Actions of Tumor Necrosis Factor-α on Oocyte Maturation and Embryonic Development in Cattle

Authors


  • 1Research was supported by a grant from the USDA National Research Initiative Grants Program (No. 2002-35203-12664). This is journal series number R-03942 of the Florida Agricultural Experiment Station.

Address reprint requests to P.J. Hansen, PO Box 110910, Gainesville, FL 32611-0910, USA.
E-mail: hansen@animal.ufl.edu

Abstract

Problem:  Infertility can accompany mastitis in cattle. Involvement of tumor necrosis factor-α (TNF-α) in this phenomenon is suggested by observations that circulating concentrations of TNF-α are elevated after intramammary infection or infusion of endotoxin. It was hypothesized that (1) TNF-α acts on the oocyte during maturation to decrease the percent of oocytes that cleave and develop following fertilization; (2) exposure of embryos to TNF-α after fertilization reduces development to the blastocyst stage; and (3) TNF-α increases the proportion of blastomeres that undergo apoptosis in a stage-of-development dependent manner.

Method of study:  In one experiment, oocytes were matured with various concentrations of TNF-α and then fertilized and cultured without TNF-α. In another study, embryos were cultured with TNF-α for 8 days beginning after fertilization. Finally, embryos were collected at the two or four-cell stage (at 28–30 hr after insemination) or when ≥9-cells (at day 4 after insemination) and cultured ± TNF-α for 24 hr. The proportion of blastomeres undergoing apoptosis was then determined by the TUNEL procedure.

Results:  Addition of TNF-α to maturation medium did not affect the proportion of oocytes that cleaved. However, the percent of oocytes that developed to the blastocyst stage at day 8 after insemination was reduced (P = 0.05) at all TNF-α concentrations tested (0.1–100 ng/mL). When added during embryo culture, there was no significant effect of TNF-α on the proportion of oocytes that became blastocysts. In addition, TNF-α did not induce apoptosis in two and four-cell embryos. For embryos ≥9-cells, however, 10 and 100 ng/mL TNF-α increased (P < 0.05) the percent of blastomeres labeling as TUNEL-positive.

Conclusion:  TNF-α can have deleterious actions on oocyte maturation that compromise development of the resultant embryo. While exposure of fertilized embryos to TNF-α did not inhibit development to the blastocyst stage, TNF-α increased the percentage of blastomeres undergoing apoptosis when exposure occurred for embryos ≥9-cells. Increased blastomere apoptosis could conceivably compromise subsequent embryo survival.

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