Cell Surface Estrogen Receptor Alpha Is Upregulated during Subchronic Metabolic Stress and Inhibits Neuronal Cell Degeneration

<div><p>In addition to the classical nuclear estrogen receptor, the expression of non-nuclear estrogen receptors localized to the cell surface membrane (mER) has recently been demonstrated. Estrogen and its receptors have been implicated in the development or progression of numerous neurodegenerative disorders. Furthermore, the pathogenesis of these diseases has been associated with disturbances of two key cellular programs: apoptosis and autophagy. An excess of apoptosis or a defect in autophagy has been implicated in neurodegeneration. The aim of this study was to clarify the role of ER in determining neuronal cell fate and the possible implication of these receptors in regulating either apoptosis or autophagy. The human neuronal cell line SH-SY5Y and mouse neuronal cells in primary culture were thus exposed to chronic minimal peroxide treatment (CMP), a form of subcytotoxic minimal chronic stress previously that mimics multiple aspects of long-term cell stress and represents a limited molecular proxy for neurodegenerative processes. We actually found that either E2 or E2-bovine serum albumin construct (E2BSA, i.e. a non-permeant form of E2) was capable of modulating intracellular cell signals and regulating cell survival and death. In particular, under CMP, the up-regulation of mERα, but not mERβ, was associated with functional signals (ERK phosphorylation and p38 dephosphorylation) compatible with autophagic cytoprotection triggering and leading to cell survival. The mERα trafficking appeared to be independent of the microfilament system cytoskeletal network but was seemingly associated with microtubular apparatus network, i.e., to MAP2 molecular chaperone. Importantly, antioxidant treatments, administration of siRNA to ERα, or the presence of antagonist of ERα hindered these events. These results support that the surface expression of mERα plays a pivotal role in determining cell fate, and that ligand-induced activation of mER signalling exerts a powerful cell-survival signal. These results shed new light on the pathogenetic mechanisms leading to neuronal cell degeneration.</p> </div

Immunofluorescence analysis of cell surface mERα in rat hippocampal neurons.

<p>mERα expression (green fluorescence) in unpermeated hippocampal neuronal cells and MAP2 expression (red fluorescence) in Triton X100 permeated hippocampal neuronal cells: (<b>A</b>) untreated, (<b>B, C</b>) CMP treated or (<b>D</b>) NAC exposed before CMP treatment. Note the yellow spots in (<b>B</b>) and (<b>C</b>) suggesting a colocalization of ERα and MAP2 in soma (<b>B</b>) and dendritic protrusions (<b>C</b>) of CMP exposed cells. No yellow spots are instead observable in untreated and NAC/CMP exposed hippocampal cells. Cells were counterstained with Hoechst dye to reveal nuclei (blue staining). Magnifications: (<b>A</b>) (<b>B</b>) (<b>D</b>) 3500×; (<b>C</b>) 6000×.</p