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International audience; ContextGut inflammation constitutes a growing health concern in developed countries. It may consist in spontaneous ailments of the gut, involving both the host immune system and microbiota, such as IBD, including ulcerative colitis and Crohn’s disease. It may be caused by a medical treatment, such as mucositis induced by cancer chemotherapy and/or radiotherapy. It coincides with a dysbiosis including a lack of anti-inflammatory bacteria. As an example, propionibacteria are lacking in the microbiota of newborns that develop necrotizing enterocolitis.Methods and resultsWe thus focused on the immunomodulatory properties of GRAS propionibacteria. Selected strains of Propionibacterium freudenreichii induced the regulatory IL-10 cytokine in human immune cells (Foligné et al., 2010, 2013), depending on surface proteins (Le Marechal et al., 2015). Mutation of the slpB gene suppressed this immunomodulatory effect and the resulting slpB mutant induced a rather proinflammatory response (Deutsch et al., 2017). Consumption of wild-type P. freudenreichii protected from colitis induced by both TNBS and by DSS. It alleviated severity of symptoms, modulated local and systemic inflammation, as well as colonic oxidative stress and epithelial cell damages (Plé et al., 2015, 2016; Rabah et al., 2020). Accordingly, consumption of Lactococcus lactis NCDO 2118 harboring pXIES-SEC:slpB and expressing the propionibacterial SlpB reduced severity of colitis, lowered weight loss, disease activity index, shortening of the colon length, and histopathological score, compared with mice treated with L. lactis NCDO 2118 wild-type strain.In the context of mucositis induced by the chemotherapy 5-FU, P. freudenreichii prevented weight loss, reduced inflammation and consequently intestinal damages. It regulated key markers, including Claudin-1 and IL-17a genes, as well as IL-12 and IL-1β cytokines levels (Cordeiro et al., 2018). Mutant strain slpB displayed opposite regulatory effect on cld1 expression and on IL-12 levels, and failed to afford protection towards 5-FU-mucositis (do Carmo et al., 2019).ConclusionThis work emphasizes the importance of SlpB in P. freudenreichii ability to reduce both mucositis and colitis inflammation. It opens perspectives for the development of probiotic products aimed at decreasing side effects of chemotherapy and at helping treatment of colitis, thanks to GRAS bacteria.ReferencesCordeiro, B. F., Oliveira, E. R., Silva, D., H, S., Savassi, B. M., Acurcio, L. B., et al. (2018). Whey Protein Isolate-Supplemented Beverage, Fermented by Lactobacillus casei BL23 and Propionibacterium freudenreichii 138, in the Prevention of Mucositis in Mice. Front. Microbiol. 9. doi:10.3389/fmicb.2018.02035.Deutsch, S.-M., Mariadassou, M., Nicolas, P., Parayre, S., Le Guellec, R., Chuat, V., et al. (2017). Identification of proteins involved in the anti-inflammatory properties of Propionibacterium freudenreichii by means of a multi-strain study. Sci Rep 7, 46409. doi:10.1038/srep46409.do Carmo, F. L. R., Rabah, H., Cordeiro, B. F., da Silva, S. H., Pessoa, R. M., Fernandes, S. O. A., et al. (2019). Probiotic Propionibacterium freudenreichii requires SlpB protein to mitigate mucositis induced by chemotherapy. Oncotarget 10, 7198–7219. doi:10.18632/oncotarget.27319.Foligné, B., Breton, J., Mater, D., and Jan, G. (2013). Tracking the microbiome functionality: focus on Propionibacterium species. Gut 62, 1227–1228.Foligné, B., Deutsch, S. M., Breton, J., Cousin, F. J., Dewulf, J., Samson, M., et al. (2010). Promising immunomodulatory effects of selected strains of dairy propionibacteria as evidenced in vitro and in vivo. Appl.Environ.Microbiol. 76, 8259–8264.Le Marechal, C., Peton, V., Ple, C., Vroland, C., Jardin, J., Briard-Bion, V., et al. (2015). Surface proteins of Propionibacterium freudenreichii are involved in its anti-inflammatory properties. J.Proteomics. 113C, 447–461.Plé, C., Breton, J., Richoux, R., Nurdin, M., Deutsch, S.-M., Falentin, H., et al. (2016). Combining selected immunomodulatory Propionibacterium freudenreichii and Lactobacillus delbrueckii strains: Reverse engineering development of an anti-inflammatory cheese. Mol Nutr Food Res 60, 935–948. doi:10.1002/mnfr.201500580.Plé, C., Richoux, R., Jardin, J., Nurdin, M., Briard-Bion, V., Parayre, S., et al. (2015). Single-strain starter experimental cheese reveals anti-inflammatory effect of Propionibacterium freudenreichii CIRM BIA 129 in TNBS-colitis model. Journal of Functional Foods 18, 575–585. doi:10.1016/j.jff.2015.08.015.Rabah, H., do Carmo, F. L. R., Carvalho, R. D. de O., Cordeiro, B. F., da Silva, S. H., Oliveira, E. R., et al. (2020). Beneficial Propionibacteria within a Probiotic Emmental Cheese: Impact on Dextran Sodium Sulphate-Induced Colitis in Mice. Microorganisms 8, 380. doi:10.3390/microorganisms8030380.- PF induces IL-10 in human PBMCs- Surface layer extraction reduces IL-10 induction- Extracted surface layer induces IL-10- Mutation of the SlpB gene reduces IL-10 induction- PF prevents colitis- PF prevents mucositis- PF slpB mutant does not prevent mucositis- Lactococcus lactis expressing SlpB prevents colitis

International audience; IntroductionGut inflammation constitutes a growing health concern in developed countries. It may consist in spontaneous ailments of the gut, involving both the host immune system and microbiota, such as IBD, including ulcerative colitis and Crohn’s disease. It may be caused by a medical treatment, such as mucositis induced by cancer chemotherapy and/or radiotherapy. It coincides with a dysbiosis including a lack of anti-inflammatory bacteria. As an example, propionibacteria are lacking in the microbiota of newborns that develop necrotizing enterocolitis.Methods Dairy propionibacteria strains were tested in vitro on human PBMCs with respect to their ability to induce immunomodulatory cytokines. Selected strains were then tested in vitro with respect to their ability to protect mice from TNBS-induced colitis, from DSS-induced colitis, and from 5FU-induced mucositis.ResultsWe thus focused on the immunomodulatory properties of GRAS propionibacteria. Selected strains of Propionibacterium freudenreichii induced the regulatory IL-10 cytokine in human immune cells (Foligné et al., 2010, 2013), depending on surface proteins (Le Marechal et al., 2015). Mutation of the slpB gene suppressed this immunomodulatory effect and the resulting slpB mutant induced a rather proinflammatory response (Deutsch et al., 2017). Consumption of wild-type P. freudenreichii protected from colitis induced by both TNBS and by DSS. It alleviated severity of symptoms, modulated local and systemic inflammation, as well as colonic oxidative stress and epithelial cell damages (Plé et al., 2015, 2016; Rabah et al., 2020). Accordingly, consumption of Lactococcus lactis NCDO 2118 harboring pXIES-SEC:slpB and expressing the propionibacterial SlpB reduced severity of colitis, lowered weight loss, disease activity index, shortening of the colon length, and histopathological score, compared with mice treated with L. lactis NCDO 2118 wild-type strain (Belo et al., 2021).In the context of mucositis induced by the chemotherapy 5-FU, P. freudenreichii prevented weight loss, reduced inflammation and consequently intestinal damages. It regulated key markers, including Claudin-1 and IL-17a genes, as well as IL-12 and IL-1β cytokines levels (Cordeiro et al., 2018). Mutant strain slpB displayed opposite regulatory effect on cld1 expression and on IL-12 levels, and failed to afford protection towards 5-FU-mucositis (do Carmo et al., 2019).P. freudenreichii was further shown to produce extracellular vesicles (EVs), which mimic the immunomodulatory features of propionibacteria in vitro by modulating NF-κB transcription factor activity and IL-8 release in cultured human intestinal epithelial cells (Rodovalho et al., 2020). Proteomic analysis revealed presence of SlpB in these EVs.DiscussionThis work emphasizes the importance of SlpB in P. freudenreichii ability to reduce both mucositis and colitis inflammation. It opens perspectives for the development of probiotic products aimed at decreasing side effects of chemotherapy and at helping treatment of colitis, thanks to GRAS bacteria.