Crosstalk between ApoE-expressing cells and genotoxic stress in the mouse brain

Apolipoprotein E (ApoE) plays an important role in cerebral lipid transport. Beyond lipid transport, ApoE also contributes to the maintenance of neuronal integrity. Although DNA damage and dysfunction in the DNA damage response are recognized as early contributors to neuropathology, the connection between ApoE and DNA damage remains poorly understood. In this study, we investigated cells expressing endogenous mouse ApoE (mApoE) in the brain under both normal condition and etoposide-induced DNA damage. Immunohistochemical analysis revealed that mApoE was predominantly expressed in astrocytes and a subset of neurons across various brain regions, with minimal expression in microglia and no detectable expression in oligodendrocytes. Induction of DNA damage through etoposide treatment did not alter the expression level or distribution pattern of mApoE in brain. However, a correlation between neuronal mApoE expression and DNA damage was observed: mApoE-positive neurons were more affected and exhibited a higher number of γH2A.X foci upon etoposide treatment. This observation warrants further investigation to determine whether the increased sensitivity of mApoE-positive neurons to DNA damage is neuroprotective or contributes to neurodegeneration. Our study provides a foundation for understanding the physiological role of mApoE in response to DNA damage and suggests a potential involvement of neuronal mApoE in neurodegeneration.