Background-Serum paraoxonase (PON1), an enzyme carried on HDL, inhibits LDL oxidation, and in human population studies, low PON1 activity is associated with atherosclerosis. In addition, PON1 knockout mice are more susceptible to lipoprotein oxidation and atherosclerosis. To evaluate whether PON1 protects against atherosclerosis and lipid oxidation in a dose-dependent manner, we generated and studied human PON1 transgenic mice. Methods and Results-Human PON1 transgenic mice were produced by using bacterial artificial chromosome genomic clones. The mice had 2-to 4-fold increased plasma PON1 levels, but plasma cholesterol levels were unchanged. Atherosclerotic lesions were significantly reduced in the transgenic mice when both dietary and apoE-null mouse models were used. HDL isolated from the transgenic mice also protected against LDL oxidation more effectively. Conclusions-Our results indicate that PON1 protects against atherosclerosis in a dose-dependent manner and suggest that it may be a potential target for developing therapeutic agents for the treatment of cardiovascular disease.

Serum paraoxonase (PON1), present on high density lipoprotein, may inhibit low density lipoprotein (LDL) oxidation and protect against atherosclerosis. We generated combined PON1 knockout (KO)/apolipoprotein E (apoE) KO and apoE KO control mice to compare atherogenesis and lipoprotein oxidation. Early lesions were examined in 3-month-old mice fed a chow diet, and advanced lesions were examined in 6-month-old mice fed a high fat diet. In both cases, the PON1 KO/apoE KO mice exhibited significantly more atherosclerosis (50 -71% increase) than controls. We examined LDL oxidation and clearance in vivo by injecting human LDL into the mice and following its turnover. LDL clearance was faster in the double KO mice as compared with controls. There was a greater rate of accumulation of oxidized phospholipid epitopes and a greater accumulation of LDL-immunoglobulin complexes in the double KO mice than in controls. Furthermore, the amounts of three bioactive oxidized phospholipids were elevated in the endogenous intermediate density lipoprotein/LDL of double KO mice as compared with the controls. Finally, the expression of heme oxygenase-1, peroxisome proliferator-activated receptor ␥, and oxidized LDL receptors were elevated in the livers of double KO mice as compared with the controls. These data demonstrate that PON1 deficiency promotes LDL oxidation and atherogenesis in apoE KO mice.

NCX3 is the third isoform of a mammalian Na ؉ -Ca 2؉ exchanger to be cloned. NCX3 was identified from rat brain cDNA by polymerase chain reaction (PCR) using degenerate primers derived from the sequences of two conserved regions of NCX1 and NCX2. The NCX3 PCR product was used to isolate two overlapping clones totalling 4.8 kilobases (kb) from a rat brain cDNA library. The overlapping clones were sequenced and joined at a unique Bsp106I restriction enzyme site to form a fulllength cDNA clone. The NCX3 cDNA clone has an open reading frame of 2.8 kb encoding a protein of 927 amino acids. At the amino acid level, NCX3 shares 73% identity with NCX1 and 75% identity with NCX2 and is predicted to share the same membrane topology as NCX1 and NCX2. Following addition of a poly(A)؉ tail to the NCX3 clone, exchanger activity could be expressed in Xenopus oocytes. NCX3 was also expressed in the mammalian BHK cell line. NCX3 transcripts are 6 kb in size and are highly restricted to brain and skeletal muscle. Linkage analysis in the mouse indicated that the NCX family of genes is dispersed, since the NCX1, NCX2, and NCX3 genes mapped to mouse chromosomes 17, 7, and 12, respectively.

In an effort to identify genetic factors contributing to atherogenesis, we have studied inbred strains of mice that are susceptible (C57BL/6J) and resistant (C3H/HeJ) to dietinduced aortic fatty streak lesions. When maintained on a low-fat diet, HDL isolated from both strain C57BL/6J (B6) and C3H/HeJ (C3H) mice protect against LDL oxidation in a coculture model of the artery wall. However, when maintained on an atherogenic diet high in fat and cholesterol, the HDL isolated from B6 mice lose the capacity to protect, whereas HDL from C3H mice protect equally well. Associated with the loss in the ability of HDL to protect is a decrease in the activity of serum paraoxonase, a serum esterase carried on HDL that has previously been shown to protect against LDL oxidation in vitro. The levels of paraoxonase mRNA decreased in B6 mice upon challenge with the atherogenic diet but increased in C3H, indicating that paraoxonase production is under genetic control. In a set of recombinant inbred strains derived from the B6 and C3H parental strains, low paraoxonase mRNA levels segregated with aortic lesion development, supporting a role for paraoxonase in atherogenesis.