A potential role of fibrillin-1 (FBN1) mRNA and asprosin in follicular development in water buffalo

Abstract

Fibrillin-1 (FBN1) functions as a structural protein in the ovary, while the role of its protein product asprosin remains unknown. Both proteins are encoded by the FBN1 gene and when it is cleaved at the C-terminal end, asprosin is produced. Asprosin is associated with various metabolic parameters and sex-related hormones in women. One goal of this research was to quantify FBN1 and the presumed asprosin receptor, olfactory receptor family 4 subfamily M member 1 (OR4M1) mRNA in water buffalo granulosa cells and correlate them to aromatase (CYP19A1) gene expression. A second goal was to determine the effect of asprosin on follicular growth in vivo. In Exp. 1, ovaries were collected from a local slaughterhouse, follicular fluid and granulosa cells from small (<6 mm) and large (6-13 mm) follicles were aspirated, cellular RNA extracted for gene expression analysis, data analyzed using ANOVA, and Pearson correlation coefficients were calculated among FBN1, OR4M1, and CYP19A1 gene expression. In Exp. 2, an intra-follicular injection of asprosin (600 ng of asprosin/194 μL of PBS) or vehicle (200 μL of PBS; Controls) was given via the theca layer of the dominant follicle of synchronized cows (n = 5/group) 1 day after injection of PGF2α, follicle sizes were measured daily via transrectal ultrasonography for 3 days, a two-way repeated measures ANOVA was used to determine the effect of asprosin on growth rate of follicles from day 0-2, and Chi-square analysis for the percentage of cows ovulated 2 days following asprosin injections. In Exp. 1, FBN1 mRNA abundance was 1.9-fold greater in cells of follicular aspirates from small than large follicles (P < 0.05), but abundance of OR4M1 and CYP19A1 mRNA did not differ (P > 0.10) between the two sizes of follicles. Abundance of FBN1 mRNA was positively correlated with CYP19A1 (r = 0.55, P < 0.05) and OR4M1 mRNA (r = 0.50, P < 0.06) across follicle sizes. In Exp. 2, cows treated with asprosin revealed a greater follicle growth rate from day 0-2 (63.4% increase in diameter) than placebo cows (36.8% increase in diameter) post-injection, and more follicles from asprosin treatment vs. control group (100% vs. 20%; P < 0.05) ovulated within 2 days. These findings suggest that FBN1 may be developmentally regulated in follicular cells, and that asprosin may induce follicular growth in buffaloes, but further studies will be required to determine if asprosin directly regulates estradiol production during follicle development.

Keywords: Asprosin; Fibrillin-1; Granulosa cells; Water buffalo.