ИСТИНА

The problem of obesity and metabolic syndrome is one of the most important in modern medicine. The main hazard of metabolic syndrome is latent inflammation in adipose tissue promoting systemic inflammation, cardiovascular risk and the development of insulin resistance which breaks biological response of tissues and cells to the action of insulin. In physiological state, the main aim of insulin action is phosphorylation of Akt kinase on Thr-308, but additional phosphorylation of Ser-473 is also required for full activation of Akt. The latter effect mostly relies on mTORC2 activity and also depends on insulin action. Complete activation of Akt results in a spectrum of physiological effects including translocation of GLUT4 into cell membrane and synthesis of glycogen. In our work we studied the influence of RAW 264.7 macrophages (Mphs) which were polarized into M1 and M2 types by LPS/INF-γ and by IL-4, respectively, on insulin-dependent phosphorylation of Akt kinase in 3T3L1 adipocytes. Mph M1/M2 polarization was characterized by real time PCR, ELISA and by estimating reactive oxygen species production. We have proved that M1-Mphs secrete and express predominantly inflammatory markers (TNF-α, CXCL9, CXCL11) and have more abundant generation of ROS than M2- and nonpolarized (M0) cells. In turn, M2-Mphs produce predominantly anti-inflammatory markers (ALOX-15, IGF-1, MCP-4) and have lesser ROS generation than M1. Basing on this divergence, we modeled paracrine effect of M0, M1 and M2 Mphs on differentiated 3T3L1 adipocytes by using macrophage conditioned media (CM). Then, after short-term loading by insulin, 3T3L1 cells were analyzed on Akt phosphorylation by Western-blotting. We have found that M1-cell CM exert a decrease of pAkt-Thr308 while increasing pAkt-Ser473 in 3T3L1 adipocytes. These effects were not observed if M2 cell’ media was used for adipocyte treatment. On the contrary, M2 Mph CM induced the increase of pAkt-Thr308 and decrease in pAkt-Ser473. The decline of Thr-308 phosphorylation in inflammatory conditions may be due to regulatory inhibitory Ser/Thr phosphorylation of IRS-1. This regulatory mechanism can be operated via a variety of protein kinases, including aPKC, S6K and proinflammatory kinase IKK. The proposed mechanism of pAkt-Ser473 increase in inflammatory conditions may be associated with IKK-dependent activation of mTORC2, the possibility of which was shown in some studies. Thus, possible mechanism mediating the influence of M1/M2-polarized Mphs on insulin-dependent Akt-phosphorylation may be associated with divergent regulation of IKK-kinase in target cells. It may be realized in latent inflammation, insulin resistance and metabolic syndrome.