Association of <i>NR3C1 Bcl1</i> gene polymorphism with impaired programmed cell death of lymphocytes in patients with atopic bronchial asthma

Abstract

Atopic asthma is a chronic disease characterized by airway obstruction, bronchial hyperresponsiveness, and inflammation. Patients show increased activation of immune cells in the airways, especially T-lymphocytes, leading to chronic inflammation. The lymphocytes of asthma patients are known to have an impairment of the type 1 and 2 programmed cell death, i.e., apoptosis and autophagy, thus contributing to prolongation and intensification of inflammatory process. As compared to apoptosis, autophagy may also contribute to cell survival under stress conditions. Its disruption and hyperactivation leads to exacerbation of allergic responses. Glucocorticoids are the main drugs for the treatment of atopic bronchial asthma by activating the glucocorticoid receptor, thus triggering anti-inflammatory response and apoptosis of the cells. However, some patients exhibit resistance to therapy due to various factors, including single nucleotide polymorphisms of NR3C1 glucocorticoid receptor gene. The highest association between asthma severity and resistance to therapy was found for the GG variant of the NR3C1 Bcl1 polymorphism. Common molecular pathways for glucocorticoid receptor activation and programmed cell death and mediating molecules suggest a significant role for the polymorphic receptor variant in cell death. The aim of our study was to evaluate the effect of a single nucleotide polymorphism (G allele, i.e., Bcl1 polymorphism of NR3C1 gene) of glucocorticoid receptor on expression levels of genes that regulate apoptosis (BCL2, CASP3) and autophagy (BECN1, LC3) in lymphocytes of patients with moderate and severe atopic bronchial asthma. The study was performed with peripheral blood samples of 24 patients aged 20 to 45 years with an established diagnosis of moderate to severe atopic bronchial asthma. Using PCR technique with restriction fragment length polymorphism (RFLP) assay, the patients were distributed according to the genotypes of the BclI polymorphism of the NR3C1 gene: 12 patients with CC genotype, 8 persons with GC genotype, and 4 cases with GG genotype. The lymphocytes were isolated in Ficoll density gradient and cultivated with dexamethasone under the conditions of nutrient depletion. The level of gene expression was determined by real-time PCR. When studying associations between various genotypes of Bcl1 polymorphism and expression of cell death marker genes, the anti-apoptotic reactions were detected in lymphocytes of patients with GG polymorphism under the influence of dexamethasone thus being a potential mechanism for development of resistance to glucocorticosteroid therapy in asthma. Impaired activation of BECN1 gene expression in patients with the GG genotype may suggest deregulation of the autophagy in this group of patients, as a mode of programmed cell death. Moreover, in patients with GC genotype during long-term cultivation, exposure to dexamethasone increases the expression of the LC3 gene, indicating a more pronounced activation of autophagy. Hence, this work demonstrates differences in response of lymphocytes to synthetic glucocorticoid therapy, and probable effect of G allele (Bcl1 polymorphism) on dysregulation of programmed cell death under the influence of dexamethasone.