Scaffolding protein Homer1a protects against NMDA-induced neuronal injury.

Y Wang,F Han,M-D Liu,Z Fei,N Su,W Rao,H Han,L-B Yao,C Zhang,P Luo

doi:10.1038/cddis.2015.216

Abstract

Excessive N-methyl-D-aspartate receptor (NMDAR) activation and the resulting activation of neuronal nitric oxide synthase (nNOS) cause neuronal injury. Homer1b/c facilitates NMDAR-PSD95-nNOS complex interactions, and Homer1a is a negative competitor of Homer1b/c. We report that Homer1a was both upregulated by and protected against NMDA-induced neuronal injury in vitro and in vivo. The neuroprotective activity of Homer1a was associated with NMDA-induced Ca2+ influx, oxidative stress and the resultant downstream signaling activation. Additionally, we found that Homer1a functionally regulated NMDAR channel properties in neurons, but did not regulate recombinant NR1/NR2B receptors in HEK293 cells. Furthermore, we found that Homer1a detached the physical links among NR2B, PSD95 and nNOS and reduced the membrane distribution of NMDAR. NMDA-induced neuronal injury was more severe in Homer1a homozygous knockout mice (KO, Homer1a−/−) when compared with NMDA-induced neuronal injury in wild-type mice (WT, Homer1a+/+). Additionally, Homer1a overexpression in the cortex of Homer1a−/− mice alleviated NMDA-induced neuronal injury. These findings suggest that Homer1a may be a key neuroprotective endogenous molecule that protects against NMDA-induced neuronal injury by disassembling NR2B-PSD95-nNOS complexes and reducing the membrane distribution of NMDARs.

Highlights

Disrupted cortical integrity and extensive neuronal cell loss on the side ipsilateral to the NMDA injection site were detected by Nissl staining, but no changes were observed on the contralateral side 24 h after injury (Figure 1f)
Examining NR2B immunoprecipitations, we found that Flag-Homer1a upregulation reduced the NR2Bbound neuronal nitric oxide synthase (nNOS), PSD95 and Homer1b/c when compared with the empty vector group (Vector versus Flag-H1a: nNOS, 1.00 ± 0.14 versus 0.51 ± 0.10-fold; PSD95, 1.00 ± 0.11 versus 0.47 ± 0.16-fold; Homer1b/c, 1.00 ± 0.07 versus 0.38 ± 0.09-fold; Figure 6d)
We demonstrated that Homer1a conferred neuroprotection against NMDA-induced neuronal injury

Summary

Introduction

We found that Homer1a detached the physical links among NR2B, PSD95 and nNOS and reduced the membrane distribution of NMDAR. These findings suggest that Homer1a may be a key neuroprotective endogenous molecule that protects against NMDA-induced neuronal injury by disassembling NR2B-PSD95-nNOS complexes and reducing the membrane distribution of NMDARs. N-methyl-D-aspartate receptor (NMDAR), and leads to neuronal hyper-excitability and death in a dose-dependent manner.[1] NMDAR activation induces Ca2+ influx and activates neuronal nitric oxide synthase (nNOS) and downstream signaling pathways.[2,3,4] Ca2+ influx is involved in glutamate-induced apoptosis caused by the activation of apoptosis-related signaling pathways, mitochondrial dysfunction and ROS induction.[3,4] nNOS has been reported to contribute to NMDA-induced excitotoxicity.[5,6].

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