This is the first proteomic approach using the human T-lymphocytes of blood in asthmatic patients. Although the proteomic data of the T-lymphocytes of normal human has been reported, no study on T-lymphocytes in asthmatic patients has been reported.
It is known that the asthmatic process that triggers the immune system can lead to excessive release of various cytokines and inflammatory mediators, which are produced by T-cells, infiltrated mononuclear cells, eosinophils, and local mast cells into the lung. Among the inflammatory cells, T-lymphocytes play major roles in the pathogenesis of bronchial asth-ma.’ So, we performed proteomic analysis of the peripheral T-lymphocytes of asthmatic patients.
In this study, we identified several proteins that were previously unknown or known to be associated with the pathogenesis of asthma. The function of phosphodiesterase (PDE) is to hydrolyze cyclic adenosine monophosphate and/or cyclic guanosine monophosphate. Crocker et al demonstrated that the PDE activity in CD4+ T cells from asthmatic patients was elevated over that in the cells from nonatopic controls. In vivo and in vitro studies have established that selective PDE4 inhibitors suppress the activity of many proin-flammatory and immune cells. Additionally, it was reported that PDE4 inhibition decreased the MUC5AC expression induced by EGFR in cultured human airway epithelial cells and in human isolated bronchus. Our study showed the result that the proteomic expressions of EGFR and PDE4 were slightly increased in T-lymphocytes of asthmatic patients compared to healthy persons.
Oxidative stress occurs in many allergic and immunologic disorders. Asthma is also associated with reduced antioxidant defenses and glutathione is one of the most important antioxidants. Glutathione reductase is a cofactor for generating reduced glutathione. In our study, glutathione reductase was increased and GST-M3 was decreased in the asthmatic patients. Glutathione S transferases (GSTs) are components of the phase II xenobiotic defense pathway that utilizes the lipid and DNA products of oxidative stress. Several reports have shown that the reduced antioxidant capacity of GST is related to the increased risk of allergic asthma, Polymorphism at the GST genetic locus is associated with the expression of bronchial hyperresponsiveness and atopic phenotypes in asthma.
Thioredoxin was slightly increased in the asthmatic group in this study. Thioredoxin is known to possess antioxidant activity that regulates redox-sensitive molecules such as nuclear factor-kB and glucocorticoid receptors. Yamada et al first reported that the serum levels of thioredoxin were positively correlated with the severity of asthma.
Our study showed the increase of the HSP-70 in the asthma group. Heat shock protein protects the cells and tissues from the deleterious effects of numerous mediators, reactive oxygen species, or tumor necrosis factor-а. Several studies have suggested that heat shock protein is correlated with the severity of asthma exacerbation.
In our study, the decreased expression of TPR-containing protein was observed in the asthma patients. The TPR domain consists of a 34-amino-acid motif, and it has many cellular functions such as mitosis, transcription, protein transport, and development. A previous report showed that some proteins with the TPR domain negatively regulated adenosine triphosphatase and HSP-70, but any detailed association with asthma has not yet been elucidated.
Several cytoskeletal proteins were decreased in the T-lymphocytes of asthma patients. Dynein is a microtubule-dependent motor protein. Vimentin attaches to the nucleus, endoplasmic reticulum, and mitochondria. Tubulin 32, a subunit of microtubules, integrates ciliary motion with the cellular functions via the cytoskeleton. These cytoskeletal changes may illustrate the functional changes in the T-lymphocytes of asthma patient.
Some proteins related to the cell cycle were also observed in our study. PTPs work antagonistically with protein tyrosine kinases to regulate signal transduction in a cell. Protein tyrosine kinases phosphorylate the tyrosine residues on a substrate protein, and PTPs remove these phosphates from substrate tyrosines (dephosphorylation). Kamata et al reported that Src homology 2 domain-containing tyrosine phosphatase regulates the development of allergic airway inflammation. P-Arrestins are cytosolic proteins that mediate homologous desensitization of the G protein-coupled receptors by binding to agonist-occupied receptors and by uncoupling them from heterotrimeric G proteins. It was suggested in an animal study that P-arrestin 2 was associated with T-cell migration and the development of asthma. Several previous studies have shown that T-cells expressing different P receptors may play different roles in regulating the airway inflammation in asthma. Cyclin-dependent kinase is also involved in the regulation of transcription and processing of messenger RNA. Increased cyclin-dependent kinase inhibitors were discovered in the bronchial epithelium of asthmatic patients. The above-mentioned proteins show that an abnormal repair process may contribute to airway inflammation and remodeling during damage to the epithelium. Changes of several proteins (ie, pyri-doxal kinase, phenylalanine hydroxylase, zinc finger protein, pyrroline-5-carboxylate reductase) were also observed in this study, and the relation of these proteins with the asthma is not yet clear.
Several studies have shown polymorphism of the human leukocyte antigen I genes in the asthma population. However, one study showed that no definitive human leukocyte antigen association could be established with atopic or nonatopic asthma.
Our study may have some limitations. First, it is known that depending on the different physiologic conditions, such as age, gender, fasting and feeding, changes in diet, physical activity, medications, pregnancy and the disease status, 2D-PAGE can show different panels. So, we selected nonsmokers and relatively young-aged persons. Second, we discovered changes of the proteins associated with the cell cycle, inflammation, or oxidative stress. Whether the changes of such proteins are pathognomonic markers of asthma or of a reactive phenomenon is questionable. Finally, posttranslational modifications might lead to a shift of the protein spot in the electrophoresis, which could have an influence on both spot identification and spot intensity.
Despite of the above limitations, our study is a meaningful first study on the proteomic changes of T-lymphocytes of asthmatic patients. It would be interesting and informative to observe the changes of the proteome profiles after steroid treatment. Studies on other inflammatory cells in asthma patients would also be necessary to understand the overall picture of proteome behavior in asthma patients. We suggest that some of the proteins, whose expressions are differentially regulated in the T-lymphocytes of asthmatic patients, may serve as important biomarkers and therapeutic targets of asthma.
In conclusion, proteomic analysis of the peripheral T-lymphocytes of asthma patients revealed some differentially expressed proteins compared with those of normal subjects. The possibility of using the differentially expressed proteins as important biomarkers and therapeutic targets in asthma patients warrants further studies.