Behavioral and Synaptic Phenotypes of Female Prdx6-/- Mice

Abstract

Peroxiredoxin 6 (PRDX6) is expressed throughout the brain, including the hippocampus, where it plays a potential role in synaptic regulation and forming emotional and spatial memories. PRDX6 is predominantly detected in the female mouse's hippocampus; thus, we investigate the effect of the Prdx6 gene on behavioral phenotypes and synaptic functions using female Prdx6 knockout (Prdx6^-/-) mice. Our results demonstrate that female Prdx6^-/- mice exhibited anxiety-like behavior, enhanced contextual fear memory, and impaired spatial memory. We also found increased, paired-pulse facilitation ratios, and decreased long-term potentiation (LTP) in the hippocampal region of these female Prdx6^-/- mice. The present study helps to understand better the PRDX6's role in emotional response and spatial memory formation in female mice.

Keywords: antioxidation; anxiety; long-term potentiation; peroxiredoxin 6; spatial memory.

Figure 1

Experimental design and timeline. A total of 60 (12–14 week-old) mice, 29 Prdx6^+/+ and 31 Prdx6^−/−, were divided into 3 batches and used in three sets of experiments. The first batch of mice was used to test a series of behavior tests, including OFT, rotarod test, LDT, and TFC. The second batch of mice was used to measure the spatial memory to MWM test. The third batch of mice was used to investigate the hippocampal synaptic plasticity by PPF and LTP recording.

Figure 2

Female Prdx6^−/− mice have normal locomotor functions. (A) Schematic diagram of the open field arena. (B) The distance traveled and (C) moving speed in an open field arena (Prdx6^+/+, n = 9 and Prdx6^−/−, n = 9). (D) Schematic diagram of the rotarod test protocol. (E) Time remaining on an acceleration rotarod (s) before falling. (F) Rotational velocity (rpm) at the time of falling. All data are presented as mean ± SEM. PRDX6, peroxiredoxin 6.

Figure 3

Female Prdx6^−/− mice exhibit high levels of anxiety-like behavior. (A) Number of entries into the center of an open field arena (Prdx6^+/+, n = 9 and Prdx6^−/−, n = 9). Percentage of time spent in (B) center, (C) middle, and (D) outer areas in the open field arena. (E) Schematic diagram of light/dark transfer test. (F) The traveling distance and (G) moving speed in the light compartment. (H) Percentage of risk assessment during 10 min of exploration period. (I) The number of entries into the light compartment. (J) Time spent in the light compartment. All data are presented as mean ± SEM, * p < 0.05. PRDX6, peroxiredoxin 6.

Figure 4

Female Prdx6^−/− mice exhibited enhanced fear memory retrieval to context. (A) Illustration of trace fear conditioning procedure and contextual test (B) The learning curve for baseline and three trials of TFC training (Prdx6^+/+, n = 9 and Prdx6^−/−, n = 9). (C) The total percentage of freezing of training sessions. (D) The total percentage of freezing of contextual test. All data are presented as mean ± SEM, * p < 0.05. TFC, trace fear conditioning; PRDX6, peroxiredoxin 6.

Figure 5

The female Prdx6^−/− mice showed impaired spatial memory in the Morris water maze (MWM) task. (A) Illustration of a MWM. (B) Escape latency (time to reach the platform) and (C) swimming speed during the visible platform trial (Prdx6^+/+, n = 15 and Prdx6^−/−, n = 17). (D) The trial plots of escape latency for 5 days of hidden trials. (E) Percentage of time spent in each quadrant during a probe test. (F) The heat map (left panel) and swimming pattern (right panel) during a probe test. All data are presented as mean ± SEM, * p < 0.05, mixed-design repeated measure ANOVA followed by Bonferroni’s post hoc test with unpaired Student’s t test for individual differences between groups within each quadrant. NW, northwest; NE, northeast; SW, southwest; SE, southeast; PRDX6, peroxiredoxin 6; HD, hidden platform day.

Figure 6

Impaired hippocampal LTP in female Prdx6^−/− mice. (A) Representative image for the positions of stimulus and recording electrodes in the hippocampal CA1 region. (B) Input–Output curve for fFPSP amplitudes (n = 8 slices/ 5 mice in each group). (C) the paired–pulse facilitation (PPF) ratio, delivered throughout the seven selected interstimulus intervals (15, 30, 50, 100, 150, 200, and 250 ms) (n = 8 slices/ 5 mice in Prdx6^+/+ group and n = 9 slices/ 5 mice in Prdx6^−/− mice). (D) The averaged fEPSP traces of Prdx6^+/+ and Prdx6^−/− mice (n = 5 mice/group). The gray boxes represent the regions of the last 10 min of the first and third hours. (E) The averages of the percentage of normalized fEPSP slopes from the last 10 min of the first and third hours. All data are presented as mean ± SEM., * p < 0.05, mixed-design repeated measure ANOVA followed by Bonferroni’s post hoc test with unpaired Student’s t-test for individual differences between groups within each time point. fEPSP, field excitatory postsynaptic potential; PRDX6, peroxiredoxin 6; PPR, paired-pulse ratio; HFS, high frequency stimulation.

Figure 7

Graphical summary for the behavioral and synaptic phenotypes of female Prdx6^−/− mice. The female Prdx6^−/− mice exhibited high emotional responses, including anxiety-like behavior and enhanced fear expression (orange box). These mutant mice also displayed impaired spatial memory and hippocampal synaptic function (yellow box). Normal locomotion and motor coordination were also observed in female Prdx6^−/− mice (green box).