Influence of Estrogens on GH-Cell Network Dynamics in Females: A Live in Situ Imaging Approach

Anne-Cécile Meunier,Chrystel Lafont,Danielle Carmignac,David J Hodson,Elodie Gavois,Iain C Robinson,Joanne F Murray,Jérôme Birkenstock,Marie Schaeffer,Patrice Mollard,Paul Le Tissier

doi:10.1210/en.2011-1430

Abstract

The secretion of endocrine hormones from pituitary cells finely regulates a multitude of homeostatic processes. To dynamically adapt to changing physiological status and environmental stimuli, the pituitary gland must undergo marked structural and functional plasticity. Endocrine cell plasticity is thought to primarily rely on variations in cell proliferation and size. However, cell motility, a process commonly observed in a variety of tissues during development, may represent an additional mechanism to promote plasticity within the adult pituitary gland. To investigate this, we used multiphoton time-lapse imaging methods, GH-enhanced green fluorescent protein transgenic mice and sexual dimorphism of the GH axis as a model of divergent tissue demand. Using these methods to acutely (12 h) track cell dynamics, we report that ovariectomy induces a dramatic and dynamic increase in cell motility, which is associated with gross GH-cell network remodeling. These changes can be prevented by estradiol supplementation and are associated with enhanced network connectivity as evidenced by increased coordinated GH-cell activity during multicellular calcium recordings. Furthermore, cell motility appears to be sex-specific, because reciprocal alterations are not detected in males after castration. Therefore, GH-cell motility appears to play an important role in the structural and functional pituitary plasticity, which is evoked in response to changing estradiol concentrations in the female.

Highlights

Dimensional GH-cell network that wires the gland allows coordinated propagation of information between distant cell ensembles after arrival of the hypothalamic secretagogue GHRH (4 – 6)
Gonadectomy increases GH-cell motility in females We performed overnight three-dimensional time-lapse recordings of pituitary slices taken from postpubertal 60to 80-d-old male or female GH-enhanced green fluorescent protein (eGFP) mice
A significant decrease in uterus weight could be observed in OVX females (19 Ϯ 2 mg vs. 121 Ϯ 21 mg; OVX vs. sham, respectively; P Ͻ 0.05), which was reversed after EE complementation (97 Ϯ 29 mg, OVX ϩ EE, P Ͻ 0.05 vs. OVX)

Summary

Introduction

Dimensional GH-cell network that wires the gland allows coordinated propagation of information between distant cell ensembles after arrival of the hypothalamic secretagogue GHRH (4 – 6). The mechanisms underlying this functional divergence are elusive, it may be partly due to remodeling of GH-cell network connectivity by gonadal steroids, because sex differences in GH-cell topological organization are observed during sexual maturation [4, 5]. Despite the welldefined role of gonadal steroids in driving pituitary plasticity in response to both physiological and pathological demands in adults (2, 14 –18), it remains to be shown whether they can impact cell motility to induce structural remodeling and sexually differentiated function of endocrine cell populations such as GH-cells. Live imaging and cell motility analysis Thick pituitary slices (200 ␮m) were prepared from GH-eGFP animals as previously described [5]. The x, y, and z displacements of cells over a 4-h imaging period were plotted on three-dimensional plots using Chaser script for MATLAB [23]

Methods

Results

Conclusion