Publications

OBJECTIVE

Toll-like receptors (TLRs) recognize pathogens and mediate signaling pathways important for host defense. Recent studies implicate TLR polymorphisms in atherosclerosis risk in humans. Adipocyte fatty acid-binding protein (aP2) is present in macrophages and has an important role in atherosclerotic plaque development. We investigated aP2 expression in RAW 264.7 cells treated with lipopolysaccharide (LPS) and other TLR agonists and assessed lipid accumulation in these activated murine macrophages.

METHODS AND RESULTS

Stimulation with LPS, a TLR4 ligand, resulted in a 56-fold increase in aP2 mRNA expression, and zymosan, a TLR2 ligand, induced an approximately 1500-fold increase. Polyinosine: polycytidylic acid (poly I:C), a TLR3 ligand, led to a 9-fold increase. Levels of aP2 protein were significantly increased in LPS or zymosan-treated macrophages compared with control or poly I:C-treated cells. In addition, the cholesteryl ester content of LPS or zymosan-treated macrophages was approximately 5-fold greater in the presence of low-density lipoprotein, and triglyceride content was approximately 2-fold greater in the absence of exogenous lipid than control or poly I:C-treated cells.

CONCLUSIONS

Expression of macrophage aP2 is induced on TLR activation and parallels increases in cholesteryl ester and triglyceride levels. These results provide a molecular link between the known roles of TLR and aP2 in foam cell formation.

Fatty acid oxidation provides energy in tissues with high metabolic demands. During the acute-phase response (APR) induced by infection and inflammation, fatty acid oxidation is decreased associated with hypertriglyceridemia. Little is known about the mechanism by which the APR decreases fatty acid oxidation. Therefore, we investigated whether the APR affects the expression of medium-chain acyl-coenzyme A dehydrogenase (MCAD), its regulator the estrogen-related receptor alpha (ERRalpha), and a key coactivator of ERRalpha, the peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha). mRNA levels of PGC-1alpha, ERRalpha, and MCAD are markedly reduced in the liver, heart, and kidney of mice during the lipopolysaccharide (LPS)-induced APR. The decreases were rapid and occurred at very low doses of LPS. MCAD activity in liver was also reduced. Furthermore, binding of hepatic nuclear extracts to the ERRalpha response element found in the promoter region of MCAD was significantly decreased during the APR, suggesting the decreased transcription of the MCAD gene. The binding activity was identified as ERRalpha by supershift with antibody to ERRalpha. Similar decreases in mRNA levels of these genes occur during zymosan- and turpentine-induced inflammation, indicating that suppression of the PGC-1alpha, ERRalpha, and MCAD pathway is a general response during infection and inflammation. Our study provides a potential mechanism by which the APR decreases fatty acid oxidation.

The acute-phase response (APR) suppresses type II nuclear hormone receptors and alters the expression of their target genes involved in lipid metabolism in the liver and heart. Therefore, we examined the expression of liver X receptor/retinoid X receptor (LXR/RXR) and their target genes in kidney from mice treated with lipopolysaccharide (LPS) and in human proximal tubular HK-2 cells treated with interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). We found that LXRalpha and RXRalpha expression was suppressed by LPS in kidney and by IL-1beta or TNF-alpha in HK-2 cells. The decrease in LXRalpha/RXRalpha expression was associated with a decrease in the expression of several LXRalpha target genes [apolipoprotein E (apoE), ABCA1, ABCG1, and sterol-regulatory element binding protein-1c (SREBP-1c)] and a decrease in ligand-induced apoE expression. Moreover, IL-1beta and TNF-alpha significantly reduced liver X receptor response element (LXRE)-driven transcription as measured by LXRE-linked luciferase activity. However, overexpression of LXRalpha/RXRalpha only partially restored the cytokine-mediated reduction in LXRE-linked luciferase activity. Additionally, expression of the LXR coactivators peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC1alpha) and steroid receptor coactivator-2 (SRC-2) was decreased by IL-1beta or TNF-alpha. We conclude that the APR suppresses the expression of both nuclear receptors LXRalpha/RXRalpha and several LXRalpha coactivators in kidney, which could be a mechanism for coordinately regulating the expression of multiple LXR target genes that play important roles in lipid metabolism in kidney during the APR.

BACKGROUND

Data on associations of body composition with HIV disease characteristics are limited.

OBJECTIVE

We compared sex-specific associations between HIV disease characteristics and body composition in an racially-ethnically diverse cohort of antiretroviral-naive patients.

DESIGN

The study was a cross-sectional analysis of participants enrolled in a metabolic substudy of a multicenter trial. Regional fat was measured, and total body fat (TBF) was derived by using the Durnin-Womersley formula (DWF) and bioelectrical impedance analysis (BIA). Body cell mass (BCM) was measured by BIA.

RESULTS

Among 422 participants, 22% were women, 60% were African American, and 36% had prior AIDS-defining illnesses. Mean (+/-SD) age was 38.2 +/- 9.6 y, CD4+ count was 215 +/- 184 cells/mm3, and HIV RNA log10 was 5.0 +/- 0.8 copies/mL. On multivariate analysis, women with AIDS-defining illness had significantly (P < 0.005) lower regional body fat and TBF (BIA: -9.5 kg; DWF: -7.3 kg) but nonsignificantly lower BCM (-1.3 kg) than did women without such illnesses, whereas men with AIDS-defining illness had significantly (P < 0.005) lower BCM (-1.7 kg) but nonsignificantly lower TBF (BIA: -1.3 kg; DWF: -1.83 kg) than did men without such illnesses (P < 0.05 for sex differences in TBF). Significant negative associations of HIV RNA with BCM (-0.9 kg/log RNA; P = 0.03), TBF by BIA (-1.4 kg/log RNA; P = 0.05) and by DWF (-1.6 kg/log RNA; P = 0.01), and regional fat were observed in men only.

CONCLUSIONS

The effect of prior AIDS illness on body fat differed significantly between the sexes: women with prior AIDS-defining illness had significantly less fat than did women without such illnesses. An independent effect of HIV viremia on BCM and fat was seen in men. These distinctions may be due to inherent biological differences between the sexes.

During the third trimester of pregnancy, there is an increase in serum triglyceride and cholesterol levels. The mechanisms accounting for these changes in lipid metabolism during pregnancy are unknown. We hypothesized that, during pregnancy, the expression of nuclear hormone receptors involved in regulating lipid metabolism would decrease. In 19-day pregnant mice, serum triglyceride and non-HDL cholesterol levels were significantly increased, whereas total cholesterol was slightly decreased, because of a decrease in the HDL fraction. Peroxisome proliferator-activated receptor (PPAR)alpha, PPARbeta/delta, and PPARgamma, liver X receptor (LXR)alpha and LXRbeta, farnesoid X receptor (FXR), and retinoid X receptor (RXR)alpha, RXRbeta, and RXRgamma mRNA levels were significantly decreased in the livers of 19-day pregnant mice. Additionally, the expressions of thyroid receptor (TR)alpha, pregnane X receptor, sterol regulatory element-binding proteins (SREBP)-1a, SREBP-1c, SREBP-2, and liver receptor homolog 1 were also decreased, whereas the expression of TRbeta, constitutive androstane receptor, and hepatic nuclear factor 4 showed no significant change. mRNA levels of the PPAR target genes carnitine-palmitoyl transferase 1alpha and acyl-CoA oxidase, the LXR target genes SREBP1c, ATP-binding cassettes G5 and G8, the FXR target gene SHP, and the TR target genes malic enzyme and Spot14 were all significantly decreased. Finally, the expressions of PPARgamma coactivator (PGC)-1alpha and PGC-1beta, known activators of a number of nuclear hormone receptors, were also significantly decreased. The decreases in expression of RXRs, PPARs, LXRs, FXR, TRs, SREBPs, and PGC-1s could contribute to the alterations in lipid metabolism during late pregnancy.

OBJECTIVE

To evaluate the efficacy and safety of oxandrolone in promoting body weight and body cell mass (BCM) gain in HIV-associated weight loss.

METHODS

Randomized, double-blind, placebo-controlled trial. Two hundred sixty-two HIV-infected men with documented 10% to 20% weight loss or body mass index < or =20 kg/m were randomized to placebo or to 20, 40, or 80 mg of oxandrolone daily. After 12 weeks, subjects were allowed to receive open-label oxandrolone at a dose of 20 mg for another 12 weeks.

RESULTS

Body weight increased in all groups, including the group receiving placebo, during the double-blind phase (1.1 +/- 2.7, 1.8 +/- 3.9, 2.8 +/- 3.3, and 2.3 +/- 2.9 kg in placebo and 20-, 40-, and 80-mg oxandrolone groups, respectively; all P < 0.014 vs. baseline). BCM increased from baseline in all groups (0.45 +/- 1.7, 0.91 +/- 2.2, 1.5 +/- 2.5, and 1.8 +/- 1.8 kg in placebo and 20-, 40-, and 80-mg oxandrolone groups, respectively). At 12 weeks, only the gain in weight at the 40-mg dose of oxandrolone and the gain in BCM at the 40- and 80-mg doses of oxandrolone were greater than those in the placebo group, however. Oxandrolone treatment was associated with significant suppression of sex hormone-binding globulin, luteinizing hormone, follicle-stimulating hormone, and total and free testosterone levels. Treatment was generally well tolerated but accompanied by significant increases in transaminases and low-density lipoprotein as well as decreases in high-density lipoprotein.

CONCLUSION

Oxandrolone administration is effective in promoting dose-dependent gains in body weight and BCM in HIV-infected men with weight loss.

Cardiolipin (CL) is a phospholipid localized to the mitochondria, and its biosynthesis is essential for mitochondrial structure and function. We report here the identification and characterization of a cDNA encoding the first mammalian cardiolipin synthase (CLS1) in humans and mice. This cDNA exhibits sequence homology with members of a CLS gene family that share similar domain structure and chemical properties. Expression of the human CLS (hCLS1) cDNA in reticulocyte lysates or insect cells led to a marked increase in CLS activity. The enzyme is specific for CL synthesis, because no significant increase in phosphatidylglycerol phosphate synthase activity was observed. In addition, CL pool size was increased in hCLS1-overexpressing cells compared with controls. Furthermore, the hCLS1 gene was highly expressed in tissues such as heart, skeletal muscle, and liver, which have been shown to have high CLS activities. These results demonstrate that hCLS1 encodes an enzyme that synthesizes CL.

OBJECTIVE

Percent fat is often considered the reference for establishing the magnitude of adipose tissue accumulation and the risk of excess adiposity. However, the increasing recognition of a strong link between central adiposity and metabolic disturbances led us to test whether waist circumference (WC) is more highly correlated with metabolic syndrome components than percent fat and other related anthropometric measures such as BMI.

RESEARCH METHODS AND PROCEDURES

BMI, WC, and percent fat, measured by DXA, were evaluated in 1010 healthy white and African-American men and women [age, 48.3 +/- 17.2 (standard deviation) years; BMI, 27.0 +/- 5.3 kg/m(2)]. The associations of BMI, WC, and percent fat with age and laboratory-adjusted health risk indicators (i.e., serum glucose, insulin, triglycerides, high-density lipoprotein cholesterol, blood pressure) in each sex and ethnicity group were examined.

RESULTS

For 18 of 24 comparisons, the age- and laboratory-adjusted correlations were lowest for percent fat and in 16 of 24 comparisons were highest for WC. Fifteen of the between-method differences reached statistical significance. With health risk indicator as the dependent variable and anthropometric measures as the independent variable, the contribution of percent fat to the WC regression model was not statistically significant; in contrast, adding WC to the percent fat regression model did make a significant independent contribution for most health risk indicators.

DISCUSSION

WC had the strongest associations with health risk indicators, followed by BMI. Although percent fat is a useful measure of overall adiposity, health risks are best represented by the simply measured WC.

The acute-phase response (APR) leads to alterations in lipid metabolism and type II nuclear hormone receptors, which regulate lipid metabolism, are suppressed, in liver, heart, and kidney. Here, we examine the effect of the APR in adipose tissue. In mice, lipopolysaccharide produces a rapid, marked decrease in mRNA levels of nuclear hormone receptors [peroxisome proliferator-activated receptor gamma (PPARgamma), liver X receptor alpha (LXRalpha) and LXRbeta, thyroid receptor alpha (TRalpha) and TRbeta, and retinoid X receptor alpha (RXRalpha) and RXRbeta] and receptor coactivators [cAMP response element binding protein, steroid receptor coactivator 1 (SRC1) and SRC2, thyroid hormone receptor-associated protein, and peroxisome proliferator-activated receptor gamma co-activator 1alpha (PGC1alpha) and PGC1beta] along with decreased expression of target genes (adipocyte P2, phosphoenolpyruvate carboxykinase, glycerol-3-phosphate acyltransferase, ABCA1, apolipoprotein E, sterol-regulatory element binding protein-1c, glucose transport protein 4 (GLUT4), malic enzyme, and Spot14) involved in triglyceride (TG) and carbohydrate metabolism. We show that key TG synthetic enzymes, 1-acyl-sn-glycerol-3-phosphate acyltransferase-2, monoacylglycerol acyltransferase 1, and diacylglycerol acyltransferase 1, are PPARgamma-regulated genes and that they also decrease in the APR. In 3T3-L1 adipocytes, tumor necrosis factor-alpha (TNF-alpha) significantly decreases PPARgamma, LXRalpha and LXRbeta, RXRalpha and RXRbeta, SRC1 and SRC2, and PGC1alpha and PGC1beta mRNA levels, which are associated with a marked reduction in receptor-regulated genes. Moreover, TNF-alpha significantly reduces PPAR and LXR response element-driven transcription. Thus, the APR suppresses the expression of many nuclear hormone receptors and their coactivators in adipose tissue, which could be a mechanism to coordinately downregulate TG biosynthesis and thereby redirect lipids to other critical organs during the APR.