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      A Systematic Evaluation of Methods for Tailoring Genome-Scale Metabolic Models

      , , , , ,
      Cell Systems
      Elsevier BV

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          Abstract

          <p class="first" id="P1">Genome-scale models of metabolism can illuminate the molecular basis of cell phenotypes. Since many enzymes are only active in specific cell types, several algorithms use omics data to construct cell line- and tissue-specific metabolic models from genome-scale models. However, these methods have not been rigorously benchmarked, and it is unclear how algorithm and parameter selection (e.g., gene expression thresholds, metabolic constraints) impacts model content and predictive accuracy. To investigate this, we built hundreds of models of four different cancer cell lines using six algorithms, four gene expression thresholds and three sets of metabolic constraints. Model content varied substantially across different parameter sets, but model extraction method choice had the largest impact on the accuracy of model-predicted gene essentiality. We further highlight how assumptions during model development influence the accuracy of model prediction. These insights will guide further development of context-specific models, thus more accurately resolving genotype-phenotype relationships. </p><p id="P2">eTOC blurb: This study presents a comparative analysis of hundreds of models extracted for four different cancer cell lines using several prominent model extraction algorithms. The evaluation provides insights into how their assumptions impact the prediction capabilities of context-specific models. </p><p id="P3"> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/c905d7fa-d150-49e7-980b-ab9cd969d6f5/PubMedCentral/image/nihms878440u1.jpg"/> </div> </p>

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          Most cited references39

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          Quantitative prediction of cellular metabolism with constraint-based models: the COBRA Toolbox v2.0.

          Over the past decade, a growing community of researchers has emerged around the use of constraint-based reconstruction and analysis (COBRA) methods to simulate, analyze and predict a variety of metabolic phenotypes using genome-scale models. The COBRA Toolbox, a MATLAB package for implementing COBRA methods, was presented earlier. Here we present a substantial update of this in silico toolbox. Version 2.0 of the COBRA Toolbox expands the scope of computations by including in silico analysis methods developed since its original release. New functions include (i) network gap filling, (ii) (13)C analysis, (iii) metabolic engineering, (iv) omics-guided analysis and (v) visualization. As with the first version, the COBRA Toolbox reads and writes systems biology markup language-formatted models. In version 2.0, we improved performance, usability and the level of documentation. A suite of test scripts can now be used to learn the core functionality of the toolbox and validate results. This toolbox lowers the barrier of entry to use powerful COBRA methods.
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            The effects of alternate optimal solutions in constraint-based genome-scale metabolic models.

            Genome-scale constraint-based models of several organisms have now been constructed and are being used for model driven research. A key issue that may arise in the use of such models is the existence of alternate optimal solutions wherein the same maximal objective (e.g., growth rate) can be achieved through different flux distributions. Herein, we investigate the effects that alternate optimal solutions may have on the predicted range of flux values calculated using currently practiced linear (LP) and quadratic programming (QP) methods. An efficient LP-based strategy is described to calculate the range of flux variability that can be present in order to achieve optimal as well as suboptimal objective states. Sample results are provided for growth predictions of E. coli using glucose, acetate, and lactate as carbon substrates. These results demonstrate the extent of flux variability to be highly dependent on environmental conditions and network composition. In addition we examined the impact of alternate optima for growth under gene knockout conditions as calculated using QP-based methods. It was observed that calculations using QP-based methods can show significant variation in growth rate if the flux variability among alternate optima is high. The underlying biological significance and general source of such flux variability is further investigated through the identification of redundancies in the network (equivalent reaction sets) that lead to alternate solutions. Collectively, these results illustrate the variability inherent in metabolic flux distributions and the possible implications of this heterogeneity for constraint-based modeling approaches. These methods also provide an efficient and robust method to calculate the range of flux distributions that can be derived from quantitative fermentation data.
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              Network-based prediction of human tissue-specific metabolism.

              Direct in vivo investigation of mammalian metabolism is complicated by the distinct metabolic functions of different tissues. We present a computational method that successfully describes the tissue specificity of human metabolism on a large scale. By integrating tissue-specific gene- and protein-expression data with an existing comprehensive reconstruction of the global human metabolic network, we predict tissue-specific metabolic activity in ten human tissues. This reveals a central role for post-transcriptional regulation in shaping tissue-specific metabolic activity profiles. The predicted tissue specificity of genes responsible for metabolic diseases and tissue-specific differences in metabolite exchange with biofluids extend markedly beyond tissue-specific differences manifest in enzyme-expression data, and are validated by large-scale mining of tissue-specificity data. Our results establish a computational basis for the genome-wide study of normal and abnormal human metabolism in a tissue-specific manner.
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                Author and article information

                Journal
                Cell Systems
                Cell Systems
                Elsevier BV
                24054712
                March 2017
                March 2017
                : 4
                : 3
                : 318-329.e6
                Article
                10.1016/j.cels.2017.01.010
                5526624
                28215528
                41c79edf-e0e0-44d5-8c4c-edd1aedbfd8e
                © 2017
                History

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