Kalirin, a key player in synapse formation, is implicated in human diseases

GDNF facilitates cognitive function recovery following neonatal surgical-induced learning and memory impairment via activation of the RET pathway and modulation of downstream effectors PKMζ and Kalirin in rats

OBJECTIVE

The aim of this study is to elucidate the underlying mechanism through which glial cell line-derived neurotrophic factor (GDNF) improves cognitive deficits in adults resulting from neonatal surgical interventions.

METHODS

Newborn Sprague-Dawley rats, regardless of gender, were randomly allocated into seven groups on postnatal day 7 as follows (n=15): (1) Control group (not subjected to anesthesia, surgery, or any pharmaceutical interventions); (2) GDNF group (received intracerebroventricular injection of GDNF); (3) Surgery group (underwent right carotid artery exposure under anesthesia with 3 % sevoflurane); (4) Surgery plus GDNF group; (5) Surgery plus GDNF and type II JAK inhibitor NVP-BBT594 (BBT594) group (administered intraperitoneal injection of BBT594); (6) BBT group; and (7) Surgery plus BBT group. Starting from postnatal day 33, all rats underwent Barnes maze and fear conditioning tests, followed by decapitation under sevoflurane anesthesia for subsequent analyses. The left hemibrains underwent Golgi staining, while the right hemibrains were used for hippocampal protein extraction to assess Protein kinase Mζ (PKMζ) and Kalirin expression through western blotting.

RESULTS

GDNF demonstrated a mitigating effect on spatial learning and memory impairment, as well as context-related fear memory impairment, reductions in dendritic total lengths, and spinal density within the hippocampus induced by surgical intervention. Notably, all of these ameliorative effects of GDNF were reversed upon administration of the RET inhibitor BBT594. Additionally, GDNF alleviated the downregulation of protein expression of PKMζ and Kalirin in the hippocampus of rats subjected to surgery, subsequently reversed by BBT594.

CONCLUSION

The effective impact of GDNF on learning and memory impairment caused by surgical intervention appears to be mediated through the RET pathway. Moreover, GDNF may exert its influence by upregulating the expression of PKMζ and Kalirin, consequently enhancing the development of dendrites and dendritic spines.

Chronic thermal stress on Octopus maya embryos down-regulates epigenome-related genes and those involved in the nervous system development and morphogenesis

Red Octopus maya is strongly influenced by temperature. Recent studies have reported negative reproduction effects on males and females when exposed to temperatures higher than 27 °C. Embryos under thermal stress show morphological and physiological alterations; similar phenotypes have been reported in embryos from stressed females, evidencing transgenerational consequences. Transcriptomic profiles were characterized along embryo development during normal-under thermal stress and epigenetic alterations through DNA methylation and damage quantification. Total RNA in organogenesis, activation, and growth stages in control and thermal stress were sequenced with Illumina RNA-Seq. Similarly, total DNA was used for DNA methylation and damage quantification between temperatures and embryo stages. Differential gene expression analyses showed that embryos express genes associated with oxygen transport, morphogenesis, nervous system, neuroendocrine cell differentiation, spermatogenesis, and male sex differentiation. Conversely, embryos turn off genes involved mainly in nervous system development, morphogenesis, and gene expression regulation when exposed to thermal stress - consistent with O. maya embryo phenotypes showing abnormal arms, eyes, and body development. No significant differences were observed in quantifying DNA methylation between temperatures but they were for DNA damage quantification. Epigenetic alterations are hypothesized to occur since several genes found downregulated belong to the epigenetic machinery but at histone tail level.

Structural and biochemical alterations in dendritic spines as key mechanisms for severe mental illnesses

Severe mental illnesses (SMI) collectively affect approximately 20% of the global population, as estimated by the World Health Organization (WHO). Despite having diverse etiologies, clinical symptoms, and pharmacotherapies, these diseases share a common pathophysiological characteristic: the misconnection of brain areas involved in reality perception, executive control, and cognition, including the corticolimbic system. Dendritic spines play a crucial role in excitatory neurotransmission within the central nervous system. These small structures exhibit remarkable plasticity, regulated by factors such as neurotransmitter tone, neurotrophic factors, and innate immunity-related molecules, and other mechanisms - all of which are associated with the pathophysiology of SMI. However, studying dendritic spine mechanisms in both healthy and pathological conditions in patients is fraught with technical limitations. This is where animal models related to these diseases become indispensable. They have played a pivotal role in elucidating the significance of dendritic spines in SMI. In this review, the information regarding the potential role of dendritic spines in SMI was summarized, drawing from clinical and animal model reports. Also, the implications of targeting dendritic spine-related molecules for SMI treatment were explored. Specifically, our focus is on major depressive disorder and the neurodevelopmental disorders schizophrenia and autism spectrum disorder. Abundant clinical and basic research has studied the functional and structural plasticity of dendritic spines in these diseases, along with potential pharmacological targets that modulate the dynamics of these structures. These targets may be associated with the clinical efficacy of the pharmacotherapy.

Kalirin is involved in epileptogenesis by modulating the activity of the Rac1 signaling pathway

BACKGROUND AND OBJECTIVE

Epilepsy is a common chronic brain disease. Despite the availability of various anti-seizure drugs, approximately 30 % of patients do not respond to treatment. Recent research suggests that Kalirin plays a role in regulating neurological function. However, the pathogenesis of Kalirin in epileptic seizures remains unclear. This study aims to investigate the role and mechanism of Kalirin in epileptogenesis.

MATERIALS AND METHODS

An epileptic model was induced by intraperitoneal injection of pentylenetetrazole (PTZ). Endogenous Kalirin was inhibited using shRNA. The expression of Kalirin, Rac1, and Cdc42 in the hippocampal CA1 region was measured using Western blotting. Spine and synaptic structures were examined using Golgi staining and electron microscopy. Moreover, the necrotic neurons in CA1 were examined using HE staining.

RESULTS

The results indicated that the epileptic score increased in epileptic animals, while inhibition of Kalirin decreased the epileptic scores and increased the latent period of the first seizure attack. Inhibition of Kalirin attenuated the increases in Rac1 expression, dendritic spine density, and synaptic vesicle number in the CA1 region induced by PTZ. However, the increase in Cdc42 expression was not affected by the inhibition of Kalirin.

CONCLUSION

This study suggests that Kalirin is involved in the development of seizures by modulating the activity of Rac1, providing a novel anti-epileptic target.

Synaptic dysfunction in schizophrenia

Schizophrenia is a chronic disease presented with psychotic symptoms, negative symptoms, impairment in the reward system, and widespread neurocognitive deterioration. Disruption of synaptic connections in neural circuits is responsible for the disease's development and progression. Because deterioration in synaptic connections results in the impaired effective processing of information. Although structural impairments of the synapse, such as a decrease in dendritic spine density, have been shown in previous studies, functional impairments have also been revealed with the development of genetic and molecular analysis methods. In addition to abnormalities in protein complexes regulating exocytosis in the presynaptic region and impaired vesicle release, especially, changes in proteins related to postsynaptic signaling have been reported. In particular, impairments in postsynaptic density elements, glutamate receptors, and ion channels have been shown. At the same time, effects on cellular adhesion molecular structures such as neurexin, neuroligin, and cadherin family proteins were detected. Of course, the confusing effect of antipsychotic use in schizophrenia research should also be considered. Although antipsychotics have positive and negative effects on synapses, studies indicate synaptic deterioration in schizophrenia independent of drug use. In this review, the deterioration in synapse structure and function and the effects of antipsychotics on the synapse in schizophrenia will be discussed.

A Novel Cis-Regulatory lncRNA, Kalnc2, Downregulates Kalrn Protein-Coding Transcripts in Mouse Neuronal Cells

The KALRN gene encodes several multi-domain protein isoforms that localize to neuronal synapses, conferring the ability to grow and retract dendritic spines and shaping axonal outgrowth, dendrite morphology, and dendritic spine re-modeling. The KALRN genomic locus is implicated in several neurodevelopmental and neuropsychiatric diseases, including autism, schizophrenia, bipolar disease, and intellectual disability. We have previously shown that a novel brain-specific long non-coding RNA (lncRNA) arising from the 5' end of the kalrna gene, called durga, regulates neuronal morphology in zebrafish. Here, we characterized mammalian Kalrn loci, annotating and experimentally validating multiple novel non-coding RNAs, including linear and circular variants. Comparing the mouse and human loci, we show that certain non-coding RNAs and Kalrn protein-coding isoforms arising from the locus show similar expression dynamics during development. In humans, mice, and zebrafish, the 5' end of the Kalrn locus gives rise to a chromatin-associated lncRNA that is present in adult ovaries, besides being expressed during brain development and enriched in certain regions of the adult brain. Ectopic expression of this lncRNA led to the downregulation of all the major Kalrn mRNA isoforms. We propose that this lncRNA arising from the 5' end of the Kalrn locus is functionally the mammalian ortholog of zebrafish lncRNA durga.

Secreted Amyloid Precursor Protein Alpha, a Neuroprotective Protein in the Brain Has Widespread Effects on the Transcriptome and Proteome of Human Inducible Pluripotent Stem Cell-Derived Glutamatergic Neurons Related to Memory Mechanisms

Secreted amyloid precursor protein alpha (sAPPα) processed from a parent human brain protein, APP, can modulate learning and memory. It has potential for development as a therapy preventing, delaying, or even reversing Alzheimer’s disease. In this study a comprehensive analysis to understand how it affects the transcriptome and proteome of the human neuron was undertaken. Human inducible pluripotent stem cell (iPSC)-derived glutamatergic neurons in culture were exposed to 1 nM sAPPα over a time course and changes in the transcriptome and proteome were identified with RNA sequencing and Sequential Window Acquisition of All THeoretical Fragment Ion Spectra-Mass Spectrometry (SWATH-MS), respectively. A large subset (∼30%) of differentially expressed transcripts and proteins were functionally involved with the molecular biology of learning and memory, consistent with reported links of sAPPα to memory enhancement, as well as neurogenic, neurotrophic, and neuroprotective phenotypes in previous studies. Differentially regulated proteins included those encoded in previously identified Alzheimer’s risk genes, APP processing related proteins, proteins involved in synaptogenesis, neurotransmitters, receptors, synaptic vesicle proteins, cytoskeletal proteins, proteins involved in protein and organelle trafficking, and proteins important for cell signalling, transcriptional splicing, and functions of the proteasome and lysosome. We have identified a complex set of genes affected by sAPPα, which may aid further investigation into the mechanism of how this neuroprotective protein affects memory formation and how it might be used as an Alzheimer’s disease therapy.

Differential Effects of Sevoflurane Exposure on Long-Term Fear Memory in Neonatal and Adult Rats

It remains unclear whether exposure to sevoflurane produces different effects on long-term cognitive function in developing and mature brains. In the present study, Sprague-Dawley neonatal rats at postnatal day (PND) 7 and adult rats (PND 56) were used in all experiments. We performed fear conditioning testing to examine long-term fear memory following 4-h sevoflurane exposure. We assessed hippocampal synapse ultrastructure with a transmission electron microscope. Moreover, we investigated the effect of sevoflurane exposure on the expression of postsynaptic protein 95 (PSD-95) and its binding protein kalirin-7 in the hippocampus. We observed that early exposure to sevoflurane in neonatal rats impairs hippocampus-dependent fear memory, reduces hippocampal synapse density, and dramatically decreases the expressions of PSD-95 and kalirin-7 in the hippocampus of the developing brain. However, sevoflurane exposure in adult rats has no effects on hippocampus-dependent fear memory and hippocampal synapse density, and the expressions of PSD-95 and kalirin-7 in the adult hippocampus are not significantly altered following sevoflurane treatment. Our results indicate that sevoflurane exposure produces differential effects on long-term fear memory in neonatal and adult rats and that PSD-95 signaling may be involved in the molecular mechanism for early sevoflurane exposure-caused long-term fear memory impairment.

Differential Transcriptome Profiling Unveils Novel Deregulated Gene Signatures Involved in Pathogenesis of Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that is characterized by a progressive loss of cognitive functions at a higher level than normal aging. Although the apolipoprotein (APOE) gene is a major risk factor in developing AD, other genes have also been reported to be linked with complex phenotypes. Therefore, this genome-wide expression study explored differentially expressed genes as possible novel biomarkers involved in AD. The mRNA expression dataset, GSE28146, containing 15 sample data composed of 7 AD cases from the hippocampus region with age-matched control (n = 8, >80 years), was analyzed. Using “affy” R-package, mRNA expression was calculated, while pathway enrichment analysis was performed to determine related biological processes. Of 58 differentially expressed genes, 44 downregulated and 14 upregulated genes were found to be significantly (p < 0.001) altered. The pathway enrichment analysis revealed two altered genes, i.e., dynein light chain 1 (DYNLL1) and kalirin (KLRN), associated with AD in the elderly population. The majority of genes were associated with retrograde endocannabinoid as well as vascular endothelial growth factors affecting the complex phenotypes. The DYNLL1 and KLRN genes may be involved with AD and Huntington’s disease (HD) phenotypes and represent a common genetic basis of these diseases. However, the hallmark of AD is dementia, while the classic motor sign of HD includes chorea. Our data warrant further investigation to identify the role of these genes in disease pathogenesis.

Phencynonate hydrochloride exerts antidepressant effects by regulating the dendritic spine density and altering glutamate receptor expression

Phencynonate hydrochloride (PCH) is a drug that crosses the blood-brain barrier. Cellular experiments confirmed that PCH protects against glutamate toxicity and causes only weak central inhibition and limited side effects. As shown in our previous studies, PCH alleviates depression-like behaviours induced by chronic unpredictable mild stress (CUMS). Here we administered PCH at three different doses (4, 8 and 16 mg/kg) to male rats for two continuous days after CUMS and conducted behavioural tests to assess the dose-dependent antidepressant effects of PCH and its effects on the neuroplasticity in the hippocampus and medial prefrontal cortex (mPFC). Meanwhile, we measured the spine density and expression of related proteins to illustrate the mechanism of PCH. PCH treatment (8 mg/kg) significantly alleviated depression-like behaviours induced by CUMS. All doses of PCH treatment reversed the spine loss in prelimbic and CA3 regions induced by CUMS. Kalirin-7 expression was decreased in the hippocampus and mPFC of the CUMS group. The expression of the NR1 and NR2B subunits in the hippocampus, and NR2B in mPFC are increased by CUMS. PCH treatment (8 and 16 mg/kg) reversed all of these changes of Kalirin-7 in PFC and hippocampus, as well as NR1 and NR2B expression in the hippocampus. PCH is expected to be developed as a new type of rapid antidepressant. Its antidepressant effect may be closely related to the modulation of dendritic spine density in the prelimbic and CA3 regions and the regulation of Kalilin-7 and N-methyl-D-aspartic acid receptor levels in the hippocampus.

Osthole Ameliorates Estrogen Deficiency-Induced Cognitive Impairment in Female Mice

Loss of endogenous estrogen and dysregulation of the estrogen receptor signaling pathways are associated with an increase in risk for cognitive deficit and depression in women after menopause. Estrogen therapy for menopause increases the risk of breast and ovarian cancers, and stroke. Therefore, it is critical to find an alternate treatment for menopausal women. Osthole (OST), a coumarin, has been reported to have neuroprotective effects. This study examined whether OST improves ovariectomy (OVX)-induced cognitive impairment, and alleviates anxiety- and depression-like behaviors induced by OVX in mice. Adult female C57BL/6J mice were ovariectomized and then treated with OST at a dose of 30 mg/kg for 14 days. At the end of the treatment period, behavioral tests were used to evaluate spatial learning and memory, recognition memory, anxiety- and depression-like behaviors. A cohort of the mice were sacrificed after 14 days of OST treatment and their hippocampi were collected for measurement of the proteins of interest using western blot. OVX-induced alteration in the levels of proteins was accompanied by cognitive deficit, anxiety- and depression-like behaviors. OST treatment improved cognitive deficit, alleviated anxiety- and depression-like behaviors induced by OVX, and reversed OVX-induced alterations in the levels of synaptic proteins and ERα, BDNF, TrKB, p-CREB, p-Akt and Rac1 in the hippocampus. Therefore, reversal of OVX-induced decrease in the levels of hippocampal proteins by OST might contribute to the effects of OST on improving cognitive deficit and alleviating anxiety- and depression-like behaviors induced by OVX.

A newly identified small molecular compound acts as a protein kinase inhibitor to suppress metastasis of colorectal cancer

BACKGROUND

Targeted therapy has demonstrated high efficacy in the treatment of advanced cancer, and protein kinase inhibitors are a major focus of that therapy; therefore, our study aimed to identify a new protein kinase inhibitor that could be used in the treatment of advanced cancers.

METHODS

We analyzed the expression profile of colorectal cancer (CRC), combined the driver gene and drug target databases, and identified protein kinase kalirin RhoGEF kinase (kalirin/KALRN) which is related to CRC metastasis. Based on the structure of kalirin, we screened for the small molecular compound ZINC65387069. We first compared the kinase inhibitory activities and molecular properties of ZINC65387069 and tyrosine kinase inhibitors (TKIs). We then determined the effects of ZINC65387069 on the phosphorylation of protein kinase B-Raf. Finally, we determined the effects of ZINC65387069 on migration and apoptosis of HCT116 cells as well as RKO cells. The cell cytoskeleton was also determined.

RESULTS

Compared with traditional TKIs, ZINC65387069 had stronger kinase inhibitory activity, a simpler structure, higher water solubility, a smaller polar surface area, and lower molecular weight and volume. In CRC cells, ZINC65387069 could significantly inhibit the phosphorylation of B-Raf as well as inhibit cell migration, destroy the cell cytoskeleton, and promote cell apoptosis.

CONCLUSION

ZINC65387069 is a newly identified protein kinase inhibitor that deserves additional research as a lead compound for drug development to help create targeted therapy against CRC.

KALRN: A central regulator of synaptic function and synaptopathies

The synaptic regulator, kalirin, plays a key role in synaptic plasticity and formation of dendritic arbors and spines. Dysregulation of the KALRN gene has been linked to various neurological disorders, including autism spectrum disorder, Alzheimer's disease, schizophrenia, addiction and intellectual disabilities. Both genetic and molecular studies highlight the importance of normal KALRN expression for healthy neurodevelopment and function. This review aims to give an in-depth analysis of the structure and molecular mechanisms of kalirin function, particularly within the brain. These data are correlated to genetic evidence of patient mutations within KALRN and animal models of Kalrn that together give insight into the manner in which this gene may be involved in neurodevelopment and the etiology of disease. The emerging links to human disease from post-mortem, genome wide association (GWAS) and exome sequencing studies are examined to highlight the disease relevance of kalirin, particularly in neurodevelopmental diseases. Finally, we will discuss efforts to pharmacologically regulate kalirin protein activity and the implications of such endeavors for the treatment of human disease. As multiple disease states arise from deregulated synapse formation and altered KALRN expression and function, therapeutics may be developed to provide control over KALRN activity and thus synapse dysregulation. As such, a detailed understanding of how kalirin regulates neuronal development, and the manner in which kalirin dysfunction promotes neurological disease, may support KALRN as a valuable therapeutic avenue for future pharmacological intervention.

Synaptic Kalirin-7 and Trio Interactomes Reveal a GEF Protein-Dependent Neuroligin-1 Mechanism of Action

The RhoGEFs Kalirin-7 and Trio are regulators of synaptic plasticity, and their dysregulation is associated with a range of neurodevelopmental and neurodegenerative disorders. Although studies have implicated both Kalirin and Trio in certain diseases, such as tauopathies, they remarkably differ in their association with other disorders. Using unbiased proteomics, we identified interactomes of Kalirin-7 and Trio to ascertain distinct protein association networks associated with their respective function and revealed groups of proteins that preferentially interact with a particular RhoGEF. In comparison, we find Trio interacts with a range of axon guidance and presynaptic complexes, whereas Kalirin-7 associates with several synaptic adhesion molecules. Specifically, we show Kalirin-7 is an interactor of the cell adhesion molecule neuroligin-1 (NLGN1), and NLGN1-dependent synaptic function is mediated through Kalirin-7 in an interaction-dependent manner. Our data reveal not only the interactomes of two important disease-related proteins, but also provide an intracellular effector of NLGN1 function.

Paskus et al. use quantitative proteomics to determine the synaptic interactomes of the disease-associated proteins Kalirin-7 and Trio, identifying Kalirin-7 as an interactor of NLGN1. Investigation of this interaction unveils Kalirin-7 as a primary intracellular effector of NLGN1 gain of function.

Rac1 is a downstream effector of PKCα in structural synaptic plasticity

Structural and functional plasticity of dendritic spines is the basis of animal learning. The rapid remodeling of actin cytoskeleton is associated with spine enlargement and shrinkage, which are essential for structural plasticity. The calcium-dependent protein kinase C isoform, PKCα, has been suggested to be critical for this actin-dependent plasticity. However, mechanisms linking PKCα and structural plasticity of spines are unknown. Here, we examine the spatiotemporal activation of actin regulators, including small GTPases Rac1, Cdc42 and Ras, in the presence or absence of PKCα during single-spine structural plasticity. Removal of PKCα expression in the postsynapse attenuated Rac1 activation during structural plasticity without affecting Ras or Cdc42 activity. Moreover, disruption of a PDZ binding domain within PKCα led to impaired Rac1 activation and deficits in structural spine remodeling. These results demonstrate that PKCα positively regulates the activation of Rac1 during structural plasticity.

Treadmill Exercise Reverses Depression Model-Induced Alteration of Dendritic Spines in the Brain Areas of Mood Circuit

Depression is one of the most prevalent psychiatric disorders. Exercise has been shown to be effective in the amelioration of depression, but the underlying mechanism remains largely unknown. Alterations in the density and morphology of dendritic spines are associated with psychiatric diseases. Chronic unpredictable mild stress (CUMS) is an established animal model of depression. The aim of this study was to determine whether treadmill exercise reverses CUMS-induced both depression-like behaviors and alterations in spine density and morphology of the principal neurons in the brain areas of the mood circuits including the hippocampus, medial prefrontal cortex (mPFC), nucleus accumbens (NAc) and basolateral amygdala (BLA). Male rats were randomly divided into four groups: control, CUMS, exercise, and CUMS+exercise. CUMS-induced depression-like behaviors were evaluated by the sucrose preference test (SPT). Golgi staining was used to visualize dendritic spines. Our results showed that CUMS-induced depression-like behaviors characterized by a decrease in sucrose consumption were accompanied by a decrease in spine density and a change in spine morphology in the pyramidal neurons of both the hippocampal CA3 area and the mPFC, and an increase in spine density and an alteration in spine shape in both the NAc medium spiny neurons (MSNs) and the BLA neurons; exercise reversed both CUMS-induced depression-like behaviors and alterations in dendritic spines. This study provides important information for understanding the mechanism through which exercise ameliorates CUMS-induced depression-like behaviors.

Regulators of Rho GTPases in the Nervous System: Molecular Implication in Axon Guidance and Neurological Disorders

One of the fundamental steps during development of the nervous system is the formation of proper connections between neurons and their target cells-a process called neural wiring, failure of which causes neurological disorders ranging from autism to Down's syndrome. Axons navigate through the complex environment of a developing embryo toward their targets, which can be far away from their cell bodies. Successful implementation of neuronal wiring, which is crucial for fulfillment of all behavioral functions, is achieved through an intimate interplay between axon guidance and neural activity. In this review, our focus will be on axon pathfinding and the implication of some of its downstream molecular components in neurological disorders. More precisely, we will talk about axon guidance and the molecules implicated in this process. After, we will briefly review the Rho family of small GTPases, their regulators, and their involvement in downstream signaling pathways of the axon guidance cues/receptor complexes. We will then proceed to the final and main part of this review, where we will thoroughly comment on the implication of the regulators for Rho GTPases-GEFs (Guanine nucleotide Exchange Factors) and GAPs (GTPase-activating Proteins)-in neurological diseases and disorders.

Role of Cdk5 in Kalirin7-Mediated Formation of Dendritic Spines

A majority of excitatory synapses in the brain are localized on the dendritic spines. Alterations of spine density and morphology are associated with many neurological diseases. Understanding the molecular mechanisms underlying spine formation is important for understanding these diseases. Kalirin7 (Kal-7) is localized to the postsynaptic side of excitatory synapses in the neurons. Overexpression of Kal-7 causes an increase in spine density whereas knockdown expression of endogenous Kal-7 results in a decrease in spine density in primary cultured cortical neurons. However, the mechanisms underlying Kal-7-mediated spine formation are not entirely clear. Cyclin-dependent kinase 5 (Cdk5) plays a vital role in the formation of spines and synaptic plasticity. Kal-7 is phosphorylated by CDK5 at Thr¹⁵⁹⁰, the unique Cdk5 phosphorylation site in the Kal-7 protein. This study was to explore the role of CDK5-mediated phosphorylation of Kal-7 in spine formation and the underlying mechanisms. Our results showed expression of Kal-7T/D (mimicked phosphorylation), Kal-7T/A mutants (blocked phosphorylation) or wild-type (Wt) Kal-7 caused in a similar increase in spine density, while spine size of Wt Kal-7-expressing cortical neurons was bigger than that in Kal-7 T\A-expressing neurons, but smaller than that in Kal-7T/D-expressing neurons. The fluorescence intensity of NMDA receptor subunit NR2B (GluN2B) staining was stronger along the MAP2 positive dendrites of Kal-7T/D-expressing neurons than that in Kal-7T/A- or Wt Kal-7-expressing neurons. The fluorescence intensity of AMPA receptor subunit GluR1 (GluA1) staining showed the same trend as GluN2B staining. These findings suggest that Cdk5 affects the function of Kal-7 on spine morphology and function via GluN2B and GluA1 receptors during dendritic spine formation.

Kalirin-7 plays a neuroprotective role in Neuro-2A cells injured by oxygen-glucose deprivation and reperfusion through Rac1 activation

Objective(s):

The study explored the neuroprotective role of Kalirin-7 (Kal-7) in Neuro-2A cells after oxygen-glucose deprivation and reperfusion (OGD/R) treatment.

Materials and Methods:

The study used an OGD/R model of mouse Neuro-2A neuroblastoma cells in vitro. Cells were transfected with pCAGGS-Kal-7 to up-regulating kal-7. Then cell proliferation and apoptosis were respectively analyzed by Trypan blue exclusion method and flow cytometry. To examine the involvement of Rac1, cells were treated with Rac1-GTP inhibitor NSC23766 before treatment with OGD/R. Expressions of Bax, Bcl-2, Rac1, and down-stream targets of Rac1 were analyzed by Western blot.

Results:

Kal-7 significantly decreased OGD/R induced cell apoptosis (P<0.01), but no significant effects were observed on cell proliferation. Kal-7 increased the expressions of apoptosis-related protein of Bcl-2 and Rac1, but decreased the expression of Bax in Neuro-2A cells stimulated to OGD/R. Rac1 was activated by Kal-7 due to the increased levels of its down-stream targets, p-p38 and p-PAK1. NSC23766 reduced the anti-apoptotic effect of Kal-7 as the enhanced apoptotic cell rate and increased Bax/Bcl-2 ratio.

Conclusion:

These findings suggest that the protective effects of Kal-7 against OGD/R injury in Neuro-2A cells were dependent in a Rac1 activation signaling.

Genetic Variation of the Kalirin Gene is Associated with ICAS in the Chinese Population

Intracranial atherosclerotic stenosis (ICAS) is one of the most common causes of ischemic stroke (IS), especially in recurrent patients. Several studies have demonstrated an intimate association between the genetic mutation of the KALRN gene and IS. The main aim of this study was to clarify the relationship between three single nucleotide polymorphisms (SNPs) of KALRN and ICAS in a northern Chinese population and further explore the underlining mechanism. The relationship between each SNP and ICAS and the related components were examined in five models (co-dominant, dominant, recessive, heterozygous, and additive). Multivariate logistic regression models were applied and adjusted for 10,000 permutation tests. Haplotype regression analysis was performed to determine the associations between haplotypes and the severity of ICAS. qRT-PCR was used to confirm the mRNA level of Kalirin. SNP rs6438833 of the Kalirin gene in the additive model was associated with ICAS (OR = 1.642, 95%CI: 1.129-2.388, P_Dom = 0.048). After performing 10,000 permutations, the result showed a trend toward statistical significance (Pper = 0.048). Haplotypes of the KALRN gene were not significantly associated with ICAS (global significance, p = 0.090). qRT-PCR showed that the expression of KALRN 9 in IS patients was almost threefold the control group (p < 0.0005). SNPs of the KALRN gene are associated with ICAS in the northern Chinese population.

Modulation of Kalirin-7 expression by hippocampal CA1 5-HT1B receptors in spatial memory consolidation

Serotonin 5-HT1B receptors (5-HT1BRs) are distributed in hippocampal CA1 and play a pivotal role in cognitive function. Activation of 5-HT1BRs regulates synaptic plasticity at the excitatory synapses in the hippocampus. However, the role and its underlying mechanism of 5-HT1BR activation-mediated glutamatergic synaptic plasticity in spatial memory are not fully understood. In this study, spatial memory of Sprague-Dawley (SD) rats was assessed in a Morris water maze after bilateral dorsal hippocampal CA1 infusion of the 5-HT1BR antagonist GR55562 (25 μg/μL) or agonist CP93129 (25 μg/μL). GR55562 did not affect the spatial memory acquisition but significantly increased the target quadrant preference during the memory consolidation probe performed 14 d after the training session, while CP93129 impaired the memory consolidation process. Moreover, GR55562 significantly increased, while CP93129 significantly decreased, the density of dendritic spines on the distal apical dendrites of CA1 pyramidal neurons. Furthermore, western blot experiments indicated that GR55562 significantly increased, but CP93129 significantly reduced, the expression of Kalirin-7 (Kal-7), PSD95, and GluA2/3 subunits of AMPA receptors. Our results suggest that Kal-7 and Kal-7-mediatedalteration of AMPA receptor subtype expression may play crucial roles in the impact of hippocampal CA1 5-HT1BR activation on spatial memory consolidation.

The transcription factor XBP1s restores hippocampal synaptic plasticity and memory by control of the Kalirin-7 pathway in Alzheimer model

Neuronal network dysfunction and cognitive decline constitute the most prominent features of Alzheimer's disease (AD), although mechanisms causing such impairments are yet to be determined. Here we report that virus-mediated delivery of the active spliced transcription factor X-Box binding protein 1s (XBP1s) in the hippocampus rescued spine density, synaptic plasticity and memory function in a mouse model of AD. XBP1s transcriptionally activated Kalirin-7 (Kal7), a protein that controls synaptic plasticity. In addition, we found reduced levels of Kal7 in primary neurons exposed to Aβ oligomers, transgenic mouse models and human AD brains. Short hairpin RNA-mediated knockdown of Kal7 altered synaptic plasticity and memory formation in naive mice. Further, reduction of endogenous Kal7 compromised the beneficial effects of XBP1s in Alzheimer's model. Hence, our findings reveal that XBP1s is neuroprotective through a mechanism that engages Kal7 pathway with therapeutic implications in AD pathology.

A novel relationship for schizophrenia, bipolar and major depressive disorder Part 3: Evidence from chromosome 3 high density association screen

Familial clustering of schizophrenia (SCZ), bipolar disorder (BPD), and major depressive disorder (MDD) was systematically reported (Aukes et al, Genet Med 2012, 14, 338-341) and convergent evidence from genetics, symptomatology, and psychopharmacology imply that there are intrinsic connections between these three major psychiatric disorders, for example, any two or even three of these disorders could co-exist in some families. A total of 60, 838 single-nucleotide polymorphisms (SNPs) on chromosome 3 were genotyped by Affymetrix Genome-Wide Human SNP array 6.0 on 119 SCZ, 253 BPD (type-I), 177 MDD patients and 1,000 controls. The population of Shandong province was formed in 14 century and believed that it belongs to homogenous population. Associated SNPs were systematically revealed and outstanding susceptibility genes (CADPS, GRM7,KALRN, LSAMP, NLGN1, PRICKLE2, ROBO2) were identified. Unexpectedly, flanking genes for the associated SNPs distinctive for BPD and/or MDD were replicated in an enlarged cohort of 986 SCZ patients. The evidence from this chromosome 3 analysis supports the notion that both of bipolar and MDD might be subtypes of schizophrenia rather than independent disease entity. Also, a similar finding was detected on chromosome 5, 6, 7, and 8 (Chen et al. Am J Transl Res 2017;9 (5):2473-2491; Curr Mol Med 2016;16(9):840-854; Behav Brain Res 2015;293:241-251; Mol Neurobiol 2016. doi: 10.1007/s12035-016-0102-1). Furthermore, PRICKLE2 play an important role in the pathogenesis of three major psychoses in this population.

An autism spectrum disorder-related de novo mutation hotspot discovered in the GEF1 domain of Trio

The Rho guanine nucleotide exchange factor (RhoGEF) Trio promotes actin polymerization by directly activating the small GTPase Rac1. Recent studies suggest that autism spectrum disorder (ASD)-related behavioral phenotypes in animal models of ASD can be produced by dysregulation of Rac1’s control of actin polymerization at glutamatergic synapses. Here, in humans, we discover a large cluster of ASD-related de novo mutations in Trio’s Rac1 activating domain, GEF1. Our study reveals that these mutations produce either hypofunctional or hyperfunctional forms of Trio in rodent neurons in vitro. In accordance with pathological increases or decreases in glutamatergic neurotransmission observed in animal models of ASD, we find that these mutations result in either reduced synaptic AMPA receptor expression or enhanced glutamatergic synaptogenesis. Together, our findings implicate both excessive and reduced Trio activity and the resulting synaptic dysfunction in ASD-related pathogenesis, and point to the Trio-Rac1 pathway at glutamatergic synapses as a possible key point of convergence of many ASD-related genes.

Trio is a RhoGEF protein that promotes actin polymerization and is implicated in the regulation of glutamatergic synapses in autism spectrum disorder (ASD). Here the authors identify a large cluster of de novo mutations in the GEF1 domain of Trio in whole-exome sequencing data from individuals with ASD, and confirm that some of these mutations lead to glutamatergic dysregulation in vitro.

Genetic Variant of Kalirin Gene Is Associated with Ischemic Stroke in a Chinese Han Population

INTRODUCTION

Ischemic stroke is a complex disorder resulting from the interplay of genetic and environmental factors. Previous studies showed that kalirin gene variations were associated with cardiovascular disease. However, the association between this gene and ischemic stroke was unknown. We performed this study to confirm if kalirin gene variation was associated with ischemic stroke.

METHODS

We enrolled 385 ischemic stroke patients and 362 controls from China. Three SNPs of kalirin gene were genotyped by means of ligase detection reaction-PCR method. Data was processed with SPSS and SHEsis platform.

RESULTS

SNP rs7620580 (dominant model: OR = 1.590, p = 0.002 and adjusted OR = 1.662, p = 0.014; additive model: OR = 1.490, p = 0.002 and adjusted OR = 1.636, p = 0.005; recessive model: OR = 2.686, p = 0.039) and SNP rs1708303 (dominant model: OR = 1.523, p = 0.007 and adjusted OR = 1.604, p = 0.028; additive model: OR = 1.438, p = 0.01 and adjusted OR = 1.476, p = 0.039) were associated with ischemic stroke. The GG genotype and G allele of SNP rs7620580 were associated with a risk for ischemic stroke with an adjusted OR of 3.195 and an OR of 1.446, respectively. Haplotype analysis revealed that A-T-G,G-T-A, and A-T-A haplotypes were associated with ischemic stroke.

CONCLUSIONS

Our results provide evidence that kalirin gene variations were associated with ischemic stroke in the Chinese Han population.

A Novel Long Non-coding RNA, durga Modulates Dendrite Density and Expression of kalirin in Zebrafish

Kalirin, a key player in axonal development, nerve growth and synaptic re-modeling, is implicated in many pathological conditions like schizophrenia and autism-spectrum disorders. Alternative promoters and splicing lead to functionally distinct isoforms, but the post-transcriptional regulation of Kalirin has not been studied. Here, we report a novel non-coding RNA, which we name durga, arising from the first exon of kalirin a (kalrna) in the antisense orientation in zebrafish. The kalrna and durga transcripts are barely detectable during early development, but steadily increase by 24 hours post-fertilization (hpf) as the brain develops. Over-expression of durga in the zebrafish embryo led to an increase in kalrna expression. The morphology of the neurons cultured from durga injected embryos had significantly fewer and shorter dendrites. Although durga has no apparent sequence homolog in mammals, based on gene synteny, we found a non-coding RNA arising from the 5′ end of the human Kalrn gene and expressed in the human neuronal cell line, SH-SY5Y. We propose that the zebrafish lncRNA durga maintains dendritic length and density through regulation of kalrna expression and this may have further implications in mammalian systems.

Synaptic Plasticity, Metaplasticity and Depression

The development of a persistent depressive affective state has for some time been thought to result from persistent alterations in neurotransmitter-mediated synaptic transmission. While the identity of those transmitters has changed over the years, the literature has lacked mechanistic connections between the neurophysiological mechanisms they regulate, and how these mechanisms alter neuronal function, and, hence, affective homeostasis. This review will examine recent work that suggests that both long-term activity-dependent changes in synaptic strength (“plasticity”), and shifting set points for the ease of induction of future long-term changes (“metaplasticity”), may be critical to establishing and reversing a depressive behavioral state. Activity-dependent long-term synaptic plasticity involves both strengthening and weakening of synaptic connections associated with a dizzying array of neurochemical alterations that include synaptic insertion and removal of a number of subtypes of AMPA, NMDA and metabotropic glutamate receptors, changes in presynaptic glutamate release, and structural changes in dendritic spines. Cellular mechanisms of metaplasticity are far less well understood. Here, we will review the growing evidence that long-term synaptic changes in glutamatergic transmission, in brain regions that regulate mood, are key determinants of affective homeostasis and therapeutic targets with immense potential for drug development.

Long-Term Potentiation: From CaMKII to AMPA Receptor Trafficking

For more than 20 years, we have known that Ca(2+)/calmodulin-dependent protein kinase (CaMKII) activation is both necessary and sufficient for the induction of long-term potentiation (LTP). During this time, tremendous effort has been spent in attempting to understand how CaMKII activation gives rise to this phenomenon. Despite such efforts, there is much to be learned about the molecular mechanisms involved in LTP induction downstream of CaMKII activation. In this review, we highlight recent developments that have shaped our current thinking about the molecular mechanisms underlying LTP and discuss important questions that remain in the field.

Exome sequencing discloses KALRN homozygous variant as likely cause of intellectual disability and short stature in a consanguineous pedigree

BACKGROUND

The recent availability of whole-exome sequencing has opened new possibilities for the evaluation of individuals with genetically undiagnosed intellectual disability.

RESULTS

We report two affected siblings, offspring of first-cousin parents, with intellectual disability, hypotonia, short stature, growth hormone deficiency, and delayed bone age. All members of the nuclear family were genotyped, and exome sequencing was performed in one of the affected individuals. We used an in-house algorithm (CATCH v1.1) that combines homozygosity mapping with exome sequencing results and provides a list of candidate variants. One identified novel homozygous missense variant in KALRN (NM_003947.4:c.3644C>A: p.(Thr1215Lys)) was predicted to be pathogenic by all pathogenicity prediction software used (SIFT, PolyPhen, Mutation Taster). KALRN encodes the protein kalirin, which is a GTP-exchange factor protein with a reported role in cytoskeletal remodeling and dendritic spine formation in neurons. It is known that mice with ablation of Kalrn exhibit age-dependent functional deficits and behavioral phenotypes.

CONCLUSION

Exome sequencing provided initial evidence linking KALRN to monogenic intellectual disability in man, and we propose that KALRN is the causative gene for the autosomal recessive phenotype in this family.

Mouse and Human Genetic Analyses Associate Kalirin with Ventral Striatal Activation during Impulsivity and with Alcohol Misuse

Impulsivity is associated with a spectrum of psychiatric disorders including drug addiction. To investigate genetic associations with impulsivity and initiation of drug taking, we took a two-step approach. First, we identified genes whose expression level in prefrontal cortex, striatum and accumbens were associated with impulsive behavior in the 5-choice serial reaction time task across 10 BXD recombinant inbred (BXD RI) mouse strains and their progenitor C57BL/6J and DBA2/J strains. Behavioral data were correlated with regional gene expression using GeneNetwork (www.genenetwork.org), to identify 44 genes whose probability of association with impulsivity exceeded a false discovery rate of < 0.05. We then interrogated the IMAGEN database of 1423 adolescents for potential associations of SNPs in human homologs of those genes identified in the mouse study, with brain activation during impulsive performance in the Monetary Incentive Delay task, and with novelty seeking scores from the Temperament and Character Inventory, as well as alcohol experience. There was a significant overall association between the human homologs of impulsivity-related genes and percentage of premature responses in the MID task and with fMRI BOLD-response in ventral striatum (VS) during reward anticipation. In contrast, no significant association was found between the polygenic scores and anterior cingulate cortex activation. Univariate association analyses revealed that the G allele (major) of the intronic SNP rs6438839 in the KALRN gene was significantly associated with increased VS activation. Additionally, the A-allele (minor) of KALRN intronic SNP rs4634050, belonging to the same haplotype block, was associated with increased frequency of binge drinking.

Dendritic Spines in Depression: What We Learned from Animal Models

Depression, a severe psychiatric disorder, has been studied for decades, but the underlying mechanisms still remain largely unknown. Depression is closely associated with alterations in dendritic spine morphology and spine density. Therefore, understanding dendritic spines is vital for uncovering the mechanisms underlying depression. Several chronic stress models, including chronic restraint stress (CRS), chronic unpredictable mild stress (CUMS), and chronic social defeat stress (CSDS), have been used to recapitulate depression-like behaviors in rodents and study the underlying mechanisms. In comparison with CRS, CUMS overcomes the stress habituation and has been widely used to model depression-like behaviors. CSDS is one of the most frequently used models for depression, but it is limited to the study of male mice. Generally, chronic stress causes dendritic atrophy and spine loss in the neurons of the hippocampus and prefrontal cortex. Meanwhile, neurons of the amygdala and nucleus accumbens exhibit an increase in spine density. These alterations induced by chronic stress are often accompanied by depression-like behaviors. However, the underlying mechanisms are poorly understood. This review summarizes our current understanding of the chronic stress-induced remodeling of dendritic spines in the hippocampus, prefrontal cortex, orbitofrontal cortex, amygdala, and nucleus accumbens and also discusses the putative underlying mechanisms.

Mechanisms for spatiotemporal regulation of Rho-GTPase signaling at synapses

Synapses mediate information flow between neurons and undergo plastic changes in response to experience, which is critical for learning and memory. Conversely, synaptic defects impair information processing and underlie many brain pathologies. Rho-family GTPases control synaptogenesis by transducing signals from extracellular stimuli to the cytoskeleton and nucleus. The Rho-GTPases Rac1 and Cdc42 promote synapse development and the growth of axons and dendrites, while RhoA antagonizes these processes. Despite its importance, many aspects of Rho-GTPase signaling remain relatively unknown. Rho-GTPases are activated by guanine nucleotide exchange factors (GEFs) and inhibited by GTPase-activating proteins (GAPs). Though the number of both GEFs and GAPs greatly exceeds that of Rho-GTPases, loss of even a single GEF or GAP often has profound effects on cognition and behavior. Here, we explore how the actions of specific GEFs and GAPs give rise to the precise spatiotemporal activation patterns of Rho-GTPases in neurons. We consider the effects of coupling GEFs and GAPs targeting the same Rho-GTPase and the modular pathways that connect specific cellular stimuli with a given Rho-GTPase via different GEFs. We discuss how the creation of sharp borders between Rho-GTPase activation zones is achieved by pairing a GEF for one Rho-GTPase with a GAP for another and the extensive crosstalk between different Rho-GTPases. Given the importance of synapses for cognition and the fundamental roles that Rho-GTPases play in regulating them, a detailed understanding of Rho-GTPase signaling is essential to the progress of neuroscience.

Neurexin-Neuroligin Synaptic Complex Regulates Schizophrenia-Related DISC1/Kal-7/Rac1 "Signalosome"

Neurexins (NXs) and neuroligins (NLs) are cell adhesion molecules that are localized at opposite sites of synaptic membranes. They interact with each other to promote the assembly, maintenance, and function of synapses in the central nervous system. Both NX and NL are cleaved from a membrane-attached intracellular domain in an activity-dependent manner, generating the soluble ectodomain of NX or NL. Expression of the NX1 and NX3 genes in the brain appears to be regulated by a schizophrenia-related protein, DISC1. Here, we show that soluble ecto-NX1β can regulate the expression of DISC1 and induce signaling downstream of DISC1. We also show that NL1 binds to a well-characterized DISC1 interaction partner, Kal-7, and this interaction can be compromised by DISC1. Our results indicate that the NX/NL synaptic complex is intrinsically involved in the regulation of DISC1 function, thus contributing to a better understanding of the pathology of schizophrenia.

KALRN Rare and Common Variants and Susceptibility to Ischemic Stroke in Chinese Han Population

Stroke is the second most common cause of mortality worldwide, and it is a major cause of physical disability. Several genome-wide association studies have yielded numerous common variants which increase the risk of ischemic stroke, including the Kalirin-coding gene, KALRN. KALRN strongly associates with early-onset coronary artery disease and atherosclerosis and plays an important role in stroke in the European population. In this study, we analyzed four KALRN gene SNPs in 503 ischemic stroke patients and 493 control subjects, separating the patients into separate research groups based on comorbidity with hypertension or diabetes and stroke type (atherosis or lacunar and combination type). We found a rare variant of KALRN, rs11712619, that associated with lacunar stroke in the northern Chinese Han population with an average-risk allele frequency 0.009 (OR 2.95, 95 % CI 1.08-8.01, p = 0.028). However, after adjusting for relevant factors, including sex, age, body mass index, dyslipidemia, alcohol consumption, and smoking, this association was not evident. Additionally, the KALRN variant rs6438833 was associated with ischemic stroke, ischemic stroke comorbid with diabetes, and lacunar stroke after adjusting for the relevant factors (p = 0.046, p = 0.019 and p = 0.046, respectively), which remained significant after 10,000 permutation procedure test (p' = 0.047, p' = 0.018 and p' = 0.048, respectively). The association of these rare and common variants of KALRN with ischemic stroke in northern Chinese Han population offers insight for potential therapeutic research.

Supervillin binds the Rac/Rho-GEF Trio and increases Trio-mediated Rac1 activation

We investigated cross-talk between the membrane-associated, myosin II-regulatory protein supervillin and the actin-regulatory small GTPases Rac1, RhoA, and Cdc42. Supervillin knockdown reduced Rac1-GTP loading, but not the GTP loading of RhoA or Cdc42, in HeLa cells with normal levels of the Rac1-activating protein Trio. No reduction in Rac1-GTP loading was observed when supervillin levels were reduced in Trio-depleted cells. Conversely, overexpression of supervillin isoform 1 (SV1) or, especially, isoform 4 (SV4) increased Rac1 activation. Inhibition of the Trio-mediated Rac1 guanine nucleotide exchange activity with ITX3 partially blocked the SV4-mediated increase in Rac1-GTP. Both SV4 and SV1 co-localized with Trio at or near the plasma membrane in ruffles and cell surface projections. Two sequences within supervillin bound directly to Trio spectrin repeats 4-7: SV1-171, which contains N-terminal residues found in both SV1 and SV4 and the SV4-specific differentially spliced coding exons 3, 4, and 5 within SV4 (SV4-E345; SV4 amino acids 276-669). In addition, SV4-E345 interacted with the homologous sequence in rat kalirin (repeats 4-7, amino acids 531-1101). Overexpressed SV1-174 and SV4-E345 affected Rac1-GTP loading, but only in cells with endogenous levels of Trio. Trio residues 771-1057, which contain both supervillin-interaction sites, exerted a dominant-negative effect on cell spreading. Supervillin and Trio knockdowns, separately or together, inhibited cell spreading, suggesting that supervillin regulates the Rac1 guanine nucleotide exchange activity of Trio, and potentially also kalirin, during cell spreading and lamellipodia extension.

Progressive alterations of hippocampal CA3-CA1 synapses in an animal model of depression

Major depressive disorder is the most prevalent psychiatric condition, but the cellular and molecular mechanisms underlying this disorder are largely unknown, although multiple hypotheses have been proposed. The aim of this study was to characterize the progressive alteration of neuronal plasticity in the male rat hippocampus during depression induced by chronic unpredictable mild stress (CUMS), an established animal model of depression. The data in the hippocampus were collected on days 7, 14 and 21 after the onset of three-week CUMS. When analyzed on day 21, three-week CUMS induced typically depressive-like behaviors, impaired LTP induction, and decreased basal synaptic transmission at hippocampal CA3-CA1 synapses recorded in vivo, which was accompanied by decreased density of dendritic spines in CA1 and CA3 pyramidal neurons. The levels of both Kalirin-7 and brain-derived neurotrophic factor (BDNF) in the hippocampus were decreased at the same time. On day 14 (middle phase), some depressive-like behaviors were observed, which was accompanied by depressed basal synaptic transmission and enhanced LTP induction at the CA3-CA1 synapses. However, BDNF expression was decreased without alteration of Kalirin7 expression in comparison with no-stress control. Depressed basal synaptic transmission occurred in the middle phase of CUMS may contribute to decreased expression of BDNF. On day 7, depressive-like behaviors were not observed, and LTP induction, spine density, Kalirin-7 and BDNF expression were not altered by CUMS in comparison with no-stress control. These results showed that the functional changes at CA3-CA1synapses occurred earlier than the structural alteration during three-week CUMS as a strategy of neural adaptation, and rats required three weeks to develop depressive-like behaviors during CUMS. Our results suggest an important role of Kalirin-7 in CUMS-mediated alterations in spine density, synaptic function and overall depressive-like behaviors on day 21.

Elimination of Kalrn expression in POMC cells reduces anxiety-like behavior and contextual fear learning

Kalirin, a Rho GDP/GTP exchange factor for Rac1 and RhoG, is known to play an essential role in the formation and maintenance of excitatory synapses and in the secretion of neuropeptides. Mice unable to express any of the isoforms of Kalrn in cells that produce POMC at any time during development (POMC cells) exhibited reduced anxiety-like behavior and reduced acquisition of passive avoidance behavior, along with sex-specific alteration in the corticosterone response to restraint stress. Strikingly, lack of Kalrn expression in POMC cells closely mimicked the effects of global Kalrn knockout on anxiety-like behavior and passive avoidance conditioning without causing the other deficits noted in Kalrn knockout mice. Our data suggest that deficits in excitatory inputs onto POMC neurons are responsible for the behavioral phenotypes observed.

The Rho-GEF Kalirin regulates bone mass and the function of osteoblasts and osteoclasts

Bone homeostasis is maintained by the balance between bone resorption by osteoclasts and bone formation by osteoblasts. Dysregulation in the activity of the bone cells can lead to osteoporosis, a disease characterized by low bone mass and an increase in bone fragility and risk of fracture. Kalirin is a novel GTP-exchange factor protein that has been shown to play a role in cytoskeletal remodeling and dendritic spine formation in neurons. We examined Kalirin expression in skeletal tissue and found that it was expressed in osteoclasts and osteoblasts. Furthermore, micro-CT analyses of the distal femur of global Kalirin knockout (Kal-KO) mice revealed significantly reduced trabecular and cortical bone parameters in Kal-KO mice, compared to WT mice, with significantly reduced bone mass in 8, 14 and 36week-old female Kal-KO mice. Male mice also exhibited a decrease in bone parameters but not to the level seen in female mice. Histomorphometric analyses also revealed decreased bone formation rate in 14week-old female Kal-KO mice, as well as decreased osteoblast number/bone surface and increased osteoclast surface/bone surface. Consistent with our in vivo findings, the bone resorbing activity and differentiation of Kal-KO osteoclasts was increased in vitro. Although alkaline phosphatase activity by Kal-KO osteoblasts was increased in vitro, Kal-KO osteoblasts showed decreased mineralizing activity, as well as decreased secretion of OPG, which was inversely correlated with ERK activity. Taken together, our findings suggest that deletion of Kalirin directly affects osteoclast and osteoblast activity, leading to decreased OPG secretion by osteoblasts which is likely to alter the RANKL/OPG ratio and promote osteoclastogenesis. Therefore, Kalirin may play a role in paracrine and/or endocrine signaling events that control skeletal bone remodeling and the maintenance of bone mass.

Rho guanine nucleotide exchange factors: regulators of Rho GTPase activity in development and disease

The aberrant activity of Ras homologous (Rho) family small GTPases (20 human members) has been implicated in cancer and other human diseases. However, in contrast to the direct mutational activation of Ras found in cancer and developmental disorders, Rho GTPases are activated most commonly in disease by indirect mechanisms. One prevalent mechanism involves aberrant Rho activation via the deregulated expression and/or activity of Rho family guanine nucleotide exchange factors (RhoGEFs). RhoGEFs promote formation of the active GTP-bound state of Rho GTPases. The largest family of RhoGEFs is comprised of the Dbl family RhoGEFs with 70 human members. The multitude of RhoGEFs that activate a single Rho GTPase reflects the very specific role of each RhoGEF in controlling distinct signaling mechanisms involved in Rho activation. In this review, we summarize the role of Dbl RhoGEFs in development and disease, with a focus on Ect2 (epithelial cell transforming squence 2), Tiam1 (T-cell lymphoma invasion and metastasis 1), Vav and P-Rex1/2 (PtdIns(3,4,5)P3 (phosphatidylinositol (3,4,5)-triphosphate)-dependent Rac exchanger).

Glutamatergic postsynaptic density protein dysfunctions in synaptic plasticity and dendritic spines morphology: relevance to schizophrenia and other behavioral disorders pathophysiology, and implications for novel therapeutic approaches

Emerging researches point to a relevant role of postsynaptic density (PSD) proteins, such as PSD-95, Homer, Shank, and DISC-1, in the pathophysiology of schizophrenia and autism spectrum disorders. The PSD is a thickness, detectable at electronic microscopy, localized at the postsynaptic membrane of glutamatergic synapses, and made by scaffolding proteins, receptors, and effector proteins; it is considered a structural and functional crossroad where multiple neurotransmitter systems converge, including the dopaminergic, serotonergic, and glutamatergic ones, which are all implicated in the pathophysiology of psychosis. Decreased PSD-95 protein levels have been reported in postmortem brains of schizophrenia patients. Variants of Homer1, a key PSD protein for glutamate signaling, have been associated with schizophrenia symptoms severity and therapeutic response. Mutations in Shank gene have been recognized in autism spectrum disorder patients, as well as reported to be associated to behaviors reminiscent of schizophrenia symptoms when expressed in genetically engineered mice. Here, we provide a critical appraisal of PSD proteins role in the pathophysiology of schizophrenia and autism spectrum disorders. Then, we discuss how antipsychotics may affect PSD proteins in brain regions relevant to psychosis pathophysiology, possibly by controlling synaptic plasticity and dendritic spine rearrangements through the modulation of glutamate-related targets. We finally provide a framework that may explain how PSD proteins might be useful candidates to develop new therapeutic approaches for schizophrenia and related disorders in which there is a need for new biological treatments, especially against some symptom domains, such as negative symptoms, that are poorly affected by current antipsychotics.

Rho GTPases in neurodegeneration diseases

Rho GTPases are molecular switches that modulate multiple intracellular signaling processes by means of various effector proteins. As a result, Rho GTPase activities are tightly spatiotemporally regulated in order to ensure homeostasis within the cell. Though the roles of Rho GTPases during neural development have been well documented, their participation during neurodegeneration has been far less characterized. Herein we discuss our current knowledge of the role and function of Rho GTPases and regulators during neurodegeneration, and highlight their potential as targets for therapeutic intervention in common neurodegenerative disorders.

Modulation of behavior by scaffolding proteins of the post-synaptic density

Scaffolding proteins of the neuronal post-synaptic density (PSD) are principal organizers of glutamatergic neurotransmission that bring together glutamate receptors and signaling molecules at discrete synaptic locations. Genetic alterations of individual PSD scaffolds therefore disrupt the function of entire multiprotein modules rather than a single glutamatergic mechanism, and thus induce a range of molecular and structural abnormalities in affected neurons. Despite such broad molecular consequences, knockout, knockdown, or knockin of glutamate receptor scaffolds typically affect a subset of specific behaviors and thereby mold and specialize the actions of the ubiquitous glutamatergic neurotransmitter system. Approaches designed to control the function of neuronal scaffolds may therefore have high potential to restore behavioral morbidities and comorbidities in patients with psychiatric disorders. Here we summarize a series of experiments with genetically modified mice revealing the roles of main N-methyl-d-aspartate (NMDA) and group I metabotropic glutamate (mGluR1/5) receptor scaffolds in behavior, discuss the clinical implications of the findings, and propose future research directions.

Neuronal Rho GEFs in synaptic physiology and behavior

In the mammalian brain, the majority of excitatory synapses are housed in micron-sized dendritic protrusions called spines, which can undergo rapid changes in shape and number in response to increased or decreased synaptic activity. These dynamic alterations in dendritic spines require precise control of the actin cytoskeleton. Within spines, multidomain Rho guanine nucleotide exchange factors (Rho GEFs) coordinate activation of their target Rho GTPases by a variety of pathways. In this review, we focus on the handful of disease-related Rho GEFs (Kalirin; Trio; Tiam1; P-Rex1,2; RasGRF1,2; Collybistin) localized at synapses and known to affect electrophysiology, spine morphology, and animal behavior. The goal is to integrate structure/function studies with measurements of synaptic function and behavioral phenotypes in animal models.

In vivo quantitative proteomics of somatosensory cortical synapses shows which protein levels are modulated by sensory deprivation

Postnatal bilateral whisker trimming was used as a model system to test how synaptic proteomes are altered in barrel cortex by sensory deprivation during synaptogenesis. Using quantitative mass spectrometry, we quantified more than 7,000 synaptic proteins and identified 89 significantly reduced and 161 significantly elevated proteins in sensory-deprived synapses, 22 of which were validated by immunoblotting. More than 95% of quantified proteins, including abundant synaptic proteins such as PSD-95 and gephyrin, exhibited no significant difference under high- and low-activity rearing conditions, suggesting no tissue-wide changes in excitatory or inhibitory synaptic density. In contrast, several proteins that promote mature spine morphology and synaptic strength, such as excitatory glutamate receptors and known accessory factors, were reduced significantly in deprived synapses. Immunohistochemistry revealed that the reduction in SynGAP1, a postsynaptic scaffolding protein, was restricted largely to layer I of barrel cortex in sensory-deprived rats. In addition, protein-degradation machinery such as proteasome subunits, E2 ligases, and E3 ligases, accumulated significantly in deprived synapses, suggesting targeted synaptic protein degradation under sensory deprivation. Importantly, this screen identified synaptic proteins whose levels were affected by sensory deprivation but whose synaptic roles have not yet been characterized in mammalian neurons. These data demonstrate the feasibility of defining synaptic proteomes under different sensory rearing conditions and could be applied to elucidate further molecular mechanisms of sensory development.

Kalrn plays key roles within and outside of the nervous system

Background

The human KALRN gene, which encodes a complex, multifunctional Rho GDP/GTP exchange factor, has been linked to cardiovascular disease, psychiatric disorders and neurodegeneration. Examination of existing Kalrn knockout mouse models has focused only on neuronal phenotypes. However, Kalirin was first identified through its interaction with an enzyme involved in the synthesis and secretion of multiple bioactive peptides, and studies in C.elegans revealed roles for its orthologue in neurosecretion.

Results

We used a broad array of tests to evaluate the effects of ablating a single exon in the spectrin repeat region of Kalrn (KalSR^KO/KO); transcripts encoding Kalrn isoforms containing only the second GEF domain can still be produced from the single remaining functional Kalrn promoter. As expected, KalSR^KO/KO mice showed a decrease in anxiety-like behavior and a passive avoidance deficit. No changes were observed in prepulse inhibition of acoustic startle or tests of depression-like behavior. Growth rate, parturition and pituitary secretion of growth hormone and prolactin were deficient in the KalSR^KO/KO mice. Based on the fact that a subset of Kalrn isoforms is expressed in mouse skeletal muscle and the observation that muscle function in C.elegans requires its Kalrn orthologue, KalSR^KO/KO mice were evaluated in the rotarod and wire hang tests. KalSR^KO/KO mice showed a profound decrease in neuromuscular function, with deficits apparent in KalSR^+/KO mice; these deficits were not as marked when loss of Kalrn expression was restricted to the nervous system. Pre- and postsynaptic deficits in the neuromuscular junction were observed, along with alterations in sarcomere length.

Conclusions

Many of the widespread and diverse deficits observed both within and outside of the nervous system when expression of Kalrn is eliminated may reflect its role in secretory granule function and its expression outside of the nervous system.