Background: Neuronal damage resulting from increased oxidative stress is important in the development of late onset/age-related Alzheimer's disease (LOAD). We have developed an oxidative stress-related mouse model of LOAD based on gene deletion of aldehyde dehydrogenase 2 (ALDH2), an enzyme important for the detoxification of endogenous aldehydes arising from lipid peroxidation. Compared to wildtype (WT) mice, the knockout (KO) mice exhibit AD-like pathologies and a progressive decline in recognition and spatial memory. This progression presumably has a morphological basis induced by oxidative damage.
Objective: We performed morphometric analyses in the dorsal hippocampal CA1 region (dCA1) to determine if altered neuronal structure can help account for the progressive cognitive impairment in 3- to 12-month-old KO mice.
Methods: Dendritic morphology was quantitatively analyzed by branched structured analysis and Sholl analysis following Golgi-Cox staining in WT mice (148 neurons) versus KO mice (180 neurons).
Results: The morphology and complexity of dCA1 pyramidal neurons were similar at age 3 months in WTs and KOs. However, by 6 months there were significant reductions in apical and basal dendritic length, dendrite complexity, and spine density in KO versus WT mice that were maintained through ages 9 and 12 months. Immunostaining for protein adducts of the lipid peroxidation product 4-hydroxynonenal revealed significant increases in staining in dCA1 (but not ventral CA1) by 3 months, increasing through 12 months.
Conclusion: This specific and progressive increase in dCA1 oxidative damage preceded detectable synaptic trimming in KO mice, in keeping with studies showing that lesions to dorsal hippocampus primarily impair cognitive memory.
Keywords: CA1; dendrite; hippocampus; morphometry; oxidative stress; pyramidal neurons; spatial memory; spines.