Caracterização da expressão gênica das subpopulações de monócitos CD14+CD16-, CD14+CD16+ e CD14dimCD16+ na obesidade

Abstract

Obesity is a low-grade inflammatory state characterized by excessive accumulation of adipose tissue which contributes to inflammatory process. Adipose tissue macrophages (ATMs) secret different factors and are polarized into pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes. Most of the ATMs derive from circulating monocytes, so monocytes play an important role in this low-grade inflammatory condition. In recent years, three subsets of monocytes have been identified: The CD14+CD16- (CMI), the CD14+CD16+ (IM) and the CD14dim CD16+ (NCM). Studies have shown an increase in CD16+ (CD14+CD16+ and CD14dimCD16+) subset in human inflammatory chronic pathologies. Recently, it was demonstrated an increase in CD16+ subsets in obesity decreasing after weight loss. Here, we show a set of data of the increased percentages and numbers of IM and NCM in obese subjects that decreased with weight loss (Poitou et al. 2011), and characterize gene expression profile of the monocyte subpopulations in obesity and suggest for the first time that the secretion derived from the obese adipose tissue induces the differentiation of CM into CD16+ monocytes. Furthermore we characterize the frequencies of the three monocytes subpopulations in obese and overweight children. The CM, IM and NCM of 6 obese subjects (OB) before and three-month after the gastric bypass, 6 obese subjects with type II diabetes (OB/D) and 7 lean subjects (C) were sorted by flow cytometry. The expression of several genes involved in monocyte functions (migration, adhesion, phagocytosis and cytokines production) was analyzed by Low Density Array. We observed an increase in the frequency of CD16+ monocytes in obese and diabetic obese subjects which decreased three months after the weight loss. The gene expression of CX3CR1 (fractalkine receptor) and of TLR8 (Toll Like Receptor 8) was highly increased in the CM, IM and NCM of the OB group and decreased after surgery. The three subsets displayed different gene expression profiles in the OB group compared to the C group: the NCM expressed high levels of CSF1R (Colony Stimulating Factor 1 receptor), TLR4, SELPLG (selectin P ligand) TNFα and IL1, the IM were characterized by over-expression of CCR2, CX3CR1, CCR5, TNFα and MCP1 and the CM expressed high levels of CCR2 (C-C chemokine receptor type 2) and CD36. Our results showed that CD14+CD16- monocytes can differentiate into CD16+ monocytes when stimulated with the conditioning media of visceral adipose tissue, suggesting a pivotal role for adipose tissue in the increased frequency of these monocytes during obesity. The three subpopulations display different gene expression patterns of molecules involved in migration, inflammation and antibody capture. CX3CR1 and TLR8 could be considered as a molecular signature reflecting modified functions of monocytes in obesity.