Differential responses of neurons, astrocytes, and microglia to G-quadruplex stabilization.

Natalie Tabor,Liang Zhu,Andrey S Tsvetkov,Conelius Ngwa,David Monchaud,Matthew D Meyer,Jeremie Mitteaux,Fudong Liu,Jose F Moruno-Manchon,Louise D Mccullough

doi:10.18632/aging.203222

Abstract

The G-quadruplex (G4-DNA or G4) is a secondary DNA structure formed by DNA sequences containing multiple runs of guanines. While it is now firmly established that stabilized G4s lead to enhanced genomic instability in cancer cells, whether and how G4s contribute to genomic instability in brain cells is still not clear. We previously showed that, in cultured primary neurons, small-molecule G4 stabilizers promote formation of DNA double-strand breaks (DSBs) and downregulate the Brca1 gene. Here, we determined if G4-dependent Brca1 downregulation is unique to neurons or if the effects in neurons also occur in astrocytes and microglia. We show that primary neurons, astrocytes and microglia basally exhibit different G4 landscapes. Stabilizing G4-DNA with the G4 ligand pyridostatin (PDS) differentially modifies chromatin structure in these cell types. Intriguingly, PDS promotes DNA DSBs in neurons, astrocytes and microglial cells, but fails to downregulate Brca1 in astrocytes and microglia, indicating differences in DNA damage and repair pathways between brain cell types. Taken together, our findings suggest that stabilized G4-DNA contribute to genomic instability in the brain and may represent a novel senescence pathway in brain aging.

Highlights

Guanine (G)-rich sequences in the human genome and transcriptome can fold into non-canonical structures known as G-quadruplexes [1, 2]
We found that pyridostatin (PDS), a selective G4-DNA-binding small molecule designed to form a stable complex with G4-DNA structures [33], induces significant chromatin re-arrangements in cultured cortical neurons, astrocytes, and to less extent microglia
Our findings indicate that G4DNA might be an important mechanism that induces genomic instability in brain cells in aging and neurodegeneration

Summary

Introduction

Guanine (G)-rich sequences in the human genome and transcriptome can fold into non-canonical structures known as G-quadruplexes (or G4s, G4-DNA and G4-RNA, respectively) [1, 2]. These sequences contain at least four G runs, which enable the four Gs to associate via Hoogsteen-type hydrogen-bonds to form self-stacking G-quartets, forming a columnar G4 structure, further stabilized by potassium cations in its inner channel [1]. G4-DNA-binding transcription factors, G4DNA-associated proteins, and G4-DNA helicases bind to the G4-DNA structures and modulate G4 landscapes in cells [11,12,13]. The G4 helicase PIF1 cooperates with breast cancer type 1 susceptibility protein (BRCA1) to unfold the G4-DNA structures at DNA double-strand breaks (DSBs) [24]

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Results

Conclusion