Human adipose tissue macrophages display activation of cancer-related pathways.

Obesity is associated with a significantly increased risk for cancer suggesting that adipose tissue dysfunctions might play a crucial role therein. Macrophages play important roles in adipose tissue as well as in cancers. Here, we studied whether human adipose tissue macrophages (ATM) modulate cancer cell function. Therefore, ATM were isolated and compared with monocyte-derived macrophages (MDM) from the same obese patients. ATM, but not MDM, were found to secrete factors inducing inflammation and lipid accumulation in human T47D and HT-29 cancer cells. Gene expression profile comparison of ATM and MDM revealed overexpression of functional clusters, such as cytokine-cytokine receptor interaction (especially CXC-chemokine) signaling as well as cancer-related pathways, in ATM. Comparison with gene expression profiles of human tumor-associated macrophages showed that ATM, but not MDM resemble tumor-associated macrophages. Indirect co-culture experiments demonstrated that factors secreted by preadipocytes, but not mature adipocytes, confer an ATM-like phenotype to MDM. Finally, the concentrations of ATM-secreted factors related to cancer are elevated in serum of obese subjects. In conclusion, ATM may thus modulate the cancer cell phenotype.

Association between a thyroid hormone receptor-α gene polymorphism and blood pressure but not with coronary heart disease risk.

BACKGROUND: Thyroid hormones (THs) exert multiple biological roles including effects on the cardiovascular system (lipid profile, blood pressure (BP) and cardiac output). The lipid-lowering actions of TH are mediated by the TH receptor-ß whereas the mechanisms explaining the BP variations concomitant with the thyroid disorders are less understood. As the TH receptor-α (TR-α) has been associated with many of TH actions on the cardiovascular system in mice models, we hypothesized that it could be involved in the latter. We thus tested whether polymorphisms in TR-α (THRA gene) could be associated with BP level variation. Secondarily, we tested for association with coronary heart disease (CHD) risk. METHODS: We analyzed the associations between five THRA polymorphisms and (i) BP level in two population-based studies (MONICA Lille n = 1,155; MONICA Toulouse n = 1,170) and (ii) the risk of CHD in two case-control studies (Lille CHD n = 558 cases/568 controls; PRIME n = 527 cases/584 controls). RESULTS: Individuals carrying the rs939348 T allele had higher systolic BP (~+1.3 mm Hg) than CC individuals in both the MONICA Lille (P = 0.02) and Toulouse (P = 0.03) studies. The odds ratio (OR) for hypertension was 1.25 (P = 0.02) in the combined sample. Concerning the CHD risk, no significant association could be detected. CONCLUSIONS: For the first time, our study showed associations between the THRA rs939348 polymorphism and systolic BP and the risk of hypertension but not with CHD, although we admit that the statistical power available to study any relationship with CHD was very limited. Further larger association studies are needed to confirm our findings.

Liver X Receptor (LXR) activation negatively regulates visfatin expression in macrophages.

Adipose tissue macrophages (ATM) are the major source of visfatin, a visceral fat adipokine upregulated during obesity. Also known to play a role in B cell differentiation (pre-B cell colony-enhancing factor (PBEF)) and NAD biosynthesis (nicotinamide phosphoribosyl transferase (NAMPT)), visfatin has been suggested to play a role in inflammation. Liver X Receptor (LXR) and Peroxisome Proliferator-Activated Receptor (PPAR)γ are nuclear receptors expressed in macrophages controlling the inflammatory response. Recently, we reported visfatin as a PPARγ target gene in human macrophages. In this study, we examined whether LXR regulates macrophage visfatin expression. Synthetic LXR ligands decreased visfatin gene expression in a LXR-dependent manner in human and murine macrophages. The decrease of visfatin mRNA was paralleled by a decrease of protein secretion. Consequently, a modest and transient decrease of NAD(+) concentration was observed. Interestingly, LXR activation decreased the PPARγ-induced visfatin gene and protein secretion in human macrophages. Our results identify visfatin as a gene oppositely regulated by the LXR and PPARγ pathways in human macrophages.

Visfatin is induced by peroxisome proliferator-activated receptor gamma in human macrophages.

Obesity is a low-grade chronic inflammatory disease associated with an increased number of macrophages (adipose tissue macrophages) in adipose tissue. Within the adipose tissue, adipose tissue macrophages are the major source of visfatin/pre-B-cell colony-enhancing factor/nicotinamide phosphoribosyl transferase. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) exerts anti-inflammatory effects in macrophages by inhibiting cytokine production and enhancing alternative differentiation. In this study, we investigated whether PPARgamma modulates visfatin expression in murine (bone marrow-derived macrophage) and human (primary human resting macrophage, classical macrophage, alternative macrophage or adipose tissue macrophage) macrophage models and pre-adipocyte-derived adipocytes. We show that synthetic PPARgamma ligands increase visfatin gene expression in a PPARgamma-dependent manner in primary human resting macrophages and in adipose tissue macrophages, but not in adipocytes. The threefold increase of visfatin mRNA was paralleled by an increase of protein expression (30%) and secretion (30%). Electrophoretic mobility shift assay experiments and transient transfection assays indicated that PPARgamma induces visfatin promoter activity in human macrophages by binding to a DR1-PPARgamma response element. Finally, we show that PPARgamma ligands increase NAD(+) production in primary human macrophages and that this regulation is dampened in the presence of visfatin small interfering RNA or by the visfatin-specific inhibitor FK866. Taken together, our results suggest that PPARgamma regulates the expression of visfatin in macrophages, leading to increased levels of NAD(+).

Hypoxia down-regulates CCAAT/enhancer binding protein-alpha expression in breast cancer cells.

The transcription factor CCAAT/enhancer binding protein-alpha (C/EBP alpha) is involved in the control of cell differentiation and proliferation, and has been suggested to act as a tumor suppressor in several cancers. By using microarray analysis, we have previously shown that hypoxia and estrogen down-regulate C/EBP alpha mRNA in T-47D breast cancer cells. Here, we have examined the mechanism by which the down-regulation by hypoxia takes place. Using the specific RNA polymerase II inhibitor 5,6-dichlorobenzimidazole-1-beta-D-ribofuranoside, the mRNA stability was analyzed under normoxia or hypoxia by quantitative reverse transcription-PCR. Hypoxia reduced the half-life of C/EBP alpha mRNA by approximately 30%. C/EBP alpha gene promoter studies indicated that hypoxia also repressed the transcription of the gene and identified a hypoxia-responsive element (-522; -527 bp), which binds to hypoxia-inducible factor (HIF)-1 alpha, as essential for down-regulation of C/EBP alpha transcription in hypoxia. Immunocytochemical analysis showed that C/EBP alpha was localized in the nucleus at 21% O(2), but was mostly cytoplasmic under 1% O(2). Knockdown of HIF-1 alpha by RNAi restored C/EBP alpha to normal levels under hypoxic conditions. Immunohistochemical studies of 10 tumor samples did not show any colocalization of C/EBP alpha and glucose transporter 1 (used as a marker for hypoxia). Taken together, these results show that hypoxia down-regulates C/EBP alpha expression in breast cancer cells by several mechanisms, including transcriptional and posttranscriptional effects. The down-regulation of C/EBP alpha in hypoxia is mediated by HIF-1.