Identification of Potential Interacting Proteins With the Extracellular Loops of the Neuronal Glycoprotein M6a by TMT/MS

Non-synonymous single nucleotide polymorphisms (nsSNPs) within the extracellular domains of the GPM6A gene impair hippocampal neuron development

Psychiatric disorders are complex pathologies influenced by both environmental and genetic factors, ultimately leading to synaptic plasticity dysfunction. Altered expression levels of neuronal glycoprotein GPM6a or polymorphisms within the GPM6A gene are associated with neuropsychiatric disorders like schizophrenia, depression, and claustrophobia. This protein promotes neurite outgrowth, filopodia formation, dendritic spine, and synapse maintenance in vitro. Although strong evidence suggests that its extracellular domains (ECs) are responsible for its function, the molecular mechanisms linking GPM6a to the onset of such diseases remain unknown. To gain knowledge of these mechanisms, we characterized new non-synonymous polymorphisms (nsSNPs) within the ECs of GPM6a. We identified six nsSNPs (T71P, T76I, M154V, F156Y, R163Q, and T210N) that impair GPM6a-induced plasticity in neuronal cultures without affecting GPM6a expression, folding, and localization to the cell membrane. However, we observed that some of these modified GPM6a's distribution at the cell membrane. Additionally, one of the nsSNPs exhibited alterations in GPM6a oligomerization, highlighting the importance of this amino acid in establishing homophilic cis interactions. Furthermore, we observed that the ability of GPM6a's extracellular domains to interact and induce cell aggregation was significantly decreased in several of the nsSNP variants studied here. Altogether, these results provide new insights into the key residues within GPM6a's extracellular regions that are crucial for its self-association, which is essential for promoting neuronal morphogenesis. Besides, these findings highlight the importance of reverse genetics approaches to gain knowledge on GPM6a's mechanisms of action and the genetic susceptibility of certain GPM6A variants.

Mechanisms of GPM6A in Malignant Tumors

BACKGROUND

Glycoprotein M6A (GPM6A) encodes a transmembrane protein, expressing in large quantities on the cell surface of central nervous system (CNS) neurons. GPM6A acts importantly in neurodevelopment by modulating neuronal differentiation, migration, axon growth, synaptogenesis, and spine formation, but its role in malignancy remains controversial and requires further research. This article reviewed the mechanisms of GPM6A in colorectal cancer, liver cancer, lung cancer, glioblastoma, and other malignant tumors, and made a "one-stop" summary of the relevant mechanisms.

RECENT FINDINGS

Researches have indicated that GPM6A is related to malignant tumors. It affects epithelial-mesenchymal transition and induces the formation of filopodia, participating in the adhesion, migration, and metastasis of cancer cells. Its role in malignant tumors remains controversial, however. On the one hand, GPM6A may have carcinogenic properties and is related to poor prognosis of malignant tumors. It is highly expressed in lymphoblastic leukemia and is a potential oncogene. It also shows carcinogenic properties in colorectal cancer, glioblastoma, gonadotroph adenomas and so on. On the other hand, the expression of GPM6A decreases in lung adenocarcinoma, liver cancer, thyroid cancer, and so forth as the tumor progresses, and it can inhibit the progression of malignant tumors by inhibiting some signaling pathways, suggesting that it may be a tumor suppressor gene.

CONCLUSION

Carcinogenic or tumor suppressive? Although the biological function of GPM6A in the development of malignant tumors is still unclear, according to the current research progress, it is still expected to become an effective molecular marker for predicting tumor occurrence, metastasis and prognosis, as well as a new target for diagnosis and treatment.

Combined additive effects of neuronal membrane glycoprotein GPM6a and the intercellular cell adhesion molecule ICAM5 on neuronal morphogenesis

The mechanisms underlying neuronal development and synaptic formation in the brain depend on intricate cellular and molecular processes. The neuronal membrane glycoprotein GPM6a promotes neurite elongation, filopodia/spine formation, and synapse development, yet its molecular mechanisms remain unknown. Since the extracellular domains of GPM6a (ECs) command its function, we investigated the interaction between ICAM5, the neuronal member of the intercellular adhesion molecule (ICAM) family, and GPM6a's ECs. Our study aimed to explore the functional relationship between GPM6a and ICAM5 in hippocampal culture neurons and cell lines. Immunostaining of 15 days in vitro (DIV) neurons revealed significant co-localization between endogenous GPM6a clusters and ICAM5 clusters in the dendritic shaft. These results were further corroborated by overexpressing GPM6a and ICAM5 in N2a cells and hippocampal neurons at 5 DIV. Moreover, results from the co-immunoprecipitations and cell aggregation assays prove the cis and trans interaction between both proteins in GPM6a/ICAM5 overexpressing HEK293 cells. Additionally, GPM6a and ICAM5 overexpression additively enhanced neurite length, the number of neurites in N2a cells, and filopodia formation in 5 DIV neurons, indicating their cooperative role. These findings highlight the dynamic association between GPM6a and ICAM5 during neuronal development, offering insights into their contributions to neurite outgrowth, filopodia formation, and cell-cell interactions.

Astrocytic Ephrin-B1 Regulates Oligodendrocyte Development and Myelination

Astrocytes have been implicated in oligodendrocyte development and myelination, however, the mechanisms by which astrocytes regulate oligodendrocytes remain unclear. Our findings suggest a new mechanism that regulates astrocyte-mediated oligodendrocyte development through ephrin-B1 signaling in astrocytes. Using a mouse model, we examined the role of astrocytic ephrin-B1 signaling in oligodendrocyte development by deleting ephrin-B1 specifically in astrocytes during the postnatal days (P)14-P28 period and used mRNA analysis, immunohistochemistry, and mouse behaviors to study its effects on oligodendrocytes and myelination. We found that deletion of astrocytic ephrin-B1 downregulated many genes associated with oligodendrocyte development, myelination, and lipid metabolism in the hippocampus and the corpus callosum. Additionally, we observed a reduced number of oligodendrocytes and impaired myelination in the corpus callosum of astrocyte-specific ephrin-B1 KO mice. Finally, our data show reduced motor strength in these mice exhibiting clasping phenotype and impaired performance in the rotarod test most likely due to impaired myelination. Our studies provide new evidence that astrocytic ephrin-B1 positively regulates oligodendrocyte development and myelination, potentially through astrocyte-oligodendrocyte interactions.

Bulk serum extracellular vesicles from stressed mice show a distinct proteome and induce behavioral and molecular changes in naive mice

Chronic stress can trigger several pathologies including mood disorders for which no clear diagnostic molecular markers have been established yet. Attractive biomarker sources are extracellular vesicles (EVs). Evs are released by cells in health and disease and contain genetic material, proteins and lipids characteristic of the cell state. Here we show that Evs recovered from the blood of animals exposed to a repeated interrupted stress protocol (RIS) have a different protein profile compared to those obtained from control animals. Proteomic analysis indicated that proteins differentially present in bulk serum Evs from stressed animals were implicated in metabolic and inflammatory pathways and several of them were previously related to psychiatric disorders. Interestingly, these serum Evs carry brain-enriched proteins including the stress-responsive neuronal protein M6a. Then, we used an in-utero electroporation strategy to selectively overexpress M6a-GFP in brain neurons and found that M6a-GFP could also be detected in bulk serum Evs suggesting a neuronal origin. Finally, to determine if these Evs could have functional consequences, we administered Evs from control and RIS animals intranasally to naïve mice. Animals receiving stress EVs showed changes in behavior and brain M6a levels similar to those observed in physically stressed animals. Such changes could therefore be attributed, or at least in part, to EV protein transfer. Altogether these findings show that EVs may participate in stress signaling and propose proteins carried by EVs as a valuable source of biomarkers for stress-induced diseases.

Single-Cell Patch-Clamp/Proteomics of Human Alzheimer's Disease iPSC-Derived Excitatory Neurons Versus Isogenic Wild-Type Controls Suggests Novel Causation and Therapeutic Targets

Standard single-cell (sc) proteomics of disease states inferred from multicellular organs or organoids cannot currently be related to single-cell physiology. Here, a scPatch-Clamp/Proteomics platform is developed on single neurons generated from hiPSCs bearing an Alzheimer's disease (AD) genetic mutation and compares them to isogenic wild-type controls. This approach provides both current and voltage electrophysiological data plus detailed proteomics information on single-cells. With this new method, the authors are able to observe hyperelectrical activity in the AD hiPSC-neurons, similar to that observed in the human AD brain, and correlate it to ≈1400 proteins detected at the single neuron level. Using linear regression and mediation analyses to explore the relationship between the abundance of individual proteins and the neuron's mutational and electrophysiological status, this approach yields new information on therapeutic targets in excitatory neurons not attainable by traditional methods. This combined patch-proteomics technique creates a new proteogenetic-therapeutic strategy to correlate genotypic alterations to physiology with protein expression in single-cells.

Theiler's Murine Encephalomyelitis Virus Replicates in Primary Neuron Cultures and Impairs Spine Density Formation

In this study, we examined infection with the highly neurovirulent GDVII, the less neurovirulent DA strains, and with a mutant DA, which lacks the L* protein (L*-1) involved in viral persistence and demyelinating disease, to analyze the direct effects of Theiler's murine encephalomyelitis virus (TMEV) replication using primary cultures of mouse brain hippocampal neurons. All viruses replicate in cultured neurons, with GDVII having the highest titers and L*-1 the lowest. Accordingly, all were positive for viral antigen staining 3 days postinfection (dpi), and DA and L*-1 were also positive after 12 dpi. NeuN + immunostaining showed an early and almost complete absence of positive cells in cultures infected with GDVII, an approximately 50% reduction in cultures infected with DA, and fewer changes in L*-1 strains at 3 dpi. Accordingly, staining with chloromethyltetramethylrosamine orange (Mitotracker OrangeTM) as a parameter for cell viability showed similar results. Moreover, at 1 dpi, the strain DA induced higher transcript levels of neuroprotective genes such as IFN-Iβ, IRF7, and IRF8. At 3 dpi, strains GDVII and DA, but not the L*-1 mutant, showed lower PKR expression. In addition, confocal analysis showed that L*-1-infected neurons exhibited a decrease in spine density. Treatment with poly (I:C), which is structurally related to dsRNA and is known to trigger IFN type I synthesis, reduced spine density even more. These results confirmed the use of mouse hippocampal neuron cultures as a model to study neuronal responses after TMEV infection, particularly in the formation of spine density.

The Intertwining Roads between Psychological Distress and Gut Microbiota in Inflammatory Bowel Disease

Inflammatory bowel disease represents one of the most life-altering gastrointestinal pathologies, with its multifactorial nature and unclear physiopathology. The most relevant clinical forms, ulcerative colitis and Crohn's disease, clinically manifest with mild to severe flares and remission periods that alter the patient's social, familial and professional integration. The chronic inflammatory activity of the intestinal wall determines severe modifications of the local environment, such as dysbiosis, enteric endocrine, nervous and immune system disruptions and intestinal wall permeability changes. These features are part of the gastrointestinal ecosystem that modulates the bottom-to-top signaling to the central nervous system, leading to a neurobiologic imbalance and clinical affective and/or behavioral symptoms. The gut-brain link is a bidirectional pathway and psychological distress can also affect the central nervous system, which will alter the top-to-bottom regulation, leading to possible functional digestive symptoms and local inflammatory responses. In the middle of this neuro-gastrointestinal system, the microbiome is a key player, as its activities offer basic functional support for both relays. The present article presents current scientific information that links the pathophysiology and clinical aspects of inflammatory bowel disease and psychiatric symptomatology through the complex mechanism of the gut-brain axis and the modulatory effects of the gut microbiota.

Endogenous Glycoprotein GPM6a Is Involved in Neurite Outgrowth in Rat Dorsal Root Ganglion Neurons

The peripheral nervous system (PNS) has a unique ability for self-repair. Dorsal root ganglion (DRG) neurons regulate the expression of different molecules, such as neurotrophins and their receptors, to promote axon regeneration after injury. However, the molecular players driving axonal regrowth need to be better defined. The membrane glycoprotein GPM6a has been described to contribute to neuronal development and structural plasticity in central-nervous-system neurons. Recent evidence indicates that GPM6a interacts with molecules from the PNS, although its role in DRG neurons remains unknown. Here, we characterized the expression of GPM6a in embryonic and adult DRGs by combining analysis of public RNA-seq datasets with immunochemical approaches utilizing cultures of rat DRG explants and dissociated neuronal cells. M6a was detected on the cell surfaces of DRG neurons throughout development. Moreover, GPM6a was required for DRG neurite elongation in vitro. In summary, we provide evidence on GPM6a being present in DRG neurons for the first time. Data from our functional experiments support the idea that GPM6a could contribute to axon regeneration in the PNS.

Rab11 and Its Role in Neurodegenerative Diseases

Vesicles mediate the trafficking of membranes/proteins in the endocytic and secretory pathways. These pathways are regulated by small GTPases of the Rab family. Rab proteins belong to the Ras superfamily of GTPases, which are significantly involved in various intracellular trafficking and signaling processes in the nervous system. Rab11 is known to play a key role especially in recycling many proteins, including receptors important for signal transduction and preservation of functional activities of nerve cells. Rab11 activity is controlled by GEFs (guanine exchange factors) and GAPs (GTPase activating proteins), which regulate its function through modulating GTP/GDP exchange and the intrinsic GTPase activity, respectively. Rab11 is involved in the transport of several growth factor molecules important for the development and repair of neurons. Overexpression of Rab11 has been shown to significantly enhance vesicle trafficking. On the other hand, a reduced expression of Rab11 was observed in several neurodegenerative diseases. Current evidence appears to support the notion that Rab11 and its cognate proteins may be potential targets for therapeutic intervention. In this review, we briefly discuss the function of Rab11 and its related interaction partners in intracellular pathways that may be involved in neurodegenerative processes.

Assessing the effect of interaction between gut microbiome and inflammatory bowel disease on the risks of depression

Background

Gut microbiome and inflammatory bowel disease (IBD) are implicated in the development of depression, but the effect of their interactions on the risk of depression remains unclear. We aim to analyze the effect of interactions between gut microbiome and IBD on the risk of depression, and explore candidate genes involving the interactions.

Methods

Using the individual genotype and depression traits data from the UK Biobank, we calculated the polygenetic risk scores (PRS) of 114 gut microbiome, ulcerative colitis (UC), Crohn's disease (CD), and total IBD (CD + UC) respectively. The effects of interactions between gut microbiome and IBD on depression were assessed through a linear regression model. Moreover, for observed significant interactions between gut microbiome PRS and IBD PRS, PLINK software was used to test pair-wise single nucleotide polymorphisms (SNPs) interaction of corresponding gut microbiome PRS and IBD PRS on depression.

Results

We found 64 candidate interactions between gut microbiome and IBD on four phenotypes of depression, such as F_Lachnospiraceae (RNT) × (CD + UC) for patient health questionnaire-9 (PHQ-9) score (P = 1.48 × 10^-3), F_Veillonellaceae (HB) × UC for self-reported depression (P = 2.83 × 10^-3) and P_Firmicutes (RNT) × CD for age at first episode of depression (P = 8.50 × 10^-3). We observed interactions of gut-microbiome-associated SNPs × IBD-associated SNPs, such as G_Alloprevotella (HB)-associated rs147650986 (GPM6A) × IBD-associated rs114471990 (QRICH1) (P = 2.26 × 10^-4).

Conclusion

Our results support the effects of interactions between gut microbiome and IBD on depression risk, and reported several novel candidate genes for depression.

Genetic Predisposition to Schizophrenia and Depressive Disorder Comorbidity

Background: Patients with schizophrenia have an increased risk of depressive disorders compared to the general population. The comorbidity between schizophrenia and depression suggests a potential coincidence of the pathophysiology and/or genetic predictors of these mental disorders. The aim of this study was to review the potential genetic predictors of schizophrenia and depression comorbidity. Materials and Methods: We carried out research and analysis of publications in the databases PubMed, Springer, Wiley Online Library, Taylor & Francis Online, Science Direct, and eLIBRARY.RU using keywords and their combinations. The search depth was the last 10 years (2010–2020). Full-text original articles, reviews, meta-analyses, and clinical observations were analyzed. A total of 459 articles were found, of which 45 articles corresponding to the purpose of this study were analyzed in this topic review. Results: Overlap in the symptoms and genetic predictors between these disorders suggests that a common etiological mechanism may underlie the presentation of comorbid depression in schizophrenia. The molecular mechanisms linking schizophrenia and depression are polygenic. The most studied candidate genes are GRIN1, GPM6A, SEPTIN4, TPH1, TPH2, CACNA1C, CACNB2, and BCL9.Conclusion: Planning and conducting genome-wide and associative genetic studies of the comorbid conditions under consideration in psychiatry is important for the development of biological and clinical predictors and a personalized therapy strategy for schizophrenia. However, it should be recognized that the problems of predictive and personalized psychiatry in the diagnosis and treatment of schizophrenia and comorbid disorders are far from being resolved.

Neuronal Glycoprotein M6a: An Emerging Molecule in Chemical Synapse Formation and Dysfunction

The cellular and molecular mechanisms underlying neuropsychiatric and neurodevelopmental disorders show that most of them can be categorized as synaptopathies-or damage of synaptic function and plasticity. Synaptic formation and maintenance are orchestrated by protein complexes that are in turn regulated in space and time during neuronal development allowing synaptic plasticity. However, the exact mechanisms by which these processes are managed remain unknown. Large-scale genomic and proteomic projects led to the discovery of new molecules and their associated variants as disease risk factors. Neuronal glycoprotein M6a, encoded by the GPM6A gene is emerging as one of these molecules. M6a has been involved in neuron development and synapse formation and plasticity, and was also recently proposed as a gene-target in various neuropsychiatric disorders where it could also be used as a biomarker. In this review, we provide an overview of the structure and molecular mechanisms by which glycoprotein M6a participates in synapse formation and maintenance. We also review evidence collected from patients carrying mutations in the GPM6A gene; animal models, and in vitro studies that together emphasize the relevance of M6a, particularly in synapses and in neurological conditions.