Sirt1Protects Against Acute Lung And Kidney Injury In Sepsis

Sepsis，also called systemic inflammatory response syndrome, is a high morbidityand mortality disease which arises mostly from severe infection. Sepsis is alsothought to be a transition from infection to multiple organ damage. The severemultiple organ failure happens due to the excessive systemic inflammation. Sinceend-organ dysfunction can be caused by severe sepsis, furthermore, septicpatients are at great risk of developing acute lung injury (ALI) and acute kidneyinjury（AKI）.Currently, the cross talk of injured organs is getting more and moreattention in sepsis, especially related to the relationship between AKI and ALI.ALI and its severe form, acute respiratory distress syndrome (ARDS), often leadsto multi-organ failure with a mortality of approximately30-50%. In addition,kidney functions as a natural filter of blood becomes a direct target ofinflammatory injury.Sepsis-induced AKI is very common in the elderly and isassociated with high mortality, however it has been found that the expression ofSirt1decreased in elder person. In addition, it has been reported Sirt1decline iscommon in COPD patients. Therefore we speculate Sirt1exerts critical functionin regulating inflammatory disease. Cecal ligation and puncture (CLP) surgerymodel and lipopolysaccharide (LPS) challenge are the most accepted animalmodels to explore the underlying mechanisms and potential treatment insepsis-induced ALI and AKI, therefore we use these two sepsis model to investigate the mechanism of Sirt1protects mice from the sepsis induced ALIand AKI.Sirt1, a member of the Sirtuin family, is a deacetylase first found insaccharomycetes. The mechanism of deacetylation by sirtuins is difference fromthe classic deacetylation.Sirt1modulates the function of a wide variety ofproteins such as NF-kB and p53, through deacetylation of lysine residues. Therehave been increasing studies suggesting that Sirt1plays an important role ininflammation, apoptosis, stress resistance, metabolism, differentiation, and aging.However the regulation of Sirt1in sepsis is rarely studied, and the mechanism isstill not clear. In the present study, we investigated the role of Sirt1in sepsisinduced acute lung injury and acute kidney injury by inducible deletion of Sirt1in mice. Our studies demonstrated that Sirt1knockout mice are highly susceptibleto sepsis-induced inflammatory lung and kidney injury.In the first part of the study, we mainly focus on the regulation function andthe mechanism of Sirt1in ALI in sepsis model. Cecal ligation and puncture (CLP)surgery was used in Sirt1knockout mice and there littermates to induce the sepsismodel. To explain the role of Sirt1, we studied in three aspects, including theneutrophil migration、pro-inflammory cytokines releasing and the mechanism ofSirt1regulation. First, Lung homogenate myeloperoxidase (MPO) activity, as anindicator of neutrophil infiltration, was detected at24h after CLP surgery.Second, pro-inflammory cytokines IL-6and TNF-α level are measured bycommercially ELISA kits6h or24h after CLP implementing. Our results demonstrated Sirt1deletion significantly increases the MPO activity and thereleasing of pro-inflammatory cytokines. To expound the modulation mechanismof Sirt1in ALI, we use western blot to assay the express of targeted proteinmodulated by Sirt1.After the exogenous and endogenous stimulation invade thebody, NF-kB excitation happened through a complex pathway, subsequentlyregulates the transcription of all kinds of inflammatory mediator, eventuallyleading to the irreversible inflammatory reaction. Our study showed NF-kB wassignificantly activated in Sirt1deletion mice, meanwhile, the excitation ofintercellular adhesion molecule-1(ICAM-1) and vascular cell adhesionmolecule-1(VCAM-1), the phosphorylation of ERk1/2and activator oftranscription3(STAT3), and the activation of caspase3，caspase7were increasedby western immunoblot assay. Our results demonstrate the Sirt1deletion augmentthe lung injury by triggering the inflammatory signaling pathway.In the second part of the study, we focus on the regulation function and themechanism of Sirt1in AKI in sepsis model.Lipopolysaccharide (LPS) was usedin C57BL6mice to induce sepsis. Renal function is significantly compromisedduring sepsis as indicated by increased blood urea nitrogen (BUN) and urineKidney injury molecul e-1(KIM-1) levels. Sepsis also causes renal tubulardamage and inflammation as shown by histological analysis. Kidneyinflammation is associated with increased production of pro-inflammatorymediators, and up-regulation of adhesion molecules such as Intercellularadhesion molecule-1(ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Those early inflammatory responses induce leukocyte infiltrationduring kidney injury, which may lead to further damage. Increased cytokineproduction is a hallmark in many inflammatory diseases including kidney injury.In the regulation of cytokines, NF–kB is an important transcription regulationfactor which play a critical role in inflammatory reaction. In this part of study, wefound NF-kB expression augment in Sirt1deletion mice kidney, causingcytokines, including IL-6and TNF-a, increased. Subsequently, pro-inflammatorysignaling such as activation of signal transducer and activator of transcription3(STAT3), and modulate inflammatory responses through ERK/MAPK cascadewere activated. According to the results, we foundSirt1protects against the LPS-induced acute kidney injury in sepsis.In conclusion, Sirt1plays a protective role against inflammatory lung and kidneyinjury in sepsis. Sirt1exerts its function through suppressing NF-kB activation,following by the cytokines-mediated multiple pathways such as STAT3, ERK1/2,and caspase. Our studies indicate that Sirt1is a potential therapeutic target totreat sepsis-induced lung and kidney injury.