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Abstract
The objective of this study was to determine the effect of changes in diet before puberty in heifers, excess A4 in cows and VEGFA isoforms on follicle progression in bovine ovarian cortex cultures. Two different studies were conducted to better understand how these factors affect bovine follicle development. The first study we evaluated the effect of changes in diets before puberty on follicle development and determined that diet treatment beef heifers had more primordial follicles than control beef heifers at 13 months of age. VEGFA165 can stimulate follicle progression independent of diet. Diet treatment had different VE-CADHERIN and NRP-1 mRNA expression in the ovarian cortex of beef heifers at 13 months. The second study we evaluated follicle development in the ovary of cows with excess A4 in the follicular fluid (FF) and found that uncultured ovarian cortex from High A4 cows had more primordial follicles and fewer primary, secondary and antral follicles when compared to control cows. However, after 7 days of culture in PBS, High A4 ovarian cortex had more primordial follicles indicating that culture conditions did not relieve the follicular arrest in High A4 ovarian cortex compared to the control cows. There was an increase in the expression of CYP17 in the stroma of High A4 cows. There was also positive staining for oxidative stress and fibrosis in the ovarian cortex of High A4 cows. In summary, we showed that (1) the postweaning diet can affect the number of primordial follicles; (2) VEGFA165 can stimulate follicle progression independent of diet; and (3) VEGFA165B can antagonize the actions of angiogenic isoform VEGFA165. We also demonstrated that cows with androgen excess in the follicular fluid: (1) have excess A4 in the culture media from ovarian cortex as well as impaired follicle development both in vivo and in vitro; (2) have increased expression of CYP17A1 in the stroma of ovarian cortex; (3) and VEGFA165 may be a potential therapeutic to restore the ovarian microenvironment and enhance follicular maturation. Thus, excess A4 environment which may be due to aberrant expression of CYP17A1 in the stroma could potentially lead to oxidative stress and fibrosis which prevents normal follicle development.
