Spine Maturation Research Articles

Development and evaluation of an autism pig model.

Developing cost-effective and disease-relevant animal models is essential for advancing biomedical research into human disorders. Here we investigate the feasibility of a pig model for autism spectrum disorder (ASD) using embryonic exposure to valproic acid (VPA), an antiepileptic drug known to increase ASD risk. We established experimental paradigms to assess the behavioral characteristics of these pig models. Administration of VPA to Bama miniature pigs (Sus scrofa domestica) during critical embryonic stages resulted in abnormal gait, increased anxiety levels, reduced learning capabilities and altered social patterns, while largely preserving social preference of treated piglets. Notably, we detected significant neuroanatomical changes in cortical regions associated with ASD in the VPA-treated pigs, including cortical malformation, increased neuronal soma size, decreased dendritic complexity and reduced dendritic spine maturation. Transcriptome analysis of the prefrontal cortex of VPA-treated pigs further revealed substantial alterations in the expression of genes linked to ASD, especially genes of the dopamine signaling pathway, highlighting the model's relevance and potential for shedding light on ASD's underlying neuropathological and molecular mechanisms. These findings suggest that pig models could serve as a promising alternative to traditional rodent models and provide a more ethical substitute for the use of primates in translational research on neurodevelopmental disorders.

Monoallelic loss-of-function variants in GSK3B lead to autism and developmental delay.

De novo variants adjacent to the canonical splicing sites or in the well-defined splicing-related regions are more likely to impair splicing but remain under-investigated in autism spectrum disorder (ASD). By analyzing large, recent ASD genome sequencing cohorts, we find a significant burden of de novo potential splicing-disrupting variants (PSDVs) in 5048 probands compared to 4090 unaffected siblings. We identified 55 genes with recurrent de novo PSDVs that were highly intolerant to variation. Forty-six of these genes have not been strongly implicated in ASD or other neurodevelopmental disorders previously, including GSK3B. Through international, multicenter collaborations, we assembled genotype and phenotype data for 15 individuals with GSK3B variants and identified common phenotypes including developmental delay, ASD, sleeping disturbance, and aggressive behavior. Using available single-cell transcriptomic data, we show that GSK3B is enriched in dorsal progenitors and intermediate forms of excitatory neurons in the developing brain. We showed that Gsk3b knockdown in mouse excitatory neurons interferes with dendrite arborization and spine maturation which could not be rescued by de novo missense variants identified from affected individuals. In summary, our findings suggest that PSDVs may play an important role in the genetic etiology of ASD and allow for the prioritization of new ASD candidate genes. Importantly, we show that genetic variation resulting in GSK3B loss-of-function can lead to a neurodevelopmental disorder with core features of ASD and developmental delay.

Mechanisms of glutamate receptors hypofunction dependent synaptic transmission impairment in the hippocampus of schizophrenia susceptibility gene Opcml-deficient mouse model

Schizophrenia is a severe psychiatric disorder with high heritability, characterized by positive and negative symptoms as well as cognitive abnormalities. Dysfunction in glutamate synapse is strongly implicated in the pathophysiology of schizophrenia. However, the precise role of the perturbed glutamatergic system in contributing to the cognitive abnormalities of schizophrenia at the synaptic level remains largely unknown. Although our previous work found that Opcml promotes spine maturation and Opcml-deficient mice exhibit schizophrenia-related cognitive impairments, the synaptic mechanism remains unclear. By using whole-cell patch clamp recording, we found that decreased neuronal excitability and alterations in intrinsic membrane properties of CA1 PNs in Opcml-deficient mice. Furthermore, Opcml deficiency leads to impaired glutamatergic transmission in hippocampus, which is closely related to postsynaptic AMPA/NMDA receptors dysfunction, resulting in the disturbances of E/I balance. Additionally, we found that the aripiprazole which we used to ameliorate abnormal cognitive behaviors also rescued the impaired glutamatergic transmission in Opcml-deficient mice. These findings will help to understand the synaptic mechanism in schizophrenia pathogenesis, providing insights into schizophrenia therapeutics with glutamatergic disruption.

Postnatal Allergic Inhalation Induces Glial Inflammation in the Olfactory Bulb and Leads to Autism-Like Traits in Mice

Autism spectrum disorder (ASD) is one of the most prevalent neurodevelopmental disorders. To explore its pathophysiology, we investigated the association between neonatal allergic exposure and behavioral changes. Adult female C57BL/6J mice were immunized with adjuvant (aluminum hydroxide) or ovalbumin emulsified with adjuvant. After immunization, the mice were mated, and offspring were born at full term. The postnatal dams and infants were then simultaneously exposed to an allergen (ovalbumin) or vehicle via inhalation. After weaning, behavioral testing and histopathological analyses were conducted on male offspring. Compared with the vehicle-exposed offspring, the ovalbumin-exposed offspring had decreased sociability and increased repetitive behavior, thus representing an ASD-like phenotype in mice. Moreover, histopathological analyses revealed that the ovalbumin-exposed mice had increased astroglial, microglial, and eosinophilic infiltration in the olfactory bulb, as well as increased eosinophils in the nasal mucosa. The ovalbumin-exposed mice also had decreased dendritic spine density and a lower proportion of mature spines, suggesting the impairment of stimulus-induced synaptogenesis. In conclusion, postnatal allergic exposure induced an ASD-like phenotype, as well as allergic rhinitis, which was followed by glial inflammation in the olfactory bulb parenchyma.

Sex-Specific ADNP/NAP (Davunetide) Regulation of Cocaine-Induced Plasticity

Cocaine use disorder (CUD) is a chronic neuropsychiatric disorder estimated to effect 1–3% of the population. Activity-dependent neuroprotective protein (ADNP) is essential for brain development and functioning, shown to be protective in fetal alcohol syndrome and to regulate alcohol consumption in adult mice. The goal of this study was to characterize the role of ADNP, and its active peptide NAP (NAPVSIPQ), which is also known as davunetide (investigational drug) in mediating cocaine-induced neuroadaptations. Real time PCR was used to test levels of Adnp and Adnp2 in the nucleus accumbens (NAc), ventral tegmental area (VTA), and dorsal hippocampus (DH) of cocaine-treated mice (15 mg/kg). Adnp heterozygous (Adnp+/−)and wild-type (Adnp+/−) mice were further tagged with excitatory neuronal membrane-expressing green fluorescent protein (GFP) that allowed for in vivo synaptic quantification. The mice were treated with cocaine (5 injections; 15 mg/kg once every other day) with or without NAP daily injections (0.4 µg/0.1 ml) and sacrificed following the last treatment. We analyzed hippocampal CA1 pyramidal cells from 3D confocal images using the Imaris x64.8.1.2 (Oxford Instruments) software to measure changes in dendritic spine density and morphology. In silico ADNP/NAP/cocaine structural modeling was performed as before. Cocaine decreased Adnp and Adnp2 expression 2 h after injection in the NAc and VTA of male mice, with mRNA levels returning to baseline levels after 24 h. Cocaine further reduced hippocampal spine density, particularly synaptically weaker immature thin and stubby spines, in male Adnp+/+) mice while increasing synaptically stronger mature (mushroom) spines in Adnp+/−) male mice and thin and stubby spines in females. Lastly, we showed that cocaine interacts with ADNP on a zinc finger domain identical to ketamine and adjacent to a NAP-zinc finger interaction site. Our results implicate ADNP in cocaine abuse, further placing the ADNP gene as a key regulator in neuropsychiatric disorders. Ketamine/cocaine and NAP treatment may be interchangeable to some degree, implicating an interaction with adjacent zinc finger motifs on ADNP and suggestive of a potential sex-dependent, non-addictive NAP treatment for CUD.

Phosphatidylinositol-3-phosphate mediates Arc capsid secretion through the multivesicular body pathway

Activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) is an immediate early gene that plays a vital role in learning and memory. Arc protein has structural and functional properties similar to viral Group-specific antigen (Gag) protein and mediates the intercellular RNA transfer through virus-like capsids. However, the regulators and secretion pathway through which Arc capsids maneuver cargos are unclear. Here, we identified that phosphatidylinositol-3-phosphate (PI3P) mediates Arc capsid assembly and secretion through the endosomal-multivesicular body (MVB) pathway. Indeed, reconstituted Arc protein preferably binds to PI3P. In HEK293T cells, Arc forms puncta that colocalize with FYVE, an endosomal PI3P marker, as well as Rab5 and CD63, early endosomal and MVB markers, respectively. Superresolution imaging resolves Arc accumulates within the intraluminal vesicles of MVB. CRISPR double knockout of RalA and RalB, crucial GTPases for MVB biogenesis and exocytosis, severely reduces the Arc-mediated RNA transfer efficiency. RalA/B double knockdown in cultured rat cortical neurons increases the percentage of mature dendritic spines. Intake of extracellular vesicles purified from Arc-expressing wild-type, but not RalA/B double knockdown, cells in mouse cortical neurons reduces their surface GlutA1 levels. These results suggest that unlike the HIV Gag, whose membrane targeting requires interaction with plasma-membrane-specific phosphatidyl inositol (4,5) bisphosphate (PI(4,5)P2), the assembly of Arc capsids is mediated by PI3P at endocytic membranes. Understanding Arc's secretion pathway helps gain insights into its role in intercellular cargo transfer and highlights the commonality and distinction of trafficking mechanisms between structurally resembled capsid proteins.

Cyclase-associated protein (CAP) inhibits inverted formin 2 (INF2) to induce dendritic spine maturation

The morphology of dendritic spines, the postsynaptic compartment of most excitatory synapses, decisively modulates the function of neuronal circuits as also evident from human brain disorders associated with altered spine density or morphology. Actin filaments (F-actin) form the backbone of spines, and a number of actin-binding proteins (ABP) have been implicated in shaping the cytoskeleton in mature spines. Instead, only little is known about the mechanisms that control the reorganization from unbranched F-actin of immature spines to the complex, highly branched cytoskeleton of mature spines. Here, we demonstrate impaired spine maturation in hippocampal neurons upon genetic inactivation of cyclase-associated protein 1 (CAP1) and CAP2, but not of CAP1 or CAP2 alone. We found a similar spine maturation defect upon overactivation of inverted formin 2 (INF2), a nucleator of unbranched F-actin with hitherto unknown synaptic function. While INF2 overactivation failed in altering spine density or morphology in CAP-deficient neurons, INF2 inactivation largely rescued their spine defects. From our data we conclude that CAPs inhibit INF2 to induce spine maturation. Since we previously showed that CAPs promote cofilin1-mediated cytoskeletal remodeling in mature spines, we identified them as a molecular switch that control transition from filopodia-like to mature spines.

PKMζ alters oxycodone-taking in a dose- and sex-dependent manner

Opioid use disorder involves disruptions to glutamate homeostasis and dendritic spine density in the reward system. PKMζ is an atypical isoform of protein kinase C that is expressed exclusively in neurons and plays a role in postsynaptic glutamate signaling and dendritic spine maturation. As opioid use leads to alterations in glutamate transmission and dendritic spine density, we hypothesized that PKMζ deletion would alter opioid-taking behaviors. The current study examined two doses of oxycodone self-administration in male and female mice with constitutive deletion of PKMζ compared to wildtype controls. At a dose of 0.25 mg/kg/infusion, PKMζ deletion significantly potentiated oxycodone self-administration in both male and female mice. However, increases in motivation for oxycodone, as indicated by increased breakpoint on a progressive ratio schedule, were only seen in male PKMζ knockout mice and not females. When we examined a lower dose of oxycodone, 0.125 mg/kg/infusion, PKMζ knockout led to increases in oxycodone self-administration only in female mice. Additionally, female PKMζ knockout mice exhibited higher breakpoints on a progressive ratio schedule at this dose compared to all other groups. In addition to the self-administration studies, we also examined locomotor sensitization in response to experimenter administered oxycodone. PKMζ KO decreased oxycodone induced locomotion in males and potentiated oxycodone sensitization in females. Together, these results suggest that PKMζ acts to dampen oxycodone taking in both sexes, but females may be more sensitive to its effects.

Adult Human Brain Tissue Cultures to Study NeuroHIV.

HIV-associated neurocognitive disorders (HAND) persist under antiretroviral therapy as a complex pathology that has been difficult to study in cellular and animal models. Therefore, we generated an ex vivo human brain slice model of HIV-1 infection from surgically resected adult brain tissue. Brain slice cultures processed for flow cytometry showed >90% viability of dissociated cells within the first three weeks in vitro, with parallel detection of astrocyte, myeloid, and neuronal populations. Neurons within brain slices showed stable dendritic spine density and mature spine morphologies in the first weeks in culture, and they generated detectable activity in multi-electrode arrays. We infected cultured brain slices using patient-matched CD4+ T-cells or monocyte-derived macrophages (MDMs) that were exposed to a GFP-expressing R5-tropic HIV-1 in vitro. Infected slice cultures expressed viral RNA and developed a spreading infection up to 9 days post-infection, which were significantly decreased by antiretrovirals. We also detected infected myeloid cells and astrocytes within slices and observed minimal effect on cellular viability over time. Overall, this human-centered model offers a promising resource to study the cellular mechanisms contributing to HAND (including antiretroviral toxicity, substance use, and aging), infection of resident brain cells, and new neuroprotective therapeutics.

PP1β opposes classic PP1 function, inhibiting spine maturation and promoting LTP.

Protein phosphatase 1 (PP1) regulates synaptic plasticity and has been described as a molecular constraint on learning and memory. There are three neuronal isoforms, PP1α, PP1β, and PP1γ, but little is known about their individual functions. PP1α and PP1γ are assumed to mediate the effects of PP1 on learning and memory based on their enrichment at dendritic spines and their preferential binding to neurabin and spinophilin, major PP1 synaptic scaffolding proteins. However, it was recently discovered that human de novo PP1β mutations cause intellectual disability, suggesting an important but ill-defined role for PP1β. In this study, we investigated the functions of each PP1 isoform in hippocampal synaptic physiology using conditional CA1-specific knockout mice. In stark contrast to classic PP1 function, we found that PP1β promotes synaptic plasticity as well as spatial memory. These changes in synaptic plasticity and memory are accompanied by changes in GluA1 phosphorylation, GluN2A levels, and dendritic spine density and morphology, including silent synapse number. These functions of PP1β reveal a previously unidentified signaling pathway regulating spine maturation and plasticity, broadening our understanding of the complex role of PP1 in synaptic physiology.

The Small G-Protein Rac1 in the Dorsomedial Striatum Promotes Alcohol-Dependent Structural Plasticity and Goal-Directed Learning in Mice.

The small G-protein Ras-related C3 botulinum toxin substrate 1 (Rac1) promotes the formation of filamentous actin (F-actin). Actin is a major component of dendritic spines, and we previously found that alcohol alters actin composition and dendritic spine structure in the nucleus accumbens (NAc) and the dorsomedial striatum (DMS). To examine if Rac1 contributes to these alcohol-mediated adaptations, we measured the level of GTP-bound active Rac1 in the striatum of mice following 7 weeks of intermittent access to 20% alcohol. We found that chronic alcohol intake activates Rac1 in the DMS of male mice. In contrast, Rac1 is not activated by alcohol in the NAc and DLS of male mice or in the DMS of female mice. Similarly, closely related small G-proteins are not activated by alcohol in the DMS, and Rac1 activity is not increased in the DMS by moderate alcohol or natural reward. To determine the consequences of alcohol-dependent Rac1 activation in the DMS of male mice, we inhibited endogenous Rac1 by infecting the DMS of mice with an adeno-associated virus (AAV) expressing a dominant negative form of the small G-protein (Rac1-DN). We found that overexpression of AAV-Rac1-DN in the DMS inhibits alcohol-mediated Rac1 signaling and attenuates alcohol-mediated F-actin polymerization, which corresponded with a decrease in dendritic arborization and spine maturation. Finally, we provide evidence to suggest that Rac1 in the DMS plays a role in alcohol-associated goal-directed learning. Together, our data suggest that Rac1 in the DMS plays an important role in alcohol-dependent structural plasticity and aberrant learning.

Prosapip1 in the dorsal hippocampus mediates synaptic protein composition, long-term potentiation, and spatial memory.

Prosapip1 is a brain-specific protein localized to the postsynaptic density, where it promotes dendritic spine maturation in primary hippocampal neurons. However, nothing is known about the role of Prosapip1 in vivo . To examine this, we utilized the Cre-loxP system to develop a Prosapip1 neuronal knockout mouse. We found that Prosapip1 controls the synaptic localization of its binding partner SPAR, along with PSD-95 and the GluN2B subunit of the NMDA receptor (NMDAR) in the dorsal hippocampus (dHP). We next sought to identify the potential contribution of Prosapip1 to the activity and function of the NMDAR and found that Prosapip1 plays an important role in NMDAR-mediated transmission and long-term potentiation (LTP) in the CA1 region of the dHP. As LTP is the cellular hallmark of learning and memory, we examined the consequences of neuronal knockout of Prosapip1 on dHP-dependent memory. We found that global or dHP-specific neuronal knockout of Prosapip1 caused a deficit in learning and memory whereas developmental, locomotor, and anxiety phenotypes were normal. Taken together, Prosapip1 in the dHP promotes the proper localization of synaptic proteins which, in turn, facilitates LTP driving recognition, social, and spatial learning and memory.

A C-terminal motif containing a PKC phosphorylation site regulates γ-Protocadherin-mediated dendrite arborization in the cerebral cortex in vivo.

The Pcdhg gene cluster encodes 22 γ-Protocadherin (γ-Pcdh) cell adhesion molecules that critically regulate multiple aspects of neural development, including neuronal survival, dendritic and axonal arborization, and synapse formation and maturation. Each γ-Pcdh isoform has unique protein domains-a homophilically interacting extracellular domain and a juxtamembrane cytoplasmic domain-as well as a C-terminal cytoplasmic domain shared by all isoforms. The extent to which isoform-specific versus shared domains regulate distinct γ-Pcdh functions remains incompletely understood. Our previous in vitro studies identified protein kinase C (PKC)phosphorylation of a serine residue within a shared C-terminal motif as a mechanism through which γ-Pcdh promotion of dendrite arborization via myristoylated alanine-rich C-kinase substrate (MARCKS) is abrogated. Here, we used CRISPR/Cas9 genome editing to generate two new mouse lines expressing only non-phosphorylatable γ-Pcdhs, due either to a serine-to-alanine mutation (PcdhgS/A) or to a 15-amino acid C-terminal deletion resulting from insertion of an early stop codon (PcdhgCTD). Both lines are viable and fertile, and the density and maturation of dendritic spines remain unchanged in both PcdhgS/A and PcdhgCTD cortex. Dendrite arborization of cortical pyramidal neurons, however, is significantly increased in both lines, as are levels of active MARCKS. Intriguingly, despite having significantly reduced levels of γ-Pcdh proteins, the PcdhgCTD mutation yields the strongest phenotype, with even heterozygous mutants exhibiting increased arborization. The present study confirms that phosphorylation of a shared C-terminal motif is a key γ-Pcdh negative regulation point and contributes to a converging understanding of γ-Pcdh family function in which distinct roles are played by both individual isoforms and discrete protein domains.

Cognitive integrity in Non-Demented Individuals with Alzheimer's Neuropathology is associated with preservation and remodeling of dendritic spines.

Individuals referred to as Non-Demented with Alzheimer's Neuropathology (NDAN) exhibit cognitive resilience despite presenting Alzheimer's disease (AD) histopathological signs. Investigating the mechanisms behind this resilience may unveil crucial insights into AD resistance. DiI labeling technique was used to analyze dendritic spine morphology in control (CTRL), AD, and NDAN post mortem frontal cortex, particularly focusing on spine types near and far from amyloid beta (Aβ) plaques. NDAN subjects displayed a higher spine density in regions distant from Aβ plaques versus AD patients. In distal areas from the plaques, NDAN individuals exhibited more immature spines, while AD patients had a prevalence of mature spines. Additionally, our examination of levels of Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1), a protein associated with synaptic plasticity and AD, showed significantly lower expression in AD versus NDAN and CTRL. These results suggest that NDAN individuals undergo synaptic remodeling, potentially facilitated by Pin1, serving as a compensatory mechanism to preserve cognitive function despite AD pathology. Spine density is reduced near Aβ plaques compared to the distal area in CTRL, AD, and NDAN dendrites. NDAN shows higher spine density than AD in areas far from Aβ plaques. Far from Aβ plaques, NDAN has a higher density of immature spines, AD a higher density of mature spines. AD individuals show significantly lower levels of Pin1 compared to NDAN and CTRL.

Dopamine-mediated plasticity preserves excitatory connections to direct pathway striatal projection neurons and motor function in a mouse model of Parkinson's disease.

The cardinal symptoms of Parkinson's disease (PD) such as bradykinesia and akinesia are debilitating, and treatment options remain inadequate. The loss of nigrostriatal dopamine neurons in PD produces motor symptoms by shifting the balance of striatal output from the direct (go) to indirect (no-go) pathway in large part through changes in the excitatory connections and intrinsic excitabilities of the striatal projection neurons (SPNs). Here, we report using two different experimental models that a transient increase in striatal dopamine and enhanced D1 receptor activation, during 6-OHDA dopamine depletion, prevent the loss of mature spines and dendritic arbors on direct pathway projection neurons (dSPNs) and normal motor behavior for up to 5 months. The primary motor cortex and midline thalamic nuclei provide the major excitatory connections to SPNs. Using ChR2-assisted circuit mapping to measure inputs from motor cortex M1 to dorsolateral dSPNs, we observed a dramatic reduction in both experimental model mice and controls following dopamine depletion. Changes in the intrinsic excitabilities of SPNs were also similar to controls following dopamine depletion. Future work will examine thalamic connections to dSPNs. The findings reported here reveal previously unappreciated plasticity mechanisms within the basal ganglia that can be leveraged to treat the motor symptoms of PD.

Targeted rescue of synaptic plasticity improves cognitive decline in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a frequent complication of severe systemic infection resulting in delirium, premature death, and long-term cognitive impairment. We closely mimicked SAE in a murine peritoneal contamination and infection (PCI) model. We found long-lasting synaptic pathology in the hippocampus including defective long-term synaptic plasticity, reduction of mature neuronal dendritic spines, and severely affected excitatory neurotransmission. Genes related to synaptic signaling, including the gene for activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) and members of the transcription-regulatory EGR gene family, were downregulated. At the protein level, ARC expression and mitogen-activated protein kinase signaling in the brain were affected. For targeted rescue we used adeno-associated virus-mediated overexpression of ARC in the hippocampus invivo. This recovered defective synaptic plasticity and improved memory dysfunction. Using the enriched environment paradigm as a non-invasive rescue intervention, we found improvement of defective long-term potentiation, memory, and anxiety. The beneficial effects of an enriched environment were accompanied by an increase in brain-derived neurotrophic factor (BDNF) and ARC expression in the hippocampus, suggesting that activation of the BDNF-TrkB pathway leads to restoration of the PCI-induced reduction of ARC. Collectively, our findings identify synaptic pathomechanisms underlying SAE and provide a conceptual approach to target SAE-induced synaptic dysfunction with potential therapeutic applications to patients with SAE.

Genetic deletion of zinc transporter ZnT3 induces progressive cognitive deficits in mice by impairing dendritic spine plasticity and glucose metabolism.

Zinc transporter 3 (ZnT3) is abundantly expressed in the brain, residing in synaptic vesicles, where it plays important roles in controlling the luminal zinc levels. In this study, we found that ZnT3 knockout in mice decreased zinc levels in the hippocampus and cortex, and was associated with progressive cognitive impairments, assessed at 2, 6, and 9-month of age. The results of Golgi-Cox staining demonstrated that ZnT3 deficiency was associated with an increase in dendritic complexity and a decrease in the density of mature dendritic spines, indicating potential synaptic plasticity deficit. Since ZnT3 deficiency was previously linked to glucose metabolism abnormalities, we tested the expression levels of genes related to insulin signaling pathway in the hippocampus and cortex. We found that the Expression of glucose transporters, GLUT3, GLUT4, and the insulin receptor in the whole tissue and synaptosome fraction of the hippocampus of the ZnT3 knockout mice were significantly reduced, as compared to wild-type controls. Expression of AKT (A serine/threonine protein kinase) and insulin-induced AKT phosphorylation was also reduced in the hippocampus of ZnT3 knockout mice. We hypothesize that the ZnT3 deficiency and reduced brain zinc levels may cause cognitive impairment by negatively affecting glycose metabolism via decreased expression of key components of insulin signaling, as well as via changes in synaptic plasticity. These finding may provide new therapeutic target for treatments of neurodegenerative disorders.

KIS counteracts PTBP2 and regulates alternative exon usage in neurons.

Alternative RNA splicing is an essential and dynamic process in neuronal differentiation and synapse maturation, and dysregulation of this process has been associated with neurodegenerative diseases. Recent studies have revealed the importance of RNA-binding proteins in the regulation of neuronal splicing programs. However, the molecular mechanisms involved in the control of these splicing regulators are still unclear. Here, we show that KIS, a kinase upregulated in the developmental brain, imposes a genome-wide alteration in exon usage during neuronal differentiation in mice. KIS contains a protein-recognition domain common to spliceosomal components and phosphorylates PTBP2, counteracting the role of this splicing factor in exon exclusion. At the molecular level, phosphorylation of unstructured domains within PTBP2 causes its dissociation from two co-regulators, Matrin3 and hnRNPM, and hinders the RNA-binding capability of the complex. Furthermore, KIS and PTBP2 display strong and opposing functional interactions in synaptic spine emergence and maturation. Taken together, our data uncover a post-translational control of splicing regulators that link transcriptional and alternative exon usage programs in neuronal development.

The role of glia in the dysregulation of neuronal spinogenesis in Ube3a-dependent ASD

Overexpression of the Ube3a gene and the resulting increase in Ube3a protein are linked to autism spectrum disorder (ASD). However, the cellular and molecular processes underlying Ube3a-dependent ASD remain unclear. Using both male and female mice, we find that neurons in the somatosensory cortex of the Ube3a 2× Tg ASD mouse model display reduced dendritic spine density and increased immature filopodia density. Importantly, the increased gene dosage of Ube3a in astrocytes alone is sufficient to confer alterations in neurons as immature dendritic protrusions, as observed in primary hippocampal neuron cultures. We show that Ube3a overexpression in astrocytes leads to a loss of astrocyte-derived spinogenic protein, thrombospondin-2 (TSP2), due to a suppression of TSP2 gene transcription. By neonatal intraventricular injection of astrocyte-specific virus, we demonstrate that Ube3a overexpression in astrocytes in vivo results in a reduction in dendritic spine maturation in prelimbic cortical neurons, accompanied with autistic-like behaviors in mice. These findings reveal an astrocytic dominance in initiating ASD pathobiology at the neuronal and behavior levels. Significance statementIncreased gene dosage of Ube3a is tied to autism spectrum disorders (ASDs), yet cellular and molecular alterations underlying autistic phenotypes remain unclear. We show that Ube3a overexpression leads to impaired dendritic spine maturation, resulting in reduced spine density and increased filopodia density. We find that dysregulation of spine development is not neuron autonomous, rather, it is mediated by an astrocytic mechanism. Increased gene dosage of Ube3a in astrocytes leads to reduced production of the spinogenic glycoprotein thrombospondin-2 (TSP2), leading to abnormalities in spines. Astrocyte-specific Ube3a overexpression in the brain in vivo confers dysregulated spine maturation concomitant with autistic-like behaviors in mice. These findings indicate the importance of astrocytes in aberrant neurodevelopment and brain function in Ube3a-depdendent ASD.

Restoration of norepinephrine release, cognitive performance, and dendritic spines by amphetamine in aged rat brain.

Age-related dysfunctions in specific neurotransmitter systems likely play an important role in cognitive decline even in its most subtle forms. Therefore, preservation or improvement of cognition via augmentation of neurotransmission is a potential therapeutic strategy to prevent further cognitive deficits. Here we identified a particular neuronal vulnerability in the aged Fischer 344 rat brain, an animal model of neurocognitive aging. Specifically, we demonstrated a marked impairment in glutamate-stimulated release of norepinephrine (NE) in the hippocampus and cerebral cortex of aged rats, and established that this release was mediated by N-methyl-D-aspartate (NMDA) receptors. Further, we also demonstrated that this decrease in NE release is fully rescued by the psychostimulant drug amphetamine (AMPH). Moreover, we showed that AMPH increases dendritic spine maturation, and importantly shows preclinical efficacy in restoring memory deficits in the aged rat through its actions to potentiate NE neurotransmission at β-adrenergic receptors. Taken together, our results suggest that deficits in glutamate-stimulated release of NE may contribute to and possibly be a determinant of neuronal vulnerability underlying cognitive decline during aging, and that these deficits can be corrected with currently available drugs. Overall these studies suggest that repurposing of psychostimulants for age-associated cognitive deficits is a potential avenue to delay or prevent cognitive decline and/or frank dementia later in life.