RESUMO
A common feature seen in acute infections is a severe atrophy of the thymus. This occurs in the murine model of acute Chagas disease. Moreover, in thymuses from Trypanosoma cruzi acutely infected mice, thymocytes exhibit an increase in the density of fibronectin and laminin integrin-type receptors, with an increase in migratory response ex vivo. Thymic epithelial cells (TEC) play a major role in the intrathymic T cell differentiation. To date, the consequences of molecular changes promoted by parasite infection upon thymus have not been elucidated. Considering the importance of microRNA for gene expression regulation, 85 microRNAs (mRNAs) were analyzed in TEC from T. cruzi acutely infected mice. The infection significantly modulated 29 miRNAs and modulation of 9 was also dependent whether TEC sorted out from the thymus exhibited cortical or medullary phenotype. In silico analysis revealed that these miRNAs may control target mRNAs known to be responsible for chemotaxis, cell adhesion, and cell death. Considering that we sorted TEC in the initial phase of thymocyte loss, it is conceivable that changes in TEC miRNA expression profile are functionally related to thymic atrophy, providing new clues to better understanding the mechanisms of the thymic involution seen in experimental Chagas disease.
RESUMO
O timo é um órgão linfoide primário no qual ocorre o desenvolvimento de células T. Distúrbios nesse processo podem levar a doenças diversas inclusive à autoimunidade. [...] Nesse sentido, essa tese aborda os aspectos moleculares envolvidos na linfopoiese T sob a perspectiva das células progenitoras e das TEC. Nosso estudod e meta-análise utilizando microarranjos de timócitos em estágios de desenvolvimento definidos pela expressão de moléculas CD4 e CD8 permitiu a identificação de 14 agrupamentos gênicos,os quais se relacionam intimamente às etapas do desenvolvimento dessas células. A modulaçãodesses genes está vinculada à sinalização via receptor de células T (TCR) e pode sercorrelacionada com a afinidade pelo complexo formado entre peptídeo e o complexo principal dehistocompatibilidade (MHC). Destacam-se ainda, vias de sinalização relacionadas a outrosreceptores de superfície, evidenciando a importância dos estímulos externos no desenvolvimentode células T. Através da integração de dados, nós identificamos as vias e moléculas com maiorimpacto para a diferenciação de timócitos, bem como complementamos a compreensão de comoos eventos envolvidos nesse processo se organizam temporalmente, apresentando umaperspectiva global das ondas de modulação gênica. Já em outra perspectiva, estudamos aregulação gênica em TEC comparando células corticais e medulares, mas também focamos nainvolução tímica, uma resposta natural a diversas fontes de estresse e ao envelhecimento.Nessa tese, esse fenômeno foi estudado em modelos experimentais de fase aguda da doençade Chagas, pois existem evidências de que as alterações no timo durante a fase aguda podemser responsáveis pelo desfecho da doença anos mais tarde...
The thymus is a primary lymphoid organ, where the T cell development takes place. Disturbanceson this process can lead to a diversity of diseases, including autoimmunity. [...] In this sense, this thesis addresses the molecular aspects involved on Tlymphopoiesis under the progenitor cells and TEC perspective. Our meta-analysis study usingmicroarrays of thymocytes sorted based on the developmental stages defined by the CD4 andCD8 expression allowed to identify 14 gene clusters, which are closely related to thedevelopmental stages of these cells. Those genes modulation is linked to the T cell receptor(TCR) signaling pathway and it can be related to the TCR affinity for the complex formed betweenthe peptide and the major histocompatibility complex (MHC). Moreover, other signaling pathwaysrelated to surface receptors stand out, highlighting the importance of external stimuli on the T celldevelopment. Through data integration, we identify pathways and molecules that have morerelevant impact on the thymocyte differentiation, as well as, we improved the comprehension onhow the events are organized temporally, providing a global perspective on the gene modulationwaves. In another perspective, we have studied the gene regulation on TEC by comparingcortical and medullary cells, but also focused on thymic involution, a natural response to varioussources of stress and aging. In this thesis, this phenomenon was studied using Chagas' diseaseacute phase experimental model because there are evidences showing that the thymic alterationsduring the acute phase can be responsible for the disease outcome years later...
