Materials
Asiatic acid (C30H48O5, MW: 488.70) was purchased from Guangxi Changzhou Natural Products Development Co. Ltd (>95% purity, Guangxi, China). Antibiotic-antimycotic solution (10,000 units/ml of penicillin, 10,000 ug/ml of streptomycin) Ang II was obtained from Sigma Chemical Co. (St Louis, MO, USA). Antibodies against ANP, β-MHC, PIK3R2, PI3K, p-PI3K, Akt, p-Akt, GAPDH were purchased from Abcam CO (Cambrige, UK).
Animal
8-week-old male Sprague Dawley (SD) rats (150-170 g body weight) were purchased from Beijing Vital River Laboratory Animal Technology Company (Beijing, China). All experiments involving rats were approved by the Institutional Animal Care Research Advisory Committee of the National Institute of Biological Science (NIBS) and Animal Care Committee of Zhengzhou University. All rats were maintained on a 12:12-h light-dark cycle and have free access to water and food.
Experimental design and treatment protocol
A rat model of Ang-II infusion induced cardiac hypertrophy were established. In brief, SD rats were quickly anesthetized with an intraperitoneal injection of sodium pentobarbital (50 mg/kg), then the prefilled osmotic minipumps (Alzet, Model 2002) were implanted into the subcutaneous tissue to deliver Ang II (Sigma-Aldrich, A9525) at 400 ng/kg/min for 4 weeks. Rats were randomly divided into two groups (10 mice/group) for different treatments by oral gavage for 4 weeks: Ang II group and Ang II +AA (AA 20mg/kg) group. Another ten SD rats as the wild control group sham group.
Cell culture
Rat cardiomyoblast H9c2 cells were cultured in DMEM with 15% FBS, 100 U/mL penicillin and 100 μg/mL streptomycin in a humidified atmosphere of 5% CO2 and 95% air at 37℃. Cells were incubated with AA 160uM with or without AngII 10uM for 24 h in a 6 well plate. Cell surface area analysis was performed using confocal microscopy as described previously [19].
Echocardiographic study
Transthoracic echocardiography was performed to access left ventricular (LV) function variables. Briefly, after the induction of general anesthesia, rats were placed in a supine position. Rats were underwent transthoracic two dimensional guided M-mode echocardiography with a 12L MHz transducer (Sibiscape Co. Ltd.). From the cardiac short axis, the LV anterior wall end-diastolic thickness (LVAWd), the systolic LV anterior wall thickness (LVAWs),the LV internal dimension at end-diastole (LVIDd), the LV internal dimension at end-systole (LVIDs), the LV posterior wall end-diastolic thickness (LVPWd), the LV posterior wall end-systolic thickness (LVPWs), the ejection fraction (EF), and fractional shortening (FS) were measured.
Histological analysis
The left ventricle were fixed in 10% formalin and embedded in paraffin. Tissue sections (4um) were stained with 1.0 mg/ml Alexa Fluor 488®conjugete of wheat germ agglutinin (WGA) solution(MolecularProbes, Eugene, OR, USA)to demonstrate the size of cardiomyocytes. The collagen deposition in the left ventricle was detected by Masson staining. Ten fields in each region of the heart were selected randomly from four nonconsecutive serial sections, and collagen content was quantified by measuring the total blue area per square millimeter using the ImageJ.
Dual-luciferase gene reporter assays
Based on the PIK3R2-wild type (wt), a complementary sequence mutation site of the seed sequence was designed as mutant type (mut). PIK3R2 wt and mut were amplified and cloned into a pGL3 vector containing the firefly luciferase reporter gene (ObiO, Shanghai, China). Human embryonic kidney (HEK) 293 cells were co-transfected with 100ng of recombinant luciferase reporter plasmid, 10ng of pRL-TK as an internal control, 50nM miR-126-3p mimic, or mimic control respectively. Luciferase activity and renilla luciferase were measured 24h after transfection using a dual-luciferase reporter assay. And the ratio of firefly luciferase/renilla luciferase was calculated and were used to reveal the interactions between miR-126 and PIK3R2.
Western blotting
At the end of experiment, rats were sacrificed and the heart were quickly removed. Left ventricle tissue were lysed by RIPA lysis buffer and phenylmethylsulfonyl fluoride (Beyotime, China). The protein concentration was detected by using a BCA protein assay kit. Equal amounts of protein (30μg) were separated using 10 or 12% SDS-PAGE and were transferred onto a polyvinylidene difluoride membrane (PVDF). Next, PVDF membranes were blocked with 5% fat-free milk and incubated with primary antibodies overnight at 4℃. Subsequently, the membranes were washed and incubated with secondary antibodies at room temperature. The optical density of the bands were visualized by an ECL system (Pierce). GAPDH was used as an endogenous control. Data was normalized to GAPDH levels.
RNA isolation and quantitative real-time PCR
Total RNA was extracted from the frozen tissues or treated H9c2 cells using Trizol reagent (Invitrogen, USA). First strand cDNA was synthesized using an RT kit (Invitrogen, USA). miRNA from heart was converted to cDNA using the miRNA 1st Strand cDNA Synthisis Kit (Vazyme, Nanjing, China) according to the manufacturer’s protocol. Amplifications were performed using an opticon continuous fluorescence detection system with SYBR green fluorescence (Molecular Probes, Eugene, USA). A single melting curve peak confirmed the presence of a single product. Results were expressed as fold differences relative to GAPDH or U6 using the 2-ΔΔCT method. All the primers were synthesized by Sangon Biotech (Shanghai, China) and the sequence are listed in Table 1.
Table 1. Primers used for reverse transcription and real-time PCR
Primer Names
|
|
Sequences
|
ANP
|
Sense
Anti-Sense
|
CCTTCTCCATCACCAA
TGTTATCTTCGGTACCG
|
PIK3R2
|
Sense
Anti-Sense
|
ACTCACCTTCTGCTCCGTT
TCTGGTCCTGCTGGTATTTGG
|
U6
|
Stem-loop
Sense
Anti-Sense
|
GTCGTATCCAGTGCAGGGTCCGAGGTATTCGCACTGGATACGACAA
AGAGAAGATTAGCATGGCCCCTG
ATCCAGTGCAGGGTCCGAGG
|
miR-126
|
Stem-loop
Sense
Anti-Sense
|
GTCGTATCCAGTGCAGGGTCCGAGGTATTCGCACTGGATACGACCGCATT
CGCGTCGTACCGTGAGTAAT
AGTGCAGGGTCCGAGGTATT
|
pri-miR-126
|
Sense
Anti-Sense
|
AAGGACCATTGTTGGCACTCAGG
TCTCACCACGCTGTCCACTCC
|
β-MHC
|
Sense
Anti-Sense
|
GCCGAGTCCCAGGTCAACAA
GTAATTCGAGGGCAGGAACCC
|
Co1 I
|
Sense
Anti-Sense
|
ACTCAGCCCTCTGTGCCT
CCTTCGCTTCCATACTCG
|
Co1 III
|
Sense
Anti-Sense
|
AGATGCTGGTGCTGAGAAG
TGGAAAGAAGTCTGAGGAAGG
|
GAPDH
|
Sense
Anti-Sense
|
GACATCAAGAAGGTGGTGAAGC
TGTCATTGAGAGCAATGCCAGC
|
Statistical analysis
All data are presented as means ± SEM. SPSS 21.0 was used to perform statistical analysis of the data. Statistical differences were calculated with the 2-tailed Student t test when comparing 2 conditions, and ANOVA was used when comparing >2 conditions. A value of P <0.05 was considered statistically significant.