Identification and characterization of Slitrk, a novel neuronal transmembrane protein family controlling neurite outgrowth

Insight into the Association between Slitrk Protein and Neurodevelopmental and Neuropsychiatric Conditions

Slitrk proteins belong the leucine-rich repeat transmembrane family and share structural similarities with the Slits and tropomyosin receptor kinase families, which regulate the development of the nervous system. Slitrks are highly expressed in the developing nervous system of vertebrates, modulating neurite outgrowth and enhancing synaptogenesis; however, the expression and function of Slitrk protein members differ. Slitrk protein variations have been associated with various sensory and neuropsychiatric conditions, including myopia, deafness, obsessive-compulsive disorder, autism spectrum disorders, schizophrenia, attention-deficit/hyperactivity disorder, glioma, and Tourette syndrome; however, the underlying mechanism remains unclear. Therefore, the Slitrk family members' protein expression, roles in the signaling cascade, functions, and gene mutations need to be comprehensively studied to develop therapeutics against neurodegenerative diseases. This study presents complete and pertinent information demonstrating the relationship between Slitrk family proteins and neuropsychiatric illnesses. This review briefly discusses neurodevelopmental disorders, the leucine-rich repeat family, the Slitrk family, and the association of Slitrk with the neuropathology of representative disorders.

Satellite glial contact enhances differentiation and maturation of human iPSC-derived sensory neurons

Sensory neurons generated from induced pluripotent stem cells (iSNs) are used to model human peripheral neuropathies, however current differentiation protocols produce sensory neurons with an embryonic phenotype. Peripheral glial cells contact sensory neurons early in development and contribute to formation of the canonical pseudounipolar morphology, but these signals are not encompassed in current iSN differentiation protocols. Here, we show that terminal differentiation of iSNs in co-culture with rodent Dorsal Root Ganglion satellite glia (rSG) advances their differentiation and maturation. Co-cultured iSNs develop a pseudounipolar morphology through contact with rSGs. This transition depends on semaphorin-plexin guidance cues and on glial gap junction signaling. In addition to morphological changes, iSNs terminally differentiated in co-culture exhibit enhanced spontaneous action potential firing, more mature gene expression, and increased susceptibility to paclitaxel induced axonal degeneration. Thus, iSNs differentiated in coculture with rSGs provide a better model for investigating human peripheral neuropathies.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Slitrk4 is required for the development of inhibitory neurons in the fear memory circuit of the lateral amygdala

The Slitrk family consists of six synaptic adhesion molecules, some of which are associated with neuropsychiatric disorders. In this study, we aimed to investigate the physiological role of Slitrk4 by analyzing Slitrk4 knockout (KO) mice. The Slitrk4 protein was widely detected in the brain and was abundant in the olfactory bulb and amygdala. In a systematic behavioral analysis, male Slitrk4 KO mice exhibited an enhanced fear memory acquisition in a cued test for classical fear conditioning, and social behavior deficits in reciprocal social interaction tests. In an electrophysiological analysis using amygdala slices, Slitrk4 KO mice showed enhanced long-term potentiation in the thalamo-amygdala afferents and reduced feedback inhibition. In the molecular marker analysis of Slitrk4 KO brains, the number of calretinin (CR)-positive interneurons was decreased in the anterior part of the lateral amygdala nuclei at the adult stage. In in vitro experiments for neuronal differentiation, Slitrk4-deficient embryonic stem cells were defective in inducing GABAergic interneurons with an altered response to sonic hedgehog signaling activation that was involved in the generation of GABAergic interneuron subsets. These results indicate that Slitrk4 function is related to the development of inhibitory neurons in the fear memory circuit and would contribute to a better understanding of osttraumatic stress disorder, in which an altered expression of Slitrk4 has been reported.

Human mutations in SLITRK3 implicated in GABAergic synapse development in mice

This study reports on biallelic homozygous and monoallelic de novo variants in SLITRK3 in three unrelated families presenting with epileptic encephalopathy associated with a broad neurological involvement characterized by microcephaly, intellectual disability, seizures, and global developmental delay. SLITRK3 encodes for a transmembrane protein that is involved in controlling neurite outgrowth and inhibitory synapse development and that has an important role in brain function and neurological diseases. Using primary cultures of hippocampal neurons carrying patients' SLITRK3 variants and in combination with electrophysiology, we demonstrate that recessive variants are loss-of-function alleles. Immunostaining experiments in HEK-293 cells showed that human variants C566R and E606X change SLITRK3 protein expression patterns on the cell surface, resulting in highly accumulating defective proteins in the Golgi apparatus. By analyzing the development and phenotype of SLITRK3 KO (SLITRK3-/-) mice, the study shows evidence of enhanced susceptibility to pentylenetetrazole-induced seizure with the appearance of spontaneous epileptiform EEG as well as developmental deficits such as higher motor activities and reduced parvalbumin interneurons. Taken together, the results exhibit impaired development of the peripheral and central nervous system and support a conserved role of this transmembrane protein in neurological function. The study delineates an emerging spectrum of human core synaptopathies caused by variants in genes that encode SLITRK proteins and essential regulatory components of the synaptic machinery. The hallmark of these disorders is impaired postsynaptic neurotransmission at nerve terminals; an impaired neurotransmission resulting in a wide array of (often overlapping) clinical features, including neurodevelopmental impairment, weakness, seizures, and abnormal movements. The genetic synaptopathy caused by SLITRK3 mutations highlights the key roles of this gene in human brain development and function.

Loss-of-function variant in the LRR domain of SLITRK2 implicated in a neurodevelopmental disorder

Background: Neurodevelopmental disorders are characterized by different combinations of intellectual disability (ID), communication and social skills deficits, and delays in achieving motor or language milestones. SLITRK2 is a postsynaptic cell-adhesion molecule that promotes neurite outgrowth and excitatory synapse development. Methods and Results: In the present study, we investigated a single patient segregating Neurodevelopmental disorder. SLITRK2 associated significant neuropsychological issues inherited in a rare X-linked fashion have recently been reported. Whole-exome sequencing and data analysis revealed a novel nonsense variant [c.789T>A; p.(Cys263*); NM_032539.5; NP_115928.1] in exon 5 of the SLITRK2 gene (MIM# 300561). Three-dimensional protein modeling revealed substantial changes in the mutated SLITRK2 protein, which might lead to nonsense-medicated decay. Conclusion: This study confirms the role of SLITRK2 in neuronal development and highlights the importance of including the SLITRK2 gene in the screening of individuals presenting neurodevelopmental disorders.

Small molecule regulators of microRNAs identified by high-throughput screen coupled with high-throughput sequencing

MicroRNAs (miRNAs) regulate fundamental biological processes by silencing mRNA targets and are dysregulated in many diseases. Therefore, miRNA replacement or inhibition can be harnessed as potential therapeutics. However, existing strategies for miRNA modulation using oligonucleotides and gene therapies are challenging, especially for neurological diseases, and none have yet gained clinical approval. We explore a different approach by screening a biodiverse library of small molecule compounds for their ability to modulate hundreds of miRNAs in human induced pluripotent stem cell-derived neurons. We demonstrate the utility of the screen by identifying cardiac glycosides as potent inducers of miR-132, a key neuroprotective miRNA downregulated in Alzheimer's disease and other tauopathies. Coordinately, cardiac glycosides downregulate known miR-132 targets, including Tau, and protect rodent and human neurons against various toxic insults. More generally, our dataset of 1370 drug-like compounds and their effects on the miRNome provides a valuable resource for further miRNA-based drug discovery.

In Cerebellar Atrophy of 12-Month-Old ATM-Null Mice, Transcriptome Upregulations Concern Most Neurotransmission and Neuropeptide Pathways, While Downregulations Affect Prominently Itpr1, Usp2 and Non-Coding RNA

The autosomal recessive disorder Ataxia-Telangiectasia is caused by a dysfunction of the stress response protein, ATM. In the nucleus of proliferating cells, ATM senses DNA double-strand breaks and coordinates their repair. This role explains T-cell dysfunction and tumour risk. However, it remains unclear whether this function is relevant for postmitotic neurons and underlies cerebellar atrophy, since ATM is cytoplasmic in postmitotic neurons. Here, we used ATM-null mice that survived early immune deficits via bone-marrow transplantation, and that reached initial neurodegeneration stages at 12 months of age. Global cerebellar transcriptomics demonstrated that ATM depletion triggered upregulations in most neurotransmission and neuropeptide systems. Downregulated transcripts were found for the ATM interactome component Usp2, many non-coding RNAs, ataxia genes Itpr1, Grid2, immediate early genes and immunity factors. Allelic splice changes affected prominently the neuropeptide machinery, e.g., Oprm1. Validation experiments with stressors were performed in human neuroblastoma cells, where ATM was localised only to cytoplasm, similar to the brain. Effect confirmation in SH-SY5Y cells occurred after ATM depletion and osmotic stress better than nutrient/oxidative stress, but not after ATM kinase inhibition or DNA stressor bleomycin. Overall, we provide pioneer observations from a faithful A-T mouse model, which suggest general changes in synaptic and dense-core vesicle stress adaptation.

Pivotal Role of Slitrk1 in Adult Striatal Cholinergic Neurons in Mice: Implication in Tourette Syndrome

OBJECTIVE

The SLIT and NTRK-like 1 (SLITRK1) gene mutation and striatal cholinergic interneurons (ChIs) loss are associated with Tourette syndrome (TS). ChIs comprise only 1 to 2% of striatal neurons but project widely throughout the stratum to impact various striatal neurotransmission, including TS-related dopaminergic transmission. Here, we link striatal Slitrk1, ChI function, and dopaminergic transmission and their associations with TS-like tic behaviors.

METHODS

Slitrk1-KD mice were induced by bilaterally injecting Slitrk1 siRNA into their dorsal striatum. Control mice received scrambled siRNA injection. Their TS-like tic behaviors, prepulse inhibition, sensory-motor function and dopamine-related behaviors were compared. We also compared dopamine and ACh levels in microdialysates, Slitrk protein and dopamine transporter levels, and numbers of Slitrk-positive ChIs and activated ChIs in the striatum between two mouse groups, and electrophysiological properties between Slitrk-positive and Slitrk-negative striatal ChIs.

RESULTS

Slitrk1-KD mice exhibit TS-like haloperidol-sensitive stereotypic tic behaviors, impaired prepulse inhibition, and delayed sensorimotor response compared with the control group. These TS-like characteristics correlate with lower striatal Slitrk1 protein levels, fewer Slitrk1-containing ChIs, and fewer activated ChIs in Slitrk1-KD mice. Based on their electrophysiological properties, Slitrk1-negative ChIs are less excitable than Slitrk1-positive ChIs. Slitrk1-KD mice have lower evoked acetylcholine and dopamine levels, higher tonic dopamine levels, and downregulated dopamine transporters in the striatum, increased apomorphine-induced climbing behaviors, and impaired methamphetamine-induced hyperlocomotion compared with controls.

INTERPRETATION

Slitrk1 is pivotal in maintaining striatal ChIs activity and subsequent dopaminergic transmission for normal motor functioning. Furthermore, conditional striatal Slitrk1-KD mice may serve as a translational modality with aspects of TS phenomenology. ANN NEUROL 2023.

Upregulation of SLITRK5 in patients with epilepsy and in a rat model

SLIT and NTRK-like protein-5 (SLITRK5) is one of the six members of SLITRK protein family, which is widely expressed in central nervous system (CNS). In brain, SLITRK5 plays important roles in neurite outgrowth, dendritic branching, neuron differentiation, synaptogenesis, and signal transmission of neurons. Epilepsy is a common, chronic neurological disorder characterized by recurrent spontaneous seizures. The pathophysiological mechanism of epilepsy remains unclear. Neuronal apoptosis, abnormal nerve excitatory transmission, and synaptic remodeling are thought to be involved in the development of epilepsy. To explore whether there is a potential relationship between SLITRK5 and epilepsy, we investigated the expression and distribution of SLITRK5 in patients with temporal lobe epilepsy (TLE) and a rat model of epilepsy. We collected cerebral cortex samples from patients with drug-refractory temporal lobe epilepsy, and a rat model of epilepsy induced by lithium chloride/pilocarpine was established. The ways of immunohistochemistry, double-immunofluorescence labeling and western blot have been used in our study to research the expression and distribution of SLITRK5 in the temporal lobe epilepsy patients and epilepsy animal model. All of the results have shown that SLITRK5 is mainly localized in the cell cytoplasm of neurons both in patients with TLE and in epilepsy model. In addition, compared with nonepileptic controls, the expression of SLITRK5 was upregulated in the temporal neocortex of TLE patients. And both in the temporal neocortex and hippocampus of pilocarpine-induced epilepsy rats, the expression of SLITRK5 was increased at 24 h after status epilepticus (SE), with a relatively high level within 30 days, and reached the peak on the 7th day after SE. Our preliminary results revealed that SLITRK5 may have a potential relationship with epilepsy, which may be a foundation for the further study of the underlying mechanism between SLITRK5 and epilepsy and the therapeutic targets of antiepileptic drugs.

Differential expression of SLITRK6 gene as a potential therapeutic target Urothelial cancer in particular upper tract cancer

BACKGROUND

Urinary bladder urothelial carcinoma (UBUC) and upper tract urothelial carcinoma (UTUC) harbor analogous morphology with comparable cytogenetic changes as well as prognostic factors but their similar biological activities still remain controversial. SLITRK6 gene has been demonstrated to have distinct role in urothelial cancers with a distinction between UTUC and UBUC.

METHOD

The study included a total of 80 patients of urothelial carcinoma including 60 UBUC and 20 UTUC cases. The tumor tissues from both the groups were evaluated for gene expression at mRNA level by qRT-PCR and protein expression by immunohistochemistry (IHC) and western blot.

RESULTS

Significantly more than 4-fold high mRNA expression of SLITRK6 was observed in UTUC against 1.2-fold in UBUC (p<0.0001). The overall SLITRK6 expression by IHC was observed in 80% of the UBUC cases in comparison to 100% strong expression in UTUC patients and among two groups expression exhibited a significant difference for moderate to strong expression (p=0.0005). The protein expression by western blot analysis in UTUC samples was considerably higher as compared to UBUC samples (1.64 vs. 0.76 respectively: p=0.01). A strong concordance exhibited for the higher mRNA and protein expression in both UTUC and UBUC cases (∼75%) wherein 80%, 75% and 70% higher expression of SLITRK6 was detected by qRT-PCR, Western blot and IHC respectively.

CONCLUSION

To conclude, although SLITRK6 exhibits a strong expression in both UTUC and UBUC but was considerably observed higher in majority of UTUC cases. Therefore, SLITRK6 appears as a promising novel possible gene target for urothelial carcinoma in particular UTUC.

SLITRK6 promotes the progression of lung adenocarcinoma by regulating PI3K/AKT/mTOR signaling and Warburg effect

To investigate the role of SLITRK6 in lung adenocarcinoma (LUAD) and the underlying mechanism in it, clinical tissues and tissue microarray of LUAD were used to detect the expression of SLITRK6. In vitro cell viability assay and colony formation assay in LUAD cells were conducted to investigate SLITRK6 related biological functions. In vivo subcutaneous model was used to determine the role of SLITRK6 in LUAD growth. It was found that the expression of SLITRK6 was significantly upregulated in LUAD tissues compared with that in para-cancerous tissues. Knockdown of SLITRK6 suppressed the proliferation and colony formation of LUAD cells in vitro. Meanwhile, the growth of LUAD cells was also inhibited by SLITRK6 knockdown in vivo. Furthermore, we found that SLITRK6 knockdown could suppress the glycolysis of LUAD cells by regulating the phosphorylation of AKT and mTOR. All results suggest that SLITRK6 promotes LUAD cell proliferation and colony formation by regulating PI3K/AKT/mTOR signaling and Warburg effect. SLITRK6 may serve as a potential therapeutic target for LUAD in future.

Rapid effects of valproic acid on the fetal brain transcriptome: Implications for brain development and autism

There is an increased incidence of autism among the children of women who take the anti-epileptic, mood stabilizing drug, valproic acid (VPA) during pregnancy; moreover, exposure to VPA in utero causes autistic-like symptoms in rodents and non-human primates. Analysis of RNAseq data obtained from fetal mouse brains 3 hr after VPA administration revealed that VPA significantly [p(FDR) ≤ 0.025] increased or decreased the expression of approximately 7,300 genes. No significant sex differences in VPA-induced gene expression were observed. Expression of genes associated with neurodevelopmental disorders such as autism as well as neurogenesis, axon growth and synaptogenesis, GABAergic, glutaminergic and dopaminergic synaptic transmission, perineuronal nets, and circadian rhythms was dysregulated by VPA. Moreover, expression of 400 autism risk genes was significantly altered by VPA as was expression of 247 genes that have been reported to play fundamental roles in the development of the nervous system, but are not linked to autism by GWAS. The goal of this study was to identify mouse genes that are: (a) significantly up- or down-regulated by VPA in the fetal brain and (b) known to be associated with autism and/or to play a role in embryonic neurodevelopmental processes, perturbation of which has the potential to alter brain connectivity in the postnatal and adult brain. The set of genes meeting these criteria provides potential targets for future hypothesis-driven approaches to elucidating the proximal underlying causes of defective brain connectivity in neurodevelopmental disorders such as autism.

Small Molecule Regulators of microRNAs Identified by High-Throughput Screen Coupled with High-Throughput Sequencing

MicroRNAs (miRNAs) regulate fundamental biological processes by silencing mRNA targets and are dysregulated in many diseases. Therefore, miRNA replacement or inhibition can be harnessed as potential therapeutics. However, existing strategies for miRNA modulation using oligonucleotides and gene therapies are challenging, especially for neurological diseases, and none have yet gained clinical approval. We explore a different approach by screening a biodiverse library of small molecule compounds for their ability to modulate hundreds of miRNAs in human induced pluripotent stem cell-derived neurons. We demonstrate the utility of the screen by identifying cardiac glycosides as potent inducers of miR-132, a key miRNA downregulated in Alzheimer's disease and other tauopathies. Coordinately, cardiac glycosides downregulate known miR-132 targets, including Tau, and protect rodent and human neurons against various toxic insults. More generally, our dataset of 1370 drug-like compounds and their effects on the miRNome provide a valuable resource for further miRNA-based drug discovery.

Developmental control of noradrenergic system by SLITRK1 and its implications in the pathophysiology of neuropsychiatric disorders

SLITRK1 is a neuronal transmembrane protein with neurite development-and synaptic formation-controlling abilities. Several rare variants of SLITRK1 have been identified and implicated in the pathogenesis of Tourette's syndrome, trichotillomania, and obsessive-compulsive disorder, which can be collectively referred to as obsessive-compulsive-spectrum disorders. Recent studies have reported a possible association between bipolar disorder and schizophrenia, including a revertant of modern human-specific amino acid residues. Although the mechanisms underlying SLITRK1-associated neuropsychiatric disorders are yet to be fully clarified, rodent studies may provide some noteworthy clues. Slitrk1-deficient mice show neonatal dysregulation of the noradrenergic system, and later, anxiety-like behaviors that can be attenuated by an alpha 2 noradrenergic receptor agonist. The noradrenergic abnormality is characterized by the excessive growth of noradrenergic fibers and increased noradrenaline content in the medial prefrontal cortex, concomitant with enlarged serotonergic varicosities. Slitrk1 has both cell-autonomous and cell-non-autonomous functions in controlling noradrenergic fiber development, and partly alters Sema3a-mediated neurite control. These findings suggest that transiently enhanced noradrenergic signaling during the neonatal stage could cause neuroplasticity associated with neuropsychiatric disorders. Studies adopting noradrenergic signal perturbation via pharmacological or genetic means support this hypothesis. Thus, Slitrk1 is a potential candidate genetic linkage between the neonatal noradrenergic signaling and the pathophysiology of neuropsychiatric disorders involving anxiety-like or depression-like behaviors.

Correlations between single nucleotide polymorphisms in obsessive-compulsive disorder with the clinical features or response to therapy

Obsessive-compulsive disorder (OCD) is a debilitating neuropsychiatric disorder, in which the patient endures intrusive thoughts or is compelled to perform repetitive or ritualized actions. Many cases of OCD are considered to be familial or heritable in nature. It has been shown that a variety of internal and external risk factors are involved in the pathogenesis of OCD. Among the internal factors, genetic modifications play a critical role in the pathophysiological process. Despite many investigations performed to determine the candidate genes, the precise genetic factors involved in the disease remain largely undetermined. The present review summarizes the single nucleotide polymorphisms that have been proposed to be associated with OCD symptoms, early onset disease, neuroimaging results, and response to therapy. This information could help us to draw connections between genetics and OCD symptoms, better characterize OCD in individual patients, understand OCD prognosis, and design more targeted personalized treatment approaches.

Genomic imprinting-like monoallelic paternal expression determines sex of channel catfish

The X and Y chromosomes of channel catfish have the same gene contents. Here, we report allelic hypermethylation of the X chromosome within the sex determination region (SDR). Accordingly, the X-borne hydin-1 gene was silenced, whereas the Y-borne hydin-1 gene was expressed, making monoallelic expression of hydin-1 responsible for sex determination, much like genomic imprinting. Treatment with a methylation inhibitor, 5-aza-dC, erased the epigenetic marks within the SDR and caused sex reversal of genetic females into phenotypic males. After the treatment, hydin-1 and six other genes related to cell cycle control and proliferative growth were up-regulated, while three genes related to female sex differentiation were down-regulated in genetic females, providing additional support for epigenetic sex determination in catfish. This mechanism of sex determination provides insights into the plasticity of genetic sex determination in lower vertebrates and its connection with temperature sex determination where DNA methylation is broadly involved.

SLITRK1-mediated noradrenergic projection suppression in the neonatal prefrontal cortex

SLITRK1 is an obsessive-compulsive disorder spectrum-disorders-associated gene that encodes a neuronal transmembrane protein. Here we show that SLITRK1 suppresses noradrenergic projections in the neonatal prefrontal cortex, and SLITRK1 functions are impaired by SLITRK1 mutations in patients with schizophrenia (S330A, a revertant of Homo sapiens-specific residue) and bipolar disorder (A444S). Slitrk1-KO newborns exhibit abnormal vocalizations, and their prefrontal cortices show excessive noradrenergic neurites and reduced Semaphorin3A expression, which suppresses noradrenergic neurite outgrowth in vitro. Slitrk1 can bind Dynamin1 and L1 family proteins (Neurofascin and L1CAM), as well as suppress Semaphorin3A-induced endocytosis. Neurofascin-binding kinetics is altered in S330A and A444S mutations. Consistent with the increased obsessive-compulsive disorder prevalence in males in childhood, the prefrontal cortex of male Slitrk1-KO newborns show increased noradrenaline levels, and serotonergic varicosity size. This study further elucidates the role of noradrenaline in controlling the development of the obsessive-compulsive disorder-related neural circuit.

SLITRK2 variants associated with neurodevelopmental disorders impair excitatory synaptic function and cognition in mice

SLITRK2 is a single-pass transmembrane protein expressed at postsynaptic neurons that regulates neurite outgrowth and excitatory synapse maintenance. In the present study, we report on rare variants (one nonsense and six missense variants) in SLITRK2 on the X chromosome identified by exome sequencing in individuals with neurodevelopmental disorders. Functional studies showed that some variants displayed impaired membrane transport and impaired excitatory synapse-promoting effects. Strikingly, these variations abolished the ability of SLITRK2 wild-type to reduce the levels of the receptor tyrosine kinase TrkB in neurons. Moreover, Slitrk2 conditional knockout mice exhibited impaired long-term memory and abnormal gait, recapitulating a subset of clinical features of patients with SLITRK2 variants. Furthermore, impaired excitatory synapse maintenance induced by hippocampal CA1-specific cKO of Slitrk2 caused abnormalities in spatial reference memory. Collectively, these data suggest that SLITRK2 is involved in X-linked neurodevelopmental disorders that are caused by perturbation of diverse facets of SLITRK2 function.

The Role of SliTrk5 in Central Nervous System

SLIT and NTRK-like protein-5 (SliTrk5) is one of the six members of SliTrk protein family, which is widely expressed in the central nervous system (CNS), regulating and participating in many essential steps of central nervous system development, including axon and dendritic growth, neuron differentiation, and synaptogenesis. SliTrk5, as a neuron transmembrane protein, contains two important conservative domains consisting of leucine repeats (LRRs) located at the amino terminal in the extracellular region and tyrosine residues (Tyr) located at the carboxyl terminal in the intracellular domains. These special structures make SliTrk5 play an important role in the pathological process of the CNS. A large number of studies have shown that SliTrk5 may be involved in the pathogenesis of CNS diseases, such as obsessive-compulsive-disorder (OCD), attention deficit/hyperactivity disorder (ADHD), glioma, autism spectrum disorders (ASDs), and Parkinson's disease (PD). Targeting SliTrk5 is expected to become a new target for the treatment of CNS diseases, promoting the functional recovery of CNS. The purpose of this article is to review the current research progression of the role of SliTrk5 in CNS and its potential mechanisms in CNS diseases.

Slitrk2 deficiency causes hyperactivity with altered vestibular function and serotonergic dysregulation

SLITRK2 encodes a transmembrane protein that modulates neurite outgrowth and synaptic activities and is implicated in bipolar disorder. Here, we addressed its physiological roles in mice. In the brain, the Slitrk2 protein was strongly detected in the hippocampus, vestibulocerebellum, and precerebellar nuclei—the vestibular-cerebellar-brainstem neural network including pontine gray and tegmental reticular nucleus. Slitrk2 knockout (KO) mice exhibited increased locomotor activity in novel environments, antidepressant-like behaviors, enhanced vestibular function, and increased plasticity at mossy fiber–CA3 synapses with reduced sensitivity to serotonin. A serotonin metabolite was increased in the hippocampus and amygdala, and serotonergic neurons in the raphe nuclei were decreased in Slitrk2 KO mice. When KO mice were treated with methylphenidate, lithium, or fluoxetine, the mood stabilizer lithium showed a genotype-dependent effect. Taken together, Slitrk2 deficiency causes aberrant neural network activity, synaptic integrity, vestibular function, and serotonergic function, providing molecular-neurophysiological insight into the brain dysregulation in bipolar disorders.

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Slitrk2 KO mice showed antidepressant-like behaviors and enhanced vestibular function

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Mossy fiber-CA3 synaptic sensitivity to serotonin was reduced in Slitrk2 KO mice

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Serotonin metabolite was increased in hippocampus and amygdala of Slitrk2 KO mice

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Numbers of serotonergic neurons in raphe nuclei were decreased in Slitrk2 KO mice

Upscaling biological complexity to boost neuronal and oligodendroglia maturation and improve in vitro developmental neurotoxicity (DNT) evaluation

Human induced pluripotent stem cell (iPSC)-derived neuronal and glial cell models are suitable to assess the effects of environmental chemicals on the developing brain. Such test systems can recapitulate several key neurodevelopmental features, such as neural stem cell formation and differentiation towards different neuronal subtypes and astrocytes, neurite outgrowth, synapse formation and neuronal network formation and function, which are crucial for brain development. While monolayer, two-dimensional (2D) cultures of human iPSC-neuronal or glial derivatives are generally suited for high-throughput testing, they also show some limitations. In particular, differentiation towards myelinating oligodendrocytes can only be achieved after extended periods in differentiation. In recent years, the implementation of three-dimensional (3D) neuronal and glial models obtained from human iPSCs has been shown to compensate for such limitations, enabling robust differentiation towards both neuronal and glial cell populations, myelination and formation of more mature neuronal network activity. Here we compared the differentiation capacity of human iPSC-derived neural stem cells cultured either as 2D monolayer or as 3D neurospheres, and assessed chlorpyrifos (CPF) effects. Data indicate that 3D neurospheres differentiate towards neurons and oligodendroglia more rapidly than 2D cultures; however, the 2D model is more suitable to assess neuronal functionality by analysis of spontaneous electrical activity using multielectrode array. Moreover, 2D and 3D test systems are diversely susceptible to CPF treatment. In conclusion, the selection of the most suitable in vitro test system (either 2D or 3D) should take into account the context of use and intended research goals ('fit for purpose' principle).

Pigment Epithelium Derived Factor Is Involved in the Late Phase of Osteosarcoma Metastasis by Increasing Extravasation and Cell-Cell Adhesion

Organ tropism of metastatic cells is not well understood. To determine the key factors involved in the selection of a specific organ upon metastasis, we established metastatic cell lines and analyzed their homing to specific tissues. Toward this, 143B osteosarcoma cells were injected intracardially until the kidney-metastasizing sub-cell line Bkid was established, which significantly differed from the parental 143B cells. The candidate genes responsible for kidney metastasis were validated, and SerpinF1/Pigment epithelium derived factor (PEDF) was identified as the primary target. Bkid cells with PEDF knockdown injected intracardially did not metastasize to the kidneys. In contrast, PEDF overexpressing 143B cells injected into femur metastasized to the lungs and kidneys. PEDF triggered mesenchymal-to-epithelial transition (MET) in vitro as well as in vivo. Based on these results, we hypothesized that the MET might be a potential barrier to extravasation. PEDF overexpression in various osteosarcoma cell lines increased their extravasation to the kidneys and lungs. Moreover, when cultured close to the renal endothelial cell line TKD2, Bkid cells disturbed the TKD2 layer and hindered wound healing via the PEDF-laminin receptor (lamR) axis. Furthermore, novel interactions were observed among PEDF, lamR, lysyl oxidase-like 1 (Loxl1), and SNAI3 (Snail-like transcription factor) during endothelial-to-mesenchymal transition (EndoMT). Collectively, our results show that PEDF induces cancer cell extravasation by increasing the permeability of kidney and lung vasculature acting via lamR and its downstream genes. We also speculate that PEDF promotes extravasation via inhibiting EndoMT, and this warrants investigation in future studies.

Autism risk gene POGZ promotes chromatin accessibility and expression of clustered synaptic genes

Deleterious genetic variants in POGZ, which encodes the chromatin regulator Pogo Transposable Element with ZNF Domain protein, are strongly associated with autism spectrum disorder (ASD). Although it is a high-confidence ASD risk gene, the neurodevelopmental functions of POGZ remain unclear. Here we reveal the genomic binding of POGZ in the developing forebrain at euchromatic loci and gene regulatory elements (REs). We profile chromatin accessibility and gene expression in Pogz-/- mice and show that POGZ promotes the active chromatin state and transcription of clustered synaptic genes. We further demonstrate that POGZ forms a nuclear complex and co-occupies loci with ADNP, another high-confidence ASD risk gene, and provide evidence that POGZ regulates other neurodevelopmental disorder risk genes as well. Our results reveal a neurodevelopmental function of an ASD risk gene and identify molecular targets that may elucidate its function in ASD.

Fine Breakpoint Mapping by Genome Sequencing Reveals the First Large X Inversion Disrupting the NHS Gene in a Patient with Syndromic Cataracts

Inversions are structural variants that are generally balanced. However, they could lead to gene disruptions or have positional effects leading to diseases. Mutations in the NHS gene cause Nance-Horan syndrome, an X-linked disorder characterised by congenital cataracts and dental anomalies. Here, we aimed to characterise a balanced pericentric inversion X(p22q27), maternally inherited, in a child with syndromic bilateral cataracts by breakpoint mapping using whole-genome sequencing (WGS). 30× Illumina paired-end WGS was performed in the proband, and breakpoints were confirmed by Sanger sequencing. EdU assays and FISH analysis were used to assess skewed X-inactivation patterns. RNA expression of involved genes in the breakpoint boundaries was evaluated by droplet-digital PCR. We defined the breakpoint position of the inversion at Xp22.13, with a 15 bp deletion, disrupting the unusually large intron 1 of the canonical NHS isoform, and also perturbing topologically-associated domains (TADs). Moreover, a microhomology region of 5 bp was found on both sides. RNA analysis confirmed null and reduced NHS expression in the proband and his unaffected mother, respectively. In conclusion, we report the first chromosomal inversion disrupting NHS, fine-mapped by WGS. Our data expand the clinical spectrum and the pathogenic mechanisms underlying the NHS defects.

SLITRK2, an X-linked modifier of the age at onset in C9orf72 frontotemporal lobar degeneration

The G4C2-repeat expansion in C9orf72 is the most common cause of frontotemporal dementia and of amyotrophic lateral sclerosis. The variability of age at onset and phenotypic presentations is a hallmark of C9orf72 disease. In this study, we aimed to identify modifying factors of disease onset in C9orf72 carriers using a family-based approach, in pairs of C9orf72 carrier relatives with concordant or discordant age at onset. Linkage and association analyses provided converging evidence for a locus on chromosome Xq27.3. The minor allele A of rs1009776 was associated with an earlier onset (P = 1 × 10-5). The association with onset of dementia was replicated in an independent cohort of unrelated C9orf72 patients (P = 0.009). The protective major allele delayed the onset of dementia from 5 to 13 years on average depending on the cohort considered. The same trend was observed in an independent cohort of C9orf72 patients with extreme deviation of the age at onset (P = 0.055). No association of rs1009776 was detected in GRN patients, suggesting that the effect of rs1009776 was restricted to the onset of dementia due to C9orf72. The minor allele A is associated with a higher SLITRK2 expression based on both expression quantitative trait loci (eQTL) databases and in-house expression studies performed on C9orf72 brain tissues. SLITRK2 encodes for a post-synaptic adhesion protein. We further show that synaptic vesicle glycoprotein 2 and synaptophysin, two synaptic vesicle proteins, were decreased in frontal cortex of C9orf72 patients carrying the minor allele. Upregulation of SLITRK2 might be associated with synaptic dysfunctions and drives adverse effects in C9orf72 patients that could be modulated in those carrying the protective allele. How the modulation of SLITRK2 expression affects synaptic functions and influences the disease onset of dementia in C9orf72 carriers will require further investigations. In summary, this study describes an original approach to detect modifier genes in rare diseases and reinforces rising links between C9orf72 and synaptic dysfunctions that might directly influence the occurrence of first symptoms.

Proteomic discovery in sickle cell disease: Elevated neurogranin levels in children with sickle cell disease

PURPOSE

Sickle cell disease (SCD) is an inherited hemoglobinopathy that causes stroke and silent cerebral infarct (SCI). Our aim was to identify markers of brain injury in SCD.

EXPERIMENTAL DESIGN

Plasma proteomes were analyzed using a sequential separation approach of hemoglobin (Hb) and top abundant plasma protein depletion, followed by reverse phase separation of intact proteins, trypsin digestion, and tandem mass spectrometry. We compared plasma proteomes of children with SCD with and without SCI in the Silent Cerebral Infarct Multi-Center Clinical Trial (SIT Trial) to age-matched, healthy non-SCD controls.

RESULTS

From the SCD group, 1172 proteins were identified. Twenty-five percent (289/1172) were solely in the SCI group. Twenty-five proteins with enriched expression in the human brain were identified in the SCD group. Neurogranin (NRGN) was the most abundant brain-enriched protein in plasma of children with SCD. Using a NRGN sandwich immunoassay and SIT Trial samples, median NRGN levels were higher at study entry in children with SCD (0.28 ng/mL, N = 100) compared to control participants (0.12 ng/mL, N = 25, p < 0.0004).

CONCLUSIONS AND CLINICAL RELEVANCE

NRGN levels are elevated in children with SCD. NRGN and other brain-enriched plasma proteins identified in plasma of children with SCD may provide biochemical evidence of neurological injury.

Quantitative Proteomics Reveals Significant Differences between Mouse Brain Formations in Expression of Proteins Involved in Neuronal Plasticity during Aging

Aging is associated with a general decline in cognitive functions, which appears to be due to alterations in the amounts of proteins involved in the regulation of synaptic plasticity. Here, we present a quantitative analysis of proteins involved in neurotransmission in three brain regions, namely, the hippocampus, the cerebral cortex and the cerebellum, in mice aged 1 and 22 months, using the total protein approach technique. We demonstrate that although the titer of some proteins involved in neurotransmission and synaptic plasticity is affected by aging in a similar manner in all the studied brain formations, in fact, each of the formations represents its own mode of aging. Generally, the hippocampal and cortical proteomes are much more unstable during the lifetime than the cerebellar proteome. The data presented here provide a general picture of the effect of physiological aging on synaptic plasticity and might suggest potential drug targets for anti-aging therapies.

SLITRK5 is a negative regulator of hedgehog signaling in osteoblasts

Hedgehog signaling is essential for bone formation, including functioning as a means for the growth plate to drive skeletal mineralization. However, the mechanisms regulating hedgehog signaling specifically in bone-forming osteoblasts are largely unknown. Here, we identified SLIT and NTRK-like protein-5(Slitrk5), a transmembrane protein with few identified functions, as a negative regulator of hedgehog signaling in osteoblasts. Slitrk5 is selectively expressed in osteoblasts and loss of Slitrk5 enhanced osteoblast differentiation in vitro and in vivo. Loss of SLITRK5 in vitro leads to increased hedgehog signaling and overexpression of SLITRK5 in osteoblasts inhibits the induction of targets downstream of hedgehog signaling. Mechanistically, SLITRK5 binds to hedgehog ligands via its extracellular domain and interacts with PTCH1 via its intracellular domain. SLITRK5 is present in the primary cilium, and loss of SLITRK5 enhances SMO ciliary enrichment upon SHH stimulation. Thus, SLITRK5 is a negative regulator of hedgehog signaling in osteoblasts that may be attractive as a therapeutic target to enhance bone formation.

MiR-139-5p influences hepatocellular carcinoma cell invasion and proliferation capacities via decreasing SLITRK4 expression

The microRNA, miR-139-5p, has been proved to play important roles in regulating tumor progression, including prostate cancer, osteosarcoma, esophageal cancer, and so on, but its correlation of hepatocellular carcinoma (HCC) still remains unclear. Here we found that hsa-miR-139-5p (miR-139-5p) was decreased in HCC samples compared with normal liver tissues, and a lower expression of miR-139-5p was connected to a poorer prognosis. Mechanism study indicated that a decreased/increased miR-139-5p could increase/decrease HCC cells invasion and proliferation capacities via increasing SLITRK4 expression, what’s more, the reverse assays also confirmed the conclusion when we knocked down SLITRK4 in the miR-139-5p low-expression cells. Luciferase assay confirmed that miR-139-5p could directly bind to the 3′UTR of SLITRK4 mRNA to regulate its expression. Together, these findings show the importance of miR-139-5p/SLITRK4 pathway in HCC growth and progression and may provide new targets for us to better arrange the progression of HCC.

Opposite Control of Excitatory and Inhibitory Synapse Formation by Slitrk2 and Slitrk5 on Dopamine Neurons Modulates Hyperactivity Behavior

The neurodevelopmental origin of hyperactivity disorder has been suggested to involve the dopaminergic system, but the underlying mechanisms are still unknown. Here, transcription factors Lmx1a and Lmx1b are shown to be essential for midbrain dopaminergic (mDA) neuron excitatory synaptic inputs and dendritic development. Strikingly, conditional knockout (cKO) of Lmx1a/b in postmitotic mDA neurons results in marked hyperactivity. In seeking Lmx1a/b target genes, we identify positively regulated Slitrk2 and negatively regulated Slitrk5. These two synaptic adhesion proteins promote excitatory and inhibitory synapses on mDA neurons, respectively. Knocking down Slitrk2 reproduces some of the Lmx1a/b cKO cellular and behavioral phenotypes, whereas Slitrk5 knockdown has opposite effects. The hyperactivity caused by this imbalance in excitatory/inhibitory synaptic inputs on dopamine neurons is reproduced by chronically inhibiting the ventral tegmental area during development using pharmacogenetics. Our study shows that alterations in developing dopaminergic circuits strongly impact locomotor activity, shedding light on mechanisms causing hyperactivity behaviors.

Proper synaptic adhesion signaling in the control of neural circuit architecture and brain function

Trans-synaptic cell-adhesion molecules are critical for governing various stages of synapse development and specifying neural circuit properties via the formation of multifarious signaling pathways. Recent studies have pinpointed the putative roles of trans-synaptic cell-adhesion molecules in mediating various cognitive functions. Here, we review the literature on the roles of a diverse group of central synaptic organizers, including neurexins (Nrxns), leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-RPTPs), and their associated binding proteins, in regulating properties of specific type of synapses and neural circuits. In addition, we highlight the findings that aberrant synaptic adhesion signaling leads to alterations in the structures, transmission, and plasticity of specific synapses across diverse brain areas. These results seem to suggest that proper trans-synaptic signaling pathways by Nrxns, LAR-RPTPs, and their interacting network is likely to constitute central molecular complexes that form the basis for cognitive functions, and that these complexes are heterogeneously and complexly disrupted in many neuropsychiatric and neurodevelopmental disorders.

Synaptic Organizers in Alzheimer's Disease: A Classification Based on Amyloid-β Sensitivity

Synaptic pathology is one of the major hallmarks observed from the early stage of Alzheimer’s disease (AD), leading to cognitive and memory impairment characteristic of AD patients. Synaptic connectivity and specificity are regulated by multiple trans-bindings between pre- and post-synaptic organizers, the complex of which exerts synaptogenic activity. Neurexins (NRXs) and Leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-RPTPs) are the major presynaptic organizers promoting synaptogenesis through their distinct binding to a wide array of postsynaptic organizers. Recent studies have shown that amyloid-β oligomers (AβOs), a major detrimental molecule in AD, interact with NRXs and neuroligin-1, an NRX-binding postsynaptic organizer, to cause synaptic impairment. On the other hand, LAR-RPTPs and their postsynaptic binding partners have no interaction with AβOs, and their synaptogenic activity is maintained even in the presence of AβOs. Here, we review the current evidence regarding the involvement of synaptic organizers in AD, with a focus on Aβ synaptic pathology, to propose a new classification where NRX-based and LAR-RPTP-based synaptic organizing complexes are classified into Aβ-sensitive and Aβ-insensitive synaptic organizers, respectively. We further discuss how their different Aβ sensitivity is involved in Aβ vulnerability and tolerance of synapses for exploring potential therapeutic approaches for AD.

The role of SLITRK6 in the pathogenesis of Tourette syndrome: From the conclusion of a family-based study in the Chinese Han population

BACKGROUND

Tourette syndrome (TS) is a complex neuropsychiatric disorder coupled with obvious genetic heterogeneity. Studies in recent years have confirmed the association of SLITRK genes with sensory and neuropsychiatric diseases. To detect whether SLITRK6 is involved in the progress of TS, a family-based association study was performed to explore the possible genetic association between SLITRK6 and TS in the Chinese Han population.

METHODS

We genotyped 399 TS nuclear families trios, and then analyzed three tag SLITRK6 single nucleotide polymorphisms using the transmission disequilibrium test (TDT) haplotype relative risk (HRR) and haplotype-based haplotype relative risk (HHRR) methods.

RESULTS

The TDT showed no statistically significant allele transfer for the three polymorphisms. The HRR and HHRR also showed a negative association.

CONCLUSIONS

Despite the results suggesting that these polymorphisms may not be associated with susceptibility to TS in the Chinese Han population, we are still unable to determine the potential role of SLITRK6 in the pathogenesis of TS. Furthermore, the results still need to be confirmed in a larger sample size and in different populations.

Marble-burying behavior test as a murine model of compulsive-like behavior

Object burying by rodents is a popular screening tool for anxiolytic agents. However, modulation of marble-burying by serotonin reuptake inhibitors prompted its link to obsessive-compulsive disorder/compulsive-like behavior. The Marble-burying behavior test is an acute test; however, some investigators incorporate the sub-acute treatment regimen as an essential component for screening anti-compulsive agents. The test exhibits between-laboratory methodological differences and demonstrates positive treatment responses to an array of pharmacotherapies, creating doubts about its predictive validity and construct validity. Numerous reviews are available on marble-burying behavior test, which incorporates the test as a part of anti-compulsive behavior-like screens, but none has made it a sole subject-matter for discussion. This review attempts to provide a comprehensive account of the marble-burying test as a model of compulsive-like disorders. It envisages the model's scientific origins, the preclinical research done and its correlation with the clinical research outcomes, and a detailed discussion about its validity. In conclusion, there appears a need to address the issue of construct and predictive validity of the model authoritatively; or the paradigm may remain squandered in the field of obsessive-compulsive disorder research.

Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

Background

Genes involved in Tourette syndrome (TS) remain largely unknown. We aimed to identify genetic factors contributing to TS in a French cohort of 120 individuals using a combination of hypothesis-driven and exome-sequencing approaches.

Methods

We first sequenced exons of SLITRK1-6 and HDC in the TS cohort and subsequently sequenced the exome of 12 individuals harboring rare variants in these genes to find additional rare variants contributing to the disorder under the hypothesis of oligogenic inheritance. We further screened three candidate genes (OPRK1, PCDH10, and NTSR2) preferentially expressed in the basal ganglia, and three additional genes involved in neurotensin and opioid signaling (OPRM1, NTS, and NTSR1), and compared variant frequencies in TS patients and 788 matched control individuals. We also investigated the impact of altering the expression of Oprk1 in zebrafish.

Results

Thirteen ultrarare missense variants of SLITRK1-6 and HDC were identified in 12 patients. Exome sequencing in these patients revealed rare possibly deleterious variants in 3,041 genes, 54 of which were preferentially expressed in the basal ganglia. Comparison of variant frequencies altering selected candidate genes in TS and control individuals revealed an excess of potentially disrupting variants in OPRK1, encoding the opioid kappa receptor, in TS patients. Accordingly, we show that downregulation of the Oprk1 orthologue in zebrafish induces a hyperkinetic phenotype in early development.

Discussion

These results support a heterogeneous and complex genetic etiology of TS, possibly involving rare variants altering the opioid pathway in some individuals, which could represent a novel therapeutic target in this disorder.

Slitrk2 controls excitatory synapse development via PDZ-mediated protein interactions

Members of the Slitrk (Slit- and Trk-like protein) family of synaptic cell-adhesion molecules control excitatory and inhibitory synapse development through isoform-dependent extracellular interactions with leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-RPTPs). However, how Slitrks participate in activation of intracellular signaling pathways in postsynaptic neurons remains largely unknown. Here we report that, among the six members of the Slitrk family, only Slitrk2 directly interacts with the PDZ domain-containing excitatory scaffolds, PSD-95 and Shank3. The interaction of Slitrk2 with PDZ proteins is mediated by the cytoplasmic COOH-terminal PDZ domain-binding motif (Ile-Ser-Glu-Leu), which is not found in other Slitrks. Mapping analyses further revealed that a single PDZ domain of Shank3 is responsible for binding to Slitrk2. Slitrk2 forms in vivo complexes with membrane-associated guanylate kinase (MAGUK) family proteins in addition to PSD-95 and Shank3. Intriguingly, in addition to its role in synaptic targeting in cultured hippocampal neurons, the PDZ domain-binding motif of Slitrk2 is required for Slitrk2 promotion of excitatory synapse formation, transmission, and spine development in the CA1 hippocampal region. Collectively, our data suggest a new molecular mechanism for conferring isoform-specific regulatory actions of the Slitrk family in orchestrating intracellular signal transduction pathways in postsynaptic neurons.

The Neuronal Glutamate Transporter EAAT3 in Obsessive-Compulsive Disorder

Obsessive compulsive disorder (OCD) is a heterogeneous psychiatric disorder affecting 1%–3% of the population worldwide. About half of OCD afflicted individuals do not respond to currently available pharmacotherapy, which is mainly based on serotonin reuptake inhibition. Therefore, there is a critical need to search novel and improved therapeutic targets to treat this devastating disorder. In recent years, accumulating evidence has supported the glutamatergic hypothesis of OCD, and particularly pointing a potential role for the neuronal glutamate transporter EAAT3. This mini-review summarizes recent findings regarding the neurobiological basis of OCD, with an emphasis on the glutamatergic neurotransmission and EAAT3 as a key player in OCD etiology.

Transcranial Current Stimulation Alters the Expression of Immune-Mediating Genes

Despite its extensive use in clinical studies, the molecular mechanisms underlying the effects of transcranial direct current stimulation (tDCS) remain to be elucidated. We previously described subacute effects of tDCS on immune- and stem cells in the rat brain. To investigate the more immediate effects of tDCS regulating those cellular responses, we treated rats with a single session of either anodal or cathodal tDCS, and analyzed the gene expression by microarray; sham-stimulated rats served as control. Anodal tDCS increased expression of several genes coding for the major histocompatibility complex I (MHC I), while cathodal tDCS increased the expression of the immunoregulatory protein osteopontin (OPN). We confirmed the effects of gene upregulation by immunohistochemistry at the protein level. Thus, our data show a novel mechanism for the actions of tDCS on immune- and inflammatory processes, providing a target for future therapeutic studies.

A Conserved Tyrosine Residue in Slitrk3 Carboxyl-Terminus Is Critical for GABAergic Synapse Development

Single-passing transmembrane protein, Slitrk3 (Slit and Trk-like family member 3, ST3), is a synaptic cell adhesion molecule highly expressed at inhibitory synapses. Recent studies have shown that ST3, through its extracellular domain, selectively regulates inhibitory synapse development via the trans-synaptic interaction with presynaptic cell adhesion molecule, receptor protein tyrosine phosphatase δ (PTPδ) and the cis-interaction with postsynaptic cell adhesion molecule, Neuroligin 2 (NL2). However, little is known about the physiological function of ST3 intracellular, carboxyl (C)-terminal region. Here we report that in heterologous cells, ST3 C-terminus is not required for ST3 homo-dimerization and trafficking to the cell surface. In contrast, in hippocampal neurons, ST3 C-terminus, more specifically, the conserved tyrosine Y969 (in mice), is critical for GABAergic synapse development. Indeed, overexpression of ST3 Y969A mutant markedly reduced the gephyrin puncta density and GABAergic transmission in hippocampal neurons. In addition, single-cell genetic deletion of ST3 strongly impaired GABAergic transmission. Importantly, wild-type (WT) ST3, but not the ST3 Y969A mutant, could fully rescue GABAergic transmission deficits in neurons lacking endogenous ST3, confirming a critical role of Y969 in the regulation of inhibitory synapses. Taken together, our data identify a single critical residue in ST3 C-terminus that is important for GABAergic synapse development and function.

Regional Gene Expression Profile Comparison Reveals the Unique Transcriptome of the Optic Fissure

Purpose

The optic fissure (OF) is a transient opening in the ventral optic cup (OC) that acts as a passage for blood vessels and retinal ganglion cell axons during early eye development. Failure to close the OF is the developmental basis for uveal coloboma, a congenital blinding eye disease that significantly contributes to childhood blindness. Genes specifically expressed in the OF region may play important roles in OF development and function. The aim of this study was to characterize the transcriptome of OC cells in the OF region and investigate the function of OF-specific genes during OF closure.

Methods

Laser-assisted microdissection was used to collect different regions of OC tissues. Microarray analysis was used to obtain and compare gene expression profiles of different OC regions. RNA in situ hybridization (ISH) was used to further characterize OF-specific gene expression patterns. Morpholino knockdown in zebrafish was used to study the function of a newly discovered OF-specific gene during OF closure.

Results

Microarray comparison revealed that the OC at the OF region exhibited a unique gene expression profile. OC expression patterns of a number of newly discovered OF-specific genes were confirmed by ISH. Morpholino knockdown and downstream target expression and function analysis demonstrated that afap1l2, a newly discovered OF-specific gene, controls OF closure by regulating pax2a expression.

Conclusions

Our study characterized the unique transcriptome of the OF region of the OC and demonstrated the essential role of a newly discovered OF-specific gene in OF closure. This study provides a valuable foundation for future mechanism dissection in OF development and physiology, and for human coloboma etiology exploration.

Targeting advanced urothelial carcinoma-developing strategies

PURPOSE OF REVIEW

Advanced urothelial carcinoma is a heterogeneous disease with high burden of morbidity, mortality, and cost. Significant progress has been made in understanding the biology of the disease and the development of immunotherapies and targeted therapies. In this review, we summarize the current and future therapeutic approaches in the management of urothelial carcinoma.

RECENT FINDINGS

Advances in immune checkpoint inhibitors resulted in the Food and Drug Administration (FDA) approvals of atezolizumab in 2016, and pembrolizumab, avelumab, durvalumab, and nivolumab in 2017 for the treatment of advanced urothelial carcinoma. More recently, development of inhibitors targeting the fibroblast growth factor receptor genetic alterations and antibody-drug conjugates targeting specific cell surface antigens (trop2, nectin4, and SLITRK6) resulted in several FDA breakthrough designations for urothelial carcinoma.

CONCLUSION

The development of novel therapies targeting the immune and molecular pathways of advanced urothelial carcinoma is promising for the improvement of outcomes in this lethal disease. Ongoing efforts are poised to optimize therapeutic options in the post-chemotherapy arena. In the era of precision medicine, the future of urothelial carcinoma lies in using less cytotoxic chemotherapy, more targeted therapy and immunotherapy, and possibly a combination of these therapeutic approaches.

Genome-wide association meta-analysis of functional outcome after ischemic stroke

OBJECTIVE

To discover common genetic variants associated with poststroke outcomes using a genome-wide association (GWA) study.

METHODS

The study comprised 6,165 patients with ischemic stroke from 12 studies in Europe, the United States, and Australia included in the GISCOME (Genetics of Ischaemic Stroke Functional Outcome) network. The primary outcome was modified Rankin Scale score after 60 to 190 days, evaluated as 2 dichotomous variables (0-2 vs 3-6 and 0-1 vs 2-6) and subsequently as an ordinal variable. GWA analyses were performed in each study independently and results were meta-analyzed. Analyses were adjusted for age, sex, stroke severity (baseline NIH Stroke Scale score), and ancestry. The significance level was p < 5 × 10-8.

RESULTS

We identified one genetic variant associated with functional outcome with genome-wide significance (modified Rankin Scale scores 0-2 vs 3-6, p = 5.3 × 10-9). This intronic variant (rs1842681) in the LOC105372028 gene is a previously reported trans-expression quantitative trait locus for PPP1R21, which encodes a regulatory subunit of protein phosphatase 1. This ubiquitous phosphatase is implicated in brain functions such as brain plasticity. Several variants detected in this study demonstrated suggestive association with outcome (p < 10-5), some of which are within or near genes with experimental evidence of influence on ischemic stroke volume and/or brain recovery (e.g., NTN4, TEK, and PTCH1).

CONCLUSIONS

In this large GWA study on functional outcome after ischemic stroke, we report one significant variant and several variants with suggestive association to outcome 3 months after stroke onset with plausible mechanistic links to poststroke recovery. Future replication studies and exploration of potential functional mechanisms for identified genetic variants are warranted.

Gene variations in PBX1, LMX1A and SLITRK1 are associated with obsessive-compulsive disorder and its clinical features

Genetic factors probably influence OCD development and a current hypothesis proposes that genes involved in the development of the central nervous system (CNS) are related to OCD. The aim of this study was to analyze six Single Nucleotide Polymorphisms (SNPs) in five genes with functions related to neurodevelopment in OCD. A total of 203 patient and 203 control samples were genotyped using the TaqMan® methodology. Statistically significant associations between OCD and PBX1 (rs2275558) in total sample (P = 0.002) and in males (P = 0.0003) were observed. Concerning symptom dimensions, the expression of neutralization showed a statistical significant association with LMX1A (rs4657411, P = 0.004) in total sample. We also observed significant association between LMX1A (rs4657411) and washing dimension in females (P = 0.01). Additionally, SLITRK1 (rs9593835) was significantly associated with checking dimension in male patients (P = 0.04). Our results indicate an important influence of neurodevelopment genes in the OCD susceptibility. Additional studies with larger samples are needed to confirm these results.

Synaptic organizer: Slitrks and type IIa receptor protein tyrosine phosphatases

Slit-like and Trk-like (Slitrk) family members are leucine-rich repeat (LRR)-containing neuronal transmembrane proteins. Slitrks have been highlighted as key synapse organizers at neuronal synapses through interactions with specific members of the presynaptic type IIa receptor protein tyrosine phosphatase (RPTP) family. Recent structural studies on type IIa RPTP/Slitrk1 complexes have unveiled molecular insights into their binding selectivity and have established the role of higher-order receptor clustering in their synaptogenic activity. Here, we will discuss key structural aspects of Slitrk interactions with type IIa RPTP family members, the biological roles of Slitrks in neurons, and our current knowledge of SLITRK mutations in human diseases.

Application of ex-vivo spheroid model system for the analysis of senescence and senolytic phenotypes in uterine leiomyoma

Cellular senecence is an important biologic endpoint. Naturally occuring (aging) senescence is common in uterine leiomyoma (ULM). AKT is one of major pathways in promoting ULM growth and survival. Inactivation of AKT by MK2206 in ULM resulted in stress-induced senescence in vitro. Study of the senescent phenotypes and molecular changes in ULM may greatly facilitate the understanding of the tumor biology and potential clinical therapy for this common disease associated with high morbidity. To study senescence in a model system that closely resembles primary ULM in vivo, we applied an ex vivo model of three-dimensional (3D) spheroid culture system which maintained the molecular and cellular characteristics of primary ULM and matched myometrium as seen in vivo. Gene expression profiling done on ULM induced to undergo replication (passaging) or stress-induced (MK2206) senescence revealed that ROS and hypoxic-related genes were upregulated in the two types of senescences. Overexpression of two selected genes, WIPI1 and SLITKR4, induced cellular senescence in ULM spheroids. Additionally, administration of ABT263 (a BH3 mimetic) effectively reduced the senescent cells induced in ULM spheroids. This study identified novel genes associated with senescence in ULM and demonstrated a BH3 mimetic to act as a senolytic to remove senescent cells.

Born This Way: Using Intrinsic Disorder to Map the Connections between SLITRKs, TSHR, and Male Sexual Orientation

Recently, genome-wide association study reveals a significant association between specific single nucleotide polymorphisms (SNPs) in men and their sexual orientation. These SNPs (rs9547443 and rs1035144) reside in the intergenic region between the SLITRK5 and SLITRK6 genes and in the intronic region of the TSHR gene and might affect functionality of SLITRK5, SLITRK6, and TSHR proteins that are engaged in tight control of key developmental processes, such as neurite outgrowth and modulation, cellular differentiation, and hormonal regulation. SLITRK5 and SLITRK6 are single-pass transmembrane proteins, whereas TSHR is a heptahelical G protein-coupled receptor (GPCR). Mutations in these proteins are associated with various diseases and are linked to phenotypes found at a higher rate in homosexual men. A bioinformatics analysis of SLITRK5, SLITRK6, and TSHR proteins is conducted to look at their structure, protein interaction networks, and propensity for intrinsic disorder. It is assumed that this information might improve understanding of the roles that SLITRK5, SLITRK6, and TSHR play within neuronal and thyroidal tissues and give insight into the phenotypes associated with male homosexuality.