Overexpression of netrin-1 increases the expression of tight junction-associated proteins, claudin-5, occludin, and ZO-1, following traumatic brain injury in rats.

Jianfeng Wen,Ye Mo,Suokai Qian,Qifan Yang,Yuefei Yu,Lei Deng

doi:10.3892/etm.2014.1818

Abstract

The function of the blood-brain barrier (BBB) depends on the integrity of tight junction (TJ)-associated proteins. Netrin-1 is known to promote angiogenesis and may also regulate the BBB. To understand the association between netrin-1 and the TJ-associated proteins, the expression levels of proteins involved in maintaining the integrity of the BBB, including netrin-1, claudin-5, occludin and zonula occluden (ZO)-1, were investigated in the present study using quantitative polymerase chain reaction, western blot analysis and immunofluorescence. The aim of the present study was to determine the changes in BBB permeability and whether pZsGreen1-N1 mediated overexpression of netrin-1 increased the expression of the TJ-associated proteins following traumatic brain injury (TBI). The results demonstrated that the levels of mRNA transcription and protein expression of the TJ-associated proteins, claudin-5, occludin and ZO-1, were significantly reduced following TBI. Furthermore, the changes in the expression of these three TJ proteins were consistent with the changes in the BBB permeability, indicating that weakening intercellular junctions leads to BBB opening. The present study also demonstrated that netrin-1 significantly increased the downregulation of claudin-5, occludin and ZO-1 expression levels induced by TBI, which provided a basis for further investigation on the role of netrin-1 in the integrity of TJs and proper functioning of the BBB.

Highlights

Traumatic brain injury (TBI) is the main cause of mortality and disability in young individuals, and can directly cause pathophysiological changes in the blood‐brain barrier (BBB)
The ability to maintain the BBB integrity depends on adequate structural support from the tight junction (TJ)‐associated proteins, which include claudin‐5, occludin and zonula occludens (ZO)‐1
TJ‐associated proteins, including claudin‐5, occludin and ZO‐1, have critical roles in the maintenance of BBB functions; the expression levels of these TJ proteins following TBI were investigated in the present study

Summary

Introduction

Traumatic brain injury (TBI) is the main cause of mortality and disability in young individuals, and can directly cause pathophysiological changes in the blood‐brain barrier (BBB). The endothelial cells come into contact with each other at what are known as tight junctions (TJs). TJs consist of the transmembrane proteins, occludins and claudins, that interact on adjacent endothelial cells to form a physical barrier against paracellular diffusion [1,2,3], and the accessory proteins, zonula occludens (ZO) family (ZO‐1 and ZO‐2), that anchor the transmembrane proteins to the cytoskeleton [4,5,6]. Netrin‐1, one of three members in the mammalian netrin family, stimulates angiogenesis and augments the response to vascular endothelial growth factor [7]. Netrin‐1 has been found to be superior to vascular endothelial growth factor in restoring nerve conduction velocity, possibly due to the potent effects on vascular and neural biology [8]. The angiogenic effect of netrin‐1 offers unique therapeutic potentials in restoring the BBB under pathological conditions, including TBI

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