Genetic effect of single-nucleotide polymorphisms in the PPARGC1B gene on airway hyperreactivity in asthmatic patients

Abstract

Background Peroxisome proliferator-activated receptor gamma coactivator 1 beta (PPARGC1B) is a co-activator for intracellular receptors such as the estrogen receptor, PPAR, and glucocorticoid receptor, which are involved in asthma development.Objectives Genetic association of single-nucleotide polymorphisms (SNPs) in the PPARGC1B gene with the risk of asthma and airway hyperreactivity (AHR) was investigated, as well as the functional effects of these SNPs on PPARGC1B gene and protein expression. Methods Direct sequencing of DNA from 24 Korean was performed to identify PPARGC1B SNPs. Genotyping was done in 264 controls and 949 asthmatics using single-base extension methods. PPARGC1B, cholinergic receptor muscarinic 2 (CHRM2), and cholinergic receptor muscarinic 3 (CHRM3) mRNA levels were measured using real-time PCR. Dual luciferase reporter assays were performed to analyze +102525G>A SNPs on exon 5. Results 18 SNPs and 1 insertion/deletion polymorphism were identified, and 7 SNPs were genotyped. No significant difference existed in the distribution of SNPs and haplotypes between the asthmatics and controls. However, the allele frequency of -427C>T and +102525G>A; R265Q showed a significant association with log-transformed PC20 methacholine values in the asthmatics (P = 0.005-0.0004). Real-time PCR demonstrated higher PPARGC1B mRNA levels in asthmatics having -427CC allele than in those having -427TT or CT alleles (P = 0.048). The ratio of the mRNA expression for each PPARGC1B exon4-mRNA compared to the wild type was similar in peripheral blood mononuclear cells carrying the +102525G>A allele. Dual luciferase reporter assays revealed that +102525A allele caused higher activation of ERa with estrogen than +102525G allele. The ratio of the CHRM2 and CHRM3 mRNA expression for +102525A of PPARGC1B/ERa co-transfected 293T cells mRNA showed a significant up regulation when compared to +102525G of PPARGC1B /ERa co-tansfected 293T cells mRNA. Conclusions and Clinical Relevance Polymorphisms of +102525G>A on exon 5 of the PPARGC1B gene may affect the development of AHR through the modulation of PPARGC1B gene products. The PPARGC1B genotypes may serve as genetic markers for AHR.