Accelerated puberty and late-onset hypothalamic hypogonadism in female transgenic skinny mice overexpressing leptin

Abstract

Excess or loss of body fat can be associated with infertility, suggesting that adequate fat mass is essential for proper reproductive function. Leptin is an adipocyte-derived hormone that is involved in the regulation of food intake and energy expenditure, and its synthesis and secretion are markedly increased in obesity. Short-term administration of leptin accelerates the onset of puberty in normal mice and corrects the sterility of leptin-deficient ob/ob mice. These findings suggest a role for leptin as an endocrine signal between fat depots and the reproductive axis, but the effect of hyperleptinemia on the initiation and maintenance of reproductive function has not been elucidated. To address this issue, we examined the reproductive phenotypes of female transgenic skinny mice with elevated plasma leptin concentrations comparable to those in obese subjects. With no apparent adipose tissue, female transgenic skinny mice exhibit accelerated puberty and intact fertility at younger ages followed by successful delivery of healthy pups. However, at older ages, they develop hypothalamic hypogonadism characterized by prolonged menstrual cycles, atrophic ovary, reduced hypothalamic gonadotropin releasing hormone contents, and poor pituitary luteinizing hormone secretion. This study has demonstrated for the first time to our knowledge that accelerated puberty and late-onset hypothalamic hypogonadism are associated with chronic hyperleptinemia, thereby leading to a better understanding of the pathophysiological and therapeutic implication of leptin.

Figure 1

Reproductive profile of transgenic skinny mice overexpressing leptin (filled columns) and their nontransgenic littermates (open columns). (a) Number of mice with vaginal opening (n = 9); P < 0.05 by log-rank test. (b) Organ weights of ovaries on day 21 (21 d) (filled columns, n = 4; open columns, n = 7) day 29 (29 d) (filled columns, n = 4; open columns, n = 6), and on the diestrus day at 11 weeks (11W) (filled and open columns, n = 4) and 21 weeks (21W) (filled and open columns, n = 4) of age. (c) Organ weights of uteri. Uteri were collected from the same animals in b. (d) Durations of estrous cycle by vaginal smears. Daily observation was performed for 20 days from 8 weeks (8 W) (filled and open columns, n = 4) and 30 weeks (30 W) (filled and open columns, n = 5) of age. ^AP < 0.05, ^BP < 0.01, and ^CP < 0.005 compared with nontransgenic littermates by ANOVA with Fisher’s least significance difference test.

Figure 2

Gross histological findings of ovaries from transgenic skinny mice overexpressing leptin (Tg: e–h) and their nontransgenic littermates (nonTg: a–d). Hematoxylin-eosin staining was performed on paraffin sections. a and e were collected from mice aged 21 days; b and f were from those aged 11 weeks; c and g were from those aged 17 weeks; and d and h were from those aged 25 weeks after 2 cycles of gonadotropin stimulation. Scale bar = 0.5 mm.

Figure 3

Hormonal profile of transgenic skinny mice overexpressing leptin (filled columns) and their nontransgenic littermates (open columns). (a) Hypothalamic GnRH contents. Hypothalami were collected from the same animals in Figure 1b. (b) Serum LH concentrations 15 minutes after intraperitoneal administrations of GnRH. Procedures were performed on day 21 (21 d) (filled columns, n = 10; open columns, n = 8), on the diestrus day at 13 weeks (13 W) (filled columns, n = 6; open columns, n = 4), and on the diestrus day at 25 weeks (25 W) (filled and open columns, n = 10) of age. (c) Serum LH concentrations at 2000 hours on the proestrus day between 13 and 18 weeks of age (filled columns, n = 6; open columns, n = 4). ^AP < 0.05 compared with nontransgenic littermates by ANOVA with Fisher’s least significance difference test. ^BP < 0.005 by Student’s t test.