Alpha-1 antitrypsin inhibits fractalkine-mediated monocyte-lung endothelial cell interactions

Chronic obstructive pulmonary disease (COPD) is characterized by nonresolving inflammation fueled by breach in the endothelial barrier and leukocyte recruitment into the airspaces. Among the ligand-receptor axes that control leukocyte recruitment, the full-length fractalkine ligand (CX3CL1)-receptor (CX3CR1) ensures homeostatic endothelial-leukocyte interactions. Cigarette smoke (CS) exposure and respiratory pathogens increase expression of endothelial sheddases, such as a-disintegrin-and-metalloproteinase-domain 17 (ADAM17, TACE), inhibited by the anti-protease α-1 antitrypsin (AAT). In the systemic endothelium, TACE cleaves CX3CL1 to release soluble CX3CL1 (sCX3CL1). During CS exposure, it is not known whether AAT inhibits sCX3CL1 shedding and CX3CR1+ leukocyte transendothelial migration across lung microvasculature. We investigated the mechanism of sCX3CL1 shedding, its role in endothelial-monocyte interactions, and AAT effect on these interactions during acute inflammation. We used two, CS and lipopolysaccharide (LPS) models of acute inflammation in transgenic Cx3cr1gfp/gfp mice and primary human endothelial cells and monocytes to study sCX3CL1-mediated CX3CR1+ monocyte adhesion and migration. We measured sCX3CL1 levels in plasma and bronchoalveolar lavage (BALF) of individuals with COPD. Both sCX3CL1 shedding and CX3CR1+ monocytes transendothelial migration were triggered by LPS and CS exposure in mice, and were significantly attenuated by AAT. The inhibition of monocyte-endothelial adhesion and migration by AAT was TACE-dependent. Compared with healthy controls, sCX3CL1 levels were increased in plasma and BALF of individuals with COPD, and were associated with clinical parameters of emphysema. Our results indicate that inhibition of sCX3CL1 as well as AAT augmentation may be effective approaches to decrease excessive monocyte lung recruitment during acute and chronic inflammatory states.NEW & NOTEWORTHY Our novel findings that AAT and other inhibitors of TACE, the sheddase that controls full-length fractalkine (CX3CL1) endothelial expression, may provide fine-tuning of the CX3CL1-CX3CR1 axis specifically involved in endothelial-monocyte cross talk and leukocyte recruitment to the alveolar space, suggests that AAT and inhibitors of sCX3CL1 signaling may be harnessed to reduce lung inflammation.

Subcutaneous administration of neutralizing antibodies to endothelial monocyte-activating protein II attenuates cigarette smoke-induced lung injury in mice

Proapoptotic and monocyte chemotactic endothelial monocyte-activating protein 2 (EMAPII) is released extracellularly during cigarette smoke (CS) exposure. We have previously demonstrated that, when administered intratracheally during chronic CS exposures, neutralizing rat antibodies to EMAPII inhibited endothelial cell apoptosis and lung inflammation and reduced airspace enlargement in mice (DBA/2J strain). Here we report further preclinical evaluation of EMAPII targeting using rat anti-EMAPII antibodies via either nebulization or subcutaneous injection. Both treatment modalities efficiently ameliorated emphysema-like disease in two different strains of CS-exposed mice, DBA/2J and C57BL/6. Of relevance for clinical applicability, this treatment showed therapeutic and even curative potential when administered either during or following CS-induced emphysema development, respectively. In addition, a fully humanized neutralizing anti-EMAPII antibody administered subcutaneously to mice during CS exposure retained anti-apoptotic and anti-inflammatory effects similar to that of the parent rat antibody. Furthermore, humanized anti-EMAPII antibody treatment attenuated CS-induced autophagy and restored mammalian target of rapamycin signaling in the lungs of mice, despite ongoing CS exposure. Together, our results demonstrate that EMAPII secretion is involved in CS-induced lung inflammation and cell injury, including apoptosis and autophagy, and that a humanized EMAPII neutralizing antibody may have therapeutic potential in emphysema.

Xeroderma Pigmentosum Group C Deficiency Alters Cigarette Smoke DNA Damage Cell Fate and Accelerates Emphysema Development

Cigarette smoke (CS) exposure is a major risk factor for the development of emphysema, a common disease characterized by loss of cells comprising the lung parenchyma. The mechanisms of cell injury leading to emphysema are not completely understood but are thought to involve persistent cytotoxic or mutagenic DNA damage induced by CS. Using complementary cell culture and mouse models of CS exposure, we investigated the role of the DNA repair protein, xeroderma pigmentosum group C (XPC), on CS-induced DNA damage repair and emphysema. Expression of XPC was decreased in mouse lungs after chronic CS exposure and XPC knockdown in cultured human lung epithelial cells decreased their survival after CS exposure due to activation of the intrinsic apoptosis pathway. Similarly, cell autophagy and apoptosis were increased in XPC-deficient mouse lungs and were further increased by CS exposure. XPC deficiency was associated with structural and functional changes characteristic of emphysema, which were worsened by age, similar to levels observed with chronic CS exposure. Taken together, these findings suggest that repair of DNA damage by XPC plays an important and previously unrecognized role in the maintenance of alveolar structures. These findings support that loss of XPC, possibly due to chronic CS exposure, promotes emphysema development and further supports a link between DNA damage, impaired DNA repair, and development of emphysema.

AMD3100 ameliorates cigarette smoke-induced emphysema-like manifestations in mice

We have shown that cigarette smoke (CS)-induced pulmonary emphysema-like manifestations are preceded by marked suppression of the number and function of bone marrow hematopoietic progenitor cells (HPCs). To investigate whether a limited availability of HPCs may contribute to CS-induced lung injury, we used a Food and Drug Administration-approved antagonist of the interactions of stromal cell-derived factor 1 (SDF-1) with its chemokine receptor CXCR4 to promote intermittent HPC mobilization and tested its ability to limit emphysema-like injury following chronic CS. We administered AMD3100 (5mg/kg) to mice during a chronic CS exposure protocol of up to 24 wk. AMD3100 treatment did not affect either lung SDF-1 levels, which were reduced by CS, or lung inflammatory cell counts. However, AMD3100 markedly improved CS-induced bone marrow HPC suppression and significantly ameliorated emphysema-like end points, such as alveolar airspace size, lung volumes, and lung static compliance. These results suggest that antagonism of SDF-1 binding to CXCR4 is associated with protection of both bone marrow and lungs during chronic CS exposure, thus encouraging future studies of potential therapeutic benefit of AMD3100 in emphysema.

Inhibition of acid sphingomyelinase disrupts LYNUS signaling and triggers autophagy

Activation of the lysosomal ceramide-producing enzyme, acid sphingomyelinase (ASM), by various stresses is centrally involved in cell death and has been implicated in autophagy. We set out to investigate the role of the baseline ASM activity in maintaining physiological functions of lysosomes, focusing on the lysosomal nutrient-sensing complex (LYNUS), a lysosomal membrane-anchored multiprotein complex that includes mammalian target of rapamycin (mTOR) and transcription factor EB (TFEB). ASM inhibition with imipramine or sphingomyelin phosphodiesterase 1 (SMPD1) siRNA in human lung cells, or by transgenic Smpd1^+/- haploinsufficiency of mouse lungs, markedly reduced mTOR- and P70-S6 kinase (Thr 389)-phosphorylation and modified TFEB in a pattern consistent with its activation. Inhibition of baseline ASM activity significantly increased autophagy with preserved degradative potential. Pulse labeling of sphingolipid metabolites revealed that ASM inhibition markedly decreased sphingosine (Sph) and Sph-1-phosphate (S1P) levels at the level of ceramide hydrolysis. These findings suggest that ASM functions to maintain physiological mTOR signaling and inhibit autophagy and implicate Sph and/or S1P in the control of lysosomal function.

Sphingolipid regulation of lung epithelial cell mitophagy and necroptosis during cigarette smoke exposure

The mechanisms by which lung structural cells survive toxic exposures to cigarette smoke (CS) are not well defined but may involve proper disposal of damaged mitochondria by macro-autophagy (mitophagy), processes that may be influenced by pro-apoptotic ceramide (Cer) or its precursor dihydroceramide (DHC). Human lung epithelial and endothelial cells exposed to CS exhibited mitochondrial damage, signaled by phosphatase and tensin homolog-induced putative kinase 1 (PINK1) phosphorylation, autophagy, and necroptosis. Although cells responded to CS by rapid inhibition of DHC desaturase, which elevated DHC levels, palmitoyl (C16)-Cer also increased in CS-exposed cells. Whereas DHC augmentation triggered autophagy without cell death, the exogenous administration of C16-Cer was sufficient to trigger necroptosis. Inhibition of Cer-generating acid sphingomyelinase reduced both CS-induced PINK1 phosphorylation and necroptosis. When exposed to CS, Pink1-deficient ( Pink1^-/-) mice, which are protected from airspace enlargement compared with wild-type littermates, had blunted C16-Cer elevations and less lung necroptosis. CS-exposed Pink1^-/- mice also exhibited significantly increased levels of lignoceroyl (C24)-DHC, along with increased expression of Cer synthase 2 ( CerS2), the enzyme responsible for its production. This suggested that a combination of high C24-DHC and low C16-Cer levels might protect against CS-induced necroptosis. Indeed, CerS2^-/- mice, which lack C24-DHC at the expense of increased C16-Cer, were more susceptible to CS, developing airspace enlargement following only 1 month of exposure. These results implicate DHCs, in particular, C24-DHC, as protective against CS toxicity by enhancing autophagy, whereas C16-Cer accumulation contributes to mitochondrial damage and PINK1-mediated necroptosis, which may be amplified by the inhibition of C24-DHC-producing CerS2.-Mizumura, K., Justice, M. J., Schweitzer, K. S., Krishnan, S., Bronova, I., Berdyshev, E. V., Hubbard, W. C., Pewzner-Jung, Y., Futerman, A. H., Choi, A. M. K., Petrache, I. Sphingolipid regulation of lung epithelial cell mitophagy and necroptosis during cigarette smoke exposure.

Oncostatin M and TNF-α Induce Alpha-1 Antitrypsin Production in Undifferentiated Adipose Stromal Cells

Alpha-1 antitrypsin (A1AT), a circulating acute-phase reactant antiprotease, is produced and secreted by cells of endodermal epithelial origin, primarily hepatocytes, and by immune cells. Deficiency of A1AT is associated with increased risk of excessive lung inflammation and injury, especially following chronic cigarette smoke (CS) exposure. Exogenous administration of mesenchymal progenitor cells, including adipose tissue-derived stromal/stem cells (ASC), alleviates CS-induced lung injury through paracrine effectors such as growth factors. It is unknown, however, if mesodermal ASC can secrete functional A1AT and if CS exposure affects their A1AT production. Human ASC collected via liposuction from nonsmoking or smoking donors were stimulated by inflammatory cytokines tumor necrosis alpha (TNFα), oncostatin M (OSM), and/or dexamethasone (DEX) or were exposed to sublethal concentrations of ambient air control or CS extract (0.5%-2%). We detected minimal expression and secretion of A1AT by cultured ASC during unstimulated conditions, which significantly increased following stimulation with TNFα or OSM. Furthermore, TNFα and OSM synergistically enhanced A1AT expression and secretion, which were further increased by DEX. The A1AT transcript variant produced by stimulated ASC resembled that produced by bronchial epithelial cells rather than the variant produced by monocytes/macrophages. While the cigarette smoking status of the ASC donor had no measurable effect on the ability of ASC to induce A1AT expression, active exposure to CS extract markedly reduced A1AT expression and secretion by cultured ASC, as well as human tracheobronchial epithelial cells. ASC-secreted A1AT covalently complexed with neutrophil elastase in control ASC, but not in cells transfected with A1AT siRNA. Undifferentiated ASC may require priming to secrete functional A1AT, a potent antiprotease that may be relevant to stem cell therapeutic effects.

Alpha-1 antitrypsin supplementation improves alveolar macrophages efferocytosis and phagocytosis following cigarette smoke exposure

Cigarette smoking (CS), the main risk factor for COPD (chronic obstructive pulmonary disease) in developed countries, decreases alveolar macrophages (AM) clearance of both apoptotic cells and bacterial pathogens. This global deficit of AM engulfment may explain why active smokers have worse outcomes of COPD exacerbations, episodes characterized by airway infection and inflammation that carry high morbidity and healthcare cost. When administered as intravenous supplementation, the acute phase-reactant alpha-1 antitrypsin (A1AT) reduces the severity of COPD exacerbations in A1AT deficient (AATD) individuals and of bacterial pneumonia in murine models, but the effect of A1AT on AM scavenging functions has not been reported. Apoptotic cell clearance (efferocytosis) was measured in human AM isolated from patients with COPD, in primary rat AM or differentiated monocytes exposed to CS ex vivo, and in AM recovered from mice exposed to CS. A1AT (100 μg/mL, 16 h) significantly ameliorated efferocytosis (by ~50%) in AM of active smokers or AM exposed ex vivo to CS. A1AT significantly improved AM global engulfment, including phagocytosis, even when cells were simultaneously challenged with apoptotic and Fc-coated (bacteria-like) targets. The improved efferocytosis in A1AT-treated macrophages was associated with inhibition of tumor necrosis factor-α converting enzyme (TACE) activity, decreased mannose receptor shedding, and markedly increased abundance of efferocytosis receptors (mannose- and phosphatidyl serine receptors and the scavenger receptor B2) on AM plasma membrane. Directed airway A1AT treatment (via inhalation of a nebulized solution) restored in situ airway AM efferocytosis after CS exposure in mice. The amelioration of CS-exposed AM global engulfment may render A1AT as a potential therapy for COPD exacerbations.

Human adipose-derived stem cells ameliorate cigarette smoke-induced murine myelosuppression via secretion of TSG-6

OBJECTIVE

Bone marrow-derived hematopoietic stem and progenitor cells (HSC/HPC) are critical to homeostasis and tissue repair. The aims of this study were to delineate the myelotoxicity of cigarette smoking (CS) in a murine model, to explore human adipose-derived stem cells (hASC) as a novel approach to mitigate this toxicity, and to identify key mediating factors for ASC activities.

METHODS

C57BL/6 mice were exposed to CS with or without i.v. injection of regular or siRNA-transfected hASC. For in vitro experiments, cigarette smoke extract was used to mimic the toxicity of CS exposure. Analysis of bone marrow HPC was performed both by flow cytometry and colony-forming unit assays.

RESULTS

In this study, we demonstrate that as few as 3 days of CS exposure results in marked cycling arrest and diminished clonogenic capacity of HPC, followed by depletion of phenotypically defined HSC/HPC. Intravenous injection of hASC substantially ameliorated both acute and chronic CS-induced myelosuppression. This effect was specifically dependent on the anti-inflammatory factor TSG-6, which is induced from xenografted hASC, primarily located in the lung and capable of responding to host inflammatory signals. Gene expression analysis within bone marrow HSC/HPC revealed several specific signaling molecules altered by CS and normalized by hASC.

CONCLUSION

Our results suggest that systemic administration of hASC or TSG-6 may be novel approaches to reverse CS-induced myelosuppression.

Scavenger receptor class B, type I-mediated uptake of A1AT by pulmonary endothelial cells

In addition to exerting a potent anti-elastase function, α-1 antitrypsin (A1AT) maintains the structural integrity of the lung by inhibiting endothelial inflammation and apoptosis. A main serpin secreted in circulation by hepatocytes, A1AT requires uptake by the endothelium to achieve vasculoprotective effects. This active uptake mechanism, which is inhibited by cigarette smoking (CS), involves primarily clathrin- but also caveola-mediated endocytosis and may require active binding to a receptor. Because circulating A1AT binds to high-density lipoprotein (HDL), we hypothesized that scavenging receptors are candidates for endothelial uptake of the serpin. Although the low-density lipoprotein (LDL) receptor-related protein 1 (LRP1) internalizes only elastase-bound A1AT, the scavenger receptor B type I (SR-BI), which binds and internalizes HDL and is modulated by CS, may be involved in A1AT uptake. Transmission electron microscopy imaging of colloidal gold-labeled A1AT confirmed A1AT endocytosis in both clathrin-coated vesicles and caveolae in endothelial cells. SR-BI immunoprecipitation identified binding to A1AT at the plasma membrane. Pretreatment of human lung microvascular endothelial cells with SR-B ligands (HDL or LDL), knockdown of SCARB1 expression, or neutralizing SR-BI antibodies significantly reduced A1AT uptake by 30-50%. Scarb1 null mice exhibited decreased A1AT lung content following systemic A1AT administration and reduced lung anti-inflammatory effects of A1AT supplementation during short-term CS exposure. In turn, A1AT supplementation increased lung SR-BI expression and modulated circulating lipoprotein levels in wild-type animals. These studies indicate that SR-BI is an important mediator of A1AT endocytosis in pulmonary endothelium and suggest a cross talk between A1AT and lipoprotein regulation of vascular functions.

Endothelial disruptive proinflammatory effects of nicotine and e-cigarette vapor exposures

The increased use of inhaled nicotine via e-cigarettes has unknown risks to lung health. Having previously shown that cigarette smoke (CS) extract disrupts the lung microvasculature barrier function by endothelial cell activation and cytoskeletal rearrangement, we investigated the contribution of nicotine in CS or e-cigarettes (e-Cig) to lung endothelial injury. Primary lung microvascular endothelial cells were exposed to nicotine, e-Cig solution, or condensed e-Cig vapor (1-20 mM nicotine) or to nicotine-free CS extract or e-Cig solutions. Compared with nicotine-containing extract, nicotine free-CS extract (10-20%) caused significantly less endothelial permeability as measured with electric cell-substrate impedance sensing. Nicotine exposures triggered dose-dependent loss of endothelial barrier in cultured cell monolayers and rapidly increased lung inflammation and oxidative stress in mice. The endothelial barrier disruptive effects were associated with increased intracellular ceramides, p38 MAPK activation, and myosin light chain (MLC) phosphorylation, and was critically mediated by Rho-activated kinase via inhibition of MLC-phosphatase unit MYPT1. Although nicotine at sufficient concentrations to cause endothelial barrier loss did not trigger cell necrosis, it markedly inhibited cell proliferation. Augmentation of sphingosine-1-phosphate (S1P) signaling via S1P1 improved both endothelial cell proliferation and barrier function during nicotine exposures. Nicotine-independent effects of e-Cig solutions were noted, which may be attributable to acrolein, detected along with propylene glycol, glycerol, and nicotine by NMR, mass spectrometry, and gas chromatography, in both e-Cig solutions and vapor. These results suggest that soluble components of e-Cig, including nicotine, cause dose-dependent loss of lung endothelial barrier function, which is associated with oxidative stress and brisk inflammation.

Effects of lipid interactions on model vesicle engulfment by alveolar macrophages

The engulfment function of macrophages relies on complex molecular interactions involving both lipids and proteins. In particular, the clearance of apoptotic bodies (efferocytosis) is enabled by externalization on the cell target of phosphatidylserine lipids, which activate receptors on macrophages, suggesting that (local) specific lipid-protein interactions are required at least for the initiation of efferocytosis. However, in addition to apoptotic cells, macrophages can engulf foreign bodies that vary substantially in size from a few nanometers to microns, suggesting that nonspecific interactions over a wide range of length scales could be relevant. Here, we use model lipid membranes (made of phosphatidylcholine, phosphatidylserine, and ceramide) and rat alveolar macrophages to show how lipid bilayer properties probed by small-angle x-ray scattering and solid-state (2)H NMR correlate with engulfment rates measured by flow cytometry. We find that engulfment of protein-free model lipid vesicles is promoted by the presence of phosphatidylserine lipids but inhibited by ceramide, in accord with a previous study of apoptotic cells. We conclude that the roles of phosphatidylserine and ceramide in phagocytosis is based, at least in part, on lipid-mediated modification of membrane physical properties, including interactions at large length scales as well as local lipid ordering and possible domain formation.

Transient and persistent metabolomic changes in plasma following chronic cigarette smoke exposure in a mouse model

Cigarette smoke exposure is linked to the development of a variety of chronic lung and systemic diseases in susceptible individuals. Metabolomics approaches may aid in defining disease phenotypes, may help predict responses to treatment, and could identify biomarkers of risk for developing disease. Using a mouse model of chronic cigarette smoke exposure sufficient to cause mild emphysema, we investigated whether cigarette smoke induces distinct metabolic profiles and determined their persistence following smoking cessation. Metabolites were extracted from plasma and fractionated based on chemical class using liquid-liquid and solid-phase extraction prior to performing liquid chromatography mass spectrometry-based metabolomics. Metabolites were evaluated for statistically significant differences among group means (p-value≤0.05) and fold change ≥1.5). Cigarette smoke exposure was associated with significant differences in amino acid, purine, lipid, fatty acid, and steroid metabolite levels compared to air exposed animals. Whereas 60% of the metabolite changes were reversible, 40% of metabolites remained persistently altered even following 2 months of smoking cessation, including nicotine metabolites. Validation of metabolite species and translation of these findings to human plasma metabolite signatures induced by cigarette smoking may lead to the discovery of biomarkers or pathogenic pathways of smoking-induced disease.

Smoking exposure induces human lung endothelial cell adaptation to apoptotic stress

Prolonged exposure to cigarette smoking is the main risk factor for emphysema, a component of chronic obstructive pulmonary diseases (COPDs) characterized by destruction of alveolar walls. Moreover, smoking is associated with pulmonary artery remodeling and pulmonary hypertension, even in the absence of COPD, through as yet unexplained mechanisms. In murine models, elevations of intra- and paracellular ceramides in response to smoking have been implicated in the induction of lung endothelial cell apoptosis, but the role of ceramides in human cell counterparts is yet unknown. We modeled paracrine increases (outside-in) of palmitoyl ceramide (Cer16) in primary human lung microvascular cells. In naive cells, isolated from nonsmokers, Cer16 significantly reduced cellular proliferation and induced caspase-independent apoptosis via mitochondrial membrane depolarization, apoptosis-inducing factor translocation, and poly(ADP-ribose) polymerase cleavage. In these cells, caspase-3 was inhibited by ceramide-induced Akt phosphorylation, and by the induction of autophagic microtubule-associated protein-1 light-chain 3 lipidation. In contrast, cells isolated from smokers exhibited increased baseline proliferative features associated with lack of p16(INK4a) expression and Akt hyperphosphorylation. These cells were resistant to Cer16-induced apoptosis, despite presence of both endoplasmic reticulum stress response and mitochondrial membrane depolarization. In cells from smokers, the prominent up-regulation of Akt pathways inhibited ceramide-triggered apoptosis, and was associated with elevated sphingosine and high-mobility group box 1, skewing the cell's response toward autophagy and survival. In conclusion, the cell responses to ceramide are modulated by an intricate cross-talk between Akt signaling and sphingolipid metabolites, and profoundly modified by previous cigarette smoke exposure, which selects for an apoptosis-resistant phenotype.

In vivo knockdown of intersectin-1s alters endothelial cell phenotype and causes microvascular remodeling in the mouse lungs

Intersectin-1s (ITSN-1s) is a general endocytic protein involved in regulating lung vascular permeability and endothelial cells (ECs) survival, via MEK/Erk1/2^MAPK signaling. To investigate the in vivo effects of ITSN-1s deficiency and the resulting ECs apoptosis on pulmonary vasculature and lung homeostasis, we used an ITSN-1s knocked-down (KD_ITSN) mouse generated by repeated delivery of a specific siRNA targeting ITSN-1 gene (siRNA_ITSN). Biochemical and histological analyses as well as electron microscopy (EM) revealed that acute KD_ITSN [3-days (3d) post-siRNA_ITSN treatment] inhibited Erk1/2^MAPK pro-survival signaling, causing significant ECs apoptosis and lung injury; at 10d of KD_ITSN, caspase-3 activation was at peak, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive ECs showed 3.4-fold increase, the mean linear intercept (MLI) showed 48 % augment and pulmonary microvessel density as revealed by aquaporin-1 staining (AQP-1) decreased by 30 %, all compared to controls; pulmonary function was altered. Concomitantly, expression of several growth factors known to activate Erk1/2^MAPK and suppress Bad pro-apoptotic activity increased. KD_ITSN altered Smads activity, downstream of the transforming growth factor beta-receptor-1 (TβR1), as shown by subcellular fractionation and immunoblot analyses. Moreover, 24d post-siRNA_ITSN, surviving ECs became hyper-proliferative and apoptotic-resistant against ITSN-1s deficiency, as demonstrated by EM imaging, 5-bromo-deoxyuridine (BrdU) incorporation and Bad-Ser^112/155 phosphorylation, respectively, leading to increased microvessel density and repair of the injured lungs, as well as matrix deposition. In sum, ECs endocytic dysfunction and apoptotic death caused by KD_ITSN contribute to the initial lung injury and microvascular loss, followed by endothelial phenotypic changes and microvascular remodeling in the remaining murine pulmonary microvascular bed.

Ceramide synthases expression and role of ceramide synthase-2 in the lung: insight from human lung cells and mouse models

Increases in ceramide levels have been implicated in the pathogenesis of both acute or chronic lung injury models. However, the role of individual ceramide species, or of the enzymes that are responsible for their synthesis, in lung health and disease has not been clarified. We now show that C24- and C16-ceramides are the most abundant lung ceramide species, paralleled by high expression of their synthetic enzymes, ceramide synthase 2 (CerS2) and CerS5, respectively. Furthermore, the ceramide species synthesis in the lung is homeostatically regulated, since mice lacking very long acyl chain C24-ceramides due to genetic deficiency of CerS2 displayed a ten-fold increase in C16-ceramides and C16-dihydroceramides along with elevation of acid sphingomyelinase and CerS5 activities. Despite relatively preserved total lung ceramide levels, inhibition of de novo sphingolipid synthesis at the level of CerS2 was associated with significant airflow obstruction, airway inflammation, and increased lung volumes. Our results suggest that ceramide species homeostasis is crucial for lung health and that CerS2 dysfunction may predispose to inflammatory airway and airspace diseases.

Cigarette smoke-induced CXCR3 receptor up-regulation mediates endothelial apoptosis

Endothelial monocyte-activating polypeptide II (EMAP II) and interferon-inducible protein (IP)-10 are proinflammatory mediators, which in addition to their chemokine activities, selectively induce apoptosis in endothelial cells and are up-regulated in the lungs of cigarette smoke-exposed humans. Previously, we showed that EMAP II is an essential mediator of cigarette smoke-induced lung emphysema in mice linking endothelial cell apoptosis with inflammation. Here we addressed the role of the CXCR3 receptor in EMAP II-induced and IP-10-induced apoptosis in endothelial cells and its regulation by cigarette smoke. We found that both neutralizing antibodies and small inhibitory RNA to CXCR3 abrogated EMAP II-induced and IP-10-induced endothelial caspase-3 activation and DNA fragmentation. CXCR3 receptor surface expression in human lung microvascular endothelial cells and in lung tissue endothelium was up-regulated by exposure to cigarette smoke. In tissue culture conditions, EMAP II-induced and IP-10-induced apoptosis was enhanced by preincubation with cigarette smoke extract. Interestingly, serum starvation also induced CXCR3 up-regulation and enhanced EMAP II-induced endothelial apoptosis. Signal transduction via p38 mitogen-activated protein kinase activation was essential for CXCR3-induced cell death, but not for CXCR3 receptor up-regulation by cigarette smoke. In turn, protein nitration was required for CXCR3 receptor up-regulation by cigarette smoke and consequently for subsequent CXCR3-induced cell death. In conclusion, the concerted up-regulation of proinflammatory EMAP II, IP-10, and CXCR3 by cigarette smoke could sustain a cascade of cell death that may promote the alveolar tissue loss noted in human emphysema.

17β-Estradiol attenuates hypoxic pulmonary hypertension via estrogen receptor-mediated effects

RATIONALE

17β-Estradiol (E2) attenuates hypoxic pulmonary vasoconstriction and hypoxic pulmonary hypertension (HPH) through an unknown mechanism that may involve estrogen receptors (ER) or E2 conversion to catecholestradiols and methoxyestradiols with previously unrecognized effects on cardiopulmonary vascular remodeling.

OBJECTIVES

To determine the mechanism by which E2 exerts protective effects in HPH.

METHODS

Male rats were exposed to hypobaric hypoxia while treated with E2 (75 μg/kg/d) or vehicle. Subgroups were cotreated with pharmacologic ER-antagonist or with inhibitors of E2-metabolite conversion. Complementary studies were performed in rats cotreated with selective ERα- or ERβ-antagonist. Hemodynamic and pulmonary artery (PA) and right ventricular (RV) remodeling parameters, including cell proliferation, cell cycle, and autophagy, were measured in vivo and in cultured primary rat PA endothelial cells.

MEASUREMENTS AND MAIN RESULTS

E2 significantly attenuated HPH endpoints. Hypoxia increased ERβ but not ERα lung vascular expression. Co-treatment with nonselective ER inhibitor or ERα-specific antagonist rendered hypoxic animals resistant to the beneficial effects of E2 on cardiopulmonary hemodynamics, whereas ERα- and ERβ-specific antagonists opposed the remodeling effects of E2. In contrast, inhibition of E2-metabolite conversion did not abolish E2 protection. E2-treated hypoxic animals exhibited reduced ERK1/2 activation and increased expression of cell-cycle inhibitor p27(Kip1) in lungs and RV, with up-regulation of lung autophagy. E2-induced signaling was recapitulated in hypoxic but not normoxic endothelial cells, and was associated with decreased vascular endothelial growth factor secretion and cell proliferation.

CONCLUSIONS

E2 attenuates hemodynamic and remodeling parameters in HPH in an ER-dependent manner, through direct antiproliferative mechanisms on vascular cells, which may provide novel nonhormonal therapeutic targets for HPH.

Mechanisms of lung endothelial barrier disruption induced by cigarette smoke: role of oxidative stress and ceramides

The epithelial and endothelial cells lining the alveolus form a barrier essential for the preservation of the lung respiratory function, which is, however, vulnerable to excessive oxidative, inflammatory, and apoptotic insults. Whereas profound breaches in this barrier function cause pulmonary edema, more subtle changes may contribute to inflammation. The mechanisms by which cigarette smoke (CS) exposure induce lung inflammation are not fully understood, but an early alteration in the epithelial barrier function has been documented. We sought to investigate the occurrence and mechanisms by which soluble components of mainstream CS disrupt the lung endothelial cell barrier function. Using cultured primary rat microvascular cell monolayers, we report that CS induces endothelial cell barrier disruption in a dose- and time-dependent manner of similar magnitude to that of the epithelial cell barrier. CS exposure triggered a mechanism of neutral sphingomyelinase-mediated ceramide upregulation and p38 MAPK and JNK activation that were oxidative stress dependent and that, along with Rho kinase activation, mediated the endothelial barrier dysfunction. The morphological changes in endothelial cell monolayers induced by CS included actin cytoskeletal rearrangement, junctional protein zonula occludens-1 loss, and intercellular gap formation, which were abolished by the glutathione modulator N-acetylcysteine and ameliorated by neutral sphingomyelinase inhibition. The direct application of ceramide recapitulated the effects of CS, by disrupting both endothelial and epithelial cells barrier, by a mechanism that was redox and apoptosis independent and required Rho kinase activation. Furthermore, ceramide induced dose-dependent alterations of alveolar microcirculatory barrier in vivo, measured by two-photon excitation microscopy in the intact rat. In conclusion, soluble components of CS have direct endothelial barrier-disruptive effects that could be ameliorated by glutathione modulators or by inhibitors of neutral sphingomyelinase, p38 MAPK, JNK, and Rho kinase. Amelioration of endothelial permeability may alleviate lung and systemic vascular dysfunction associated with smoking-related chronic obstructive lung diseases.

Prdm14 initiates lymphoblastic leukemia after expanding a population of cells resembling common lymphoid progenitors

Understanding the heterogeneous genetic mechanisms of tumor initiation in lymphoid leukemias (LL) will lead to improvements in prognostic classification and treatment regimens. In previous studies of mouse leukemias, we showed that retroviral insertion at the ecotropic viral insertion site 32 locus leads to increased expression of Prdm14, a pluripotency gene implicated in the self-renewal capacity of embryonic stem cells and the early stages of breast cancer. Here, we show that PRDM14 is also overexpressed in ∼25% of human lymphoid neoplasms, with increased frequencies in T-cell acute LL and hyperdiploid precursor B-cell acute LL. To test if Prdm14 overexpression could initiate leukemia, mice were transduced with bone marrow cells transfected with a Prdm14 expression vector. LLs developed in 96% of female mice and 42% of male mice. Before the onset of leukemia, differentiation of transduced cells was biased up to 1000-fold toward cells with features of common lymphoid progenitors (CLPs), and lymphoid differentiation showed a relative block at the pro-B stage. Microarray gene expression analysis of expanded CLP-like cells before the onset of leukemia demonstrated upregulation of genes involved in pluripotency, tumor initiation, early B-lineage commitment, Wnt/Ras signaling and the epithelial-to-mesenchymal transition. Among the dysregulated genes were imprinted genes and non-coding RNAs including Dlk1 and Meg3, which are also key pluripotency mediators. Heightened expression of the estrogen-dependent oncogene, Myb, in tumors suggests a basis for the increased frequency of cancer in female mice. These data provide the first direct evidence for the association of Prdm14 with cancer initiation in an in vivo mouse model and in human lymphoid malignancies, while suggesting mechanisms for Prdm14's mode of action.

Solid-state ²H NMR shows equivalence of dehydration and osmotic pressures in lipid membrane deformation

Lipid bilayers represent a fascinating class of biomaterials whose properties are altered by changes in pressure or temperature. Functions of cellular membranes can be affected by nonspecific lipid-protein interactions that depend on bilayer material properties. Here we address the changes in lipid bilayer structure induced by external pressure. Solid-state ²H NMR spectroscopy of phospholipid bilayers under osmotic stress allows structural fluctuations and deformation of membranes to be investigated. We highlight the results from NMR experiments utilizing pressure-based force techniques that control membrane structure and tension. Our ²H NMR results using both dehydration pressure (low water activity) and osmotic pressure (poly(ethylene glycol) as osmolyte) show that the segmental order parameters (S(CD)) of DMPC approach very large values of ≈ 0.35 in the liquid-crystalline state. The two stresses are thermodynamically equivalent, because the change in chemical potential when transferring water from the interlamellar space to the bulk water phase corresponds to the induced pressure. This theoretical equivalence is experimentally revealed by considering the solid-state ²H NMR spectrometer as a virtual osmometer. Moreover, we extend this approach to include the correspondence between osmotic pressure and hydrostatic pressure. Our results establish the magnitude of the pressures that lead to significant bilayer deformation including changes in area per lipid and volumetric bilayer thickness. We find that appreciable bilayer structural changes occur with osmotic pressures in the range of 10-100 atm or lower. This research demonstrates the applicability of solid-state ²H NMR spectroscopy together with bilayer stress techniques for investigating the mechanism of pressure sensitivity of membrane proteins.

Investigation of a catalyst ink dispersion using both ultra-small-angle X-ray scattering and cryogenic TEM

The dispersion of Nafion ionomer particles and Pt/C catalyst aggregates in liquid media was studied using both ultra-small-angle X-ray scattering (USAXS) and cryogenic TEM. A systematic approach was taken to study first the dispersion of each component (i.e., ionomer particles and Pt/C aggregates), then the combination of the components, and last the catalyst ink. Multiple-level curve fitting was used to extract the particle size, size distribution, and geometry of the Pt/C aggregates and the Nafion particles in liquid media from the scattering data. The results suggest that the particle size, size distribution, and geometry are not uniform throughout the systems but rather vary significantly. It was found that the interaction of each component (i.e., the Nafion ionomer particles and the Pt/C aggregates) occurs in the dispersion. Cryogenic TEM was used to observe the size and geometry of the particles in liquid directly and to validate the scattering results. The TEM results showed excellent agreement.

Phase separation in binary mixtures of bipolar and monopolar lipid dispersions revealed by 2H NMR spectroscopy, small angle x-ray scattering, and molecular theory

Binary mixtures of C(20)BAS and POPC membranes were studied by solid-state (2)H NMR spectroscopy and small angle x-ray scattering (SAXS) over a wide range of concentrations and at different temperatures. Three specifically deuterated C(20)BAS derivatives--[1',1',20',20'-(2)H(4)]C(20)BAS, [2',2',19',19'-(2)H(4)]C(20)BAS, and [10',11'-(2)H(2)]C(20)BAS--combined with protiated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), as well as membranes containing POPC-d(31) and fully protiated bolalipid, were used in NMR experiments to obtain structural information for the mixtures. The (2)H NMR spectra of [10',11'-(2)H(2)]C(20)BAS/POPC membrane dispersions reveal that the bolalipid is predominantly in the transmembrane conformation at high bolalipid concentrations (100, 90, and 70 mol %). At < or =50 mol % C(20)BAS, smaller quadrupolar couplings appear in the spectra, indicating the presence of U-shaped conformers. The proportion of U-shaped bolalipids increases as the amount of POPC in the membrane increases; however, the transmembrane component remains the dominant bolalipid conformation in the membrane even at 45 degrees C and 10 mol % C(20)BAS, where it accounts for approximately 50% of the bolalipid population. The large fraction of C(20)BAS transmembrane conformers, regardless of the C(20)BAS/POPC ratio, together with the findings from molecular mean-field theory calculations, suggests the coexistence of phase-separated bolalipid-rich domains and POPC-rich domains. A single lamellar repeat distance was observed in SAXS experiments corresponding to the average repeat spacing expected for C(20)BAS- and POPC-rich domains. These observations are consistent with the presence of microphase-separated domains in the mixed membrane samples that arise from POPC-C(20)BAS hydrophobic mismatch.

Gene defect in ectodermal dysplasia implicates a death domain adapter in development

Members of the tumour-necrosis factor receptor (TNFR) family that contain an intracellular death domain initiate signalling by recruiting cytoplasmic death domain adapter proteins. Edar is a death domain protein of the TNFR family that is required for the development of hair, teeth and other ectodermal derivatives. Mutations in Edar-or its ligand, Eda-cause hypohidrotic ectodermal dysplasia in humans and mice. This disorder is characterized by sparse hair, a lack of sweat glands and malformation of teeth. Here we report the identification of a death domain adapter encoded by the mouse crinkled locus. The crinkled mutant has an hypohidrotic ectodermal dysplasia phenotype identical to that of the edar (downless) and eda (Tabby) mutants. This adapter, which we have called Edaradd (for Edar-associated death domain), interacts with the death domain of Edar and links the receptor to downstream signalling pathways. We also identify a missense mutation in its human orthologue, EDARADD, that is present in a family affected with hypohidrotic ectodermal dysplasia. Our findings show that the death receptor/adapter signalling mechanism is conserved in developmental, as well as apoptotic, signalling.

Isolation and characterization of Vsx1, a novel mouse CVC paired-like homeobox gene expressed during embryogenesis and in the retina

Gastrula stage mouse embryo RNA was screened by degenerate RT-PCR to yield a novel paired-like homeobox gene. The open reading frame encoded by the cDNA was most similar to human VSX1. Mouse Vsx1 encodes a protein of 363 amino acid residues that contains a CVC domain that was originally identified as a conserved motif among mouse CHX10, goldfish VSX-1 and C. elegans CEH-10. Linkage analysis showed that mouse Vsx1 mapped to the distal region of chromosome 2. RT-PCR analysis detected mouse Vsx1 transcripts from gastrulation and post-gastrulation stage mouse embryos, suggesting a role for Vsx1 during mouse embryogenesis. Analysis of the eyes of mouse chimeras generated with embryonic stem cells in which a lacZ reporter was targeted to the Vsx1 locus suggested that Vsx1 is expressed in the inner nuclear layer of the retina.

Ltap, a mammalian homolog of Drosophila Strabismus/Van Gogh, is altered in the mouse neural tube mutant Loop-tail

Neural tube defects (NTDs) such as spina bifida and anencephaly are common congenital malformations in humans (1/1,000 births) that result from failure of the neural tube to close during embryogenesis. The etiology of NTDs is complex, with both genetic and environmental contributions; the genetic component has been extensively studied with mouse models. Loop-tail (Lp) is a semidominant mutation on mouse chromosome 1 (ref. 4). In the two known Lp alleles (Lp, Lpm1Jus), heterozygous mice exhibit a characteristic looped tail, and homozygous embryos show a completely open neural tube in the hindbrain and spinal region, a condition similar to the severe craniorachischisis defect in humans. Morphological and neural patterning studies indicate a role for the Lp gene product in controlling early morphogenesis and patterning of both axial midline structures and the developing neural plate. The 0.6-cM/0.7-megabase (Mb) Lp interval is delineated proximally by D1Mit113/Apoa2/Fcer1g and distally by Fcer1a/D1Mit149/Spna1 and contains a minimum of 17 transcription units. One of these genes, Ltap, encodes a homolog of Drosophila Strabismus/Van Gogh (Stbm/Vang), a component of the frizzled/dishevelled tissue polarity pathway. Ltap is expressed broadly in the neuroectoderm throughout early neurogenesis and is altered in two independent Lp alleles, identifying this gene as a strong candidate for Lp.

The winged helix/forkhead transcription factor Foxq1 regulates differentiation of hair in satin mice

Satin (sa) homozygous mice have a silky coat with high sheen arising from structurally abnormal medulla cells and defects in differentiation of the hair shaft. We demonstrate that the winged helix/forkhead transcription factor, Foxq1 (Forkhead box, subclass q, member 1) is mutant in sa mice. An intragenic deletion was identified in the radiation-induced satin mutant of the SB/Le inbred strain; a second allele, identified by an N-ethyl-N-nitrosourea (ENU) mutagenesis screen, has a missense mutation in the conserved winged helix DNA-binding domain. Homozygous mutants of the two alleles are indistinguishable. We show that Foxq1 is expressed during embryogenesis and exhibits a tissue-restricted expression pattern in adult tissues. The hair defects appear to be restricted to the inner structures of the hair; consequently, Foxq1 has a unique and distinct function involved in differentiation and development of the hair shaft. Despite an otherwise healthy appearance, satin mice have been reported to exhibit suppressed NK-cell function and alloimmune cytotoxic T-cell function. We show instead that the immune defects are attributable to genetic background differences.

Identification of a new chemically induced allele (Lp(m1Jus)) at the loop-tail locus: morphology, histology, and genetic mapping

Loop-tail (Lp) is a semidominant mutation that affects neurulation in mice. Heterozygous animals are characterized by a looped-tail appearance (pig tail) and wobbly head movements while homozygous embryos exhibit a neural tube closure defect that extends from the caudal midbrain to the tip of the tail. The Lp gene has been finely mapped to the distal part of chromosome 1, and a positional cloning strategy has been initiated to isolate the defective gene. This study represents the characterization of a new Lp allele (Lp(m1Jus)) induced by N-ethyl-N-nitrosurea mutagenesis. Lp(m1Jus)/+ mice have a looped-tail appearance, and both Lp(m1Jus)/Lp(m1Jus) homozygotes and Lp/Lp(m1Jus) compound heterozygotes fail to initiate neural tube closure along most of the embryonic axis. These data indicate that the Lp(m1Jus) allele causes a neural tube defect and overall phenotype similar to that of the original Lp allele. Segregation analysis of 90 (Lp(m1Jus)/+ x C57BL/6J)F(1) x C57BL/6J looped-tail mice with seven markers that define the Lp genetic map (D1Mit455/D1Mit146/D1Mit148/D1Mit270-1 cM-D1Mit113-0.4 cM-Lp-0.2 cM-D1Mit149-0.8 cM-D1Mit115) showed significant linkage between Lp(m1Jus) and all loci analyzed (P < 0.0001). Eight crossovers were detected with the proximal cluster of D1Mit455, D1Mit146, D1Mit148, and D1Mit270, indicating a recombination rate higher than expected in this region, and a single recombinant was encountered with the distal markers D1Mit149 and D1Mit115. Based on these phenotypic and genetic data, Lp(m1Jus) is most likely allelic to Lp, thereby representing a valuable additional tool for the positional cloning of the Lp gene and its subsequent molecular characterization.

Capitalizing on large-scale mouse mutagenesis screens

Variation is the crux of genetics. Mutagenesis screens in organisms from bacteria to fish have provided a battery of mutants that define protein functions within complex pathways. Large-scale mutation isolation has been carried out in Caenorhabditis elegans, Drosophila melanogaster and zebrafish, and has been recently reported in the mouse in two screens that have generated many new, clinically relevant mutations to reveal the power of phenotype-driven screens in a mammal.

Developmental eye and neural tube defects in the eye blebs mouse

In the mouse, eye blebs (eb) is a spontaneous mutation that presents a useful model for the study of abnormal eye development. Since its initial description three decades ago, little information has been generated regarding the developmental course of eb eyes. Although the gene for eb has not been identified, much can be learned from the developmental defects present in the eb mouse. First detected in the eye at embryonic day 11.5 (E11.5), the eb defect is observed as an increased vascularization throughout the developing eye and head region. As development proceeds, the embryonic eye fills with blood, and the resulting hematoma distorts the shape of the iris. The eyelids fail to close, and animals are born with open eyes. Lens degeneration and retinal folding are characteristic of eb, as are microphthalmia and thick, disorganized irises. A second presentation of the eb defect is disruption of neural tube closure in the anterior and hindbrain neuropores. These eb animals are born with open neural tubes but with apparently normal eyes.

Mouse ENU mutagenesis

The progress of human genome sequencing is driving genetic approaches to define gene function. Strategies such as gene traps and chemical mutagenesis will soon generate a large mutant mouse resource. Point mutations induced by N -ethyl- N -nitrosourea (ENU) provide a unique mutant resource because they: (i) reflect the consequences of single gene change independent of position effects; (ii) provide a fine-structure dissection of protein function; (iii) display a range of mutant effects from complete or partial loss of function to exaggerated function; and (iv) discover gene functions in an unbiased manner. Phenotype-driven ENU screens in the mouse are emphasizing relevance to human clinical disease by targeting cardiology, physiology, neurology, immunity, hematopoiesis and mammalian development. Such approaches are extremely powerful in understanding complex human diseases and traits: the base-pair changes may accurately model base changes found in human diseases, and subtle mutant alleles in a standard genetic background provide the ability to analyze the consequences of compound genotypes. Ongoing mouse ENU mutagenesis experiments are generating a treasure trove of new mutations to allow an in-depth study of a single gene, a chromosomal region or a biological system.

Effects of ENU dosage on mouse strains

The germline supermutagen, N-ethyl-N-nitrosourea (ENU), has a variety of effects on mice. ENU is a toxin and carcinogen as well as a mutagen, and strains differ in their susceptibility to its effects. Therefore, it is necessary to determine an appropriate mutagenic, non-toxic dose of ENU for strains that are to be used in experiments. In order to provide some guidance, we have compiled data from a number of laboratories that have exposed male mice from inbred and non-inbred strains or their F(1) hybrids to ENU. The results show that most F(1) hybrid animals tolerate ENU well, but that inbred strains of mice vary in their longevity and in their ability to recover fertility after treatment with ENU.

Mouse as the measure of man?

The humble house mouse's cohabitation with humans has been noted since the birth of agriculture, about 10 000 years ago, in the fertile flood plains of the Middle East. In recent times, however, the mouse has been elevated from pest to model for the study of human health and disease. Recent genomics and genetics initiatives will ensure the continued growth of the house mouse as a disease model.

Optimal N-ethyl-N-nitrosourea (ENU) doses for inbred mouse strains

ENU is a powerful germline mutagen in the mouse, providing the opportunity to analyze the functions of large numbers of genes in the mammalian genome. In many mutagenesis experiments, it would be beneficial to exploit the advantages of inbred mouse strains. To perform an effective ENU mutagenesis screen using inbred mice, a dosage regimen is required to determine the optimal dose of ENU for that inbred strain, a time-consuming preliminary process. We have carried out dosage regimens for mutagenizing doses of ENU in ten inbred strains of mouse: 129X1/SvJ, 129S6/SvEv, A/J, BALB/cJ, BTBR/N, C3He/J, C3HeB/FeJ, C57BL/6J, C57BR/cdJ, and CBA/CaJ, and determined an optimal dose for each strain, defined by length of sterile period and number of males to survive treatment. Three strains: A/J, BALB/cJ and C57BL/6J, are able to tolerate high doses, up to 300 mg/kg body weight, and are highly recommended for mutagenesis studies.

Genetic profile of insertion mutations in mouse leukemias and lymphomas

Murine leukemia retroviruses (MuLVs) cause leukemia and lymphoma in susceptible strains of mice as a result of insertional mutation of cellular proto-oncogenes or tumor suppressor genes. Using a novel approach to amplify and sequence viral insertion sites, we have sequenced >200 viral insertion sites from which we identify >35 genes altered by viral insertion in four AKXD mouse strains. The class of genes most frequently altered are transcription factors, however, insertions are found near genes involved in signal transduction, cell cycle control, DNA repair, cell division, hematopoietic differentiation, and near many ESTs and novel loci. Many of these mutations identify genes that have not been implicated in cancer. By isolating nearly all the somatic viral insertion mutations contributing to disease in these strains we show that each AKXD strain displays a unique mutation profile, suggesting strain-specific susceptibility to mutations in particular genetic pathways.

A comparative transcript map and candidates for mutant phenotypes in the Tyrp1 (brown) deletion complex homologous to human 9p21-23

The mouse Tyrp1 deletion complex is a valuable resource for high-resolution mapping of genes and phenotypes to the central region of Chromosome (Chr) 4. The distal part of the complex is homologous to human Chr 9p21-23, and we have used the available radiation hybrid maps to identify human transcripts in the region. We localize seven genes to a human YAC contig that spans the full extent of the distal deletion complex and show that the mouse homologs of four of these, including Cer1, map within the complex. On the basis of location and/or expression, we exclude genes as candidates for several known phenotypes in the region and identify a candidate transcript for the neonatal lethal phenotype l(4)Rn2.

Activation of Hex and mEg5 by retroviral insertion may contribute to mouse B-cell leukemia

AKXD recombinant inbred mice develop a variety of leukemias and lymphomas due to retrovirally mediated insertional activation of cellular proto-oncogenes. We describe a new retroviral insertion site that is the most frequent genetic alteration in AKXD B-cell leukemias. Multiple genes flank the site of viral insertion, but the expression of just two, Hex and mEg5, is significantly upregulated. Hex is a divergent homeobox gene that is transiently expressed in many hematopoietic lineages, suggesting an involvement in cellular differentiation. mEg5 is a member of the bim-C subfamily of kinesin related proteins that are necessary for spindle formation and stabilization during mitosis. Our data provide the first genetic evidence for the activation of these genes in leukemia, and suggest that unscheduled expression of Hex and mEg5 contributes to the development of B-cell leukemia. In addition, this work highlights the use of genomic approaches for the study of position effect mutations.

Contrasting effects of ENU induced embryonic lethal mutations of the quaking gene

Multiple alleles of the quaking (qk) gene have a variety of phenotypes ranging in severity from early embryonic death to viable dysmyelination. A previous study identified a candidate gene, QKI, that contains an RNA-binding domain and encodes at least three protein isoforms (QKI-5, -6 and -7). We have determined the genomic structure of QKI, identifying an additional alternative end in cDNAs. Further we have examined the exons and splice sites for mutations in the lethal alleles qkl-1, qkkt1, qkk2, and qkkt3. The mutation in qkl-1 creates a splice site in the terminal exon of the QKI-6 isoform. Missense mutations in the KH domain and the QUA1 domains in qkk2 and qkkt3, respectively, indicate that these domains are of critical functional importance. Although homozygotes for each ENU induced allele die as embryos, their phenotypes as viable compound heterozygotes with qkv differ. Compound heterozygous qkv animals carrying qkkt1, qkk2, and qkkt3 all exhibit a permanent quaking phenotype similar to that of qkv/qkv animals, whereas qkv/qkl-1 animals exhibit only a transient quaking phenotype. The qkl-1 mutation eliminates the QKI-5 isoform, showing that this isoform plays a crucial role in embryonic survival. The transient quaking phenotype observed in qkv/qkl-1 mice indicates that the QKI-6 and QKI-7 isoforms function primarily during myelination, but that QKI-5 may have a concentration-dependent role in early myelination. This mutational analysis demonstrates the power of series of alleles to examine the function of complex loci and suggests that additional mutant alleles of quaking could reveal additional functions of this complex gene.

A mouse chromosome 19 genetic map including the Lvis1 viral insertion site

Somatic insertion mutations, such as those caused by the insertion of a proviral element, can contribute to abnormal cell growth by activating cellular proto-oncogenes or inactivating tumor suppressor genes. Lvis1 is a genomic locus frequently disrupted by viral insertion in AKXD B-cell lymphomas (manuscript submitted for publication). To determine whether insertion mutations at Lvis1 affect a known proto-oncogene or tumor suppressor gene, we mapped Lvis1 to distal mouse chromosome 19. A detailed molecular genetic map of this region was constructed, localizing Lvis1 relative to 20 gene and microsatellite markers, 3 of which have not been mapped in the mouse (Nfkb2, Nlz, and Wnt8b). This analysis revealed that Lvis1 maps between two previously identified viral insertion sites, His2 and Frat1, and does not cosegregate with known gene markers. In addition, our study refines the gene order for distal mouse chromosome 19 and expands the comparative map between mouse chromosome 19 and the human chromosome 10q23-q26 homology region.