Innate immune response of human pluripotent stem cell-derived airway epithelium

The acquisition of innate immune response is requisite to having bona fide differentiation of airway epithelium. Procedures developed to differentiate lung airway from human pluripotent stem cells (hPSCs) have demonstrated anecdotal evidence for innate immune response, but an in-depth exploration of response levels is lacking. Herein, using an established method of airway epithelial generation from hPSCs, we show that hPSC-derived epithelial cells are able to up-regulate expression of TNFα, IL8 and IL1β in response to challenge with bacterial endotoxin LPS, but lack response from genes associated with innate immune response in other cell types. Further, stimulation of cells with TNF-α resulted in auto-induction of TNFα transcript, as well as cytokine responses of IL8 and IL1β. The demonstration of innate immune induction in hPSC-derived airway epithelia gives further strength to the functionality of in vitro protocols aimed at generating differentiated airway cells that can potentially be used in a translational setting. Finally, we propose that innate immune challenge of airway epithelium from human pluripotent stem cell sources be used as a robust validation of functional in vitro differentiation.

Expansive generation of functional airway epithelium from human embryonic stem cells

Production of human embryonic stem cell (hESC)-derived lung progenitors has broad applicability for drug screening and cell therapy; however, this is complicated by limitations in demarcating phenotypic changes with functional validation of airway cell types. In this paper, we reveal the potential of hESCs to produce multipotent lung progenitors using a combined growth factor and physical culture approach, guided by the use of novel markers LIFRα and NRP1. Lung specification of hESCs was achieved by priming differentiation via matrix-specific support, followed by air-liquid interface to allow generation of lung progenitors capable of in vitro maturation into airway epithelial cell types, resulting in functional characteristics such as secretion of pulmonary surfactant, ciliation, polarization, and acquisition of innate immune activity. This approach provided a robust expansion of lung progenitors, allowing in vivo assessment, which demonstrated that only fully differentiated hESC-derived airway cells were retained in the distal airway, where they aided in physiological recovery in immunocompromised mice receiving airway injury. Our study provides a basis for translational applications of hESCs for lung diseases.

Nonhematopoietic cells represent a more rational target of in vivo hedgehog signaling affecting normal or acute myeloid leukemia progenitors

Recent work has shown that leukemic stem cell self-renewal in chronic myeloid leukemia is dependent on cell-intrinsic hedgehog (Hh) signaling, and early clinical trials suggest that targeting this pathway is also therapeutic in patients with acute myeloid leukemia (AML). In this study, we aimed to better understand Hh signaling in normal hematopoiesis and AML by molecularly and functionally analyzing more than 200 primary human AML patient samples compared with nonleukemic controls. Gene expression analysis indicated that Hh pathway transcripts were similarly regulated in AML and nonleukemic controls, regardless of whether samples were purified based on primitive phenotypes. Consistent with these results, pharmacologic inhibition of Smoothened (SMO) did not preferentially reduce in vitro colony formation of AML versus normal progenitors. Using a unique analytic approach, messenger RNA expression of membrane receptor SMO was found to be unexpectedly rare within all hematopoietic samples analyzed, which is indicative of heterogeneity at the level of Hh signaling machinery. In contrast, abundant SMO expression could be readily detected in the nonhematopoietic fraction of human and murine bone marrow (BM) cells. Our predictions of increased SMO(+) cell frequencies within nonhematopoietic BM fractions were further supported by single-cell protein analyses. Although we did not find support for cell-autonomous sensitivity of AML cells to Hh pathway inhibition, we alternatively suggest that nonhematopoietic BM cells represent an indirect target through which primitive normal and leukemic cells can be modulated. These findings suggest current approaches to applying Hh inhibition should be carefully reevaluated to account for BM niche cell regulation that might be selectively Hh responsive.

Somatic uniparental isodisomy explains multifocality of glomuvenous malformations

Inherited vascular malformations are commonly autosomal dominantly inherited with high, but incomplete, penetrance; they often present as multiple lesions. We hypothesized that Knudson's two-hit model could explain this multifocality and partial penetrance. We performed a systematic analysis of inherited glomuvenous malformations (GVMs) by using multiple approaches, including a sensitive allele-specific pairwise SNP-chip method. Overall, we identified 16 somatic mutations, most of which were not intragenic but were cases of acquired uniparental isodisomy (aUPID) involving chromosome 1p. The breakpoint of each aUPID is located in an A- and T-rich, high-DNA-flexibility region (1p13.1-1p12). This region corresponds to a possible new fragile site. Occurrences of these mutations render the inherited glomulin variant in 1p22.1 homozygous in the affected tissues without loss of genetic material. This finding demonstrates that a double hit is needed to trigger formation of a GVM. It also suggests that somatic UPID, only detectable by sensitive pairwise analysis in heterogeneous tissues, might be a common phenomenon in human cells. Thus, aUPID might play a role in the pathogenesis of various nonmalignant disorders and might explain local impaired function and/or clinical variability. Furthermore, these data suggest that pairwise analysis of blood and tissue, even on heterogeneous tissue, can be used for localizing double-hit mutations in disease-causing genes.

Activin A promotes hematopoietic fated mesoderm development through upregulation of brachyury in human embryonic stem cells

The development of the hematopoietic system involves multiple cellular steps beginning with the formation of the mesoderm from the primitive streak, followed by emergence of precursor populations that become committed to either the endothelial or hematopoietic lineages. A number of growth factors such as activins and fibroblast growth factors (FGFs) are known to regulate the early specification of hematopoietic fated mesoderm, notably in amphibians. However, the potential roles of these factors in the development of mesoderm and subsequent hematopoiesis in the human have yet to be delineated. Defining the cellular and molecular mechanisms by which combinations of mesoderm-inducing factors regulate this stepwise process in human cells in vitro is central to effectively directing human embryonic stem cell (hESC) hematopoietic differentiation. Herein, using hESC-derived embryoid bodies (EBs), we show that Activin A, but not basic FGF/FGF2 (bFGF), promotes hematopoietic fated mesodermal specification from pluripotent human cells. The effect of Activin A treatment relies on the presence of bone morphogenetic protein 4 (BMP4) and both of the hematopoietic cytokines stem cell factor and fms-like tyrosine kinase receptor-3 ligand, and is the consequence of 2 separate mechanisms occurring at 2 different stages of human EB development from mesoderm to blood. While Activin A promotes the induction of mesoderm, as indicated by the upregulation of Brachyury expression, which represents the mesodermal precursor required for hematopoietic development, it also contributes to the expansion of cells already committed to a hematopoietic fate. As hematopoietic development requires the transition through a Brachyury+ intermediate, we demonstrate that hematopoiesis in hESCs is impaired by the downregulation of Brachyury, but is unaffected by its overexpression. These results demonstrate, for the first time, the functional significance of Brachyury in the developmental program of hematopoietic differentiation from hESCs and provide an in-depth understanding of the molecular cues that orchestrate stepwise development of hematopoiesis in a human system.

Pulmonary hypertension in the newborn GTP cyclohydrolase I-deficient mouse

Tetrahydrobiopterin (BH4) is a regulator of endothelial nitric oxide synthase (eNOS) activity. Deficient levels result in eNOS uncoupling, with a shift from nitric oxide to superoxide generation. The hph-1 mutant mouse has deficient GTP cyclohydrolase I (GTPCH1) activity, resulting in low BH4 tissue content. The adult hph-1 mouse has pulmonary hypertension, but whether such condition is present from birth is not known. Thus, we evaluated newborn animals' pulmonary arterial medial thickness, biopterin content (BH4+BH2), H(2)O(2) and eNOS, right ventricle-to-left ventricle+septum (RV/LV+septum) ratio, near-resistance pulmonary artery agonist-induced force, and endothelium-dependent and -independent relaxation. The lung biopterin content was inversely related to age for both types, but significantly lower in hph-1 mice, compared to wild-type animals. As judged by the RV/LV+septum ratio, newborn hph-1 mice have pulmonary hypertension and, after a 2-week 13% oxygen exposure, the ratios were similar in both types. The pulmonary arterial agonist-induced force was reduced (P<0.01) in hph-1 animals and no type-dependent difference in endothelium-dependent or -independent vasorelaxation was observed. Compared to wild-type mice, the lung H(2)O(2) content was increased, whereas the eNOS expression was decreased (P<0.01) in hph-1 animals. The pulmonary arterial medial thickness, a surrogate marker of vascular remodeling, was increased (P<0.01) in hph-1 compared to wild-type mice. In conclusion, our data suggest that pulmonary hypertension is present from birth in the GTPCH1-deficient mice, not as a result of impaired vasodilation, but secondary to vascular remodeling.

Pulmonary hypertension in adult Alk1 heterozygous mice due to oxidative stress

AIMS

Mutations in the ALK1 gene, coding for an endothelial-specific receptor of the transforming growth factor-β superfamily, are the underlying cause of hereditary haemorrhagic telangiectasia type 2, but are also associated with familial pulmonary hypertension (PH). We assessed the lung vasculature of mice with a heterozygous deletion of Alk1 (Alk1(+/-)) for disease manifestations and levels of reactive O(2) species (ROS) implicated in both disorders.

METHODS AND RESULTS

Several signs of PH, including elevated right ventricular (RV) systolic pressure leading to RV hypertrophy, reduced vascular density, and increased thickness and outward remodelling of pulmonary arterioles, were observed in 8- to 18-week-old Alk1(+/-) mice relative to wild-type littermate controls. Higher ROS lung levels were also documented. At 3 weeks, Alk1(+/-) mice were indistinguishable from controls and were prevented from subsequently developing PH when treated with the anti-oxidant Tempol for 6 weeks, confirming a role for ROS in pathogenesis. Levels of NADPH oxidases and superoxide dismutases were higher in adults than newborns, but unchanged in Alk1(+/-) mice vs. controls. Prostaglandin metabolites were also normal in adult Alk1(+/-) lungs. In contrast, NO production was reduced, while endothelial NO synthase (eNOS)-dependent ROS production was increased in adult Alk1(+/-) mice. Pulmonary near resistance arteries from adult Alk1(+/-) mice showed less agonist-induced force and greater acetylcholine-induced relaxation; the later was normalized by catalase or Tempol treatment.

CONCLUSION

The increased pulmonary vascular remodelling in Alk1(+/-) mice leads to signs of PH and is associated with eNOS-dependent ROS production, which is preventable by anti-oxidant treatment.

Pulmonary vascular and cardiac effects of peroxynitrite decomposition in newborn rats

Evidence implicates oxidative stress as playing a prominent role in the pathogenesis of pulmonary hypertension, to which peroxynitrite anion (ONOO(-)) may make a major contribution. Hypothesizing that removal of ONOO(-) would attenuate chronic neonatal pulmonary hypertension, we examined the effects of a ONOO(-) decomposition catalyst (FeTPPS) on pulmonary arteries in vitro, on primary cultured pulmonary artery smooth muscle cell (PASMC) and cardiomyocyte survival and growth, and on central hemodynamics in rat pups exposed to hypoxia (13% O(2)) for 7 days from birth. Daily FeTPPS (30 mg/kg ip) reduced lung nitrotyrosine content, attenuated vascular remodeling, and normalized pulmonary vascular resistance in hypoxia-exposed animals. FeTPPS attenuated proliferation and increased apoptosis of neonatal PASMCs in vitro. Isolated neonatal pulmonary arteries treated with FeTPPS showed reduced agonist-induced force development and enhanced endothelium-dependent and -independent relaxation, possibly via increased nitrate. However, we observed endothelial dysfunction, enhanced lung tissue phosphodiesterase 5 activity, and biventricular cardiac hypertrophy in air-exposed animals receiving FeTPPS. Further, in contrast to PASMCs, FeTPPS enhanced survival of newborn cardiomyocytes. We conclude that decomposition of ONOO(-) with FeTPPS attenuates chronic hypoxia-induced pulmonary hypertension; however, it may negatively influence the modulation of normal pulmonary arterial relaxation function, cell survival, and growth.

Spontaneous adult-onset pulmonary arterial hypertension attributable to increased endothelial oxidative stress in a murine model of hereditary hemorrhagic telangiectasia

OBJECTIVE

Loss-of-function mutations in genes coding for transforming growth factor-beta/bone morphogenetic protein receptors and changes in nitric oxide(*) (NO(*)) bioavailability are associated with hereditary hemorrhagic telangiectasia and some forms of pulmonary arterial hypertension. How these abnormalities lead to seemingly disparate pulmonary pathologies remains unknown. Endoglin (Eng), a transforming growth factor-beta coreceptor, is mutated in hereditary hemorrhagic telangiectasia and involved in regulating endothelial NO(*) synthase (eNOS)-derived NO(*) production and oxidative stress. Because some patients with pulmonary arterial hypertension harbor ENG mutations leading to haplo insufficiency, we investigated the pulmonary vasculature of Eng(+/-) mice and the potential contribution of abnormal eNOS activation to pulmonary arterial hypertension.

METHODS AND RESULTS

Hemodynamic, histological, and biochemical assessments and x-ray micro-CT imaging of adult Eng(+/-) mice indicated signs of pulmonary arterial hypertension including increased right ventricular systolic pressure, degeneration of the distal pulmonary vasculature, and muscularization of small arteries. These findings were absent in 3-week-old Eng(+/-) mice and were attributable to constitutively uncoupled eNOS activity in the pulmonary circulation, as evidenced by reduced eNOS/heat shock protein 90 association and increased eNOS-derived superoxide ((*)O(2)(-)) production in a BH(4)-independent manner. These changes render eNOS unresponsive to regulation by transforming growth factor-beta/bone morphogenetic protein and underlie the signs of pulmonary arterial hypertension that were prevented by Tempol.

CONCLUSIONS

Adult Eng(+/-) mice acquire signs of pulmonary arterial hypertension that are attributable to uncoupled eNOS activity and increased (*)O(2)(-) production, which can be prevented by antioxidant treatment. Eng links transforming growth factor/bone morphogenetic protein receptors to the eNOS activation complex, and its reduction in the pulmonary vasculature leads to increased oxidative stress and pulmonary arterial hypertension.

Airway epithelial-derived factor relaxes pulmonary vascular smooth muscle

The factors controlling the pulmonary vascular resistance under physiological conditions are poorly understood. We have previously reported on an apparent cross talk between the airway and adjacent pulmonary arterial bed where a factor likely derived from the bronchial epithelial cells reduced the magnitude of agonist-stimulated force in the vascular smooth muscle. The main purpose of this investigation was to evaluate whether bronchial epithelial cells release a pulmonary arterial smooth muscle relaxant factor. Conditioned media from SPOC-1 or BEAS-2B, a rat- and a human-derived bronchial epithelial cell line, respectively, were utilized. This media significantly relaxed precontracted adult but not fetal pulmonary arterial muscle in an oxygen tension-dependent manner. This response was mediated via soluble guanylate cyclase, involving AKT/PI3-kinase and neuronal nitric oxide synthase. Airway epithelial cell-conditioned media increased AKT phosphorylation in pulmonary smooth muscle cells (SMC) and reduced intracellular calcium change following ATP stimulation to a significantly greater extent than observed for bronchial SMC. The present data strongly support the evidence for bronchial epithelial cells releasing a stable and soluble factor capable of inducing pulmonary arterial SMC relaxation. We speculate that under physiological conditions, the maintenance of a low pulmonary vascular resistance, postnatally, is in part modulated by the airway epithelium.

Expression profiling of circulating non-red blood cells in embryonic blood

Background

In addition to erythrocytes, embryonic blood contains other differentiated cell lineages and potential progenitor or stem cells homed to changing niches as the embryo develops. Using chicken as a model system, we have isolated an enriched pool of circulating non red blood cells (nRBCs) from E4 and E6 embryos; a transition period when definitive hematopoietic lineages are being specified in the peri-aortic region.

Results

Transcriptome analysis of both nRBC and RBC enriched populations was performed using chicken Affymetrix gene expression arrays. Comparison of transcript profiles of these two populations, with verification by RT-PCR, reveals in nRBCs an expression signature indicative of hematopoietic stem cells (HSCs) and progenitor cells of myeloid and lymphoid lineages, as well as a number of previously undescribed genes possibly involved in progenitor and stem cell maintenance.

Conclusion

This data indicates that early circulating embryonic blood contains a full array of hematopoietic progenitors and stem cells. Future studies on their heterogeneity and differentiation potentials may provide a useful alternative to ES cells and perinatal blood.

Glomulin is predominantly expressed in vascular smooth muscle cells in the embryonic and adult mouse

Mutations in the glomulin gene result in dominantly inherited vascular lesions of the skin known as glomuvenous malformations (GVMs). These lesions are histologically distinguished by their distended vein-like channels containing characteristic 'glomus cells', which appear to be incompletely or improperly differentiated vascular smooth muscle cells (VSMCs). The function of glomulin is currently unknown. We studied glomulin expression during murine development (E9.5 days post-coitum until adulthood) by non-radioactive in situ hybridization. Glomulin was first detected at E10.5 dpc in cardiac outflow tracts. Later, it showed strong expression in VSMCs as well as a limited expression in the perichondrium. At E11.5-14.5 dpc glomulin RNA was most abundant in the walls of the large vessels. At E16.5 dpc expression was also detectable in smaller arteries and veins. The high expression of glomulin in murine vasculature suggests an important role for glomulin in blood vessel development and/or maintenance, which is supported by the vascular phenotype seen in GVM patients with mutations in this gene.