Mary E. Sunday

Thrombospondin-1 is required for normal murine pulmonary homeostasis and its absence causes pneumonia.

The thrombospondins are a family of extracellular calcium-binding proteins that modulate cellular phenotype. Thrombospondin-1 (TSP-1) reportedly regulates cellular attachment, proliferation, migration, and differentiation in vitro. To explore its function in vivo, we have disrupted the TSP-1 gene by homologous recombination in the mouse genome. Platelets from these mice are completely deficient in TSP-1 protein; however, thrombin-induced platelet aggregation is not diminished. TSP-1-deficient mice display a mild and variable lordotic curvature of the spine that is apparent from birth. These mice also display an increase in the number of circulating white blood cells, with monocytes and eosinophils having the largest percent increases. The brain, heart, kidney, spleen, stomach, intestines, aorta, and liver of TSP-1-deficient mice showed no major abnormalities. However, consistent with high levels of expression of TSP-1 in lung, we observe abnormalities in the lungs of mice that lack the protein. Although normal at birth, histopathological analysis of lungs from 4-wk-old TSP-1-deficient mice reveals extensive acute and organizing pneumonia, with neutrophils and macrophages. The macrophages stain for hemosiderin, indicating that diffuse alveolar hemorrhage is occurring. At later times, the number of neutrophils decreases and a striking increase in the number of hemosiderin-containing macrophages is observed associated with multiple-lineage epithelial hyperplasia and the deposition of collagen and elastin. A thickening and ruffling of the epithelium of the airways results from increasing cell proliferation in TSP-1-deficient mice. These results indicate that TSP-1 is involved in normal lung homeostasis.

Differential expression of VEGF isoforms in mouse during development and in the adult.

Vascular endothelial growth factor (VEGF), a factor that is critical for development of the vascular system in mouse embryos, exists as at least three isoforms, VEGF120, VEGF164, and VEGF188. The isoforms have different affinities for heparan sulfate as well as for the three known VEGF receptors, VEGFR‐1 (Flt‐1), VEGFR‐2 (Flk‐1), and neuropilin‐1, suggesting that different VEGF isoforms may play distinct roles in vascular development. To determine whether there are differences in the organ‐specific expression patterns that would support this concept, we used a quantitative RNase protection assay (RPA) to determine the distribution of different VEGF isoform mRNA in developing and adult mouse organs. Results revealed that the ratios of the three VEGF isoforms changed during organ development and that adult organs expressed different levels of the three VEGF isoforms. Because the lung expressed the highest levels of VEGF188 isoform, we used VEGF isoform‐specific in situ hybridization in the developing lung and determined that type II alveolar epithelial cells were expressing high levels of VEGF188 mRNA. Finally, targeted exon deletion of the VEGF gene revealed that mice that developed in the absence of the heparan sulfate binding isoforms VEGF164 and VEGF188, displayed a variety of vascular defects, including abnormal pulmonary vascular development. Our results support the concept that different VEGF isoforms have distinct functions in vascular development.

Gastrin-Releasing Peptide (Mammalian Bombesin) Gene Expression in Health and Disease

In recent years much attention has been focused on gastrin-releasing peptide (GRP), the mammalian homologue of bombesin, both as a neuroregulatory hormone and as a tissue-specific growth factor in normal and neoplastic tissues. This paper will analyze the distribution and role of GRP in normal mammalian tissues and examine the potential involvement of GRP in diverse pathologic processes.

Control of Basement Membrane Remodeling and Epithelial Branching Morphogenesis in Embryonic Lung by Rho and Cytoskeletal Tension

Local alterations in the mechanical compliance of the basement membrane that alter the level of isometric tension in the cell have been postulated to influence tissue morphogenesis. To explore whether cell tension contributes to tissue pattern formation in vivo, we modulated cytoskeletal force generation in embryonic mouse lung (embryonic days 12–14) rudiments using inhibitors of Rho‐associated kinase (ROCK), myosin light chain kinase, myosin ATPase, and microfilament integrity, or a Rho stimulator (cytotoxic necrotizing factor‐1). Tension inhibition resulted in loss of normal differentials in basement membrane thickness, inhibition of new terminal bud formation, and disorganization of epithelial growth patterns as well as disruption of capillary blood vessels. In contrast, increasing cell tension through Rho activation, as confirmed by quantitation of myosin light chain phosphorylation and immunohistocytochemical analysis of actin organization, accelerated lung branching and increase capillary elongation. These data suggest that changes in cytoskeletal tension mediated by Rho signaling through ROCK may play an important role in the establishment of the spatial differentials in cell growth and extracellular matrix remodeling that drive embryonic lung development. Developmental Dynamics 232:268–281, 2005.

Suppression of tumor formation in vivo by expression of the JE gene in malignant cells.

The early growth response gene JE encodes a monocyte chemoattractant, MCP-1. The JE/MCP-1 protein attracts and stimulates human monocytes and induces monocyte-mediated inhibition of tumor cell growth in vitro. Expression of human or murine JE/MCP-1 in Chinese hamster ovary (CHO) cells completely suppressed their ability to form tumors in nude mice. Coinjection of JE/MCP-1-expressing cells with nonexpressing CHO cells or with HeLa cells also prevented tumor formation. Since JE/MCP-1 expression had no discernible effect on the tranformed phenotype of these cells in vitro, the suppressive effect depends on host animal factors. These factors are likely to be components of the inflammatory response, because JE/MCP-1-expressing cells elicited a predominantly monocytic infiltrate at the site of injection. Our results suggest that JE/MCP-1 protein may be useful in cancer therapy.

Airway epithelial cells: current concepts and challenges.

The adult human bronchial tree is covered with a continuous layer of epithelial cells that play a critical role in maintaining the conduit for air, and which are central to the defenses of the lung against inhaled environmental concomitants. The epithelial sheet functions as an interdependent unit with the other lung components. Importantly, the structure and/or function of airway epithelium is deranged in major lung disorders, including chronic obstructive pulmonary disease, asthma, and bronchogenic carcinoma. Investigations regarding the airway epithelium have led to many advances over the past few decades, but new developments in genetics and stem cell/progenitor cell biology have opened the door to understanding how the airway epithelium is developed and maintained, and how it responds to environmental stress. This article provides an overview of the current state of knowledge regarding airway epithelial stem/progenitor cells, gene expression, cell-cell interactions, and less frequent cell types, and discusses the challenges for future areas of investigation regarding the airway epithelium in health and disease.

An intrinsic adrenergic system in mammalian heart.

We have identified a previously undescribed intrinsic cardiac adrenergic (ICA) cell type in rodent and human heart. Northern and Western blot analyses demonstrated that ICA cell isolates contain mRNA and protein of enzymes involved in catecholamine biosynthesis. Radioenzymatic catecholamine assays also revealed that the catecholamine profile of adult rat ICA cell isolates differed from that of sympathetic neurons. Unlike sympathetic neuronal cells, isolated ICA cells have abundant clear vesicles on electron microscopy. Endogenous norepinephrine and epinephrine constitutively released by ICA cells in vitro affect the spontaneous beating rate of neonatal rat cardiac myocytes in culture. Finally, ICA cells could be identified in human fetal hearts at a developmental stage before sympathetic innervation of the heart has been documented to occur. These findings support the concept that these cells constitute an ICA signaling system capable of participating in cardiac regulation that appears to be independent of sympathetic innervation.

Embryonic mouse lung epithelial progenitor cells co-express immunohistochemical markers of diverse mature cell lineages.

Developmental expression of marker genes representative of different mature cell types can be used to study differentiation of cell lineages. We used immunohistochemistry to study expression in developing mouse lung of calcitonin gene-related peptide (CGRP), Clara cell 10-KD protein (CC10), and surfactant protein-A (SP-A), markers that are differentially expressed in neuroendocrine cells, Clara cells, and Type II alveolar cells. Two distinct developmental phases were revealed. The earlier phase (embryonic days 13-15; E13-E15) was characterized by CGRP, CC10, and SP-A immunostaining in all epithelial cells of the distal airways, with the three patterns being virtually identical in adjacent sections. The later phase (E16-E18) was characterized by emergence of staining of the differentiated cell types. These expression patterns were recapitulated in serumless organ culture, demonstrating that information necessary to generate both phases of gene expression is present within the lung analage by E11. We conclude that CGRP, CC10, and SP-A are co-expressed in most or all cells of the distal lung epithelium at E13-E15 and later become restricted to different cell lineages. This transient expression in progenitor cells of gene products characteristic of diverse differentiated cell types may reflect an underlying mechanism of gene regulation.

Transient elevation of messenger RNA encoding gastrin-releasing peptide, a putative pulmonary growth factor in human fetal lung.

Gastrin-releasing peptide (GRP), the mammalian homologue of the amphibian peptide bombesin, is present in pulmonary neuroendocrine cells and appears to be a growth factor for both normal and neoplastic pulmonary cells. Previously we have reported the cloning of the messenger RNAs (mRNAs) and gene that encode human GRP. We now report that GRP mRNAs are markedly elevated in human fetal lung during the canalicular phase of pulmonary development (from approximately 16 to 30 wk gestation). By RNA blot and in situ hybridization analyses, GRP mRNAs were first detectable in fetal lung at 9-10 wk, plateaued at levels 25-fold higher than in adult lungs from 16 to approximately 30 wk and then declined to near adult levels by 34 wk gestation. By contrast, GRP peptide levels remain elevated until several months after birth. Consistent with this, in situ hybridization and immunohistochemical studies showed that GRP mRNA and peptide consistently colocalized in early gestation lung but that in neonatal lung, many cells that contained GRP peptide no longer contained GRP mRNA. The transient expression of high levels of GRP mRNAs during an approximately 12-wk phase of fetal lung development suggests that the secretion of GRP or its COOH-terminal peptides from pulmonary neuroendocrine cells may play a role in normal lung development.

CD10/neutral endopeptidase 24.11 in developing human fetal lung. Patterns of expression and modulation of peptide-mediated proliferation.

The cell membrane-associated enzyme CD10/neutral endopeptidase 24.11 (CD10/NEP) functions in multiple organ systems to downregulate responses to peptide hormones. Recently, CD10/NEP was found to hydrolyze bombesin-like peptides (BLP), which are mitogens for normal bronchial epithelial cells and small cell lung carcinomas. Growth of BLP-responsive small cell lung carcinomas was potentiated by CD10/NEP inhibition, implicating CD10/NEP in regulation of BLP-mediated tumor growth. BLP are also likely to participate in normal lung development because high BLP levels are found in fetal lung, and bombesin induces proliferation and maturation of human fetal lung in organ cultures and murine fetal lung in utero. To explore potential roles for CD10/NEP in regulating peptide-mediated human fetal lung development, we have characterized temporal and cellular patterns of CD10/NEP expression and effects of CD10/NEP inhibition in organ cultures. Peak CD10/NEP transcript levels are identified at 11-13 wk gestation by Northern blots and localized to epithelial cells and mesenchyme of developing airways by in situ hybridization. CD10/NEP immunostaining is most intense in undifferentiated airway epithelium. In human fetal lung organ cultures, inhibition of CD10/NEP with either phosphoramidon or SCH32615 increases thymidine incorporation by 166-182% (P < 0.025). The specific BLP receptor antagonist, [Leu13-psi(CH2NH)Leu14]bombesin abolishes these effects on fetal lung growth, suggesting that CD10/NEP modulates BLP-mediated proliferation. CD10/NEP expression in the growing front of airway epithelium and the effects of CD10/NEP inhibitors in lung explants implicate the enzyme in the regulation of peptide-mediated fetal lung growth.