The miR-455-5p/ERα36 axis regulates mammalian neuronal viability and axonal regeneration

Estrogen signal transduction plays an important role in regulating neuronal cell growth and axonal regeneration. Estrogen receptor alpha 36 (ERα36) is a truncated isoform of the estrogen receptor that inhibits aspects of estrogen transduction. Here, we investigated the role of ERα36 in neuronal viability as well as axonal growth and regeneration using SH-SY5Y neuroblastoma cells and murine sensory neurons. We identified an ERα36-targeting microRNA, miR-455-5p, that negatively regulates ERα36 levels. miR-455-5p inhibition increased cell viability, PCNA, cyclin D1, and Bcl-2 levels and decreased apoptosis and Bax levels in SH-SY5Y neuroblastoma cells. Moreover, miR-455-5p inhibition upregulated the phosphorylation of the intracellular signaling mediators MEK, ERK, Akt, and mTOR in SH-SY5Y neuroblastoma cells. miR-455-5p inhibition promoted axonal growth and regeneration and downregulated activation of the glycogen synthase kinase-3β (GSK3β)/Tau protein pathway in murine sensory neurons. ERα36 silencing was sufficient to reverse the phenotypic characteristics produced by miR-455-5p inhibition, suggesting that ERα36 is mechanistically linked to miR-455-5p. We provide additional mechanistic evidence showing that GSK3β is the mediator of miR-455-5p/ERα36-induced axonal growth. Together, these findings elucidate a novel miR-455-5p/ERα36 axis that regulates mammalian neuronal viability and axonal regeneration.