Modeling and high-throughput experimental data uncover the mechanisms underlying Fshb gene sensitivity to gonadotropin-releasing hormone pulse frequency

Estee Stern,Frederique Ruf-Zamojski,Lisa Zalepa-King,Hanna Pincas,Soon Gang Choi,Charles S Peskin,Fernand Hayot,Judith L Turgeon,Stuart C Sealfon

doi:10.1074/jbc.m117.783886

Abstract

Neuroendocrine control of reproduction by brain-secreted pulses of gonadotropin-releasing hormone (GnRH) represents a longstanding puzzle about extracellular signal decoding mechanisms. GnRH regulates the pituitary gonadotropin's follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which are heterodimers specified by unique β subunits (FSHβ/LHβ). Contrary to Lhb, Fshb gene induction has a preference for low-frequency GnRH pulses. To clarify the underlying regulatory mechanisms, we developed three biologically anchored mathematical models: 1) parallel activation of Fshb inhibitory factors (e.g. inhibin α and VGF nerve growth factor-inducible), 2) activation of a signaling component with a refractory period (e.g. G protein), and 3) inactivation of a factor needed for Fshb induction (e.g. growth differentiation factor 9). Simulations with all three models recapitulated the Fshb expression levels obtained in pituitary gonadotrope cells perifused with varying GnRH pulse frequencies. Notably, simulations altering average concentration, pulse duration, and pulse frequency revealed that the apparent frequency-dependent pattern of Fshb expression in model 1 actually resulted from variations in average GnRH concentration. In contrast, models 2 and 3 showed "true" pulse frequency sensing. To resolve which components of this GnRH signal induce Fshb, we developed a high-throughput parallel experimental system. We analyzed over 4,000 samples in experiments with varying near-physiological GnRH concentrations and pulse patterns. Whereas Egr1 and Fos genes responded only to variations in average GnRH concentration, Fshb levels were sensitive to both average concentration and true pulse frequency. These results provide a foundation for understanding the role of multiple regulatory factors in modulating Fshb gene activity.

Highlights

Neuroendocrine control of reproduction by brain-secreted pulses of gonadotropin-releasing hormone (GnRH) represents a longstanding puzzle about extracellular signal decoding mechanisms
We previously reported that G␣s activation by gonadotropin-release hormone (GnRH) promoted Lhb but suppressed Fshb gene expression in L␤T2 cells and found that this differential effect was mediated, at least in part, via the secretion of autocrine factors including inhibin ␣ [13] and VGF nerve growth factor-inducible (VGF)/neuroendocrine regulatory peptide-1 (NERP-1) [14]
In contrast with Fshb gene expression, Inha and Vgf were preferentially induced by high GnRH pulse frequency

Summary

Introduction

Neuroendocrine control of reproduction by brain-secreted pulses of gonadotropin-releasing hormone (GnRH) represents a longstanding puzzle about extracellular signal decoding mechanisms. Simulations with all three models recapitulated the Fshb expression levels obtained in pituitary gonadotrope cells perifused with varying GnRH pulse frequencies. Fshb levels were sensitive to both average concentration and true pulse frequency These results provide a foundation for understanding the role of multiple regulatory factors in modulating Fshb gene activity. The mechanisms of information coding and decoding of many concentration-based biological chemical signals are well understood, the frequency and pulse pattern-signal information transfer protocols are largely unknown. Since the discovery of this apparently frequency-sensitive, brain-endocrine information transfer system in the 1970s, the mechanisms underlying the GnRH signal information decoding by the recipient pituitary gonadotrope cell have been an area of widespread research interest. GnRH pulse frequency decoding tive disorders such as hypogonadotropic hypogonadism and anosmia (Kallmann syndrome) show impaired GnRH pulse secretion and subsequent abnormal FSH and LH levels; treatment with either pulsatile GnRH or gonadotropins restores fertility in those patients (for a review, see Ref. 2)

Objectives

Results

Conclusion