P16 AND METABOLISM · The role of p16INK4a in the development of obesity and insulin resistance

The role of p16INK4a in the development of obesity and insulin resistance

The Metabolic Syndrome (MetS) increases the risk for developing heart disease, stroke, and type 2 diabetes (T2D). However, therapeutical possibilities of these consequences remain limited. The MetS is an inflammatory disease in which a particular cell type, the macrophage, plays a key role. Macrophages are important effectors of inflammation and are a heterogeneous cell population, of which the activation state can be influenced by a variety of inflammatory factors and microbial products. Pro-inflammatory mediators induce polarisation towards "M1" or "classically activated" macrophages. M1 macrophages display an enhanced pro-inflammatory cytokine production and are able to generate reactive oxygen species. "M2" or "alternatively activated" macrophages contribute to a more anti-inflammatory environment by exerting immunosuppressive functions. It is now becoming increasingly evident that macrophage polarisation plays an important role in obesity, IR and cardiovascular disease development. Genome-wide association studies have shown that the locus encoding for p16ink4a is linked to increased risk of T2D and cardiovascular disease development. This protein is known as a tumor suppressor since it arrests the cell cycle and induces growth arrest and senescence. The goal of current project was to identify the role of p16INK4a in macrophages and to elucidate its potential role in MetS-related conditions, such as obesity, IR and atherosclerosis. We found that macrophages isolated from mice that do not express p16INK4a (p16 -/-) resemble M2 macrophages, without any effects on cell cycle status: i. e. M2 marker genes were found to be higher expressed while M1 markers were lower expressed in p16 -/- macrophages compared to controls. Moreover, p16 -/- macrophages were less responsive to M1 stimuli but were more responsive to M2 stimuli. Additionally, p16 -/- macrophages had anti-inflammatory effects on neighboring macrophages, a feature typical for M2 macrophages. The mechanism behind this phenotype involves the interference of p16INK4a with 2 major inflammatory signaling pathways (JAK2-STAT1 and NF-?B). To evaluate the role of p16INK4a in macrophages in the complete organism (in vivo), we created animals that lack p16INK4a only in their immune cells (such as macrophages) by using the technique of bone marrow transplantation. Using these animals, we performed several in vivo studies to identify the role of macrophage p16INK4a. First, we infected animals with the parasite Schistosoma Mansoni, which induces M2 macrophage polarisation. In line with our pervious results, mice with p16 -/- macrophages displayed increased M2 polarisation. Second, we assessed the development of obesity and IR in mice with p16 -/- immune cells. Interestingly, no difference on the development of parameters relevant to the MetS was observed, suggesting that p16INK4a in immune cells does not directly affect MetS development. Third, we evaluated whether p16INK4a in immune cells affects atherosclerosis development, one of the complications of the MetS. In line with our observations that immune cell p16INK4a deficiency did not affect MetS development, no effect was observed in the development of atherosclerosis. Finally, to examine the relevance to the human situation, we investigated the role of p16INK4a in macrophages isolated from human subjects. Interestingly, we found that p16INK4a also plays a role in macrophage polarisation of human macrophages and that p16INK4a inhibits the differentiation into a specific subset of macrophages found in adipose tissue. In conclusion, we have shown that p16INK4a is an important modulator of the inflammatory state of macrophages. However, the exact contribution to disease development remains to be elucidated. These results may lead to therapeutic targets to modulate macrophage polarisation and inflammatory status

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз