Development of the GnRH neuronal network and effects of prenatal androgen exposure

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Project Summary Gonadotropin-releasing hormone (GnRH) neurons form the final common central pathway regulating fertility. Properly patterned GnRH release is required for fertility and is often disrupted in women with polycystic ovary syndrome (PCOS). Hyperandrogenic PCOS affects ~8-10% of women. In these women, there is a persistent high frequency of luteinizing hormone (LH), and likely GnRH, release. Prenatally androgenized (PNA) mice have neuroendocrine phenotypes similar to women with PCOS, including high LH pulse frequency, and can be used to study mechanisms of this increase. Pathophysiology similar to PCOS is being detected at younger ages, suggesting the antecedents of this disorder may be developmentally programmed. In the previous work from a different funding mechanism (NCTRI), we characterized the development of GnRH neuron activity and GABA transmission to these cells, showing that PNA disrupts both parameters before puberty, and that PNA- induced changes before and after puberty are different. The neurobiological mechanisms underlying these observations are largely unknown. Our working model to explain these findings is that 1) PNA alters the biophysical properties of GnRH neurons and their afferents; 2) altered epigenetic programing at least in part underlies these changes; 3) PNA increases excitatory GABA synaptic drive to GnRH neurons before puberty and this increase continues in adults; 4) before puberty in PNA mice, GnRH neurons initiate intrinsic changes to adapt to the increased GABA drive, and firing output is reduced; 5) developmental changes in PNA mice lead to failure of these GnRH neuron adaptations, so that in PNA adults, increased GABA drive contributes to increased GnRH neuron firing; 6) the increased neuroendocrine drive increases androgens, which are critical to maintain neuroendocrine PNA phenotypes in adults. We will test this model in two aims. Aim 1 will identify the mechanisms underlying prepubertal adaptation of GnRH neurons in PNA mice to increased GABA drive. Aim 2 will characterize the epigenetic landscape in GnRH neurons during development, and changes induced by PNA. The role of the ovary and androgen replacement in establishing and maintaining epigenetic changes will also be assessed. Preliminary data indicate that GnRH neuron action potential firing, calcium currents and potassium currents are all differentially regulated in prepubertal vs adult PNA mice compared to controls. To complement the electrophysiology studies, we have adapted epigenetic profiling to libraries made from a few hundred neurons and established fluorescent cell sorting protocols that yield sufficient numbers of enriched GnRH neurons for these analyses. We are thus positioned to examine the molecular and biophysical underpinnings of the functional changes of GnRH neurons observed in PNA mice. This work will provide mechanistic insight currently lacking on the typical functional development of GnRH neurons through the pubertal process, associated epigenetic changes, and how these parameters may be altered in hyperandrogenic disorders; is not possible to obtain these insights from human studies.