An NFIX-mediated regulatory network governs the balance of hematopoietic stem and progenitor cells during hematopoiesis.

The transcription factor (TF) nuclear factor I-X (NFIX) is a positive regulator of hematopoietic stem and progenitor cell (HSPC) transplantation. Nfix-deficient HSPCs exhibit a severe loss of repopulating activity, increased apoptosis, and a loss of colony-forming potential. However, the underlying mechanism remains elusive. Here, we performed cellular indexing of transcriptomes and epitopes by high-throughput sequencing (CITE-seq) on Nfix-deficient HSPCs and observed a loss of long-term hematopoietic stem cells and an accumulation of megakaryocyte and myelo-erythroid progenitors. The genome-wide binding profile of NFIX in primitive murine hematopoietic cells revealed its colocalization with other hematopoietic TFs, such as PU.1. We confirmed the physical interaction between NFIX and PU.1 and demonstrated that the 2 TFs co-occupy super-enhancers and regulate genes implicated in cellular respiration and hematopoietic differentiation. In addition, we provide evidence suggesting that the absence of NFIX negatively affects PU.1 binding at some genomic loci. Our data support a model in which NFIX collaborates with PU.1 at super-enhancers to promote the differentiation and homeostatic balance of hematopoietic progenitors.

Murine fetal bone marrow does not support functional hematopoietic stem and progenitor cells until birth.

While adult bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs) and their extrinsic regulation is well studied, little is known about the composition, function, and extrinsic regulation of the first HSPCs to enter the BM during development. Here, we functionally interrogate murine BM HSPCs from E15.5 through P0. Our work reveals that fetal BM HSPCs are present by E15.5, but distinct from the HSPC pool seen in fetal liver, both phenotypically and functionally, until near birth. We also generate a transcriptional atlas of perinatal BM HSPCs and the BM niche in mice across ontogeny, revealing that fetal BM lacks HSPCs with robust intrinsic stem cell programs, as well as niche cells supportive of HSPCs. In contrast, stem cell programs are preserved in neonatal BM HSPCs, which reside in a niche expressing HSC supportive factors distinct from those seen in adults. Collectively, our results provide important insights into the factors shaping hematopoiesis during this understudied window of hematopoietic development.

Chemotherapy-induced transposable elements activate MDA5 to enhance haematopoietic regeneration.

Haematopoietic stem cells (HSCs) are normally quiescent, but have evolved mechanisms to respond to stress. Here, we evaluate haematopoietic regeneration induced by chemotherapy. We detect robust chromatin reorganization followed by increased transcription of transposable elements (TEs) during early recovery. TE transcripts bind to and activate the innate immune receptor melanoma differentiation-associated protein 5 (MDA5) that generates an inflammatory response that is necessary for HSCs to exit quiescence. HSCs that lack MDA5 exhibit an impaired inflammatory response after chemotherapy and retain their quiescence, with consequent better long-term repopulation capacity. We show that the overexpression of ERV and LINE superfamily TE copies in wild-type HSCs, but not in Mda5-/- HSCs, results in their cycling. By contrast, after knockdown of LINE1 family copies, HSCs retain their quiescence. Our results show that TE transcripts act as ligands that activate MDA5 during haematopoietic regeneration, thereby enabling HSCs to mount an inflammatory response necessary for their exit from quiescence.

3' UTR-truncated HMGA2 overexpression induces non-malignant in vivo expansion of hematopoietic stem cells in non-human primates.

Vector-mediated mutagenesis remains a major safety concern for many gene therapy clinical protocols. Indeed, lentiviral-based gene therapy treatments of hematologic disease can result in oligoclonal blood reconstitution in the transduced cell graft. Specifically, clonal expansion of hematopoietic stem cells (HSCs) highly expressing HMGA2, a chromatin architectural factor found in many human cancers, is reported in patients undergoing gene therapy for hematologic diseases, raising concerns about the safety of these integrations. Here, we show for the first time in vivo multilineage and multiclonal expansion of non-human primate HSCs expressing a 3' UTR-truncated version of HMGA2 without evidence of any hematologic malignancy >7 years post-transplantation, which is significantly longer than most non-human gene therapy pre-clinical studies. This expansion is accompanied by an increase in HSC survival, cell cycle activation of downstream progenitors, and changes in gene expression led by the upregulation of IGF2BP2, a mRNA binding regulator of survival and proliferation. Thus, we conclude that prolonged ectopic expression of HMGA2 in hematopoietic progenitors is not sufficient to drive hematologic malignancy and is not an acute safety concern in lentiviral-based gene therapy clinical protocols.

Alu retrotransposons modulate Nanog expression through dynamic changes in regional chromatin conformation via aryl hydrocarbon receptor.

Transcriptional repression of Nanog is an important hallmark of stem cell differentiation. Chromatin modifications have been linked to the epigenetic profile of the Nanog gene, but whether chromatin organization actually plays a causal role in Nanog regulation is still unclear. Here, we report that the formation of a chromatin loop in the Nanog locus is concomitant to its transcriptional downregulation during human NTERA-2 cell differentiation. We found that two Alu elements flanking the Nanog gene were bound by the aryl hydrocarbon receptor (AhR) and the insulator protein CTCF during cell differentiation. Such binding altered the profile of repressive histone modifications near Nanog likely leading to gene insulation through the formation of a chromatin loop between the two Alu elements. Using a dCAS9-guided proteomic screening, we found that interaction of the histone methyltransferase PRMT1 and the chromatin assembly factor CHAF1B with the Alu elements flanking Nanog was required for chromatin loop formation and Nanog repression. Therefore, our results uncover a chromatin-driven, retrotransposon-regulated mechanism for the control of Nanog expression during cell differentiation.

GPRASP proteins are critical negative regulators of hematopoietic stem cell transplantation.

Hematopoietic stem cell (HSC) transplantation (HSCT) is often exploited to treat hematologic disease. Donor HSCs must survive, proliferate, and differentiate in the damaged environment of the reconstituting niche. Illuminating molecular mechanisms regulating the activity of transplanted HSCs will inform efforts to improve HSCT. Here, we report that G-protein-coupled receptor-associated sorting proteins (GPRASPs) function as negative regulators of HSCT. Silencing of Gprasp1 or Gprasp2 increased the survival, quiescence, migration, niche retention, and hematopoietic repopulating activity of hematopoietic stem and progenitor cells (HSPCs) posttransplant. We further show that GPRASP1 and GPRASP2 promote the degradation of CXCR4, a master regulator of HSC function during transplantation. CXCR4 accumulates in Gprasp-deficient HSPCs, boosting their function posttransplant. Thus, GPRASPs negatively regulate CXCR4 stability in HSCs. Our work reveals GPRASP proteins as negative regulators of HSCT and CXCR4 activity. Disruption of GPRASP/CXCR4 interactions could be exploited in the future to enhance the efficiency of HSCT.

Elevated Oxidative Stress Impairs Hematopoietic Progenitor Function in C57BL/6 Substrains.

C57BL/6N (N) and C57BL/6J (J) mice possess key genetic differences, including a deletion in the Nicotinamide nucleotide transhydrogenase (Nnt) gene that results in a non-functional protein in J mice. NNT regulates mitochondrial oxidative stress. Although elevated oxidative stress can compromise hematopoietic stem and progenitor cell (HSPC) function, it is unknown whether N- and J-HSPCs are functionally equivalent. Here, we report that J-HSPCs display compromised short-term hematopoietic repopulating activity relative to N-HSPCs that is defined by a delay in lymphoid reconstitution and impaired function of specific multi-potent progenitor populations post transplant. J-HSPCs also displayed elevated reactive oxygen species (ROS) relative to N-HSPCs post transplant and upregulate ROS levels more in response to hematopoietic stress. Nnt knockdown in N-HSPCs recapitulated J-HSPCs' short-term repopulating defect, indicating that NNT loss contributes to this defect. In summary, C57BL/6N and C57BL/6J HSPCs are not functionally equivalent, which should be considered when determining the substrain most appropriate for investigations of HSPC biology.

Lung regeneration after toxic injury is improved in absence of dioxin receptor.

Recent experimental evidences from cellular systems and from mammalian and non-mammalian animal models highlight novel functions for the aryl hydrocarbon/dioxin receptor (AhR) in maintaining cell differentiation and tissue homeostasis. Notably, AhR depletion stimulates an undifferentiated and pluripotent phenotype likely associated to a mesenchymal transition in epithelial cells and to increased primary tumorigenesis and metastasis in melanoma. In this work, we have used a lung model of epithelial regeneration to investigate whether AhR regulates proper tissue repair by adjusting the expansion of undifferentiated stem-like cells. AhR-null mice developed a faster and more efficient repair of the lung bronchiolar epithelium upon naphthalene injury that required increased cell proliferation and the earlier activation of stem-like Clara, Basal and neuroepithelial cells precursors. Increased basal content in multipotent Sca1+/CD31-/CD4- cells and in cells expressing pluripotency factors NANOG and OCT4 could also improve re-epithelialization in AhR-null lungs. The reduced response of AhR-deficient lungs to Sonic Hedgehog (Shh) repression shortly after injury may also help their improved bronchiolar epithelium repair. These results support a role for AhR in the regenerative response against toxins, and open the possibility of modulating its activation level to favor recovery from lesions caused by environmental contaminants.

Dioxin Receptor Adjusts Liver Regeneration After Acute Toxic Injury and Protects Against Liver Carcinogenesis.

The aryl hydrocarbon receptor (AhR) has roles in cell proliferation, differentiation and organ homeostasis, including the liver. AhR depletion induces undifferentiation and pluripotency in normal and transformed cells. Here, AhR-null mice (AhR-/-) were used to explore whether AhR controls liver regeneration and carcinogenesis by restricting the expansion of stem-like cells and the expression of pluripotency genes. Short-term CCl4 liver damage was earlier and more efficiently repaired in AhR-/- than in AhR+/+ mice. Stem-like CK14 + and TBX3 + and pluripotency-expressing OCT4 + and NANOG + cells expanded sooner in AhR-/- than in AhR+/+ regenerating livers. Stem-like side population cells (SP) isolated from AhR-/- livers had increased ß-catenin (ß-Cat) signaling with overexpression of Axin2, Dkk1 and Cyclin D1. Interestingly, ß-Cat, Axin2 and Dkk1 also increased during regeneration but more notably in AhR-null livers. Liver carcinogenesis induced by diethylnitrosamine (DEN) produced large carcinomas in all AhR-/- mice but mostly premalignant adenomas in less than half of AhR+/+ mice. AhR-null tumoral tissue, but not their surrounding non-tumoral parenchyma, had nuclear ß-Cat and Axin2 overexpression. OCT4 and NANOG were nevertheless similarly expressed in AhR+/+ and AhR-/- lesions. We suggest that AhR may serve to adjust liver repair and to block tumorigenesis by modulating stem-like cells and ß-Cat signaling.

AhR-dependent 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in human neuronal cell line SHSY5Y.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a xenobiotic agent with high persistency that induces neurotoxic effects altering neurodevelopment and behavior. The molecular mechanisms and the signaling pathways involved in TCDD-mediated neurotoxicity, together with the search of its molecular targets in neurons are under intense study. We have previously shown that high nanomolar concentrations of TCDD for incubation times of minutes induce apoptosis in SHSY5Y human neuroblastoma cells by the disruption of calcium homeostasis, affecting membrane structural integrity. In this work, we have analyzed the effect of low nanomolar concentrations of TCDD for incubation times of hours to define the role of aryl hydrocarbon receptor which can be activated at those concentrations. TCDD induces toxicity in SHSY5Y human neuroblastoma cells under these experimental conditions with an EC50 value of approximately 3nM at 24h of incubation time. Transient transfection of a hairpin RNA for AhR protects against TCDD neurotoxicity, suggesting that AhR is mediating the dioxin effect. Altogether, these results support the hypothesis that TCDD toxicity in SHSY5Y neuroblastoma cells depends on dioxin concentration and time of incubation, with a main role of aryl hydrocarbon receptor at low nanomolar TCDD concentrations.

RNA-Seq Analysis to Measure the Expression of SINE Retroelements.

The intrinsic features of retroelements, like their repetitive nature and disseminated presence in their host genomes, demand the use of advanced methodologies for their bioinformatic and functional study. The short length of SINE (short interspersed elements) retrotransposons makes such analyses even more complex. Next-generation sequencing (NGS) technologies are currently one of the most widely used tools to characterize the whole repertoire of gene expression in a specific tissue. In this chapter, we will review the molecular and computational methods needed to perform NGS analyses on SINE elements. We will also describe new methods of potential interest for researchers studying repetitive elements. We intend to outline the general ideas behind the computational analyses of NGS data obtained from SINE elements, and to stimulate other scientists to expand our current knowledge on SINE biology using RNA-seq and other NGS tools.

Alu retrotransposons promote differentiation of human carcinoma cells through the aryl hydrocarbon receptor.

Cell differentiation is a central process in development and in cancer growth and dissemination. OCT4 (POU5F1) and NANOG are essential for cell stemness and pluripotency; yet, the mechanisms that regulate their expression remain largely unknown. Repetitive elements account for almost half of the Human Genome; still, their role in gene regulation is poorly understood. Here, we show that the dioxin receptor (AHR) leads to differentiation of human carcinoma cells through the transcriptional upregulation of Alu retrotransposons, whose RNA transcripts can repress pluripotency genes. Despite the genome-wide presence of Alu elements, we provide evidences that those located at the NANOG and OCT4 promoters bind AHR, are transcribed by RNA polymerase-III and repress NANOG and OCT4 in differentiated cells. OCT4 and NANOG repression likely involves processing of Alu-derived transcripts through the miRNA machinery involving the Microprocessor and RISC. Consistently, stable AHR knockdown led to basal undifferentiation, impaired Alus transcription and blockade of OCT4 and NANOG repression. We suggest that transcripts produced from AHR-regulated Alu retrotransposons may control the expression of stemness genes OCT4 and NANOG during differentiation of carcinoma cells. The control of discrete Alu elements by specific transcription factors may have a dynamic role in genome regulation under physiological and diseased conditions.

Dioxin receptor regulates aldehyde dehydrogenase to block melanoma tumorigenesis and metastasis.

BACKGROUND: The dioxin (AhR) receptor can have oncogenic or tumor suppressor activities depending on the phenotype of the target cell. We have shown that AhR knockdown promotes melanoma primary tumorigenesis and lung metastasis in the mouse and that human metastatic melanomas had reduced AhR levels with respect to benign nevi. METHODS: Mouse melanoma B16F10 cells were engineered by retroviral transduction to stably downregulate AhR expression, Aldh1a1 expression or both. They were characterized for Aldh1a1 activity, stem cell markers and migration and invasion in vitro. Their tumorigenicity in vivo was analyzed using xenografts and lung metastasis assays as well as in vivo imaging. RESULTS: Depletion of aldehyde dehydrogenase 1a1 (Aldh1a1) impairs the pro-tumorigenic and pro-metastatic advantage of melanoma cells lacking AhR expression (sh-AhR). Thus, Aldh1a1 knockdown in sh-AhR cells (sh-AhR + sh-Aldh1a1) diminished their migration and invasion potentials and blocked tumor growth and metastasis to the lungs in immunocompetent AhR+/+ recipient mice. However, Aldh1a1 downmodulation in AhR-expressing B16F10 cells did not significantly affect tumor growth in vivo. Aldh1a1 knockdown reduced the high levels of CD133(+)/CD29(+)/CD44(+) cells, melanosphere size and the expression of the pluripotency marker Sox2 in sh-AhR cells. Interestingly, Sox2 increased Aldh1a1 expression in sh-AhR but not in sh-AhR + sh-Aldh1a1 cells, suggesting that Aldh1a1 and Sox2 may be co-regulated in melanoma cells. In vivo imaging revealed that mice inoculated with AhR + Aldh1a1 knockdown cells had reduced tumor burden and enhanced survival than those receiving Aldh1a1-expressing sh-AhR cells. CONCLUSIONS: Aldh1a1 overactivation in an AhR-deficient background enhances melanoma progression. Since AhR may antagonize the protumoral effects of Aldh1a1, the AhR(low)-Aldh1a1(high) phenotype could be indicative of bad outcome in melanoma.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induces apoptosis by disruption of intracellular calcium homeostasis in human neuronal cell line SHSY5Y.

The persistent xenobiotic agent 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces neurotoxic effects that alters neurodevelopment and behavior both during development and adulthood. There are many ongoing efforts to determine the molecular mechanisms of TCDD-mediated neurotoxicity, the signaling pathways involved and its molecular targets in neurons. In this work, we have used SHSY5Y human neuroblastoma cells to characterize the TCDD-induced toxicity. TCDD produces a loss of viability linked to an increased caspase-3 activity, PARP-1 fragmentation, DNA laddering, nuclear fragmentation and hypodiploid (apoptotic) DNA content, in a similar way than staurosporine, a prototypical molecule of apoptosis induction. In addition, TCDD produces a decrease of mitochondrial membrane potential and an increase of intracellular calcium concentration (P < 0.05). Finally, based on the high lipophilic properties of the dioxin, we test the TCDD effect on the membrane integrity using sarcoplasmic reticulum vesicles as a model. TCDD produces calcium efflux through the membrane and an anisotropy decrease (P < 0.05) that reflects an increase in membrane fluidity. Altogether these results support the hypothesis that TCDD toxicity in SHSY5Y neuroblastoma cells provokes the disruption of calcium homeostasis, probably affecting membrane structural integrity, leading to an apoptotic process.

Ablación del nodo aurículo-ventricular por radiofrecuencia en una paciente con cirrosis / Radiofrequency catheter ablation of the atrioventricular junction in a cirrhotic patient

El uso de la radiofrecuencia en el tratamiento de las arritmias, ha cambiado las perspectivas en este capítulo de la cardiología, otrora limitado seriamente por el pobre alcance terapéutico de los fármacos antiarrítmicos y el quirúrgico, que en el caso de una cirugía mayor, quedaba restringida a un selecto grupo de pacientes. El empleo de esta técnica, en sujetos portadores de patologías que no sean consecuencia de una cardiopatía estructural, parece ofrecer un beneficio terapéutico valioso. Presentamos el caso de una mujer con daño hepático importante y sin cardiopatía subyacente, que estaba gravemente limitada por paroxismo de taquiarritmias supraventriculares diversas rebeldes a tratamiento farmacológico. Fue sometida a una ablación exitosa del nodo atrio-ventricular por medio de radiofrecuencia. La paciente fue egresada sin medicación antiarrítmica, y con un sistema definitivo de marcapaso. Hubo evidentes mejorías clínicas y de calidad de vida de nuestra paciente que permitió extender los beneficios más alla de la simple resolución de los trastornos del ritmo