SorCS2 is required for BDNF-dependent plasticity in the hippocampus

Lithium response in bipolar disorder: Epigenome-wide DNA methylation signatures and epigenetic aging

Lithium (Li) is the first-line treatment for bipolar disorder (BD) even though only 30 % of BD patients are considered excellent responders. The mechanisms by which Li exerts its action are not clearly understood, but it has been suggested that specific epigenetic mechanisms, such as methylation processes, may play a role. In this regard, DNA methylation patterns can be used to estimate epigenetic age (EpiAge), which is accelerated in BD patients and reversed by Li treatment. Our first aim was to compare the DNA methylation profile in peripheral blood between BD patients categorized as excellent responders to Li (Ex-Rp) and non-responders (N-Rp). Secondly, EpiAge was estimated to detect differential age acceleration between the two groups. A total of 130 differentially methylated positions (DMPs) and 16 differentially methylated regions (DMRs) between Ex-Rp (n = 26) and N-Rp (n = 37) were identified (FDR adjusted p-value < 0.05). We found 122 genes mapping the DMPs and DMRs, nine of which (HOXB6, HOXB3, HOXB-AS3, TENM2, CACNA1B, ANK3, EEF2K, CYP1A1, and SORCS2) had previously been linked to Li response. We found genes related to the GSK3β pathway to be highly represented. Using FUMA, we found enrichment in Gene Ontology Cell Component for the synapse. Gene network analysis highlighted functions related to the cell cycle, nervous system development and function, and gene expression. No significant differences in age acceleration were found between Ex-Rp and N-Rp for any of the epigenetic clocks analysed. Our findings indicate that a specific methylation pattern could determine the response to Li in BD patients. We also found that a significant portion of the differentially methylated genes are closely associated with the GSK3β pathway, reinforcing the role of this system in Li response. Future longitudinal studies with larger samples will help to elucidate the epigenetic mechanisms underlying Li response.

SorCS2 is involved in promoting periodontitis-induced depression-like behaviour in mice

BACKGROUND

Emerging evidence supports the association between periodontitis and depression, although the mechanisms are unclear. This study investigated the role of SorCS2 in the pathogenesis of periodontitis-induced depression.

MATERIALS AND METHODS

An experimental periodontitis model was established using SorCS2 knockout mice and their wild-type littermates, and depression-like behaviour was evaluated. The expression of proBDNF signalling, neuronal activity, and glutamate-associated signalling pathways were further measured by western blotting and immunofluorescence. In addition, neuroinflammatory status, astrocytic and microglial markers, and the expression of corticosterone-related factors were measured by immunofluorescence, western blotting, and enzyme-linked immunosorbent assays.

RESULTS

SorCS2 deficiency alleviated periodontitis-induced depression-like behaviour in mice. Further results suggested that SorCS2 deficiency downregulated the expression of pro-BDNF and glutamate signalling and restored neuronal activities in mice with periodontitis. Neuroinflammation in the mouse hippocampus was triggered by experimental periodontitis but was not affected by SorCS2 deficiency. The levels of corticosterone and the expression of glucocorticoid receptors were also not altered.

CONCLUSION

Our study, for the first time, reveals the critical role of SorCS2 in the pathogenesis of periodontitis-induced depression. The underlying mechanism involves proBDNF and glutamate signalling in the hippocampus, providing a novel therapeutic target for periodontitis-associated depression.

Spatial transcriptomic analysis of the mouse brain following chronic social defeat stress

Depression is a highly prevalent and disabling mental disorder, involving numerous genetic changes that are associated with abnormal functions in multiple regions of the brain. However, there is little transcriptomic-wide characterization of chronic social defeat stress (CSDS) to comprehensively compare the transcriptional changes in multiple brain regions. Spatial transcriptomics (ST) was used to reveal the spatial difference of gene expression in the control, resilient (RES) and susceptible (SUS) mouse brains, and annotated eight anatomical brain regions and six cell types. The gene expression profiles uncovered that CSDS leads to gene synchrony changes in different brain regions. Then it was identified that inhibitory neurons and synaptic functions in multiple regions were primarily affected by CSDS. The brain regions Hippocampus (HIP), Isocortex, and Amygdala (AMY) present more pronounced transcriptional changes in genes associated with depressive psychiatric disorders than other regions. Signalling communication between these three brain regions may play a critical role in susceptibility to CSDS. Taken together, this study provides important new insights into CSDS susceptibility at the ST level, which offers a new approach for understanding and treating depression.

Reduced mastication during growth inhibits cognitive function by affecting trigeminal ganglia and modulating Wnt signaling pathway and ARHGAP33 molecular transmission

Binding of brain-derived neurotrophic factor (BDNF) to its receptor tyrosine kinase B (TrkB) is essential for the development of the hippocampus, which regulates memory and learning. Decreased masticatory stimulation during growth reportedly increases BDNF expression while decreasing TrkB expression in the hippocampus. Increased BDNF expression is associated with Wnt family member 3A (Wnt3a) expression and decreased expression of Rho GTPase Activating Protein 33 (ARHGAP33), which regulates intracellular transport of TrkB. TrkB expression may be decreased at the cell surface and affects the hippocampus via BDNF/TrkB signaling. Mastication affects cerebral blood flow and the neural cascade that occurs through the trigeminal nerve and hippocampus. In the current study, we hypothesized that decreased masticatory stimulation reduces memory/learning in mice due to altered Wnt3a and ARHGAP33 expression, which are related to memory/learning functions in the hippocampus. To test this hypothesis, we fed mice a powdered diet until 14 weeks of age and analyzed the BDNF and TrkB mRNA expression in the right hippocampus using real-time polymerase chain reaction and Wnt3a and ARHGAP33 levels in the left hippocampus using western blotting. Furthermore, we used staining to assess BDNF and TrkB expression in the hippocampus and the number of nerve cells, the average size of each single cell and the area of intercellular spaces of the trigeminal ganglion (TG). We found that decreased masticatory stimulation affected the expression of BDNF, Wnt3a, ARHGAP33, and TrkB proteins in the hippocampus, as well as memory/learning. The experimental group showed significantly decreased numbers of neurons and increased the area of intercellular spaces in the TG. Our findings suggest that reduced masticatory stimulation during growth induces a decline in memory/learning by modulating molecular transmission mechanisms in the hippocampus and TG.

The molecular cytoarchitecture of the adult mouse brain

The function of the mammalian brain relies upon the specification and spatial positioning of diversely specialized cell types. Yet, the molecular identities of the cell types and their positions within individual anatomical structures remain incompletely known. To construct a comprehensive atlas of cell types in each brain structure, we paired high-throughput single-nucleus RNA sequencing with Slide-seq1,2-a recently developed spatial transcriptomics method with near-cellular resolution-across the entire mouse brain. Integration of these datasets revealed the cell type composition of each neuroanatomical structure. Cell type diversity was found to be remarkably high in the midbrain, hindbrain and hypothalamus, with most clusters requiring a combination of at least three discrete gene expression markers to uniquely define them. Using these data, we developed a framework for genetically accessing each cell type, comprehensively characterized neuropeptide and neurotransmitter signalling, elucidated region-specific specializations in activity-regulated gene expression and ascertained the heritability enrichment of neurological and psychiatric phenotypes. These data, available as an online resource ( www.BrainCellData.org ), should find diverse applications across neuroscience, including the construction of new genetic tools and the prioritization of specific cell types and circuits in the study of brain diseases.

SorCS2 binds progranulin to regulate motor neuron development

Motor neuron (MN) development and nerve regeneration requires orchestrated action of a vast number of molecules. Here, we identify SorCS2 as a progranulin (PGRN) receptor that is required for MN diversification and axon outgrowth in zebrafish and mice. In zebrafish, SorCS2 knockdown also affects neuromuscular junction morphology and fish motility. In mice, SorCS2 and PGRN are co-expressed by newborn MNs from embryonic day 9.5 until adulthood. Using cell-fate tracing and nerve segmentation, we find that SorCS2 deficiency perturbs cell-fate decisions of brachial MNs accompanied by innervation deficits of posterior nerves. Additionally, adult SorCS2 knockout mice display slower motor nerve regeneration. Interestingly, primitive macrophages express high levels of PGRN, and their interaction with SorCS2-positive motor axon is required during axon pathfinding. We further show that SorCS2 binds PGRN to control its secretion, signaling, and conversion into granulins. We propose that PGRN-SorCS2 signaling controls MN development and regeneration in vertebrates.

Internally tagged Vps10p-domain receptors reveal uptake of the neurotrophin BDNF

The Vps10p-domain (Vps10p-D) receptor family consists of Sortilin, SorLA, SorCS1, SorCS2, and SorCS3. They mediate internalization and intracellular sorting of specific cargo in various cell types, but underlying molecular determinants are incompletely understood. Deciphering the dynamic intracellular itineraries of Vps10p-D receptors is crucial for understanding their role in physiological and cytopathological processes. However, studying their spatial and temporal dynamics by live imaging has been challenging so far, as terminal tagging with fluorophores presumably impedes several of their protein interactions and thus functions. Here, we addressed the lack of appropriate tools and developed functional versions of all family members internally tagged in their ectodomains. We predict folding of the newly designed receptors by bioinformatics and show their exit from the endoplasmic reticulum. We examined their subcellular localization in immortalized cells and primary cultured neurons by immunocytochemistry and live imaging. This was, as far as known, identical to that of wt counterparts. We observed homodimerization of fluorophore-tagged SorCS2 by coimmunoprecipitation and fluorescence lifetime imaging, suggesting functional leucine-rich domains. Through ligand uptake experiments, live imaging and fluorescence lifetime imaging, we show for the first time that all Vps10p-D receptors interact with the neurotrophin brain-derived neurotrophic factor and mediate its uptake, indicating functionality of the Vps10p-Ds. In summary, we developed versions of all Vps10p-D receptors, with internal fluorophore tags that preserve several functions of the cytoplasmic and extracellular domains. These newly developed fluorophore-tagged receptors are likely to serve as powerful functional tools for accurate live studies of the individual cellular functions of Vps10p-D receptors.

Spatially and temporally distinct patterns of expression for VPS10P domain receptors in human cerebral organoids

Vacuolar protein sorting 10 protein (VPS10P) domain receptors are a unique class of intracellular sorting receptors that emerge as major risk factors associated with psychiatric and neurodegenerative diseases, including bipolar disorders, autism, schizophrenia, as well as Alzheimer's disease and frontotemporal dementia. Yet, the lack of suitable experimental models to study receptor functions in the human brain has hampered elucidation of receptor actions in brain disease. Here, we have adapted protocols using human cerebral organoids to the detailed characterization of VPS10P domain receptor expression during neural development and differentiation, including single-cell RNA sequencing. Our studies uncovered spatial and temporal patterns of expression unique to individual receptor species in the human brain. While SORL1 expression is abundant in stem cells and SORCS1 peaks in neural progenitors at onset of neurogenesis, SORT1 and SORCS2 show increasing expression with maturation of neuronal and non-neuronal cell types, arguing for distinct functions in development versus the adult brain. In neurons, subcellular localization also distinguishes between types of receptor species, either mainly localized to the cell soma (SORL1 and SORT1) or also to neuronal projections (SORCS1 and SORCS2), suggesting divergent functions in protein sorting between Golgi and the endo-lysosomal system or along axonal and dendritic tracks. Taken together, our findings provide an important resource on temporal, spatial, and subcellular patterns of VPS10P domain receptor expression in cerebral organoids for further elucidation of receptor (dys) functions causative of behavioral and cognitive defects of the human brain.

Alternative splicing regulates adaptor protein binding, trafficking, and activity of the Vps10p domain receptor SorCS2 in neuronal development

The Vps10p domain receptor SorCS2 is crucial for the development and function of the nervous system and essential for brain-derived neurotrophic factor (BDNF)-induced changes in neuronal morphology and plasticity. SorCS2 regulates the subcellular trafficking of the BDNF signaling receptor TrkB as well as selected neurotransmitter receptors in a manner that is dependent on the SorCS2 intracellular domain (ICD). However, the cellular machinery and adaptor protein (AP) interactions that regulate receptor trafficking via the SorCS2 ICD are unknown. We here identify four splice variants of human SorCS2 differing in the insertion of an acidic cluster motif and/or a serine residue within the ICD. We show that each variant undergoes posttranslational proteolytic processing into a one- or two-chain receptor, giving rise to eight protein isoforms, the expression of which differs between neuronal and nonneuronal tissues and is affected by cellular stressors. We found that the only variants without the serine were able to rescue BDNF-induced branching of SorCS2 knockout hippocampal neurons, while variants without the acidic cluster showed increased interactions with clathrin-associated APs AP-1, AP-2, and AP-3. Using yeast two-hybrid screens, we further discovered that all variants bound dynein light chain Tctex-type 3; however, only variants with an acidic cluster motif bound kinesin light chain 1. Accordingly, splice variants showed markedly different trafficking properties and localized to different subcellular compartments. Taken together, our findings demonstrate the existence of eight functional SorCS2 isoforms with differential capacity for interactions with cytosolic ligands dynein light chain Tctex-type 3 and kinesin light chain 1, which potentially allows cell-type specific SorCS2 trafficking and BDNF signaling.

Molecular Mechanisms Underlying NMDARs Dysfunction and Their Role in ADHD Pathogenesis

Attention deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders, although the aetiology of ADHD is not yet understood. One proposed theory for developing ADHD is N-methyl-D-aspartate receptors (NMDARs) dysfunction. NMDARs are involved in regulating synaptic plasticity and memory function in the brain. Abnormal expression or polymorphism of some genes associated with ADHD results in NMDAR dysfunction. Correspondingly, NMDAR malfunction in animal models results in ADHD-like symptoms, such as impulsivity and hyperactivity. Currently, there are no drugs for ADHD that specifically target NMDARs. However, NMDAR-stabilizing drugs have shown promise in improving ADHD symptoms with fewer side effects than the currently most widely used psychostimulant in ADHD treatment, methylphenidate. In this review, we outline the molecular and genetic basis of NMDAR malfunction and how it affects the course of ADHD. We also present new therapeutic options related to treating ADHD by targeting NMDAR.

The history of Danish neuroscience

The history of Danish neuroscience starts with an account of impressive contributions made at the 17th century. Thomas Bartholin was the first Danish neuroscientist, and his disciple Nicolaus Steno became internationally one of the most prominent neuroscientists in this period. From the start, Danish neuroscience was linked to clinical disciplines. This continued in the 19th and first half of the 20th centuries with new initiatives linking basic neuroscience to clinical neurology and psychiatry in the same scientific environment. Subsequently, from the middle of the 20th century, basic neuroscience was developing rapidly within the preclinical university sector. Clinical neuroscience continued and was even reinforced during this period with important translational research and a close co-operation between basic and clinical neuroscience. To distinguish 'history' from 'present time' is not easy, as many historical events continue in present time. Therefore, we decided to consider 'History' as new major scientific developments in Denmark, which were launched before the end of the 20th century. With this aim, scientists mentioned will have been born, with a few exceptions, no later than the early 1960s. However, we often refer to more recent publications in documenting the developments of initiatives launched before the end of the last century. In addition, several scientists have moved to Denmark after the beginning of the present century, and they certainly are contributing to the present status of Danish neuroscience-but, again, this is not the History of Danish neuroscience.

DRD1 signaling modulates TrkB turnover and BDNF sensitivity in direct pathway striatal medium spiny neurons

Disturbed motor control is a hallmark of Parkinson's disease (PD). Cortico-striatal synapses play a central role in motor learning and adaption, and brain-derived neurotrophic factor (BDNF) from cortico-striatal afferents modulates their plasticity via TrkB in striatal medium spiny projection neurons (SPNs). We studied the role of dopamine in modulating the sensitivity of direct pathway SPNs (dSPNs) to BDNF in cultures of fluorescence-activated cell sorting (FACS)-enriched D1-expressing SPNs and 6-hydroxydopamine (6-OHDA)-treated rats. DRD1 activation causes enhanced TrkB translocation to the cell surface and increased sensitivity for BDNF. In contrast, dopamine depletion in cultured dSPN neurons, 6-OHDA-treated rats, and postmortem brain of patients with PD reduces BDNF responsiveness and causes formation of intracellular TrkB clusters. These clusters associate with sortilin related VPS10 domain containing receptor 2 (SORCS-2) in multivesicular-like structures, which apparently protects them from lysosomal degradation. Thus, impaired TrkB processing might contribute to disturbed motor function in PD.

Stable bulged G-quadruplexes in the human genome: identification, experimental validation and functionalization

DNA sequence composition determines the topology and stability of G-quadruplexes (G4s). Bulged G-quadruplex structures (G4-Bs) are a subset of G4s characterized by 3D conformations with bulges. Current search algorithms fail to capture stable G4-B, making their genome-wide study infeasible. Here, we introduced a large family of computationally defined and experimentally verified potential G4-B forming sequences (pG4-BS). We found 478 263 pG4-BS regions that do not overlap 'canonical' G4-forming sequences in the human genome and are preferentially localized in transcription regulatory regions including R-loops and open chromatin. Over 90% of protein-coding genes contain pG4-BS in their promoter or gene body. We observed generally higher pG4-BS content in R-loops and their flanks, longer genes that are associated with brain tissue, immune and developmental processes. Also, the presence of pG4-BS on both template and non-template strands in promoters is associated with oncogenesis, cardiovascular disease and stemness. Our G4-BS models predicted G4-forming ability in vitro with 91.5% accuracy. Analysis of G4-seq and CUT&Tag data strongly supports the existence of G4-BS conformations genome-wide. We reconstructed a novel G4-B 3D structure located in the E2F8 promoter. This study defines a large family of G4-like sequences, offering new insights into the essential biological functions and potential future therapeutic uses of G4-B.

ProBDNF signaling is involved in periodontitis-induced depression-like behavior in mouse hippocampus

OBJECTIVE

Increasing evidence supports the association between periodontitis and depression. However, the specific mechanisms remain to be further elucidated. The present study aimed to mechanistically investigate the regional roles of proBDNF (the precursor of brain-derived neurotrophic factor) in periodontitis induced depression-like behavior in mice.

METHODS

Experimental periodontitis model was established by periodontal injection of Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) in 8-week-old male Bdnf-HA/HA mice for 3 weeks. The depression-like behaviors, spontaneous exploratory activity and the level of anxiety were assessed by behavior tests. The activation of microglia and astrocytes, as well as the expression of Interleukin (IL)-1β and Tumor necrosis factor (TNF)-α in the hippocampus, prefrontal cortex, and cortex were further assessed by immunofluorescence and western blots. The levels of IL-1β in blood serum and expression of occludin as well as claudin5 in the hippocampus, prefrontal cortex, and cortex were further determined by enzyme-linked immunosorbent assay and western blot. Finally, the expression of proBDNF, its receptors, and mature BDNF (mBDNF), as well as neuronal activity were measured by western blots and immunofluorescence.

RESULTS

Pg-LPS successfully induced periodontitis in mice and caused obvious depression-like behavior. Furthermore, we observed an increased activation of astrocytes and microglia, as well as a significant increase in expression of IL-1β and TNF-α in the hippocampus of mice treated with Pg-LPS, with elevated level of IL-1β in serum and decreased expression of occludin and claudin5 in the hippocampus. Importantly, we found that the levels of proBDNF and its receptors, SorCS2 and p75NTR, were increased significantly; however, the level of mBDNF was decreased, therefor leading to greater ratio of proBDNF/mBDNF. In addition, we also detected decreased neuronal activity in the hippocampus of mice treated with Pg-LPS.

CONCLUSIONS

Our results indicate that Pg-LPS-induced periodontitis could cause depression-like behaviors in mice, and the proBDNF signaling is involved in the process.

Fructose Diet-Associated Molecular Alterations in Hypothalamus of Adolescent Rats: A Proteomic Approach

BACKGROUND

The enhanced consumption of fructose as added sugar represents a major health concern. Due to the complexity and multiplicity of hypothalamic functions, we aim to point out early molecular alterations triggered by a sugar-rich diet throughout adolescence, and to verify their persistence until the young adulthood phase.

METHODS

Thirty days old rats received a high-fructose or control diet for 3 weeks. At the end of the experimental period, treated animals were switched to the control diet for further 3 weeks, and then analyzed in comparison with those that were fed the control diet for the entire experimental period.

RESULTS

Quantitative proteomics identified 19 differentially represented proteins, between control and fructose-fed groups, belonging to intermediate filament cytoskeleton, neurofilament, pore complex and mitochondrial respiratory chain complexes. Western blotting analysis confirmed proteomic data, evidencing a decreased abundance of mitochondrial respiratory complexes and voltage-dependent anion channel 1, the coregulator of mitochondrial biogenesis PGC-1α, and the protein subunit of neurofilaments α-internexin in fructose-fed rats. Diet-associated hypothalamic inflammation was also detected. Finally, the amount of brain-derived neurotrophic factor and its high-affinity receptor TrkB, as well as of synaptophysin, synaptotagmin, and post-synaptic protein PSD-95 was reduced in sugar-fed rats. Notably, deregulated levels of all proteins were fully rescued after switching to the control diet.

CONCLUSIONS

A short-term fructose-rich diet in adolescent rats induces hypothalamic inflammation and highly affects mitochondrial and cytoskeletal compartments, as well as the level of specific markers of brain function; above-reported effects are reverted after switching animals to the control diet.

Blood transcriptome of Rasa Aragonesa rams with different sexual behavior phenotype reveals CRYL1 and SORCS2 as genes associated with this trait

Reproductive fitness of rams is seasonal, showing the highest libido during short days coinciding with the ovarian cyclicity resumption in the ewe. However, the remarkable variation in sexual behavior between rams impair farm efficiency and profitability. Intending to identify in vivo sexual behavior biomarkers that may aid farmers to select active rams, transcriptome profiling of blood was carried out by analyzing samples from 6 sexually active (A) and 6 nonactive (NA) Rasa Aragonesa rams using RNA-Seq technique. A total of 14,078 genes were expressed in blood but only four genes were differentially expressed (FDR < 0.10) in the A vs. NA rams comparison. The genes, acrosin inhibitor 1 (ENSOARG00020023278) and SORCS2, were upregulated (log2FC > 1) in active rams, whereas the CRYL1 and immunoglobulin lambda-1 light chain isoform X47 (ENSOARG00020025518) genes were downregulated (log2FC < -1) in this same group. Gene set Enrichment Analysis (GSEA) identified 428 signaling pathways, predominantly related to biological processes. The lysosome pathway (GO:0005764) was the most enriched, and may affect fertility and sexual behavior, given the crucial role played by lysosomes in steroidogenesis, being the SORCS2 gene related to this signaling pathway. Furthermore, the enriched positive regulation of ERK1 and ERK2 cascade (GO:0070374) pathway is associated with reproductive phenotypes such as fertility via modulation of hypothalamic regulation and GnRH-mediated production of pituitary gonadotropins. Furthermore, external side of plasma membrane (GO:0009897), fibrillar center (GO:0001650), focal adhesion (GO:0005925), and lamellipodium (GO:0030027) pathways were also enriched, suggesting that some molecules of these pathways might also be involved in rams' sexual behavior. These results provide new clues for understanding the molecular regulation of sexual behavior in rams. Further investigations will be needed to confirm the functions of SORCS2 and CRYL1 in relation to sexual behavior.

Loss of SORCS2 is Associated with Neuronal DNA Double-Strand Breaks

SORCS2 is one of five proteins that constitute the Vps10p-domain receptor family. Members of this family play important roles in cellular processes linked to neuronal survival, differentiation and function. Genetic and functional studies implicate SORCS2 in cognitive function, as well as in neurodegenerative and psychiatric disorders. DNA damage and DNA repair deficits are linked to ageing and neurodegeneration, and transient neuronal DNA double-strand breaks (DSBs) also occur as a result of neuronal activity. Here, we report a novel role for SORCS2 in DSB formation. We show that SorCS2 loss is associated with elevated DSB levels in the mouse dentate gyrus and that knocking out SORCS2 in a human neuronal cell line increased Topoisomerase IIβ-dependent DSB formation and reduced neuronal viability. Neuronal stimulation had no impact on levels of DNA breaks in vitro, suggesting that the observed differences may not be the result of aberrant neuronal activity in these cells. Our findings are consistent with studies linking the VPS10 receptors and DNA damage to neurodegenerative conditions.

Finding memo: versatile interactions of the VPS10p-Domain receptors in Alzheimer’s disease

The family of VPS10p-Domain (D) receptors comprises five members named SorLA, Sortilin, SorCS1, SorCS2 and SorCS3. While their physiological roles remain incompletely resolved, they have been recognized for their signaling engagements and trafficking abilities, navigating a number of molecules between endosome, Golgi compartments, and the cell surface. Strikingly, recent studies connected all the VPS10p-D receptors to Alzheimer’s disease (AD) development. In addition, they have been also associated with diseases comorbid with AD such as diabetes mellitus and major depressive disorder. This systematic review elaborates on genetic, functional, and mechanistic insights into how dysfunction in VPS10p-D receptors may contribute to AD etiology, AD onset diversity, and AD comorbidities. Starting with their functions in controlling cellular trafficking of amyloid precursor protein and the metabolism of the amyloid beta peptide, we present and exemplify how these receptors, despite being structurally similar, regulate various and distinct cellular events involved in AD. This includes a plethora of signaling crosstalks that impact on neuronal survival, neuronal wiring, neuronal polarity, and synaptic plasticity. Signaling activities of the VPS10p-D receptors are especially linked, but not limited to, the regulation of neuronal fitness and apoptosis via their physical interaction with pro- and mature neurotrophins and their receptors. By compiling the functional versatility of VPS10p-D receptors and their interactions with AD-related pathways, we aim to further propel the AD research towards VPS10p-D receptor family, knowledge that may lead to new diagnostic markers and therapeutic strategies for AD patients.

The evolution of BDNF is defined by strict purifying selection and prodomain spatial coevolution, but what does it mean for human brain disease?

Brain-Derived Neurotrophic Factor (BDNF) is an essential mediator of brain assembly, development, and maturation. BDNF has been implicated in a variety of brain disorders such as neurodevelopmental disorders (e.g., autism spectrum disorder), neuropsychiatric disorders (e.g., anxiety, depression, PTSD, and schizophrenia), and various neurodegenerative disorders (e.g., Parkinson's, Alzheimer's, etc.). To better understand the role of BDNF in disease, we sought to define the evolution of BDNF within Mammalia. We conducted sequence alignment and phylogenetic reconstruction of BDNF across a diverse selection of >160 mammalian species spanning ~177 million years of evolution. The selective evolutionary change was examined via several independent computational models of codon evolution including FEL (pervasive diversifying selection), MEME (episodic selection), and BGM (structural coevolution of sites within a single molecule). We report strict purifying selection in the main functional domain of BDNF (NGF domain, essentially comprising the mature BDNF protein). Additionally, we discover six sites in our homologous alignment which are under episodic selection in early regulatory regions (i.e. the prodomain) and 23 pairs of coevolving sites that are distributed across the entirety of BDNF. Coevolving BDNF sites exhibited complex spatial relationships and geometric features including triangular relations, acyclic graph networks, double-linked sites, and triple-linked sites, although the most notable pattern to emerge was that changes in the mature region of BDNF tended to coevolve along with sites in the prodomain. Thus, we propose that the discovery of both local and distal sites of coevolution likely reflects 'evolutionary fine-tuning' of BDNF's underlying regulation and function in mammals. This tracks with the observation that BDNF's mature domain (which encodes mature BDNF protein) is largely conserved, while the prodomain (which is linked to regulation and its own unique functionality) exhibits more pervasive and diversifying evolutionary selection. That said, the fact that negative purifying selection also occurs in BDNF's prodomain also highlights that this region also contains critical sites of sensitivity which also partially explains its disease relevance (via Val66Met and other prodomain variants). Taken together, these computational evolutionary analyses provide important context as to the origins and sensitivity of genetic changes within BDNF that may help to deconvolute the role of BDNF polymorphisms in human brain disorders.

Fading memories in aging and neurodegeneration: Is p75 neurotrophin receptor a culprit?

Aging and age-related neurodegenerative diseases have become one of the major concerns in modern times as cognitive abilities tend to decline when we get older. It is well known that the main cause of this age-related cognitive deficit is due to aberrant changes in cellular, molecular circuitry and signaling pathways underlying synaptic plasticity and neuronal connections. The p75 neurotrophin receptor (p75^NTR) is one of the important mediators regulating the fate of the neurons in the nervous system. Its importance in neuronal apoptosis is well documented. However, the mechanisms involving the regulation of p75^NTR in synaptic plasticity and cognitive function remain obscure, although cognitive impairment has been associated with a higher expression of p75^NTR in neurons. In this review, we discuss the current understanding of how neurons are influenced by p75^NTR function to maintain normal neuronal synaptic strength and connectivity, particularly to support learning and memory in the hippocampus. We then discuss the age-associated alterations in neurophysiological mechanisms of synaptic plasticity and cognitive function. Furthermore, we also describe current evidence that has begun to elucidate how p75^NTR regulates synaptic changes in aging and age-related neurodegenerative diseases, focusing on the hippocampus. Elucidating the role that p75^NTR signaling plays in regulating synaptic plasticity will contribute to a better understanding of cognitive processes and pathological conditions. This will in turn provide novel approaches to improve therapies for the treatment of neurological diseases in which p75^NTR dysfunction has been demonstrated.

Expression, purification and characterization of SORCS2 intracellular domain for structural studies

Neurotrophin signaling pathways are one of the major cascades in neuronal development and involved in many key processes including proliferation, differentiation, apoptosis, synaptic plasticity, axonal growth. In addition to the main classes of neurotrophin receptors, Trk and P75NTR, there are many auxiliary proteins, which can also bind neurotrophins and regulate the signaling pathways. The versatility of interactions between them could explain multiple and completely opposite biological outcomes such as cell survival or apoptosis. Membrane protein SorCS2, a vacuolar protein sorting 10 protein-domain receptor, interacts with P75NTR and controls the activity of Trk receptors. The abnormal functioning of SorCS2 is associated with neurodegenerative diseases, such as Alzheimer's and Huntington's disease. But the mechanism of SorCS2 activation and basis of the interaction with P75NTR has remained elusive. Herein, we describe two efficient approaches for the intracellular domain of the SorCS2 production employing bacterial and cell-free expression systems, as well as purification and refolding protocols. Finally, we characterized the purified protein by DLS and NMR and demonstrated that the protein sample is suitable for structural studies.

Association of Epigenetic Differences Screened in a Few Cases of Monozygotic Twins Discordant for Attention-Deficit Hyperactivity Disorder With Brain Structures

The present study examined the relationship between DNA methylation differences and variations in brain structures involved in the development of attention-deficit hyperactivity disorder (ADHD). First, we used monozygotic (MZ) twins discordant (2 pairs of 4 individuals, 2 boys, mean age 12.5 years) for ADHD to identify candidate DNA methylation sites involved in the development of ADHD. Next, we tried to replicate these candidates in a case-control study (ADHD: N = 18, 15 boys, mean age 10.0 years; Controls: N = 62, 40 boys, mean age 13.9 years). Finally, we examined how methylation rates at those sites relate to the degree of local structural alterations where significant differences were observed between cases and controls. As a result, we identified 61 candidate DNA methylation sites involved in ADHD development in two pairs of discordant MZ twins, among which elevated methylation at a site in the sortilin-related Vps10p domain containing receptor 2 (SorCS2) gene was replicated in the case-control study. We also observed that the ADHD group had significantly reduced gray matter volume (GMV) in the precentral and posterior orbital gyri compared to the control group and that this volume reduction was positively associated with SorCS2 methylation. Furthermore, the reduced GMV regions in children with ADHD are involved in language processing and emotional control, while SorCS2 methylation is also negatively associated with emotional behavioral problems in children. These results indicate that SorCS2 methylation might mediate a reduced GMV in the precentral and posterior orbital gyri and therefore influence the pathology of children with ADHD.

Superoxide Dismutase, BDNF, and Cognitive Improvement in Drug-Naive First-Episode Patients With Schizophrenia: A 12-Week Longitudinal Study

OBJECTIVE

Cognitive improvement after antipsychotic agents in patients with schizophrenia (SCZ) appears to involve redox regulation through neurotrophins such as brain derived neurotropic factor (BDNF). This study examined whether cognitive improvement was associated with the increase in superoxide dismutase (SOD) and whether higher levels of BDNF could have a permissive role in allowing SOD to improve cognition.

METHODS

We examined this hypothesis in 183 drug-naïve first-episode SCZ patients taking risperidone monotherapy for 12 weeks. We measured total copper-zinc SOD (CuZn-SOD), manganese SOD (Mn-SOD), and SOD activities and BDNF levels in these patients and compared their levels with 152 healthy controls. We assessed cognitive functioning and clinical symptoms at baseline and 12-week follow-up.

RESULTS

After treatment with risperidone, CuZn-SOD activity was significantly increased, and BDNF levels were slightly increased. Increased CuZn-SOD activity was associated with the cognitive effectiveness of risperidone monotherapy. The BDNF levels and SOD activities were correlated at baseline but not after 12-week treatment. Furthermore, baseline CuZn-SOD activity positively correlated with improvement on the delayed memory subscale of the Repeatable Battery for the Assessment of Neuropsychological Status only in the high BDNF subgroup.

CONCLUSIONS

Our longitudinal study suggests that risperidone can enhance SOD activity and that, in combination with higher baseline BDNF levels acting in a permissive role, can improve cognitive impairments in SCZ. Greater baseline CuZn-SOD activity also may have predictive value for cognitive improvement of delayed memory in SCZ patients receiving risperidone treatment.

Astrocytic microdomains from mouse cortex gain molecular control over long-term information storage and memory retention

Memory consolidation requires astrocytic microdomains for protein recycling; but whether this lays a mechanistic foundation for long-term information storage remains enigmatic. Here we demonstrate that persistent synaptic strengthening invited astrocytic microdomains to convert initially internalized (pro)-brain-derived neurotrophic factor (proBDNF) into active prodomain (BDNFpro) and mature BDNF (mBDNF) for synaptic re-use. While mBDNF activates TrkB, we uncovered a previously unsuspected function for the cleaved BDNFpro, which increases TrkB/SorCS2 receptor complex at post-synaptic sites. Astrocytic BDNFpro release reinforced TrkB phosphorylation to sustain long-term synaptic potentiation and to retain memory in the novel object recognition behavioral test. Thus, the switch from one inactive state to a multi-functional one of the proBDNF provides post-synaptic changes that survive the initial activation. This molecular asset confines local information storage in astrocytic microdomains to selectively support memory circuits.

Beatrice Vignoli et al. examine potential molecular mechanisms of long-term storage information in mice. Their results suggest that astrocytes may help convert neuronal BDNF precursor into active prodomain and mature forms to enhance post-synaptic signaling and memory, providing further insight into the development of memory circuits.

Systemic depletion of histone macroH2A1.1 boosts hippocampal synaptic plasticity and social behavior in mice

Gene expression and epigenetic processes in several brain regions regulate physiological processes such as cognitive functions and social behavior. MacroH2A1.1 is a ubiquitous variant of histone H2A that regulates cell stemness and differentiation in various organs. Whether macroH2A1.1 has a modulatory role in emotional behavior is unknown. Here, we employed macroH2A1.1 knock-out (^-/- ) mice to perform a comprehensive battery of behavioral tests, and an assessment of hippocampal synaptic plasticity (long-term potentiation) accompanied by whole hippocampus RNA sequencing. MacroH2A1.1^-/- mice exhibit a stunningly enhancement both of sociability and of active stress-coping behavior, reflected by the increased social behavior in social activity tests and higher mobility time in the forced swim test, respectively. They also display an increased hippocampal synaptic plasticity, accompanied by significant neurotransmission transcriptional networks changes. These results suggest that systemic depletion of histone macroH2A1.1 supports an epigenetic control necessary for hippocampal function and social behavior.

Single neonatal dexamethasone administration has long-lasting outcome on depressive-like behaviour, Bdnf, Nt-3, p75ngfr and sorting receptors (SorCS1-3) stress reactive expression

Elevated glucocorticoid level in the early postnatal period is associated with glucocorticoid therapy prescribed at preterm delivery most often has severe long-lasting neurodevelopmental and behavioural effects. Detailed molecular mechanisms of such programming action of antenatal glucocorticoids on behaviour are still poorly understood. To address this question we studied neurotrophins: Bdnf, Nt-3, Ngf and their receptors: p75ngfr, Sorcs3 expression changes after subcutaneous dexamethasone (DEX) 0.2 mg/kg injection to P2 rat pups. Neurotrophins expression level was studied in the hippocampus (HPC). Disturbances in these brain regions have been implicated in the emergence of multiple psychopathologies. p75ngfr and Sorcs3 expression was studied in the brainstem—region where monoamine neurons are located. Immunohistochemically P75NTR protein level changes after DEX were investigated in the brainstem Locus Coereleus norepinephrine neurons (NE). In the first hours after DEX administration elevation of neurotrophins expression in HPC and decline of receptor’s expression in the NE brainstem neurons were observed. Another critical time point during maturation is adolescence. Impact of elevated glucocorticoid level in the neonatal period and unpredictable stress (CMUS) at the end of adolescence on depressive-like behaviour was studied. Single neonatal DEX injection leads to decrease in depressive-like behaviour, observed in FST, independently from chronic stress. Neonatal DEX administration decreased Ntf3 and SorCS1 expression in the brainstem. Also Bdnf mRNA level in the brainstem of these animals didn’t decrease after FST. CMUS at the end of adolescence changed p75ngfr and SorCS3 expression in the brainstem in the animals that received single neonatal DEX administration.

SorCS2 is required for social memory and trafficking of the NMDA receptor

Social memory processing requires functional CA2 neurons, however the specific mechanisms that regulate their activity are poorly understood. Here, we document that SorCS2, a member of the family of the Vps10 family of sorting receptors, is highly expressed in pyramidal neurons of CA2, as well as ventral CA1, a circuit implicated in social memory. SorCS2 specifically localizes to the postsynaptic density and endosomes within dendritic spines of CA2 neurons. We have discovered that SorCS2 is a selective regulator of NMDA receptor surface trafficking in hippocampal neurons, without altering AMPA receptor trafficking. In addition, SorCS2 regulates dendritic spine density in CA2 neurons where SorCS2 expression is enriched, but not in dorsal CA1 neurons, which normally express very low levels of this protein. To specifically test the role of SorCS2 in behavior, we generated a novel SorCS2-deficient mouse, and identify a significant social memory deficit, with no change in sociability, olfaction, anxiety, or several hippocampal-dependent behaviors. Mutations in sorCS2 have been associated with bipolar disease, schizophrenia, and attention deficient-hyperactivity disorder, and abnormalities in social memory are core components of these neuropsychiatric conditions. Thus, our findings provide a new mechanism for social memory formation, through regulating synaptic receptor trafficking in pyramidal neurons by SorCS2.

Altered dopaminergic firing pattern and novelty response underlie ADHD-like behavior of SorCS2-deficient mice

Attention deficit hyperactivity disorder (ADHD) is the most frequently diagnosed neurodevelopmental disorder worldwide. Affected individuals present with hyperactivity, inattention, and cognitive deficits and display a characteristic paradoxical response to drugs affecting the dopaminergic system. However, the underlying pathophysiology of ADHD and how this relates to dopaminergic transmission remains to be fully understood. Sorcs2^-/- mice uniquely recapitulate symptoms reminiscent of ADHD in humans. Here, we show that lack of SorCS2 in mice results in lower sucrose intake, indicating general reward deficits. Using in-vivo recordings, we further find that dopaminergic transmission in the ventral tegmental area (VTA) is shifted towards a more regular firing pattern with marked reductions in the relative occurrence of irregular firing in Sorcs2^-/- mice. This was paralleled by abnormal acute behavioral responses to dopamine receptor agonists, suggesting fundamental differences in dopaminergic circuits and indicating a perturbation in the balance between the activities of the postsynaptic dopamine receptor DRD1 and the presynaptic inhibitory autoreceptor DRD2. Interestingly, the hyperactivity and drug response of Sorcs2^-/- mice were markedly affected by novelty. Taken together, our findings show how loss of a candidate ADHD-risk gene has marked effects on dopaminergic circuit function and the behavioral response to the environment.

SorCS2 Controls Functional Expression of Amino Acid Transporter EAAT3 and Protects Neurons from Oxidative Stress and Epilepsy-Induced Pathology

VPS10P domain receptors emerge as central regulators of intracellular protein sorting in neurons with relevance for various brain pathologies. Here, we identified a role for the family member SorCS2 in protection of neurons from oxidative stress and epilepsy-induced cell death. We show that SorCS2 acts as sorting receptor that sustains cell surface expression of the neuronal amino acid transporter EAAT3 to facilitate import of cysteine, required for synthesis of the reactive oxygen species scavenger glutathione. Lack of SorCS2 causes depletion of EAAT3 from the plasma membrane and impairs neuronal cysteine uptake. As a consequence, SorCS2-deficient mice exhibit oxidative brain damage that coincides with enhanced neuronal cell death and increased mortality during epilepsy. Our findings highlight a protective role for SorCS2 in neuronal stress response and provide a possible explanation for upregulation of this receptor seen in surviving neurons of the human epileptic brain.

Annexin A3 is necessary for parallel artery-vein alignment in the mouse retina

BACKGROUND

Annexin A3 (Anxa3) is a member of the calcium-regulated, cell membrane-binding family of annexin proteins. We previously confirmed that Anxa3 is expressed in the endothelial lineage in vertebrates and that loss of anxa3 in Xenopus laevis leads to embryonic blood vessel defects. However, the biological function of Anxa3 in mammals is completely unknown. In order to investigate Anxa3 vascular function in mammals, we generated an endothelial cell-specific Anxa3 conditional knockout mouse model (Anxa3f/f ;Tie2-Cre).

RESULTS

Anxa3f/f ;Tie2-Cre mice are born at Mendelian ratios and display morphologically normal blood vessels during development. However, loss of Anxa3 leads to artery-vein (AV) misalignment characterized by atypical AV crossovers in the postnatal and adult retina.

CONCLUSIONS

Anxa3 is not essential for embryonic blood vessel formation but is required for proper parallel AV alignment in the murine retina. AV crossovers associated with Anxa3f/f ;Tie2-Cre mice are similar to AV intersections observed in patients with branch retinal vein occlusion (BRVO), although we did not observe occluded vessels. This new Anxa3 mouse model may provide a basis for understanding AV crossover formation associated with BRVO.

Genome-wide association analysis of insomnia using data from Partners Biobank

Insomnia is one of the most prevalent and burdensome mental disorders worldwide, affecting between 10–20% of adults and up to 48% of the geriatric population. It is further associated with substance usage and dependence, as well other psychiatric disorders. In this study, we combined electronic health record (EHR) derived phenotypes and genotype information to conduct a genome wide analysis of insomnia in a 18,055 patient cohort. Diagnostic codes were used to identify 3,135 patients with insomnia. Our genome-wide association study (GWAS) identified one novel genomic risk locus on chromosome 8 (lead SNP rs17052966, p = 4.53 × 10⁻⁹, odds ratio = 1.28, se = 0.04). The heritability analysis indicated that common SNPs accounts for 7% (se = 0.02, p = 0.015) of phenotypic variation. We further conducted a large-scale meta-analysis of our results and summary statistics of two recent insomnia GWAS and 13 significant loci were identified. The genetic correlation analysis yielded a strong positive genetic correlation between insomnia and alcohol use (rG = 0.56, se = 0.14, p < 0.001), nicotine use (rG = 0.50, se = 0.12, p < 0.001) and opioid use (rG = 0.43, se = 0.18, p = 0.02) disorders, suggesting a significant common genetic risk factors between insomnia and substance use.

Sleep Deprivation Disrupts Acquisition of Contextual Fear Extinction by Affecting Circadian Oscillation of Hippocampal-Infralimbic proBDNF

Extensive evidence showed that mature brain-derived neurotrophic factor (mBDNF) levels displayed a circadian pattern. Circadian disruption, for example, sleep deprivation (SD), induced functional and behavioral deficits. However, compared with that of mature form, the biological role of the pro-peptide, proBDNF, was poorly understood. Here, we found that proBDNF was expressed under circadian rhythm in the ventral hippocampus (vHPC). SD rats exhibited deficits in acquisition of conditioned extinction and damped rhythmicity in vHPC proBDNF activity that were accompanied by SD between zeitgeber time (ZT)0 and ZT4, but not the late stage of sleep period. Furthermore, SD affected fear extinction through vHPC-IL proBDNF signaling, which was associated with NR2B subunits of NMDA receptors. More importantly, infusion of proBDNF could mitigate SD-induced abnormal neural activity, by suppressing the enhanced basal firing rate of IL-RS and elevating the depressed neural response that evoked by acquisition of conditioned extinction. Therefore, this finding provided the first evidence that circadian oscillation of vHPC proBDNF activity contributed to the effects of SD on acquisition of conditioned fear extinction, and suggested a new therapeutic target to reverse the cognitive deficits in sleep-related mental disorder, such as post-traumatic stress disorder (PTSD).

SorCS1-mediated sorting in dendrites maintains neurexin axonal surface polarization required for synaptic function

The pre- and postsynaptic membranes comprising the synaptic junction differ in protein composition. The membrane trafficking mechanisms by which neurons control surface polarization of synaptic receptors remain poorly understood. The sorting receptor Sortilin-related CNS expressed 1 (SorCS1) is a critical regulator of trafficking of neuronal receptors, including the presynaptic adhesion molecule neurexin (Nrxn), an essential synaptic organizer. Here, we show that SorCS1 maintains a balance between axonal and dendritic Nrxn surface levels in the same neuron. Newly synthesized Nrxn1α traffics to the dendritic surface, where it is endocytosed. Endosomal SorCS1 interacts with the Rab11 GTPase effector Rab11 family-interacting protein 5 (Rab11FIP5)/Rab11 interacting protein (Rip11) to facilitate the transition of internalized Nrxn1α from early to recycling endosomes and bias Nrxn1α surface polarization towards the axon. In the absence of SorCS1, Nrxn1α accumulates in early endosomes and mispolarizes to the dendritic surface, impairing presynaptic differentiation and function. Thus, SorCS1-mediated sorting in dendritic endosomes controls Nrxn axonal surface polarization required for proper synapse development and function.

Recent advances in understanding context-dependent mechanisms controlling neurotrophin signaling and function

Complex mechanisms control the signaling of neurotrophins through p75 NTR and Trk receptors, allowing cellular responses that are highly context dependent, particularly in the nervous system and particularly with regard to the neurotrophin brain-derived neurotrophic factor (BDNF). Recent reports describe a variety of sophisticated regulatory mechanisms that contribute to such functional flexibility. Mechanisms described include regulation of trafficking of alternative BDNF transcripts, regulation of post-translational processing and secretion of BDNF, engagement of co-receptors that influence localization and signaling of p75 NTR and Trk receptors, and control of trafficking of receptors in the endocytic pathway and during anterograde and retrograde axonal transport.

Reduced Alcohol Seeking and Withdrawal Symptoms in Mice Lacking the BDNF Receptor SorCS2

Alcohol use disorder (AUD) is characterized by repetitive and uncontrolled intake of alcohol with severe consequences for affected individuals, their families and society as a whole. Numerous studies have implicated brain-derived neurotrophic factor (BDNF) activity in the neurobiology underlying AUD. The BDNF signaling mechanism is complex and depends on two receptor systems, TrkB and p75NTR, which appear to have opposite effects on alcohol seeking behavior in animal models. We recently discovered that the sortilin-related receptor SorCS2 forms complexes with both TrkB and p75NTR and is important for BDNF activity in the developing and adult CNS. Moreover, the SORCS2 gene was recently identified as the top association signal for severity of alcohol withdrawal symptoms. Hence, we speculated that SorCS2 deficient mice would have an altered response to alcohol. The role of SorCS2 in the acute and adapted response to alcohol was therefore investigated by comparing SorCS2 knockout (Sorcs2^-/- ) mice to wild type (WT) mice in three paradigms modeling alcohol sensitivity and consumption; alcohol-induced conditioned place preference, two-bottle choice test as well as the behavioral response to alcohol withdrawal. We found that, when compared to the WT mice, (I) Sorcs2^-/- mice displayed complete lack of alcohol-induced place preference, (II) when given free choice between water and alcohol, Sorcs2^-/- mice consumed less alcohol, and (III) Sorcs2^-/- mice showed no handling-induced convulsion in response to alcohol withdrawal following extended alcohol exposure. Taken together, these results show that lack of the alcohol withdrawal risk gene Sorcs2 results in abnormal behavioral response to alcohol in mice. Consequently, SorCS2 may play an important role in the molecular pathways underlying AUD and complications associated with alcohol withdrawal.

Mechanisms That Modulate and Diversify BDNF Functions: Implications for Hippocampal Synaptic Plasticity

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that has pleiotropic effects on neuronal morphology and synaptic plasticity that underlie hippocampal circuit development and cognition. Recent advances established that BDNF function is controlled and diversified by molecular and cellular mechanisms including trafficking and subcellular compartmentalization of different Bdnf mRNA species, pre- vs. postsynaptic release of BDNF, control of BDNF signaling by tropomyosin receptor kinase B (TrkB) receptor interactors and conversion of pro-BDNF to mature BDNF and BDNF-propeptide. Defects in these regulatory mechanisms affect dendritic spine formation and morphology of pyramidal neurons as well as synaptic integration of newborn granule cells (GCs) into preexisting circuits of mature hippocampus, compromising the cognitive function. Here, we review recent findings describing novel dynamic mechanisms that diversify and locally control the function of BDNF in hippocampal neurons.

Risk Locus Identification Ties Alcohol Withdrawal Symptoms to SORCS2

BACKGROUND

Efforts to promote the cessation of harmful alcohol use are hindered by the affective and physiological components of alcohol withdrawal (AW), which can include life-threatening seizures. Although previous studies of AW and relapse have highlighted the detrimental role of stress, little is known about genetic risk factors.

METHODS

We conducted a genome-wide association study of AW symptom count in uniformly assessed subjects with histories of serious AW, followed by additional genotyping in independent AW subjects.

RESULTS

The top association signal for AW severity was in sortilin family neurotrophin receptor gene SORCS2 on chromosome 4 (European American meta-analysis n = 1,478, p = 4.3 × 10-9 ). There were no genome-wide significant findings in African Americans (n = 1,231). Bioinformatic analyses were conducted using publicly available high-throughput transcriptomic and epigenomic data sets, showing that in humans SORCS2 is most highly expressed in the nervous system. The identified SORCS2 risk haplotype is predicted to disrupt a stress hormone-modulated regulatory element that has tissue-specific activity in human hippocampus. We used human neural lineage cells to demonstrate in vitro a causal relationship between stress hormone levels and SORCS2 expression, and show that SORCS2 levels in culture are increased upon ethanol exposure and withdrawal.

CONCLUSIONS

Taken together, these findings indicate that the pathophysiology of withdrawal may involve the effects of stress hormones on neurotrophic factor signaling. Further investigation of these pathways could produce new approaches to managing the aversive consequences of abrupt alcohol cessation.

Structural insights into SorCS2-Nerve Growth Factor complex formation

Signaling of SorCS receptors by proneurotrophin ligands regulates neuronal plasticity, induces apoptosis and is associated with mental disorders. The detailed structure of SorCS2 and its extracellular specificity are unresolved. Here we report crystal structures of the SorCS2–NGF complex and unliganded SorCS2 ectodomain, revealing cross-braced SorCS2 homodimers with two NGF dimers bound in a 2:4 stoichiometry. Five out of six SorCS2 domains directly contribute to dimer formation and a C-terminal membrane proximal unreported domain, with an RNA recognition motif fold, locks the dimer in an intermolecular head-to-tail interaction. The complex structure shows an altered SorCS2 conformation indicating substantial structural plasticity. Both NGF dimer chains interact exclusively with the top face of a SorCS2 β-propeller. Biophysical experiments reveal that NGF, proNGF, and proBDNF bind at this site on SorCS2. Taken together, our data reveal a structurally flexible SorCS2 receptor that employs the large β-propeller as a ligand binding platform.

The Sortilin-related CNS-expressed receptor 2 (SorCS2)–proneurotrophin signaling system regulates neuronal plasticity and its dysfunction is linked to schizophrenia. Here the authors present the structures of the SorCS2 ectodomain alone and in complex with Nerve Growth Factor, which provides insights into SorCS2 ligand binding and signaling.

Motifome comparison between modern human, Neanderthal and Denisovan

BACKGROUND

The availability of the genomes of two archaic humans, Neanderthal and Denisovan, and that of modern humans provides researchers an opportunity to investigate genetic differences between these three subspecies on a genome-wide scale. Here we describe an algorithm that predicts statistically significant motifs based on the difference between a given motif's actual and expected distributions. The algorithm was previously applied to plants but was modified for this work.

RESULTS

The result of applying the algorithm to the human, Neanderthal, and Denisovan genomes is a catalog of potential regulatory motifs in these three human subspecies. We examined the distributions of these motifs in genetic elements including human retroviruses, human accelerated regions, and human accelerated conserved noncoding sequences regions. Differences in these distributions could be the origin of differences in phenotype between the three subspecies. Twenty significant motifs common to all three genomes were found; thirty-three were found in endogenous retroviruses in Neanderthal and Denisovan. Ten of these motifs mapped to the 22 bp core of MiR-1304. The core of this genetic element regulates the ENAM and AMTN genes, which take part in odontogenesis and whose 3' UTRs contained significant motifs. The introns of 20 genes were found to contain a large number of significant motifs, which were also overrepresented in 49 human accelerated regions. These genes include NAV2, SorCS2, TRAPPC9, GRID1, PRDM16, CAMTA1, and ASIC which are all involved in neuroregulation. Further analysis of these genes using the GO database indicates that many are associated with neurodevelopment. Also, varying numbers of significant motifs were found to occur in regions of the Neanderthal and Denisovan genomes that are missing from the human genome, suggesting further functional differences between modern and archaic humans.

CONCLUSION

Although Neanderthal and Denisovan are now extinct, detailed examination of elements from their genomes can shed light on possible phenotypic and cognitive differences between these two archaic human subspecies and modern humans. Genetic similarities and differences between these three subspecies and other fossil hominids would also be of interest.

Exploring the sortilin related receptor, SorLA, in depression

BACKGROUND

Studies of individual biomarkers for depression have shown insufficient sensitivity and specificity for clinical use, and most likely combinations of biomarkers may provide a better signature. The sorting-related receptor with A-type repeats (SorLA) is a well-studied pathogenic factor for Alzheimer's. SorLA belongs to the Vps10p domain receptor family, which also encompasses sortilin and SorCS1-3. All family members have been implicated in neurological and mental disorders. Notably, the SORCS3 gene is genome-wide significantly associated with depression and serum protein levels of sortilin are reduced in depressed individuals. SorLA regulates the activity of neurotrophic factors and cytokines and we hence speculated that SorLA might be implicated in depression.

METHODS

Serum SorLA levels were measured in two well-defined clinical samples using ELISA. Generalized linear models were used in the statistical analyses.

RESULTS

We identified a multivariate model to discriminate depressed individuals from healthy controls. Interestingly, the model consisted of serum SorLA levels and additional four predictors: previous depressive episode, stressful life events, serum levels of sortilin and VEGF. However, as an isolated factor, we observed no significant difference in SorLA levels between 140 depressed individuals and 140 healthy controls. Nevertheless, we observed a significant increase in SorLA levels following 12 weeks of treatment with nortriptyline, but not escitalopram.

LIMITATIONS

The number of biomarkers included in the multivariate model for depression and lack of replication limit our study.

CONCLUSIONS

Our results suggest SorLA as one of five factors that in combination may support the depression diagnosis, but not as an individual biomarker for depression or treatment response.

Behavioral, cellular, and synaptic tagging frameworks

Behavioral tagging is the transformation of a short-term memory induced by a weak experience into a long-term memory through temporal association with a novel experience. This phenomenon was discovered to recapitulate synaptic tagging and capture at the behavioral level. Significant progress has been made in determining the molecular machinery associated with synaptic tagging and capture and behavioral tagging theories. However, the tag setting and recruitment of plasticity-related proteins that occur within the spatiotemporally constrained cell ensemble at the network level (cellular tagging) in the brain where multimodal sensory information is input are just beginning to be understood. Here, we review the evidence for behavioral tagging and the mechanism underlying memory allocation at the network level leading to the overlap of cell ensembles. We also discuss the functional significance of overlapping cell ensembles in association of standard Pavlovian conditioning and distinct memories. Finally, we describe the role of neuronal ensemble overlap in behavioral tagging.

Highly segregated localization of the functionally related vps10p receptors sortilin and SorCS2 during neurodevelopment

Nervous system development is a precisely orchestrated series of events requiring a multitude of intrinsic and extrinsic cues. Sortilin and SorCS2 are members of the Vps10p receptor family with complementary influence on some of these cues including the neurotrophins (NTs). However, the developmental time points where sortilin and SorCS2 exert their activities in conjunction or independently still remain unclear. In this study we present the characterization of the spatiotemporal expression pattern of sortilin and SorCS2 in the developing murine nervous system. Sortilin is highly expressed in the fetal nervous system with expression localized to distinct cell populations. Expression was high in neurons of the cortical plate and developing allocortex, as well as subpallial structures. Furthermore, the neuroepithelium lining the ventricles and the choroid plexus showed high expression of sortilin, together with the developing retina, spinal ganglia, and sympathetic ganglia. In contrast, SorCS2 was confined in a marked degree to the thalamus and, at E13.5, the floor plate from midbrain rostrally to spinal cord caudally. SorCS2 was also found in the ventricular zones of the ventral hippocampus and nucleus accumbens areas, in the meninges and in Schwann cells. Hence, sortilin and SorCS2 are extensively present in several distinct anatomical areas in the developing nervous system and are rarely co-expressed. Possible functions of sortilin and SorCS2 pertain to NT signaling, axon guidance and beyond. The present data will form the basis for hypotheses and study designs for unravelling the functions of sortilin and SorCS2 during the establishment of neuronal structures and connections.

SORCS1 and SORCS3 control energy balance and orexigenic peptide production

SORCS1 and SORCS3 are two related sorting receptors expressed in neurons of the arcuate nucleus of the hypothalamus. Using mouse models with individual or dual receptor deficiencies, we document a previously unknown function of these receptors in central control of metabolism. Specifically, SORCS1 and SORCS3 act as intracellular trafficking receptors for tropomyosin-related kinase B to attenuate signaling by brain-derived neurotrophic factor, a potent regulator of energy homeostasis. Loss of the joint action of SORCS1 and SORCS3 in mutant mice results in excessive production of the orexigenic neuropeptide agouti-related peptide and in a state of chronic energy excess characterized by enhanced food intake, decreased locomotor activity, diminished usage of lipids as metabolic fuel, and increased adiposity, albeit at overall reduced body weight. Our findings highlight a novel concept in regulation of the melanocortin system and the role played by trafficking receptors SORCS1 and SORCS3 in this process.

In situ screening for postsynaptic cell adhesion molecules during synapse formation

Neuronal synapse formation is regulated by pre- and postsynaptic cell adhesion molecules. Presynaptic neurexins (NRXNs) and receptor protein tyrosine phosphatases (RPTPs; PTPδ, PTPσ and LAR in mammals) can induce postsynaptic differentiation through the interaction with various postsynaptic cell adhesion molecules. Here, we developed a novel in situ screening method to identify postsynaptic membranous proteins involved in synaptogenesis. Magnetic beads coated with the extracellular domains of NRXN1β(-S4) and PTPδ-A6 variants preferentially induced excitatory postsynaptic differentiation on the beads' surface when co-cultured with cortical neurons. After inducing postsynaptic sites on these beads, protein complexes including NRXN1β(-S4)/PTPδ-A6 and their ligands on the neuronal membrane were chemically cross-linked and purified using a magnetic separator. Liquid chromatography-tandem mass spectrometry analysis of the complexes revealed two types of postsynaptic ligands for NRXN1β(-S4) and PTPδ-A6, one has an activity to induce presynaptic differentiation in a trans manner, whereas the other has no such activity. These results suggest that synapse formation is regulated by the interplay between presynaptic NRXN/PTPδ and their postsynaptic ligands with functionally different impacts on pre- and postsynaptic differentiation. Thus, our in situ screening method for identifying synapse-organizing complexes will help to understand the molecular basis for elaborate neuronal networks.

Hidden Twins: SorCS Neuroreceptors Form Stable Dimers

SorCS1, SorCS2 and SorCS3 belong to the Vps10p-domain family of multiligand receptors. Genetic and functional studies have linked SorCS receptors to psychiatric disorders, Alzheimer's disease and type 2 diabetes, demonstrating critical roles in neuronal functionality and metabolic control. Surprisingly, their structural composition has so far not been studied. Here we have characterized SorCS1, SorCS2 and SorCS3 using biochemical methods and electron microscopy. We found that their purified extracellular domains co-exist in stable dimeric and monomeric populations. This was supported by co-immunoprecipitation experiments, where membrane-bound dimers were successfully pulled down from cell lysate. While dimers were virtually unbreakable, dimerization of the monomeric population was promoted through enzymatic deglycosylation. We conclude that post-translational modifications, specifically the degree and pattern of glycosylation, regulate the oligomeric state of the protein. Hence, cells may dictate ligand specificity by controlling the ratio between monomers and dimers and, therefore, regulate the multiple functions of SorCS receptors.

Neurotrophins and Proneurotrophins: Focus on Synaptic Activity and Plasticity in the Brain

Neurotrophins have been intensively studied and have multiple roles in the brain. Neurotrophins are first synthetized as proneurotrophins and then cleaved intracellularly and extracellularly. Increasing evidences demonstrate that proneurotrophins and mature neurotrophins exerts opposing role in the central nervous system. In the present review, we explore the role of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT3), and neurotrophin 4 (NT4) and their respective proform in cellular processes related to learning and memory. We focused on their roles in synaptic activity and plasticity in the brain with an emphasis on long-term potentiation, long-term depression, and basal synaptic transmission in the hippocampus and the temporal lobe area. We also discuss new findings on the role of the Val66Met polymorphism on the BDNF propeptide on synaptic activity.