Leptin attenuates follicular apoptosis and accelerates the onset of puberty in immature rats

Human and rat granulosa cells express receptors to leptin which synergies w ith glucocorticoid hormones in stimulation of ovarian steroidogenesis. To e xamine whether leptin affects follicular development and maturation, we inj ected recombinant ovine leptin (300 ng- 10 mug/animal) daily to immature 21 day-old female rats. Non-treated rats reached puberty at 44.5 +/-1.6 (n=9) days. In contrast, in leptin treated animals, puberty was reached at 34.5 +/-1.6 (n=9) days. Ovarian sections revealed hypertrophy of granulosa cells in leptin treated animals. Moreover, the number of ovulations was 2-fold h igher in the treated animals compared to controls (3-4 ovulations versus 7- 8 on the first three estrous cycles, P<0.001). Leptin dramatically reduced incidence of follicular apoptosis measured by TUNEL, and was already eviden t after 7 days of leptin injection (12% of apoptosis in leptin treated grou p compared to 52%, in controls, P<0.001). Maximal protection against apopto sis was achieved at 1-3 mug leptin/animal. The levels of FSH, LH, progester one and the steroidogenic factors ADX and STAR were elevated earlier in dev elopment in the leptin treated animals compared to control animals which is in line with the achievement of early puberty in the leptin treated animal s compared to non treated ones. To reveal whether modulation of death and s urvival genes is involved in leptin attenuation of follicular apoptosis, we examined the expression of the survival gene Bcl-2 and the death gene Bax in Western blots of ovarian homogenates. There was a pronounced elevation i n Bcl-2 expression during 7-14 days of leptin injections up to 16.3-fold (P <0.001) compared to Bcl-2 expression in controls. Bax expression was elevat ed only 3.4 fold (P<0.001), leading to an increase in the Bcl-2/Bax ratio o f 4.7 fold (P<0.001). Expression of the tumor suppressor gene p53 and the o ncogene Mdm2 did not change significantly. Our data suggests that leptin ma y be involved in accelerating follicular maturation by attenuating follicul ar atresia and increasing the ratio of Bcl-2/Bax. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.