Submission Number: MUR-4-23-4

Abstract Number: 183

TUMOR NECROSIS FACTOR UP-REGULATES MATRIX METALLOPROTEINASE-2 ACTIVITY IN PERIOVULATORY OVINE FOLLICLES: METAMORPHIC AND ENDOCRINE IMPLICATIONS.

Michelle L Gottsch, Edward A Van Kirk and William J Murdoch*

Department of Animal Science, University of Wyoming, Laramie, WY ¹

Abstract:
Collagenous tissue remodeling is associated with the processes of ovulatory follicular rupture and formation of the corpus luteum (CL). Matrix metalloproteinase-2 (MMP-2) belongs to a family of zinc endopeptidases that cleave extracellular proteins; its primary substrate is the type IV collagen of basement membranes that supports epithelial cells and endothelium. Tumor necrosis factor alpha (TNF) is a putative mediator of collagenolysis and ovulation. The objective of this investigation was to ascertain the regulatory role of TNF on MMP-2 activity relevant to the folliculo-luteal transition in ewes. Luteal regression and the preovulatory surge of gonadotropins were induced by administration of prostaglandin F and gonadotropin-releasing hormone (GnRH) on days 14 and 15.5 (= 0 h) of the estrous cycle, respectively. Ovulation occurs from the dominant follicle at approximately 24 h after GnRH. An immunocapture-urokinase detection/chromogenic peptide substrate assay was used to measure MMP-2 in tissue extracts. Follicular MMP-2 increased during the periovulatory period (0.47 0.07, 0 h; 10.12 1.92, 20 h; 19.44 3.61 ng/mg, 40 h) and after incubation with TNF (0-h explants for 20 h: 0.59 0.15 control vs. 2.39 0.64 ng/mg). Activity of MMP-2 was reduced when preovulatory follicles were incubated with TNF antiserum (12-h explants for 6 h: 4.06 0.61 control vs. 0.09 0.03 ng/mg). In-vivo ovulation was blocked by intrafollicular injection of TNF antiserum. Unruptured follicles luteinized, but produced (based on jugular serum concentrations) less progesterone than their (control) CL counterparts (0.89 0.17 vs. 1.74 0.34, day 5; 1.59 0.16 vs. 3.67 0.35 ng/ml, day 8 of the luteal phase). Mean contrasts (n = 4-5) were different at P < 0.05. Histological observations of the wall of luteinized follicles (day 8) indicated a deficiency of connective tissue trabeculae and associative blood vessels. We suggest that TNF, via MMP-2 induction, contributes to the reorganization of an ovulatory follicle into a fully-competent CL.

Keywords: tumor necrosis factor, matrix metalloproteinase-2, ovulation, corpus luteum, sheep

This abstract is being presented at: 8:00 AM in session:
Ovulation