|ABEDAL-MAJED, MOHAMED - University Of Amman|
|KURZ, SCOTT - University Of Nebraska|
|SPRINGMAN, SHELBY - University Of Nebraska|
|MCNEEL, ANTHONY - Former ARS Employee|
|LARGEN, VALERIE - University Of Nebraska|
|MAGAMAGE, MANJULA - Sabaragamuwa University Of Sri Lanka|
|SARGENT, KEVIN - College Of The Ozarks|
|WOOD, JENNIFER - University Of Nebraska|
|Cushman, Robert - Bob|
|CUPP, ANDREA - University Of Nebraska|
Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2019
Publication Date: 3/1/2020
Citation: Abedal-Majed, M.A., Kurz, S.G., Springman, S.A., McNeel, A.K., Freetly, H.C., Largen, V., Magamage, M., Sargent, K.M., Wood, J.R., Cushman, R.A., Cupp, A.S. 2020. Vascular endothelial growth factor A isoforms modulate follicle development in peripubertal heifers independent of diet through diverse signal transduction pathways. Biology of Reproduction. 102(3):680-692. https://doi.org/10.1093/biolre/ioz211.
Interpretive Summary: Over-feeding replacement heifers during the development phase can be detrimental to their reproductive longevity. Past research from our laboratories has demonstrated that placing heifers on a stair step diet between weaning and breeding decreases development costs and adapts the heifers to the reduced caloric environments they can encounter as cows on grass in some years. We have demonstrated further that feeding replacement heifers the stair step diet during the development phase increases the number of eggs in their ovaries when the heifers enter their first breeding season. One mechanism by which this might happen is a slowing of the entry of eggs into the growing pool, a process known as activation. The current study was performed to examine the rate of activation of eggs in cultured ovarian pieces from heifers that were provided the stair step diet during the development phase or from heifers that were developed at a constant rate of gain. In this culture system, there was no difference in the rate of activation between development diets; however, the increased insulin and nutrients in the culture system may have overcome the physiological differences established in the heifers prior to placing the pieces of ovary in culture. A better understanding of the physiological response to these diets is crucial to more efficiently develop highly fertile replacement heifers.
Technical Abstract: Follicular progression during peripuberty is affected by diet. Vascular endothelial growth factor A (VEGFA) induces follicle progression in many species; however, there are limited studies to determine if diet may alter the effects of angiogenic VEGFA165-stimulated follicle progression or antiangiogenic VEGFA165b follicle arrest. We hypothesized that diet affects the magnitude of angiogenic and antiangiogenic VEGFA isoform actions on follicular development through diverse signal transduction pathways. To test this hypothesis, beef heifers in our first trial received Stair-Step (restricted and refeeding) or control diets from 8 to 13 months of age. Ovaries were collected to determine follicle stages, measure vascular gene expression and conduct ovarian cortical cultures. Ovarian cortical cultures were treated with phosphate-buffered saline (control), 50 ng/ml VEGFA165, VEGFA165b, or VEGFA165 + VEGFA165b. The Stair-Step heifers had more primordial follicles (P < 0.0001), greater messenger RNA abundance of vascular markers VEcadherin (P < 0.0001) and NRP-1 (P < 0.0051) than controls at 13 months of age prior to culture. After culture, VEGFA isoforms had similar effects, independent of diet, where VEGFA165 stimulated and VEGFA165b inhibited VEGFA165-stimulated follicle progression from early primary to antral follicle stages. In vitro cultures were treated with VEGFA isoforms and signal transduction array plates were evaluated. VEGFA165 stimulated expression of genes related to cell cycle, cell proliferation, and growth while VEGFA165b inhibited expression of those genes. Thus, VEGFA isoforms can act independently of diet to alter follicle progression or arrest. Furthermore, follicle progression can be stimulated by VEGFA165 and inhibited by VEGFA165b through diverse signal transduction pathways.