Involvement of membrane protein GDE2 in retinoic acid-induced neurite formation in Neuro2A cells

Promotion of neurite outgrowth by 3,5,7,3',4'-pentamethoxyflavone is mediated through ERK signaling pathway in Neuro2a cells

In this study, the effects of 3,5,7,3',4'-pentamethoxyflavone (KP1), a major bioactive ingredient isolated from the Kaempferia parviflora rhizomes, on a neurite outgrowth in Neuro2a cells and its mechanism have been investigated. KP1 increased concentration-dependently the percentage of neurite-bearing cells. KP1 showed a remarkable capability to elicit neurite outgrowth in Neuro2a cells, as evidenced by morphological alterations and immunostaining using anti-class III β-tubulin and anti-NeuN antibodies. KP1 also displayed a higher neurogenic activity than retinoic acid (RA), a promoter of neurite outgrowth in Neuro2a cells. KP1 treatment caused significant elevation in phosphorylation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38 MAPK) and glycogen synthase kinase-3β (GSK-3β). However, KP1-triggered neurite outgrowth was markedly inhibited by treatment with the ERK inhibitor U0126, whereas p38 MAPK inhibitor SB203580 and GSK-3β inhibitor SB216763 did not influence KP1-induced neurite outgrowth. These results demonstrate that KP1 elicits neurite outgrowth and triggers cell differentiation of Neuro2a cells through ERK signal pathway.

An independent regulator of global release pathways in astrocytes generates a subtype of extracellular vesicles required for postsynaptic function

Extracellular vesicles (EVs) are heterogeneous in size, composition, and function. We show that the six-transmembrane protein glycerophosphodiester phosphodiesterase 3 (GDE3) regulates actin remodeling, a global EV biogenic pathway, to release an EV subtype with distinct functions. GDE3 is necessary and sufficient for releasing EVs containing annexin A1 and GDE3 from the plasma membrane via Wiskott-Aldrich syndrome protein family member 3 (WAVE3), a major regulator of actin dynamics. GDE3 is expressed in astrocytes but not neurons, yet mice lacking GDE3 [Gde3 knockout (KO)] have decreased miniature excitatory postsynaptic current (mEPSC) amplitudes in hippocampal CA1 neurons. EVs from cultured wild-type astrocytes restore mEPSC amplitudes in Gde3 KOs, while EVs from Gde3 KO astrocytes or astrocytes inhibited for WAVE3 actin branching activity do not. Thus, GDE3-WAVE3 is a nonredundant astrocytic pathway that remodels actin to release a functionally distinct EV subtype, supporting the concept that independent regulation of global EV release pathways differentially regulates EV signaling within the cellular EV landscape.

GDPD5 Related to Lipid Metabolism Is a Potential Prognostic Biomarker in Neuroblastoma

Neuroblastoma (NB) is an extracranial solid tumor in children with poor prognosis in high-risk patients and its pathogenesis and prognostic markers urgently need to be explored. This study aimed to explore potential biomarkers related to NB from the aspect of lipid metabolism. Fifty-eight lipid metabolism-related differentially expressed genes between high-risk NB and non-high-risk NB in the GSE49710 dataset were analyzed using bioinformatics, including 45 down-regulated genes and 13 up-regulated genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified steroid hormone biosynthesis as an abnormal metabolic pathway in high-risk NB. Survival analysis established a three-gene prognostic model, including ACHE, GDPD5 and PIK3R1. In the test data, the AUCs of the established prognostic models used to predict patient survival at 1, 3 and 5 years were 0.84, 0.90 and 0.91, respectively. Finally, in the SH-SY5Y cell line, it was verified that overexpression of GDPD5 can inhibit cell proliferation and migration, as well as affect the lipid metabolism of SH-SY5Y, but not the sugar metabolism. hsa-miR-592 was predicted to be a potential target miRNA of GDPD5 by bioinformatics. In conclusion, this study develops a lipid-metabolism-related gene-based prognostic model for NB and demonstrates that GDPD5 inhibits SH-SY5Y proliferation and migration and may be targeted by hsa-miR-592 and inhibit SH-SY5Y fat synthesis.

Alterations of serine racemase expression determine proliferation and differentiation of neuroblastoma cells

Although the role of serine racemase (SR) in neuropsychiatric disorders has been extensively studied, its role in cell proliferation and differentiation remains unclear. Deletion of Srr, the encoding gene for SR, has been shown to reduce dendritic arborization and dendritic spine density in the brains of adult mice, whereas increased SR levels have been associated with differentiation in cell cultures. Previously, we demonstrated that valproic acid induces differentiation in the N2A neuroblastoma cell line, and that this differentiation is associated with increased SR expression. These observations suggest that SR may have a role in cell proliferation and differentiation. We herein found that both valproic acid and all-trans retinoic acid induced N2A differentiation. In contrast, knockdown of SR reduced levels of differentiation, increased N2A proliferation, promoted cell cycle entry, and modulated expression of cell cycle-related proteins. To further evaluate the effects of SR expression on cell proliferation and differentiation, we used an in vivo model of neuroblastoma in nude mice. N2A cells stably expressing scramble shRNA (Srr^wt -N2A) or specific Srr shRNA (Srr^kd -N2A) were subcutaneously injected into nude mice. The weights and volumes of Srr^wt -N2A-derived tumors were lower than Srr^kd -N2A-derived tumors. Furthermore, Srr^wt -N2A-derived tumors were significantly mitigated by intraperitoneal injection of valproic acid, whereas Srr^kd -N2A-derived tumors were unaffected. Taken together, our findings demonstrate for the first time that alterations in SR expression determine the transition between proliferation and differentiation in neural progenitor cells. Thus, in addition to its well-established roles in neuropsychiatric disorders, our study has highlighted a novel role for SR in cell proliferation and differentiation.

Regulation of Neurogenesis and Neuronal Differentiation by Natural Compounds

Neuronal damage or degeneration is the main feature of neurological diseases. Regulation of neurogenesis and neuronal differentiation is important in developing therapies to promote neuronal regeneration or synaptic network reconstruction. Neurogenesis is a multistage process in which neurons are generated and integrated into existing neuronal circuits. Neuronal differentiation is extremely complex because it can occur in different cell types and can be caused by a variety of inducers. Recently, natural compounds that induce neurogenesis and neuronal differentiation have attracted extensive attention. In this paper, the potential neural induction effects of medicinal plant-derived natural compounds on neural stem/progenitor cells (NS/PCs), the cultured neuronal cells, and mesenchymal stem cells (MSCs) are reviewed. The natural compounds that are efficacious in inducing neurogenesis and neuronal differentiation include phenolic acids, polyphenols, flavonoids, glucosides, alkaloids, terpenoids, quinones, coumarins, and others. They exert neural induction effects by regulating signal factors and cell-specific genes involved in the process of neurogenesis and neuronal differentiation, including specific proteins (β-tubulin III, MAP-2, tau, nestin, neurofilaments, GFAP, GAP-43, NSE), related genes and proteins (STAT3, Hes1, Mash1, NeuroD1, notch, cyclin D1, SIRT1, reggie-1), transcription factors (CREB, Nkx-2.5, Ngn1), neurotrophins (BDNF, NGF, NT-3) and signaling pathways (JAK/STAT, Wnt/β-catenin, MAPK, PI3K/Akt, GSK-3β/β-catenin, Ca2+/CaMKII/ATF1, Nrf2/HO-1, BMP). The natural compounds with neural induction effects are of great value for neuronal regenerative medicine and provide promising prevention and treatment strategies for neurological diseases.

Neuroprotective effects of oolong tea extracts against glutamate-induced toxicity in cultured neuronal cells and β-amyloid-induced toxicity in Caenorhabditis elegans

Oolong tea, a traditional Chinese tea, is especially popular in south China and has a variety of health benefits. However, studies about its neuroprotective and neuroregenerative properties are still limited. This study explored the neuroprotective and neurite outgrowth-promoting properties of oolong tea in cultured neuronal cells (Neuro-2a and HT22) and Caenorhabditis elegans models. Ultra performance liquid chromatography was applied to identify the main natural bioactive compounds in oolong tea. Using Neuro-2a and HT22 cells, we found that oolong tea extracts had a protective effect against glutamate-induced cell death. The extracts reduced intracellular reactive oxygen species accumulation and induced gene expression of cellular antioxidant enzymes such as GPx, GSTs and SODs. These extracts also increased the average neurite length, and GAP-43 and Ten-4 mRNA expression in Neuro-2a cells. Moreover, they had protective effects against Aβ-induced paralysis, chemotaxis deficiency and α-synuclein aggregation in C. elegans. This is the first study showing the neuroregenerative and neuroprotective potential of the oolong tea extracts against glutamate/Aβ/α-synuclein-induced toxicity in vitro and in vivo. Our study may support oolong tea extracts as potential candidates for the prevention of neurodegenerative diseases.

Melatonin promotes neuroblastoma cell differentiation by activating hyaluronan synthase 3-induced mitophagy

Neuroblastoma is the second most common pediatric malignancy and has a high rate of spontaneous remission. Uncovering the mechanisms underlying neuroblastoma cell differentiation is critical for therapeutic purposes. A neuroblastoma cell line (N2a) treated with either serum withdrawal (<2.5%) or melatonin (>0.1 nmol/L) for 24 hours was used as a cell differentiation research model. Interestingly, the hyaluronan synthase 3 (HAS3) protein was induced in differentiated N2a cells. N2a-allografted nude mice received an intraperitoneal injection of melatonin (40 or 80 mg/kg/day for 3 weeks). The mean tumor volume in mice treated with 80 mg/kg melatonin was smaller than that in PBS-treated mice (1416.3 and 3041.3 mm³ , respectively, difference = 1625 mm³ , *P = 0.0003, n = 7 per group). Compared with the vector control group, N2a cells with forced HAS3 overexpression showed significantly increased neuron length (*P = 0.00082) and neurite outgrowth (*P = 0.00059). Intracellular changes in autophagy, including distorted mitochondria with abnormal circular inner membranes, were detected by transmission electron microscopy (TEM). Our study demonstrated that HAS3-mediated signaling activated by physiological concentrations of melatonin (>0.1 nmol/L) triggered significant N2a cell differentiation. These results provide molecular data with potential clinical relevance for therapeutic drug development.

Whole-Transcriptome Analysis Reveals Dysregulation of Actin-Cytoskeleton Pathway in Intellectual Disability Patients

A significant level of genetic heterogeneity has been demonstrated in intellectual disability (ID). More than 700 genes have been identified in ID patients. To identify molecular pathways underlying this heterogeneity, we applied whole-transcriptome analysis using RNA-Seq in consanguineous families with ID. Significant changes in expression of genes related to neuronal and actin cytoskeletal functions were observed in all the ID families. Remarkably, we found a significant down-regulation of SHTN1 gene and up-regulation of FGFR2 gene in all ID patients. FGFR2, but not SHTN1, was previously reported as an ID causing gene. Detailed gene ontology analyses identified pathways linked to tyrosine protein kinase, actin cytoskeleton, and axonogenesis to be affected in ID patients. The findings reported here provide new insights into the candidate genes and molecular pathways underling ID and highlight the key role of actin cytoskeleton in etiology of ID.

High-Frequency Repetitive Magnetic Stimulation Enhances the Expression of Brain-Derived Neurotrophic Factor Through Activation of Ca2+-Calmodulin-Dependent Protein Kinase II-cAMP-Response Element-Binding Protein Pathway

Repetitive transcranial magnetic stimulation (rTMS) can be used in various neurological disorders. However, neurobiological mechanism of rTMS is not well known. Therefore, in this study, we examined the global gene expression patterns depending on different frequencies of repetitive magnetic stimulation (rMS) in both undifferentiated and differentiated Neuro-2a cells to generate a comprehensive view of the biological mechanisms. The Neuro-2a cells were randomly divided into three groups—the sham (no active stimulation) group, the low-frequency (0.5 Hz stimulation) group, and high-frequency (10 Hz stimulation) group—and were stimulated 10 min for 3 days. The low- and high-frequency groups of rMS on Neuro-2a cells were characterized by transcriptome array. Differentially expressed genes were analyzed using the Database of Annotation Visualization and Integrated Discovery program, which yielded a Kyoto Encyclopedia of Genes and Genomes pathway. Amphetamine addiction pathway, circadian entrainment pathway, long-term potentiation (LTP) pathway, neurotrophin signaling pathway, prolactin signaling pathway, and cholinergic synapse pathway were significantly enriched in high-frequency group compared with low-frequency group. Among these pathways, LTP pathway is relevant to rMS, thus the genes that were involved in LTP pathway were validated by quantitative real-time polymerase chain reaction and western blotting. The expression of glutamate ionotropic receptor N-methyl d-aspartate 1, calmodulin-dependent protein kinase II (CaMKII) δ, and CaMKIIα was increased, and the expression of CaMKIIγ was decreased in high-frequency group. These genes can activate the calcium (Ca²⁺)–CaMKII–cAMP-response element-binding protein (CREB) pathway. Furthermore, high-frequency rMS induced phosphorylation of CREB, brain-derived neurotrophic factor (BDNF) transcription via activation of Ca²⁺–CaMKII–CREB pathway. In conclusion, high-frequency rMS enhances the expression of BDNF by activating Ca²⁺–CaMKII–CREB pathway in the Neuro-2a cells. These findings may help clarify further therapeutic mechanisms of rTMS.

Glycerophosphodiesterase GDE2 Promotes Neuroblastoma Differentiation through Glypican Release and Is a Marker of Clinical Outcome

Neuroblastoma is a pediatric embryonal malignancy characterized by impaired neuronal differentiation. A better understanding of neuroblastoma differentiation is essential for developing new therapeutic approaches. GDE2 (encoded by GDPD5) is a six-transmembrane-domain glycerophosphodiesterase that promotes embryonic neurogenesis. We find that high GDPD5 expression is strongly associated with favorable outcome in neuroblastoma. GDE2 induces differentiation of neuroblastoma cells, suppresses cell motility, and opposes RhoA-driven neurite retraction. GDE2 alters the Rac-RhoA activity balance and the expression of multiple differentiation-associated genes. Mechanistically, GDE2 acts by cleaving (in cis) and releasing glycosylphosphatidylinositol-anchored glypican-6, a putative co-receptor. A single point mutation in the ectodomain abolishes GDE2 function. Our results reveal GDE2 as a cell-autonomous inducer of neuroblastoma differentiation with prognostic significance and potential therapeutic value.

β-Hydroxy-β-Methylbutyrate (HMB) Promotes Neurite Outgrowth in Neuro2a Cells

β-Hydroxy-β-methylbutyrate (HMB) has been shown to enhance cell survival, differentiation and protein turnover in muscle, mainly activating phosphoinositide-3-kinase/protein kinase B (PI3K/Akt) and mitogen-activated protein kinases/ extracellular-signal-regulated kinases (MAPK/ERK) signaling pathways. Since these two pathways are related to neuronal survival and differentiation, in this study, we have investigated the neurotrophic effects of HMB in mouse neuroblastoma Neuro2a cells. In Neuro2a cells, HMB promotes differentiation to neurites independent from any effects on proliferation. These effects are mediated by activation of both the PI3K/Akt and the extracellular-signal-regulated kinases (ERK1/2) signaling as demonstrated by the use of specific inhibitors of these two pathways. As myocyte-enhancer factor 2 (MEF2) family of transcription factors are involved in neuronal survival and plasticity, the transcriptional activity and protein levels of MEF2 were also evaluated. HMB promoted MEF2-dependent transcriptional activity mediated by the activation of Akt and ERK1/2 pathways. Furthermore, HMB increases the expression of brain glucose transporters 1 (GLUT1) and 3 (GLUT3), and mTOR phosphorylation, which translates in a higher protein synthesis in Neuro2a cells. Furthermore, Torin1 and rapamycin effects on MEF2 transcriptional activity and HMB-dependent neurite outgrowth support that HMB acts through mTORC2. Together, these findings provide clear evidence to support an important role of HMB in neurite outgrowth.

Emodin induces neurite outgrowth through PI3K/Akt/GSK-3β-mediated signaling pathways in Neuro2a cells

In this study, a neurite outgrowth-inducing substance was isolated from the ethylacetate extract of the Polygonum multiflorum roots and identified as emodin by gas-liquid chromatography-mass spectrometry and (1)H NMR and (13)C NMR. Emodin displayed remarkable neurite outgrowth-inducing activity in Neuro2a cells, as demonstrated by morphological changes and immunocytochemistry for class III β-tubulin. Emodin exhibited a stronger neutrophic activity than retinoic acid (RA) known as inducer of neurite outgrowth in Neuro2a cells. Emodin treatment resulted in marked increases in phosphorylation of Akt a direct downstream signaling molecule of phosphatidylinositol 3-kinase (PI3K), but upstream of glycogen synthase kinase-3β (GSK-3β) and cAMP response element-binding protein (CREB). These augmentations and neurite-bearing cells induced by emodin were remarkably reduced by the addition of PI3K inhibitor LY294002. These results demonstrate that emodin induces neuronal differentiation of Neuro2a cells via PI3K/Akt/GSK-3β pathway.

Estudo das células Neuro2A sobre os biomateriais PCL e PLLA

Os biomateriais poli L-ácido lático (PLLA) e o poli caprolactona (PCL) são os polímeros mais estudadas na área dos materiais bioreabsorvíveis. Dentre as suas principais características que contribuem para a interação celular, temos a especificidade química da superfície, elétrica, hidrofobicidade e topografia. Ainda, observa-se o tempo de degradação, porosidade, biocompatibilidade com o tecido biológico, bem como, a confecção com as mais variadas formas e dimensões. Já a prática da cultura celular, tem como objetivo estudar a adesão, migração, diferenciação e a proliferação celular utilizando-se um determinado material ou substância. Contudo, poucos trabalhos utilizando os biomateriais ora supracitados e a aplicação em células neuro2A foram realizados. Sabe-se que este tipo celular é derivado de células embrionárias da crista neural, as quais originam em neurônios simpáticos e apresentam como característica a imortalidade, portanto, são excelentes modelos em ensaios in vitro. Nesse sentido, o presente estudo avalia a adesão e a proliferação desta linhagem celular sobre os biopolímeros poli caprolactona (PCL) e poli L-ácido lático (PLLA).

Mammalian Glycerophosphodiester Phosphodiesterases

Bacterial glycerophosphodiester phosphodiesterases (GP-PDEs), GlpQ and UgpQ, are well-characterized periplasmic and cytosolic proteins that play critical roles in the hydrolysis of deacylated glycerophospholipids to glycerol phosphate and alcohol, which are utilized as major sources of carbon and phosphate. In contrast, two novel mammalian GP-PDEs, GDE1/MIR16 and GDE3, were recently identified, and were shown to be involved in several physiological functions. GDE1/MIR16 was identified as a membrane protein interacting with RGS16, a regulator of G protein signaling, and found to hydrolyze glycerophosphoinositol preferentially. We have found that expression of GDE3 is significantly up-regulated during osteoblast differentiation and is involved in morphological changes of cells. Furthermore, five mammalian GP-PDEs were virtually identified, and very recent studies indicate that retinoic acid-induced expression of GDE2 plays essential roles in neuronal differentiation and neurite outgrowth. Thus mammalian GP-PDEs are likely to be important in controlling numerous cellular events, indicating that the GP-PDE superfamily in mammals might be a pharmacological target in the future.

The emerging physiological roles of the glycerophosphodiesterase family

The glycerophosphodiester phosphodiesterases are evolutionarily conserved proteins that have been linked to several patho/physiological functions, comprising bacterial pathogenicity and mammalian cell proliferation or differentiation. The bacterial enzymes do not show preferential substrate selectivities among the glycerophosphodiesters, and they are mainly dedicated to glycerophosphodiester hydrolysis, producing glycerophosphate and alcohols as the building blocks that are required for bacterial biosynthetic pathways. In some cases, this enzymatic activity has been demonstrated to contribute to bacterial pathogenicity, such as with Hemophilus influenzae. Mammalian glyerophosphodiesterases have high substrate specificities, even if the number of potential physiological substrates is continuously increasing. Some of these mammalian enzymes have been directly linked to cell differentiation, such as GDE2, which triggers motor neuron differentiation, and GDE3, the enzymatic activity of which is necessary and sufficient to induce osteoblast differentiation. Instead, GDE5 has been shown to inhibit skeletal muscle development independent of its enzymatic activity.

High NaCl- and urea-induced posttranslational modifications that increase glycerophosphocholine by inhibiting GDPD5 phosphodiesterase

Glycerophosphocholine (GPC) is high in cells of the renal inner medulla where high interstitial NaCl and urea power concentration of the urine. GPC protects inner medullary cells against the perturbing effects of high NaCl and urea by stabilizing intracellular macromolecules. Degradation of GPC is catalyzed by the glycerophosphocholine phosphodiesterase activity of glycerophosphodiester phosphodiesterase domain containing 5 (GDPD5). We previously found that inhibitory posttranslational modification (PTM) of GDPD5 contributes to high NaCl- and urea-induced increase of GPC. The purpose of the present studies was to identify the PTM(s). We find at least three such PTMs in HEK293 cells: (i) Formation of a disulfide bond between C25 and C571. High NaCl and high urea increase reactive oxygen species (ROS). The ROS increase disulfide bonding between GDPD5-C25 and -C571, which inhibits GDPD5 activity, as supported by the findings that the antioxidant N-acetylcysteine prevents high NaCl- and urea-induced inhibition of GDPD5; GDPD5-C25S/C571S mutation or over expression of peroxiredoxin increases GDPD5 activity; H2O2 inhibits activity of wild type GDPD5, but not of GDPD5-C25S/C571S; and peroxiredoxin is relatively low in the renal inner medulla where GPC is high. (ii) Dephosphorylation of GDPD5-T587. GDPD5 threonine 587 is constitutively phosphorylated. High NaCl and high urea dephosphorylate GDPD5-T587. Mutation of GDPD5-T587 to alanine, which cannot be phosphorylated, decreases GPC-PDE activity of GDPD5. (iii) Alteration at an unknown site mediated by CDK1. Inhibition of CDK1 protein kinase reduces GDE-PDE activity of GDPD5 without altering phosphorylation at T587, and CDK1/5 inhibitor reduces activity of GDPD5- C25S/C571S-T587A.

Involvement of P2Y13 receptor in suppression of neuronal differentiation

We examined the receptor-mediated effects of extracellular ATP on neuronal differentiation of PC12 cells, Neuro2a cells and MEB5 cells by using a series of receptor antagonists. The P2Y13 receptor antagonist MRS2211 significantly accelerated neurite outgrowth in all cases. Treatment with nerve growth factor (NGF) alone activated ERK1/2 in PC12 cells, and the activation was further increased by MRS2211. These results suggest involvement of P2Y13 receptor in suppression of neuronal differentiation. Thus, P2Y13 receptor antagonists might be candidates for treatment of neurodegenerative diseases.

The glycerophosphoinositols and their cellular functions

Interest in the glycerophosphoinositols has been increasing recently, on the basis of their biological activities. The cellular metabolism of these water-soluble bioactive phosphoinositide metabolites has been clarified, with the identification of the specific enzyme involved in their synthesis, PLA2IVα (phospholipase A2 IVα), and the definition of their phosphodiesterase-based catabolism, and thus inactivation. The functional roles and mechanisms of action of these compounds have been investigated in different cellular contexts. This has led to their definition in the control of various cell functions, such as cell proliferation in the thyroid and actin cytoskeleton organization in fibroblasts and lymphocytes. Roles for the glycerophosphoinositols in immune and inflammatory responses are also being defined. In addition to these physiological functions, the glycerophosphoinositols have potential anti-metastatic activities that should lead to their pharmacological exploitation.

Vitamin B6 regulates mRNA expression of peroxisome proliferator-activated receptor-γ target genes

We previously demonstrated that vitamin B6 suppresses tumorigenesis in the colon of mice and exerts an anti-inflammatory effect through the inhibition of NF-κB activation. As these effects resemble the pharmacological properties of thiazolidinedione (TZD), a synthetic peroxisome proliferator-activated receptor-γ (PPARγ) ligand, this study was designed to examine the effect of vitamin B6 on the activation of PPARγ and adipogenesis in 3T3-L1 adipocyte cells. Pyridoxal 5'-phosphate (PLP), one of the vitamin B6 derivatives, was shown to promote adipogenesis in the 3T3-L1 adipocytes. In addition, PLP specifically induced mRNA expression of PPARγ target genes in the 3T3-L1 adipocytes and enhanced the lipid accumulation and adipocyte fatty acid-binding protein (aP2) mRNA expression in NIH3T3 cells stably expressing PPARγ. Furthermore, the administration of vitamin B6 increased the expression of aP2 mRNA in mouse adipose tissues. Collectively, these observations suggest a novel function of vitamin B6 as an activator for PPARγ, which may contribute to the anti-tumor and anti-inflammatory effects of vitamin B6.

A novel glycerophosphodiester phosphodiesterase, GDE5, controls skeletal muscle development via a non-enzymatic mechanism

Mammalian glycerophosphodiester phosphodiesterases (GP-PDEs) have been identified recently and shown to be implicated in several physiological functions. This study isolated a novel GP-PDE, GDE5, and showed that GDE5 selectively hydrolyzes glycerophosphocholine (GroPCho) and controls skeletal muscle development. We show that GDE5 expression was reduced in atrophied skeletal muscles in mice and that decreasing GDE5 abundance promoted myoblastic differentiation, suggesting that decreased GDE5 expression has a counter-regulatory effect on the progression of skeletal muscle atrophy. Forced expression of full-length GDE5 in cultured myoblasts suppressed myogenic differentiation. Unexpectedly, a truncated GDE5 construct (GDE5DeltaC471), which contained a GP-PDE sequence identified in other GP-PDEs but lacked GroPCho phosphodiesterase activity, showed a similar inhibitory effect. Furthermore, transgenic mice specifically expressing GDE5DeltaC471 in skeletal muscle showed less skeletal muscle mass, especially type II fiber-rich muscle. These results indicate that GDE5 negatively regulates skeletal muscle development even without GroPCho phosphodiesterase activity, providing novel insight into the biological significance of mammalian GP-PDE function in a non-enzymatic mechanism.

Phosphatidylcholine biosynthesis during neuronal differentiation and its role in cell fate determination

Neuronal differentiation is characterized by neuritogenesis and neurite outgrowth, processes that are dependent on membrane biosynthesis. Thus, the production of phosphatidylcholine (PtdCho), the major membrane phospholipid, should be stimulated during neuronal differentiation. We demonstrate that during retinoic acid (RA)-induced differentiation of Neuro-2a cells, PtdCho synthesis was promoted by an ordered and sequential activation of choline kinase alpha (CK(alpha)) and choline cytidylyltransferase alpha (CCT(alpha)). Early after RA stimulation, the increase in PtdCho synthesis is mainly governed by the biochemical activation of CCT(alpha). Later, the transcription of CK(alpha)- and CCT(alpha)-encoding genes was induced. Both PtdCho biosynthesis and neuronal differentiation are dependent on ERK activation. A novel mechanism is proposed by which PtdCho biosynthesis is coordinated during neuronal differentiation. Enforced expression of either CK(alpha) or CCTalpha increased the rate of synthesis and the amount of PtdCho, and these cells initiated differentiation without RA stimulation, as evidenced by cell morphology and the expression of genes associated with neuritogenesis. The differentiation resulting from enforced expression of CCT(alpha) or CK(alpha) was dependent on persistent ERK activation. These results indicate that elevated PtdCho synthesis could mimic the RA signals and thus determine neuronal cell fate. Moreover, they could explain the key role that PtdCho plays during neuronal regeneration.

The antioxidant enzyme Prdx1 controls neuronal differentiation by thiol-redox-dependent activation of GDE2

The six-transmembrane protein GDE2 controls the onset and progression of spinal motor neuron differentiation through extracellular glycerophosphodiester phosphodiesterase metabolism. Although this process is likely to be tightly regulated, the relevant mechanisms that modulate its activity are unknown. Here we show that the antioxidant scavenger peroxiredoxin1 (Prdx1) interacts with GDE2, and that loss of Prdx1 causes motor neuron deficits analogous to GDE2 ablation. Prdx1 cooperates with GDE2 to drive motor neuron differentiation, and this synergy requires Prdx1 thiol-dependent catalysis. Prdx1 activates GDE2 through reduction of an intramolecular disulfide bond that bridges its intracellular N- and C-terminal domains. GDE2 variants incapable of disulfide bond formation acquire independence from Prdx1 and are potent inducers of motor neuron differentiation. These findings define Prdx1 as a pivotal regulator of GDE2 activity and suggest roles for coupled thiol-redox-dependent cascades in controlling neuronal differentiation in the spinal cord.

The developmentally regulated osteoblast phosphodiesterase GDE3 is glycerophosphoinositol-specific and modulates cell growth

The glycerophosphodiester phosphodiesterase enzyme family involved in the hydrolysis of glycerophosphodiesters has been characterized in bacteria and recently identified in mammals. Here, we have characterized the activity and function of GDE3, one of the seven mammalian enzymes. GDE3 is up-regulated during osteoblast differentiation and can affect cell morphology. We show that GDE3 is a glycerophosphoinositol (GroPIns) phosphodiesterase that hydrolyzes GroPIns, producing inositol 1-phosphate and glycerol, and thus suggesting specific roles for this enzyme in GroPIns metabolism. Substrate specificity analyses show that wild-type GDE3 selectively hydrolyzes GroPIns over glycerophosphocholine, glycerophosphoethanolamine, and glycerophosphoserine. A single point mutation in the catalytic domain of GDE3 (GDE3R231A) leads to loss of GroPIns enzymatic hydrolysis, identifying an arginine residue crucial for GDE3 activity. After heterologous GDE3 expression in HEK293T cells, phosphodiesterase activity is detected in the extracellular medium, with no effect on the intracellular GroPIns pool. Together with the millimolar concentrations of calcium required for GDE3 activity, this predicts an enzyme topology with an extracellular catalytic domain. Interestingly, GDE3 ectocellular activity is detected in a stable clone from a murine osteoblast cell line, further confirming the activity of GDE3 in a more physiological context. Finally, overexpression of wild-type GDE3 in osteoblasts promotes disassembly of actin stress fibers, decrease in growth rate, and increase in alkaline phosphatase activity and calcium content, indicating a role for GDE3 in induction of differentiation. Thus, we have identified the GDE3 substrate GroPIns as a candidate mediator for osteoblast proliferation, in line with the GroPIns activity observed previously in epithelial cells.

Isolation, characterization and molecular 3D model of human GDE4, a novel membrane protein containing glycerophosphodiester phosphodiesterase domain

As a transmembrane protein family, glycerophosphodiester phosphodiesterase (GDPD/GDE) catalyzes the hydrolysis of deacylated glycerophospholipids to glycerol phosphate and alcohol. To date, seven mammalian GDEs have been virtually cloned or predicted by bioinformatics analysis, however, GDE4 has not been molecular isolated and characterized in mammal. Here we report molecular cloning of human GDE4 encoding cDNA sequence, which is 945 base pairs long encoding a 314-amino acid protein with 2 transmembrane regions and a GDE motif. The human GDE1 gene is located on chromosome 19q22 and contains ten exons and nine introns. A molecular 3-D model provides the first structural information of human GDE4 and suggests a triose-phosphate-isomerase barrel core as typically found in bacterial GDPDs. Furthermore, a model of the putative catalytic residues highlights that the individual core residues Glu72, Asp74, and His87 are crucial to maintaining GDE4 catalytic activity. Western blotting shows that human GDE4 is a 36 kDa protein. Subcellular localization of GDE4 tagged with enhanced green fluorescence protein is in the cytoplasm, especially accumulated in the perinuclear region and the cell periphery. Moreover, over-expression of GDE4 did not induce neurite formation or change cell morphology. These results indicate GDE4 protein is a member of the GDE family and suggest it may play different roles from other members of GDE family.

GDPD5 is a glycerophosphocholine phosphodiesterase that osmotically regulates the osmoprotective organic osmolyte GPC

Glycerophosphocholine (GPC) is an abundant osmoprotective renal medullary organic osmolyte. We previously found that its synthesis from phosphatidylcholine is catalyzed by tonicity-regulated activity of the phospholipase B, neuropathy target esterase. We also found that its degradation is catalyzed by glycerophosphocholine phosphodiesterase (GPC-PDE) activity and that elevating osmolality from 300 to 500 mosmol/kg by adding NaCl or urea, inhibits GPC-PDE activity, which contributes to the resultant increase of GPC. In the present studies we identify GDPD5 (glycerophosphodiester phosphodiesterase domain containing 5) as a GPC-PDE that is rapidly inhibited by high NaCl or urea. Recombinant GDPD5 colocalizes with neuropathy target esterase in the perinuclear region of HEK293 cells, and immuno-precipitated recombinant GDPD5 degrades GPC in vitro. The in vitro activity is reduced when the cells from which the GDPD5 is immuno-precipitated have been exposed to high NaCl or urea. In addition, high NaCl decreases mRNA abundance of GDPD5 via an increase of its degradation rate, although high urea does not. At 300 mosmol/kg siRNA knockdown of GDPD5 increases GPC in mouse inner medullary collecting duct-3 cells, and over expression of recombinant GDPD5 increases cellular GPC-PDE activity, accompanied by decreased GPC. We conclude that GDPD5 is a GPC-PDE that contributes to osmotic regulation of cellular GPC.

Crystal structure of glycerophosphodiester phosphodiesterase (GDPD) from Thermoanaerobacter tengcongensis, a metal ion-dependent enzyme: insight into the catalytic mechanism

Glycerophosphodiester phosphodiesterase (GDPD; EC 3.1.4.46) catalyzes the hydrolysis of a glycerophosphodiester to an alcohol and glycerol 3-phosphate in glycerol metabolism. It has an important role in the synthesis of a variety of products that participate in many biochemical pathways. We report the crystal structure of the Thermoanaerobacter tengcongensis GDPD (ttGDPD) at 1.91 A resolution, with a calcium ion and glycerol as a substrate mimic coordinated at this calcium ion (PDB entry 2pz0). The ttGDPD dimer with an intermolecular disulfide bridge and two hydrogen bonds is considered as the potential functional unit. We used site-directed mutagenesis to characterize ttGDPD as a metal ion-dependent enzyme, identified a cluster of residues involved in substrate binding and the catalytic reaction, and we propose a possible general acid-base catalytic mechanism for ttGDPD. Superposing the active site with the homologous structure GDPD from Agrobacterium tumefaciens (PDB entry 1zcc), which binds a sulfate ion in the active site, the sulfate ion can represent the phosphate moiety of the substrate, simulating the binding mode of the true substrate of GDPD.