Effect Of Mesenchymal Stem Cells On Lipopolysaccharide Induced Acute Lung Injury And Its Molecular Mechanism

Acute lung injury(ALI)is a lung injury caused by a variety of direct or indirect factors(such as pneumonia,infection,toxic gases,sepsis,poisoning,etc.).It has a poor prognosis and a mortality rate of up to 50%.Studies have shown that the over-activation of the autoimmune system is an important mechanism in the pathogenesis of ALI.Mesenchymal stem cells(MSCs),with the characteristics of inflammation,tissue regeneration,low immunogenicity and the correlation between the activation of autophagy and immune regulation,have potential for the treatment of ALI.Exploring the influence and molecular mechanism of human umbilical cord blood mesenchymal stem cells(hUC-MSCs)on ALI induced by lipopolysaccharide(LPS),expect to provide a new theory basis for treatment of the acute lung injury.Methods:(1)The ALI model was successfully induced by adding LPS into the medium of human embryonic lung fibroblasts(MRC-5)and detecting the relative expression of apoptosis protein Bax and inflammatory factors IL-6,IL-1β and TNF-α.(2)MRC-5 cells in ALI model were cultured with hUC-MSCs cell medium to explore the influence of paracrine function of hUC-MSCs cells on ALI.(3)Rapamycin(RAPA),an autophagy inducer,was added into hUC-MSCs cell culture medium to explore the influence of paracrine function of hUC-MSCs cells after autophagy induction on ALI.(4)The involvement of CXCL12/CXCR4 signal axis was determined by detecting the relative expression level of CXCR4 in hUC-MSCs cells after autophagy induction and CXCL12 in MRC-5 cells of ALI model,as well as the influence of paracrine of CXCR4 gene silence in hUC-MSCs cells.Results:(1)The relative expression of apoptosis protein Bax and the inflammatory factors(IL-6,IL-1β and TNF-α)in MRC-5 cells after the addition of LPS were up-regulated.(2)Paracrine function of hUC-MSCs can down-regulate the relative expression of apoptosis protein Bax and inflammatory factors(IL-6,IL-1β and TNF-α)in MRC-5 cells in ALI model.(3)The paracrine function of hUC-MSCs,activating the autophagy,can down-regulate the relative expression of apoptosis protein Bax and inflammatory factors(IL-6,IL-1β and TNF-α)in MRC-5 cells in ALI model.(4)The relative expression of CXCR4 in hUC-MSCs cells was significantly up-regulated after inducting autophagy.The relative expression of CXCL12 in MRC-5 cells was significantly up-regulated in ALI model.The paracrine function after CXCR4 gene silence in hUC-MSCs can down-regulate the relative expression of apoptosis protein Bax and inflammatory factors(IL-6,IL-1β and TNF-α)in ALI model MRC-5 cells.Conclusion:(1)The paracrine function of hUC-MSCs can inhibit the inflammatory response of LPS-induced ALI and has a protective effect on ALI.(2)hUC-MSCs mediated the expression of CXCR4 by activating autophagy,and then participated in the protection of ALI through the CXCL12/CXCR4 axis.