The primary goal of this project is to elucidate the cross-talk between leptin and 17-estradiol signaling in kisspeptin neurons. Congenital leptin deficiency and/or loss of leptin function due to mutations in leptin can cause obesity and hypogonadotropic hypogonadism. Hypothalamic hypogonadism and its associated disturbances can be reversed by administration of leptin. Leptin signals via its cognate receptors, leptin receptors (LRs). The long isoform (LRb) is the predominant signaling form of the receptor and is abundantly expressed in hypothalamic neurons, including arcuate proopiomelanocortin (POMC) and kisspeptin neurons, but not in gonadotropin releasing-hormone (GnRH) neurons. Therefore, the effects of leptin on GnRH neurons are thought to be mediated indirectly via neurons synapsing on GnRH neurons. Hypothalamic kisspeptin neurons play a critical role in modulating GnRH release and hence the control of reproduction. Moreover, KiSS1 mRNA is reduced in obese and infertile ob/ob mice, and the levels of Kiss1 mRNA increase after administration of leptin. Furthermore, KiSS1 mRNA and kisspeptin protein are highly regulated by 17- estradiol (E2), and recently, we have found that E2 differentially regulates arcuate kisspeptin neurons in the female guinea pig, inhibiting expression during negative feedback and augmenting expression during positive feedback. In addition, we have discovered that leptin depolarizes POMC neurons via a novel signaling pathway that is coupled to activation of canonical transient receptor potential (TRPC) channels, and kisspeptin neurons may be similarly regulated. Therefore, our current work focuses on hypothalamic arcuate kisspeptin neurons and the interaction between E2 and leptin acting through multiple signaling cascades to affect kisspeptin neuronal excitability and ultimately the reproductive cycle. Our multidisciplinary approach incorporates a unique array of cellular and molecular tools and our combined expertise (electrophysiology, molecular biology, histochemistry and whole animal physiology). Our working hypothesis is that the kisspeptin neurons are the """"""""gate-keeper"""""""" of excitatory drive to GnRH neurons in the female, and it is the complex interaction of E2 and leptin in these neurons that control the ovulatory cycle in fed and fasted states. Therefore, our specific aims are the following: (1) To characterize the leptin signaling pathway in arcuate kisspeptin neurons in ovariectomized female guinea pigs. (2) To characterize the effects of E2 on arcuate kisspeptin neurons during positive feedback versus negative feedback. (3) To elucidate the actions of E2 on arcuate kisspeptin neurons during positive feedback in fasted versus fed guinea pigs. (4) To elucidate the effects of E2 and fasting on the expression of K-ATP channels in kisspeptin neurons. Understanding the convergence of leptin and E2 signaling in arcuate kisspeptin neurons will provide insight into the fundamental role of these hormones in conveying metabolic cues to the reproductive axis.

Public Health Relevance

Excessive exercise, eating disorders or weight loss in women can cause amenorrhea, which is characterized by low levels of serum 17-estradiol and anovulation. It is known that during negative energy balance the hormone leptin that is released from fat stores is drastically reduced and may contribute to hypothalamic amenorrhea conditions. However, leptin receptors are not expressed in hypothalamic gonadotropin releasing hormone (GnRH) neurons, which are directly responsible for the control of the ovulatory cycle, but in kisspeptin neurons that are essential for the excitatory input to GnRH neurons. Therefore, the current studies will characterize the cross-talk between leptin and 17-estradiol signaling in kisspeptin neurons in fed and fasted states. Understanding the convergence of leptin and estrogen signaling in arcuate kisspeptin neurons will provide insight into the fundamental role of these hormones in conveying metabolic cues to the reproductive axis.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IFCN-H (03))
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Hyde, James F
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Oregon Health and Science University
Schools of Medicine
United States
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Stincic, Todd L; Rønnekleiv, Oline K; Kelly, Martin J (2018) Diverse actions of estradiol on anorexigenic and orexigenic hypothalamic arcuate neurons. Horm Behav :
Qiu, Jian; Rivera, Heidi M; Bosch, Martha A et al. (2018) Estrogenic-dependent glutamatergic neurotransmission from kisspeptin neurons governs feeding circuits in females. Elife 7:
Qiu, Jian; Bosch, Martha A; Meza, Cecilia et al. (2018) Estradiol Protects Proopiomelanocortin Neurons Against Insulin Resistance. Endocrinology 159:647-664
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Kelly, Martin J; Qiu, Jian; Rønnekleiv, Oline K (2018) TRPCing around the hypothalamus. Front Neuroendocrinol 51:116-124
Padilla, Stephanie L; Qiu, Jian; Nestor, Casey C et al. (2017) AgRP to Kiss1 neuron signaling links nutritional state and fertility. Proc Natl Acad Sci U S A 114:2413-2418
Heppner, Kristy M; Baquero, Arian F; Bennett, Camdin M et al. (2017) GLP-1R Signaling Directly Activates Arcuate Nucleus Kisspeptin Action in Brain Slices but Does not Rescue Luteinizing Hormone Inhibition in Ovariectomized Mice During Negative Energy Balance. eNeuro 4:
Qiu, Jian; Nestor, Casey C; Zhang, Chunguang et al. (2016) High-frequency stimulation-induced peptide release synchronizes arcuate kisspeptin neurons and excites GnRH neurons. Elife 5:

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