150 α6 Integrin for evaluating sperm quality in bulls with different capacities of in vitro embryo production

Abstract

The α6 integrin, an adhesion molecule, is expressed on bovine sperm, but major questions about the role of integrins in sperm-oocyte fusion remain unsolved. In this work, we show the results of characterisation of sperm α6 integrin from 4 bulls with different capacities of in vitro embryo production using flow cytometric analysis. The bull capacities judged by the rate of blastocyst formation after in vitro embryo production with semen from 5 ejaculates per animal were 44.3, 17.1, 13.2, and 15.0% for bulls 1, 2, 3, and 4, respectively (P < 0.05). For flow cytometric analysis, surface expression of α6 integrin was evaluated using a fluorescence-activated cell sorter (FACScan, Coulter Electronics) using a 520-nm excitation from an argon laser at 150 mW for excitation. Frozen-thawed sperm were centrifuged at 700 × g for 10 min and washed once in warm phosphate buffered saline (PBS). Briefly, the spermatozoa (5 × 10⁵ cells per sample) were resuspended in 100 μL of PBS containing 1% bovine serum albumin. After washing 3 times, the live cells were incubated at room temperature for 1 h with 100 μL (1:500) of α6 monoclonal antibody (Chemicon) in PBS (0.1 M, pH 7.4) with 1% bovine serum albumin. After washing three times, the cells were incubated at 4°C for 1 h in the dark with the fluorescein isothiocyanate-conjugated F(ab)2 fragment of affinity isolated goat anti-mouse antibody (Invitrogen). The cells were washed three times, resuspended in 100 μL of PBS, and analysed. For each sample, 10 000 cells were recorded at a flow rate of 200-300 cells s⁻¹ using forward scatter (cell size) and side angle of light scatter (cell density), the first using a logarithmic amplifier and the second using a linear amplifier. The fluorescence data were collected using the logarithmic amplifier. The percentage of positive cells and the mean fluorescence channel on a 1023-channel scale were calculated using Epics Profile II software (Epics II Software). To define the forward and side-scatter regions corresponding to sperm, binding of fluorescein isothiocyanate-conjugated Pisum sativum agglutinin to the acrosome was used for setting the bitmap on the dot plot. Initially, the percentage of spermatozoa stained with α6 antibody was calculated on a per-individual basis. Subsequently, the mean ± standard deviation was calculated for each group. The Mann-Whitney U test was used to compare the differences in the expression of α6 between groups. Expression of α6 integrin was higher in bull 1 (control) than in bulls with low capacities of in vitro embryo production. The spermatozoa from bull 1 was distributed in a single broad peak with a mean fluorescence intensity of 36.16 ± 4.17%. The increased distance of the fluorescence intensity in bull 1 compared with the weak fluorescence peaks in the others bulls reflects the increased width and distance of the population distribution. In conclusion, α6 integrin may be used as a biomarker to evaluate sperm quality.

This study was supported by FAPESP grants 2010/01077-9, 2011/18085-7, and 2016/00976-6.