Homozygous Nr1h3 (nuclear receptor subfamily 1, group H, member 3) targeted mutation mice lose their ability to respond normally to dietary cholesterol. Mice maintained on cholesterol diets fail to induce transcription of the Cyp7a1 (cytochrome P450, family 7, subfamily a, polypeptide 1) gene, a rate-limiting enzyme in bile acid synthesis, and fail to induce expression of ABCG5 (ATP-binding cassette, sub-family G (WHITE), member 5) and ABCG8 (ATP-binding cassette, sub-family G (WHITE), member 8), ATP-binding cassette transporters that are required for cholesterol secretion into bile. Large amounts of cholesterol rapidly accumulate in the liver leading to impaired hepatic function. Impaired reverse cholesterol transport from peripheral tissues is also observed. The ability to regulate lipids and carbohydrates is also lost. Defects in innate immune responses by activated macrophages have also been described. Males are not infertile, but show a significantly higher number of testicular apoptotic cells than wildtype mice. Testosterone production is significantly lower. It is not known whether genetic background affects the phenotype associated with this mutation.
