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Changes in the glucose-6-phosphate dehydrogenase activity in granulosa cells during follicular atresia in ewes

Unidad de Investigación Médica en Bioquímica, Hospital de Especialidades, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Avenida Cuauhtemoc 330, Colonia Doctores, C.P. 06720 México DF, Mexico¹ Bioquímica de la Reproducción, Departamento de Producción Agrícola y Animal, Universidad Autónoma Metropolitana-Xochimilco, C.P. 04960 México DF, Mexico² Facultad de Medicina Veterinaria y Zootecnia, UNAM, C.P. 04510 México DF, Mexico³ Unidad de Investigación Médica en Inmunoquímica, Hospital de Especialidades, CMN SXXI, Instituto Mexicano del Seguro Social, C.P. 06720 México DF, Mexico⁴ Laboratorio de Biología del Desarrollo, Unidad de Morfología FES-IZTACALA, UNAM-México, C.P. 54090 México DF, Mexico

Correspondence should be addressed to M Díaz-Flores; Email: mardiaz2001{at}yahoo.com

Apoptosis of granulosa cells during follicular atresia is preceded by oxidative stress, partly due to a drop in the antioxidant glutathione (GSH). Under oxidative stress, GSH regeneration is dependent on the adequate supply of NADPH by glucose-6-phosphate dehydrogenase (G6PD). In this study, we analyzed the changes of G6PD, GSH, and oxidative stress of granulosa cells and follicular liquid and its association with apoptosis during atresia of small (4–6 mm) and large (>6 mm) sheep antral follicles. G6PD activity was found to be higher in granulosa cells of healthy small rather than large follicles, with similar GSH concentration in both cases. During atresia, increased apoptosis and protein oxidation, as well as a drop in GSH levels, were observed in follicles of both sizes. Furthermore, the activity of G6PD decreased in atretic small follicles, but not in large ones. GSH decreased and protein oxidation increased in follicular fluid. This was dependent on the degree of atresia, whereas the changes in G6PD activity were based on the type of follicle. The higher G6PD activity in the small follicles could be related to granulosa cell proliferation, follicular growth, and a lower sensitivity to oxidative stress when compared with large follicles. The results also indicate that GSH concentration in atretic follicles depends on other factors in addition to G6PD, such as de novo synthesis or activity of other NADPH-producing enzymes. Finally, lower G6PD activity in large follicles indicating a higher susceptibility to oxidative stress associated to apoptosis progression in follicle atresia.