Pre‐synaptic and post‐synaptic localization of EphA4 and EphB2 in adult mouse forebrain

Abstract

The ephrin receptors EphA4 and EphB2 have been implicated in synaptogenesis and long‐term potentiation in the cerebral cortex and hippocampus, where they are generally viewed as post‐synaptic receptors. To determine the precise distribution of EphA4 and EphB2 in mature brain synapses, we used subcellular fractionation and electron microscopy to examine the adult mouse forebrain/midbrain. EphA4 and EphB2 were both enriched in microsomes and synaptosomes. In synaptosomes, they were present in the membrane and the synaptic vesicle fractions. While EphA4 was tightly associated with PSD‐95‐enriched post‐synaptic density fractions, EphB2 was easily extracted with detergents. In contrast, both receptors were found in the pre‐synaptic active zone fraction. By electron microscopy, EphA4 was mainly detected in axon terminals, whereas EphB2 was more frequently detected in large dendritic shafts, in the hippocampus and cerebral cortex. However, in the ventrobasal thalamus, EphB2 was detected most frequently in axon terminals and thin dendritic shafts. The localization of EphA4 and EphB2 in multiple compartments of neurons and synaptic junctions suggests that they interact with several distinct scaffolding proteins and play diverse roles at synapses.

Early Changes in Hippocampal Eph Receptors Precede the Onset of Memory Decline in Mouse Models of Alzheimer's Disease

“…EphA4 receptors are highly expressed in brain structures with marked synaptic plasticity such as the hippocampus [14], and electron microscopy studies have shown that these receptors are basically localized on dendritic spines of hippocampal pyramidal neurons as well as on axon terminals [20,44]. Activation of EphA4 receptors is necessary for remodeling of CA1 dendritic spines in processes of synaptic plasticity in the adult brain [45][46][47], and EphA4 null mice have hippocampal distorted spines, confirming that EphA4 is required to maintain normal spine architecture in vivo [14,48].…”

“…The critical role of Eph receptor subtypes in synaptic plasticity has been demonstrated in numerous studies [17][18][19]. EphA4 and EphB2 are the two Eph receptors most intensively studied in the adult brain, where they have been detected in many regions, especially in the neocortex and hippocampus [20,21]. The multiple pathways involved in the regulation of synaptic function after Eph receptor activation remain to be fully elucidated.…”

“…Indeed, some reports have shown alterations in AM-PA and NMDA receptors in postsynaptic hippocampal membranes of brains from both AD patients [24] and cultured neurons of AβPP transgenic mice [25,26]. Because of the critical role of Eph receptors in synaptic plasticity, we explored the possibility that Eph receptor alterations could be correlated with cognitive deficits in these mice so we analyzed the time-course of the expression of EphA4 and EphB2 receptors, which present an overlapping distribution in the hippocampus [20], as well as AMPA and NMDA receptor subunit levels, looking for a correlation with the progression of cognitive impairment. We also sought other related molecular changes downstream of ephrin-Eph receptor signaling, such as p21-activated kinase (PAK), LIM-kinase (LIMK), and in particular alterations in the activity of cofilin, a protein of the cofilin/actin depolymerization factor family that binds and depolymerizes actin filaments [27] and is consequently implicated in the plasticity of dendritic spines.…”

Trans-synaptic EphB2–ephrin–B3 interaction regulates excitatory synapse density by inhibition of postsynaptic MAPK signaling

“…EphB2 copurifies with both presynaptic active zones and the postsynaptic density fraction (14). To identify whether a presynaptic EphB receptor mediates eB-dependent presynaptic induction, we used a modified coculture assay (9) in which axons expressing shRNA targeting potential presynaptic receptors are cocultured with eB expressing HEK293T cells (9).…”

Expression of PTPRO in the interneurons of adult mouse olfactory bulb

“…The present study also showed that the staining of PTPRO overlapped with that of EphA4 in the GL, EPL, and GCL of the adult mouse OB. Eph receptors are thought to regulate the reorganization of the actin cytoskeleton through Rho-family small G proteins (Huot, 2004), and they are known to regulate synaptogenesis Bouvier et al, 2008). Thus, PTPRO might participate in the regulation of synapse formation of OB interneurons through modulation of ephrin-Eph signaling.…”