The secretion of transforming growth factor-beta by bovine luteal cells in vitro

Bhushan K. Gangrade, Elisa D. Gotcher, John S. Davis, Jeffrey V. May

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22 Scopus citations

Abstract

Transforming growth factor-beta (TGF-β), a multifunctional polypeptide growth factor, is produced by follicular cells in the ovary. However, there is little information indicating that TGF-β is produced in the post-ovulatory follicle, i.e. the corpus luteum. In the present communication we present evidence that bovine luteal cells secrete large amounts of TGF-β when maintained in moderate-term monolayer culture. Using TGF-β1 and TGF-β2 subtype-specific antibodies to neutralize the bioactivity it was found that 80-90% TGF-β activity in luteal cell conditioned medium (LCCM) is due to TGF-β1, whereas ≤ 10% TGF-β activity in LCCM is due to TGF-β2. TGF-β subtype nonspecific antibodies effectively and completely neutralized all TGF-β activity in LCCM. The ratio of TGF-β1:TGF-β2 as estimated on the basis of neutralization studies was supported by visual observation of TGF-β1 and TGF-β2 protein bands on Western blotting. Using a modified and rapid mink lung epithelial cell bioassay and authentic TGF-β to generate standard curves, the amount of TGF-β secreted by luteal cells in vitro was quantitated. The concentration of luteal cell secreted proteins in the medium increased with time during 7 days of culture. Likewise, the TGF-β concentration in LCCM increased during 7 days. To study the effect of duration of culture on the rate of TGF-β secretion by luteal cells, conditioned medium was collected at 24 h intervals and replaced with fresh nutrient medium. The rate of TGF-β secretion increased gradually on days 2, 3 and 4 of culture and declined slowly thereafter. Interestingly, measurement of the rate of total protein secretion into the conditioned medium at 24 h intervals showed a steady decline with the duration of culture. The significant decrease in protein secretion by luteal cells during the latter part of prolonged culture resulted in an increase in TGF-β secretion per unit total protein secretion (i.e. ng TGF-β/μg protein). These studies for the first time demonstrate that bovine luteal cells secrete high amounts of latent TGF-β1 and relatively little TGF-β2. It is suggested that luteal cell secreted TGF-β may play a role as an autocrine or paracrine regulator of luteal function and may modify gonadotropin-dependent ovarian follicular functions.

Original languageEnglish (US)
Pages (from-to)117-123
Number of pages7
JournalMolecular and Cellular Endocrinology
Volume93
Issue number2
DOIs
Publication statusPublished - Jun 1993

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Keywords

  • Corpus luteum
  • Growth factor
  • Ovary
  • TGF-β
  • TGF-β bioassay

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology

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