Influence of distance from calving on the trascriptional activity of granulosa cells from preovulatory follicles of dairy cows

Negative energy balance (NEB) in dairy cattle early lactation period is associated with a multitude of endocrine, metabolic and immunological changes that not only influence animal health, but also affect fertility, and in particular ovarian function. There is a lack of information on the the transcriptional activity of granulosa cells during the first month after calving, when dairy cow pass from a severe NEB condition to a correct methabolic omeostasis. In this research, GCs of preovulatory follicles have been collected at 30 (30 d), 60 (60 d), 90 (90 d) and 120 days (120 d) after calving from 12 Holstein Freisian cows. To map the differences in genes expression and cellular functions that occur in the follicular microenvironment during the progressive recovery from NEB condition in dairy cow an analysis of the transcriptome was performed using a global bovine oligo array microarray. Considering that after 4 months from parturition the dairy cows have recovered from the NEB condition, the GC samples collected at 120 d were used as a positive control in microarray analysis. The results obtained allowed the identification of a list of differentially expressed transcripts for each GC group contrast: 30 d vs 120 d, 60 d vs 120 d and 90 d vs 120 d. To provide a comprehensive understanding on the interferences of lacatation on the the processes involved in the maturation of ovarian dominant follicle, different gene pathways and molecular and cellular function by Ingenuity Pathways Analysis (IPA) software were used to reveal the different roles of transcripts. The comparison between 30 d and 120 d groups evidenced up and down regulations differences of transcripts in small molecule biochemistry, DNA replication, recombination and repair, and cellular assembly and organization. The contrast analysis between 90 d and 120 d group revealed modifications in up and down regulations genes activities linked to cell cycle progression, cell proliferation and cell interaction, which are indicative of cells preparing for ovulation. The granulosa cells of 60 d group revealed a significant increase in up and down regulations of genes associated with apoptosis, ovarian cancer and a slow cell follicular development compared to the 120 d group; differences which suggest activaton of apoptotic chain typical of cell in suffering conditions more than those of a normal preovulatory follicular stage. Overall the results and findings of the current study lead to the conclusion that microarray analysis is a useful and valid method for the study of the different gene expression profiles in granulosa cells, from collected preovulatory follicles in dairy cow at different distance from calving. These results offer the opportunity to future studies aimed to the understanding of which molecular mechanisms or external factors negatively influence ovarian development during the time interval between the 30 d and 60 d postpartum period in dairy cow.