Is it possible to improve memory function by upregulation of the cholesterol 24S-hydroxylase (CYP46A1) in the brain?

Abstract

We previously described a heterozygous mouse model overexpressing human HA-tagged 24S-hydroxylase (CYP46A1) utilizing a ubiquitous expression vector. In this study, we generated homozygotes of these mice with circulating levels of 24OH 30-60% higher than the heterozygotes. Female homozygous CYP46A1 transgenic mice, aged 15 months, showed an improvement in spatial memory in the Morris water maze test as compared to the wild type mice. The levels of N-Methyl-D-Aspartate receptor 1, phosphorylated-N-Methyl-D-Aspartate receptor 2A, postsynaptic density 95, synapsin-1 and synapthophysin were significantly increased in the hippocampus of the CYP46A1 transgenic mice as compared to the controls. The levels of lanosterol in the brain of the CYP46A1 transgenic mice were significantly increased, consistent with a higher synthesis of cholesterol. Our results are discussed in relation to the hypothesis that the flux in the mevalonate pathway in the brain is of importance in cognitive functions.

Figure 1. Levels of 24OH in serum from heterozygous (HeZ) and homozygous (HoZ) CYP46A1 mice (females and males) 18–21 weeks of age (n = 4–6).

Figure 2. CYP46A1 overexpression enhanced spatial memory retention in aged female mice.

A) Acquisition phase in MWM test: data are shown as escape latency to locate the platform over the 4 days of acquisition. B) Probe test: data are shown as escape latency time to reach the position where the platform was located, number of crossings on the platform position and the time spent in the platform target. C) Passive avoidance test: data are shown as latency time to enter the dark compartment on the training day (day 1) and the probe day (day 2) of the test. No differences were found between the groups. Results are expressed as mean ± standard error of the mean (SEM), n = 7 animal per group (**P<0.01, *P<0.05 compared to WT control mice).

Figure 3. Levels of postsynaptic proteins were increased in the hippocampus of CYP46A1 mice.

Hippocampal samples from CYP46A1 and WT control mice were analyzed by Western blotting. NMDAR1, p-NMDAR2A and PSD95 levels were significantly increased in CYP46 mice. Data are shown as mean ± standard error of the mean (SEM) of immunoreactivity (OD x area of the band) normalizes by α-tubulin levels. N = 7 animal per group (***P<0.001, *P<0.01 compared to WT control mice).

Figure 4. Levels of presynaptic proteins were increased in the hippocampus of CYP46A1 mice.

Hippocampal samples from CYP46A1 and WT control mice were analyzed by Western blotting. Synapthophysin and synapsin-1 levels were significantly increased in CYP46A1 mice, while no differences were found in Neun among the groups. Data are shown as mean ± standard error of the mean (SEM) of immunoreactivity (OD x area of the band) normalizes by α-tubulin levels. N = 7 animal per group (*P<0.01 compared to WT control mice).