The Study Of IL-22 Protects Mice From Acute Severe Pancreatitis Via STAT3 Signaling Pathway

Objectives:Acute severe pancreatitis (SAP) is one of clinical common critical diseases with rapid progression, multiple complications and high mortality. Because its exact pathogenesis is not clear, currently, aside from supportive therapy, no active treatment exists for treating SAP. IL-22 as a protective factor, plays important roles in a variety of liver, lung, intestinal injury animal models, such as repairing tissue damage and maintaining homeostasis. This study will use large doses of L-arginine to induce SAP model in mice and investigate the effect and mechanism of IL-22 in the SAP mice.Methods60 male Balb/c mice were randomly divided into normal control group (NaCl group), severe acute pancreatitis group (SAP group), PBS treatment group (PBS group) and rIL-22 treatment group (rIL-22 group). NaCl group (10 mice):injecting the amount of normal saline; SAP group (30 mice):using 8% L-arginine (pH=7.0), 4 g/kg each,1 h apart to intraperitoneal inject; PBS group (10 mice):PBS(200 ng/dose X 5 times) was administrated to mice at the indicated times; rIL-22 group (10 mice):rIL-22 (200 ng/dose × 5 times) was administrated to mice at the indicated times. To observe pancreatic tissue pathology change, to test serum amylase activity, to detect pancreatic tissue Reg3β, Reg3γ, Bcl-2, Bcl-xL and IL-22RA1 expression level changes by Real-time PCR method and STAT3 and P-STAT3 protein expression level by Western blotting method, to statistics mice mortality in treatment groups.Results1. Pancreatic histologyIn NaCl group, pancreatic structure was clear and cells form was complete, with no inflammatory cell infiltrating. In SAP group, at 24 h, interstitial edema, inflammatory cells infiltration, and lobule platelet destruction, acinar cells necrosis were observed in pancreatic tissue. At 72 h, normal pancreatic lobule island shaped distribution, note extensive disruption of acinar architecture with necrosis and inflammatory cells infiltration; In rIL-22 group pancreatic edema necrosis, inflammatory cells infiltration were significantly reduced comparing with PBS group.2.Serum amylase activityIn NaCl group, serum amylase was in the normal range; In SAP group, serum amylase activity presented increase first and then decrease. The serum amylase level decreased significantly in the rIL-22 group in comparison with the PBS group (P< 0.05).3. Mortality in the treatment groupsThe mortality of mice in PBS group was 30%; There was no death in rIL-22 group (P<0.05).4.Levels of RegⅢβ, RegⅢγ, Bcl-2, Bcl-xL and IL-22RA1 mRNA expression in pancreatic tissueComparing with the NaCl group, RegⅢβ, RegⅢγ, Bcl-2 and Bcl-xL mRNA expression were markedly decreased, especially at 72h. IL-22RA1 mRNA expression significantly increased in 24 h and 48 h during the L-arginine induced SAP mice model. rIL-22 stimulated the expression of RegⅢβ, RegⅢγ, Bcl-2, Bcl-xL and IL-22RA1 genes comparing with mice in PBS group.5.Levels of phosphorylated STAT3 and total STAT3 expression in the pancreatic tissuerIL-22 treatment resulted in a significant increase in phosphorylated STAT3, but the total expression level of STAT3 did not change. Besides, the P-STAT3 Tyr705/total STAT3 level was markedly much higher in rIL-22 group than that in PBS group (P <0.05).Conclusion1. High doses of L-arginine successfully induced SAP mice model.2. Exogenous recombinant IL-22 protect mice from SAP induced by L-arginine, by activating the STAT3 signaling pathway and enhancing the expression of antimicrobial peptides and antiapoptotic genes.