Mixed Lineage Leukemia 1 Promoted Neuron Apoptosis in Ischemic Penumbra via Regulating ASK-1/TNF-α Complex.

Zhang Feng,Wang Xi,Lv Guimin,Liu Jie

doi:10.3389/fnana.2020.00036

Abstract

Neuron apoptosis in ischemic penumbra was proved to be involved in ischemic stroke (IS) development and contributed to the poor prognosis of IS. Recent studies showed that aberrant trimethylation of histone H3 lysine 4 (H3K4me3) level was associated with cell apoptosis. This study aimed to explore the underlying mechanism of neuron apoptosis in ischemic penumbra via histone methyltransferase (HMT) mixed lineage leukemia 1 (MLL1) mediated epigenetic pathway. Mouse IS model was established by middle cerebral artery occlusion (MCAO). Mouse primary cortical mixed cells were cultured and treated with oxygen–glucose deprivation (OGD) to simulate IS process. The expressions of apoptosis signal regulating kinase-1 (ASK-1), pASK-1, cleaved caspase-3, ASK-1/serine–threonine kinase receptor-associated protein (STRAP)/14-3-3 complex, ASK-1/tumor necrosis factor-α (TNF-α) complex, and MLL1 in mouse brain tissue and mouse primary cortical mixed cells were analyzed. The function of MLL1 was investigated using small interfering RNA (siRNA) targeting MLL1 and vector overexpressing MLL1. In vivo inhibition of MLL1 was conducted to explore its value as a therapeutic target. The prognostic value of MLL1 was investigated in IS patients. Results showed that the expressions of ASK-1, pASK-1, cleaved caspase-3, ASK-1/TNF-α complex, and MLL1 increased significantly in ischemic penumbra compared to brain tissue from the control group (P < 0.05). MCAO and OGD significantly upregulated the H3K4me3 level in ASK-1 promoter region and promoted the recruitment of MLL1 to this region (P < 0.05). siMLL1 significantly reversed the proapoptosis effects of OGD in primary cortical mixed cells, while MLL1 overexpression induced apoptosis of cells (P < 0.05). In vivo inhibition of MLL1 significantly reduced the infarct volume and the neurological score of MCAO mice (P < 0.05). Serum MLL1 level had a positive association with that in ischemic core and penumbra in mouse model and was positively correlated with the infarct volume and neurological score (P < 0.05). Besides, serum MLL1 level was also significantly correlated with the severity of IS (P < 0.05), and high serum MLL1 level indicated poor prognosis of IS patients (P < 0.05). These results revealed that MLL1 contributed to neuron cell apoptosis in ischemic penumbra after IS onset by promoting the formation of ASK-1/TNF-α complex, and its serum level was associated with poor prognosis of IS.

Highlights

Ischemic stroke (IS) is the most common type of stroke, accounting for ∼80% of all strokes (Adeoye et al, 2019)
Results showed that Mixed lineage leukemia 1 (MLL1) expression was significantly upregulated in ischemic penumbra, as well as in cells treated with oxygen–glucose deprivation (OGD) (Figures 2B,D)
We found that MLL1 was upregulated in the ischemic penumbra and OGD-treated primary cortical mixed cells, and its expression level in ischemic penumbra was positively correlated with its serum level and positively correlated with the severity of IS

Summary

Introduction

Ischemic stroke (IS) is the most common type of stroke, accounting for ∼80% of all strokes (Adeoye et al, 2019). Apoptosis signal regulating kinase 1 (ASK-1) is a component of tumor necrosis factor-α (TNF-α)-induced apoptosis complex I, and its activation (phosphorylation) is required for TNF-αinduced apoptosis in multiple cell types (Hatai et al, 2000; Han et al, 2015). The aberrant histone methylation was suggested to be associated with neuron cell apoptosis (Zhoa et al, 2016; Yung et al, 2018). As an active histone modification, the trimethylation of H3K4 (H3K4me3) can be recognized by specific proteins and further recruit downstream coregulatory components, promoting the transcription and expression of the target genes (Bochynska et al, 2018). Mixed lineage leukemia 1 (MLL1) is the main histone methyltransferase (HMT) responsible for the catalysis of H3K4me (Yang and Ernst, 2017), whose abnormal expression had been proven to be tightly associated with cell proliferation and apoptosis (Wang et al, 2014; Sengupta et al, 2019)

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