Enlarged adipocytes are associated with insulin resistance and are an independent predictor of type 2 diabetes. To understand the molecular link between these diseases and adipocyte hypertrophy, we developed a technique to separate human adipocytes from an adipose tissue sample into populations of small cells (mean 57.6+/-3.54 microm) and large cells (mean 100.1+/-3.94 microm). Microarray analysis of the cell populations separated from adipose tissue from three subjects identified 14 genes, of which five immune-related, with more than fourfold higher expression in large cells than small cells. Two of these genes were serum amyloid A (SAA) and transmembrane 4 L six family member 1 (TM4SF1). Real-time RT-PCR analysis of SAA and TM4SF1 expression in adipocytes from seven subjects revealed 19-fold and 22-fold higher expression in the large cells, respectively, and a correlation between adipocyte size and both SAA and TM4SF1 expression. The results were verified using immunohistochemistry. In comparison with 17 other human tissues and cell types by microarray, large adipocytes displayed by far the highest SAA and TM4SF1 expression. Thus, we have identified genes with markedly higher expression in large, compared with small, human adipocytes. These genes may link hypertrophic obesity to insulin resistance/type 2 diabetes.

To identify genes predominantly expressed in omental adipocytes, microarray expression profiles from 33 human tissues or cell types were analyzed, using an algorithm developed for identification of transcripts predominantly expressed in a certain tissue. Both known adipocyte-specific and more unexpected genes were among the 28 genes identified. To validate the approach, adipocyte expression of three of these genes, acute-phase serum amyloid A (A-SAA), aquaporin 7, and transport secretion protein-2.2, was compared with 17 other human tissues by real-time PCR. The unexpectedly high expression of A-SAA in adipocytes was further verified by Northern blot and immunohistochemistry. The liver, reported to be the main production site for A-SAA, displayed the second highest expression using microarray and real-time PCR. In obese subjects, adipose tissue mRNA and serum A-SAA levels were down-regulated during an 18-wk diet regime (P < 0.05 and P < 0.0001, respectively). A-SAA serum levels were highly correlated to adipose tissue mRNA levels (P < 0.001) and to the total (P < 0.0001) and sc (P < 0.0001) adipose tissue areas, as analyzed by computed tomography. We show that adipose tissue is a major expression site of A-SAA during the nonacute-phase reaction condition. This provides a direct link between adipose tissue mass and a marker for low-grade inflammation and cardiovascular risk.

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Context:We have previously identified nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1 (NQO1), an enzyme involved in the protection against oxidative stress, as a gene predominantly expressed in human adipocytes. Studies in mice deficient in NQO1 activity suggest that NQO1 may also play an important role in metabolism.Objective: The aim of this study was to explore the expression and regulation of NQO1 in human adipose tissue (AT) and isolated adipocytes. Patients and Results:The high expression of NQO1 in adipocytes was verified in human adipocytes and AT by real-time PCR. DNA microarray analysis showed that NQO1 was expressed at higher levels in large compared with small adipocytes, isolated from the same fat biopsy. Furthermore, NQO1 mRNA levels were positively correlated with adipocyte size (n ϭ 7; P Ͻ 0.002). During an 18-wk diet regime (n ϭ 24; mean weight loss 27 kg), the NQO1 expression in human sc AT was down-regulated (P Ͻ 0.0001), and mRNA levels correlated with body mass index (P ϭ 0.0005), sc, and total abdominal AT areas, as determined by computerized tomography (P Ͻ 0.0001, both) and metabolic parameters. NQO1 mRNA levels were also positively correlated with aspartate aminotransferase (P ϭ 0.0028) and alanine aminotransferase (P ϭ 0.0219), markers known to be associated with severity of hepatic steatosis.Conclusions: NQO1 is highly expressed in human AT, particularly in large adipocytes. AT NQO1 expression is reduced during dietinduced weight loss, and the expression levels positively correlate with adiposity, glucose tolerance, and markers of liver dysfunction. Together, these findings indicate a role for NQO1 in the metabolic complications of human obesity.

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Objective: To characterize brown adipose tissue (BAT) in the human perirenal adipose tissue depot. Method: Perirenal adipose tissue biopsies were obtained from 55 healthy kidney donors. Expression analysis was performed using microarray, real-time PCR, immunoblotting and immunohistochemistry. Additional studies using human stem cells were performed. Results: UCP1 gene expression analysis revealed a large intra-individual variation in the perirenal adipose tissue biopsies. Both multi-and unilocular UCP1-positive adipocytes were detected in several of the adipose tissue samples analyzed by immunohistochemical staining. Microarray analysis identified 54 genes that were overexpressed in UCP1-positive perirenal adipose tissue. Real-time PCR analysis of BAT candidate genes revealed a set of genes that were highly correlated to UCP1 and a set of three transcription factor genes (PRDM16, PGC1a, and RXRc) that were highly correlated to each other. RXRc displayed nuclear immunoreactivity in brown adipocytes and an increased gene expression during brown adipogenesis in human stem cells. Conclusion: Our data provides the first molecular characterization of BAT in the perirenal adipose tissue depot. Furthermore, it highlights the transcription factor RXRc as a new player in BAT development.