Fetal Liver Cells Research Articles

SATB1 Regulates GATA1 Protein Expression in Early Hematopoiesis and Is Deregulated in Diamond Blackfan Anemia

The induction of the master erythroid transcription factor, GATA1 during early erythropoiesis is critical for efficient red blood cell production. However, GATA1 is expressed at low levels in hematopoietic stem cells (HSCs) and is moderately induced at both the common myeloid progenitor (CMP) and megakaryocyte/erythroid progenitor (MEP) stages prior to lineage commitment. Diamond Blackfan Anemia is a rare disease, usually associated with ribosomal gene mutations, leading to significant decrease in GATA1 expression and block in early committed erythroid differentiation. Mild defects in other myeloid lineages are also observed, with limited clinical relevance. The importance of GATA1 downregulation in disease pathogenesis is manifested by rare patients with DBA carrying GATA1 mutations. To understand signaling pathways that contribute to the pathogenesis DBA, we perform RNA-seq with mRNA from human CD34+ fetal liver cells and found that the chromatin organizer, Special AT-rich sequence binding protein 1 (SATB1) was prematurely downregulated. Our results further demonstrated that sustained SATB1 expression is critical to maintain required levels of GATA1 protein at both the CMP and MEP stages of differentiation, but not in committed erythroid progenitors. In mice, SATB1 is modestly expressed in HSCs and upregulated during lymphopoiesis. SATB1 is downregulated during myeloid and erythroid differentiation and antagonizes myeloid and erythroid expansion. However, in human hematopoietic stem and progenitor cells (HSPCs), SATB1 is required for efficient expansion of these lineages. SATB1 maintains 78% expression in human MEPs, but is undetectable in early committed erythroid progenitors. In RPS19-insufficient human HSPCs, SATB1 was downregulated to 22% in MEPs (p=0.02). Re-expression of SATB1 corrected a significant subset of deregulated mRNAs, including GATA1 regulators. In the absence of SATB1, one such GATA1 regulator, heat shock protein 70 (HSP70), failed to be induced in ribosome-competent human MEPs, reducing GATA1 protein expression by 35.7% (p= 0.026). Concurrently, MEP expansion was inhibited by 64.5% (p=0.023), reducing erythroid and megakaryocyte expansion by 18.2% (p=0.024) and 20.4% (p=0.183) respectively. SATB1 facilitated the formation of chromatin loops linking together an enhancer element with HSP70 promoters required for HSP70 induction in early differentiation. Although GATA1 is significantly upregulated in committed erythroid progenitors, RPS19-insufficient human CD235+ erythrocytes express GATA1 28.4% of controls (p= 0.011). SATB1 re-expression increased GATA1 expression to 31.4% (p=0.089). Similarly, SATB1 re-expression increased CD235+ expansion from 13.9% to 39.5% (p=0.02) compared to controls. Our data indicate that premature SATB1 downregulation contributes to erythroid failure in DBA by reducing MEP expansion, but aberrant GATA1 expression observed in more mature erythrocytes is predominantly SATB1-independent. However, SATB1-re-expression improved CD11b+ myeloid expansion from 81.2% to 90.4% (p=0.045) and CD41a+ megakaryocyte expansion from 76.7% to 214.7% (p=0.038) respectively. Our results demonstrate that SATB1 plays an important role in human hematopoiesis and is an important regulator of GATA1. Disclosures Glader: Agios Pharmaceuticals, Inc.: Consultancy.

Transcriptional, Protein-Level and Functional Profiling of Human Fetal Liver (FL)-Derived Hematopoietic Stem Cells (HSCs) at Single Cell Resolution

Intro: The complex and tightly regulated process of human hematopoietic development culminates in the production of hematopoietic stem cells (HSCs), which subsequently acquire functional competence and undergo expansion in the fetal liver (FL). The establishment of a high-resolution molecular signature of FL HSCs provides insights into HSC biology with potential utility in the purification and expansion of engraftable HSCs ex vivo and the generation of HSCs from pluripotent cell sources. To profile HSCs at this developmental stage, we performed CITE-Seq, a technique that combines single cell RNA sequencing (scRNAseq) and cell surface marker interrogation using oligo-tagged antibodies to simultaneously map transcriptional and protein-level expression in individual cells. To connect expression profiles with functional engraftment, we have coupled this with transplantation assays in immunocompromised mice. Methods: In these studies, three populations of human FL cells were used: CD34- cells, CD34+ cells and CD34+ cells furtherenrichedby expression of GPI-80, a marker tightly linked to engraftment potential, to explicitly identify HSCs capable of long-term engraftment. These populations were stained with a panel of oligo-tagged antibodies, processed via the 10X Genomics platform, and sequenced (26,407 total cells). Results: Transplantation experiments using the same sorted fractions that were assayed by CITE-seq revealed superior engraftment potential of the GPI-80+ fraction, and thus enrichment for bona fide HSCs at the functional level. This functional signature coincided with enrichment for known HSC markers such as ITGA6 (CD49f), PROCR (EPCR), CD164, MLLT3, HLF, CLEC9A and HMGA2 at the transcriptional level. As such, by profiling >7000 GPI-80+ cells, we have achieved unprecedented resolution of the engraftable HSC compartment within the FL. Combined analysis of all captured FL fractions accurately recapitulated the hematopoietic landscape of the FL at this developmental stage, representing the expected hematopoietic lineages and cell types. To gain further insight into FL HSCs, we next focused on the CD34+ HSC/progenitor compartment where we tracked cluster dynamics upon functional HSC enrichment between the CD34+ bulk and GPI-80+ sample. We noted a prominent (4-fold) increase in a cluster marked by enrichment for genes including RGCC, LMNA, VIM, ID1 and ID3 as well as components of the AHR pathway, suggesting that this expression profile strongly correlates with engraftment potential. Notably, LMNA is expressed in postnatal HSCs and its expression has been shown to decrease upon aging (Grigoryan et al., 2018). In line with this, we also found that LMNA is more highly expressed in our prenatal FL HSPCs compared to postnatal HSPCs. This data suggests a potential role for LMNA in endowing FL HSCs with their superior engraftment potential compared to postnatal HSCs. To complement our transcriptomic characterization of engraftment potential, we also collected cell surface marker expression data based on sequencing of a series of antibody-derived tags (ADTs). This additional layer of information uncovered expression patterns that weren't readily apparent based on mRNA expression data and inspired us to use this ADT information to gate out populations of interest via in silico sorting. This enabled us to compare the transcriptional profiles associated with well-described HSC enrichment signatures to assess whether they represent equivalent cell populations. We compared CD34+CD90+CD49f+ (~Notta et al., 2011) vs CD34+CD133+GPI-80+ (~Sumide et al., 2018) vs CD34+EPCR+ (~Subramaniam et al., 2019) in silico sorted cells and found a strong overlap in enriched genes, suggesting that the transcriptomic signature corresponding to engraftment potential identified in this work is not exclusive to GPI-80+ sorted cells but represents engraftable HSCs beyond this enrichment strategy. Conclusion: We have achieved unprecedented resolution of the engraftable HSC compartment in the human FL. Combining transcriptional profiling of the engraftment potential of FL HSCs with cell surface level expression data provides an in-depth characterization of this unique and developmentally relevant HSC source. This data will be valuable in optimizing the purification and expansion of engraftable HSCs ex vivo as well as in guiding the in vitro generation of HSCs from pluripotent cell sources. Disclosures No relevant conflicts of interest to declare.

DOCK8 controls survival of group 3 innate lymphoid cells in the gut through Cdc42 activation.

Innate lymphoid cells (ILCs) are a family of developmentally related leukocytes that rapidly secrete polarized sets of cytokines to combat infection and promote tissue repair at mucosal barriers. Among them, group 3 ILCs (ILC3s) play an important role in maintenance of the gut homeostasis by producing IL-22, and their development and function critically depend on the transcription factor RORγt. Although recent evidence indicates that RORγt+ ILC3s are reduced in the gut in the absence of the Cdc42 activator DOCK8 (dedicator of cytokinesis 8), the underlying mechanism remains unclear. We found that genetic deletion of Dock8 in RORγt+-lineage cells markedly reduced ILC3s in the lamina propria of the small intestine. By analyzing BrdU incorporation, it was revealed that DOCK8 deficiency did not affect the cell proliferation. Furthermore, when lineage marker-negative (Lin-) α4β7+ CD127+ RORγt- fetal liver cells were cultured with OP9 stromal cells in the presence of stem cell factor (SCF) and IL-7 in vitro, RORγt+ ILC3s normally developed irrespective of DOCK8 expression. However, DOCK8-deficient ILC3s exhibited a severe defect in survival of ILC3s under the condition with or without IL-7. Similar defects were observed when we analyzed Dock8VAGR mice having mutations in the catalytic center of DOCK8, thereby failing to activate Cdc42. Thus, DOCK8 acts in cell-autonomous manner to control survival of ILC3s in the gut through Cdc42 activation.

Identification of hepatic progenitor cells in the canine fetal liver

The liver plays essential roles in human and animal organisms, such as the storage, release, metabolism, and elimination of various endogenous or exogenous substances. Although its vital importance, few treatments are yet available when a hepatic failure occurs, and hence, the use of stem cells has arisen as a possible solution for both human and veterinary medicines. Previous studies have shown the existence of hepatic progenitor cells in human fetuses that were positive for EpCAM and NCAM. There is limited evidence, however, further identification and characterization of these cells in other species. Considering the similarity between dogs and humans regarding physiology, and also the increasing importance of developing new treatments for both veterinary and translational medicine, this study attempted to identify hepatic progenitor cells in canine fetal liver. For that, livers from canine fetuses were collected, cells were isolated by enzymatic digestion and cultured. Cells were characterized regarding morphology and expression of EpCAM, NCAM, Nestin, and Thy-1/CD90 markers. Our results suggest that it is possible to identify hepatic progenitor cells in the canine fetal liver; however, for therapeutic use, further techniques for cellular isolation and culture are necessary to obtain enriched populations of hepatic progenitors from the canine fetal liver.

Expansion of mouse primitive hematopoietic cells in three-dimensional cultures on chemically fixed stromal cell layers

To establish a practical and convenient method to expand hematopoietic cells (HCs), we applied chemically-fixed stromal cell layers formed within three-dimensional (3D) scaffolds to feeder of HC cultures. The HCs were expanded using two successive cultures. First, stromal cells were cultured within porous polymer scaffolds and formed tissue-engineered constructs (TECs); the scaffolds containing stromal cells, were fixed using aldehyde (formaldehyde or glutaraldehyde) or organic solvents (acetone, methanol or ethanol). Second, mouse fetal liver cells (FLCs), as a source of HCs, were cultured on the TECs for 2weeks, and the effects of fixative solutions on expansion of primitive HCs (c-kit+ and CD34+ cells) were examined. In the cultures on aldehyde-fixed TECs, primitive HCs were expanded 2.5- to 5.1-fold in the cultures on TECs fixed with glutaraldehyde, whereas no expansions were detected in those fixed with formaldehyde. However, we achieved expansion of primitive HCs > fivefold in the cultures using TECs fixed with organic solvents. Among these solvents, the highest expansions-of roughly tenfold-were obtained using acetone fixation. Ethanol-fixed TECs also supported the expansion of the primitive HCs well (6.6- to 8.0-fold). In addition to these sufficient expansions, the procedure and storage of fixed TECs is fairly easy. Thus, HC expansion on chemically-fixed TECs may be a practical method for expanding primitive HCs.

Effect of methylsulfonylmethane on oxidative stress and CYP3A93 expression in fetal horse liver cells.

ObjectiveStress-induced cytotoxicity caused by xenobiotics and endogenous metabolites induces the production of reactive oxygen species and often results in damage to cellular components such as DNA, proteins, and lipids. The cytochrome P450 (CYP) family of enzymes are most abundant in hepatocytes, where they play key roles in regulating cellular stress responses. We aimed to determine the effects of the antioxidant compound, methylsulfonylmethane (MSM), on oxidative stress response, and study the cytochrome P450 family 3 subfamily A (CYP3A) gene expression in fetal horse hepatocytes.MethodsThe expression of hepatocyte markers and CYP3A family genes (CYP3A89, CYP3A93, CYP3A94, CYP3A95, CYP3A96, and CYP3A97) were assessed in different organ tissues of the horse and fetal horse liver-derived cells (FHLCs) using quantitative reverse transcription polymerase chain reaction. To elucidate the antioxidant effects of MSM on FHLCs, cell viability, levels of oxidative markers, and gene expression of CYP3A were investigated in H2O2-induced oxidative stress in the presence and absence of MSM.ResultsFHLCs exhibited features of liver cells and simultaneously maintained the typical genetic characteristics of normal liver tissue; however, the expression profiles of some liver markers and CYP3A genes, except that of CYP3A93, were different. The expression of CYP3A93 specifically increased after the addition of H2O2 to the culture medium. MSM treatment reduced oxidative stress as well as the expression of CYP3A93 and heme oxygenase 1, an oxidative marker in FHLCs.ConclusionMSM could reduce oxidative stress and hepatotoxicity in FHLCs by altering CYP3A93 expression and related signaling pathways.

Hyperphosphorylation of fetal liver IGFBP-1 precedes slowing of fetal growth in nutrient-restricted baboons and may be a mechanism underlying IUGR.

In cultured fetal liver cells, insulin-like growth factor (IGF) binding protein (IGFBP)-1 hyperphosphorylation in response to hypoxia and amino acid deprivation is mediated by inhibition of mechanistic target of rapamycin (mTOR) and activation of amino acid response (AAR) signaling and casein kinase (CK)2. We hypothesized that fetal liver mTOR inhibition, activation of AAR and CK2, and IGFBP-1 hyperphosphorylation occur before development of intrauterine growth restriction (IUGR). Pregnant baboons were fed a control (C) or a maternal nutrient restriction (MNR; 70% calories of control) diet starting at gestational day (GD) 30 (term GD 185). Umbilical blood and fetal liver tissue were obtained at GD 120 (C, n = 7; MNR, n = 10) and 165 (C, n = 7; MNR, n = 8). Fetal weights were unchanged at GD 120 but decreased at GD 165 in the MNR group (-13%, P = 0.03). IGFBP-1 phosphorylation, as determined by parallel reaction monitoring mass spectrometry (PRM-MS), immunohistochemistry, and/or Western blot, was enhanced in MNR fetal liver and umbilical plasma at GD 120 and 165. IGF-I receptor autophosphorylationTyr1135 (-64%, P = 0.05) was reduced in MNR fetal liver at GD 120. Furthermore, fetal liver CK2 (α/α'/β) expression, CK2β colocalization, proximity with IGFBP-1, and CK2 autophosphorylationTyr182 were greater at GD 120 and 165 in MNR vs. C. Additionally, mTOR complex (mTORC)1 (p-P70S6KThr389, -52%, P = 0.05) and mTORC2 (p-AktSer473, -56%, P < 0.001) activity were decreased and AAR was activated (p-GCN2Thr898, +117%, P = 0.02; p-eIF2αSer51, +294%, P = 0.002; p-ERKThr202, +111%, P = 0.03) in MNR liver at GD 120. Our data suggest that fetal liver IGFBP-1 hyperphosphorylation, mediated by mTOR inhibition and both AAR and CK2 activation, is a key link between restricted nutrient and oxygen availability and the development of IUGR.

3144 – ECTOPIC EXPRESSION OF THE HOMEOBOX GENE MNX1 IS THE TRANSFORMING EVENT IN A MOUSE MODEL OF PEDIATRIC T(7;12)(Q36;P13) PEDIATRIC ACUTE MYELOID LEUKEMIA

Pediatric acute myeloid leukemia (AML) with the translocation t(7;12)(q36;p13) is a form of childhood leukemia associated with inferior outcome. In the current investigation we have studied the gene alterations that are induced by this chromosomal translocation, a gene fusion MNX1-ETV6 but also ectopic expression of the homeobox gene MNX1. In a murine bone marrow transplantation model, our results showed that ectopic expression of MNX1 was able to induce AML, but not the MNX1-ETV6 gene fusion. However, this transformation to AML was only seen using hematopoietic progenitor cells from fetal liver and not adult bone marrow cells. This was accompanied with an alteration of cell differentiation towards myeloid lineage, increased proliferation and colony formation capacity induced by MNX1. Our data also showed that ectopic expression of MNX1, and to a lower extend MNX1-ETV6 fusion, induced DNA damage and cell cycle arrest, where we saw an increased expression and binding of the MNX1 and the MNX1-ETV6 fusion to the gene CEP164 that has a critical role in cell cycle regulation and DNA damage response, and the transcriptional pioneer factor gene PBX1 that is important in development and differentiation. Furthermore, global histone modifications, specifically H3K4me3 and H3K27me, were induced by MNX1 but also the MNX1-ETV6 fusion. We could also see an enrichment of methylation/methionine proteins from mass spectrometry analysis of proteins associated with MNX1. In conclusion, these results suggest a possible mechanism by which MNX1 mediates its transforming effect through abnormal methylation of proteins that result in changed histone modifications and subsequent dysregulation of gene expression. Our finding that only fetal liver cells were able to transform into AML is also in concordance with the clinical finding that this AML subtype is only found in very young children.

3139 – TRANSCRIPTIONAL, PROTEIN-LEVEL AND FUNCTIONAL PROFILING OF HUMAN FETAL LIVER-DERIVED HEMATOPOIETIC STEM CELLS AT SINGLE CELL RESOLUTION

The complex and tightly regulated process of human hematopoietic development culminates in the production of hematopoietic stem cells (HSCs), which subsequently undergo expansion in the fetal liver (FL). The establishment of a high-resolution molecular signature of FL-HSCs would provide insights into HSC biology with potential utility in the purification and expansion of engraftable HSCs ex vivo and the generation of HSCs from pluripotent cell sources. To profile HSCs at this developmental stage, we performed CITE-Seq, a technique that combines single cell RNA sequencing (scRNAseq) and cell surface marker interrogation using oligo-tagged antibodies. To connect expression profiles with functional engraftment, we have coupled this with transplantation assays in immunocompromised mice. In these studies, three populations of human FL cells were used: CD34- cells, CD34+ cells and CD34+ cells further enriched by expression of GPI-80, a marker tightly linked to engraftment potential, to acquire additional resolution of HSCs capable of long-term engraftment. These populations were stained with a panel of oligo-tagged antibodies, processed via the 10X platform, and sequenced (26.582 total cells). Simultaneous transplantation experiments of these three populations revealed superior engraftment potential of the CD34+GPI-80+ fraction, and thus enrichment for bona fide HSCs at the functional level. This coincided with enrichment for known HSC markers such as ITGA6 (CD49f), PROCR (EPCR), CD164, MLLT3, HLF and HMGA2 at the transcriptional level. As such, by profiling profiling >7000 GPI-80+CD34+ cells, we have achieved unprecedented resolution of the engraftable HSC compartment within the FL. Studying the transcriptional profile in combination with protein level expression of key HSC-related genes, will allow for an accurate characterization of these cells and provide insights into the biology behind their remarkable engraftment potential.

STEM CELL CORRECTION OF TOXIC LIVER LESIONS

Assessment of the feasibility of fetal liver cells (FLC) for correction of a CCl4-induced acute toxic hepatitis was performed. Exposure to Cl4 in a dose of 3000 mg/kg caused well-defined centrilobular necrosis, hydropic, protein, carbohydrate, and adipose degeneration, as well as vascular disorders. The dynamics of morphological changes in the liver was studied, and the role of their intrinsic regenerative potential was assessed using pathomorphological, histochemical, and immunofluorescence methods. Phenotyping the cellular material was carried out to reveal expression of endodermal and mesodermal markers characteristic for the hepatic epithelium, hematopoietic stem cells, and mesenchymal cells. Three days after FLC transplantation, slowing down of necrotic and dystrophic processes in the liver parenchyma was observed. In some animals, the trabecular structure of the central hepatic zones was restored and, by 5th to 7th day of post-implantation, vascular disorders were eliminated. The resulting data can be considered as evidence for the use of fetal liver cells in the treatment of acute toxic hepatitis.

Bmi1 Maintains the Self-Renewal Property of Innate-like B Lymphocytes.

The self-renewal ability is a unique property of fetal-derived innate-like B-1a lymphocytes, which survive and function without being replenished by bone marrow (BM) progenitors. However, the mechanism by which IgM-secreting mature B-1a lymphocytes self-renew is poorly understood. In this study, we showed that Bmi1 was critically involved in this process. Although Bmi1 is considered essential for lymphopoiesis, the number of mature conventional B cells was not altered when Bmi1 was deleted in the B cell lineage. In contrast, the number of peritoneal B-1a cells was significantly reduced. Peritoneal cell transfer assays revealed diminished self-renewal ability of Bmi1-deleted B-1a cells, which was restored by additional deletion of Ink4-Arf, the well-known target of Bmi1 Fetal liver cells with B cell-specific Bmi1 deletion failed to repopulate peritoneal B-1a cells, but not other B-2 lymphocytes after transplantation assays, suggesting that Bmi1 may be involved in the developmental process of B-1 progenitors to mature B-1a cells. Although Bmi1 deletion has also been shown to alter the microenvironment for hematopoietic stem cells, fat-associated lymphoid clusters, the reported niche for B-1a cells, were not impaired in Bmi1 -/- mice. RNA expression profiling suggested lysine demethylase 5B (Kdm5b) as another possible target of Bmi1, which was elevated in Bmi1-/- B-1a cells in a stress setting and might repress B-1a cell proliferation. Our work has indicated that Bmi1 plays pivotal roles in self-renewal and maintenance of fetal-derived B-1a cells.

Hemoglobin switching in mice carrying the Klf1Nan variant.

Haploinsufficiency for transcription factor KLF1 causes a variety of human erythroid phenotypes, such as the In(Lu) blood type, increased HbA2 levels, and hereditary persistence of fetal hemoglobin. Severe dominant congenital dyserythropoietic anemia IV (CDA-IV) (OMIM 613673) is associated with the KLF1 p.E325K variant. CDA-IV patients display ineffective erythropoiesis and hemolysis resulting in anemia, accompanied by persistently high levels of embryonic and fetal hemoglobin. The mouse Nan strain carries a variant in the orthologous residue, KLF1 p.E339D. Klf1Nan causes dominant hemolytic anemia with many similarities to CDA-IV. Here we investigated the impact of Klf1Nan on the developmental expression patterns of the endogenous α-like and β-like globins, and the human β-like globins carried on a HBB locus transgene. We observe that the switch from primitive, yolk sac-derived, erythropoiesis to definitive, fetal liver-derived, erythropoiesis is delayed in Klf1wt/Nan embryos. This is reflected in globin expression patterns measured between embryonic day 12.5 (E12.5) and E14.5. Cultured Klf1wt/Nan E12.5 fetal liver cells display growth- and differentiation defects. These defects likely contribute to the delayed appearance of definitive erythrocytes in the circulation of Klf1wt/Nan embryos. After E14.5, expression of the embryonic/fetal globin genes is silenced rapidly. In adult Klf1wt/Nan animals, silencing of the embryonic/fetal globin genes is impeded, but only minute amounts are expressed. Thus, in contrast to human KLF1 p.E325K, mouse KLF1 p.E339D does not lead to persistent high levels of embryonic/fetal globins. Our results support the notion that KLF1 affects gene expression in a variant-specific manner, highlighting the necessity to characterize KLF1 variant-specific phenotypes of patients in detail.

Contribution of a GATA4-Expressing Hematopoietic Progenitor Lineage to the Adult Mouse Endothelium.

Different sources have been claimed for the embryonic origin of the coronary endothelium. Recently, the potential of circulating cells as progenitors of the cardiac endothelium has also been suggested. In a previous study we have shown that circulating progenitors are recruited by the embryonic endocardium and incorporated into the coronary vessels. These progenitors derive from a mesodermal lineage characterized by the expression of Gata4 under control of the enhancer G2. Herein, we aim to trace this specific lineage throughout postnatal stages. We have found that more than 50% of the adult cardiac endothelium derives from the G2-GATA4 lineage. This percentage increases from embryos to adults probably due to differential proliferation and postnatal recruitment of circulating endothelial progenitors. In fact, injection of fetal liver or placental cells in the blood stream of neonates leads to incorporation of G2-GATA4 lineage cells to the coronary endothelium. On the other hand, labeling of the hematopoietic lineage by the stage E7.5 also resulted in positive coronary endothelial cells from both, embryos and adults. Our results suggest that early hematopoietic progenitors recruited by the embryonic ventricular endocardium can become the predominant source of definitive endothelium during the vascularization of the heart.

TFEB regulates murine liver cell fate during development and regeneration

It is well established that pluripotent stem cells in fetal and postnatal liver (LPCs) can differentiate into both hepatocytes and cholangiocytes. However, the signaling pathways implicated in the differentiation of LPCs are still incompletely understood. Transcription Factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy, is known to be involved in osteoblast and myeloid differentiation, but its role in lineage commitment in the liver has not been investigated. Here we show that during development and upon regeneration TFEB drives the differentiation status of murine LPCs into the progenitor/cholangiocyte lineage while inhibiting hepatocyte differentiation. Genetic interaction studies show that Sox9, a marker of precursor and biliary cells, is a direct transcriptional target of TFEB and a primary mediator of its effects on liver cell fate. In summary, our findings identify an unexplored pathway that controls liver cell lineage commitment and whose dysregulation may play a role in biliary cancer.

Fc receptor-like 6 (FCRL6) delineates innate-like B cell progenitors that undergo pre-BCR dependent and independent pathways of natural antibody selection

Abstract Innate-like B-1a B cells produce ‘natural’ antibodies (Abs) to neutralize pathogens and clear neo self-antigens, but the early selection mechanisms that shape their polyreactive repertoires are poorly understood. Fc receptor-like (Fcrl) genes encode surface regulatory proteins preferentially expressed by B cells. Here, we identified a B cell progenitor subset defined by FCRL6 expression, harboring emerging Ighv repertoire, migration, and differentiation properties conducive for natural Ab generation. Receptor-specific monoclonal antibodies identified subpopulations of FCRL6+ pro B cells in E18 fetal liver (FL), neonatal tissues, and adult bone marrow (BM). While it was absent on Hardy Fr. A cells, FCRL6 expression became evident in Fr. B, peaked in Fr. C, and declined in Fr. C′. By the Dorshkind scheme, FCRL6 marked subsets of B-1P and pro B cells in the FL and BM, but was not detected on B-2P cells. Compared to FCRL6− pro B cells, the repressed mitotic, DNA damage repair, and signaling activity of FCRL6+ progenitors, yielded VH repertoires with biased distal Ighv segment accessibility, constrained diversity, and hydrophobic and charged CDR-H3 sequences. Similar features were apparent among B-1a and chronic lymphocytic leukemia (CLL) Ighv sequences. Beyond nascent autoreactivity, VH11 productivity, which predominates phosphatidylcholine-specific B-1a B cell receptors (BCRs), was higher for FCRL6+ cells as was pre-BCR formation, which was required for Myc induction and VH11, but not VH12, B-1a development. Thus, FCRL6 revealed unexpected heterogeneity in the developmental origins, regulation, and selection of natural Abs at the pre-BCR checkpoint with implications for autoimmunity and lymphoproliferative disorders.

Ly6cLo non-classical monocytes promote resolution of rhesus rotavirus-mediated perinatal hepatic inflammation

Perinatal hepatic inflammation can have devastating consequences. Monocytes play an important role in the initiation and resolution of inflammation, and their diverse functions can be attributed to specific cellular subsets: pro-inflammatory or classical monocytes (Ly6cHi) and pro-reparative or non-classical monocytes (Ly6cLo). We hypothesized that inherent differences in Ly6cHi classical monocytes and Ly6cLo non-classical monocytes determine susceptibility to perinatal hepatic inflammation in late gestation fetuses and neonates. We found an anti-inflammatory transcriptional profile expressed by Ly6cLo non-classical monocytes, and a physiologic abundance of these cells in the late gestation fetal liver. Unlike neonatal pups, late gestation fetuses proved to be resistant to rhesus rotavirus (RRV) mediated liver inflammation. Furthermore, neonatal pups were rendered resistant to RRV-mediated liver injury when Ly6cLo non-classical monocytes were expanded. Pharmacologic inhibition of Ly6cLo non-classical monocytes in this setting restored susceptibility to RRV-mediated disease. These data demonstrate that Ly6cLo monocytes promote resolution of perinatal liver inflammation in the late gestation fetus, where there is a physiologic expansion of non-classical monocytes, and in the neonatal liver upon experimental expansion of these cells. Therapeutic strategies directed towards enhancing Ly6cLo non-classical monocyte function may mitigate the detrimental effects of perinatal liver inflammation.

Growth and albumin secretion of mouse fetal liver cells cryopreserved within porous polymer scaffolds as a viable cell source for bioartificial livers

To clinically apply bioartificial livers (BALs), an effective liver cell cryopreservation method is required for a stable cell supply. In this study, we performed tissue-engineered construct (TEC) cryopreservation of fetal liver cells (FLCs) in which FLCs cultured within a porous polymer scaffold were cryopreserved. Growth and albumin secretion in TEC-cryopreserved FLCs after thawing were compared to freshly isolated FLCs (control experiments). The effect of preculture duration prior to cryopreservation (0-3 weeks) on these functions was also examined. In the three-dimensional cultures, the TEC-cryopreserved FLCs with preculturing showed constant growth, and this growth was comparable to controls. On the contrary, the TEC-cryopreserved FLCs without preculturing did not proliferate after thawing. Albumin secretion of TEC-cryopreserved FLCs with preculturing rapidly increased up to day 12 and high secretory activity comparable to controls was maintained thereafter in FLCs with 1- or 2-week preculturing, suggesting this as an appropriate preculture duration. Compared to conventionally cryopreserved FLCs, growth and albumin secretion in the TEC-cryopreserved FLCs were significantly higher, indicating their usefulness as a potent cell source for BALs.

BMP2K dysregulation promotes abnormal megakaryopoiesis in acute megakaryoblastic leukemia

BackgroundForced polyploidization is an effective strategy for acute megakaryoblastic leukemia (AMKL) therapy and factors controlling polyploidization are potential targets for drug development. Although bone morphology protein 2-inducible kinase (BMP2K) has been implied to be a potential target for fasudil, a potent polyploidy-inducing compound, the function of BMP2K in megakaryopoiesis and AMKL remains unknown. This study aimed to investigate the role of BMP2K as a novel regulator in megakaryocyte polyploidization and differentiation and its implication in AMKL therapy.ResultsBMP2K upregulation was observed in human megakaryopoiesis and leukemia cells whereas BMP2K was downregulated in AMKL cells forced to undergo terminal differentiation. Functionally, BMP2K suppressed MLN8237-induced megakaryocytic differentiation in AMKL cells and dampened megakaryocyte differentiation in primary mouse fetal liver cells. Furthermore, BMP2K overexpression conferred resistance to multiple chemotherapy compounds in AMKL cells. Mechanistically, cyclin-dependent kinase 2 (CDK2) interacted with BMP2K and partially mediated its function. In transient MLN8237 and nocodazole challenge cell model, BMP2K reduced cell percentage of G2/M phase but increased G1 phase, suggesting a role of BMP2K antagonizing polyploidization and promoting mitosis by regulating cell cycle in megakaryopoiesis.ConclusionsBMP2K negatively regulates polyploidization and megakaryocyte differentiation by interacting CDK2 and promoting mitosis in megakaryopoiesis. BMP2K may serve as a potential target for improvement of AMKL therapy.

RNA Binding Motif Protein RBM45 Regulates Expression of the 11-Kilodalton Protein of Parvovirus B19 through Binding to Novel Intron Splicing Enhancers.

During infection of human parvovirus B19 (B19V), one viral precursor mRNA (pre-mRNA) is transcribed by a single promoter and is alternatively spliced and alternatively polyadenylated. Here, we identified a novel cis-acting sequence (5'-GUA AAG CUA CGG GAC GGU-3'), intronic splicing enhancer 3 (ISE3), which lies 72 nucleotides upstream of the second splice acceptor (A2-2) site of the second intron that defines the exon of the mRNA encoding the 11-kDa viral nonstructural protein. RNA binding motif protein 45 (RBM45) specifically binds to ISE3 with high affinity (equilibrium dissociation constant [KD ] = 33 nM) mediated by its RNA recognition domain and 2-homo-oligomer assembly domain (RRM2-HOA). Knockdown of RBM45 expression or ectopic overexpression of RRM2-HOA in human erythroid progenitor cells (EPCs) expanded ex vivo significantly decreased the level of viral mRNA spliced at the A2-2 acceptor but not that of the mRNA spliced at A2-1 that encodes VP2. Moreover, silent mutations of ISE3 in an infectious DNA of B19V significantly reduced 11-kDa expression. Notably, RBM45 also specifically interacts in vitro with ISE2, which shares the octanucleotide (GGGACGGU) with ISE3. Taken together, our results suggest that RBM45, through binding to both ISE2 and ISE3, is an essential host factor for maturation of 11-kDa-encoding mRNA.IMPORTANCE Human parvovirus B19 (B19V) is a human pathogen that causes severe hematological disorders in immunocompromised individuals. B19V infection has a remarkable tropism with respect to human erythroid progenitor cells (EPCs) in human bone marrow and fetal liver. During B19V infection, only one viral precursor mRNA (pre-mRNA) is transcribed by a single promoter of the viral genome and is alternatively spliced and alternatively polyadenylated, a process which plays a key role in expression of viral proteins. Our studies revealed that a cellular RNA binding protein, RBM45, binds to two intron splicing enhancers and is essential for the maturation of the small nonstructural protein 11-kDa-encoding mRNA. The 11-kDa protein plays an important role not only in B19V infection-induced apoptosis but also in viral DNA replication. Thus, the identification of the RBM45 protein and its cognate binding site in B19V pre-mRNA provides a novel target for antiviral development to combat B19V infection-caused severe hematological disorders.

Retroviral Gene Transduction into T Cell Progenitors for Analysis of T Cell Development in the Thymus.

The thymus is an organ where T cells develop throughout life. Using mice as a model animal, molecular mechanisms of intrathymic T cell development have been studied. Fetal thymus organ culture technique enables ex vivo reconstitution of fetal-specific T cell development, while bone marrow chimera technique allows in vivo reconstitution of T cell development in adult thymus. These techniques can be combined with retroviral gene transduction into the T cell progenitors to evaluate the function of genes of interest in developing T cells. Here, we describe the basic protocols for retrovirus gene transduction into fetal or adult T cell progenitors and reconstitution of thymic T cell development including experimental tips such as using cryopreserved fetal liver or bone marrow cells as sources of T cell progenitors.