Immunoelectron-microscopic demonstration of elastase in emphysematous lungs of tight-skin mice

Complex integration of matrix, oxidative stress, and apoptosis in genetic emphysema

Alveolar enlargement, which is characteristic of bronchopulmonary dysplasia, congenital matrix disorders, and cigarette smoke-induced emphysema, is thought to result from enhanced inflammation and ensuing excessive matrix proteolysis. Although there is recent evidence that cell death and oxidative stress punctuate these diseases, the mechanistic link between abnormal lung extracellular matrix and alveolar enlargement is lacking. We hypothesized that the tight-skin (TSK) mouse, which harbors a spontaneous internal duplication in the microfibrillar glycoprotein fibrillin-1, might show whether matrix alterations are sufficient to promote oxidative stress and cell death, injury cascades central to the development of clinical emphysema. We observed no evidence of increased metalloprotease activation by histochemical and zymographic methods. We did find initial oxidative stress followed by increased apoptosis in the postnatal TSK lung. Both blunted antioxidant production and reduced extracellular superoxide dismutase activity were evident in the neonatal lung. High-dose antioxidant treatment with N-acetylcysteine improved airspace caliber and attenuated oxidative stress and apoptosis in neonatal and adult TSK mice. These data establish that an abnormal extracellular matrix without overt elastolysis is sufficient to confer susceptibility to postnatal normoxia, reminiscent of bronchopulmonary dysplasia. The resultant oxidative stress and apoptosis culminate in profound airspace enlargement. The TSK lung exemplifies the critical interplay between extracellular matrix, oxidative stress, and cell-death cascades that may contribute to genetic and acquired airspace enlargement.

The effect of caloric restriction on the aortic tissue of aging rats

Connective tissue shows peculiar and complex age-related modifications, which can be, at least in part, responsible for altered functions and increased susceptibility to diseases. Food restriction has long been known to prolong life in rodents, having antiaging effects on a variety of physiologic and pathologic processes. Therefore, the aorta has been investigated in rats fed normal or hypocaloric diet, from weaning to senescence. Compared with controls, caloric-restricted animals showed less pronounced age-dependent alterations such as elastic fiber degradation, collagen accumulation and cellular modifications. Immunocytochemical analyses revealed that elastic fibers were positively labelled for biglycan, decorin, ApoB100 (LDL), ApoA1 (HDL) and elastase and that the intensity of the reactions was time- and diet-dependent. With age, the major changes affecting aortic elastic fibers were increased positivity for decorin, LDL and elastase. Compared with age-matched normal fed rats, caloric restricted animals revealed lower content of LDL, decorin and elastase and higher positivity for HDL. These data suggest that a caloric restricted diet might influence the aging process of the arterial wall in rats, delaying the appearance of age-related degenerative features, such as structural alterations of cells and matrix and modified interactions of elastin with cells and with other extracellular matrix molecules.

Neutrophil influx into the lungs of beige mice is followed by elastolytic damage and emphysema

The beige mouse is currently used as a model of elastase and cathepsin G deficiency to demonstrate or exclude the role of these proteases in a variety of pathologic conditions. We recently demonstrated that beige cathepsin G is tightly bound to neutrophil lysosomal membranes but is released in near normal quantities during exocytosis. Also, beige neutrophils contain a latent form of elastase that undergoes spontaneous activation when released under in vitro or in vivo conditions. However, the pathogenic potential of this enzyme in matrix degradation has not been ascertained previously. The possibility that in beige mice elastolytic proteases from neutrophils recruited into the lung have the capability to damage alveolar septa was investigated following an intratracheal instillation of N-formyl-L-methionyl-L-leucyl-L-phenylalanine (200 microg). Neutrophil influx was followed by a decrease in lung elastin content (-18%) and by a significant increase of the mean linear intercept (+30%) and of morphologic emphysema. The onset of pulmonary lesion was preceded by a marked increase of neutrophil elastase burden on the alveolar interstitium. The appearance of emphysema was prevented by administration of the serine protease inhibitor 4-(2-aminoetyl)-benzenesulfonyl fluoride hydrochloride (2. 4 microg/ml saline). These results demonstrate that the lung elastin degradation and emphysema can occur in beige lungs. The fact that the beige mouse does develop lung elastolytic changes after neutrophil recruitment indicates that this mutant cannot be considered a model of neutrophil function deficiency and used as a model of elastase deficiency.

Neutrophils in beige mice secrete normal amounts of cathepsin G and a 46 kDa latent form of elastase that can be activated extracellularly by proteolytic activity

Among other phenotypic defects, the beige mouse is susceptible to infection and has large neutrophil granules that apparently secrete a decreased amount of elastolytic activity. We have shown using in vitro methods that cytosolic inhibitors in beige neutrophils are normal. Although cathepsin G is tightly bound to lysosomal membranes, normal amounts of activity are released in response to degranulating agents. Decreased elastolytic activity is secreted by beige neutrophils because elastase is present in the granules as a 46 kDa proenzyme, which can be activated extracellularly by a protease-dependent mechanism. The current experiments were undertaken to explore the in vivo functions of neutrophils from C57 BI/6J (bg/bg) beige mice using the model of casein-induced acute peritonitis; normal C57 BI/6J (+/+) mice served as controls. The kinetics of neutrophil accumulation in the peritoneum were normal, suggesting normal neutrophil migration. Cathepsin G activity in the cell-free supernatant of peritoneal lavage fluid was normal; elastolytic activity was initially very low but increased to about twice baseline level after 4 h at 25 degrees C and to about 20-fold at 36 h. The appearance of this activity was inhibited to varying degree (54 to 83%) by different protease inhibitors (pepstatin, antipain, aprotinin, leupeptin and chymostatin). We conclude that the decreased amount of elastolytic activity secreted by beige neutrophils into an inflammatory exudate is due to a genetic defect that results in production of a 46 kDa proelastase rather than the normal 29 kDa active elastase; the proelastase can be spontaneously activated by a protease-dependent mechanism. In light of these data, the use of the beige mouse as a model for the Chediak-Higashi syndrome, and as a model in which neutrophils do not produce elastase, must be reconsidered.

A human SP-C promoter fragment targets alpha 1-proteinase inhibitor gene expression to lung alveolar type II cells in transgenic mice

A 1.277 kb promoter fragment of the gene encoding one of the lung surfactant proteins, SP-C, was cloned from a human genomic library and characterized using the human alpha 1-proteinase inhibitor (alpha 1PI) gene as reporter. Messenger RNA for human alpha 1PI isolated from a single transgenic mouse line was detected solely in lung tissue. Using immunogold electron microscopy, accumulation of human alpha 1PI was shown unambiguously to occur only in type II pulmonary cells and, in discrete amounts, in the alveolar lining fluid. The protein was secreted and glycosylated showing a molecular weight close to that of plasma-derived human alpha 1PI.

Effect of elastase on the directional migration of lung fibroblasts within a three-dimensional collagen matrix

Interactions between airway epithelial cells and bronchial fibroblasts often require close proximity between these cells. Previous studies have demonstrated that airway epithelial cells direct the migration of lung fibroblasts, but the factors that regulate this process during airway injury are not clear. We hypothesized that exposure of culture substrates to proteolytic enzymes, like those present in the inflamed airway, would increase fibroblast recruitment. We also postulated that elastase might affect the epithelium's ability to attract fibroblasts. We used an in vitro model with fibroblasts embedded between two layers of collagen gel to investigate their migration. Embedded fibroblasts exposed to culture medium alone (baseline) had a slight downward migration (migration directed to the upper gel layer expressed as a percentage of total migration was -2.8 +/- 1.4), but medium supplemented with porcine pancreatic elastase (PPE) resulted in a slight upward migration (2.0 +/- 1.4). When airway epithelial cells were cultured on the upper gel surface, the index of directed migration toward them was 15.9 +/- 1.3. Addition of PPE to the culture medium resulted in a significant increase to 22.3 +/- 1.5 (p < .05). Human neutrophil elastase (HNE) produced similar results, and these effects were inhibited by alpha 1-proteinase inhibitor. Similarly, total fibroblasts per 20 high-powered fields were counted in all conditions, suggesting that mitogenic interactions were not important in this system. The percentage of the total fibroblasts migrating at least 5 microns in any direction was also similar in all groups, suggesting chemokinetic mechanisms were not involved. These data suggest that elastase exposure in a model of the human airway increases directed fibroblast migration through the extracellular matrix. This phenomenon may play a role in the development of subepithelial fibrosis seen in inflammatory airway diseases like asthma.

Neutrophil lysosomal dysfunctions in mutant C57 Bl/6J mice: interstrain variations in content of lysosomal elastase, cathepsin G and their inhibitors

In this paper we report the serum antiprotease screening and the biochemical and functional characteristics of neutrophils in a variety of mouse strains with different susceptibilities for developing a protease-mediated injury. C57Bl/6J mice and their mutants tight-skin and pallid have a lower serum elastase inhibitory capacity (-30, -65 and -70% respectively) than other inbred strains (i.e. NMRI and Balb/c, which both have similar values). We demonstrate that these values are a consequence of a decreased concentration of the alpha 1-protease inhibitor for elastase [PI(E)], which is the major serum inhibitor of elastase and cathepsin G. In addition, neutrophil lysosomal dysfunctions characterized by abnormally high contents of elastase and cathepsin G, or defective lysosomal secretion are observed in tight-skin and pallid mice respectively. Another C57Bl/6J mutant with lysosomal abnormalities is the beige mouse. Negligible amounts of elastase and cathepsin G, as well as defective neutrophil degranulation, have been described previously in this strain. We found, however, discrete amounts of a latent form of neutrophil elastase that undergoes a spontaneous activation by a protease-dependent mechanism. We also report that neutrophil cathepsin G in this mouse is tightly bound to lysosomal membranes, but is released in near normal quantities during exocytosis. Cytosolic elastase and cathepsin G inhibitors, which were previously reported as being specific for the beige neutrophils, have also been detected in all the examined strains. Neutrophil functions, lysosomal enzyme content and serum antiprotease screening may represent key elements in the protease-antiprotease balance and may explain the different interstrain susceptibility to developing lesions in which an elastolytic activity has been implicated.

Lung collagen synthesis and deposition in tight-skin mice with genetic emphysema

The tight-skin (Tsk) mouse is a genetic model of pulmonary emphysema linked to a deficiency of serum antielastase. In this mouse occurrence of connective tissue abnormalities in various organs (systemic scleroderma) has been reported. The aim of the present work was to study lung collagen synthesis and deposition in Tsk mice. No differences in the collagen synthesis rate and morphology at the ultrastructural level were found in Tsk mice at birth. At 2 months of age, a marked increase in collagen was observed within the alveolar septa. At this time, an increased lung collagen synthesis, assessed by determining prolyl hydroxylase activity and incorporation of radiolabeled proline, was found in Tsk mice with respect to control mice. However, due to the ongoing parenchymal destruction, the values of total lung collagen at 6 and 12 months of age were only moderately but significantly increased with respect to those observed at 2 months. As a consequence, a progressive accumulation of lung collagen fibers was observed in the residual septa. The increase in collagen deposition was accompanied by a relative increase in type I collagen. Although the data in the literature would suggest a genetic cause for the lung collagen change in Tsk mice, the data presented here indicate that the change in lung collagen metabolism may be a part of a remodeling process taking place after lung destruction.

Michaelis complexes of porcine pancreatic elastase with 7-[(alkylcarbamoyl)amino]-4-chloro-3-ethoxyisocoumarins: translational sampling of inhibitor position and kinetic measurements

A step leading to the formation of the covalent complexes between porcine pancreatic elastase (PPE) and 7-[(alkylcarbamoyl)amino]-4-chloro-3-ethoxyisocoumarins (alkylHNCO-EICs) is the formation of the noncovalent Michaelis complex. No average structures are available for the Michaelis complexes of PPE with alkylHNCO-EICs. We present the results of an initial step in obtaining these structures and have determined kinetic constants as well. The kinetic results indicate that formation of the Michaelis complex is what differentiates the effectiveness of these inhibitors in inactivating PPE. The structural and kinetic results together suggest that the structure of the Michaelis complex is necessary for the design of potent alkylHNCO-EIC inhibitors of PPE. Two novel alkylHNCO-EICs are predicted to be the best inhibitors of this series. An alternate mechanism for serine protease inhibition is also proposed. Evidence for, and studies that may add support to, the hypothesized mechanism are discussed.

Serum antielastase deficiency in tight-skin mice with genetic emphysema

The tight-skin (Tsk) mouse is a model of genetically determined emphysema. The cause for the development of the lung lesion is unknown. In the present study we investigated the lung morphometry and the serum elastase inhibitory capacity (EIC) of Tsk mice. Mean interalveolar distance was significantly greater (+60%) in Tsk mice than in C57 Bl/6J, NMRI, and Balb/c mice, which have similar values. Serum of Tsk mice against mouse leukocyte elastase (MLE) has significantly lower EIC values than that of NMRI, Balb/c (-64%), and C57 Bl/6J (-50%) mice. Similar results were obtained when porcine pancreatic elastase (PPE) was used. Against human leukocyte elastase (HLE), however, there was no difference among the strains, all of which had high EIC values. Preincubation of mouse (C57 Bl/6J) serum with chloramine-T (CT) resulted in an almost complete inhibition of EIC against MLE and PPE but only in a 20% inhibition against HLE using a synthetic substrate. Using elastin Congo Red as substrate, CT inhibited EIC against MLE and PPE by approximately 70% but did not affect the EIC against HLE. These results indicate that (1) the Tsk mouse can be considered a model of severe inborn deficiency of serum antielastase activity which is associated with emphysema; and (2) MLE and PPE can be considered interchangeable in studies of serum EIC in the mouse. On the other hand, the differences between MLE and HLE preclude the use of HLE for EIC determination in this species.