Martin Post

Induction of the heat shock response reduces mortality rate and organ damage in a sepsis-induced acute lung injury model.

ObjectiveTo test the hypothesis that induction of heat shock proteins before the onset of sepsis could prevent or reduce organ injury and death in a rat model of intra-abdominal sepsis and sepsis-induced acute lung injury produced by cecal ligation and perforation. DesignProspective, blind, randomized, controlled trial. SettingUniversity research laboratory. SubjectsOne-hundred forty-two adult Sprague-Dawley rats (weight range 200 to 300 g). InterventionsProduction of intra-abdominal sepsis and exposure to heat stress. Animals were randomly divided into four groups: heated and septic, heated and sham-septic, unheated and septic, and unheated and sham-septic. Measurements and Main ResultsWe evaluated the mortality rate and pathologic changes in lung, heart, and liver at 18 hrs after cecal perforation, at 24 hrs after removal of the cecum, and at 7 days after perforation. Heated animals exhibited a maximum increase in heat shock protein of 72 kilodalton molecular weight protein concentrations in the lungs and heart 6 to 24 hrs after the hyperthermic stress. By 18 hrs after perforation, 25% of the septic, unheated animals had died whereas none of the septic heated animals had died (p < .005). Septic, heated animals showed a marked decrease in 7-day mortality rate (21%) compared with septic unheated animals (69%) (p < .01). Furthermore, septic heated animals showed less histologic evidence of lung and liver damage than septic unheated animals. ConclusionsThese data suggest that thermal pretreatment, associated with the synthesis of heat shock proteins, reduces organ damage and enhances animal survival in experimental sepsis-induced acute lung injury. Although the mechanisms by which heat shock proteins exert a protective effect are not well understood, these data raise interesting questions regarding the importance of fever in the protection of the whole organism during bacterial infection. (Crit Care Med 1994; 22:914–921)

Improvement of outcomes after coronary artery bypass: A randomized trial comparing intraoperative high versus low mean arterial pressure

BACKGROUND The objective of this randomized clinical trial of elective coronary artery bypass grafting was to investigate whether intraoperative mean arterial pressure below autoregulatory limits of the coronary and cerebral circulations was a principal determinant of postoperative complications. The trial compared the impact of two strategies of hemodynamic management during cardiopulmonary bypass on outcome. Patients were randomized to a low mean arterial pressure of 50 to 60 mm Hg or a high mean arterial pressure of 80 to 100 mm Hg during cardiopulmonary bypass. METHODS A total of 248 patients undergoing primary, nonemergency coronary bypass were randomized to either low (n = 124) or high (n = 124) mean arterial pressure during cardiopulmonary bypass. The impact of the mean arterial pressure strategies on the following outcomes was assessed: mortality, cardiac morbidity, neurologic morbidity, cognitive deterioration, and changes in quality of life. All patients were observed prospectively to 6 months after the operation. RESULTS The overall incidence of combined cardiac and neurologic complications was significantly lower in the high pressure group at 4.8% than in the low pressure group at 12.9% (p = 0.026). For each of the individual outcomes, the trend favored the high pressure group. At 6 months after coronary bypass for the high and low pressure groups, respectively, total mortality rate was 1.6% versus 4.0%, stroke rate 2.4% versus 7.2%, and cardiac complication rate 2.4% versus 4.8%. Cognitive and functional status outcomes did not differ between the groups. CONCLUSION Higher mean arterial pressures during cardiopulmonary bypass can be achieved in a technically safe manner and effectively improve outcomes after coronary bypass.

Mechanical force-induced signal transduction in lung cells

The lung is a unique organ in that it is exposed to physical forces derived from breathing, blood flow, and surface tension throughout life. Over the past decade, significant progress has been made at the cellular and molecular levels regarding the mechanisms by which physical forces affect lung morphogenesis, function, and metabolism. With the use of newly developed devices, mechanical forces have been applied to a variety of lung cells including fetal lung cells, adult alveolar epithelial cells, fibroblasts, airway epithelial and smooth muscle cells, pulmonary endothelial and smooth muscle cells, and mesothelial cells. These studies have led to new insights into how cells sense mechanical stimulation, transmit signals intra- and intercellularly, and regulate gene expression at the transcriptional and posttranscriptional levels. These advances have significantly increased our understanding of the process of mechanotransduction in lung cells. Further investigation in this exciting research field will facilitate our understanding of pulmonary physiology and pathophysiology at the cellular and molecular levels.The lung is a unique organ in that it is exposed to physical forces derived from breathing, blood flow, and surface tension throughout life. Over the past decade, significant progress has been made at the cellular and molecular levels regarding the mechanisms by which physical forces affect lung morphogenesis, function, and metabolism. With the use of newly developed devices, mechanical forces have been applied to a variety of lung cells including fetal lung cells, adult alveolar epithelial cells, fibroblasts, airway epithelial and smooth muscle cells, pulmonary endothelial and smooth muscle cells, and mesothelial cells. These studies have led to new insights into how cells sense mechanical stimulation, transmit signals intra- and intercellularly, and regulate gene expression at the transcriptional and posttranscriptional levels. These advances have significantly increased our understanding of the process of mechanotransduction in lung cells. Further investigation in this exciting research field will facilitate our understanding of pulmonary physiology and pathophysiology at the cellular and molecular levels.

Dual-hit hypothesis explains pulmonary hypoplasia in the nitrofen model of congenital diaphragmatic hernia.

Pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) remains a major therapeutic problem. Moreover, the pathogenesis of pulmonary hypoplasia in case of CDH is controversial. In particular, little is known about early lung development in this anomaly. To investigate lung development separate from diaphragm development we used an in vitro modification of the 2, 4-dichlorophenyl-p-nitrophenylether (Nitrofen) animal model for CDH. This enabled us to investigate the direct effects of Nitrofen on early lung development and branching morphogenesis in an organotypic explant system without the influence of impaired diaphragm development. Epithelial cell differentiation of the lung explants was assessed using surfactant protein-C and Clara cell secretory protein-10 mRNA expression as markers. Furthermore, cell proliferation and apoptosis were investigated. Our results indicate that Nitrofen negatively influences branching morphogenesis of the lung. Initial lung anlage formation is not affected. In addition, epithelial cell differentiation and cell proliferation are attenuated in lungs exposed to Nitrofen. These data indicate that Nitrofen interferes with early lung development before and separate from (aberrant) diaphragm development. Therefore, we postulate the dual-hit hypothesis, which explains pulmonary hypoplasia in CDH by two insults, one affecting both lungs before diaphragm development and one affecting the ipsilateral lung after defective diaphragm development.

Defective lung vascular development and fatal respiratory distress in endothelial NO synthase-deficient mice: A model of alveolar capillary dysplasia?

Abstract— Endothelium-derived NO plays a critical role in the regulation of cardiovascular function and structure, as well as acting as a downstream mediator of the angiogenic response to numerous vascular growth factors. Although endothelial NO synthase (eNOS)–deficient mice are viable, minor congenital cardiac abnormalities have been reported and homozygous offspring exhibit high neonatal mortality out of proportion to the severity of these defects. The aim of the present report was to determine whether abnormalities of the pulmonary vascular development could contribute to high neonatal loss in eNOS-deficient animals. We now report that eNOS-deficient mice display major defects in lung morphogenesis, resulting in respiratory distress and death within the first hours of life in the majority of animals. Histological and molecular examination of preterm and newborn mutant lungs demonstrated marked thickening of saccular septae, with evidence of reduced surfactant material. Lungs of eNOS-deficient mice also exhibited a striking paucity of distal arteriolar branches and extensive regions of capillary hypoperfusion, together with misalignment of pulmonary veins, which represent the characteristic features of alveolar capillary dysplasia. We conclude that eNOS plays a previously unrecognized role in lung development, which may have relevance for clinical syndromes of neonatal respiratory distress.

Changes in structure, mechanics, and insulin-like growth factor-related gene expression in the lungs of newborn rats exposed to air or 60% oxygen.

Exposure of neonatal rats to ≥95% O2 for 2 wk, a widely used model of oxidant/antioxidant interactions in neonatal lung injury, results in arrested lung growth without the dysplastic lesions observed in chronic human neonatal lung injury. To determine whether dysplastic lung cell growth would be seen at lesser O2 concentrations, we exposed newborn rats to either 95% O2 for 1 wk followed by 60% O2 for 1 wk, or to 60% O2 for 2 wk. Exposure to 95% O2 for 1 wk profoundly inhibited lung DNA synthesis. Recovery of synthesis did not occur during the 2nd wk in 60% O2, nor were areas of dysplastic growth evident in lung tissue. In contrast, a continuous 2-wk exposure to 60% O2 resulted in a slight increase in lung weight with a significant reduction in lung volume over a range of inflation pressures. Also seen was an overall, but inhomogeneous, reduction in lung cell DNA synthesis. A preliminary analysis of affected cell types suggested that inhibition of DNA synthesis affected endothelial cells more than interstitial cells, whereas DNA synthesis increased in type II pneumocytes. Areas of reduced DNA synthesis were interspersed with patchy areas of parenchymal thickening and active DNA synthesis. These areas of parenchymal thickening, but not other areas, had increased immunoreactive IGF-I and the type I IGF receptor. These data are consistent with a direct effect of O2 on growth factor and growth factor receptor expression in causing dysplastic lung cell growth in chronic neonatal lung injury.

Dexamethasone prevents hypoxic-ischemic brain damage in the neonatal rat.

ABSTRACT: Glucocorticoid therapy is frequently used in perinatology and neonatology for its beneficial pulmonary effects. We investigated the influence of neonatal glucocorticoid administration on brain damage caused by a concurrent episode of cerebral hypoxia-ischemia. Various doses of dexamethasone in several treatment schedules were administered to 7-d-old rats that were also subjected to unilateral cerebral hypoxia-ischemia. In 79% of control rats, a large unilateral cerebral infarction occurred, whereas all rats pretreated with dexamethasone in doses of 0.01 to 0.5 mg/kg/d for 3 d had no infarction (p < 0.001). The neuroprotective effect of dexamethasone pretreatment was dose- and time-dependent. Treatment with dexamethasone after the insult or with lower doses before the insult did not prevent infarction. The neuroprotective effect was not immediate: single doses 0 to 3 h prehypoxia were not effective but a single dose 24 h before hypoxiaischemia prevented cerebral infarction. The results demonstrate that glucocorticoid administration in the neonatal period, even in low doses, protects the brain during subsequent periods of hypoxia-ischemia.

Dynamic HIF1A Regulation During Human Placental Development

Abstract The human placenta is a unique organ in terms of oxygenation as it undergoes a transition from a low to a more oxygenated environment. This physiological switch in oxygen tension is a prerequisite for proper placental development and involves the hypoxia inducible factor (HIF). HIF is stable and initiates gene transcription under hypoxia, whereas in normoxia, interaction with the von Hippel-Lindau tumor suppressor protein (VHL) leads to rapid degradation of the HIF1A subunit. The degradation requires formation of a multiprotein complex (VHLCBC) and hydroxylation of HIF1A proline residues via members of the egg-laying-defective nine (EGLN) family. Herein, we have investigated the regulatory mechanisms of HIF1A expression during human placental development. Expression of HIF1A and VHL was high at 7–9 wk of gestation, when oxygen tension is low, and decreased when placental oxygen tension increases (10–12 wk of gestation). During early placentation, HIF1A localized in cytotrophoblasts, while VHL was present in syncytiotrophoblasts. At 10–12 wk, VHL appeared in cytotrophoblast cells, which coincided with the disappearance of HIF1A. At the same time the association of VHL and Cullin 2 as well as ubiquitination of HIF1A was maximal. EGLN1, EGLN2, and EGLN3 were also temporally expressed in an oxygen-dependent fashion, with greatest mRNA expression at 10–12 wk of gestation. Inhibition of EGLN activity increased HIF1A stability in villous explants and stimulated transforming growth factor beta 3 (TGFB3) expression consistent with promoter analyses showing that HIF1A transactivates TGFB3. These data demonstrate that during placental development, HIF1A is regulated by temporal and spatial changes in expression and association of molecules forming the multi-protein VHLCBC complex as well as prolyl hydroxylase activities.

Expression of Basic Fibroblast Growth Factor and Receptor: Immunolocalization Studies in Developing Rat Fetal Lung

ABSTRACT: To study the role of basic fibroblast growth factor (bFGF) in fetal lung development, the distribution of bFGF peptide and FGF receptor (FGF-R) was examined by immunohistochemistry in embryonic and fetal rat lung [d 12 to term (term = 22 d)). Throughout development bFGF was localized to airway epithelial cells, their basement membranes, and their extracellular matrix. FGF-R was also detected in airway epithelial cells, especially in the branching areas, and in interstitial cells as early as d 13. The number of FGF-R immunoreactive cells increased during the embryonic and pseudoglandular stages of lung development, followed by fluctuations in reactivity during the canalicular stage. No FGF-R was detected in tissue from the saccular stage of lung development. The presence of bFGF and FGF-R in developing airway epithelium and mesenchyme is compatible with a role for this growth factor during fetal lung development. In the developing lung, bFGF seems to be sequestered and stored in the extracellular matrix, and may be released at times of need. Furthermore, FGF-R up- and down-regulation offers another mechanism by which the growth of specific cell populations may be controlled during fetal lung development.

Stretch-activated signaling pathways responsible for early response gene expression in fetal lung epithelial cells.

High‐tidal volume ventilation has been shown to increase the expression of several inflammation‐associated genes prior to overt physiologic lung injury. Herein, using an in vitro stretch system, we investigated the mechanotransduction pathways involved in ventilation‐induced expression of these early response genes (i.e., early growth response gene (Egr)1, heat‐shock protein (HSP)70, and the pro‐inflammatory cytokines interleukin (IL)‐1β, IL‐6, and MIP‐2). Mechanical stretch of fetal lung epithelial cells activated various signaling pathways, resulting in transient or progressive increases in gene expression of the early response genes. The transient increase in Egr1 and IL‐6 expression was mediated via p44/42 mitogen‐activated protein kinase (p44/42 MAPK), while nuclear factor‐kappaB (NF‐κB) was responsible for the sustained and progressive increase in expression of HSP70 and MIP‐2. Blockage of Egr‐1 expression did not affect the upregulation of IL‐6, HSP70, MIP‐2, and itself by stretch. Inhibition of calcium mobilization abolished stretch‐induced p44/42 MAPK activation and NF‐κB nuclear translocation as well as increased expression of all early response genes. Similar results were obtained with an inhibitor of Ras. These results suggest that mechanical stretch of fetal lung epithelial cells evokes a complex network of signaling molecules, which diverge downstream to regulate the temporal expression of a unique set of early response genes, but upstream converge at calcium. Thus, calcium mobilization may be a point of hierarchical integration of mechanotransduction in lung epithelial cells. J. Cell. Physiol. 210: 133–143, 2007.