Sex-dependent influence of postweaning environmental enrichment in Angelman syndrome model mice

Abstract

Introduction: Angelman syndrome (AS) is a rare neurodevelopmental disorder caused by mutation or loss of UBE3A and marked by intellectual disability, ataxia, autism-like symptoms, and other atypical behaviors. One route to treatment may lie in the role that environment plays early in postnatal life. Environmental enrichment (EE) is one manipulation that has shown therapeutic potential in preclinical models of many brain disorders, including neurodevelopmental disorders. Here, we examined whether postweaning EE can rescue behavioral phenotypes in Ube3a maternal deletion mice (AS mice), and whether any improvements are sex-dependent.

Methods: Male and female mice (C57BL/6J Ube3a^tm1Alb mice and wild-type (WT) littermates; ≥10 mice/group) were randomly assigned to standard housing (SH) or EE at weaning. EE had a larger footprint, a running wheel, and a variety of toys that promoted foraging, burrowing, and climbing. Following 6 weeks of EE, animals were submitted to a battery of tests that reliably elicit behavioral deficits in AS mice, including rotarod, open field, marble burying, and forced swim; weights were also monitored.

Results: In male AS-EE mice, we found complete restoration of motor coordination, marble burying, and forced swim behavior to the level of WT-SH mice. We also observed a complete normalization of exploratory distance traveled in the open field, but we found no rescue of vertical behavior or center time. AS-EE mice also had weights comparable to WT-SH mice. Intriguingly, in the female AS-EE mice, we found a failure of EE to rescue the same behavioral deficits relative to female WT-SH mice.

Conclusions: Environmental enrichment is an effective route to correcting the most penetrant phenotypes in male AS mice but not female AS mice. This finding has important implications for the translatability of early behavioral intervention for AS patients, most importantly the potential dependency of treatment response on sex.

Keywords: behavior therapy; mouse; neurodevelopmental disorders; sex differences; transgenic.

FIGURE 1

Experimental setup. (a) Angelman syndrome (AS, Ube3a^m‐/p+) mice on the C57BL/6J (C57) background and their wild‐type (WT) littermates arising from mothers carrying the paternal deletion (Ube3a^m+/p–) and WT males (left) were randomly assigned to standard housing (SH) or larger enriched housing (EE) (right). Dashed line indicates the relative size of EE housing. (b) Timeline for behavioral testing. Following the beginning of enrichment at weaning at postnatal day 21, marble burying (MB), open field (OF), accelerating rotarod (RR), and forced swim (FS) tasks were administered

FIGURE 2

Environmental enrichment normalizes weight deficit at week 6. Improvements in excessive weights were observed in male (a) and female (b) AS mice in the enriched environment. Abbreviations: AS, Angelman syndrome mice; EE, enriched environment; SH, standard housing; WT, wild‐type littermates. Weights, in grams, displayed as mean ± SEM. Two‐way analysis of variance (ANOVA) followed by Bonferroni‐corrected planned comparisons: *p < .05, **p < .01

FIGURE 3

Environmental enrichment normalizes marble burying in male AS mice after 8 weeks. Improvement in the deficit in the number of marbles buried was observed at week 6 in male (a) and female (b) AS mice in the enriched environment, with this improvement strengthened in male AS mice (c) but not female AS mice (d) at a week 8 retest. Abbreviations: AS, Angelman syndrome mice; EE, enriched environment; SH, standard housing; WT, wild‐type littermates. Number of marbles ≥50% buried displayed as mean ± SEM. Two‐way analysis of variance (ANOVA) followed by Bonferroni‐corrected planned comparisons: *p < .05, **p < .01, ***p < .001

FIGURE 4

Environmental enrichment improves some aspects of exploratory activity in the open field in male AS mice after 7 weeks. Male AS mice in the enriched environment showed improvements in distance traveled (a), with no statistically significant improvement in deficient rearing behaviors (b) or thigmotaxis (c). Female AS mice in the enriched environment showed no statistically significant improvements in distance traveled (d), rearing behaviors (e), or thigmotaxis (f) relative to standard housing. Abbreviations: AS, Angelman syndrome mice; EE, enriched environment; SH, standard housing; WT, wild‐type littermates. All quantities displayed as mean ± SEM. Two‐way analysis of variance (ANOVA) followed by Bonferroni‐corrected planned comparisons: *p < .05, **p < .01, ***p < .001

FIGURE 5

Environmental enrichment normalizes rotarod performance in male mice after 9 weeks. Improvement in the motor coordination deficit on the accelerating rotarod was observed in male AS mice (a and b) but not female mice (c and d) in environmental enrichment. Data show the training period (a and c) and a retest of motor learning 48 h later (b and d). Abbreviations: AS, Angelman syndrome mice; EE, enriched environment; SH, standard housing; WT, wild‐type littermates. Latency to fall, in seconds (maximum, 300 s), displayed as mean ± SEM. Two‐way analysis of variance (ANOVA) followed by Bonferroni‐corrected planned comparisons: *p < .05, **p < .01, ***p < .001

FIGURE 6

Environmental enrichment corrects forced swim performance in male mice after 11 weeks. The forced swim deficit in male AS mice improved with environmental enrichment (a), but similar changes were not seen in female mice (b). Abbreviations: AS, Angelman syndrome mice; EE, enriched environment; SH, standard housing; WT, wild‐type littermates. Floating time, as a percentage of 4 min, displayed as mean ± SEM. Two‐way analysis of variance (ANOVA) followed by Bonferroni‐corrected planned comparisons: *p < .05, **p < .01, ***p < .001