The Role of Gonadotropin Pulsations in the Regulation of Puberty and Fertility The key initiating factors for reproductive development remain among the great mysteries of pediatric and reproductive endocrinology. The onset of puberty is initiated by pulsatile secretion of GnRH from the hypothalamus. GnRH secretion is fully active during the neonatal period, quiescent throughout most of childhood, and is reactivated at the time of puberty to induce sexual maturation and subsequent fertility. The neuroendocrine events leading to increased GnRH secretion and the resultant onset of puberty remain largely unknown. Isolated deficiency of GnRH results in the rare clinical syndrome of isolated hypogonadotropic hypogonadism (IHH), where decreased secretion of GnRH results in impaired secretion of luteinizing hormone and follicle-stimulating hormone from the pituitary gland. The resultant hypogonadism presents with delayed, incomplete, or absent sexual maturation. In addition, non-reproductive phenotypic features of this spectrum have been identified in some individuals, including anosmia, auditory defects, and skeletal, neurological and renal anomalies. Defining the physiology of GnRH is critical to understanding the clinical heterogeneity of IHH, particularly in light of emerging gene discoveries that elucidate genotype-phenotype correlations. Careful human phenotyping of patients with mutations in genes known to cause IHH has provided insight into developmental pathways involved in the ontogeny of GnRH neurons, but the neuroendocrine regulation of this system is still not well understood. Our collaboration has resulted in the addition of the NIH as the second site in an existing protocol at MGH to phenotypically characterize subjects with IHH. Clinical studies are now actively underway, enrolling males and females 14 years of age or older with clinical signs suggestive of IHH for comprehensive phenotyping to include neuroendocrine profiling via an LH pulsatility study, as well as identification of other non-reproductive findings. In collaboration with Jay Giedd, we are also evaluating the effect of sex steroid (e.g. testosterone and estrogen) exposure during puberty on neurocognitive outcomes in these patients. We are utilizing the disease model of IHH to increase our understanding of the physiology of GnRH secretion, including the neuroendocrine regulation of GnRH pulsatility, as well as other unknown aspects of GnRH biology, which may be illuminated through the non-reproductive characteristics of these patients. Examining the baseline characteristics of subjects with isolated GnRH deficiency will allow us to make genotype-phenotype correlations that will expand our current paradigm of the hypothalamic-pituitary-gonadal axis, which may have important implications for human disorders of puberty and fertility. The Molecular Basis of Inherited Reproductive Disorders Human and animal models have identified a number of genes responsible for IHH, but more than half of patients with clinical evidence of the disorder do not have a detectable mutation. In addition, there is significant clinical heterogeneity among affected individuals, including members of the same family harboring the same mutations. Recent evidence has expanded our understanding of this spectrum of disorders to include oligo-digenic inheritence, as well as reversibility of the condition, and has provided insight into developmental pathways involved in the ontogeny of GnRH neurons. Genetic analysis of subjects with unknown mutations is likely to yield important insights into additional pathways involved in the regulation of GnRH secretion, as was the case with the identification of mutations in the kisspeptin receptor (KISS1R, or GPR54) in families with IHH, leading to the emergence of kisspeptin (KISS1) as an important gatekeeper of puberty. This is merely one example among many critical discoveries that have been made in this field through molecular exploration. We are conducting genetic investigations of subjects with IHH to characterize further the phenotypic effect of previously described genetic variants, as well as to identify novel genes involved in congenital GnRH deficiency, using both candidate gene and whole exome approaches, as well as linkage analysis. We are also conducting these molecular investigations in individuals with precocious puberty as well as delayed puberty, even in the absence of meeting diagnostic criteria for IHH, in order to explore the molecular mechanisms underlying these more common variants of pubertal development. Patients with IHH provide a unique human disease model, which will elucidate the physiology of GnRH secretion, including the neuroendocrine regulation of GnRH secretion. Examining the genetic characteristics of subjects with isolated GnRH deficiency, as well as other pubertal disorders, and correlating these findings with detailed phenotypic characteristics will reveal insights into the mechanisms underlying the reawakening of the hypothalamic-pituitary-gonadal axis at puberty. This will provide opportunities for new diagnostic capabilities and therapeutic interventions for disorders of puberty and reproduction. Blockade of Kisspeptin Signaling in Women The neuropeptide hormone kisspeptin potently stimulates secretion of GnRH from neurons in the hypothalamus. While single doses of kisspeptin stimulate the reproductive endocrine axis, animal models suggest that continuous administration of kisspeptin paradoxically suppresses the reproductive endocrine axis temporarily through desensitization of the kisspeptin receptor. By administering 24-hour infusions of kisspeptin to healthy women and to patients with reproductive disorders, we hope to learn more about the role of kisspeptin both in normal physiology and in pathological conditions. Polycystic ovary syndrome (PCOS) is a common condition characterized by ovulatory dysfunction and hyperandrogenism, and is frequently associated with obesity and insulin resistance. Among other disturbances of hormonal regulation, patients with PCOS have high amplitude, high frequency LH pulses which may contribute to the oligo-anovulation characteristic of this disorder. Here, we also seek to determine if abnormal kisspeptin signaling is involved in these disturbed endocrine dynamics, as greater understanding of how kisspeptin modulates GnRH secretion in this condition could lead to novel therapeutic interventions for this patient population. In collaboration with Stephanie Seminara, and funded by NICHD through a Bench to Bedside project proposal, we are developing a new clinical trial to explore the use of continuous kisspeptin to manipulate the reproductive cascade in healthy female volunteers, as well as in women with chronic anovulation due to PCOS. The study will begin with healthy postmenopausal women to determine the safety and effectiveness of continuous kisspeptin administration in women. Subsequently, the peptide will be given to women in the periovulatory phase of the menstrual cycle and to women with PCOS. Subjects will undergo a frequent blood sampling study to determine the effect of a 24-hour infusion of kisspeptin on GnRH-induced LH pulsatility. In summary, this study will utilize a cutting-edge physiologic tool to answer key questions about the neuroendocrine control of reproduction in the human female. The information gained from these protocols has the potential to significantly broaden our knowledge of the neuroendocrine control of human reproduction.
| Lippincott, Margaret F; Chan, Yee-Ming; Delaney, Angela et al. (2016) Kisspeptin Responsiveness Signals Emergence of Reproductive Endocrine Activity: Implications for Human Puberty. J Clin Endocrinol Metab 101:3061-9 |
