Study Population
We enrolled a total of 300 patients with T2DM who were referred for diagnostic coronary angiography between January 2014 and November 2017. The diagnoses of T2DM and dyslipidemia were according to the published guidelines from the American Diabetes Association. We grouped the patients with T2DM into Group I (n=80, control group: subjects without evidence of cardiovascular diseases or diabetes, who received annual physical checkups.), Group II: subjects with no coronary artery stenosis or stenosis. Group III: subjects with coronary artery stenosis or stenosis. This study complied with the Declaration of Helsinki. The study protocol was approved by the local hospital ethics committee, and we obtained written informed consent from all the participants.
Isolation of HDL, and quantification of CML.
To circumvent the interference and masking effects of albumin and immunoglobulins in plasma, we obtained apo A-IV by immunoprecipitating it from isolated HDL. We analyzed apo A-IV glycation (CML) through Western blotting. HDL was isolated from 50 ml of fresh plasma by ultracentrifugation, as previously described (17). The HDL solution was then incubated with an anti–apo A-IV and CML antibody (1:1000, Santa Cruz, California). Western blotting was repeated 3 times for each HDL sample. The absolute intensity of apo A-IV glycation and the content of apo A-IV were calculated as density values, which was calculated as the ratio of the normalized absolute intensity of apo A-IV glycation to the normalized content of apo A-IV ([apo A-IV sample glycation/apo A-IV standard glycation]/[apo A-IV sample/apo A-IV standard]).The relative intensity of apo A-IV glycation was determined in all participants.
Preparation of the glycated apo A-IV recombinant protein.
We performed apo A-IV glycation by incubating apo A-IV in a solution containing 0.01% ethylene diamenete tracetic acid, 0.01% sodium azide and 20 mmol/l glyoxal for 7 days, after which we dialyzed the solution.
Ischemic Hind-Limb Model and Blood Flow Monitoring
(i) The animal studies were approved by the animal care committee of Shanghai Jiao Tong University. And (ii) all procedures must conform to the guidelines from Directive 2010/63/EU of the European Parliament on the protection of animals used for scientific purposes or the NIH Guide for the Care and Use of Laboratory Animals. Overall, 40 C57BL/6 male mice aged 5 weeks were purchased from the Model Animal Center of Nanjing University and housed in a pathogen-free isolation facility under a 12/12-hour light–dark cycle with free access to water and food. Streptozotocin (STZ)(obtained from Sigma Aldrich Milan Italy) was dissolved in 0.01 M sodium citrate buffer (pH 4.5) and administrated i.p. at a dose of 40 mg/kg body weight (bw) , continuous 4 days , and by feeding the animals (n = 24) with a high fat diet (HFD: 59% fat, 15% protein, 20% carbohydrates),to induce Diabetes[21]. The diabetes mice were divided into 4 groups: the control group (n=10), the saline group (n=10)( intraperitoneal injection), the ApoA4 group (n=10)(i.p.) (20μg, as cilinical)and the G-APOA4 group (n=10) (i.p.) (20μg). Drug was injected 4 times per week. After 2 weeks of administration, unilateral hind-limb ischemia was surgically performed by left femoral vessel (artery and vein) removal and excision of femoral bifurcation with all branches, details were described previous (19). Hind-limb blood perfusion was measured with laser Doppler perfusion imaging. The results were expressed as the ratio of perfusion in the ischemic (left) versus nonischemic (right) hind limb.
Tissue Preparation and Immunochemistry
1%(m/V, or 5mg/kg) Pentobarbital was I.P to anesthesia mice, Depth of anesthesia was determined by the pedal reflex test, the animals were euthanized by decapitation t, and the Gastrocnemius tissue was removed from the ischemic hind limb at21 days. For mouse capillary density identification, the tissues were stained with monoclonal CD31 antibodies. For quantification, the capillaries were counted in 5 randomly selected microscopic fields. For downstream signal, the tissues were stained at 80℃,and detected with Western Blot. The experimental protocol was approved by the Committee on Animal Resources from Shanghai Jiao Tong University.
Cell Culture
We obtained Human Umbilical Vein Endothelial Cells (HUVECs) from company (Portland, OR). The cells were maintained in Medium 200 supplemented with growth factors and cultured in a humidified atmosphere of 5% CO2 at 37°C.
Glycation treatment
Medium Cell culture medium mix with different concentrations of glycate APOA-IV and APOA-IV (10, 50, and 100 mmol/ L) for 24 hours at 37°C.
Overexpression plasmid and GFP of Nur77 was obtain from Shanghai Jima Pharmaceutical Technology Co., Ltd, which (Final concentration 50nM) was transferred into HUVECs, which was verified in 48h by qPCR.
Wound-Healing Assay
HUVECs were plated on 6-well plates and incubated with glycated APOA-IV and APOA-IV (10, 50, and 100 mmol/L) or serum media (control) for 24 hours. The HUVECs were then wounded with a sterile pipette tip, and the width of each wound line was photographed (Olympus) at 0 and 24 hours.
Cell Migration
Assay Cell migration assays were performed using a Boyden chamber (Millipore). The HUVECs were either incubated with glycate APOA-IV and APOA-IV medium or serum. Cells (0.5*106 cells per mL) were then harvested and placed in the upper chamber, with the lower chamber filled with 500uL of cell culture medium containing 10% FBS. After 8 hours of incubation, the non-migrated HUVECs on the upper side of the membrane surface were removed by wiping with a cotton swab. The migratory cells were then fixed and stained with crystal violet solution and quantified by optical density (560 nm) measurement.
Tube Formation Assay
Matrigel (BD Bioscience) was added to 96-well plates, with 50uL in each well. After treatment with glycated apo A-IV or apo A-IV for 24 hours, HUVECs were added to the 96-well plates. Cells plated on Growth Factor-Reduced Matrigel served as the negative control. Cells were examined in 4 random microscopic fields, and total length of the capillary structures and branch point numbers were measured by Image-Pro Plus version 6.2 (Media Cybernetics).
Western Blot
Proteins from cell lysates at equal loadings were subjected to 7.5% to 12.5% SDS-PAGE and then transferred to polyvinylidene difluoride membranes. Membranes were further blocked in 5% nonfat milk, followed by incubation with the corresponding primary antibodies overnight at 4°C and with horseradish peroxidase–conjugated secondary antibodies for 1 hour at room temperature. The PI3K antibody (abcam,1:1000), Akt antibody (abcam,1:1000), VEGFR2 antibody (abcam,1:1000), VEGFA antibody (abcam,1:1000), Blots were detected using an electrochemiluminescence system (GE Healthcare Biosciences) and qualified with Quantity One (Bio-Rad) software. We also detected β-actin as the protein loading control.
Statistical Analysis
Statistical analyses were performed with SPSS software (version 20.0) and GraphPad Prism 5. Continuous variables were expressed as mean SD. For normally distributed continuous variables, we use unpaired Student t tests to assess differences. One-way ANOVA was used for multiple comparisons. P value of <0.05 was considered statistically significant.
Data and Resource Availability
The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request. All data generated or analyzed during this study are included in the published article (and its online supplementary files).