Role of GPS2 in the regulation of adipocyte fate and function : a multi-omics approach

Abstract: The escalating prevalence of obesity and its association with comorbidities like insulin resistance and type 2 diabetes have raised the interest in adipose tissue biology and its therapeutic potential. Adipose tissue remodeling during the development of obesity is an important regulator of systemic metabolic homeostasis, and dysfunctional adipose tissue is linked to the risk of developing type 2 diabetes. Adipocyte differentiation and function are orchestrated by a complex network of transcription factors and coregulators that transduce regulatory signals into epigenome alterations and transcriptional responses. While the role of transcription factors involved in adipogenic pathways is well established, the role of their associated coregulators remains poorly understood. Of particular interest is G protein pathway suppressor 2 (GPS2), a core subunit of the HDAC3 corepressor complex, which is downregulated in humans with obesity and implicated in regulating metabolic and antiinflammatory pathways in various tissues. The overall aim of this thesis was to identify hitherto unknown functions of GPS2 in the adipose tissue, with a particular emphasis on mechanisms underlying adipocyte dysfunction in the context of obesity and type 2 diabetes. In Paper I, by generating a unique loss-of-function model using human multipotent adiposederived stem cells, we showed that loss of GPS2 triggers the commitment of fibroblast-like progenitors towards the adipogenic lineage and induces hypertrophy of mature adipocytes associated with a deep remodeling of the adipocyte lipidome. Furthermore, we demonstrated that adipocyte hypertrophy was likely the consequence of the increased expression of ATPbinding cassette subfamily G member 1 (ABCG1) that mediates sphingomyelin efflux from adipocytes and modulates the activity of lipoprotein lipase (LPL). We validated the cellderived findings by gene expression analysis of an obese cohort, where GPS2 is downregulated in diabetic patients and negatively correlated with the expression of ABCG1. In Paper II, by characterizing adipocyte-specific Gps2 knockout mice, we discovered a hitherto unknown function of GPS2 in the induction of adipocyte hypertrophy, inflammation and mitochondrial dysfunction. The knockout phenotype was driven by over-activation of the transcription factor HIF1A that orchestrates an inadequate white adipose tissue remodeling and disrupts mitochondrial activity. The validation of the experimental mouse data in a human cohort of non-obese and obese individuals with or without diagnosed type 2 diabetes showed a negative correlation between the expression of GPS2 and HIF1A, adipocyte hypertrophy and insulin resistance. In Paper III, we found that the expression of GPS2 in the white adipose tissue of humans was strongly correlated with the insulin secretion rate. The causality of this relationship was confirmed using adipocyte-specific Gps2 knockout mice, in which adipocyte dysfunction caused by the loss of GPS2 triggered the secretion of factors that provoked pancreatic islet inflammation and impaired beta cell function. In conclusion, the research within this thesis revealed novel insights into the multifaceted regulatory roles of GPS2 in altering the epigenome and the transcriptome linked to adipose tissue metabolism and inflammation. These discoveries increase our understanding of the mechanisms underlying the development of obesity and its link with type 2 diabetes, and they may help to define novel potential targets for treating these metabolic diseases.