The expression of apelin and its receptor APJ during different physiological stages in the bovine ovary

Abstract

Recent studies implicate that apelin and its receptor APJ may have important role for the modulation of angiogenesis. The aim of this study was to further characterise the regulation of apelin/APJ system in bovine ovary. Experiment 1: corpora lutea (CL) were assigned to the following stages: days 1-2, 3-4, 5-7, 8-12, 13-16, >18 (after regression) of oestrous cycle and of gravidity (month <3, 3-5, 6-7 and >8). Experiment 2: Follicles during maturation were divided into granulosa cells (GC) and theca interna (TI) and were examined separately. Classification of follicles occurred by follicle size and oestradiol-17beta (E2) concentration in the follicular fluid (FF) (<0.5 ng/ml, 0.5-5 ng/ml; 5-40 ng/ml; 40-180 ng/ml; >180 ng/ml). Real-time RT-PCR (qPCR) was applied to investigate mRNA expression of examined factors. In general, the expression level of apelin during the oestrous cycle was significantly higher compared to the one during pregnancy. Apelin mRNA levels were always high during the cycle with a tendency of decrease after CL regression. The APJ mRNA in the CL was significantly up regulated on days 5-7 and 8-12 followed by a decrease on days 13-16, and further on days >18. The expression of APJ does not show any significant regulation in the CL throughout pregnancy. The expression of apelin and APJ was not statistically regulated in GC, but was significantly up regulated in follicles with an E2 concentration of more than 5 ng/ml and showed an increase according to growth and maturation of follicles. In conclusion, our data suggest that apelin/APJ system is involved in the mechanism regulating angiogenesis during follicle maturation as well as during CL formation and function in the bovine ovary.

Keywords: angiogenesis; apelin; bovine ovary; corpus luteum; follicle.

Figure 1

Expression of mRNA of (A) apelin and (B) APJ in the CL of oestrus cycle and gravidity. Results are presented by 40 minus mean of crossing points (cp) ± SEM (n=6-7). Different superscripts denote statistically different values (P<0.05).

Figure 2

Expression of mRNA of (A) apelin and (B) APJ in the theka interna (TI) in follicles of different stages of follicle development and maturation. Results are presented by 40 minus mean of crossing points (cp) ± SEM (n=7-12). Different superscripts denote statistically different values (P<0.05). Classification of follicles occurred by follicle size and oestradiol-17β concentration in the FF (<0.5 ng/ml, 0.5-5 ng/ml; 5-40 ng/ml; 40-180 ng/ml; >180 ng/ml).

Figure 3

Expression of mRNA of (A) apelin and (B) APJ in granulosa cells (GC) in follicles of different stages of follicle development and maturation. Results are presented by 40 minus mean of crossing points (cp) ± SEM (n=7-12). Classification of follicles occurred by follicle size and oestradiol-17β concentration in the FF (<0.5 ng/ml, 0.5-5 ng/ml; 5-40 ng/ml; 40-180 ng/ml; >180 ng/ml).