Effect of overexpression of inhibin α (1-32) fragment on bovine granulosa cell proliferation, apoptosis, steroidogenesis, and development of co-cultured oocytes

The objective was to determine the effects of an inhibin α (1-32) fragment gene on proliferation, apoptosis, and steroidogenesis of bovine granulosa cells (GC) isolated from medium and small follicles (diameter >4-8 and 1-4 mm, respectively), and the effect of GC, previously transfected with pEGISI, on oocyte maturation and in vitro embryo development. To enhance expression of the inhibin α (1-32) fragment, GC were transfected with pEGISI. Transfection inhibited (P < 0.05) GC proliferation (88.8 ± 2.1%; mean ± S.E.M.) compared to the control and EGFP groups (100% and 97.5 ± 2.1%) from medium follicles, with no significant effect on GC from small follicles. Apoptosis was higher (P < 0.01) in transfected GC than in controls. Transfection increased (P < 0.05) estradiol synthesis from both medium and small follicles (0.57 ± 0.13 and 0.86 ± 0.13 pg/mL vs. 0.19 ± 0.05 and 0.35 ± 0.09 pg/mL in controls) after culturing for 48 h, with suppression (P < 0.05) in transfected GC after 96 h. Transfection reduced (P < 0.05) progesterone synthesis in GC from both medium and small follicles (24.5 ± 3.4 and 75.4 ± 4.6 ng/mL vs. 45.42 ± 5.33 and 117.32 ± 11.99 ng/mL in controls) after culture for 48 h, with no significant difference after 96 h. Maturation rate of oocytes co-cultured with transfected GC from medium follicles was decreased relative to control (61.5 ± 6.8% vs. 71.2 ± 5.7%, P < 0.05), with no significant effect on embryo development. In conclusion, overexpression of inhibin α (1-32) fragment regulated GC development; effects on subsequent oocyte maturation were both time- and stage-dependent.