Lipopolysaccharide Reduces the Primordial Follicle Pool in the Bovine Ovarian Cortex Ex Vivo and in the Murine Ovary In Vivo

Infections of the uterus or mammary gland with Gram-negative bacteria cause infertility in cattle, not only during disease but also for some time afterward. Even though these infections are in organs distant from the ovary, metritis and mastitis perturb antral follicle development and function in vivo. Although granulosa cells from antral follicles express toll-like receptor 4 (TLR4), and detect and mount an inflammatory response to lipopolysaccharide (LPS) from Gram-negative bacteria, it is not known whether LPS impacts preantral follicle development. The present study tested the hypothesis that LPS perturbs the development of primordial ovarian follicles. Exposure of bovine ovarian cortex ex vivo to LPS reduced the primordial follicle pool associated with increased primordial follicle activation. Ovarian cortex culture supernatants accumulated the inflammatory mediators IL-1beta, IL-6, and IL-8 in an LPS concentration-dependent manner. In addition, LPS exposure modulated key intracellular regulators of follicle activation with loss of the primordial follicle PTEN and cytoplasmic translocation of FOXO3. Acute exposure of mice in vivo to LPS also reduced the primordial follicle pool associated with increased follicle atresia. The increased follicle atresia was TLR4-dependent as Tlr4-deficient mice were insensitive to LPS-mediated follicle atresia. However, LPS did not affect the diameter of individually cultured bovine secondary follicles or their enclosed oocytes. In conclusion, LPS reduced the primordial ovarian follicle pool in the bovine ovarian cortex ex vivo and in the murine ovary in vivo. These observations provide an insight into how bacterial infections distant from the ovary have long term effects on fertility.