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The loss of pancreatic β-cell identity emerges as an important feature of type 2 diabetes development, but the molecular mechanisms are still elusive. Here, we explore the cell-autonomous role of the cell cycle regulator and transcription factor E2F1 in the maintenance of β-cell identity, insulin secretion and glucose homeostasis. We show that the β-cell-specific loss of E2f1 function in mice triggers glucose intolerance associated with defective insulin secretion, an altered endocrine cell mass, a downregulation of many β-cell genes and a concomitant increase of non-β-cell markers. Mechanistically, the epigenomic profiling of promoters of these non-β-cell upregulated genes identified an enrichment of bivalent H3K4me3/H3K27me3 or H3K27me3 marks. Conversely, promoters of downregulated genes were enriched in active chromatin H3K4me3 and H3K27ac histone marks. We find that specific E2f1 transcriptional, cistromic and epigenomic signatures are associated with these β-cell dysfunctions, with E2F1 directly regulating several β-cell genes at the chromatin level. Finally, the pharmacological inhibition of E2F transcriptional activity in human islets also impairs insulin secretion and the expression of β-cell identity genes. Our data suggest that E2F1 is critical for maintaining β-cell identity and function through a sustained control of β-cell and non β-cell transcriptional programs.

The loss of pancreatic β-cell identity emerges as an important feature of type 2 diabetes development, but the molecular mechanisms are still elusive. Here, we explore the cellautonomous role of the cell cycle regulator and transcription factor E2F1 in the maintenance of β-cell identity, insulin secretion and glucose homeostasis. We show that the β-cell-specific loss of E2f1 function in mice triggers glucose intolerance associated with defective insulin secretion, an altered endocrine cell mass, a downregulation of many β-cell genes and a concomitant increase of non-β-cell markers. Mechanistically, the epigenomic profiling of promoters of these non-β-cell upregulated genes identified an enrichment of bivalent H3K4me3/H3K27me3 or H3K27me3 marks. Conversely, promoters of downregulated genes were enriched in active chromatin H3K4me3 and H3K27ac histone marks. We find that specific E2f1 transcriptional, cistromic and epigenomic signatures are associated with these β-cell dysfunctions, with E2F1 directly regulating several β-cell genes at the chromatin level. Finally, the pharmacological inhibition of E2F transcriptional activity in human islets also impairs insulin secretion and the expression of β-cell identity genes. Our data suggest that E2F1 is critical for maintaining β-cell identity and function through a sustained control of β-cell and non β-cell transcriptional programs.

Adipose tissue is a complex organ consisting of a mixture of mature adipocytes and stromal vascular cells. It displays a remarkable ability to adapt to environmental and dietary cues by changing its morphology and metabolic capacity. This plasticity is demonstrated by the emergence of interspersed thermogenic beige adipocytes within white depots in response to catecholamines secretion. Coordinated cellular interaction between different cell types within the tissue and a fine-tuned transcriptional program synergistically take place to promote beige remodeling. However, both cell–cell interactions and molecular mechanisms governing beige adipocyte appearance and maintenance are poorly understood. In this and the previous issue of Genes & Development, Shao and colleagues (pp. 1461–1474) and Shan and colleagues (pp. 1333–1338) advance our understanding of these issues and, in doing so, highlight potential therapeutic strategies to combat obesity-associated diseases.

Obesity and metabolic diseases, such as insulin resistance and type 2 diabetes (T2D), are associated with metastatic breast cancer in post-menopausal women. Here, we investigated the critical cellular and molecular factors behind this link. We found that primary human adipocytes shed extracellular vesicles—specifically exosomes—that induced the expression of genes associated with epithelial-to-mesenchymal transition (EMT) and cancer stem-like cell (CSC) traits in cocultured breast cancer cell lines. Transcription of these genes was further increased in cells exposed to exosomes shed from T2D patient-derived adipocytes or insulin-resistant adipocytes and required the epigenetic reader proteins BRD2 and BRD4 in recipient cells. The thrombospondin family protein TSP5, which is associated with cancer, was more abundant in exosomes from T2D or insulin-resistant adipocytes and partially contributed to EMT in recipient cells. Bioinformatic analysis of breast cancer patient tissue showed that greater co-expression of COMP (which encodes TSP5) and BRD2 or BRD3 correlated with poorer prognosis, specifically decreased distant metastasis-free survival. Our findings reveal a mechanism of exosome-mediated crosstalk between metabolically abnormal adipocytes and breast cancer cells that may promote tumor aggressiveness in T2D patients.

Most strategies to treat obesity-related disorders have involved prevention of diet-induced weight gain in lean mice. Treatment of obese individuals will require therapies that reverse the detrimental effects of excess body weight. Here, we show that roscovitine given to mice during the last six weeks of a 19-week high fat diet, reduced weight gain and prevented accompanying insulin resistance, hepatic steatosis, visceral adipose tissue (eWAT) inflammation/fibrosis as well as restored insulin secretion and enhanced whole body energy expenditure. Proteomics and phosphoproteomics analysis of eWAT demonstrated that roscovitine suppressed expression of peptides and phosphopeptides linked to inflammation and extracellular matrix proteins. It also identified 17 putative protein kinases perturbed by roscovitine, including CMGC kinases, AGC kinases and CAMK kinases. Pathway enrichment analysis showed that lipid metabolism, TCA cycle, fatty acid beta oxidation and creatine biosynthesis are enriched following roscovitine treatment. For brown adipose tissue (BAT), analysis of upstream kinases controlling the phosphoproteome revealed two major kinase groups, AGC and CMGC kinases. Among the top enriched pathways were insulin signaling, regulation of lipolysis in adipocytes, thyroid hormone signaling, thermogenesis and cAMP-PKG signaling. We conclude that roscovitine is effective at reversing prolonged diet-induced metabolic disruption and restoring mitochondrial activity in BAT and eWAT.

The glucagon-like peptide 1 (Glp-1) has emerged as a hormone with broad pharmacological potential in type 2 diabetes (T2D) treatment, notably by improving β cell functions. The cell-cycle regulator and transcription factor E2f1 is involved in glucose homeostasis by modulating β cell mass and function. Here, we report that β cell-specific genetic ablation of E2f1 (E2f1

Compromised β-cell function contributes to type 2 diabetes (T2D) development. The glucagon like peptide 1 (Glp-1) has emerged as a hormone with broad pharmacological potential toward T2D treatment, notably by improving β-cell functions. Recent data have shown that the transcription factor E2f1, besides its role as a cell cycle regulator, is involved in glucose homeostasis by modulating β-cell mass, function and identity. Here, we demonstrate a crosstalk between the E2F1, phosphorylation of retinoblastoma protein (pRb) and Glp-1 signaling pathways. We found that β-cell specificE2f1deficient mice (E2f1β−/−) presented with impaired glucose homeostasis and decreased glucose stimulated-insulin secretion mediated by exendin 4 (i.e., GLP1R agonist), which were associated with decreased expression ofGlp1rencoding Glp-1 receptor (GLP1R) inE2f1β−/−pancreatic islets. Decreasing E2F1 transcriptional activity with an E2F inhibitor in islets from nondiabetic humans decreasedGLP1Rlevels and blunted the incretin effect of exendin 4 on insulin secretion. Conversely, overexpressingE2f1in pancreatic β cells increasedGlp1rexpression associated with enhanced insulin secretion mediated by GLP1R agonist. Interestingly, kinome analysis of mouse islets demonstrated that an acute treatment with exendin 4 increased pRb phosphorylation and subsequent E2f1 transcriptional activity. This study suggests a molecular crosstalk between the E2F1/pRb and GLP1R signaling pathways that modulates insulin secretion and glucose homeostasis.

Cancer cachexia (CC) presents itself as a syndrome with multiple manifestations, causing a marked multi-organ metabolic imbalance. Recently, cachectic wasting has been proposed to be stimulated by several inflammatory mediators, which may disrupt the integrative physiology of adipose tissues and other tissues such as the brain and muscle. In this scenario, the tumor can survive at the host's expense. In recent clinical research, the intensity of depletion of the different fat deposits has been negatively correlated with the patient's survival outcome. Studies have also shown that various metabolic disorders can alter white adipose tissue (WAT) remodeling, especially in the early stages of cachexia development. WAT dysfunction resulting from tissue remodeling is a contributor to overall cachexia, with the main modifications in WAT consisting of morpho-functional changes, increased adipocyte lipolysis, accumulation of immune cells, reduction of adipogenesis, changes in progenitor cell population, and the increase of "niches" containing beige/brite cells. To study the various facets of cachexia-induced WAT remodeling, particularly the changes progenitor cells and beige remodeling, two-dimensional (2D) culture has been the first option for in vitro studies. However, this approach does not adequately summarize WAT complexity. Improved assays for the reconstruction of functional AT ex vivo help the comprehension of physiological interactions between the distinct cell populations. This protocol describes an efficient three-dimensional (3D) printing tissue culture system based on magnetic nanoparticles. The protocol is optimized for investigating WAT remodeling induced by cachexia induced factors (CIFs). The results show that a 3D culture is an appropriate tool for studying WAT modeling ex vivo and may be useful for functional screens to identify bioactive molecules for individual adipose cell populations applications and aid the discovery of WAT-based cell anticachectic therapy.

Made available in DSpace on 2022-05-01T10:18:54Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-01 Bundesministerium für Bildung und Forschung American Historical Association Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Deutsche Forschungsgemeinschaft National Institutes of Health Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Adipose tissue has been classified based on its morphology and function as white, brown, or beige/brite. It plays an essential role as a regulator of systemic metabolism through paracrine and endocrine signals. Recently, multiple adipocyte subtypes have been revealed using RNA sequencing technology, going beyond simply defined morphology but also by their cellular origin, adaptation to metabolic stress, and plasticity. Here, we performed an in-depth analysis of publicly available single-nuclei RNAseq from adipose tissue and utilized a workflow template to characterize adipocyte plasticity, heterogeneity, and secretome profiles. The reanalyzed dataset led to the identification of different subtypes of adipocytes including three subpopulations of thermogenic adipocytes, and provided a characterization of distinct transcriptional profiles along the adipocyte trajectory under thermogenic challenges. This study provides a useful resource for further investigations regarding mechanisms related to adipocyte plasticity and trans-differentiation. Department of Genetics Ribeirão Preto Medical School University of São Paulo Center for Cell-Based Therapy (CEPID/FAPESP) National Institute of Science and Technology in Stem Cell and Cell Therapy (INCTC/CNPq) Regional Blood Center of Ribeirão Preto Institute for Cancer Research IPEC Department of Structural and Functional Biology Institute of Biosciences São Paulo State University (UNESP) Department of Translational Genomics Medical Faculty University of Cologne Department of Biochemistry School of Medicine Boston University Department of Integrated Biotechnology University of Mogi das Cruzes Department of Structural and Functional Biology Institute of Biosciences São Paulo State University (UNESP) Bundesministerium für Bildung und Forschung: 01ZX1901A American Historical Association: 17POST33660875 CNPq: 311319/2018-1 CNPq: 311530/2019-2 Deutsche Forschungsgemeinschaft: 413326622 CNPq: 870415/1997-2 National Institutes of Health: DK117161 National Institutes of Health: DK117163 National Institutes of Health: P30-DK-046200 Deutsche Forschungsgemeinschaft: SFB1399

Adipose tissue fibrosis is regulated by the chronic and progressive metabolic imbalance caused by differences in caloric intake and energy expenditure. By exploring the cellular heterogeneity within fibrotic adipose tissue, we demonstrate that early adipocyte progenitor cells expressing both platelet derived growth factor receptor (PDGFR) α and β are the major contributors to extracellular matrix deposition. We show that the fibrotic program is promoted by senescent macrophages. These macrophages are highly enriched in the fibrotic stroma and exhibit a distinct expression profile . Furthermore, we demonstrate that these cells display a blunted phagocytotic capacity and acquire a senescence associated secretory phenotype. Finally, we determined that senescent macrophage-derived osteopontin in the fibrotic environment promoted progenitor cell proliferation, fibrotic gene expression, and inhibited adipogenesis. Our work reveals that obesity promotes macrophage senescence and provides a conceptual framework for the discovery of rational therapeutic targets for metabolic and inflammatory disease associated with obesity.

Summary White adipose tissue (WAT) is a dynamic tissue, which responds to environmental stimuli and dietary cues by changing its morphology and metabolic capacity. The ability of WAT to undergo a beige remodeling has become an appealing strategy to combat obesity and its comorbidities. Here, by using single-cell RNA sequencing, we provide a comprehensive atlas of the cellular dynamics during beige remodeling. We reveal drastic changes both in the overall cellular composition and transcriptional states of individual cell subtypes between Adrb3- and cold-induced beiging. Moreover, we demonstrate that cold induces a myeloid to lymphoid shift of the immune compartment compared to Adrb3 activation. Further analysis showed that, Adrb3 stimulation leads to activation of the interferon/Stat1 pathways favoring infiltration of myeloid immune cells, while repression of this pathway by cold promotes lymphoid immune cell recruitment. These findings highlight that pharmacological mimetics may not provide the same beneficial effects as physiological stimuli., Graphical Abstract, Highlights • ScSeq reveals an extensive remodeling during browning of white adipose tissue • Cold and β3Adr agonist treatment results in distinct brown/beige remodeling • Cold induces a myeloid to lymphoid shift of the immune compartment • β3Adr agonism leads to an interferon/Stat response and infiltration of myeloid cells, Biological Sciences; Endocrinology; Omics; Transcriptomics

The loss of pancreatic β-cell identity emerges as an important feature of type 2 diabetes development, but the molecular mechanisms are still elusive. Here, we explore the cell-autonomous role of the cell cycle regulator and transcription factor E2F1 in the maintenance of β-cell identity and insulin secretion. We show that the β-cell-specific loss ofE2f1function in mice triggers glucose intolerance associated with defective insulin secretion, an altered α-to-β-cell ratio, a downregulation of many β-cell genes and a concomitant increase of non-β-cell markers. Mechanistically, the epigenomic profiling of non-beta cell upregulated gene promoters identified an enrichment of bivalent H3K4me3/H3K27me3 or H3K27me3 marks. Conversely, downregulated genes were enriched in active chromatin H3K4me3 and H3K27ac histone marks. We find that histone deacetylase inhibitors modulate E2F1 transcriptional and epigenomic signatures associated with these β-cell dysfunctions. Finally, the pharmacological inhibition of E2F transcriptional activity in human islets also impairs insulin secretion and the expression of β-cell identity genes. Our data suggest that E2F1 is critical for maintaining β-cell identity through a sustained repression of non β-cell transcriptional programs.

SUMMARYWhite adipose tissue (WAT) is a dynamic tissue, which responds to environmental stimuli and dietary cues by changing its morphology and metabolic capacity. The ability of WAT to undergo a beige remodeling has become an appealing strategy to combat obesity and its related metabolic complications. Within the cell mixture that constitutes the stromal vascular fraction (SVF), WAT beiging is initiated through expansion and differentiation of adipocytes progenitor cells, however, the extent of the SVF cellular changes is still poorly understood. Additionally, direct beta 3 adrenergic receptor (Adrb3) stimulation has been extensively used to mimic physiological cold- induced beiging, yet it is still unknown whether Adrb3 activation induces the same WAT remodeling as cold exposure. Here, by using single cell RNA sequencing, we provide a comprehensive atlas of the cellular dynamics during beige remodeling within white adipose tissue. We reveal drastic changes both in the overall cellular composition and transcriptional states of individual cell subtypes between Adrb3- and cold-induced beiging. Moreover, we demonstrate that cold exposure induces a myeloid to lymphoid shift of the immune compartment compared to Adrb3 activation. Further analysis, showed that Adrb3 stimulation leads to activation of the interferon/Stat1 pathways favoring infiltration of myeloid immune cells, while repression of this pathway by cold promotes lymphoid immune cells recruitment. These findings provide new insight into the cellular dynamics during WAT beige remodeling and could ultimately lead to novel strategies to identify translationally-relevant drug targets to counteract obesity and T2D.

The vascular adventitia contains numerous cell types including fibroblasts, adipocytes, inflammatory cells, and progenitors embedded within a complex extracellular matrix (ECM) network. In response to vascular injury, adventitial progenitors and fibroblasts become activated and exhibit increased proliferative capacity and differentiate into contractile cells that remodel the ECM. These processes can lead to vascular fibrosis and disease progression. Our previous work established that the ECM protein aortic carboxypeptidase-like protein (ACLP) promotes fibrotic remodeling in the lung and is activated by vascular injury. It is currently unknown what controls vascular adventitial cell differentiation and if ACLP has a role in this process. Using purified mouse aortic adventitia Sca1+ progenitors, ACLP repressed stem cell markers (CD34, KLF4) and upregulated smooth muscle actin (SMA) and collagen I expression. ACLP enhanced myocardin-related transcription factor A (MRTFA) activity in adventitial cells by promoting MRTFA nuclear translocation. Sca1 cells from MRTFA-null mice exhibited reduced SMA and collagen expression induced by ACLP, indicating Sca1 cell differentiation is regulated in part by the ACLP-MRTFA axis. We determined that ACLP induced vessel contraction and increased adventitial collagen in an explant model. Collectively these studies identified ACLP as a mediator of adventitial cellular differentiation, which may result in pathological vessel remodeling.

Summary Adipose tissue fibrosis is associated with inflammation and insulin resistance in human obesity. In particular, visceral fat fibrosis is correlated with hyperlipidemia and ectopic fat accumulation. Myocardin-related transcription factor A (MRTFA) is an important coactivator that mediates the transcription of extracellular matrix and other fibrogenic genes. Here, we examine the role of MRTFA in the development of adipose tissue fibrosis and identify a signaling pathway that regulates the fate of vascular progenitors. We demonstrate that obesity induces the formation of Sca1−, Sma+, ITGA5+ fibrogenic progenitor cells (FPCs) in adipose tissue. MRTFA deficiency in mice shifts the fate of perivascular progenitors from FPCs to adipocyte precursor cells and protects against chronic obesity-induced fibrosis and accompanying metabolic dysfunction, without a shift in energy expenditure. Our findings highlight the ITGA5-MRTFA pathway as a potential target to ameliorate obesity-associated metabolic disease.

Visceral white adipose tissue (vWAT) expands and undergoes extensive remodeling during diet-induced obesity. Much is known about the contribution of various stromal vascular cells to the remodeling process, but less is known of the changes that occur within the adipocyte as it becomes progressively dysfunctional. Here, we performed a transcriptome analysis of isolated vWAT adipocytes to assess global pathway changes occurring in response to a chronic high fat diet (HFD). The data demonstrate that the adipocyte responds to the HFD by adopting a fibroblast-like phenotype, characterized by enhanced expression of ECM, focal adhesion and cytoskeletal genes and suppression of many adipocyte programs most notably those associated with mitochondria. This study reveals that during obesity the adipocyte progressively becomes metabolically dysfunctional due to its acquisition of fibrogenic functions. We propose that mechano-responsive transcription factors such as MRTFA and SRF contribute to both upregulation of morphological genes as well as suppression of mitochondrial programs.

The prevalence of obesity—and thus the incidence of metabolic diseases, including type 2 diabetes and cardiovascular disease—is dramatically increasing worldwide. Despite the critical role of adipose tissues in nutrient metabolism, there are surprisingly few clinically-approved medications targeting adipose tissue. Thiazolidinediones (TZDs), PPARγ agonists are exceptions that act in adipose tissue, but they are associated with adverse effects such as weight gain, and heart failure. An exciting series of studies demonstrate that posttranslational modifications can selectively enhance the insulin sensitizing activity of PPARγ. Our laboratory previously showed that roscovitine (RS), a CDK inhibitor, prevents diet-induced obesity by blocking PPARγ S273 phosphorylation, which promotes formation of UCP1+ (brite) adipocytes in WAT. RNA profiling reveals that brite adipocytes are distinct from beige adipocytes, which arise through catecholamine signaling suggesting that brown-like adipocytes in WAT may arise from multiple origins. Using adipocytes and progenitor’s lineage tracing mice, we demonstrate that brite adipocytes originate from mature white adipocytes through trans-differentiation. Inhibition of S273 phosphorylation of PPARγ in obese mice prevents weight gain, restores insulin and glucose sensitivity and a normal pancreatic β-cells response to glucose as well as prevents liver steatosis and adipocytes formation in bone. Moreover, mass spectrometry analysis of extracellular matrix proteins showed a reduced adipose tissues fibrosis following RS treatment. Mechanistically, inhibition of PPARγ phosphorylation shifts its interaction with cofactors favoring a brown-like healthy remodeling of adipose tissue, which includes suppression of genes associated with inflammation and fibrosis. Overall, we demonstrate targeting PPARγ phosphorylation using RS can constitute a new therapy for obesity and its metabolic complications. Disclosure N. Rabhi: None. S.R. Farmer: None. Funding American Heart Association (17POST33660875); Francophone Society of Diabetes (R01DK102199-01)

International audience; Innate immune responses are intricately linked with intracellular metabolism of myeloid cells. Toll-like receptor (TLR) stimulation shifts intracellular metabolism toward glycolysis, while anti-inflammatory signals depend on enhanced mitochondrial respiration. How exogenous metabolic signals affect the immune response is unknown. We demonstrate that TLR-dependent responses of dendritic cells (DCs) are exacerbated by a high-fatty-acid (FA) metabolic environment. FAs suppress the TLR-induced hexokinase activity and perturb tricarboxylic acid cycle metabolism. These metabolic changes enhance mitochondrial reactive oxygen species (mtROS) production and, in turn, the unfolded protein response (UPR), leading to a distinct transcriptomic signature with IL-23 as hallmark. Interestingly, chemical or genetic suppression of glycolysis was sufficient to induce this specific immune response. Conversely, reducing mtROS production or DC-specific deficiency in XBP1 attenuated IL-23 expression and skin inflammation in an IL-23-dependent model of psoriasis. Thus, fine-tuning of innate immunity depends on optimization of metabolic demands and minimization of mtROS-induced UPR.

A recent study (Girousse et al. Cell Rep. 2019;27:323–333) shows that CXCR4+ adipose progenitors (APCs) contribute to lipid spillover during high-fat feeding through their release from subcutaneous fat depots (ScATs) and migration to skeletal muscle where they differentiate into adipocytes. Pharmacological antagonism of CXCR4, which prevents the CXCL12-dependent retention of APCs in ScAT, mimics the effects of overfeeding.

Adipose tissue fibrosis is associated with inflammation and insulin resistance in human obesity. In particular, visceral fat fibrosis is correlated with hyperlipidemia and ectopic fat accumulation. Myocardin-related transcription factor A (MRTFA) is an important coactivator that mediates the transcription of extracellular matrix and other fibrogenic genes. Here, we examine the role of MTRFA in the development of adipose tissue fibrosis and identify a novel signaling pathway that regulates myofibroblast differentiation. We demonstrate that obesity induces the formation of Sca1-, PDGFRa+, Sma+, ITGA5+ fibrogenic progenitors in adipose tissue. MRTFA deficiency in mice shifts the fate of perivascular progenitors from fibrogenic to adipocyte precursor cells and protects against diet-induced fibrosis and accompanying metabolic dysfunction. Our findings highlight the MRTFA-ITGA5 pathway as a potential target to ameliorate obesity associated metabolic disease.

International audience; Hepatitis B virus (HBV) is a small DNA virus that replicates by reverse transcription of a terminally redundant RNA, the pregenome. Specific packaging of this transcript into viral capsids is mediated by interaction of the reverse transcriptase, P protein, with the 5'-proximal encapsidation signal epsilon, epsilon-function is correlated with the formation of a hairpin structure containing a bulge and a loop, each consisting of 6 nt. To analyse the importance of primary sequence in these regions, we have combined selection of encapsidation competent individuals from pools of randomized epsilon-sequences in transfected cells with in vitro amplification, thus bypassing the current experimental limitations of the HBV system. While no alterations of the authentic loop sequence were detectable, many different sequences were tolerated in the 3'-part of the bulge. However, at the two 5'-proximal bulge positions the wt sequence was strongly selected for, indicating that for RNA packaging close contacts between protein and the 5'- but not the 3'-part of the bulge are important. Such a bipartite organisation provides a structural basis for the recently demonstrated special role of the 3'-part of the bulge as template for the first nucleotides of (-)-strand DNA in HBV reverse transcription.

The endoplasmic reticulum (ER) unfolded protein response (UPR(er)) pathway plays an important role in helping pancreatic β cells to adapt their cellular responses to environmental cues and metabolic stress. Although altered UPR(er) gene expression appears in rodent and human type 2 diabetic (T2D) islets, the underlying molecular mechanisms remain unknown. We show here that germline and β cell-specific disruption of the lysine acetyltransferase 2B (Kat2b) gene in mice leads to impaired insulin secretion and glucose intolerance. Genome-wide analysis of Kat2b-regulated genes and functional assays reveal a critical role for Kat2b in maintaining UPR(er) gene expression and subsequent β cell function. Importantly, Kat2b expression is decreased in mouse and human diabetic β cells and correlates with UPR(er) gene expression in normal human islets. In conclusion, Kat2b is a crucial transcriptional regulator for adaptive β cell function during metabolic stress by controlling UPR(er) and represents a promising target for T2D prevention and treatment.

Pancreaticβcell failure leads to diabetes development. During disease progression,βcells adapt their secretory capacity to compensate the elevated glycaemia and the peripheral insulin resistance. This compensatory mechanism involves a fine-tuned regulation to modulate the endoplasmic reticulum (ER) capacity and quality control to prevent unfolded proinsulin accumulation, a major protein synthetized within theβcell. These signalling pathways are collectively termed unfolded protein response (UPR). The UPR machinery is required to preserve ER homeostasis andβcell integrity. Moreover, UPR actors play a key role by regulating ER folding capacity, increasing the degradation of misfolded proteins, and limiting the mRNA translation rate. Recent genetic and biochemical studies on mouse models and human UPR sensor mutations demonstrate a clear requirement of the UPR machinery to preventβcell failure and increaseβcell mass and adaptation throughout the progression of diabetes. In this review we will highlight the specific role of UPR actors inβcell compensation and failure during diabetes.

The ARF/INK4A (Cdkn2a) locus includes the linked tumour suppressor genes p16INK4a and p14ARF (p19ARF in mice) that trigger the antiproliferative activities of both RB and p53. With beta cell self-replication being the primary source for new beta cell generation in adult animals, the network by which beta cell replication could be increased to enhance beta cell mass and function is one of the approaches in diabetes research. In this review, we show a general view of the regulation points at transcriptional and posttranslational levels of Cdkn2a locus. We describe the molecular pathways and functions of Cdkn2a in beta cell cycle regulation. Given that aging reveals increased p16Ink4a levels in the pancreas that inhibit the proliferation of beta cells and decrease their ability to respond to injury, we show the state of the art about the role of this locus in beta cell senescence and diabetes development. Additionally, we focus on two approaches in beta cell regeneration strategies that rely on Cdkn2a locus negative regulation: long noncoding RNAs and betatrophin.

Objectif Le diabete de type 2 (DT2) resulte d'un defaut fonctionnel des cellules β pancreatiques dont les mecanismes sont encore mysterieux, ce qui limite nos capacites therapeutiques. La dedifferenciation partielle ou totale des cellules β liee a la plasticite cellulaire endocrine pourrait contribuer a la perte de masse de ces cellules dans le DT2 et impliquerait les facteurs de transcription Pax4, specifique de la cellule β, ou Arx, specifique de la cellule α. Nous avons egalement montre que le regulateur du cycle cellulaire E2F1 joue un role cle dans le controle de la proliferation post-natale des cellules β, ainsi que sur leur masse et leur fonction. Cependant, le role de E2F1 dans la plasticite des cellules β et leur dedifferenciation reste inconnu. Materiels et Methodes Nous avons etudie par immunofluorescence la proportion de cellules α et β dans des modeles de souris invalidees pour E2f1 (+/+ et −/−) et des souris (Db/Db). Nous avons invalide E2F1 dans les cellules MIN6, par shRNA et siRNA, avec transfections transitoires et immunopre-cipitations de la chromatine. Nous avons egalement traite pendant 24 h des ilots humains avec un inhibiteur de E2F1 (E2F1i). Resultats L'inactivation genique de E2f1 chez la souris entraine une diminution des cellules β et une augmentation des cellules α. Ce phenomene est amplifie par l'inactivation de E2f1 dans des souris Db/Db, ou des mecanismes de dedifferenciation ont ete decrits. L'extinction de l'expression de E2f1 dans les MIN6 induit une diminution de l'expression des marqueurs de la cellule β et une forte augmentation de l'expression du facteur de transcription Arx. Enfin, le traitement d'ilots humains avec E2F1i diminue l'expression de genes cles de la cellule β. Conclusions Nos donnees suggerent que E2F1 pourrait etre necessaire au maintien de l'identite des cellules s pancreatiques. Son absence entrainerait une diminution de marqueurs specifiques de la cellule β et une re-expression du marqueurs α Arx, et pourraient etre a l'origine de la dedifferenciation observee dans le DT2.

Introduction Le locus CDKN2A code pour deux suppresseurs de tumeur p16Ink4a et p19Arf, acteurs cles dans la regulation du cycle cellulaire et de la senescence en modulant l'activite de pRB et p53. Des etudes d'association pangenomiques (GWAS) ont demontre une forte association du locus CDKN2A avec le diabete de type 2 (DT2). Chez la souris l'augmentation de l'expression de p16Ink4a dans les cellules â pancreatiques au cours du vieillissement induit une perte de la masse et du potentiel regeneratif des ilots. De plus, p16Ink4a controle la neoglucogenese hepatique induite par le jeune. Cependant, l'implication de Cdkn2a dans le developpement du DT2 n'a pas ete clairement demontree. L'objectif de cette etude etait d'etudier l'implication du locus Cdkn2a dans le developpement de l'obesite et du DT2. Materiels et methodes Des tests de tolerance au glucose et a l'insuline ont ete realises sur des souris Cdkn2a-/- soumises un regime standard ou riche en graisse. Le metabolisme energetique a ete etudie par mesure de calorimetrie indirecte. Les mecanismes moleculaires ont ete analyses sur les tissus adipeux blancs (WAT) et bruns (BAT), ainsi que sur des cultures primaires de pre-adipocytes. L'expression genique a ete analysee par PCR quantitative. Resultats Les souris Cdkn2a-/- sont resistantes a une obesite induite par un regime riche en graisse et sont insulino-sensibles. Ces effets semblent etre lies a une augmentation de leur depense d'energetique. L'analyse du WAT des souris Cdkn2a-/- montre une augmentation de l'expression de genes thermogeniques (Ucp1, Prdm16, Cox5a, Pgc1a). Des cultures primaires issues du WAT Cdkn2a-/- confirment les resultats obtenus in vivo et suggerent un role important de Cdkn2a dans la conversion de WAT en BAT. Conclusion Nous montrons pour la premiere fois un lien direct entre cycle cellulaire et la conversion des cellules du WAT en BAT. p16Ink4a et p19Arf semblent donc controler la destinee des cellules du tissu adipeux. Declaration d’interet Les auteurs declarent ne pas avoir d'interet direct ou indirect (financier ou en nature) avec un organisme prive, industriel ou commercial en relation avec le sujet presente.

Introduction P16Ink4a et p19Arf, codes par le locus Cdkn2a, controle la proliferation cellulaire via les voies CDK4-CyclinD-pRb-E2F et p53, respectivement. Des etudes de « Genome-Wide Association » ont identifie une association entre le locus Cdkn2a et le diabete de type 2 (DT2). Dans des conditions physiologiques, les niveaux de p16 dans le pancreas diminuent avec l’âge, inhibant la proliferation des cellules beta pancreatiques, les rendant incapables de s’adapter aux besoins metaboliques. Cependant, le role de Cdkn2a dans les tissus insulino-sensibles demeure inconnu. L’objectif principal de ce travail est d’etudier la fonction de Cdkn2a dans des conditions diabetogenes. Materiels et methodes Des souris controles et inactivees specifiquement pourþCdkn2a (KO) ont ete soumises a un regime riche en graisse pendant 12 semaines. Des tests de tolerance au glucose et a l’insuline ont ete realises pour mesurer la resistance au glucose et la sensibilite a l’insuline, respectivement. Afin de mesurer le metabolisme energetique in vivo, ces souris ont ete mises dans des cages metaboliques. Resultats Les souris Cdkn2a KO sont resistantes a une obesite induite par un regime riche en graisse, bien que leur prise alimentaire soit augmentee. Cependant, bien qu’intolerantes au glucose, les KO restent sensibles l’insuline, suggerant que, contrairement aux souris controles, les Cdkn2a KO ne developpent pas de DT2. Les souris Cdkn2a KO demontrent une augmentation de leur depense energetique, secondaire a une augmentation de l’activite du tissu adipeux brun. Conclusion P16Ink4a et p19Arf controle la depense energetique et le metabolisme oxydatif. En consequence, les souris invalidees pour Cdkn2a sont resistantes a l’obesite et ne developpent pas de DT2. Les mecanismes moleculaires sous-jacents (regulation via E2F1) sont en cours d’analyse.

Introduction Le diabete de type 2 (T2D) est caracterise par une insulino-resistance peripherique et un dysfonctionnement des cellules β pancreatiques. La stimulation des cellules β par le glucose augmente la secretion et la synthese d’insuline, induisant un stress du reticulum endoplasmique (RE). Ce dernier active une reponse adaptative au stress (UPR) afin de retablir l’equilibre cellulaire. Au cours d’un stress chronique comme au cours du T2D, l’UPR ne parvient plus a arreter les perturbations du RE et les cellules β entrent en apoptose. Afin de determiner le role de PCAF dans la regulation de la reponse UPR et la secretion d’insuline, nous avons realise un phenotypage metabolique des souris deficientes pour Pcaf (Pcaf-/-) et mesure ex vivo (ilots isoles) la reponse au glucose, ainsi que les mecanismes moleculaires impliques. Materiels et methodes Des tests de tolerance au glucose et a l’insuline ont ete realises sur des souris Pcaf +/+ et -/-. Des tests de secretion d’insuline ont ete realises sur des ilots isoles de ces souris. L’expression des genes a ete mesuree par RT-PCR quantitative. L’interactome a ete etudie sur une lignee Min6 apres immunoprecipitation et MALDI-Tof-Tof. Resultats Les souris Pcaf-/- sont gluco-intolerantes et resistantes a une obesite induite par un regime riche en graisse. Les cellules β pancreatiques de souris Pcaf -/- sont incapables de secreter de l’insuline en reponse au glucose, lie a une diminution de l’expression genique des acteurs clef de l’UPR. De plus, l’etude de l’interactome revele une interaction de PCAF avec des proteines de l’UPR, suggerant ainsi l’implication de PCAF dans la maturation de l’insuline. Conclusion Nous montrons que PCAF controle la secretion d’insuline en agissant sur l’UPR. L’utilisation d’un agoniste de PCAF pourrait constituer ainsi une nouvelle strategie therapeutique pour le traitement du T2D.

Introduction Les cellules β pancreatiques controlent la secretion d’insuline par un mecanisme finement regule. La physiopathologie du diabete de type 1 (auto-immun) ou de type 2 se caracterise par une diminution du nombre et de la masse des ilots de Langerhans, et plus precisement de la masse des cellules β. Par consequent, une meilleure comprehension des mecanismes controlant non seulement la proliferation mais egalement la fonction est necessaire pour le developpement de nouvelles strategies pour le traitement du diabete. Nous avons demontre que les acteurs du cycle cellulaire, en particulier E2F1, CDK4 et pRb, jouaient un role crucial dans le tissu adipeux, le muscle et la cellule s pancreatique. L’histone acetyl-transferase PCAF controle la transcription de certains genes par des mecanismes epigenetiques, via son interaction avec des facteurs de transcription comme E2F1, HNF-1 et USF-1. PCAF est egalement implique dans la modulation d’un programme transcriptionnel en reponse a l’insuline, suggerant que ce cofacteur pourrait jouer un role metabolique important. Materiels et methodes Dans ce projet, nous avons utilise des souris invalidees pour le gene Pcaf. Des experimentations de biologie moleculaire et de microscopie ont ete effectuees in vitro sur ilots isoles. Le phenotypage metabolique a ete realise sur des souris Pcaf+/+ et -/-. Resultats Nous avons observe que les souris Pcaf-/- etaient intolerantes au glucose et resistantes a une obesite induite par un regime riche en graisse. Nous avons remarque que les cellules β pancreatiques isolees des souris Pcaf -/- etaient incapables de secreter de l’insuline en reponse a une hyperglycemie. De plus, l’observation des structures cellulaires par microscopie electronique a transmission a revele un defaut de crystallisation et/ou de maturation des granules contenant l’insuline, suggerant que PCAF controle ce mecanisme. Finalement, des etudes genetiques utilisant les donnees issues de DIAGRAM semblent montrer une association entre 2 polymorphismes du gene Kat2B et le diabete de type 2. Conclusion Bien que les mecanismes moleculaires restent inconnus, toutes ces donnees convergent malgre cela vers un role potentiel de PCAF dans le controle de l’homeostasie du glucose et suggere une implication de cette proteine dans le developpement du diabete de type 2.