Excessive Laughter-like Vocalizations, Microcephaly, and Translational Outcomes in theUbe3aDeletion Rat Model of Angelman Syndrome

Abstract

Angelman Syndrome (AS) is a rare genetic neurodevelopmental disorder characterized by intellectual disabilities, motor and balance deficits, impaired communication, and a happy, excitable demeanor with frequent laughter. We sought to elucidate a preclinical outcome measure in male and female rats that addressed communication abnormalities of AS and other neurodevelopmental disorders in which communication is atypical and/or lack of speech is a core feature. We discovered, and herein report for the first time, excessive laughter-like 50-kHz ultrasonic emissions in the Ube3a mat-/pat+ rat model of AS, which suggests an excitable, playful demeanor and elevated positive affect, similar to the demeanor of individuals with AS. Also in line with the AS phenotype, Ube3a mat-/pat+ rats demonstrated aberrant social interactions with a novel partner, distinctive gait abnormalities, impaired cognition, an underlying long-term potentiation deficit, and profound reductions in brain volume. These unique, robust phenotypes provide advantages compared to currently available mouse models and will be highly valuable as outcome measures in the evaluation of therapies for AS. Significance StatementAngelman Syndrome (AS) is a severe neurogenetic disorder for which there is no cure, despite decades of research using mouse models. This study utilized a recently developed rat model of AS to delineate disease-relevant outcome measures in order to facilitate therapeutic development. We found the rat to be a strong model of AS, offering several advantages over mouse models by exhibiting numerous AS-relevant phenotypes including overabundant laughter-like vocalizations, reduced hippocampal longterm potentiation, and volumetric anomalies across the brain. These findings are unconfounded by detrimental motor abilities and background strain, issues plaguing mouse models. This rat model represents an important advancement in the field of AS and the outcome metrics reported herein will be central to the therapeutic pipeline.

Response Calls Evoked by Playback of Natural 50-kHz Ultrasonic Vocalizations in Rats

“…Importantly, the emission of response calls was clearly linked to 50-kHz USV playback. In fact, response calls were seen specifically in response to 50-kHz USV but not in response to time-and amplitude-matched noise, replicating previous results (Willadsen et al, 2014;Willuhn et al, 2014;Engelhardt et al, 2017Engelhardt et al, , 2018Berg et al, 2018Berg et al, , 2021Kisko et al, 2020;Olszyński et al, 2020Olszyński et al, , 2021. When exposed to 50-kHz USV, receiver rats often started emitting response calls within the first minute of playback and emission rates were typically peaking after around 2-3 min, often outlasting playback for up to 5 min.…”

“…In this study, we characterized response calls emitted by rats exposed to playback of appetitive 50-kHz USV, previously shown to function as social contact calls (Wöhr, 2018). The phenomenon that rats respond to playback of species-specific 50-kHz calls by emitting response calls has been repeatedly reported before, but has not been described in detail yet Schwarting, 2007, 2009;Willadsen et al, 2014;Willuhn et al, 2014;Engelhardt et al, 2017Engelhardt et al, , 2018Berg et al, 2018Berg et al, , 2021Kisko et al, 2020;Olszyński et al, 2020Olszyński et al, , 2021 for an overview see Supplementary Table 1). First, we described the emission of response calls in reaction toward 50-kHz USV playback in WI rats.…”

“…Although echoing the reciprocal nature of acoustic communication and repeatedly observed in studies applying the 50-kHz USV playback paradigm, still little is known about such response calls. In previous studies, response calls toward 50-kHz USV were observed in males and females (Berg et al, 2018(Berg et al, , 2021, albeit the emission of calls in response to 50-kHz USV playback was found to be more prominent in males than females in one study (Kisko et al, 2020). A developmental study further suggests that age is another relevant factor, with juvenile rats emitting more response calls than adult rats (Wöhr and Schwarting, 2009).…”

“…At the behavioral level, the social approach response toward 50-kHz USV playback can be accompanied by the emission of response calls Schwarting, 2007, 2009;Willadsen et al, 2014;Willuhn et al, 2014;Engelhardt et al, 2017Engelhardt et al, , 2018Berg et al, 2018Berg et al, , 2021Kisko et al, 2020;Olszyński et al, 2020Olszyński et al, , 2021. Although echoing the reciprocal nature of acoustic communication and repeatedly observed in studies applying the 50-kHz USV playback paradigm, still little is known about such response calls.…”

Gait as a quantitative translational outcome measure in Angelman syndrome

“…In mice, this behavioral phenotype has been well reported as reduced locomotor activity, poor balance and coordination, and impairment of performance on the accelerated rotarod (Born et al, 2017;Huang et al, 2013;Jiang et al, 1998;Miura et al, 2002). Recently, a novel rat model of a full deletion of Ube3a recapitulated these motor deficits including the aforementioned accelerated rotarod motor learning deficit as well as additional nuanced impairments in rearing and fine forelimb motor skills (Berg et al, 2020(Berg et al, , 2021Dodge et al, 2020).…”