Letrozole regulates actin cytoskeleton polymerization dynamics in a SRC-1 dependent manner in the hippocampus of mice

In the hippocampus, local estrogens (E-2) derived from testosterone that is catalyzed by aromatase play important roles in the regulation of hippocampal neural plasticity, but the underlying mechanisms remain unclear. The actin cytoskeleton contributes greatly to hippocampal synaptic plasticity; however, whether it is regulated by local E-2 and the related mechanisms remain to be elucidated. In this study, we first examined the postnatal developmental profiles of hippocampal aromatase and specific proteins responsible for actin cytoskeleton dynamics. Then we used aromatase inhibitor letrozole (LET) to block local E-2 synthesis and examined the changes of these proteins and steroid receptor coactivator-1 (SRC-1), the predominant coactivator for steroid nuclear receptors. Finally, SRC-1 specific RNA interference was used to examine the effects of SRC-1 on the expression of these actin remodeling proteins. The results showed a V-type profile for aromatase and increased profiles for actin cytoskeleton proteins in both male and female hippocampus without obvious sex differences. LET treatment dramatically decreased the Factin/G-actin ratio, the expression of Rictor, phospho-AKT (ser473), Profilin-1, phospho-Cofilin (Sera), and SRC-1 in a dose-dependent manner. In vitro studies demonstrated that LET induced downregulation of these proteins could be reversed by E2, and E-2 induced increase of these proteins were significantly suppressed by SRC-1 shRNA interference. These results for the first time clearly demonstrated that local E-2 inhibition could induce aberrant actin polymerization; they also showed an important role of SRC-1 in the mediation of local E-2 action on hippocampal synaptic plasticity by regulation of actin cytoskeleton dynamics. (C) 2016 Elsevier Ltd. All rights reserved.