Aberrant DNA methylation of the toll-like receptors 2 and 6 genes in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) is a syndrome leading to chronic intermittent hypoxia, and the up-regulation of toll-like receptors (TLR) 2 and 6 on peripheral blood cells has been reported. We hypothesized that DNA methylation in TLR2 and TLR6 genes may play a role in the development of OSA and its excessive daytime sleepiness (EDS) phenotype. DNA methylation over 28 cytosine-phosphate-guanine (CpG) sites of the TLR2 promoter region and 3 CpG sites of the TLR6 gene body, and their protein expressions were measured by using pyrosequencing and ELISA methods in 18 heathy subjects (HS) and 58 patients with severe OSA (divided into 18 non-EDS and 40 EDS group). Patients with severe OSA had higher DNA methylation levels over five CpG sites (#1, #2, #3, #25 and #28) and lower DNA methylation levels over CpG site #18 of the TLR2 promoter region, higher DNA methylation levels over two CpG sites (#1 and #3) of the TLR6 gene body, and higher protein expressions of TLR6 than HS. The CpG site #2 of the TLR6 gene body was hypermethylated in severe OSA patients with EDS. Both DNA methylation levels over CpG site #1 of the TLR6 gene body and protein expressions of TLR6 were reduced after more than 6 months of nasal CPAP treatment in seven selected patients. Aberrant DNA methylation of the TLR2 promoter region and TLR6 gene body are associated with the consequence of severe OSA and its EDS phenotype.