Sergei B. Koralov

Ten-Eleven-Translocation 2 (TET2) negatively regulates homeostasis and differentiation of hematopoietic stem cells in mice

The Ten-Eleven-Translocation 2 (TET2) gene encodes a member of TET family enzymes that alters the epigenetic status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Somatic loss-of-function mutations of TET2 are frequently observed in patients with diverse myeloid malignancies, including myelodysplastic syndromes, myeloproliferative neoplasms, and chronic myelomonocytic leukemia. By analyzing mice with targeted disruption of the Tet2 catalytic domain, we show here that Tet2 is a critical regulator of self-renewal and differentiation of hematopoietic stem cells (HSCs). Tet2 deficiency led to decreased genomic levels of 5hmC and augmented the size of the hematopoietic stem/progenitor cell pool in a cell-autonomous manner. In competitive transplantation assays, Tet2-deficient HSCs were capable of multilineage reconstitution and possessed a competitive advantage over wild-type HSCs, resulting in enhanced hematopoiesis into both lymphoid and myeloid lineages. In vitro, Tet2 deficiency delayed HSC differentiation and skewed development toward the monocyte/macrophage lineage. Our data indicate that Tet2 has a critical role in regulating the expansion and function of HSCs, presumably by controlling 5hmC levels at genes important for the self-renewal, proliferation, and differentiation of HSCs.

Halofuginone Inhibits TH17 Cell Differentiation by Activating the Amino Acid Starvation Response

Starving T Cells The TH17 lineage of CD4+ helper T cells, characterized by the ability to secrete IL-17, is an important mediator of inflammation and autoimmunity. Dampening the responses of these cells or inhibiting their differentiation is of great therapeutic interest. Sundrud et al. (p. 1334; see the Perspective by Blander and Amsen) now show that the small molecule halofuginone inhibits the differentiation of TH17 cells but not other CD4+ T cell helper lineages both in vitro and in a mouse model of multiple sclerosis. This selective inhibition was mediated by activation of the amino acid starvation response. Amino acid depletion mimicked the effects of halofuginone, whereas excess amino acids rescued TH17 differentiation. The results highlight the importance of amino acid metabolism in regulating inflammation. Activation of the amino acid starvation response inhibits differentiation of a subset of inflammatory T cells. A central challenge for improving autoimmune therapy is preventing inflammatory pathology without inducing generalized immunosuppression. T helper 17 (TH17) cells, characterized by their production of interleukin-17, have emerged as important and broad mediators of autoimmunity. Here we show that the small molecule halofuginone (HF) selectively inhibits mouse and human TH17 differentiation by activating a cytoprotective signaling pathway, the amino acid starvation response (AAR). Inhibition of TH17 differentiation by HF is rescued by the addition of excess amino acids and is mimicked by AAR activation after selective amino acid depletion. HF also induces the AAR in vivo and protects mice from TH17-associated experimental autoimmune encephalomyelitis. These results indicate that the AAR pathway is a potent and selective regulator of inflammatory T cell differentiation in vivo.

Activation of Stat3 Signaling in AgRP Neurons Promotes Locomotor Activity

Leptin, an adipocyte-derived hormone, acts on hypothalamic neurons located in the arcuate nucleus (ARC) of the hypothalamus to regulate energy homeostasis. One of the leptin-regulated neuronal subtypes in the ARC are agouti-related peptide (AgRP)-expressing neurons, which are involved in the regulation of food intake and are directly inhibited by leptin. Leptin activates the signal transducer and activator of transcription 3 (Stat3), but the role of Stat3 in the regulation of AgRP neurons is unclear. Here we show that mice expressing a constitutively active version of Stat3 selectively in AgRP neurons are lean and exhibit relative resistance to diet-induced obesity. Surprisingly, this phenotype arises from increased locomotor activity in the presence of unaltered AgRP expression. These data demonstrate that Stat3-dependent signaling in AgRP neurons in the ARC controls locomotor activity independently of AgRP regulation.

TET proteins and 5-methylcytosine oxidation in hematological cancers

DNA methylation has pivotal regulatory roles in mammalian development, retrotransposon silencing, genomic imprinting, and X‐chromosome inactivation. Cancer cells display highly dysregulated DNA methylation profiles characterized by global hypomethylation in conjunction with hypermethylation of promoter CpG islands that presumably lead to genome instability and aberrant expression of tumor suppressor genes or oncogenes. The recent discovery of ten‐eleven‐translocation (TET) family dioxygenases that oxidize 5mC to 5‐hydroxymethylcytosine (5hmC), 5‐formylcytosine (5fC), and 5‐carboxylcytosine (5caC) in DNA has led to profound progress in understanding the mechanism underlying DNA demethylation. Among the three TET genes, TET2 recurrently undergoes inactivating mutations in a wide range of myeloid and lymphoid malignancies. TET2 functions as a bona fide tumor suppressor particularly in the pathogenesis of myeloid malignancies resembling chronic myelomonocytic leukemia (CMML) and myelodysplastic syndromes (MDS) in human. Here we review diverse functions of TET proteins and the novel epigenetic marks that they generate in DNA methylation/demethylation dynamics and normal and malignant hematopoietic differentiation. The impact of TET2 inactivation in hematopoiesis and various mechanisms modulating the expression or activity of TET proteins are also discussed. Furthermore, we also present evidence that TET2 and TET3 collaborate to suppress aberrant hematopoiesis and hematopoietic transformation. A detailed understanding of the normal and pathological functions of TET proteins may provide new avenues to develop novel epigenetic therapies for treating hematological malignancies.

IL35-Producing B Cells Promote the Development of Pancreatic Neoplasia

UNLABELLED A salient feature of pancreatic ductal adenocarcinoma (PDAC) is an abundant fibroinflammatory response characterized by the recruitment of immune and mesenchymal cells and the consequent establishment of a protumorigenic microenvironment. Here, we report the prominent presence of B cells in human pancreatic intraepithelial neoplasia and PDAC lesions as well as in oncogenic Kras-driven pancreatic neoplasms in the mouse. The growth of orthotopic pancreatic neoplasms harboring oncogenic Kras was significantly compromised in B-cell-deficient mice (μMT), and this growth deficiency could be rescued by the reconstitution of a CD1d(hi)CD5(+) B-cell subset. The protumorigenic effect of B cells was mediated by their expression of IL35 through a mechanism involving IL35-mediated stimulation of tumor cell proliferation. Our results identify a previously unrecognized role for IL35-producing CD1d(hi)CD5(+) B cells in the pathogenesis of pancreatic cancer and underscore the potential significance of a B-cell/IL35 axis as a therapeutic target. SIGNIFICANCE This study identifies a B-cell subpopulation that accumulates in the pancreatic parenchyma during early neoplasia and is required to support tumor cell growth. Our findings provide a rationale for exploring B-cell-based targeting approaches for the treatment of pancreatic cancer.

T cell-derived IL-17 mediates epithelial changes in the airway and drives pulmonary neutrophilia.

Th17 cells are a proinflammatory subset of effector T cells that have been implicated in the pathogenesis of asthma. Their production of the cytokine IL-17 is known to induce local recruitment of neutrophils, but the direct impact of IL-17 on the lung epithelium is poorly understood. In this study, we describe a novel mouse model of spontaneous IL-17–driven lung inflammation that exhibits many similarities to asthma in humans. We have found that STAT3 hyperactivity in T lymphocytes causes an expansion of Th17 cells, which home preferentially to the lungs. IL-17 secretion then leads to neutrophil infiltration and lung epithelial changes, in turn leading to a chronic inflammatory state with increased mucus production and decreased lung function. We used this model to investigate the effects of IL-17 activity on airway epithelium and identified CXCL5 and MIP-2 as important factors in neutrophil recruitment. The neutralization of IL-17 greatly reduces pulmonary neutrophilia, underscoring a key role for IL-17 in promoting chronic airway inflammation. These findings emphasize the role of IL-17 in mediating neutrophil-driven pulmonary inflammation and highlight a new mouse model that may be used for the development of novel therapies targeting Th17 cells in asthma and other chronic pulmonary diseases.

Elucidating the role of interleukin-17F in cutaneous T-cell lymphoma

Inappropriately regulated expression of interleukin (IL)-17A is associated with the development of inflammatory diseases and cancer. However, little is known about the role of other IL-17 family members in carcinogenesis. Here, we show that a set of malignant T-cell lines established from patients with cutaneous T-cell lymphoma (CTCL) spontaneously secrete IL-17F and that inhibitors of Janus kinases and Signal transducer and activator of transcription 3 are able to block that secretion. Other malignant T-cell lines produce IL-17A but not IL-17F. Upon activation, however, some of the malignant T-cell lines are able to coexpress IL-17A and IL-17F, leading to formation of IL-17A/F heterodimers. Clinically, we demonstrate that IL-17F messenger RNA expression is significantly increased in CTCL skin lesions compared with healthy donors and patients with chronic dermatitis. IL-17A expression is also increased and a significant number of patients express high levels of both IL-17A and IL-17F. Concomitantly, we observed that the expression of the IL-17 receptor is significantly increased in CTCL skin lesions compared with control subjects. Importantly, analysis of a historic cohort of 60 CTCL patients indicates that IL-17F expression is associated with progressive disease. These findings implicate IL-17F in the pathogenesis of CTCL and suggest that IL-17 cytokines and their receptors may serve as therapeutic targets.

Tyk2 and Stat3 Regulate Brown Adipose Tissue Differentiation and Obesity

Mice lacking the Jak tyrosine kinase member Tyk2 become progressively obese due to aberrant development of Myf5+ brown adipose tissue (BAT). Tyk2 RNA levels in BAT and skeletal muscle, which shares a common progenitor with BAT, are dramatically decreased in mice placed on a high-fat diet and in obese humans. Expression of Tyk2 or the constitutively active form of the transcription factor Stat3 (CAStat3) restores differentiation in Tyk2(-/-) brown preadipocytes. Furthermore, Tyk2(-/-) mice expressing CAStat3 transgene in BAT also show improved BAT development, normal levels of insulin, and significantly lower body weights. Stat3 binds to PRDM16, a master regulator of BAT differentiation, and enhances the stability of PRDM16 protein. These results define Tyk2 and Stat3 as critical determinants of brown fat lineage and suggest that altered levels of Tyk2 are associated with obesity in both rodents and humans.

Direct in vivo VH to JH rearrangement violating the 12/23 rule

V(D)J recombination at the immunoglobulin heavy chain (IgH) locus follows the 12/23 rule to ensure the correct assembly of the variable region gene segments. Here, we report characterization of an in vivo model that allowed us to study recombination violating the 12/23 rule, namely a mouse strain lacking canonical D elements in its IgH locus. We demonstrate that VH to JH joining can support the generation of all B cell subsets. However, the process is inefficient in that B cells and antibodies derived from the DH-less allele are not detectable if the latter is combined with a wild-type IgH allele. There is no preferential usage of any particular VH gene family or JH element in VHJH junctions, indicating that 23/23-guided recombination is possible, but is a low frequency event at the IgH locus in vivo.

Simultaneous deletion of the methylcytosine oxidases Tet1 and Tet3 increases transcriptome variability in early embryogenesis

Significance Development of preimplantation embryos entails global DNA demethylation on the zygotic genome. The original thought was that TET-deficient embryos would be unlikely to survive early embryogenesis because they would be unable to mediate genome-wide demethylation in the zygote and preimplantation embryo. However, mice lacking the individual TET proteins Tet1, Tet2, or Tet3 have survived until birth and beyond, suggesting redundancy among TET proteins in the early embryogenesis. Here we report that preimplantation embryos doubly disrupted for Tet1 and Tet3 show abnormal embryonic phenotypes, whose incomplete penetrance correlates with a high variability of transcriptional profiles and DNA methylation status. Our data suggest that in addition to facilitating DNA demethylation, TET proteins and oxidized methylcytosines may regulate the consistency of gene transcription during embryogenesis. Dioxygenases of the TET (Ten-Eleven Translocation) family produce oxidized methylcytosines, intermediates in DNA demethylation, as well as new epigenetic marks. Here we show data suggesting that TET proteins maintain the consistency of gene transcription. Embryos lacking Tet1 and Tet3 (Tet1/3 DKO) displayed a strong loss of 5-hydroxymethylcytosine (5hmC) and a concurrent increase in 5-methylcytosine (5mC) at the eight-cell stage. Single cells from eight-cell embryos and individual embryonic day 3.5 blastocysts showed unexpectedly variable gene expression compared with controls, and this variability correlated in blastocysts with variably increased 5mC/5hmC in gene bodies and repetitive elements. Despite the variability, genes encoding regulators of cholesterol biosynthesis were reproducibly down-regulated in Tet1/3 DKO blastocysts, resulting in a characteristic phenotype of holoprosencephaly in the few embryos that survived to later stages. Thus, TET enzymes and DNA cytosine modifications could directly or indirectly modulate transcriptional noise, resulting in the selective susceptibility of certain intracellular pathways to regulation by TET proteins.