Expression of human cholesterol 7 alpha-hydroxylase in atherosclerosis-susceptible mice via adenovirus infection

Adenovirus is a vector for the delivery of genes mainly to the liver. Short-term (similar to 3 days) studies using adenovirus transfection have provided valuable insights into how genes can complement normal and pathological phenotypes. When atherosclerosis-susceptible C57BL/6 mice were infected with an adenovirus vector containing the human 7 alpha-hydroxylase cDNA (AV17hl) and fed on a chow diet, human 7 alpha-hydroxylase mRNA and enzyme activity doubled compared with that in mice infected with an adenovirus vector (AVINull) alone. In AV17hl-infected mice fed on a high fat cholic acid (HFCA) diet, mRNA expression and activity of both the endogenous and adenovirus (human) 7 alpha-hydroxylase were repressed. AV17hl-infected mice fed on a HFCA diet and killed at mid-light had increased 7 alpha-hydroxylase activity and mRNA compared with mice killed at mid-dark. Since expression of AV17hl is driven by a constitutive Rous sarcoma virus promoter, the repression of human 7 alpha-hydroxylase by the HFCA diet was unexpected. In spite of this posttranscriptional repression by the HFCA diet, AVl7hl-infected mice expressed the human 7 alpha-hydroxylase mRNA, causing its enzyme activity to be 3-fold greater than in AV1Null-infected mice. In AV17hl-infected mice, the 7 alpha-hydroxylase enzyme activity varied as a linear function of human mRNA abundance. In conclusion, the accumulation of apolipoprotein B-containing lipoproteins in plasma of C57BL/6 mice fed on the HFCA diet was not reduced by longer-term (2 weeks) 7 alpha-hydroxylase expression, probably because of its diminished expression caused by the diet and hepatic inflammation from the adenovirus infection. These results may suggest that adenovirus is effective in promoting longer-term (2 weeks) expression of 7 alpha-hydroxylase.