Correlation of methylation of toll-like receptor 4 (TLR4) and interleukin-6 (IL6) promoter with insulin resistance in obese adolescents

Abstract

Chronic inflammation can lead to insulin resistance in obesity. Increased mRNA expression
of inflammatory markers such as toll-like receptor 4 (TLR4) and interleukin 6 (IL6) were
reported both in the tissue and the peripheral blood of obese adolescent and correlated
with insulin resistance. DNA methylation surrounding TSS region is known to regulate the
level of a gene expression. The aim of the study was to investigate the methylation status
of TLR4 and IL6 promoter in peripheral blood of obese adolescent and its correlation to
insulin resistance. This was a cross sectional study with observational analytic approached.
Fifty adolescents with obesity from Yogyakarta Special Region, aged 15-18 years,
z-score value >2 SD, no experience of any acute infections within 2 weeks and signed in
informed consent, were selected in this study. Subjects with diabetic mellitus, incomplete
data and DNA concentration of <20 μg/mL were excluded. DNA samples were extracted
from peripheral blood of the subjects. The bisulfite converted DNA was analyzed for
methylation level with direct sequencing. Correlation analysis using Spearman test was
performed with significance value was set at p<0.05. No methylation in TLR4 promoter
was detected in all subjects. The methylation level of IL6 was transformed to categorical
variable. Four (8%) subjects with insulin resistance and 2 (4%) without insulin resistance
had methylation on a CpG site. Methylation of IL6 was not statisticaly different between
insulin resistance and non-resistance adolescent (p=0.635). The significant correlation
was not found between methylation level in IL6 promoter with insulin resistance (HOMAIR)
(r=0.051). Cell specific of methylation mechanism, characteristic of subjects and
types of samples were suspected causing those results. In conclusion, no correlation
between methylation levels of TLR4 promoter and IL6 with insulin resistance in obese
adolescent was observed in this study.