Irradiation-Induced Upregulation of miR-711 Inhibits DNA Repair and Promotes Neurodegeneration Pathways.

Boris Sabirzhanov,Alan I Faden,James P Barrett,Ethan P Glaser,Isabel L Jackson,Bogdan A Stoica,Oleg Makarevich

doi:10.3390/ijms21155239

Abstract

Radiotherapy for brain tumors induces neuronal DNA damage and may lead to neurodegeneration and cognitive deficits. We investigated the mechanisms of radiation-induced neuronal cell death and the role of miR-711 in the regulation of these pathways. We used in vitro and in vivo models of radiation-induced neuronal cell death. We showed that X-ray exposure in primary cortical neurons induced activation of p53-mediated mechanisms including intrinsic apoptotic pathways with sequential upregulation of BH3-only molecules, mitochondrial release of cytochrome c and AIF-1, as well as senescence pathways including upregulation of p21WAF1/Cip1. These pathways of irradiation-induced neuronal apoptosis may involve miR-711-dependent downregulation of pro-survival genes Akt and Ang-1. Accordingly, we demonstrated that inhibition of miR-711 attenuated degradation of Akt and Ang-1 mRNAs and reduced intrinsic apoptosis after neuronal irradiation; likewise, administration of Ang-1 was neuroprotective. Importantly, irradiation also downregulated two novel miR-711 targets, DNA-repair genes Rad50 and Rad54l2, which may impair DNA damage responses, amplifying the stimulation of apoptotic and senescence pathways and contributing to neurodegeneration. Inhibition of miR-711 rescued Rad50 and Rad54l2 expression after neuronal irradiation, enhancing DNA repair and reducing p53-dependent apoptotic and senescence pathways. Significantly, we showed that brain irradiation in vivo persistently elevated miR-711, downregulated its targets, including pro-survival and DNA-repair molecules, and is associated with markers of neurodegeneration, not only across the cortex and hippocampus but also specifically in neurons isolated from the irradiated brain. Our data suggest that irradiation-induced miR-711 negatively modulates multiple pro-survival and DNA-repair mechanisms that converge to activate neuronal intrinsic apoptosis and senescence. Using miR-711 inhibitors to block the development of these regulated neurodegenerative pathways, thus increasing neuronal survival, may be an effective neuroprotective strategy.

Highlights

Ionizing radiation (IR) is an important treatment for brain tumors [1]
We observed that X-ray exposure in Rat primary cortical neurons (RCNs) activated DNA damage responses with sequential phosphorylation/activation of ATM(Ser1981), γH2A.X and Ph-p53(S15) (Figure 3)
A key intrinsic apoptosis pathway involves p53 binding to and transactivating the promoters of pro-apoptotic B-cell lymphoma 2 (Bcl-2) family members, such as Puma, Noxa and Bim [46,47,48], a mechanism confirmed by our detection of p53 interaction with the Noxa promoter and IR-induced upregulation of the p53-dependent genes, Noxa, Puma and Bim (Figure 4)

Summary

Introduction

IR-induced DNA damage may initiate neuronal apoptotic pathways leading to neuronal cell death [2,3,5] via various mechanisms such as activation of p53 and caspase activation [11]. Activated p53 binds to the promoters of its target genes and upregulates the transcription of pro-apoptotic Bcl-2 family members Puma, Noxa and Bim. The role of p53 and downstream apoptotic pathways in irradiation-mediated neurotoxicity is suggested by studies showing that the absence of p53 attenuated apoptosis and volume loss after radiation therapy [15]. Agents that downregulate the expression of pro-apoptotic Bcl-2 genes, such as valproic acid [16] and lithium [17,18], may attenuate IR-induced neuronal apoptosis and improve cognitive performance

Methods

Results

Conclusion