The disruption of the blood-brain barrier (BBB) caused by cerebral ischemia determines the extent of injury and patient prognosis. Inhibitors of Src can markedly minimize the infarct size and preserve neurological function. The Src protein tyrosine kinase (PTK) inhibitor, PP2, protects the rat brain against ischemic injury, possibly through the reduction of vascular endothelial growth factor A (VEGFA) expression and the upregulation of claudin-5 expression, which preserves the integrity of the BBB. In this study, the expression levels of phosphorylated (p)-Src, VEGFA and claudin-5 were determined to investigate the changes occurring in the levels of these proteins and to determine the benefits of PP2 treatment following cerebral ischemia/reperfusion (I/R). Our study included a sham-operated group, an I/R group, a vehicle-treated group (V) and a PP2-treated group (PP2). We found that the rats in the PP2 group exhibited greater preservation of neurological function and reduced VEGFA and p-Src protein expression compared with the rats in the I/R and V groups. Moreover, the mRNA and protein levels of claudin-5 were markedly higher in the PP2 group than in the I/R group or the V group after 3 days of reperfusion. Immunofluorescence staining revealed that the co-localized immunostaining of fibrinogen and claudin-5 was reduced in the PP2 group, which suggests that the exudation of fibrinogen in this group was less than that in the I/R and V groups. Furthermore, the reduced co-localization of immunostaining of glial fibrillary acidic protein (GFAP) and claudin-5 indicated that the rats in the PP2 group had only a slight disruption of the BBB. These findings suggested that PP2 treatment attenuated the disruption of the BBB following ischemia and minimized the neurological deficit; these effects were associated with a decreased VEGFA expression and an increased claudin-5 expression. Members of the Src PTK family may be critical targets for the protection of the BBB following cerebral ischemia.
Minocycline, a semi-synthetic second-generation derivative of tetracycline, has been reported to exert neuroprotective effects both in animal models and in clinic trials of neurological diseases. In the present study, we first investigated the protective effects of minocycline on oxygen-glucose deprivation and reoxygenation-induced impairment of neurite outgrowth and its potential mechanism in the neuronal cell line, PC12 cells. We found that minocycline significantly increased cell viability, promoted neurite outgrowth and enhanced the expression of growth-associated protein-43 (GAP-43) in PC12 cells exposed to oxygen-glucose deprivation/reoxygenation injury. In addition, immunoblots revealed that minocycline reversed the overexpression of phosphorylated myosin light chain (MLC) and the suppression of activated extracellular signal-regulated kinase 1/2 (ERK1/2) caused by oxygen-glucose deprivation/reoxygenation injury. Moreover, the minocycline-induced neurite outgrowth was significantly blocked by Calyculin A (1 nM), an inhibitor of myosin light chain phosphatase (MLCP), but not by an ERK1/2 inhibitor (U0126; 10 μM). These findings suggested that minocycline activated the MLCP/MLC signaling pathway in PC12 cells after oxygen-glucose deprivation/reoxygenation injury, which resulted in the promotion of neurite outgrowth.
Ischemia/reperfusion (I/R) injury after middle cerebral artery occlusion (MCAO) induces detrimental processes such as oxidative stress, inflammation, and apoptosis. All parts of the neurovascular unit are involved in these pathological processes. Fibulin-5 is a 66-kD glycoprotein secreted by various vascular cells, including vascular smooth muscle cells (SMCs), fibroblasts, and endothelial cells. As an extracellular matrix protein involved in cell adhesion, fibulin-5 has been widely studied in tumor growth and invasion. However, the effects of fibulin-5 on brain injury following ischemia/reperfusion have not been reported. In this study, we examined the effect of overexpressed fibulin-5 on reactive oxygen species (ROS) production. Fibulin-5 overexpression attenuated ROS expression, which in turn decreased apoptosis and blood-brain barrier (BBB) permeability following MCAO and reperfusion. Fibulin-5 also improved neurological deficits but had no effect on infarction volume. T2-weighted MRI and electron microscopy further confirmed brain edema reduction and decreased BBB disruption in fibulin-5 overexpression recombinant adenovirus (Ad-FBLN) treated rats. In addition, tight junction protein occludin was significantly degraded and matrix metalloproteinase 9 (MMP-9) immunoreactivity was significantly increased. Fibulin-5-mediated ROS decrease was not due to increased total superoxide dismutase levels but was instead correlated with the activation of Rac-1 pathway. The findings highlight the importance of antioxidant mechanism underlying cerebral ischemia/reperfusion.
Minocycline has been recently implicated in protection against focal cerebral ischemia reperfusion (I/R), but the protective effects on neurobehavioral abnormalities remains contradictory. In the present study, we investigate whether minocycline improves axonal regeneration and neurological function recovery by inhibiting the expression of the repulsive guidance molecular A (RGMa) after focal cerebral ischemia reperfusion. Male Sprague-Dawley (SD) rats were subjected to occlusion of the right middle cerebral artery (MCAO) for 2 h and 3 mg kg⁻¹ minocycline was injected intravenously immediately after reperfusion twice a day for 14 days. The staircase test and modified neurological severity score (mNSS) were performed to evaluate functional outcome and blood-brain barrier (BBB) permeability was assessed by Evan's blue dye extravasation (EB) at the expected time point. The expression of RGMa in ischemic cortex was measured by immunohistochemical staining and Western blot 2 weeks after MCAO. Neurofilament protein 200 (NF-200) immunohistochemical staining was used to assess axonal damage. Treatment with minocycline at a dose of 3 mg kg⁻¹ via the caudal vein significantly reduced the extravasation of EB, elevated mNSS and improved forelimb motor function as assessed by the staircase test when compared to the I/R group (P < 0.05). Moreover, axonal regrowth was enhanced in the minocycline treatment group when compared to the I/R group (P < 0.05). In addition, minocycline significantly reduced the expression of RGMa protein 2 weeks after MCAO as assessed by both immunostaining and Western blot. Our studies suggest that early minocycline treatment promotes neurological functional recovery and axonal regeneration in rats after MCAO, which might be mediated by down-regulating RGMa expression.
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