Structural organization of the gene encoding apolipoprotein A-II in an amyloidotic strain of senescence-accelerated mouse

Dramatically decreased high density lipoprotein cholesterol, increased remnant clearance, and insulin hypersensitivity in apolipoprotein A-II knockout mice suggest a complex role for apolipoprotein A-II in atherosclerosis susceptibility

Apolipoprotein (apo) A-II is the second most abundant apolipoprotein in high density lipoprotein (HDL). To study its role in lipoprotein metabolism and atherosclerosis susceptibility, apo A-II knockout mice were created. Homozygous knockout mice had 67% and 52% reductions in HDL cholesterol levels in the fasted and fed states, respectively, and HDL particle size was reduced. Metabolic turnover studies revealed the HDL decrease to be due to both decreased HDL cholesterol ester and apo A-I transport rate and increased HDL cholesterol ester and apo A-I fractional catabolic rate. The apo A-II deficiency trait was bred onto the atherosclerosis-prone apo E-deficient background, which resulted in a surprising 66% decrease in cholesterol levels due primarily to decreased atherogenic lipoprotein remnant particles. Metabolic turnover studies indicated increased remnant clearance in the absence of apo A-II. Finally, apo A-II deficiency was associated with lower free fatty acid, glucose, and insulin levels, suggesting an insulin hypersensitivity state. In summary, apo A-II plays a complex role in lipoprotein metabolism, with some antiatherogenic properties such as the maintenance of a stable HDL pool, and other proatherogenic properties such as decreasing clearance of atherogenic lipoprotein remnants and promotion of insulin resistance.

Polymorphism of apolipoprotein A-II (apoA-II) among inbred strains of mice. Relationship between the molecular type of apoA-II and mouse senile amyloidosis

Three types of apolipoprotein A-II (apoA-II) proteins (A, B and C) were predicted from the nucleotide sequence of apoA-II cDNA. Substitution of amino acid residues was noted at four positions (type A: Pro-5, Asp-20, Met-26, Ala-38; B: Pro-5, Glu-20, Val-26, Val-38; C: Gln-5, Glu-20, Val-26, Ala-38). Each type was identifiable by digestion of amplified apoA-II DNA by PCR, using restriction-fragment-length polymorphism of the apoA-II gene for restriction enzymes Cfr13I and MspI. The molecular type of apoA-II was determined among 23 strains of mice including nine of the senescence accelerated mouse series developed in our laboratory. Examination of types of apoA-II and amyloid deposition in the F2 and F3 hybrid mice showed that apoA-II amyloid deposition was present only in the mice homozygous for type C apoA-II and which were 12-17 months of age. The molecular type of apoA-II may be a factor involved in the development of senile amyloidosis in mice.