Netrin-1 Ameliorates Blood-Brain Barrier Impairment Secondary to Ischemic Stroke via the Activation of PI3K Pathway

Abstract

Secondary impairment of blood-brain barrier (BBB) occurs in the remote thalamus after ischemic stroke. Netrin-1, an axonal guidance molecule, presents bifunctional effects on blood vessels through receptor-dependent pathways. This study investigates whether netrin-1 protects BBB against secondary injury. Netrin-1 (600 ng/d for 7 days) was intracerebroventricularly infused 24 h after middle cerebral artery occlusion (MCAO) in hypertensive rats. Neurological function was assessed 8 and 14 days after MCAO, and the permeability of BBB in the ipsilateral thalamus was detected. The viability of brain microvascular endothelial cells was determined after being disposed with netrin-1 (50 ng/mL) before oxygen-glucose deprivation (OGD). The role of netrin-1 was further explored by examining its receptors and their function. We found that netrin-1 infusion improved neurological function, attenuated secondary impairment of BBB by up-regulating the levels of tight junction proteins and diminishing extravasation of albumin, with autophagy activation 14 days after MCAO. Netrin-1 also enhanced cell survival and autophagy activity in OGD-treated cells, inhibited by UNC5H2 siRNA transfection. Furthermore, the beneficial effects of netrin-1 were suppressed by PI3K inhibitors 3-Methyladenine and LY294002. Our results showed that netrin-1 ameliorated BBB impairment secondary to ischemic stroke by promoting tight junction function and endothelial survival. PI3K-mediated autophagy activation depending on UNC5H2 receptor could be an underlying mechanism.

Inflammatory Responses in the Secondary Thalamic Injury After Cortical Ischemic Stroke

“…In other studies, albumin staining in the ipsilesional thalamus has revealed changes in BBB permeability (50,69). Increased albumin extravasation and decreased tight-junction protein expression, such as zona occludin 1 (ZO-1) and occludin are shown in the ipsilesional thalamus as early as 24 h after cortical stroke, and persist through Day 14 after cortical stroke (50,69). Aberrant angiogenesis resulting in a loss of BBB integrity may contribute to inflammatory responses and injuries in the thalamus after cortical stroke.…”

“…Emerging studies have shown multiple pathological changes associated with the secondary thalamic degenerative injury after cortical ischemic stroke, including excitotoxicity (17,30), apoptosis (27,49), Aβ accumulation, BBB breakdown (50), and inflammatory responses (5,25). We will discuss them in detail in the following sections.…”

“…Angiogenesis is prevalent at Day 7 post-stroke in the degenerative thalamus using bromodeoxyuridine (BrdU) costaining with laminin, a common blood vessel marker (68). In other studies, albumin staining in the ipsilesional thalamus has revealed changes in BBB permeability (50,69). Increased albumin extravasation and decreased tight-junction protein expression, such as zona occludin 1 (ZO-1) and occludin are shown in the ipsilesional thalamus as early as 24 h after cortical stroke, and persist through Day 14 after cortical stroke (50,69).…”

“…Aberrant angiogenesis resulting in a loss of BBB integrity may contribute to inflammatory responses and injuries in the thalamus after cortical stroke. It is important to assess BBB dysregulation in the secondary thalamic injury as it relates to inflammatory responses and neurodegeneration (50,69). There have been a few reports of BBB disruption in the ipsilesional thalamus in chronic post-stroke time points.…”

“…Some studies have shown that interventions to prevent secondary thalamic injury may be beneficial for recovery of function after stroke. Below is a summary of studies that investigate the role of secondary thalamic injury through manipulating specific molecules involved in inflammatory responses, autophagy, Aβ deposition, and neuronal apoptosis (5,26,50,59,60,(99)(100)(101).…”