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Ornithine deficiency in the arginase double knockout mouse
Joshua L Deignan1, Justin C Livesay, Paul K Yoo
1Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
Molecular Genetics and Metabolism
|June 7, 2006
Summary
Arginase AI deficiency in mice causes fatal hyperammonemia due to low ornithine levels, crucial for the urea cycle. This study links ornithine deficiency to arginase AI knockout, impacting urea cycle function.
Area of Science:
- Biochemistry
- Genetics
- Physiology
Background:
- Arginase enzymes (AI and AII) are critical for urea metabolism.
- Deficiency in arginase AI leads to hyperammonemia in knockout mice.
- Arginase AII knockout mice show no apparent phenotype.
Purpose of the Study:
- To investigate the roles of arginase AI and AII in vivo.
- To determine the cause of hyperammonemia in arginase AI-deficient mice.
- To explore the impact of combined arginase AI and AII deficiency.
Main Methods:
- Generation and analysis of arginase AI and AII single and double knockout mice.
- Phenotypic characterization of knockout models.
- Measurement of plasma and tissue amino acid levels (arginine, ornithine).
Main Results:
- Arginase AI knockout mice exhibit fatal hyperammonemia by 14 days.
- Double knockout mice show similar phenotypes to AI knockout mice.
- Plasma and tissue ornithine levels are significantly decreased, while arginine levels are elevated in double knockout mice.
- Ornithine deficiency is identified as the cause of hyperammonemia in AI knockout mice.
Conclusions:
- The fatal hyperammonemia in arginase AI knockout mice is primarily caused by ornithine deficiency.
- Ornithine is essential for urea cycle function.
- Ornithine aminotransferase (OAT) plays a critical role in maintaining ornithine homeostasis.
- Clinically significant ornithine deficiency may be present in human arginase AI deficiency patients even without neonatal hyperammonemia.
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