Characterization of Inflammatory Gene Expression and Chemotaxis of Macrophages Expressing Guanylin and Guanylyl Cyclase-C

Depending upon the environment, macrophages can show at least two different phenotypes, including the inflammatory (M1) phenotype and the anti-inflammatory (M2) phenotype. CD11c–positive M1 macrophages produce proinflammatory cytokines such as interleukin (IL) 1β, IL-6, tumor necrosis factor α, and monocyte chemoattractant protein (MCP) 1, which are linked to the development of obesity-associated insulin resistance. Recently, we showed that double-transgenic (dTg) rats overexpressing guanylin (Gn) and its receptor, guanylyl cyclase-C (GC-C), specifically in macrophages did not become obese even when fed a high-fat diet. In the present study, to characterize macrophages expressing Gn and GC-C (i.e., Gn/GC-C macrophages), we analyzed the expression of the M1 and M2 markers of peritoneal macrophages isolated from dTg and wild type (WT) rats. We also examined the chemotaxis of these macrophages after incubation with MCP-1 or fatty acids. The expression of CD11c, an M1 macrophage marker were expressed at a significantly lower level in the peritoneal macrophages of dTg rats than in those of wild-type (WT) rats. In addition, the expression of IL-1, MCP-1 and chemokine receptor 2 were expressed at a significantly lower level in the peritoneal macrophages of dTg rats than in those of WT rats. On the other hand, there were no significant differences in the expression of M2 markers such as CD206, IL10, and arginine 1 between dTg and WT rats. We also found that the chemotaxis of Gn/GC-C macrophages incubated with fatty acids significantly increases compared to the macrophages of WT rats. Our results suggest that the low levels of proinflammatory cytokines and M1 markers in Gn/GC-C macrophages at least in part contribute to the anti-obese phenotype of Gn/GC-C Tg rats. In addition, the accelerated chemotaxis of Gn/GC-C macrophages in response to fatty acids suggests that these macrophages can uniquely react to excess fatty acids.