Neuroprotective Effect of Protein Phosphatase 2A/Tristetraprolin Following Subarachnoid Hemorrhage in Rats.

Jian Yin,Ran Li,Wenchao Liu,Yunchang Chen,Xin Zhang,Xifeng Li,Chuanzhi Duan,Xuying He

doi:10.3389/fnins.2018.00096

Abstract

Early brain injury (EBI) following subarachnoid hemorrhage (SAH) can lead to inflammation and neuronal dysfunction. There is a need for effective strategies to mitigate these effects and improve the outcome of patients who experience SAH. The mRNA-destabilizing protein tristetraprolin (TTP) is an anti-inflammatory factor that induces the decay of cytokine transcripts and has been implicated in diseases such as glioma. However, the mechanism of action of TTP in EBI after SAH is unclear. The present study investigated the effects of TTP regulation via phosphorylation in a rat model of SAH by protein phosphatase (PP)2A, which is a pleiotropic enzyme complex with multiple substrate phospho-proteins. We hypothesized that inhibitory phosphorylation of TTP by PP2A would reduce neuroinflammation and apoptosis. To evaluate the function of each factor, the PP2A agonist FTY720, short interfering (si)RNAs targeting TTP and PP2A were administered to rats by intracerebroventricular injection 24 h before SAH. Rats were evaluated with SAH grade, neurological score, brain water content and by western blotting, and terminal deoxynucleotidyltransferase dUTP nick-end labeling. We found that endogenous PP2A and TTP levels were increased after SAH. FTY720 induced PP2A activation would lead to dephosphorylation and activation of TTP and decreased production of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-8. SiRNA-mediated TTP knockdown abolished anti-inflammatory effects of FTY720 treatment, indicating that PP2A was associated with TTP activation in vivo. Decreased TNF-α, IL-6, and IL-8 levels were associated with improvement of neurological function, reduction of brain edema, suppression of caspase-3, and up-regulation of B cell lymphoma-2. These results demonstrated that PP2A activation could enhance the anti-inflammatory and anti-apoptotic effects of TTP, by which it might shed light on the development of an effective therapeutic strategy against EBI following SAH.

Highlights

Subarachnoid hemorrhage (SAH) is an acute cerebrovascular event that can have devastating consequences including disability and mortality (Chen et al, 2014)
We investigated the role of PP2A and TTP in Early brain injury (EBI) after subarachnoid hemorrhage (SAH) and found that silencing PP2A or TTP exacerbated brain edema and reduced neurological scores following SAH
PP2A and TTP knockdown abolished the beneficial effects of TTP in mitigating EBI by suppressing the expression of tumor necrosis factor (TNF)-α and IL-6 and IL-8 in the cortex

Summary

Introduction

Subarachnoid hemorrhage (SAH) is an acute cerebrovascular event that can have devastating consequences including disability and mortality (Chen et al, 2014). Levels of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-8 are increased after SAH These factors can activate microglia and increase inflammatory cell infiltration into the brain, causing neuronal dysfunction (Chang et al, 2015; Niwa et al, 2016; Wu et al, 2016). Expression of these inflammationrelated proteins may be affected by means of RNA-binding proteins, which could regulate mRNA stability by binding to AUrich elements (AREs) in the 3′ untranslated region of transcripts and counter the increase of cytokine levels (Hollams et al, 2002; Stoecklin and Anderson, 2006). This mechanism might be used as a therapeutic approach for preventing EBI after SAH

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