Pathogenic mutations in cyclin-dependent kinase-like 5 (
) result in CDKL5 deficiency disorder (CDD), a rare disease marked by early-life seizures, autistic behaviors, and intellectual disability. ...Although mouse models of CDD exhibit dendritic instability and alterations in synaptic scaffolding proteins, studies of glutamate receptor levels and function are limited. Here we used a novel mouse model of CDD, the
knock-in mouse (R59X), to investigate changes in synaptic glutamate receptor subunits and functional consequences. Male mice were used for all experiments to avoid the confounding effects of X-inactivation that would be present in female heterozygous mice. We showed that adult male R59X mice recapitulated the behavioral outcomes observed in other mouse models of CDD, including social deficits and memory and learning impairments, and exhibited decreased latency to seizure upon pentylenetetrazol administration. Furthermore, we observed a specific increase in GluA2-lacking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)-type glutamate receptors (AMPARs) in the adult R59X hippocampus, which is accompanied electrophysiologically by increased rectification ratio of AMPAR EPSCs and elevated early-phase long term potentiation (LTP). Finally, we showed that acute treatment with the GluA2-lacking AMPAR blocker IEM-1460 decreased AMPAR currents, and rescued social deficits, working memory impairments, and seizure behavior latency in R59X mice.
CDKL5 deficiency disorder (CDD) is a rare disease marked by autistic-like behaviors, intellectual disability, and seizures. While synaptic dysfunction has been observed in mouse models of CDD, there is limited information on how synaptic alterations contribute to behavioral and functional changes in CDD. Here we reveal elevated hippocampal GluA2-lacking AMPAR expression in a novel mouse model of CDD that is accompanied by changes in synaptic AMPAR function and plasticity. We also show, for the first time, that acutely targeting GluA2-lacking AMPAR dysregulation rescues core synaptic and neurobehavioral deficits in CDD.
Mutation rates can evolve through genetic drift, indirect selection due to genetic hitchhiking, or direct selection on the physicochemical cost of high fidelity. However, for many systems, it has ...been difficult to disentangle the relative impact of these forces empirically. In RNA viruses, an observed correlation between mutation rate and virulence has led many to argue that their extremely high mutation rates are advantageous because they may allow for increased adaptability. This argument has profound implications because it suggests that pathogenesis in many viral infections depends on rare or de novo mutations. Here, we present data for an alternative model whereby RNA viruses evolve high mutation rates as a byproduct of selection for increased replicative speed. We find that a poliovirus antimutator, 3DG64S, has a significant replication defect and that wild-type (WT) and 3DG64S populations have similar adaptability in 2 distinct cellular environments. Experimental evolution of 3DG64S under selection for replicative speed led to reversion and compensation of the fidelity phenotype. Mice infected with 3DG64S exhibited delayed morbidity at doses well above the lethal level, consistent with attenuation by slower growth as opposed to reduced mutational supply. Furthermore, compensation of the 3DG64S growth defect restored virulence, while compensation of the fidelity phenotype did not. Our data are consistent with the kinetic proofreading model for biosynthetic reactions and suggest that speed is more important than accuracy. In contrast with what has been suggested for many RNA viruses, we find that within-host spread is associated with viral replicative speed and not standing genetic diversity.
Cyclin‐dependent kinase‐like 5 (CDKL5) deficiency disorder (CDD) is caused by a loss‐of‐function mutation in CDKL5 gene, encoding a serine–threonine kinase highly expressed in the brain. CDD ...manifests with early‐onset epilepsy, autism, motor impairment and severe intellectual disability. While there are no known treatments for CDD, the use of cannabidiol has recently been introduced into clinical practice for neurodevelopmental disorders. Given the increased clinical utilization of cannabidiol, we examined its efficacy in the CDKL5R59X knock‐in (R59X) mice, a CDD model based on a human mutation that exhibits both lifelong seizure susceptibility and behavioural deficits. We found that cannabidiol pre‐treatment rescued the increased seizure susceptibility in response to the chemoconvulsant pentylenetetrazol (PTZ), attenuated working memory and long‐term memory impairments, and rescued social deficits in adult R59X mice. To elucidate a potential mechanism, we compared the developmental hippocampal and cortical expression of common endocannabinoid (eCB) targets in R59X mice and their wild‐type littermates, including cannabinoid type 1 receptor (CB1R), transient receptor potential vanilloid type 1 (TRPV1) and 2 (TRPV2), G‐coupled protein receptor 55 (GPR55) and adenosine receptor 1 (A1R). Many of these eCB targets were developmentally regulated in both R59X and wild‐type mice. In addition, adult R59X mice demonstrated significantly decreased expression of CB1R and TRPV1 in the hippocampus, and TRPV2 in the cortex, while TRPV1 was increased in the cortex. These findings support the potential for dysregulation of eCB signalling as a plausible mechanism and therapeutic target in CDD, given the efficacy of cannabidiol to attenuate hyperexcitability and behavioural deficits in this disorder.
CDKL5 deficiency disorder (CDD) is a genetic disease that produces lifelong neurological dysfunction, including autism, intellectual disability and epilepsy. This study employed a clinically relevant mouse model of CDD to investigate the effects of cannabidiol (CBD) on behavioural outcomes and found that it attenuates seizure susceptibility, memory impairments and social behavioural deficits. The clinical impact of this research is potentially very high, as CBD is already FDA‐approved for epilepsy. The study also demonstrates altered signalling related to the endogenous endocannabinoid system in CDD, which could inform the development of novel therapies with more specific endocannabinoid receptor modulators.
Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is caused by a loss-of-function mutation in CDKL5 gene, encoding a serine-threonine kinase highly expressed in the brain. CDD ...manifests with early-onset epilepsy, autism, motor impairment and severe intellectual disability. While there are no known treatments for CDD, the use of cannabidiol has recently been introduced into clinical practice for neurodevelopmental disorders. Given the increased clinical utilization of cannabidiol, we examined its efficacy in the CDKL5
knock-in (R59X) mice, a CDD model based on a human mutation that exhibits both lifelong seizure susceptibility and behavioural deficits. We found that cannabidiol pre-treatment rescued the increased seizure susceptibility in response to the chemoconvulsant pentylenetetrazol (PTZ), attenuated working memory and long-term memory impairments, and rescued social deficits in adult R59X mice. To elucidate a potential mechanism, we compared the developmental hippocampal and cortical expression of common endocannabinoid (eCB) targets in R59X mice and their wild-type littermates, including cannabinoid type 1 receptor (CB1R), transient receptor potential vanilloid type 1 (TRPV1) and 2 (TRPV2), G-coupled protein receptor 55 (GPR55) and adenosine receptor 1 (A1R). Many of these eCB targets were developmentally regulated in both R59X and wild-type mice. In addition, adult R59X mice demonstrated significantly decreased expression of CB1R and TRPV1 in the hippocampus, and TRPV2 in the cortex, while TRPV1 was increased in the cortex. These findings support the potential for dysregulation of eCB signalling as a plausible mechanism and therapeutic target in CDD, given the efficacy of cannabidiol to attenuate hyperexcitability and behavioural deficits in this disorder.
CDKL5 Deficiency Disorder (CDD) is a rare disease that presents as a set of neurological deficits including early-life epilepsy, intellectual disability, and autistic-like behaviors. It results from ...pathogenic mutations in the gene for cyclin-dependent kinase-like 5 (CDKL5), a protein that is highly expressed in brain. There is no cure for CDD and seizures in this disorder are typically resistant to traditional anti-epileptic drugs, although some patients respond well to cannabidiol. However, underlying mechanisms of what causes hyperexcitability and neurological deficits in CDD is poorly understood. We investigated the novel Cdkl5R59X mouse (R59X), and observed that mutant mice have social interaction and memory deficits, and decreased latency to seizure after administration of pentylenetetrazol. Given the observed behavioral alterations and hyperexcitability in R59X mice, we hypothesized that mutant mice would exhibit underlying molecular and functional alterations in proteins involved in regulating the E:I balance. Indeed, we observed a specific decrease in membrane-bound AMPA receptor (AMPAR) subunit GluA2 as well as decreased GluA2:GluA1 in the hippocampus of R59X mice, suggesting an increase in hippocampal GluA2-lacking AMPARs, which are calcium permeable and have significant roles in regulating neuronal plasticity and excitability. Indeed, decreased hippocampal GluA2 was accompanied by inward rectification of AMPAR currents in whole-cell patch recordings from hippocampal CA1 neurons, indicative of an increased population of functional GluA2-lacking AMPARs, and elevated early-phase long-term potentiation at Schaffer collateral-CA1 synapses. Finally, we evaluated the therapeutic potential of GluA2-lacking AMPAR blocker IEM-1460 as well as cannabidiol to observe 1) whether blocking increased hippocampal GluA2-lacking AMPARs would attenuate behavioral alterations and hyperexcitability in R59X mice and 2) whether cannabidiol shows therapeutic efficacy in R59X mice similar to human CDD patients, thus validating R59X mice as a relevant model to test potential therapeutics in CDD. Indeed, IEM-1460 significantly rescued deficits in social behavior, short-term memory, and latency to seizure while cannabidiol significantly rescued deficits in short and long-term memory and latency to seizure. These results verify that blocking increased GluA2-lacking AMPARs may be a successful therapeutic strategy in CDD, and that both IEM-1460 and cannabidiol may attenuate hyperexcitability as well as autistic-like behaviors and memory deficits in CDD.
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