Oxidatively modified RNA in mild cognitive impairment

Area of Science:

• Neuroscience
• Biochemistry
• Pathology

Background:

• Oxidative damage is a known hallmark of Alzheimer's disease (AD) and mild cognitive impairment (MCI).
• The specific role of RNA oxidation in the early stages of neurodegeneration, such as MCI, remains largely unexplored.

Purpose of the Study:

• To investigate the presence and significance of RNA oxidation in the hippocampus/parahippocampal gyrus (HPG) of subjects with MCI.
• To compare RNA oxidation levels in MCI with those in late-stage AD (LAD) and age-matched normal controls (NC).

Main Methods:

• Immunohistochemistry was performed on HPG sections from MCI, LAD, and NC subjects using antibodies for 8-hydroxyguanine (8-OHG) and 1-N2-propanodeoxyguanosine (NPrG).
• Confocal microscopy was used to quantify immunostaining.
• RNase and DNase-I treatments were employed to determine the association of adducts with RNA or DNA.

Main Results:

• Significantly elevated levels of 8-OHG and NPrG immunostaining were observed in the HPG of MCI and LAD subjects compared to NC subjects (p<0.05).
• The observed adducts were predominantly localized to neurons exhibiting early tau alterations (MC-1 antibody positive).
• Enzymatic pretreatment indicated that the adducts were primarily associated with RNA, and RNA oxidation levels in MCI were comparable to LAD.

Conclusions:

• RNA oxidation is significantly increased in mild cognitive impairment and is associated with early neurodegenerative changes in tau.
• These findings suggest that RNA oxidation is an early event in the pathogenesis of neuronal degeneration in Alzheimer's disease.