Human embryonic stem cells and embryonal carcinoma cells have overlapping and distinct metabolic signatures

Transcriptomic and metabolomic insights into the roles of exogenous β-hydroxybutyrate acid for the development of rumen epithelium in young goats

Beta-hydroxybutyric acid (BHBA), as one of the main metabolic ketones in the rumen epithelium, plays critical roles in cellular growth and metabolism. The ketogenic capacity is associated with the maturation of rumen in young ruminants, and the exogenous BHBA in diet may promote the rumen development. However, the effects of exogenous BHBA on rumen remain unknown. This is the first study to investigate the mechanisms of BHBA on gene expression and metabolism of rumen epithelium using young goats as a model through multi-omics techniques. Thirty-two young goats were divided into control, low dose, middle dose, and high dose groups by supplementation of BHBA in starter (0, 3, 6, and 9 g/day, respectively). Results demonstrated the dietary of BHBA promoted the growth performance of young goats and increased width and length of the rumen papilla (P < 0.05). Hub genes in host transcriptome that were positively related to rumen characteristics and BHBA concentration were identified. Several upregulated hub genes including NDUFC1, NDUFB4, NDUFB10, NDUFA11 and NDUFA1 were enriched in the gene ontology (GO) pathway of nicotinamide adenine dinucleotide (NADH) dehydrogenase (ubiquinone) activity, while ATP5ME, ATP5PO and ATP5PF were associated with ATP synthesis. RT-PCR revealed the expression of genes (HMGCS2, BDH1, SLC16A3, etc.) associated with lipolysis increased significantly by BHBA supplementation (P < 0.05). Metabolomics indicated that some metabolites such as glucose, palmitic acid, cortisol and capric acid were also increased (P < 0.05). This study revealed that BHBA promoted rumen development through altering NADH balance and accelerating lipid metabolism, which provides a theoretical guidance for the strategies of gastrointestinal health and development of young ruminants.

Lactate promotes survival and hepatocyte differentiation of human induced pluripotent stem cells in a medium without glucose and supplemented with galactose

Human induced pluripotent stem (iPS) cells initiate hepatocyte differentiation in a medium without glucose and supplemented with galactose, oncostatin M and small molecules [hepatocyte differentiation inducer (HDI)]. To clarify the metabolic differences between iPS cells in HDI and ReproFF (undifferentiated state), a metabolome analysis was performed. iPS cells were cultured in a medium without glucose and supplemented with galactose, as well as 1 mM of calcium lactate, sodium lactate or lactic acid. After 7 days of culture, the cells were subjected to reverse transcription-quantitative PCR analysis. The galactose-1-phosphate concentration was significantly higher in cells cultured in HDI than in those cultured with ReproFF. The lactate concentration in the HDI group was significantly lower than that in the ReproFF group. The expression levels of α-feto protein and albumin were significantly higher in the groups cultured with calcium lactate, sodium lactate and lactic acid as compared with ReproFF. It was suggested that lactate promoted the survival of iPS cells cultured in a medium without glucose and supplemented with galactose. Under these conditions, iPS cells begin to differentiate into a hepatocyte lineage. Lactate may be applied to produce hepatocytes from iPS cells more efficiently.

NDUFC1 Is Upregulated in Gastric Cancer and Regulates Cell Proliferation, Apoptosis, Cycle and Migration

Gastric cancer is one of the most common primary tumors of the digestive system. NADH: ubiquinone oxidoreductase subunit C1 (NDUFC1), which is an accessory subunit of the NADH dehydrogenase (complex I), is responsible for the transportation of electrons from NADH to the respiratory chain essential for the oxidative phosphorylation. However, little is known about the roles of NDUFC1 in carcinogenesis. In this study, NDUFC1 protein level in NSCLC tissues was tested by immunohistochemistry (IHC) staining. NDUFC1 mRNA level in gastric cancer cell lines was determined by qRT-PCR. MGC-803 and SGC-7901 cells were transfected with shNDUFC1 lentivirus designed to silence NDUFC1. MTT assay, CCK8 assay, wound healing assay and transwell migration assay were conducted. Cell cycle and apoptosis were detected by flow cytometry. In vivo experiments were performed using nude mice. The results indicated that overexpressed NDUFC1 in gastric cancer was related to more serious tumor infiltrates, a higher risk of lymphatic metastasis, a higher proportion of positive lymph nodes, and a more advanced tumor stage. Compared with shCtrl groups, MGC-803 and SGC-7901 of shNDUFC1 groups had lower abilities of proliferation and migration, higher levels of apoptosis. NDUFC1 knockdown also inhibited SGC-7901 cell growth in vivo and suppressed Ki67 expression in xenograft tumors. More importantly, we found that NDUFC1 downregulation made the levels of P-Akt, P-mTOR, CCND1, CDK6, PIK3CA, Bcl-2, Survivin, and XIAP decreased, and that PI3K/AKT signaling pathway agonist SC79 rescued the inhibitory effects on cell proliferation and migration, reversed the promoted effects on cell apoptosis caused by NDUFC1 knockdown. More importantly, compared with NDUFC1 knockdown group, the expression of P-Akt, Bcl-2, Survivin, and XIAP was raised in shNDUFC1 + SC79 group. Thus, our suspicion was that NDUFC1 exacerbates NSCLC progression via PI3K/Akt pathway. Taken together, our study indicated that targeting NDUFC1 could open innovative perspectives for new multi-targeting approaches in the treatment of gastric cancer.

Regulation of mRNA translation in stem cells; links to brain disorders

Translational control of gene expression is emerging as a cardinal step in the regulation of protein abundance. Especially for embryonic (ESC) and neuronal stem cells (NSC), regulation of mRNA translation is involved in the maintenance of pluripotency but also differentiation. For neuronal stem cells this regulation is linked to the various neuronal subtypes that arise in the developing brain and is linked to numerous brain disorders. Herein, we review translational control mechanisms in ESCs and NSCs during development and differentiation, and briefly discuss their link to brain disorders.

Role of PIWI-like 4 in modulating neuronal differentiation from human embryonal carcinoma cells

PIWI homologs constitute a subclass of the Argonaute family. Traditionally, they have been shown to associate with a specific class of small RNAs, piRNAs, to suppress transposable elements and protect genomic integrity in germ cells. Recent studies imply that PIWI proteins may also exert important biological functions in somatic contexts, including the brain. However, their exact role in neural development remains unknown. Hence we investigated whether PIWI proteins are involved in neuronal differentiation. By using an established cell model for studying neurogenesis, NTera2/D1 (NT2) cells, we found that a particular PIWI homolog, PIWIL4 was increasingly upregulated throughout the course of all-trans retinoic acid (RA)-mediated neuronal differentiation. During this process, PIWIL4 knockdown led to partial recovery of embryonic stem cell markers, while suppressing RA-induced expression of neuronal markers. Consistently, PIWIL4 overexpression further elevated their expression levels. Furthermore, co-immunoprecipitation revealed an RA-induced interaction between PIWIL4 and the H3K27me3 demethylase UTX. Chromatin immunoprecipitation showed that this interaction could be essential for the removal of H3K27me3 from the promoters of RA-inducible genes. By a similar mechanism, PIWIL4 knockdown also suppressed the expression of PTN and NLGN3, two important neuronal factors secreted to regulate glioma activity. We further noted that the conditioned medium collected from PIWIL4-silenced NT2 cells significantly reduced the proliferation of glioma cells. Thus, our data suggest a novel somatic role of PIWIL4 in modulating the expression of neuronal genes that can be further characterized to promote neuronal differentiation and to modulate the activity of glioma cells.

The metabolic network model of primed/naive human embryonic stem cells underlines the importance of oxidation-reduction potential and tryptophan metabolism in primed pluripotency

Background

Pluripotency is proposed to exist in two different stages: Naive and Primed. Conventional human pluripotent cells are essentially in the primed stage. In recent years, several protocols have claimed to generate naive human embryonic stem cells (hESCs). To the best of our knowledge, none of these protocols is currently recognized as the gold standard method. Furthermore, the consistency of the resulting cells from these diverse protocols at the molecular level is yet to be shown. Additionally, little is known about the principles that govern the metabolic differences between naive and primed pluripotency. In this work, using a computational approach, we tried to shed light on these basic issues.

Results

We showed that, after batch effect removal, the transcriptome data of eight different protocols which supposedly produce naive hESCs are clustered consistently when compared to the primed ones. Next, by integrating transcriptomes of all hESCs obtained by these protocols, we reconstructed p-hESCNet and n-hESCNet, the first metabolic network models representing hESCs. By exploiting reporter metabolite analysis we showed that the status of NAD\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{+}$$\end{document}+ and the metabolites involved in the TCA cycle are significantly altered between naive and primed hESCs. Furthermore, using flux variability analysis (FVA), the models showed that the kynurenine-mediated metabolism of tryptophan is remarkably downregulated in naive human pluripotent cells.

Conclusion

The aim of the present paper is twofold. Firstly, our findings confirm the applicability of all these protocols for generating naive hESCs, due to their consistency at the transcriptome level. Secondly, we showed that in silico metabolic models of hESCs can be used to simulate the metabolic states of naive and primed pluripotency. Our models confirmed the OXPHOS activation in naive cells and showed that oxidation-reduction potential vary between naive and primed cells. Tryptophan metabolism is also outlined as a key pathway in primed pluripotency and the models suggest that decrements in the activity of this pathway might be an appropriate marker for naive pluripotency.

Metabolomic profiles in yak mammary gland tissue during the lactation cycle

The yak is one of the most important domestic animals in Tibetan life for providing basic resources such as milk, meat and transportation. Although yak milk production is not elevated, yak milk is superior to dairy cow milk in nutrient composition (protein and fat). However, the understanding of the metabolic mechanisms of yak mammary gland tissue during the lactation cycle remains elusive. In this study, GC-MS-based metabolomics was employed to study the metabolic variations in the yak mammary gland during the lactation cycle (pregnancy, lactation and dry period). Twenty-nine metabolites were up or downregulated during the lactation period. Compared to the dry period, during the lactation period the levels of oxalic acid were upregulated, while glycine and uridine were downregulated. Thirty-seven pathways were obtained when the 29 differential metabolites were imported into the KEGG pathway analysis. The most impacted pathways during the lactation cycle were glycine, serine and threonine metabolism; alanine, aspartate and glutamate metabolism; TCA cycle; glyoxylate and dicarboxylate metabolism; and pyrimidine metabolism. Our results provide important insights into the metabolic events involved in yak mammary gland development, lactogenesis and lactation, which can guide further research to improve milk yield and enhance the constituents of yak milk.

miRNA-302s may act as oncogenes in human testicular germ cell tumours

Testicular germ cell tumour (TGCT) represents the most common malignancy in young men in large parts of the world, but the aetiology is yet unclear. Multiple TGCT susceptibility loci have been identified, and we have shown that one of these, SPRY4, may act as a TGCT oncogene. Furthermore, many of the loci are in non-coding regions of the genome. miRNAs, a class of non-coding RNAs may play a crucial role in cell proliferation, differentiation, and apoptosis, and alteration in their expression may lead to oncogenesis. Differential expression of miRNAs in TGCT and normal testis has been reported in previous studies. In this study, we used qPCR to analyse, in normal and malignant testis tissue, the expression of the ten miRNAs that we had previously identified by sequencing to be the most upregulated in TGCT. We found high expression of these miRNAs also by qPCR analysis. The levels of miR-302a-3p, miR-302b-3p, and miR-302c-3p were downregulated after treatment of the TGCT cell lines NT2-D1 and 833 K with the chemotherapy drug cisplatin. By using miRNA inhibitor-mediated transient transfection, we inhibited the expression of the three members of miR-302 family (miR-302s). Inhibition of miR-302s resulted in a decreased cell proliferation in NT2-D1 cells, but not in 833 K cells. In both cell lines, inhibition of miR-302s resulted in decreased expression of SPRY4, which we have previously shown to regulate MAPK/ERK and PI3K/Akt signalling pathways in these cells. Inhibition of miR-302b-3p and miR-302c-3p decreased phosphorylation of ERK1/2, whereas inhibition of miR-302a-3p and miR-302b-3p led to decreased expression of the apoptosis inhibitor, survivin. Our findings suggest that miR-302s act as TGCT oncogenes by inducing the expression of SPRY4 and activating MAPK/ERK pathway while inhibiting apoptosis via increased survivin expression.

Metabolism of Stem and Progenitor Cells: Proper Methods to Answer Specific Questions

Stem cells can stay quiescent for a long period of time or proliferate and differentiate into multiple lineages. The activity of stage-specific metabolic programs allows stem cells to best adapt their functions in different microenvironments. Specific cellular phenotypes can be, therefore, defined by precise metabolic signatures. Notably, not only cellular metabolism describes a defined cellular phenotype, but experimental evidence now clearly indicate that also rewiring cells towards a particular cellular metabolism can drive their cellular phenotype and function accordingly. Cellular metabolism can be studied by both targeted and untargeted approaches. Targeted analyses focus on a subset of identified metabolites and on their metabolic fluxes. In addition, the overall assessment of the oxygen consumption rate (OCR) gives a measure of the overall cellular oxidative metabolism and mitochondrial function. Untargeted approach provides a large-scale identification and quantification of the whole metabolome with the aim to describe a metabolic fingerprinting. In this review article, we overview the methodologies currently available for the study of invitro stem cell metabolism, including metabolic fluxes, fingerprint analyses, and single-cell metabolomics. Moreover, we summarize available approaches for the study of in vivo stem cell metabolism. For all of the described methods, we highlight their specificities and limitations. In addition, we discuss practical concerns about the most threatening steps, including metabolic quenching, sample preparation and extraction. A better knowledge of the precise metabolic signature defining specific cell population is instrumental to the design of novel therapeutic strategies able to drive undifferentiated stem cells towards a selective and valuable cellular phenotype.

Cancer Etiology: A Metabolic Disease Originating from Life's Major Evolutionary Transition?

A clear understanding of the origins of cancer is the basis of successful strategies for effective cancer prevention and management. The origin of cancer at the molecular and cellular levels is not well understood. Is the primary cause of the origin of cancer the genomic instability or impaired energy metabolism? An attempt was made to present cancer etiology originating from life's major evolutionary transition. The first evolutionary transition went from simple to complex cells when eukaryotic cells with glycolytic energy production merged with the oxidative mitochondrion (The Endosymbiosis Theory first proposed by Lynn Margulis in the 1960s). The second transition went from single-celled to multicellular organisms once the cells obtained mitochondria, which enabled them to obtain a higher amount of energy. Evidence will be presented that these two transitions, as well as the decline of NAD+ and ATP levels, are the root of cancer diseases. Restoring redox homeostasis and reactivation of mitochondrial oxidative metabolism are important factors in cancer prevention.

Purinergic receptors in neurogenic processes

Neurogenesis is a process of generating functional neurons, which occurs during embryonic and adult stages in mammals. While neurogenesis during development phase is characterized by intensive proliferation activity in all regions of the brain to form the architecture and neural function of the nervous system, adult neurogenesis occurs with less intensity in two brain regions and is involved in the maintenance of neurogenic niches, local repair, memory and cognitive functions in the hippocampus. Taking such differences into account, the understanding of molecular mechanisms involved in cell differentiation in developmental stages and maintenance of the nervous system is an important research target. Although embryonic and adult neurogenesis presents several differences, signaling through purinergic receptors participates in this process throughout life. For instance, while embryonic neurogenesis involves P2X7 receptor down-regulation and calcium waves triggered by P2Y1 receptor stimulation, adult neurogenesis may be enhanced by increased activity of A_2A and P2Y1 receptors and impaired by A₁, P2Y13 and P2X7 receptor stimulation.

βcatenin is a marker of poor clinical characteristics and suppressed immune infiltration in testicular germ cell tumors

BACKGROUND

WNT/βcatenin (WNTβ) pathway is activated in early stages of embryonic development. We aimed to evaluate the significance of βcatenin in germ cell tumors (GCTs) and explore associations with the inflamed environment.

METHODS

Surgical specimens from 247 patients were analyzed. Βcatenin expression was detected in the tumor tissue by immunohistochemistry and correlated with clinical characteristics, outcome, PD-L1 expression and systemic immune-inflammation index (SII). The Ingenuity Pathway Analysis (IPA) was used to investigate the immune-cell related effects of βcatenin and PD-L1 encoding genes.

RESULTS

βcatenin was expressed in 86.2% of GCTs. The expression in seminomas was significantly lower compared to all subtypes of non-seminoma (all P <  0.0001). A high expression (weighted histoscore > 150) was associated with primary mediastinal non-seminoma (P = 0.035), intermediate/poor risk disease (P = 0.033) and high tumor markers (P = 0.035). We observed a positive correlation with the PD-L1 in tumor and an inverse correlation with the SII. IPA uncovered relationships of CTNNB (βcatenin) and CD274 (PD-L1) genes and their effects on differentiation, proliferation and activation of lymphocyte subtypes.

CONCLUSION

Herein, we showed that βcatenin is associated with male adult GCT characteristics as well as supressed immune environment.

Pluripotency Transcription Factors and Metabolic Reprogramming of Mitochondria in Tumor-Initiating Stem-like Cells

Significance: Neoplasms contain tumor-initiating stem-like cells (TICs) that drive malignant progression and tumor growth with drug resistance. TICs proliferate through a self-renewal process in which the two daughter cells differ in their proliferative potential, with one retaining the self-renewing phenotype and another displaying the differentiated phenotype. Recent Advances: Cancer traits (hepatocellular carcinoma) are triggered by alcoholism, obesity, and hepatitis B or C virus (HBV and HCV), including genetic changes, angiogenesis, defective tumor immunity, immortalization, metabolic reprogramming, excessive and prolonged inflammation, migration/invasion/metastasis, evasion of cell cycle arrest, anticell death, and compensatory regeneration/proliferation. Critical Issues: This review describes how metabolic reprogramming in mitochondria promotes self-renewal and oncogenicity of TICs. Pluripotency transcription factors (TFs), NANOG, OCT4, MYC, and SOX2, contribute to cancer progression by mitochondrial reprogramming, leading to the genesis of TICs and cancer. For example, oxidative phosphorylation (OXPHOS) and fatty acid metabolism are identified as major pathways contributing to pluripotency TF-mediated oncogenesis. Future Directions: Identification of novel metabolic pathways provides potential drug targets for neutralizing the activity of highly malignant TICs found in cancer patients. Antioxid. Redox Signal. 28, 1080-1089.

Metabolic Pathways of the Warburg Effect in Health and Disease: Perspectives of Choice, Chain or Chance

Focus on the Warburg effect, initially descriptive of increased glycolysis in cancer cells, has served to illuminate mitochondrial function in many other pathologies. This review explores our current understanding of the Warburg effect’s role in cancer, diabetes and ageing. We highlight how it can be regulated through a chain of oncogenic events, as a chosen response to impaired glucose metabolism or by chance acquisition of genetic changes associated with ageing. Such chain, choice or chance perspectives can be extended to help understand neurodegeneration, such as Alzheimer’s disease, providing clues with scope for therapeutic intervention. It is anticipated that exploration of Warburg effect pathways in extreme conditions, such as deep space, will provide further insights crucial for comprehending complex metabolic diseases, a frontier for medicine that remains equally significant for humanity in space and on earth.

Effect of the epiphytic bacterium Bacillus sp. WPySW2 on the metabolism of Pyropia haitanensis

A variety of different symbiotic microbial communities are harbored on the surface of seaweeds, the interactions of which depend upon nutritional exchanges between the microbes and the hosts. Metabolomic profiling is able to provide a comprehensive and unbiased snapshot of the metabolites associated with seaweed-microbe interactions. In this study, the relationships between phycosphere bacteria and the red alga Pyropia haitanensis were investigated on a metabolomic basis using gas chromatography-mass spectrometry, and the pathways of the interactions between the seaweed and its associated phycospheric microbes were revealed. Bacillus sp. WPySW2, one bacterial species isolated from the phycosphere of Pyropia species, had a significant influence on the metabolomic profile of the algae. Some of the intracellular metabolites such as phenylalanine, leucine, isoleucine, valine, proline, tyrosine, threonine, octadecanoic acid, hexadecanoic acid, and citric acid were downregulated in the thalli of P. haitanensis when it was co-cultured with Bacillus sp. WPySW2, while several special metabolites including melibiose, serine, glycerol-3-phosphate, galactosylglycerol, and alanine were upregulated. The results demonstrated that P. haitanensis grew better when it was co-cultured with Bacillus sp. WPySW2 at 20 °C. In conclusion, several main intracellular metabolites were downregulated and upregulated, which might have facilitated bacterial colonization.

The fate of lysine: Non-targeted stable isotope analysis reveals parallel ways for lysine catabolization in Phaeobacter inhibens

For a detailed investigation of the degradation of lysine in Phaeobacter inhibens DSM 17395, stable isotope experiments with uniformly ¹³C labeled L-lysine were carried out with lysine adapted cells and the metabolites were analyzed using GC/MS and HPLC/MS. A non-targeted stable isotope analysis was used which compares labeled and not labeled samples to determine the Mass Isotopomer Distribution not only for known metabolites but for all labeled compounds in our GC/MS analysis. We show that P. inhibens uses at least two parallel pathways for the first degradation steps of lysine. Further investigations identified L-pipecolate as an L-lysine degradation intermediate in P. inhibens. The analysis of HPLC/MS data as well as the labeling data of tricarboxylic acid (TCA) cycle intermediates show that L-lysine is not only catabolized directly to acetyl-CoA but also via the ethylmalonyl-CoA-pathway, leading to entry points into the TCA cycle via acetyl-CoA, succinyl-CoA, and malate. Altogether the presented data give a detailed insight into the catabolization of L-lysine following the fate of ¹³C labeled carbon via several ways into the TCA cycle.

Cell cycle and pluripotency: Convergence on octamer‑binding transcription factor 4 (Review)

Embryonic stem cells (ESCs) have unlimited expansion potential and the ability to differentiate into all somatic cell types for regenerative medicine and disease model studies. Octamer-binding transcription factor 4 (OCT4), encoded by the POU domain, class 5, transcription factor 1 gene, is a transcription factor vital for maintaining ESC pluripotency and somatic reprogramming. Many studies have established that the cell cycle of ESCs is featured with an abbreviated G1 phase and a prolonged S phase. Changes in cell cycle dynamics are intimately associated with the state of ESC pluripotency, and manipulating cell-cycle regulators could enable a controlled differentiation of ESCs. The present review focused primarily on the emerging roles of OCT4 in coordinating the cell cycle progression, the maintenance of pluripotency and the glycolytic metabolism in ESCs.

2102Ep embryonal carcinoma cells have compromised respiration and shifted bioenergetic profile distinct from H9 human embryonic stem cells

Recent studies have shown that cellular bioenergetics may be involved in stem cell differentiation. Considering that during cancerogenesis cells acquire numerous properties of stem cells, it is possible to assume that the energy metabolism in tumorigenic cells might be differently regulated. The aim of this study was to compare the mitochondrial bioenergetic profile of normal pluripotent human embryonic stem cells (hESC) and relatively nullipotent embryonal carcinoma cells (2102Ep cell line). We examined three parameters related to cellular bioenergetics: phosphotransfer system, aerobic glycolysis, and oxygen consumption. Activities and expression levels of main enzymes that facilitate energy transfer were measured. The oxygen consumption rate studies were performed to investigate the respiratory capacity of cells. 2102Ep cells showed a shift in energy distribution towards adenylate kinase network. The total AK activity was almost 3 times higher in 2102Ep cells compared to hESCs (179.85±5.73 vs 64.39±2.55mU/mg of protein) and the expression of AK2 was significantly higher in these cells, while CK was downregulated. 2102Ep cells displayed reduced levels of oxygen consumption and increased levels of aerobic glycolysis compared to hESCs. The compromised respiration of 2102Ep cells is not the result of increased mitochondrial mass, increased proton leak, and reduced respiratory reserve capacity of the cells or impairment of respiratory chain complexes. Our data showed that the bioenergetic profile of 2102Ep cells clearly distinguishes them from normal hESCs. This should be considered when this cell line is used as a reference, and highlight the importance of further research concerning energy metabolism of stem cells.

Metabolic and fitness determinants for in vitro growth and intestinal colonization of the bacterial pathogen Campylobacter jejuni

Campylobacter jejuni is one of the leading infectious causes of food-borne illness around the world. Its ability to persistently colonize the intestinal tract of a broad range of hosts, including food-producing animals, is central to its epidemiology since most infections are due to the consumption of contaminated food products. Using a highly saturated transposon insertion library combined with next-generation sequencing and a mouse model of infection, we have carried out a comprehensive genome-wide analysis of the fitness determinants for growth in vitro and in vivo of a highly pathogenic strain of C. jejuni. A comparison of the C. jejuni requirements to colonize the mouse intestine with those necessary to grow in different culture media in vitro, combined with isotopologue profiling and metabolic flow analysis, allowed us to identify its metabolic requirements to establish infection, including the ability to acquire certain nutrients, metabolize specific substrates, or maintain intracellular ion homeostasis. This comprehensive analysis has identified metabolic pathways that could provide the basis for the development of novel strategies to prevent C. jejuni colonization of food-producing animals or to treat human infections.

Advances in Applications of Metabolomics in Pluripotent Stem Cell Research

Stem cells undergo extensive metabolic rewiring during reprogramming, proliferation and differentiation, and numerous studies have demonstrated a significant role of metabolism in controlling stem cell fates. Recent applications of metabolomics, the study of concentrations and fluxes of small molecules in cells, have advanced efforts to characterize and maturate stem cell fates, assess drug toxicity in stem cell tissue models, identify biomarkers, and study the effects of environment on metabolic pathways in stem cells and their progeny. Looking to the future, combining metabolomics with other -omics approaches will provide a deeper understanding of the complex regulatory mechanisms of stem cells.

Targeting PDK1 with dichloroacetophenone to inhibit acute myeloid leukemia (AML) cell growth

Pyruvate dehydrogenase kinase-1 (PDK1), a key metabolic enzyme involved in aerobic glycolysis, is highly expressed in many solid tumors. Small molecule compound DAP (2,2-dichloroacetophenone) is a potent inhibitor of PDK1. Whether targeting PDK1 with DAP can inhibit acute myeloid leukemia (AML) and how it works remains unknown. In this study, we evaluated the effect of inhibition of PDK1 with DAP on cell growth, apoptosis and survival in AML cells and identified the underlying mechanisms. We found that treatment with DAP significantly inhibited cell proliferation, increased apoptosis induction and suppressed autophagy in AML cells in vitro, and inhibited tumor growth in an AML mouse model in vivo. We also showed that inhibition of PDK1 with DAP increased the cleavage of pro-apoptotic proteins (PARP and Caspase 3) and decreased the expression of the anti-apoptotic proteins (BCL-xL and BCL-2) and autophagy regulators (ULK1, Beclin-1 and Atg). In addition, we found that DAP inhibited the PI3K/Akt signaling pathway. Furthermore, we demonstrated that PDK1 interacted with ULK1, BCL-xL and E3 ligase CBL-b in AML cells, and DPA treatment could inhibit the interactions. Collectively, our results indicated that targeting PDK1 with DAP inhibited AML cell growth via multiple signaling pathways and suggest that targeting PDK1 may be a promising therapeutic strategy for AMLs.

A systems biology approach reveals major metabolic changes in the thermoacidophilic archaeon Sulfolobus solfataricus in response to the carbon source L-fucose versus D-glucose

Archaea are characterised by a complex metabolism with many unique enzymes that differ from their bacterial and eukaryotic counterparts. The thermoacidophilic archaeon Sulfolobus solfataricus is known for its metabolic versatility and is able to utilize a great variety of different carbon sources. However, the underlying degradation pathways and their regulation are often unknown. In this work, the growth on different carbon sources was analysed, using an integrated systems biology approach. The comparison of growth on L-fucose and D-glucose allows first insights into the genome-wide changes in response to the two carbon sources and revealed a new pathway for L-fucose degradation in S. solfataricus. During growth on L-fucose major changes in the central carbon metabolic network, as well as an increased activity of the glyoxylate bypass and the 3-hydroxypropionate/4-hydroxybutyrate cycle were observed. Within the newly discovered pathway for L-fucose degradation the following key reactions were identified: (i) L-fucose oxidation to L-fuconate via a dehydrogenase, (ii) dehydration to 2-keto-3-deoxy-L-fuconate via dehydratase, (iii) 2-keto-3-deoxy-L-fuconate cleavage to pyruvate and L-lactaldehyde via aldolase and (iv) L-lactaldehyde conversion to L-lactate via aldehyde dehydrogenase. This pathway as well as L-fucose transport shows interesting overlaps to the D-arabinose pathway, representing another example for pathway promiscuity in Sulfolobus species.

Effects of whole genome duplication on cell size and gene expression in mouse embryonic stem cells

Alterations in ploidy tend to influence cell physiology, which in the long-term, contribute to species adaptation and evolution. Polyploid cells are observed under physiological conditions in the nerve and liver tissues, and in tumorigenic processes. Although tetraploid cells have been studied in mammalian cells, the basic characteristics and alterations caused by whole genome duplication are still poorly understood. The purpose of this study was to acquire basic knowledge about the effect of whole genome duplication on the cell cycle, cell size, and gene expression. Using flow cytometry, we demonstrate that cell cycle subpopulations in mouse tetraploid embryonic stem cells (TESCs) were similar to those in embryonic stem cells (ESCs). We performed smear preparations and flow cytometric analysis to identify cell size alterations. These indicated that the relative cell volume of TESCs was approximately 2.2–2.5 fold that of ESCs. We also investigated the effect of whole genome duplication on the expression of housekeeping and pluripotency marker genes using quantitative real-time PCR with external RNA. We found that the target transcripts were 2.2 times more abundant in TESCs than those in ESCs. This indicated that gene expression and cell volume increased in parallel. Our findings suggest the existence of a homeostatic mechanism controlling the cytoplasmic transcript levels in accordance with genome volume changes caused by whole genome duplication.

miR-302 regulates pluripotency, teratoma formation and differentiation in stem cells via an AKT1/OCT4-dependent manner

Pluripotency makes human pluripotent stem cells (hPSCs) promising for regenerative medicine, but the teratoma formation has been considered to be a major obstacle for their clinical applications. Here, we determined that the downregulation of miR-302 suppresses the teratoma formation, hampers the self-renewal and pluripotency, and promotes hPSC differentiation. The underlying mechanism is that the high endogenous expression of miR-302 suppresses the AKT1 expression by directly targeting its 3'UTR and subsequently maintains the pluripotent factor OCT4 at high level. Our findings reveal that miR-302 regulates OCT4 by suppressing AKT1, which provides hPSCs two characteristics related to their potential for clinical applications: the benefit of pluripotency and the hindrance of teratoma formation. More importantly, we demonstrate that miR-302 upregulation cannot lead OCT4 negative human adult mesenchymal stem cells (hMSCs) to acquire the teratoma formation in vivo. Whether miR-302 upregulation can drive hMSCs to acquire a higher differentiation potential is worthy of deep investigation.

Mitochondrial resetting and metabolic reprogramming in induced pluripotent stem cells and mitochondrial disease modeling

BACKGROUND

Nuclear reprogramming with pluripotency factors enables somatic cells to gain the properties of embryonic stem cells. Mitochondrial resetting and metabolic reprogramming are suggested to be key early events in the induction of human skin fibroblasts to induced pluripotent stem cells (iPSCs).

SCOPE OF REVIEW

We review recent advances in the study of the molecular basis for mitochondrial resetting and metabolic reprogramming in the regulation of the formation of iPSCs. In particular, the recent progress in using iPSCs for mitochondrial disease modeling was discussed.

MAJOR CONCLUSIONS

iPSCs rely on glycolysis rather than oxidative phosphorylation as a major supply of energy. Mitochondrial resetting and metabolic reprogramming thus play crucial roles in the process of generation of iPSCs from somatic cells.

GENERAL SIGNIFICANCE

Neurons, myocytes, and cardiomyocytes are cells containing abundant mitochondria in the human body, which can be differentiated from iPSCs or trans-differentiated from fibroblasts. Generating these cells from iPSCs derived from skin fibroblasts of patients with mitochondrial diseases or by trans-differentiation with cell-specific transcription factors will provide valuable insights into the role of mitochondrial DNA heteroplasmy in mitochondrial disease modeling and serves as a novel platform for screening of drugs to treat patients with mitochondrial diseases.

Metabolite Profiling of adh1 Mutant Response to Cold Stress in Arabidopsis

As a result of global warming, vegetation suffers from repeated freeze-thaw cycles caused by more frequent short-term low temperatures induced by hail, snow, or night frost. Therefore, short-term freezing stress of plants should be investigated particularly in light of the current climatic conditions. Alcohol dehydrogenase (ADH) plays a central role in the metabolism of alcohols and aldehydes and it is a key enzyme in anaerobic fermentation. ADH1 responds to plant growth and environmental stress; however, the function of ADH1 in the response to short-term freezing stress remains unknown. Using real-time quantitative fluorescence PCR, the expression level of ADH1 was analyzed at low temperature (4°C). The lethal temperature was calculated based on the electrolyte leakage tests for both ADH1 deletion mutants (adh1) and wild type (WT) plants. To further investigate the relationship between ADH1 and cold tolerance in plants, low-Mr polar metabolite analyses of Arabidopsis adh1 and WT were performed at cold temperatures using gas chromatography-mass spectrometry. This investigation focused on freezing treatments (cold acclimation group: -6°C for 2 h with prior 4°C for 7 d, cold shock group: -6°C for 2 h without cold acclimation) and recovery (23°C for 24 h) with respect to seedling growth at optimum temperature. The experimental results revealed a significant increase in ADH1 expression during low temperature treatment (4°C) and at a higher lethal temperature in adh1 compared to that in the WT. Retention time indices and specific mass fragments were used to monitor 263 variables and annotate 78 identified metabolites. From these analyses, differences in the degree of metabolite accumulation between adh1 and WT were detected, including soluble sugars (e.g., sucrose) and amino acids (e.g., asparagine). In addition, the correlation-based network analysis highlighted some metabolites, e.g., melibiose, fumaric acid, succinic acid, glycolic acid, and xylose, which enhanced connectedness in adh1 network under cold chock. When considered collectively, the results showed that adh1 possessed a metabolic response to freezing stress and ADH1 played an important role in the cold stress response of a plant. These results expands our understanding of the short-term freeze response of ADH1 in plants.

Highly proliferative primitive fetal liver hematopoietic stem cells are fueled by oxidative metabolic pathways

Hematopoietic stem cells (HSCs) in the fetal liver (FL) unlike adult bone marrow (BM) proliferate extensively, posing different metabolic demands. However, metabolic pathways responsible for the production of energy and cellular building blocks in FL HSCs have not been described. Here, we report that FL HSCs use oxygen dependent energy generating pathways significantly more than their BM counterparts. RNA-Seq analysis of E14.5 FL versus BM derived HSCs identified increased expression levels of genes involved in oxidative phosphorylation (OxPhos) and the citric acid cycle (TCA). We demonstrated that FL HSCs contain more mitochondria than BM HSCs, which resulted in increased levels of oxygen consumption and reactive oxygen species (ROS) production. Higher levels of DNA repair and antioxidant pathway gene expression may prevent ROS-mediated (geno)toxicity in FL HSCs. Thus, we here for the first time highlight the underestimated importance of oxygen dependent pathways for generating energy and building blocks in FL HSCs.

Effect of fatty acids on human bone marrow mesenchymal stem cell energy metabolism and survival

Successful stem cell therapy requires the optimal proliferation, engraftment, and differentiation of stem cells into the desired cell lineage of tissues. However, stem cell therapy clinical trials to date have had limited success, suggesting that a better understanding of stem cell biology is needed. This includes a better understanding of stem cell energy metabolism because of the importance of energy metabolism in stem cell proliferation and differentiation. We report here the first direct evidence that human bone marrow mesenchymal stem cell (BMMSC) energy metabolism is highly glycolytic with low rates of mitochondrial oxidative metabolism. The contribution of glycolysis to ATP production is greater than 97% in undifferentiated BMMSCs, while glucose and fatty acid oxidation combined only contribute 3% of ATP production. We also assessed the effect of physiological levels of fatty acids on human BMMSC survival and energy metabolism. We found that the saturated fatty acid palmitate induces BMMSC apoptosis and decreases proliferation, an effect prevented by the unsaturated fatty acid oleate. Interestingly, chronic exposure of human BMMSCs to physiological levels of palmitate (for 24 hr) reduces palmitate oxidation rates. This decrease in palmitate oxidation is prevented by chronic exposure of the BMMSCs to oleate. These results suggest that reducing saturated fatty acid oxidation can decrease human BMMSC proliferation and cause cell death. These results also suggest that saturated fatty acids may be involved in the long-term impairment of BMMSC survival in vivo.

Comparative computational analysis of pluripotency in human and mouse stem cells

Pluripotent cells can be subdivided into two distinct states, the naïve and the primed state, the latter being further advanced on the path of differentiation. There are substantial differences in the regulation of pluripotency between human and mouse, and in humans only stem cells that resemble the primed state in mouse are readily available. Reprogramming of human stem cells into a more naïve-like state is an important research focus. Here, we developed a pipeline to reanalyze transcriptomics data sets that describe both states, naïve and primed pluripotency, in human and mouse. The pipeline consists of identifying regulated start-ups/shut-downs in terms of molecular interactions, followed by functional annotation of the genes involved and aggregation of results across conditions, yielding sets of mechanisms that are consistently regulated in transitions towards similar states of pluripotency. Our results suggest that one published protocol for naïve human cells gave rise to human cells that indeed share putative mechanisms with the prototypical naïve mouse pluripotent cells, such as DNA damage response and histone acetylation. However, cellular response and differentiation-related mechanisms are similar between the naïvehuman state and the primedmouse state, so the naïvehuman state did not fully reflect the naïvemouse state.

GC-MS based targeted metabolic profiling identifies changes in the wheat metabolome following deoxynivalenol treatment

Fusariumgraminearum and related species commonly infest grains causing the devastating plant disease Fusarium head blight (FHB) and the formation of trichothecene mycotoxins. The most relevant toxin is deoxynivalenol (DON), which acts as a virulence factor of the pathogen. FHB is difficult to control and resistance to this disease is a polygenic trait, mainly mediated by the quantitative trait loci (QTL) Fhb1 and Qfhs.ifa-5A. In this study we established a targeted GC-MS based metabolomics workflow comprising a standardized experimental setup for growth, treatment and sampling of wheat ears and subsequent GC-MS analysis followed by data processing and evaluation of QC measures using tailored statistical and bioinformatics tools. This workflow was applied to wheat samples of six genotypes with varying levels of Fusarium resistance, treated with either DON or water, and harvested 0, 12, 24, 48 and 96 h after treatment. The results suggest that the primary carbohydrate metabolism and transport, the citric acid cycle and the primary nitrogen metabolism of wheat are clearly affected by DON treatment. Most importantly significantly elevated levels of amino acids and derived amines were observed. In particular, the concentrations of the three aromatic amino acids phenylalanine, tyrosine, and tryptophan increased. No clear QTL specific difference in the response could be observed except a generally faster increase in shikimate pathway intermediates in genotypes containing Fhb1. The overall workflow proved to be feasible and facilitated to obtain a more comprehensive picture on the effect of DON on the central metabolism of wheat.

Blastocyst metabolism

The mammalian blastocyst exhibits an idiosyncratic metabolism, reflecting its unique physiology and its ability to undergo implantation. Glucose is the primary nutrient of the blastocyst, and is metabolised both oxidatively and through aerobic glycolysis. The production of significant quantities of lactate by the blastocyst reflects specific metabolic requirements and mitochondrial regulation; it is further proposed that lactate production serves to facilitate several key functions during implantation, including biosynthesis, endometrial tissue breakdown, the promotion of new blood vessel formation and induction of local immune-modulation of the uterine environment. Nutrient availability, oxygen concentration and the redox state of the blastocyst tightly regulate the relative activities of specific metabolic pathways. Notably, a loss of metabolic normality is associated with a reduction in implantation potential and subsequent fetal development. Even a transient metabolic stress at the blastocyst stage culminates in low fetal weights after transfer. Further, it is evident that there are differences between male and female embryos, with female embryos being characterised by higher glucose consumption and differences in their amino acid turnover, reflecting the presence of two active X-chromosomes before implantation, which results in differences in the proteomes between the sexes. In addition to the role of Hypoxia-Inducible Factors, the signalling pathways involved in regulating blastocyst metabolism are currently under intense analysis, with the roles of sirtuins, mTOR, AMP-activated protein kinase and specific amino acids being scrutinised. It is evident that blastocyst metabolism regulates more than the production of ATP; rather, it is apparent that metabolites and cofactors are important regulators of the epigenome, putting metabolism at centre stage when considering the interactions of the blastocyst with its environment.

Oct4 maintains the pluripotency of human embryonic stem cells by inactivating p53 through Sirt1-mediated deacetylation

Oct4 is critical to maintain the pluripotency of human embryonic stem cells (hESCs); however, the underlying mechanism remains to be fully understood. Here, we report that silencing of Oct4 in hESCs leads to the activation of tumor suppressor p53, inducing the differentiation of hESCs since acute disruption of p53 in p53 conditional knockout (p53CKO) hESCs prevents the differentiation of hESCs after Oct4 depletion. We further discovered that the silencing of Oct4 significantly reduces the expression of Sirt1, a deacetylase known to inhibit p53 activity and the differentiation of ESCs, leading to increased acetylation of p53 at lysine 120 and 164. The importance of Sirt1 in mediating Oct4-dependent pluripotency is revealed by the finding that the ectopic expression of Sirt1 in Oct4-silenced hESCs prevents p53 activation and hESC differentiation. In addition, using knock-in approach, we revealed that the acetylation of p53 at lysine 120 and 164 is required for both stabilization and activity of p53 in hESCs. In summary, our findings reveal a novel role of Oct4 in maintaining the pluripotency of hESCs by suppressing pathways that induce differentiation. Considering that p53 suppresses pluripotency after DNA damage response in ESCs, our findings further underscore the stringent mechanism to coordinate DNA damage response pathways and pluripotency pathways in order to maintain the pluripotency and genomic stability of hESCs.

Cancer stem cell theory and the warburg effect, two sides of the same coin?

Over the last 100 years, many studies have been performed to determine the biochemical and histopathological phenomena that mark the origin of neoplasms. At the end of the last century, the leading paradigm, which is currently well rooted, considered the origin of neoplasms to be a set of genetic and/or epigenetic mutations, stochastic and independent in a single cell, or rather, a stochastic monoclonal pattern. However, in the last 20 years, two important areas of research have underlined numerous limitations and incongruities of this pattern, the hypothesis of the so-called cancer stem cell theory and a revaluation of several alterations in metabolic networks that are typical of the neoplastic cell, the so-called Warburg effect. Even if this specific “metabolic sign” has been known for more than 85 years, only in the last few years has it been given more attention; therefore, the so-called Warburg hypothesis has been used in multiple and independent surveys. Based on an accurate analysis of a series of considerations and of biophysical thermodynamic events in the literature, we will demonstrate a homogeneous pattern of the cancer stem cell theory, of the Warburg hypothesis and of the stochastic monoclonal pattern; this pattern could contribute considerably as the first basis of the development of a new uniform theory on the origin of neoplasms. Thus, a new possible epistemological paradigm is represented; this paradigm considers the Warburg effect as a specific “metabolic sign” reflecting the stem origin of the neoplastic cell, where, in this specific metabolic order, an essential reason for the genetic instability that is intrinsic to the neoplastic cell is defined.

Solving the differential biochemical Jacobian from metabolomics covariance data

High-throughput molecular analysis has become an integral part in organismal systems biology. In contrast, due to a missing systematic linkage of the data with functional and predictive theoretical models of the underlying metabolic network the understanding of the resulting complex data sets is lacking far behind. Here, we present a biomathematical method addressing this problem by using metabolomics data for the inverse calculation of a biochemical Jacobian matrix, thereby linking computer-based genome-scale metabolic reconstruction and in vivo metabolic dynamics. The incongruity of metabolome coverage by typical metabolite profiling approaches and genome-scale metabolic reconstruction was solved by the design of superpathways to define a metabolic interaction matrix. A differential biochemical Jacobian was calculated using an approach which links this metabolic interaction matrix and the covariance of metabolomics data satisfying a Lyapunov equation. The predictions of the differential Jacobian from real metabolomic data were found to be correct by testing the corresponding enzymatic activities. Moreover it is demonstrated that the predictions of the biochemical Jacobian matrix allow for the design of parameter optimization strategies for ODE-based kinetic models of the system. The presented concept combines dynamic modelling strategies with large-scale steady state profiling approaches without the explicit knowledge of individual kinetic parameters. In summary, the presented strategy allows for the identification of regulatory key processes in the biochemical network directly from metabolomics data and is a fundamental achievement for the functional interpretation of metabolomics data.

The identification of mitochondrial DNA variants in glioblastoma multiforme

BACKGROUND

Mitochondrial DNA (mtDNA) encodes key proteins of the electron transfer chain (ETC), which produces ATP through oxidative phosphorylation (OXPHOS) and is essential for cells to perform specialised functions. Tumor-initiating cells use aerobic glycolysis, a combination of glycolysis and low levels of OXPHOS, to promote rapid cell proliferation and tumor growth. Glioblastoma multiforme (GBM) is an aggressively malignant brain tumor and mitochondria have been proposed to play a vital role in GBM tumorigenesis.

RESULTS

Using next generation sequencing and high resolution melt analysis, we identified a large number of mtDNA variants within coding and non-coding regions of GBM cell lines and predicted their disease-causing potential through in silico modeling. The frequency of variants was greatest in the D-loop and origin of light strand replication in non-coding regions. ND6 was the most susceptible coding gene to mutation whilst ND4 had the highest frequency of mutation. Both genes encode subunits of complex I of the ETC. These variants were not detected in unaffected brain samples and many have not been previously reported. Depletion of HSR-GBM1 cells to varying degrees of their mtDNA followed by transplantation into immunedeficient mice resulted in the repopulation of the same variants during tumorigenesis. Likewise, de novo variants identified in other GBM cell lines were also incorporated. Nevertheless, ND4 and ND6 were still the most affected genes. We confirmed the presence of these variants in high grade gliomas.

CONCLUSIONS

These novel variants contribute to GBM by rendering the ETC. partially dysfunctional. This restricts metabolism to anaerobic glycolysis and promotes cell proliferation.

Functional characterisation of osteosarcoma cell lines and identification of mRNAs and miRNAs associated with aggressive cancer phenotypes

Background:

Osteosarcoma is the most common primary malignant bone tumour, predominantly affecting children and adolescents. Cancer cell line models are required to understand the underlying mechanisms of tumour progression and for preclinical investigations.

Methods:

To identify cell lines that are well suited for studies of critical cancer-related phenotypes, such as tumour initiation, growth and metastasis, we have evaluated 22 osteosarcoma cell lines for in vivo tumorigenicity, in vitro colony-forming ability, invasive/migratory potential and proliferation capacity. Importantly, we have also identified mRNA and microRNA (miRNA) gene expression patterns associated with these phenotypes by expression profiling.

Results:

The cell lines exhibited a wide range of cancer-related phenotypes, from rather indolent to very aggressive. Several mRNAs were differentially expressed in highly aggressive osteosarcoma cell lines compared with non-aggressive cell lines, including RUNX2, several S100 genes, collagen genes and genes encoding proteins involved in growth factor binding, cell adhesion and extracellular matrix remodelling. Most notably, four genes—COL1A2, KYNU, ACTG2 and NPPB—were differentially expressed in high and non-aggressive cell lines for all the cancer-related phenotypes investigated, suggesting that they might have important roles in the process of osteosarcoma tumorigenesis. At the miRNA level, miR-199b-5p and mir-100-3p were downregulated in the highly aggressive cell lines, whereas miR-155-5p, miR-135b-5p and miR-146a-5p were upregulated. miR-135b-5p and miR-146a-5p were further predicted to be linked to the metastatic capacity of the disease.

Interpretation:

The detailed characterisation of cell line phenotypes will support the selection of models to use for specific preclinical investigations. The differentially expressed mRNAs and miRNAs identified in this study may represent good candidates for future therapeutic targets. To our knowledge, this is the first time that expression profiles are associated with functional characteristics of osteosarcoma cell lines.

Analysis of metabolism to select viable human embryos for transfer

As we move to reducing the number of embryos transferred in a given IVF cycle, ideally down to one, there is an ever-increasing need for noninvasive quantitative markers of embryo viability. Although stage-specific morphologic markers and grading systems have been developed, such an approach is unable to assess the physiological status of the embryo. Analysis of metabolism has proved to be a valuable marker of embryo viability after transfer in animal models. We therefore reviewed what is known about human embryo metabolism, how media systems can affect the patterns of nutrient utilization and the activities of metabolic pathways, and how this relates to the developmental competence of the embryo. It is proposed that a unifying hypothesis of metabolism for the entire preimplantation period is not realistic, given the dramatic changes in embryo physiology that occur from fertilization to blastocyst development, and that the concept of a "quiet metabolism" can be interpreted as stress induced by the presence of high oxygen in the embryo culture/analysis system. Further research is required to fully understand the origins of metabolic stress in embryos for it to be alleviated and to develop a comprehensive range of markers that not only reflect embryo viability, but also sex-specific differences in physiology.

Contribution of amino acid catabolism to the tissue specific persistence of Campylobacter jejuni in a murine colonization model

Campylobacter jejuni is a major cause of food-borne disease in industrialized countries. Carbohydrate utilization by C. jejuni is severely restricted, and knowledge about which substrates fuel C. jejuni infection and growth is limited. Some amino acids have been shown to serve as carbon sources both in vitro and in vivo. In the present study we investigated the contribution of serine and proline catabolism to the invitro and invivo growth of C. jejuni 81-176. We confirmed that the serine transporter SdaC and the serine ammonia-lyase SdaA are required for serine utilization, and demonstrated that a predicted proline permease PutP and a bifunctional proline/delta-1-pyrroline-5-carboxylate dehydrogenase PutA are required for proline utilization by C. jejuni 81-176. C. jejuni 81-176 mutants unable to utilize serine were shown to be severely defective for colonization of the intestine and systemic tissues in a mouse model of infection. In contrast, C. jejuni 81-176 mutants unable to utilize proline were only defective for intestinal colonization. These results further emphasize the importance of amino acid utilization in C. jejuni colonization of various tissues.