Background Nasal polyps (NP) are characterized by pseudocysts derived from stromal tissue edema and cause persistent infections in patients with chronic rhinosinusitis (CRS). A low level of tissue-type plasminogen activator (gene name PLAT) is considered a cause of stromal tissue edema because of insufficient plasmin activation in NP; however, the mechanism regulating PLAT gene expression levels is still unclear. The epigenetic mechanism regulating the PLAT gene expression has been studied in other tissues. Objective We aimed to investigate the methylation levels in the proximal PLAT promoter and their effects on gene expression in NP tissue. Methods We investigated the methylation levels at 3 CpG sites in the proximal PLAT promoter regions (-618, -121, and -105 with respect to the transcription initiation site) by bisulfite pyrosequencing and their effects on the gene expression by quantitative real-time polymerase chain reaction (qPCR) in 20 paired samples of NP and inferior turbinate tissue (IT) from patients with CRS. Results The DNA methylation levels at all CpG sites were higher ( P < .01), and the PLAT expression was lower ( P < .001) in NP compared with IT. The methylation changes at the -618 site showed a negative correlation with the gene expression changes between NP and IT ( r = -.65, P < .01). Conclusions Hypermethylation of PLAT promoter may downregulate the gene expression in NP, leading to excessive fibrin deposition by aberrant coagulation cascade. DNA methylation of proximal PLAT promoter may contribute to NP growth and have a potential as a new therapeutic target.
Keywords: DNA methylation; chronic rhinosinusitis; coagulation cascade; epigenesis; inferior turbinate; nasal polyps; promoter regions; pyrosequence; qPCR; tissue plasminogen activator.