Crohn's disease (CD) is a chronic and debilitating inflammatory bowel disease with unknown etiology;however, it is clear that there are both genetic components as well as environmental factors that are required for its development. Tremendous advances have been made recently in understanding the genetics of CD. Although several chromosomal loci have been associated with IBD susceptibility, until last year, only one gene had been conclusively identified as a CD susceptibility gene. This gene is NOD2 (nucleotide-binding, oligomerization domain 2), which encodes an intracellular sensor of bacteria in the innate immune system. Recent genome-wide association scans have identified multiple, novel CD susceptibility genes. Many of these new CD susceptibility genes also modulate immune responses, suggesting that dysregulation of an immune pathway rather than a single gene may be important in CD pathogenesis. One of these processes is autophagy. Autophagy (literally """"""""self-eating"""""""") is best known as a cell survival mechanism in response to starvation, where organelles are broken down and recycled to provide nutrients. This mechanism also plays a crucial role in the clearance of intracellular bacteria by the innate immune system. Bacteria and bacterial components induce autophagy, linking innate immune microbial sensors to autophagy. One of these microbial sensors is Nod2, which detects a specific component of the bacterial cell wall called muramyl dipeptide (MDP). Our preliminary data demonstrates that stimulation of cells with MDP not only activates autophagy, but suggests autophagy may also be involved in activation of Nod2 by MDP. These results provide a link between two separate classes of molecules mutated in CD and lead us to propose the following central hypothesis: CD- associated mutations in the autophagy genes, ATG16L1 (autophagy related 16-like protein 1) and IRGM (immunity-related GTPase family, M), and NOD2 impair the same critical innate immune pathway and impairment of this pathway contributes to CD pathogenesis. We hypothesize autophagy and Nod2 function together in two non-exclusive ways: (1) MDP stimulation of Nod2 activates autophagy as an essential anti-microbial response, and (2) autophagy is involved in MDP internalization and Nod2 activation. This hypothesis will be tested by the following three specific aims using both primary cells and cell lines: 1) Determine the role of Nod2 in activation of autophagy - is autophagy a component of Nod2 stimulated anti- microbial responses?, 2) Characterize the mechanism of MDP internalization - is it autophagy?, 3) Analyze alterations in autophagy in phagocytic cells of CD patients. The results of our proposed studies may benefit individuals with CD by identifying a crucial processes altered in CD, leading to the design and use of more specific CD therapies targeting this pathway.
Recent advances in the genetics of Crohn's disease (CD) indicate that alterations in an immune pathway rather than a single gene may be important in CD pathogenesis. We propose to study the interactions of three genes associated with CD susceptibility and define if they are a part of the same innate immune system pathway. The results of our proposed studies may benefit individuals with CD by identifying a crucial process altered in the disease, leading to the design and use of more specific therapies targeting this pathway.
|Schuster, Andrew T; Homer, Craig R; Kemp, Jacqueline R et al. (2015) Chromosome-associated protein D3 promotes bacterial clearance in human intestinal epithelial cells by repressing expression of amino acid transporters. Gastroenterology 148:1405-16.e3|
|Dixon, Laura J; Kabi, Amrita; Nickerson, Kourtney P et al. (2015) Combinatorial effects of diet and genetics on inflammatory bowel disease pathogenesis. Inflamm Bowel Dis 21:912-22|
|Scarpa, Melania; Kessler, Sean; Sadler, Tammy et al. (2015) The epithelial danger signal IL-1Î± is a potent activator of fibroblasts and reactivator of intestinal inflammation. Am J Pathol 185:1624-37|
|Nickerson, Kourtney P; Chanin, Rachael; McDonald, Christine (2015) Deregulation of intestinal anti-microbial defense by the dietary additive, maltodextrin. Gut Microbes 6:78-83|
|Thapaliya, Samjhana; Runkana, Ashok; McMullen, Megan R et al. (2014) Alcohol-induced autophagy contributes to loss in skeletal muscle mass. Autophagy 10:677-90|
|Warner, Neil; Burberry, Aaron; Pliakas, Maria et al. (2014) A genome-wide small interfering RNA (siRNA) screen reveals nuclear factor-ÎºB (NF-ÎºB)-independent regulators of NOD2-induced interleukin-8 (IL-8) secretion. J Biol Chem 289:28213-24|
|Nickerson, Kourtney P; Homer, Craig R; Kessler, Sean P et al. (2014) The dietary polysaccharide maltodextrin promotes Salmonella survival and mucosal colonization in mice. PLoS One 9:e101789|
|Schirbel, Anja; Kessler, Sean; Rieder, Florian et al. (2013) Pro-angiogenic activity of TLRs and NLRs: a novel link between gut microbiota and intestinal angiogenesis. Gastroenterology 144:613-623.e9|
|Warner, Neil; Burberry, Aaron; Franchi, Luigi et al. (2013) A genome-wide siRNA screen reveals positive and negative regulators of the NOD2 and NF-ÎºB signaling pathways. Sci Signal 6:rs3|
|Qiu, Jia; Thapaliya, Samjhana; Runkana, Ashok et al. (2013) Hyperammonemia in cirrhosis induces transcriptional regulation of myostatin by an NF-ÎºB-mediated mechanism. Proc Natl Acad Sci U S A 110:18162-7|
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