Publications

2014
Mayo L, Trauger SA, Blain M, Nadeau M, Patel B, Alvarez JI, Mascanfroni ID, Yeste A, Kivisakk P, Kallas K, et al. Regulation of astrocyte activation by glycolipids drives chronic CNS inflammation. Nat MedNat MedNat Med. 2014.Abstract
Astrocytes have complex roles in health and disease, thus it is important to study the pathways that regulate their function. Here we report that lactosylceramide (LacCer) synthesized by beta-1,4-galactosyltransferase 6 (B4GALT6) is upregulated in the central nervous system (CNS) of mice during chronic experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). LacCer acts in an autocrine manner to control astrocyte transcriptional programs that promote neurodegeneration. In addition, LacCer in astrocytes controls the recruitment and activation of microglia and CNS-infiltrating monocytes in a non-cell autonomous manner by regulating production of the chemokine CCL2 and granulocyte-macrophage colony-stimulating factor (GM-CSF), respectively. We also detected high B4GALT6 gene expression and LacCer concentrations in CNS MS lesions. Inhibition of LacCer synthesis in mice suppressed local CNS innate immunity and neurodegeneration in EAE and interfered with the activation of human astrocytes in vitro. Thus, B4GALT6 regulates astrocyte activation and is a potential therapeutic target for MS and other neuroinflammatory disorders.
Deguchi H, Elias DJ, Trauger S, Zhang HM, Kalisiak E, Siuzdak G, Griffin JH. Warfarin untargeted metabolomics study identifies novel procoagulant ethanolamide plasma lipids. Br J HaematolBr J HaematolBr J Haematol. 2014;165:409-12.
Chin RM, Fu X, Pai MY, Vergnes L, Hwang H, Deng G, Diep S, Lomenick B, Meli VS, Monsalve GC, et al. The metabolite alpha-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR. NatureNatureNature. 2014;510:397-401.Abstract
Metabolism and ageing are intimately linked. Compared with ad libitum feeding, dietary restriction consistently extends lifespan and delays age-related diseases in evolutionarily diverse organisms. Similar conditions of nutrient limitation and genetic or pharmacological perturbations of nutrient or energy metabolism also have longevity benefits. Recently, several metabolites have been identified that modulate ageing; however, the molecular mechanisms underlying this are largely undefined. Here we show that alpha-ketoglutarate (alpha-KG), a tricarboxylic acid cycle intermediate, extends the lifespan of adult Caenorhabditis elegans. ATP synthase subunit beta is identified as a novel binding protein of alpha-KG using a small-molecule target identification strategy termed drug affinity responsive target stability (DARTS). The ATP synthase, also known as complex V of the mitochondrial electron transport chain, is the main cellular energy-generating machinery and is highly conserved throughout evolution. Although complete loss of mitochondrial function is detrimental, partial suppression of the electron transport chain has been shown to extend C. elegans lifespan. We show that alpha-KG inhibits ATP synthase and, similar to ATP synthase knockdown, inhibition by alpha-KG leads to reduced ATP content, decreased oxygen consumption, and increased autophagy in both C. elegans and mammalian cells. We provide evidence that the lifespan increase by alpha-KG requires ATP synthase subunit beta and is dependent on target of rapamycin (TOR) downstream. Endogenous alpha-KG levels are increased on starvation and alpha-KG does not extend the lifespan of dietary-restricted animals, indicating that alpha-KG is a key metabolite that mediates longevity by dietary restriction. Our analyses uncover new molecular links between a common metabolite, a universal cellular energy generator and dietary restriction in the regulation of organismal lifespan, thus suggesting new strategies for the prevention and treatment of ageing and age-related diseases.
Ciolino JB, Stefanescu CF, Ross AE, Salvador-Culla B, Cortez P, Ford EM, Wymbs KA, Sprague SL, Mascoop DR, Rudina SS, et al. In vivo performance of a drug-eluting contact lens to treat glaucoma for a month. BiomaterialsBiomaterialsBiomaterials. 2014;35:432-9.Abstract
For nearly half a century, contact lenses have been proposed as a means of ocular drug delivery, but achieving controlled drug release has been a significant challenge. We have developed a drug-eluting contact lens designed for prolonged delivery of latanoprost for the treatment of glaucoma, the leading cause of irreversible blindness worldwide. Latanoprost-eluting contact lenses were created by encapsulating latanoprost-poly(lactic-co-glycolic acid) films in methafilcon by ultraviolet light polymerization. In vitro and in vivo studies showed an early burst of drug release followed by sustained release for one month. Contact lenses containing thicker drug-polymer films demonstrated released a greater amount of drug after the initial burst. In vivo, single contact lenses were able to achieve, for at least one month, latanoprost concentrations in the aqueous humor that were comparable to those achieved with topical latanoprost solution, the current first-line treatment for glaucoma. The lenses appeared safe in cell culture and animal studies. This contact lens design can potentially be used as a treatment for glaucoma and as a platform for other ocular drug delivery applications.
Mayo L1, Trauger SA2 BNPAJI4 MID1 YKKEM3 M1 B1.

Regulation of astrocyte activation by glycolipids drives chronic CNS inflammation

. Nature Medicine. 2014;Sep 14.Abstract
Astrocytes have complex roles in health and disease, thus it is important to study the pathways that regulate their function. Here we report that lactosylceramide (LacCer) synthesized by β-1,4-galactosyltransferase 6 (B4GALT6) is upregulated in the central nervous system (CNS) of mice during chronic experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). LacCer acts in an autocrine manner to control astrocyte transcriptional programs that promote neurodegeneration. In addition, LacCer in astrocytes controls the recruitment and activation of microglia and CNS-infiltrating monocytes in a non-cell autonomous manner by regulating production of the chemokine CCL2 and granulocyte-macrophage colony-stimulating factor (GM-CSF), respectively. We also detected high B4GALT6 gene expression and LacCer concentrations in CNS MS lesions. Inhibition of LacCer synthesis in mice suppressed local CNS innate immunity and neurodegeneration in EAE and interfered with the activation of human astrocytes in vitro. Thus, B4GALT6 regulates astrocyte activation and is a potential therapeutic target for MS and other neuroinflammatory disorders.
2013
Kirby DP, Buckley M, Promise E, Trauger SA, Holdcraft TR. Identification of collagen-based materials in cultural heritage. AnalystAnalystAnalyst. 2013;138:4849-58.Abstract
All stakeholders in cultural heritage share an interest in fabrication methods and material technology. Until now methods for analysis of organic materials, particularly proteins, have not been widely available to researchers at cultural institutions. This paper will describe an analytical method for the identification of collagen-based materials from soft tissue sources and show examples of its application to diverse museum objects. The method, peptide mass fingerprinting (PMF), uses enzymatic digestion of extracted proteins to produce a mixture of peptides. The mass spectrum of the mixture contains characteristic marker ions-a peptide mass fingerprint-which are compared to species-specific markers from references as the basis of identification. Preliminary results indicate that analysis of materials from aged samples, several different tissue types, and tanned or untanned materials yields comparable PMF results. Significantly, PMF is simple, rapid, sensitive and specific, has been implemented in a museum laboratory, and is being practiced successfully by non-specialists.
Koudelka KJ, Ippoliti S, Medina E, Shriver LP, Trauger SA, Catalano CE, Manchester M. Lysine addressability and mammalian cell interactions of bacteriophage lambda procapsids. BiomacromoleculesBiomacromoleculesBiomacromolecules. 2013;14:4169-76.Abstract
Chemically or genetically modified virus particles, termed viral nanoparticles (VNPs), are being explored in applications such as drug delivery, vaccine development, and materials science. Each virus platform has inherent properties and advantages based on its structure, molecular composition, and biomolecular interactions. Bacteriophage lambda was studied for its lysine addressability, stability, cellular uptake, and the ability to modify its cellular uptake. lambda procapsids could be labeled primarily at a single residue on the gpE capsid protein as determined by tandem mass spectrometry, providing a unique attachment site for further capsid modification. Bioconjugation of transferrin to the procapsids mediated specific interaction with transferrin receptor-expressing cells. These studies demonstrate the utility of bacteriophage lambda procapsids and their potential use as targeted drug delivery vehicles.
Blankman JL, Long JZ, Trauger SA, Siuzdak G, Cravatt BF. ABHD12 controls brain lysophosphatidylserine pathways that are deregulated in a murine model of the neurodegenerative disease PHARC. Proc Natl Acad Sci U S AProc Natl Acad Sci U S AProc Natl Acad Sci U S A. 2013;110:1500-5.Abstract
Advances in human genetics are leading to the discovery of new disease-causing mutations at a remarkable rate. Many such mutations, however, occur in genes that encode for proteins of unknown function, which limits our molecular understanding of, and ability to devise treatments for, human disease. Here, we use untargeted metabolomics combined with a genetic mouse model to determine that the poorly characterized serine hydrolase alpha/beta-hydrolase domain-containing (ABHD)12, mutations in which cause the human neurodegenerative disorder PHARC (polyneuropathy, hearing loss, ataxia, retinosis pigmentosa, and cataract), is a principal lysophosphatidylserine (LPS) lipase in the mammalian brain. ABHD12(-/-) mice display massive increases in a rare set of very long chain LPS lipids that have been previously reported as Toll-like receptor 2 activators. We confirm that recombinant ABHD12 protein exhibits robust LPS lipase activity, which is also substantially reduced in ABHD12(-/-) brain tissue. Notably, elevations in brain LPS lipids in ABHD12(-/-) mice occur early in life (2-6 mo) and are followed by age-dependent increases in microglial activation and auditory and motor defects that resemble the behavioral phenotypes of human PHARC patients. Taken together, our data provide a molecular model for PHARC, where disruption of ABHD12 causes deregulated LPS metabolism and the accumulation of proinflammatory lipids that promote microglial and neurobehavioral abnormalities.
2011
Powers ME, Smith PA, Roberts TC, Fowler BJ, King CC, Trauger SA, Siuzdak G, Romesberg FE. Type I signal peptidase and protein secretion in Staphylococcus epidermidis. J BacteriolJ BacteriolJ Bacteriol. 2011;193:340-8.Abstract
Bacterial protein secretion is a highly orchestrated process that is essential for infection and virulence. Despite extensive efforts to predict or experimentally detect proteins that are secreted, the characterization of the bacterial secretome has remained challenging. A central event in protein secretion is the type I signal peptidase (SPase)-mediated cleavage of the N-terminal signal peptide that targets a protein for secretion via the general secretory pathway, and the arylomycins are a class of natural products that inhibit SPase, suggesting that they may be useful chemical biology tools for characterizing the secretome. Here, using an arylomycin derivative, along with two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identify 11 proteins whose secretion from stationary-phase Staphylococcus epidermidis is dependent on SPase activity, 9 of which are predicted to be translated with canonical N-terminal signal peptides. In addition, we find that the presence of extracellular domains of lipoteichoic acid synthase (LtaS) and the beta-lactam response sensor BlaR1 in the medium is dependent on SPase activity, suggesting that they are cleaved at noncanonical sites within the protein. In all, the data define the proteins whose stationary-phase secretion depends on SPase and also suggest that the arylomycins should be valuable chemical biology tools for the study of protein secretion in a wide variety of different bacteria.
Pendyala G, Trauger SA, Siuzdak G, Fox HS. Short communication: quantitative proteomic plasma profiling reveals activation of host defense to oxidative stress in chronic SIV and methamphetamine comorbidity. AIDS Res Hum RetrovirusesAIDS Res Hum RetrovirusesAIDS Res Hum Retroviruses. 2011;27:179-82.Abstract
The double epidemic of substance abuse and HIV infection is a multifaceted problem To investigate mechanistic clues to the effects of substance abuse on infected individuals we preformed quantitative proteomic profiling of plasma in a methamphetamine treated nonhuman primate model for AIDS. A nontargeted quantitative approach identified extracellular superoxide dismutase to be significantly upregulated by SIV and methamphetamine treatment, and targeted studies revealed an increase in expression in the antioxidant glutathione S-transferase, thus pointing to a compensatory response to increased oxidative stress in methamphetamine-treated animals.
Long JZ, Cisar JS, Milliken D, Niessen S, Wang C, Trauger SA, Siuzdak G, Cravatt BF. Metabolomics annotates ABHD3 as a physiologic regulator of medium-chain phospholipids. Nat Chem BiolNat Chem BiolNat Chem Biol. 2011;7:763-5.Abstract
All organisms, including humans, possess a huge number of uncharacterized enzymes. Here we describe a general cell-based screen for enzyme substrate discovery by untargeted metabolomics and its application to identify the protein alpha/beta-hydrolase domain-containing 3 (ABHD3) as a lipase that selectively cleaves medium-chain and oxidatively truncated phospholipids. Abhd3(-/-) mice possess elevated myristoyl (C14)-phospholipids, including the bioactive lipid C14-lysophosphatidylcholine, confirming the physiological relevance of our substrate assignments.
Lancaster WA, Praissman JL, Poole, F. L. 2nd, Cvetkovic A, Menon AL, Scott JW, Jenney, F. E. J, Thorgersen MP, Kalisiak E, Apon JV, et al. A computational framework for proteome-wide pursuit and prediction of metalloproteins using ICP-MS and MS/MS data. BMC BioinformaticsBMC BioinformaticsBMC Bioinformatics. 2011;12:64.Abstract
BACKGROUND: Metal-containing proteins comprise a diverse and sizable category within the proteomes of organisms, ranging from proteins that use metals to catalyze reactions to proteins in which metals play key structural roles. Unfortunately, reliably predicting that a protein will contain a specific metal from its amino acid sequence is not currently possible. We recently developed a generally-applicable experimental technique for finding metalloproteins on a genome-wide scale. Applying this metal-directed protein purification approach (ICP-MS and MS/MS based) to the prototypical microbe Pyrococcus furiosus conclusively demonstrated the extent and diversity of the uncharacterized portion of microbial metalloproteomes since a majority of the observed metal peaks could not be assigned to known or predicted metalloproteins. However, even using this technique, it is not technically feasible to purify to homogeneity all metalloproteins in an organism. In order to address these limitations and complement the metal-directed protein purification, we developed a computational infrastructure and statistical methodology to aid in the pursuit and identification of novel metalloproteins. RESULTS: We demonstrate that our methodology enables predictions of metal-protein interactions using an experimental data set derived from a chromatography fractionation experiment in which 870 proteins and 10 metals were measured over 2,589 fractions. For each of the 10 metals, cobalt, iron, manganese, molybdenum, nickel, lead, tungsten, uranium, vanadium, and zinc, clusters of proteins frequently occurring in metal peaks (of a specific metal) within the fractionation space were defined. This resulted in predictions that there are from 5 undiscovered vanadium- to 13 undiscovered cobalt-containing proteins in Pyrococcus furiosus. Molybdenum and nickel were chosen for additional assessment producing lists of genes predicted to encode metalloproteins or metalloprotein subunits, 22 for nickel including seven from known nickel-proteins, and 20 for molybdenum including two from known molybdo-proteins. The uncharacterized proteins are prime candidates for metal-based purification or recombinant approaches to validate these predictions. CONCLUSIONS: We conclude that the largely uncharacterized extent of native metalloproteomes can be revealed through analysis of the co-occurrence of metals and proteins across a fractionation space. This can significantly impact our understanding of metallobiochemistry, disease mechanisms, and metal toxicity, with implications for bioremediation, medicine and other fields.
Pendyala G, Trauger SA, Siuzdak G, Fox HS. Short communication: quantitative proteomic plasma profiling reveals activation of host defense to oxidative stress in chronic SIV and methamphetamine comorbidity. AIDS Res Hum Retroviruses [Internet]. 2011;27:179-82. WebsiteAbstract
The double epidemic of substance abuse and HIV infection is a multifaceted problem To investigate mechanistic clues to the effects of substance abuse on infected individuals we preformed quantitative proteomic profiling of plasma in a methamphetamine treated nonhuman primate model for AIDS. A nontargeted quantitative approach identified extracellular superoxide dismutase to be significantly upregulated by SIV and methamphetamine treatment, and targeted studies revealed an increase in expression in the antioxidant glutathione S-transferase, thus pointing to a compensatory response to increased oxidative stress in methamphetamine-treated animals.
Powers ME, Smith PA, Roberts TC, Fowler BJ, King CC, Trauger SA, Siuzdak G, Romesberg FE. Type I signal peptidase and protein secretion in Staphylococcus epidermidis. J Bacteriol [Internet]. 2011;193:340-8. WebsiteAbstract
Bacterial protein secretion is a highly orchestrated process that is essential for infection and virulence. Despite extensive efforts to predict or experimentally detect proteins that are secreted, the characterization of the bacterial secretome has remained challenging. A central event in protein secretion is the type I signal peptidase (SPase)-mediated cleavage of the N-terminal signal peptide that targets a protein for secretion via the general secretory pathway, and the arylomycins are a class of natural products that inhibit SPase, suggesting that they may be useful chemical biology tools for characterizing the secretome. Here, using an arylomycin derivative, along with two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identify 11 proteins whose secretion from stationary-phase Staphylococcus epidermidis is dependent on SPase activity, 9 of which are predicted to be translated with canonical N-terminal signal peptides. In addition, we find that the presence of extracellular domains of lipoteichoic acid synthase (LtaS) and the beta-lactam response sensor BlaR1 in the medium is dependent on SPase activity, suggesting that they are cleaved at noncanonical sites within the protein. In all, the data define the proteins whose stationary-phase secretion depends on SPase and also suggest that the arylomycins should be valuable chemical biology tools for the study of protein secretion in a wide variety of different bacteria.
Lancaster WA, Praissman JL, Poole, F. L. 2nd, Cvetkovic A, Menon AL, Scott JW, Jenney, F. E. J, Thorgersen MP, Kalisiak E, Apon JV, et al. A computational framework for proteome-wide pursuit and prediction of metalloproteins using ICP-MS and MS/MS data. BMC Bioinformatics [Internet]. 2011;12:64. WebsiteAbstract
BACKGROUND: Metal-containing proteins comprise a diverse and sizable category within the proteomes of organisms, ranging from proteins that use metals to catalyze reactions to proteins in which metals play key structural roles. Unfortunately, reliably predicting that a protein will contain a specific metal from its amino acid sequence is not currently possible. We recently developed a generally-applicable experimental technique for finding metalloproteins on a genome-wide scale. Applying this metal-directed protein purification approach (ICP-MS and MS/MS based) to the prototypical microbe Pyrococcus furiosus conclusively demonstrated the extent and diversity of the uncharacterized portion of microbial metalloproteomes since a majority of the observed metal peaks could not be assigned to known or predicted metalloproteins. However, even using this technique, it is not technically feasible to purify to homogeneity all metalloproteins in an organism. In order to address these limitations and complement the metal-directed protein purification, we developed a computational infrastructure and statistical methodology to aid in the pursuit and identification of novel metalloproteins. RESULTS: We demonstrate that our methodology enables predictions of metal-protein interactions using an experimental data set derived from a chromatography fractionation experiment in which 870 proteins and 10 metals were measured over 2,589 fractions. For each of the 10 metals, cobalt, iron, manganese, molybdenum, nickel, lead, tungsten, uranium, vanadium, and zinc, clusters of proteins frequently occurring in metal peaks (of a specific metal) within the fractionation space were defined. This resulted in predictions that there are from 5 undiscovered vanadium- to 13 undiscovered cobalt-containing proteins in Pyrococcus furiosus. Molybdenum and nickel were chosen for additional assessment producing lists of genes predicted to encode metalloproteins or metalloprotein subunits, 22 for nickel including seven from known nickel-proteins, and 20 for molybdenum including two from known molybdo-proteins. The uncharacterized proteins are prime candidates for metal-based purification or recombinant approaches to validate these predictions. CONCLUSIONS: We conclude that the largely uncharacterized extent of native metalloproteomes can be revealed through analysis of the co-occurrence of metals and proteins across a fractionation space. This can significantly impact our understanding of metallobiochemistry, disease mechanisms, and metal toxicity, with implications for bioremediation, medicine and other fields.
Long JZ, Cisar JS, Milliken D, Niessen S, Wang C, Trauger SA, Siuzdak G, Cravatt BF. Metabolomics annotates ABHD3 as a physiologic regulator of medium-chain phospholipids. Nat Chem Biol [Internet]. 2011;7:763-5. WebsiteAbstract
All organisms, including humans, possess a huge number of uncharacterized enzymes. Here we describe a general cell-based screen for enzyme substrate discovery by untargeted metabolomics and its application to identify the protein alpha/beta-hydrolase domain-containing 3 (ABHD3) as a lipase that selectively cleaves medium-chain and oxidatively truncated phospholipids. Abhd3(-/-) mice possess elevated myristoyl (C14)-phospholipids, including the bioactive lipid C14-lysophosphatidylcholine, confirming the physiological relevance of our substrate assignments.
2010
Yanes O, Clark J, Wong DM, Patti GJ, Sanchez-Ruiz A, Benton HP, Trauger SA, Desponts C, Ding S, Siuzdak G. Metabolic oxidation regulates embryonic stem cell differentiation. Nat Chem BiolNat Chem BiolNat Chem Biol. 2010;6:411-7.Abstract
Metabolites offer an important unexplored complementary approach to understanding the pluripotency of stem cells. Using MS-based metabolomics, we show that embryonic stem cells are characterized by abundant metabolites with highly unsaturated structures whose levels decrease upon differentiation. By monitoring the reduced and oxidized glutathione ratio as well as ascorbic acid levels, we demonstrate that the stem cell redox status is regulated during differentiation. On the basis of the oxidative biochemistry of the unsaturated metabolites, we experimentally manipulated specific pathways in embryonic stem cells while monitoring the effects on differentiation. Inhibition of the eicosanoid signaling pathway promoted pluripotency and maintained levels of unsaturated fatty acids. In contrast, downstream oxidized metabolites (for example, neuroprotectin D1) and substrates of pro-oxidative reactions (for example, acyl-carnitines), promoted neuronal and cardiac differentiation. We postulate that the highly unsaturated metabolome sustained by stem cells allows them to differentiate in response to in vivo oxidative processes such as inflammation.
Pendyala G, Trauger SA, Siuzdak G, Fox HS. Quantitative plasma proteomic profiling identifies the vitamin E binding protein afamin as a potential pathogenic factor in SIV induced CNS disease. J Proteome ResJ Proteome ResJ Proteome Res. 2010;9:352-8.Abstract
Investigating, predicting, diagnosing, and treating HIV-1-associated neurocognitive disorder (HAND) has been hindered by the lack of disease-related molecular markers. In this study, plasma from rhesus monkeys (n = 6), before and after infection with simian immunodeficiency virus (SIV), was profiled to obtain differential fingerprints in protein expression during SIV-induced central nervous system (CNS) disease. A quantitative proteomic analysis was performed by means of isobaric tag for relative and absolute quantification (iTRAQ) labeling, using multidimensional liquid chromatography tandem mass spectrometry (LC-MS/MS) run on a linear ion trap mass spectrometer in an integrated mode comprising pulsed-Q-dissociation (PQD) and CID. Among a panel of proteins showing differential expression following SIV infection, we identified afamin, a member of the albumin superfamily, to be significantly down regulated after infection. Validation by Western blot confirmed this observation and, given its potential implication in neuroprotection by transport of alpha-tocopherol (alphaTocH), provides new avenues into further understanding HIV induced CNS disease. iTRAQ-based LC-MS/MS provides a valuable platform for plasma protein profiling and has important implications in identifying molecular markers relevant for the pathogenesis of neurodegenerative diseases. Using such an approach, we show its successful application in identifying differential fingerprints in SIV/HIV induced CNS disease.
Kopp F, Komatsu T, Nomura DK, Trauger SA, Thomas JR, Siuzdak G, Simon GM, Cravatt BF. The glycerophospho metabolome and its influence on amino acid homeostasis revealed by brain metabolomics of GDE1(-/-) mice. Chem BiolChem BiolChem Biol. 2010;17:831-40.Abstract
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.
Dorrell MI, Aguilar E, Jacobson R, Trauger SA, Friedlander J, Siuzdak G, Friedlander M. Maintaining retinal astrocytes normalizes revascularization and prevents vascular pathology associated with oxygen-induced retinopathy. GliaGliaGlia. 2010;58:43-54.Abstract
Astrocytes are well known modulators of normal developmental retinal vascularization. However, relatively little is known about the role of glial cells during pathological retinal neovascularization (NV), a leading contributor to vision loss in industrialized nations. We demonstrate that the loss of astrocytes and microglia directly correlates with the development of pathological NV in a mouse model of oxygen-induced retinopathy (OIR). These two distinct glial cell populations were found to have cooperative survival effects in vitro and in vivo. The intravitreal injection of myeloid progenitor cells, astrocytes, or astrocyte-conditioned media rescued endogenous astrocytes from degeneration that normally occurs within the hypoxic, vaso-obliterated retina following return to normoxia. Protection of the retinal astrocytes and microglia was directly correlated with accelerated revascularization of the normal retinal plexuses and reduction of pathological intravitreal NV normally associated with OIR. Using astrocyte-conditioned media, several factors were identified that may contribute to the observed astrocytic protection and subsequent normalization of the retinal vasculature, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Injection of VEGF or bFGF at specific doses rescued the retinas from developing OIR-associated pathology, an effect that was also preceded by protection of endogenous glia from hypoxia-induced degeneration. Together, these data suggest that vascular-associated glia are also required for normalized revascularization of the hypoxic retina. Methods developed to target and protect glial cells may provide a novel strategy by which normalized revascularization can be promoted and the consequences of abnormal NV in retinal vascular diseases can be prevented.