Cell cycle reentry triggers hyperploidization and synaptic dysfunction followed by delayed cell death in differentiated cortical neurons

E Barrio-Alonso,J M Frade,C C Walton,A Hernández-Vivanco,G Perea

doi:10.1038/s41598-018-32708-4

Abstract

Cell cycle reentry followed by neuronal hyperploidy and synaptic failure are two early hallmarks of Alzheimer’s disease (AD), however their functional connection remains unexplored. To address this question, we induced cell cycle reentry in cultured cortical neurons by expressing SV40 large T antigen. Cell cycle reentry was followed by hyperploidy in ~70% of cortical neurons, and led to progressive axon initial segment loss and reduced density of dendritic PSD-95 puncta, which correlated with diminished spike generation and reduced spontaneous synaptic activity. This manipulation also resulted in delayed cell death, as previously observed in AD-affected hyperploid neurons. Membrane depolarization by high extracellular potassium maintained PSD-95 puncta density and partially rescued both spontaneous synaptic activity and cell death, while spike generation remained blocked. This suggests that AD-associated hyperploid neurons can be sustained in vivo if integrated in active neuronal circuits whilst promoting synaptic dysfunction. Thus, cell cycle reentry might contribute to cognitive impairment in early stages of AD and neuronal death susceptibility at late stages.

Highlights

Alzheimer’s disease (AD), the most common cause of dementia, is an irreversible neurological disorder characterized by progressive cognitive decline and degeneration of brain regions crucial for learning and memory[1]
To confirm that T antigen (TAg) expression can trigger neuronal cell cycle reentry, cortical neurons maintained for 6–8 days in vitro (DIV) were lipofected with red fluorescent protein (RFP) and either TAg or LacZ and treated with BrdU, a nucleoside analog that becomes incorporated into the DNA during S-phase
This is followed by a gradual decrease of neuronal viability starting 3 days after transfection, which is independent of caspase-3-mediated apoptosis and oxidative stress

Summary

Introduction

Alzheimer’s disease (AD), the most common cause of dementia, is an irreversible neurological disorder characterized by progressive cognitive decline and degeneration of brain regions crucial for learning and memory[1]. Neuronal expression of TAg in vivo recapitulates the hallmarks of AD, including the presence of neurofibrillary tangle-like profiles and plaque-like amyloid deposits[13] In this latter study, TAg was widely expressed in neurons, resulting in widespread neuronal cell cycle reentry. TAg was widely expressed in neurons, resulting in widespread neuronal cell cycle reentry This situation differs from AD, a condition characterized by a small proportion of neurons becoming hyperploid[5,6,7], which remains surrounded by non-affected neurons. TAg-expressing neurons initially survive, but cell cycle reentry and progressively triggers non-apoptotic/oxidative stress-independent death. We provide evidence that facilitating membrane depolarization after addition of high extracellular potassium prevents further loss of PSD-95 puncta and partially restores spontaneous activity in neurons that reactivate the cell cycle, which is concomitant with survival facilitation

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Conclusion