TRAP Induces Obesity Figure 3. Expression of TRAP mRNA and protein in human adipose tissue. (A) Expression of TRAP mRNA and monomeric TRAP protein in obesity compared to the lean state. (B) TRAP mRNA, (C) total TRAP protein and (D) monomeric TRAP protein expression in hyperplastic and hypertrophic obesity. doi:10.1371/journal.pone.0001713.g003 whether macrophages can secrete monomeric TRAP. The supernatant of the mouse macrophage cell line RAW 264.7 stimulated with LPS and IFN-c was shown to contain exclusively monomeric TRAP (Figure 5G). TRAP overexpression affects adipokine- and cytokine profile in mouse adipose tissue and serum Obesity in humans is associated with a so-called metabolic syndrome which involves alterations in circulating levels of a wide range of adipocyte and immune cell-derived cytokines, and eventually with insulin resistance. We measured mRNA and serum protein levels of cytokines and adipokines known to be altered in obesity in TRAP+ and WT mice. These factors can be divided into two groups: those only expressed by adipocytes (adiponectin, leptin) [28] and those thought to be expressed by several different cells in adipose tissue (TNFa, IL1b, MMP9, IL6, CCL2) [28] The mRNA levels of leptin and adiponectin in adipose tissue were found to be unchanged between the TRAP+ mice and WT littermates (Figure 6A). The serum leptin levels were two-fold increased (Figure 6A; Z = 22.83 p = 0.004) in the TRAP+ compared to WT mice, probably reflecting the overall increase in total body fat (and total fat cell number). The mRNA level of TNFa in adipose tissue was increased (Figure 6B; Z = 2.34 p = 0.019) in TRAP+ mice compared to WT littermates although serum TNFa levels were not (data not shown). The mRNA levels for CCL2, MMP9, IL1b, IFNc, IL12b, TGFb and IL6 were not significantly affected in the adipose tissue of TRAP+ mice (Figure 6B), suggesting that there is not a global activation of macrophages to produce inflammatory cytokines. Transgenic mice over expressing TRAP have normal adipocyte lipid metabolism and insulin sensitivity Adipocytes isolated from TRAP+ mice exhibited normal spontaneous basal lipolysis (Figure 6C, D), normal responses to addition of noradrenaline (Figure 6C) and insulin (Figure 6D) on lipolysis and unchanged basal or maximum insulin induced lipogenesis (Figure 6E). Half-maximum effective concentrations of insulin and noradrenaline to elicit metabolic responses were also similar in adipocytes from WT and TRAP+ mice (data not shown). Thus, adipocyte metabolism and insulin sensitivity were normal in TRAP+ mice. In line with the finding in adipocytes, serum levels of glucose and insulin as well as HOMA index did not differ between the TRAP+ mice and their non-transgenic WT controls (Figure 6F). PLoS ONE | www.plosone.org 5 March 2008 | Volume 3 | Issue 3 | e1713