A PCR protocol to establish standards for routine mycoplasma testing that by design detects over ninety percent of all known mycoplasma species

Mycoplasma infection leads to false and non-reproducible scientific data and poses a risk to human health. Despite strict guidelines calling for regular mycoplasma screening, there is no universal and widely established standard procedure. Here, we describe a reliable and cost-effective PCR method that establishes a universal protocol for mycoplasma testing. The applied strategy utilizes ultra-conserved eukaryotic and mycoplasma sequence primers covering by design 92% of all species in the six orders of the class Mollicutes within the phylum Mycoplasmatota and is applicable to mammalian and many non-mammalian cell types. This method can stratify mycoplasma screening and is suitable as a common standard for routine mycoplasma testing.

Wnt1 Boosts Fracture Healing by Enhancing Bone Formation in the Fracture Callus

Despite considerable improvement in fracture care, 5%-10% of all fractures still heal poorly or result in nonunion formation. Therefore, there is an urgent need to identify new molecules that can be used to improve bone fracture healing. One activator of the Wnt-signaling cascade, Wnt1, has recently gained attention for its intense osteoanabolic effect on the intact skeleton. The aim of the present study was to investigate whether Wnt1 might be a promising molecule to accelerate fracture healing both in skeletally healthy and osteoporotic mice that display a diminished healing capacity. Transgenic mice for a temporary induction of Wnt1 specifically in osteoblasts (Wnt1-tg) were subjected to femur osteotomy. Non-ovariectomized and ovariectomized Wnt1-tg mice displayed significantly accelerated fracture healing based on a strong increase in bone formation in the fracture callus. Transcriptome profiling revealed that Hippo/yes1-associated transcriptional regulator (YAP)-signaling and bone morphogenetic protein (BMP) signaling pathways were highly enriched in the fracture callus of Wnt1-tg animals. Immunohistochemical staining confirmed increased activation of YAP1 and expression of BMP2 in osteoblasts in the fracture callus. Therefore, our data indicate that Wnt1 boosts bone formation during fracture healing via YAP/BMP signaling both under healthy and osteoporotic conditions. To further test a potential translational application of Wnt1, we applied recombinant Wnt1 embedded into a collagen gel during critical-size bone-defect repair. Mice treated with Wnt1 displayed increased bone regeneration compared to control mice accompanied by increased YAP1/BMP2 expression in the defect area. These findings are of high clinical relevance because they indicate that Wnt1 could be used as a new therapeutic agent to treat orthopedic complications in the clinic. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

The WNT1G177C mutation specifically affects skeletal integrity in a mouse model of osteogenesis imperfecta type XV

The recent identification of homozygous WNT1 mutations in individuals with osteogenesis imperfecta type XV (OI-XV) has suggested that WNT1 is a key ligand promoting the differentiation and function of bone-forming osteoblasts. Although such an influence was supported by subsequent studies, a mouse model of OI-XV remained to be established. Therefore, we introduced a previously identified disease-causing mutation (G177C) into the murine Wnt1 gene. Homozygous Wnt1^G177C/G177C mice were viable and did not display defects in brain development, but the majority of 24-week-old Wnt1^G177C/G177C mice had skeletal fractures. This increased bone fragility was not fully explained by reduced bone mass but also by impaired bone matrix quality. Importantly, the homozygous presence of the G177C mutation did not interfere with the osteoanabolic influence of either parathyroid hormone injection or activating mutation of LRP5, the latter mimicking the effect of sclerostin neutralization. Finally, transcriptomic analyses revealed that short-term administration of WNT1 to osteogenic cells induced not only the expression of canonical WNT signaling targets but also the expression of genes encoding extracellular matrix modifiers. Taken together, our data demonstrate that regulating bone matrix quality is a primary function of WNT1. They further suggest that individuals with WNT1 mutations should profit from existing osteoanabolic therapies.

Definitive evidence for Club cells as progenitors for mutant Kras/Trp53-deficient lung cancer

Accumulating evidence suggests that both the nature of oncogenic lesions and the cell-of-origin can strongly influence cancer histopathology, tumor aggressiveness and response to therapy. Although oncogenic Kras expression and loss of Trp53 tumor suppressor gene function have been demonstrated to initiate murine lung adenocarcinomas (LUADs) in alveolar type II (AT2) cells, clear evidence that Club cells, representing the second major subset of lung epithelial cells, can also act as cells-of-origin for LUAD is lacking. Equally, the exact anatomic location of Club cells that are susceptible to Kras transformation and the resulting tumor histotype remains to be established. Here, we provide definitive evidence for Club cells as progenitors for LUAD. Using in vivo lineage tracing, we find that a subset of Kras^12V -expressing and Trp53-deficient Club cells act as precursors for LUAD and we define the stepwise trajectory of Club cell-initiated tumors leading to lineage marker conversion and aggressive LUAD. Our results establish Club cells as cells-of-origin for LUAD and demonstrate that Club cell-initiated tumors have the potential to develop aggressive LUAD.

Wnt1 Promotes Cementum and Alveolar Bone Growth in a Time-Dependent Manner

The WNT/β-catenin signaling pathway plays a central role in the biology of the periodontium, yet the function of specific extracellular WNT ligands remains poorly understood. By using a Wnt1-inducible transgenic mouse model targeting Col1a1-expressing alveolar osteoblasts, odontoblasts, and cementoblasts, we demonstrate that the WNT ligand WNT1 is a strong promoter of cementum and alveolar bone formation in vivo. We induced Wnt1 expression for 1, 3, or 9 wk in Wnt1Tg mice and analyzed them at the age of 6 wk and 12 wk. Micro–computed tomography (CT) analyses of the mandibles revealed a 1.8-fold increased bone volume after 1 and 3 wk of Wnt1 expression and a 3-fold increased bone volume after 9 wk of Wnt1 expression compared to controls. In addition, the alveolar ridges were higher in Wnt1Tg mice as compared to controls. Nondecalcified histology demonstrated increased acellular cementum thickness and cellular cementum volume after 3 and 9 wk of Wnt1 expression. However, 9 wk of Wnt1 expression was also associated with periodontal breakdown and ectopic mineralization of the pulp. The composition of this ectopic matrix was comparable to those of cellular cementum as demonstrated by quantitative backscattered electron imaging and immunohistochemistry for noncollagenous proteins. Our analyses of 52-wk-old mice after 9 wk of Wnt1 expression revealed that Wnt1 expression affects mandibular bone and growing incisors but not molar teeth, indicating that Wnt1 influences only growing tissues. To further investigate the effect of Wnt1 on cementoblasts, we stably transfected the cementoblast cell line (OCCM-30) with a vector expressing Wnt1-HA and performed proliferation as well as differentiation experiments. These experiments demonstrated that Wnt1 promotes proliferation but not differentiation of cementoblasts. Taken together, our findings identify, for the first time, Wnt1 as a critical regulator of alveolar bone and cementum formation, as well as provide important insights for harnessing the WNT signal pathway in regenerative dentistry.

Nano-Enhanced Cancer Immunotherapy: Immunology Encounters Nanotechnology

Cancer immunotherapy utilizes the immune system to fight cancer and has already moved from the laboratory to clinical application. However, and despite excellent therapeutic outcomes in some hematological and solid cancers, the regular clinical use of cancer immunotherapies reveals major limitations. These include the lack of effective immune therapy options for some cancer types, unresponsiveness to treatment by many patients, evolving therapy resistance, the inaccessible and immunosuppressive nature of the tumor microenvironment (TME), and the risk of potentially life-threatening immune toxicities. Given the potential of nanotechnology to deliver, enhance, and fine-tune cancer immunotherapeutic agents, the combination of cancer immunotherapy with nanotechnology can overcome some of these limitations. In this review, we summarize innovative reports and novel strategies that successfully combine nanotechnology and cancer immunotherapy. We also provide insight into how nanoparticular combination therapies can be used to improve therapy responsiveness, to reduce unwanted toxicity, and to overcome adverse effects of the TME.

Wheat Consumption Aggravates Colitis in Mice via Amylase Trypsin Inhibitor-mediated Dysbiosis

BACKGROUND & AIMS

Wheat has become the world's major staple and its consumption correlates with prevalence of noncommunicable disorders such as inflammatory bowel diseases. Amylase trypsin inhibitors (ATIs), a component of wheat, activate the intestine's innate immune response via toll-like receptor 4 (TLR4). We investigated the effects of wheat and ATIs on severity of colitis and fecal microbiota in mice.

METHODS

C57BL/6 wild-type and Tlr4^-/- mice were fed wheat- or ATI-containing diets or a wheat-free (control) diet and then given dextran sodium sulfate to induce colitis; we also studied Il10^-/- mice, which develop spontaneous colitis. Changes in fecal bacteria were assessed by taxa-specific quantitative polymerase chain reaction and 16S ribosomal RNA metagenomic sequencing. Feces were collected from mice on wheat-containing, ATI-containing, control diets and transplanted to intestines of mice with and without colitis on control or on ATI-containing diets. Intestinal tissues were collected and analyzed by histology, immunohistochemistry, and flow cytometry. Bacteria with reported immunomodulatory effects were incubated with ATIs and analyzed in radial diffusion assays.

RESULTS

The wheat- or ATI-containing diets equally increased inflammation in intestinal tissues of C57BL/6 mice with colitis, compared with mice on control diets. The ATI-containing diet promoted expansion of taxa associated with development of colitis comparable to the wheat-containing diet. ATIs inhibited proliferation of specific human commensal bacteria in radial diffusion assays. Transplantation of microbiota from feces of mice fed the wheat- or ATI-containing diets to intestines of mice on control diets increased the severity of colitis in these mice. The ATI-containing diet did not increase the severity of colitis in Tlr4^-/- mice.

CONCLUSIONS

Consumption of wheat or wheat ATIs increases intestinal inflammation in mice with colitis, via TLR4, and alters their fecal microbiota. Wheat-based, ATI-containing diets therefore activate TLR4 signaling and promote intestinal dysbiosis.

A subset of flavaglines inhibits KRAS nanoclustering and activation

The RAS oncogenes are frequently mutated in human cancers and among the three isoforms (KRAS, HRAS and NRAS), KRAS is the most frequently mutated oncogene. Here, we demonstrate that a subset of flavaglines, a class of natural anti-tumour drugs and chemical ligands of prohibitins, inhibit RAS GTP loading and oncogene activation in cells at nanomolar concentrations. Treatment with rocaglamide, the first discovered flavagline, inhibited the nanoclustering of KRAS, but not HRAS and NRAS, at specific phospholipid-enriched plasma membrane domains. We further demonstrate that plasma membrane-associated prohibitins directly interact with KRAS, phosphatidylserine and phosphatidic acid, and these interactions are disrupted by rocaglamide but not by the structurally related flavagline FL1. Depletion of prohibitin-1 phenocopied the rocaglamide-mediated effects on KRAS activation and stability. We also demonstrate that flavaglines inhibit the oncogenic growth of KRAS-mutated cells and that treatment with rocaglamide reduces non-small-cell lung carcinoma (NSCLC) tumour nodules in autochthonous KRAS-driven mouse models without severe side effects. Our data suggest that it will be promising to further develop flavagline derivatives as specific KRAS inhibitors for clinical applications.

Wnt1 is an Lrp5-independent bone-anabolic Wnt ligand

WNT1 mutations in humans are associated with a new form of osteogenesis imperfecta and with early-onset osteoporosis, suggesting a key role of WNT1 in bone mass regulation. However, the general mode of action and the therapeutic potential of Wnt1 in clinically relevant situations such as aging remain to be established. Here, we report the high prevalence of heterozygous WNT1 mutations in patients with early-onset osteoporosis. We show that inactivation of Wnt1 in osteoblasts causes severe osteoporosis and spontaneous bone fractures in mice. In contrast, conditional Wnt1 expression in osteoblasts promoted rapid bone mass increase in developing young, adult, and aged mice by rapidly increasing osteoblast numbers and function. Contrary to current mechanistic models, loss of Lrp5, the co-receptor thought to transmit extracellular WNT signals during bone mass regulation, did not reduce the bone-anabolic effect of Wnt1, providing direct evidence that Wnt1 function does not require the LRP5 co-receptor. The identification of Wnt1 as a regulator of bone formation and remodeling provides the basis for development of Wnt1-targeting drugs for the treatment of osteoporosis.

A conditional inducible JAK2V617F transgenic mouse model reveals myeloproliferative disease that is reversible upon switching off transgene expression

Aberrant activation of the JAK/STAT pathway is thought to be the critical event in the pathogenesis of the chronic myeloproliferative neoplasms, polycythemia vera, essential thrombocythemia and primary myelofibrosis. The most frequent genetic alteration in these pathologies is the activating JAK2^V617F mutation, and expression of the mutant gene in mouse models was shown to cause a phenotype resembling the human diseases. Given the body of genetic evidence, it has come as a sobering finding that JAK inhibitor therapy only modestly suppresses the JAK2^V617F allele burden, despite showing clear benefits in terms of reducing splenomegaly and constitutional symptoms in patients. To gain a better understanding if JAK2^V617F is required for maintenance of myeloproliferative disease once it has evolved, we generated a conditional inducible transgenic JAK2^V617F mouse model using the SCL-tTA-2S tet-off system. Our model corroborates that expression of JAK2^V617F in hematopoietic stem and progenitor cells recapitulates key hallmarks of human myeloproliferative neoplasms, and exhibits gender differences in disease manifestation. The disease was found to be transplantable, and importantly, reversible when transgenic JAK2^V617F expression was switched off. Our results indicate that mutant JAK2^V617F-specific inhibitors should result in profound disease modification by disabling the myeloproliferative clone bearing mutant JAK2.

Abstract 267: Targeting the alt-NHEJ DNA repair pathway selectively sensitizes KRAS-mutant cancer cells to chemotherapy

Genomic instability is considered as a hallmark of human cancer. Whereas the oncogene-induced emergence of genetic lesions caused by increased levels of reactive oxygen species (ROS) and/or replicative stress is well characterised, the impact of defined driver mutations on individual DNA damage response and repair pathways is poorly understood. Recently, we have shown that oncogenic Kirsten-rat sarcoma (KRAS) dysregulates the repair of DNA double-strand breaks (DSB) and shifts the balance from canonical non-homologous end-joining (c-NHEJ) towards the highly error-prone alternative-NHEJ (alt-NHEJ) repair pathway by upregulation of XRCC1, PARP1 and DNA ligase 3α (Lig3α).

In this study, we wanted to investigate, whether KRAS-mutant (KRASmut) lung cancer cells rely on alt-NHEJ to repair genotoxic stress-induced DSBs. In addition, we addressed the question whether targeting essential component of the alt-NHEJ pathways sensitises KRASmut cells toward genotoxic agents.

The presence of oncogenic KRAS associates with increased expression of essential components of the error-prone alt-NHEJ pathway and causes enhanced alt-NHEJ activity compared to KRAS-wild-type (KRASwt) lung cancer cells as revealed by in vivo host cell reactivation assays. Pharmacologic inhibition of PARP, which has been shown to promote end joining by alt-NHEJ, resulted in increased apoptosis upon combined treatment with standard genotoxic agents in KRASmut cells but not KRASwt cells. Moreover, mice bearing tumor xenografts derived from KRASmut lung cancer cell lines but not KRASwt tumors experienced attenuated tumor growth and longer overall survival upon treatment with the PARP-inhibitor Olaparib and chemotherapy compared to single agent therapy, respectively. Similar results were obtained using a genetically modified mouse model of inducible, KRASmut-dependent lung cancer. Mice bearing KRASmut lung tumors showed a significantly reduced tumor burden when treated with the combination therapy of Olaparib and the topoisomerase II inhibitor VP-16 compared to animals treated only with single agents alone. Mechanistically, the DNA damage sensor protein KU70 is trapped in the cytoplasm in a KRASmut-dependent manner. siRNA-mediated knockdown of KRAS caused a shift of KU70 into the nucleus allowing access of KU70 to DSBs and to initiate DNA repair via the c-NHEJ repair pathway.

Our data provide evidence for a novel synthetic lethal interaction between oncogenic KRAS and DNA damage repair. Targeting components of the alt-NHEJ represents a so far not recognized therapeutic strategy to induce synthetic vulnerability in cells harbouring otherwise non-druggable KRAS mutations.

Citation Format: Patricia S. Haehnel, Sarah Swoboda, Nadine Lehmann, Sebastian Rosigkeit, Hernike Gothe, Danial I. Sasca, Dennis Strand, Matthias Theobald, Vassilis Roukos, Ernesto Bockamp, Thomas Kindler. Targeting the alt-NHEJ DNA repair pathway selectively sensitizes KRAS-mutant cancer cells to chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 267.

IL-4 Receptor Alpha Signaling through Macrophages Differentially Regulates Liver Fibrosis Progression and Reversal

Chronic hepatitis leads to liver fibrosis and cirrhosis. Cirrhosis is a major cause of worldwide morbidity and mortality. Macrophages play a key role in fibrosis progression and reversal. However, the signals that determine fibrogenic vs fibrolytic macrophage function remain ill defined. We studied the role of interleukin-4 receptor α (IL-4Rα), a potential central switch of macrophage polarization, in liver fibrosis progression and reversal. We demonstrate that inflammatory monocyte infiltration and liver fibrogenesis were suppressed in general IL-4Rα^−/− as well as in macrophage-specific IL-4Rα^−/− (IL-4Rα^ΔLysM) mice. However, with deletion of IL-4Rα^ΔLysM spontaneous fibrosis reversal was retarded. Results were replicated by pharmacological intervention using IL-4Rα-specific antisense oligonucleotides. Retarded resolution was linked to the loss of M2-type resident macrophages, which secreted MMP-12 through IL-4 and IL-13-mediated phospho-STAT6 activation. We conclude that IL-4Rα signaling regulates macrophage functional polarization in a context-dependent manner. Pharmacological targeting of macrophage polarization therefore requires disease stage-specific treatment strategies.

Research in Context

Alternative (M2-type) macrophage activation through IL-4Rα promotes liver inflammation and fibrosis progression but speeds up fibrosis reversal. This demonstrates context dependent, opposing roles of M2-type macrophages. During reversal IL-4Rα induces fibrolytic MMPs, especially MMP-12, through STAT6. Liver-specific antisense oligonucleotides efficiently block IL-4Rα expression and attenuate fibrosis progression.

•

IL-4Rα is considered a central switch for alternative macrophage polarization.

•

IL-4Rα on macrophages is shown to differentially regulate liver fibrosis progression vs reversal.

•

Therapeutic IL-4Rα antisense oligonucleotides replicate these findings.

•

MMP-12 induced via macrophage IL-4Rα is a key promoter of fibrosis reversal.

Enhanced protection of C57 BL/6 vs Balb/c mice to melanoma liver metastasis is mediated by NK cells

The B16F10 murine melanoma cell line displays a low expression of MHC class I molecules favoring immune evasion and metastases in immunocompetent C57 BL/6 wild-type mice. Here, we generated metastases to the liver, an organ that is skewed towards immune tolerance, by intrasplenic injection of B16F10 cells in syngeneic C57 BL/6 compared to allogeneic Balb/c mice. Surprisingly, Balb/c mice, which usually display a pronounced M2 macrophage and Th2 T cell polarization, were ∼3 times more susceptible to metastasis than C57 BL/6 mice, despite a much higher M1 and Th1 T cell immune response. The anti-metastatic advantage of C57 BL/6 mice could be attributed to a more potent NK-cell mediated cytotoxicity against B16F10 cells. Our findings highlight the role of NK cells in innate anti-tumor immunity in the context of the liver – particularly against highly aggressive MHC I-deficient cancer cells. Moreover, the B16F10 model of melanoma liver metastasis is suited for developing novel therapies targeting innate NK cell related immunity in liver metastases and liver cancer.

Characterization of a Fetal Liver Cell Population Endowed with Long-Term Multiorgan Endothelial Reconstitution Potential

Stable reconstitution of vascular endothelial beds upon transplantation of progenitor cells represents an important challenge due to the paucity and generally limited integration/expansion potential of most identified vascular related cell subsets. We previously showed that mouse fetal liver (FL) hemato/vascular cells from day 12 of gestation (E12), expressing the Stem Cell Leukaemia (SCL) gene enhancer transgene (SCL‐PLAP⁺ cells), had robust endothelial engraftment potential when transferred to the blood stream of newborns or adult conditioned recipients, compared to the scarce vascular contribution of adult bone marrow cells. However, the specific SCL‐PLAP⁺ hematopoietic or endothelial cell subset responsible for the long‐term reconstituting endothelial cell (LTR‐EC) activity and its confinement to FL developmental stages remained unknown. Using a busulfan‐treated newborn transplantation model, we show that LTR‐EC activity is restricted to the SCL‐PLAP⁺VE‐cadherin⁺CD45⁻ cell population, devoid of hematopoietic reconstitution activity and largely composed by Lyve1⁺ endothelial‐committed cells. SCL‐PLAP⁺ Ve‐cadherin⁺CD45⁻ cells contributed to the liver sinusoidal endothelium and also to the heart, kidney and lung microvasculature. LTR‐EC activity was detected at different stages of FL development, yet marginal activity was identified in the adult liver, revealing unknown functional differences between fetal and adult liver endothelial/endothelial progenitors. Importantly, the observations that expanding donor‐derived vascular grafts colocalize with proliferating hepatocyte‐like cells and participate in the systemic circulation, support their functional integration into young livers. These findings offer new insights into the engraftment, phonotypical, and developmental characterization of a novel endothelial/endothelial progenitor cell subtype with multiorgan LTR‐EC activity, potentially instrumental for the treatment/genetic correction of vascular diseases. Stem Cells2017;35:507–521

Genetic enhancement of microsomal epoxide hydrolase improves metabolic detoxification but impairs cerebral blood flow regulation

Microsomal epoxide hydrolase (mEH) is a detoxifying enzyme for xenobiotic compounds. Enzymatic activity of mEH can be greatly increased by a point mutation, leading to an E404D amino acid exchange in its catalytic triad. Surprisingly, this variant is not found in any vertebrate species, despite the obvious advantage of accelerated detoxification. We hypothesized that this evolutionary avoidance is due to the fact that the mEH plays a dualistic role in detoxification and control of endogenous vascular signaling molecules. To test this, we generated mEH E404D mice and assessed them for detoxification capacity and vascular dynamics. In liver microsomes from these mice, turnover of the xenobiotic compound phenanthrene-9,10-oxide was four times faster compared to WT liver microsomes, confirming accelerated detoxification. mEH E404D animals also showed faster metabolization of a specific class of endogenous eicosanoids, arachidonic acid-derived epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs). Significantly higher DHETs/EETs ratios were found in mEH E404D liver, urine, plasma, brain and cerebral endothelial cells compared to WT controls, suggesting a broad impact of the mEH mutant on endogenous EETs metabolism. Because EETs are strong vasodilators in cerebral vasculature, hemodynamics were assessed in mEH E404D and WT cerebral cortex and hippocampus using cerebral blood volume (CBV)-based functional magnetic resonance imaging (fMRI). Basal CBV₀ levels were similar between mEH E404D and control mice in both brain areas. But vascular reactivity and vasodilation in response to the vasodilatory drug acetazolamide were reduced in mEH E404D forebrain compared to WT controls by factor 3 and 2.6, respectively. These results demonstrate a critical role for mEH E404D in vasodynamics and suggest that deregulation of endogenous signaling pathways is the undesirable gain of function associated with the E404D variant.

Instruction of haematopoietic lineage choices, evolution of transcriptional landscapes and cancer stem cell hierarchies derived from an AML1-ETO mouse model

The t(8;21) chromosomal translocation activates aberrant expression of the AML1-ETO (AE) fusion protein and is commonly associated with core binding factor acute myeloid leukaemia (CBF AML). Combining a conditional mouse model that closely resembles the slow evolution and the mosaic AE expression pattern of human t(8;21) CBF AML with global transcriptome sequencing, we find that disease progression was characterized by two principal pathogenic mechanisms. Initially, AE expression modified the lineage potential of haematopoietic stem cells (HSCs), resulting in the selective expansion of the myeloid compartment at the expense of normal erythro- and lymphopoiesis. This lineage skewing was followed by a second substantial rewiring of transcriptional networks occurring in the trajectory to manifest leukaemia. We also find that both HSC and lineage-restricted granulocyte macrophage progenitors (GMPs) acquired leukaemic stem cell (LSC) potential being capable of initiating and maintaining the disease. Finally, our data demonstrate that long-term expression of AE induces an indolent myeloproliferative disease (MPD)-like myeloid leukaemia phenotype with complete penetrance and that acute inactivation of AE function is a potential novel therapeutic option.

STAT5 is crucial to maintain leukemic stem cells in acute myelogenous leukemias induced by MOZ-TIF2

MOZ-TIF2 is a leukemogenic fusion oncoprotein that confers self-renewal capability to hematopoietic progenitor cells and induces acute myelogenous leukemia (AML) with long latency in bone marrow transplantation assays. Here, we report that FLT3-ITD transforms hematopoietic cells in cooperation with MOZ-TIF2 in vitro and in vivo. Coexpression of FLT3-ITD confers growth factor independent survival/proliferation, shortens disease latency, and results in an increase in the number of leukemic stem cells (LSC). We show that STAT5, a major effector of aberrant FLT3-ITD signal transduction, is both necessary and sufficient for this cooperative effect. In addition, STAT5 signaling is essential for MOZ-TIF2-induced leukemic transformation itself. Lack of STAT5 in fetal liver cells caused rapid differentiation and loss of replating capacity of MOZ-TIF2-transduced cells enriched for LSCs. Furthermore, mice serially transplanted with Stat5(-/-) MOZ-TIF2 leukemic cells develop AML with longer disease latency and finally incomplete penetrance when compared with mice transplanted with Stat5(+/+) MOZ-TIF2 leukemic cells. These data suggest that STAT5AB is required for the self-renewal of LSCs and represents a combined signaling node of FLT3-ITD and MOZ-TIF2 driven leukemogenesis. Therefore, targeting aberrantly activated STAT5 or rewired downstream signaling pathways may be a promising therapeutic option.

Endothelial Wnt/β-catenin signaling inhibits glioma angiogenesis and normalizes tumor blood vessels by inducing PDGF-B expression

Wnt modulates glioma vascularization by regulating PDGF-B expression.

Endothelial Wnt/β-catenin signaling is necessary for angiogenesis of the central nervous system and blood–brain barrier (BBB) differentiation, but its relevance for glioma vascularization is unknown. In this study, we show that doxycycline-dependent Wnt1 expression in subcutaneous and intracranial mouse glioma models induced endothelial Wnt/β-catenin signaling and led to diminished tumor growth, reduced vascular density, and normalized vessels with increased mural cell attachment. These findings were corroborated in GL261 glioma cells intracranially transplanted in mice expressing dominant-active β-catenin specifically in the endothelium. Enforced endothelial β-catenin signaling restored BBB characteristics, whereas inhibition by Dkk1 (Dickkopf-1) had opposing effects. By overactivating the Wnt pathway, we induced the Wnt/β-catenin–Dll4/Notch signaling cascade in tumor endothelia, blocking an angiogenic and favoring a quiescent vascular phenotype, indicated by induction of stalk cell genes. We show that β-catenin transcriptional activity directly regulated endothelial expression of platelet-derived growth factor B (PDGF-B), leading to mural cell recruitment thereby contributing to vascular quiescence and barrier function. We propose that reinforced Wnt/β-catenin signaling leads to inhibition of angiogenesis with normalized and less permeable vessels, which might prove to be a valuable therapeutic target for antiangiogenic and edema glioma therapy.

Desmoglein 2 mutant mice develop cardiac fibrosis and dilation

Desmosomes are cell–cell adhesion sites and part of the intercalated discs, which couple adjacent cardiomyocytes. The connection is formed by the extracellular domains of desmosomal cadherins that are also linked to the cytoskeleton on the cytoplasmic side. To examine the contribution of the desmosomal cadherin desmoglein 2 to cardiomyocyte adhesion and cardiac function, mutant mice were prepared lacking a part of the extracellular adhesive domain of desmoglein 2. Most live born mutant mice presented normal overall cardiac morphology at 2 weeks. Some animals, however, displayed extensive fibrotic lesions. Later on, mutants developed ventricular dilation leading to cardiac insufficiency and eventually premature death. Upon histological examination, cardiomyocyte death by calcifying necrosis and replacement by fibrous tissue were observed. Fibrotic lesions were highly proliferative in 2-week-old mutants, whereas the fibrotic lesions of older mutants showed little proliferation indicating the completion of local muscle replacement by scar tissue. Disease progression correlated with increased mRNA expression of c-myc, ANF, BNF, CTGF and GDF15, which are markers for cardiac stress, remodeling and heart failure. Taken together, the desmoglein 2-mutant mice display features of dilative cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, an inherited human heart disease with pronounced fibrosis and ventricular arrhythmias that has been linked to mutations in desmosomal proteins including desmoglein 2.

Tetracycline-controlled transgene activation using the ROSA26-iM2-GFP knock-in mouse strain permits GFP monitoring of DOX-regulated transgene-expression

Background

Conditional gene activation is an efficient strategy for studying gene function in genetically modified animals. Among the presently available gene switches, the tetracycline-regulated system has attracted considerable interest because of its unique potential for reversible and adjustable gene regulation.

Results

To investigate whether the ubiquitously expressed Gt(ROSA)26Sor locus enables uniform DOX-controlled gene expression, we inserted the improved tetracycline-regulated transcription activator iM2 together with an iM2 dependent GFP gene into the Gt(ROSA)26Sor locus, using gene targeting to generate ROSA26-iM2-GFP (R26^t1Δ) mice. Despite the presence of ROSA26 promoter driven iM2, R26^t1Δ mice showed very sparse DOX-activated expression of different iM2-responsive reporter genes in the brain, mosaic expression in peripheral tissues and more prominent expression in erythroid, myeloid and lymphoid lineages, in hematopoietic stem and progenitor cells and in olfactory neurons.

Conclusions

The finding that gene regulation by the DOX-activated transcriptional factor iM2 in the Gt(ROSA)26Sor locus has its limitations is of importance for future experimental strategies involving transgene activation from the endogenous ROSA26 promoter. Furthermore, our ROSA26-iM2 knock-in mouse model (R26^t1Δ) represents a useful tool for implementing gene function in vivo especially under circumstances requiring the side-by-side comparison of gene manipulated and wild type cells. Since the ROSA26-iM2 mouse allows mosaic gene activation in peripheral tissues and haematopoietic cells, this model will be very useful for uncovering previously unknown or unsuspected phenotypes.

Hematopoietic stem cells reversibly switch from dormancy to self-renewal during homeostasis and repair

Bone marrow hematopoietic stem cells (HSCs) are crucial to maintain lifelong production of all blood cells. Although HSCs divide infrequently, it is thought that the entire HSC pool turns over every few weeks, suggesting that HSCs regularly enter and exit cell cycle. Here, we combine flow cytometry with label-retaining assays (BrdU and histone H2B-GFP) to identify a population of dormant mouse HSCs (d-HSCs) within the lin(-)Sca1+cKit+CD150+CD48(-)CD34(-) population. Computational modeling suggests that d-HSCs divide about every 145 days, or five times per lifetime. d-HSCs harbor the vast majority of multilineage long-term self-renewal activity. While they form a silent reservoir of the most potent HSCs during homeostasis, they are efficiently activated to self-renew in response to bone marrow injury or G-CSF stimulation. After re-establishment of homeostasis, activated HSCs return to dormancy, suggesting that HSCs are not stochastically entering the cell cycle but reversibly switch from dormancy to self-renewal under conditions of hematopoietic stress.

Conditional transgenic mouse models: from the basics to genome-wide sets of knockouts and current studies of tissue regeneration

Many mouse models are currently available, providing avenues to elucidate gene function and to recapitulate specific pathological conditions. To a large extent, successful translation of clinical evidence or analytical data into appropriate mouse models is possible through progress in transgenic or gene-targeting technology. Beginning with a review of standard mouse transgenics and conventional gene targeting, this article will move on to discussing the basics of conditional gene expression: the tetracycline (tet)-off and tet-on systems based on the transactivators tet-controlled transactivator (Tta) and reverse tet-on transactivator (rtTA) that allow downregulation or induction of gene expression; Cre or Flp recombinase-mediated modifications, including excision, inversion, insertion and interchromosomal translocation; combination of the tet and Cre systems, permitting inducible knockout, reporter gene activation or activation of point mutations; the avian retroviral system based on delivery of rtTA specifically into cells expressing the avian retroviral receptor, which enables cell type-specific, inducible gene expression; the tamoxifen system, one of the most frequently applied steroid receptor-based systems, allows rapid activation of a fusion protein between the gene of interest and a mutant domain of the estrogen receptor, whereby activation does not depend on transcription; and techniques for cell type-specific ablation. The diphtheria toxin receptor system offers the advantage that it can be combined with the ‘zoo’ of Cre recombinase driver mice. Having described the basics we move on to the cutting edge: generation of genome-wide sets of conditional knockout mice. To this end, large ongoing projects apply two strategies: gene trapping based on random integration of trapping vectors into introns leading to truncation of the transcript, and gene targeting, representing the directed approach using homologous recombination. It can be expected that in the near future genome-wide sets of such mice will be available. Finally, the possibilities of conditional expression systems for investigating gene function in tissue regeneration will be illustrated by examples for neurodegenerative disease, liver regeneration and wound healing of the skin.

Toxicity of ligand-dependent Cre recombinases and generation of a conditional Cre deleter mouse allowing mosaic recombination in peripheral tissues

Ligand-activated Cre recombinases are widely used for studying gene function in vitro and in conditional mouse models. To compare ligand-dependent Cre recombinases, different Cre estrogen receptor fusions were introduced into the ROSA26 locus of embryonic stem (ES) cells and assayed for genotoxicity and recombination efficiency. Of the tested recombinases, the CreERT2 variant showed no toxicity and was highly responsive to ligand induction. To constitutively express CreERT2 in mice and also to clarify whether the CreERT2 system displays background activity, we generated a knock-in mouse line harboring the CreERT2 coding region under the control of the ROSA26 locus. Analysis of this ROSA26-CreERT2 deleter mouse with different reporter strains revealed ubiquitous recombination in the embryo and partial recombination in peripheral and hematopoietic tissues but no effective CreERT2 expression in the brain. Furthermore, using flow cytometry, we found low-level background recombination in noninduced bitransgenic ROSA26-CreERT2/EGFP reporter mice. To determine whether background activity poses a general problem for conducting conditional in vivo experiments with the ROSA26-CreERT2 deleter, we used a sensitive conditional skin cancer model. In this assay, cancer induction was completely restricted to induced bitransgenic CreERT2/K-Ras(V12) mice, whereas noninduced control animals did not show any sign of cancer, indicating the usefulness of the ROSA-CreERT2 system for regulating conditional gene expression in vivo. The ROSA26-CreERT2 deleter strain will be a convenient experimental tool for studying gene function under circumstances requiring partial induction of recombination in peripheral tissues and will be useful for uncovering previously unknown or unsuspected phenotypes.

Generation and characterization of tTS-H4: a novel transcriptional repressor that is compatible with the reverse tetracycline-controlled TET-ON system

BACKGROUND

Conditional gene regulatory systems ensuring tight and adjustable expression of therapeutic genes are central for developing future gene therapy strategies. Among various regulatory systems, tetracycline-controlled gene expression has emerged as a safe and reliable option. Moreover, the tightness of tetracycline-regulated gene switches can be substantially improved by complementing transcriptional activators with antagonizing repressors.

METHODS

To develop novel tetracycline-responsive transcriptional repressors, we fused various transcriptional silencing domains to the TetR (B/E) DNA-binding and dimerization domain of the Tn10-encoded tetracycline resistance operon (TetR (B/E)). The resulting fusion proteins were individually tested for their ability to repress transcription of the constitutively active hypoxanthine phosphoribosyltransferase (HPRT) promoter. In addition, compatibility with the commonly used reverse tetracycline-controlled transactivator system (rtTA-system) and responsiveness to the pharmacological effector doxycycline (DOX) were evaluated. Finally, inducibility, effector-dependent promoter activity and the modification of histone H3 and H4 of the active versus the repressed target promoter were determined.

RESULTS

Fusion of the human deacetylase 4 (HDAC4) carboxy-terminal silencing domain to TetR (B/E) resulted in a functional transcriptional repressor. This novel repressor, termed tTS-H4, efficiently reduced the activity of the murine HPRT promoter and a constitutively active human cytomegalovirus (hCMV) minimal promoter. Furthermore, combining tTS-H4 with the rtTA transcriptional activator allowed for grading, turning off and resuming target gene expression over several orders of magnitude without background.

CONCLUSIONS

The tTS-H4 repressor is compatible with the commonly used rtTA transcriptional activation system and is a versatile new tool for tightly and adjustably regulating conditional gene expression.

Generation of human hepatocytes by stem cell technology: definition of the hepatocyte

Since 1999, numerous articles have reported the generation of hepatocytes from different types of extrahepatic stem or precursor cells. This opens exciting new possibilities for pharmacology and toxicology, as well as for cell therapy. Hepatocyte marker expression, including albumin, cytokeratin 18, c-met, alpha-fetoprotein and cytochrome P450 3A4 and -2B6, has been observed after transplantation of different types of human stem cells into the liver of laboratory animals or in vitro after incubation with cytokines. These intriguing observations have prompted scientists to classify stem cell-derived cell populations as hepatocytes. However, this conclusion may be premature. It has been shown that factors of the liver microenvironment can induce expression of a limited number of hepatocyte marker genes in nonhepatic cell types. To conclude on the grounds of a limited number of markers that these cells are true hepatocytes is not indicated. In this case one should carefully evaluate crucial hepatocyte-defining enzymatic properties. The present article: i) reviews studies describing the fate of extrahepatic human stem and precursor cells in livers of laboratory animals, including the possibility of cell fusion; and ii) critically discusses the phenotype of stem cells after application of various differentiation protocols aimed at generating human hepatocytes. In addition, the necessary criteria needed for defining a true hepatocyte are suggested. Establishing the necessary properties for stem cell-derived hepatocytes is timely and reasonable, and thus avoids further misleading semantic confusion. Finally, it is essential to understand that the definition of a bona fide hepatocyte should not be limited to qualitative assays, such as reverse transcriptase polymerase chain reaction and immunohistochemistry, but has to include a quantitative analysis of enzymatic activities, which allows direct comparison with primary hepatocytes. Although the stem cell-derived-hepatocyte does not yet exist there is a good chance that this aim may be achieved in the future.

Tetracycline-controlled transgenic targeting from the SCL locus directs conditional expression to erythrocytes, megakaryocytes, granulocytes, and c-kit-expressing lineage-negative hematopoietic cells

The stem cell leukemia gene SCL, also known as TAL-1, encodes a basic helix-loop-helix transcription factor expressed in erythroid, myeloid, megakaryocytic, and hematopoietic stem cells. To be able to make use of the unique tissue-restricted and spatio-temporal expression pattern of the SCL gene, we have generated a knock-in mouse line containing the tTA-2S tetracycline transactivator under the control of SCL regulatory elements. Analysis of this mouse using different tetracycline-dependent reporter strains demonstrated that switchable transgene expression was restricted to erythrocytes, megakaryocytes, granulocytes, and, importantly, to the c-kit-expressing and lineage-negative cell fraction of the bone marrow. In addition, conditional transgene activation also was detected in a very minor population of endothelial cells and in the kidney. However, no activation of the reporter transgene was found in the brain of adult mice. These findings suggested that the expression of tetracycline-responsive reporter genes recapitulated the known endogenous expression pattern of SCL. Our data therefore demonstrate that exogenously inducible and reversible expression of selected transgenes in myeloid, megakaryocytic, erythroid, and c-kit-expressing lineage-negative bone marrow cells can be directed through SCL regulatory elements. The SCL knock-in mouse presented here represents a powerful tool for studying normal and malignant hematopoiesis in vivo.

Aryl hydrocarbon receptor activation by cAMP vs. dioxin: divergent signaling pathways

Even before the first vertebrates appeared on our planet, the aryl hydrocarbon receptor (AHR) gene was present to carry out one or more critical life functions. The vertebrate AHR then evolved to take on functions of detecting and responding to certain classes of environmental toxicants. These environmental pollutants include polycyclic aromatic hydrocarbons (e.g., benzo[a]pyrene), polyhalogenated hydrocarbons, dibenzofurans, and the most potent small-molecular-weight toxicant known, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin). After binding of these ligands, the activated AHR translocates rapidly from the cytosol to the nucleus, where it forms a heterodimer with aryl hydrocarbon nuclear translocator, causing cellular responses that lead to toxicity, carcinogenesis, and teratogenesis. The nuclear form of the activated AHR/aryl hydrocarbon nuclear translocator complex is responsible for alterations in immune, endocrine, reproductive, developmental, cardiovascular, and central nervous system functions whose mechanisms remain poorly understood. Here, we show that the second messenger, cAMP (an endogenous mediator of hormones, neurotransmitters, and prostaglandins), activates the AHR, moving the receptor to the nucleus in some ways that are similar to and in other ways fundamentally different from AHR activation by dioxin. We suggest that this cAMP-mediated activation may reflect the true endogenous function of AHR; disruption of the cAMP-mediated activation by dioxin, binding chronically to the AHR for days, weeks, or months, might be pivotal in the mechanism of dioxin toxicity. Understanding this endogenous activation of the AHR by cAMP may help in developing methods to counteract the toxicity caused by numerous environmental and food-borne toxic chemicals that act via the AHR.

RNAi knock-down mice: an emerging technology for post-genomic functional genetics

RNA interference (RNAi) has been extensively used for sequence-specific silencing of gene function in mammalian cells. The latest major breakthrough in the application of RNAi technology came from experiments demonstrating RNAi-mediated gene repression in mice and rats. After more than two decades of functional mouse research aimed at developing and continuously improving transgenic and knock-out technology, the advent of RNAi knock-down mice represents a valuable new alternative for studying gene function in vivo. In this review we provide some basic insight as to how RNAi can induce gene silencing to then focus on recent findings concerning the applicability of RNAi for regulating gene function in the mouse. Reviewed topics will include delivery methods for RNAi-mediating molecules, a comparison between traditional knock-out and innovative transgenic RNAi technology and the generation of graded RNAi knock-down phenotypes. Apart from the exciting possibilities RNAi provides for studying gene function in mice, we discuss several caveats and limitations to be considered. Finally, we present prospective strategies as to how RNAi technology might be applied for generating conditional and tissue-restricted knock-down mice.

Of mice and models: improved animal models for biomedical research

The ability to engineer the mouse genome has profoundly transformed biomedical research. During the last decade, conventional transgenic and gene knockout technologies have become invaluable experimental tools for modeling genetic disorders, assigning functions to genes, evaluating drugs and toxins, and by and large helping to answer fundamental questions in basic and applied research. In addition, the growing demand for more sophisticated murine models has also become increasingly evident. Good state-of-principle knowledge about the enormous potential of second-generation conditional mouse technology will be beneficial for any researcher interested in using these experimental tools. In this review we will focus on practice, pivotal principles, and progress in the rapidly expanding area of conditional mouse technology. The review will also present an internet compilation of available tetracycline-inducible mouse models as tools for biomedical research (http://www.zmg.uni-mainz.de/tetmouse/).

Distinct 5' SCL enhancers direct transcription to developing brain, spinal cord, and endothelium: neural expression is mediated by GATA factor binding sites

The SCL gene encodes a basic helix-loop-helix transcription factor with a pivotal role in the development of endothelium and of all hematopoietic lineages. SCL is also expressed in the central nervous system, although its expression pattern has not been examined in detail and its function in neural development is unknown. In this article we present the first analysis of SCL transcriptional regulation in vivo. We have identified three spatially distinct regulatory modules, each of which was both necessary and sufficient to direct reporter gene expression in vivo to three different regions within the normal SCL expression domain, namely, developing endothelium, midbrain, and hindbrain/spinal cord. In addition we have demonstrated that GATA factor binding sites are essential for neural expression of the SCL constructs. The midbrain element was particularly powerful and axonal lacZ expression revealed the details of axonal projections, thus implicating SCL in the development of occulomotor, pupillary, or retinotectal pathways. The neural expression pattern of the SCL gene was highly conserved in mouse, chicken, and zebrafish embryos and the 5' region of the chicken SCL locus exhibited a striking degree of functional conservation in transgenic mice. These data suggest that SCL performs critical functions in neural development. The regulatory elements identified here provide important tools for analyzing these functions.