National Heart, Lung, and Blood Institute perspective: lung progenitor and stem cells--gaps in knowledge and future opportunities

Because the lung stem cell field is so new, there remain many unanswered questions that are being addressed regarding the identification, location, and role of exogenous and endogenous stem and progenitor cell populations in growth, regeneration, and repair of the lung. Advancing lung stem cell biology will require multidisciplinary teams and a long term effort to unravel the biologic processes of stem cells in the lung. While no clinical research in lung stem cell therapies are currently funded by NHLBI, the knowledge gained by understanding the basic biology of the lung stem cell populations will be needed to translate to diagnostic and therapeutic strategies in the future.

Past achievements and future directions of sarcoidosis research: a NHLBI perspective

This history of research on sarcoidosis is largely from the perspective of the National Heart, Lung, and Blood Institute of the National Insititutes of Health which has had an interest in this disease since the inception of the Lung Program in 1969.

BACKGROUND

Cutaneous sarcoidosis was described over 130 years ago and, subsequently, many reports have documented this illness affecting many organs or body sites. But a definitive cause has remained elusive. Multiple research stimuli converged in the early 1970s to begin an era of active investigation into the immunopathogensis of this granulomatous disease that included: new insights into host cellular immunity and lymphocytes; program analysis of lung research in 1971-72; new technology, especially the fiberoptic bronchoscope; and a focus by the NIH Intramural Pulmonary Branch to conduct research on interstitial lung diseases begun in 1974. During the mid 1970-80s, research into lung cellular immunity of sarcoidosis patients developed rapidly at NIH and at many other centers across the US, England, Europe, and Asia.

PRESENT AND FUTURE DIRECTIONS

NHLBI has continued active support of research in sarcoidosis, both basic and clinical, such as the A Case Control Etiologic Study of Sarcoidosis (ACCESS) program, 1995-2003, whose conclusions are continuing to be published. A workshop on "Future Directions in Sarcoidosis Research" provided new research ideas to explore basic immunity mechanisms in human sarcoidosis tissue and search for latent microbial agents in tissue. The organization of sarcoidosis patient support groups has heightened awareness of the need for research on multiple organs affected by the disease in addition to the respiratory tract. In response, a trans-NIH sarcoidosis working group has been formed to assess this need and to better coordinate NIH research efforts.

Interstitial lung diseases--where we started from and are now going

BACKGROUND AND AIM

Research into mechanisms causing interstitial lung diseases (ILD) began 35 years ago with the advent of cellular immunology and techniques to sample airways for biologic materials. After an analysis of lung research programs by the then National Heart and Lung Institute in 1972 identified as a priority the study of fibrotic and immunologic lung diseases, this began in the Pulmonary Branch (1974) of the Institute's intramural program. The Division of Lung Diseases initiated extramural research support also. ILD research developed quickly at many centers in the US and throughout the world. This review focuses on idiopathic pulmonary fibrosis (IPF) and highlights some of the initial research from the Pulmonary Branch.

RECENT RESEARCH PARADIGM

In the 1990s research emphasis changed from a focus on inflammation to alveolar epithelial injury, fibrogenesis in fibroblastic foci, myofibroblast function, cytokine secretion and disordered matrix remodeling. More precise classification of ILD was advocated, especially for IPF. New strategies for therapy of IPF followed, including anti-fibrotic agents and interferon gamma treatment. However, therapy is still not sufficiently effective. Much is still left to do.

FUTURE DIRECTIONS

The NHLBI research support continues for ILD, especially IPF. Current programs include: searching for new molecular therapeutic targets; establishing of a clinical network for IPF patients to assess combinations of therapy and new agents as appropriate; identifying genomic and genetic susceptibility factors; and creating a repository for lung tissue and biologic samples to aid investigators.

Future directions in sarcoidosis research: summary of an NHLBI working group

Sarcoidosis is a systemic granulomatous disease of unknown etiology that primarily affects the lungs. The etiology remains unclear; however, environmental, genetic, ethnic, and familial factors probably modify expression of the disease. As an example, African Americans are at greater risk of mortality and morbidity than are white Americans, and more often have a family history of sarcoidosis. Most patients with sarcoidosis recover spontaneously, but some develop chronic, debilitating disease. Corticosteroids and other drugs, although effective at controlling disease activity, may not influence the overall course of disease. Because of the many uncertainties about the pathogenesis, course, and management of sarcoidosis, the National Heart, Lung, and Blood Institute convened a working group to identify future research directions and opportunities for sarcoidosis. These include developing a tissue bank, using novel methods to identify genetic factors, studying the immunopathogenesis with human tissue and animal models, exploring new approaches to diagnose and manage disease, and, finally, conducting randomized controlled trials to assess new therapies.

Future research directions in acute lung injury: summary of a National Heart, Lung, and Blood Institute working group

Acute lung injury (ALI) and its more severe form, the acute respiratory distress syndrome (ARDS), are syndromes of acute respiratory failure that result from acute pulmonary edema and inflammation. The development of ALI/ARDS is associated with several clinical disorders including direct pulmonary injury from pneumonia and aspiration as well as indirect pulmonary injury from trauma, sepsis, and other disorders such as acute pancreatitis and drug overdose. Although mortality from ALI/ARDS has decreased in the last decade, it remains high. Despite two major advances in treatment, low VT ventilation for ALI/ARDS and activated protein C for severe sepsis (the leading cause of ALI/ARDS), additional research is needed to develop specific treatments and improve understanding of the pathogenesis of these syndromes. The NHLBI convened a working group to develop specific recommendations for future ALI/ARDS research. Improved understanding of disease heterogeneity through use of evolving biologic, genomic, and genetic approaches should provide major new insights into pathogenesis of ALI. Cellular and molecular methods combined with animal and clinical studies should lead to further progress in the detection and treatment of this complex disease.

Determination of disaturated lecithin in rhesus monkey amniotic fluid as an index of fetal lung maturity

Although increased concentrations of total lecithin in amniotic fluid allow prenatal assessment of fetal lung maturation, it has become clear that routine use of the L/S index may lead to a substantial number of inaccurate predictions. Since disaturated lecithin (DL) is a more specific marker of pulmonary surfactant than total lecithin, we developed a convenient method for measuring this phospholipid in amniotic fluid, and then evaluated its level in pregnant rhesus monkeys of 120 to 163 days of gestation. The method involves osmic acid destruction of unsaturated lipids, chromatographic isolation of disaturated lecithin, and quantitation by phosphorus assay. It can be performed in approximately 5 hours on 4 ml. of amniotic fluid and yield 67 +/- 3 per cent average recovery of added 14C-dipalmitolyl lecithin. The results of analyzing 36 rhesus amniotic fluid specimens showed the disaturated lecithin and the disaturated lecithin/sphingomyelin ratio (DL/S) increase sharply after 150 days of gestation, consistent with the pattern of lung maturation in this species. We conclude that disaturated lecithin can be readily quantitated in primate amniotic fluid and that its concentration, the DL/S ratio, and percentage of disaturated lecithin are potentially useful indices of fetal lung maturity for the clinical laboratory.

Interspecies variation in lung lavage and tissue saturated phosphatidylcholine

We measured the saturated phosphatidylcholine in lung lavage fluid and in lung tissue after lavage in five vertebrate species. The amount of saturated phosphatidylcholine recovered by lung lavage and from lung tissue showed a direct log linear correlation with species alveolar surface area. The saturated phosphatidylcholine content of lung lavage fluid per square meter of alveolar surface area varied in the sequence: mouse greater than rat greater than rabbit greater than dog greater than cat, and showed a direct correlation with species respiratory rate. We compared the lavage (presumably mainly alveolar) and tissue saturated phosphatidylcholine with the theoretical minimum amount required to produce a monomolecular layer over an area equal to the computed alveolar surface area. The data suggest that there is an alveolar and a tissue reserve of saturated phosphatidylcholine. The size of the alveolar reserve varied in the sequence: mouse greater than rat greater than rabbit greater than dog greater than cat. We conclude that in each species studied there is an alveolar and tissue reserve of saturated phosphatidylcholine and that both reserves are larger in animals with rapid ventilatory rates and small alveoli than in animals with slower breathing rates and larger alveoli.

Influence of fasting on the lung

We examined the following in fed rats and in rats fasted for 72 h: 1) the dipalmitoyl lecithin (DPL) content of lung lavage fluid and of the remaining lung tissue, 2) descending air and saline pressure-volume curves of excised lungs, and 3) the volume density of granular pneumocyte lamellar bodies. Lung tissue DPL was decreased by 27% and lavage DPL was decreased by 40% in lungs of fasted rats. The decreased lung DPL content was associated with a 20% decrease in the volume density of lamellar bodies of granular pneumocytes. In spite of the decrease in lavage DPL content, air pressure-volume curves of excised lungs were the same as curves of lungs of fed rats. Saline pressure-volume curves of excised lungs were also the same in fed and fasted rats. The amount of lavage DPL obtained from both fed (1.1 +/- 0.1 mg, n=6) and fasted (0.7 +/- 0.1 mg, n=7) rats exceeded the theoretical minimum amount of DPL (0.5 mg) required for a monomolecular film to cover the alveolar surface of the rat at functional residual capacity. If we assume that lavage DPL represents mainly DPL lining the alveolus (surface film and hypophase) the data suggest that there is an alveolar reserve of DPL above that amount needed to maintain normal alveolar stability.

Oxygen consumption by rat lung after in vivo hyperoxia

We studied the influence of 48 and 96 hours of in vivo hyperoxia (O2 greater than 98 per cent) on O2 consumption by rat lung slices. After 48 hours of hyperoxia, lung O2 consumption expressed per mg of deoxyribonucleic acid or per left lung decreased to approximately 70 per cent of that of lungs from rats exposed to compressed air. After 96 hours of hyperoxia, there was no difference in lung O2 consumption per mg of deoxyribonucleic acid between rats exposed to O2 and those exposed to air, but lung O2 consumption per left lung was higher in rats exposed to O2 than in those exposed to compressed air. Lung ribonucleic acid content and the ratio of ribonucleic acid to deoxyribonucleic acid were significantly increased after 96 hours of hyperoxia. We concluded that the rate of lung metabolism is altered after in vivo exposure to high PO2.

Influence of fasting on lung oxygen consumption and respiratory quotient

We measured the oxygen consumption (QO2) of lung slices from rats and rabbits and the respiratory quotient (RQ) of lung slices from fed and fasted rats. The QO2 of lung slices is lowered within 24 h after the onset of food deprivation; this decrease in QO2 lasts during at least 2 additional days of fasting and is not eliminated by addition of glucose to the reaction medium. In fed rats the RQ of lung slices after 30 min of incubation without glucose is 0.75 +/- 0.01 (mean +/- SE) and 0.96 +/- 0.02 with glucose present. Fasting for 72 h lowers the RQ of lung slices after 30 min of incubation without glucose to 0.68 +/- 0.03; addition of glucose raises the RQ of lung slices from 72-h-fasted rats to 0.76 +/- 0.02. We conclude that fasting depresses lung oxidative metabolism. In the fed rat glucose is a major substrate for oxidative processes but in the fasting rat the oxidation of glucose is impaired and lipids are an important source of lung energy.

Lung oxygen consumption and mitochondria of alveolar epithelial and endothelial cells

We examined oxygen consumption by lung slices and measured the volume density of mitochondria of granular pneumocytes, alveolar type I cells, and alveolar capillary endothelial cells in several species. We found that lung oxygen consumption (mu-1 02 times h-1 times mg DNA-1) varies inversely with the log of animal body weight and with the species alveolar diameter and directly with the species respiratory rate. The volume density of granular pneumocyte mitochondria show a direct linear correlation with the lung's oxygen consumption and the species respiratory rate, and an inverse linear correlation with the species alveolar diameter. The volume density of mitochondria in type I alveolar epithelial cells and capillary endothelial cells, considered together, did not differ in the two species studied (mouse and rat). We conclude that there are interspecies differences in oxygen consumption by lung cells and that granular pneumocytes contribute to these differences. We suggest that, at least part of these differences, are related to interspecies differences in surfactant secretory activity.

Influence of cycloheximide on the lung

We examined the time course of the influence of cycloheximide on descending pressure-volume curves of excised lungs and on protein and lecithin synthesis and oxygen consumption by lung slices. We also looked at the influence of cycloheximide on granular pneumocyte ultrastructure. Excised lungs from cycloheximide-treated animals are more compliant than controls. After ventilation with air, lungs from control and cycloheximide animals show increased retractive forces and a shift to the right of the deflation P-V curve. Incubation at 38 degrees C for 30 min reverses these changes in control lungs, but not in lungs from cycloheximide-treated rabbits. There is no change in liquid delfation P-V curves after cycloheximide. Cycloheximide causes an immediate decrease of 50% in incorporation of radioactive leucine into protein by lung slices. Incorporation of radioactive palmitate into lecithin and oxygen consumption are also decreased by 50% 6 h after cycloheximide. Lamellar bodies in granular pneumocytes are smaller after cycloheximide. Cycloheximide causes a significant increase in the surface density of the lamellar body envelope. Cytoplasmic area of granular pneumocytes is increased after cycloheximide.

Intraspecies differences in lung metabolism and granular pneumocyte mitochondria

The authors used waltzing and nonwaltzing mice to examine granular pneumocyte mitochondria and lung oxygen consumption and protein synthesis. They found that the oxygen consumption of lung slices from waltzing mice is higher than that of lung slices from nonwaltzing mice. The volume density of granular pneumocyte mitochondria is higher in waltzing than nonwaltzing mice as is their number per 100 mum-3 of cytoplasm. The mean, length, width, volume and surface density of individual mitochondria are the same in both groups. The incorporation of [14-C]leucine by lung slices into protein in a surface active lung fraction is greater in lung slices from waltzing than nonwaltzing mice. This difference occurs in the face of similar levels of free leucine in both groups. The authors conclude that there are intraspecies differences in lung oxygen consumption and protein synthesis and in the volume density and number of granular pneumocyte mitochondria.