👤 G D Barish

Adiponectin (APN), a pleiotropic adipokine that exerts anti-inflammatory, antidiabetic, and antiatherogenic effects through its receptors (AdipoRs), AdipoR1 and AdipoR2, is an important therapeutic target. Factors regulating AdipoR expression in monocyte/macrophages are poorly understood, and the significance of polarized macrophage activation in controlling AdipoR expression and the APN-mediated inflammatory response has not been investigated. The aim of this study was to investigate whether the macrophage polarization phenotype controls the AdipoR expression and APN-mediated inflammatory response. With the use of mouse bone marrow and peritoneal macrophages, we demonstrate that classical activation (M1) of macrophages suppressed (40-60% of control) AdipoR expression, whereas alternative activation (M2) preserved it. Remarkably, the macrophage polarization phenotypes produced contrasting inflammatory responses to APN (EC50 5 µg/ml). In M1 macrophages, APN induced proinflammatory cytokines, TNF-α, IL-6, and IL-12 (>10-fold of control) and AdipoR levels. In contrast, in M2 macrophages, APN induced the anti-inflammatory cytokine IL-10 without altering AdipoR expression. Furthermore, M1 macrophages adapt to a cytokine environment by reversing AdipoR expression. APN induced AdipoR mRNA and protein expression by up-regulating liver X receptor-α (LXRα) in macrophages. These results provide the first evidence that macrophage polarization is a key determinant regulating AdipoR expression and differential APN-mediated macrophage inflammatory responses, which can profoundly influence their pathogenic role in inflammatory and metabolic disorders. Show less

In Wnt signaling, beta-catenin and plakoglobin transduce signals to the nucleus through interactions with TCF-type transcription factors. However, when plakoglobin is artificially engineered to restrict it to the cytoplasm by fusion with the transmembrane domain of connexin (cnxPg), it efficiently induces a Wnt-like axis duplication phenotype in Xenopus. In Xenopus embryos, maternal XTCF3 normally represses ventral expression of the dorsalizing gene Siamois. Two models have been proposed to explain the Wnt-like activity of cnxPg: 1) that cnxPg inhibits the machinery involved in the turnover of cytosolic beta-catenin, which then accumulates and inhibits maternal XTCF3, and 2) that cnxPg directly acts to inhibit XTCF3 activity. To distinguish between these models, we created a series of N-terminal deletion mutations of cnxPg and examined their ability to induce an ectopic axis in Xenopus, activate a TCF-responsive reporter (OT), stabilize beta-catenin, and colocalize with components of the Wnt signaling pathway. cnxPg does not colocalize with the Wnt pathway component Dishevelled, but it does lead to the redistribution of APC and Axin, two proteins involved in the regulation of beta-catenin turnover. Expression of cnxPg increases levels of cytosolic beta-catenin; however, this effect does not completely explain its signaling activity. Although cnxPg and Wnt-1 stabilize beta-catenin to similar extents, cnxPg activates OT to 10- to 20-fold higher levels than Wnt-1. Moreover, although LEF1 and TCF4 synergize with beta-catenin and plakoglobin to activate OT, both suppress the signaling activity of cnxPg. In contrast, XTCF3 suppresses the signaling activity of both beta-catenin and cnxPg. Both exogenous XLEF1 and XTCF3 are sequestered in the cytoplasm of Xenopus cells by cnxPg. Based on these data, we conclude that, in addition to its effects on beta-catenin, cnxPg interacts with other components of the Wnt pathway, perhaps TCFs, and that these interactions contribute to its signaling activity. Show less