| Background and objectiveSepsis induced cardiac dysfunction remains a major cause of morbidity and mortality in patients suffered from severe trauma. Mesenchymal stem cells(MSCs) based treatment has been verified as a promising approach to mitigate the sepsis induced cardiac dysfunction, but the mechanism is still ambiguous. Thus, our study was designed to evaluate therapeutic efficacy and mechanism of MSCs in sepsis induced cardiac dysfunction. MethodsIn this study, BMSCsFluc+/GFP+were isolated from Tg(Fluc-egfp) mice which constitutively expressed enhanced green fluorescent protein(eGFP) and Firefly luciferase(Fluc). Cardiac fibroblasts(Fbs) were isolated from 1- 3 day-old C57BL/6 mice. Cardiac specidic Raptor knock out(K.O.) or overexpressed(O.E.) transgenetic mice were made by mating across for veral generations or by cardiac specific injecting adenovirus. Sepsis was induced by a intraperitoneal injection of high dose LPS(20mg/Kg) to subject mice, followed 1 hour later by intraperitoneal injection of BMSCs, Fbs or PBS. In vivo BLI was applied to monitor the survival and proliferation of transplanted BMSCsFluc+/GFP+. Echocardiography was performed after LPS intraperitoneal injection as a baseline, and then, post LPS injection 24 and 96 hours were also measured. Tissues and Serum were collected for analysing the density of neutrophil and macrophages infiltration,as well as the secretion of proinflammatory cytokines and the expression of proteins. We assessed survival after surgery every 12 h for 96 h. Cardiomyocytes apoptosis was observed by TUNEL staining. ResultsIn vivo biolumiescence imaging revealed 80% acute donor cell death of bone marrow derived MSCs(BMSCs) within 7 days after transplantation. However, echocardiography demonstrated that systolic function in wild type mice group were reduced 24 hours after sepsis while the cardiac function was relatively well persevered in cadiac-conditional deletion of Raptor(component of mTORC1 complex) mice group. The cardiac function was more severely undermined in the Raptor overexpression(O.E) mice group. Raptor KO mice group treated with BMSCs appeared better cardiac function than other groups(P<0.05). In vitro cell study revealed that co-culture of H9C2(Raptor-Knock down) and BMSCS could attenuate the level of pro-inflammatory cytokines and promote the expression of anti-inflammatory cytokine accompanied by mTORC2-Akt activation(p<0.05). On the contrary, co-culture H9C2(Raptor-O.E) and BMSCS could aggravate the inflammatory response accompanied by the activation of mTORC1- p70S6 K and inhibition of mTORC2-Akt(p<0.05). The immunomodulatory property of MSC is related to the inhibition of mTORC1-p70S6 K and activation of mTORC2-Akt signaling pathway. Conclusion: mTORC1-p70S6 K and mTORC2-Akt pathways were involved in the therapeutic adjuncts of MSC. The possible mechanism due to MSC`s immunomodulatory property through activation of mTORC2-Akt and inhibition of mTORC1-p70S6 K signal pathways which may lead to modulate the expression of inflammation cytokines. ConclusionIn conclusion, our studies demonstrated that BMSCs can modulate sepsis induced inflammation through mTORC1-S6 K and mTORC2-Akt pathway, alleviating sepsis induced cardiac dysfunction. Furthermore, a subtle balance of mTORC1 and mTORC2 was revealed, which was indispensable for the modulating of inflammation. In addition, TLR-4/NF-κB pathway was also involved in this process, and BMSCs could decrease this proinflammatory signal pathway. These data leads us to better understand the mechanism of MSC’s immunomodulatory effect, facilitating the progress of clinical translation of cell-based sepsis treatment. |
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