Critical Roles of Kisspeptin in Female Puberty and Preovulatory Gonadotropin Surges as Revealed by a Novel Antagonist.

Kisspeptins (Kp) have recently emerged as master regulators of the reproductive axis and among the most potent elicitors of GnRH-gonadotropin secretion. Despite their paramount importance in reproductive physiology and their potential therapeutic implications, development of Kp antagonists has remained elusive, and only recently has the first compound with the ability to blockKpactions invitro and invivo ,namelyp234,beenreported.However,previous invivo studiesallusedacutecentralinjections, whereas characterization of the effects of the antagonist after continuous or systemic administration, which poses pharmaco-logical challenges, is still pending. We report herein a comprehensive series of analyses on the impact of continuous intracerebroventricular infusion of p234 on puberty onset and the preovulatory surge of gonadotropins in the female rat. In addition, the effectsofsystemic(ip)administrationofataggedp234-penetratin,withapredictedhigherpermeabilityattheblood-brainbarrier, on Kp-10 induced gonadotropin secretion were evaluated. Central infusion of p234 to pubertal females delayed vaginal opening and decreased uterine and ovarian weights at the expected time of puberty, without affecting body weight. Likewise, chronic intracerebroventricular administration of p234 for 4 d prevented the preovulatory surges of LH and FSH. In addition, systemic (ip) administration of p234-penetratin significantly attenuated acute LH and FSH responses to Kp-10, either after intracerebroventricular or ip injection of Kp. Our data document the validity of p234 for antagonizing Kp actions in vivo and provide direct experimental evidence for the important role of Kp signaling in the key events of female reproduction, such as puberty onset and the preovulatory surge of gonadotropins. ABSTRACT Aromatase, the enzyme that catalyzes estrogen synthesis, is critical for the progression of estrogen receptor-positive breast cancer (BCa) in postmenopausal women. We show that calcitriol, the hormonally active form of vitamin D, regulates the expression of aromatase in a tissue-selective manner. Calcitriol significantly decreased aromatase expression in human BCa cells and adipocytes and caused substantial increases in human osteosarcoma cells (a bone cell model exhibiting osteoblast phenotype in culture) and modest increases in ovarian cancer cells. Calcitriol administration to immunocompromised mice bearing human BCa xenografts decreasedaromatasemRNAlevelsinthetumorsandthesurroundingmammaryadiposetissuebutdidnotalterovarianaromatase expression. In BCa cells, calcitriol also reduced the levels of prostaglandins (PGs), major stimulators of aromatase transcription, by suppressing the expression of cyclooxygenase-2 (which catalyzes PG synthesis) and increasing that of 15-hydroxyprostaglandin dehydrogenase (which catalyzes PG degradation). The mechanism of aromatase down-regulation by calcitriol in BCa cells is therefore 2-fold: a direct repression of aromatase transcription via promoter II through the vitamin D-responsive elements identifiedinthispromoterandanindirectsuppressionbyreducingthelevelsofPGs.Combinationsofcalcitriolwiththreedifferent aromatase inhibitors (AIs) caused enhanced inhibition of BCa cell growth. The combination of calcitriol and an AI may have potentialbenefitsforBCatherapy.InadditiontoaugmentingtheabilityofAIstoinhibitBCagrowth,calcitriolactingasaselective