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Evidence for Autocrine or Paracrine Roles of ₂-Macroglobulin in Regulation of Estradiol Production by Granulosa Cells and Development of Dominant Follicles

Molecular Reproductive Endocrinology Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan 48824-1225

Address all correspondence and requests for reprints to: J. J. Ireland, Molecular Reproductive Endocrinology Laboratory, Department of Animal Science, Michigan State University, East Lansing, Michigan 48824-1225. E-mail: ireland{at}msu.edu.

₂-Macroglobulin (₂-M) inhibits proteinases and modulates the actions of growth factors and cytokines. Despite the key roles proteinases, growth factors, and cytokines have in folliculogenesis, the role of ₂-M in follicular development is unknown. Our objectives were to: 1) determine whether granulosa cells produce ₂-M and have ₂-M receptors, 2) examine the effect of ₂-M on estradiol production by granulosa cells, 3) establish whether amounts of ₂-M and ₂-M receptors were altered during dominant nonovulatory follicle development, and 4) examine ₂-M’s mechanism of action. The results demonstrated that bovine granulosa cells contain 5.2- and 15-kb mRNAs and 720- and 500-kDa proteins that correspond, respectively, to sizes of mRNAs and proteins for ₂-M and the ₂-M receptor. Treatment of granulosa cells with ₂-M resulted in a specific dose-responsive increase in estradiol production. Cell viability, cell number, and the amount of aromatase in granulosa cells were not altered by ₂-M. Treatment of granulosa cells with factors that bind ₂-M or its receptor did not mimic ₂-M action. Although intrafollicular amounts of ₂-M remained unchanged, amounts of ₂-M receptor in granulosa cells were strongly inversely associated with concentrations of estradiol in dominant and subordinate follicles. Based on these results, we concluded that ₂-M may have autocrine or paracrine roles in granulosa cells potentially important for regulation of estradiol production and development of dominant follicles.

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