1317-P: Intermittent Hypoxia Increased the Expression of DBH and PNMT in Neuronal Cells via MicroRNA-Mediated Mechanism

Abstract

Sleep apnea syndrome (SAS) , characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]) , is a risk factor for hypertension and insulin resistance. We have reported correlation between IH and insulin resistance. However, why hypertension is induced by IH has been elusive. Here, we investigated the effect of IH on the expression of catecholamine metabolizing enzymes using in vitro IH system. Human and mouse neuronal cells, NB-1 and Neuro-2a, were exposed to IH (70 cycles of 5 min hypoxia [1% O2] and min normoxia [21% O2]) or normoxia for 24 hours. Real-time RT-PCR revealed that IH significantly increased the mRNA levels of dopamine β-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) in both NB-1 (P=0.0271 and P<0.0001, respectively) and Neuro-2a (P=0.0135 and P=0.0341, respectively) . Western blot showed that the expression of DBH and PNMT in the NB-1 cells significantly increased by IH (P=0.0296 and P=0.0007, respectively) . We next prepared reporter plasmids containing human DBH (-1018˜+10) and PNMT (-600˜+67) upstream of luciferase reporter gene and transfected them into NB-1 cells. The promoter activities of these genes were not increased by IH. Target mRNA search of microRNA (miR) s using MicroRNA.org program revealed that the mRNAs have a potential target sequence for miR-375. The miR-375 level of IH-treated cells was significantly decreased than that of normoxia-treated cells (P=0.0222) . To clarify the role of miR-375, miR-375 mimic and non-specific control RNA (miR-375 mimic NC) were introduced into NB-1 cells. The IH-induced up-regulation of mRNAs of DBH and PNMT was abolished by introduction of miR-375 mimic but not by miR-375 mimic NC. Theses results strongly suggest that IH stress down-regulates the miR-375 in neuronal cells, resulting in the increased levels of DBH and PNMT via the inhibition of the miR-375-mediated mRNA degradation, leading SAS patients to hypertension. Disclosure S.Takasawa: None. R.Shobatake: None. Y.Takeda: None. T.Uchiyama: None. A.Yamauchi: None. M.Makino: None. K.Asai: None. H.Ota: None.