2 TRANSCRIPTOME ANALYSIS OF GRANULOSA CELLS FROM GROWING DOMINANT FOLLICLE REVEALS AGE-ASSOCIATED CHANGES AT THE TIME OF FOLLICLE SELECTION IN AGED BEEF CATTLE

Abstract

Growing dominant follicles at the time of selection from aged (n = 3; 15 ± 1.5 years) and young (n = 3; 6 ± 1.1 years) Hereford cows were compared using bovine-specific microarrays containing 40 000 targets. The objective of the study was to determine age-associated changes in transcriptome of granulosa cells at the time of dominant follicle selection. Cows were given prostaglandin F_2α to cause ovulation (Day 0) and granulosa cells from dominant follicles were collected on Day 3 either by ultrasound-guided follicle aspiration or after ovariectomy. The mRNA was extracted, analyzed for quality, converted into antisense RNA, amplified, labelled with red and green florescent dyes, and hybridized with microarrays. Feature intensities were measured using Array-Pro software (Media Cybernetics Inc., Rockville, MD), and differentially expressed genes were obtained using FlexArray 1.6. A total of 169 transcripts were differentially expressed with a fold change of ≥2 (P ≤ 0.05) in aged cows v. young cows. Ingenuity System Pathway (IPA; Ingenuity Systems Inc., Redwood City, CA) analysis of these transcripts revealed that granulosa cells of aged cows exhibit (1) reduced capability to regulate gonadotropins [↓follistatin (FST), ↓inhibin beta A (INHBA), ↓inhibin beta B (INHBB)] and reduced responsiveness to gonadotropin-induced changes in cytoskeleton [↑tropomyosin 2 (TPM2), ↑actin gamma 2 (ACTG2), ↓tubulin beta] and extracellular matrix [↓tumor necrosis factor alpha-induced protein 6 (TNFAIP6), ↓versican (VCAN)], (2) inefficiency in processing lipids [↓low-density lipoprotein receptor (LDLR), ↓stearoyl-coenzyme A desaturase (SCD), ↑cluster of differentiation 36 (CD36), ↓sterol-C4-methyl oxidase-like (SC4MOL)] and synthesizing steroids [↓cytochrome P450, family 19, subfamily A, polypeptide 1 (CYP19A1), ↓cytochrome P450, family 51, subfamily A, polypeptide 1 (CYP51A1)], (3) decreased proliferation [↓proliferating cell nuclear antigen (PCNA)] and control of cell cycle check points [↓checkpoint kinase 1 (CHEK1), ↓centromere-associated protein E (CENPE)] and have poor intercellular communication [↓gap junction protein alpha 1 (GJA1)], and (4) higher expression of oxidative stress responsive genes [↑vanin-1 (VNN1), ↑vanin-2 (VNN2), and ↑glutathione peroxidase 3 (GPX3)]. A total of 6 transcripts: CYP19A1 (aromatase; P ≤ 0.1), VNN1 (P ≤ 0.05), INHBA (P ≥ 0.1), PCNA (P ≤ 0.001), TPM2 (P ≤ 0.1), and GJA1 (P ≤ 0.05) were selected to validate the microarray results via quantitative real-time PCR. In conclusion, granulosa cells of growing dominant follicles exhibit age-related changes in the transcriptome at the time of selection relative to young cows; changes that may explain follicle-associated loss of oocyte competence in aged cows.

Research was supported by the Natural Sciences and Engineering Research Council of Canada (Ottawa, ON, Canada).