Constrictive bronchiolitis obliterans. Characterisation of fibrogenesis and lysyl oxidase expression patterns

[Small airway diseases and immune deficiency]

INTRODUCTION

Innate or acquired immune deficiency may show respiratory manifestations, often characterized by small airway involvement. The purpose of this article is to provide an overview of small airway disease across the major causes of immune deficiency.

BACKGROUND

In patients with common variable immune deficiency, recurrent lower airway infections may lead to bronchiolitis and bronchiectasis. Follicular and/or granulomatous bronchiolitis of unknown origin may also occur. Bronchiolitis obliterans is the leading cause of death after the first year in patients with lung transplantation. Bronchiolitis obliterans also occurs in patients with allogeneic haematopoietic stem cell transplantation, especially in the context of systemic graft-versus-host disease.

VIEWPOINT AND CONCLUSION

Small airway diseases have different clinical expression and pathophysiology across various causes of immune deficiency. A better understanding of small airways disease pathogenesis in these settings may lead to the development of novel targeted therapies.

Gene expression in obliterative bronchiolitis-like lesions in 2,3-pentanedione-exposed rats

Obliterative bronchiolitis (OB) is an irreversible lung disease characterized by progressive fibrosis in the small airways with eventual occlusion of the airway lumens. OB is most commonly associated with lung transplant rejection; however, OB has also been diagnosed in workers exposed to artificial butter flavoring (ABF) vapors. Research has been limited by the lack of an adequate animal model of OB, and as a result the mechanism(s) is unclear and there are no effective treatments for this condition. Exposure of rats to the ABF component, 2,3-pentanedione (PD) results in airway lesions that are histopathologically similar to those in human OB. We used this animal model to evaluate changes in gene expression in the distal bronchi of rats with PD-induced OB. Male Wistar Han rats were exposed to 200 ppm PD or air 6 h/d, 5 d/wk for 2-wks. Bronchial tissues were laser microdissected from serial sections of frozen lung. In exposed lungs, both fibrotic and non-fibrotic airways were collected. Following RNA extraction and microarray analysis, differential gene expression was evaluated. In non-fibrotic bronchi of exposed rats, 4683 genes were significantly altered relative to air-exposed controls with notable down-regulation of many inflammatory cytokines and chemokines. In contrast, in fibrotic bronchi, 3807 genes were significantly altered with a majority of genes being up-regulated in affected pathways. Tgf-β2 and downstream genes implicated in fibrosis were significantly up-regulated in fibrotic lesions. Genes for collagens and extracellular matrix proteins were highly up-regulated. In addition, expression of genes for peptidases and peptidase inhibitors were significantly altered, indicative of the tissue remodeling that occurs during airway fibrosis. Our data provide new insights into the molecular mechanisms of OB. This new information is of potential significance with regard to future therapeutic targets for treatment.

Challenges in pulmonary fibrosis. 2: Bronchiolocentric fibrosis

Bronchiolocentric fibrosis is essentially represented by the pathological pattern of constrictive fibrotic bronchiolitis obliterans. The corresponding clinical condition (obliterative bronchiolitis) is characterised by dyspnoea, airflow obstruction at lung function testing and air trapping with characteristic mosaic features on expiratory high resolution CT scans. Bronchiolitis obliterans may result from many causes including acute diffuse bronchiolar damage after inhalation of toxic gases or fumes, alloimmune chronic processes after lung or haematopoietic stem cell transplantation, or connective tissue disease (especially rheumatoid arthritis). Airway-centred interstitial fibrosis and bronchiolar metaplasia are other features of bronchiolocentric fibrosis.

Immune Cell Infiltration and Broncovascular Remodeling After Nitric Acid Nasal Instillation in a Mouse Bronchiolitis Obliterans Model

Immune cell airway infiltration and the bronchovascular remodeling process have shown to be promising in the understanding of bronchiolitis obliterans (BO) pathogenesis. In this study we sought to validate the importance of immune cells, whether diffusely distributed or forming lymphoid follicles, collagen density, and vascular factors. Eight weeks after a single nitric acid (NA) nasal instillation, lung changes were characterized by lumen distortion, epithelial layer folding, reduction or total obliteration of terminal bronchiole (TB) lumen, and wall thickness increase. The morphologic changes in the TB and TA (terminal artery) lumen coincide with the measurement difference in the three groups. The TB diameter and lumen were significantly decreased in BO when compared with non-BO lungs (0.76 +/- 0.05 microm vs. 0.81 +/- 0.05 microm and 12,286.13 +/- 378.83 microm vs. 18,182.27 +/- 5,593.98 microm, p = 0.05 and p = 0.01, respectively). Equally significant was the increase in TB thickness in BO when compared with the non-BO group (201.72 +/- 35.75 microm vs. 149.75 +/- 40.61 microm, p = 0.007). The morphologic changes in immune cells seen in TB, TA, and bronchus-associated lymphoid tissue (BALT) also coincide with the quantification differences observed in the three groups. We concluded that immune cell infiltration and collagen/vascular remodeling are related to the spectrum of histologic changes in a BO nasal-induced model in mice and may be an appropriate target for prospective studies of human bronchiolitis.

Bleomycin-induced pulmonary fibrosis susceptibility genes in AcB/BcA recombinant congenic mice

The genetic basis of susceptibility to pulmonary fibrosis is largely unknown. Initially, in this study, loci regulating the response of bleomycin-induced pulmonary fibrosis were mapped using a set of recombinant congenic strains bred from pulmonary fibrosis-resistant A/J and susceptible C57BL/6J (B6) mice. Linkage was identified (logarithm of the odds score = 4.9) on chromosome 9, and other suggestive loci were detected. The putative loci included alleles from both the B6 and A/J strains as increasing the fibrosis response of congenic mice. Gene expression analysis with microarrays revealed 3,304 genes or expressed sequence tags to be differentially expressed (P < 0.01) in lung tissue between bleomycin-treated B6 and A/J mice, and 246 of these genes mapped to potential susceptibility loci. Pulmonary genes differentially expressed between bleomycin-treated B6 and A/J mice included those of heparin binding and extracellular matrix deposition pathways. A review of available genomic sequences revealed 809 (43% of total) genes in the linkage intervals to have variations predicted to alter the encoded proteins or their regulation, 68 (8.4%) of which were also differentially expressed. Genomic approaches were combined to produce a set of candidate genes that may influence susceptibility to bleomycin-induced pulmonary fibrosis in the A/J:B6 mouse model.

Transforming growth factor-beta-regulated gene transcription and protein expression in human GFAP-negative lamina cribrosa cells

Primary open-angle glaucoma (POAG) is a progressive optic neuropathy, which is a major cause of worldwide visual impairment and blindness. Pathological hallmarks of the glaucomatous optic nerve head (ONH) include retinal ganglion cell axon loss and extracellular matrix (ECM) remodeling of the lamina cribrosa layer. Transforming growth factor-beta (TGF-beta) is an important pro-fibrotic modulator of ECM metabolism, whose levels are elevated in human POAG lamina cribrosa tissue compared with non-glaucomatous controls. We hypothesize that in POAG, lamina cribrosa (LC) glial cells respond to elevated TGF-beta, producing a remodeled ONH ECM. Using Affymetrix microarrays, we report the first study examining the effect of TGF-beta1 on global gene expression profiles in glial fibrillary acidic acid (GFAP)-negative LC glial cells in vitro. Prominent among the differentially expressed genes were those with established fibrogenic potential, including CTGF, collagen I, elastin, thrombospondin, decorin, biglycan, and fibromodulin. Independent TaqMan and Sybr Green quantitative PCR analysis significantly validated genes involved in regulation of cell proliferation (platelet-derived growth factor [PDGF-alpha]), angiogenesis (vascular endothelial growth factor [VEGF]), ECM accumulation and degradation (CTGF, IL-11, and ADAMT-S5), and growth factor binding (ESM-1). Bioinformatic analysis of the ESM-1 promoter identified putative Smad and Runx transcription factor binding sites, and luciferase assays confirmed that TGF-beta1 drives transcription of the ESM-1 gene. TGF-beta1 induces expression and release of ECM components in LC cells, which may be important in regulating matrix remodeling in the lamina cribrosa. In disease states such as POAG, the LC cell may represent an important pro-fibrotic cell type and an attractive target for novel therapeutic strategies.

Transforming growth factor-β1 mediated up-regulation of lysyl oxidase in the kidneys of hereditary nephrotic mouse with chronic renal fibrosis

Lysyl oxidase (LOX), an extracellular enzyme, plays a key role in the post-translational modification of collagens and elastin, catalyzing inter- and intra-crosslinking reactions. Because the crosslinked extracellular matrices (ECMs) are highly resistant to degradative enzymes, it is considered that the over-expression of LOX may cause severe fibrotic degeneration. In the present study, we addressed the role of LOX-mediated crosslinking in chronic renal tubulointerstitial fibrosis using an animal model of hereditary nephrotic syndrome, the Institute of Cancer Research (ICR)-derived glomerulonephritis (ICGN) mouse. Ribonuclease protection assay (RPA) revealed that LOX mRNA expression was up-regulated in the kidneys of ICGN mice as compared with control ICR mice. High-level expression of LOX and transforming growth factor (TGF)-beta1 (an up-regulator of LOX) mRNA was detected in tubular epithelial cells of ICGN mouse kidneys by in situ hybridization. Type-I and -III collagens, major substrates for LOX, were accumulated in tubulointerstitium of ICGN mouse kidneys. The present findings imply that TGF-beta1 up-regulates the production of LOX in tubular epithelial cells of ICGN mouse kidneys, and the excessive LOX acts on interstitial collagens and catalyzes crosslinking reactions. As a result, the highly crosslinked collagens induce an irreversible progression of chronic renal tubulointerstitial fibrosis in the kidneys of ICGN mice.

Comparative immunocytochemical localization of lysyl oxidase (LOX) and the lysyl oxidase-like (LOXL) proteins: changes in the expression of LOXL during development and growth of mouse tissues

Lysyl oxidase (LOX) and lysyl oxidase-like (LOXL) are extracellular enzymes that deaminate peptidyl lysyl residues involved in the cross-linking of fibrillar collagens and elastin. While LOX is required for the survival of newborn mice, the role of LOXL during development remains unclear. Studies have shown that the same cell types express LOX and LOXL in the same tissues, but no functional differences have been established. We have compared the immunohistochemical localization of LOX and LOXL in various tissues from normal, young adult mice. LOX and LOXL were co-localized in the skin, aorta, heart, lung, liver and cartilage, but were localized to different areas in the kidney, stomach, small intestine, colon, retina, ovary, testis and brain. LOXL expression was further examined in tissues from different developmental stages. In embryonic mice (10.5-14.5 dpc), LOXL immunostaining was abundant in the heart, liver, intestine, and neural tube. LOXL was present in most major organs in late fetal (16.5 dpc) and newborn mice, but generally diminished as animals aged. Immunoreactivity was significantly reduced in the heart, lung, kidney and liver of 2 year-old mice, but remained prevalent in the skin and tongue. LOX and LOXL were also found in the nuclei of cells in a number of tissues. These results indicate that LOXL has a role during mouse development and in the maintenance of adult tissues.

Synthesis and characterization of model compounds of the lysine tyrosyl quinone cofactor of lysyl oxidase

4-n-Butylamino-5-ethyl-1,2-benzoquinone (1(ox)) has been synthesized as a model compound for the LTQ (lysine tyrosyl quinone) cofactor of lysyl oxidase (LOX). At pH 7, 1(ox) has a lambda(max) at 504 nm and exists as a neutral o-quinone in contrast to a TPQ (2,4,5-trihydroxyphenylalanine quinone) model compound, 4, which is a resonance-stabilized monoanion. Despite these structural differences 1(ox) and 4 have the same redox potential (ca. -180 mV vs SCE). The structure of the phenylhydrazine adduct of 1(ox) (2) is reported, and 2D NMR spectroscopy has been used to show that the position of nucleophilic addition is at C(1). UV-vis spectroscopic pH titration of phenylhydrazine adducts of 1(ox) and 4, 2, and 11, respectively, reveals a similar red shift in lambda(max) at alkaline pH with the same pK(a) (approximately 11.8). In contrast, the red shift in lambda(max) at acidic pH conditions yields different pK(a) values (2.12 for 2 vs -0.28 for 11), providing a means to distinguish LTQ from TPQ. Reactions between in situ generated 4-ethyl-1,2-benzoquinone and primary amines give a mixture of products, indicating that the protein environment must play an essential role in LTQ biogenesis by directing the nucleophilic addition of the epsilon-amino group of a lysine residue to the C(4) position of a putative dopaquinone intermediate. Characterization of a 1,6-adduct between an o-quinone and butylamine (3-n-butylamino-5-ethyl-1,2-benzoquinone, 13) confirms the assignment of LTQ as a 1,4-addition product.

Synovial Remodeling Process Induced by Type V Collagen Immunization in Rabbits

The pathogenesis of diffuse connective tissue diseases is still unknown despite studies of the autoimmunity aspects related to extracellular matrix elements, mainly the collagens. Articulations are frequently affected by the synovitis process in these diseases. The objective of the present study was to verify the morphologic aspects of the synovial membrane of rabbits immunized with type V collagen, which has some particular characteristics 75 days after the first antigen inoculation and when compared to control animals. The synovial membrane of the animals sacrificed after 75 days of immunization presented an intense remodeling phenomenon along the connective tissue screen and interlobular septa of the adipose-muscle tissue screen compartment. The remodeling process determined type I and III collagen fiber depositions in the vascular and connective tissue compartments of the synovial membrane. The nutrient vessels of the adipose-muscle compartment showed a similar remodeling process, which resulted in small vessel occlusion. Few residual inflammatory foci consisting of monocytes and eosinophils were observed. Thus, our experimental model reproduces morphologic changes in different tissues, characterized by an extracellular matrix remodeling process similar to those observed in many diffuse connective tissue diseases such as systemic lupus erytematosus and scleroderma. Therefore, this model could be useful in understanding the pathogenesis and the treatment of these diseases.