Regulation of AMPA receptor function by the human memory-associated gene KIBRA

WWC1 mutation drives dopamine dysregulation and synaptic imbalance in Tourette's syndrome

Tourette's syndrome (TS) is a major neurodevelopmental disorder characterized by childhood-onset motor and vocal tics. A W88C mutation in WWC1 gene is a notable risk factor for TS, but the underlying molecular mechanisms remain unclear due to the lack of suitable animal models. Here, we generate a mutant mouse line with human W88C mutation (W88CMut mice), which exhibits behavioral deficits similar to those observed in patients with TS, including repetitive motor behaviors and sensorimotor gating abnormalities. The W88C mutation leads to the degradation of kidney and brain (KIBRA) protein via a proteasomal pathway, evokes dopamine release in the dorsal striatum, and disrupts synaptic function through the dysregulation of Hippo pathway. Neuron-specific overexpression of wild-type WWC1 rescues synaptic and behavioral phenotypes in W88CMut mice. Together, this study not only provides a valuable mouse model for studying TS but also offers fresh insights into the molecular and synaptic mechanisms underlying neurodevelopmental abnormalities in TS.

PICK1 links KIBRA and AMPA receptor subunit GluA2 in coiled-coil-driven supramolecular complexes

The human memory-associated protein KIBRA regulates synaptic plasticity and trafficking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors, and is implicated in multiple neuropsychiatric and cognitive disorders. How KIBRA forms complexes with and regulates AMPA receptors remains unclear. Here, we show that KIBRA does not interact directly with the AMPA receptor subunit GluA2, but that protein interacting with C kinase 1 (PICK1), a key regulator of AMPA receptor trafficking, can serve as a bridge between KIBRA and GluA2. In contrast, KIBRA can form a complex with GluA1 independent of PICK1. We identified structural determinants of KIBRA-PICK1-AMPAR complexes by investigating interactions and cellular expression patterns of different combinations of KIBRA and PICK1 domain mutants. We find that the PICK1 BAR domain, a coiled-coil structure, is sufficient for interaction with KIBRA, whereas mutation of the PICK1 BAR domain disrupts KIBRA-PICK1-GluA2 complex formation. In addition, KIBRA recruits PICK1 into large supramolecular complexes, a process which requires KIBRA coiled-coil domains. These findings reveal molecular mechanisms by which KIBRA can organize key synaptic signaling complexes.

AMPA Receptors in Synaptic Plasticity, Memory Function, and Brain Diseases

Tetrameric AMPA-type ionotropic glutamate receptors are primary transducers of fast excitatory synaptic transmission in the central nervous system, and their properties and abundance at the synaptic surface are crucial determinants of synaptic efficacy in neuronal communication across the brain. The induction of long-term potentiation (LTP) leads to the insertion of GluA1-containing AMPA receptors at the synaptic surface, whereas during long-term depression (LTD), these receptors are internalized into the cytoplasm of the spine. Disruptions in the trafficking of AMPA receptors to and from the synaptic surface attenuate both forms of synaptic plasticity. Homeostatic scaling up and scaling down, which are additional types of plasticity similar to LTP and LTD, are also regulated by the insertion and removal of GluA1-containing AMPA receptors from the synaptic surface. The trafficking of AMPA receptors is an intricate process assisted by various proteins. Furthermore, AMPA receptors are critical for the formation and consolidation of various types of memory, and alterations in their function are intimately associated with cognitive dysfunction in aging and several neurological and psychiatric diseases. In this review, we will provide an overview of the current understanding of how AMPA receptors regulate various forms of synaptic plasticity, their contribution to memory functions, and their role in aging and brain diseases.

WWC2 modulates GABAA-receptor-mediated synaptic transmission, revealing class-specific mechanisms of synapse regulation by WWC family proteins

The WW and C2 domain-containing protein (WWC2) is implicated in several neurological disorders. Here, we demonstrate that WWC2 interacts with inhibitory, but not excitatory, postsynaptic scaffolds, consistent with prior proteomic identification of WWC2 as a putative component of the inhibitory postsynaptic density. Using mice lacking WWC2 expression in excitatory forebrain neurons, we show that WWC2 suppresses γ-aminobutyric acid type-A receptor (GABAAR) incorporation into the plasma membrane and regulates HAP1 and GRIP1, which form a complex promoting GABAAR recycling to the membrane. Inhibitory synaptic transmission is increased in CA1 pyramidal cells lacking WWC2. Furthermore, unlike the WWC2 homolog KIBRA (kidney/brain protein; WWC1), a key regulator of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking at excitatory synapses, the deletion of WWC2 does not affect synaptic AMPAR expression. In contrast, loss of KIBRA does not affect GABAAR membrane expression. These data reveal synapse class-selective functions for WWC proteins as regulators of ionotropic neurotransmitter receptors and provide insight into mechanisms regulating GABAAR membrane expression.

Interaction between the TBC1D24 TLDc domain and the KIBRA C2 domain is disrupted by two epilepsy-associated TBC1D24 missense variants

Mutations of human TBC1D24 are associated with deafness, epilepsy, or DOORS syndrome (deafness, onychodystrophy, osteodystrophy, cognitive disability, and seizures). The causal relationships between TBC1D24 variants and the different clinical phenotypes are not understood. Our hypothesis is that phenotypic heterogeneity of missense mutations of TBC1D24 results, in part, from perturbed binding of different protein partners. To discover novel protein partners of TBC1D24, we conducted yeast two-hybrid (Y2H) screen using mouse full-length TBC1D24 as bait. Kidney and brain protein (KIBRA), a scaffold protein encoded by Wwc1, was identified as a partner of TBC1D24. KIBRA functions in the Hippo signaling pathway and is important for human cognition and memory. The TBC1D24 TLDc domain binds to KIBRA full-length and to its C2 domain, confirmed by Y2H assays. No interaction was detected with Y2H assays between the KIBRA C2 domain and TLDc domains of NCOA7, MEAK7, and OXR1. Moreover, the C2 domains of other WWC family proteins do not interact with the TLDc domain of TBC1D24, demonstrating specificity. The mRNAs encoding TBC1D24 and KIBRA proteins in mouse are coexpressed at least in a subset of hippocampal cells indicating availability to interact in vivo. As two epilepsy-associated recessive variants (Gly511Arg and Ala515Val) in the TLDc domain of human TBC1D24 disrupt the interaction with the human KIBRA C2 domain, this study reveals a pathogenic mechanism of TBC1D24-associated epilepsy, linking the TBC1D24 and KIBRA pathways. The interaction of TBC1D24-KIBRA is physiologically meaningful and necessary to reduce the risk of epilepsy.

Myosin Va-dependent Transport of NMDA Receptors in Hippocampal Neurons

N-methyl-D-aspartate receptor (NMDAR) trafficking is a key process in the regulation of synaptic efficacy and brain function. However, the molecular mechanism underlying the surface transport of NMDARs is largely unknown. Here we identified myosin Va (MyoVa) as the specific motor protein that traffics NMDARs in hippocampal neurons. We found that MyoVa associates with NMDARs through its cargo binding domain. This association was increased during NMDAR surface transport. Knockdown of MyoVa suppressed NMDAR transport. We further demonstrated that Ca2+/calmodulin-dependent protein kinase II (CaMKII) regulates NMDAR transport through its direct interaction with MyoVa. Furthermore, MyoVa employed Rab11 family-interacting protein 3 (Rab11/FIP3) as the adaptor proteins to couple themselves with NMDARs during their transport. Accordingly, the knockdown of FIP3 impairs hippocampal memory. Together, we conclude that in hippocampal neurons, MyoVa conducts active transport of NMDARs in a CaMKII-dependent manner.

KIBRA anchoring the action of PKMζ maintains the persistence of memory

How can short-lived molecules selectively maintain the potentiation of activated synapses to sustain long-term memory? Here, we find kidney and brain expressed adaptor protein (KIBRA), a postsynaptic scaffolding protein genetically linked to human memory performance, complexes with protein kinase Mzeta (PKMζ), anchoring the kinase's potentiating action to maintain late-phase long-term potentiation (late-LTP) at activated synapses. Two structurally distinct antagonists of KIBRA-PKMζ dimerization disrupt established late-LTP and long-term spatial memory, yet neither measurably affects basal synaptic transmission. Neither antagonist affects PKMζ-independent LTP or memory that are maintained by compensating PKCs in ζ-knockout mice; thus, both agents require PKMζ for their effect. KIBRA-PKMζ complexes maintain 1-month-old memory despite PKMζ turnover. Therefore, it is not PKMζ alone, nor KIBRA alone, but the continual interaction between the two that maintains late-LTP and long-term memory.

Tweaking synaptic plasticity: Deciphering the role of WWC1 in memory opens new therapeutic horizons

WWC1 is a scaffolding protein in the evolutionarily conserved Hippo signaling network and is genetically linked to human memory and synaptic plasticity. In the archives of Science Signaling, Stepan et al. demonstrate the translational potential of modulating WWC1 through pharmacological inhibition of Hippo-pathway kinases to enhance cognition.

Human mutations in high-confidence Tourette disorder genes affect sensorimotor behavior, reward learning, and striatal dopamine in mice

Tourette disorder (TD) is poorly understood, despite affecting 1/160 children. A lack of animal models possessing construct, face, and predictive validity hinders progress in the field. We used CRISPR/Cas9 genome editing to generate mice with mutations orthologous to human de novo variants in two high-confidence Tourette genes, CELSR3 and WWC1. Mice with human mutations in Celsr3 and Wwc1 exhibit cognitive and/or sensorimotor behavioral phenotypes consistent with TD. Sensorimotor gating deficits, as measured by acoustic prepulse inhibition, occur in both male and female Celsr3 TD models. Wwc1 mice show reduced prepulse inhibition only in females. Repetitive motor behaviors, common to Celsr3 mice and more pronounced in females, include vertical rearing and grooming. Sensorimotor gating deficits and rearing are attenuated by aripiprazole, a partial agonist at dopamine type II receptors. Unsupervised machine learning reveals numerous changes to spontaneous motor behavior and less predictable patterns of movement. Continuous fixed-ratio reinforcement shows that Celsr3 TD mice have enhanced motor responding and reward learning. Electrically evoked striatal dopamine release, tested in one model, is greater. Brain development is otherwise grossly normal without signs of striatal interneuron loss. Altogether, mice expressing human mutations in high-confidence TD genes exhibit face and predictive validity. Reduced prepulse inhibition and repetitive motor behaviors are core behavioral phenotypes and are responsive to aripiprazole. Enhanced reward learning and motor responding occur alongside greater evoked dopamine release. Phenotypes can also vary by sex and show stronger affection in females, an unexpected finding considering males are more frequently affected in TD.

Inhibiting Hippo pathway kinases releases WWC1 to promote AMPAR-dependent synaptic plasticity and long-term memory in mice

The localization, number, and function of postsynaptic AMPA-type glutamate receptors (AMPARs) are crucial for synaptic plasticity, a cellular correlate for learning and memory. The Hippo pathway member WWC1 is an important component of AMPAR-containing protein complexes. However, the availability of WWC1 is constrained by its interaction with the Hippo pathway kinases LATS1 and LATS2 (LATS1/2). Here, we explored the biochemical regulation of this interaction and found that it is pharmacologically targetable in vivo. In primary hippocampal neurons, phosphorylation of LATS1/2 by the upstream kinases MST1 and MST2 (MST1/2) enhanced the interaction between WWC1 and LATS1/2, which sequestered WWC1. Pharmacologically inhibiting MST1/2 in male mice and in human brain-derived organoids promoted the dissociation of WWC1 from LATS1/2, leading to an increase in WWC1 in AMPAR-containing complexes. MST1/2 inhibition enhanced synaptic transmission in mouse hippocampal brain slices and improved cognition in healthy male mice and in male mouse models of Alzheimer's disease and aging. Thus, compounds that disrupt the interaction between WWC1 and LATS1/2 might be explored for development as cognitive enhancers.

PICK1 links KIBRA and AMPA receptors in coiled-coil-driven supramolecular complexes

The human memory-associated protein KIBRA regulates synaptic plasticity and trafficking of AMPA-type glutamate receptors, and is implicated in multiple neuropsychiatric and cognitive disorders. How KIBRA forms complexes with and regulates AMPA receptors remains unclear. Here, we show that KIBRA does not interact directly with the AMPA receptor subunit GluA2, but that PICK1, a key regulator of AMPA receptor trafficking, can serve as a bridge between KIBRA and GluA2. We identified structural determinants of KIBRA-PICK1-AMPAR complexes by investigating interactions and cellular expression patterns of different combinations of KIBRA and PICK1 domain mutants. We find that the PICK1 BAR domain, a coiled-coil structure, is sufficient for interaction with KIBRA, whereas mutation of the BAR domain disrupts KIBRA-PICK1-GluA2 complex formation. In addition, KIBRA recruits PICK1 into large supramolecular complexes, a process which requires KIBRA coiled-coil domains. These findings reveal molecular mechanisms by which KIBRA can organize key synaptic signaling complexes.

Modulation of GABA A receptor trafficking by WWC2 reveals class-specific mechanisms of synapse regulation by WWC family proteins

WWC2 (WW and C2 domain-containing protein) is implicated in several neurological disorders, however its function in the brain has yet to be determined. Here, we demonstrate that WWC2 interacts with inhibitory but not excitatory postsynaptic scaffolds, consistent with prior proteomic identification of WWC2 as a putative component of the inhibitory postsynaptic density. Using mice lacking WWC2 expression in excitatory forebrain neurons, we show that WWC2 suppresses GABA A R incorporation into the plasma membrane and regulates HAP1 and GRIP1, which form a complex promoting GABA A R recycling to the membrane. Inhibitory synaptic transmission is dysregulated in CA1 pyramidal cells lacking WWC2. Furthermore, unlike the WWC2 homolog KIBRA (WWC1), a key regulator of AMPA receptor trafficking at excitatory synapses, deletion of WWC2 does not affect synaptic AMPAR expression. In contrast, loss of KIBRA does not affect GABA A R membrane expression. These data reveal unique, synapse class-selective functions for WWC proteins as regulators of ionotropic neurotransmitter receptors and provide insight into mechanisms regulating GABA A R membrane expression.

KIBRA repairs synaptic plasticity and promotes resilience to tauopathy-related memory loss

Synaptic plasticity is obstructed by pathogenic tau in the brain, representing a key mechanism that underlies memory loss in Alzheimer's disease (AD) and related tauopathies. Here, we found that reduced levels of the memory-associated protein KIdney/BRAin (KIBRA) in the brain and increased KIBRA protein levels in cerebrospinal fluid are associated with cognitive impairment and pathological tau levels in disease. We next defined a mechanism for plasticity repair in vulnerable neurons using the C-terminus of the KIBRA protein (CT-KIBRA). We showed that CT-KIBRA restored plasticity and memory in transgenic mice expressing pathogenic human tau; however, CT-KIBRA did not alter tau levels or prevent tau-induced synapse loss. Instead, we found that CT-KIBRA stabilized the protein kinase Mζ (PKMζ) to maintain synaptic plasticity and memory despite tau-mediated pathogenesis. Thus, our results distinguished KIBRA both as a biomarker of synapse dysfunction and as the foundation for a synapse repair mechanism to reverse cognitive impairment in tauopathy.

KIBRA single nucleotide polymorphism is associated with hippocampal subfield volumes and cognition across development

The hippocampus (Hc) consists of cytoarchitectonically and functionally distinct subfields: dentate gyrus (DG), cornu ammonis (CA1-3), and subiculum. In adults, a single nucleotide polymorphism (rs17070145, C→ T) in KIBRA, a gene encoding the eponymous (KIdney-BRAin) protein, is associated with variability in Hc subfield volumes and episodic memory. T-allele carriers have larger DG and CA volumes and better episodic memory compared to C-homozygotes. Little is known, however, about KIBRA's role in the development of the brain and cognition. In a sample of children, adolescents, and young adults (N = 176, ages 5- 25 years), we replicated the adult association between KIBRA T-allele and larger DG and CA volumes but observed no relationship between KIBRA rs17070145 polymorphism and episodic memory. We noted, however, that a general cognitive performance index (IQ) differed across the allelic groups, with the lowest scores among T-homozygotes and the highest among C-homozygotes. Thus, in this developmental sample, KIBRA appears to have opposing effects on regional brain volume and cognition. These influences of KIBRA SNP may stem from associations between developmental reduction in brain volume and gains in cognitive performance-a hypothesis to be tested in longitudinal studies.

Human mutations in high-confidence Tourette disorder genes affect sensorimotor behavior, reward learning, and striatal dopamine in mice

Tourette disorder (TD) is poorly understood, despite affecting 1/160 children. A lack of animal models possessing construct, face, and predictive validity hinders progress in the field. We used CRISPR/Cas9 genome editing to generate mice with mutations orthologous to human de novo variants in two high-confidence Tourette genes, CELSR3 and WWC1 . Mice with human mutations in Celsr3 and Wwc1 exhibit cognitive and/or sensorimotor behavioral phenotypes consistent with TD. Sensorimotor gating deficits, as measured by acoustic prepulse inhibition, occur in both male and female Celsr3 TD models. Wwc1 mice show reduced prepulse inhibition only in females. Repetitive motor behaviors, common to Celsr3 mice and more pronounced in females, include vertical rearing and grooming. Sensorimotor gating deficits and rearing are attenuated by aripiprazole, a partial agonist at dopamine type II receptors. Unsupervised machine learning reveals numerous changes to spontaneous motor behavior and less predictable patterns of movement. Continuous fixed-ratio reinforcement shows Celsr3 TD mice have enhanced motor responding and reward learning. Electrically evoked striatal dopamine release, tested in one model, is greater. Brain development is otherwise grossly normal without signs of striatal interneuron loss. Altogether, mice expressing human mutations in high-confidence TD genes exhibit face and predictive validity. Reduced prepulse inhibition and repetitive motor behaviors are core behavioral phenotypes and are responsive to aripiprazole. Enhanced reward learning and motor responding occurs alongside greater evoked dopamine release. Phenotypes can also vary by sex and show stronger affection in females, an unexpected finding considering males are more frequently affected in TD.

Significance Statement

We generated mouse models that express mutations in high-confidence genes linked to Tourette disorder (TD). These models show sensorimotor and cognitive behavioral phenotypes resembling TD-like behaviors. Sensorimotor gating deficits and repetitive motor behaviors are attenuated by drugs that act on dopamine. Reward learning and striatal dopamine is enhanced. Brain development is grossly normal, including cortical layering and patterning of major axon tracts. Further, no signs of striatal interneuron loss are detected. Interestingly, behavioral phenotypes in affected females can be more pronounced than in males, despite male sex bias in the diagnosis of TD. These novel mouse models with construct, face, and predictive validity provide a new resource to study neural substrates that cause tics and related behavioral phenotypes in TD.

WWC1/2 regulate spinogenesis and cognition in mice by stabilizing AMOT

WWC1 regulates episodic learning and memory, and genetic nucleotide polymorphism of WWC1 is associated with neurodegenerative diseases such as Alzheimer's disease. However, the molecular mechanism through which WWC1 regulates neuronal function has not been fully elucidated. Here, we show that WWC1 and its paralogs (WWC2/3) bind directly to angiomotin (AMOT) family proteins (Motins), and recruit USP9X to deubiquitinate and stabilize Motins. Deletion of WWC genes in different cell types leads to reduced protein levels of Motins. In mice, neuron-specific deletion of Wwc1 and Wwc2 results in reduced expression of Motins and lower density of dendritic spines in the cortex and hippocampus, in association with impaired cognitive functions such as memory and learning. Interestingly, ectopic expression of AMOT partially rescues the neuronal phenotypes associated with Wwc1/2 deletion. Thus, WWC proteins modulate spinogenesis and cognition, at least in part, by regulating the protein stability of Motins.

Experience alters hippocampal and cortical network communication via a KIBRA-dependent mechanism

Synaptic plasticity is hypothesized to underlie "replay" of salient experience during hippocampal sharp-wave/ripple (SWR)-based ensemble activity and to facilitate systems-level memory consolidation coordinated by SWRs and cortical sleep spindles. It remains unclear how molecular changes at synapses contribute to experience-induced modification of network function. The synaptic protein KIBRA regulates plasticity and memory. To determine the impact of KIBRA-regulated plasticity on circuit dynamics, we recorded in vivo neural activity from wild-type (WT) mice and littermates lacking KIBRA and examined circuit function before, during, and after novel experience. In WT mice, experience altered population activity and oscillatory dynamics in a manner consistent with incorporation of new information content in replay and enhanced hippocampal-cortical communication. While baseline SWR features were normal in KIBRA conditional knockout (cKO) mice, experience-dependent alterations in SWRs were absent. Furthermore, intra-hippocampal and hippocampal-cortical communication during SWRs was disrupted following KIBRA deletion. These results indicate molecular mechanisms that underlie network-level adaptations to experience.

KIBRA repairs synaptic plasticity and promotes resilience to tauopathy-related memory loss

Synaptic plasticity is obstructed by pathogenic tau in the brain, representing a key mechanism that underlies memory loss in Alzheimer's disease (AD) and related tauopathies. Here, we define a mechanism for plasticity repair in vulnerable neurons using the C-terminus of the KIdney/BRAin (KIBRA) protein (CT-KIBRA). We show that CT-KIBRA restores plasticity and memory in transgenic mice expressing pathogenic human tau; however, CT-KIBRA did not alter tau levels or prevent tau-induced synapse loss. Instead, we find that CT-KIBRA binds to and stabilizes protein kinase Mζ (PKMζ) to maintain synaptic plasticity and memory despite tau-mediated pathogenesis. In humans we find that reduced KIBRA in brain and increased KIBRA in cerebrospinal fluid are associated with cognitive impairment and pathological tau levels in disease. Thus, our results distinguish KIBRA both as a novel biomarker of synapse dysfunction in AD and as the foundation for a synapse repair mechanism to reverse cognitive impairment in tauopathy.

A Lightweight Drive Implant for Chronic Tetrode Recordings in Juvenile Mice

In vivo electrophysiology provides unparalleled insight into the sub-second-level circuit dynamics of the intact brain and represents a method of particular importance for studying mouse models of human neuropsychiatric disorders. However, such methods often require large cranial implants, which cannot be used in mice at early developmental time points. As such, virtually no studies of in vivo physiology have been performed in freely behaving infant or juvenile mice, despite the fact that a better understanding of neurological development in this critical window would likely provide unique insights into age-dependent developmental disorders such as autism or schizophrenia. Here, a micro-drive design, surgical implantation procedure, and post-surgery recovery strategy are described that allow for chronic field and single-unit recordings from multiple brain regions simultaneously in mice as they age from postnatal day 20 (p20) to postnatal day 60 (p60) and beyond, a time window roughly corresponding to the human ages of 2 years old through to adulthood. The number of recording electrodes and final recording sites can be easily modified and expanded, thus allowing flexible experimental control of the in vivo monitoring of behavior- or disease-relevant brain regions across development.

WWC2 expression in the testis: Implications for spermatogenesis and male fertility

The family of WWC proteins is known to regulate cell proliferation and organ growth control via the Hippo signaling pathway. As WWC proteins share a similar domain structure and a common set of interacting proteins, they are supposed to fulfill compensatory functions in cells and tissues. While all three WWC family members WWC1, WWC2, and WWC3 are found co-expressed in most human organs including lung, brain, kidney, and liver, in the testis only WWC2 displays a relatively high expression. In this study, we investigated the testicular WWC2 expression in spermatogenesis and male fertility. We show that the Wwc2 mRNA expression level in mouse testes is increased during development in parallel with germ cell proliferation and differentiation. The cellular expression of each individual WWC family member was evaluated in published single-cell mRNA datasets of murine and human testes demonstrating a high WWC2 expression predominantly in early spermatocytes. In line with this, immunohistochemistry revealed cytosolic WWC2 protein expression in primary spermatocytes from human testes displaying full spermatogenesis. In accordance with these findings, markedly lower WWC2 expression levels were detected in testicular tissues from mice and men lacking germ cells. Finally, analysis of whole-exome sequencing data of male patients affected by infertility and unexplained severe spermatogenic failure revealed several heterozygous, rare WWC2 gene variants with a proposed damaging function and putative impact on WWC2 protein structure. Taken together, our findings provide novel insights into the testicular expression of WWC2 and show its cell-specific expression in spermatocytes. As rare WWC2 variants were identified in the background of disturbed spermatogenesis, WWC2 may be a novel candidate gene for male infertility.

Dendritic spinule-mediated structural synaptic plasticity: Implications for development, aging, and psychiatric disease

Dendritic spines are highly dynamic and changes in their density, size, and shape underlie structural synaptic plasticity in cognition and memory. Fine membranous protrusions of spines, termed dendritic spinules, can contact neighboring neurons or glial cells and are positively regulated by neuronal activity. Spinules are thinner than filopodia, variable in length, and often emerge from large mushroom spines. Due to their nanoscale, spinules have frequently been overlooked in diffraction-limited microscopy datasets. Until recently, our knowledge of spinules has been interpreted largely from single snapshots in time captured by electron microscopy. We summarize herein the current knowledge about the molecular mechanisms of spinule formation. Additionally, we discuss possible spinule functions in structural synaptic plasticity in the context of development, adulthood, aging, and psychiatric disorders. The literature collectively implicates spinules as a mode of structural synaptic plasticity and suggests the existence of morphologically and functionally distinct spinule subsets. A recent time-lapse, enhanced resolution imaging study demonstrated that the majority of spinules are small, short-lived, and dynamic, potentially exploring their environment or mediating retrograde signaling and membrane remodeling via trans-endocytosis. A subset of activity-enhanced, elongated, long-lived spinules is associated with complex PSDs, and preferentially contacts adjacent axonal boutons not presynaptic to the spine head. Hence, long-lived spinules can form secondary synapses with the potential to alter synaptic connectivity. Published studies further suggest that decreased spinules are associated with impaired synaptic plasticity and intellectual disability, while increased spinules are linked to hyperexcitability and neurodegenerative diseases. In summary, the literature indicates that spinules mediate structural synaptic plasticity and perturbations in spinules can contribute to synaptic dysfunction and psychiatric disease. Additional studies would be beneficial to further delineate the molecular mechanisms of spinule formation and determine the exact role of spinules in development, adulthood, aging, and psychiatric disorders.

A novel, lightweight drive implant for chronic tetrode recordings in juvenile mice

SHORT ABSTRACT

We describe a novel micro-drive design, surgical implantation procedure, and post-surgery recovery strategy that allows for chronic field and single-unit recordings from up to sixteen brain regions simultaneously in juvenile and adolescent mice across a critical developmental window from p20 to p60 and beyond.

LONG ABSTRACT

In vivo electrophysiology provides unparalleled insight into sub-second-level circuit dynamics of the intact brain and represents a method of particular importance for studying mouse models of human neuro-psychiatric disorders. However, such methods often require large cranial implants which cannot be used in mice at early developmental timepoints. As such, virtually no studies of in vivo physiology have been performed in freely behaving infant or juvenile mice, despite the fact that a better understanding of neurological development in this critical window is likely to provide unique insights into age-dependent developmental disorders such as autism or schizophrenia. Here, we describe a novel micro-drive design, surgical implantation procedure, and post-surgery recovery strategy that allows for chronic field and single-unit recordings from up to sixteen brain regions simultaneously in mice as they age from postnatal day 20 (p20) to postnatal day 60 (p60) and beyond, a time window roughly corresponding to human ages 2-years-old through adult. The number of recording electrodes and final recording sites can be easily modified and expanded, allowing flexible experimental control of in vivo monitoring of behavior- or disease-relevant brain regions across development.

Co-culturing Immune Cells and Mouse-Derived Mixed Cortical Cultures with Oxygen-Glucose Deprivation to In Vitro Simulate Neuroinflammatory Interactions After Stroke

Studying interactions between neural cells and glial cells in vitro remains an essential tool for scientists worldwide, and with the addition of oxygen-glucose deprivation (OGD) can be particularly useful for identifying mechanisms related to ischemic stroke-related injury and repair. In developing these protocols in the lab, however, we discovered the limitation of co-culturing immune cells with pure neuronal cultures as the standard media for immune cells impair neuronal growth and vice versa. Thus, we optimized a mixed cortical cell culture system that does not require the use of glial-conditioned media to support the viability and growth of neurons but can nonetheless be used to quantify neuronal survival and dendritic arborization. The following methods provide a guide as to how to culture mixed cortical cells from mouse pups (postnatal day 0-2). Additionally, we demonstrate how to co-culture mixed cortical cells with immune cells (e.g., B cells) to study neuro-immune interactions in vitro.

KIBRA regulates activity-induced AMPA receptor expression and synaptic plasticity in an age-dependent manner

A growing body of human literature implicates KIBRA in memory and neurodevelopmental disorders. Memory and the cellular substrates supporting adaptive cognition change across development. Using an inducible KIBRA knockout mouse, we demonstrate that adult-onset deletion of KIBRA in forebrain neurons impairs long-term spatial memory and long-term potentiation (LTP). These LTP deficits correlate with adult-selective decreases in extrasynaptic AMPA receptors under basal conditions, and we identify a role for KIBRA in LTP-induced AMPAR upregulation. In contrast, juvenile-onset deletion of KIBRA in forebrain neurons did not affect LTP and had minimal effects on basal AMPAR expression. LTP did not increase AMPAR protein expression in juvenile WT mice, providing a potential explanation for juvenile resilience to KIBRA deletion. These data suggest that KIBRA serves a unique role in adult hippocampal function through regulation of basal and activity-dependent AMPAR proteostasis that supports synaptic plasticity.

Hippo-released WWC1 facilitates AMPA receptor regulatory complexes for hippocampal learning

Learning and memory rely on changes in postsynaptic glutamergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type receptor (AMPAR) number, spatial organization, and function. The Hippo pathway component WW and C2 domain-containing protein 1 (WWC1) regulates AMPAR surface expression and impacts on memory performance. However, synaptic binding partners of WWC1 and its hierarchical position in AMPAR complexes are largely unclear. Using cell-surface proteomics in hippocampal tissue of Wwc1-deficient mice and by generating a hippocampus-specific interactome, we show that WWC1 is a major regulatory platform in AMPAR signaling networks. Under basal conditions, the Hippo pathway members WWC1 and large tumor-suppressor kinase (LATS) are associated, which might prevent WWC1 effects on synaptic proteins. Reduction of WWC1/LATS binding through a point mutation at WWC1 elevates the abundance of WWC1 in AMPAR complexes and improves hippocampal-dependent learning and memory. Thus, uncoupling of WWC1 from the Hippo pathway to AMPAR-regulatory complexes provides an innovative strategy to enhance synaptic transmission.

Multiphase coalescence mediates Hippo pathway activation

The function of biomolecular condensates is often restricted by condensate dissolution. Whether condensates can be suppressed without condensate dissolution is unclear. Here, we show that upstream regulators of the Hippo signaling pathway form functionally antagonizing condensates, and their coalescence into a common phase provides a mode of counteracting the function of biomolecular condensates without condensate dissolution. Specifically, the negative regulator SLMAP forms Hippo-inactivating condensates to facilitate pathway inhibition by the STRIPAK complex. In response to cell-cell contact or osmotic stress, the positive regulators AMOT and KIBRA form Hippo-activating condensates to facilitate pathway activation. The functionally antagonizing SLMAP and AMOT/KIBRA condensates further coalesce into a common phase to inhibit STRIPAK function. These findings provide a paradigm for restricting the activity of biomolecular condensates without condensate dissolution, shed light on the molecular principles of multiphase organization, and offer a conceptual framework for understanding upstream regulation of the Hippo signaling pathway.

Trafficking of NMDA receptors is essential for hippocampal synaptic plasticity and memory consolidation

NMDA receptor (NMDAR) plays a vital role in brain development and normal physiological functions. Surface trafficking of NMDAR contributes to the modulation of synaptic functions and information processing. However, it remains unclear whether NMDAR trafficking is independent of long-term potentiation (LTP) and whether it regulates behavior. Here, we report that LTP of AMPAR and NMDAR can occur concurrently and that NMDAR trafficking can regulate AMPAR trafficking and AMPAR-mediated LTP. By contrast, AMPAR trafficking does not impact NMDAR-mediated LTP. Using SAP97-interfering peptide and SAP97 knockin (KI) rat, we show that the effect is mediated by GluN2A-subunit-containing NMDARs. At the behavior level, impaired NMDAR trafficking results in deficits in consolidation, but not acquisition, of fear memory. Collectively, our results suggest the essential role of NMDAR trafficking in LTP and memory consolidation.

Thalamic gray matter volume mediates the association between KIBRA polymorphism and olfactory function among older adults: a population-based study

The kidney and brain expressed protein (KIBRA) rs17070145 polymorphism is associated with both structure and activation of the olfactory cortex. However, no studies have thus far examined whether KIBRA can be linked with olfactory function and whether brain structure plays any role in the association. We addressed these questions in a population-based cross-sectional study among rural-dwelling older adults. This study included 1087 participants derived from the Multidomain Interventions to Delay Dementia and Disability in Rural China, who underwent the brain MRI scans in August 2018 to October 2020; of these, 1016 took the 16-item Sniffin' Sticks identification test and 634 (62.40%) were defined with olfactory impairment (OI). Data were analyzed using the voxel-based morphometry analysis and general linear, logistic, and structural equation models. The KIBRA rs17070145 C-allele (CC or CT vs. TT genotype) was significantly associated with greater gray matter volume (GMV) mainly in the bilateral orbitofrontal cortex and left thalamus (P < 0.05) and with the multi-adjusted odds ratio of 0.73 (95% confidence interval 0.56-0.95) for OI. The left thalamic GMV could mediate 8.08% of the KIBRA-olfaction association (P < 0.05). These data suggest that the KIBRA rs17070145 C-allele is associated with a reduced likelihood of OI among older adults, partly mediated through left thalamic GMV.

KIBRA regulates amyloid β metabolism by controlling extracellular vesicles secretion

Background

Previous research has revealed that KIBRA controls secretion of extracellular vesicles (EVs) by inhibiting the proteasomal degradation of Rab27a and EVs play an important role in amyloid β (Aβ) metabolism and transmission during Alzheimer's disease (AD) pathogenesis. Here, we further test the hypothesis that KIBRA regulates Aβ metabolism via the endosomal-lysosomal system.

Methods

We generated KIBRA knockout mice on a 5XFAD background and KIBRA knockdown cells in murine HT22 cells with stably overexpressing APP. Various forms of Aβ and quantification of EVs were analyzed by biochemical methods and nanoparticle tracking analysis, respectively. Multivesicular bodies (MVBs) were visualized by electron microscopy and confocal fluorescent microscopy. In a population-based cohort (n = 1419), KIBRA genotypes and plasma Aβ levels were analyzed using multiple-PCR amplification and Simoa, respectively.

Findings

Multiple forms of Aβ were dramatically attenuated in KIBRA knockout mouse brain, including monomers, oligomers, and extracellular deposition, but KIBRA knockout had no effect on intraneuronal APP C-terminal fragment β (APP-CTFβ)/Aβ levels. KIBRA depletion also decreased APP-CTFβ/Aβ-associated EVs secretion and subsequently enhanced MVBs number. Furthermore, we found that excessive accumulation of MVBs harboring APP-CTFβ/Aβ promoted the MVBs-lysosome fusion for degradation and inhibition of lysosomal function rescued secretion of APP-CTFβ/Aβ-associated EVs. More importantly, whole exon sequencing of KIBRA in a large population-based cohort identified the association of KIBRA rs28421695 polymorphism with plasma Aβ levels.

Interpretation

These results demonstrate that KIBRA regulates Aβ metabolism via controlling the secretion of APP-CTFβ/Aβ-associated EVs.

Funding

National Key R&D Program of China, and National Natural Science Foundation of China.

AMPA Receptors: A Key Piece in the Puzzle of Memory Retrieval

Retrieval constitutes a highly regulated and dynamic phase in memory processing. Its rapid temporal scales require a coordinated molecular chain of events at the synaptic level that support transient memory trace reactivation. AMPA receptors (AMPAR) drive the majority of excitatory transmission in the brain and its dynamic features match the singular fast timescales of memory retrieval. Here we provide a review on AMPAR contribution to memory retrieval regarding its dynamic movements along the synaptic compartments, its changes in receptor number and subunit composition that take place in activity dependent processes associated with retrieval. We highlight on the differential regulations exerted by AMPAR subunits in plasticity processes and its impact on memory recall.

NMDA and AMPA receptors dysregulation in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative condition characterized by cognitive dysfunction and synaptic failure. The current therapeutic approaches are mainly focused on symptomatic treatment and possess limited effectiveness in addressing the pathophysiology of AD. It is known that neurodegeneration is negatively correlated with synaptic plasticity. This negative correlation highlights glutamatergic neurotransmission via N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors and (AMPA) receptors as a critical mediator of synaptic plasticity. Despite this favorable role, extensive extracellular glutamate concentration induces excitotoxicity and neurodegeneration. NMDA receptors containing GluN2A subunits are located at synaptic sites, implicated in the protective pathways. In comparison, GluN2B containing receptors are located mainly at extrasynaptic sites and increase neuronal vulnerability. AMPA receptors are consistently endocytosed and recycled back to the membrane. An increase in the rate of endocytosis has been implicated as a part of AD pathophysiology through inducing long-term depression (LTD) and synaptic disintegration. In the present review, we focused on the mechanisms of glutamatergic system dysregulation in AD, particularly on its interaction with amyloid-beta. We concluded that assigning a specific role to an individual subtype of either NMDA receptors or AMPA receptors might be an oversimplification as they are not static receptors. Therefore, any imbalance between synaptic and extrasynaptic NMDA receptors and a reduced number of surface AMPA receptors will lead to synaptopathy.

Pyk2 suppresses contextual fear memory in an autophosphorylation-independent manner

Clustered protocadherins (Pcdhs) are a large family of cadherin-like cell adhesion proteins that are central for neurite self-avoidance and neuronal connectivity in the brain. Their downstream non-receptor tyrosine kinase Pyk2 (proline-rich tyrosine kinase 2, also known as Ptk2b, Cakb, Raftk, Fak2, and Cadtk) is predominantly expressed in the hippocampus. We constructed Pyk2 null mouse lines and found that these mutant mice showed enhancement in contextual fear memory, without any change in auditory-cued and spatial-referenced learning and memory. In addition, by preparing Y402F mutant mice, we observed that Pyk2 suppressed contextual fear memory in an autophosphorylation-independent manner. Moreover, using high-throughput RNA sequencing, we found that immediate early genes, such as Npas4, cFos, Zif268/Egr1, Arc, and Nr4a1, were enhanced in Pyk2 null mice. We further showed that Pyk2 disruption affected pyramidal neuronal complexity and spine dynamics. Thus, we demonstrated that Pyk2 is a novel fear memory suppressor molecule and Pyk2 null mice provide a model for understanding fear-related disorders. These findings have interesting implications regarding dysregulation of the Pcdh‒Pyk2 axis in neuropsychiatric disorders.

Synaptic tau: A pathological or physiological phenomenon?

In this review, we discuss the synaptic aspects of Tau pathology occurring during Alzheimer's disease (AD) and how this may relate to memory impairment, a major hallmark of AD. Whilst the clinical diagnosis of AD patients is a loss of working memory and long-term declarative memory, the histological diagnosis is the presence of neurofibrillary tangles of hyperphosphorylated Tau and Amyloid-beta plaques. Tau pathology spreads through synaptically connected neurons to impair synaptic function preceding the formation of neurofibrillary tangles, synaptic loss, axonal retraction and cell death. Alongside synaptic pathology, recent data suggest that Tau has physiological roles in the pre- or post- synaptic compartments. Thus, we have seen a shift in the research focus from Tau as a microtubule-stabilising protein in axons, to Tau as a synaptic protein with roles in accelerating spine formation, dendritic elongation, and in synaptic plasticity coordinating memory pathways. We collate here the myriad of emerging interactions and physiological roles of synaptic Tau, and discuss the current evidence that synaptic Tau contributes to pathology in AD.

Dendritic/Post-synaptic Tau and Early Pathology of Alzheimer's Disease

Microtubule-associated protein tau forms insoluble neurofibrillary tangles (NFTs), which is one of the major histopathological hallmarks of Alzheimer's disease (AD). Many studies have demonstrated that tau causes early functional deficits prior to the formation of neurofibrillary aggregates. The redistribution of tau from axons to the somatodendritic compartment of neurons and dendritic spines causes synaptic impairment, and then leads to the loss of synaptic contacts that correlates better with cognitive deficits than amyloid-β (Aβ) aggregates do in AD patients. In this review, we discuss the underlying mechanisms by which tau is mislocalized to dendritic spines and contributes to synaptic dysfunction in AD. We also discuss the synergistic effects of tau and oligomeric forms of Aβ on promoting synaptic dysfunction in AD.

Lack of WWC2 Protein Leads to Aberrant Angiogenesis in Postnatal Mice

The WWC protein family is an upstream regulator of the Hippo signalling pathway that is involved in many cellular processes. We examined the effect of an endothelium-specific WWC1 and/or WWC2 knock-out on ocular angiogenesis. Knock-outs were induced in C57BL/6 mice at the age of one day (P1) and evaluated at P6 (postnatal mice) or induced at the age of five weeks and evaluated at three months of age (adult mice). We analysed morphology of retinal vasculature in retinal flat mounts. In addition, in vivo imaging and functional testing by electroretinography were performed in adult mice. Adult WWC1/2 double knock-out mice differed neither functionally nor morphologically from the control group. In contrast, the retinas of the postnatal WWC knock-out mice showed a hyperproliferative phenotype with significantly enlarged areas of sprouting angiogenesis and a higher number of tip cells. The branching and end points in the peripheral plexus were significantly increased compared to the control group. The deletion of the WWC2 gene was decisive for these effects; while knocking out WWC1 showed no significant differences. The results hint strongly that WWC2 is an essential regulator of ocular angiogenesis in mice. As an activator of the Hippo signalling pathway, it prevents excessive proliferation during physiological angiogenesis. In adult animals, WWC proteins do not seem to be important for the maintenance of the mature vascular plexus.

Increased expression of dendrin in the dorsal horn of the spinal cord during stress is regulated by sex hormones

Chronic stress has various effects on organisms and is sex-specific. The aim of the study was to describe the expression of synapse strengthening protein, dendrin, in the spinal cord (SC) and the dependence of its expression on chronic stress and sex hormones. Thirteen-month-old female and male rats were castrated (ovariectomy [F-OVX] or orchidectomy [M-ORX]) or sham-operated (F-SH or M-SH), respectively. At age 15 months, three 10-day-sessions of sham stress (control, C) or chronic stress (S) were conducted. Dendrin expression was present in the thoracic SC segments and the dorsal root ganglia (DRG). In the SC, dendrin expression was prominent in superficial laminae of the dorsal horn and lamina X (central canal). The M-ORX-S group had the highest dendrin expression in the dorsal horn, being significantly higher than the M-ORX-C or M-SH-S groups (P < 0.05). Dendrin expression was significantly higher in the F-SH-S group than the F-SH-C group (P < 0.05), as well as in the F-SH-S than the M-SH-S (P < 0.05). Co-localization with the α-d-galactosyl-specific isolectin B4 (IB4) in central projections of the DRG neurons in the dorsal horn of the SC was 7.43 ± 3.36%, while with the calcitonin gene-related peptide (CGRP) was 8.47 ± 4.45%. Localization of dendrin was observed in soma and nuclei of neurons in the dorsal horn. Dendrin expression in pain-processing areas of the SC, the DRG neurons and their peripheral projections suggest possible roles in pain perception and modulation. Stress-induced increase in dendrin expression and its dependence on sex hormones may partially explain sex-specific pain hypersensitivity induced by stress.

The Hippo pathway component Wwc2 is a key regulator of embryonic development and angiogenesis in mice

The WW-and-C2-domain-containing (WWC) protein family is involved in the regulation of cell differentiation, cell proliferation, and organ growth control. As upstream components of the Hippo signaling pathway, WWC proteins activate the Large tumor suppressor (LATS) kinase that in turn phosphorylates Yes-associated protein (YAP) and its paralog Transcriptional coactivator-with-PDZ-binding motif (TAZ) preventing their nuclear import and transcriptional activity. Inhibition of WWC expression leads to downregulation of the Hippo pathway, increased expression of YAP/TAZ target genes and enhanced organ growth. In mice, a ubiquitous Wwc1 knockout (KO) induces a mild neurological phenotype with no impact on embryogenesis or organ growth. In contrast, we could show here that ubiquitous deletion of Wwc2 in mice leads to early embryonic lethality. Wwc2 KO embryos display growth retardation, a disturbed placenta development, impaired vascularization, and finally embryonic death. A whole-transcriptome analysis of embryos lacking Wwc2 revealed a massive deregulation of gene expression with impact on cell fate determination, cell metabolism, and angiogenesis. Consequently, a perinatal, endothelial-specific Wwc2 KO in mice led to disturbed vessel formation and vascular hypersprouting in the retina. In summary, our data elucidate a novel role for Wwc2 as a key regulator in early embryonic development and sprouting angiogenesis in mice.

Emerging roles for angiomotin in the nervous system

Angiomotins are a family of molecular scaffolding proteins that function to organize contact points (called tight junctions in vertebrates) between adjacent cells. Some angiomotin isoforms bind to the actin cytoskeleton and are part of signaling pathways that influence cell morphology and migration. Others cooperate with components of the Hippo signaling pathway and the associated networks to control organ growth. The 130-kDa isoform, AMOT-p130, has critical roles in neural stem cell differentiation, dendritic patterning, and synaptic maturation-attributes that are essential for normal brain development and are consistent with its association with autism. Here, we review and discuss the evidence that supports a role for AMOT-p130 in neuronal development in the central nervous system.

Wwc2 Is a Novel Cell Division Regulator During Preimplantation Mouse Embryo Lineage Formation and Oogenesis

Formation of the hatching mouse blastocyst marks the end of preimplantation development, whereby previous cell cleavages culminate in the formation of three distinct cell lineages (trophectoderm, primitive endoderm and epiblast). We report that dysregulated expression of Wwc2, a genetic paralog of Kibra/Wwc1 (a known activator of Hippo-signaling, a key pathway during preimplantation development), is specifically associated with cell autonomous deficits in embryo cell number and cell division abnormalities. Division phenotypes are also observed during mouse oocyte meiotic maturation, as Wwc2 dysregulation blocks progression to the stage of meiosis II metaphase (MII) arrest and is associated with spindle defects and failed Aurora-A kinase (AURKA) activation. Oocyte and embryo cell division defects, each occurring in the absence of centrosomes, are fully reversible by expression of recombinant HA-epitope tagged WWC2, restoring activated oocyte AURKA levels. Additionally, clonal embryonic dysregulation implicates Wwc2 in maintaining the pluripotent epiblast lineage. Thus, Wwc2 is a novel regulator of meiotic and early mitotic cell divisions, and mouse blastocyst cell fate.

WWC1 and NF2 Prevent the Development of Intrahepatic Cholangiocarcinoma by Regulating YAP/TAZ Activity through LATS in Mice

Hippo signaling acts as a tumor suppressor pathway by inhibiting the proliferation of adult stem cells and progenitor cells in various organs. Liver-specific deletion of Hippo pathway components in mice induces liver cancer development through activation of the transcriptional coactivators, YAP and TAZ, which exhibit nuclear enrichment and are activated in numerous types of cancer. The upstream-most regulators of Warts, the Drosophila ortholog of mammalian LATS1/2, are Kibra, Expanded, and Merlin. However, the roles of the corresponding mammalian orthologs, WWC1, FRMD6 and NF2, in the regulation of LATS1/2 activity and liver tumorigenesis in vivo are not fully understood. Here, we show that deletion of both Wwc1 and Nf2 in the liver accelerates intrahepatic cholangiocarcinoma (iCCA) development through activation of YAP/TAZ. Additionally, biliary epithelial cell-specific deletion of both Lats1 and Lats2 using a Sox9-CreERT2 system resulted in iCCA development through hyperactivation of YAP/TAZ. These findings suggest that WWC1 and NF2 cooperate to promote suppression of cholangiocarcinoma development by inhibiting the oncogenic activity of YAP/TAZ via LATS1/2.

Interaction of COMT and KIBRA modulates the association between hippocampal structure and episodic memory performance in healthy young adults

Genetic variations of COMT and KIBRA, which were reported to be expressed in the hippocampus, have been linked to memory function. However, their interaction on the hippocampal structure remains unknown. This study aimed to explore the interaction effects of COMT rs4680 and KIBRA rs17070145 on the hippocampal subfield volumes and test their associations with hippocampus-memory relationship in 187 healthy young adults. Two-way analysis of covariance was applied to the alterations in hippocampal subfield volumes among COMT and KIBRA genotypes. Significant interaction effects of these two genes were found in the right CA1 and CA3 subfields. Among KIBRA C-allele carriers, COMT Val/Val homozygotes showed greater volume in these regions than COMT Met-allele carriers. Furthermore, the slope of the correlation between right CA1 volume and immediate recall on the California Verbal Learning Test-II (CVLT-II) (F = 4.36, p = 0.041) as well as CVLT-II delayed recall (F = 6.44, p = 0.014) were significantly different between COMT Val/Val homozygotes and Met-allele carriers, which were positive or tend to be positive in COMT Val/Val group (CVLT immediate recall, r = 0.319, p = 0.040; CVLT delayed recall, r = 0.304, p = 0.051), but absent in COMT Met-allele carriers (CVLT immediate recall, r = -0.263, p = 0.205; CVLT delayed recall, r = -0.351, p = 0.086). These findings may provide a novel insight into the genetic effects upon the hippocampal structure and suggest that the conjoint effects of COMT and KIBRA played a modulatory role in the hippocampus-episodic memory correlation.

Kibra Modulates Learning and Memory via Binding to Dendrin

Kibra is a synaptic scaffold protein regulating learning and memory. Alterations of Kibra-encoding gene WWC1 cause various neuronal disorders, including Alzheimer's disease and Tourette syndrome. However, the molecular mechanism underlying Kibra's function in neurons is poorly understood. Here we discover that Kibra, via its N-terminal WW12 tandem domains, binds to a postsynaptic density enriched protein, Dendrin, with a nanomolar dissociation constant. On the basis of the structure of Kibra WW12 in complex with Dendrin PY motifs, we developed a potent peptide inhibitor capable of specifically blocking the binding between Kibra and Dendrin in neurons. Systematic administration of the inhibitory peptide attenuated excitatory synaptic transmission, completely blocked long-term potentiation induction, and impaired spatial learning and memory. A Kibra mutation found in Tourette syndrome patients causes defects in binding to Dendrin. Thus, Kibra can modulate spatial learning and memory via binding to Dendrin.

CAMDI interacts with the human memory-associated protein KIBRA and regulates AMPAR cell surface expression and cognition

Little is known about the molecular mechanisms of cognitive deficits in psychiatric disorders. CAMDI is a psychiatric disorder-related factor, the deficiency of which in mice results in delayed neuronal migration and psychiatrically abnormal behaviors. Here, we found that CAMDI-deficient mice exhibited impaired recognition memory and spatial reference memory. Knockdown of CAMDI in hippocampal neurons increased the amount of internalized alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor (AMPAR) and attenuated the chemical long-term potentiation (LTP)-dependent cell surface expression of AMPAR. KIBRA was identified as a novel CAMDI-binding protein that retains AMPAR in the cytosol after internalization. KIBRA inhibited CAMDI-dependent Rab11 activation, thereby attenuating AMPAR cell surface expression. These results suggest that CAMDI regulates AMPAR cell surface expression during LTP. CAMDI dysfunction may partly explain the mechanism underlying cognitive deficits in psychiatric diseases.

Isoform Specificity of PKMs during Long-Term Facilitation in Aplysia Is Mediated through Stabilization by KIBRA

Persistent activity of protein kinase M (PKM), the truncated form of protein kinase C (PKC), can maintain long-term changes in synaptic strength in many systems, including the hermaphrodite marine mollusk, Aplysia californica Moreover, different types of long-term facilitation (LTF) in cultured Aplysia sensorimotor synapses rely on the activities of different PKM isoforms in the presynaptic sensory neuron and postsynaptic motor neuron. When the atypical PKM isoform is required, the kidney and brain expressed adaptor protein (KIBRA) is also required. Here, we explore how this isoform specificity is established. We find that PKM overexpression in the motor neuron, but not the sensory neuron, is sufficient to increase synaptic strength and that this activity is not isoform-specific. KIBRA is not the rate-limiting step in facilitation since overexpression of KIBRA is neither sufficient to increase synaptic strength, nor to prolong a form of PKM-dependent intermediate synaptic facilitation. However, the isoform specificity of dominant-negative-PKMs to erase LTF is correlated with isoform-specific competition for stabilization by KIBRA. We identify a new conserved region of KIBRA. Different splice isoforms in this region stabilize different PKMs based on the isoform-specific sequence of an α-helix "handle" in the PKMs. Thus, specific stabilization of distinct PKMs by different isoforms of KIBRA can explain the isoform specificity of PKMs during LTF in Aplysia SIGNIFICANCE STATEMENT Long-lasting changes in synaptic plasticity associated with memory formation are maintained by persistent protein kinases. We have previously shown in the Aplysia sensorimotor model that distinct isoforms of persistently active protein kinase Cs (PKMs) maintain distinct forms of long-lasting synaptic changes, even when both forms are expressed in the same motor neuron. Here, we show that, while the effects of overexpression of PKMs are not isoform-specific, isoform specificity is defined by a "handle" helix in PKMs that confers stabilization by distinct splice forms in a previously undefined domain of the adaptor protein KIBRA. Thus, we define new regions in both KIBRA and PKMs that define the isoform specificity for maintaining synaptic strength in distinct facilitation paradigms.

The AMPA Receptor Code of Synaptic Plasticity

Changes in the properties and postsynaptic abundance of AMPA-type glutamate receptors (AMPARs) are major mechanisms underlying various forms of synaptic plasticity, including long-term potentiation (LTP), long-term depression (LTD), and homeostatic scaling. The function and the trafficking of AMPARs to and from synapses is modulated by specific AMPAR GluA1-GluA4 subunits, subunit-specific protein interactors, auxiliary subunits, and posttranslational modifications. Layers of regulation are added to AMPAR tetramers through these different interactions and modifications, increasing the computational power of synapses. Here we review the reliance of synaptic plasticity on AMPAR variants and propose "the AMPAR code" as a conceptual framework. The AMPAR code suggests that AMPAR variants will be predictive of the types and extent of synaptic plasticity that can occur and that a hierarchy exists such that certain AMPARs will be disproportionally recruited to synapses during LTP/homeostatic scaling up, or removed during LTD/homeostatic scaling down.

Dendritic Tau in Alzheimer's Disease

The microtubule-associated protein tau and amyloid-β (Aβ) are key players in Alzheimer's disease (AD). Aβ and tau are linked in a molecular pathway at the post-synapse with tau-dependent synaptic dysfunction being a major pathomechanism in AD. Recent work on site-specific modification of dendritic and more specifically post-synaptic tau has revealed new endogenous functions of tau that limits synaptic Aβ toxicity. Thus, molecular studies opened a new perspective on tau, placing it at the center of neurotoxic and neuroprotective signaling at the post-synapse. Here, we review recent advances on tau in the dendritic compartments, with implications for understanding and treatment of AD and related neurological conditions.

AMPA receptors and their minions: auxiliary proteins in AMPA receptor trafficking

To correctly transfer information, neuronal networks need to continuously adjust their synaptic strength to extrinsic stimuli. This ability, termed synaptic plasticity, is at the heart of their function and is, thus, tightly regulated. In glutamatergic neurons, synaptic strength is controlled by the number and function of AMPA receptors at the postsynapse, which mediate most of the fast excitatory transmission in the central nervous system. Their trafficking to, at, and from the synapse, is, therefore, a key mechanism underlying synaptic plasticity. Intensive research over the last 20 years has revealed the increasing importance of interacting proteins, which accompany AMPA receptors throughout their lifetime and help to refine the temporal and spatial modulation of their trafficking and function. In this review, we discuss the current knowledge about the roles of key partners in regulating AMPA receptor trafficking and focus especially on the movement between the intracellular, extrasynaptic, and synaptic pools. We examine their involvement not only in basal synaptic function, but also in Hebbian and homeostatic plasticity. Included in our review are well-established AMPA receptor interactants such as GRIP1 and PICK1, the classical auxiliary subunits TARP and CNIH, and the newest additions to AMPA receptor native complexes.

The Neuroprotection of KIBRA in Promoting Neuron Survival and Against Amyloid β-Induced Apoptosis

Background: Recent research has identified the nucleotide polymorphisms of KIdney and BRAin expressed protein (KIBRA) to be associated with cognitive performance, suggesting its vital role in Alzheimer’s disease (AD); however, the underlying molecular mechanism of KIBRA in AD remains obscure.

Methods: The AD animal model (APP/PS1 transgenic mice) and KIBRA knockout (KIBRA KO) mice were used to investigate pathophysiological changes of KIBRA in vivo. Mouse hippocampal cell line (HT22) was used to explore its molecular mechanism through KIBRA CRISPR/Cas9-sgRNA system and KIBRA overexpression lentivirus in vitro.

Results: Aged APP/PS1 mice displayed increased neuronal apoptosis in the hippocampus, as did KIBRA KO mice. KIBRA deficiency was closely related to neuronal loss in the brain. In addition, knockdown of KIBRA in neuronal cell lines suppressed its growth and elevated apoptosis-associated protein levels under the stress of Aβ_1–42 oligomers. On the contrary, overexpression of KIBRA significantly promoted cell proliferation and reduced its apoptosis. Moreover, through screening several survival-related signaling pathways, we found that KIBRA inhibited apoptosis by activating the Akt pathway other than ERK or PKC pathways, which was further confirmed by Akt-specific inhibitor MK2206.

Conclusion: Our data indicate that KIBRA may function as a neuroprotective gene in promoting neuron survival and inhibiting Aβ-induced neuronal apoptosis.

Glutamate-Releasing SWELL1 Channel in Astrocytes Modulates Synaptic Transmission and Promotes Brain Damage in Stroke

By releasing glutamate, astrocytes actively regulate synaptic transmission and contribute to excitotoxicity in neurological diseases. However, the mechanisms of astrocytic glutamate release have been debated. Here, we report non-vesicular release of glutamate through the glutamate-permeable volume-regulated anion channel (VRAC). Both cell swelling and receptor stimulation activated astrocytic VRAC, which requires its only obligatory subunit, Swell1. Astrocyte-specific Swell1 knockout mice exhibited impaired glutamatergic transmission due to the decreases in presynaptic release probability and ambient glutamate level. Consistently, the mutant mice displayed hippocampal-dependent learning and memory deficits. During pathological cell swelling, deletion of astrocytic Swell1 attenuated glutamate-dependent neuronal excitability and protected mice from brain damage after ischemic stroke. Our identification of a new molecular mechanism for channel-mediated glutamate release establishes a role for astrocyte-neuron interactions in both synaptic transmission and brain ischemia. It provides a rationale for targeting VRAC for the treatment of stroke and other neurological diseases associated with excitotoxicity.

KIBRA controls exosome secretion via inhibiting the proteasomal degradation of Rab27a

Exosomes are nanosized membrane vesicles released from cells after fusion of multivesicular bodies (MVBs) with the plasma membrane (PM) and play important roles in intercellular communication and numerous biological processes. However, the molecular mechanisms regulating exosome secretion remain poorly understood. Here we identify KIBRA as an adaptor-like protein that stabilizes Rab27a, which in turn controls exosome secretion both in vitro and in vivo. Knockdown or overexpression of KIBRA in neuronal and podocyte cell lines leads to a decrease or increase of exosome secretion, respectively, and KIBRA depletion increases MVB size and number. Comparing protein profiles between KIBRA knockout and wild-type mouse brain showed significantly decreased Rab27a, a small GTPase that regulates MVB-PM docking. Rab27a is stabilized by interacting with KIBRA, which prevents ubiquitination and degradation via the ubiquitin-proteasome pathway. In conclusion, we show that KIBRA controls exosome secretion via inhibiting the proteasomal degradation of Rab27a.

Exosomes are intercellular signaling vesicles created by fusion of multivesicular bodies (MVBs) and the plasma membrane (PM), but secretory regulation is ill-defined. Song et al. show that KIBRA controls exosome secretion by protecting Rab27a from proteasomal degradation, promoting MVB-PM docking.