DNA damage and transcriptional regulation in iPSC-derived neurons from Ataxia Telangiectasia patients

Alessandro Corti,Benedetta Terragni,Matteo Dugo,Raina Sota,Domenico Delia,Silvana Franceschetti,Massimo Mantegazza,Raffaele A Calogero,Daniele Lecis,Patrizia Gasparini,Michela Restelli,Krystyna H Chrzanowska

doi:10.1038/s41598-018-36912-0

Abstract

Ataxia Telangiectasia (A-T) is neurodegenerative syndrome caused by inherited mutations inactivating the ATM kinase, a master regulator of the DNA damage response (DDR). What makes neurons vulnerable to ATM loss remains unclear. In this study we assessed on human iPSC-derived neurons whether the abnormal accumulation of DNA-Topoisomerase 1 adducts (Top1ccs) found in A-T impairs transcription elongation, thus favoring neurodegeneration. Furthermore, whether neuronal activity-induced immediate early genes (IEGs), a process involving the formation of DNA breaks, is affected by ATM deficiency. We found that Top1cc trapping by CPT induces an ATM-dependent DDR as well as an ATM-independent induction of IEGs and repression especially of long genes. As revealed by nascent RNA sequencing, transcriptional elongation and recovery were found to proceed with the same rate, irrespective of gene length and ATM status. Neuronal activity induced by glutamate receptors stimulation, or membrane depolarization with KCl, triggered a DDR and expression of IEGs, the latter independent of ATM. In unperturbed A-T neurons a set of genes (FN1, DCN, RASGRF1, FZD1, EOMES, SHH, NR2E1) implicated in the development, maintenance and physiology of central nervous system was specifically downregulated, underscoring their potential involvement in the neurodegenerative process in A-T patients.

Highlights

Ataxia Telangiectasia (A-T) is an inherited syndrome manifesting early onset neurodegeneration, cancer predisposition, immunodeficiency, telangiectasias, and at cellular level radiosensitivity, chromosomal instability and cell cycle checkpoint defects[1]
We previously reported that human postmitotic A-T neurons exhibit an abnormal accumulation of topoisomerase 1 covalently bound to DNA (Top1-cc)[16], in agreement with findings in mouse Atm−/− neural and MEF cells[15,17,22]
A-T is an inherited multisystemic disorder with early onset brain degeneration, caused by mutations inactivating the ATM kinase best known for its apical role in DNA damage response (DDR) signalling

Summary

Introduction

Ataxia Telangiectasia (A-T) is an inherited syndrome manifesting early onset neurodegeneration, cancer predisposition, immunodeficiency, telangiectasias, and at cellular level radiosensitivity, chromosomal instability and cell cycle checkpoint defects[1]. Cytoplasmic ATM was shown to segregate with and regulate endocytosis of synaptic vesicles, as opposite to ATR which associates with inhibitory vesicles[7] It is uncertain what renders neurons hypersensitive to ATM deficiency. Patient-derived induced pluripotent stem cells (iPSCs) differentiating into mature neurons offer a powerful in vitro system to model neurological diseases[19,20]. Using this approach, we investigated the response of A-T and normal (WT) neurons to various stimuli and impact on transcription, to identify factors and mechanisms of neuropathological relevance for A-T

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Results

Conclusion