Mammalian Glycerophosphodiester Phosphodiesterases

Physiological regulation of neuronal Wnt activity is essential for TDP-43 localization and function

Nuclear exclusion of the RNA- and DNA-binding protein TDP-43 can induce neurodegeneration in different diseases. Diverse processes have been implicated to influence TDP-43 mislocalization, including disrupted nucleocytoplasmic transport (NCT); however, the physiological pathways that normally ensure TDP-43 nuclear localization are unclear. The six-transmembrane enzyme glycerophosphodiester phosphodiesterase 2 (GDE2 or GDPD5) cleaves the glycosylphosphatidylinositol (GPI) anchor that tethers some proteins to the membrane. Here we show that GDE2 maintains TDP-43 nuclear localization by regulating the dynamics of canonical Wnt signaling. Ablation of GDE2 causes aberrantly sustained Wnt activation in adult neurons, which is sufficient to cause NCT deficits, nuclear pore abnormalities, and TDP-43 nuclear exclusion. Disruption of GDE2 coincides with TDP-43 abnormalities in postmortem tissue from patients with amyotrophic lateral sclerosis (ALS). Further, GDE2 deficits are evident in human neural cell models of ALS, which display erroneous Wnt activation that, when inhibited, increases mRNA levels of genes regulated by TDP-43. Our study identifies GDE2 as a critical physiological regulator of Wnt signaling in adult neurons and highlights Wnt pathway activation as an unappreciated mechanism contributing to nucleocytoplasmic transport and TDP-43 abnormalities in disease.

GDE5/Gpcpd1 activity determines phosphatidylcholine composition in skeletal muscle and regulates contractile force in mice

Glycerophosphocholine (GPC) is an important precursor for intracellular choline supply in phosphatidylcholine (PC) metabolism. GDE5/Gpcpd1 hydrolyzes GPC into choline and glycerol 3-phosphate; this study aimed to elucidate its physiological function in vivo. Heterozygous whole-body GDE5-deficient mice reveal a significant GPC accumulation across tissues, while homozygous whole-body knockout results in embryonic lethality. Skeletal muscle-specific GDE5 deletion (Gde5 skKO) exhibits reduced passive force and improved fatigue resistance in electrically stimulated gastrocnemius muscles in vivo. GDE5 deficiency also results in higher glycolytic metabolites and glycogen levels, and glycerophospholipids alteration, including reduced levels of phospholipids that bind polyunsaturated fatty acids (PUFAs), such as DHA. Interestingly, this PC fatty acid compositional change is similar to that observed in skeletal muscles of denervated and Duchenne muscular dystrophy mouse models. These are accompanied by decrease of GDE5 expression, suggesting a regulatory role of GDE5 activity for glycerophospholipid profiles. Furthermore, a DHA-rich diet enhances contractile force and lowers fatigue resistance, suggesting a functional relationship between PC fatty acid composition and muscle function. Finally, skinned fiber experiments show that GDE5 loss increases the probability of the ryanodine receptor opening and lowers the maximum Ca2+-activated force. Collectively, GDE5 activity plays roles in PC and glucose/glycogen metabolism in skeletal muscle.

Loss of GDE2 leads to complex behavioral changes including memory impairment

BACKGROUND

Alzheimer's disease (AD) and amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) are debilitating neurodegenerative diseases for which there are currently no cures. Familial cases with known genetic causes make up less than 10% of these diseases, and little is known about the underlying mechanisms that contribute to sporadic disease. Accordingly, it is important to expand investigations into possible pathways that may contribute to disease pathophysiology. Glycerophosphodiester phosphodiesterase 2 (GDE2 or GDPD5) is a membrane-bound enzyme that acts at the cell surface to cleave the glycosylphosphatidylinositol (GPI)-anchor that tethers distinct proteins to the membrane. GDE2 abnormally accumulates in intracellular compartments in the brain of patients with AD, ALS, and ALS/FTD, indicative of GDE2 dysfunction. Mice lacking GDE2 (Gde2KO) show neurodegenerative changes such as neuronal loss, reduced synaptic proteins and synapse loss, and increased Aβ deposition, raising the possibility that GDE2 disruption in disease might contribute to disease pathophysiology. However, the effect of GDE2 loss on behavioral function and learning/memory has not been characterized.

RESULTS

Here, we show that GDE2 is expressed throughout the adult mouse brain in areas including the cortex, hippocampus, habenula, thalamus, and amygdala. Gde2KO and WT mice were tested in a set of behavioral tasks between 7 and 16 months of age. Compared to WT, Gde2KO mice display moderate hyperactivity that becomes more pronounced with age across a variety of behavioral tests assessing novelty-induced exploratory activity. Additionally, Gde2KO mice show reduced startle response, with females showing additional defects in prepulse inhibition. No changes in anxiety-associated behaviors were found, but Gde2KOs show reduced sociability. Notably, aged Gde2KO mice demonstrate impaired short/long-term spatial memory and cued fear memory/secondary contextual fear acquisition.

CONCLUSIONS

Taken together, these observations suggest that loss of GDE2 leads to behavioral deficits, some of which are seen in neurodegenerative disease models, implying that loss of GDE2 may be an important contributor to phenotypes associated with neurodegeneration.

An update on Glycerophosphodiester Phosphodiesterases; From Bacteria to Human

The hydrolysis of deacylated glycerophospholipids into sn-glycerol 3-phosphate and alcohol is facilitated by evolutionarily conserved proteins known as glycerophosphodiester phosphodiesterases (GDPDs). These proteins are crucial for the pathogenicity of bacteria and for bioremediation processes aimed at degrading organophosphorus esters that pose a hazard to both humans and the environment. Additionally, GDPDs are enzymes that respond to multiple nutrients and could potentially serve as candidate genes for addressing deficiencies in zinc, iron, potassium, and especially phosphate in important plants like rice. In mammals, glycerophosphodiesterases (GDEs) play a role in regulating osmolytes, facilitating the biosynthesis of anandamine, contributing to the development of skeletal muscle, promoting the differentiation of neurons and osteoblasts, and influencing pathological states. Due to their capacity to enhance a plant's ability to tolerate various nutrient deficiencies and their potential as pharmaceutical targets in humans, GDPDs have received increased attention in recent times. This review provides an overview of the functions of GDPD families as vital and resilient enzymes that regulate various pathways in bacteria, plants, and humans.

Goods and Bads of the Endocannabinoid System as a Therapeutic Target: Lessons Learned after 30 Years

The cannabis derivative marijuana is the most widely used recreational drug in the Western world and is consumed by an estimated 83 million individuals (∼3% of the world population). In recent years, there has been a marked transformation in society regarding the risk perception of cannabis, driven by its legalization and medical use in many states in the United States and worldwide. Compelling research evidence and the Food and Drug Administration cannabis-derived cannabidiol approval for severe childhood epilepsy have confirmed the large therapeutic potential of cannabidiol itself, Δ9-tetrahydrocannabinol and other plant-derived cannabinoids (phytocannabinoids). Of note, our body has a complex endocannabinoid system (ECS)-made of receptors, metabolic enzymes, and transporters-that is also regulated by phytocannabinoids. The first endocannabinoid to be discovered 30 years ago was anandamide (N-arachidonoyl-ethanolamine); since then, distinct elements of the ECS have been the target of drug design programs aimed at curing (or at least slowing down) a number of human diseases, both in the central nervous system and at the periphery. Here a critical review of our knowledge of the goods and bads of the ECS as a therapeutic target is presented to define the benefits of ECS-active phytocannabinoids and ECS-oriented synthetic drugs for human health. SIGNIFICANCE STATEMENT: The endocannabinoid system plays important roles virtually everywhere in our body and is either involved in mediating key processes of central and peripheral diseases or represents a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of the components of this complex system, and in particular of key receptors (like cannabinoid receptors 1 and 2) and metabolic enzymes (like fatty acid amide hydrolase and monoacylglycerol lipase), will advance our understanding of endocannabinoid signaling and activity at molecular, cellular, and system levels, providing new opportunities to treat patients.

Lysophosphatidylglycerol (LPG) phospholipase D maintains membrane homeostasis in Staphylococcus aureus by converting LPG to lysophosphatidic acid

Lysophospholipids are deacylated derivatives of their bilayer forming phospholipid counterparts that are present at low concentrations in cells. Phosphatidylglycerol (PG) is the principal membrane phospholipid in Staphylococcus aureus and lysophosphatidylglycerol (LPG) is detected in low abundance. Here, we used a mass spectrometry screen to identify locus SAUSA300_1020 as the gene responsible for maintaining low concentrations of 1-acyl-LPG in S. aureus. The SAUSA300_1020 gene encodes a protein with a predicted amino terminal transmembrane α-helix attached to a globular glycerophosphodiester phosphodiesterase (GDPD) domain. We determined that the purified protein lacking the hydrophobic helix (LpgDΔN) possesses cation-dependent lysophosphatidylglycerol phospholipase D activity that generates both lysophosphatidic acid (LPA) and cyclic-LPA products and hydrolyzes cyclic-LPA to LPA. Mn2+ was the highest affinity cation and stabilized LpgDΔN to thermal denaturation. LpgDΔN was not specific for the phospholipid headgroup and degraded 1-acyl-LPG, but not 2-acyl-LPG. Furthermore, a 2.1 Å crystal structure shows that LpgDΔN adopts the GDPD variation of the TIM barrel architecture except for the length and positioning of helix α6 and sheet β7. These alterations create a hydrophobic diffusion path for LPG to access the active site. The LpgD active site has the canonical GDPD metal binding and catalytic residues, and our biochemical characterization of site-directed mutants support a two-step mechanism involving a cyclic-LPA intermediate. Thus, the physiological function of LpgD in S. aureus is to convert LPG to LPA, which is re-cycled into the PG biosynthetic pathway at the LPA acyltransferase step to maintain membrane PG molecular species homeostasis.

The distribution and function of GDE2, a regulator of spinal motor neuron survival, are disrupted in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that affects the viability of upper and lower motor neurons. Current options for treatment are limited, necessitating deeper understanding of the mechanisms underlying ALS pathogenesis. Glycerophosphodiester phosphodiesterase 2 (GDE2 or GDPD5) is a six-transmembrane protein that acts on the cell surface to cleave the glycosylphosphatidylinositol (GPI)-anchor that tethers some proteins to the membrane. GDE2 is required for the survival of spinal motor neurons but whether GDE2 neuroprotective activity is disrupted in ALS is not known. We utilized a combination of mouse models and patient post-mortem samples to evaluate GDE2 functionality in ALS. Haplogenetic reduction of GDE2 exacerbated motor neuron degeneration and loss in SOD1G93A mice but not in control SOD1WT transgenic animals, indicating that GDE2 neuroprotective function is diminished in the context of SOD1G93A. In tissue samples from patients with ALS, total levels of GDE2 protein were equivalent to healthy controls; however, membrane levels of GDE2 were substantially reduced. Indeed, GDE2 was found to aberrantly accumulate in intracellular compartments of ALS motor cortex, consistent with a disruption of GDE2 function at the cell surface. Supporting the impairment of GDE2 activity in ALS, tandem-mass-tag mass spectrometry revealed a pronounced reduction of GPI-anchored proteins released into the CSF of patients with ALS compared with control patients. Taken together, this study provides cellular and biochemical evidence that GDE2 distribution and activity is disrupted in ALS, supporting the notion that the failure of GDE2-dependent neuroprotective pathways contributes to neurodegeneration and motor neuron loss in disease. These observations highlight the dysregulation of GPI-anchored protein pathways as candidate mediators of disease onset and progression and accordingly, provide new insight into the mechanisms underlying ALS pathogenesis.

Tiki proteins are glycosylphosphatidylinositol-anchored proteases

Wnt signalling pathways play pivotal roles in development, homeostasis and human diseases, and are tightly regulated. We previously identified Tiki as a novel family of Wnt inhibitory proteases. Tiki proteins were predicted as type I transmembrane proteins and can act in both Wnt-producing and Wnt-responsive cells. Here, we characterize Tiki proteins as glycosylphosphatidylinositol (GPI)-anchored proteases. TIKI1/2 proteins are enriched on the detergent-resistant membrane microdomains and can be released from the plasma membrane by GPI-specific glycerophosphodiesterases GDE3 and GDE6, but not by GDE2. The GPI anchor determines the cellular localization of Tiki proteins and their regulation by GDEs, but not their inhibitory activity on Wnt signalling. Our study uncovered novel characteristics and potential regulations of the Tiki family proteases.

Hepatotoxicity induced by PPⅥ and PPⅦ in zebrafish were related to the Cholesterol disorder

BACKGROUND

PPⅥ² and PPⅦ³ were a group of Pennogenin compounds extracted from the Paris polyphylla and caused hepatotoxicity in human, while the potential underlying mechanism was unclear.

PURPOSE

To evaluated the adverse effects of PPⅥ and PPⅦ on the liver in the zebrafish.

METHOD

In this study, 4dpf zebrafish were used for acute toxicity test, LC₀ was calculated, and 1/2LC₀ and 3/5LC₀ were selected for pathological section and liver area measurement to verify the hepatotoxicity of PPⅥ and PPⅦ. Etabonomics study was then conducted to further explore the mechanism of hepatotoxicity of PPⅥ and PPⅦ. Lovastatin was used as an inhibitor, and PCR was used to verify the results.

RESULT

The result showed that under the condition of sub-lethal concentration exposure, hepatotoxicity-included changes in liver phenotype (liver area), hepatocyte swelling and degeneration, liver cell apoptosis and disturbed biochemical index were observed in zebrafish treated with PPⅥ and PPⅦ. Furthermore, the transcriptome was conducted to confirm the toxicity mechanism shared with PPⅥ and PPⅦ, and we found that steroid biosynthesis process and the related target genes were mainly affected. While, lovastatin treatment effectively ameliorated PPⅦ-induced zebrafish liver injury by improving the liver tissue structure and regulate the expression of associated genes including HMGCRA, SREBP, LSS, CYP2R1, PIK3R3A, GDPD1 and PFKFB-2.

CONCLUSION

This study was the first investigation to provide the direct evidence of hepatotoxicity of PPⅥ and PPⅦ in vivo zebrafish model, which were related to the steroid biosynthesis. furthermore, in lovastatin played an important role in protection against hepatotoxicity induced by PPVI and PPⅦ by regulating the cholesterol metabolism.

An extensive and dynamic trans-omic network illustrating prominent regulatory mechanisms in response to insulin in the liver

An effective combination of multi-omic datasets can enhance our understanding of complex biological phenomena. To build a context-dependent network with multiple omic layers, i.e., a trans-omic network, we perform phosphoproteomics, transcriptomics, proteomics, and metabolomics of murine liver for 4 h after insulin administration and integrate the resulting time series. Structural characteristics and dynamic nature of the network are analyzed to elucidate the impact of insulin. Early and prominent changes in protein phosphorylation and persistent and asynchronous changes in mRNA and protein levels through non-transcriptional mechanisms indicate enhanced crosstalk between phosphorylation-mediated signaling and protein expression regulation. Metabolic response shows different temporal regulation with transient increases at early time points across categories and enhanced response in the amino acid and nucleotide categories at later time points as a result of process convergence. This extensive and dynamic view of the trans-omic network elucidates prominent regulatory mechanisms that drive insulin responses through intricate interlayer coordination.

PacBio Iso-Seq Improves the Rainbow Trout Genome Annotation and Identifies Alternative Splicing Associated With Economically Important Phenotypes

Rainbow trout is an important model organism that has received concerted international efforts to study the transcriptome. For this purpose, short-read sequencing has been primarily used over the past decade. However, these sequences are too short of resolving the transcriptome complexity. This study reported a first full-length transcriptome assembly of the rainbow trout using single-molecule long-read isoform sequencing (Iso-Seq). Extensive computational approaches were used to refine and validate the reconstructed transcriptome. The study identified 10,640 high-confidence transcripts not previously annotated, in addition to 1,479 isoforms not mapped to the current Swanson reference genome. Most of the identified lncRNAs were non-coding variants of coding transcripts. The majority of genes had multiple transcript isoforms (average ∼3 isoforms/locus). Intron retention (IR) and exon skipping (ES) accounted for 56% of alternative splicing (AS) events. Iso-Seq improved the reference genome annotation, which allowed identification of characteristic AS associated with fish growth, muscle accretion, disease resistance, stress response, and fish migration. For instance, an ES in GVIN1 gene existed in fish susceptible to bacterial cold-water disease (BCWD). Besides, under five stress conditions, there was a commonly regulated exon in prolyl 4-hydroxylase subunit alpha-2 (P4HA2) gene. The reconstructed gene models and their posttranscriptional processing in rainbow trout provide invaluable resources that could be further used for future genetics and genomics studies. Additionally, the study identified characteristic transcription events associated with economically important phenotypes, which could be applied in selective breeding.

GDE2-RECK controls ADAM10 α-secretase-mediated cleavage of amyloid precursor protein

A disintegrin and metalloprotease 10 (ADAM10) is the α-secretase for amyloid precursor protein (APP). ADAM10 cleaves APP to generate neuroprotective soluble APPα (sAPPα), which precludes the generation of Aβ, a defining feature of Alzheimer's disease (AD) pathophysiology. Reduced ADAM10 activity is implicated in AD, but the mechanisms mediating ADAM10 modulation are unclear. We find that the plasma membrane enzyme glycerophosphodiester phosphodiesterase 2 (GDE2) stimulates ADAM10 APP cleavage by shedding and inactivating reversion-inducing cysteine-rich protein with Kazal motifs (RECK), a glycosylphosphatidylinositol (GPI)-anchored inhibitor of ADAM10. In AD, membrane-tethered RECK is highly elevated and GDE2 is abnormally sequestered inside neurons. Genetic ablation of GDE2 phenocopies increased membrane RECK in AD, which is causal for reduced sAPPα, increased Aβ, and synaptic protein loss. RECK reduction restores the balance of APP processing and rescues synaptic protein deficits. These studies identify GDE2 control of RECK surface activity as essential for ADAM10 α-secretase function and physiological APP processing. Moreover, our results suggest the involvement of the GDE2-RECK-ADAM10 pathway in AD pathophysiology and highlight RECK as a potential target for therapeutic development.

Transcriptomic analysis of a near-isogenic line of melon with high fruit flesh firmness during ripening

BACKGROUND

A near-isogenic line (NIL) of melon (SC10-2) with introgression in linkage group X was studied from harvest (at firm-ripe stage of maturity) until day 18 of postharvest storage at 20.5 °C together with its parental control ('Piel de Sapo', PS).

RESULTS

SC10-2 showed higher flesh firmness and whole fruit hardness but lower juiciness than its parental. SC10-2 showed a decrease in respiration rate accompanied by a decrease in ethylene production during ripening, both of which fell to a greater extent than in PS. The introgression affected 11 volatile organic compounds (VOCs), the levels of which during ripening were generally higher in SC10-2 than in PS. Transcriptomic analysis from RNA-Seq revealed differentially expressed genes (DEGs) associated with the effects studied. For example, 909 DEGs were exclusive to the introgression, and only 23 DEGs were exclusive to postharvest ripening time. Major functions of the DEGs associated with introgression or ripening time were identified by cluster analysis. About 37 genes directly and/or indirectly affected the delay in ripening of SC10-2 compared with PS in general and, more particularly, the physiological and quality traits measured and, probably, the differential non-climacteric response. Of the former genes, we studied in more detail at least five that mapped in the introgression in linkage group (LG) X, and 32 outside it.

CONCLUSION

There is an apparent control of textural changes, VOCs and fruit ripening by an expression quantitative trait locus located in LG X together with a direct control on them due to genes presented in the introgression (CmTrpD, CmNADH1, CmTCP15, CmGDSL esterase/lipase, and CmHK4-like) and CmNAC18. © 2020 Society of Chemical Industry.

GDE2 expression in oligodendroglia regulates the pace of oligodendrocyte maturation

BACKGROUND

Oligodendrocytes generate specialized lipid-rich sheaths called myelin that wrap axons and facilitate the rapid, saltatory transmission of action potentials. Extrinsic signals and surface-mediated pathways coordinate oligodendrocyte development to ensure appropriate axonal myelination, but the mechanisms involved are not fully understood. Glycerophosphodiester phosphodiesterase 2 (GDE2 or GDPD5) is a six-transmembrane enzyme that regulates the activity of surface glycosylphosphatidylinositol (GPI)-anchored proteins by cleavage of the GPI-anchor. GDE2 is expressed in neurons where it promotes oligodendrocyte maturation through the release of neuronally-derived soluble factors. GDE2 is also expressed in oligodendrocytes but the function of oligodendroglial GDE2 is not known.

RESULTS

Using Cre-lox technology, we generated mice that lack GDE2 expression in oligodendrocytes (O-Gde2KO). O-Gde2KOs show normal production and proliferation of oligodendrocyte precursor cells. However, oligodendrocyte maturation is accelerated leading to the robust increase of myelin proteins and increased myelination during development. These in vivo observations are recapitulated in vitro using purified primary oligodendrocytes, supporting cell-autonomous functions for GDE2 in oligodendrocyte maturation.

CONCLUSIONS

These studies reveal that oligodendroglial GDE2 expression is required for controlling the pace of oligodendrocyte maturation. Thus, the cell-type specific expression of GDE2 is important for the coordination of oligodendrocyte maturation and axonal myelination during neural development.

Glycerophosphodiesterase 3 (GDE3) is a lysophosphatidylinositol-specific ectophospholipase C acting as an endocannabinoid signaling switch

Endocannabinoid signaling plays a regulatory role in various (neuro)biological functions. 2-arachidonoylglycerol (2-AG) is the most abundant endocannabinoid, and although its canonical biosynthetic pathway involving phosphoinositide-specific phospholipase C and diacylglycerol lipase α is known, alternative pathways remain unsettled. Here, we characterize a noncanonical pathway implicating glycerophosphodiesterase 3 (GDE3, from GDPD2 gene). Human GDE3 expressed in HEK293T cell membranes catalyzed the conversion of lysophosphatidylinositol (LPI) into monoacylglycerol and inositol-1-phosphate. The enzyme was equally active against 1-acyl and 2-acyl LPI. When using 2-acyl LPI, where arachidonic acid is the predominant fatty acid, LC-MS analysis identified 2-AG as the main product of LPI hydrolysis by GDE3. Furthermore, inositol-1-phosphate release into the medium occurred upon addition of LPI to intact cells, suggesting that GDE3 is actually an ecto-lysophospholipase C. In cells expressing G-protein-coupled receptor GPR55, GDE3 abolished 1-acyl LPI-induced signaling. In contrast, upon simultaneous ex-pression of GDE3 and cannabinoid receptor CB2, 2-acyl LPI evoked the same signal as that induced by 2-AG. These data strongly suggest that, in addition to degrading the GPR55 LPI ligand, GDE3 can act as a switch between GPR55 and CB2 signaling. Coincident with a major expression of both GDE3 and CB2 in the spleen, spleens from transgenic mice lacking GDE3 displayed doubling of LPI content compared with WT mice. Decreased production of 2-AG in whole spleen was also observed, supporting the in vivo relevance of our findings. These data thus open a new research avenue in the field of endocannabinoid generation and reinforce the view of GPR55 and LPI being genuine actors of the endocannabinoid system.

Identification of human glycerophosphodiesterase 3 as an ecto phospholipase C that converts the G protein-coupled receptor 55 agonist lysophosphatidylinositol to bioactive monoacylglycerols in cultured mammalian cells

A family of glycerol-based lysolipid mediators comprises lysophosphatidic acid as a representative phospholipidic member but also a monoacylglycerol as a non-phosphorus-containing member. These critical lysolipid mediators are known to be produced from different lysophospholipids by actions of lysophospholipases C and D in mammals. Some members of the glycerophosphodiesterase (GDE) family have attracted recent attention due to their phospholipid-metabolizing activity. In this study, we found selective depletion of lysophosphatidylinositol among lysophospholipids in the culture medium of COS-7 cells transfected with a vector containing glycerophosphodiester phosphodiesterase 2 (GDPD2, GDE3). Thin-layer chromatography and liquid chromatography-tandem mass spectrometry of lipids extracted from GDE3-transfected COS-7 cells exposed to fluorescent analogs of phosphatidylinositol (PI) revealed that GDE3 acted as an ecto-type lysophospholipase C preferring endogenous lysophosphatidylinositol and PI having a long-chain acyl and a short-chain acyl group rather than endogenous PI and its fluorescent analog having two long chain acyl groups. In MC3T3-E1 cells cultured with an osteogenic or mitogenic medium, mRNA expression of GDE3 was increased by culturing in 10% fetal bovine serum for several days, concomitant with increased activity of ecto-lysophospholipase C, converting arachidonoyl-lysophosphatidylinositol, a physiological agonist of G protein-coupled receptor 55, to arachidonoylglycerol, a physiological agonist of cannabinoid receptors 1 and 2. We suggest that GDE3 acts as an ecto-lysophospholipase C, by switching signaling from lysophosphatidylinositol to that from arachidonoylglycerol in an opposite direction in mouse bone remodeling.

GDE3 regulates oligodendrocyte precursor proliferation via release of soluble CNTFRα

Oligodendrocyte development is tightly controlled by extrinsic signals; however, mechanisms that modulate cellular responses to these factors remain unclear. Six-transmembrane glycerophosphodiester phosphodiesterases (GDEs) are emerging as central regulators of cellular differentiation via their ability to shed glycosylphosphatidylinositol (GPI)-anchored proteins from the cell surface. We show here that GDE3 controls the pace of oligodendrocyte generation by negatively regulating oligodendrocyte precursor cell (OPC) proliferation. GDE3 inhibits OPC proliferation by stimulating ciliary neurotrophic factor (CNTF)-mediated signaling through release of CNTFRα, the ligand-binding component of the CNTF-receptor multiprotein complex, which can function as a soluble factor to activate CNTF signaling. GDE3 releases soluble CNTFRα by GPI-anchor cleavage from the plasma membrane and from extracellular vesicles (EVs) after co-recruitment of CNTFRα in EVs. These studies uncover new physiological roles for GDE3 in gliogenesis and identify GDE3 as a key regulator of CNTF-dependent regulation of OPC proliferation through release of CNTFRα.

Identification of multiple male reproductive tract-specific proteins that regulate sperm migration through the oviduct in mice

While the emergence of gene modification technologies has produced major discoveries in biomedical sciences, the recent development of the CRISPR/Cas9 system has dramatically altered the trajectory of phenotypic analysis in animal models. In this study, we identified male-specific gene clusters (Cst and Pate) and family genes (Gdpd and Lypd) and found specific members to be required for male fertility, especially for sperm fertilizing ability. Our findings support the important roles of these proteins in sperm function and could be used to develop novel infertility treatments as well as contraceptives.

CRISPR/Cas9-mediated genome editing technology enables researchers to efficiently generate and analyze genetically modified animals. We have taken advantage of this game-changing technology to uncover essential factors for fertility. In this study, we generated knockouts (KOs) of multiple male reproductive organ-specific genes and performed phenotypic screening of these null mutant mice to attempt to identify proteins essential for male fertility. We focused on making large deletions (dels) within 2 gene clusters encoding cystatin (CST) and prostate and testis expressed (PATE) proteins and individual gene mutations in 2 other gene families encoding glycerophosphodiester phosphodiesterase domain (GDPD) containing and lymphocyte antigen 6 (Ly6)/Plaur domain (LYPD) containing proteins. These gene families were chosen because many of the genes demonstrate male reproductive tract-specific expression. Although Gdpd1 and Gdpd4 mutant mice were fertile, disruptions of Cst and Pate gene clusters and Lypd4 resulted in male sterility or severe fertility defects secondary to impaired sperm migration through the oviduct. While absence of the epididymal protein families CST and PATE affect the localization of the sperm membrane protein A disintegrin and metallopeptidase domain 3 (ADAM3), the sperm acrosomal membrane protein LYPD4 regulates sperm fertilizing ability via an ADAM3-independent pathway. Thus, use of CRISPR/Cas9 technologies has allowed us to quickly rule in and rule out proteins required for male fertility and expand our list of male-specific proteins that function in sperm migration through the oviduct.

GDE5 inhibition accumulates intracellular glycerophosphocholine and suppresses adipogenesis at a mitotic clonal expansion stage

Mammalian glycerophosphodiesterases (GDEs) were recently shown to be involved in multiple cellular signaling pathways. This study showed that decreased GDE5 expression results in accumulation of intracellular glycerophosphocholine (GPC), showing that GDE5 is actively involved in GPC/choline metabolism in 3T3-L1 adipocytes. Using 3T3-L1 adipocytes, we further studied the biological significance of GPC/choline metabolism during adipocyte differentiation. Inhibition of GDE5 suppressed the formation of lipid droplets, which is accompanied by the decreased expression of adipocyte differentiation markers. We further showed that the decreased GDE5 expression suppressed mitotic clonal expansion (MCE) of preadipocytes. Decreased expression of CTP: phosphocholine cytidylyltransferase (CCTβ), a rate-limiting enzyme for phosphatidylcholine (PC) synthesis, is similarly able to inhibit MCE and PC synthesis; however, the decreased GDE5 expression resulted in accumulation of intracellular GPC but did not affect PC synthesis. Furthermore, we showed that mRNAs of proteoglycans and transporters for organic osmolytes are significantly upregulated and that intracellular amino acids and urea levels are altered in response to GDE5 inhibition. Finally, we showed that reduction of GDE5 expression increased lactate dehydrogenase release from preadipocytes. These observations indicate that decreased GDE5 expression can suppress adipocyte differentiation not through the PC pathway but possibly by intracellular GPC accumulation. These results provide insight into the roles of mammalian GDEs and their dependence upon osmotic regulation by altering intracellular GPC levels.

Deficiency of the Endocytic Protein Hip1 Leads to Decreased Gdpd3 Expression, Low Phosphocholine, and Kypholordosis

Deficiency of huntingtin-interacting protein 1 (Hip1) results in degenerative phenotypes. Here we generated a Hip1 deficiency allele where a floxed transcriptional stop cassette and a human HIP1 cDNA were knocked into intron 1 of the mouse Hip1 locus. CMV-Cre-mediated germ line excision of the stop cassette resulted in expression of HIP1 and rescue of the Hip1 knockout phenotype. Mx1-Cre-mediated excision led to HIP1 expression in spleen, kidney and liver, and also rescued the phenotype. In contrast, hGFAP-Cre-mediated, brain-specific HIP1 expression did not rescue the phenotype. Metabolomics and microarrays of several Hip1 knockout tissues identified low phosphocholine (PC) levels and low glycerophosphodiester phosphodiesterase domain containing 3 (Gdpd3) gene expression. Since Gdpd3 has lysophospholipase D activity that results in the formation of choline, a precursor of PC, Gdpd3 downregulation could lead to the low PC levels. To test whether Gdpd3 contributes to the Hip1 deficiency phenotype, we generated Gdpd3 knockout mice. Double knockout of Gdpd3 and Hip1 worsened the Hip1 phenotype. This suggests that Gdpd3 compensates for Hip1 loss. More-detailed knowledge of how Hip1 deficiency leads to low PC will improve our understanding of HIP1 in choline metabolism in normal and disease states.

An involvement of phospholipase A/acyltransferase family proteins in peroxisome regulation and plasmalogen metabolism

The H-Ras-like suppressor (HRASLS) is a protein family consisting of five members in humans. Despite their discovery as tumor suppressors, we demonstrated that all these proteins are phospholipid-metabolizing enzymes, such as phospholipase (PL) A₁ /A₂ and acyltransferase. We thus proposed to rename HRASLS1-5 as PLA/acyltransferase (PLAAT)-1-5. Notably, PLAATs exhibit N-acyltransferase activity to biosynthesize N-acylated ethanolamine phospholipids, including N-acyl-plasmalogen, which serve as precursors of bioactive N-acylethanolamines. Furthermore, the overexpression of PLAAT-3 in animal cells causes disappearance of peroxisomes and a remarkable reduction in plasmalogen levels. This finding might be related to the inhibitory effect of PLAAT-3 on the chaperone activity of the peroxin PEX19. In this article, we will review our recent findings about PLAAT proteins, with special reference to their roles in peroxisome biogenesis and plasmalogen metabolism.

Mammalian enzymes responsible for the biosynthesis of N-acylethanolamines

Bioactive N-acylethanolamines (NAEs) are ethanolamides of long-chain fatty acids, including palmitoylethanolamide, oleoylethanolamide and anandamide. In animal tissues, NAEs are biosynthesized from membrane phospholipids. The classical "transacylation-phosphodiesterase" pathway proceeds via N-acyl-phosphatidylethanolamine (NAPE), which involves the actions of two enzymes, NAPE-generating Ca²⁺-dependent N-acyltransferase (Ca-NAT) and NAPE-hydrolyzing phospholipase D (NAPE-PLD). Recent identification of Ca-NAT as Ɛ isoform of cytosolic phospholipase A₂ enabled the further molecular biological approaches toward this enzyme. In addition, Ca²⁺-independent NAPE formation was shown to occur by N-acyltransferase activity of a group of proteins named phospholipase A/acyltransferases (PLAAT)-1-5. The analysis of NAPE-PLD-deficient mice confirmed that NAEs can be produced through multi-step pathways bypassing NAPE-PLD. The NAPE-PLD-independent pathways involved three members of the glycerophosphodiesterase (GDE) family (GDE1, GDE4 and GDE7) as well as α/β-hydrolase domain-containing protein (ABHD)4. In this review article, we will focus on recent progress made and latest insights in the enzymes involved in NAE synthesis and their further characterization.

GDE2 is essential for neuronal survival in the postnatal mammalian spinal cord

Background

Glycerophosphodiester phosphodiesterase 2 (GDE2) is a six-transmembrane protein that cleaves glycosylphosphatidylinositol (GPI) anchors to regulate GPI-anchored protein activity at the cell surface. In the developing spinal cord, GDE2 utilizes its enzymatic function to regulate the production of specific classes of motor neurons and interneurons; however, GDE2’s roles beyond embryonic neurogenesis have yet to be defined.

Method

Using a panel of histological, immunohistochemical, electrophysiological, behavioral, and biochemistry techniques, we characterized the postnatal Gde2^−/− mouse for evidence of degenerative neuropathology. A conditional deletion of Gde2 was used to study the temporal requirements for GDE2 in neuronal survival. Biochemical approaches identified deficits in the processing of GPI-anchored GDE2 substrates in the SOD1^G93A mouse model of familial Amyotrophic Lateral Sclerosis that shows robust motor neuron degeneration.

Results

Here we show that GDE2 expression continues postnatally, and adult mice lacking GDE2 exhibit a slow, progressive neuronal degeneration with pathologies similar to human neurodegenerative disease. Early phenotypes include vacuolization, microgliosis, cytoskeletal accumulation, and lipofuscin deposition followed by astrogliosis and cell death. Remaining motor neurons exhibit peripheral motor unit restructuring causing behavioral motor deficits. Genetic ablation of GDE2 after embryonic neurogenesis is complete still elicits degenerative pathology, signifying that GDE2’s requirement for neuronal survival is distinct from its involvement in neuronal differentiation. Unbiased screens identify impaired processing of Glypican 4 and 6 in Gde2 null animals, and Glypican release is markedly reduced in SOD1^G93A mice.

Conclusions

This study identifies a novel function for GDE2 in neuronal survival and implicates deregulated GPI-anchored protein activity in pathways mediating neurodegeneration. These findings provide new molecular insight for neuropathologies found in multiple disease settings, and raise the possibility of GDE2 hypofunctionality as a component of neurodegenerative disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0148-1) contains supplementary material, which is available to authorized users.

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.

Expression and Characterization of a Novel Glycerophosphodiester Phosphodiesterase from Pyrococcus furiosus DSM 3638 That Possesses Lysophospholipase D Activity

Glycerophosphodiester phosphodiesterases (GDPD) are enzymes which degrade various glycerophosphodiesters to produce glycerol-3-phosphate and the corresponding alcohol moiety. Apart from this, a very interesting finding is that this enzyme could be used in the degradation of toxic organophosphorus esters, which has resulted in much attention on the biochemical and application research of GDPDs. In the present study, a novel GDPD from Pyrococcus furiosus DSM 3638 (pfGDPD) was successfully expressed in Escherichia coli and biochemically characterized. This enzyme hydrolyzed bis(p-nitrophenyl) phosphate, one substrate analogue of organophosphorus diester, with an optimal reaction temperature 55 °C and pH 8.5. The activity of pfGDPD was strongly dependent on existing of bivalent cations. It was strongly stimulated by Mn(2+) ions, next was Co(2+) and Ni(2+) ions. Further investigations were conducted on its substrate selectivity towards different phospholipids. The results indicated that except of glycerophosphorylcholine (GPC), this enzyme also possessed lysophospholipase D activity toward both sn1-lysophosphatidylcholine (1-LPC) and sn2-lysophosphatidylcholine (2-LPC). Higher activity was found for 1-LPC than 2-LPC; however, no hydrolytic activity was found for phosphatidylcholine (PC). Molecular docking based on the 3D-modeled structure of pfGDPD was conducted in order to provide a structural foundation for the substrate selectivity.

CD4 memory T cells develop and acquire functional competence by sequential cognate interactions and stepwise gene regulation

Memory CD4(+) T cells promote protective humoral immunity; however, how memory T cells acquire this activity remains unclear. This study demonstrates that CD4(+) T cells develop into antigen-specific memory T cells that can promote the terminal differentiation of memory B cells far more effectively than their naive T-cell counterparts. Memory T cell development requires the transcription factor B-cell lymphoma 6 (Bcl6), which is known to direct T-follicular helper (Tfh) cell differentiation. However, unlike Tfh cells, memory T cell development did not require germinal center B cells. Curiously, memory T cells that develop in the absence of cognate B cells cannot promote memory B-cell recall responses and this defect was accompanied by down-regulation of genes associated with homeostasis and activation and up-regulation of genes inhibitory for T-cell responses. Although memory T cells display phenotypic and genetic signatures distinct from Tfh cells, both had in common the expression of a group of genes associated with metabolic pathways. This gene expression profile was not shared to any great extent with naive T cells and was not influenced by the absence of cognate B cells during memory T cell development. These results suggest that memory T cell development is programmed by stepwise expression of gatekeeper genes through serial interactions with different types of antigen-presenting cells, first licensing the memory lineage pathway and subsequently facilitating the functional development of memory T cells. Finally, we identified Gdpd3 as a candidate genetic marker for memory T cells.

GPI-AP release in cellular, developmental, and reproductive biology

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) contain a covalently linked GPI anchor located on outer cell membranes. GPI-APs are ubiquitously conserved from protozoa to vertebrates and are critical for physiological events such as development, immunity, and neurogenesis in vertebrates. Both membrane-anchored and soluble GPI-APs play a role in regulating their protein conformation and functional properties. Several pathways mediate the release of GPI-APs from the plasma membrane by vesiculation or cleavage. Phospholipases and putative substrate-specific GPI-AP-releasing enzymes, such as NOTUM, glycerophosphodiesterase 2, and angiotensin-converting enzyme, have been characterized in mammals. Here, the protein modifications resulting from the cleavage of the GPI anchor are discussed in the context of its physiological functions.

Prdx4 is a compartment-specific H2O2 sensor that regulates neurogenesis by controlling surface expression of GDE2

Neural progenitors and terminally differentiated neurons show distinct redox profiles, suggesting that coupled-redox cascades regulate the initiation and progression of neuronal differentiation. Discrete cellular compartments have different redox environments and how they contribute to differentiation is unclear. Here we show that Prdx4, an endoplasmic reticulum (ER) enzyme that metabolizes H₂O₂, acts as a tunable regulator of neurogenesis via its compartmentalized thiol-oxidative function. Prdx4 ablation causes premature motor neuron differentiation and progenitor depletion, leading to imbalances in subtype-specific motor neurons. GDE2, a six-transmembrane protein that induces differentiation by downregulating Notch signalling through surface cleavage of GPI-anchored proteins, is targeted by Prdx4 oxidative activity. Prdx4 dimers generated by H₂O₂ metabolism oxidize two cysteine residues within the GDE2 enzymatic domain, which blocks GDE2 trafficking to the plasma membrane and prevents GDE2 neurogeneic function. Thus, Prdx4 oxidative activity acts as a sensor to directly couple neuronal differentiation with redox environments in the ER.

Neuron differentiation is marked by changes in intracellular redox status. Here Yan et al. show that ER-resident peroxiredoxin 4 senses increased H₂O₂ and prevents the surface expression of differentiation-promoting GDE2 by modifying cysteine residues within GDE2.

Coincidental loss of DOCK8 function in NLRP10-deficient and C3H/HeJ mice results in defective dendritic cell migration

Dendritic cells (DCs) are the primary leukocytes responsible for priming T cells. To find and activate naïve T cells, DCs must migrate to lymph nodes, yet the cellular programs responsible for this key step remain unclear. DC migration to lymph nodes and the subsequent T-cell response are disrupted in a mouse we recently described lacking the NOD-like receptor NLRP10 (NLR family, pyrin domain containing 10); however, the mechanism by which this pattern recognition receptor governs DC migration remained unknown. Using a proteomic approach, we discovered that DCs from Nlrp10 knockout mice lack the guanine nucleotide exchange factor DOCK8 (dedicator of cytokinesis 8), which regulates cytoskeleton dynamics in multiple leukocyte populations; in humans, loss-of-function mutations in Dock8 result in severe immunodeficiency. Surprisingly, Nlrp10 knockout mice crossed to other backgrounds had normal DOCK8 expression. This suggested that the original Nlrp10 knockout strain harbored an unexpected mutation in Dock8, which was confirmed using whole-exome sequencing. Consistent with our original report, NLRP3 inflammasome activation remained unaltered in NLRP10-deficient DCs even after restoring DOCK8 function; however, these DCs recovered the ability to migrate. Isolated loss of DOCK8 via targeted deletion confirmed its absolute requirement for DC migration. Because mutations in Dock genes have been discovered in other mouse lines, we analyzed the diversity of Dock8 across different murine strains and found that C3H/HeJ mice also harbor a Dock8 mutation that partially impairs DC migration. We conclude that DOCK8 is an important regulator of DC migration during an immune response and is prone to mutations that disrupt its crucial function.

New members of the mammalian glycerophosphodiester phosphodiesterase family: GDE4 and GDE7 produce lysophosphatidic acid by lysophospholipase D activity

The known mammalian glycerophosphodiester phosphodiesterases (GP-PDEs) hydrolyze glycerophosphodiesters. In this study, two novel members of the mammalian GP-PDE family, GDE4 and GDE7, were isolated, and the molecular basis of mammalian GP-PDEs was further explored. The GDE4 and GDE7 sequences are highly homologous and evolutionarily close. GDE4 is expressed in intestinal epithelial cells, spermatids, and macrophages, whereas GDE7 is particularly expressed in gastro-esophageal epithelial cells. Unlike other mammalian GP-PDEs, GDE4 and GDE7 cannot hydrolyze either glycerophosphoinositol or glycerophosphocholine. Unexpectedly, both GDE4 and GDE7 show a lysophospholipase D activity toward lysophosphatidylcholine (lyso-PC). We purified the recombinant GDE4 and GDE7 proteins and show that these enzymes can hydrolyze lyso-PC to produce lysophosphatidic acid (LPA). Further characterization of purified recombinant GDE4 showed that it can also convert lyso-platelet-activating factor (1-O-alkyl-sn-glycero-3-phosphocholine; lyso-PAF) to alkyl-LPA. These data contribute to our current understanding of mammalian GP-PDEs and of their physiological roles via the control of lyso-PC and lyso-PAF metabolism in gastrointestinal epithelial cells and macrophages.

Metabolic remodeling of white adipose tissue in obesity

Adipose tissue metabolism is a critical regulator of adiposity and whole body energy expenditure; however, metabolic changes that occur in white adipose tissue (WAT) with obesity remain unclear. The purpose of this study was to understand the metabolic and bioenergetic changes occurring in WAT with obesity. Wild-type (C57BL/6J) mice fed a high-fat diet (HFD) showed significant increases in whole body adiposity, had significantly lower V̇(O₂), V̇(CO₂), and respiratory exchange ratios, and demonstrated worsened glucose and insulin tolerance compared with low-fat-fed mice. Metabolomic analysis of WAT showed marked changes in lipid, amino acid, carbohydrate, nucleotide, and energy metabolism. Tissue levels of succinate and malate were elevated, and metabolites that could enter the Krebs cycle via anaplerosis were mostly diminished in high-fat-fed mice, suggesting altered mitochondrial metabolism. Despite no change in basal oxygen consumption or mitochondrial DNA abundance, citrate synthase activity was decreased by more than 50%, and responses to FCCP were increased in WAT from mice fed a high-fat diet. Moreover, Pgc1a was downregulated and Cox7a1 upregulated after 6 wk of HFD. After 12 wk of high-fat diet, the abundance of several proteins in the mitochondrial respiratory chain or matrix was diminished. These changes were accompanied by increased Parkin and Pink1, decreased p62 and LC3-I, and ultrastructural changes suggestive of autophagy and mitochondrial remodeling. These studies demonstrate coordinated restructuring of metabolism and autophagy that could contribute to the hypertrophy and whitening of adipose tissue in obesity.

New players in the fatty acyl ethanolamide metabolism

Fatty acyl ethanolamides represent a class of endogenous bioactive lipid molecules and are generally referred to as N-acylethanolamines (NAEs). NAEs include palmitoylethanolamide (anti-inflammatory and analgesic substance), oleoylethanolamide (anorexic substance), and anandamide (endocannabinoid). The endogenous levels of NAEs are mainly regulated by enzymes responsible for their biosynthesis and degradation. In mammalian tissues, the major biosynthetic pathway starts from glycerophospholipids and is composed of two enzyme reactions. The first step is N-acylation of ethanolamine phospholipids catalyzed by Ca(2+)-dependent N-acyltransferase and the second step is the release of NAEs from N-acylated ethanolamine phospholipids by N-acylphosphatidylethanolamine (NAPE)-hydrolyzing phospholipase D (NAPE-PLD). As for the degradation of NAEs, fatty acid amide hydrolase plays the central role. However, recent studies strongly suggest the involvement of other enzymes in the NAE metabolism. These enzymes include members of the HRAS-like suppressor family (also called phospholipase A/acyltransferase family), which were originally discovered as tumor suppressors but can function as Ca(2+)-independent NAPE-forming N-acyltransferases; multiple enzymes involved in the NAPE-PLD-independent multi-step pathways to generate NAE from NAPE, which came to light by the analysis of NAPE-PLD-deficient mice; and a lysosomal NAE-hydrolyzing acid amidase as a second NAE hydrolase. These newly recognized enzymes may become the targets for the development of new therapeutic drugs. Here, we focus on recent enzymological findings in this area.

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.

Glycerophosphocholine utilization by Candida albicans: role of the Git3 transporter in virulence

Candida albicans contains four ORFs (GIT1,2,3,4) predicted to encode proteins involved in the transport of glycerophosphodiester metabolites. Previously, we reported that Git1, encoded by ORF 19.34, is responsible for the transport of intact glycerophosphoinositol but not glycerophosphocholine (GroPCho). Here, we report that a strain lacking both GIT3 (ORF 19.1979) and GIT4 (ORF 19.1980) is unable to transport [(3)H]GroPCho into the cell. In the absence of a GroPCho transporter, C. albicans can utilize GroPCho via a mechanism involving extracellular hydrolysis. Upon reintegration of either GIT3 or GIT4 into the genome, measurable uptake of [(3)H]GroPCho is observed. Transport assays and kinetic analyses indicate that Git3 has the greater transport velocity. We present evidence that GDE1 (ORF 19.3936) codes for an enzyme with glycerophosphodiesterase activity against GroPCho. Homozygous deletion of GDE1 results in a buildup of internal GroPCho that is restored to wild type levels by reintegration of GDE1 into the genome. The transcriptional regulator, Pho4, is shown to regulate the expression of GIT3, GIT4, and GDE1. Finally, Git3 is shown to be required for full virulence in a mouse model of disseminated candidiasis, and Git3 sequence orthologs are present in other pathogenic Candida species. In summary, we have characterized multiple aspects of GroPCho utilization by C. albicans and have demonstrated that GroPCho transport plays a key role in the growth of the organism in the host.

The glycerophosphoinositols: from lipid metabolites to modulators of T-cell signaling

Glycerophosphoinositols (GPIs) are bioactive, diffusible phosphoinositide metabolites of phospholipase A₂ that act both intracellularly and in a paracrine fashion following their uptake by specific transporters. The most representative compound, glycerophosphoinositol (GroPIns), is a ubiquitous component of eukaryotic cells that participates in central processes, including cell proliferation and survival. Moreover, glycerophosphoinositol 4-phosphate (GroPIns4P) controls actin dynamics in several cell systems by regulating Rho GTPases. Recently, immune cells have emerged as targets of the biological activities of the GPIs. We have shown that exogenous GroPIns4P enhances CXCL12-induced T-cell chemotaxis through activation of the kinase Lck in a cAMP/PKA-dependent manner. While highlighting the potential of GroPIns4P as an immunomodulator, this finding raises questions on the role of endogenously produced GroPIns4P as well as of other GPIs in the regulation of the adaptive immune responses under homeostatic and pathological settings. Here we will summarize our current understanding of the biological activities of the GPIs, with a focus on lymphocytes, highlighting open questions and potential developments in this promising new area.

The role of phosphatidylcholine and choline metabolites to cell proliferation and survival

The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.

A multi-omic systems-based approach reveals metabolic markers of bacterial vaginosis and insight into the disease

BACKGROUND

Bacterial vaginosis (BV) is the most common vaginal disorder of reproductive-age women. Yet the cause of BV has not been established. To uncover key determinants of BV, we employed a multi-omic, systems-biology approach, including both deep 16S rRNA gene-based sequencing and metabolomics of lavage samples from 36 women. These women varied demographically, behaviorally, and in terms of health status and symptoms.

PRINCIPAL FINDINGS

16S rRNA gene-based community composition profiles reflected Nugent scores, but not Amsel criteria. In contrast, metabolomic profiles were markedly more concordant with Amsel criteria. Metabolomic profiles revealed two distinct symptomatic BV types (SBVI and SBVII) with similar characteristics that indicated disruption of epithelial integrity, but each type was correlated to the presence of different microbial taxa and metabolites, as well as to different host behaviors. The characteristic odor associated with BV was linked to increases in putrescine and cadaverine, which were both linked to Dialister spp. Additional correlations were seen with the presence of discharge, 2-methyl-2-hydroxybutanoic acid, and Mobiluncus spp., and with pain, diethylene glycol and Gardnerella spp.

CONCLUSIONS

The results not only provide useful diagnostic biomarkers, but also may ultimately provide much needed insight into the determinants of BV.

GDE2 promotes neurogenesis by glycosylphosphatidylinositol-anchor cleavage of RECK

The six-transmembrane protein glycerophosphodiester phosphodiesterase 2 (GDE2) induces spinal motor neuron differentiation by inhibiting Notch signaling in adjacent motor neuron progenitors. GDE2 function requires activity of its extracellular domain that shares homology with glycerophosphodiester phosphodiesterases (GDPDs). GDPDs metabolize glycerophosphodiesters into glycerol-3-phosphate and corresponding alcohols, but whether GDE2 inhibits Notch signaling by this mechanism is unclear. Here, we show that GDE2, unlike classical GDPDs, cleaves glycosylphosphatidylinositol (GPI) anchors. GDE2 GDPD activity inactivates the Notch activator RECK (reversion-inducing cysteine-rich protein with kazal motifs) by releasing it from the membrane through GPI-anchor cleavage. RECK release disinhibits ADAM (a disintegrin and metalloproteinase) protease-dependent shedding of the Notch ligand Delta-like 1 (Dll1), leading to Notch inactivation. This study identifies a previously unrecognized mechanism to initiate neurogenesis that involves GDE2-mediated surface cleavage of GPI-anchored targets to inhibit Dll1-Notch signaling.

Characterization of a glycerophosphodiesterase with an unusual tripartite distribution and an important role in the asexual blood stages of Plasmodium falciparum

Catabolism of glycerophospholipids during the rapid growth of the asexual intraerythrocytic malaria parasite may contribute to membrane recycling and the acquisition of lipid biosynthetic precursors from the host. To better understand the scope of lipid catabolism in Plasmodium falciparum, we have characterized a malarial homolog of bacterial glycerophosphodiesterases. These enzymes catalyze the hydrolysis of glycerophosphodiesterases that are generated by phospholipase-catalyzed removal of the two acyl groups from glycerophospholipids. The P. falciparum glycerophosphodiesterase (PfGDPD) exhibits an unusual tripartite distribution during the asexual blood stage with pools of enzyme in the parasitophorous vacuole, food vacuole and cytosol. Efforts to disrupt the chromosomal PfGDPD coding sequence were unsuccessful, which implies that the enzyme is important for efficient parasite growth. Tagging of the endogenous pool of PfGDPD with a conditional aggregation domain partially perturbed the distribution of the enzyme in the parasitophorous vacuole but had no discernable effect on growth in culture. Kinetic characterization of the hydrolysis of glycerophosphocholine by recombinant PfGDPD, an Mg(2+)-dependent enzyme, yielded steady-state parameters that were comparable to those of a homologous bacterial glycerophosphodiesterase. Together, these results suggest a physiological role for PfGDPD in glycerophospholipid catabolism in multiple subcellular compartments. Possibilities for what this role might be are discussed.

Choline-releasing glycerophosphodiesterase EDI3 drives tumor cell migration and metastasis

Metastasis from primary tumors remains a major problem for tumor therapy. In the search for markers of metastasis and more effective therapies, the tumor metabolome is relevant because of its importance to the malignant phenotype and metastatic capacity of tumor cells. Altered choline metabolism is a hallmark of cancer. More specifically, a decreased glycerophosphocholine (GPC) to phosphocholine (PC) ratio was reported in breast, ovarian, and prostate cancers. Improved strategies to exploit this altered choline metabolism are therefore required. However, the critical enzyme cleaving GPC to produce choline, the initial step in the pathway controlling the GPC/PC ratio, remained unknown. In the present work, we have identified the enzyme, here named EDI3 (endometrial differential 3). Purified recombinant EDI3 protein cleaves GPC to form glycerol-3-phosphate and choline. Silencing EDI3 in MCF-7 cells decreased this enzymatic activity, increased the intracellular GPC/PC ratio, and decreased downstream lipid metabolites. Downregulating EDI3 activity inhibited cell migration via disruption of the PKCα signaling pathway, with stable overexpression of EDI3 showing the opposite effect. EDI3 was originally identified in our screening study comparing mRNA levels in metastasizing and nonmetastasizing endometrial carcinomas. Both Kaplan-Meier and multivariate analyses revealed a negative association between high EDI3 expression and relapse-free survival time in both endometrial (P < 0.001) and ovarian (P = 0.029) cancers. Overall, we have identified EDI3, a key enzyme controlling GPC and choline metabolism. Because inhibition of EDI3 activity corrects the GPC/PC ratio and decreases the migration capacity of tumor cells, it represents a possible target for therapeutic intervention.

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.

Characterization of the Arabidopsis glycerophosphodiester phosphodiesterase (GDPD) family reveals a role of the plastid-localized AtGDPD1 in maintaining cellular phosphate homeostasis under phosphate starvation

Glycerophosphodiester phosphodiesterase (GDPD), which hydrolyzes glycerophosphodiesters into sn-glycerol-3-phosphate (G-3-P) and the corresponding alcohols, plays an important role in various physiological processes in both prokaryotes and eukaryotes. However, little is known about the physiological significance of GDPD in plants. Here, we characterized the Arabidopsis GDPD family that can be classified into canonical GDPD (AtGDPD1-6) and GDPD-like (AtGDPDL1-7) subfamilies. In vitro analysis of enzymatic activities showed that AtGDPD1 and AtGDPDL1 hydrolyzed glycerolphosphoglycerol, glycerophosphocholine and glycerophosphoethanolamine, but the maximum activity of AtGDPD1 was much higher than that of AtGDPDL1 under our assay conditions. Analyses of gene expression patterns revealed that all AtGDPD genes except for AtGDPD4 were transcriptionally active in flowers and siliques. In addition, the gene family displayed overlapping and yet distinguishable patterns of expression in roots, leaves and stems, indicating functional redundancy as well as specificity of GDPD genes. AtGDPDs but not AtGDPDLs are up-regulated by inorganic phosphate (P(i) ) starvation. Loss-of-function of the plastid-localized AtGDPD1 leads to a significant decrease in GDPD activity, G-3-P content, P(i) content and seedling growth rate only under P(i) starvation compared with the wild type (WT). However, membrane lipid compositions in the P(i) -deprived seedlings remain unaltered between the AtGDPD1 knockout mutant and WT. Thus, we suggest that the GDPD-mediated lipid metabolic pathway may be involved in release of P(i) from phospholipids during P(i) starvation.

The glycerophospho metabolome and its influence on amino acid homeostasis revealed by brain metabolomics of GDE1(-/-) mice

GDE1 is a mammalian glycerophosphodiesterase (GDE) implicated by in vitro studies in the regulation of glycerophophoinositol (GroPIns) and possibly other glycerophospho (GroP) metabolites. Here, we show using untargeted metabolomics that GroPIns is profoundly (>20-fold) elevated in brain tissue from GDE1(-/-) mice. Furthermore, two additional GroP metabolites not previously identified in eukaryotic cells, glycerophosphoserine (GroPSer) and glycerophosphoglycerate (GroPGate), were also highly elevated in GDE1(-/-) brains. Enzyme assays with synthetic GroP metabolites confirmed that GroPSer and GroPGate are direct substrates of GDE1. Interestingly, our metabolomic profiles also revealed that serine (both L-and D-) levels were significantly reduced in brains of GDE1(-/-) mice. These findings designate GroPSer as a previously unappreciated reservoir for free serine in the nervous system and suggest that GDE1, through recycling serine from GroPSer, may impact D-serine-dependent neural signaling processes in vivo.

CGDEase, a Pseudomonas fluorescens protein of the PLC/APase superfamily with CDP-ethanolamine and (dihexanoyl)glycerophosphoethanolamine hydrolase activity induced by osmoprotectants under phosphate-deficient conditions

A novel enzyme, induced by choline, ethanolamine, glycine betaine or dimethylglycine, was released at low temperature and phosphate from Pseudomonas fluorescens (CECT 7229) suspensions at low cell densities. It is a CDP-ethanolamine pyrophosphatase/(dihexanoyl)glycerophosphoethanolamine phosphodiesterase (CGDEase) less active on choline derivatives, and inactive on long-chain phospholipids, CDP-glycerol and other NDP-X compounds. The reaction pattern was typical of phospholipase C (PLC), as either phosphoethanolamine or phosphocholine was produced. Peptide-mass analyses, gene cloning and expression provided a molecular identity for CGDEase. Bioinformatic studies assigned it to the PLC branch of the phospholipase C/acid phosphatase (PLC/APase) superfamily, revealed an irregular phylogenetic distribution of close CGDEase relatives, and suggested their genes are not in operons or conserved contexts. A theoretical CGDEase structure was supported by mutagenesis of two predicted active-site residues, which yielded essentially inactive mutants. Biological relevance is supported by comparisons with CGDEase relatives, induction by osmoprotectants (not by osmotic stress itself) and repression by micromolar phosphate. The low bacterial density requirement was related to phosphate liberation from lysed bacteria in denser populations, rather than to a classical quorum-sensing effect. The results fit better a CGDEase role in phosphate scavenging than in osmoprotection.

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.

GDP-bound Galphai2 regulates spinal motor neuron differentiation through interaction with GDE2

Galphai proteins play major roles in the developing and mature nervous system, ranging from the control of cellular proliferation to modulating synaptic plasticity. Although best known for transducing signals from activated seven transmembrane G-protein coupled receptors (GPCRs) when bound to GTP, key cellular functions for Galphai-GDP are beginning to emerge. Here, we show that Galphai2 is expressed in motor neuron progenitors that are differentiating to form postmitotic motor neurons in the developing spinal cord. Ablation of Galphai2 causes deficits in motor neuron generation but no changes in motor neuron progenitor patterning or specification, consistent with a function for Galphai2 in regulating motor neuron differentiation. We show that Galphai2 function is mediated in part by its interaction with GDE2, a known regulator of motor neuron differentiation, and that disruption of the GDE2/Galphai2 complex in vivo causes motor neuron deficits analogous to Galphai2 ablation. Galphai2 preferentially associates with GDE2 when bound to GDP, invoking GPCR-independent functions for Galphai2 in the control of spinal motor neuron differentiation.