L-serine synthesis in the central nervous system: a review on serine deficiency disorders

D-Serine as the gatekeeper of NMDA receptor activity: implications for the pharmacologic management of anxiety disorders

Fear, anxiety, and trauma-related disorders, including post-traumatic stress disorder (PTSD), are quite common and debilitating, with an estimated lifetime prevalence of ~28% in Western populations. They are associated with excessive fear reactions, often including an inability to extinguish learned fear, increased avoidance behavior, as well as altered cognition and mood. There is an extensive literature demonstrating the importance of N-methyl-D-aspartate receptor (NMDAR) function in regulating these behaviors. NMDARs require the binding of a co-agonist, D-serine or glycine, at the glycine modulatory site (GMS) to function. D-serine is now garnering attention as the primary NMDAR co-agonist in limbic brain regions implicated in neuropsychiatric disorders. L-serine is synthesized by astrocytes, which is then transported to neurons for conversion to D-serine by serine racemase (SR), a model we term the 'serine shuttle.' The neuronally-released D-serine is what regulates NMDAR activity. Our review discusses how the systems that regulate the synaptic availability of D-serine, a critical gatekeeper of NMDAR-dependent activation, could be targeted to improve the pharmacologic management of anxiety-related disorders where the desired outcomes are the facilitation of fear extinction, as well as mood and cognitive enhancement.

Inhibition of Serine Metabolism Promotes Resistance to Cisplatin in Gastric Cancer

Background

Serine provides important precursors of protein, lipid, and nucleotide synthesis needed for tumor cell growth. Phosphoglycerate dehydrogenase (PHGDH), a key rate-limiting enzyme in the serine de novo synthesis pathway, is highly expressed in many tumor types (including gastric cancer) and negatively correlated with overall survival. Cisplatin is a chemotherapeutic drug commonly used in the treatment of gastric cancer. In this study, we mainly investigated the relationship between serine metabolism and resistance to cisplatin in gastric cancer cells, as well as the regulatory mechanism involved in this process.

Materials and Methods

We determined the effect of different concentrations of serine or a PHGDH inhibitor combined with cisplatin or oxaliplatin on the viability and apoptosis of SGC7901, BGC823, and MGC803 cells via the Cell Counting Kit-8 and Hoechst 33258 staining, respectively. Western blotting was utilized to detect the relative protein expression. Furthermore, we investigated DNA damage through the micrococcal nuclease sensitivity assay detected using agarose gels.

Results

We found that reduced concentrations of serine or inhibition of PHGDH hindered the toxicity and pro-apoptotic effects of cisplatin on gastric cancer cells. Moreover, the addition of serine could reverse the sensitivity of gastric cancer cells to cisplatin. Moreover, we found that DNA damage was reduced by treatment with PHGDH inhibitor NCT-503 or CBR-5884. Inhibition of serine metabolism induced a decrease in H3K4 tri-methylation, which was reversed by JIB-04 (inhibitor of H3K4 demethylase). The tolerance of gastric cancer cells to cisplatin was relieved by JIB-04. Through micrococcal nuclease experiments, we further found that inhibiting the activity of PHGDH strengthened chromatin tightness.

Conclusion

Inhibition of serine metabolism reduced H3K4 tri-methylation and increased the density of chromatin, which leads to decreased toxicity and pro-apoptotic effect of platinum chemotherapeutic drugs on gastric cancer cells.

Investigation of bound and unbound phosphoserine phosphatase conformations through elastic network models and molecular dynamics simulations

The human phosphoserine phosphatase (hPSP) catalyses the last step in the biosynthesis of L-serine. It involves conformational changes of the enzyme lid once the substrate, phosphoserine (PSer), is bound in the active site. Here, Elastic Network Model (ENM) is applied to the crystal structure of hPSP to probe the transition between open and closed conformations of hPSP. Molecular Dynamics (MD) simulations are carried out on several PSer-hPSP systems to characterise the intermolecular interactions and their effect on the dynamics of the enzyme lid. Systems involving either Ca⁺⁺ or Mg⁺⁺ are considered. The first ENM normal mode shows that an open-closed transition can be explained from a simple description of the enzyme in terms of harmonic potentials. Principal Component Analyses applied to the MD trajectories also highlight a trend for a closing/opening motion. Different PSer orientations inside the enzyme cavity are identified, i.e. either the carboxylate, the phosphate group of PSer, or both, are oriented towards the cation. The interaction patterns are analysed in terms of hydrogen bonds, electrostatics, and bond critical points of the electron density distributions. The latter approach yields a global description of the bonding intermolecular interactions. The PSer orientation determines the content of the cation coordination shell and the mobility of the substrate, while Lys158 and Thr182, involved in the reaction mechanism, are always in interaction with the substrate. Closed enzyme conformations involve Met52-Gln204, Arg49-Glu29, and Arg50-Glu29 interactions. Met52, as well as Arg49 and Arg50, also stabilize PSer inside the cavity. Communicated by Ramaswamy H. Sarma.

A reconnaissance DFT study of the full conformational analysis of N-formyl-L-serine-L-alanine-NH2 dipeptide

Theoretical conformational analysis of N-formyl-L-serine-L-alanine-NH₂ dipeptide model was investigated using B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) calculations. In this research, 243 total possible conformations of the dipeptide model were optimized including 87 stable conformers and the other disappeared ones migrated to more stable geometries. Migration pattern suggests more stability of the dipeptide model with the serine (ser) in β_L, γ_L, and γ_D and the alanine (ala) in γ_D and γ_L configurations, along with 26 of the found conformers having β-turn structures. Our calculations reveal that the most stable conformer, γ_L⁺γ_D, is in β-turn region of Ramachandran map; therefore, serine-alanine (ser-ala) dipeptide model should be adopted with a β-turn conformation. The atoms in molecules (AIM) topological analysis was carried out to characterize the nature of the intramolecular hydrogen bonding in β-turn structures. The γ_L⁺γ_D, including three hydrogen bonds, has the highest stability, while α_L^aγ_L as the most unstable β-turn conformer bears two and one hydrogen bonds at the B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) levels of theory, respectively. Graphical abstract.

The Role of D-3-Phosphoglycerate Dehydrogenase in Cancer

Serine, a non-essential amino acid, can be imported from the extracellular environment by transporters and de novo synthesized from glycolytic 3-phosphoglycerate (3-PG) in the serine biosynthetic pathway (SSP). It has been reported that active serine synthesis might be needed for the synthesis of proteins, lipids, and nucleotides and the balance of folate metabolism and redox homeostasis, which are necessary for cancer cell proliferation. Human D-3-phosphoglycerate dehydrogenase (PHGDH), the first and only rate-limiting enzyme in the de novo serine biosynthetic pathway, catalyzes the oxidation of 3-PG derived from glycolysis to 3-phosphohydroxypyruvate (3-PHP). PHGDH is highly expressed in tumors as a result of amplification, transcription, or its degradation and stability alteration, which dysregulates the serine biosynthesis pathway via metabolic enzyme activity to nourish tumors. And some recent researches reported that PHGDH promoted some tumors growth via non-metabolic way by upregulating target cancer-promoting genes. In this article, we reviewed the type, structure, expression and inhibitors of PHGDH, as well as the role it plays in cancer and tumor resistance to chemotherapy.

The synthesis of unnatural α-alkyl- and α-aryl-substituted serine derivatives

The synthesis of α-aryl- and α-alkyl-substituted serine derivatives via [3,3]-sigmatropic rearrangement of allyl carbamates as a key step is reported. Allyl carbamates were obtained from the corresponding allyl alcohols. The former were prepared through three approaches. Aryl-substituted ones were synthesized via the Stille coupling reaction of aryl iodides with enantiomerically enriched vinyl stannanes. Conversely, alkyl-substituted allyl alcohols were prepared by an analogous strategy involving the Negishi coupling reaction of enantiomerically enriched vinyl iodides or by enzymatic kineric resolution of the corresponding racemic alcohols.

Overexpression of PSAT1 promotes metastasis of lung adenocarcinoma by suppressing the IRF1-IFNγ axis

An increasing number of enzymes involved in serine biosynthesis have been identified and correlated with malignant evolution in various types of cancer. Here we showed that the overexpression of phosphoserine aminotransferase 1 (PSAT1) is widely found in lung cancer tissues compared with nontumor tissues and predicts a poorer prognosis in patients with lung adenocarcinoma. PSAT1 expression was examined in a tissue microarray by immunohistochemistry. The data show that the knockdown of PSAT1 dramatically inhibits the in vitro and in vivo metastatic potential of highly metastatic lung cancer cells; conversely, the enforced expression of exogenous PSAT1 predominantly enhances the metastatic potential of lung cancer cells. Importantly, manipulating PSAT1 expression regulates the in vivo tumor metastatic abilities in lung cancer cells. Adjusting the glucose and glutamine concentrations did not alter the PSAT1-driven cell invasion properties, indicating that this process might not rely on the activation of its enzymatic function. RNA microarray analysis of transcriptional profiling from PSAT1 alternation in CL1-5 and CL1-0 cells demonstrated that interferon regulatory factor 1 (IRF1) acts as a crucial regulator of PSAT1-induced gene expression upon metastatic progression. Decreasing the IRF1-IFIH1 axis compromised the PSAT1-prompted transcriptional reprogramming in cancer cells. Our results identify PSAT1 as a key regulator by a novel PSAT1/IRF1 axis in lung cancer progression, which may serve as a potential biomarker and therapeutic target for the treatment of lung cancer patients.

Amino Acid Transport Defects in Human Inherited Metabolic Disorders

Amino acid transporters play very important roles in nutrient uptake, neurotransmitter recycling, protein synthesis, gene expression, cell redox balance, cell signaling, and regulation of cell volume. With regard to transporters that are closely connected to metabolism, amino acid transporter-associated diseases are linked to metabolic disorders, particularly when they involve different organs, cell types, or cell compartments. To date, 65 different human solute carrier (SLC) families and more than 400 transporter genes have been identified, including 11 that are known to include amino acid transporters. This review intends to summarize and update all the conditions in which a strong association has been found between an amino acid transporter and an inherited metabolic disorder. Many of these inherited disorders have been identified in recent years. In this work, the physiological functions of amino acid transporters will be described by the inherited diseases that arise from transporter impairment. The pathogenesis, clinical phenotype, laboratory findings, diagnosis, genetics, and treatment of these disorders are also briefly described. Appropriate clinical and diagnostic characterization of the underlying molecular defect may give patients the opportunity to avail themselves of appropriate therapeutic options in the future.

Metabolomics facilitates the discovery of metabolic biomarkers and pathways for ischemic stroke: a systematic review

INTRODUCTION

Ischemic stroke (IS) is a major contributor to the global disease burden, and effective biomarkers for IS management in clinical practice are urgently needed. Metabolomics can detect metabolites that are small enough to cross the blood-brain barrier in a high-throughput manner, and thus represents a powerful tool for discovering biomarkers of IS.

OBJECTIVES

In this study, we conducted a systematic review to identify potential metabolic biomarkers and pathways that might facilitate risk predictions, clinical diagnoses, the recognition of complications, predictions of recurrence and an understanding of the pathogenesis of IS.

METHODS

The PubMed and Web of Science databases were searched for relevant studies published between January 2000 and July 2019. The study objectives, study designs and reported metabolic biomarkers were systematically examined and compared. Pathway analysis was performed using the MetaboAnalyst online software.

RESULTS

Twenty-eight studies were included in this systematic review. Many consistent metabolites, including isoleucine, leucine, valine, glycine, lysine, glutamate, LysoPC(16:0), LysoPC(18:2), serine, uric acid, citrate and palmitic acid, possess potential as biomarkers of IS. Metabolic pathways and dysregulations that are implicated in excitotoxicity, inflammation, apoptosis, oxidative stress, neuroprotection, energy failure, and elevation of intracellular Ca²⁺ levels, were indicated as playing important roles in the development and progression of IS.

CONCLUSIONS

This systematic review summarizes potential metabolic biomarkers and pathways related to IS, which may provide opportunities for the construction of diagnostic or predictive models for IS and the discovery of novel therapeutic targets.

Integrated Epigenetics, Transcriptomics, and Metabolomics to Analyze the Mechanisms of Benzo[a]pyrene Neurotoxicity in the Hippocampus

Benzo[a]pyrene (B[a]P) is a common environmental pollutant that is neurotoxic to mammals, which can cause changes to hippocampal function and result in cognitive disorders. The mechanisms of B[a]P-induced impairments are complex .To date there have been no studies on the association of epigenetic, transcriptomic, and metabolomic changes with neurotoxicity after B[a]P exposure. In the present study, we investigated the global effect of B[a]P on DNA methylation patterns, noncoding RNAs (ncRNAs) expression, coding RNAs expression, and metabolites in the rat hippocampus. Male Sprague Dawley rats (SD rats) received daily gavage of B[a]P (2.0 mg/kg body weight [BW]) or corn oil for 7 weeks. Learning and memory ability was analyzed using the Morris water maze (MWM) test and change to cellular ultrastructure in the hippocampus was analyzed using electron microscope observation. Integrated analysis of epigenetics, transcriptomics, and metabolomics was conducted to investigate the effect of B[a]P exposure on the signaling and metabolic pathways. Our results suggest that B[a]P could lead to learning and memory deficits, likely as a result of epigenetic and transcriptomic changes that further affected the expression of CACNA1C, Tpo, etc. The changes in expression ultimately affecting LTP, tyrosine metabolism, and other important metabolic pathways.

pLG72 levels increase in early phase of Alzheimer's disease but decrease in late phase

pLG72, named as D-amino acid oxidase activator (although it is not an activator of D-amino acid oxidase demonstrated by later studies), in mitochondria has been regarded as an important modulator of D-amino acid oxidase that can regulate the N-methyl-D-aspartate receptor (NMDAR). Both oxidative stress in mitochondria and NMDAR neurotransmission play essential roles in the process of neurodegenerative dementia. The aim of the study was to investigate whether pLG72 levels changed with the severity of neurodegenerative dementia. We enrolled 376 individuals as the overall cohort, consisting of five groups: healthy elderly, amnestic mild cognitive impairment [MCI], mild Alzheimer's disease [AD], moderate AD, and severe AD. pLG72 levels in plasma were measured using Western blotting. The severity of cognitive deficit was principally evaluated by Clinical Dementia Rating Scale. A gender- and age- matched cohort was selected to elucidate the effects of gender and age. pLG72 levels increased in the MCI and mild AD groups when compared to the healthy group. However, pLG72 levels in the moderate and severe AD groups were lower than those in the mild AD group. D-serine level and D- to total serine ratio were significantly different among the five groups. L-serine levels were correlated with the pLG72 levels. The results in the gender- and age- matched cohort were similar to those of the overall cohort. The finding supports the hypothesis of NMDAR hypofunction in early-phase dementia and NMDAR hyperfunction in late-phase dementia. Further studies are warranted to test whether pLG72 could reflect the function of NMDAR.

Phosphoserine Phosphatase Promotes Lung Cancer Progression through the Dephosphorylation of IRS-1 and a Noncanonical L-Serine-Independent Pathway

Phosphoserine phosphatase (PSPH) is one of the key enzymes of the L-serine synthesis pathway. PSPH is reported to affect the progression and survival of several cancers in an L-serine synthesis-independent manner, but the mechanism remains elusive. We demonstrate that PSPH promotes lung cancer progression through a noncanonical L-serine-independent pathway. PSPH was significantly associated with the prognosis of lung cancer patients and regulated the invasion and colony formation of lung cancer cells. Interestingly, L-serine had no effect on the altered invasion and colony formation by PSPH. Upon measuring the phosphatase activity of PSPH on a serine-phosphorylated peptide, we found that PSPH dephosphorylated phospho-serine in peptide sequences. To identify the target proteins of PSPH, we analyzed the protein phosphorylation profile and the PSPH-interacting protein profile using proteomic analyses and found one putative target protein, IRS-1. Immunoprecipitation and immunoblot assays validated a specific interaction between PSPH and IRS1 and the dephosphorylation of phospho-IRS-1 by PSPH in lung cancer cells. We suggest that the specific interaction and dephosphorylation activity of PSPH have novel therapeutic potential for lung cancer treatment, while the metabolic activity of PSPH, as a therapeutic target, is controversial.

Crystal structures and snapshots along the reaction pathway of human phosphoserine phosphatase

The equilibrium between phosphorylation and dephosphorylation is one of the most important processes that takes place in living cells. Human phosphoserine phosphatase (hPSP) is a key enzyme in the production of serine by the dephosphorylation of phospho-L-serine. It is directly involved in the biosynthesis of other important metabolites such as glycine and D-serine (a neuromodulator). hPSP is involved in the survival mechanism of cancer cells and has recently been found to be an essential biomarker. Here, three new high-resolution crystal structures of hPSP (1.5–2.0 Å) in complexes with phosphoserine and with serine, which are the substrate and the product of the reaction, respectively, and in complex with a noncleavable substrate analogue (homocysteic acid) are presented. New types of interactions take place between the enzyme and its ligands. Moreover, the loop involved in the open/closed state of the enzyme is fully refined in a totally unfolded conformation. This loop is further studied through molecular-dynamics simulations. Finally, all of these analyses allow a more complete reaction mechanism for this enzyme to be proposed which is consistent with previous publications on the subject.

Genetic determinants of beverage consumption: Implications for nutrition and health

Beverages make important contributions to nutritional intake and their role in health has received much attention. This review focuses on the genetic determinants of common beverage consumption and how research in this field is contributing insight to what and how much we consume and why this genetic knowledge matters from a research and public health perspective. The earliest efforts in gene-beverage behavior mapping involved genetic linkage and candidate gene analysis but these approaches have been largely replaced by genome-wide association studies (GWAS). GWAS have identified biologically plausible loci underlying alcohol and coffee drinking behavior. No GWAS has identified variants specifically associated with consumption of tea, juice, soda, wine, beer, milk or any other common beverage. Thus far, GWAS highlight an important behavior-reward component (as opposed to taste) to beverage consumption which may serve as a potential barrier to dietary interventions. Loci identified have been used in Mendelian randomization and gene×beverage interaction analysis of disease but results have been mixed. This research is necessary as it informs the clinical relevance of SNP-beverage associations and thus genotype-based personalized nutrition, which is gaining interest in the commercial and public health sectors.

Poly(I:C) alters placental and fetal brain amino acid transport in a rat model of maternal immune activation

PROBLEM

Maternal immune activation (MIA) during pregnancy is associated with increased chances of neurodevelopmental disorders including schizophrenia and autism spectrum disorder (ASD). However, the exact mechanism through which MIA contributes to altered neurodevelopment is unknown. Due to the important role that amino acids play in neurodevelopment, altered amino acid transport could play a role in neurodevelopmental disorders. Indeed, altered plasma concentrations of multiple amino acids have been reported in individuals with ASD or schizophrenia. Therefore, our objective was to determine whether virally mediated MIA induces changes in amino acid transporters in the placenta and fetal brain.

METHOD OF STUDY

Pregnant rats were administered poly(I:C) on gestational day 14, and placental and fetal tissues were collected 6, 24, and 48 hours later. Amino acid transporter expression was measured in the placenta and fetal brain using qPCR, Western blotting, and Simple Western. Free amino acid concentrations in the fetal brain were quantified using HPLC.

RESULTS

Poly(I:C) increased mRNA expression of several amino acid transporters in the placenta and fetal brain over these timepoints. Conversely, poly(I:C) imposed significant decreases in the protein expression of ASCT1 and EAAT2 in placenta and expression of SNAT5, EAAT1, and GLYT1 in fetal brain. Functional consequences of altered transporter expression were demonstrated through widespread changes in the concentrations of free amino acids in the fetal brains.

CONCLUSION

Together, these results represent novel findings with the poly(I:C) MIA model and contribute to the understanding of how MIA during pregnancy potentially leads to neurodevelopmental disorders.

Prostate cancer-specific hallmarks of amino acids metabolism: Towards a paradigm of precision medicine

So far multiple differences in prostate cancer-specific amino acids metabolism have been discovered. Moreover, attempts to utilize these alterations for prostate cancer diagnosis and treatment have been made. The prostate cancer metabolism and biosynthesis of amino acids are particularly focused on anaplerosis more than on energy production. Other crucial requirements on amino acids pool come from the serine, one‑carbon cycle, glycine synthesis pathway and folate metabolism forming major sources of interproducts for synthesis of nucleobases necessary for rapidly proliferating cells. Considering the lack of some amino acids biosynthetic pathways and/or their extraordinary importance for prostate cancer cells, there is a widespread potential for targeted therapeutic applications with no effect on non-malignant cells. This review summarizes the up-to-date knowledge of the importance of amino acids for prostate cancer pathogenesis with a special emphasis on potential applications of metabolic variabilities in the new oncologic paradigm of precision medicine.

The effect of repeated isoflurane exposure on serine synthesis pathway during the developmental period in Caenorhabditis elegans

BACKGROUND

Serine synthetic pathway plays an essential role in the development and function of the nervous system. This study investigated whether the serine synthetic pathway was affected by repeated volatile anesthetic exposure using C. elegans and its relationship with anesthesia-induced neurotoxicity.

METHODS

Synchronized worms were divided into two groups: the control and isoflurane groups. Worms in the isoflurane group were exposed to isoflurane for 1 h at each larval stage. The chemotaxis index was evaluated when they reached the young adult-stage in both groups. Also, RNA was extracted from the young adult-worms, and the expressions of C31C9.2, F26H9.5, and Y62E10 A.13 were evaluated using real-time polymerase chain reaction in both groups. At the same time, the l-serine level was measured. After phosphoserine phosphatase inhibitor - glycerophosphorylcholine (GPC) - and l-serine were treated, the change of chemotaxis index was determined.

RESULTS

In young adult worms exposed to isoflurane, the genetic expressions of C31C9.2, F26H9.5, and Y62E10 A.13 were decreased, and a significant decrease was shown in Y62E10 A.13. The serine level in worms was also lower in the isoflurane group than in the control group (5.13 ± 1.44 vs. 7.65 ± 0.81 pM, n = 5 in each group, p = 0.009). Exposure to GPC reduced the chemotaxis index to a similar degree as repeated isoflurane exposure (52.9% in GPC group vs 58.7% in the isoflurane group). The chemotaxis index (61.1%) was not decreased by repeated isoflurane anesthesia in GPC-treated worms. In this condition, the l-serine level was low similarly in both groups (5.22 ± 1.19 vs. 4.90 ± 1.36 pM, n = 5 in each group, p = 0.702). When l-serine was supplied to C. elegans, the deteriorated chemotaxis index by isoflurane exposure recovered (78.1% in the control group vs. 75.5% in the isoflurane group, p = 0.465).

CONCLUSION

Serine synthetic pathway was negatively affected in C. elegans by repeated isoflurane exposure. Y62E10 A.13, which corresponds to phosphoserine phosphatase, was mostly influenced, followed by low l-serine level. Supplementation with l-serine could restore the chemotaxis index.

PSPH Mediates the Metastasis and Proliferation of Non-small Cell Lung Cancer through MAPK Signaling Pathways

Growing evidence indicates that phosphoserine phosphatase (PSPH) is up-regulated and correlates with prognosis in multiple types of cancer. However, little is known about the roles of PSPH in NSCLC. Thus, the aim of the present study was to demonstrate the expression of PSPH in human NSCLC and reveal its biological functions and the underlying mechanisms. qRT-PCR, western blot and immunohistochemistry were used to assess the expression of NSCLC patient specimens and NSCLC cell lines. The functions of PSPH in migration and invasion were determined using trans-well and wound-healing assays. Cell proliferation capacity was performed by cell counting kit-8 (CCK-8), colony formation assays and cell cycle analysis. We demonstrated that PSPH was overexpressed in NSCLC specimens compared with the adjacent non-tumorous specimens, and high expression of PSPH was associated with clinical stage, metastasis and gender in NSCLC. Decreased expression of PSPH inhibited NSCLC cells migration, invasion and proliferation. Most importantly, further experiments demonstrated that PSPH might regulate NSCLC progress through MAPK signaling pathways. Lastly, immunohistochemistry (IHC) revealed that the PSPH expression level was positively correlated with the clinical stage in NSCLC patients. These results suggest that PSPH may act as a putative oncogene and a potential therapeutic target in NSCLC.

D-3-Phosphoglycerate Dehydrogenase

l-Serine is the immediate precursor of d-serine, a major agonist of the N-methyl-d-aspartate (NMDA) receptor. l-Serine is a pivotal amino acid since it serves as a precursor to a large number of essential metabolites besides d-serine. In all non-photosynthetic organisms, including mammals, a major source of l-serine is the phosphorylated pathway of l-serine biosynthesis. The pathway consists of three enzymes, d-3-phosphoglycerate dehydrogenase (PGDH), phosphoserine amino transferase (PSAT), and l-phosphoserine phosphatase (PSP). PGDH catalyzes the first step in the pathway by converting d-3-phosphoglycerate (PGA), an intermediate in glycolysis, to phosphohydroxypyruvate (PHP) concomitant with the reduction of NAD⁺. In some, but not all organisms, the catalytic activity of PGDH can be regulated by feedback inhibition by l-serine. Three types of PGDH can be distinguished based on their domain structure. Type III PGDHs contain only a nucleotide binding and substrate binding domain. Type II PGDHs contain an additional regulatory domain (ACT domain), and Type I PGDHs contain a fourth domain, termed the ASB domain. There is no consistent pattern of domain content that correlates with organism type, and even when additional domains are present, they are not always functional. PGDH deficiency results in metabolic defects of the nervous system whose systems range from microcephaly at birth, seizures, and psychomotor retardation. Although deficiency of any of the pathway enzymes have similar outcomes, PGDH deficiency is predominant. Dietary or intravenous supplementation with l-serine is effective in controlling seizures but has little effect on psychomotor development. An increase in PGDH levels, due to overexpression, is also associated with a wide array of cancers. In culture, PGDH is required for tumor cell proliferation, but extracellular l-serine is not able to support cell proliferation. This has led to the hypothesis that the pathway is performing some function related to tumor growth other than supplying l-serine. The most well-studied PGDHs are bacterial, primarily from Escherichia coli and Mycobacterium tuberculosis, perhaps because they have been of most interest mechanistically. However, the relatively recent association of PGDH with neuronal defects and human cancers has provoked renewed interest in human PGDH.

Neuroprotective effect of l-serine against white matter demyelination by harnessing and modulating inflammation in mice

Demyelination in white matter is the end product of numerous pathological processes. This study was designed to evaluate the neuroprotective effect of l-serine and the underlying mechanisms against the demyelinating injury of white matter. A model of focal demyelinating lesions (FDL) was established using the two-point stereotactic injection of 0.25% lysophosphatidylcholine (LPC, 10 μg per point) into the corpus callosum of mice. Mice were then intraperitoneally injected with one of three doses of l-serine (114, 342, or 1026 mg/kg) 2 h after FDL, and then twice daily for the next five days. Behavior tests and histological analysis were assessed for up to twenty-eight days post-FDL induction. Electron microscopy was used for ultrastructural investigation. In vitro, we applied primary co-cultures of microglia and oligodendrocytes for oxygen glucose deprivation (OGD). After establishing FDL, l-serine treatment: 1) improved spatial learning, memory and cognitive ability in mice, and relieved anxiety for 4 weeks post-FDL induction; 2) reduced abnormally dephosphorylated neurofilament proteins, increased myelin basic protein, and preserved anatomic myelinated axons; 3) inhibited microglia activation and reduced the release of inflammatory factors; 4) promoted recruitment and proliferation of oligodendrocyte progenitor cells, and the efficiency of subsequent remyelination on day twenty-eight post-FDL induction. In vitro experiments, showed that l-serine not only directly protected against oligodendrocytes from OGD damage, but also provided an indirect protective effect by regulating microglia. In our study, l-serine offered long-lasting behavioral and oligodendrocyte protection and promoted remyelination. Therefore, l-serine may be an effective clinical treatment aganist white matter injury.

Metabolism of amino acid neurotransmitters: the synaptic disorder underlying inherited metabolic diseases

Amino acids are involved in various metabolic pathways and some of them also act as neurotransmitters. Since biosynthesis of L-glutamate and γ-aminobutyric acid (GABA) requires 2-oxoglutarate while 3-phosphoglycerate is the precursor of L-glycine and D-serine, evolutionary selection of these amino acid neurotransmitters might have been driven by their capacity to provide important information about the glycolytic pathway and Krebs cycle. Synthesis and recycling of amino acid neurotransmitters as well as composition and function of their receptors are often compromised in inherited metabolic diseases. For instance, increased plasma L-phenylalanine concentrations impair cerebral biosynthesis of protein and bioamines in phenylketonuria, while elevated cerebral L-phenylalanine directly acts via ionotropic glutamate receptors. In succinic semialdehyde dehydrogenase deficiency, the neurotransmitter GABA and neuromodulatory γ-hydroxybutyric acid are elevated. Chronic hyperGABAergic state results in progressive downregulation of GABA_A and GABA_B receptors and impaired mitophagy. In glycine encephalopathy, the neurological phenotype is precipitated by L-glycine acting both via cortical NMDA receptors and glycine receptors in spinal cord and brain stem neurons. Serine deficiency syndromes are biochemically characterized by decreased biosynthesis of L-serine, an important neurotrophic factor, and the neurotransmitters D-serine and L-glycine. Supplementation with L-serine and L-glycine has a positive effect on seizure frequency and spasticity, while neurocognitive development can only be improved if treatment starts in utero or immediately postnatally. With novel techniques, the study of synaptic dysfunction in inherited metabolic diseases has become an emerging research field. More and better therapies are needed for these difficult-to-treat diseases.

Deletion of PHGDH in adipocytes improves glucose intolerance in diet-induced obese mice

Serine is a nonessential amino acid and plays an important role in cellular metabolism. In mammalian serine biosynthesis, 3-phosphoglycerate dehydrogenase (PHGDH) is considered a rate-limiting enzyme and is required for normal development. Although the biological functions of PHGHD in the nervous system have been intensively studied, its function in adipose tissue is unknown. In this study, we found that PHGDH is abundantly expressed in mature adipocytes of white adipose tissue. We generated an adipocyte-specific PHGDH knockout mouse (PHGDH FKO) and used it to investigate the role of serine biosynthesis in adipose tissues. Although PHGDH FKO mice had no apparent defects in adipose tissue development, these mice ameliorated glucose intolerance upon diet-induced obesity. Additionally, we found that the serine levels increase drastically in the adipose tissues of obese wild type mice, whereas no significant rise was observed in PHGDH FKO mice. Furthermore, wild type mice fed a serine-deficient diet also exhibited better glucose tolerance. These results suggest that PHGDH-mediated serine biosynthesis has important roles in adipose tissue glucose metabolism and could be a therapeutic target for diabetes in humans.

Metabolic reprogramming for cancer cells and their microenvironment: Beyond the Warburg Effect

While metabolic reprogramming of cancer cells has long been considered from the standpoint of how and why cancer cells preferentially utilize glucose via aerobic glycolysis, the so-called Warburg Effect, the progress in the following areas during the past several years has substantially advanced our understanding of the rewired metabolic network in cancer cells that is intertwined with oncogenic signaling. First, in addition to the major nutrient substrates glucose and glutamine, cancer cells have been discovered to utilize a variety of unconventional nutrient sources for survival. Second, the deregulated biomass synthesis is intertwined with cell cycle progression to coordinate the accelerated progression of cancer cells. Third, the reciprocal regulation of cancer cell's metabolic alterations and the microenvironment, involving extensive host immune cells and microbiota, have come into view as critical mechanisms to regulate cancer progression. These and other advances are shaping the current and future paradigm of cancer metabolism.

Serine metabolism in the brain regulates starvation-induced sleep suppression in Drosophila melanogaster

Foraging and sleep are two conflicting behaviors in starved animals; however, it remains elusive how metabolic status governs sleep drive. In this study, we show that a biosynthetic pathway for the amino acid serine is transcriptionally up-regulated by starvation in adult fly brains. The behavioral response to genetic manipulation of key enzymes involved in serine metabolism supports the sleep-suppressing effect of serine in response to starvation. In a society where daily diet is becoming increasingly important to the sleep quality of individuals, our study defines an amino acid metabolic pathway that underlies adaptive sleep behaviors upon dietary stress.

Sleep and metabolism are physiologically and behaviorally intertwined; however, the molecular basis for their interaction remains poorly understood. Here, we identified a serine metabolic pathway as a key mediator for starvation-induced sleep suppression. Transcriptome analyses revealed that enzymes involved in serine biosynthesis were induced upon starvation in Drosophila melanogaster brains. Genetic mutants of astray (aay), a fly homolog of the rate-limiting phosphoserine phosphatase in serine biosynthesis, displayed reduced starvation-induced sleep suppression. In contrast, a hypomorphic mutation in a serine/threonine-metabolizing enzyme, serine/threonine dehydratase (stdh), exaggerated starvation-induced sleep suppression. Analyses of double mutants indicated that aay and stdh act on the same genetic pathway to titrate serine levels in the head as well as to adjust starvation-induced sleep behaviors. RNA interference-mediated depletion of aay expression in neurons, using cholinergic Gal4 drivers, phenocopied aay mutants, while a nicotinic acetylcholine receptor antagonist selectively rescued the exaggerated starvation-induced sleep suppression in stdh mutants. Taken together, these data demonstrate that neural serine metabolism controls sleep during starvation, possibly via cholinergic signaling. We propose that animals have evolved a sleep-regulatory mechanism that reprograms amino acid metabolism for adaptive sleep behaviors in response to metabolic needs.

Analysis of Gene Expression Variance in Schizophrenia Using Structural Equation Modeling

Schizophrenia (SCZ) is a psychiatric disorder of unknown etiology. There is evidence suggesting that aberrations in neurodevelopment are a significant attribute of schizophrenia pathogenesis and progression. To identify biologically relevant molecular abnormalities affecting neurodevelopment in SCZ we used cultured neural progenitor cells derived from olfactory neuroepithelium (CNON cells). Here, we tested the hypothesis that variance in gene expression differs between individuals from SCZ and control groups. In CNON cells, variance in gene expression was significantly higher in SCZ samples in comparison with control samples. Variance in gene expression was enriched in five molecular pathways: serine biosynthesis, PI3K-Akt, MAPK, neurotrophin and focal adhesion. More than 14% of variance in disease status was explained within the logistic regression model (C-value = 0.70) by predictors accounting for gene expression in 69 genes from these five pathways. Structural equation modeling (SEM) was applied to explore how the structure of these five pathways was altered between SCZ patients and controls. Four out of five pathways showed differences in the estimated relationships among genes: between KRAS and NF1, and KRAS and SOS1 in the MAPK pathway; between PSPH and SHMT2 in serine biosynthesis; between AKT3 and TSC2 in the PI3K-Akt signaling pathway; and between CRK and RAPGEF1 in the focal adhesion pathway. Our analysis provides evidence that variance in gene expression is an important characteristic of SCZ, and SEM is a promising method for uncovering altered relationships between specific genes thus suggesting affected gene regulation associated with the disease. We identified altered gene-gene interactions in pathways enriched for genes with increased variance in expression in SCZ. These pathways and loci were previously implicated in SCZ, providing further support for the hypothesis that gene expression variance plays important role in the etiology of SCZ.

Inflammatory cytokine-mediated induction of serine racemase in atopic dermatitis

Serine racemase (SR) is an enzyme that catalyses the synthesis of d‐serine, an endogenous coagonist for N‐methyl‐D‐aspartate (NMDA)‐type glutamate receptor in the central nervous system. Our previous study demonstrated that SR was expressed in the epidermis of wild‐type (WT) mice but not in SR knockout (KO) mice. In addition, SR immune‐reactivity was only found in the granular and cornified layers of the epidermis in WT mice. These findings suggested that SR is involved in the differentiation of epidermal keratinocytes and the formation of the skin barrier. However, its role in skin barrier dysfunction such as atopic dermatitis (AD) remains elusive. AD is a chronic inflammatory disease of skin, and the clinical presentation of AD has been reported to be occasionally associated with psychological factors. Therefore, this study examined the content of d‐serine in stratum corneum in AD patients and healthy controls using a tape‐stripping method. Skin samples were collected from the cheek and upper arm skin of AD patient's lesion and healthy individuals. The d‐serine content was significantly increased in the involved skin of AD in comparison with healthy individuals. An immunohistochemical analysis also revealed an increased SR expression in the epidermis of AD patients. Furthermore, the SR expression in cultured human keratinocytes was significantly increased by the stimulation with tumour necrosis factor ‐α or macrophage migration inhibitory factor. Taken together, these findings suggest that d‐serine expressed particularly strongly in AD lesional skin and that the SR expression in the keratinocytes is linked to inflammatory cytokines.

[Changes of cerebral cortical metabolomics in rats following benzo[a]pyrene exposure]

OBJECTIVE

To analyze the changes in endogenous small molecule metabolites after benzo[a]pyrene (B[a]P) exposure in rat cerebral cortex and explore the mechanism of B[a]P neurotoxicity.

METHODS

Five-day-old SD rats were subjected to gavage administration of 2 mg/kg B[a]P for 7 consecutive weeks. After the exposure, the rats were assessed for spatial learning ability using Morris water maze test, ultrastructural changes of the cortical neurons under electron microscope, and metabolite profiles of the cortex using GC/MS. The differential metabolites between the exposed and control rats were identified with partial least squares discriminant analysis (PLS-DA) and the metabolic pathways related with the differential metabolites were analyzed using Cytoscape software.

RESULTS

Compared with the control group, the rats exposed to B[a]P showed significantly increased escape latency (P<0.05) and decreased time spent in the target area (P<0.05). The exposed rats exhibited widened synaptic cleft, thickened endplate membrane and swollen cytoplasm compared with the control rats. Eighteen differential metabolites (VIP>1, P<0.05) in the cortex were identified between the two groups, and 9 pathways associated with B[a]P neurotoxicity were identified involving amino acid metabolism, tricarboxylic acid cycle and Vitamin B3 (niacin and nicotinamide) metabolism.

CONCLUSION

B[a]P can cause disturbance in normal metabolisms and its neurotoxicity is possibly related with disorders in amino acid metabolism, tricarboxylic acid cycle and vitamin metabolism.

Disruption of De Novo Serine Synthesis in Müller Cells Induced Mitochondrial Dysfunction and Aggravated Oxidative Damage

De novo serine synthesis plays important roles in normal mitochondrial function and cellular anti-oxidative capacity. It is reported to be mainly activated in glial cells of the central nervous system, but its role in retinal Müller glia remains unclear. In this study, we inhibited de novo serine synthesis using CBR-5884, a specific inhibitor of phosphoglycerate dehydrogenase (PHGDH, a rate limiting enzyme in de novo serine metabolism) in MIO-M1 cells (immortalized human Müller cells) and huPMCs (human primary Müller cells) under mild oxidative stress. Alamar blue and LDH (lactate dehydrogenase) assays showed significantly reduced metabolic activities and increased cellular damage of Müller cells, when exposed to CBR-5884 accompanied by mild oxidative stress; however, CBR-5884 alone had little effect. The increased cellular damage was partially reversed by supplementation with exogenous serine/glycine. HSP72 (an oxidative stress marker) and reactive oxygen species (ROS) levels were significantly increased; glutathione and NADPH/NADP⁺ levels were pronouncedly reduced under PHGDH inhibition accompanied by oxidative stress. JC-1 staining and Seahorse respiration experiments showed that inhibition of de novo serine synthesis in Müller cells can also increase mitochondrial stress and decrease mitochondrial ATP production. qPCR and Western blot demonstrated an increased expression of HSP60 (a key mitochondrial stress-related gene), and this was further validated in human retinal explants. Our study suggests that de novo serine synthesis is important for Müller cell survival, particularly when they are exposed to mild oxidative stress, possibly by maintaining mitochondrial function and generating glutathione and NADPH to counteract ROS.

Natural Variation in SER1 and ENA6 Underlie Condition-Specific Growth Defects in Saccharomyces cerevisiae

Despite their ubiquitous use in laboratory strains, naturally occurring loss-of-function mutations in genes encoding core metabolic enzymes are relatively rare in wild isolates of Saccharomyces cerevisiae. Here, we identify a naturally occurring serine auxotrophy in a sake brewing strain from Japan. Through a cross with a honey wine (white tecc) brewing strain from Ethiopia, we map the minimal medium growth defect to SER1, which encodes 3-phosphoserine aminotransferase and is orthologous to the human disease gene, PSAT1. To investigate the impact of this polymorphism under conditions of abundant external nutrients, we examine growth in rich medium alone or with additional stresses, including the drugs caffeine and rapamycin and relatively high concentrations of copper, salt, and ethanol. Consistent with studies that found widespread effects of different auxotrophies on RNA expression patterns in rich media, we find that the SER1 loss-of-function allele dominates the quantitative trait locus (QTL) landscape under many of these conditions, with a notable exacerbation of the effect in the presence of rapamycin and caffeine. We also identify a major-effect QTL associated with growth on salt that maps to the gene encoding the sodium exporter, ENA6. We demonstrate that the salt phenotype is largely driven by variation in the ENA6 promoter, which harbors a deletion that removes binding sites for the Mig1 and Nrg1 transcriptional repressors. Thus, our results identify natural variation associated with both coding and regulatory regions of the genome that underlie strong growth phenotypes.

Mechanisms of L-Serine Neuroprotection in vitro Include ER Proteostasis Regulation

β-N-methylamino-L-alanine (L-BMAA) is a neurotoxic non-protein amino acid produced by cyanobacteria. Recently, chronic dietary exposure to L-BMAA was shown to trigger neuropathology in nonhuman primates consistent with Guamanian ALS/PDC, a paralytic disease that afflicts Chamorro villagers who consume traditional food items contaminated with L-BMAA. However, the addition of the naturally occurring amino acid L-serine to the diet of the nonhuman primates resulted in a significant reduction in ALS/PDC neuropathology. L-serine is a dietary amino acid that plays a crucial role in central nervous system development, neuronal signaling, and synaptic plasticity and has been shown to impart neuroprotection from L-BMAA-induced neurotoxicity both in vitro and in vivo. We have previously shown that L-serine prevents the formation of autofluorescent aggregates and death by apoptosis in human cell lines and primary cells. These effects are likely imparted by L-serine blocking incorporation of L-BMAA into proteins hence preventing proteotoxic stress. However, there are likely other mechanisms for L-serine-mediated neuroprotection. Here, we explore the molecular mechanisms of L-serine neuroprotection using a human unfolded protein response real-time PCR array with genes from the ER stress and UPR pathways, and western blotting. We report that L-serine caused the differential expression of many of the same genes as L-BMAA, even though concentrations of L-serine in the culture medium were ten times lower than that of L-BMAA. We propose that L-serine may be functioning as a small proteostasis regulator, in effect altering the cells to quickly respond to a possible oxidative insult, thus favoring a return to homeostasis.

Amino acid synthesis deficiencies

In recent years the number of disorders known to affect amino acid synthesis has grown rapidly. Nor is it just the number of disorders that has increased: the associated clinical phenotypes have also expanded spectacularly, primarily due to the advances of next generation sequencing diagnostics. In contrast to the "classical" inborn errors of metabolism in catabolic pathways, in which elevated levels of metabolites are easily detected in body fluids, synthesis defects present with low values of metabolites or, confusingly, even completely normal levels of amino acids. This makes the biochemical diagnosis of this relatively new group of metabolic diseases challenging. Defects in the synthesis pathways of serine metabolism, glutamine, proline and, recently, asparagine have all been reported. Although these amino acid synthesis defects are in unrelated metabolic pathways, they do share many clinical features. In children the central nervous system is primarily affected, giving rise to (congenital) microcephaly, early onset seizures and varying degrees of mental disability. The brain abnormalities are accompanied by skin disorders such as cutis laxa in defects of proline synthesis, collodion-like skin and ichthyosis in serine deficiency, and necrolytic erythema in glutamine deficiency. Hypomyelination with accompanying loss of brain volume and gyration defects can be observed on brain MRI in all synthesis disorders. In adults with defects in serine or proline synthesis, spastic paraplegia and several forms of polyneuropathy with or without intellectual disability appear to be the major symptoms in these late-presenting forms of amino acid disorders. This review provides a comprehensive overview of the disorders in amino acid synthesis.

Epileptogenesis in organotypic hippocampal cultures has limited dependence on culture medium composition

Rodent organotypic hippocampal cultures spontaneously develop epileptiform activity after approximately 2 weeks in vitro and are increasingly used as a model of chronic post-traumatic epilepsy. However, organotypic cultures are maintained in an artificial environment (culture medium), which contains electrolytes, glucose, amino acids and other components that are not present at the same concentrations in cerebrospinal fluid (CSF). Therefore, it is possible that epileptogenesis in organotypic cultures is driven by these components. We examined the influence of medium composition on epileptogenesis. Epileptogenesis was evaluated by measurements of lactate and lactate dehydrogenase (LDH) levels (biomarkers of ictal activity and cell death, respectively) in spent culture media, immunohistochemistry and automated 3-D cell counts, and extracellular recordings from CA3 regions. Changes in culture medium components moderately influenced lactate and LDH levels as well as electrographic seizure burden and cell death. However, epileptogenesis occurred in any culture medium that was capable of supporting neural survival. We conclude that medium composition is unlikely to be the cause of epileptogenesis in the organotypic hippocampal culture model of chronic post-traumatic epilepsy.

An archaeal ADP-dependent serine kinase involved in cysteine biosynthesis and serine metabolism

Routes for cysteine biosynthesis are still unknown in many archaea. Here we find that the hyperthermophilic archaeon Thermococcus kodakarensis generates cysteine from serine via O-phosphoserine, in addition to the classical route from 3-phosphoglycerate. The protein responsible for serine phosphorylation is encoded by TK0378, annotated as a chromosome partitioning protein ParB. The TK0378 protein utilizes ADP as the phosphate donor, but in contrast to previously reported ADP-dependent kinases, recognizes a non-sugar substrate. Activity is specific towards free serine, and not observed with threonine, homoserine and serine residues within a peptide. Genetic analyses suggest that TK0378 is involved in serine assimilation and clearly responsible for cysteine biosynthesis from serine. TK0378 homologs, present in Thermococcales and Desulfurococcales, are most likely not ParB proteins and constitute a group of kinases involved in serine utilization.

Archaea metabolism has unique adaptations to hostile environments. Here Makino et al. describe an unusual ADP-dependent kinase that phosphorylates free serine to O-phosphoserine and participates in an additional cysteine biosynthetic pathway in the archaeon Thermococcus kodakarensis.

Epilepsy in Inborn Errors of Metabolism With Therapeutic Options

Inborn errors of metabolism (IEM) are rare conditions that represent more than 1000 diseases, with a global prevalence of approximately 1:2000 individuals. Approximately, 40%-60% of IEM may present with epilepsy as one of the main neurologic signs. Epilepsy in IEM may appear at any age (fetal, newborn, infant, adolescent, or even adult). Different pathophysiological mechanisms may be responsible for the clinical phenotype, such as disturbances in energy metabolism (mitochondrial and fatty oxidation disorders, GLUT-1, and cerebral creatine deficiency), accumulation of complex molecules (lysosomal storage disorders), toxic mechanisms (organic acidurias and urea cycle disorders), or impairment of neurotransmission. Early diagnosis and, in some cases, an effective treatment may result in an excellent evolution of the IEM, in particularly seizure control. This review attempts to delineate a summary of IEM that may present with seizures or epilepsy and emphasizes the management in treatable conditions.

Phase I clinical trial of safety of L-serine for ALS patients

We performed a randomized, double-blind phase I clinical trial for six months on the effects of oral L-serine in patients with ALS. The protocol called for enrollment of patients with a diagnosis of probable or definite ALS, age 18-85 years, disease duration of less than three years and forced vital capacity (FVC) ≥ 60%. Patients were randomly assigned to four different oral twice-daily dose regimens (0.5, 2.5, 7.5, or 15 g/dose). Blood, urine and CSF samples, ALS Functional Rating Scale-Revised (ALSFRS-R) scores and forced vital capacity (FVC) were obtained throughout the trial. Disease progression was compared with matched historical placebo controls from five previous ALS therapeutic trials. Of 20 patients enrolled, one withdrew before receiving study drug and two withdrew with gastro-intestinal problems. Three patients died during the trial. L-serine was generally well tolerated by the patients and L-serine did not appear to accelerate functional decline of patients as measured by slope of their ALSFRS-R scores. Based on this small study, L-serine appears to be generally safe for patients with ALS.

Amenable Treatable Severe Pediatric Epilepsies

Vitamin-dependent epilepsies and multiple metabolic epilepsies are amenable to treatment that markedly improves the disease course. Knowledge of these amenably treatable severe pediatric epilepsies allows for early identification, testing, and treatment. These disorders present with various phenotypes, including early onset epileptic encephalopathy (refractory neonatal seizures, early myoclonic encephalopathy, and early infantile epileptic encephalopathy), infantile spasms, or mixed generalized seizure types in infancy, childhood, or even adolescence and adulthood. The disorders are presented as vitamin responsive epilepsies such as pyridoxine, pyridoxal-5-phosphate, folinic acid, and biotin; transportopathies like GLUT-1, cerebral folate deficiency, and biotin thiamine responsive disorder; amino and organic acidopathies including serine synthesis defects, creatine synthesis disorders, molybdenum cofactor deficiency, and cobalamin deficiencies; mitochondrial disorders; urea cycle disorders; neurotransmitter defects; and disorders of glucose homeostasis. In each case, targeted intervention directed toward the underlying metabolic pathophysiology affords for the opportunity to significantly effect the outcome and prognosis of an otherwise severe pediatric epilepsy.

Neuropädiatrische Differenzialdiagnostik der Mikrozephalie im Kindesalter

Eine Mikrozephalie betrifft 2–3 % der Bevölkerung und geht oftmals mit einer Intelligenzminderung einher. Die zugrunde liegende Reduktion des Gehirnvolumens kann sowohl durch exogene Faktoren als auch durch genetische Ursachen bedingt sein. Problematisch sind sowohl die uneinheitliche Klassifikation als auch die große Heterogenität der hinter dem klinischen Zeichen Mikrozephalie stehenden Erkrankungen. Im vorliegenden Artikel stellen wir unseren Vorschlag für die diagnostische Herangehensweise an ein Kind mit Mikrozephalie aus neuropädiatrischer Sicht vor.

Adaptive response to l-serine deficiency is mediated by p38 MAPK activation via 1-deoxysphinganine in normal fibroblasts

Reduced availability of l‐serine limits cell proliferation and leads to an adaptation to l‐serine‐deficient environment, the underlying molecular mechanism of which remain largely unexplored. Genetic ablation of 3‐phosphoglycerate dehydrogenase (Phgdh), which catalyzes the first step of de novo l‐serine synthesis, led to diminished cell proliferation and the activation of p38 MAPK and stress‐activated protein kinase/Jun amino‐terminal kinase in mouse embryonic fibroblasts under l‐serine depletion. The resultant l‐serine deficiency induced cyclin‐dependent kinase inhibitor 1a (Cdkn1a; p21) expression, which was mediated by p38 MAPK. Survival of the Phgdh‐deficient mouse embryonic fibroblasts was markedly reduced by p38 MAPK inhibition under l‐serine depletion, whereas p38 MAPK could be activated by 1‐deoxysphinganine, an atypical alanine‐derived sphingoid base that was found to accumulate in l‐serine‐depleted mouse embryonic fibroblasts. These observations provide persuasive evidence that when the external l‐serine supply is limited, l‐serine synthesized de novo in proliferating cells serves as a metabolic gatekeeper to maintain cell survival and the functions necessary for executing cell cycle progression.

Database

Gene Expression Omnibus, accession number GSE55687.

Division of labour: how does folate metabolism partition between one-carbon metabolism and amino acid oxidation?

One-carbon metabolism is usually represented as having three canonical functions: purine synthesis, thymidylate synthesis and methylation reactions. There is however a fourth major function: the metabolism of some amino acids (serine, glycine, tryptophan and histidine), as well as choline. These substrates can provide cells with more one-carbon groups than they need for these three canonical functions. Therefore, there must be mechanisms for the disposal of these one-carbon groups (when in excess) which maintain the complement of these groups required for the canonical functions. The key enzyme for these mechanisms is 10-formyl-THF (tetrahydrofolate) dehydrogenase (both mitochondrial and cytoplasmic isoforms) which oxidizes the formyl group to CO2 with the attendant reduction of NADP(+) to NADPH and release of THF. In addition to oxidizing the excess of these compounds, this process can reduce substantial quantities of NADP(+) to NADPH.

Electrochemical Imprinted Polycrystalline Nickel-Nickel Oxide Half-Nanotube-Modified Boron-Doped Diamond Electrode for the Detection of L-Serine

This paper presents a novel and versatile method for the fabrication of half nanotubes (HNTs) using a flexible template-based nanofabrication method denoted as electrochemical imprinting. With use of this method, polycrystalline nickel and nickel(II) oxide (Ni-NiO) HNTs were synthesized using pulsed electrodeposition to transfer Ni, deposited by radio frequency magnetron sputtering on a porous polytetrafluoroethylene template, onto a boron-doped diamond (BDD) film. The Ni-NiO HNTs exhibited semicircular profiles along their entire lengths, with outer diameters of 50-120 nm and inner diameters of 20-50 nm. The HNT walls were formed of Ni and NiO nanoparticles. A biosensor for the detection of L-serine was fabricated using a BDD electrode modified with Ni-NiO HNTs, and the device demonstrated satisfactory analytical performance with high sensitivity (0.33 μA μM(-1)) and a low limit of detection (0.1 μM). The biosensor also exhibited very good reproducibility and stability, as well as a high anti-interference ability against amino acids such as L-leucine, L-tryptophan, L-cysteine, L-phenylalanine, L-arginine, and L-lysine.