Sleep apnea syndrome is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]), and it is a known risk factor for hypertension. The upregulation of the renin-angiotensin system has been reported in IH, and the correlation between renin and CD38 has been noted. We exposed human HEK293 and mouse As4.1 renal cells to experimental IH or normoxia for 24 h and then measured the mRNA levels using a real-time reverse transcription polymerase chain reaction. The mRNA levels of Renin (Ren) and Cd38 were significantly increased by IH, indicating that they could be involved in the CD38-cyclic ADP-ribose signaling pathway. We next investigated the promotor activities of both genes, which were not increased by IH. Yet, a target mRNA search of the microRNA (miRNA) revealed both mRNAs to have a potential target sequence for miR-203. The miR-203 level of the IH-treated cells was significantly decreased when compared with the normoxia-treated cells. The IH-induced upregulation of the genes was abolished by the introduction of the miR-203 mimic, but not the miR-203 mimic NC negative control. These results indicate that IH stress downregulates the miR-203 in renin-producing cells, thereby resulting in increased mRNA levels of Ren and Cd38, which leads to hypertension.

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 report a correlation between IH and insulin resistance/diabetes. However, the reason why hypertension is induced by IH is elusive. Here, we investigated the effect of IH on the expression of catecholamine-metabolizing enzymes using an in vitro IH system. Human and mouse neuroblastoma cells (NB-1 and Neuro-2a) were exposed to IH or normoxia for 24 h. 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 and Neuro-2a. Western blot showed that the expression of DBH and PNMT in the NB-1 cells was significantly increased by IH. Reporter assays revealed that promoter activities of DBH and PNMT were not increased by IH. The miR-375 level of IH-treated cells was significantly decreased relative to that of normoxia-treated cells. The IH-induced up-regulation of DBH and PNMT was abolished by the introduction of the miR-375 mimic, but not by the control RNA. These results indicate that IH stress increases levels of DBH and PNMT via the inhibition of miR-375-mediated mRNA degradation, potentially playing a role in the emergence of hypertension in SAS patients.

Sleep apnea syndrome (SAS) is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]) and is a risk factor for hypertension. Among several mechanisms of hypertension in IH, up-regulation of renin (Ren)-angiotensin system has been reported. However, the detailed mechanism of how IH increases Ren remains elusive. We exposed human embryonic renal HEK293 and mouse juxtaglomerular As4.1 cells either to IH or normoxia for 24 hours and then measured mRNA and protein levels by real-time RT-PCR, ELISA and Western blot. We found that the mRNA and protein levels of Ren and Cd38 were significantly increased by IH. Introduction of small interfering RNA against Cd38 and addition of cell permeable cyclic ADP-ribose (cADPR) antagonist, 8-bromo-cADPR, attenuated the IH-induced increases of Ren expression, indicating an essential role of the CD38-cADPR signal in Ren expression in response to IH. Promotor activities of Ren and Cd38 were not increased by IH, suggesting the up-regulation is caused by post-transcriptional mechanism. We found that both mRNAs have a potential target sequence for miR-203. The miR-203 level of IH-treated cells was significantly decreased compared to normoxia-treated cells. Thus, we introduced miR-203 mimic and non-specific control RNA (miR-203 mimic NC) into As4.1 cells, exposed the cells to IH/normoxia. The IH-induced up-regulation of the mRNA levels of Ren and Cd38 was abolished by introduction of the miR-203 mimic but not by the miR-203 mimic NC. These results indicate that IH stress down-regulates the miR-203 in Ren-producing cells, resulting in increased levels of Ren and Cd38 mRNAs, leading SAS patients to hypertension.

Intermittent hypoxia (IH) is a central characteristic of sleep apnea syndrome (SAS), and it subjects cells in the body to repetitive apnea, chronic hypoxia, oxygen desaturation, and hypercapnia. Since SAS is linked to various serious cardiovascular complications, especially hypertension, many studies have been conducted to elucidate the mechanism of hypertension induced by SAS/IH. Hypertension in SAS is associated with numerous cardiovascular disorders. As hypertension is the most common complication of SAS, cell and animal models to study SAS/IH have developed and provided lots of hints for elucidating the molecular mechanisms of hypertension induced by IH. However, the detailed mechanisms are obscure and under investigation. This review outlines the molecular mechanisms of hypertension in IH, which include the regulation systems of reactive oxygen species (ROS) that activate the renin–angiotensin system (RAS) and catecholamine biosynthesis in the sympathetic nervous system, resulting in hypertension. And hypoxia-inducible factors (HIFs), Endotheline 1 (ET-1), and inflammatory factors are also mentioned. In addition, we will discuss the influences of SAS/IH in cardiovascular dysfunction and the relationship of microRNA (miRNA)s to regulate the key molecules in each mechanism, which has become more apparent in recent years. These findings provide insight into the pathogenesis of SAS and help in the development of future treatments.

Sleep apnea syndrome (SAS) is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia, IH), and it is a risk factor for cardiovascular disease (CVD) and insulin resistance/type 2 diabetes. However, the mechanisms linking IH stress and CVD remain elusive. We exposed rat H9c2 and mouse P19.CL6 cardiomyocytes to experimental IH or normoxia for 24 h to analyze the mRNA expression of the components of Cd38-cyclic ADP-ribose (cADPR) signaling. We found that the mRNA levels of cluster of differentiation 38 (Cd38), type 2 ryanodine receptor (Ryr2), and FK506-binding protein 12.6 (Fkbp12.6) in H9c2 and P19.CL6 cardiomyocytes were significantly decreased by IH, whereas the promoter activities of these genes were not decreased. By contrast, the expression of phosphatase and tensin homolog deleted from chromosome 10 (Pten) was upregulated in IH-treated cells. The small interfering RNA for Pten (siPten) and a non-specific control RNA were introduced into the H9c2 cells. The IH-induced downregulation of Cd38, Ryr2, and Fkbp12.6 was abolished by the introduction of the siPten, but not by the control RNA. These results indicate that IH stress upregulated the Pten in cardiomyocytes, resulting in the decreased mRNA levels of Cd38, Ryr2, and Fkbp12.6, leading to the inhibition of cardiomyocyte functions in SAS patients.

Deubiquitinase USP28 is a target gene of the transcription factor HNF1 homeobox β (HNF‑1β), which promotes the survival of ovarian clear cell carcinoma (OCCC) cell lines. However, the pharmacological inhibition of HNF‑1β can cause several adverse effects as it is abundantly expressed in numerous organ systems, including the kidney, liver, pancreas and digestive tract. Therefore, small interfering RNA (siRNA) screening was performed in the current study to identify other potential downstream targets of the HNF‑1β‑mediated pathway. The results revealed that glycogen synthase kinase‑3β (GSK‑3β) may be a potential downstream target affecting cell viability. To further clarify the effects of GSK‑3β, two human OCCC cell lines, TOV‑21G (HNF‑1β overexpressing line) and ES2 (HNF‑1β negative) were transfected with siRNA targeting GSK‑3β or control vectors. Loss‑of‑function studies using RNAi‑mediated gene silencing indicated that HNF‑1β facilitated GSK‑3β expression, resulting in the loss of phosphorylated nuclear factor‑κB (p‑NFκB) and the reduction of TOV‑21G cell proliferation. The cell proliferation assay also revealed that GSK‑3β inhibitors rescued the effects of HNF‑1β silencing on cell viability in a dose‑dependent manner. Furthermore, the GSK‑3β inhibitor, AR‑A014418, effectively inhibited tumor cell proliferation in a xenograft mouse model. In conclusion and to the best of our knowledge, the current study was the first to determine that GSK‑3β is a target gene of HNF‑1β. In addition, the results of the present study revealed the novel HNF‑1β‑GSK‑3β‑p‑NFκB pathway, occurring in response to DNA damage. Targeting this pathway may therefore represent a putative, novel, anticancer strategy in patients with OCCC.