DNA glycosylase Neil2 contributes to genomic responses in the spleen during clinical prion disease

Katja Scheffler,Clara M.O Jalland,Sylvie L Benestad,Torfinn Moldal,Cecilie Ersdal,Gjermund Gunnes,Rajikala Suganthan,Magnar Bjørås,Michael A Tranulis

doi:10.1016/j.freeradbiomed.2020.03.030

Abstract

The DNA glycosylase Neil2 is a member of the base excision repair (BER) family of enzymes, which are important for repair of oxidative DNA damage. Specifically, Neil2 participates in repair of oxidized bases in single-stranded DNA of transcriptionally active genes. Mice with genetic ablation of Neil2 (Neil2−/−) display no overt phenotypes, but an age-dependent accumulation of oxidative DNA damage and increased inflammatory responsiveness. In young mice intra-cerebrally inoculated with prions, vigorous prion propagation starts rapidly in the germinal follicles of the spleen due to inoculum spillover. Here, we compare experimental prion disease in Neil2−/− mice with that in wild-type mice at disease onset and end-stage. Specifically, we investigated disease progression, accumulation of DNA damage, and mitochondrial respiratory complex activity in brain and spleen. We used genome-wide RNA sequencing of the spleen to compare the immune responses to prion propagation between the two groups of mice, at both onset and end-stage prion disease. The Neil2−/− mice deteriorated more rapidly than wild-type mice after onset of clinical signs. Levels of DNA damage in brain increased in both mouse groups, slightly more in the Neil2−/− mice. Transcriptome data from spleen at disease onset were similar between the mouse groups with moderate genomic responses. However, at end-stage a substantial response was evident in the wild-type mice but not in Neil2−/− mice. Our data show that Neil2 counteracts toxic signaling in clinical prion disease, and this is separate from gross pathological manifestations and PrPSc accumulation.

Highlights

Prion diseases are invariably fatal, neurodegenerative maladies caused by disease-provoking protein complexes, known as prions
We found no difference in nuclear DNA and mitochondrial DNA damage level in brain between the mouse genotypes, mtDNA damage accumulated significantly during disease development (Fig. 2A)
As has previously been observed in experimental prion disease in mice with compromised DNA glycosylase activity [22,23], the overall features of prion disease were similar in Neil2−/− mice and wild-type mice

Summary

Introduction

Prion diseases are invariably fatal, neurodegenerative maladies caused by disease-provoking protein complexes, known as prions. These consist of misfolded conformers of the host-encoded cellular prion protein PrPC [1,2]. In some naturally occurring prion diseases, such as classical scrapie in sheep and chronic wasting disease in deer, PrPSc aggregates are often abundantly present in peripheral lymphoid tissues along the gastrointestinal tract and in the spleen long before onset of clinical signs [3,4,5]. We have observed active prion propagation in the spleen in RML-infected mice that are compromised regarding repair of oxidative DNA damage. Gene knockout of downstream effectors, such as APE1 or pol β are embryonic lethal, suggesting that accumulation of BER pathway intermediates is lethal [19,20,21]

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Results

Conclusion