Altered DNA repair; an early pathogenic pathway in Alzheimer\u2019s disease and obesity

Hao Yu,Fen Xia,Fiona Edith Harrison

doi:10.1038/s41598-018-23644-4

Abstract

Unrepaired DNA double-strand breaks (DSBs) are lethal. The present study compared the extent of DSBs, neuronal apoptosis, and status of two major DSB repair pathways - homologous combinational repair (HR) and nonhomologous end-joining (NHEJ) - in hippocampus of 5–6 month and 16–18 month-old wild-type and APP/PSEN1 mice fed control diet or high fat diet (60% fat from lard). We performed immunohistochemical staining and quantification for nuclear foci formation of γ-H2AX for DSBs, RAD51, and 53BP1, which represent the functional status of HR and NHEJ, respectively. Increased γ-H2AX and caspase-3 staining indicated greater DSBs and associated neuronal apoptosis in APP/PSEN1 mice at both ages studied. RAD51-positive foci were fewer in APP/PSEN1 indicating that HR processes may be diminished in these mice, although NHEJ (53BP1 staining) appeared unchanged. High fat diet in young wild-type mice led to similar changes to those observed in APP/PSEN1 mice (γ-H2AX and caspase-3 staining, and fewer RAD51-positive foci). Overall, these data suggest that APP/PSEN1- and high fat diet-associated early accumulation of DSBs and neuronal cell death, resulted at least in part, from inhibition of HR, one of the major DSB repair pathways.

Highlights

The typical pathological hallmarks of Alzheimer’s disease include accumulation of β-amyloid, tau hyperphosphorylation, synaptic damage, and cell death
In this study we report that increases in DNA double-strand breaks (DSBs) (γ-H2AX nuclear foci) and apoptosis (Caspase3) in hippocampal neurons, were accompanied by decreased evidence of homologous recombination-directed repair (HR) DSB repair (RAD51) in young and aged APP/PSEN1 mice, and in young mice fed a high fat diet
Data are analyzed by separate 2-tailed t-tests within each comparison pair. *P < 0.05, ***P < 0.001 all HFD mice, APP/PSEN1 compared to wild-type as marked; +P < 0.05, ++P < 0.01 high fat diet-fed wild-type mice compared to age-matched control fed-wild-types

Summary

Introduction

The typical pathological hallmarks of Alzheimer’s disease include accumulation of β-amyloid, tau hyperphosphorylation, synaptic damage, and cell death. One downstream effect of DSBs, which can be detected histochemically and quantified based on the level of phosphorylation of a histone protein (H2A variant X, at Ser[139] (γ-H2AX))[6], is neuronal death It is still not clear what are the downstream effects of DSBs that can be detected histochemically and quantified, whether these DSB repair mechanisms are altered in Alzheimer’s disease, and at which stage this particular lethal form of DNA damage is involved in the pathologic process[7]. In the present study we investigated persistent DSBs, and markers of two repair pathways - non-homologous end joining (NHEJ) and homologous recombination-directed repair (HR) - in APP/PSEN1 mice, a model of Alzheimer’s disease-related amyloidosis These mice exhibit escalating β-amyloid accumulation, oxidative stress, neuroinflammation and cognitive decline from around 6 months of age[8]. Our data suggest that these repair process were impacted by both age and genotype, as well as the high fat diet

Methods

Results

Conclusion