Structural Bases of Atypical Whisker Responses in a Mouse Model of CDKL5 Deficiency Disorder

A new knockin mouse carrying the E364X patient mutation for CDKL5 deficiency disorder: neurological, behavioral and molecular profiling

CDKL5 deficiency disorder (CDD) is a rare neurodevelopmental syndrome caused by mutations in the X-linked CDKL5 gene. Hundreds of pathogenic variants have been described, associated with a significant phenotypic heterogeneity observed among patients. To date, different knockout mouse models have been generated. Here we present a new knockin CDKL5 mouse model carrying a humanized, well-characterized nonsense variant (c.1090G > T; p.E364X) described in the C-terminal domain of the CDKL5 protein in a female patient with a milder phenotype. Both male and female Cdkl5 E364X mice were analyzed. The novel Cdkl5 E364X mouse showed altered neurological and motor neuron maturation, hyperactivity, defective coordination and impaired memory and cognition. Gene expression analysis highlighted an unexpected reduction of Cdkl5 expression in Cdkl5 E364X mice brain tissues, with a significant increase in overall neuron-specific gene expression and an area-dependent alteration of astrocyte- and oligodendrocyte-specific transcripts. Moreover, our results showed that the loss of CDKL5 protein had the most significant impact on the cerebellum and hippocampus, compared to other analyzed tissues. A targeted analysis to study synaptic plasticity in cerebellum and hippocampus showed reduced Gabra1 and Gabra5 expression levels in females, whereas Gabra1 expression was increased in males, suggesting an opposite, sex-dependent regulation of the GABA receptor expression already described in humans. In conclusion, the novel Cdkl5E364X mouse model is characterized by robust neurological and neurobehavioral alterations, associated with a molecular profile related to synaptic function indicative of a cerebellar GABAergic hypofunction, pointing to Gabra1 and Gabra5 as novel druggable target candidates for CDD.

Involvement of sphingosine-1-phosphate receptor 1 in pain insensitivity in a BTBR mouse model of autism spectrum disorder

BACKGROUND

Abnormal sensory perception, particularly pain insensitivity (PAI), is a typical symptom of autism spectrum disorder (ASD). Despite the role of myelin metabolism in the regulation of pain perception, the mechanisms underlying ASD-related PAI remain unclear.

METHODS

The pain-associated gene sphingosine-1-phosphate receptor 1 (S1PR1) was identified in ASD samples through bioinformatics analysis. Its expression in the dorsal root ganglion (DRG) tissues of BTBR ASD model mice was validated using RNA-seq, western blot, RT-qPCR, and immunofluorescence. Pain thresholds were assessed using the von Frey and Hargreaves tests. Patch-clamp techniques measured KCNQ/M channel activity and neuronal action potentials. The expression of S1PR1, KCNQ/M, mitogen-activated protein kinase (MAPK), and cyclic AMP/protein kinase A (cAMP/PKA) signaling proteins was analyzed before and after inhibiting the S1P-S1PR1-KCNQ/M pathway via western blot and RT-qPCR.

RESULTS

Through integrated transcriptomic analysis of ASD samples, we identified the upregulated gene S1PR1, which is associated with sphingolipid metabolism and linked to pain perception, and confirmed its role in the BTBR mouse model of ASD. This mechanism involves the regulation of KCNQ/M channels in DRG neurons. The enhanced activity of KCNQ/M channels and the decreased action potentials in small and medium DRG neurons were correlated with PAI in a BTBR mouse model of ASD. Inhibition of the S1P/S1PR1 pathway rescued baseline insensitivity to pain by suppressing KCNQ/M channels in DRG neurons, mediated through the MAPK and cAMP/PKA pathways. Investigating the modulation and underlying mechanisms of the non-opioid pathway involving S1PR1 will provide new insights into clinical targeted interventions for PAI in ASD.

CONCLUSIONS

S1PR1 may contribute to PAI in the PNS in ASD. The mechanism involves KCNQ/M channels and the MAPK and cAMP/PKA signaling pathways. Targeting S1PR1 in the PNS could offer novel therapeutic strategies for the intervention of pain dysesthesias in individuals with ASD.

Novel CDKL5 targets identified in human iPSC-derived neurons

CDKL5 Deficiency Disorder (CDD) is a debilitating epileptic encephalopathy disorder affecting young children with no effective treatments. CDD is caused by pathogenic variants in Cyclin-Dependent Kinase-Like 5 (CDKL5), a protein kinase that regulates key phosphorylation events in neurons. For therapeutic intervention, it is essential to understand molecular pathways and phosphorylation targets of CDKL5. Using an unbiased phosphoproteomic approach we identified novel targets of CDKL5, including GTF2I, PPP1R35, GATAD2A and ZNF219 in human iPSC-derived neuronal cells. The phosphoserine residue in the target proteins lies in the CDKL5 consensus motif. We validated direct phosphorylation of GTF2I and PPP1R35 by CDKL5 using complementary approaches. GTF2I controls axon guidance, cell cycle and neurodevelopment by regulating expression of neuronal genes. PPP1R35 is critical for centriole elongation and cilia morphology, processes that are impaired in CDD. PPP1R35 interacts with CEP131, a known CDKL5 phospho-target. GATAD2A and ZNF219 belong to the Nucleosome Remodelling Deacetylase (NuRD) complex, which regulates neuronal activity-dependent genes and synaptic connectivity. In-depth knowledge of molecular pathways regulated by CDKL5 will allow a better understanding of druggable disease pathways to fast-track therapeutic development.

Alterations of Perineuronal Net Expression and Abnormal Social Behavior and Whisker-dependent Texture Discrimination in Mice Lacking the Autism Candidate Gene Engrailed 2

GABAergic interneurons and perineuronal nets (PNNs) are important regulators of plasticity throughout life and their dysfunction has been implicated in the pathogenesis of several neuropsychiatric conditions, including autism spectrum disorders (ASD). PNNs are condensed portions of the extracellular matrix (ECM) that are crucial for neural development and proper formation of synaptic connections. We previously showed a reduced expression of GABAergic interneuron markers in the hippocampus and somatosensory cortex of adult mice lacking the Engrailed2 gene (En2-/- mice), a mouse model of ASD. Since alterations in PNNs have been proposed as a possible pathogenic mechanism in ASD, we hypothesized that the PNN dysfunction may contribute to the neural and behavioral abnormalities of En2-/- mice. Here, we show an increase in the PNN fluorescence intensity, evaluated by Wisteria floribunda agglutinin, in brain regions involved in social behavior and somatosensory processing. In addition, we found that En2-/- mice exhibit altered texture discrimination through whiskers and display a marked decrease in the preference for social novelty. Our results raise the possibility that altered expression of PNNs, together with defects of GABAergic interneurons, might contribute to the pathogenesis of social and sensory behavioral abnormalities.

Gene Expression Profiling in Trigeminal Ganglia from Cntnap2-/- and Shank3b-/- Mouse Models of Autism Spectrum Disorder

Sensory difficulties represent a crucial issue in the life of autistic individuals. The diagnostic and statistical manual of mental disorders describes both hyper- and hypo-responsiveness to sensory stimulation as a criterion for the diagnosis autism spectrum disorders (ASD). Among the sensory domain affected in ASD, altered responses to tactile stimulation represent the most commonly reported sensory deficits. Although tactile abnormalities have been reported in monogenic cohorts of patients and genetic mouse models of ASD, the underlying mechanisms are still unknown. Traditionally, autism research has focused on the central nervous system as the target to infer the neurobiological bases of such tactile abnormalities. Nonetheless, the peripheral nervous system represents the initial site of processing of sensory information and a potential site of dysfunction in the sensory cascade. Here we investigated the gene expression deregulation in the trigeminal ganglion (which directly receives tactile information from whiskers) in two genetic models of syndromic autism (Shank3b and Cntnap2 mutant mice) at both adult and juvenile ages. We found several neuronal and non-neuronal markers involved in inhibitory, excitatory, neuroinflammatory and sensory neurotransmission to be differentially regulated within the trigeminal ganglia of both adult and juvenile Shank3b and Cntnap2 mutant mice. These results may help in disentangling the multifaced complexity of sensory abnormalities in autism and open avenues for the development of peripherally targeted treatments for tactile sensory deficits exhibited in ASD.

mGluR5 PAMs rescue cortical and behavioural defects in a mouse model of CDKL5 deficiency disorder

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a devastating rare neurodevelopmental disease without a cure, caused by mutations of the serine/threonine kinase CDKL5 highly expressed in the forebrain. CDD is characterized by early-onset seizures, severe intellectual disabilities, autistic-like traits, sensorimotor and cortical visual impairments (CVI). The lack of an effective therapeutic strategy for CDD urgently demands the identification of novel druggable targets potentially relevant for CDD pathophysiology. To this aim, we studied Class I metabotropic glutamate receptors 5 (mGluR5) because of their important role in the neuropathological signs produced by the lack of CDKL5 in-vivo, such as defective synaptogenesis, dendritic spines formation/maturation, synaptic transmission and plasticity. Importantly, mGluR5 function strictly depends on the correct expression of the postsynaptic protein Homer1bc that we previously found atypical in the cerebral cortex of Cdkl5^-/y mice. In this study, we reveal that CDKL5 loss tampers with (i) the binding strength of Homer1bc-mGluR5 complexes, (ii) the synaptic localization of mGluR5 and (iii) the mGluR5-mediated enhancement of NMDA-induced neuronal responses. Importantly, we showed that the stimulation of mGluR5 activity by administering in mice specific positive-allosteric-modulators (PAMs), i.e., 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) or RO6807794, corrected the synaptic, functional and behavioral defects shown by Cdkl5^-/y mice. Notably, in the visual cortex of 2 CDD patients we found changes in synaptic organization that recapitulate those of mutant CDKL5 mice, including the reduced expression of mGluR5, suggesting that these receptors represent a promising therapeutic target for CDD.

Anxiety and Gene Expression Enhancement in Mice Exposed to Glyphosate-Based Herbicide

Growing evidence demonstrates that serotonin (5-HT) depletion increases activity in the amygdala and medial prefrontal cortex (mPFC), ultimately leading to anxiety behavior. Previously, we showed that glyphosate-based herbicides (GBHs) increased anxiety levels and reduced the number of serotoninergic fibers within the mPFCs and amygdalas of exposed mice. However, the impact of this 5-HT depletion following GBH exposure on neuronal activity in these structures is still unknown. In this study, we investigated the effects of GBH on immediate early gene (IEG) activation within the mPFCs and amygdalas of treated mice from juvenile age to adulthood and its subsequent effects on anxiety levels. Mice were treated for subchronic (6 weeks) and chronic (12 weeks) periods with 250 or 500 mg/kg/day of GBH and subjected to behavioral testing using the open field and elevated plus maze paradigms. Then, we analyzed the expression levels of c-Fos and pCREB and established the molecular proxies of neuronal activation within the mPFC and the amygdala. Our data revealed that repeated exposure to GBH triggers anxiogenic behavior in exposed mice. Confocal microscopy investigations into the prelimbic/infralimbic regions of the mPFC and in basolateral/central nuclei of the amygdala disclosed that the behavioral alterations are paralleled by a robust increase in the density and labelling intensity of c-Fos- and pCREB-positive cells. Taken together, these data show that mice exposed to GBH display the hyperactivation of the mPFC–amygdala areas, suggesting that this is a potential mechanism underlying the anxiety-like phenotype.

Somatosensory cortex hyperconnectivity and impaired whisker-dependent responses in Cntnap2-/- mice

Sensory abnormalities are a common feature in autism spectrum disorders (ASDs). Tactile responsiveness is altered in autistic individuals, with hypo-responsiveness being associated with the severity of ASD core symptoms. Similarly, sensory abnormalities have been described in mice lacking ASD-associated genes. Loss-of-function mutations in CNTNAP2 result in cortical dysplasia-focal epilepsy syndrome (CDFE) and autism. Likewise, Cntnap2^-/- mice show epilepsy and deficits relevant with core symptoms of human ASDs, and are considered a reliable model to study ASDs. Altered synaptic transmission and synchronicity found in the cerebral cortex of Cntnap2^-/- mice would suggest a network dysfunction. Here, we investigated the neural substrates of whisker-dependent responses in Cntnap2^+/+ and Cntnap2^-/- adult mice. When compared to controls, Cntnap2^-/- mice showed focal hyper-connectivity within the primary somatosensory cortex (S1), in the absence of altered connectivity between S1 and other somatosensory areas. This data suggests the presence of impaired somatosensory processing in these mutants. Accordingly, Cntnap2^-/- mice displayed impaired whisker-dependent discrimination in the textured novel object recognition test (tNORT) and increased c-fos mRNA induction within S1 following whisker stimulation. S1 functional hyperconnectivity might underlie the aberrant whisker-dependent responses observed in Cntnap2^-/- mice, indicating that Cntnap2 mice are a reliable model to investigate sensory abnormalities that characterize ASDs.

Abnormal Whisker-Dependent Behaviors and Altered Cortico-Hippocampal Connectivity in Shank3b-/- Mice

Abnormal tactile response is an integral feature of Autism Spectrum Disorders (ASDs), and hypo-responsiveness to tactile stimuli is often associated with the severity of ASDs core symptoms. Patients with Phelan-McDermid syndrome (PMS), caused by mutations in the SHANK3 gene, show ASD-like symptoms associated with aberrant tactile responses. The neural underpinnings of these abnormalities are still poorly understood. Here we investigated, in Shank3b^−/− adult mice, the neural substrates of whisker-guided behaviors, a key component of rodents’ interaction with the surrounding environment. We assessed whisker-dependent behaviors in Shank3b^−/− adult mice and age-matched controls, using the textured novel object recognition (tNORT) and whisker nuisance (WN) test. Shank3b^−/− mice showed deficits in whisker-dependent texture discrimination in tNORT and behavioral hypo-responsiveness to repetitive whisker stimulation in WN. Sensory hypo-responsiveness was accompanied by a significantly reduced activation of the primary somatosensory cortex (S1) and hippocampus, as measured by c-fos mRNA induction, a proxy of neuronal activity following whisker stimulation. Moreover, resting-state fMRI showed a significantly reduced S1-hippocampal connectivity in Shank3b mutants, in the absence of altered connectivity between S1 and other somatosensory areas. Impaired crosstalk between hippocampus and S1 might underlie Shank3b^−/− hypo-reactivity to whisker-dependent cues, highlighting a potentially generalizable somatosensory dysfunction in ASD.

Whole genome sequencing of nearly isogenic WMI and WLI inbred rats identifies genes potentially involved in depression and stress reactivity

The WMI and WLI inbred rats were generated from the stress-prone, and not yet fully inbred, Wistar Kyoto (WKY) strain. These were selected using bi-directional selection for immobility in the forced swim test and were then sib-mated for over 38 generations. Despite the low level of genetic diversity among WKY progenitors, the WMI substrain is significantly more vulnerable to stress relative to the counter-selected WLI strain. Here we quantify numbers and classes of genomic sequence variants distinguishing these substrains with the long term goal of uncovering functional and behavioral polymorphism that modulate sensitivity to stress and depression-like phenotypes. DNA from WLI and WMI was sequenced using Illumina xTen, IonTorrent, and 10X Chromium linked-read platforms to obtain a combined coverage of ~ 100X for each strain. We identified 4,296 high quality homozygous SNPs and indels between the WMI and WLI. We detected high impact variants in genes previously implicated in depression (e.g. Gnat2), depression-like behavior (e.g. Prlr, Nlrp1a), other psychiatric disease (e.g. Pou6f2, Kdm5a, Reep3, Wdfy3), and responses to psychological stressors (e.g. Pigr). High coverage sequencing data confirm that the two substrains are nearly coisogenic. Nonetheless, the small number of sequence variants contributes to numerous well characterized differences including depression-like behavior, stress reactivity, and addiction related phenotypes. These selected substrains are an ideal resource for forward and reverse genetic studies using a reduced complexity cross.

Age-Related Cognitive and Motor Decline in a Mouse Model of CDKL5 Deficiency Disorder is Associated with Increased Neuronal Senescence and Death

CDKL5 deficiency disorder (CDD) is a severe neurodevelopmental disease caused by mutations in the X-linked CDKL5 gene. Children affected by CDD display a clinical phenotype characterized by early-onset epilepsy, intellectual disability, motor impairment, and autistic-like features. Although the clinical aspects associated with CDKL5 mutations are well described in children, adults with CDD are still under-characterized. Similarly, most animal research has been carried out on young adult Cdkl5 knockout (KO) mice only. Since age represents a risk factor for the worsening of symptoms in many neurodevelopmental disorders, understanding age differences in the development of behavioral deficits is crucial in order to optimize the impact of therapeutic interventions. Here, we compared young adult Cdkl5 KO mice with middle-aged Cdkl5 KO mice, at a behavioral, neuroanatomical, and molecular level. We found an age-dependent decline in motor, cognitive, and social behaviors in Cdkl5 KO mice, as well as in breathing and sleep patterns. The behavioral decline in older Cdkl5 KO mice was not associated with a worsening of neuroanatomical alterations, such as decreased dendritic arborization or spine density, but was paralleled by decreased neuronal survival in different brain regions such as the hippocampus, cortex, and basal ganglia. Interestingly, we found increased β-galactosidase activity and DNA repair protein levels, γH2AX and XRCC5, in the brains of older Cdkl5 KO mice, which suggests that an absence of Cdkl5 accelerates neuronal senescence/death by triggering irreparable DNA damage. In summary, this work provides evidence that CDKL5 may play a fundamental role in neuronal survival during brain aging and suggests a possible worsening with age of the clinical picture in CDD patients.

A GABAB receptor antagonist rescues functional and structural impairments in the perirhinal cortex of a mouse model of CDKL5 deficiency disorder

CDKL5 (cyclin-dependent kinase-like 5) deficiency disorder (CDD) is a severe neurodevelopmental encephalopathy characterized by early-onset epilepsy and intellectual disability. Studies in mouse models have linked CDKL5 deficiency to defects in neuronal maturation and synaptic plasticity, and disruption of the excitatory/inhibitory balance. Interestingly, increased density of both GABAergic synaptic terminals and parvalbumin inhibitory interneurons was recently observed in the primary visual cortex of Cdkl5 knockout (KO) mice, suggesting that excessive GABAergic transmission might contribute to the visual deficits characteristic of CDD. However, the functional relevance of cortical GABAergic circuits abnormalities in these mutant mice has not been investigated so far. Here we examined GABAergic circuits in the perirhinal cortex (PRC) of Cdkl5 KO mice, where we previously observed impaired long-term potentiation (LTP) associated with deficits in novel object recognition (NOR) memory. We found a higher number of GABAergic (VGAT)-immunopositive terminals in the PRC of Cdkl5 KO compared to wild-type mice, suggesting that increased inhibitory transmission might contribute to LTP impairment. Interestingly, while exposure of PRC slices to the GABA_A receptor antagonist picrotoxin had no positive effects on LTP in Cdkl5 KO mice, the selective GABA_B receptor antagonist CGP55845 restored LTP magnitude, suggesting that exaggerated GABA_B receptor-mediated inhibition contributes to LTP impairment in mutants. Moreover, acute in vivo treatment with CGP55845 increased the number of PSD95 positive puncta as well as density and maturation of dendritic spines in PRC, and restored NOR memory in Cdkl5 KO mice. The present data show the efficacy of limiting excessive GABA_B receptor-mediated signaling in improving synaptic plasticity and cognition in CDD mice.