Estudio del papel de los micrornas en la diferenciación terminal de células B y el establecimiento de la tolerancia inmunológica

• Autores: Laura Belver Miguel
• Directores de la Tesis: A. Ramiro (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2011
• Idioma: español
• Tribunal Calificador de la Tesis: María Luisa Toribio García (presid.), Ignacio Moreno Alborán (secret.), Óscar Fernández Capetillo (voc.), Thomas Graf (voc.), Susana Minguet García (voc.)
• Materias:
  • Ciencias de la vida
    • Biología molecular
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • MicroRNAs (miRNAs) are small non coding RNA molecules that regulate gene expression post-transcriptionally and have been demonstrated to control several biological processes including immune regulation. The endonuclease Dicer is essential for the generation of mature miRNAs. To address the role of miRNAs in terminal B cell differentiation we generated CD19-CreKi/+ Dicerfl/fl mice where Dicer is specifically ablated in B cells.

    Early B cell differentiation was completely normal in CD19-CreKi/+ Dicerfl/fl mice but instead these animals showed a global reduction of B cell numbers in the peripheral lymphoid tissues. We found that in the absence of Dicer the transitional and marginal zone B cell compartments were overrepresented, and follicular B cell generation was impaired. By analyzing miRNA expression profile of follicular and marginal zone wild type cells we found 31 miRNAs that were differentially expressed. All of them were upregulated in the follicular compartment suggesting that miRNA expression is more critical for follicular than marginal zone differentiation. We found that one such miRNA, miR185, could target Bruton¿s tyrosine kinase (Btk), a protein involved in BCR signalling. Indeed, Btk levels were increased in CD19-CreKi/+ Dicerfl/fl cells, which resulted in an enhanced signalling response through the BCR. Finally, we analyzed the antibody repertoire in these animals and observed an increased proportion of positive charges within the CDR3, that are characteristic of autoreactivity. When testing aged mice sera for the reactivity against autoantigens, we found that CD19-CreKi/+ Dicerfl/fl females showed high titers of autoreactive antibodies. These autoantibodies accumulated in the kidney forming immunocomplexes and resulting in renal damage.

    In summary, our results show that miRNA-based regulation is essential for a correct terminal B cell differentiation and activation. These data suggest that the upregulation of Btk due to the absence of miR185 is responsible for an abnormal BCR signalling that results in a biased terminal B cell differentiation and compromises B cell tolerance in CD19-CreKi/+ Dicerfl/fl mice. These results reveal a novel function for miRNA-mediated regulation of gene expression that can be essential to the understanding of autoimmune diseases.