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Reconfiguration of amino acid biosynthesis in TGF-β1-induced myofibroblasts

Contento, Gregorio; (2021) Reconfiguration of amino acid biosynthesis in TGF-β1-induced myofibroblasts. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

At sites of tissue injury, the differentiation of fibroblasts into highly synthetic extracellular matrix (ECM)-producing myofibroblasts is essential for tissue repair and chiefly mediated by the pro-fibrotic cytokine, TGF-β1. In a fibrotic setting, these myofibroblasts fail to respond to pro-apoptotic signals during the resolution phase and relentlessly deposit ECM components, leading to destruction of healthy tissue and, in the case of lung fibrosis, respiratory failure and death. Differentiating myofibroblasts exhibit a reprograming in their metabolic networks which, like cancer cells, is believed to support the biosynthetic and bioenergetic needs of a highly protein-synthesizing cell. Evidence suggests that the changes observed in glucose and glutamine metabolic networks are critical for fibrogenesis. The present study shows that TGF-β1 induces ATF4 protein levels via mTOR to upregulate the serine-glycine biosynthetic axis enzymes (PHGDH, PSAT1, PSPH, SHMT2) which are required for enhanced collagen synthesis. Pharmacological inhibition of PHGDH and siRNA-mediated silencing of PSAT1 both prevent TGF-β1-stimulated pHLFs from synthesizing enhanced levels of collagen protein. Glycine is essential in the growth media for pHLFs to synthesize TGF-β1-enhanced collagen I levels. Glutamine, which supports the serine-glycine biosynthetic axis via its generation of glutamate, is critical for collagen synthesis and compensates for a withdrawal of glucose for pHLFs to synthesize TGF-β1-induced collagen I. TGF-β1 accelerates glutamine consumption and increases intracellular glutamate synthesis, an even facilitated by upregulating GLS1 and downregulating GLUL. GLS1-derived glutamate supports the biosynthetic pathways for alanine and proline, the latter mediated by GPT2 and required for TGF-β1-induced mTORC1 activation via a mechanism which is independent of the amino acid sensing Rag-GTPases. Furthermore, the group of enzymes to which GPT2 and PSAT1 belong, the aminotransferases, prevent TGF-β1-induced collagen synthesis upon pharmacological inhibition, an event rescued by exogenous addition of nonessential amino acids and α-ketoglutarate. Together, this work identifies the aminotransferases as a promising therapeutic target for fibrotic conditions by limiting the capacity for enhanced collagen synthesis in fibroblasts. Further understanding the pro-fibrotic functions of the members of this enzyme family may yield promising results to aid in the development of therapeutic approaches and strategies.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Reconfiguration of amino acid biosynthesis in TGF-β1-induced myofibroblasts
Event: UCL (University College London)
Language: English
Additional information: Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences > Div of Medicine
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences > Div of Medicine > Respiratory Medicine
URI: https://discovery.ucl.ac.uk/id/eprint/10137540
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