Utilization of single-cell RNA-Seq and genome-scale modeling for investigating cancer metabolism
Doctoral thesis, 2022

Cancer remains a leading cause of death worldwide, and its dysregulated metabolism is a promising target for therapy. However, metabolism is complex to study – the metabolism of a cell involves the interplay of thousands of chemical reactions that are combined in different ways across tissues and cell types. Genome-scale metabolic models (GEMs), where the reaction networks of cells are described using a mathematical formulation, have been developed to help in such studies.

In this thesis, methods were developed for determining the active metabolic network (the context-specific model) in individual cell types, followed by studies of cancer metabolism. To enable identification of the active metabolic network per cell type, single-cell RNA sequencing (scRNA-Seq) was employed to detect the presence of individual genes. However, the technical and biological variation in scRNA-Seq data poses a major challenge to the identification of the active reaction network in a cell type. The variability of gene expression due to technical and biological factors was therefore examined, concluding that data from thousands of cells is often required to provide enough stability for robust model generation. An improved quantification method for scRNA-Seq data, called BUTTERFLY, was also developed and implemented as part of the kallisto-bustools scRNA-Seq workflow. A new optimized version of tINIT, which enables generation of context-specific models, was also developed. It allowed for generation of models based on bootstrapped cell populations, which were used to acquire the statistical uncertainty of models generated from scRNA-Seq data. Finally, the method was applied to a lung cancer dataset, identifying both known and unknown features of cancer metabolism.

To further explore cancer metabolism, a study was conducted to investigate the most optimal metabolic behavior under different degrees of hypoxia. To this end, a diffusion-based model for estimating nutrient availability was developed, as well as a light-weight version of the tool GECKO that enables constraining the total enzyme usage in the model. The model could explain the glutamine addiction phenomenon in cancers and was used to show that metabolic collaboration between cell types in tumors is likely not important for growth.

single-cell RNA-Seq

cancer

metabolism

genome-scale metabolic modeling

KB, Kemigården 4
Opponent: Rickard Sandberg, Karolinska institutet

Author

Johan Gustafsson

Chalmers, Biology and Biological Engineering, Systems and Synthetic Biology

Sources of variation in cell-type RNA-Seq profiles

PLoS ONE,; Vol. 15(2020)p. e0239495-

Journal article

Gustafsson J, Robinson J.L, Roshanzamir F, Jörnsten R, Kerkhoven E.J, Nielsen J Generation and analysis of context-specific genome-scale metabolic models derived from single-cell RNA-Seq data

Gustafsson J, Roshanzamir F, Hagnestål A, Robinson J.L, Nielsen J Cellular limitation of enzymatic capacity explains glutamine addiction in cancers

Mathematical models can help explain cancer

Metabolism describes the complex processes by which living cells acquire energy and building blocks from their surroundings to sustain cellular function and growth. Human metabolism involves thousands of different chemical reactions that form a complex reaction network, and in this thesis, mathematical modeling of the reaction network was used to study the metabolic behavior of cells. Methods were developed for utilizing a technology called single-cell RNA sequencing to detect the presence of enzymes that can catalyze reactions, enabling specialization of the reaction network for individual cell types. Furthermore, a method for improving the quantification of single-cell RNA sequencing data was developed. Mathematical modeling was then applied to study the metabolism of the environment within tumors, which unraveled why many cancers use amino acids instead of glucose as an energy source. Furthermore, it has been proposed that healthy cell types within a tumor assist cancer cells metabolically by supplying them with resources. Our models showed that such metabolic collaboration scenarios likely have a small or non-existent positive effect on cancer cell growth. The results from this thesis show that mathematical modeling is a powerful tool for investigating human health and disease, and that combining such modeling with single-cell RNA sequencing shows promise to advance our understanding of human metabolism even further.

Subject Categories

Bioinformatics (Computational Biology)

Cancer and Oncology

Areas of Advance

Life Science Engineering (2010-2018)

ISBN

978-91-7905-651-3

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5117

Publisher

Chalmers

KB, Kemigården 4

Online

Opponent: Rickard Sandberg, Karolinska institutet

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Latest update

5/6/2022 6