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Special Issue "Sleep Apnea and Intermittent Hypoxia"

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Pathology, Diagnostics, and Therapeutics".

Deadline for manuscript submissions: closed (31 July 2019).

Special Issue Editor

Guest Editor
Prof. Dr. Shin Takasawa

Department of Biochemistry, Nara Medical University (NMU), 840Shijo-cho, Kashihara 634-8521, Nara, Japan
E-Mail
Interests: diabetes and its complication; sleep apnea; cancer cell biology; CD38-cyclic ADP-ribose signal system; insulin secretion; regeneration biology; regenerating gene (Reg) family

Special Issue Information

Dear Colleagues,

Sleep apnea syndrome (SAS) is a clinical syndrome characterized by repeated episodes of pharyngeal obstruction during sleep, that leads to intermittent hypoxia (IH), sleep fragmentation, and excessive daytime sleepiness. It is a highly prevalent disorder affecting about 14% of men and 5% of women, and its prevalence is rapidly rising because of the strong association of SAS with obesity. The major health burden in SAS patients is an increased risk of cardiovascular diseases, such as systemic arterial hypertension, coronary artery disease, heart failure, and stroke, which is an association that is corroborated by numerous large-scale epidemiological and prospective studies. Furthermore, there is increasing evidence of an independent association of SAS with metabolic dysfunction, and in particular, with alterations in glucose metabolism. Subjects with SAS seem to be at greater risk of developing type 2 diabetes mellitus, insulin resistance, and metabolic syndrome, an association that seems to be, at least in part, irrespective of the degree of obesity. Indeed, SAS and obesity may exert synergistic negative effects on glucose metabolisms. However, there are few molecular studies about SAS/IH. The aim of this Special Issue is to provide new findings regarding the molecular events in SAS/IH, as well as their mechanisms.

Prof. Dr. Shin Takasawa
Guest Editor

Manuscript Submission Information

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Keywords

  • Sleep apnea syndrome
  • Intermittent hypoxia
  • Oxidative stress
  • Gene expression
  • Diabetes
  • Appetite
  • Obesity
  • Hypertension

Published Papers (7 papers)

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Research

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Open AccessCommunication
Hypoxia Modulates Effects of Fatty Acids on NES2Y Human Pancreatic β-cells
Int. J. Mol. Sci. 2019, 20(14), 3441; https://doi.org/10.3390/ijms20143441
Received: 28 June 2019 / Accepted: 11 July 2019 / Published: 12 July 2019
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Abstract
Saturated fatty acids (FAs) induce apoptosis in the human pancreatic NES2Y β-cell line while unsaturated FAs have nearly no detrimental effect. Moreover, unsaturated FAs are capable of inhibiting the pro-apoptotic effect of saturated FAs. Hypoxia is also known to have deleterious effects on [...] Read more.
Saturated fatty acids (FAs) induce apoptosis in the human pancreatic NES2Y β-cell line while unsaturated FAs have nearly no detrimental effect. Moreover, unsaturated FAs are capable of inhibiting the pro-apoptotic effect of saturated FAs. Hypoxia is also known to have deleterious effects on β-cells function and viability. In the present study, we have tested the modulatory effect of hypoxia on the effect of FAs on the growth and viability of the human pancreatic NES2Y β-cells. This study represents the first study testing hypoxia effect on effects of FAs in pancreatic β-cells as well as in other cell types. We showed that hypoxia increased the pro-apoptotic effect of saturated stearic acid (SA). Endoplasmic reticulum stress signaling seemed to be involved while redistribution of FA transporters fatty acid translocase/cluster of differentiation 36 (FAT/CD36) and fatty acid-binding protein (FABP) do not seem to be involved in this effect. Hypoxia also strongly decreased the protective effect of unsaturated oleic acid (OA) against the pro-apoptotic effect of SA. Thus, in the presence of hypoxia, OA was unable to save SA-treated β-cells from apoptosis induction. Hypoxia itself had only a weak detrimental effect on NES2Y cells. Our data suggest that hypoxia could represent an important factor in pancreatic β-cell death induced and regulated by FAs and thus in the development of type 2 diabetes mellitus. Full article
(This article belongs to the Special Issue Sleep Apnea and Intermittent Hypoxia)
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Open AccessArticle
Intermittent Hypoxia Up-Regulates CCL2, RETN, and TNFα mRNAs in Adipocytes via Down-regulation of miR-452
Int. J. Mol. Sci. 2019, 20(8), 1960; https://doi.org/10.3390/ijms20081960
Received: 23 March 2019 / Revised: 18 April 2019 / Accepted: 19 April 2019 / Published: 22 April 2019
Cited by 2 | PDF Full-text (2299 KB) | HTML Full-text | XML Full-text
Abstract
Sleep apnea syndrome (SAS), characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]), is a risk factor for insulin resistance. Recently, IH is considered to independently cause adipose tissue inflammation/dysfunction, leading to worsening insulin resistance; however, the detailed mechanism remains [...] Read more.
Sleep apnea syndrome (SAS), characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]), is a risk factor for insulin resistance. Recently, IH is considered to independently cause adipose tissue inflammation/dysfunction, leading to worsening insulin resistance; however, the detailed mechanism remains unknown. We exposed mouse 3T3-L1 and human SW872 adipocytes to experimental IH or normoxia for 24 h, and analyzed mRNA expression of several adipokines. We found that the mRNA levels of RETN, TNFα, and CCL2 in SW872 and 3T3-L1 adipocytes were significantly increased by IH, whereas the promoter activities of these genes were not increased. A target mRNA search of microRNA (miR)s revealed that all human mRNAs have a potential target sequence for miR-452. The miR-452 level of IH-treated cells was significantly decreased compared to normoxia-treated cells. MiR-452 mimic and non-specific control RNA (miR-452 mimic NC) were introduced into SW872 cells, and the IH-induced up-regulation of the genes was abolished by introduction of the miR-452 mimic but not by the miR-452 mimic NC. These results indicate that IH stress down-regulates the miR-452 in adipocytes, resulting in increased levels of RETN, TNFα, and CCL2 mRNAs, leading to insulin resistance in SAS patients. Full article
(This article belongs to the Special Issue Sleep Apnea and Intermittent Hypoxia)
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Open AccessArticle
Intermittent Hypoxia Up-Regulates Gene Expressions of Peptide YY (PYY), Glucagon-like Peptide-1 (GLP-1), and Neurotensin (NTS) in Enteroendocrine Cells
Int. J. Mol. Sci. 2019, 20(8), 1849; https://doi.org/10.3390/ijms20081849
Received: 23 March 2019 / Revised: 8 April 2019 / Accepted: 11 April 2019 / Published: 15 April 2019
Cited by 1 | PDF Full-text (1677 KB) | HTML Full-text | XML Full-text
Abstract
The patients with sleep apnea syndrome are exposed to intermittent hypoxia (IH) during sleep. We previously demonstrated the IH-induced up-regulation of the mRNA levels of anorexigenic peptides proopiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) in human neuronal cells. Appetite is regulated not [...] Read more.
The patients with sleep apnea syndrome are exposed to intermittent hypoxia (IH) during sleep. We previously demonstrated the IH-induced up-regulation of the mRNA levels of anorexigenic peptides proopiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) in human neuronal cells. Appetite is regulated not only by the central nervous system but also by the peptides from gastrointestinal tract. Here, we investigated the effects of IH on the gene expression(s) of appetite-inhibiting gut hormones. Human enteroendocrine Caco-2 and mouse STC-1 cells were exposed to IH [64 cycles of 5 min hypoxia (1% O2) and 10 min normoxia (21% O2)] or normoxia for 24 h. Real-time RT-PCR revealed that IH significantly increased the mRNA levels of peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and neurotensin (NTS) in Caco-2 and STC-1 cells. ELISA showed that the concentrations of PYY, GLP-1, and NTS in the culture medium were significantly increased by IH. The mRNA levels of PYY, GLP-1, and NTS were significantly up-regulated even in normoxia by Trichostatin A (TSA) and were significantly decreased even in IH by 5-azacytidine (5AZC), suggesting that IH increases PYY, GLP-1, and NTS mRNAs via alterations in the chromatin structure in enteroendocrine cells. IH might have an anorexigenic influence on the enteric nervous system. Full article
(This article belongs to the Special Issue Sleep Apnea and Intermittent Hypoxia)
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Open AccessArticle
Obstructive Sleep Apnea Activates HIF-1 in a Hypoxia Dose-Dependent Manner in HCT116 Colorectal Carcinoma Cells
Int. J. Mol. Sci. 2019, 20(2), 445; https://doi.org/10.3390/ijms20020445
Received: 20 December 2018 / Revised: 17 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
Cited by 1 | PDF Full-text (2944 KB) | HTML Full-text | XML Full-text
Abstract
Obstructive sleep apnea (OSA) affects a significant proportion of the population and is linked to increased rates of cancer development and a worse cancer outcome. OSA is characterized by nocturnal intermittent hypoxia and animal models of OSA-like intermittent hypoxia show increased tumor growth [...] Read more.
Obstructive sleep apnea (OSA) affects a significant proportion of the population and is linked to increased rates of cancer development and a worse cancer outcome. OSA is characterized by nocturnal intermittent hypoxia and animal models of OSA-like intermittent hypoxia show increased tumor growth and metastasis. Advanced tumors typically have regions of chronic hypoxia, activating the transcription factor, HIF-1, which controls the expression of genes involved in cancer progression. Rapid intermittent hypoxia from OSA has been proposed to increase HIF-1 activity and this may occur in tumors. The effect of exposing a developing tumor to OSA-like intermittent hypoxia is largely unknown. We have built a cell-based model of physiological OSA tissue oxygenation in order to study the effects of intermittent hypoxia in HCT116 colorectal cancer cells. We found that HIF-1α increases following intermittent hypoxia and that the expression of HIF-target genes increases, including those involved in glycolysis, the hypoxic pathway and extracellular matrix remodeling. Expression of these genes acts as a ‘hypoxic’ signature which is associated with a worse prognosis. The total dose of hypoxia determined the magnitude of change in the hypoxic signature rather than the frequency or duration of hypoxia-reoxygenation cycles per se. Finally, transcription of HIF1A mRNA differs in response to chronic and intermittent hypoxia suggesting that HIF-1α may be regulated at the transcriptional level in intermittent hypoxia and not just by the post-translational oxygen-dependent degradation pathway seen in chronic hypoxia. Full article
(This article belongs to the Special Issue Sleep Apnea and Intermittent Hypoxia)
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Review

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Open AccessReview
Epigenetics: A Potential Mechanism Involved in the Pathogenesis of Various Adverse Consequences of Obstructive Sleep Apnea
Int. J. Mol. Sci. 2019, 20(12), 2937; https://doi.org/10.3390/ijms20122937
Received: 28 April 2019 / Revised: 9 June 2019 / Accepted: 13 June 2019 / Published: 15 June 2019
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Abstract
Epigenetics is defined as the heritable phenotypic changes which do not involve alterations in the DNA sequence, including histone modifications, non-coding RNAs, and DNA methylation. Recently, much attention has been paid to the role of hypoxia-mediated epigenetic regulation in cancer, pulmonary hypertension, adaptation [...] Read more.
Epigenetics is defined as the heritable phenotypic changes which do not involve alterations in the DNA sequence, including histone modifications, non-coding RNAs, and DNA methylation. Recently, much attention has been paid to the role of hypoxia-mediated epigenetic regulation in cancer, pulmonary hypertension, adaptation to high altitude, and cardiorenal disease. In contrast to sustained hypoxia, chronic intermittent hypoxia with re-oxygenation (IHR) plays a major role in the pathogenesis of various adverse consequences of obstructive sleep apnea (OSA), resembling ischemia re-perfusion injury. Nevertheless, the role of epigenetics in the pathogenesis of OSA is currently underexplored. This review proposes that epigenetic processes are involved in the development of various adverse consequences of OSA by influencing adaptive potential and phenotypic variability under conditions of chronic IHR. Improved understanding of the interaction between genetic and environmental factors through epigenetic regulations holds great value to give deeper insight into the mechanisms underlying IHR-related low-grade inflammation, oxidative stress, and sympathetic hyperactivity, and clarify their implications for biomedical research. Full article
(This article belongs to the Special Issue Sleep Apnea and Intermittent Hypoxia)
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Open AccessReview
Proliferative Pathways of Vascular Smooth Muscle Cells in Response to Intermittent Hypoxia
Int. J. Mol. Sci. 2019, 20(11), 2706; https://doi.org/10.3390/ijms20112706
Received: 28 April 2019 / Revised: 20 May 2019 / Accepted: 30 May 2019 / Published: 1 June 2019
PDF Full-text (2690 KB) | HTML Full-text | XML Full-text
Abstract
Obstructive sleep apnea (OSA) is characterized by intermittent hypoxia (IH) and is a risk factor for cardiovascular diseases (e.g., atherosclerosis) and chronic inflammatory diseases (CID). The excessive proliferation of vascular smooth muscle cells (VSMCs) plays a pivotal role in the progression of atherosclerosis. [...] Read more.
Obstructive sleep apnea (OSA) is characterized by intermittent hypoxia (IH) and is a risk factor for cardiovascular diseases (e.g., atherosclerosis) and chronic inflammatory diseases (CID). The excessive proliferation of vascular smooth muscle cells (VSMCs) plays a pivotal role in the progression of atherosclerosis. Hypoxia-inducible factor-1 and nuclear factor-κB are thought to be the main factors involved in responses to IH and in regulating adaptations or inflammation pathways, however, further evidence is needed to demonstrate the underlying mechanisms of this process in VSMCs. Furthermore, few studies of IH have examined smooth muscle cell responses. Our previous studies demonstrated that increased interleukin (IL)-6, epidermal growth factor family ligands, and erbB2 receptor, some of which amplify inflammation and, consequently, induce CID, were induced by IH and were involved in the proliferation of VSMCs. Since IH increased IL-6 and epiregulin expression in VSMCs, the same phenomenon may also occur in other smooth muscle cells, and, consequently, may be related to the incidence or progression of several diseases. In the present review, we describe how IH can induce the excessive proliferation of VSMCs and we develop the suggestion that other CID may be related to the effects of IH on other smooth muscle cells. Full article
(This article belongs to the Special Issue Sleep Apnea and Intermittent Hypoxia)
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Open AccessReview
Obstructive Sleep Apnea and Inflammation: Proof of Concept Based on Two Illustrative Cytokines
Int. J. Mol. Sci. 2019, 20(3), 459; https://doi.org/10.3390/ijms20030459
Received: 21 December 2018 / Revised: 12 January 2019 / Accepted: 15 January 2019 / Published: 22 January 2019
Cited by 1 | PDF Full-text (521 KB) | HTML Full-text | XML Full-text
Abstract
Obstructive sleep apnea syndrome (OSAS) is a markedly prevalent condition across the lifespan, particularly in overweight and obese individuals, which has been associated with an independent risk for neurocognitive, behavioral, and mood problems as well as cardiovascular and metabolic morbidities, ultimately fostering increases [...] Read more.
Obstructive sleep apnea syndrome (OSAS) is a markedly prevalent condition across the lifespan, particularly in overweight and obese individuals, which has been associated with an independent risk for neurocognitive, behavioral, and mood problems as well as cardiovascular and metabolic morbidities, ultimately fostering increases in overall mortality rates. In adult patients, excessive daytime sleepiness (EDS) is the most frequent symptom leading to clinical referral for evaluation and treatment, but classic EDS features are less likely to be reported in children, particularly among those with normal body-mass index. The cumulative evidence collected over the last two decades supports a conceptual framework, whereby sleep-disordered breathing in general and more particularly OSAS should be viewed as low-grade chronic inflammatory diseases. Accordingly, it is assumed that a proportion of the morbid phenotypic signature in OSAS is causally explained by underlying inflammatory processes inducing end-organ dysfunction. Here, the published links between OSAS and systemic inflammation will be critically reviewed, with special focus on the pro-inflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), since these constitute classical prototypes of the large spectrum of inflammatory molecules that have been explored in OSAS patients. Full article
(This article belongs to the Special Issue Sleep Apnea and Intermittent Hypoxia)
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