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| Author(s): |
Bruno de Melo Carvalho
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Ciências Médicas |
| Defense date: | 2012-03-15 |
| Examining board members: |
Mario José Abdalla Saad;
Anibal Eugenio Vercesi;
Antonio Carlos Boschero;
Rui Curi;
William Tadeu Lara Festuccia
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| Advisor: | Mario José Abdalla Saad |
| Abstract | |
A high-fat diet intake induces obesity and chronic subclinical inflammation, which play important roles in insulin resistance. Increased circulating levels of proinflammatory cytokines, free fatty acids and lipopolysaccharides activate innate immune system, which triggers inflammation and cytokine expression, leading to insulin resistance. Thus, we investigated the effect of gut microbiota modulation, on insulin resistance and evaluated the spleen as a novel source of inflammation and immune cells, responsible for the obesity-induced insulin resistance, which roles are not yet fully understood. To investigate microbiota modulation effects, we submitted Swiss mice to a high-fat diet with antibiotics or pair-feeding for eight weeks and performed metagenomic analyses from mice fecal DNA samples. In order to evaluate the spleen influence over the metabolism, we performed splenectomy in Swiss mice and induced obesity with a high-fat diet and performed proteomic approaches to determine novel molecules that could promote inflammation and immune cell migration. In both experiments, blood glucose, serum insulin and cytokines were evaluated, as well as liver, muscle and adipose tissue insulin and inflammatory signaling pathway, and liver and adipose tissue macrophage infiltration. Gut microbiota was greatly modified by the antibiotic treatment, reducing Bacteroidetes and Firmicutes prevalence, overall bacterial count and circulating LPS, as well as fasting blood glucose and serum insulin and cytokines. It also promoted TLR4 downregulation and reduction in inflammation, which promoted improvement in insulin sensitivity, besides a striking reduction in macrophage infiltration in antibiotic-treated mice. In splenectomized obese mice, a great improvement in insulin sensitivity was seen, reflected by blood glucose, serum insulin and TNF-'alpha' levels reduction. Inflammation was reduced in the liver, muscle and adipose tissue of obese splenectomized mice, in consequence, insulin signaling was improved when compared to obese mice that maintained the spleen. There was an immense reduction in liver and adipose tissue macrophage infiltration in splenectomized mice after obesity induction, which was repeated when we observed lipolysis-induced adipose tissue macrophage infiltration. Spleen proteomic studies indicated that GMF-'gamma' is overexpressed in obese mice compared to lean ones. In conclusion, gut microbiota modulation by antibiotic therapy reduced circulating LPS levels, inflammation and macrophage infiltration, improving insulin sensitivity in mice fed a high-fat diet. In addition, splenectomy also reduced inflammation and promoted insulin sensitization, as well as inhibited obesity-induced macrophage infiltration, which can be ruled by the spleen and chemokines, and possibly by GMF-'gamma', a novel protein, that could be involved in the regulation of cell migration and insulin resistance settlement (AU) | |