Current TH17 projects in the lab are focused on characterizing the role of local tissue factors in the differentiation and tuning of TH17 responses and on understanding the signaling pathways and effector functions of homeostatic and pathogenic Th17 cells. We previously discovered that epithelium-derived serum amyloid A (SAA) proteins enhance the effector functions of TH17 cells induced in the small intestine upon colonization with segmented filamentous bacteria (SFB). This niche-specific anti-commensal TH17 response protects the intestinal barrier, and is not inflammatory even in the absence of induced Treg cells or upon blockade of IL-10 function. We have further investigated the functions of the SAAs in conditions under which TH17 cells exert pathological functions. We found that SAA1,2, and 3 synergize with IL-6 to induce both RORγt and a pro-inflammatory transcriptional program in mouse and human T cells. Using a variety of engineered mouse strains, we showed that SAAs that are liver-derived and secreted into serum or produced locally in inflamed tissues contribute to the pathogenic functions of TH17 in models for inflammatory bowel disease and multiple sclerosis. A key goal is to identify the receptor molecule(s) for the SAAs and characterize its downstream signaling pathway. We are performing CRISPR/Cas9 genome-wide screens in both mouse and human cells to identify novel receptors and pathways critical for distinct modes of TH17 programming.
To gain a better understanding of RORγt mechanisms of action in different cell types, we have engineered mice with tagged versions of the transcription factor, allowing for both proteomics and chromatin occupancy studies. We have similarly targeted the gene encoding RORa, allowing us to examine shared versus distinct functions of the closely related nuclear receptors. We have studied the transcriptional regulatory networks of in vitro-generated TH17 cells and of intestinal innate lymphoid cells, and are using new genomics tools to investigated RORγt-dependent networks in ex vivo cells with homeostatic versus inflammatory properties. In bulk and single cell transcriptomics analyses of ex vivo TH17 cells, we have found that glycolysis pathway enzymes are much more highly expressed in pathogenic cells than in SFB-specific TH17 cells. We are studying the metabolic requirements for the programming of these functionally distinct but related cells. Recent results suggest that the glycolytic pathway blockade that preserves the pentose phosphate pathway is tolerated in homeostatic TH17 cell differentiation, but not the differentiation of colitogenic or encephalitogenic TH17 cells. This is because homeostatic commenal bacteria-specific TH17 cells are localized in normoxic microenvironments, where the mitochondrial oxidative phosphorylation pathway becomes essential when glycolysis is not fully enabled. The relatively hypoxic microenvironments in inflamed tissue appear to result in greater demand for glycolytic flux, which suggests that it may be possible to target this pathway in proinflammatory cells without blocking homeostatic functions.
Related Publications:
Lee, J-Y., Hall, J.AA., Kroehling, L., Wu, L., Najar, T., Nguyen, H.H., Lin, W-Y., Yeung, S.T., Moura Silva, H., Li, D., Hine, A., Loke, P., Hudesman, D., Martin, J.C., Kenigsberg, E., Merad, M., Khanna, K.M., & Littman, D.R. (2019) Serum Amyloid A Proteins Induce Pathogenic TH17 Cells and Promote Inflammatory Disease. Cell in press 2019. bioRxiv 681346
Miraldi, E.R., Pokrovskii, M., Watters, A., Castro, D.M., DeVeaux, N., Hall, J., Lee, J-Y., Ciofani, M., Madar, A., Carrierro, N., Littman, D.R., & Bonneau, R. (2018) Leveraging chromatin accessibility for transcriptional regulatory network inference in T helper 17 cells. bioRxiv 292987 Genome Research, 29, 449-463s.
Sano, T., Huang, W., Hall, J.A., Yang, Y., Chen, A., Gavzy, S.J., Lee, J.Y., Ziel, J., Miraldi, E., Bonneau, R. & Littman, D.R. (2015) An IL-23R/IL-22 circuit regulates epithelial serum amyloid A to promote local effector Th17 responses. Cell, 163, 381-93. PMID: 26411290
Longman, R.S., Diehl, G.E., Victorio, D., Huh, J.R., Galan, C., Miraldi, E., Swaminath, A., Bonneau, R., Scherl, E.J. & Littman, D.R. (2014) CX3CR1+ mononuclear phagocytes support colitis-associated innate lymphoid cell production of IL-22. J. Exp. Med. 211, 1571-83. PMC4113938
Ciofani, M., Madar, A., Galan, C., Sellars, M., Mace, K., Pauli, F., Agarwal, A., Huang, W., Parkurst, C.N., Muratet, M., Newberry, K.M., Meadows, S., Greenfield, A., Yang, Y., Jain, P., Kirigin, F.F., Birchmeier, C., Wagner, E.F., Murphy, K.M., Myers, R.M., Bonneau, R. & Littman, D.R. (2012) A validated regulatory network for Th17 cell specification. Cell, 151:289-303. PMID: 23021777
Huh, J.R., Leung, M.W.L., Huang, P., Ryan, D.A., Krout, M.R., Malapaka, R.R., Chow, J., Manel, N., Ciofani, M., Kim, S.V., Cuesta, A., Santori, F.R., Lafaille, J.J., Gin, D.Y., Rastinejad, F., & Littman, D.R. (2011) Digoxin and its derivatives suppress Th17 cell differentiation by antagonizing RORgt activity. Nature 472(7344), 486-90. PMID: 21441909
Zhou, L., Lopes, J., Chong, M.M.W., Ivanov, I.I., Min, R., Victora, G.D., Shen, Y., Du, J., Rubtsov, Y.P., Rudensky, A.Y., Ziegler, S.F. & Littman, D.R. (2008) TGF-b-induced Foxp3 inhibits Th17 cell differentiation by antagonizing RORgt function. Nature 453(7192), 236-40. Epub 2008 Mar26. PMC2597437
Zhou, L., Ivanov, I.I., Spolski, R., Min, R., Shenderov, K., Egawa, T., Levy, D.E., Leonard, W.J. & Littman, D.R. (2007) IL-6 programs Th17 cell differentiation by promoting the sequential engagement of the IL-21 and IL-23 pathways. Nat. Immunol. 8(9), 967-74.
Manel, N., Unutmaz, D., & Littman, D.R. (2008) The differentiation of human Th17 cells requires transforming growth factor-b and induction of the nuclear receptor RORT. Nat. Immunol. 9(6), 641-9. Epub 2008 May 4. PMC2597394.
Ivanov, I.I., McKenzie, B.S., Zhou, L., Tadokoro, C.E., Lepelley, A., Lafaille, J.J., Cua, D.J. & Littman, D.R. (2006) The orphan nuclear receptor RORgt directs the differentiation program of pro-inflammatory IL-17+ T helper cells. Cell 126, 1121-33.