Aspartic proteinases in normal lung and interstitial pulmonary diseases

Aspiration Pneumonia and Related Syndromes

Aspiration is a syndrome with variable respiratory manifestations that span acute, life-threatening illnesses, such as acute respiratory distress syndrome, to chronic, sometimes insidious, respiratory disorders such as aspiration bronchiolitis. Diagnostic testing is limited by the insensitivity of histologic testing, and although gastric biomarkers for aspiration are increasingly available, none have been clinically validated. The leading mechanism for microaspiration is thought to be gastroesophageal reflux disease, largely driven by the increased prevalence of gastroesophageal reflux across a variety of respiratory disorders, including chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis, and chronic cough. Failure of therapies targeting gastric acidity in clinical trials, in addition to increasing concerns about both the overuse of and adverse events associated with proton pump inhibitors, raise questions about the precise mechanism and causal link between gastroesophageal reflux and respiratory disease. Our review summarizes key aspiration syndromes with a focus on reflux-mediated aspiration and highlights the need for additional mechanistic studies to find more effective therapies for aspiration syndromes.

Cathepsin E promotes pulmonary emphysema via mitochondrial fission

Emphysema is characterized by loss of lung elasticity and irreversible air space enlargement, usually in the later decades of life. The molecular mechanisms of emphysema remain poorly defined. We identified a role for a novel cathepsin, cathepsin E, in promoting emphysema by inducing mitochondrial fission. Unlike previously reported cysteine cathepsins, which have been implicated in cigarette smoke-induced lung disease, cathepsin E is a nonlysosomal intracellular aspartic protease whose function has been described only in antigen processing. We examined lung tissue sections of persons with chronic obstructive pulmonary disease, a clinical entity that includes emphysematous change. Human chronic obstructive pulmonary disease lungs had markedly increased cathepsin E protein in the lung epithelium. We generated lung epithelial-targeted transgenic cathepsin E mice and found that they develop emphysema. Overexpression of cathepsin E resulted in increased E3 ubiquitin ligase parkin, mitochondrial fission protein dynamin-related protein 1, caspase activation/apoptosis, and ultimately loss of lung parenchyma resembling emphysema. Inhibiting dynamin-related protein 1, using a small molecule inhibitor in vitro or in vivo, inhibited cathepsin E-induced apoptosis and emphysema. To the best of our knowledge, our study is the first to identify links between cathepsin E, mitochondrial fission, and caspase activation/apoptosis in the pathogenesis of pulmonary emphysema. Our data expand the current understanding of molecular mechanisms of emphysema development and may provide new therapeutic targets.

High Expression of Cathepsin E is Associated with the Severity of Airflow Limitation in Patients with COPD

BACKGROUND

It was reported that Cathepsin E (Cat E) plays a critical role in antigen processing and in the development of pulmonary emphysema. The aim of this study was to investigate the role of Cat E and airflow limitation in the pathogenesis of COPD.

METHODS

Sixty-five patients with COPD, 20 smoking control subjects without COPD and 15 non-smoking healthy control subjects were enrolled. Cat E and EIC (Elastase inhibitory capacity) expressions were measured by ELISA in sputum and serum samples and compared according to different subgroups.

RESULTS

Cat E concentrations were significantly higher in patients with COPD than smoking control and non-smoking control subjects (P < 0.01). The levels of CatE were inversely correlated with FEV1% predicted in COPD patients (r = -0.95, P < 0.01). The levels of EIC were inversely positively correlated with FEV1% predicted in COPD patients (r = 0.926, P < 0.01). Levels of Cat E were also inversely correlated with the levels of EIC (r = -0.922, P < 0.01).

CONCLUSIONS

Cat E contributes to the severity of airflow limitation during progression of COPD.

Progastriscin: structure, function, and its role in tumor progression

Progastricsin (PGC) is a major seminal plasma protein having aspartyl proteinases-like activity and showing close sequence similarity to pepsins. PGC is also present as zymogen in gastric mucosa. In this article, we have reviewed all important features of PGC. Furthermore, we have compared all features of PGC with those of different aspartyl proteinases. The complete amino acid sequence of PGC reveals that it is composed of 374 residues (gastricsin moiety of 331 residues and the activation segment of 43 residues). The gene of human PGC is located at single locus on chromosome 6, whereas the human pepsinogen genetic locus is polymorphic and codes for at least three distinct polypeptide sequences on chromosome 11. The major useful function of PGC includes production of pro-antimicrobial substance in seminal plasma. The crystal structure of human PGC is known, which shows that it is quite similar to that of porcine pepsinogen. The tertiary structure of PGC is comprised of commonly bilobal structure with a large active-site cleft between the lobes. Two aspartate residues in the center of the cleft, namely Asp32 and Asp215, function as catalytic residues. The sequence and structural features of PGC indicate that it is diverged from its pepsinogen ancestor in the early phase of the evolution of gastric aspartyl proteinases. Our detailed review of PGC structure, function and activation mechanism will also be of interest to cancer biologists as well as gastroenterologists.

Cathepsin E Deficiency Induces a Novel Form of Lysosomal Storage Disorder Showing the Accumulation of Lysosomal Membrane Sialoglycoproteins and the Elevation of Lysosomal pH in Macrophages

Cathepsin E, an endolysosomal aspartic proteinase predominantly expressed in cells of the immune system, has an important role in immune responses. However, little is known about the precise roles of cathepsin E in this system. Here we report that cathepsin E deficiency (CatE(-/-)) leads to a novel form of lysosome storage disorder in macrophages, exhibiting the accumulation of the two major lysosomal membrane sialoglycoproteins LAMP-1 and LAMP-2 and the elevation of lysosomal pH. These striking features were also found in wild-type macrophages treated with pepstatin A and Ascaris inhibitor. Whereas there were no obvious differences in their expression, biosynthesis, and trafficking between wild-type and CatE(-/-) macrophages, the degradation rates of these two membrane proteins were apparently decreased as a result of cathepsin E deficiency. Because there was no difference in the vacuolar-type H(+)-ATPase activity in both cell types, the elevated lysosomal pH in CatE(-/-) macrophages is most likely due to the accumulation of these lysosomal membrane glycoproteins highly modified with acidic monosaccharides, thereby leading to the disruption of non-proton factors controlling lysosomal pH. Furthermore, the selective degradation of LAMP-1 and LAMP-2, as well as LIMP-2, was also observed by treatment of the lysosomal membrane fraction isolated from wild-type macrophages with purified cathepsin E at pH 5. Our results thus suggest that cathepsin E is important for preventing the accumulation of these lysosomal membrane sialoglycoproteins that can induce a new form of lysosomal storage disorder.

Gene Expression Profiling of Progressive Papillary Noninvasive Carcinomas of the Urinary Bladder

PURPOSE

The aim of the present study was to define gene expression profiles of noninvasive and invasive bladder cancer, to identify potential therapeutic or screening targets in bladder cancer, and to define genetic changes relevant for tumor progression of recurrent papillary bladder cancer (pTa).

EXPERIMENTAL DESIGN

Overall, 67 bladder neoplasms (46 pTa, 3 pTis, 10 pT1, and 8 pT2) and eight normal bladder specimens were investigated by a combination of laser microdissection and gene expression profiling. Eight of 16 patients with recurrent noninvasive papillary bladder tumors developed carcinoma in situ (pTis) or invasive bladder cancer (> or = pT1G2) in the course of time. RNA expression results of the putative progression marker cathepsin E (CTSE) were confirmed by immunohistochemistry using high-throughput tissue microarray analysis (n = 776). Univariate analysis of factors regarding overall survival, progression-free survival, and recurrence-free survival in patients with urothelial bladder cancer was done.

RESULTS

Hierarchical cluster analyses revealed no differences between pTaG1 and pTaG2 tumors. However, distinct groups of invasive cancers with different gene expression profiles in papillary and solid tumors were found. Progression-associated gene profiles could be defined (e.g., FABP4 and CTSE) and were already present in the preceding noninvasive papillary tumors. CTSE expression (P = 0.003) and a high Ki-67 labeling index of at least 5% (P = 0.01) were the only factors that correlated significantly with progression-free survival of pTa tumors in our gene expression approach.

CONCLUSIONS

Gene expression profiling revealed novel genes with potential clinical utility to select patients that are more likely to develop aggressive disease.

Regulation of human and mouse procathepsin E gene expression

Cathepsin E is an intracellular aspartic proteinase that is considered to have a number of physiological roles including antigen processing. Quantitation of procathepsin E mRNA by LightCyclertrade mark technology indicated that the gene was transcribed in lung but not in kidney of both human and mouse origin. In contrast, the transcript was present in mouse spleen and alveolar macrophages but not in the counterpart tissue/cells from humans. Regulation of human and mouse procathepsin E gene expression was shown not to be influenced by the extent of CpG methylation but depended on the recognition of potential binding motifs in each promoter region by transcription factors such as GATA1, PU1 and YY1, as revealed by functional analysis using a series of promoter/luciferase reporter gene fusion constructs. Thus the extent to which the procathepsin E gene is expressed in a particular cell type may depend on the balance between the effects produced by positive-acting, cell-specific transcription factors such as GATA1 and PU1 and the negative influence of the ubiquitous YY1 factor. In this way, the relative abundance and influence of general and cell-specific transcription factors can govern the production of cathepsin E and thereby account for the sporadic cell and tissue distribution of this enzyme in different species.

Proteinases and proteinase inhibitors during the development of pulmonary fibrosis in rat

Changes in the activities of several proteinases and their inhibitors were investigated during the development of bleomycin-induced pulmonary fibrosis in rat. Studies on the proteinase-anti-proteinase-ratio may contribute to the understanding of the mechanism of the development of pulmonary fibrosis and may help to develop therapeutic strategies to prevent tissue damage by proteolytic attack. In the acute inflammatory period the activity of metalloelastase in lung tissue increased by about 10-fold. The time course of changes in the activity of 72 kD gelatinase indicates that this gelatinase accounts at least partially for the elastolytic activity. Elastase inhibitory activity in lung tissue showed maxima at days 1 and 5 and high levels in the fibrotic phase. The increase of the elastase inhibitory activity at the beginning of the fibrotic period corresponds with elevated activity of alpha 2-macroglobulin. Alveolar fluid and alveolar macrophages did not contain elastase activity but contained high elastase inhibitory activity. During the period of chronic inflammation, the activities of the cathepsins L, B, H and S in lung tissue and in isolated alveolar macrophages were found to be strongly increased.

Immunolocalization of cathepsin D in pneumocytes of normal human lung and in pulmonary fibrosis

Cathepsin D expression has been assessed by immunohistochemistry and immunoelectron microscopy in fetal, normal adult and injured lungs of human beings. In addition to the well known positivity of alveolar macrophages and the bronchial epithelial cells, normal type I and to a lesser extent type II pneumocytes showed a granular, cytoplasmic staining pattern. Using immunogold labelling of lowicryl embedded human lung, cathepsin D was present in lysosomes of epithelial cells. Double immunofluorescence labelling employing type I and type II specific antibodies or lectins confirmed the epithelial staining for cathepsin D. At the terminal sac period during lung development cathepsin D appears in the alveolar epithelium. In fibrotic specimens, enhanced immunoreactivity was found in epithelial and non-epithelial cells. Proliferative epithelial formations were strongly stained with cathepsin D antibodies, whereas detached, desquamated epithelial cells were weakly positive or negative. We suggest that cathepsin D plays a role in the remodelling process during fibrogenesis.

Cervical adenocarcinomas express markers common to gastric, intestinal, and pancreatobiliary epithelial cells

Frequency and pattern of expression of eight markers of gastric, intestinal, and pancreatobiliary duct epithelial cells have been investigated by histochemical and immunohistochemical techniques in 85 cases of cervical adenocarcinomas. M1, a mucin antigen, and Cathepsin E (CaE), an aspartic proteinase, markers of normal gastric superficial/foveolar epithelial cells, are expressed in 40 and 55 tumors, respectively. Periodic acid-concanavalin A-reactive mucin or Pepsinogen (PG) II, markers of gastric mucus neck and pyloric gland cells, are found in 24 tumors, 13 of which also express M1 and CaE. CAR-5 and M3SI, markers of intestinal mucin, are expressed in 68 and 12 tumors and DU-PAN-2, marker of normal pancreatobiliary duct cells, is found in 46 tumors. All but two tumors express at least one of the eight markers studied, none express PG I, marker of gastric chief cells. The different histologic subtypes of cervical adenocarcinomas expressed to a variable degree both gastrointestinal and pancreatobiliary markers. Only endocervical type tumors, however, showed the full spectrum of mucosal pyloric type differentiation, including the expression of PGII which is not present in any other histotype. A correlation between expression of gastroenteropancreatic markers and tumor grade is not apparent in our series.

Cathepsin E in follicle associated epithelium of intestine and tonsils: localization to M cells and possible role in antigen processing

A specific rabbit anti-human serum was used selectively to localize the aspartic proteinase cathepsin E to follicle associated epithelium (FAE) of human and rat intestine, including jejunum, ileum, appendix, colon and rectum, as well as of human palatine, pharyngeal and lingual tonsils. Coexpression of class II histocompatibility antigen HLA-DR antigen has been observed in some of the cathepsin E-positive epithelial cells. In addition, cathepsin E has been detected in a few mononuclear cells of intestinal lymphoid structures and tonsils resembling interdigitating reticulum cells of lymph nodes. Another aspartic proteinase, cathepsin D, has been found to be poorly represented in FAE and intensely expressed by macrophages. Electron immunocytochemistry localized cathepsin E to endosomal vesicles and endoplasmic reticulum of M cells in rat and human ileum as well as of M-like cells in human palatine tonsil. The results suggest a possible role of endosomal cathepsin E in the processing of macromolecules and microorganisms transported by M cells and related epithelial cells to mucosal associated lymphoid tissue (MALT).