Periodic Reporting for period 3 - MAIT (Tissue repair functions of MAIT cells: integrating thymic pre-commitment and peripheral signals)
Período documentado: 2023-10-01 hasta 2025-03-31
In this project, we study the development and the functions of an innate like T cell subset called Mucosal Associated Invariant T (MAIT) cells which recognize an ubiquitous bacterial compounds derived from the vitamin B2 biosynthetic pathway. Both the TCR and the restricting molecule presenting the bacterial compound are conserved in mammalian species, indicating important functions. MAIT cells display immediate effector activities.
Contrary to mainstream (i.e."conventional") T cells that are selected on epithelial cells, MAIT cells are selected on CD4+CD8+ thymocytes leading to the acquisition of a particular differentiation program linked to the expression of the PLZF transcription factor. In the murine thymus, two subsets of MAIT cells are generated: Tbet+ MAIT1 cells and RORgt+ MAIT17 cells. Both subsets are readily able to produce effector cytokines (IFN and IL-17, respectively) in the thymus. Both subsets then populate different tissues: liver and spleen for MAIT1; lung, skin and gut mucosae for MAIT17.
The molecular mechanisms leading to these two outcomes have not been fully deciphered and are studied in this project.
Once in the periphery, MAIT cells are involved in antibacterial defense and in tissue homeostasis by sensing bacterial invasion or even just the metabolic status of the gut microbiota. The interplay between gut microbiota and MAIT cells is another topic studied in this project. Notably, the frequency of MAIT cells in the blood is modified in many diseases in which the microbiota is disturbed such as obesity, diabetes and inflammatory bowel diseases suggesting that MAIT cell may play a direct or indirect role in these diseases. The study of MAIT cells may allow a better understanding and treatment of the diseases seen above as MAIT triggering or inhibition may be beneficial.
MAIT cells seems also to be involved in tissue repair in the skin after wound while MAIT cells are protective during flu infection. The study of MAIT cells in experimental models will enable to decipher the involved mechanisms.
Contrary to mainstream (i.e."conventional") T cells that are selected on epithelial cells, MAIT cells are selected on CD4+CD8+ thymocytes leading to the acquisition of a particular differentiation program linked to the expression of the PLZF transcription factor. In the murine thymus, two subsets of MAIT cells are generated: Tbet+ MAIT1 cells and RORgt+ MAIT17 cells. Both subsets are readily able to produce effector cytokines (IFN and IL-17, respectively) in the thymus. Both subsets then populate different tissues: liver and spleen for MAIT1; lung, skin and gut mucosae for MAIT17.
The molecular mechanisms leading to these two outcomes have not been fully deciphered and are studied in this project.
Once in the periphery, MAIT cells are involved in antibacterial defense and in tissue homeostasis by sensing bacterial invasion or even just the metabolic status of the gut microbiota. The interplay between gut microbiota and MAIT cells is another topic studied in this project. Notably, the frequency of MAIT cells in the blood is modified in many diseases in which the microbiota is disturbed such as obesity, diabetes and inflammatory bowel diseases suggesting that MAIT cell may play a direct or indirect role in these diseases. The study of MAIT cells may allow a better understanding and treatment of the diseases seen above as MAIT triggering or inhibition may be beneficial.
MAIT cells seems also to be involved in tissue repair in the skin after wound while MAIT cells are protective during flu infection. The study of MAIT cells in experimental models will enable to decipher the involved mechanisms.
To analyze the mechanisms of MAIT1 versus MAIT17 commitment during development, we analyzed the TCR repertoire of developing MAIT cells. The results dismissed the hypothesis that TCR avidity for the selecting ligand would be responsible for MAIT1/17 commitment as the same TCRs were found in both MAIT1 and MAIT17 subsets. The CDR3 beta sequences were similar in MAIT1 and MAIT17 subsets. In several instances, the same clonal expanded TCRs were found in both MAIT1 and MAIT17 subsets. Quantitative simulation indicated that the number of such cases is best explained by a MAIT-1 vs -17 subset choice independently of TCR characteristics. Further simulations demonstrated that MAIT lineage commitment cannot occur exclusively before or after proliferation. Altogether, our results support a two-stage model of MAIT development: non-committed intermediate-stage MAIT cells undergo a first round of proliferation associated with differentiation into either MAIT1 or MAIT17 in a TCR-feature independent manner, followed by an additional round of proliferation.
Analysis of MAIT cell relationship with the microbial environment has been completed. At steady-state, MAIT antigens were synthesized by aerotolerant bacteria residing in the colon mucosa. Experimental colitis triggered a luminal expansion of riboflavin-producing bacteria, leading to increased production of MAIT ligands. Modulation of intestinal oxygen levels suggested a role for oxygen in inducing MAIT ligand production. MAIT antigens produced in the colon rapidly crossed the intestinal barrier and activated MAIT cells, which expressed a tissue-repair genes and produced barrier-promoting mediators during colitis. Consequently, mice lacking MAIT cells were more susceptible to colitis and colitis-driven colorectal cancer. Thus, MAIT cells monitor a bacterial metabolic pathway indicative of intestinal inflammation, providing host protection in return.
We have analyzed the mechanisms underlying the tissue repair-capacity of MAIT cells to show that: 1) MAIT cell repair function does not rely on cognate interaction with MR1 in the skin; 2) MAIT cells are not long-term resident in the skin; 3) the repair functions are expressed at steady state; 4) MAIT cells rely on CXCR6 and CCL16 to populate the skin; 5) MAIT cells promote epithelial proliferation and angiogenesis during wound healing; 6) amphiregulin secreted by MAIT cells is necessary to accelerate skin wound healing; 7) MR1 expression on non-hematopoietic cells is not necessary for the repaire functon of MAIT cells.
In parallel, we have completed a study of MAIT cell development in various mammalian species. Cross-species comparative analyses revealed a conserved sequence of transcriptional events underlying the maturation of 5-OP-RU-specific thymocytes, marked by the early expression of ZBTB16 in all species. MAIT cells also co-expressed the transcription factors TBX21 (Tbet) and RORC (RORt) in human, sheep, cattle and opossum. By contrast, Tbet and RORt were expressed by distinct subsets of MAIT cells in the thymus of rodents, including pet mice and >30 genetically diverse mouse strains, dismissing a laboratory mouse artifact. In mice, RORt+ MAIT cells further matured in the mesenteric lymph nodes and intestines to acquire a transcriptional program remarkably conserved in MAIT cells from non-rodent species and characterized by co-expression of type 1 and type 17 effector genes, but also genes associated with cytotoxicity and tissue repair. Thus, we define a deeply conserved transcriptional program for 5-OP-RU-specific T cells, which may help understand their functions.
Our results suggest that MAIT cells promotes survival of influenza-infected animals but are not involved in direct anti-viral immunity. The analysis is still ongoing.
Analysis of MAIT cell relationship with the microbial environment has been completed. At steady-state, MAIT antigens were synthesized by aerotolerant bacteria residing in the colon mucosa. Experimental colitis triggered a luminal expansion of riboflavin-producing bacteria, leading to increased production of MAIT ligands. Modulation of intestinal oxygen levels suggested a role for oxygen in inducing MAIT ligand production. MAIT antigens produced in the colon rapidly crossed the intestinal barrier and activated MAIT cells, which expressed a tissue-repair genes and produced barrier-promoting mediators during colitis. Consequently, mice lacking MAIT cells were more susceptible to colitis and colitis-driven colorectal cancer. Thus, MAIT cells monitor a bacterial metabolic pathway indicative of intestinal inflammation, providing host protection in return.
We have analyzed the mechanisms underlying the tissue repair-capacity of MAIT cells to show that: 1) MAIT cell repair function does not rely on cognate interaction with MR1 in the skin; 2) MAIT cells are not long-term resident in the skin; 3) the repair functions are expressed at steady state; 4) MAIT cells rely on CXCR6 and CCL16 to populate the skin; 5) MAIT cells promote epithelial proliferation and angiogenesis during wound healing; 6) amphiregulin secreted by MAIT cells is necessary to accelerate skin wound healing; 7) MR1 expression on non-hematopoietic cells is not necessary for the repaire functon of MAIT cells.
In parallel, we have completed a study of MAIT cell development in various mammalian species. Cross-species comparative analyses revealed a conserved sequence of transcriptional events underlying the maturation of 5-OP-RU-specific thymocytes, marked by the early expression of ZBTB16 in all species. MAIT cells also co-expressed the transcription factors TBX21 (Tbet) and RORC (RORt) in human, sheep, cattle and opossum. By contrast, Tbet and RORt were expressed by distinct subsets of MAIT cells in the thymus of rodents, including pet mice and >30 genetically diverse mouse strains, dismissing a laboratory mouse artifact. In mice, RORt+ MAIT cells further matured in the mesenteric lymph nodes and intestines to acquire a transcriptional program remarkably conserved in MAIT cells from non-rodent species and characterized by co-expression of type 1 and type 17 effector genes, but also genes associated with cytotoxicity and tissue repair. Thus, we define a deeply conserved transcriptional program for 5-OP-RU-specific T cells, which may help understand their functions.
Our results suggest that MAIT cells promotes survival of influenza-infected animals but are not involved in direct anti-viral immunity. The analysis is still ongoing.
1. We showed that MAIT cells are rapidly recruited into the skin inflamed site and that they promote wound healing repair
2. We evidenced a two-stage model of MAIT development: non-committed intermediate-stage MAIT cells undergo a first round of proliferation associated with differentiation into either MAIT1 or MAIT17 in a TCR-feature independent manner, followed by an additional round of proliferation.
3. We evidenced that intestinal oxygen levels modulate MAIT ligand production in the intestine. MAIT antigens produced in the colon rapidly crossed the intestinal barrier and activated MAIT cells, which expressed a tissue-repair genes and produced barrier-promoting mediators during colitis. Consequently, mice lacking MAIT cells were more susceptible to colitis and colitis-driven colorectal cancer. Thus, MAIT cells monitor a bacterial metabolic pathway indicative of intestinal inflammation, providing host protection in return.
4. Using scRNAseq of MAIT cells from mice, rats, cattle, sheep, humans and opossum. Integration of the different datasets allowed us to define a common core gene signature characterizing MAIT cell development.
Before the end of the project, we will further decipher the molecular mechanisms leading to either MAIT1 and MAIT17 subsets.
We will also define the way particular MAIT cell subsetss seed particular tissues and lymph nodes.
We also study the mechanisms involved in the protection imparted by MAIT cells during flu infection in mice.
2. We evidenced a two-stage model of MAIT development: non-committed intermediate-stage MAIT cells undergo a first round of proliferation associated with differentiation into either MAIT1 or MAIT17 in a TCR-feature independent manner, followed by an additional round of proliferation.
3. We evidenced that intestinal oxygen levels modulate MAIT ligand production in the intestine. MAIT antigens produced in the colon rapidly crossed the intestinal barrier and activated MAIT cells, which expressed a tissue-repair genes and produced barrier-promoting mediators during colitis. Consequently, mice lacking MAIT cells were more susceptible to colitis and colitis-driven colorectal cancer. Thus, MAIT cells monitor a bacterial metabolic pathway indicative of intestinal inflammation, providing host protection in return.
4. Using scRNAseq of MAIT cells from mice, rats, cattle, sheep, humans and opossum. Integration of the different datasets allowed us to define a common core gene signature characterizing MAIT cell development.
Before the end of the project, we will further decipher the molecular mechanisms leading to either MAIT1 and MAIT17 subsets.
We will also define the way particular MAIT cell subsetss seed particular tissues and lymph nodes.
We also study the mechanisms involved in the protection imparted by MAIT cells during flu infection in mice.