Histone marks regulate the epithelial-to-mesenchymal transition via alternative splicing

International audienceHistone modifications impact final splicing decisions. However, there is little evidence of the driving role of these marks in inducing cell-specific splicing changes. Using CRISPR epigenome editing tools, we show in an epithelial-to-mesenchymal cell reprogramming system (epithelial-to-mesenchymal transition [EMT]) that a single change in H3K27ac or H3K27me3 levels right at the alternatively spliced exon is necessary and sufficient to induce a splicing change capable of recapitulating important aspects of EMT, such as cell motility and invasiveness. This histone-mark-dependent splicing effect is highly dynamic and mediated by direct recruitment of the splicing regulator PTB to its RNA binding sites. These results support a role for H3K27 marks in inducing a change in the cell's phenotype via regulation of alternative splicing. We propose the dynamic nature of chromatin as a rapid and reversible mechanism to coordinate the splicing response to cell-extrinsic cues, such as induction of EMT

Adipose tissue mitochondrial dysfunction in human obesity is linked to a specific DNA methylation signature in adipose-derived stem cells

Background: A functional population of adipocyte precursors, termed adipose-derived stromal/stem cells (ASCs), is crucial for proper adipose tissue (AT) expansion, lipid handling, and prevention of lipotoxicity in response to chronic positive energy balance. We previously showed that obese human subjects contain a dysfunctional pool of ASCs. Elucidation of the mechanisms underlying abnormal ASC function might lead to therapeutic interventions for prevention of lipotoxicity by improving the adipogenic capacity of ASCs. Methods: Using epigenome-wide association studies, we explored the impact of obesity on the methylation signature of human ASCs and their differentiated counterparts. Mitochondrial phenotyping of lean and obese ASCs was performed. TBX15 loss- and gain-of-function experiments were carried out and western blotting and electron microscopy studies of mitochondria were performed in white AT biopsies from lean and obese individuals. Results: We found that DNA methylation in adipocyte precursors is significantly modified by the obese environment, and adipogenesis, inflammation, and immunosuppression were the most affected pathways. Also, we identified TBX15 as one of the most differentially hypomethylated genes in obese ASCs, and genetic experiments revealed that TBX15 is a regulator of mitochondrial mass in obese adipocytes. Accordingly, morphological analysis of AT from obese subjects showed an alteration of the mitochondrial network, with changes in mitochondrial shape and number. Conclusions: We identified a DNA methylation signature in adipocyte precursors associated with obesity, which has a significant impact on the metabolic phenotype of mature adipocytes

Survivin, a key player in cancer progression, increases in obesity and protects adipose tissue stem cells from apoptosis

Adipose tissue (AT) has a central role in obesity-related metabolic imbalance through the dysregulated production of cytokines and adipokines. In addition to its known risk for cardiovascular disease and diabetes, obesity is also a major risk for cancer. We investigated the impact of obesity for the expression of survivin, an antiapoptotic protein upregulated by adipokines and a diagnostic biomarker of tumor onset and recurrence. In a cross-sectional study of 111 subjects classified by body mass index, circulating levels of survivin and gene expression in subcutaneous ATwere significantly higher in obese patients and positively correlated with leptin. Within AT, survivin was primarily detected in human adipocyte-derived stem cells (hASCs), the adipocyte precursors that determine AT expansion. Remarkably, survivin expression was significantly higher in hASCs isolated from obese patients that fromlean controls and was increased by proinflammatory M1 macrophage soluble factors including IL-1β. Analysis of survivin expression in hASCs revealed a complex regulation including epigenetic modifications and protein stability. Surprisingly, obese hASCs showed survivin promoter hypermethylation that correlated with a significant decrease in its mRA levels. Nonetheless, a lower level ofmir-203, which inhibits survivin protein translation, and higher protein stability, was found in obese hASCs compared with their lean counterparts. We discovered that survivin levels determine the susceptibility of hASCs to apoptotic stimuli (including leptin and hypoxia). Accordingly, hASCs from an obese setting were protected from apoptosis. Collectively, these data shed new light on the molecular mechanisms governing AT expansion in obesity through promotion of hASCs that are resistant to apoptosis, and point to survivin as a potential new molecular player in the communication between AT and tumor cells. Thus, inhibition of apoptosis targeting survivin might represent an effective strategy for both obesity and cancer therapy

Caveolin-1 is down-regulated in alveolar habdomyosarcomas and negatively regulates tumor growth

Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence. Despite advances in therapy, patients with histological variant of rhabdomyosarcoma known as alveolar rhabdomyosarcoma (ARMS) have a 5-year survival of less than 30%. Caveolin-1 (CAV1), encoding the structural component of cellular caveolae, is a suggested tumor suppressor gene involved in cell signaling. In the present study we report that compared to other forms of rhabdomyosarcoma (RMS) CAV1 expression is either undetectable or very low in ARMS cell lines and tumor samples. DNA methylation analysis of the promoter region and azacytidine-induced re-expression suggest the involvement of epigenetic mechanisms in the silencing of CAV1. Reintroduction of CAV1 in three of these cell lines impairs their clonogenic capacity and promotes features of muscular differentiation. In vitro, CAV1-expressing cells show high expression of Caveolin-3 (CAV3), a muscular differentiation marker. Blockade of MAPK signaling is also observed. In vivo, CAV1-expressing xenografts show growth delay, features of muscular differentiation and increased cell death. In summary, our results suggest that CAV1 could function as a potent tumor suppressor in ARMS tumors. Inhibition of CAV1 function therefore, could contribute to aberrant cell proliferation, leading to ARMS development

Diagnostic Accuracy of Abdominal CT for Locally Advanced Colon Tumors: Can We Really Entrust Certain Decisions to the Reliability of CT?

Many different options of neoadjuvant treatments for advanced colon cancer are emerging. An accurate preoperative staging is crucial to select the most appropriate treatment option. A retrospective study was carried out on a national series of operated patients with T4 tumors. Considering the anatomo-pathological analysis of the surgical specimen as the gold standard, a diagnostic accuracy study was carried out on the variables T and N staging and the presence of peritoneal metastases (M1c). The parameters calculated were sensitivity, specificity, positive and negative predictive values, and positive and negative likelihood ratios, as well as the overall accuracy. A total of 50 centers participated in the study in which 1950 patients were analyzed. The sensitivity of CT for correct staging of T4 colon tumors was 57%. Regarding N staging, the overall accuracy was 63%, with a sensitivity of 64% and a specificity of 62%; however, the positive and negative likelihood ratios were 1.7 and 0.58, respectively. For the diagnosis of peritoneal metastases, the accuracy was 94.8%, with a sensitivity of 40% and specificity of 98%; in the case of peritoneal metastases, the positive and negative likelihood ratios were 24.4 and 0.61, respectively. The diagnostic accuracy of CT in the setting of advanced colon cancer still has some shortcomings for accurate diagnosis of stage T4, correct classification of lymph nodes, and preoperative detection of peritoneal metastases

Role of HDAC11 in muscle cell differentiation and regeneration = Paper de HDAC11 en la diferenciació i regeneració musculars

[eng] HDAC11 is the newest member of the histone deacetylase (HDAC) family and one of the less studied. Its expression was described to be enriched in skeletal muscle tissues from the first moment of its discovery, yet now after 15 years, its roles in myogenesis remain unknown. We started this thesis by analyzing the expression changes of all HDAC’s’ members between proliferation and early differentiation conditions, which constitutes a crucial cell fate point in which cells have to decide whether to continue proliferating or enter to irreversible G0 arrest state to differentiate. With this analysis, we found HDAC11 as the HDAC family member the most upregulated in the skeletal muscle differentiation process. By CRISPR/Cas9 knock-in tagging of endogenous HDAC11, we show that HDAC11 protein levels are absent in proliferating cells and increased through differentiation. The silencing of HDAC11 in proliferation conditions is mediated, at least in part, by class I HDAC’s deacetylation of MYOD. In differentiation conditions, acetylated MYOD and myogenin, the two master regulators of muscle differentiation, bind to HDAC11 promoter regions and trigger its expression. HDAC11 deficient myoblasts did not present major alterations in cell proliferation or differentiation capacities but show reduced fusion ability. Genome-wide transcriptomic analysis of differentiating HDAC11 deficient myoblasts revealed an upregulation of genes involved in proliferation and a decreased expression of genes involved in muscle contraction, suggesting a delayed entry in G0 irreversible arrest state. Our ChIP results suggest that HDAC11 would mediate repression of proliferation related genes by deacetylation of H3 in their promoter regions. Moreover, HDAC11 expression is also highly expressed in additional G0 states, like in reversible arrested quiescent satellite cells. In skeletal muscle tissues, HDAC11 is higher expressed in fast muscles than slow ones, especially in males. The analysis of HDAC11 deficient mice concludes that HDAC11 absence do not cause major alterations in muscle development, adult myofiber growth or fiber type composition in basal conditions. In regeneration conditions, HDAC11 deficient mice show advanced regeneration capacity at 7 days post injury, probably mediated at least in part, by an increased expression of Il-10 by HDAC11 deficient macrophages. Finally, we show that HDAC11 upregulation through differentiation is conserved in human myoblast and its expression is reduced in rhabdomyosarcoma cells, which present impaired differentiation capabilities. Altogether, our results place HDAC11 as a new epigenetic regulator in in vitro an in vivo myogenesis.[cat] HDAC11 és el membre més recentment descobert de la família de deacetilases d'histones (HDAC) i un dels menys estudiats. En el moment del seu descobriment es va veure que estava altament expressada en teixits de múscul esquelètic encara que després de 15 anys, les seves funcions en la miogènesi resten encara desconegudes. Vam començar aquesta tesi analitzant els canvis d'expressió de tots els membres de la família HDAC entre les condicions de proliferació i diferenciació primerenca, un moment crucial on les cèl·lules han de decidir si continuen dividint-se o entren en l'estat d'aturada irreversible G0 per diferenciar-se. Amb aquesta anàlisi vam trobar HDAC11 com el membre de la família HDAC que augmentava més la seva expressió en aquest procés. Amb la tècnica d'enginyeria genètica CRISPR/Cas9 vam aconseguir inserir un epítop en el locus genòmic de HDAC11, que ens permeté demostrar que la proteïna HDAC11 està absent en condicions de proliferació i augmenta amb la diferenciació. El silenciament de l'expressió de HDAC11 durant la proliferació està mitjançada, almenys en part, per la deacetilació de MYOD per part de la classe I de HDACs. Durant la diferenciació, MYOD acetilat i miogenina, els dos reguladors responsables d’iniciar la diferenciació muscular, s'uneixen al promotor de HDAC11 i activen la seva expressió. Els mioblasts deficients en HDAC11 no presenten greus alteracions en la proliferació cel·lular o en la seva capacitat de diferenciar-se però mostren una reduïda capacitat de fusió. L'estudi transcriptòmic a escala global de mioblasts deficients en HDAC11 va revelar una sobreexpressió de gens involucrats en la proliferació cel·lular i una reducció en l'expressió de gens amb funcions en la contracció muscular, suggerint una entrada més tardana en la fase G0 d'aturada irreversible. Els nostres resultats de ChIP suggereixen que HDAC11 podria intervindre en la repressió dels gens involucrats en la proliferació cel·lular mitjançant la deacetilació de les histones H3 dels seus promotors. A més, l'expressió d'HDAC11 també és alta en estats addicionals de G0 com l'arrest reversible de les cèl·lules satèl·lit quiescents. En teixits de múscul esquelètic, HDAC11 està més expressada en músculs ràpids que lents, especialment en mascles. L'anàlisi de ratolins deficients en HDAC11 conclogué que l'absència de HDAC11 no causa greus alteracions en el desenvolupament muscular, el creixement de miofibres adultes o en la composició en tipus de fibres en condicions basals. Durant la regeneració muscular, els ratolins deficients en HDAC11 mostren un avanç en la seva capacitat de regeneració 7 dies després de la lesió, probablement mitjançat en part per un increment en l’expressió de Il-10 per part dels macròfags deficients en HDAC11. Finalment, mostrem que l’augment d’expressió de HDAC11 està conservat en la diferenciació de mioblasts humans i que la seva expressió està reduïda en rabdomiosarcoma, patologia tumoral que presenta un impediment en la diferenciació muscular. En conjunt, els nostres resultats situen HDAC11 com un nou regulador epigenètic en la miogènesi in vitro i in vivo

HDAC11 is a novel regulator of fatty acid oxidative metabolism in skeletal muscle

Skeletal muscle is the largest tissue in mammalian organisms and is a key determinant of basal metabolic rate and whole‐body energy metabolism. Histone deacetylase 11 (HDAC11) is the only member of the class IV subfamily of HDACs, and it is highly expressed in skeletal muscle, but its role in skeletal muscle physiology has never been investigated. Here, we describe for the first time the consequences of HDAC11 genetic deficiency in skeletal muscle, which results in the improvement of muscle function enhancing fatigue resistance and muscle strength. Loss of HDAC11 had no obvious impact on skeletal muscle structure but increased the number of oxidative myofibers by promoting a glycolytic‐to‐oxidative muscle fiber switch. Unexpectedly, HDAC11 was localized in muscle mitochondria and its deficiency enhanced mitochondrial content. In particular, we showed that HDAC11 depletion increased mitochondrial fatty acid β‐oxidation through activating the AMP‐activated protein kinase‐acetyl‐CoA carboxylase pathway and reducing acylcarnitine levels in vivo, thus providing a mechanistic explanation for the improved muscle strength and fatigue resistance. Overall, our data reveal a unique role of HDAC11 in the maintenance of muscle fiber‐type balance and the mitochondrial lipid oxidation. These findings shed light on the mechanisms governing muscle metabolism and may have implications for chronic muscle metabolic disease management.We thank Rosa Mª Ampudia and Dr. Sara Capdevila for excellent technical assistance with mice. We also thank Dr. Pilar Armengol for its technological support with the confocal microscopy. We thank Drs. Dolors Serra and Coral Sanfeliu for kindly providing ACC/pACC and TOM20, and COXIV antibodies, respectively. We thank Drs. Mercè Jardí and Monserrat Batlle for sharing with us the grip strength and treadmill equipments, respectively. Finally, we are also very grateful to Drs. Dolors Serra for her advice and helpful discussions. This work was supported by Ministerio de Economía y Competitividad (BFU2016‐80748 to MS and BFU2017‐89408‐R to AMP) and Ministerio de Ciencia, Innovación y Universidades (RTI2018‐094009‐B‐I00 to MAP), Feder funds, Generalitat de Catalunya (2017 SGR969 and 2017 SGR206), and Junta de Castilla y Leon (CSI239P18). EH was supported in part by BFU2016‐80748, and YNA was supported by Ministerio de Educación, Cultura y Deport (FPU12/05668).Peer reviewe

Adipose tissue mitochondrial dysfunction in human obesity is linked to a specific DNA methylation signature in adipose-derived stem cells

Background: A functional population of adipocyte precursors, termed adipose-derived stromal/stem cells (ASCs), is crucial for proper adipose tissue (AT) expansion, lipid handling, and prevention of lipotoxicity in response to chronic positive energy balance. We previously showed that obese human subjects contain a dysfunctional pool of ASCs. Elucidation of the mechanisms underlying abnormal ASC function might lead to therapeutic interventions for prevention of lipotoxicity by improving the adipogenic capacity of ASCs. Methods: Using epigenome-wide association studies, we explored the impact of obesity on the methylation signature of human ASCs and their differentiated counterparts. Mitochondrial phenotyping of lean and obese ASCs was performed. TBX15 loss- and gain-of-function experiments were carried out and western blotting and electron microscopy studies of mitochondria were performed in white AT biopsies from lean and obese individuals. Results: We found that DNA methylation in adipocyte precursors is significantly modified by the obese environment, and adipogenesis, inflammation, and immunosuppression were the most affected pathways. Also, we identified TBX15 as one of the most differentially hypomethylated genes in obese ASCs, and genetic experiments revealed that TBX15 is a regulator of mitochondrial mass in obese adipocytes. Accordingly, morphological analysis of AT from obese subjects showed an alteration of the mitochondrial network, with changes in mitochondrial shape and number. Conclusions: We identified a DNA methylation signature in adipocyte precursors associated with obesity, which has a significant impact on the metabolic phenotype of mature adipocytes