Current views on regulation and function of plasticity-related genes (PRGs/LPPRs) in the brain

Neuroplasticity-related genes correlate with individual differences in distinct phases of oxycodone self-administration in male rats

Opioid use disorder (OUD) is a chronic condition associated with long-lasting molecular and behavioral changes. Animals with prolonged access to opioids develop behaviors similar to human OUD. Identifying associated molecular changes can provide insight to underpinnings that lead to or maintain OUD. In pilot studies, we identified several miRNA targets that are altered by the administration of oxycodone. We selected mir182 for follow up as it was recently shown to be dysregulated in plasma of men administered oxycodone. In addition, mir182 is increased in reward-related brain regions of male rats following exposure to various addictive substances. The present study utilizes a long-access oxycodone self-administration paradigm to examine changes in mir182 and its mRNA targets associated with neuroplasticity, which may be involved in the maintenance of OUD-like phenotype in rats. Male rats were trained to self-administer oxycodone (0.1 mg/kg/infusion, i. v.) for 6 h daily sessions for 12 days. Each animal had a yoked saline control that received matched saline infusions. Animals were then tested on a progressive ratio schedule to measure motivation to obtain a single infusion of oxycodone. Drug seeking was measured following 28 days of forced abstinence using a 90-min cued/test. RTqPCR was utilized to measure mir182 and mRNA targets related to neuroplasticity (wnt3, plppr4, pou3f3, tle4, cacna2d, and bdnf) from the nucleus accumbens. Data revealed that animals responded on a continuum for oxycodone. When divided into two groups termed high- and low responders, animals diverged during self-administration acquisition and maintained differences in behavior and gene expression throughout the study. mir182 was upregulated in the nucleus accumbens of both high and low responders and negatively correlated with tle4, which showed a strong negative correlation with reinstatement behavior. mRNA target levels were correlated with behaviors associated with increased severity of OUD behavior in male rats.

Spotlight on plasticity-related genes: Current insights in health and disease

The development of the central nervous system is highly complex, involving numerous developmental processes that must take place with high spatial and temporal precision. This requires a series of complex and well-coordinated molecular processes that are tighly controlled and regulated by, for example, a variety of proteins and lipids. Deregulations in these processes, including genetic mutations, can lead to the most severe maldevelopments. The present review provides an overview of the protein family Plasticity-related genes (PRG1-5), including their role during neuronal differentiation, their molecular interactions, and their participation in various diseases. As these proteins can modulate the function of bioactive lipids, they are able to influence various cellular processes. Furthermore, they are dynamically regulated during development, thus playing an important role in the development and function of synapses. First studies, conducted not only in mouse experiments but also in humans, revealed that mutations or dysregulations of these proteins lead to changes in lipid metabolism, resulting in severe neurological deficits. In recent years, as more and more studies have shown their involvement in a broad range of diseases, the complexity and broad spectrum of known and as yet unknown interactions between PRGs, lipids, and proteins make them a promising and interesting group of potential novel therapeutic targets.

PLPPR4 haploinsufficiency causes neurodevelopmental disorders by disrupting synaptic plasticity via mTOR signalling

Phospholipid phosphatase related 4 (PLPPR4), a neuron-specific membrane protein located at the postsynaptic density of glutamatergic synapses, is a putative regulator of neuronal plasticity. However, PLPPR4 dysfunction has not been linked to genetic disorders. In this study, we report three unrelated patients with intellectual disability (ID) or autism spectrum disorder (ASD) who harbour a de novo heterozygous copy number loss of PLPPR4 in 1p21.2p21.3, a heterozygous nonsense mutation in PLPPR4 (NM_014839, c.4C > T, p.Gln2*) and a homozygous splice mutation in PLPPR4 (NM_014839: c.408 + 2 T > C), respectively. Bionano single-molecule optical mapping confirmed PLPPR4 deletion contains no additional pathogenic genes. Our results suggested that the loss of function of PLPPR4 is associated with neurodevelopmental disorders. To test the pathogenesis of PLPPR4, peripheral blood mononuclear cells obtained from the patient with heterozygous deletion of PLPPR4 were induced to specific iPSCs (CHWi001-A) and then differentiated into neurons. The neurons carrying the deletion of PLPPR4 displayed the reduced density of dendritic protrusions, shorter neurites and reduced axon length, suggesting the causal role of PLPPR4 in neurodevelopmental disorders. As the mTOR signalling pathway was essential for regulating the axon maturation and function, we found that mTOR signalling was inhibited with a higher level of p-AKT, p-mTOR and p-ERK1/2, decreased p-PI3K in PLPPR4-iPSCs neurons. Additionally, we found silencing PLPPR4 disturbed the mTOR signalling pathway. Our results suggested PLPPR4 modulates neurodevelopment by affecting the plasticity of neurons via the mTOR signalling pathway.

Lysophosphatidic acid, a simple phospholipid with myriad functions

Lysophosphatidic acid (LPA) is a simple phospholipid consisting of a phosphate group, glycerol moiety, and only one hydrocarbon chain. Despite its simple chemical structure, LPA plays an important role as an essential bioactive signaling molecule via its specific six G protein-coupled receptors, LPA_1-6. Recent studies, especially those using genetic tools, have revealed diverse physiological and pathological roles of LPA and LPA receptors in almost every organ system. Furthermore, many studies are illuminating detailed mechanisms to orchestrate multiple LPA receptor signaling pathways and to facilitate their coordinated function. Importantly, these extensive "bench" works are now translated into the "bedside" as exemplified by approaches targeting LPA₁ signaling to combat fibrotic diseases. In this review, we discuss the physiological and pathological roles of LPA signaling and their implications for clinical application by focusing on findings revealed by in vivo studies utilizing genetic tools targeting LPA receptors.

PRG3 and PRG5 C-Termini: Important Players in Early Neuronal Differentiation

The functional importance of neuronal differentiation of the transmembrane proteins’ plasticity-related genes 3 (PRG3) and 5 (PRG5) has been shown. Although their sequence is closely related, they promote different morphological changes in neurons. PRG3 was shown to promote neuritogenesis in primary neurons; PRG5 contributes to spine induction in immature neurons and the regulation of spine density and morphology in mature neurons. Both exhibit intracellularly located C-termini of less than 50 amino acids. Varying C-termini suggested that these domains shape neuronal morphology differently. We generated mutant EGFP-fusion proteins in which the C-termini were either swapped between PRG3 and PRG5, deleted, or fused to another family member, plasticity-related gene 4 (PRG4), that was recently shown to be expressed in different brain regions. We subsequently analyzed the influence of overexpression in immature neurons. Our results point to a critical role of the PRG3 and PRG5 C-termini in shaping early neuronal morphology. However, the results suggest that the C-terminus alone might not be sufficient for promoting the morphological effects induced by PRG3 and PRG5.

Plasma membrane phospholipid phosphatase-related proteins as pleiotropic regulators of neuron growth and excitability

Neuronal plasma membrane proteins are essential for integrating cell extrinsic and cell intrinsic signals to orchestrate neuronal differentiation, growth and plasticity in the developing and adult nervous system. Here, we shed light on the family of plasma membrane proteins phospholipid phosphatase-related proteins (PLPPRs) (alternative name, PRGs; plasticity-related genes) that fine-tune neuronal growth and synaptic transmission in the central nervous system. Several studies uncovered essential functions of PLPPRs in filopodia formation, axon guidance and branching during nervous system development and regeneration, as well as in the control of dendritic spine number and excitability. Loss of PLPPR expression in knockout mice increases susceptibility to seizures, and results in defects in sensory information processing, development of psychiatric disorders, stress-related behaviors and abnormal social interaction. However, the exact function of PLPPRs in the context of neurological diseases is largely unclear. Although initially described as active lysophosphatidic acid (LPA) ecto-phosphatases that regulate the levels of this extracellular bioactive lipid, PLPPRs lack catalytic activity against LPA. Nevertheless, they emerge as atypical LPA modulators, by regulating LPA mediated signaling processes. In this review, we summarize the effects of this protein family on cellular morphology, generation and maintenance of cellular protrusions as well as highlight their known neuronal functions and phenotypes of KO mice. We discuss the molecular mechanisms of PLPPRs including the deployment of phospholipids, actin-cytoskeleton and small GTPase signaling pathways, with a focus on identifying gaps in our knowledge to stimulate interest in this understudied protein family.

PRG-1 prevents neonatal stimuli-induced persistent hyperalgesia and memory dysfunction via NSF/Glu/GluR2 signaling

Neonatal repetitive noxious stimuli (RNS) has been shown to cause long-term harmful effects on nociceptive processing, learning, and memory which persist until adulthood. Plasticity-related gene 1 (PRG-1) regulates synaptic plasticity and functional reorganization in the brain during neuronal development. In this study, neonatal RNS rats were established by repetitive needle pricks to neonatal rats on all four feet to model repetitive pain exposure in infants. Neonatal RNS caused thermal hyperalgesia, mechanical allodynia, learning, and memory impairments which manifested in young rats and persisted until adulthood. Hippocampal PRG-1/N-ethylmaleimide sensitive fusion protein (NSF) interaction was determined to be responsible for the RNS-induced impairment via enhanced extracellular glutamate release and AMPAR GluR2 trafficking deficiency in a cell-autonomous manner. These pathways likely act synergistically to cause changes in dendritic spine density. Our findings suggest that PRG-1 prevents the RNS-induced hyperalgesia, learning, and memory impairment by regulating synaptic plasticity via NSF/Glu/GluR2 signaling.

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Neonatal RNS induced hyperalgesia, learning, and memory impairment until adulthood.

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PRG-1 attenuated RNS-induced impairments by dendritic spine regulation.

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PRG-1 prevents RNS-induced impairments via NSF/Glu/GluR2 signaling.

Plasticity-Related Gene 5 Is Expressed in a Late Phase of Neurodifferentiation After Neuronal Cell-Fate Determination

During adult neurogenesis, neuronal stem cells differentiate into mature neurons that are functionally integrated into the existing network. One hallmark during the late phase of this neurodifferentiation process is the formation of dendritic spines. These morphological specialized structures form the basis of most excitatory synapses in the brain, and are essential for neuronal communication. Additionally, dendritic spines are affected in neurological disorders, such as Alzheimer’s disease or schizophrenia. However, the mechanisms underlying spinogenesis, as well as spine pathologies, are poorly understood. Plasticity-related Gene 5 (PRG5), a neuronal transmembrane protein, has previously been linked to spinogenesis in vitro. Here, we analyze endogenous expression of the PRG5 protein in different mouse brain areas, as well as on a subcellular level. We found that native PRG5 is expressed dendritically, and in high abundance in areas characterized by their regenerative capacity, such as the hippocampus and the olfactory bulb. During adult neurogenesis, PRG5 is specifically expressed in a late phase after neuronal cell-fate determination associated with dendritic spine formation. On a subcellular level, we found PRG5 not to be localized at the postsynaptic density, but at the base of the synapse. In addition, we showed that PRG5-induced formation of membrane protrusions is independent from neuronal activity, supporting a possible role in the morphology and stabilization of spines.

Histopathology is required to identify and characterize myopathies in high-throughput phenotype screening of genetically engineered mice

The development of mouse models that replicate the genetic and pathological features of human disease is important in preclinical research because these types of models enable the completion of meaningful pharmacokinetic, safety, and efficacy studies. Numerous relevant mouse models of human disease have been discovered in high-throughput screening programs, but there are important specific phenotypes revealed by histopathology that are not reliably detected by any other physiological or behavioral screening tests. As part of comprehensive phenotypic analyses of over 4000 knockout (KO) mice, histopathology identified 12 lines of KO mice with lesions indicative of an autosomal recessive myopathy. This report includes a brief summary of histological and other findings in these 12 lines. Notably, the inverted screen test detected muscle weakness in only 4 of these 12 lines (Scyl1, Plpp7, Chkb, and Asnsd1), all 4 of which have been previously recognized and published. In contrast, 6 of 8 KO lines showing negative or inconclusive findings on the inverted screen test (Plppr2, Pnpla7, Tenm1, Srpk3, Sidt2, Yif1b, Mrs2, and Pnpla2) had not been previously identified as having myopathies. These findings support the need to include histopathology in phenotype screening protocols in order to identify novel genetic myopathies that are not clinically evident or not detected by the inverted screen test.

PRG-1 relieves pain and depressive-like behaviors in rats of bone cancer pain by regulation of dendritic spine in hippocampus

Rationale: Pain and depression, which tend to occur simultaneously and share some common neural circuits and neurotransmitters, are highly prevalent complication in patients with advanced cancer. Exploring the underlying mechanisms is the cornerstone to prevent the comorbidity of chronic pain and depression in cancer patients. Plasticity-related gene 1 (PRG-1) protein regulates synaptic plasticity and brain functional reorganization during neuronal development or after cerebral lesion. Purinergic P2X7 receptor has been proposed as a therapeutic target for various pain and neurological disorders like depression in rodents. In this study, we investigated the roles of PRG-1 in the hippocampus in the comorbidity of pain and depressive-like behaviors in rats with bone cancer pain (BCP). Methods: The bone cancer pain rat model was established by intra-tibial cell inoculation of SHZ-88 mammary gland carcinoma cells. The animal pain behaviors were assessed by measuring the thermal withdrawal latency values by using radiant heat stimulation and mechanical withdrawal threshold by using electronic von Frey anesthesiometer, and depressive-like behavior was assessed by sucrose preference test and forced swim test. Alterations in the expression levels of PRG-1 and P2X7 receptor in hippocampus were separately detected by using western blot, immunofluorescence and immunohistochemistry analysis. The effects of intra-hippocampal injection of FTY720 (a PRG-1/PP2A interaction activator), PRG-1 overexpression or intra-hippocampal injection of A438079 (a selective competitive P2X₇ receptor antagonist) were also observed. Results: Carcinoma intra-tibia injection caused thermal hyperalgesia, mechanical allodynia and depressive-like behaviors in rats, and also induced the deactivation of neurons and dendritic spine structural anomalies in the hippocampus. Western blot, immunofluorescence and immunohistochemistry analysis showed an increased expression of PRG-1 and P2X₇ receptor in the hippocampus of BCP rats. Intra-hippocampal injection of FTY720 or A438079 attenuated both pain and depressive-like behaviors. Furthermore, overexpression of PRG-1 in hippocampus has similar analgesic efficacy to FTY720. In addition, they rescued neuron deactivation and dendritic spine anomalies. Conclusion: The results suggest that both PRG-1 and P2X₇ receptor in the hippocampus play important roles in the development of pain and depressive-like behaviors in bone cancer condition in rats by dendritic spine regulation via P2X₇R/PRG-1/PP2A pathway.

Systematic expression analysis of plasticity-related genes in mouse brain development brings PRG4 into play

BACKGROUND

Plasticity-related genes (Prgs/PRGs) or lipid phosphate phosphatase-related proteins (LPPRs) comprise five known members, which have been linked to neuronal differentiation processes, such as neurite outgrowth, axonal branching, or dendritic spine formation. PRGs are highly brain-specific and belong to the lipid phosphate phosphatases (LPPs) superfamily, which influence lipid metabolism by dephosphorylation of bioactive lipids. PRGs, however, do not possess enzymatic activity, but modify lipid metabolism in a way that is still under investigation.

RESULTS

We analyzed mRNA expression levels of all Prgs during mouse brain development, in the hippocampus, neocortex, olfactory bulbs, and cerebellum. We found different spatio-temporal expression patterns for each of the Prgs, and identified a high expression of the uncharacterized Prg4 throughout brain development. Unlike its close family members PRG3 and PRG5, PRG4 did not induce filopodial outgrowth in non-neuronal cell lines, and does not localize to the plasma membrane of filopodia.

CONCLUSION

We showed PRG4 to be highly expressed in the developing and the adult brain, suggesting that it is of vital importance for normal brain function. Despite its similarities to other family members, it seems not to be involved in changes of cell morphology; instead, it is more likely to be associated with intracellular signaling.

RNA splicing and aggregate gene expression differences in lung squamous cell carcinoma between patients of West African and European ancestry

OBJECTIVES

Despite disparities in lung cancer incidence and mortality, the molecular landscape of lung cancer in patients of African ancestry remains underexplored, and race-related differences in RNA splicing remain unexplored.

MATERIALS AND METHODS

We identified differentially spliced genes (DSGs) and differentially expressed genes (DEGs) in biobanked lung squamous cell carcinoma (LUSC) between patients of West African and European ancestry, using ancestral genotyping and Affymetrix Clariom D array. DSGs and DEGs were validated independently using the National Cancer Institute Genomic Data Commons. Associated biological processes, overlapping canonical pathways, enriched gene sets, and cancer relevance were identified using Gene Ontology Consortium, Ingenuity Pathway Analysis, Gene Set Enrichment Analysis, and CancerMine, respectively. Association with LUSC survival was conducted using The Cancer Genome Atlas.

RESULTS

4,829 DSGs and 267 DEGs were identified, including novel targets in NSCLC as well as genes identified previously to have relevance to NSCLC. RNA splicing events within 3 DSGs as well as 1 DEG were validated in the independent cohort. 853 DSGs and 29 DEGs have been implicated as potential drivers, oncogenes and/or tumor suppressor genes. Biological processes enriched among DSGs and DEGs included metabolic process, biological regulation, and multicellular organismal process and, among DSGs, ion transport. Overlapping canonical pathways among DSGs included neuronal signaling pathways and, among DEGs, cell metabolism involving biosynthesis. Gene sets enriched among DSGs included KRAS Signaling, UV Response, E2 F Targets, Glycolysis, and Coagulation. 355 RNA splicing events within DSGs and 18 DEGs show potential association with LUSC patient survival.

CONCLUSION

These DSGs and DEGs, which show potential biological and clinical relevance, could have the ability to drive novel biomarker and therapeutic development to mitigate LUSC disparities.

Lysophosphatidic Acid Signalling in Nervous System Development and Function

One class of molecules that are now coming to be recognized as essential for our understanding of the nervous system are the lysophospholipids. One of the major signaling lysophospholipids is lysophosphatidic acid, also known as LPA. LPA activates a variety of G protein-coupled receptors (GPCRs) leading to a multitude of physiological responses. In this review, I describe our current understanding of the role of LPA and LPA receptor signaling in the development and function of the nervous system, especially the central nervous system (CNS). In addition, I highlight how aberrant LPA receptor signaling may underlie neuropathological conditions, with important clinical application.

The Axonal Membrane Protein PRG2 Inhibits PTEN and Directs Growth to Branches

In developing neurons, phosphoinositide 3-kinases (PI3Ks) control axon growth and branching by positively regulating PI3K/PI(3,4,5)P₃, but how neurons are able to generate sufficient PI(3,4,5)P₃ in the presence of high levels of the antagonizing phosphatase PTEN is difficult to reconcile. We find that normal axon morphogenesis involves homeostasis of elongation and branch growth controlled by accumulation of PI(3,4,5)P₃ through PTEN inhibition. We identify a plasma membrane-localized protein-protein interaction of PTEN with plasticity-related gene 2 (PRG2). PRG2 stabilizes membrane PI(3,4,5)P₃ by inhibiting PTEN and localizes in nanoclusters along axon membranes when neurons initiate their complex branching behavior. We demonstrate that PRG2 is both sufficient and necessary to account for the ability of neurons to generate axon filopodia and branches in dependence on PI3K/PI(3,4,5)P₃ and PTEN. Our data indicate that PRG2 is part of a neuronal growth program that induces collateral branch growth in axons by conferring local inhibition of PTEN.

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Neuronal axon growth and branching is globally regulated by PI3K/PTEN signaling

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PRG2 inhibits PTEN and stabilizes PIP3 and F-actin

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PRG2 localizes to nanoclusters on the axonal membrane and coincides with branching

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PRG2 promotes axonal filopodia and branching dependent on PI3K/PTEN

Harnessing PTEN's Growth Potential in Neuronal Development and Disease

PTEN is a powerful regulator of neuronal growth. It globally suppresses axon extension and branching during both nervous system development and regeneration, by antagonizing growth-promoting PI3K/PI(3,4,5)P3 signaling. We recently identified that the transmembrane protein PRG2/LPPR3 functions as a modulator of PTEN function during axon morphogenesis. Our work demonstrates that through inhibition of PTEN activity, PRG2 stabilizes membrane PI(3,4,5)P3. In turn, PRG2 deficiency attenuates the formation of branches in a PTEN-dependent manner, albeit without affecting the overall growth capacity of extending axons. Thus, PRG2 is poised to temporally and locally relieve growth suppression mediated by PTEN in neurons and, in effect, to redirect growth specifically to axonal branches. In this commentary, we discuss potential implications and unresolved questions regarding the regulation of axonal PTEN in neurons. Given their widespread implication during neuronal development and regeneration, identification of mechanisms that confer spatiotemporal control of PTEN may unveil new approaches to reprogram PI3K signaling in neurodevelopmental disorders and regeneration research.

Transcriptome profiling reveals signaling conditions dictating human spermatogonia fate in vitro

Spermatogonial stem cells (SSCs) are essential for the generation of sperm and have potential therapeutic value for treating male infertility, which afflicts >100 million men world-wide. While much has been learned about rodent SSCs, human SSCs remain poorly understood. Here, we molecularly characterize human SSCs and define conditions favoring their culture. To achieve this, we first identified a cell-surface protein, PLPPR3, that allowed purification of human primitive undifferentiated spermatogonia (uSPG) highly enriched for SSCs. Comparative RNA-sequencing analysis of these enriched SSCs with differentiating SPG (KIT⁺ cells) revealed the full complement of genes that shift expression during this developmental transition, including genes encoding key components in the TGF-β, GDNF, AKT, and JAK-STAT signaling pathways. We examined the effect of manipulating these signaling pathways on cultured human SPG using both conventional approaches and single-cell RNA-sequencing analysis. This revealed that GDNF and BMP8B broadly support human SPG culture, while activin A selectively supports more advanced human SPG. One condition-AKT pathway inhibition-had the unique ability to selectively support the culture of primitive human uSPG. This raises the possibility that supplementation with an AKT inhibitor could be used to culture human SSCs in vitro for therapeutic applications.

A Membranome-Centered Approach Defines Novel Biomarkers for Cellular Subtypes in the Intervertebral Disc

OBJECTIVE

Lack of specific marker-sets prohibits definition and functional distinction of cellular subtypes in the intervertebral disc (IVD), such as those from the annulus fibrosus (AF) and the nucleus pulposus (NP).

DESIGN

We recently generated immortalized cell lines from human NP and AF tissues; these comprise a set of functionally distinct clonal subtypes. Whole transcriptome analyses were performed of 12 phenotypically distinct clonal cell lines (4× NP-Responder, 4× NP-nonResponder, 2× AF-Sheet forming, and 2× AF-nonSheet forming). Data sets were filtered for membrane-associated marker genes and compared to literature.

RESULTS

Comparison of our immortal cell lines to published primary NP, AF, and articular chondrocytes (AC) transcriptome datasets revealed preservation of AF and NP phenotypes. NP-specific membrane-associated genes were defined by comparison to AF cells in both the primary dataset (46 genes) and immortal cell-lines (161 genes). Definition of AF-specific membrane-associated genes yielded 125 primary AF cell and 92 immortal cell-line markers. Overlap between primary and immortal NP cells yielded high-confidence NP-specific marker genes for NP-R (CLDN11, TMEFF2, CA12, ANXA2, CD44) and NP-nR (EFNA1, NETO2, SLC2A1). Overlap between AF and immortal AF subtypes yielded specific markers for AF-S (COLEC12, LPAR1) and AF-nS (CHIC1).

CONCLUSIONS

The current study provides a reference platform for preclinical evaluation of novel membrane-associated cell type-specific markers in the IVD. Future research will focus on their biological relevance for IVD function in development, homeostasis, and degenerate conditions.

Co-expression of TIMP-1 and its cell surface binding partner CD63 in glioblastomas

Background

We have previously identified tissue inhibitor of metalloproteinases-1 (TIMP-1) as a prognostic marker in glioblastomas. TIMP-1 has been associated with chemotherapy resistance, and CD63, a known TIMP-1-binding protein, has been suggested to be responsible for this effect. The aim of this study was to assess CD63 expression in astrocytomas focusing on the prognostic potential of CD63 alone and in combination with TIMP-1.

Methods

CD63 expression was investigated immunohistochemically in a cohort of 111 astrocytomas and correlated to tumor grade and overall survival by semi-quantitative scoring. CD63 expression in tumor-associated microglia/macrophages was examined by double-immunofluorescence with ionized calcium-binding adapter molecule 1 (Iba1). The association between CD63 and TIMP-1 was investigated using previously obtained TIMP-1 data from our astrocytoma cohort. Cellular co-expression of TIMP-1 and CD63 as well as TIMP-1 and the tumor stem cell-related markers CD133 and Sox2 was investigated with immunofluorescence. TIMP-1 and CD63 protein interaction was detected by an oligonucleotide-based proximity ligation assay and verified using co-immunoprecipitation.

Results

The expression of CD63 was widely distributed in astrocytomas with a significantly increased level in glioblastomas. CD63 levels did not significantly correlate with patient survival at a protein level, and CD63 did not augment the prognostic significance of TIMP-1. Up to 38% of the CD63+ cells expressed Iba1; however, Iba1 did not appear to impact the prognostic value of CD63. A significant correlation was found between TIMP-1 and CD63, and the TIMP-1 and CD63 proteins were co-expressed at the cellular level and located in close molecular proximity, suggesting that TIMP-1 and CD63 could be co-players in glioblastomas. Some TIMP-1+ cells expressed CD133 and Sox2.

Conclusion

The present study suggests that CD63 is highly expressed in glioblastomas and that TIMP-1 and CD63 interact. CD63 does not add to the prognostic value of TIMP-1. Co-expression of TIMP-1 and stem cell markers as well as the wide expression of CD63 might suggest a role for TIMP-1 and CD63 in glioblastoma stemness.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4179-y) contains supplementary material, which is available to authorized users.

Dysregulation of zinc/lipid metabolism‑associated genes in the rat hippocampus and cerebral cortex in early adulthood following recurrent neonatal seizures

Although it has been established that recurrent or prolonged clinical seizures during infancy may cause lifelong brain damage, the underlying molecular mechanism is still not well elucidated. The present study, to the best of our knowledge, is the first to investigate the expression of twenty zinc (Zn)/lipid metabolism-associated genes in the hippocampus and cerebral cortex of rats following recurrent neonatal seizures. In the current study, 6-day-old Sprague-Dawley rats were randomly divided into control (CONT) and recurrent neonatal seizure (RS) groups. On postnatal day 35 (P35), mossy fiber sprouting and gene expression were assessed by Timm staining and reverse transcription-quantitative polymerase chain reaction, respectively. Of the twenty genes investigated, seven were significantly downregulated, while four were significantly upregulated in the RS group compared with CONT rats, which was observed in the hippocampus but not in the cerebral cortex. Meanwhile, aberrant mossy fiber sprouting was observed in the supragranular region of the dentate gyrus and Cornu Ammonis 3 subfield of the hippocampus in the RS group. In addition, linear correlation analysis identified significant associations between the expression of certain genes in the hippocampus, which accounted for 40% of the total fifty-five gene pairs among the eleven regulated genes. However, only eight gene pairs in the cerebral cortex exhibited significant positive associations, which accounted for 14.5% of the total. The results of the present study indicated the importance of hippocampal Zn/lipid metabolism-associated genes in recurrent neonatal seizure-induced aberrant mossy fiber sprouting, which may aid the identification of novel potential targets during epileptogenesis.

Synaptic lipids in cortical function and psychiatric disorders

Psychiatric disorders, which include a variety of distinct infirmities, affect millions of people worldwide. Without intervention, the impact of these conditions is devastating, compromising the daily life of patients and their relatives. Although insights into the underlying cortical circuitry of psychiatric diseases have emerged over the years, our understanding of their pathophysiology, elucidation of pathophysiologic mechanisms and relevant advancements in clinical therapeutic strategies have been hampered by the complexity of these neural networks and the lack of reliable biomarkers in human subjects and animal models. In this issue of EMBO Molecular Medicine, Vogt and colleagues add significant new insights to the understanding of the etiology of psychiatric conditions by revealing novel contribution of synaptic lipids to altered circuit function and behavior in mice (Vogt et al, 2016).

Tumor DNA in cerebral spinal fluid reflects clinical course in a patient with melanoma leptomeningeal brain metastases

Cerebral spinal fluid (CSF) from brain tumor patients contains tumor cellular and cell-free DNA (cfDNA), which provides a less-invasive and routinely accessible method to obtain tumor genomic information. In this report, we used droplet digital PCR to test mutant tumor DNA in CSF of a patient to monitor the treatment response of metastatic melanoma leptomeningeal disease (LMD). The primary melanoma was known to have a BRAF (V600E) mutation, and the patient was treated with whole brain radiotherapy and BRAF inhibitors. We collected 9 CSF samples over 6 months. The mutant cfDNA fraction gradually decreased from 53 % (time of diagnosis) to 0 (time of symptom alleviation) over the first 6 time points. Three months after clinical improvement, the patient returned with severe symptoms and the mutant cfDNA was again detected in CSF at high levels. The mutant DNA fraction corresponded well with the patient's clinical response. We used whole exome sequencing to examine the mutation profiles of the LMD tumor DNA in CSF before therapeutic response and after disease relapse, and discovered a canonical cancer mutation PTEN (R130*) at both time points. The cellular and cfDNA revealed similar mutation profiles, suggesting cfDNA is representative of LMD cells. This study demonstrates the potential of using cellular or cfDNA in CSF to monitor treatment response for LMD.

NT-3 protein levels are enhanced in the hippocampus of PRG1-deficient mice but remain unchanged in PRG1/LPA2 double mutants

The plasticity-related gene 1 (PRG1) modulates bioactive lipids at the postsynaptic density and is a novel player in neuronal plasticity and regulation of glutamatergic transmission at principal neurons. PRG1, a neuronal molecule, is highly expressed during development and regeneration processes at the postsynaptic density, modulates synaptic lysophosphatidic acid (LPA) levels and is related to epilepsy and brain injury. In the present study, we analyzed the interaction between the synaptic molecules PRG1 and LPA2R with other plasticity-related molecules the neurotrophins. The protein levels of NGF, BDNF and NT-3 were measured using ELISA in hippocampal tissue of homozygous (PRG(-/-)) and heterozygous (PRG(+/-)) PRG1 deficient mice and compared to their wild type (PRG(+/+)/WT) littermates. In the hippocampus, protein levels of NT-3 were significantly increased in PRG(-/-) mice (compared to WT-litters) while protein levels of NGF and BDNF were not affected. Since PRG1 deficiency leads to increased neuronal excitability and higher hippocampal network activity, which may well influence neurotrophin levels, we further assessed PRG1 deficient mice on an LPA2-receptor (LPA2R) deficient background, reported to normalize hippocampal over-excitability in PRG1(-/-) mice. However, on an LPA2R deficient background, protein levels of NT-3 in PRG1(-/-) mice (PRG1(-/-)/LPA2R(-/-)) were not significantly different when compared to WT animals. Since PRG1 deficient mice showed over-excitability in glutamatergic neurons. This was normalized by additional LPA2R deletion, and we conclude the increased NT3-levels were directly or indirectly attributable to increased hippocampal network activity, possibly exerting a protective effect against over-excitability.

Cooperative interactions of LPPR family members in membrane localization and alteration of cellular morphology

The lipid phosphate phosphatase-related proteins (LPPRs), also known as plasticity-related genes (PRGs), are classified as a new brain-enriched subclass of the lipid phosphate phosphatase (LPP) superfamily. They induce membrane protrusions, neurite outgrowth or dendritic spine formation in cell lines and primary neurons. However, the exact roles of LPPRs and the mechanisms underlying their effects are not certain. Here, we present the results of a large-scale proteome analysis to determine LPPR1-interacting proteins using co-immunoprecipitation coupled to mass spectrometry. We identified putative LPPR1-binding proteins involved in various biological processes. Most interestingly, we identified the interaction of LPPR1 with its family member LPPR3, LPPR4 and LPPR5. Their interactions were characterized by co-immunoprecipitation and colocalization analysis using confocal and super-resolution microscopy. Moreover, co-expressing two LPPR members mutually elevated their protein levels, facilitated their plasma membrane localization and resulted in an increased induction of membrane protrusions as well as the phosphorylation of S6 ribosomal protein. Taken together, we revealed a new functional cooperation between LPPR family members and discovered for the first time that LPPRs likely exert their function through forming complex with its family members.

Lysophosphatidic Acid signaling in the nervous system

The brain is composed of many lipids with varied forms that serve not only as structural components but also as essential signaling molecules. Lysophosphatidic acid (LPA) is an important bioactive lipid species that is part of the lysophospholipid (LP) family. LPA is primarily derived from membrane phospholipids and signals through six cognate G protein-coupled receptors (GPCRs), LPA1-6. These receptors are expressed on most cell types within central and peripheral nervous tissues and have been functionally linked to many neural processes and pathways. This Review covers a current understanding of LPA signaling in the nervous system, with particular focus on the relevance of LPA to both physiological and diseased states.

Association of new deletion/duplication region at chromosome 1p21 with intellectual disability, severe speech deficit and autism spectrum disorder-like behavior: an all-in approach to solving the DPYD enigma

We describe an as yet unreported neocentric small supernumerary marker chromosome (sSMC) derived from chromosome 1p21.3p21.2. It was present in 80% of the lymphocytes in a male patient with intellectual disability, severe speech deficit, mild dysmorphic features, and hyperactivity with elements of autism spectrum disorder (ASD).

Several important neurodevelopmental genes are affected by the 3.56 Mb copy number gain of 1p21.3p21.2, which may be considered reciprocal in gene content to the recently recognized 1p21.3 microdeletion syndrome. Both 1p21.3 deletions and the presented duplication display overlapping symptoms, fitting the same disorder category. Contribution of coding and non-coding genes to the phenotype is discussed in the light of cellular and intercellular homeostasis disequilibrium. In line with this the presented 1p21.3p21.2 copy number gain correlated to 1p21.3 microdeletion syndrome verifies the hypothesis of a cumulative effect of the number of deregulated genes - homeostasis disequilibrium leading to overlapping phenotypes between microdeletion and microduplication syndromes.

Although miR-137 appears to be the major player in the 1p21.3p21.2 region, deregulation of the DPYD (dihydropyrimidine dehydrogenase) gene may potentially affect neighboring genes underlying the overlapping symptoms present in both the copy number loss and copy number gain of 1p21. Namely, the all-in approach revealed that DPYD is a complex gene whose expression is epigenetically regulated by long non-coding RNAs (lncRNAs) within the locus. Furthermore, the long interspersed nuclear element-1 (LINE-1) L1MC1 transposon inserted in DPYD intronic transcript 1 (DPYD-IT1) lncRNA with its parasites, TcMAR-Tigger5b and pair of Alu repeats appears to be the “weakest link” within the DPYD gene liable to break. Identification of the precise mechanism through which DPYD is epigenetically regulated, and underlying reasons why exactly the break (FRA1E) happens, will consequently pave the way toward preventing severe toxicity to the antineoplastic drug 5-fluorouracil (5-FU) and development of the causative therapy for the dihydropyrimidine dehydrogenase deficiency.

Plasticity-related gene 5 promotes spine formation in murine hippocampal neurons

The transmembrane protein plasticity-related genes 3 and 5 (PRG3 and PRG5) increase filopodial formation in various cell lines, independently of Cdc42. However, information on the effects of PRG5 during neuronal development is sparse. Here, we present several lines of evidence for the involvement of PRG5 in the genesis and stabilization of dendritic spines. First, PRG5 was strongly expressed during mouse brain development from embryonic day 14 (E14), peaked around the time of birth, and remained stable at least until early adult stages (i.e. P30). Second, on a subcellular level, PRG5 expression shifted from an equal distribution along all neurites toward accumulation only along dendrites during hippocampal development in vitro. Third, overexpression of PRG5 in immature hippocampal neurons induced formation of spine-like structures ahead of time. Proper amino acid sequences in the extracellular domains (D1 to D3) of PRG5 were a prerequisite for trafficking and induction of spine-like structures, as shown by mutation analysis. Fourth, at stages when spines are present, knockdown of PRG5 reduced the number but not the length of protrusions. This was accompanied by a decrease in the number of excitatory synapses and, consequently, by a reduction of miniature excitatory postsynaptic current frequencies, although miniature excitatory postsynaptic current amplitudes remained similar. In turn, overexpressing PRG5 in mature neurons not only increased Homer-positive spine numbers but also augmented spine head diameters. Mechanistically, PRG5 interacts with phosphorylated phosphatidylinositols, phospholipids involved in dendritic spine formation by different lipid-protein assays. Taken together, our data propose that PRG5 promotes spine formation.