Chemicals
All chemicals and reagents were obtained from Qiagen (Hilden, Germany), Thermo Fisher Scientific(Wilmington, USA), unless otherwise stated.
Ethical approval for use of animals
The present study was approved by the Ethical Use and Animal Care Committee of faculty of veterinary medicine, Cairo University.
Animals and management
This study was conducted on 80 Arabian mares; young (4–7 years), and old (8–14 years). These mares were divided into 48 sub-fertile mares {young (n = 16), old (n = 32)} suspected of endometritis (diseased group) and 32 fertile mares {control; young (n = 24), old (n = 8)} not suspected of endometritis that served as control group between November 2019 and April 2020 at a number of stud farms nearby Giza, Egypt. Uterine swabs and blood samples were collected only once from each mare after owner's permission. The selected mares experienced normal physical and vital signs where the normal range of vital signs including rectal body temperatures (37.5–38.5°C), heart rate (36–40 beats/min), respiratory rate (8–15 breaths/min), capillary refill times (1–2 sec) and a moist with a healthy pink color mucus membrane of the buccal cavity. An orthopedic examination was also performed to exclude mares with lameness or active laminitis. None of the mares had dystocia, retained fetal membranes or problems during puerperium. Additionally, none of the mares was in foaling heat. All animals were submitted to transrectal ultrasonographic (US) uterine examination using real-time B-mode machine (Esaote Mylab30- Netherlands) equipped with 5-7.5 MHz linear-array transducer.
Blood and endometrial swabs sampling
Blood samples were collected from the jugular vein into untreated vacutainer tubes and the tubes were maintained for 20 min at room temperature in an inclined position. The samples were subsequently centrifuged at 3000 ×g for 10 min (4°C) until clear serum was separated. Afterwards, serum was divided into two portions; 1st part was kept at – 20°C for measuring IL-6, PGF2α and PGE2 concentrations, and the 2nd part was kept at – 80°C for RNA isolation.
Endometrial swabs were collected as described before[16] using a sterilized double guarded uterine swab (Minitub GmbH, Germany), Briefly, after removing the feaces, the tail was bandaged, and then vulva and perineum were cleaned with iodopovidine (Betadine, EGIS, Warsaw, Poland), rinsed three times with water, and dried with a paper towel.
The tip of the swab was held and covered in the palm, and using a slight rotatory movement, the hand passed into the vagina till enabling palpation of the external cervical os, the index finger passed gently into the external cervical os followed by the uterine swab.
After passing the cervical canal, the cotton swab pushed forward through the outer then the inner guards to be contacted with the endometrium then gently rotated for 10–15 seconds. Finally, the swab was retracted back inside the inner guard then into the outer guard and the swab directly immersed into commercial transportation media.
Cytological examination
After the collection of uterine smears, the cytological samples were fixed and stained with a special commercial cytological stain; Papanicolaou method (Biodiagnostic, Egypt) according to the instruction’s recommendation within two hours at the laboratory. Samples were evaluated in regard to quality of cell morphology, cellularity, number of inflammatory cells per 400× field, as well as any other remarkable features (Zeiss Axioskopmicroscobe, Carl Zeiss, Thornwood, NY)[17].Uterine samples were considered as marker for inflammation (endometritis) if the amount of PMNs was greater than 2% as described by Aguilar et al.[18], data not shown.
Microbial culturing
Immediately after immersing the uterine smears into the transportation media, samples were transported to the laboratory for further microbial analysis. Both bacterial and fungal culturing protocol were carried out to identify the pathologically infected mares showing endometritis according to the general guidelines[19], data not shown.
Here in the current work, the criteria for mares to be enrolled in the diseased group (endometritis) were that they had been bred three or more times unsuccessfully in the breeding season, or had a history more than one year of reproductive failure. In addition, two or more of the following criteria on a checklist were present: abnormal clinical findings, US scanning showed abnormal fluid in the uterus (echogenic or ≥ 2 cm in diameter), positive endometrial cytology; and bacterial and/or fungal growth, as indicated by Amorim et al. [20].
Serum IL-6, PGF2α and PGE2 estimation
Serum concentrations of IL-6 were determined by horse IL-6 ELISA kit (SunLong Biotech Co., LTD, Zhejiang, China) and as used according to the manufacturer’s instructions.
The assay sensitivity and range were 0.5 pg/ml and 1.6 pg/ml to 100 pg/ml, respectively. For PGF2α measurement, the commercial PGF2α high sensitivity horse prostaglandin F2 alpha ELISA kit (SunLong Biotech Co., LTD, Zhejiang, China) was used and run according to the manufacturer’s instructions. The assay sensitivity and range were 0.5 pg/ml and 3 pg/ml to 210 pg/ml. For PGE2 measurements, the commercial PGE2 high sensitivity horse prostaglandin E2 ELISA kit (SunLong Biotech Co., LTD, Zhejiang, China) was used and run in accordance to the manufacturer’s instructions. The assay sensitivity and range were 0.1 pg/ml and 0.8 pg/ml to 50 pg/ml, respectively.
In-silico analysis for the selected candidate miRNA
The miRNA prediction tools such as: DIANA-microT v3.0 (http://diana.cslab.ece.ntua.gr/microT/) and miRecords (http://mirecords.biolead.org/) were used for filterations miRNAs hits according to their potential relevance for targeting inflammatory immune response in mammalian uterine tissue at least in four different search algorithms. We found that of eca-miR-155, eca-miR-223, eca-miR-17, eca-miR-200a, and eca-miR-205could be selected as potential targets. Moreover, these targets were shown different expression pattern in response to inflammation[14, 21–23].
Serum miRNA isolation, cDNA synthesis, and quantitative real-time PCR (qRT-PCR)
For purification of cell-free miRNAs, we used a miRNeasy serum/plasma kit. 200 µl of thawed serum samples on ice were used for purification total RNA according to manufactures protocol. During purification steps, a 3.5 µl of lyophilized C. elegans miR-39 miRNA mimic (miRNeasy Serum/PlasmaSpike-In Control) were added, at concentration 1.6×108 copies/µl. In order to elute cell-free RNA, 14µl of RNase-free water was added to the center of the spin column membrane. Afterwards, the purified serum free total RNA was kept at -80°C.The concentration of total RNA was checked by Nano-drop 2000/c (Thermo Fisher Scientific, Wilmington, USA).We selected the samples, which their ratios of absorbance at 260 and 280 nm (A260/280), and 260 and 230 nm (A260/230) were above 1.7. Furthermore, the integrity of RNA was evaluated by denaturing 1.5% agarose gel electrophoresis and ethidium bromide staining.
Around Ten ng of total RNA was reverse transcribed using MultiScribe reverse transcriptase, and RT primers were performed separately for each miRNA according to the supplier’s instructions.
Real-time PCR was done in a final volume of 10 µl, using 0.7 µl of RT product, 0.5 µl of specific primers with probes (Table 1), and TaqMan Universal PCR Master Mix II. Amplification was performed with initial denaturation for 10 min at 95°C, followed by 40 cycles of 15 sec at 95°C and 60 sec at 60°C with Stratagene Mx3000P (Agilent Technologies, USA), PCR reactions were performed in quadruplicates. The data were analyzed by the comparative threshold cycle (ΔCt) method and normalization was performed using geometric means of cel-miR-39-3p, eca-miR-195, and U6.
Table 1
List of miRNA names, miRBase accession numbers and mature sequences.
miR name
|
Accession number
|
Mature miRNA sequence
|
eca-miR-223
|
MIMAT0013205
|
UGUCAGUUUGUCAAAUACCCCA
|
eca-miR-155
|
MIMAT0013182
|
UUAAUGCUAAUCGUGAUAGGGGU
|
eca-miR-200a
|
MIMAT0012909
|
UAACACUGUCUGGUAACGAUGU
|
eca-miR-17
|
MIMAT0013084
|
CAAAGUGCUUACAGUGCAGGUAG
|
eca-miR-205
|
MIMAT0012962
|
UCCUUCAUUCCACCGGAGUCUG
|
Statistical analysis
The NormFinder was used to select the most stable reference gene for normalization miRNA data[24].The raw data of fluorescence values (Rn) were imported into PCR Miner in order to calculate efficiency[25].The normal distribution was checked via Shapiro-Wilk test and Gaussian distribution; and all data was passed normality test (alpha = 0.05), (GraphPad Software, Inc., San Diego, CA, USA). The expression of selected miRNAs and the levels of serum IL-6, PGF2α and PGE2were analyzed using two-way ANOVA, followed by Sidak's multiple comparisons test. The values shown in graphs are presented as the mean ± standard error of the mean (S.E.M) of at least five independent experiments each done in quadruplicate, P values ≤ 0.05 were considered statistically significant. GraphPad Prism 9.0 was used to perform statistical analysis as well as generating bar graphs