Increased expression of vascular endothelial growth factor and hypoxia inducible factor-1α in lung tissue of patients with chronic bronchitis
Introduction
Chronic obstructive pulmonary disease (COPD) is characterized by persistent airflow limitation that is not fully reversible, usually progressive and associated with an abnormal inflammatory response of the lungs [1]. It is a major health problem and the fourth leading cause of death worldwide; its prevalence is expected to increase [2]. Despite the various influencing genetic and environmental factors, cigarette smoking is the most important risk factor for COPD. The pathologic changes of COPD are largely categorized as airway inflammation and parenchymal destruction, which are traditionally known as chronic bronchitis (CB) and emphysema, respectively. The relative contributions of those two phenotypes to airflow obstruction vary from one person to another, and the mechanism of lung injury by cigarette smoke that results in the predominance of CB or emphysema remains unclear [3].
Vascular endothelial growth factor (VEGF) is one of the potent mediators of vascular regulation in angiogenesis and vascular permeability [4]. VEGF is also involved in lung development, maintenance of normal lung structure, thus it plays a crucial role in the lung homeostasis [5]. Several studies have raised the possibility that VEGF may be related with development of COPD. In an animal model, VEGF blockade with an inhibitor of VEGFR resulted in endothelial cell apoptosis and morphologic changes which is consistent with emphysema [6]. Moreover, the different expression patterns according to the different phenotypes of COPD were reported; VEGF level was increased in the induced sputum and bronchial biopsy specimen in CB patients, while being decreased in emphysema patients [7], [8], [9], [10].
Hypoxia inducible factor-1alpha (HIF-1α) is a transcription factor that induces VEGF expression which is affected by both hypoxia and inflammation. Although VEGF expression is induced by variety of factors that include cytokines, chemokines and growth factors, HIF-1α is the major mechanism of VEGF regulation [11], [12]. Taken together, VEGF and HIF-1α seem to be involved in the pathogenesis of COPD but their expression in lung tissue of CB patients has not been studied. We therefore investigated the expression of VEGF, its receptors and HIF-1α in lung tissue of CB patients and evaluated the relationship between VEGF expression and that of HIF-1α as a possible mechanism of VEGF regulation in CB.
Section snippets
Study population
We used non-tumorous lung tissues donated from the Korea Lung Tissue Bank which has been assigned and supported by the Korean Science and Engineering Foundation. The tissues were obtained from patients who underwent lobectomy or pneumonectomy and immediately frozen at − 80 °C until use. All patients gave their consent and the study protocol was approved by the Clinical Research Ethics Committee of the Korea University Medical Center (AN10139-001). Thirty subjects were enrolled: non-smokers with
Clinical characteristics
The clinical data and lung functions of all subjects are shown in Table 1. The mean age was 67.8 years and no age difference was observed among groups. More females were enrolled in non-smokers. The smoking intensity between healthy smokers and CB patients was not significantly different. FEV1 and FEV1/FVC were significantly reduced in CB patients compared with healthy smokers (p = 0.032 and p = 0.028, respectively). The diffusing lung capacity for carbon monoxide (DLCO) in CB patients was also
Discussion
In the present study, CB was associated with increased expression of VEGF in the bronchiolar epithelium, bronchiolar smooth muscle and vascular smooth muscle. VEGFR-2 was also increased in bronchiolar smooth muscle, vascular endothelium and vascular smooth muscle. In addition, VEGF expression was correlated with HIF-1α expression. To the best of our knowledge, this is the first study to document the increased expression of VEGF and VEGFR in different compartments of lung tissues in patients
Acknowledgments
This work was supported by grant from the National Research Resource Bank Program of the Korea Science & Engineering Foundation in the Ministry of Science & Technology (No. R21-2007-000-10058-0) and by the Korea University Grant (Nos. K1032051 and R1205861).
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