Macrophage Infiltration in Human Adipose Tissue

Obesity results from a disequilibrium in energy balance and an inability to adapt to lifestyles which encourage increased energy intake and sedentariness. These last years, numerous studies contributed to show that obesity is the pathology of an organ, the white adipose tissue (AT), characterized by a low grade inflammation when it is enlarged. The fact that adipocytes secrete a number of inflammatory factors or "adipokines" has forced several groups to reassess the involvement of the AT in wide range of physiological and pathophysiological processes. Adipose tissue probably contributes to the links between obesity, inflammation and insulin-resistance. Our previous results based on transcriptomics studies, showed that genes encoding inflammatory molecules are mobilized in adipose tissue of obese subjects and that caloric restriction improves greatly inflammatory profile. Our preliminary studies on the morphology of adipose tissue lead us to observe a major infiltration of macrophages in morbidly obese subjects. This project is based on a clinical protocol performed in massively obese subjects (BMI>40 kg/m²), where drastic weight loss is achieved by gastric bypass. This project has several objectives. It will allow us to characterize the infiltration of macrophages in the subcutaneous adipose tissue of 60 obese subjects compared with 20 normal-weight subjects, to study the evolution during surgically-induced weight loss and to compare the infiltration observed in adipose tissue to that of other tissues (visceral adipose tissue, muscle, liver, bowel and stomach). This study will be not only quantitative (number of macrophages) but also qualitative by characterizing the phenotype of macrophages with transcriptomics and immunohistochemical approaches. We will analyze the relationships between morphological characteristics of adipose tissue and clinical and biochemical parameters related to insulin sensitivity. More generally, this project might lead us to go thoroughly into the knowledge of the link between obesity and associated comorbidities, particularly metabolic complications, and to consider novels therapeutic strategies.