising for studying the in vivo role of elevated levels of homocyst(e)ine in the etiology of cardiovascular diseases.