G-protein coupled estrogen receptor 1 mediated estrogenic neuroprotection against spinal cord injury*

Abstract

What underlies the protection of estrogen against spinal cord injury remains largely unclear. Here, we investigated the expression pattern of a new estrogen receptor, G-protein coupled estrogen receptor 1 in the spinal cord and its role in estrogenic protection against spinal cord injury. Department of Neurosurgery and Key Laboratory of Neurotrauma, Southwest Hospital. Male Sprague-Dawley rats. The animals subjected to spinal cord injury were divided into six groups and given vehicle solution, 17β-estradiol, or G-protein coupled estrogen receptor 1 agonist G-1 at 15 mins and 24 hrs postinjury, or given nuclear estrogen receptor antagonist ICI 182,780 at 1 hr before spinal cord injury followed by 17β-estradiol administration at 15 mins and 24 hrs postinjury, or given G-protein coupled estrogen receptor 1 specific antisense or random control oligonucleotide at 4 days before spinal cord injury followed by 17β-estradiol administration at 15 mins and 24 hrs postinjury. Male Sprague-Dawley rats were subjected to spinal cord injury using a weight-drop injury approach. Immunohistochemical assays were used to observe the distribution and cell-type expression pattern of G-protein coupled estrogen receptor 1. The terminal deoxynucleotidyl transferase dUTP nick-end labeling-staining assay and behavior tests were employed to assess the role of G-protein coupled estrogen receptor 1 in mediating estrogenic protection against spinal cord injury. We show that G-protein coupled estrogen receptor 1 is mainly distributed in the ventral horn and white matter of the spinal cord, which is totally different from nuclear estrogen receptors. We also show that G-protein coupled estrogen receptor 1 is specifically expressed by neurons, oligodendrocytes, and microglial cells, but not astrocytes. Furthermore, estrogen treatment prevents spinal cord injury-induced apoptotic cell death and enhances functional recovery after spinal cord injury, which can be mimicked by the specific G-protein coupled estrogen receptor 1 agonist G-1 and inhibited by specific knockdown of G-protein coupled estrogen receptor 1 expression, but not pure nuclear ER antagonist ICI 182,780. Finally, we show that estrogen or G-1 up-regulates the protein expression level of G-protein coupled estrogen receptor 1 to intensify estrogenic effects during spinal cord injury. These results reveal that G-protein coupled estrogen receptor 1 may mediate estrogenic neuroprotection against spinal cord injury, and underline the promising potential of estrogen with its new target G-protein coupled estrogen receptor 1 for the treatment of spinal cord injury patients.