Developmental regulation of the expression of genes encoding proteins involved in cholesterol homeostasis.

The developmental patterns of expression of HMG-CoA reductase, farnesyl pyrophosphate synthase, cholesterol 7 alpha-hydroxylase, and LDL receptor were investigated using Northern blotting analysis to quantitate mRNA levels. It was found that HMG-CoA reductase and farnesyl pyrophosphate synthase mRNA levels in brain reached peaks at age 4 days which correlates with the time of peak enzyme activity and the onset of rapid brain growth and myelination. In liver, HMG-CoA reductase and cholesterol 7 alpha-hydroxylase mRNA both rose dramatically at weaning. This is consistent with the concept that de novo synthesized cholesterol is the preferred substrate for cholesterol 7 alpha-hydroxylase and may also be involved in the induction of the enzyme. In testes, HMG-CoA reductase activity was highest at age 21 days and then declined, while LDL receptor mRNA levels rose from age 31 to 120 days. These studies suggest a major role for de novo cholesterol synthesis in developing brain, liver, and testes.