Increased secretion of lipoproteins in transgenic mice expressing human D374Y PCSK9 under physiological genetic...

To produce transgenic mice expressing the D374Y variant of the human proprotein convertase subtilisin/kexin type 9 (PCSK9) gene at physiological levels to investigate the mechanisms causing hypercholesterolemia and accelerated atherosclerosis.

A bacterial artificial chromosome containing PCSK9 and its flanking regions was modified to introduce the D374Y mutation and a C-terminal myc(2) tag. Transgenic mice that expressed 1 copy of the mutant or wild-type (WT) PCSK9 bacterial artificial chromosome were produced. Human PCSK9 mRNA was expressed at levels comparable to endogenous pcsk9 and with the same tissue specificity. The expression of D374Y or WT human PCSK9 increased the serum cholesterol level and reduced hepatic low-density lipoprotein receptor protein levels in the transgenic mice compared with bacterial artificial chromosome-negative controls; however, the effects were more marked in D374Y mice. The effect of a high-cholesterol diet on increasing serum cholesterol level was greater in D374Y mice, and atherosclerotic plaques after 15 weeks were more extensive in mice expressing D374Y than in WT PCSK9. D374Y mice secreted more triglyceride-rich lipoproteins into the circulation than WT mice.

The expression of human D374Y PCSK9 at physiological levels produced a phenotype that closely matched that found in heterozygous D374Y patients and suggested that reduced low-density lipoprotein receptor activity is not the sole cause of their hypercholesterolemia.