A phosphoglycolate phosphatase/AUM-dependent link between triacylglycerol turnover and epidermal growth factor signaling

Glycolytic flux control by drugging phosphoglycolate phosphatase

Targeting the intrinsic metabolism of immune or tumor cells is a therapeutic strategy in autoimmunity, chronic inflammation or cancer. Metabolite repair enzymes may represent an alternative target class for selective metabolic inhibition, but pharmacological tools to test this concept are needed. Here, we demonstrate that phosphoglycolate phosphatase (PGP), a prototypical metabolite repair enzyme in glycolysis, is a pharmacologically actionable target. Using a combination of small molecule screening, protein crystallography, molecular dynamics simulations and NMR metabolomics, we discover and analyze a compound (CP1) that inhibits PGP with high selectivity and submicromolar potency. CP1 locks the phosphatase in a catalytically inactive conformation, dampens glycolytic flux, and phenocopies effects of cellular PGP-deficiency. This study provides key insights into effective and precise PGP targeting, at the same time validating an allosteric approach to control glycolysis that could advance discoveries of innovative therapeutic candidates.

Hepatic glycerol shunt and glycerol-3-phosphate phosphatase control liver metabolism and glucodetoxification under hyperglycemia

OBJECTIVE

Glycerol-3-phosphate (Gro3P) phosphatase (G3PP) hydrolyzes Gro3P to glycerol that exits the cell, thereby operating a "glycerol shunt", a metabolic pathway that we identified recently in mammalian cells. We have investigated the role of G3PP and the glycerol shunt in the regulation of glucose metabolism and lipogenesis in mouse liver.

METHODS

We generated hepatocyte-specific G3PP-KO mice (LKO), by injecting AAV8-TBG-iCre to male G3PP^fl/fl mice. Controls received AAV8-TBG-eGFP. Both groups were fed chow diet for 10 weeks. Hyperglycemia (16-20 mM) was induced by glucose infusion for 55 h. Hepatocytes were isolated from normoglycemic mice for ex vivo studies and targeted metabolomics were measured in mice liver after glucose infusion.

RESULTS

LKO mice showed no change in body weight, food intake, fed and fasted glycemia but had increased fed plasma triglycerides. Hepatic glucose production from glycerol was increased in fasted LKO mice. LKO mouse hepatocytes displayed reduced glycerol production, elevated triglyceride and lactate production at high glucose concentration. Hyperglycemia in LKO mice led to increased liver weight and accumulation of triglycerides, glycogen and cholesterol together with elevated levels of Gro3P, dihydroxyacetone phosphate, acetyl-CoA and some Krebs cycle intermediates in liver. Hyperglycemic LKO mouse liver showed elevated expression of proinflammatory cytokines and M1-macrophage markers accompanied by increased plasma triglycerides, LDL/VLDL, urea and uric acid and myocardial triglycerides.

CONCLUSIONS

The glycerol shunt orchestrated by G3PP acts as a glucose excess detoxification pathway in hepatocytes by preventing metabolic disturbances that contribute to enhanced liver fat, glycogen storage, inflammation and lipid build-up in the heart. We propose G3PP as a novel therapeutic target for hepatic disorders linked to nutrient excess.

Identification of Phosphorus Stress Related Proteins in the Seedlings of Dongxiang Wild Rice (Oryza Rufipogon Griff.) Using Label-Free Quantitative Proteomic Analysis

Phosphorus (P) deficiency tolerance in rice is a complex character controlled by polygenes. Through proteomics analysis, we could find more low P tolerance related proteins in unique P-deficiency tolerance germplasm Dongxiang wild rice (Oryza Rufipogon, DXWR), which will provide the basis for the research of its regulation mechanism. In this study, a proteomic approach as well as joint analysis with transcriptome data were conducted to identify potential unique low P response genes in DXWR during seedlings. The results showed that 3589 significant differential accumulation proteins were identified between the low P and the normal P treated root samples of DXWR. The degree of change was more than 1.5 times, including 60 up-regulated and 15 downregulated proteins, 24 of which also detected expression changes of more than 1.5-fold in the transcriptome data. Through quantitative trait locus (QTLs) matching analysis, seven genes corresponding to the significantly different expression proteins identified in this study were found to be uncharacterized and distributed in the QTLs interval related to low P tolerance, two of which (LOC_Os12g09620 and LOC_Os03g40670) were detected at both transcriptome and proteome levels. Based on the comprehensive analysis, it was found that DXWR could increase the expression of purple acid phosphatases (PAPs), membrane location of P transporters (PTs), rhizosphere area, and alternative splicing, and it could decrease reactive oxygen species (ROS) activity to deal with low P stress. This study would provide some useful insights in cloning the P-deficiency tolerance genes from wild rice, as well as elucidating the molecular mechanism of low P resistance in DXWR.

New Mammalian Glycerol-3-Phosphate Phosphatase: Role in β-Cell, Liver and Adipocyte Metabolism

Cardiometabolic diseases, including type 2 diabetes, obesity and non-alcoholic fatty liver disease, have enormous impact on modern societies worldwide. Excess nutritional burden and nutri-stress together with sedentary lifestyles lead to these diseases. Deranged glucose, fat, and energy metabolism is at the center of nutri-stress, and glycolysis-derived glycerol-3-phosphate (Gro3P) is at the crossroads of these metabolic pathways. Cellular levels of Gro3P can be controlled by its synthesis, utilization or hydrolysis. The belief that mammalian cells do not possess an enzyme that hydrolyzes Gro3P, as in lower organisms and plants, is challenged by our recent work showing the presence of a Gro3P phosphatase (G3PP) in mammalian cells. A previously described phosphoglycolate phosphatase (PGP) in mammalian cells, with no established physiological function, has been shown to actually function as G3PP, under physiological conditions, particularly at elevated glucose levels. In the present review, we summarize evidence that supports the view that G3PP plays an important role in the regulation of gluconeogenesis and fat storage in hepatocytes, glucose stimulated insulin secretion and nutri-stress in β-cells, and lipogenesis in adipocytes. We provide a balanced perspective on the pathophysiological significance of G3PP in mammals with specific reference to cardiometabolic diseases.

Metabolite Repair Enzymes Control Metabolic Damage in Glycolysis

Hundreds of metabolic enzymes work together smoothly in a cell. These enzymes are highly specific. Nevertheless, under physiological conditions, many perform side-reactions at low rates, producing potentially toxic side-products. An increasing number of metabolite repair enzymes are being discovered that serve to eliminate these noncanonical metabolites. Some of these enzymes are extraordinarily conserved, and their deficiency can lead to diseases in humans or embryonic lethality in mice, indicating their central role in cellular metabolism. We discuss how metabolite repair enzymes eliminate glycolytic side-products and prevent negative interference within and beyond this core metabolic pathway. Extrapolating from the number of metabolite repair enzymes involved in glycolysis, hundreds more likely remain to be discovered that protect a wide range of metabolic pathways.

Human melanoma brain metastases cell line MUG-Mel1, isolated clones and their detailed characterization

Melanoma is a leading cause of high mortality that frequently spreads to the brain and is associated with deterioration in quality and quantity of life. Treatment opportunities have been restricted until now and new therapy options are urgently required. Our focus was to reveal the potential heterogeneity of melanoma brain metastasis. We succeeded to establish a brain melanoma metastasis cell line, namely MUG-Mel1 and two resulting clones D5 and C8 by morphological variety, differences in lipidome, growth behavior, surface, and stem cell markers. Mutation analysis by next-generation sequencing, copy number profiling, and cytogenetics demonstrated the different genetic profile of MUG-Mel1 and clones. Tumorigenicity was unsuccessfully tested in various mouse systems and finally established in a zebra fish model. As innovative treatment option, with high potential to pass the blood-brain barrier a peptide isolated from lactoferricin was studied in potential toxicity. Brain metastases are a major clinical challenge, therefore the development of relevant in vitro and in vivo models derived from brain melanoma metastases provides valuable information about tumor biology and offers great potential to screen for new innovative therapies.

Phosphoglycolate has profound metabolic effects but most likely no role in a metabolic DNA response in cancer cell lines

Repair of a certain type of oxidative DNA damage leads to the release of phosphoglycolate, which is an inhibitor of triose phosphate isomerase and is predicted to indirectly inhibit phosphoglycerate mutase activity. Thus, we hypothesized that phosphoglycolate might play a role in a metabolic DNA damage response. Here, we determined how phosphoglycolate is formed in cells, elucidated its effects on cellular metabolism and tested whether DNA damage repair might release sufficient phosphoglycolate to provoke metabolic effects. Phosphoglycolate concentrations were below 5 µM in wild-type U2OS and HCT116 cells and remained unchanged when we inactivated phosphoglycolate phosphatase (PGP), the enzyme that is believed to dephosphorylate phosphoglycolate. Treatment of PGP knockout cell lines with glycolate caused an up to 500-fold increase in phosphoglycolate concentrations, which resulted largely from a side activity of pyruvate kinase. This increase was much higher than in glycolate-treated wild-type cells and was accompanied by metabolite changes consistent with an inhibition of phosphoglycerate mutase, most likely due to the removal of the priming phosphorylation of this enzyme. Surprisingly, we found that phosphoglycolate also inhibits succinate dehydrogenase with a Ki value of <10 µM. Thus, phosphoglycolate can lead to profound metabolic disturbances. In contrast, phosphoglycolate concentrations were not significantly changed when we treated PGP knockout cells with Bleomycin or ionizing radiation, which are known to lead to the release of phosphoglycolate by causing DNA damage. Thus, phosphoglycolate concentrations due to DNA damage are too low to cause major metabolic changes in HCT116 and U2OS cells.