Synopsis Speakers in this symposium presented examples of respiratory regulation that broadly ill... more Synopsis Speakers in this symposium presented examples of respiratory regulation that broadly illustrate principles of evolution from whole organ to genes. The swim bladder and lungs of aquatic and terrestrial organisms arose independently from a common primordial ''respiratory pharynx'' but not from each other. Pathways of lung evolution are similar between crocodiles and birds but a low compliance of mammalian lung may have driven the development of the diaphragm to permit lung inflation during inspiration. To meet the high oxygen demands of flight, bird lungs have evolved separate gas exchange and pump components to achieve unidirectional ventilation and minimize dead space. The process of ''screening'' (removal of oxygen from inspired air prior to entering the terminal units) reduces effective alveolar oxygen tension and potentially explains why nonathletic large mammals possess greater pulmonary diffusing capacities than required by their oxygen consumption. The ''primitive'' central admixture of oxygenated and deoxygenated blood in the incompletely divided reptilian heart is actually co-regulated with other autonomic cardiopulmonary responses to provide flexible control of arterial oxygen tension independent of ventilation as well as a unique mechanism for adjusting metabolic rate. Some of the most ancient oxygen-sensing molecules, i.e., hypoxiainducible factor-1alpha and erythropoietin, are up-regulated during mammalian lung development and growth under apparently normoxic conditions, suggesting functional evolution. Normal alveolarization requires pleiotropic growth factors acting via highly conserved cell-cell signal transduction, e.g., parathyroid hormone-related protein transducing at least partly through the Wingless/int pathway. The latter regulates morphogenesis from nematode to mammal. If there is commonality among these diverse respiratory processes, it is that all levels of organization, from molecular signaling to structure to function, co-evolve progressively, and optimize an existing gas-exchange framework.
Abstract Rationale: Animal models demonstrate that aberrant gene expression in utero can result i... more Abstract Rationale: Animal models demonstrate that aberrant gene expression in utero can result in abnormal pulmonary phenotypes. Objectives: We sought to identify genes that are differentially expressed during in utero airway development and test the hypothesis that variants in these genes influence lung function in patients with asthma.
ABSTRACT Although alveolar wall thinning has been attributed to apoptosis of interstitial lung li... more ABSTRACT Although alveolar wall thinning has been attributed to apoptosis of interstitial lung lipofibroblasts (LFs), the underlying molecular mechanism(s) remains unknown. Although the physiological vitamin D steroid hormone 1alpha,25(OH)(2)D(3) (1,25D) has been suggested as a local paracrine/autocrine effector of fetal lung maturation and is known to affect fibroblast apoptosis, its effects on LF apoptosis are unknown. We determined the role of 1,25D and its metabolite, C-3-epimer (3-epi-1,25D), on LF and alveolar type II (ATII) cell differentiation, proliferation, and apoptosis. Embryonic day 19 Sprague-Dawley fetal rat lung LFs and ATII cells were treated with 1,25D or 3-epi-1,25D (1 x 10(-10) to 1 x 10(-8) M) for 24 h, and cell proliferation, apoptosis, and differentiation were assessed. Both 1,25D and 3-epi-1,25D exhibited dose-dependent increases in expression of the key homeostatic epithelial-mesenchymal differentiation markers, increased LF and ATII cell proliferation, and decreased apoptosis. Furthermore, rat pups administered 1,25D from postnatal days 0 to 14 showed increased expressions of key LF and ATII cell differentiation markers, increased Bcl-2-to-Bax ratio as an index of decreased spontaneous alveolar LF and ATII cell apoptosis, increased alveolar count, and a paradoxical increase in septal thickness. We conclude that spatial- and temporal-specific actions of vitamin D play a critical role in perinatal lung maturation by stimulating key alveolar epithelial-mesenchymal interactions and by modulating LF proliferation/apoptosis. These data not only provide the biological rationale for the presence of an alveolar vitamin D paracrine system, but also provide the first integrated molecular mechanism for increased surfactant synthesis and alveolar septal thinning during perinatal lung maturation.
Functional maturation of pulmonary alveolar epithelial cells is crucial for extrauterine survival... more Functional maturation of pulmonary alveolar epithelial cells is crucial for extrauterine survival. Mechanical distension and mesenchymal-epithelial interactions play important roles in this process. We hypothesized that mechanical stretch simulating fetal breathing movements is an important regulator of pulmonary epithelial cell differentiation. Using a Flexercell Strain Unit, we analyzed effects of stretch on primary cultures of type II cells and cocultures of epithelial and mesenchymal cells isolated from fetal rat lungs during late development. Cyclic stretch of isolated type II cells increased surfactant protein (SP) C mRNA expression by 150 +/- 30% over controls (P < 0.02) on gestational day 18 and by 130 +/- 30% on day 19 (P < 0.03). Stretch of cocultures with fibroblasts increased SP-C expression on days 18 and 19 by 170 +/- 40 and 270 +/- 40%, respectively, compared with unstretched cocultures. On day 19, stretch of isolated type II cells increased SP-B mRNA expression by 50% (P < 0.003). Unlike SP-C, addition of fibroblasts did not produce significant additional effects on SP-B mRNA levels. Under these conditions, we observed only modest increases in cellular immunoreactive SP-B, but secreted saturated phosphatidylcholine rose by 40% (P < 0.002). These results indicate that cyclic stretch promotes developmentally timed differentiation of fetal type II cells, as a direct effect on epithelial cell function and via mesenchymal-epithelial interactions. Expression of the SP-C gene appears to be highly responsive to mechanical stimulation.
American Journal of Respiratory and Critical Care Medicine, Feb 15, 2010
At-a-Glance Commentary: Scientific Knowledge on the Subject: The trajectory of lung function grow... more At-a-Glance Commentary: Scientific Knowledge on the Subject: The trajectory of lung function growth appears to be set early in life. Animal models demonstrate that abnormal in utero expression of genes implicated in normal lung development can result in abnormal pulmonary phenotypes after birth.
In the post-genomic era the complex problem of evolutionary biology can be tackled from the top-d... more In the post-genomic era the complex problem of evolutionary biology can be tackled from the top-down, the bottom-up, or from the middle-out. Given the emergent and contingent nature of this process, we have chosen to take the latter approach, both as a mechanistic link to developmental biology and as a rational means of identifying signaling mechanisms based on their functional genomic significance. Using this approach, we have been able to configure a working model for lung evolution by reverse-engineering lung surfactant from the mammalian lung to the swim bladder of fish. Based on this archetypal cell-molecular model, we have reduced evolutionary biology to cell communication, starting with unicellular organisms communicating with the environment, followed by cell-cell communication to generate metazoa, culminating in the communication of genetic information between generations, i.e. reproduction. This model predicts the evolution of physiologic systems-including development, homeostasis, disease, regeneration/ repair, and aging-as a logical consequence of biology reducing entropy. This approach provides a novel and robust way of formulating refutable, testable hypotheses to determine the ultimate origins and first principles of physiology, providing candidate genes for phenotypes hypothesized to have mediated evolutionary changes in structure and/or function. Ultimately, it will form the basis for predictive medicine and molecular bioethics, rather than merely showing associations between genes and pathology, which is an unequivocal Just So Story. In this new age of genomics, our reach must exceed our grasp.
We have taken a basic biologic approach to elucidate the pathophysiology of bronchopulmonary dysp... more We have taken a basic biologic approach to elucidate the pathophysiology of bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, based on cell/molecular mechanisms of physiologic lung development. Stretch coordinates parathyroid hormone-related protein (PTHrP) signaling between the alveolar type II cell and the mesoderm to coordinately up-regulate key genes for the homeostatic fibroblast phenotype-including peroxisome proliferator activated receptor gamma (PPAR␥), adipocyte differentiation related protein (ADRP), and leptin-and the retrograde stimulation of type II cell surfactant synthesis by leptin. Each of these paracrine interactions requires cell-specific receptors on adjacent cells derived from the mesoderm or endoderm, respectively, to serially up-regulate the signaling pathways between and within each cell-type. It is this functional compartmentation that is key to understanding how specific agonists and antagonists can predictably affect this mechanism of alveolar homeostasis. Using a wide variety of pathophysiologic insults associated with BPD-barotrauma, oxotrauma, and infection, we have found that there are type II cell and/or fibroblast cell/molecular effects generated by these insults, which can lead to the BPD phenotype. We have exploited these cell-specific mechanisms to effectively prevent and treat lung injuries using PPAR␥ agonists to sustain this signaling pathway. It is critically important to judiciously select physiologically and developmentally relevant interventions when treating the preterm neonate. (Pediatr Res 62: 2-7, 2007) Abbreviations: ADRP, adipocyte differentiation related protein; ␣SMA, alpha smooth muscle actin; BPD, bronchopulmonary dysplasia; FRLF, fetal rat lung fibroblast; PGJ 2 , prostaglandin J 2 ; PPAR␥, peroxisome proliferator activated receptor gamma; RGZ, rosiglitazone; VLBWI, very low birth weight infant 0031-3998/07/6201-0002 PEDIATRIC RESEARCH
Synopsis Speakers in this symposium presented examples of respiratory regulation that broadly ill... more Synopsis Speakers in this symposium presented examples of respiratory regulation that broadly illustrate principles of evolution from whole organ to genes. The swim bladder and lungs of aquatic and terrestrial organisms arose independently from a common primordial ''respiratory pharynx'' but not from each other. Pathways of lung evolution are similar between crocodiles and birds but a low compliance of mammalian lung may have driven the development of the diaphragm to permit lung inflation during inspiration. To meet the high oxygen demands of flight, bird lungs have evolved separate gas exchange and pump components to achieve unidirectional ventilation and minimize dead space. The process of ''screening'' (removal of oxygen from inspired air prior to entering the terminal units) reduces effective alveolar oxygen tension and potentially explains why nonathletic large mammals possess greater pulmonary diffusing capacities than required by their oxygen consumption. The ''primitive'' central admixture of oxygenated and deoxygenated blood in the incompletely divided reptilian heart is actually co-regulated with other autonomic cardiopulmonary responses to provide flexible control of arterial oxygen tension independent of ventilation as well as a unique mechanism for adjusting metabolic rate. Some of the most ancient oxygen-sensing molecules, i.e., hypoxiainducible factor-1alpha and erythropoietin, are up-regulated during mammalian lung development and growth under apparently normoxic conditions, suggesting functional evolution. Normal alveolarization requires pleiotropic growth factors acting via highly conserved cell-cell signal transduction, e.g., parathyroid hormone-related protein transducing at least partly through the Wingless/int pathway. The latter regulates morphogenesis from nematode to mammal. If there is commonality among these diverse respiratory processes, it is that all levels of organization, from molecular signaling to structure to function, co-evolve progressively, and optimize an existing gas-exchange framework.
Abstract Rationale: Animal models demonstrate that aberrant gene expression in utero can result i... more Abstract Rationale: Animal models demonstrate that aberrant gene expression in utero can result in abnormal pulmonary phenotypes. Objectives: We sought to identify genes that are differentially expressed during in utero airway development and test the hypothesis that variants in these genes influence lung function in patients with asthma.
ABSTRACT Although alveolar wall thinning has been attributed to apoptosis of interstitial lung li... more ABSTRACT Although alveolar wall thinning has been attributed to apoptosis of interstitial lung lipofibroblasts (LFs), the underlying molecular mechanism(s) remains unknown. Although the physiological vitamin D steroid hormone 1alpha,25(OH)(2)D(3) (1,25D) has been suggested as a local paracrine/autocrine effector of fetal lung maturation and is known to affect fibroblast apoptosis, its effects on LF apoptosis are unknown. We determined the role of 1,25D and its metabolite, C-3-epimer (3-epi-1,25D), on LF and alveolar type II (ATII) cell differentiation, proliferation, and apoptosis. Embryonic day 19 Sprague-Dawley fetal rat lung LFs and ATII cells were treated with 1,25D or 3-epi-1,25D (1 x 10(-10) to 1 x 10(-8) M) for 24 h, and cell proliferation, apoptosis, and differentiation were assessed. Both 1,25D and 3-epi-1,25D exhibited dose-dependent increases in expression of the key homeostatic epithelial-mesenchymal differentiation markers, increased LF and ATII cell proliferation, and decreased apoptosis. Furthermore, rat pups administered 1,25D from postnatal days 0 to 14 showed increased expressions of key LF and ATII cell differentiation markers, increased Bcl-2-to-Bax ratio as an index of decreased spontaneous alveolar LF and ATII cell apoptosis, increased alveolar count, and a paradoxical increase in septal thickness. We conclude that spatial- and temporal-specific actions of vitamin D play a critical role in perinatal lung maturation by stimulating key alveolar epithelial-mesenchymal interactions and by modulating LF proliferation/apoptosis. These data not only provide the biological rationale for the presence of an alveolar vitamin D paracrine system, but also provide the first integrated molecular mechanism for increased surfactant synthesis and alveolar septal thinning during perinatal lung maturation.
Functional maturation of pulmonary alveolar epithelial cells is crucial for extrauterine survival... more Functional maturation of pulmonary alveolar epithelial cells is crucial for extrauterine survival. Mechanical distension and mesenchymal-epithelial interactions play important roles in this process. We hypothesized that mechanical stretch simulating fetal breathing movements is an important regulator of pulmonary epithelial cell differentiation. Using a Flexercell Strain Unit, we analyzed effects of stretch on primary cultures of type II cells and cocultures of epithelial and mesenchymal cells isolated from fetal rat lungs during late development. Cyclic stretch of isolated type II cells increased surfactant protein (SP) C mRNA expression by 150 +/- 30% over controls (P < 0.02) on gestational day 18 and by 130 +/- 30% on day 19 (P < 0.03). Stretch of cocultures with fibroblasts increased SP-C expression on days 18 and 19 by 170 +/- 40 and 270 +/- 40%, respectively, compared with unstretched cocultures. On day 19, stretch of isolated type II cells increased SP-B mRNA expression by 50% (P < 0.003). Unlike SP-C, addition of fibroblasts did not produce significant additional effects on SP-B mRNA levels. Under these conditions, we observed only modest increases in cellular immunoreactive SP-B, but secreted saturated phosphatidylcholine rose by 40% (P < 0.002). These results indicate that cyclic stretch promotes developmentally timed differentiation of fetal type II cells, as a direct effect on epithelial cell function and via mesenchymal-epithelial interactions. Expression of the SP-C gene appears to be highly responsive to mechanical stimulation.
American Journal of Respiratory and Critical Care Medicine, Feb 15, 2010
At-a-Glance Commentary: Scientific Knowledge on the Subject: The trajectory of lung function grow... more At-a-Glance Commentary: Scientific Knowledge on the Subject: The trajectory of lung function growth appears to be set early in life. Animal models demonstrate that abnormal in utero expression of genes implicated in normal lung development can result in abnormal pulmonary phenotypes after birth.
In the post-genomic era the complex problem of evolutionary biology can be tackled from the top-d... more In the post-genomic era the complex problem of evolutionary biology can be tackled from the top-down, the bottom-up, or from the middle-out. Given the emergent and contingent nature of this process, we have chosen to take the latter approach, both as a mechanistic link to developmental biology and as a rational means of identifying signaling mechanisms based on their functional genomic significance. Using this approach, we have been able to configure a working model for lung evolution by reverse-engineering lung surfactant from the mammalian lung to the swim bladder of fish. Based on this archetypal cell-molecular model, we have reduced evolutionary biology to cell communication, starting with unicellular organisms communicating with the environment, followed by cell-cell communication to generate metazoa, culminating in the communication of genetic information between generations, i.e. reproduction. This model predicts the evolution of physiologic systems-including development, homeostasis, disease, regeneration/ repair, and aging-as a logical consequence of biology reducing entropy. This approach provides a novel and robust way of formulating refutable, testable hypotheses to determine the ultimate origins and first principles of physiology, providing candidate genes for phenotypes hypothesized to have mediated evolutionary changes in structure and/or function. Ultimately, it will form the basis for predictive medicine and molecular bioethics, rather than merely showing associations between genes and pathology, which is an unequivocal Just So Story. In this new age of genomics, our reach must exceed our grasp.
We have taken a basic biologic approach to elucidate the pathophysiology of bronchopulmonary dysp... more We have taken a basic biologic approach to elucidate the pathophysiology of bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, based on cell/molecular mechanisms of physiologic lung development. Stretch coordinates parathyroid hormone-related protein (PTHrP) signaling between the alveolar type II cell and the mesoderm to coordinately up-regulate key genes for the homeostatic fibroblast phenotype-including peroxisome proliferator activated receptor gamma (PPAR␥), adipocyte differentiation related protein (ADRP), and leptin-and the retrograde stimulation of type II cell surfactant synthesis by leptin. Each of these paracrine interactions requires cell-specific receptors on adjacent cells derived from the mesoderm or endoderm, respectively, to serially up-regulate the signaling pathways between and within each cell-type. It is this functional compartmentation that is key to understanding how specific agonists and antagonists can predictably affect this mechanism of alveolar homeostasis. Using a wide variety of pathophysiologic insults associated with BPD-barotrauma, oxotrauma, and infection, we have found that there are type II cell and/or fibroblast cell/molecular effects generated by these insults, which can lead to the BPD phenotype. We have exploited these cell-specific mechanisms to effectively prevent and treat lung injuries using PPAR␥ agonists to sustain this signaling pathway. It is critically important to judiciously select physiologically and developmentally relevant interventions when treating the preterm neonate. (Pediatr Res 62: 2-7, 2007) Abbreviations: ADRP, adipocyte differentiation related protein; ␣SMA, alpha smooth muscle actin; BPD, bronchopulmonary dysplasia; FRLF, fetal rat lung fibroblast; PGJ 2 , prostaglandin J 2 ; PPAR␥, peroxisome proliferator activated receptor gamma; RGZ, rosiglitazone; VLBWI, very low birth weight infant 0031-3998/07/6201-0002 PEDIATRIC RESEARCH
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