Inflammation during oocyte maturation reduces developmental competence and increases apoptosis in blastocysts†.

Abstract

Uterine infections cause ovarian dysfunction and infertility. The bacterial endotoxin, lipopolysaccharide, accumulates in the follicular fluid of dominant follicles of cows with uterine infections. Granulosa cells produce an innate inflammatory response to lipopolysaccharide, altering the follicular microenvironment of the oocyte. We hypothesized that developmental competence and embryo quality would be reduced when oocytes are matured in an inflammatory environment. Bovine mural granulosa cells were exposed to either 1 μg/mL of lipopolysaccharide or medium alone for 24 h to produce a conditioned medium. Inflammatory responses of mural granulosa cells were confirmed by increased expression of CXCL8, IL1B, IL6, and TNF. Bovine cumulus-oocyte complexes were matured for 22 ± 1 h in a medium supplemented with either 1 μg/mL of lipopolysaccharide, 10% v/v conditioned medium of granulosa cells treated with either lipopolysaccharide (LCM) or medium alone, or no supplementation. In addition, polymyxin B (20 μg/mL) was added to the maturation medium to sequester LPS. Following maturation, cumulus-oocyte complexes were fertilized and cultured for 7.5 days with no further treatment. Oocyte maturation using lipopolysaccharide or LCM impaired development to the blastocysts stage, reduced the number of total and CDX2-negative blastomeres, and increased TUNEL-positive cells in blastocysts. Polymyxin B could rescue these effects in the lipopolysaccharide group but not in the LCM group, indicating factors produced by granulosa cells and not lipopolysaccharide alone compromised oocyte development. These findings suggest that the inflammatory milieu produced by granulosa cells in response to lipopolysaccharide impairs oocyte competence and the quality of resultant blastocyst-stage embryos.