Enhanceosomes as integrators of hypoxia inducible factor (HIF) and other transcription factors in the hypoxic transcriptional response

Omega-3 polyunsaturated fatty acids and pulmonary arterial hypertension: Insights and perspectives

Pulmonary arterial hypertension (PAH) is a rare and progressive disorder that affects the pulmonary vasculature. Although recent developments in pharmacotherapy have extended the life expectancy of PAH patients, their 5-year survival remains unacceptably low, underscoring the need for multitarget and more comprehensive approaches to managing the disease. This should incorporate not only medical, but also lifestyle interventions, including dietary changes and the use of nutraceutical support. Among these strategies, n-3 polyunsaturated fatty acids (n-3 PUFAs) are emerging as promising agents able to counteract the inflammatory component of PAH. In this narrative review, we aim at analysing the preclinical evidence for the impact of n-3 PUFAs on the pathogenesis and the course of PAH. Although evidence for the role of n-3 PUFAs deficiencies in the development and progression of PAH in humans is limited, preclinical studies suggest that these dietary components may influence several aspects of the pathobiology of PAH. Further clinical research should test the efficacy of n-3 PUFAs on top of approved clinical management. These studies will provide evidence on whether n-3 PUFAs can genuinely serve as a valuable tool to enhance the efficacy of pharmacotherapy in the treatment of PAH.

Up-Regulation of Non-Homologous End-Joining by MUC1

Ionizing radiation (IR) and chemotherapy with DNA-damaging drugs such as cisplatin are vital cancer treatment options. These treatments induce double-strand breaks (DSBs) as cytotoxic DNA damage; thus, the DSB repair activity in each cancer cell significantly influences the efficacy of the treatments. Pancreatic cancers are known to be resistant to these treatments, and the overexpression of MUC1, a member of the glycoprotein mucins, is associated with IR- and chemo-resistance. Therefore, we investigated the impact of MUC1 on DSB repair. This report examined the effect of the overexpression of MUC1 on homologous recombination (HR) and non-homologous end-joining (NHEJ) using cell-based DSB repair assays. In addition, the therapeutic potential of NHEJ inhibitors including HDAC inhibitors was also studied using pancreatic cancer cell lines. The MUC1-overexpression enhances NHEJ, while partially suppressing HR. Also, MUC1-overexpressed cancer cell lines are preferentially killed by a DNA-PK inhibitor and HDAC1/2 inhibitors. Altogether, MUC1 induces metabolic changes that create an imbalance between NHEJ and HR activities, and this imbalance can be a target for selective killing by HDAC inhibitors. This is a novel mechanism of MUC1-mediated IR-resistance and will form the basis for targeting MUC1-overexpressed pancreatic cancer.

Drusen in AMD from the Perspective of Cholesterol Metabolism and Hypoxic Response

Drusen are one of the most characteristic pathologies of precursor lesion of age-related macular degeneration (AMD). Drusen comprise a yellowish white substance that accumulates typically under the retinal pigment epithelium (RPE), and their constituents are lipids, complement, amyloid, crystallin, and others. In the past, many researchers have focused on drusen and tried to elucidate the pathophysiology of AMD because they believed that disease progression from early AMD to advanced AMD might be based on drusen or drusen might cause AMD. In fact, it is well established that drusen are the hallmark of precursor lesion of AMD and a major risk factor for AMD progression mainly based on their size and number. However, the existence of advanced AMD without drusen has long been recognized. For example, polypoidal choroidal vasculopathy (PCV), which comprises the majority of AMD cases in Asians, often lacks drusen. Thus, there is the possibility that drusen might be no more than a biomarker of AMD and not a cause of AMD. Now is the time to reconsider the relationship between AMD and drusen. In this review, we focus on early AMD pathogenesis based on basic research from the perspective of cholesterol metabolism and hypoxic response in the retina, and we discuss the role of drusen.

Aerobic Glycolysis Induced by mTOR/HIF-1α Promotes Early Brain Injury After Subarachnoid Hemorrhage via Activating M1 Microglia

M1 microglial activation is crucial for the pathogenesis of early brain injury (EBI) following subarachnoid hemorrhage (SAH), and there is growing evidence that glucose metabolism is frequently involved in microglial activation. However, the molecular mechanism of glycolysis and its role in M1 microglial activation in the context of EBI are not yet fully understood. In this study, firstly, the relationship between aerobic glycolysis and M1 microglial activation as well as SAH-induced EBI was researched in vivo. Then, intervention on mammalian target of rapamycin (mTOR) was performed to investigate the effects on glycolysis-dependent M1 microglial activation and EBI and its relationship with hypoxia-inducible factor-1α (HIF-1α) in vivo. Next, Hif-1α was inhibited to analyze its role in aerobic glycolysis, M1 microglial activation, and EBI in vivo. Lastly, both in vivo and in vitro, mTOR inhibition and Hif-1α enhancement were administered simultaneously, and the combined effects were further confirmed again. The results showed that aerobic glycolysis and M1 microglial polarization were increased after SAH, and glycolytic inhibition could attenuate M1 microglial activation and EBI. Inhibition of mTOR reduced glycolysis-dependent M1 microglial polarization and EBI severity by down-regulating HIF-1α expression, while enhancement had the opposite effects. Blockading HIF-1α had the similar effects as suppressing mTOR, while HIF-1α agonist worked against mTOR antagonist when administered simultaneously. In conclusion, the present study showed new evidence that aerobic glycolysis induced by mTOR/HIF-1α might promote EBI after SAH by activating M1 microglia. This finding provided new insights for the treatment of EBI.

Expression of EPO and related factors in the liver and kidney of plain and Tibetan sheep

Erythropoietin (EPO), hypoxia-inducible factor-1α (HIF-1α), hypoxia-inducible factor-2α (HIF-2α), and vascular endothelial growth factor (VEGF) are key factors in the regulation of hypoxia, and can transcriptionally activate multiple genes under hypoxic conditions, thereby initiating large hypoxic stress in the network. The liver and kidneys are important metabolic organs of the body. We assessed the expression of EPO, HIF-1α, HIF-2α, and VEGF in liver and kidney tissues of plain and Tibetan sheep using hematoxylin and eosin staining, immunohistochemistry, and RT-qPCR. The results showed that EPO, HIF-1α, HIF-2α, and VEGF were expressed in tubular epithelial cells, collecting duct epithelial cells, mural epithelial cells, and the glomerular cytoplasm of Tibetan sheep, and their expression was significantly higher in Tibetan sheep than in plain sheep (P<0.05). EPO, HIF-1α, HIF-2α, and VEGF are expressed in hepatocytes, interlobular venous endothelial cells, and interlobular bile duct epithelial cells. In plain sheep, positive signals for EPO, HIF-1α, HIF-2α, and VEGF were localized mainly in interlobular venous endothelial cells, whereas VEGF and HIF-2α were negatively expressed in interlobular bile duct epithelial cells and positively expressed in EPO and HIF-1α. The differences in EPO, HIF-1α, and HIF-2α in Tibetan sheep were significantly higher than those in plain sheep (P<0.001). In the liver and kidney tissues of Tibetan sheep, EPO was associated with HIF-1α, HIF-2α, and VEGF (P<0.05). RT-qPCR results showed that EPO was not expressed, and HIF-1α, HIF-2α, and VEGF were expressed (P<0.05). The results showed that the expression of EPO, HIF-1α, HIF-2α, and VEGF in the kidney and liver of Tibetan sheep was higher than that in of plain sheep. Therefore, EPO, HIF-1α, HIF-2α, and VEGF may be involved in the adaptive response of plateau animals, which provides theoretical clarity to further explore the adaptive mechanism of plateau hypoxia in Tibetan sheep.

SIRT6 deficiency in endothelial cells exacerbates oxidative stress by enhancing HIF1α accumulation and H3K9 acetylation at the Ero1α promoter

BACKGROUND

SIRT6, an important NAD+ -dependent protein, protects endothelial cells from inflammatory and oxidative stress injuries. However, the role of SIRT6 in cardiac microvascular endothelial cells (CMECs) under ischemia-reperfusion injury (IRI) remains unclear.

METHODS

The HUVECs model of oxygen-glucose deprivation/reperfusion (OGD/R) was established to simulate the endothelial IRI in vitro. Endoplasmic reticulum oxidase 1 alpha (Ero1α) mRNA and protein levels in SIRT6-overexpressing or SIRT6-knockdown cells were measured by qPCR and Western blotting. The levels of H2 O2 and mitochondrial reactive oxygen species (ROS) were detected to evaluate the status of oxidative stress. The effects of SIRT6 deficiency and Ero1α knockdown on cellular endoplasmic reticulum stress (ERS), inflammation, apoptosis and barrier function were detected by a series of molecular biological experiments and functional experiments in vitro. Chromatin immunoprecipitation, Western blotting, qPCR, and site-specific mutation experiments were used to examine the underlying molecular mechanisms. Furthermore, endothelial cell-specific Sirt6 knockout (ecSirt6-/- ) mice were subjected to cardiac ischemia-reperfusion surgery to investigate the effects of SIRT6 in CMECs in vivo.

RESULTS

The expression of Ero1α was significantly upregulated in SIRT6-knockdown endothelial cells, and high Ero1α expression correlated with the accumulation of H2 O2 and mitochondrial ROS. In addition, SIRT6 deficiency increased ERS, inflammation, apoptosis and endothelial permeability, and these effects could be significantly attenuated by Ero1α knockdown. The deacetylase catalytic activity of SIRT6 was important in regulating Ero1α expression and these biological processes. Mechanistically, SIRT6 inhibited the enrichment of HIF1α and p300 at the Ero1α promoter through deacetylating H3K9, thereby antagonizing HIF1α/p300-mediated Ero1α expression. Compared with SIRT6-wild-type (SIRT6-WT) cells, cells expressing the SIRT6-H133Y-mutant and SIRT6-R65A-mutant exhibited increased Ero1α expression. Furthermore, ecSirt6-/- mice subjected to ischemia-reperfusion surgery exhibited increased Ero1α expression and ERS in CMECs and worsened injuries to microvascular barrier function and cardiac function.

CONCLUSIONS

Our results revealed an epigenetic mechanism associated with SIRT6 and Ero1α expression and highlighted the therapeutic potential of targeting the SIRT6-HIF1α/p300-Ero1α axis.

The Effect of Hypoxia-inducible Factor Inhibition on the Phenotype of Fibroblasts in Human and Bovine Pulmonary Hypertension

Hypoxia-inducible factor (HIF) has received much attention as a potential pulmonary hypertension (PH) treatment target because inhibition of HIF reduces the severity of established PH in rodent models. However, the limitations of small-animal models of PH in predicting the therapeutic effects of pharmacologic interventions in humans PH are well known. Therefore, we sought to interrogate the role of HIFs in driving the activated phenotype of PH cells from human and bovine vessels. We first established that pulmonary arteries (PAs) from human and bovine PH lungs exhibit markedly increased expression of direct HIF target genes (CA9, GLUT1, and NDRG1), as well as cytokines/chemokines (CCL2, CSF2, CXCL12, and IL6), growth factors (FGF1, FGF2, PDGFb, and TGFA), and apoptosis-resistance genes (BCL2, BCL2L1, and BIRC5). The expression of the genes found in the intact PAs was determined in endothelial cells, smooth muscle cells, and fibroblasts cultured from the PAs. The data showed that human and bovine pulmonary vascular fibroblasts from patients or animals with PH (termed PH-Fibs) were the cell type that exhibited the highest level and the most significant increases in the expression of cytokines/chemokines and growth factors. In addition, we found that human, but not bovine, PH-Fibs exhibit consistent misregulation of HIFα protein stability, reduced HIF1α protein hydroxylation, and increased expression of HIF target genes even in cells grown under normoxic conditions. However, whereas HIF inhibition reduced the expression of direct HIF target genes, it had no impact on other "persistently activated" genes. Thus, our study indicated that HIF inhibition alone is not sufficient to reverse the persistently activated phenotype of human and bovine PH-Fibs.

The tissue-specific transcriptional landscape underlines the involvement of endothelial cells in health and disease

Endothelial cells (ECs) that line vascular and lymphatic vessels are being increasingly recognized as important to organ function in health and disease. ECs participate not only in the trafficking of gases, metabolites, and cells between the bloodstream and tissues but also in the angiocrine-based induction of heterogeneous parenchymal cells, which are unique to their specific tissue functions. The molecular mechanisms regulating EC heterogeneity between and within different tissues are modeled during embryogenesis and become fully established in adults. Any changes in adult tissue homeostasis induced by aging, stress conditions, and various noxae may reshape EC heterogeneity and induce specific transcriptional features that condition a functional phenotype. Heterogeneity is sustained via specific genetic programs organized through the combinatory effects of a discrete number of transcription factors (TFs) that, at the single tissue-level, constitute dynamic networks that are post-transcriptionally and epigenetically regulated. This review is focused on outlining the TF-based networks involved in EC specialization and physiological and pathological stressors thought to modify their architecture.

Transcriptional Response to Hypoxia: The Role of HIF-1-Associated Co-Regulators

The Hypoxia Inducible Factor 1 (HIF-1) plays a major role in the cellular response to hypoxia by regulating the expression of many genes involved in adaptive processes that allow cell survival under low oxygen conditions. Adaptation to the hypoxic tumor micro-environment is also critical for cancer cell proliferation and therefore HIF-1 is also considered a valid therapeutical target. Despite the huge progress in understanding regulation of HIF-1 expression and activity by oxygen levels or oncogenic pathways, the way HIF-1 interacts with chromatin and the transcriptional machinery in order to activate its target genes is still a matter of intense investigation. Recent studies have identified several different HIF-1- and chromatin-associated co-regulators that play important roles in the general transcriptional activity of HIF-1, independent of its expression levels, as well as in the selection of binding sites, promoters and target genes, which, however, often depends on cellular context. We review here these co-regulators and examine their effect on the expression of a compilation of well-characterized HIF-1 direct target genes in order to assess the range of their involvement in the transcriptional response to hypoxia. Delineating the mode and the significance of the interaction between HIF-1 and its associated co-regulators may offer new attractive and specific targets for anticancer therapy.

HIF‑1α inhibits ferroptosis and promotes malignant progression in non‑small cell lung cancer by activating the Hippo‑YAP signalling pathway

Ferroptosis and hypoxia-inducible factor 1α (HIF-1α) have critical roles in human tumors. The aim of the present study was to investigate the associations between ferroptosis, HIF-1α and cell growth in non-small cell lung cancer (NSCLC) cells. The lung cancer cell lines SW900 and A549 were evaluated using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) to detect the expression of HIF-1α. Cell Counting Kit-8, flow cytometry and Transwell migration assays were used to measure cell viability, apoptosis and invasion, respectively. The production of reactive oxygen species (ROS) and levels of malondialdehyde (MDA), glutathione (GSH) and ferrous ion (Fe²⁺) were determined using detection kits. The expression levels of glutathione peroxidase 4 (GPX4) and Yes-associated protein 1 (YAP1) were detected using RT-qPCR and western blotting. The results showed that the expression of HIF-1α was significantly upregulated in NSCLC cells compared with normal human bronchial epithelial cells. Small interfering RNA specific to HIF-1α (si-HIF-1α) significantly decreased the proliferation and invasion of NSCLC cells and increased their apoptosis. si-HIF-1α also increased the levels of ROS, MDA and Fe²⁺ but decreased GSH and GPX4 levels in A549 cells. Additionally, si-HIF-1α increased phosphorylated (p-)YAP1 levels, suppressed GPX4 and YAP1 expression, and attenuated the YAP1 overexpression-induced changes in YAP1, p-YAP1 and GPX4 levels and cell viability. The ferroptosis antagonist ferrostatin-1 partially attenuated the effects of si-HIF-1α on the NSCLC cells, while the ferroptosis agonist erastin further inhibited NSCLC growth by blocking HIF-1α expression. In conclusion, the silencing of HIF-1α induces ferroptosis by suppressing Hippo-YAP pathway activation in NSCLC cells. The present study provides novel insights into the malignant progression of NSCLC and suggests that HIF-1α is an effective target for the treatment of NSCLC.

Interaction Among Noncoding RNAs, DNA Damage Reactions, and Genomic Instability in the Hypoxic Tumor: Is it Therapeutically Exploitable Practice?

Hypoxia is a classical function of the tumor's microenvironment with a substantial effect on the development and therapeutic response of cancer. When put in hypoxic environments, cells undergo several biological reactions, including activation of signaling pathways that control proliferation, angiogenesis, and death. These pathways have been adapted by cancer cells to allow tumors to survive and even develop in hypoxic conditions, and poor prognosis is associated with tumor hypoxia. The most relevant transcriptional regulator in response to hypoxia, Hypoxia-inducible factor-1 alpha (HIF-1α), has been shown to modulate hypoxic gene expression and signaling transduction networks significantly. The significance of non-coding RNAs in hypoxic tumor regions has been revealed in an increasing number of studies over the past few decades. In regulating hypoxic gene expression, these hypoxia-responsive ncRNAs play pivotal roles. Hypoxia, a general characteristic of the tumor's microenvironment, significantly affects the expression of genes and is closely associated with the development of cancer. Indeed, the number of known hypoxia-associated lncRNAs has increased dramatically, demonstrating the growing role of lncRNAs in cascades and responses to hypoxia signaling. Decades of research have helped us create an image of the shift in hypoxic cancer cells' DNA repair capabilities. Emerging evidence suggests that hypoxia can trigger genetic instability in cancer cells because of microenvironmental tumor stress. Researchers have found that critical genes' expression is coordinately repressed by hypoxia within the DNA damage and repair pathways. In this study, we include an update of current knowledge on the presentation, participation, and potential clinical effect of ncRNAs in tumor hypoxia, DNA damage reactions, and genomic instability, with a specific emphasis on their unusual cascade of molecular regulation and malignant progression induced by hypoxia.

Hypoxia induces docetaxel resistance in triple-negative breast cancer via the HIF-1α/miR-494/Survivin signaling pathway

Cytotoxic chemotherapy is the major strategy to prevent and reduce triple-negative breast cancer (TNBC) progression and metastasis. Hypoxia increases chemoresistance and is associated with a poor prognosis for patients with cancer. Based on accumulating evidence, microRNAs (miRNAs) play an important role in acquired drug resistance. However, the role of miRNAs in hypoxia-induced TNBC drug resistance remains to be clarified. Here, we found that hypoxia induced TNBC docetaxel resistance by decreasing the miR-494 level. Modulating miR-494 expression altered the sensitivity of TNBC cells to DTX under hypoxic conditions. Furthermore, we identified Survivin as a direct miR-494 target. Hypoxia upregulated survivin expression. In a clinical study, the HIF-1α/miR-494/Survivin signaling pathway was also active in primary human TNBC, and miR-494 expression negatively correlated with HIF-1α and survivin expression. Finally, in a xenograft model, both miR-494 overexpression and the HIF-1α inhibitor PX-478 increased the sensitivity of TNBC to DTX by suppressing the HIF-1α/miR-494/Survivin signaling pathway in vivo. In conclusion, treatments targeting the HIF-1α/miR-494/Survivin signaling pathway potentially reverse hypoxia-induced drug resistance in TNBC.

Effects of Altitude and Duration of Differing Levels of Hypoxic Exposure on Hypoxia-Inducible Factor-1α in Rat Tissues

Li, Xiao-lin, Wei-gang Wang, Mao-xing Li, Tian-long Liu, Xiu-yu Tian, and Lan Wu. Effects of altitude and duration of differing levels of hypoxic exposure on hypoxia-inducible factor-1α in rat tissues. High Alt Med Biol. 23:173-184, 2022. Objective: This research aimed to evaluate the effects of hypoxia at different altitudes and durations on the expression of hypoxia-inducible factor-1α (HIF-1α) in rat tissues. Methods: A total of 72 Wistar rats were used to investigate the effect of hypoxia at different durations on rat tissues and 72 Wistar rats were used to investigate the effect of hypoxia at different altitudes. Hematoxylin and Eosin (HE) staining was performed to observe the pathological changes of hippocampus tissues, and the expression of HIF-1α of rats under conditions of hypoxia was detected by quantitative real-time polymerase chain reaction and western blotting. Results: According to the pathological results, we found that the degree of the brain, lung, and heart damage and HIF-1α expression, showed an increasing trend as the altitude (1,500, 3,000, 4,500, 6,000, 7,500, and 8,000 m for 12 hours) and duration (0, 6, 12, 24, 36, and 72 hours at 7,500 m) of hypoxia increased. Although there is a significant difference at 8,000 m, considering model stability, animal ethics and cost, we chose 7,500 m as a fixed altitude during hypoxia at different durations. Compared with the normoxic group, the expression of HIF-1α mRNA in the 7,500 m significantly increased by 30.48%, 21.00%, and 12.62%, in brain, lung, and heart tissue (p < 0.01), and HIF-1α mRNA in the 72-hour hypoxic exposure group significantly increased by 52.58%, 20.39%, 27.88% in tissues (p < 0.05). Compared with the normoxic group, HIF-1α protein expressions in the 7,500 m significantly increased by 10.26%, 31.71%, and 13.33% in brain, lung, and heart tissue (p < 0.01, p < 0.01, p < 0.05), and HIF-1α protein expressions in the 72-hour hypoxic exposure group significantly increased by 18.89%, 22.89%, and 29.75% in tissues (p < 0.05). Conclusion: HIF-1α expression in the rat was correlated with altitude and duration of hypoxic exposure.

Total flavones from Sceptridium ternatum alleviate pulmonary hypertension through inhibiting the proliferation of vascular endothelial cells

Background

Sceptridium ternatum is a traditional Chinese medicine that is prescribed to treat respiratory diseases in China. Our previous study confirmed that total flavones from Sceptridium ternatum (FST) have preventive and therapeutic effects on pulmonary hypertension (PH). The present study sought to investigate the mechanism underpinning the therapeutic efficacy of FST in PH.

Methods

Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) assays, real-time quantitative PCR (RT-qPCR), western blot, flow cytometry, high-throughput sequencing, and bioinformatics analysis were performed to study the therapeutic mechanism of FST in PH at the gene, cell, and animal levels.

Results

The results showed that FST could inhibit the proliferation of both human pulmonary artery smooth muscle cells (HPASMCs) and human pulmonary microvascular endothelial cells (HPMECs), and downregulate the expression of HIF1α and HIF2α, which are the key factors in the pathogenesis and occurrence of PH. FST could also inhibit the activation of the downstream JAK2-STAT3 signaling pathway and upregulate the expression of the negative regulator SOCS1. Vascular endothelial cell and smooth muscle cell proliferation was inhibited and the symptoms of PH were relieved by FST.

Conclusions

The findings of this study offer important clues for the identification of new molecular targets in FST treatment and the development of treatment strategies for PH.

Hypoxia-Inducible Factors and Burn-Associated Acute Kidney Injury-A New Paradigm?

O₂ deprivation induces stress in living cells linked to free-radical accumulation and oxidative stress (OS) development. Hypoxia is established when the overall oxygen pressure is less than 40 mmHg in cells or tissues. However, tissues and cells have different degrees of hypoxia. Hypoxia or low O₂ tension may be present in both physiological (during embryonic development) and pathological circumstances (ischemia, wound healing, and cancer). Meanwhile, the kidneys are major energy-consuming organs, being second only to the heart, with an increased mitochondrial content and O₂ consumption. Furthermore, hypoxia-inducible factors (HIFs) are the key players that orchestrate the mammalian response to hypoxia. HIFs adapt cells to low oxygen concentrations by regulating transcriptional programs involved in erythropoiesis, angiogenesis, and metabolism. On the other hand, one of the life-threatening complications of severe burns is acute kidney injury (AKI). The dreaded functional consequence of AKI is an acute decline in renal function. Taking all these aspects into consideration, the aim of this review is to describe the role and underline the importance of HIFs in the development of AKI in patients with severe burns, because kidney hypoxia is constant in the presence of severe burns, and HIFs are major players in the adaptative response of all tissues to hypoxia.

Retinal Diseases Regulated by Hypoxia-Basic and Clinical Perspectives: A Comprehensive Review

In recent years, the number of patients with age-related macular degeneration (AMD) is increasing worldwide along with increased life expectancy. Currently, the standard treatment for wet-AMD is intravitreal injection of anti-vascular endothelial growth factor (VEGF) drugs. The upstream of VEGF is hypoxia-inducible factor (HIF), a master regulator of hypoxia-responsive genes responsive to acute and chronic hypoxia. HIF activation induces various pathological pro-angiogenic gene expressions including VEGF under retinal hypoxia, ultimately leading to the development of ocular ischemic neovascular diseases. In this regard, HIF is considered as a promising therapeutic target in ocular ischemic diseases. In clinical ophthalmology, abnormal hypofluorescent areas have been detected in the late-phase of indocyanine green angiography, which are thought to be lipid deposits at the level of Bruch’s membrane to choriocapillaris in vitreoretinal diseases. These deposits may interfere with the oxygen and nutrients that should be supplied to the retinal pigment epithelium, and that HIF/VEGF is highly suspected to be expressed in the hypoxic retinal pigment epithelium, leading to neovascularization. In this review, we comprehensively summarize pathophysiology of AMD-related ocular diseases with the HIF/VEGF pathway from basic and clinic researches with recent findings.

The molecular basis for IL-31 production and IL-31-mediated itch transmission: from biology to drug development

Atopic dermatitis (AD) is one of the most prevalent chronic inflammatory skin diseases in the world. It is characterized by recurrent eczematous lesions and intense itch, and many cytokines are involved in the pathogenesis of AD. Among them, much attention has been paid to interleukin 31 (IL-31) as an AD-associated itch mediator. IL-31 is mainly produced by CD4⁺ helper T cells and transmits the signals via a heterodimeric receptor composed of IL-31 receptor A (IL-31RA) and oncostatin M receptor (OSMR), both of which are expressed in dorsal root ganglion (DRG) neurons. However, the molecular mechanisms of how IL-31 is produced in helper T cells upon stimulation and transmits the itch sensation to the brain were largely unknown. Recently, by using original mouse models of AD, we have identified endothelial PAS domain 1 (EPAS1) and neurokinin B (NKB) as key molecules critical for IL-31 production and IL-31-mediated itch transmission, respectively. These molecules could be novel drug targets for AD-associated itch. This review highlights our recent findings, which show the functional significance of these molecules in the IL-31-induced itch sensation, referring to their application to drug development.

Targeted inhibition of EPAS1-driven IL-31 production by a small-molecule compound

BACKGROUND

IL-31 is a major pruritogen associated with atopic dermatitis (AD). Although a specific antibody for IL-31 receptor has been shown to alleviate pruritus in patients with AD, therapeutic approaches to inhibition of IL-31 production remain unexploited. IL-31 production by T_H cells critically depends on the transcription factor EPAS1, which mediates IL31 promoter activation in collaboration with SP1.

OBJECTIVE

We aimed at developing small-molecule inhibitors that selectively block IL-31 production by T_H cells.

METHODS

We generated the reporter cell line that inducibly expressed EPAS1 in the presence of doxycycline to mediate Il31 promoter activation, and we screened 9600 chemical compounds. The selected compounds were further examined by using T_H cells from a spontaneous mouse model of AD and T_H cells from patients with AD.

RESULTS

We have identified 4-(2-(4-isopropylbenzylidene)hydrazineyl)benzoic acid (IPHBA) as an inhibitor of IL31 induction. Although IPHBA did not affect nonspecific T-cell proliferation, IPHBA inhibited antigen-induced IL-31 production by T_H cells from both an AD mouse model and patients with AD without affecting other cytokine production and hypoxic responses. In line with this, itch responses induced by adoptive transfer of IL-31-producing T_H cells were attenuated when mice were orally treated with IPHBA. Mechanistically, IPHBA inhibited the association between EPAS1 and SP1, resulting in defective recruitment of both transcription factors to the specific sites of the IL31 promoter. We also determined the structure-activity relationship of IPHBA by synthesizing and analyzing 201 analogous compounds.

CONCLUSION

IPHBA could be a potential drug leading to inhibition of EPAS1-driven IL-31 production.

Sanguinarine combats hypoxia-induced activation of EphB4 and HIF-1α pathways in breast cancer

BACKGROUND

Breast cancer is the most common female cancer worldwide. Large hypoxic area is one of the features of tumor microenvironment. Highly activated hypoxia-induced pathways positively correlate with poor clinical response to chemo- and radiotherapy and high mortality in breast cancer patients.

PURPOSE

We explore the effect of sanguinarine on hypoxia-induced activation of Ephrin type-B receptor 4 (EphB4) and hypoxia inducible factor-1α (HIF-1α) pathways in breast cancer.

RESULTS

Hypoxia-induced expression of a receptor tyrosine kinase EphB4 was observed in hypoxic breast cancer cell models. Sanguinarine, a natural alkaloid, could effectively combat hypoxia-induced EphB4 and HIF-1α expression. Sanguinarine inhibited the activation of downstream protein signal transducer and activator of transcription-3 (STAT3), thereby blocking hypoxia-induced HIF-1α/STAT3 interaction and downregulating the mRNA levels of their target genes. Mechanically, sanguinarine attenuated HIF-1α protein levels via inhibition of MAPK/ERK pathways and promotion of HIF-1α proteasome degradation. Sanguinarine inhibited STAT3 activation through targeting its upstream EphB4 and accelerating STAT3 dephosphorylation. Correspondingly, xenograft models confirmed that sanguinarine treatment disrupted hypoxia-induced pathways and inhibited tumor growth in vivo.

CONCLUSIONS

Our results may bring insights to the hypoxia-induced pathways in breast cancers, and suggest sanguinarine as a promising candidate for EphB4 and HIF-1α-targeted inhibition.

Hypoxia-inducible factor signaling in pulmonary hypertension

Pulmonary hypertension (PH) is characterized by pulmonary artery remodeling that can subsequently culminate in right heart failure and premature death. Emerging evidence suggests that hypoxia-inducible factor (HIF) signaling plays a fundamental and pivotal role in the pathogenesis of PH. This Review summarizes the regulation of HIF isoforms and their impact in various PH subtypes, as well as the elaborate conditional and cell-specific knockout mouse studies that brought the role of this pathway to light. We also discuss the current preclinical status of pan- and isoform-selective HIF inhibitors, and propose new research areas that may facilitate HIF isoform-specific inhibition as a novel therapeutic strategy for PH and right heart failure.

Myeloid-Derived Suppressor Cell Differentiation in Cancer: Transcriptional Regulators and Enhanceosome-Mediated Mechanisms

Myeloid-derived Suppressor Cells (MDSCs) are a sub-population of leukocytes that are important for carcinogenesis and cancer immunotherapy. During carcinogenesis or severe infections, inflammatory mediators induce MDSCs via aberrant differentiation of myeloid precursors. Although several transcription factors, including C/EBPβ, STAT3, c-Rel, STAT5, and IRF8, have been reported to regulate MDSC differentiation, none of them are specifically expressed in MDSCs. How these lineage-non-specific transcription factors specify MDSC differentiation in a lineage-specific manner is unclear. The recent discovery of the c-Rel−C/EBPβ enhanceosome in MDSCs may help explain these context-dependent roles. In this review, we examine several transcriptional regulators of MDSC differentiation, and discuss the concept of non-modular regulation of MDSC signature gene expression by transcription factors such as c-Rel and C/EBPß.

Hypoxia and the phenomenon of immune exclusion

Over the last few years, cancer immunotherapy experienced tremendous developments and it is nowadays considered a promising strategy against many types of cancer. However, the exclusion of lymphocytes from the tumor nest is a common phenomenon that limits the efficiency of immunotherapy in solid tumors. Despite several mechanisms proposed during the years to explain the immune excluded phenotype, at present, there is no integrated understanding about the role played by different models of immune exclusion in human cancers. Hypoxia is a hallmark of most solid tumors and, being a multifaceted and complex condition, shapes in a unique way the tumor microenvironment, affecting gene transcription and chromatin remodeling. In this review, we speculate about an upstream role for hypoxia as a common biological determinant of immune exclusion in solid tumors. We also discuss the current state of ex vivo and in vivo imaging of hypoxic determinants in relation to T cell distribution that could mechanisms of immune exclusion and discover functional-morphological tumor features that could support clinical monitoring.

The Drug-Resistance Mechanisms of Five Platinum-Based Antitumor Agents

Platinum-based anticancer drugs, including cisplatin, carboplatin, oxaliplatin, nedaplatin, and lobaplatin, are heavily applied in chemotherapy regimens. However, the intrinsic or acquired resistance severely limit the clinical application of platinum-based treatment. The underlying mechanisms are incredibly complicated. Multiple transporters participate in the active transport of platinum-based antitumor agents, and the altered expression level, localization, or activity may severely decrease the cellular platinum accumulation. Detoxification components, which are commonly increasing in resistant tumor cells, can efficiently bind to platinum agents and prevent the formation of platinum–DNA adducts, but the adducts production is the determinant step for the cytotoxicity of platinum-based antitumor agents. Even if adequate adducts have formed, tumor cells still manage to survive through increased DNA repair processes or elevated apoptosis threshold. In addition, autophagy has a profound influence on platinum resistance. This review summarizes the critical participators of platinum resistance mechanisms mentioned above and highlights the most potential therapeutic targets or predicted markers. With a deeper understanding of the underlying resistance mechanisms, new solutions would be produced to extend the clinical application of platinum-based antitumor agents largely.

Sanguinarine disrupts the colocalization and interaction of HIF-1α with tyrosine and serine phosphorylated-STAT3 in breast cancer

Breast cancer is one leading cause of death in females, especially triple‐negative breast cancer (TNBC). Hypoxia is a key feature leading to tumour progression driven by hypoxia‐inducible factor (HIF)‐1α. The aim is to investigate the mechanism of HIF‐1α and signal transducer and activator of transcription‐3 (STAT3) interaction and discover a compound to disrupt the interaction in breast cancer cells. The regulation pattern of HIF‐1α and STAT3 was analysed in hypoxic TNBC cells and patient samples. The effects of a natural alkaloid, sanguinarine, on HIF‐1α and STAT3 colocalization and interaction were evaluated in vitro and mouse xenograft models. We observed strong colocalization of HIF‐1α, p‐STAT3‐Tyr and p‐STAT3‐Ser in TNBC patient samples. Sanguinarine could inhibit the nuclear colocalization and interaction of HIF‐1α with p‐STAT3‐Tyr and p‐STAT3‐Ser in vivo and in vitro. Our results may bring insights to the HIF‐1α/STAT3 interaction in breast cancers and suggest sanguinarine as a promising candidate for HIF‐α/STAT3 inhibition.

Hypoxia Induces Drug Resistance in Colorectal Cancer through the HIF-1α/miR-338-5p/IL-6 Feedback Loop

Hypoxia is associated with poor prognosis and therapeutic resistance in cancer patients. Accumulating evidence has shown that microRNA (miRNA) plays an important role in the acquired drug resistance in colorectal carcinoma (CRC). However, the role of miRNA in hypoxia-induced CRC drug resistance remains to be elucidated. Here, we identified a hypoxia-triggered feedback loop that involves hypoxia-inducible transcription factor 1α (HIF-1α)-mediated repression of miR-338-5p and confers drug resistance in CRC. In this study, the unbiased miRNA array screening revealed that miR-338-5p is downregulated in both hypoxic CRC cell lines tested. Repression of miR-338-5p was required for hypoxia-induced CRC drug resistance. Furthermore, we identified interleukin-6 (IL-6), which mediates STAT3/Bcl2 activation under hypoxic conditions, as a direct miR-338-5p target. The resulting HIF-1α/miR-338-5p/IL-6 feedback loop was necessary for drug resistance in colon cancer cell lines. Using CRC patient samples, we found miR-338-5p has a negative correlation with HIF-1α and IL-6. Finally, in a xenograft model, overexpressing miR-338-5p in CRC cells and HIF-1α inhibitor PX-478 were able to enhance the sensitivity of CRC to oxaliplatin (OXA) via suppressing the HIF-1α/miR-338-5p/IL-6 feedback loop in vivo. Taken together, our results uncovered an HIF-1α/miR-338-5p/IL-6 feedback circuit that is critical in hypoxia-mediated drug resistance in CRC; targeting each member of this feedback loop could potentially reverse hypoxia-induced drug resistance in CRC.

Plexiform Arteriopathy in Rodent Models of Pulmonary Arterial Hypertension

As time progresses, our understanding of disease pathology is propelled forward by technological advancements. Much of the advancements that aid in understanding disease mechanics are based on animal studies. Unfortunately, animal models often fail to recapitulate the entirety of the human disease. This is especially true with animal models used to study pulmonary arterial hypertension (PAH), a disease with two distinct phases. The first phase is defined by nonspecific medial and adventitial thickening of the pulmonary artery and is commonly reproduced in animal models, including the classic models (ie, hypoxia-induced pulmonary hypertension and monocrotaline lung injury model). However, many animal models, including the classic models, fail to capture the progressive, or second, phase of PAH. This is a stage defined by plexogenic arteriopathy, resulting in obliteration and occlusion of the small- to mid-sized pulmonary vessels. Each of these two phases results in severe pulmonary hypertension that directly leads to right ventricular hypertrophy, decompensated right-sided heart failure, and death. Fortunately, newly developed animal models have begun to address the second, more severe, side of PAH and aid in our ability to develop new therapeutics. Moreover, p38 mitogen-activated protein kinase activation emerges as a central molecular mediator of plexiform lesions in both experimental models and human disease. Therefore, this review will focus on plexiform arteriopathy in experimental animal models of PAH.

Hypoxia Signaling in the Skeleton: Implications for Bone Health

PURPOSE OF REVIEW

We reviewed recent literature on oxygen sensing in osteogenic cells and its contribution to development of a skeletal phenotype, the coupling of osteogenesis with angiogenesis and integration of hypoxia into canonical Wnt signaling, and opportunities to manipulate oxygen sensing to promote skeletal repair.

RECENT FINDINGS

Oxygen sensing in osteocytes can confer a high bone mass phenotype in murine models; common and unique targets of HIF-1α and HIF-2α and lineage-specific deletion of oxygen sensing machinery suggest differentia utilization and requirement of HIF-α proteins in the differentiation from mesenchymal stem cell to osteoblast to osteocyte; oxygen-dependent but HIF-α-independent signaling may contribute to observed skeletal phenotypes. Manipulating oxygen sensing machinery in osteogenic cells influences skeletal phenotype through angiogenesis-dependent and angiogenesis-independent pathways and involves HIF-1α, HIF-2α, or both proteins. Clinically, an FDA-approved iron chelator promotes angiogenesis and osteogenesis, thereby enhancing the rate of fracture repair.

Adenylate kinase 4 modulates oxidative stress and stabilizes HIF-1α to drive lung adenocarcinoma metastasis

Background

Adenylate kinase 4 (AK4) has been identified as a biomarker of metastasis in lung cancer. However, the impacts of AK4 on metabolic genes and its translational value for drug repositioning remain unclear.

Methods

Ingenuity upstream analyses were used to identify potential transcription factors that regulate the AK4 metabolic gene signature. The expression of AK4 and its upstream regulators in lung cancer patients was examined via immunohistochemistry. Pharmacological and gene knockdown/overexpression approaches were used to investigate the interplay between AK4 and its upstream regulators during epithelial-to-mesenchymal transition (EMT). Drug candidates that reversed AK4-induced gene expression were identified by querying a connectivity map. Orthotopic xenograft mouse models were established to evaluate the therapeutic efficacy of drug candidates for metastatic lung cancer.

Results

We found that HIF-1α is activated in the AK4 metabolic gene signature. IHC analysis confirmed this positive correlation, and the combination of both predicts worse survival in lung cancer patients. Overexpression of AK4 exaggerates HIF-1α protein expression by increasing intracellular ROS levels and subsequently induces EMT under hypoxia. Attenuation of ROS production with N-acetylcysteine abolishes AK4-induced invasion potential under hypoxia. Pharmacogenomics analysis of the AK4 gene signature revealed that withaferin-A could suppress the AK4-HIF-1α signaling axis and serve as a potent anti-metastatic agent in lung cancer.

Conclusions

Overexpression of AK4 promotes lung cancer metastasis by enhancing HIF-1α stability and EMT under hypoxia. Reversing the AK4 gene signature with withaferin-A may serve as a novel therapeutic strategy to treat metastatic lung cancer.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0698-5) contains supplementary material, which is available to authorized users.

Hypoxia and hyperbaric oxygen therapy: a review

Hypoxia causes a cascade of activity from the level of the individual down to the regulation and function of the cell nucleus. Prolonged periods of low oxygen tension are a core feature of several disease states. Advances in the study of molecular biology have begun to bridge the gap between the cellular response to hypoxia and physiology. Hyperbaric oxygen therapy is a treatment for hypoxic- and inflammatory-driven conditions, in which patients are treated with 100% oxygen at pressures greater than atmospheric pressure. This review discusses hypoxia, the physiologic changes associated with hypoxia, the responses that occur in the cells during hypoxic conditions, and the role that hyperbaric oxygen therapy can play as part of the treatment for many patients suffering from diseases with underlying hypoxia.

Mechanisms contributing to persistently activated cell phenotypes in pulmonary hypertension

Chronic pulmonary hypertension (PH) is characterized by the accumulation of persistently activated cell types in the pulmonary vessel exhibiting aberrant expression of genes involved in apoptosis resistance, proliferation, inflammation and extracellular matrix (ECM) remodelling. Current therapies for PH, focusing on vasodilatation, do not normalize these activated phenotypes. Furthermore, current approaches to define additional therapeutic targets have focused on determining the initiating signals and their downstream effectors that are important in PH onset and development. Although these approaches have produced a large number of compelling PH treatment targets, many promising human drugs have failed in PH clinical trials. Herein, we propose that one contributing factor to these failures is that processes important in PH development may not be good treatment targets in the established phase of chronic PH. We hypothesize that this is due to alterations of chromatin structure in PH cells, resulting in functional differences between the same factor or pathway in normal or early PH cells versus cells in chronic PH. We propose that the high expression of genes involved in the persistently activated phenotype of PH vascular cells is perpetuated by an open chromatin structure and multiple transcription factors (TFs) via the recruitment of high levels of epigenetic regulators including the histone acetylases P300/CBP, histone acetylation readers including BRDs, the Mediator complex and the positive transcription elongation factor (Abstract figure). Thus, determining how gene expression is controlled by examining chromatin structure, TFs and epigenetic regulators associated with aberrantly expressed genes in pulmonary vascular cells in chronic PH, may uncover new PH therapeutic targets.

Aryl Hydrocarbon Receptor Nuclear Translocator in Vascular Smooth Muscle Cells Is Required for Optimal Peripheral Perfusion Recovery

BACKGROUND

Limb ischemia resulting from peripheral vascular disease is a common cause of morbidity. Vessel occlusion limits blood flow, creating a hypoxic environment that damages distal tissue, requiring therapeutic revascularization. Hypoxia-inducible factors (HIFs) are key transcriptional regulators of hypoxic vascular responses, including angiogenesis and arteriogenesis. Despite vascular smooth muscle cells' (VSMCs') importance in vessel integrity, little is known about their functional responses to hypoxia in peripheral vascular disease. This study investigated the role of VSMC HIF in mediating peripheral ischemic responses.

METHODS AND RESULTS

We used ArntSMKO mice with smooth muscle-specific deletion of aryl hydrocarbon receptor nuclear translocator (ARNT, HIF-1β), required for HIF transcriptional activity, in a femoral artery ligation model of peripheral vascular disease. ArntSMKO mice exhibit impaired perfusion recovery despite normal collateral vessel dilation and angiogenic capillary responses. Decreased blood flow manifests in extensive tissue damage and hypoxia in ligated limbs of ArntSMKO mice. Furthermore, loss of aryl hydrocarbon receptor nuclear translocator changes the proliferation, migration, and transcriptional profile of cultured VSMCs. ArntSMKO mice display disrupted VSMC morphologic features and wrapping around arterioles and increased vascular permeability linked to decreased local blood flow.

CONCLUSIONS

Our data demonstrate that traditional vascular remodeling responses are insufficient to provide robust peripheral tissue reperfusion in ArntSMKO mice. In all, this study highlights HIF responses to hypoxia in arteriole VSMCs critical for the phenotypic and functional stability of vessels that aid in the recovery of blood flow in ischemic peripheral tissues.

Hypoxia Induces Hypoxia-Inducible Factor 1α and Potential HIF-Responsive Gene Expression in Uterine Leiomyoma

Uterine leiomyoma is characterized by abundant extracellular matrix and broad avascular areas, both constantly resulting in hypoxia, suggesting some hypoxia-induced response function. Here, we examined whether hypoxia-inducible factor 1α (HIF-1α)- mediated hypoxic response function in uterine leiomyoma. Immunoblotting detected higher basal HIF-1α protein expression in nuclear extracts from uterine leiomyoma tissues than in those from the adjacent myometrium ( P = .0011). Immunohistochemical analysis revealed the presence of HIF-1α-positive cellular components in both leiomyoma and surrounding myometrial tissues. Hypoxia decreased HIF-1α messenger RNA (mRNA), but increased HIF-1α protein in primary culture leiomyoma smooth muscle cells, and caused translocation of HIF-1α from the cytoplasm to the nucleus. Hypoxia upregulated mRNAs of 6 potential HIF-responsive genes ( ALDOA, ENO1, LDHA, VEGFA, PFKFB3, and SLC2A1). Chromatin immunoprecipitation quantitative polymerase chain reaction revealed that hypoxia significantly increased recruitment of HIF-1α binding to putative HIF-responsive elements in the HIF-responsive genes, suggesting that the HIF transcriptional complex initiates hypoxia-induced transcription of HIF-responsive genes. These results demonstrated a HIF-1α-mediated hypoxic response in uterine leiomyoma.

The Transcription Factor Hif-1 Enhances the Radio-Resistance of Mouse MSCs

Mesenchymal stromal cells (MSCs) are multipotent progenitors supporting bone marrow hematopoiesis. MSCs have an efficient DNA damage response (DDR) and are consequently relatively radio-resistant cells. Therefore, MSCs are key to hematopoietic reconstitution following total body irradiation (TBI) and bone marrow transplantation (BMT). The bone marrow niche is hypoxic and via the heterodimeric transcription factor Hypoxia-inducible factor-1 (Hif-1), hypoxia enhances the DDR. Using gene knock-down, we have previously shown that the Hif-1α subunit of Hif-1 is involved in mouse MSC radio-resistance, however its exact mechanism of action remains unknown. In order to dissect the involvement of Hif-1α in the DDR, we used CRISPR/Cas9 technology to generate a stable mutant of the mouse MSC cell line MS5 lacking Hif-1α expression. Herein, we show that it is the whole Hif-1 transcription factor, and not only the Hif-1α subunit, that modulates the DDR of mouse MSCs. This effect is dependent upon the presence of a Hif-1α protein capable of binding to both DNA and its heterodimeric partner Arnt (Hif-1β). Detailed transcriptomic and proteomic analysis of Hif1a KO MS5 cells leads us to conclude that Hif-1α may be acting indirectly on the DNA repair process. These findings have important implications for the modulation of MSC radio-resistance in the context of BMT and cancer.

Improved oxygenation dramatically alters metabolism and gene expression in cultured primary mouse hepatocytes

Primary hepatocyte culture is an important in vitro system for the study of liver functions. In vivo, hepatocytes have high oxidative metabolism. However, oxygen supply by means of diffusion in in vitro static cultures is much less than that by blood circulation in vivo. Therefore, we investigated whether hypoxia contributes to dedifferentiation and deregulated metabolism in cultured hepatocytes. To this end, murine hepatocytes were cultured under static or shaken (60 revolutions per minute) conditions in a collagen sandwich. The effect of hypoxia on hepatocyte cultures was examined by metabolites in media and cells, hypoxia-inducible factors (HIF)-1/2α western blotting, and real-time quantitative polymerase chain reaction for HIF target genes and key genes of glucose and lipid metabolism. Hepatocytes in shaken cultures showed lower glycolytic activity and triglyceride accumulation than static cultures, compatible with improved oxygen delivery and mitochondrial energy metabolism. Consistently, static cultures displayed significant HIF-2α expression, which was undetectable in freshly isolated hepatocytes and shaken cultures. Transcript levels of HIF target genes (glyceraldehyde 3-phosphate dehydrogenase [Gapdh], glucose transporter 1 [Glut1], pyruvate dehydrogenase kinase 1 [Pdk1], and lactate dehydrogenase A [Ldha]) and key genes of lipid metabolism, such as carnitine palmitoyltransferase 1 (Cpt1), apolipoprotein B (Apob), and acetyl-coenzyme A carboxylase 1 (Acc1), were significantly lower in shaken compared to static cultures. Moreover, expression of hepatocyte nuclear factor 4α (Hnf4α) and farnesoid X receptor (Fxr) were better preserved in shaken cultures as a result of improved oxygen delivery. We further revealed that HIF-2 signaling was involved in hypoxia-induced down-regulation of Fxr. Conclusion: Primary murine hepatocytes in static culture suffer from hypoxia. Improving oxygenation by simple shaking prevents major changes in expression of metabolic enzymes and aberrant triglyceride accumulation; in addition, it better maintains the differentiation state of the cells. The shaken culture is, therefore, an advisable strategy for the use of primary hepatocytes as an in vitro model. (Hepatology Communications 2018;2:299-312).

An Experimental Study on Repeated Brief Ischemia in Promoting Sciatic Nerve Repair and Regeneration in Rats

BACKGROUND

Research has shown that ischemic preconditioning reduced the severity of ischemia-reperfusion injury in brain in rats, we have a hypothesis that repeated brief ischemia has positive effects on peripheral nerve damage. This study was conducted to investigate the potential protective effects of repeated brief ischemia on peripheral nerve regeneration using a rat model of experimental sciatic nerve transection injury.

METHODS

Treatment groups (groups A-D) received repeated, brief ischemia every 1 day/2 days/3 days/7 days. After surgery for 4, 8, 12 weeks, we evaluated sciatic functional index test, gastrocnemius muscle wet mass, axon and nerve fiber diameter, density, G-ratio, immunohistochemistry of S-100, vascular endothelial growth factor (VEGF), and the ultrastructure of the nerves.

RESULTS

Sciatic functional index test and muscle wet mass were improved on the repeated brief ischemia groups. Ischemia treatment resulted in a significant increase in axon and nerve fiber density as well as S-100 and VEGF-positive cell, which indicated that repeated brief ischemia promotes Schwann cell proliferation and reconstruction.

CONCLUSIONS

This study exhibits the positive effects of repeated brief ischemia in sciatic nerve transection injury, possibly in part because it can improve VEGF and the physiologic state of Schwann cells in the ischemic environment and then accelerate the ability of neurite outgrow.

Elevated d-2-hydroxyglutarate during colitis drives progression to colorectal cancer

d-2-hydroxyglutarate (D2HG) is produced in the tricarboxylic acid cycle and is quickly converted to α-ketoglutarate by d-2-hydroxyglutarate dehydrogenase (D2HGDH). In a mouse model of colitis-associated colon cancer (CAC), urine level of D2HG during colitis correlates positively with subsequent polyp counts and severity of dysplasia. The i.p. injection of D2HG results in delayed recovery from colitis and severe tumorigenesis. The colonic expression of D2HGDH is decreased in ulcerative colitis (UC) patients at baseline who progress to cancer. Hypoxia-inducible factor (Hif)-1α is a key regulator of D2HGDH transcription. Our study identifies urine D2HG and tissue D2HGDH expression as biomarkers to identify patients at risk for progressing from colitis to cancer. The D2HG/D2HGDH pathway provides potential therapeutic targets for the treatment of CAC.

Transcription factors, transcriptional coregulators, and epigenetic modulation in the control of pulmonary vascular cell phenotype: therapeutic implications for pulmonary hypertension (2015 Grover Conference series)

Pulmonary hypertension (PH) is a complex and multifactorial disease involving genetic, epigenetic, and environmental factors. Numerous stimuli and pathological conditions facilitate severe vascular remodeling in PH by activation of a complex cascade of signaling pathways involving vascular cell proliferation, differentiation, and inflammation. Multiple signaling cascades modulate the activity of certain sequence-specific DNA-binding transcription factors (TFs) and coregulators that are critical for the transcriptional regulation of gene expression that facilitates PH-associated vascular cell phenotypes, as demonstrated by several studies summarized in this review. Past studies have largely focused on the role of the genetic component in the development of PH, while the presence of epigenetic alterations such as microRNAs, DNA methylation, histone levels, and histone deacetylases in PH is now also receiving increasing attention. Epigenetic regulation of chromatin structure is also recognized to influence gene expression in development or disease states. Therefore, a complete understanding of the mechanisms involved in altered gene expression in diseased cells is vital for the design of novel therapeutic strategies. Recent technological advances in DNA sequencing will provide a comprehensive improvement in our understanding of mechanisms involved in the development of PH. This review summarizes current concepts in TF and epigenetic control of cell phenotype in pulmonary vascular disease and discusses the current issues and possibilities in employing potential epigenetic or TF-based therapies for achieving complete reversal of PH.

The transcription factor EPAS1 links DOCK8 deficiency to atopic skin inflammation via IL-31 induction

Mutations of DOCK8 in humans cause a combined immunodeficiency characterized by atopic dermatitis with high serum IgE levels. However, the molecular link between DOCK8 deficiency and atopic skin inflammation is unknown. Here we show that CD4⁺ T cells from DOCK8-deficient mice produce large amounts of IL-31, a major pruritogen associated with atopic dermatitis. IL-31 induction critically depends on the transcription factor EPAS1, and its conditional deletion in CD4⁺ T cells abrogates skin disease development in DOCK8-deficient mice. Although EPAS1 is known to form a complex with aryl hydrocarbon receptor nuclear translocator (ARNT) and control hypoxic responses, EPAS1-mediated Il31 promoter activation is independent of ARNT, but in collaboration with SP1. On the other hand, we find that DOCK8 is an adaptor and negative regulator of nuclear translocation of EPAS1. Thus, EPAS1 links DOCK8 deficiency to atopic skin inflammation via IL-31 induction in CD4⁺ T cells.

Infiltrating bone marrow mesenchymal stem cells (BM-MSCs) increase prostate cancer cell invasion via altering the CCL5/HIF2α/androgen receptor signals

Several infiltrating cells in the tumor microenvironment could influence the cancer progression via secreting various cytokines. Here, we found the CCL5 secreted from BM-MSCs suppressed androgen receptor (AR) signals via enhancing the expression of hypoxia inducible factor 2α (HIF2α) in prostate cancer (PCa) cells. Mechanism dissection revealed that the increased HIF2α might alter the AR-HSP90 interaction to suppress the AR transactivation, and inhibition of HIF2α reversed the BM-MSCs-increased PCa stem cell population and PCa cells invasion. Importantly, CCL5 could suppress the prolyl hydroxylases (PHDs) expression, which might then lead to suppress VHL-mediated HIF2α ubiquitination. Together, these results demonstrated that the CCL5 signals from infiltrating BM-MSC cells to HIF2α signals within PCa cells might play a key role to increase PCa stem cell population and PCa metastasis via altering the AR signals. Targeting this newly identified CCL5/HIF2α/AR axis signal axis may allow us to develop a novel way to suppress PCa metastasis.

The impact of high co-expression of Sp1 and HIF1α on prognosis of patients with hepatocellular cancer

Transcription factor specificity protein 1 (Sp1) and hypoxia-inducible factor 1α (HIF1α) serve vital roles in tumor growth and metastasis. The present study aimed to evaluate the impact of co-expression of Sp1 and HIF1α on the prognosis of patients with hepatocellular cancer (HCC) using The Cancer Genome Atlas (TCGA) database and to validate the association between the expression levels of Sp1/HIF1α in HCC specimens and patient survival using immunohistochemical analysis. A total of 214 eligible patients with HCC from TCGA database were collected for the study. The expression profile of Sp1 and HIF1α were obtained from the TCGA RNAseq database. Clinicopathological characteristics, including age, height, weight, gender, race, ethnicity, family cancer history, serum α-fetoprotein (AFP), surgical procedures and TNM stage were collected. The Cox proportional hazards regression model and Kaplan-Meier curves were used to assess the relative factors. Receiver operating characteristic (ROC) curves for cancer-specific survival (CSS) prediction were plotted to compare the prediction ability of expression of Sp1 and HIF1α and their co-expression. The location and expression of Sp1 and HIF1α in the HCC tissues were detected by immunohistochemistry (IHC) to verify the association between these two genes and CSS. The results demonstrated that the expressions of Sp1 and HIF1α were significantly increased in the succumbed group (P=0.001), compared with the surviving group. The CSS rates were 60.1% at 3 years (1,067 days), 35.8% at 5 years (1,823 days) and 9.5% at 10 years (3,528 days). Multivariate Cox regression analysis demonstrated that only the high expression levels of Sp1 and HIF1α (≥2×10³) were independent predictors for cancer mortality, with P=0.001 and P=0.029, respectively. The area under the curve for the ROC was found to be higher using the combination testing for two genes (0.751) in predicting cancer mortality, compared to a single gene (0.632 for Sp1 and 0.717 for HIF1α). Based on the cutoff points for gene expression, patients were divided into 3 groups: G1 (both genes <2×10³), G2 (either gene ≥2×10³) and G3 (both genes ≥2×10³). The risk of cancer mortality increased with high expression of genes, and G3 exhibited a greater risk than G2 when compared with the G1 group (HR=5.420, 95% CI 2.767–10.616, P=0.001; HR=3.270, 95% CI 1.843–5.803, P=0.001). The IHC staining results indicated that patients who died of cancer presented with significantly higher expression levels of these genes compared with those that did not (P=0.001). In summary, high expression levels of Sp1 and HIF1α in HCC tissues were associated with poor prognosis; in particular, the co-expression of these two genes increased the risk of cancer mortality.

Macrophages During the Fibrotic Process: M2 as Friend and Foe

Macrophages play essential activities in homeostasis maintenance during different organism’s conditions. They may be polarized according to various stimuli, which subsequently subdivide them into distinct populations. Macrophages with inflammatory activity function mainly during pathological context, while those with regulatory activity control inflammation and also remodel the repairing process. Here, we propose to review and to present a concise discuss on the role of different components during tissue repair, including those related to innate immune receptors and metabolic modifications. The scar formation is directly related to the degree of inflammation, but also with the appearance of M2 macrophages. In spite of greater numbers of macrophages in the fibrotic phase, regulatory macrophages present some characteristics related to promotion of fibrosis but also with the control of scar formation. These regulatory macrophages present an oxidative metabolism, and differ from the initial inflammatory macrophages, which in turn, present a glycolytic characteristic, which allow regulatory ones to optimize the oxygen consumption and minimizing their ROS production. We will emphasize the difference in macrophage subpopulations and the origin and plasticity of these cells during fibrotic processes.

The twisted survivin connection to angiogenesis

Survivin, a member of the inhibitor of apoptosis family of proteins (IAPs) that controls cell division, apoptosis, metastasis and angiogenesis, is overexpressed in essentially all human cancers. As a consequence, the gene/protein is considered an attractive target for cancer treatment. Here, we discuss recent findings related to the regulation of survivin expression and its role in angiogenesis, particularly in the context of hypoxia. We propose a novel role for survivin in cancer, whereby expression of the protein in tumor cells promotes VEGF synthesis, secretion and angiogenesis. Mechanistically, we propose the existence of a positive feed-back loop involving PI3-kinase/Akt activation and enhanced β-Catenin-TCF/LEF-dependent VEGF expression followed by secretion. Finally, we elaborate on the possibility that this mechanism operating in cancer cells may contribute to enhanced tumor vascularization by vasculogenic mimicry together with conventional angiogenesis.

Restoration of Opa1-long isoform inhibits retinal injury-induced neurodegeneration

Optic atrophy 1 (Opa1) is a critical factor that regulates fusion and other important functions of mitochondria. In mitochondrion, the N-terminal mitochondrial targeting sequence of Opa1 precursors is removed to generate Opa1 long isoforms (L-Opa1), which are further cleaved into short isoforms (S-Opa1). In the present study, we found that retinal ischemia-reperfusion (I/R) injury and intravitreal injection of carbonylcyanide m-chlorophenyl hydrazone (CCCP) both dramatically induced Opa1 cleavage and caused loss of L-Opa1. In cultured neuronal cells under hypoxia-reoxygenation (H/R) injury, similar changes for Opa1 were also observed. In contrast, restoration of L-Opa1 level by overexpression of S1 cleavage site deletion Opa1 splice 1 (Opa1-ΔS1) not only normalized the H/R-induced mitochondrial morphology changes, but also inhibited the H/R-induced apoptosis, necrosis, and the intracellular ATP loss. Furthermore, recovering L-Opa1 level in the I/R-injured retina by intravitreal injection of genipin or overexpression of Opa1-ΔS1 inhibited apoptosis, necrosis, cell loss in the ganglion cell layer and retinal thickness reduction. Together, our data demonstrated the loss of L-Opa1 is involved in the development of retinal I/R injury, indicating restoring L-Opa1 level may be considered as a therapeutic target for I/R injury-related diseases, at least for the retina. Key messages: Retinal ischemia-reperfusion (I/R) or hypoxia-reoxygenation (H/R) injury induces L-Opa1 loss. Opa1-ΔS1 overexpression inhibits H/R-induced L-Opa1 loss. Opa1-ΔS1 overexpression inhibits H/R-induced mitochondria morphology change. Opa1-ΔS1 and genipin inhibit retinal I/R injury-induced necroptosis. Opa1-ΔS1 and genipin inhibit retinal I/R injury-induced neurodegeneration.

Activating Injury-Responsive Genes with Hypoxia Enhances Axon Regeneration through Neuronal HIF-1α

Injured peripheral neurons successfully activate a proregenerative transcriptional program to enable axon regeneration and functional recovery. How transcriptional regulators coordinate the expression of such program remains unclear. Here we show that hypoxia-inducible factor 1α (HIF-1α) controls multiple injury-induced genes in sensory neurons and contribute to the preconditioning lesion effect. Knockdown of HIF-1α in vitro or conditional knock out in vivo impairs sensory axon regeneration. The HIF-1α target gene Vascular Endothelial Growth Factor A (VEGFA) is expressed in injured neurons and contributes to stimulate axon regeneration. Induction of HIF-1α using hypoxia enhances axon regeneration in vitro and in vivo in sensory neurons. Hypoxia also stimulates motor neuron regeneration and accelerates neuromuscular junction re-innervation. This study demonstrates that HIF-1α represents a critical transcriptional regulator in regenerating neurons and suggests hypoxia as a tool to stimulate axon regeneration.

ACLY and ACC1 Regulate Hypoxia-Induced Apoptosis by Modulating ETV4 via α-ketoglutarate

In order to propagate a solid tumor, cancer cells must adapt to and survive under various tumor microenvironment (TME) stresses, such as hypoxia or lactic acidosis. To systematically identify genes that modulate cancer cell survival under stresses, we performed genome-wide shRNA screens under hypoxia or lactic acidosis. We discovered that genetic depletion of acetyl-CoA carboxylase (ACACA or ACC1) or ATP citrate lyase (ACLY) protected cancer cells from hypoxia-induced apoptosis. Additionally, the loss of ACLY or ACC1 reduced levels and activities of the oncogenic transcription factor ETV4. Silencing ETV4 also protected cells from hypoxia-induced apoptosis and led to remarkably similar transcriptional responses as with silenced ACLY or ACC1, including an anti-apoptotic program. Metabolomic analysis found that while α-ketoglutarate levels decrease under hypoxia in control cells, α-ketoglutarate is paradoxically increased under hypoxia when ACC1 or ACLY are depleted. Supplementation with α-ketoglutarate rescued the hypoxia-induced apoptosis and recapitulated the decreased expression and activity of ETV4, likely via an epigenetic mechanism. Therefore, ACC1 and ACLY regulate the levels of ETV4 under hypoxia via increased α-ketoglutarate. These results reveal that the ACC1/ACLY-α-ketoglutarate-ETV4 axis is a novel means by which metabolic states regulate transcriptional output for life vs. death decisions under hypoxia. Since many lipogenic inhibitors are under investigation as cancer therapeutics, our findings suggest that the use of these inhibitors will need to be carefully considered with respect to oncogenic drivers, tumor hypoxia, progression and dormancy. More broadly, our screen provides a framework for studying additional tumor cell stress-adaption mechanisms in the future.

During the development of most solid tumors, there are characteristic physiological differences in the tumor that result from tumor cells outgrowing their local blood supply. Two of these physiological differences, or “stresses,” that occur in the tumor are low oxygen levels (hypoxia) and an accumulation of lactic acidic (lactic acidosis). Cancer cells experiencing hypoxia and lactic acidosis tend to be more resistant to chemo- and radio-therapy and metastasize more readily. Therefore, it is important to understand how tumor cells adapt to and survive these stresses. We used a large scale screening experiment in order to find which genes and proteins are involved in tumor cell adaptation and survival under hypoxia or lactic acidosis. We found that inhibiting either of two genes involved in lipid synthesis allowed tumor cells to survive hypoxia. This occurred because silencing these genes led to an increase in the metabolite α-ketoglutarate, which repressed a transcription factor that contributed to cell death under hypoxia. This research specifically advances our understanding of how tumor cells survive hypoxia and lactic acidosis and more broadly enhances our understanding of the cellular biology of solid tumors.

Mitochondrial Aldehyde Dehydrogenase 2 Regulates Revascularization in Chronic Ischemia: Potential Impact on the Development of Coronary Collateral Circulation

OBJECTIVE

Revascularization is an essential process to compensate for cardiac underperfusion and, therefore, preserves cardiac function in the face of chronic ischemic injury. Recent evidence suggested a vital role of aldehyde dehydrogenase 2 (ALDH2) in cardiac protection after ischemia. This study was designed to determine whether ALDH2 regulates chronic ischemia-induced angiogenesis and to explore the underlying mechanism involved. Moreover, the clinical impact of the ALDH2 mutant allele on the development of coronary collateral circulation (CCC) was evaluated.

APPROACH AND RESULTS

Mice limb ischemia was performed. Compared with wild-type, ALDH2 deletion significantly reduced perfusion recovery, small artery and capillary density, and increased muscle atrophy in this ischemic model. In vitro, ALDH2-knockdown reduced proliferation, migration and hypoxia triggered endothelial tube formation of endothelial cells, the effects of which were restored by ALDH2 transfection. Further examination revealed that ALDH2 regulated angiogenesis possibly through hypoxia-inducible factor-1α/vascular endothelial growth factor pathways. To further discern the role of ALDH2 deficiency in the function of bone marrow stem/progenitor cells, cross bone marrow transplantation was performed between wild-type and ALDH2-knockout mice. However, there was no significant improvement for wild-type bone marrow transplantation into knockout mice. ALDH2 genotyping was screened in 139 patients with chronic total occlusion recruited to Zhongshan Hospital (2011.10-2014.4). Patients with poor CCC (Rentrop 0-1; n=51) exhibited a higher frequency of the AA genotype than those with enriched CCC (Rentrop 2-3; n=88; 11.76% versus 1.14%; P=0 0.01). However, the AA group displayed less enriched CCC frequency in Logistic regression model when compared with the GG group (odds ratio=0.08; 95% confidence interval, 0.009-0.701; P=0 0.026). Furthermore, serum vascular endothelial growth factor level tended to be lower in patients with ALDH2 mutation.

CONCLUSIONS

This study demonstrated that ALDH2 possesses an intrinsic capacity to regulate angiogenesis via hypoxia-inducible factor-1α and vascular endothelial growth factor. Patients with ALDH2-deficient genotype displayed a higher risk of developing poor CCC. Therapeutic individualization based on ALDH2 allele distribution may thus improve the therapeutic benefit, especially in the East Asian decedents.

Sp3/REST/HDAC1/HDAC2 Complex Represses and Sp1/HIF-1/p300 Complex Activates ncx1 Gene Transcription, in Brain Ischemia and in Ischemic Brain Preconditioning, by Epigenetic Mechanism

The Na(+)-Ca(2+) exchanger 1 (NCX1) is reduced in stroke by the RE1-silencing transcription factor (REST), whereas it is increased in ischemic brain preconditioning (PC) by hypoxia-inducible factor 1 (HIF-1). Because ncx1 brain promoter (ncx1-Br) has five putative consensus sequences, named Sp1A-E, for the specificity protein (Sp) family of transcription factors (Sp1-4), we investigated the role of this family in regulating ncx1 transcription in rat cortical neurons. Here we found that Sp1 is a transcriptional activator, whereas Sp3 is a transcriptional repressor of ncx1, and that both bind ncx1-Br in a sequence-specific manner, modulating ncx1 transcription through the Sp1 sites C-E. Furthermore, by transient middle cerebral artery occlusion (tMCAO) in rats, the transcriptional repressors Sp3 and REST colocalized with the two histone-deacetylases (HDACs) HDAC1 and HDAC2 on the ncx1-Br, with a consequent hypoacetylation. Contrarily, in PC+tMCAO the transcriptional activators Sp1 and HIF-1 colocalized with histone acetyltransferase p300 on ncx1-Br with a consequent hyperacetylation. In addition, in neurons silenced with siRNA of NCX1 and subjected to oxygen and glucose deprivation (OGD) (3 h) plus reoxygenation (RX) (24 h), the neuroprotection of Class I HDAC inhibitor MS-275 was counteracted, whereas in neurons overexpressing NCX1 and subjected to ischemic preconditioning (PC+OGD/RX), the neurotoxic effect of p300 inhibitor C646 was prevented. Collectively, these results demonstrate that NCX1 expression is regulated by the Sp3/REST/HDAC1/HDAC2 complex in tMCAO and by the Sp1/HIF-1/p300 complex in PC+tMCAO and that epigenetic intervention, by modulating the acetylation of ncx1-Br, may be a strategy for the development of innovative therapeutic intervention in stroke.

Metabolic reprogramming in macrophages and dendritic cells in innate immunity

Activation of macrophages and dendritic cells (DCs) by pro-inflammatory stimuli causes them to undergo a metabolic switch towards glycolysis and away from oxidative phosphorylation (OXPHOS), similar to the Warburg effect in tumors. However, it is only recently that the mechanisms responsible for this metabolic reprogramming have been elucidated in more detail. The transcription factor hypoxia-inducible factor-1α (HIF-1α) plays an important role under conditions of both hypoxia and normoxia. The withdrawal of citrate from the tricarboxylic acid (TCA) cycle has been shown to be critical for lipid biosynthesis in both macrophages and DCs. Interference with this process actually abolishes the ability of DCs to activate T cells. Another TCA cycle intermediate, succinate, activates HIF-1α and promotes inflammatory gene expression. These new insights are providing us with a deeper understanding of the role of metabolic reprogramming in innate immunity.