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The capacity of the brain to elicit sustained remission of hyperglycemia in rodent models of type 2 diabetes following intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1) is well established. Here, we show that following icv FGF1 injection, hypothalamic signaling by extracellular signal-regulated kinases 1 and 2 (ERK1/2), members of the mitogen-activated protein kinase (MAPK) family is induced for at least 24h. Further, we show that in diabetic Lepob/ob mice, this prolonged response is required for the sustained antidiabetic action of FGF1, since it is abolished by sustained (but not acute) pharmacologic blockade of hypothalamic MAPK/ERK signaling. We also demonstrate that FGF1 R50E, a FGF1 mutant that activates FGF receptors but induces only transient hypothalamic MAPK/ERK signaling, fails to mimic the sustained glucose lowering induced by FGF1. These data identify sustained activation of hypothalamic MAPK/ERK signaling as playing an essential role in the mechanism underlying diabetes remission induced by icv FGF1 administration.

In rodent models of type 2 diabetes (T2D), sustained remission of hyperglycemia can be induced by a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1), and the mediobasal hypothalamus (MBH) was recently implicated as the brain area responsible for this effect. To better understand the cellular response to FGF1 in the MBH, we sequenced >79,000 single-cell transcriptomes from the hypothalamus of diabetic Lepob/ob mice obtained on Days 1 and 5 after icv injection of either FGF1 or vehicle. A wide range of transcriptional responses to FGF1 was observed across diverse hypothalamic cell types, with glial cell types responding much more robustly than neurons at both time points. Tanycytes and ependymal cells were the most FGF1-responsive cell type at Day 1, but astrocytes and oligodendrocyte lineage cells subsequently became more responsive. Based on histochemical and ultrastructural evidence of enhanced cell-cell interactions between astrocytes and Agrp neurons (key components of the melanocortin system), we performed a series of studies showing that intact melanocortin signaling is required for the sustained antidiabetic action of FGF1. These data collectively suggest that hypothalamic glial cells are leading targets for the effects of FGF1 and that sustained diabetes remission is dependent on intact melanocortin signaling., In rodent models of type 2 diabetes, sustained remission of hyperglycemia can be induced by FGF1 action in the mediobasal hypothalamus. Here, the authors show that FGF1-injection is followed by marked changes in glial cell populations and that the sustained glycemic response is dependent on intact melanocortin signaling.

Summary Gain-of-function Notch mutations are recurrent in mature small B cell lymphomas such as mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL), but the Notch target genes that contribute to B cell oncogenesis are largely unknown. We performed integrative analysis of Notch-regulated transcripts, genomic binding of Notch transcription complexes, and genome conformation data to identify direct Notch target genes in MCL cell lines. This B cell Notch regulome is largely controlled through Notch-bound distal enhancers and includes genes involved in B cell receptor and cytokine signaling and the oncogene MYC , which sustains proliferation of Notch-dependent MCL cell lines via a Notch-regulated lineage-restricted enhancer complex. Expression of direct Notch target genes is associated with Notch activity in an MCL xenograft model and in CLL lymph node biopsies. Our findings provide key insights into the role of Notch in MCL and other B cell malignancies and have important implications for therapeutic targeting of Notch-dependent oncogenic pathways.

Lasting remission of hyperglycemia can be achieved in rodent models of type 2 diabetes by a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF-1), and the mediobasal hypothalamus (MBH) was recently identified as a target for this effect. To investigate the cellular basis of FGF-1 action in the MBH, we combined whole tissue RNA-sequencing with large-scale single cell and single nuclei RNA-sequencing to generate >60,000 single cell transcriptomes from diabetic ob/ob mice harvested 5d after a single icv injection of either FGF-1 or vehicle. Of the 4 known FGF receptor genes, 3 were expressed in the MBH, primarily by glial cells rather than neurons. Employing weighted gene co-expression network analysis, distinct modules that correlated with icv FGF-1 treatment were identified, again primarily in glial cells. In astrocytes, the response to FGF-1 closely paralleled the neuroprotective “A2” transcriptional phenotype induced by stroke, and both the proportion of differentiating oligodendrocytes and genes involved in extracellular matrix remodeling of the perivascular space were also upregulated by FGF-1. By comparison, the neuronal response to icv FGF-1 was one of generalized inhibition, including decreased expression of Agrp and Pmch (encoding agouti-related peptide and pro-melanin-concentrating hormone (MCH), respectively). Since Agrp and MCH neurons are activated in ob/ob mice, and since this effect predisposes to hyperglycemia, these findings support a model in which sustained inhibition of these and perhaps other neuronal subsets underlies diabetes remission induced by icv FGF-1. Moreover, this neuronal inhibition appears to be driven by neuroprotective glial responses elicited by FGF-1. These data add to growing evidence of a crucial role for neuron-glia interactions in hypothalamic control of glucose homeostasis. Disclosure M.A. Bentsen: None. D. Rausch: None. Z. Mirzadeh: Consultant; Self; Novo Nordisk A/S. J. Scarlett: None. J.M. Brown: None. K.M. Alonge: Research Support; Self; Novo Nordisk Inc. T.H. Meek: Employee; Self; Novo Nordisk Inc. A. Secher: Employee; Spouse/Partner; Gubra. Employee; Self; Novo Nordisk A/S. Speaker's Bureau; Spouse/Partner; Gubra. Stock/Shareholder; Self; Novo Nordisk A/S. R. Jorgensen: Employee; Self; Novo Nordisk A/S. T. Pers: None. M.W. Schwartz: Consultant; Self; Novo Nordisk A/S. Research Support; Self; Novo Nordisk A/S. Funding National Institutes of Health; Novo Nordisk Foundation; Lundbeck Foundation; Novo Nordisk A/S

While much is known about the enzymes that deposit and remove epigenetic modifications, less is known about the trans-acting system that determines when and where these modifications occur. By looking at four diverse... The epigenetic landscape varies greatly among cell types. Although a variety of writers, readers, and erasers of epigenetic features are known, we have little information about the underlying regulatory systems controlling the establishment and maintenance of these features. Here, we have explored how natural genetic variation affects the epigenome in mice. Studying levels of H3K4me3, a histone modification at sites such as promoters, enhancers, and recombination hotspots, we found tissue-specific trans-regulation of H3K4me3 levels in four highly diverse cell types: male germ cells, embryonic stem cells, hepatocytes, and cardiomyocytes. To identify the genetic loci involved, we measured H3K4me3 levels in male germ cells in a mapping population of 59 BXD recombinant inbred lines. We found extensive trans-regulation of H3K4me3 peaks, including six major histone quantitative trait loci (QTL). These chromatin regulatory loci act dominantly to suppress H3K4me3, which at hotspots reduces the likelihood of subsequent DNA double-strand breaks. QTL locations do not correspond with genes encoding enzymes known to metabolize chromatin features. Instead their locations match clusters of zinc finger genes, making these possible candidates that explain the dominant suppression of H3K4me3. Collectively, these data describe an extensive, set of chromatin regulatory loci that control the epigenetic landscape.

Gain-of-function mutations in Notch receptor genes occur in 10-15% of cases of chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), and are associated with inferior clinical outcomes. Nearly all Notch mutations reported in B cell tumors lead to loss of the C-terminal negative regulatory PEST domain and result in stabilization of the activated form of Notch (intracellular Notch [ICN]), whereas mutations that lead to ligand-independent Notch activation (which are common in T cell acute lymphoblastic leukemia [T-ALL]) are rare. ICN can be detected in tumor cells within lymph nodes of >80% of patients with CLL, suggesting that Notch may have a broader oncogenic role than the incidence of Notch mutations would suggest. However, the downstream targets of Notch in B-cell tumors have not been identified. We used a gamma-secretase inhibitor (GSI) washout strategy to determine the immediate, direct effects of Notch activation in three MCL cell lines with Notch gain-of-function mutations, including two cell lines with unusual Notch gene rearrangements that lead to ligand-independent Notch activation, as well as a third line with a Notch PEST domain mutation in which signaling was activated with recombinant Notch ligand. Using these models, we identified likely direct target genes and their associated genomic Notch response elements using RNA-seq and ChIP-Seq in the Notch-on and Notch-off states. Most of these response elements corresponded to long-range enhancers that showed Notch-dependent changes in H3K27 acetylation, and were bound by components of the Notch transcription complex (NTC) in both cell lines. We confirmed these associations by performing ChIP-Seq on primary CLL and MCL biopsies, and by identifying specific looping interactions with Notch target gene promoters in public genome-wide proximity ligation datasets (RNA Pol2 ChIA-PET) from a lymphoblastoid cell line expressing the EBV-encoded Notch surrogate protein EBNA2. MYC was among the most strongly Notch-activated genes in Notch-dependent MCL cell lines and was associated with NTC binding at two B cell-specific 5' enhancers distinct from the Notch-dependent MYC enhancer previously identified in T-ALL. MCL cell line proliferation was blocked by Cas9 nuclease or epigenetic repressors targeting the 5' MYC enhancers, whereas cells were rescued from Notch inhibition by GSI via transduction with MYC. Gene set enrichment analysis of other direct Notch target genes identified in MCL models showed enrichment for regulators of B cell receptor (BCR) signaling, including the Src family kinase genes FYN, LYN, and BLK, and the signaling complex adaptor BLNK, as well as regulators of CD40 and cytokine signaling. RNA-seq analysis of primary CLL lymph node biopsies revealed significantly higher expression of many Notch target genes in biopsies with high levels of ICN. To functionally validate Notch target genes in primary tumors, we co-cultured CLL and MCL cells obtained from peripheral blood with Notch ligand-expressing stromal cells in the presence ("notch off") or absence ("notch on") of GSI, and demonstrated increased expression of Notch target genes, including MYC, in the "notch-on" cells. Furthermore, "notch-on" CLL cells showed increased phosphorylation of the BCR signaling intermediates SYK and PLCg2 upon BCR crosslinking compared to GSI-treated cells. Finally, we validated Notch-dependent regulation of target genes in vivo in a patient-derived xenograft model of NOTCH1-mutant MCL. Notch target gene expression was significantly higher in MCL cells within the spleen versus bone marrow or blood, but was markedly reduced in animals treated for five days with GSI. Additional xenograft studies are ongoing, and will be described at the meeting. Our data link active Notch signaling to two well-characterized oncogenic drivers in B cell lymphoma, MYC and BCR signaling, and may have important implications for the development of treatment strategies involving Notch antagonists and other targeted therapeutics, such as BCR targeting agents. Disclosures Weinstock: Novartis: Consultancy, Research Funding.

Recurrent gain-of-function mutations in genes encoding Notch receptors are associated with poor clinical outcome in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), but genome-wide functional targets of Notch signaling in B cells have not been characterized. We identified genome-wide binding sites for Notch transcription factor (TF) complexes, using antibodies specific for intracellular NOTCH1 and its binding partner RBPJ, in CLL and MCL lymph node biopsies, and lymphoma cell lines. We employed a gamma-secretase inhibitor washout strategy to rapidly modulate mutant NOTCH1 protein activation in complementary lymphoma cell line models of ligand-dependent and ligand-independent Notch signaling, and performed RNA-sequencing and genome-wide enhancer acetylation profiling in both the “notch on” and “notch off” states. These data identify a common set of functional Notch target genes in B-cell lymphoma that includes both canonical Notch targets as well as B-cell-specific target genes. The latter are frequently associated with adjacent B-cell-specific enhancers that show direct Notch TF binding and Notch-signaling-dependent histone acetylation. Notch-activated target genes include MYC and other TFs implicated in B-cell lymphoma, and are significantly enriched for mediators of targetable oncogenic lymphoma signaling pathways, (B-cell receptor, toll-like receptor, JAK-STAT, MAP kinase, and G-protein signaling pathways, all FDR q-value < 1e-3 in KEGG and / or Reactome analyses). Many B-cell Notch target genes show significantly increased expression in lymph nodes from patients with NOTCH1 mutant vs. wild-type CLL. Notch target genes are also up-regulated in lymph node- versus peripheral blood-derived CLL cells, consistent with immunohistochemical evidence for microenvironment-dependent Notch signaling activation in the CLL lymph node. Combined small-molecule inhibition of Notch and B-cell receptor signaling showed a synergistic anti-proliferative effect in Notch-dependent lymphoma cells. Our data reveal the functional regulome of Notch signaling in small B-cell lymphoma, and may have implications for the role of Notch signaling in normal B-cell development. These findings suggest novel strategies for rational combination therapy in CLL and MCL. Citation Format: Russell J. Ryan, Jelena Petrovic, Dylan M. Rausch, Winston Lee, Michael Kluk, Laura Donohue, Shawn Gillespie, Jon C. Aster, Warren S. Pear, Bradley E. Bernstein. Notch signaling activates B-cell specific enhancers to drive oncogene targets in B-cell lymphoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 886.

The study of brain development in humans is limited by the lack of tissue samples and suitable in vitro models. Here, we model early human neural tube development using human embryonic stem cells cultured in a microfluidic device. The approach, named microfluidic-controlled stem cell regionalization (MiSTR), exposes pluripotent stem cells to signaling gradients that mimic developmental patterning. Using a WNT-activating gradient, we generated a neural tissue exhibiting progressive caudalization from forebrain to midbrain to hindbrain, including formation of isthmic organizer characteristics. Single-cell transcriptomics revealed that rostro-caudal organization was already established at 24 h of differentiation, and that the first markers of a neural-specific transcription program emerged in the rostral cells at 48 h. The transcriptomic hallmarks of rostro-caudal organization recapitulated gene expression patterns of the early rostro-caudal neural plate in mouse embryos. Thus, MiSTR will facilitate research on the factors and processes underlying rostro-caudal neural tube patterning.