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Title: A human pluripotent stem cell-derived model for the investigation of thermogenic adipocyte development and function
Author: Samuelson, Isabella
ISNI:       0000 0004 9353 8909
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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Obesity and associated metabolic complications are growing health challenges in today’s society. New therapies, which do not rely on surgical interventions, are required to treat obesity and/or to ameliorate the metabolic syndrome. Expressly, safe and efficient interventions for weight loss, which can contribute to the positive changes induced by currently recommended lifestyle changes, are warranted. Brown adipose tissue (BAT) has emerged in the last two decades as a relevant therapeutic target due to the unique thermogenic properties of this tissue. Specifically, activated BAT is able to increase whole body energy expenditure, clearing lipids from the circulation and activating lipolysis in white adipose tissue (WAT) in order to fuel the process of non-shivering thermogenesis and burn nutrients as heat. Thus, mechanisms to safely activate BAT and thereby increase energy expenditure could represent promising anti-obesity therapeutics. The challenge is to identify a way to increase energy dissipation without side effects, as previous strategies involving mitochondrial uncouplers or sympathomimetic drugs have been unsafe and associated with cardiovascular problems due to increased sympathetic activation. Other mechanisms of BAT activation must thus be identified. In the quest to increase understanding of human BAT, in my lab we have developed a novel protocol for the in vitro differentiation of human pluripotent stem cells (hPSCs) to brown adipocytes (BAs). This thesis describes how this protocol can be employed to investigate candidate genes with proposed roles in BAT regulation. The thesis also investigates how integration of alternative cell culture systems can help optimise this in vitro BA model by potentially enabling the culture of mature adipocytes in a physiological microenvironment. Finally, this thesis examines whether the recapitulation of a physiological or pathophysiological environment can affect BA differentiation. In chapter 3, I investigate the role of one of these candidate genes in regulation of BAs. The bone morphogenetic protein 8B (BMP8B) has been identified in the mouse as a potential regulator of BA activity; however, its role in human BA function is unknown. Through the generation of a loss of function model of BMP8B I found that while a direct effect on BA differentiation and function was not detected, cells lacking BMP8B showed a downregulation of cardiac and extracellular matrix (ECM)-related processes. In chapter 4, I look into the differentiation of hPSC-derived BAs in 3D culture systems in an attempt to increase BA differentiation efficiency and maturity. I test three synthetic 3D culture systems and identify the PuraMatrix hydrogel as suitable for hPSC-derived BA culture. This hydrogel was able to increase differentiation efficiency of hPSC-derived BAs. Finally, having shown that a synthetic hydrogel scaffold is able to affect BA differentiation, in chapter 5 I investigate how addition of BAT ECM components from lean (physiological) or obese (pathophysiological) mice affects the differentiation of murine brown preadipocytes. I show that contrary to hPSCs, 3D culture did not improve murine brown preadipocyte differentiation, although a functional improvement was observed. Compared to lean ECM, obese ECM impaired BA differentiation and function.
Supervisor: Vidal-Puig, Antonio Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: brown adipose tissue ; adipose tissue ; thermogenic adipocyte ; BMP8B ; fibrosis ; 3D cell culture ; obesity ; bone morphogenetic protein ; stem cells