Uticaj mezenhimalnih matičnih ćelija na signalni put IL-17 u modelima akutnog hepatitisa i fibroze jetre

Abstract

Mezenhimalne matične ćelije (MSCs), parakrinim mehanizmima, redukuju akutno oštećenje i fibrozu jetre. S obzirom da uticaj mezenhimalnih matičnih ćelija (MSCs) na IL-17 signalni put u akutnom hepatitisu i fibrozi jetre nije poznat, analizirani su molekulski mehanizmi odgovorni za MSCs-zavisnu modulaciju IL-17 u ovim bolestima. U eksperimentalnim modelima akutnog hepatitisa izazvanim α-galaktoceramidom (αGalCer) i ugljen tetra hloridom (CCl4), MSCs su redukovale hepatotoksičnost NKT ćelija parakrinim mehanizmom koji zavisi od aktivnosti indolamin 2, 3-dioksigenaze (IDO). Smanjena koncentracija inflamacijskog IL-17 i povećana koncentracija imunsupresivnog IL-10, manji broj IL-17-produkujućih NKT ćelija (NKT17) i veće prisustvo IL-10-produkujućih FoxP3+NKT ćelija (NKTreg) uočeni su u jetrama obolelih miševa koji su primili MSCs. Primena kondicioniranog medijuma MSCs (MSC-CM) značajno je redukovala akutni hepatitis uzrokujući konverziju hepatotoksičnih NKT17 u imunosupresivne NKTreg. Primena 1-metil triptofana (1-MT), farmakološkog inhibitora IDO-a, u potpunosti je suprimirala imunomodulatorne efekte MSC-CM. U modelu CCl4-indukovane fibroze jetre, MSCs su značajno redukovale fibrozu jetre smanjenjem serumske koncentracije IL-17 i povećanjem koncentracije imunosupresivnih IL-10, IDO i kinurenina. MSCs su značajno smanjile broj intrahepatičnih Th17 limfocita i povećale procenat CD4+IL-10+ T ćelija. Slično kao i MSCs, i MSC-CM značajno je redukovao broj Th17 limfocita u jetri, smanjio koncentraciju IL-17 u serumu i pospešio ekspanziju CD4+FoxP3+IL-10+ regulatornih T limfocita. Primena 1-MT u potpunosti je suprimirala hepatoprotektivni i imunomodulacijski efekat MSC-CM. Najvažniji zaključak ove doktorske disertacije je da MSCs, aktivnošću IDO-a, redukuju akutni hepatitis indukujući konverziju hepatotoksičnih NKT17 ćelija u imunosupresivne NKTreg, dok u fibrozi jetre inhibiraju oslobađanje IL-17 iz Th17 limfocita i povećavaju prisustvo imunomosupresivnih IL-10-produkujućih Tregs u jetri, doprinoseći značajnom smanjenju fibroze.

Interleukin 17 (IL-17) plays an important role in the pathogenesis of acute hepatitis and liver fibrosis. Due to immunomodulatory characteristics, mesenchymal stem cells (MSCs) reduce acute and chronic liver failure, however, the molecular mechanism by which MSCs suppress inflammation in these diseases is still unknown To evaluate effects of MSCs on IL-17 signaling, in acute hepatitis and liver fibrosis, we used carbon tetrachloride (CCl4)- and alphagalactoceramide (α-GalCer)- induced acute hepatitis and CCl4- induced liver fibrosis. In acute hepatitis experimental models, MSCs attenuate hepatotoxicity of NKT cells in paracrine, indoleamine 2,3-dioxygenase (IDO)-dependent manner. Liver intracellular staining and cytokine serum measuring showed decreased concentration of inflammatory IL-17, increasing immunosuppressive IL-10, reduced number of IL-17 producing NKT (NKT17) cells and increased number of FoxP3+ IL-10 producing NKT regulatory (NKTreg) cells in the injured livers of MSC-treated mice. Injection of MSC conditioned medium (MSC-CM) resulted with increased NKTreg/NKT17 ratio in the liver and attenuated hepatitis in vivo and significantly reduced hepatotoxicity of NKT cells in vitro. This phenomenon was completely abrogated in the presence of IDO inhibitor, 1-methyltryptophan. In liver fibrosis experimental model, MSCs significantly attenuated CCl4-induced liver fibrosis by decreasing serum levels of inflammatory IL-17, increasing immunosuppressive IL-10, IDO and kynurenine. MSCs reduce number of IL-17 producing Th17 cells and increasing percentage of CD4+IL-10+ T cells. Injection of MSC-CM decrease number of Th17 cells in the liver and serum levels of IL-17. MSC-CM promoted expansion of CD4+FoxP3+IL-10+ T regulatory cells and suppressed proliferation Iof Th17 cells. in the presence of IDO inhibitor, 1-methyltryptophan, this immunomodulatory phenomenon was completely abrogated. In conclusion, MSCs in acute hepatitis, decrease NKT production of IL-17, while in liver fibrosis reduces number of IL-17 producing CD4+ T cells, thus reducing hepatocyte damage.