mTOR inhibitor improves autistic-like behaviors related to Tsc2 haploinsufficiency but not following developmental status epilepticus

Abstract

Background: Tuberous Sclerosis Complex (TSC), a multi-system genetic disorder often associated with Autism Spectrum Disorder (ASD), is caused by mutations of TSC1 or TSC2, which lead to constitutive overactivation of mammalian Target of Rapamycin (mTOR). In several Tsc1+/- and Tsc2+/- animal models, cognitive and social behavior deficits were reversed by mTOR inhibitors. However, phase II studies have not shown amelioration of ASD and cognitive deficits in individuals with TSC during mTOR inhibitor therapy. We asked here if developmental epilepsy, common in the majority of individuals with TSC, but absent in most animal models, could explain the discrepancy. Methods: At postnatal day P12, developmental status epilepticus (DSE) was induced in male Tsc2+/- (Eker) and wild-type rats, establishing four experimental groups including controls. In adult animals (n = 36), behavior was assessed in the paradigms of social interaction test, elevated plus-maze, light-dark test, Y-maze and novel object recognition. The testing was carried out before medication (T1), during a 2-week treatment with the mTOR inhibitor everolimus (T2) and after an 8-week washing-out (T3). Electroencephalographic (EEG) activity was recorded in a separate set of animals (n = 18). Results: Both Tsc2+/- mutation and DSE caused social behavior deficits and epileptiform EEG abnormalities (T1). Everolimus led to persistent improvement of the social deficit induced by Tsc2+/-, while deficits related to DSE did not respond to everolimus (T2, T3). Conclusions: These findings may contribute to an explanation why ASD symptoms in individuals with TSC, where comorbid early-onset epilepsy is common, were in clinical studies not reliably ameliorated by mTOR inhibitors.

Developmental effects of constitutive mTORC1 hyperactivity and environmental enrichment on structural synaptic plasticity and behaviour in a rat model of autism spectrum disorder

“…Petrasek and co‐workers recently reported a deficit of anogenital social exploration in Eker rats from the same breeding colony (Petrasek et al, 2021). The discrepancy between the results of the previous study with the current report can perhaps be explained by the fact that the rats in this study (both genotypes) generally were socially less active (compare Figure 2b, c in Petrasek et al, 2021, with Figure 3a, b in the present study), seemingly contributed by differences in housing conditions. Also, the earlier studies used non‐IVC cages, with cage type known to influence rat performance in behavioural tests (Brain & Benton, 1979; Van de Weerd et al, 2002; Wurbel, 2001).…”

“…Waltereit et al showed a reduction in social interactions in rats after induction of status epilepticus at a very young age (Waltereit et al, 2011). Petrasek and co‐workers recently reported a deficit of anogenital social exploration in Eker rats from the same breeding colony (Petrasek et al, 2021). The discrepancy between the results of the previous study with the current report can perhaps be explained by the fact that the rats in this study (both genotypes) generally were socially less active (compare Figure 2b, c in Petrasek et al, 2021, with Figure 3a, b in the present study), seemingly contributed by differences in housing conditions.…”

“…Waltereit and co‐workers were the first to study social behaviour in Eker rats, showing that the neurobehavioural phenotype with the deficit in social interactions in adult animals can be influenced by the history of drug‐induced seizures during early development (Waltereit et al, 2011). The same group has shown recently that the social deficit, but not seizure‐induced impairments in the Tsc2 +/ − Eker rats could be ameliorated by selective inhibition of mTORC1 activity (Petrasek et al, 2021). Evidence from behavioural studies in other models with TSC2 deficiency has demonstrated that autism‐like phenotype with characteristic stereotypic behaviour can be achieved by targeted depletion of TSC2 protein in cerebellar Purkinje cells at a later developmental stage (Fu & Ess, 2013; Kutna et al, 2021).…”

“…Importantly, the pharmacological block of mTORC1 also failed to counter the effects of Tsc2 haploinsufficiency (Yasuda et al, 2014), inferring a functional redundancy of this key kinase in regulating synaptic plasticity. Given that the preclinical reports of autism‐like symptoms in Tsc2 deficient models have been limited to a single point or a single age group analysis (Gadad et al, 2013; Kutna et al, 2021; Petrasek et al, 2021; Reith et al, 2013; Schneider et al, 2017; Tsai et al, 2012; Waltereit et al, 2011), it is unclear how various developmental stages and environmental changes can influence the impact of Tsc2 deficiency on the neuroplasticity mechanisms and behavioural characteristics.…”