2.1 The Citrobacter rodentium infection and hypoxia mice model
64 (32 WT and 32 MPO-/-) C57BL/6 mice (SPF grade, 8 week olds, female, 18-20 g) in total were purchased from Hu’nan SJA Laboratory Animal Co., Ltd. (WT mice) and Cyagen Biosciences (Suzhou) Inc. (MPO-/- mice). The mice were kept in a specific-pathogen-free (SPF) facility with the Individual Ventilated Cage Animal Experiment System (H6, Su Hang Technology Equipment Co., Ltd., Suzhou) with autoclaved water and food. Animal care was provided under protocols endorsed by the Institutional Animal Care and Utilize Committee at the Medical College of Qinghai University. All animal experiments comply with the ARRIVE guidelines. Citrobactercolitis was induced by oral feeding with C. rodentium (strain DBS100, ATCC number 51459, 5×108 CFU/mouse).The hypoxia environment was made with a hypobaric chamber (Fukang Air Purification Equipment Engineering Co., Ltd., Shaanxi) at 5,000 m (atmospheric pressure was 405 mmHg, PO2 was 84.7 mmHg) [8]. Mice were randomly divided into 8 groups with simple randomization method:WT normoxia control group (NC,n=8), MPO-/- normoxia control group (KC ,n=8), WT C. rodentium infection group (NI, n=8), MPO-/- C. rodentium infection group (KI,n=8), WT hypoxia control group (HC,n=8), MPO-/- hypoxia control group (HKC,n=8),WT hypoxia C. rodentium -infected group (HI,n=8) and MPO-/- hypoxia C. rodentium -infected group (HKI,n=8). 8 mice were kept in one cage. Only feeder was aware of the group allocation at the different stages of the experiment.