Increased PDGFRB and NF-κB signaling caused by highly prevalent somatic mutations in intracranial aneurysms.

Intracranial aneurysms (IAs) are a high-risk factor for life-threatening subarachnoid hemorrhage. Their etiology, however, remains mostly unknown at present. We conducted screening for sporadic somatic mutations in 65 IA tissues (54 saccular and 11 fusiform aneurysms) and paired blood samples by whole-exome and targeted deep sequencing. We identified sporadic mutations in multiple signaling genes and examined their impact on downstream signaling pathways and gene expression in vitro and an arterial dilatation model in mice in vivo. We identified 16 genes that were mutated in at least one IA case and found that these mutations were highly prevalent (92%: 60 of 65 IAs) among all IA cases examined. In particular, mutations in six genes (PDGFRB, AHNAK, OBSCN, RBM10, CACNA1E, and OR5P3), many of which are linked to NF-κB signaling, were found in both fusiform and saccular IAs at a high prevalence (43% of all IA cases examined). We found that mutant PDGFRBs constitutively activated ERK and NF-κB signaling, enhanced cell motility, and induced inflammation-related gene expression in vitro. Spatial transcriptomics also detected similar changes in vessels from patients with IA. Furthermore, virus-mediated overexpression of a mutant PDGFRB induced a fusiform-like dilatation of the basilar artery in mice, which was blocked by systemic administration of the tyrosine kinase inhibitor sunitinib. Collectively, this study reveals a high prevalence of somatic mutations in NF-κB signaling pathway-related genes in both fusiform and saccular IAs and opens a new avenue of research for developing pharmacological interventions.

GPR55 contributes to neutrophil recruitment and mechanical pain induction after spinal cord compression in mice.

Pain transmission and processing in the nervous system are modulated by various biologically active substances, including lysophospholipids, through direct and indirect actions on the somatosensory pathway. Lysophosphatidylglucoside (LysoPtdGlc) was recently identified as a structurally unique lysophospholipid that exerts biological actions via the G protein-coupled receptor GPR55. Here, we demonstrated that GPR55-knockout (KO) mice show impaired induction of mechanical pain hypersensitivity in a model of spinal cord compression (SCC) without the same change in the models of peripheral tissue inflammation and peripheral nerve injury. Among these models, only SCC recruited peripheral inflammatory cells (neutrophils, monocytes/macrophages, and CD3+ T-cells) in the spinal dorsal horn (SDH), and GPR55-KO blunted these recruitments. Neutrophils were the first cells recruited to the SDH, and their depletion suppressed the induction of SCC-induced mechanical hypersensitivity and inflammatory responses in compressed SDH. Furthermore, we found that PtdGlc was present in the SDH and that intrathecal administration of an inhibitor of secretory phospholipase A2 (an enzyme required for producing LysoPtdGlc from PtdGlc) reduced neutrophil recruitment to compressed SDH and suppressed pain induction. Finally, by screening compounds from a chemical library, we identified auranofin as a clinically used drug with an inhibitory effect on mouse and human GPR55. Systemically administered auranofin to mice with SCC effectively suppressed spinal neutrophil infiltration and pain hypersensitivity. These results suggest that GPR55 signaling contributes to the induction of inflammatory responses and chronic pain after SCC via the recruitment of neutrophils and may provide a new target for reducing pain induction after spinal cord compression, such as spinal canal stenosis.

Protecting-group-free glycosylation of phosphatidic acid in aqueous media.

The glycosylation of unprotected carbohydrates has emerged as an area of significant interest because it obviates the need for long reaction sequences involving protecting-group manipulations. Herein, we report the one-pot synthesis of anomeric glycosyl phosphates through the condensation of unprotected carbohydrates with phospholipid derivatives while retaining high stereo- and regioselective control. The anomeric center was activated using 2-chloro-1,3-dimethylimidazolinium chloride to facilitate condensation with glycerol-3-phosphate derivatives in an aqueous solution. A water/propionitrile mixture provided superior stereoselectivity while maintaining good yields. Under these optimized conditions, the condensation of stable isotope-labeled glucose with phosphatidic acid provided efficient access to labeled glycophospholipids as an internal standard for mass spectrometry.

Molecular machinery regulating organelle dynamics during axon growth and guidance.

Axon growth and guidance in the developing nervous system rely on intracellular membrane dynamics that involve endosome maturation and transport, as well as its regulated tethering to the endoplasmic reticulum (ER). Recent studies have identified several key molecules, such as protrudin, which plays a dynamic role at membrane contact sites between the ER and endosomes/lysosomes, and myosin Va, which acts as a sensor for ER-derived Ca2+ that triggers peri-ER membrane export. These molecules form different types of multiprotein complexes at the interface of organelles and, in response to their surrounding microenvironments, such as Ca2+ concentrations and lipid contents, regulate the directional movement of endosomal vesicles in extending axons. Here, we review the molecular mechanisms underlying membrane dynamics and inter-organelle interactions during neuronal morphogenesis.

Selective involvement of UGGT variant: UGGT2 in protecting mouse embryonic fibroblasts from saturated lipid-induced ER stress.

Secretory proteins and lipids are biosynthesized in the endoplasmic reticulum (ER). The "protein quality control" system (PQC) monitors glycoprotein folding and supports the elimination of terminally misfolded polypeptides. A key component of the PQC system is Uridine diphosphate glucose:glycoprotein glucosyltransferase 1 (UGGT1). UGGT1 re-glucosylates unfolded glycoproteins, to enable the re-entry in the protein-folding cycle and impede the aggregation of misfolded glycoproteins. In contrast, a complementary "lipid quality control" (LQC) system that maintains lipid homeostasis remains elusive. Here, we demonstrate that cytotoxic phosphatidic acid derivatives with saturated fatty acyl chains are one of the physiological substrates of UGGT2, an isoform of UGGT1. UGGT2 produces lipid raft-resident phosphatidylglucoside regulating autophagy. Under the disruption of lipid metabolism and hypoxic conditions, UGGT2 inhibits PERK-ATF4-CHOP-mediated apoptosis in mouse embryonic fibroblasts. Moreover, the susceptibility of UGGT2 KO mice to high-fat diet-induced obesity is elevated. We propose that UGGT2 is an ER-localized LQC component that mitigates saturated lipid-associated ER stress via lipid glucosylation.

Transcriptome analysis of human neural cells derived from isogenic embryonic stem cells with 16p11.2 deletion.

16p11.2 deletion is one of the most influential copy number variations (CNVs) associated with autism spectrum disorder (ASD). Previous studies have investigated the pathophysiology of 16p11.2 deletion both in vitro and in vivo, and have identified features such as NMDAR dysfunction, excitation-inhibition imbalance, transcriptional dysregulation, and impaired cortical development. However, little is known about the transcriptional profiles of human neural cells. Here, we constructed an isogenic human embryonic stem (hES) cell model with 16p11.2 deletion using a CRISPR/Cas9 system and performed transcriptome analyses of hES-derived 2-dimensional neural cells. We identified several characteristics which may correlate with the neuropathology of 16p11.2 deletion: predisposition to differentiate into neural lineages, enhanced neurogenesis, and dysregulation of G protein-coupled receptor signaling and RAF/MAPK pathway. We also found upregulation of fragile X mental retardation protein (FMRP) target genes including GRM5, which is implicated as a common trait between 16p11.2 deletion and fragile X syndrome. Extending our knowledge into other ASD models would help us to understand the molecular pathology of this disorder.

Lipids as new players in axon guidance and circuit development.

The formation of functional neuronal circuitry depends on axon guidance, in which extracellular chemotropic cues provide directional instructions to developing axons in the embryonic nervous system. Recently lipids, in particular lysolipids, are being appraised as a new class of axon guidance cues. Most lysolipids are formed by enzymatic hydrolysis of membrane phospholipids, and signal via a wide variety of mechanisms including specific G protein-coupled receptors. For example, lysophosphatidylglucoside released from a specific type of glia activates neuronal GPR55 to regulate axon tract patterning. However, demonstrating the in vivo mechanisms of lysolipid axon guidance is often challenging and complex. Here we will review in detail lysolipids that have been identified or proposed as axon guidance cues in the developing nervous system.

Galabiosylceramide is present in human cerebrospinal fluid.

Cerebrospinal fluid (CSF) contains glycosphingolipids, including lactosylceramide (LacCer, Galß(1,4)Glcß-ceramide). LacCer and its structural isomer, galabiosylceramide (Gb2, Galα(1,4)Galß-ceramide), are classified as ceramide dihexosides (CDH). Gb2 is degraded by α-galactosidase A (GLA) in lysosomes, and genetic GLA deficiency causes Fabry disease, an X-linked lysosomal storage disorder. In patients with Fabry disease, Gb2 accumulates in organs throughout the body. While Gb2 has been reported to be in the liver, kidney, and urine of healthy individuals, its presence in CSF has not been reported, either in patients with Fabry disease or healthy controls. Here, we isolated CDH fractions from CSF of patients with idiopathic normal pressure hydrocephalus. Purified CDH fractions showed positive reaction with Shiga toxin, which specifically binds to the Galα(1,4)Galß structure. The isolated CDH fractions were analyzed by hydrophilic interaction chromatography (HILIC)-electrospray ionization tandem mass spectrometry (ESI-MS/MS). HILIC-ESI-MS/MS separated LacCer and Gb2 and revealed the presence of Gb2 and LacCer in the fractions. We also found Gb2 in CSF from neurologically normal control subjects. This is the first report to show Gb2 exists in human CSF.

Systematic synthesis of novel phosphoglycolipid analogues as potential agonists of GPR55.

Rhodopsin-like G protein-coupled receptor (GPCR) GPR55 is attracting attention as a pharmaceutical target, because of its relationship with various physiological and pathological events. Although GPR55 was initially deorphanized as a cannabinoid receptor, lysophosphatidylinositol (LPI) is now widely perceived to be an endogenous ligand of GPR55. Recently, lysophosphatidyl-ß-d-glucoside (LPGlc) has been found to act on GPR55 to repel dorsal root ganglion (DRG) neurons. In this study, we designed and synthesized various LPGlc analogues having the squaryldiamide group as potential agonists of GPR55. By the axon turning assay, several analogues exhibited similar activities to that of LPGlc. These results will provide valuable information for understanding the mode of action of LPGlc and its analogues and for the discovery of potent and selective antagonists or agonists of GPR55.

Lysolipid Chain Length Switches Agonistic to Antagonistic G Protein-Coupled Receptor Modulation.

Activation of lysolipid-sensitive G protein-coupled receptors (GPCR) depends not only on lysolipid class but also on the length and degree of saturation of their respective hydrophobic tails. Positive regulation of these signaling networks caused by the lipid chain length specificity of upstream phospholipases is firmly established. Nonagonistic lysolipid homologues, featuring incompatible lipid tails, have been suggested to indirectly modulate GPCR signaling by delaying agonist catabolism. Nonetheless, recent results seem inconsistent with this hypothesis. Utilizing a simplified lysolipid-GPCR signaling assay based on the established lysophosphatidylglucoside-GPR55 signaling axis in primary sensory neurons, we demonstrate that short-chain ligand homologues directly modulate receptor activation via a potent competitive antagonistic activity. Considering the well-documented tissue-specific concentration of lysolipid homologues, we propose that endogenous lysolipids with insufficient chain length for stable receptor activation exert an antagonistic activity, effectively representing a negative control mechanism for GPCR-associated lysolipid signaling.

Hyperactive and impulsive behaviors of LMTK1 knockout mice.

Lemur tail kinase 1 (LMTK1), previously called Apoptosis-Associated Tyrosine Kinase (AATYK), remains an uncharacterized Ser/Thr protein kinase that is predominantly expressed in the brain. It is recently reported that LMTK1A, an isoform of LMTK1, binds to recycling endosomes through its palmitoylation and regulates endosomal trafficking by suppressing the activity of Rab11 small GTPase. In neurons, knockdown or knockout of LMTK1 results in longer axons, greater branching of dendrites and increased number of spines, suggesting that LMTK1 plays a role in neuronal circuit formation. However, its in vivo function remained to be investigated. Here, we examined the brain structures and behaviors of LMTK1 knockout (KO) mice. LMTK1 was expressed in most neurons throughout the brain. The overall brain structure appeared to be normal in LMTK1 KO mice, but the numbers of synapses were increased. LMTK1 KO mice had a slight impairment in memory formation and exhibited distinct psychiatric behaviors such as hyperactivity, impulsiveness and high motor coordination without social interaction deficits. Some of these abnormal behaviors represent core features of attention deficit hyperactive disorder (ADHD), suggesting the possible involvement of LMTK1 in the pathogenesis of ADHD.

Glucocerebrosidases catalyze a transgalactosylation reaction that yields a newly-identified brain sterol metabolite, galactosylated cholesterol.

ß-Glucocerebrosidase (GBA) hydrolyzes glucosylceramide (GlcCer) to generate ceramide. Previously, we demonstrated that lysosomal GBA1 and nonlysosomal GBA2 possess not only GlcCer hydrolase activity, but also transglucosylation activity to transfer the glucose residue from GlcCer to cholesterol to form ß-cholesterylglucoside (ß-GlcChol) in vitro ß-GlcChol is a member of sterylglycosides present in diverse species. How GBA1 and GBA2 mediate ß-GlcChol metabolism in the brain is unknown. Here, we purified and characterized sterylglycosides from rodent and fish brains. Although glucose is thought to be the sole carbohydrate component of sterylglycosides in vertebrates, structural analysis of rat brain sterylglycosides revealed the presence of galactosylated cholesterol (ß-GalChol), in addition to ß-GlcChol. Analyses of brain tissues from GBA2-deficient mice and GBA1- and/or GBA2-deficient Japanese rice fish (Oryzias latipes) revealed that GBA1 and GBA2 are responsible for ß-GlcChol degradation and formation, respectively, and that both GBA1 and GBA2 are responsible for ß-GalChol formation. Liquid chromatography-tandem MS revealed that ß-GlcChol and ß-GalChol are present throughout development from embryo to adult in the mouse brain. We found that ß-GalChol expression depends on galactosylceramide (GalCer), and developmental onset of ß-GalChol biosynthesis appeared to be during myelination. We also found that ß-GlcChol and ß-GalChol are secreted from neurons and glial cells in association with exosomes. In vitro enzyme assays confirmed that GBA1 and GBA2 have transgalactosylation activity to transfer the galactose residue from GalCer to cholesterol to form ß-GalChol. This is the first report of the existence of ß-GalChol in vertebrates and how ß-GlcChol and ß-GalChol are formed in the brain.

Inositol 1,4,5-Trisphosphate Receptor Type 3 Regulates Neuronal Growth Cone Sensitivity to Guidance Signals.

During neurodevelopment, the growth cone deciphers directional information from extracellular guidance cues presented as shallow concentration gradients via signal amplification. However, it remains unclear how the growth cone controls this amplification process during its navigation through an environment in which basal cue concentrations vary widely. Here, we identified inositol 1,4,5-trisphosphate (IP3) receptor type 3 as a regulator of axonal sensitivity to guidance cues in vitro and in vivo. Growth cones lacking the type 3 subunit are hypersensitive to nerve growth factor (NGF), an IP3-dependent attractive cue, and incapable of turning toward normal concentration ranges of NGF to which wild-type growth cones respond. This is due to globally, but not asymmetrically, activated Ca2+ signaling in the hypersensitive growth cones. Remarkably, lower NGF concentrations can polarize growth cones for turning if IP3 receptor type 3 is deficient. These data suggest a subtype-specific IP3 receptor function in sensitivity adjustment during axon navigation.

Control of cell migration by the novel protein phosphatase-2A interacting protein inka2.

Cell migration is essential for many physiological and pathological processes, including embryonic development, wound healing, immune response and cancer metastasis. Inka2 transcripts are observed in migrating cells during embryonic development, suggesting the involvement of inka2 in cell migration. However, its precise role remains unclear. Here, we found that inka2 controlled focal adhesion dynamics and cell migration, likely by regulating protein phosphatase-2A (PP2A) function. A scratch assay revealed that inka2 shRNA-transfected NIH3T3 cells showed rapid wound closure, indicating an inhibitory effect by inka2 on cell migration. Live-cell imaging of NIH3T3 cells expressing EGFP-paxillin using total internal reflection fluorescence microscopy revealed that inka2 knockdown increased the turnover rate of focal adhesions. Given that PP2A, which consists of catalytic (C), regulatory (B) and scaffolding (A) subunits, is known to regulate focal adhesions, we examined the inka2-PP2A interaction. Immunoprecipitation revealed an association between inka2 and the PP2A C subunit. Binding of Inka2 to the C subunit prevented the association between the A and C subunits, suggesting that inka2 can inhibit PP2A function. Furthermore, both inka2 expression and PP2A inhibition decreased focal adhesion kinase-paxillin interaction, resulting in reduced formation of focal adhesions. We assessed the effect of pharmacological PP2A inhibition on the inka2 knockdown-induced increase in cell migration speed and found that treatment with a PP2A inhibitor negated the accelerated migration of inka2 knockdown cells. These results suggest that inka2 knockdown exerts its effects through PP2A-dependent regulation of focal adhesions. Our findings contribute to a better understanding of the molecular mechanisms underlying cell migration.

Spatially restricted long-term transgene expression in the developing skin used for studying the interaction of epidermal development and sensory innervation.

Skin development is tightly temporally coordinated with its sensory innervation, which consists of the peripheral branches of the dorsal root ganglion (DRG) axons. Various studies suggest that the skin produces a long-range attractant for the sensory axons. However, the exact identity of the guidance cue(s) remains unclear. To reveal the detailed molecular mechanism that controls DRG axon guidance and targeting, manipulation of specific skin layers at specific time points are required. To test a variety of attractants that can be expressed in specific skin layers at specific timepoints, we combined in utero electroporation with the Tol2 transposon system to induce long-term transgene expression in the developing mouse skin, including in the highly proliferative epidermal stem cells (basal layer) and their descendants (spinous and granular layer cells). The plasmid solution was injected as close to the hindpaw plantar surface as possible. Immediately, electric pulses were passed through the embryo to transduce the plasmid DNA into hindpaw skin cells. Balancing outcome measurements including: embryo survival, transfection efficiency, and the efficiency of transgene integration into host cells, we found that IUE was best performed on E13.5, and using an electroporation voltage of 34V. After immunostaining embryonic and early postnatal skin tissue sections for keratinocyte and sensory axon markers, we observe the growth of axons into skin epidermal layers including areas expressing EGFP. Therefore, this method is useful for studying the interaction between axon growth and epidermal cell division/differentiation.

Preference for Glucose over Inositol Headgroup during Lysolipid Activation of G Protein-Coupled Receptor 55.

G protein-coupled receptor 55 (GPR55) is highly expressed in brain and peripheral nervous system. Originally deorphanized as a cannabinoid receptor, recently GPR55 has been described as a lysophospholipid-responsive receptor, specifically toward lysophosphatidylinositol and lysophosphatidyl-ß-d-glucoside (LysoPtdGlc). To characterize lysolipid-GPR55 interaction, synthetic access to LysoPtdGlc and selected analogues was established utilizing a phosphorus(III)-based chemical approach. The biological activity of each synthetic lipid was assessed using a GPR55-dependent chemotropism assay in primary sensory neurons. Combined with molecular dynamics simulations the potential ligand entry port and binding pocket specifics are discussed. These results highlight the preference for gluco- over inositol- and galacto-configured headgroups.

Squaryl group modified phosphoglycolipid analogs as potential modulators of GPR55.

Lysophosphatidyl glucoside (LPGlc) is a structurally unique glycolipid that acts as a guidance cue for extending axons during central nervous system development by activating the class A G protein coupled receptor (GPR) 55 of spinal cord sensory axons. GPR55 not only plays an important role during development, but is also implicated in many disease states, rendering molecules that target GPR55 of widespread interest. In this study, we developed synthetic access to a novel class of LPGlc analogues featuring a squaryl diamide group as surrogate for the phosphodiester. We report the facile synthesis of a series of LPGlc analogues, their GPR dependent biological activity and a systematic analysis of the structure-activity relationship in regards to GPR55 modulation. The lead compound featuring identical configuration at all stereocenters compared to natural LPGlc exhibits an activity to repel axons of dorsal root ganglion (DGR) nociceptive neurons.