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

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

Unravelling genetic variants of a swedish family with high risk of prostate cancer

Abstract Background Prostate cancer is the most prevalent cancer in men worldwide. It is a polygenic disease with a substantial proportion of heritability. Identification of novel candidate biomarkers is crucial for clinical cancer prevention and the development of therapeutic strategies. Here, we describe the analysis of rare and common genetic variants that can predispose to the development of prostate cancer. Methods Whole-genome sequencing was performed on germline DNA of five Swedish siblings which were diagnosed with prostate cancer. The high-risk variants were identified setting the minor allele frequency  10 and if tested in PRACTICAL, OR > 1.5, while the low-risk variants were identified minor allele frequency > 0.01, CADD > 10 and if tested in PRACTICAL, OR > 1.1. Results We identified 38 candidate high-risk gene variants and 332 candidate low-risk gene variants, where 2 and 14 variants were in coding regions, respectively, that were shared by the brothers with prostate cancer. Conclusions This study expanded the knowledge of potential risk factor candidates involved in hereditary and familial prostate cancer. Our findings can be beneficial when applying targeted screening in families with a high risk of developing the disease

Loss of G protein pathway suppressor 2 in human adipocytes triggers lipid remodeling by upregulating ATP binding cassette subfamily G member 1

International audienceObjective: Adipogenesis is critical for adipose tissue remodeling during the development of obesity. While the role of transcription factors in the orchestration of adipogenic pathways is already established, the involvement of coregulators that transduce regulatory signals into epigenome alterations and transcriptional responses remains poorly understood. The aim of our study was to investigate which pathways are controlled by G protein pathway suppressor 2 (GPS2) during the differentiation of human adipocytes.Methods: We generated a unique loss-of-function model by RNAi depletion of GPS2 in human multipotent adipose-derived stem (hMADS) cells. We thoroughly characterized the coregulator depletion-dependent pathway alterations during adipocyte differentiation at the level of transcriptome (RNA-seq), epigenome (ChIP-seq H3K27ac), cistrome (ChIP-seq GPS2), and lipidome. We validated the in vivo relevance of the identified pathways in non-diabetic and diabetic obese patients.Results: The loss of GPS2 triggers the reprogramming of cellular processes related to adipocyte differentiation by increasing the responses to the adipogenic cocktail. In particular, GPS2 depletion increases the expression of BMP4, an important trigger for the commitment of fibroblast-like progenitors toward the adipogenic lineage and increases the expression of inflammatory and metabolic genes. GPS2-depleted human adipocytes are characterized by hypertrophy, triglyceride and phospholipid accumulation, and sphingomyelin depletion. These changes are likely a consequence of the increased expression of ATP-binding cassette subfamily G member 1 (ABCG1) that mediates sphingomyelin efflux from adipocytes and modulates lipoprotein lipase (LPL) activity. We identify ABCG1 as a direct transcriptional target, as GPS2 depletion leads to coordinated changes of transcription and H3K27 acetylation at promoters and enhancers that are occupied by GPS2 in wild-type adipocytes. We find that in omental adipose tissue of obese humans, GPS2 levels correlate with ABCG1 levels, type 2 diabetic status, and lipid metabolic status, supporting the in vivo relevance of the hMADS cell-derived in vitro data.Conclusion: Our study reveals a dual regulatory role of GPS2 in epigenetically modulating the chromatin landscape and gene expression during human adipocyte differentiation and identifies a hitherto unknown GPS2-ABCG1 pathway potentially linked to adipocyte hypertrophy in humans

Hepatocyte-specific loss of GPS2 in mice reduces non-alcoholic steatohepatitis via activation of PPARα

Dysregulation of PPARα dependent fatty acid oxidation promotes hepatic steatosis. Here the authors show that GPS2 inhibits PPARα activity and that ablation of GPS2 ameliorates hepatic steatosis in mice