AAV-mediated expression of mouse or human GLDC normalises metabolic biomarkers in a GLDC-deficient mouse model of Non-Ketotic Hyperglycinemia.

Non-Ketotic Hyperglycinemia (NKH) is a rare inborn error of metabolism caused by impaired function of the glycine cleavage system (GCS) and characterised by accumulation of glycine in body fluids and tissues. NKH is an autosomal recessive condition and the majority of affected individuals carry mutations in GLDC (glycine decarboxylase). Current treatments for NKH have limited effect and are not curative. As a monogenic condition with known genetic causation, NKH is potentially amenable to gene therapy. An AAV9-based expression vector was designed to target sites of GCS activity. Using a ubiquitous promoter to drive expression of a GFP reporter, transduction of liver and brain was confirmed following intra-venous and/or intra-cerebroventricular administration to neonatal mice. Using the same capsid and promoter with transgenes to express mouse or human GLDC, vectors were then tested in GLDC-deficient mice that provide a model of NKH. GLDC-deficient mice exhibited elevated plasma glycine concentration and accumulation of glycine in liver and brain tissues as previously observed. Moreover, the folate profile indicated suppression of folate one­carbon metabolism (FOCM) in brain tissue, as found at embryonic stages, and reduced abundance of FOCM metabolites including betaine and choline. Neonatal administration of vector achieved reinstatement of GLDC mRNA and protein expression in GLDC-deficient mice. Treated GLDC-deficient mice showed significant lowering of plasma glycine, confirming functionality of vector expressed protein. AAV9-GLDC treatment also led to lowering of brain tissue glycine, and normalisation of the folate profile indicating restoration of glycine-derived one­carbon supply. These findings support the hypothesis that AAV-mediated gene therapy may offer potential in treatment of NKH.

Homozygosity for disease-causing variants in AMT and GLDC in a patient with severe nonketotic hyperglycinemia.

Nonketotic hyperglycinemia (NKH) is a relatively well-characterized inborn error of metabolism that results in a combination of lethargy, hypotonia, seizures, developmental arrest, and, in severe cases, death early in life. Three genes encoding components of the glycine cleavage enzyme system-GLDC, AMT, and GCSH-are independently associated with NKH. We report on a patient with severe NKH in whom the homozygous pathogenic variant in AMT (NM_000481.3):c.602_603del (p.Lys201Thrfs*75) and the homozygous likely pathogenic variant in GLDC(NM_000170.2):c.2852C>A (p.Ser951Tyr) were both identified. Our patient demonstrates a novel combination of two homozygous disease-causing variants impacting the glycine cleavage pathway at two different components, and elicits management- and genetic counseling-related challenges for the family.

Metabolic Rewiring and Altered Glial Differentiation in an iPSC-Derived Astrocyte Model Derived from a Nonketotic Hyperglycinemia Patient.

The pathophysiology of nonketotic hyperglycinemia (NKH), a rare neuro-metabolic disorder associated with severe brain malformations and life-threatening neurological manifestations, remains incompletely understood. Therefore, a valid human neural model is essential. We aimed to investigate the impact of GLDC gene variants, which cause NKH, on cellular fitness during the differentiation process of human induced pluripotent stem cells (iPSCs) into iPSC-derived astrocytes and to identify sustainable mechanisms capable of overcoming GLDC deficiency. We developed the GLDC27-FiPS4F-1 line and performed metabolomic, mRNA abundance, and protein analyses. This study showed that although GLDC27-FiPS4F-1 maintained the parental genetic profile, it underwent a metabolic switch to an altered serine-glycine-one-carbon metabolism with a coordinated cell growth and cell cycle proliferation response. We then differentiated the iPSCs into neural progenitor cells (NPCs) and astrocyte-lineage cells. Our analysis showed that GLDC-deficient NPCs had shifted towards a more heterogeneous astrocyte lineage with increased expression of the radial glial markers GFAP and GLAST and the neuronal markers MAP2 and NeuN. In addition, we detected changes in other genes related to serine and glycine metabolism and transport, all consistent with the need to maintain glycine at physiological levels. These findings improve our understanding of the pathology of nonketotic hyperglycinemia and offer new perspectives for therapeutic options.

Transposable elements contribute to the establishment of the glycine shuttle in Brassicaceae species.

C3 -C4 intermediate photosynthesis has evolved at least five times convergently in the Brassicaceae, despite this family lacking bona fide C4 species. The establishment of this carbon concentrating mechanism is known to require a complex suite of ultrastructural modifications, as well as changes in spatial expression patterns, which are both thought to be underpinned by a reconfiguration of existing gene-regulatory networks. However, to date, the mechanisms which underpin the reconfiguration of these gene networks are largely unknown. In this study, we used a pan-genomic association approach to identify genomic features that could confer differential gene expression towards the C3 -C4 intermediate state by analysing eight C3 species and seven C3 -C4 species from five independent origins in the Brassicaceae. We found a strong correlation between transposable element (TE) insertions in cis-regulatory regions and C3 -C4 intermediacy. Specifically, our study revealed 113 gene models in which the presence of a TE within a gene correlates with C3 -C4 intermediate photosynthesis. In this set, genes involved in the photorespiratory glycine shuttle are enriched, including the glycine decarboxylase P-protein whose expression domain undergoes a spatial shift during the transition to C3 -C4 photosynthesis. When further interrogating this gene, we discovered independent TE insertions in its upstream region which we conclude to be responsible for causing the spatial shift in GLDP1 gene expression. Our findings hint at a pivotal role of TEs in the evolution of C3 -C4 intermediacy, especially in mediating differential spatial gene expression.

Glycine Decarboxylase (GLDC) Plays a Crucial Role in Regulating Energy Metabolism, Invasion, Metastasis and Immune Escape for Prostate Cancer.

Glycine decarboxylase (GLDC) is one of the core enzymes for glycine metabolism, and its biological roles in prostate cancer (PCa) are unclear. First, we found that GLDC plays a central role in glycolysis in 540 TCGA PCa patients. Subsequently, a metabolomic microarray showed that GLDC enhanced aerobic glycolysis in PCa cells, and GLDC and its enzyme activity enhanced glucose uptake, lactate production and lactate dehydrogenase (LDH) activity in PCa cells. Next, we found that GLDC was highly expressed in PCa, was directly regulated by hypoxia-inducible factor (HIF1-α) and regulated downstream LDHA expression. In addition, GLDC and its enzyme activity showed a strong ability to promote the migration and invasion of PCa both in vivo and in vitro. Furthermore, we found that the GLDC-high group had a higher TP53 mutation frequency, lower CD8+ T-cell infiltration, higher immune checkpoint expression, and higher immune exclusion scores than the GLDC-low group. Finally, the GLDC-based prognostic risk model by applying LASSO Cox regression also showed good predictive power for the clinical characteristics and survival in PCa patients. This evidence indicates that GLDC plays crucial roles in glycolytic metabolism, invasion and metastasis, and immune escape in PCa, and it is a potential therapeutic target for prostate cancer.

Genetic variants in ALDH1L1 and GLDC influence the serine-to-glycine ratio in Hispanic children.

BACKGROUND: Glycine is a proteogenic amino acid that is required for numerous metabolic pathways, including purine, creatine, heme, and glutathione biosynthesis. Glycine formation from serine, catalyzed by serine hydroxy methyltransferase, is the major source of this amino acid in humans. Our previous studies in a mouse model have shown a crucial role for the 10-formyltetrahydrofolate dehydrogenase enzyme in serine-to-glycine conversion. OBJECTIVES: We sought to determine the genomic influence on the serine-glycine ratio in 803 Hispanic children from 319 families of the Viva La Familia cohort. METHODS: We performed a genome-wide association analysis for plasma serine, glycine, and the serine-glycine ratio in Sequential Oligogenic Linkage Analysis Routines while accounting for relationships among family members. RESULTS: All 3 parameters were significantly heritable (h2 = 0.22-0.78; P < 0.004). The strongest associations for the serine-glycine ratio were with single nucleotide polymorphisms (SNPs) in aldehyde dehydrogenase 1 family member L1 (ALDH1L1) and glycine decarboxylase (GLDC) and for glycine with GLDC (P < 3.5 × 10-8; effect sizes, 0.03-0.07). No significant associations were found for serine. We also conducted a targeted genetic analysis with ALDH1L1 exonic SNPs and found significant associations between the serine-glycine ratio and rs2886059 (ß = 0.68; SE, 0.25; P = 0.006) and rs3796191 (ß = 0.25; SE, 0.08; P = 0.003) and between glycine and rs3796191 (ß = -0.08; SE, 0.02; P = 0.0004). These exonic SNPs were further associated with metabolic disease risk factors, mainly adiposity measures (P < 0.006). Significant genetic and phenotypic correlations were found for glycine and the serine-glycine ratio with metabolic disease risk factors, including adiposity, insulin sensitivity, and inflammation-related phenotypes [estimate of genetic correlation = -0.37 to 0.35 (P < 0.03); estimate of phenotypic correlation = -0.19 to 0.13 (P < 0.006)]. The significant genetic correlations indicate shared genetic effects among glycine, the serine-glycine ratio, and adiposity and insulin sensitivity phenotypes. CONCLUSIONS: Our study suggests that ALDH1L1 and GLDC SNPs influence the serine-to-glycine ratio and metabolic disease risk.

Meeting in the Middle: Lessons and Opportunities from Studying C3-C4 Intermediates.

The discovery of C3-C4 intermediate species nearly 50 years ago opened up a new avenue for studying the evolution of photosynthetic pathways. Intermediate species exhibit anatomical, biochemical, and physiological traits that range from C3 to C4. A key feature of C3-C4 intermediates that utilize C2 photosynthesis is the improvement in photosynthetic efficiency compared with C3 species. Although the recruitment of some core enzymes is shared across lineages, there is significant variability in gene expression patterns, consistent with models that suggest numerous evolutionary paths from C3 to C4 photosynthesis. Despite the many evolutionary trajectories, the recruitment of glycine decarboxylase for C2 photosynthesis is likely required. As technologies enable high-throughput genotyping and phenotyping, the discovery of new C3-C4 intermediates species will enrich comparisons between evolutionary lineages. The investigation of C3-C4 intermediate species will enhance our understanding of photosynthetic mechanisms and evolutionary processes and will potentially aid in crop improvement.

Metabolic profiles in C3, C3-C4 intermediate, C4-like, and C4 species in the genus Flaveria.

C4 photosynthesis concentrates CO2 around Rubisco in the bundle sheath, favouring carboxylation over oxygenation and decreasing photorespiration. This complex trait evolved independently in >60 angiosperm lineages. Its evolution can be investigated in genera such as Flaveria (Asteraceae) that contain species representing intermediate stages between C3 and C4 photosynthesis. Previous studies have indicated that the first major change in metabolism probably involved relocation of glycine decarboxylase and photorespiratory CO2 release to the bundle sheath and establishment of intercellular shuttles to maintain nitrogen stoichiometry. This was followed by selection for a CO2-concentrating cycle between phosphoenolpyruvate carboxylase in the mesophyll and decarboxylases in the bundle sheath, and relocation of Rubisco to the latter. We have profiled 52 metabolites in nine Flaveria species and analysed 13CO2 labelling patterns for four species. Our results point to operation of multiple shuttles, including movement of aspartate in C3-C4 intermediates and a switch towards a malate/pyruvate shuttle in C4-like species. The malate/pyruvate shuttle increases from C4-like to complete C4 species, accompanied by a rise in ancillary organic acid pools. Our findings support current models and uncover further modifications of metabolism along the evolutionary path to C4 photosynthesis in the genus Flaveria.

Hormonal regulation of glycine decarboxylase and its relationship to oxidative stress.

In both humans and rodent models, circulating glycine levels are significantly reduced in obesity, glucose intolerance, type II diabetes, and non-alcoholic fatty liver disease. The glycine cleavage system and its rate-limiting enzyme, glycine decarboxylase (GLDC), is a major determinant of plasma glycine levels. The goals of this study were to determine if the increased expression of GLDC contributes to the reduced plasma glycine levels seen in disease states, to characterize the hormonal regulation of GLDC gene expression, and to determine if altered GLDC expression has physiological effects that might affect the development of diabetes. The findings presented here show that hepatic GLDC gene expression is elevated in mouse models of obesity and diabetes, as well as by fasting. We demonstrated that GLDC gene expression is strongly regulated by the metabolic hormones glucagon and insulin, and we identified the signaling pathways involved in this regulation. Finally, we found that GLDC expression is linked to glutathione levels, with increased expression associated with elevated levels of glutathione and reduced expression associated with a suppression of glutathione and increased cellular ROS levels. These findings suggest that the hormonal regulation of GLDC contributes not only to the changes in circulating glycine levels seen in metabolic disease, but also affects glutathione production, possibly as a defense against metabolic disease-associated oxidative stress.

Genomic analyses of glycine decarboxylase neurogenic mutations yield a large-scale prediction model for prenatal disease.

Hundreds of mutations in a single gene result in rare diseases, but why mutations induce severe or attenuated states remains poorly understood. Defect in glycine decarboxylase (GLDC) causes Non-ketotic Hyperglycinemia (NKH), a neurological disease associated with elevation of plasma glycine. We unified a human multiparametric NKH mutation scale that separates severe from attenuated neurological disease with new in silico tools for murine and human genome level-analyses, gathered in vivo evidence from mice engineered with top-ranking attenuated and a highly pathogenic mutation, and integrated the data in a model of pre- and post-natal disease outcomes, relevant for over a hundred major and minor neurogenic mutations. Our findings suggest that highly severe neurogenic mutations predict fatal, prenatal disease that can be remedied by metabolic supplementation of dams, without amelioration of persistent plasma glycine. The work also provides a systems approach to identify functional consequences of mutations across hundreds of genetic diseases. Our studies provide a new framework for a large scale understanding of mutation functions and the prediction that severity of a neurogenic mutation is a direct measure of pre-natal disease in neurometabolic NKH mouse models. This framework can be extended to analyses of hundreds of monogenetic rare disorders where the underlying genes are known but understanding of the vast majority of mutations and why and how they cause disease, has yet to be realized.

Obesity increases hepatic glycine dehydrogenase and aminomethyltransferase expression while dietary glycine supplementation reduces white adipose tissue in Zucker diabetic fatty rats.

Obesity is associated with altered glycine metabolism in humans. This study investigated the mechanisms regulating glycine metabolism in obese rats. Eight-week-old Zucker diabetic fatty rats (ZDF; a type-II diabetic animal model) received either 1% glycine or 1.19% L-alanine (isonitrogenous control) in drinking water for 6 weeks. An additional group of lean Zucker rats also received 1.19% L-alanine as a lean control. Glycine concentrations in serum and liver were markedly lower in obese versus lean rats. Enteral glycine supplementation restored both serum and hepatic glycine levels, while reducing mesenteric and internal white fat mass compared with alanine-treated ZDF rats. Blood glucose and non-esterified fatty acid (NEFA) concentrations did not differ between the control and glycine-supplemented ZDF rats (P > 0.10). Both mRNA and protein expression of aminomethyltransferase (AMT) and glycine dehydrogenase, decarboxylating (GLDC) were increased in the livers of obese versus lean rats (P < 0.05). In contrast, glycine cleavage system H (GCSH) hepatic mRNA expression was downregulated in obese versus lean rats, although there was no change in protein expression. These findings indicate that reduced quantities of glycine observed in obese subjects likely results from an upregulation of the hepatic glycine cleavage system and that dietary glycine supplementation potentially reduces obesity in ZDF rats.

Regulation of glycine metabolism by the glycine cleavage system and conjugation pathway in mouse models of non-ketotic hyperglycinemia.

Glycine abundance is modulated in a tissue-specific manner by use in biosynthetic reactions, catabolism by the glycine cleavage system (GCS), and excretion via glycine conjugation. Dysregulation of glycine metabolism is associated with multiple disorders including epilepsy, developmental delay, and birth defects. Mutation of the GCS component glycine decarboxylase (GLDC) in non-ketotic hyperglycinemia (NKH) causes accumulation of glycine in body fluids, but there is a gap in our knowledge regarding the effects on glycine metabolism in tissues. Here, we analysed mice carrying mutations in Gldc that result in severe or mild elevations of plasma glycine and model NKH. Liver of Gldc-deficient mice accumulated glycine and numerous glycine derivatives, including multiple acylglycines, indicating increased flux through reactions mediated by enzymes including glycine-N-acyltransferase and arginine: glycine amidinotransferase. Levels of dysregulated metabolites increased with age and were normalised by liver-specific rescue of Gldc expression. Brain tissue exhibited increased abundance of glycine, as well as derivatives including guanidinoacetate, which may itself be epileptogenic. Elevation of brain tissue glycine occurred even in the presence of only mildly elevated plasma glycine in mice carrying a missense allele of Gldc. Treatment with benzoate enhanced hepatic glycine conjugation thereby lowering plasma and tissue glycine. Moreover, administration of a glycine conjugation pathway intermediate, cinnamate, similarly achieved normalisation of liver glycine derivatives and circulating glycine. Although exogenous benzoate and cinnamate impact glycine levels via activity of glycine-N-acyltransferase, that is not expressed in brain, they are sufficient to lower levels of glycine and derivatives in brain tissue of treated Gldc-deficient mice.

Large scale analyses of genotype-phenotype relationships of glycine decarboxylase mutations and neurological disease severity.

Monogenetic diseases provide unique opportunity for studying complex, clinical states that underlie neurological severity. Loss of glycine decarboxylase (GLDC) can severely impact neurological development as seen in non-ketotic hyperglycinemia (NKH). NKH is a neuro-metabolic disorder lacking quantitative predictors of disease states. It is characterized by elevation of glycine, seizures and failure to thrive, but glycine reduction often fails to confer neurological benefit, suggesting need for alternate tools to distinguish severe from attenuated disease. A major challenge has been that there are 255 unique disease-causing missense mutations in GLDC, of which 206 remain entirely uncharacterized. Here we report a Multiparametric Mutation Score (MMS) developed by combining in silico predictions of stability, evolutionary conservation and protein interaction models and suitable to assess 251 of 255 mutations. In addition, we created a quantitative scale of clinical disease severity comprising of four major disease domains (seizure, cognitive failure, muscular and motor control and brain-malformation) to comprehensively score patient symptoms identified in 131 clinical reports published over the last 15 years. The resulting patient Clinical Outcomes Scores (COS) were used to optimize the MMS for biological and clinical relevance and yield a patient Weighted Multiparametric Mutation Score (WMMS) that separates severe from attenuated neurological disease (p = 1.2 e-5). Our study provides understanding for developing quantitative tools to predict clinical severity of neurological disease and a clinical scale that advances monitoring disease progression needed to evaluate new treatments for NKH.

Identification of a new GLDC gene alternative splicing variant and its protumorigenic roles in lung cancer.

Aim: To clarify the regulatory roles of GLDCV1, the first identified truncated glycine decarboxylase (GLDC), on cancer stem cells and tumorigenesis. Materials & methods: RT-PCR or RT-qPCR, immunoblotting and immunohistochemical staining were applied to assess gene expression. MTT, BrdU incorporation and colony formation assays were used to examine cell proliferation capacity. Soft agar colony formation and in vivo transplantation were applied to evaluate cellular transformation and tumorigenesis. Results & conclusion: Expression of GLDCV1 or GLDC was enhanced in non-small-cell lung cancer cell line and clinical samples. GLDCV1 overexpression induced MRC5 cell proliferation, transformation and tumorigenesis. Additionally, GLDCV1 increased lactate production and cancer stem cell marker expression and activated ERK and P38 pathways. Our study gained deeper insight into GLDC oncogene.

Transition from C3 to proto-Kranz to C3-C4 intermediate type in the genus Chenopodium (Chenopodiaceae).

The Chenopodiaceae is one of the families including C4 species among eudicots. In this family, the genus Chenopodium is considered to include only C3 species. However, we report here a transition from C3 photosynthesis to proto-Kranz to C3-C4 intermediate type in Chenopodium. We investigated leaf anatomical and photosynthetic traits of 15 species, of which 8 species showed non-Kranz anatomy and a CO2 compensation point (Γ) typical of C3 plants. However, 5 species showed proto-Kranz anatomy and a C3-like Γ, whereas C. strictum showed leaf anatomy and a Γ typical of C3-C4 intermediates. Chenopodium album accessions examined included both proto-Kranz and C3-C4 intermediate types, depending on locality. Glycine decarboxylase, a key photorespiratory enzyme that is involved in the decarboxylation of glycine, was located predominantly in the mesophyll (M) cells of C3 species, in both M and bundle-sheath (BS) cells in proto-Kranz species, and exclusively in BS cells in C3-C4 intermediate species. The M/BS tissue area ratio, number of chloroplasts and mitochondria per BS cell, distribution of these organelles to the centripetal region of BS cells, the degree of inner positioning (vacuolar side of chloroplasts) of mitochondria in M cells, and the size of BS mitochondria also changed with the change in glycine decarboxylase localization. All Chenopodium species examined were C3-like regarding activities and amounts of C3 and C4 photosynthetic enzymes and δ13C values, suggesting that these species perform photosynthesis without contribution of the C4 cycle. This study demonstrates that Chenopodium is not a C3 genus and is valuable for studying evolution of C3-C4 intermediates.

Glycine decarboxylase is a transcriptional target of MYCN required for neuroblastoma cell proliferation and tumorigenicity.

Genomic amplification of the oncogene MYCN is a major driver in the development of high-risk neuroblastoma, a pediatric cancer with poor prognosis. Given the challenge in targeting MYCN directly for therapy, we sought to identify MYCN-dependent metabolic vulnerabilities that can be targeted therapeutically. Here, we report that the gene encoding glycine decarboxylase (GLDC), which catalyzes the first and rate-limiting step in glycine breakdown with the production of the one-carbon unit 5,10-methylene-tetrahydrofolate, is a direct transcriptional target of MYCN. As a result, GLDC expression is markedly elevated in MYCN-amplified neuroblastoma tumors and cell lines. This transcriptional upregulation of GLDC expression is of functional significance, as GLDC depletion by RNA interference inhibits the proliferation and tumorigenicity of MYCN-amplified neuroblastoma cell lines by inducing G1 arrest. Metabolomic profiling reveals that GLDC knockdown disrupts purine and central carbon metabolism and reduces citrate production, leading to a decrease in the steady-state levels of cholesterol and fatty acids. Moreover, blocking purine or cholesterol synthesis recapitulates the growth-inhibitory effect of GLDC knockdown. These findings reveal a critical role of GLDC in sustaining the proliferation of neuroblastoma cells with high-level GLDC expression and suggest that MYCN amplification is a biomarker for GLDC-based therapeutic strategies against high-risk neuroblastoma.

Redox-Regulation of Photorespiration through Mitochondrial Thioredoxin o1.

Photorespiration sustains photosynthesis in the presence of oxygen due to rapid metabolization of 2-phosphoglycolate, the major side-product of the oxygenase activity of Rubisco that also directly impedes carbon assimilation and allocation. Despite the fact that both the biochemical reactions and the underlying genetics are well characterized, information concerning the regulatory mechanisms that adjust photorespiratory flux is rare. Here, we studied the impact of mitochondrial-localized thioredoxin o1 (TRXo1) on photorespiratory metabolism. The characterization of an Arabidopsis (Arabidopsis thaliana) transfer DNA insertional line (trxo1-1) revealed an increase in the stoichiometry of photorespiratory CO2 release and impaired Gly-to-Ser turnover after a shift from high-to-low CO2 without changes in Gly decarboxylase (GDC) gene or protein expression. These effects were distinctly pronounced in a double mutant, where the TRXo1 mutation was combined with strongly reduced GDC T-protein expression. The double mutant (TxGT) showed reduced growth in air but not in high CO2, decreased photosynthesis, and up to 54-fold more Gly alongside several redox-stress-related metabolites. Given that GDC proteins are potential targets for redox-regulation, we also examined the in vitro properties of recombinant GDC l-proteins (lipoamide dehydrogenase) from plants and the cyanobacterium Synechocystis species strain PCC6803 and observed a redox-dependent inhibition by either artificial reducing agents or TRXo1 itself. Collectively, our results demonstrate that TRXo1 potentially adjusts photorespiration via redox-regulation of GDC in response to environmental changes.

Targeted Treatment of Individuals With Psychosis Carrying a Copy Number Variant Containing a Genomic Triplication of the Glycine Decarboxylase Gene.

BACKGROUND: The increased mutational burden for rare structural genomic variants in schizophrenia and other neurodevelopmental disorders has so far not yielded therapies targeting the biological effects of specific mutations. We identified two carriers (mother and son) of a triplication of the gene encoding glycine decarboxylase, GLDC, presumably resulting in reduced availability of the N-methyl-D-aspartate receptor coagonists glycine and D-serine and N-methyl-D-aspartate receptor hypofunction. Both carriers had a diagnosis of a psychotic disorder. METHODS: We carried out two double-blind, placebo-controlled clinical trials of N-methyl-D-aspartate receptor augmentation of psychotropic drug treatment in these two individuals. Glycine was used in the first clinical trial, and D-cycloserine was used in the second one. RESULTS: Glycine or D-cycloserine augmentation of psychotropic drug treatment each improved psychotic and mood symptoms in placebo-controlled trials. CONCLUSIONS: These results provide two independent proof-of-principle demonstrations of symptom relief by targeting a specific genotype and explicitly link an individual mutation to the pathophysiology of psychosis and treatment response.

Methionine is a metabolic dependency of tumor-initiating cells.

Understanding cellular metabolism holds immense potential for developing new classes of therapeutics that target metabolic pathways in cancer. Metabolic pathways are altered in bulk neoplastic cells in comparison to normal tissues. However, carcinoma cells within tumors are heterogeneous, and tumor-initiating cells (TICs) are important therapeutic targets that have remained metabolically uncharacterized. To understand their metabolic alterations, we performed metabolomics and metabolite tracing analyses, which revealed that TICs have highly elevated methionine cycle activity and transmethylation rates that are driven by MAT2A. High methionine cycle activity causes methionine consumption to far outstrip its regeneration, leading to addiction to exogenous methionine. Pharmacological inhibition of the methionine cycle, even transiently, is sufficient to cripple the tumor-initiating capability of these cells. Methionine cycle flux specifically influences the epigenetic state of cancer cells and drives tumor initiation. Methionine cycle enzymes are also enriched in other tumor types, and MAT2A expression impinges upon the sensitivity of certain cancer cells to therapeutic inhibition.

Glycine decarboxylase induces autophagy and is downregulated by miRNA-30d-5p in hepatocellular carcinoma.

Glycine decarboxylase (GLDC) belongs to the glycine cleavage system and is involved in one-carbon metabolism. We previously reported that GLDC downregulation enhances hepatocellular carcinoma (HCC) progression and intrahepatic metastasis through decreasing ROS-mediated ubiquitination of cofilin. The role of autophagy in cancer metastasis is still controversial. Redox-dependent autophagy largely relies on the magnitude and the rate of ROS generation. Thus, we aimed to explore the role of GLDC in cellular autophagy during HCC progression. We showed that a high GLDC expression level is associated with better overall survival and is an independent factor for the favorable prognosis of HCC patients. GLDC overexpression significantly induced cell autophagy, whereas GLDC downregulation reduced cell autophagy. Of note, GLDC is the post-transcriptional target of miR-30d-5p. GLDC overexpression could rescue miR-30d-5p-mediated cell metastasis and increase autophagy. Furthermore, upregulation of GLDC could significantly decrease p62 expression and impair intrahepatic metastasis in vivo. Taken together, our results suggest that GLDC may play an important role to increasing miR-30d-5p-reduced autophagy to suppress HCC progress.