Tumour necrosis factor alpha up-regulates matrix metalloproteinase-2 activity in periovulatory ovine follicles: metamorphic and endocrine implications

Abstract

The collagenous matrix of the wall of periovulatory follicles is degraded and remodelled during ovulatory ovarian rupture and luteinization. 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. Tumour necrosis factor α (TNFα) is a putative mediator of collagenolysis and ovulation. The objective of this investigation was to ascertain the regulatory role of TNFa 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 ₂ α and gonadotropin-releasing hormone (GnRH) on Days 14 and 15.5 (= 0 h) of the oestrous cycle, respectively. Ovulation occurs from the dominant follicle approximately 24 h after GnRH. An immunocapture-activity assay was used to measure MMP-2 in follicular extracts. Bioactive MMP-2 increased from 0 to 20 to 40 h after GnRH. Enzyme was immunolocalized at 40 h to the connective tissue framework that invades the parenchyma of the formative corpus luteum. Activity of MMP-2 was up-regulated by incubation (20 h) of 0-h follicular explants with TNFα; this response was suppressed by the transcriptional inhibitor actinomycin D. Activity of MMP-2 was reduced when preovulatory follicular tissues were incubated (12-h explants for 6 h) with TNFα antiserum. Ovulation was blocked by intrafollicular injection of TNFα antiserum. Unruptured follicles luteinized, but were deficient in collagenous/vascularized trabeculae, and produced less progesterone than their control luteal counterparts. It is suggested that TNFα, via MMP-2 induction, contributes to the reorganization of an ovulatory follicle into a fully competent corpus luteum.