Requires Reactive Oxygen Species Research Articles

The Role of Vitamins A and E Level in Chronic Suppurative Otitis Media with and without Cholesteatoma.

High expression of lytic enzymes and cytokines is related to cell proliferation in Otitis Media Chronic Suppurative (CSOM) with cholesteatoma. In addition, the process of inflammation healing and maintenance of homeostatic conditions requires Reactive Oxygen Species (ROS), which can cause significant damage to cells. To address this issue, secondary antioxidants such as Vitamins A and E are used to inhibit and neutralize the occurrence of oxidation reactions. These vitamins complement each other, with vitamin A working effectively at low concentrations of oxygen, while vitamin E functions in the opposite manner. This study aims to investigate the roles of vitamin A and E levels in CSOM patients with Cholesteatoma. The study was conducted between July and December 2020, and the method used was an analytical observational approach with a case-control design. The sample population comprised 60 CSOM patients divided into 2 groups. These included those with and without cholesteatoma. The results showed that there was no significant difference between these two groups in terms of the impact of vitamin A and E levels (respectively, p = 0.626, p = 0.864). Considering these results, it was discovered that vitamins A and E levels do not influence the occurrence of CSOM with or without cholesteatoma.

Glutathione administration reduces the DNA fragmentation index in sperm preparation with the Swim-Up (SU) and mini-Density Gradient Centrifugation (mini-DGC) methods at Doctor Soetomo General Hospital, Surabaya, Indonesia

Background: Spermatozoa requires Reactive Oxygen Species (ROS) in physiological quantities for capacitation for fertilization purposes. However, if the balance between ROS production and antioxidant capacity is disrupted, it can result in oxidative stress, negatively affecting chromatin spermatozoa, leading to male infertility. This study evaluates the glutathione administration reduces the DNA fragmentation index in sperm preparation with the Swim-Up (SU) and mini-Density Gradient Centrifugation (mini-DGC) methods at Doctor Soetomo General Hospital, Surabaya, Indonesia.Methods: A true experimental study by post-test only control group was conducted using ejaculate fluid of 9 infertile patients with normozoospermic at the Department of Medical Biology, Faculty of Medicine, Universitas Indonesia, Jakarta in January - February 2019 period. The spermatozoa DNA fragmentation was examined by following the instructions for using Spermfunc® DNAf Kit for Determination of the DNA Fragmentation Level in Spermatozoa by Sperm Chromatin Dispersion (SCD) for both preparation methods. Data were analyzed using SPSS version 16.0 for Windows.Results: SU vs. SU+glutathione method gave a lower but insignificant DNA fragmentation effect (p>0.05). The mini-DGC vs. mini-DGC+glutathione method showed significant results (p<0.05). SU+glutathione vs mini-DGC+glutathione showed no significant results (p>0.05). Meanwhile, the SU vs. mini-DGC method showed significant results (p <0.05). The recovery rate (RR) of the mini-DGC method has a higher value and is even better if glutathione is given compared to the SU method.Conclusion: Spermatozoa preparation in the SU method gives a lower DNA fragmentation effect than the mini-DGC method. The administration of glutathione can be a particular consideration in carrying out spermatozoa preparation to protect spermatozoa from damage during preparation.

Adaptive effects of prolonged mitochondrial‐targeted catalase on adipocyte differentiation

One cause of obesity is an increase in the total number adipocytes by hyperplasia. To increase fat cell number, adipocyte precursors undergo differentiation into mature fat cells, a process which requires reactive oxygen species (ROS). ROS are generated in the mitochondria during oxidative phosphorylation, and previous studies have shown that short‐term treatment with mitochondria‐targeted antioxidants can reduce adipogenesis. This suggests that antioxidant therapy might be useful to treat obesity, although the efficacy of antioxidants for long‐term treatment has not been investigated. Mice that have catalase targeted to mitochondria (mCAT mice) have increased levels of the antioxidant enzyme throughout life. We tested whether mCAT mice would display reduced fat pad mass or body weight due to a reduction in mitochondrial hydrogen peroxide. At 12 weeks of age, mCAT mice showed no significant decrease in size or weight of subcutaneous fat depots compared to wild‐type mice, which suggests that mCAT pre‐adipocytes were able to bypass the requirement for ROS and differentiate normally. To test this, we isolated preadipocytes from subcutaneous fat pads of mCAT mice and compared their differentiation profiles to cells transiently transfected with a plasmid encoding mitochondrial catalase. As expected, short‐term antioxidant treatment resulted in little to no differentiation. Although preadipocytes from mCAT mice differentiated more slowly in culture, they were ultimately able to reach full differentiation. Gene expression profiles of regulatory proteins that function during differentiation in cells with short‐term antioxidant treatment were different than those with long‐term exposure. Current work involves understanding how these gene expression changes are directly affected by mitochondrial hydrogen peroxide.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract 3950: Small molecule NSC59984 synergizes with ROS-generating agents to induce cell death via reduced GSH in cancer cells

Abstract NSC59984 is a small molecule with a duel capability to induce mutant p53 degradation and restore p53 pathway signaling in cancer cells. NSC59984 requires reactive oxygen species (ROS) to induce mutant p53 degradation via ERK2. ROS regulates cell growth and death with tumor cells having higher ROS levels than normal cells. Increasing ROS level is a promising therapeutic strategy applied in cancer clinical trials. However, the toxicity of high ROS levels is a limitation that needs to be solved urgently. We investigated the synergy between NSC59984 and ROS in cancer cells. To increase ROS, cells were treated with BSO, an ROS-generating agent. Our data reveal that ROS sensitizes cells to NSC59984 treatment including enhanced-p53 restoration and mutant p53 degradation induced by NSC59984. Combination of NSC59984 and BSO shows a synergy to induce cell death in cancer cells with an antagonism observed in normal cells at the tested doses. Consistent with the in vitro experiments, our in vivo experiments show that the combination of NSC59984 and BSO significantly suppresses tumor growth. Immunohistochemical staining shows a decrease in Ki67 and an increase in cleaved caspase 3 in xenografted tumors following combination treatment, suggesting that the tumor suppression is due to the induction of cell death and the inhibition of cell growth. Furthermore, the combination of NSC59984 and BSO shows a significant reduction in glutathione (GSH) levels in cancer cells, suggesting that the synergy between NSC59984 and BSO is due to the inhibition of the antioxidant system in mutant p53-expressing cancer cells. Our data indicate that a high level of ROS can be considered as a biomarker for NSC59984 administration in cancer therapy and supports further evaluation of the combination of NSC59984 and ROS-generating agents. Citation Format: Shengliang Zhang, Lanlan Zhou, Wafik S. El-Deiry. Small molecule NSC59984 synergizes with ROS-generating agents to induce cell death via reduced GSH in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3950.

The intracellular and intercellular cross-talk during subsidiary cell formation in Zea mays: existing and novel components orchestrating cell polarization and asymmetric division.

Formation of stomatal complexes in Poaceae is the outcome of three asymmetric and one symmetric cell division occurring in particular leaf protodermal cells. In this definite sequence of cell division events, the generation of subsidiary cells is of particular importance and constitutes an attractive model for studying local intercellular stimulation. In brief, an induction stimulus emitted by the guard cell mother cells (GMCs) triggers a series of polarization events in their laterally adjacent protodermal cells. This signal determines the fate of the latter cells, forcing them to divide asymmetrically and become committed to subsidiary cell mother cells (SMCs). This article summarizes old and recent structural and molecular data mostly derived from Zea mays, focusing on the interplay between GMCs and SMCs, and on the unique polarization sequence occurring in both cell types. Recent evidence suggests that auxin operates as an inducer of SMC polarization/asymmetric division. The intercellular auxin transport is facilitated by the distribution of a specific transmembrane auxin carrier and requires reactive oxygen species (ROS). Interestingly, the local differentiation of the common cell wall between SMCs and GMCs is one of the earliest features of SMC polarization. Leucine-rich repeat receptor-like kinases, Rho-like plant GTPases as well as the SCAR/WAVE regulatory complex also participate in the perception of the morphogenetic stimulus and have been implicated in certain polarization events in SMCs. Moreover, the transduction of the auxin signal and its function are assisted by phosphatidylinositol-3-kinase and the products of the catalytic activity of phospholipases C and D. In the present review, the possible role(s) of each of the components in SMC polarization and asymmetric division are discussed, and an overall perspective on the mechanisms beyond these phenomena is provided.

A Case-Control Study of the Genetic Variability in Reactive Oxygen Species-Metabolizing Enzymes in Melanoma Risk.

Recent studies have shown that ultraviolet (UV)-induced chemiexcitation of melanin fragments leads to DNA damage; and chemiexcitation of melanin fragments requires reactive oxygen species (ROS), as ROS excite an electron in the melanin fragments. In addition, ROS also cause DNA damages on their own. We hypothesized that ROS producing and metabolizing enzymes were major contributors in UV-driven melanomas. In this case-control study of 349 participants, we genotyped 23 prioritized single nucleotide polymorphisms (SNPs) in nicotinamide adenine dinucleotide phosphate (NADPH) oxidases 1 and 4 (NOX1 and NOX4, respectively), CYBA, RAC1, superoxide dismutases (SOD1, SOD2, and SOD3) and catalase (CAT), and analyzed their associated melanoma risk. Five SNPs, namely rs1049255 (CYBA), rs4673 (CYBA), rs10951982 (RAC1), rs8031 (SOD2), and rs2536512 (SOD3), exhibited significant genotypic frequency differences between melanoma cases and healthy controls. In simple logistic regression, RAC1 rs10951982 (odds ratio (OR) 8.98, 95% confidence interval (CI): 5.08 to 16.44; p < 0.001) reached universal significance (p = 0.002) and the minor alleles were associated with increased risk of melanoma. In contrast, minor alleles in SOD2 rs8031 (OR 0.16, 95% CI: 0.06 to 0.39; p < 0.001) and SOD3 rs2536512 (OR 0.08, 95% CI: 0.01 to 0.31; p = 0.001) were associated with reduced risk of melanoma. In multivariate logistic regression, RAC1 rs10951982 (OR 6.15, 95% CI: 2.98 to 13.41; p < 0.001) remained significantly associated with increased risk of melanoma. Our results highlighted the importance of RAC1, SOD2, and SOD3 variants in the risk of melanoma.

Pancreatic Cancer-Induced Neutrophil Extracellular Traps: A Potential Contributor to Cancer-Associated Thrombosis.

Pancreatic cancer (PaCa) is a highly metastatic cancer, and patients are at high risk of developing venous thromboembolism (VTE). Neutrophil extracellular traps (NETs) have been associated with cancer metastasis and cancer-associated thrombosis, but the ability of cancer to stimulate NET release is not known. The release of NETs has been shown to be a slow process and requires reactive oxygen species (ROS) production. Studies suggest that activated platelets are important mediators in the release. Here, we show that PaCa cells can stimulate the rapid release of NETs, independently of ROS production. We further assessed the role of platelets in PaCa-induced NETs and observed a trend of increased the NET release by PaCa-primed platelets. Additionally, NETs promoted thrombus formation under venous shear stress ex vivo. Taken together, our results suggest that PaCa-induced NETs can contribute to the high risk of venous thromboembolism development in PaCa patients, and reveal NETs as a potential therapeutic target.

LSD1 and HY5 antagonistically regulate red light induced-programmed cell death in Arabidopsis.

Programmed cell death (PCD) in plant is triggered by abiotic and biotic stress. Light-dependent PCD is unique to plants. Light-induced PCD also requires reactive oxygen species (ROS) and salicylic acid (SA). In this study, lesion simulating disease1 (LSD1) and elongated hypocotyl 5 (HY5) perform opposite roles to regulate excess red light (RL)-triggered PCD associated with ROS and SA production. Under RL, the lsd1 mutant released more ROS and SA and displayed a stronger cell death rate than the hy5 mutant. It was shown that active LSD1 converted into inactive form by changing the redox status of the plastoquinone pool, and HY5 interacted with phytochrome B (phyB) to promote PCD in response to RL. LSD1 inhibited the enhanced disease susceptibility 1 (EDS1) expression by upregulating SR1, whereas HY5 enhanced the enhanced EDS1 expression by binding to the G-box of the EDS1 promoter. This study suggested that LSD1 and HY5 antagonistically modulated EDS1-dependent ROS and SA signaling; thus, PCD was mediated in response to RL.

HIF‐2α Deficiency Induces Carotid Body Sensory Long‐Term Facilitation

Chronic intermittent hypoxia (CIH) induces carotid body plasticity manifested as sensory long term facilitation (sLTF). CIH‐induced sLTF requires reactive oxygen species (ROS) signaling. Mice partially deficient in the transcriptional activator hypoxia‐inducible factor‐2α subunit (Hif‐2α+/‐) exhibit oxidative stress and augmented carotid body sensitivity to hypoxia, which are similar to CIH‐exposed wild‐type mice. We hypothesized that Hif‐2α deficiency would evoke sLTF of the carotid body due to increased ROS levels. Consistent with this possibility, Hif‐2α+/‐ mice displayed sLTF compared to their wild type littermates and systemic administration of the membrane permeable antioxidant MnTMPyP prevented both oxidative stress as well as sLTF. CIH decreased Hif‐2α protein levels in the carotid body and induced oxidative stress. Blocking CIH‐induced HIF‐2α degradation by ALLM treatment inhibited ROS generation and prevented CIH‐evoked sLTF in rats. Taken together, these results suggest that Hif‐2α degradation in response to CIH is a critical molecular mechanism leading to ROS‐dependent induction of carotid body sLTF. Supported by NIH‐ HL‐90554.

The Role of Rac and Pak in Neutrophil Histone Hypercitrullination and Neutrophil Extracellular Traps Formation

Under specific activating conditions, polymorphonuclear neutrophils (PMNs) release neutrophil extracellular traps (NETs) composed of decondensed chromatin lined with microbicidal protein such as neutrophil elastase and myeloperoxidase. NETs contribute to innate immunity but can also foster autoimmune diseases and thrombus formation. NET formation (NETosis) requires reactive oxygen species (ROS) production by NADPH oxidase and histone hypercitrullination by peptidylarginine deiminase 4 (PAD4), allowing for chromatin decondensation. Rac GTPases are expressed in three isoforms: Rac1 is ubiquitously expressed and plays a role in PMN migration and oxidase function; Rac2 is hematopoietic-specific and the major isoform in PMNs and Rac3 is mostly neuronal. Rac1 and Rac2 regulate the cytoskeleton in PMNs, controlling actin polymerization, cell shape, adhesion and migration and are essential components of the NADPH oxidase complex. The present study aimed to explore the role of the Rac pathway on NETosis in PMNs, including the upstream guanosine exchange factor (GEF) activator, Vav, and a downstream effector of Rac, p21 activated kinase, Pak. We developed a flow cytometry-based quantification of H3 hypercitrullination (H3Cit). In response to phorbol myristate ester (PMA) stimulation, H3Cit is increased to 136% of basal in WT cells, compared with 103% in Rac2-/- (P<0.01) (Table). H3Cit levels observed by flow were confirmed in a NET formation assay. Rac2-/- PMNs formed significantly fewer NETs both spontaneously and after PMA stimulation (WT unstimulated 2.79%, Rac2-/- unstimulated 0.72%, WT+PMA 10.84%, Rac2-/-+PMA 1.39%, P< 0.05 for all pair comparisons). Furthermore, Rac2-/- mice demonstrated a trend towards reduced frequency of provoked thrombosis in an in vivo vena cava stenosis model (WT 78% and Rac2-/- 56% of mice with thrombus). Deletion of floxed Rac1 sequences in a Rac2-/- background in vivoallows generation and purification of PMNs lacking both Rac isoforms. Rac1Δ/Δ,Rac2-/- PMNs, which are defective in actin polymerization, had reduced basal H3Cit and a nearly complete lack of PMA-induced increase in H3Cit (136% vs 69%, WT vs Rac1Δ/Δ,Rac2-/-, P<0.01) (Table). Null knockouts of the GEFs Vav1 (hematopoietic-specific), Vav2, Vav3 or both Vav1 and 3 did not impair H3Cit response to PMA (Table). We next studied downstream effectors of Rac. Group A Paks include Pak1, 2 and 3 isoforms. Pretreatment of wild-type PMNs with either PF3758309 or IPA-3, two group A Pak inhibitors with distinct mechanisms of action, led to reduced H3Cit after PMA stimulation (induction reduced from 36% to 11% for both PF3758309 and IPA-3 treated (Table). To validate this in a genetic model, we studied Pak2Δ/Δ PMNs, since we have recently demonstrated the dependence of hematopoietic stem cell migration on Pak2. Pak2Δ/Δ demonstrated a reduced basal level of H3Cit and a significantly reduced PMA-induced increase in H3Cit (136% vs 94%, WT vs Pak2Δ/Δ, P<0.05, Table). In summary, we describe a flow-based assay that quantitates the early processes of NET formation and validated that this assay reliably predicts agonist-induced NET formation in a genetic model. The results establish that both Rac1 and Rac2, and the downstream effector Pak2, regulate histone H3 hypercitrullination and NET formation in PMNs, while suggesting that Vav does not activate the Rac pathway in PMA-induced NET formation. These data further delineate the role of the Rac pathway in NETosis, linking cytoskeleton and oxidase functions. Furthermore, these data indicate Pak could represent a therapeutic target for a wide array of pathological processes related to NETosis such as thrombosis and numerous autoimmune diseases.TableIntensity of H3Cit staining as determined by flow cytometry-based assay.Basal H3Cit levelPMA-induced H3CitPMA-induced changeWT PMN100±2%136±5%36%Rac2-/-82±9% ns103±15.3%**21%Rac1Δ/Δ, Rac2-/-64±10%***69±10%**5%Vav1-/-86±9% ns145±15% ns59%Vav2-/-91±4% ns134±18% ns43%Vav3-/-153±30%*171±28% ns18%Vav1,3-/-125±20% ns144±24% ns19%WT+PF 5nM76±17% ns87±8%*11%WT+ IPA 5µM100±4% ns111±10% ns11%Pak2Δ/Δ75±7%*94±11%*19%Results are expressed as mean±SEM % of the untreated WT control of each experiment. Results are from ≥3 independent experiments. * P<0.05, **P<0.01. P<0.001, ns non-significant, by two-tailed t-test. DisclosuresNo relevant conflicts of interest to declare.

A Myeloperoxidase-Containing Complex Regulates Neutrophil Elastase Release and Actin Dynamics during NETosis

SummaryNeutrophils contain granules loaded with antimicrobial proteins and are regarded as impermeable organelles that deliver cargo via membrane fusion. However, during the formation of neutrophil extracellular traps (NETs), neutrophil elastase (NE) translocates from the granules to the nucleus via an unknown mechanism that does not involve membrane fusion and requires reactive oxygen species (ROS). Here, we show that the ROS triggers the dissociation of NE from a membrane-associated complex into the cytosol and activates its proteolytic activity in a myeloperoxidase (MPO)-dependent manner. In the cytosol, NE first binds and degrades F-actin to arrest actin dynamics and subsequently translocates to the nucleus. The complex is an example of an oxidative signaling scaffold that enables ROS and antimicrobial proteins to regulate neutrophil responses. Furthermore, granules contain protein machinery that transports and delivers cargo across membranes independently of membrane fusion.

Roles of ROS/TACE in neutrophil elastase-induced mucus hypersecretion in NCI-H292 airway epithelial cells.

Complications arise in chronic obstructive pulmonary diseases (COPD) with excessive mucus production, especially during the exacerbation period, which contributes to airway blockage and bacterial infection. Neutrophil elastase (NE) is detected at high levels in airway secretions, and is the primary inducer of mucin production. Understanding the mechanism of NE-induced overproduction of mucin may lead to new therapies for COPD. It is known that activation of epidermal growth factor receptor (EGFR) and its downstream signaling cascade are involved in mucin production. However, the mechanism of NE-induced EGFR activation remains unclear. Tumor necrosis factor-α-converting enzyme (TACE) cleaves pro-transforming growth factor (TGF)-α in airway epithelial cells to release the mature, soluble TGF-α form, which subsequently binds to and activates EGFR. In this investigation, we demonstrate that NE-induced mucin production requires reactive oxygen species (ROS) production, which activates TACE, resulting in TGF-α shedding, and EGFR phosphorylation in NCI-H292 epithelial cells.

P53 Represses Class Switch Recombination to IgG2a through Its Antioxidant Function

Ig class switch recombination (CSR) occurs in activated mature B cells, and causes an exchange of the IgM isotype for IgG, IgE, or IgA isotypes, which increases the effectiveness of the humoral immune response. DNA ds breaks in recombining switch (S) regions, where CSR occurs, are required for recombination. Activation-induced cytidine deaminase initiates DNA ds break formation by deamination of cytosines in S regions. This reaction requires reactive oxygen species (ROS) intermediates, such as hydroxyl radicals. In this study we show that the ROS scavenger N-acetylcysteine inhibits CSR. We also demonstrate that IFN-gamma treatment, which is used to induce IgG2a switching, increases intracellular ROS levels, and activates p53 in switching B cells, and show that p53 inhibits IgG2a class switching through its antioxidant-regulating function. Finally, we show that p53 inhibits DNA breaks and mutations in S regions in B cells undergoing CSR, suggesting that p53 inhibits the activity of activation-induced cytidine deaminase.

Vasoconstriction‐induced inward remodeling of isolated arterioles involves reactive oxygen species‐dependent activation of matrix metalloproteinases

We previously demonstrated that inward remodeling induced by prolonged agonist‐induced vasoconstriction in isolated arterioles requires reactive oxygen species (ROS) generation and activation of matrix metalloproteinases (MMPs). We hypothesize that ROS participate in the vasoconstriction‐induce inward remodeling process in part by promoting MMP activation. This hypothesis was tested in isolated and pressurized (60 mmHg) rat cremaster arterioles exposed to norepinephrine (NE, 10−5.5 M) plus angiotensin‐II (Ang‐II, 10−7 M) for 4 hours. Prolonged vasoconstriction induced inward remodeling and increased the gelatinolytic activity of arterioles (P&lt;0.05). ROS‐inhibition with apocynin, tempol, or the Rac‐inhibitor, NSC, significantly affected the development of inward remodeling and reduced the arteriolar gelatinolytic activity induced by NE and Ang‐II. These results indicate that during prolonged vasoconstriction MMPs are in part activated through a pathway dependent on the generation of ROS, and that ROS are required for the acute remodeling of the vascular wall. As MMP‐inhibition prevents the development of inward remodeling, these results suggest that vasoconstriction‐induced inward remodeling in resistance vessels is associated with ROS‐dependent activation of MMPs.Funded by AHA and NIH.

NADPH oxidase activity is necessary for acute intermittent hypoxia‐induced phrenic long‐term facilitation

Phrenic long-term facilitation (pLTF) following acute intermittent hypoxia (AIH) is a form of spinal, serotonin-dependent synaptic plasticity that requires reactive oxygen species (ROS) formation. We tested the hypothesis that spinal NADPH oxidase activity is a necessary source of ROS for pLTF. Sixty minutes post-AIH (three 5-min episodes of 11% O(2), 5 min intervals), integrated phrenic and hypoglossal (XII) nerve burst amplitudes were increased from baseline, indicative of phrenic and XII LTF. Intrathecal injections (approximately C(4)) of apocynin or diphenyleneiodonium chloride (DPI), two structurally and functionally distinct inhibitors of the NADPH oxidase complex, attenuated phrenic, but not XII, LTF. Immunoblots from soluble (cytosolic) and particulate (membrane) fractions of ventral C(4) spinal segments revealed predominantly membrane localization of the NADPH oxidase catalytic subunit, gp91(phox), whereas membrane and cytosolic expression were both observed for the regulatory subunits, p47(phox) and RAC1. Immunohistochemical analysis of fixed tissues revealed these same subunits in presumptive phrenic motoneurons of the C(4) ventral horn, but not in neighbouring astrocytes or microglia. Collectively, these data demonstrate that NADPH oxidase subunits localized within presumptive phrenic motoneurons are a major source of ROS necessary for AIH-induced pLTF. Thus, NADPH oxidase activity is a key regulator of spinal synaptic plasticity, and may be a useful pharmaceutical target in developing therapeutic strategies for respiratory insufficiency in patients with, for example, cervical spinal injury.

Transcriptional responses to intermittent hypoxia

Recurrent apneas are characterized by transient repetitive cessations of breathing (two breaths duration or longer) resulting in periodic decreases in arterial blood PO2 or chronic intermittent hypoxia (IH). Patients with recurrent apneas and experimental animals exposed to chronic IH exhibit cardio-respiratory morbidities. The purpose of this article is to highlight the current information on the transcriptional mechanisms associated with chronic IH. Studies on rodents and cell cultures have shown that IH activates a variety of transcription factors including the hypoxia-inducible factor-1 (HIF-1), c-fos (immediate early gene), nuclear factor of activated T-cells (NFAT), and nuclear factor kB (NF-kB). The signaling pathways associated with transcriptional activation associated with IH differ from continuous hypoxia (CH). Compared to same duration and intensity of CH, IH is more potent in activating HIF-1 and c-fos and also results in long-lasting accumulation of HIF-1alpha and c-fos mRNA, a phenomenon that was not seen with CH. IH-evoked transcriptional activation by HIF-1, c-fos as well as the resulting activator protein-1 (AP-1) requires reactive oxygen species (ROS)-mediated signaling and involves complex feed forward interactions between HIF-1 and ROS. Chronic IH-evoked cardio-respiratory responses are absent in Hif-1alpha+/- mice, and hypertension elicited by chronic IH is absent in mice lacking NFAT3c. These studies indicate that cardiorespiratory responses to chronic IH depend on complex interactions between various transcription factors resulting in alterations in several down stream genes and their protein products.