Abstract
Luteal angiogenesis is regulated by pro-angiogenic hormones including fibroblast growth factor 2 (FGF2) and angiopoietin 1 (Ang1), which are regulated by the adipokine leptin during development. Another adipokine, adiponectin, exhibits an inverse relationship with leptin and has been identified in the CL. Therefore, it is hypothesized that adiponectin will influence pro-angiogenic hormones in the developing porcine CL. Crossbred sows were randomly allocated to one of two days of the estrous cycle, day 5 (D5; n = 4) or day 7 (D7; n = 5) for CL collection. Tissue was processed for immunohistochemical localization of adiponectin receptor 2 (AdipoR2), gene expression of FGF2, Ang1, leptin, AdipoR2, and cell culture for adiponectin treatment. The expression of AdipoR2 tended (p = 0.09) to be higher in D7 lutea and was more prevalently localized to the cell surface of large and small luteal cells than in D5 tissue. Adiponectin influenced (p ≤ 0.05) FGF2, leptin, and AdipoR2 gene expression relative to the dose and day (D5 or D7). Collectively, the evidence supports the supposition that adiponectin influences angiogenic factors in the developing CL.
Highlights
The corpus luteum (CL) is a highly vascular ovarian structure formed from an ovulated Graafian follicle that is essential for pregnancy maintenance
Leptin is a potent adipokine with angiogenic properties [6] that regulates the expression of fibroblast growth factor 2 (FGF2) and angiopoietin 1 (Ang1) in dispersed lutea cell cultures, decreasing FGF2 in cells obtained from day 7 (D7) lutea [4]
Both leptin and its receptor are expressed in the bovine, caprine, and porcine CL [4,7,8], but changes relative to the day of development have not been detected despite a reported association with luteal angiogenesis [7,9]
Summary
The corpus luteum (CL) is a highly vascular ovarian structure formed from an ovulated Graafian follicle that is essential for pregnancy maintenance. The daily expression of FGF2 in the developing CL has not been reported in other species; the anti-angiogenic glycoprotein thrombospondin exhibits a similar pattern of expression in granulosa cells of antral follicles [5] This suggests that ovarian angiogenesis may be a precisely timed mechanism associated with the regulation of growth and developmental processes. Leptin is a potent adipokine with angiogenic properties [6] that regulates the expression of FGF2 and Ang in dispersed lutea cell cultures, decreasing FGF2 in cells obtained from D7 lutea [4] Both leptin and its receptor are expressed in the bovine, caprine, and porcine CL [4,7,8], but changes relative to the day of development have not been detected despite a reported association with luteal angiogenesis [7,9]. It is well-documented that adiponectin often exhibits an inverse and antagonistic relationship with leptin in vascular-related processes [11]
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