RESUMO

The nuclear receptor PPARγ acts as a key modulator of lipid metabolism, inflammation and pathogenesis in BCG-infected macrophages. However, the molecular mechanisms involved in PPARγ expression and functions during infection are not completely understood. Here, we investigate signaling pathways triggered by TLR2, the involvement of co-receptors and lipid rafts in the mechanism of PPARγ expression, lipid body formation and cytokine synthesis in macrophages during BCG infection. BCG induces NF-κB activation and increased PPARγ expression in a TLR2-dependent manner. Furthermore, BCG-triggered increase of lipid body biogenesis was inhibited by the PPARγ antagonist GW9662, but not by the NF-κB inhibitor JSH-23. In contrast, KC/CXCL1 production was largely dependent on NF-κB but not on PPARγ. BCG infection induced increased expression of CD36 in macrophages in vitro. Moreover, CD36 co-immunoprecipitates with TLR2 in BCG-infected macrophages, suggesting its interaction with TLR2 in BCG signaling. Pretreatment with CD36 neutralizing antibodies significantly inhibited PPARγ expression, lipid body formation and PGE2 production induced by BCG. Involvement of CD36 in lipid body formation was further confirmed by decreased BCG-induced lipid body formation in CD36 deficient macrophages. Similarly, CD14 and CD11b/CD18 blockage also inhibited BCG-induced lipid body formation, whereas TNF-α synthesis was not affected. Disruption of rafts recapitulates the latter result, inhibiting lipid body formation, but not TNF-α synthesis in BCG-infected macrophages. In conclusion, our results suggest that CD36-TLR2 cooperation and signaling compartmentalization within rafts, divert host response signaling through PPARγ-dependent and NF-κB-independent pathways, leading to increased macrophage lipid accumulation and down-modulation of macrophage response.

Assuntos

Quimiocina CXCL1/biossíntese , Metabolismo dos Lipídeos , Mycobacterium bovis , Transdução de Sinais , Receptor 2 Toll-Like/metabolismo , Tuberculose , Fator de Necrose Tumoral alfa/biossíntese , Anilidas/farmacologia , Animais , Antígeno CD11b/biossíntese , Antígeno CD11b/genética , Antígenos CD18/biossíntese , Antígenos CD18/genética , Antígenos CD36/biossíntese , Antígenos CD36/genética , Quimiocina CXCL1/genética , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/genética , Receptores de Lipopolissacarídeos/biossíntese , Receptores de Lipopolissacarídeos/genética , Macrófagos/metabolismo , Macrófagos/microbiologia , Macrófagos/patologia , Microdomínios da Membrana/genética , Microdomínios da Membrana/metabolismo , Microdomínios da Membrana/patologia , Camundongos , Camundongos Knockout , NF-kappa B/antagonistas & inibidores , NF-kappa B/genética , NF-kappa B/metabolismo , PPAR gama/antagonistas & inibidores , PPAR gama/biossíntese , PPAR gama/genética , Fenilenodiaminas/farmacologia , Receptor 2 Toll-Like/genética , Tuberculose/metabolismo , Tuberculose/patologia , Tuberculose/veterinária , Fator de Necrose Tumoral alfa/genética