Killer immunoglobulin-like receptors (KIR) bind self–major histocompatibility complex class I molecules, allowing natural killer (NK) cells to recognize aberrant cells that have down-regulated class I. NK cells express variable numbers and combinations of highly homologous clonally restricted KIR genes, but uniformly express KIR2DL4. We show that NK clones express both 2DL4 alleles and either one or both alleles of the clonally restricted KIR 3DL1 and 3DL2 genes. Despite allele-independent expression, 3DL1 alleles differed in the core promoter by only one or two nucleotides. Allele-specific 3DL1 gene expression correlated with promoter and 5′ gene DNA hypomethylation in NK cells in vitro and in vivo. The DNA methylase inhibitor, 5-aza-2′-deoxycytidine, induced KIR DNA hypomethylation and heterogeneous expression of multiple KIR genes. Thus, NK cells use DNA methylation to maintain clonally restricted expression of highly homologous KIR genes and alleles.

Mature human NK lymphocytes express the highly homologous killer Ig-like receptor (KIR) genes in a stochastic fashion, and KIR transcription precisely correlates with allele-specific DNA methylation. In this study, we demonstrate that CpG methylation of a minimal KIR promoter inhibited transcription. In human peripheral blood NK cells and long-term cell lines, expressed KIR genes were associated with a moderate level of acetylated histone H3 and H4 and trimethylated histone H3 lysine 4. Histone modifications were preferentially associated with the transcribed allele in NK cell lines with monoallelic KIR expression. Although reduced, a substantial amount of histone acetylation and H3 lysine 4 trimethylation also was associated with nonexpressed KIR genes. DNA hypomethylation correlated with increased chromatin accessibility, both in vitro and in vivo. Treatment of NK cell lines and developing NK cells with the DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine, caused a dramatic increase in KIR RNA and protein expression, but little change in histone modification. Our findings suggest that KIR transcription is primarily controlled by DNA methylation.

The epidemic of obesity sweeping developed nations is accompanied by an increase in atherosclerotic cardiovascular diseases. Dyslipidemia, diabetes, hypertension, and obesity are risk factors for cardiovascular disease. However, delineating the mechanism of obesity‐accelerated atherosclerosis has been hampered by a paucity of animal models. Similar to humans, apolipoprotein E–deficient (apoE−/−) mice spontaneously develop atherosclerosis over their lifetime. To determine whether apoE−/− mice would develop obesity with accelerated atherosclerosis, we fed mice diets containing 10 (low fat (LF)) or 60 (high fat (HF)) kcal % from fat for 17 weeks. Mice fed the HF diet had a marked increase in body weight and atherosclerotic lesion formation compared to mice fed the LF diet. There were no significant differences between groups in serum total cholesterol, triglycerides, or leptin concentrations. Plasma concentrations of the acute‐phase reactant serum amyloid A (SAA) are elevated in both obesity and cardiovascular disease. Accordingly, plasma SAA concentrations were increased fourfold (P < 0.01) in mice fed the HF diet. SAA was associated with both pro‐ and antiatherogenic lipoproteins in mice fed the HF diet compared to those fed the LF diet, in which SAA was primarily associated with the antiatherogenic lipoprotein high‐density lipoprotein (HDL). Moreover, SAA was localized with apoB‐containing lipoproteins and biglycan in the vascular wall. Taken together, these data suggest male apoE‐deficient mice are a model of metabolic syndrome and that chronic low level inflammation associated with increased SAA concentrations may mediate atherosclerotic lesion formation.

Background Despite numerous clinical and animal studies, the role of sex steroid hormones on lipoprotein metabolism and atherosclerosis remain controversial. Objective We sought to determine the effects of endogenous estrogen and testosterone on lipoprotein levels and atherosclerosis using mice fed a low-fat diet with no added cholesterol. Methods Male and female low-density lipoprotein receptor-deficient mice were fed an open stock low-fat diet (10% of kcals from fat) for 2, 4, or 17 weeks. Ovariectomy, orchidectomy, or sham surgeries were performed to evaluate the effects of the presence or absence of endogenous hormones on lipid levels, lipoprotein distribution, and atherosclerosis development. Results Female mice fed the study diet for 17 weeks had a marked increase in levels of total cholesterol, triglycerides, apolipoprotein-B containing lipoproteins, and atherosclerosis compared with male mice. Surprisingly, ovariectomy in female mice had no effect on any of these parameters. In contrast, castration of male mice markedly increased total cholesterol concentrations, triglycerides, apolipoprotein B-containing lipoproteins, and atherosclerotic lesion formation compared with male and female mice. Conclusions These data suggest that endogenous androgens protect against diet-induced increases in cholesterol concentrations, formation of proatherogenic lipoproteins, and atherosclerotic lesions formation. Conversely orchidectomy, which decreases androgen concentrations, promotes increases in cholesterol concentrations, proatherogenic lipoprotein formation, and atherosclerotic lesion formation in lowdensity lipoprotein receptor-deficient mice in response to a low-fat diet.