Our understanding of the chronic stages of tuberculosis on a molecular level is incomplete and definitely needs improvement. Comparative analysis of gene expression profiled during early vs. late stages of tuberculosis will enrich our understanding of various stages of tuberculosis. The main objective of this project is to identify gene regulatory networks responsible for establishing chronic tuberculosis in mice. Based on a strong set of preliminary results, we hypothesize that the tuberculous bacilli are actively transcribing specific sets of genes to regulate their metabolic activity inside the host despite remaining at a constant level during the chronic stase of the disease. To identify key components of the mycobacterial gene regulatory network during chronic infection, we will employ the in vivo microarray analysis to: ? 1. Identify M.tb. genes responsible for entering into the chronic stage of tuberculosis. We will employ the mouse model of chronic tuberculosis combined with microarray analysis to identify differentially expressed genes in mice during the first 220 days of infection as well as during in vitro cultures. A reactivation model of mouse tuberculosis also will be assessed to mimic human tuberculosis during immune suppression. ? 2. Characterize the role of putative persistence genes in establishing chronic tuberculosis. We will follow organ colonization of M.tb. strains with defective persistence genes (generated by allelic exchange) after aerosol infection of BALB/c mice in comparison to the wild type strain of M.tb. H37Rv. Also, the transcriptional profile of mutants growing under defined in vitro stress conditions will be assessed using DNA microarrays. ? We believe that the approaches exploited in this proposal will generate a wealth of information related to the metabolic states of M.tb. during chronic stages of infection. The proposed studies will further improve our understanding of the nature of the host-pathogen interactions that can provide potential targets for drug development. Outcomes from this project will provide the necessary foundation for more detailed and focused studies on specific sets of genes utilizing human tissues. Transcriptional regulators that could contribute to both chronic and reactivation stages of tuberculosis will be the target for future analysis. ? ? ? ?
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