Human Molecular Genetics Advance Access originally published online on June 22, 2005
Human Molecular Genetics 2005 14(15):2201-2208; doi:10.1093/hmg/ddi224
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Expression of mutant human cystathionine ß-synthase rescues neonatal lethality but not homocystinuria in a mouse model
Division of Population Science, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA
* To whom correspondence should be addressed. Tel: +1 2157283030; Fax: +1 2152141623; Email: warren.kruger{at}fccc.edu
Received May 10, 2005; Revised June 9, 2005; Accepted June 16, 2005
Cystathionine ß-synthase (CBS) deficiency is a recessive genetic disorder in humans characterized by elevated levels of total plasma homocysteine (tHcy) and frequent thrombosis in humans. The I278T mutation is the most common mutation found in human CBS-deficient patients. The T424N mutation was identified as a mutation in human CBS that could restore function to I278T in Saccharomyces cerevisiae. In this report, we have engineered mice that express human I278T and I278T/T424N proteins from a metallotheinein-driven transgene. These transgene-containing mice were then bred to CBS knockout animals (Cbs-) to generate mice that express only human I278T or I278T/T424N protein. Both the I278T and the I278T/T424N transgenes are able to entirely rescue the previously described neonatal mortality phenotype despite the animals having a mean tHcy of 250 µM. The transgenic Cbs–/– animals exhibit facial alopecia, have moderate liver steatosis and are slightly smaller than heterozygous littermates. In contrast to human CBS deficiency, these mice do not exhibit extreme methioninemia. The mutant proteins are stable in the liver, kidney and colon, and liver extracts have only 2–3% of the CBS enzyme activity found in wild-type mice. Surprisingly, the I278T/T424N enzyme had exactly the same activity as the I278T enzyme indicating that T424N is unable to suppress I278T in mice. Our results show that elevated tHcy per se is not responsible for the neonatal lethality observed in Cbs–/– animals and suggests that CBS protein may have a function in addition to its role in homocysteine catabolism. These transgenic animals should be useful in the study of homocysteine related human disease.
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