Study of the mechanisms and effectors triggering the fragmentation of mitochondrion in eukaryotic cells infected by Brucella spp

Brucella are gram-negative facultative intracellular bacteria responsible for the zoonotic disease known as brucellosis. Many researches have been devoted to study the interactions between Brucella and intracellular organelles in order to identify the molecular mechanisms by which Brucella infection and trafficking leads to perversion of the intracellular traffic and the escape from lysosomal degradation allowing Brucella survival and replication in the ER. However, the relationship between Brucella and mitochondria is still poorly understood while we know that, other facultative intracellular bacteria such as L. monocytogenes transiently modify mitochondrial dynamics and activity during infection. In addition, it is now well established that mitochondrial activity and metabolism in general are linked to innate immunity. Preliminary data clearly demonstrate that B. abortus leads to the fragmentation of mitochondria in myeloid (RAW264.7) and non-myeloid (HeLa) infected cells but the mechanisms are totally unknown. The major goal of this proposal is to investigate, both in vitro and in vivo, the mechanisms by which Brucella induces mitochondrial fragmentation in eukaryotic host cells. The main specific objectives of this research are to study the putative role of endoplasmic reticulum stress and/or changes in the cytoskeleton (actin filament and microtubule remodeling known to control the morphology of mitochondria) triggered during infection on the modifications of the mitochondrial morphology observed during infection. In addition, the active contribution of the bacteria will be tested by the hypothesis-driven work using a mutant Brucella for the Bsp-L, a Brucella effector. A collaborator has recently shown that the over- expression of the gene encoding this protein is able to trigger the fragmentation of mitochondria in HeLa cells. Finally, we will determine whether a physical interaction between Brucella Containing Vacuole (BCV) and mitochondria does exist or not.