Estrogen and aging affect synaptic distribution of phosphorylated LIM kinase (pLIMK) in CA1 region of female rat hippocampus

Abstract

Abstract17β-Estradiol (E) increases axospinous synapse density in the hippocampal CA1 region of young female rats, but not in aged rats. This may be linked to age-related alterations in signaling pathways activated by synaptic estrogen receptor α (ER-α) that potentially regulate spine formation, such as LIM-Kinase (LIMK), an actin depolymerizing factor/cofilin kinase. We hypothesized that, as with ER-α, phospho-LIMK (pLIMK) may be less abundant or responsive to E in CA1 synapses of aged female rats. To address this, cellular and subcellular distribution of pLIMK-immunoreactivity (pLIMK-IR) in CA1 was analyzed by light and electron microscopy in young and aged female rats that were ovariectomized and treated with either vehicle or E. pLIMK-IR was found primarily in perikarya within the pyramidal cell layer and dendritic shafts and spines in stratum radiatum (SR). While pLIMK-IR was occasionally present in terminals, post-embedding quantitative analysis of SR showed that pLIMK had a predominant post-synaptic localization and was preferentially localized within the postsynaptic density (PSD). The percentage of pLIMK-labeled synapses increased (30%) with E treatment (p<0.02) in young animals, and decreased (43%) with age (p<0.002) regardless of treatment. The pattern of distribution of pLIMK-IR within dendritic spines and synapses was unaffected by age or E treatment, with the exception of an E-induced increase in the non-synaptic core of spines in young females. These data suggest that age-related synaptic alterations similar to those seen with ER-α occur with signaling molecules such as pLIMK, and support the hypothesis that age-related failure of E treatment to increase synapse number in CA1 may be due to changes in the molecular profile of axospinous synapses with respect to signaling pathways linked to formation of additional spines and synapses in response to E. NY, 10029. Tel: 212-659-5985, Fax: 212-849-2510, Email: john.morrison@mssm.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. In the female rat hippocampus, dendritic spine density and synapse number in CA1 pyramidal neurons increase when levels of estrogen increase (Gould et al., 1990, Woolley and McEwen, 1992, Woolley et al., 1996, and the size of CA1 spines is also affected by estrogen (Mukai et al., 2007). ER-α and ER-β are both present in these same spines and synapses (Milner et al., 2001, Adams et al., 2002, Milner et al., 2005 and while ER-β also impacts synaptic plasticity in CA1 (Day et al., 2005, Szymczak et al., 2006, the estrogen-induced spinogenesis in CA1 is thought to be mediated primarily b...

Reversal of Behavioral Deficits and Synaptic Dysfunction in Mice Overexpressing Neuregulin 1

“…The kinase is localized in both presynaptic terminals and postsynaptic densities (Wang et al, 2000; Yildirim et al, 2008) and has been implicated in the regulation of glutamatergic transmission (Meng et al, 2004; Meng et al, 2002). Intriguingly, LIMK1 and p-cofilin were increased in synaptosomes of ctoNrg1 mice (Figures 5C and 5D) and reduced upon aDox treatment (Figure 5E).…”

A role for hippocampal actin rearrangement in object placement memory in female rats

“…Conversely, much of the in vitro work linking estradiol to actin dynamics relies on acute non-genomic fast acting effects of estradiol. However, in addition to acute in vitro evidence linking estradiol to actin rearrangement, results of another in vivo study revealed that levels of p-LIMK-immunoreactivity were increased in CA1 of the hippocampus in ovariectomized rats that received two days of chronic estradiol treatment via implanted capsules (Yildirim et al, 2008). In the present study, we saw no effects of estradiol on hippocampal levels of p-cofilin.…”

“…Hippocampal slices treated with estradiol showed increased dendritic spine density that was blocked by addition of latrunculin A, suggesting that estradiol effects change in dendrite morphology through actin polymerization (Kramar et al, 2009). Both in vivo and in vitro molecular evidence demonstrate that estradiol increases phosphorylation of cofilin in the hippocampus, thereby promoting actin polymerization (Kramar et al, 2009;Yildirim et al, 2008;Yuen, McEwen, & Akama, 2011). In addition to its impacts on the hippocampus, estradiol enhances hippocampus dependent memory across a variety of tasks (Daniel, Fader, Spencer, & Dohanich, 1997;Daniel, Roberts, & Dohanich, 1999;Korol & Kolo, 2002;Luine, Richards, Wu, & Beck, 1998;Sandstrom, 2004) including the object placement task used in the current study (Frye, Duffy, & Walf, 2007;Luine, Jacome, & Maclusky, 2003).…”

Insights into Rapid Modulation of Neuroplasticity by Brain Estrogens

“…A number of studies have also demonstrated that estrogenic signaling can activate LIM-kinase (p-LIMK) and subsequently phosphorylate cofilin (p-cofilin), resulting in the inhibition of cofilin activity (Yildirim et al, 2008;Kramar et al, 2009;Yuen et al, 2011). In the dorsal hippocampus of mice, p-LIMK levels were increased during the high-estradiol phase of proestrus (Spencer et al, 2008).…”