Periodic Reporting for period 4 - EpiFAT (Epigenomic Reprogramming of Adipose Tissue Function and Energy Metabolism in Type 2 Diabetes)
Periodo di rendicontazione: 2021-12-01 al 2023-05-31
Type 2 diabetes (T2D) develops due to insulin resistance and impaired insulin secretion, predominantly exposed to non-genetic risk factors like obesity, physical inactivity and ageing. These environmental factors are sensed by our genome through epigenetic modifications influencing gene transcription and organ dysfunction. Emerging data suggest that epigenetic alterations in the adipose tissue of T2D subjects (compared with non-diabetic controls) substantially contribute to the susceptibility to T2D. Therefore, the identification of epigenomic modifiers that are involved in the control of adipose tissue function and energy metabolism and also impact on T2D pathogenesis is of importance.
The objective of EPIFAT proposal is to decode the function of the candidate epigenomic modifiers GPS2 and KDM6B in white adipocytes and in macrophages, for a better understanding and treatment of adipose tissue dysfunction linked to obesity and T2D.
Our hypothesis is that the clinically documented deregulation of GPS2 and KDM6B expression and function during obesity and T2D leads to an epigenomic reprogramming (linked to the key enhancer mark H3K27) of adipocytes and macrophages. The resulting changes in gene expression programs and downstream pathways will affect the fate of white adipose tissue, thereby enhancing the susceptibility to metabolic and inflammatory disturbances and the progression towards insulin resistance and T2D.
The successful completion of the proposed studies will define a novel concept in molecular metabolic control. In particular, the expected outputs will for the first time highlight an epigenomic sensitization to metabolic dysfunction via the combinatorial impact of GPS2 and KDM6B as molecular checkpoints. The unprecedented combination of in vivo and in vitro tools for the epigenomic analysis will thus establish a novel layer of metabolic control and at the same time define tissue-specific target sites for preventive and therapeutic approaches towards obesity, insulin resistance and T2D.
The objective of EPIFAT proposal is to decode the function of the candidate epigenomic modifiers GPS2 and KDM6B in white adipocytes and in macrophages, for a better understanding and treatment of adipose tissue dysfunction linked to obesity and T2D.
Our hypothesis is that the clinically documented deregulation of GPS2 and KDM6B expression and function during obesity and T2D leads to an epigenomic reprogramming (linked to the key enhancer mark H3K27) of adipocytes and macrophages. The resulting changes in gene expression programs and downstream pathways will affect the fate of white adipose tissue, thereby enhancing the susceptibility to metabolic and inflammatory disturbances and the progression towards insulin resistance and T2D.
The successful completion of the proposed studies will define a novel concept in molecular metabolic control. In particular, the expected outputs will for the first time highlight an epigenomic sensitization to metabolic dysfunction via the combinatorial impact of GPS2 and KDM6B as molecular checkpoints. The unprecedented combination of in vivo and in vitro tools for the epigenomic analysis will thus establish a novel layer of metabolic control and at the same time define tissue-specific target sites for preventive and therapeutic approaches towards obesity, insulin resistance and T2D.
#1 GPS2 Deficiency Triggers Maladaptive White Adipose Tissue Expansion in Obesity via HIF1A Activation
Hypertrophic white adipose tissue (WAT) represents a maladaptive mechanism linked to the risk for developing type 2 diabetes in humans. However, the molecular events that predispose WAT to hypertrophy are poorly defined. Here, we demonstrate that adipocyte hypertrophy is triggered by loss of the corepressor GPS2 during obesity. Adipocyte-specific GPS2 deficiency in mice (GPS2 AKO) causes adipocyte hypertrophy, inflammation, and mitochondrial dysfunction during surplus energy. Increased mitochondrial activity and biogenesis is an essential biological processinvolved in WAT remodeling and browning following cold exposure and β-adrenergic receptor stimulation. To visualize the faults in mitochondrial activity and adaptation in vivo, WT and GPS2 AKO mice were subjected either to treatment with an agonist of β3 adrenergic receptor or cold exposure for 5 days. Cold exposure or β3-adrenergic stimulation provoked, in WT mice, increased mitochondrial biogenesis and adipose tissue beiging characterized by increasing MTCO2 and UCP-1 staining, respectively. In contrast, GPS2 AKO mice upon those conditions did not respond as WT control mice. Adipose tissue maladaptation to cold exposure of GPS2 AKO mice was characterized at the whole-body level by a significant decrease in body temperature and alteration of O2 consumption. Collectively, these data suggest that the dysfunctional adipose tissue observed in GPS2 AKO mice could be in part driven by disrupted mitochondrial activity .We propose therefore that the obesity-associated loss of GPS2 in adipocytes predisposes for a maladaptive WAT expansion and a pro-diabetic status.
#2 GPS2 Deficiency in Adipocytes Potentiates HIF1A-Dependent Pathways
RNA sequencing from isolated adipocytes of eWAT from WT control and GPS2 AKO mice fed an HFD for 12 weeks revealed that 2,239 transcripts were induced in isolated adipocytes of eWAT from GPS2 AKO mice relative to WT mice. Among these upregulated transcripts were genes involved in inflammation, as expected, but also genes likely involved in adipose tissue expansion,suggesting a crucial function of GPS2 in adipocyte remodeling. Network analysis of genes significantly increased in eWAT adipocytes of GPS2 AKO mice indicated that HIF1A-dependent pathways could play a central role in the disrupted adipocyte adaptation in GPS2 AKO mice.
#3 Early macrophage response to obesity encompasses Interferon Regulatory Factor 5 regulated mitochondrial architecture remodelling
We demonstrate that Interferon Regulatory Factor 5 (IRF5) is a key regulator of macrophage oxidative capacity in response to caloric excess. ATMs from mice with genetic-deficiency of Irf5 are characterised by increased oxidative respiration and mitochondrial membrane potential. We find that the highly oxidative nature of Irf5-deficient macrophages results from transcriptional de-repression of the mitochondrial matrix component Growth Hormone Inducible Transmembrane Protein (GHITM) gene. The Irf5-deficiency-associated high oxygen consumption could be alleviated by experimental suppression of Ghitm expression. ATMs and monocytes from patients with obesity or with type-2 diabetes retain the reciprocal regulatory relationship between Irf5 and Ghitm. Thus, our study provides insights into the mechanism of how the inflammatory transcription factor IRF5 controls physiological adaptation to diet-induced obesity via regulating mitochondrial architecture in macrophages.
Hypertrophic white adipose tissue (WAT) represents a maladaptive mechanism linked to the risk for developing type 2 diabetes in humans. However, the molecular events that predispose WAT to hypertrophy are poorly defined. Here, we demonstrate that adipocyte hypertrophy is triggered by loss of the corepressor GPS2 during obesity. Adipocyte-specific GPS2 deficiency in mice (GPS2 AKO) causes adipocyte hypertrophy, inflammation, and mitochondrial dysfunction during surplus energy. Increased mitochondrial activity and biogenesis is an essential biological processinvolved in WAT remodeling and browning following cold exposure and β-adrenergic receptor stimulation. To visualize the faults in mitochondrial activity and adaptation in vivo, WT and GPS2 AKO mice were subjected either to treatment with an agonist of β3 adrenergic receptor or cold exposure for 5 days. Cold exposure or β3-adrenergic stimulation provoked, in WT mice, increased mitochondrial biogenesis and adipose tissue beiging characterized by increasing MTCO2 and UCP-1 staining, respectively. In contrast, GPS2 AKO mice upon those conditions did not respond as WT control mice. Adipose tissue maladaptation to cold exposure of GPS2 AKO mice was characterized at the whole-body level by a significant decrease in body temperature and alteration of O2 consumption. Collectively, these data suggest that the dysfunctional adipose tissue observed in GPS2 AKO mice could be in part driven by disrupted mitochondrial activity .We propose therefore that the obesity-associated loss of GPS2 in adipocytes predisposes for a maladaptive WAT expansion and a pro-diabetic status.
#2 GPS2 Deficiency in Adipocytes Potentiates HIF1A-Dependent Pathways
RNA sequencing from isolated adipocytes of eWAT from WT control and GPS2 AKO mice fed an HFD for 12 weeks revealed that 2,239 transcripts were induced in isolated adipocytes of eWAT from GPS2 AKO mice relative to WT mice. Among these upregulated transcripts were genes involved in inflammation, as expected, but also genes likely involved in adipose tissue expansion,suggesting a crucial function of GPS2 in adipocyte remodeling. Network analysis of genes significantly increased in eWAT adipocytes of GPS2 AKO mice indicated that HIF1A-dependent pathways could play a central role in the disrupted adipocyte adaptation in GPS2 AKO mice.
#3 Early macrophage response to obesity encompasses Interferon Regulatory Factor 5 regulated mitochondrial architecture remodelling
We demonstrate that Interferon Regulatory Factor 5 (IRF5) is a key regulator of macrophage oxidative capacity in response to caloric excess. ATMs from mice with genetic-deficiency of Irf5 are characterised by increased oxidative respiration and mitochondrial membrane potential. We find that the highly oxidative nature of Irf5-deficient macrophages results from transcriptional de-repression of the mitochondrial matrix component Growth Hormone Inducible Transmembrane Protein (GHITM) gene. The Irf5-deficiency-associated high oxygen consumption could be alleviated by experimental suppression of Ghitm expression. ATMs and monocytes from patients with obesity or with type-2 diabetes retain the reciprocal regulatory relationship between Irf5 and Ghitm. Thus, our study provides insights into the mechanism of how the inflammatory transcription factor IRF5 controls physiological adaptation to diet-induced obesity via regulating mitochondrial architecture in macrophages.
Specific transcriptomic and epigenomic programs govern tissue inflammation in diabetes
Transcriptomic and Epigenetic processes tightly regulate cellular function in health and disease, such as obesity and type 2 diabetes. Recent studies from our team have allowed detailed characterization of the transcriptional circuitry underlying monocyte and macrophage regulation. We discovered the unexpected function of the transcription factors, IRF5 (Interferon Regulatory Factor 5), in the control of macrophage activation in the liver and the adipose tissue in mice and humans upon metabolic stress. We revealed increased IRF5 activity in metabolic tissue macrophages (liver and adipose tissue) that contributes to pathologic tissue alterations and promotes the development of T2D through immune and metabolic mechanisms. Upon differentiation and activation, genomic regions called enhancers are selected by lineage-determining and signal-dependent transcription factors. Enhancers are shown to be very dynamic, and activation of these enhancers underlies difference in gene transcription between monocytes, macrophages and their different subtypes. We identified the transcriptional co-regulator G-Protein Pathway Suppressor (GPS) 2 as a key sensor of metabolic stress that influences adipose tissue metabolism and macrophage activation in T2D. Through the modulation of enhancer accessibility and activity, GPS2 controls gene expression and hypersensitivity toward metabolic stress signals. Thus, our data reveal a potentially reversible disease mechanism that links co-repressor-dependent epigenomic alterations in adipose tissue phenotype and interorgan signalling to the development of T2D.
Transcriptomic and Epigenetic processes tightly regulate cellular function in health and disease, such as obesity and type 2 diabetes. Recent studies from our team have allowed detailed characterization of the transcriptional circuitry underlying monocyte and macrophage regulation. We discovered the unexpected function of the transcription factors, IRF5 (Interferon Regulatory Factor 5), in the control of macrophage activation in the liver and the adipose tissue in mice and humans upon metabolic stress. We revealed increased IRF5 activity in metabolic tissue macrophages (liver and adipose tissue) that contributes to pathologic tissue alterations and promotes the development of T2D through immune and metabolic mechanisms. Upon differentiation and activation, genomic regions called enhancers are selected by lineage-determining and signal-dependent transcription factors. Enhancers are shown to be very dynamic, and activation of these enhancers underlies difference in gene transcription between monocytes, macrophages and their different subtypes. We identified the transcriptional co-regulator G-Protein Pathway Suppressor (GPS) 2 as a key sensor of metabolic stress that influences adipose tissue metabolism and macrophage activation in T2D. Through the modulation of enhancer accessibility and activity, GPS2 controls gene expression and hypersensitivity toward metabolic stress signals. Thus, our data reveal a potentially reversible disease mechanism that links co-repressor-dependent epigenomic alterations in adipose tissue phenotype and interorgan signalling to the development of T2D.