Estudo do papel modulador de adipócitos na ativação macrofágica durante a infecção por Mycobacterium bovis BCG in vitro

Abstract

Obesity is a chronic multifactorial disease characterized by excess of body fat and a low- grade inflammatory state, known as meta-inflammation. It is currently one of the world's leading public health problems. WHO data indicate that 13% of the world population is obese, in Brazil, the obesity index was 17.9% of the population in 2014. In addition to genetic factors, diet and metabolic disorders, such as glucose intolerance, dyslipidemia, systemic arterial hypertension, hormonal imbalance and changes in the intestinal microbiota have been proposed as triggers for inflammation involving adipocytes. Recent studies have shown that obese adipose tissue is characterized by increased infiltration of macrophages, suggesting that these are an important source of inflammation in this tissue. Transcriptional factors with immunoregulatory properties are involved in inflammatory processes and adipogenesis. Such as the PPARγ, is a receptor activated by lipid ligands, central regulator of adipogenesis, with functions in the immune cells activation and lipid metabolism. Data from our group, demonstrated that PPARγ activation induces the biogenesis of dynamic organelles, the Lipid Droplets (LD) during mycobacterial infection. These organelles have functions in lipid storage for energy generation, membrane synthesis, inflammatory mediators synthesis, cell signaling and inflammation. Moreover, the LD in macrophages are niches for the pathogens survival. Although the impact of obesity on metabolic and cardiovascular diseases is understood, the mechanisms involved in the interactions between adipocytes and macrophages infected with intracellular pathogens are not known. In this study we differentiated NIH3T3-L1 cells into adipocytes and used the supernatant obtained to stimulate peritoneal macrophages infected or not with M. bovis BCG. We analyze the lipids droplets formation, PPARγ expression, cytokine, adipokines and NO synthesis. The results have shown that NIH3T3-L1 cells differentiation into adipocytes is an efficient process involving changes in cell morphology and LD storage. The macrophages stimulation with adipocyte supernatant was able to potentiated LD biogenesis, as well as, PPARγ activation, during mycobacterial infection. After 6 and 48 hours of stimulation and infection, the TNF-α levels were also potentiated, although a significant decrease was observed after 24 hours of infection. The IL-10 levels, was increase in the presence of infection and supernatant stimulation at 6, 24 and 48 hours after infection. To nitrite analysis, we observe that after 24 h of infection, there was an increase of levels secreted by macrophages, however this effect was independent of the supernatant stimulation. The adipokines, as leptin and adiponectin, are important factors in the obesity and metabolic syndrome development. Therefore, we analyzed the levels of leptin and adiponectin produced by macrophages during BCG infection. The Leptin levels were not detect, while adiponectin production, was increased in the control macrophages in presence of supernatant, an effect that was inhibited during BCG infection. Thus, our results suggest a modulating effect of secreted factors by adipocytes on the macrophages activation, attributed to the lipid droplets formation, PPARγ expression, cytokines synthesis as TNF-α and IL-10 and a dowmodulation of adiponectin during M. bovis BCG, infection.