GGPPS1 Regulates Inflammation In Ventilator-induced Lung Injury By Activating TLRs Signal Passway

Acute respiratory distress syndrome(ARDS),characterized by acute and diffuse pulmonary inflammation,is a life-threatening form of severe hypoxemia that affects almost other organs of the whole body,resulting in multiple organ dysfunction syndrome.Therefore,ARDS can also be considered as a systemic disease with high morbidity and mortality.The mortality of ARDS is closely related to the severity of the disease.Although the protective strategy of mechanical ventilation reduces the mortality of patients with ARDS,these factors such as the complex causes complexity of ARDS and the rapid progress of injury,together with the interindividual variation,cause a great challenge in mechanical ventilation for ARDS treatment.Ventilator-induced lung injury(VILI)is a severe complication in ARDS treatment,resulting in excessive release of inflammatory mediators,further aggravating lung injury in ARDS patients.Alveolar epithelial cells play an important role in VILI.Alveolar epithelial cells participate in alveolar damage and repair process,on the other hand,are closely related to neutrophil activation that plays a key role in VILI.The protein isoprenoid regulate organ damage and inflammation.FPP and GGPP are important intermediates in the mevalonate pathway.Geranylgeranyl diphosphate synthase 1(GGPPS1)is a key enzyme which catalyzing FPP to synthesize GGPP,and is also closely related to fetal lung development.However,the mechanism of GGPPS1 expression in ARDS and VILI remains unclear.Therefore,we detected the expression of GGPPS1 in BALF in ARDS with mechanical ventilation and non-ARDS group to verify the association between GGPPS1 and ARDS.Next,we detected GGPPS1 expression,inflammation and injury in VILI mode induced by high tidal volume MV by the methods,such as electron microscope,H&E,IHC,ELISA,Western,blotting,q-PCR,flow cytometry.Finally,GGPPS1 knocked out mice and mRNA sequencing were performed to verify the mechanism of GGPPS1 regulating the damage and inflammation in VILI.In this study,we found that GGPPS1 concentration of BALF in ARDS patients was significantly higher than in the control group,the expression of GGPPS 1 in lung tissue of VILI model was also increased.Mechanical ventilation with high tidal volume damaged alveolar epithelial cells,electron microscopy assay showed serious swelling and deformation of alveolar type ? epithelial cell,however,knockdown of GGPPS1 improved the injury of both alveolar type II epithelial cell and lung tissue,reduced the protein content in BALF and leakage of lung tissue,decreased neutrophil infiltration and increased neutrophil apoptosis,improved acute lung injury score.The levels of IL-6,IL-1?,IL-18,TNF-a and CXCL2 were lower in GGPPS1 knockout mice than in wild type mice.Further study showed that toll like receptors pathway were affected by GGPPS1.Knockout of GGPPS 1 inhibited TLR2 and TLR4,but enhanced TLR5 expression,inhibited the downstream proteins expression of TLRs relating to inflammation,such as MyD88,TRAF6,TAK1,AP1,meanwhile,enhanced proteins relating to apoptosis,such as FADD,Caspase8,Fas expression and inhibited Bcl-2 expression.In summary,this study confirms that GGPPS1 participates in the process of inflammation and injury of ARDS and VILI.Knockout of GGPPS1 inhibits inflammation through TLRs and their downstream MyD88-TRAF6-TAKl-AP1 pathway.In addition,it may also promote apoptosis of neutrophils through FADD-Caspase8 pathway.