Mycobacterium tuberculosis (Mtb) is the leading infectious cause of death worldwide. Our inability to control the spread of this disease and the absence of new effective chemotherapeutic agents are due in part to the limited knowledge about host genes that control granuloma formation and other aspects of the host's response to this pathogen in lung. One host response considered important in tuberculosis is that of tissue remodeling which is characterized by alterations in extracellular matrix expression and degradation. Tissue remodeling is responsible for the development of Mtb- mediated fibrosis, bronchiectasis, and cavitation. Although these processes are often considered late manifestations of pulmonary tuberculosis, mounting evidence suggests that the genes involved in the control of tissue remodeling (TR genes) are expressed very early in lung after Mtb infection, and are involved in other key processes including leukocyte recruitment and granuloma formation. Consistent with this, we have demonstrated that: 1) Mtb Erdman bacilli and isolated cell wall components of Mtb induce the expression of TR genes encoding for extracellular matrices, matrix-degrading proteases, and pro-fibrotic growth factors in vitro (i.e., human monocyte/macrophages) and in vivo (C57BL/6 mice). In mice, the induction of TR genes correlated both spatially and temporally with the inflammatory response. 2) The induction of TR genes in monocyte/macrophages by Mtb occurs via receptor-mediated protein kinase pathways and requires the induction of specific transcription factors (e.g., AP-1). 3) The injection of trehalose-6,6'-dimycolate (previously called mycobacterial cord factor) or live Mtb Erdman strain into mice with knockout mutations in a TR gene (Matrix Metalloproteinase-9) resulted in increased inflammation and granuloma formation. Together, this information suggests that the interaction between Mtb and host cells triggers TR gene expression; in turn, the products of TR genes play important roles in the host response to Mtb. The overall goal of this application is to identify the TR genes that are differentially expressed in pulmonary tuberculosis and study their function. This will be accomplished in 3 specific aims designed to: 1) Identify host TR genes differentially expressed in vitro in human monocyte/macrophages after infection with Mtb using High Density Oligonucleotide Array or HDOA. 2) Identify the TR genes differentially expressed in the lungs of infected mice and in the lungs of humans with pulmonary tuberculosis using HDOA. 3) Determine the function of specific TR genes identified in Specific Aims I and II by infection of mice with gene knockout mutations. We propose to study the function of 3 (at the most 4) TR genes. We will begin exploring the function of 2 TR genes encoding for matrix metalloproteinases which we have demonstrated to be differentially expressed in Mtb-infected lungs and for which knockout animals are already available in our laboratory.
|Garg, Pallavi; Ravi, Anupama; Patel, Neal R et al. (2007) Matrix metalloproteinase-9 regulates MUC-2 expression through its effect on goblet cell differentiation. Gastroenterology 132:1877-89|
|Castaneda, Florencia E; Walia, Baljit; Vijay-Kumar, Matam et al. (2005) Targeted deletion of metalloproteinase 9 attenuates experimental colitis in mice: central role of epithelial-derived MMP. Gastroenterology 129:1991-2008|