Sleep apnea syndrome (SAS) is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]) and is a risk factor for insulin resistance/type 2 diabetes. However, the mechanisms linking IH stress and insulin resistance remain elusive. We exposed human RD and mouse C2C12 muscle cells either to 70 cycles/24 h of IH (5 min hypoxia [1% O2]/10 min normoxia [21% O2]), mimicking SAS patients, or normoxia for 24 h, measured mRNA levels by real-time reverse transcription polymerase chain reaction, and found that IH significantly increased the mRNA levels of interleukin-8 (IL-8), osteonectin (ON), and myonectin (MN). IL-8, ON, and MN in IH-treated RD cell medium were also increased (P<0.0001, P<0.0001, and P=0.0079, respectively). We further analyzed the IH-induced expression mechanisms of IL-8, ON, and MN genes in RD muscle cells. Deletion analyses revealed that -152 to -151 region in IL-8, -105∼-99 region in ON, and -3,741∼-3,738 region in MN promoter(s) were responsible for the activation by IH. The promoters contain consensus transcription factor binding sequences for octamer binding transcription factor 1 (OCT1) in IL-8 and MN, and for nuclear factor erythroid 2-related factor 2 (NRF2) in ON, respectively. The introduction of siRNA for OCT1, and NRF2 abolished the increase of mRNAs for IL-8 and MN, and ON, respectively. As IL-8, ON, and MN are reported to be myokines and associated with glucose intolerance, insulin resistance, and diabetes, the results could well explain a mechanism of glucose intolerance, insulin resistance, and diabetes in SAS patients.
S. Takasawa: None. R. Shobatake: None. A. Itaya-Hironaka: None. M. Makino: None. S. Sakuramoto-Tsuchida: None. T. Uchiyama: None. H. Ota: None. A. Yamauchi: None.