The Expression of Hippocampal NRG1/ErbB4 Correlates With Neuronal Apoptosis, but Not With Glial Activation During Chronic Cerebral Hypoperfusion.

Yue Hei,Xicai Yi,Rong Chen,Lizhou Wei,Qianfa Long,Weiping Liu

doi:10.3389/fnagi.2018.00149

Abstract

Permanent bilateral common carotid occlusion (2VO) is well-established to investigate the chronic cerebral hypoperfusion (CCH)-induced cognitive deficits. Besides, previous studies suggested that disturbance of Neuregulin1 (NRG1)/ErbB4 signaling is associated with cognitive impairments, as well as neuronal apoptosis and neuroinflammation in CNS. However, the expression pattern of hippocampal NRG1/ErbB4 has not been systematically investigated during CCH. Here, we aim to investigate the temporal changes of hippocampal NRG1/ErbB4 during CCH and their possible relationship with neuronal apoptosis and glial activation. Morris water maze (MWM) and Radial arm water maze (RAWM) tests were used to analyze cognitive impairment in 2VO rats at 28 days post-surgery, and Enzyme-Linked Immunosorbent Assay (ELISA), western blotting and immunostaining were performed at different time points (24 h, 7 days, 14 days, 28 days) to detect the expression pattern of NRG1/ErbB4 and the distribution of ErbB4. Neuronal nuclei (NeuN), NeuN/TUNEL, Iba1 and GFAP immunostaining and caspase activity in hippocampal CA1 subarea were assessed during CCH as well. We found that the expression of NRG1 and phosphorylated ErbB4 (pErbB4)/ErbB4 changed in a time-dependent manner (up-regulated in the acute phase and then decreased in the chronic phase of CCH). Besides, ErbB4-expressed neurons and selective types of GABAergic cells decreased after CCH, but the distribution pattern of ErbB4 remained unchanged. In addition, the expression of hippocampal NRG1/ErbB4 positively correlated with the level of neuronal apoptosis (both NeuN/TUNEL immunostaining and caspase-3 activity), but not with glial activation according to Pearson’s correlation. These findings indicated that hippocampal NRG1/ErbB4 may be involved in the pathogenesis of CCH, especially neuronal apoptosis during CCH.

Highlights

Chronic cerebral hypoperfusion (CCH) may cause dramatic cognitive decline and neurodegenerative changes that are closely associated with Alzheimer’s disease and vascular dementia (Farkas et al, 2007; Zhao and Gong, 2015), but the underlying mechanisms are poorly understood so far
We further performed Neuronal nuclei (NeuN) immunostaining to see the neuronal loss in the hippocampal CA1 subarea at different time points during chronic cerebral hypoperfusion (CCH) (Figures 2A,B)
We analyzed the dynamic changes of NeuN/TUNEL, Iba1 and GFAP-positive cells at different time points (Figure 7)

Summary

Introduction

Chronic cerebral hypoperfusion (CCH) may cause dramatic cognitive decline and neurodegenerative changes that are closely associated with Alzheimer’s disease and vascular dementia (Farkas et al, 2007; Zhao and Gong, 2015), but the underlying mechanisms are poorly understood so far. Activated microglia and astrocytes take an essential role in neuroinflammation by producing inflammatory chemokines and cytokines (such as IL-1β, IL-6 and TNF-α) (Cechetti et al, 2012; Yang et al, 2014; Du et al, 2017), which may further accelerate the disease progression. These findings suggest the key role of both hippocampal neuronal apoptosis and glial activation in CCH

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