Pubertal lead exposure affects ovary development, folliculogenesis and steroidogenesis by activation of IRE1α-JNK signaling pathway in rat

Abstract

Epidemic studies showed that lead exposures are associated with various female reproductive dysfunctions, including infertility, miscarriage, preterm delivery, and early menopause. However, the mechanism involved is still unclear. In the current study, SD rats were exposed to lead at doses of 0, 5, 25, 50 or 250 mg/L through drinking water from postnatal day 21–56. Lead exposures did not affect the body weight or ovary weight. However, the puberty initiation (ages by which vagina opens and estrous cycle occurs) was significantly delayed by as many as 5.8 and 6.8 days respectively (P < 0.05). Also, lead exposures disrupted the estrous cycles, reduced the numbers of primordial and primary follicles and increased the number of atretic follicles by adult. Furthermore, for the highest does group, serum levels of progesterone and testosterone decreased by 80.2% (P < 0.01) and 49.9% (P < 0.05) respectively, while estradiol level increased by 69.8% (P < 0.01). Western blot analyses indicated that lead exposures specifically down-regulated the expressions of steroidogenic protein STAR, CYP17A1, and HSD3B1, while up-regulated FSHR and CYP19A1. Also, the exposure stimulated the endoplasmic reticulum stress (ERS)-related IRE1α-JNK signaling pathway members. Such activation may also result in apoptosis since the death-signaling molecules CHOP and cleaved-CASP3 were up-regulated while BCL2 was down-regulated. In conclusion, lead exposure during juvenile and puberty significantly affected ovary development and functions. The effects may relate to ERS response since the 6 members related to the pathway were all consistently activated.

Keywords

• Lead
• Ovarian development
• Sex steroid hormone synthesis
• Theca cells
• Endoplasmic reticulum stress
• IRE1α-JNK signaling