Evaluation of the effects of simulated hypoxia by CoCl2 on radioresistance and change of hypoxia-inducible factors in human glioblastoma U87 tumor cell line

PURPOSE

Glioblastoma (GBM) is considered the most common and lethal type of brain tumor with a poor prognosis. GBM treatment has challenges due to its aggressive nature, which often causes treatment failure and recurrence. Hypoxia is one of the characteristics of glioblastoma tumors that contribute to radioresistance and malignant phenotypes of GBM. In this study, we aimed to determine the effects of hypoxia on the radiosensitivity of U87 GBM cells by the hypoxia-mimicking model.

METHODS

Following the treatment of cells with different concentrations of CoCl2, an MTT assay was used to evaluate the cytotoxicity of CoCl2. To understand the effects of Ionizing radiation on CoCl2-treated groups, cells were exposed to irradiation after pretreating with 100 μM CoCl2, and a clonogenic survival assay was performed to determine the radiosensitivity of U87 cells. Also, the intracellular Reactive oxygen level was measured by 2',7'-dichlorofluorescein diacetate (DCFDA) probe staining. Additionally, the expression of hypoxia-associated genes, including HIF-1α, HIF-2α, and their target genes (GLUT-1), was monitored by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Our study revealed that the cell viability of CoCl2-treated cells was decreased in a concentration-dependent manner. Also, CoCl2 did not cause any cytotoxicity on U87 cells at a concentration of 100 μM after treatment for 24 h. Colony formation assay showed that CoCl2 pretreatment induced radioresistance of tumor cells compared to non-treated cells. Also, CoCl2 can protect cells against irradiation by the clearance of ROS. Moreover, Real-time results showed that the mRNA expression of HIF-1α and GLUT-1 were significantly upregulated following hypoxia induction and/or irradiation condition. However, the level of HIF-2α mRNA did not change significantly in hypoxia or irradiation alone conditions, but it increased significantly only in hypoxia + irradiation conditions.

CONCLUSION

Taken together, our results indicated that simulating hypoxia by CoCl2 can effectively increase hypoxia-associated genes, specially HIF-1α and GLUT-1, but did not affect HIF-2α gene expression. Also, it can increase the clearance of ROS, respectively, and it leads to inducing radioresistance of U87 cells.

Tumor microenvironment diversity and plasticity in cancer multidrug resistance

Multidrug resistance (MDR) poses a significant obstacle to effective cancer treatment, and the tumor microenvironment (TME) is crucial for MDR development and reversal. The TME plays an active role in promoting MDR through several pathways. However, a promising therapeutic approach for battling MDR involves targeting specific elements within the TME. Therefore, this comprehensive review elaborates on the research developments regarding the dual role of the TME in promoting and reversing MDR in cancer. Understanding the complex role of the TME in promoting and reversing MDR is essential to developing effective cancer therapies. Utilizing the adaptability of the TME by targeting novel TME-specific factors, utilizing combination therapies, and employing innovative treatment strategies can potentially combat MDR and achieve personalized treatment outcomes for patients with cancer.

Inverse correlation between Alzheimer's disease and cancer from the perspective of hypoxia

Sporadic Alzheimer's disease and cancer remain epidemiologically inversely related, and exploring the reverse pathogenesis is important for our understanding of both. Cognitive dysfunctions in Alzheimer's disease (AD) might result from the depletion of adaptive reserves in the brain. Energy storage in the brain is limited and is dynamically regulated by neurovascular and neurometabolic coupling. The research on neurodegenerative diseases has been dominated by the neurocentric view that neuronal defects cause the diseases. However, the proposal of the 2-hit vascular hypothesis in AD led us to focus on alterations in the vasculature, especially hypoperfusion. Chronic hypoxia is a feature shared by AD and cancer. It is interesting how contradicting chronic hypoxia's effects on both cancer and AD are. In this article, we discuss the potential links between the 2 diseases' etiology, from comparable upstream circumstances to diametrically opposed downstream effects. We suggest opposing potential mechanisms, including upregulation and downregulation of hypoxia-inducible factor-1α, the Warburg and reverse-Warburg effects, lactate-mediated intracellular acidic and alkaline conditions, and VDAC1-mediated apoptosis and antiapoptosis, and search for regulators that may be identified as the crossroads between cancer and AD.

Travelling under pressure - hypoxia and shear stress in the metastatic journey

Cancer cell invasion, intravasation and survival in the bloodstream are early steps of the metastatic process, pivotal to enabling the spread of cancer to distant tissues. Circulating tumor cells (CTCs) represent a highly selected subpopulation of cancer cells that tamed these critical steps, and a better understanding of their biology and driving molecular principles may facilitate the development of novel tools to prevent metastasis. Here, we describe key research advances in this field, aiming at describing early metastasis-related processes such as collective invasion, shedding, and survival of CTCs in the bloodstream, paying particular attention to microenvironmental factors like hypoxia and mechanical stress, considered as important influencers of the metastatic journey.

Hypoxia and panvascular diseases: exploring the role of hypoxia-inducible factors in vascular smooth muscle cells under panvascular pathologies

As an emerging discipline, panvascular diseases are a set of vascular diseases with atherosclerosis as the common pathogenic hallmark, which mostly affect vital organs like the heart, brain, kidney, and limbs. As the major responser to the most common stressor in the vasculature (hypoxia)-hypoxia-inducible factors (HIFs), and the primary regulator of pressure and oxygen delivery in the vasculature-vascular smooth muscle cells (VSMCs), their own multifaceted nature and their interactions with each other are fascinating. Abnormally active VSMCs (e.g., atherosclerosis, pulmonary hypertension) or abnormally dysfunctional VSMCs (e.g., aneurysms, vascular calcification) are associated with HIFs. These widespread systemic diseases also reflect the interdisciplinary nature of panvascular medicine. Moreover, given the comparable proliferative characteristics exhibited by VSMCs and cancer cells, and the delicate equilibrium between angiogenesis and cancer progression, there is a pressing need for more accurate modulation targets or combination approaches to bolster the effectiveness of HIF targeting therapies. Based on the aforementioned content, this review primarily focused on the significance of integrating the overall and local perspectives, as well as temporal and spatial balance, in the context of the HIF signaling pathway in VSMC-related panvascular diseases. Furthermore, the review discussed the implications of HIF-targeting drugs on panvascular disorders, while considering the trade-offs involved.

Hypoxia-inducible factors and essential hypertension: narrative review of experimental and clinical data

Hypoxia-inducible factor (HIFs) is a new class of drug developed for the management of anemia in chronic kidney disease (CKD) patients. HIFs increase the production of erythropoietin in the kidney and liver, enhance the absorption and utilization of iron, and stimulate the maturation and proliferation of erythroid progenitor cells. Besides, HIFs regulate many physiologic processes by orchestrating the transcription of hundreds of genes. Essential hypertension (HT) is an epidemic worldwide. HIFs play a role in many biological processes involved in the regulation of blood pressure (BP). In the current review, we summarize pre-clinical and clinical studies investigating the relationship between HIFs and BP regulation in patients with CKD, conflicting issues, and discuss future potential strategies.

The Intriguing Role of Hypoxia-Inducible Factor in Myocardial Ischemia and Reperfusion: A Comprehensive Review

Hypoxia-inducible factors (HIFs) play a crucial role in cellular responses to low oxygen levels during myocardial ischemia and reperfusion injury. HIF stabilizers, originally developed for treating renal anemia, may offer cardiac protection in this context. This narrative review examines the molecular mechanisms governing HIF activation and function, as well as the pathways involved in cell protection. Furthermore, we analyze the distinct cellular roles of HIFs in myocardial ischemia and reperfusion. We also explore potential therapies targeting HIFs, emphasizing their possible benefits and limitations. Finally, we discuss the challenges and opportunities in this research area, underscoring the need for continued investigation to fully realize the therapeutic potential of HIF modulation in managing this complex condition.

Spontaneous spheroids from alveolar bone-derived mesenchymal stromal cells maintain pluripotency of stem cells by regulating hypoxia-inducible factors

BACKGROUND

Spontaneous spheroid culture is a novel three-dimensional (3D) culture strategy for the rapid and efficient selection of progenitor cells. The objectives of this study are to investigate the pluripotency and differentiation capability of spontaneous spheroids from alveolar bone-derived mesenchymal stromal cells (AB-MSCs); compare the advantages of spontaneous spheroids to those of mechanical spheroids; and explore the mechanisms of stemness enhancement during spheroid formation from two-dimensional (2D) cultured cells.

METHODS

AB-MSCs were isolated from the alveolar bones of C57BL/6 J mice. Spontaneous spheroids formed in low-adherence specific culture plates. The stemness, proliferation, and multi-differentiation capacities of spheroids and monolayer cultures were investigated by reverse transcription quantitative polymerase chain reaction (RT-qPCR), immunofluorescence, alkaline phosphatase (ALP) activity, and oil-red O staining. The pluripotency difference between the spontaneous and mechanical spheroids was analyzed using RT-qPCR. Hypoxia-inducible factor (HIFs) inhibition experiments were performed to explore the mechanisms of stemness maintenance in AB-MSC spheroids.

RESULTS

AB-MSCs successfully formed spontaneous spheroids after 24 h. AB-MSC spheroids were positive for MSC markers and pluripotency markers (Oct4, KLF4, Sox2, and cMyc). Spheroids showed higher Ki67 expression and lower Caspase3 expression at 24 h. Under the corresponding conditions, the spheroids were successfully differentiated into osteogenic and adipogenic lineages. AB-MSC spheroids can induce neural-like cells after neurogenic differentiation. Higher expression of osteogenic markers, adipogenic markers, and neurogenic markers (NF-M, NeuN, and GFAP) was found in spheroids than in the monolayer. Spontaneous spheroids exhibited higher stemness than mechanical spheroids did. HIF-1α and HIF-2α were remarkably upregulated in spheroids. After HIF-1/2α-specific inhibition, spheroid formation was significantly reduced. Moreover, the expression of the pluripotency genes was suppressed.

CONCLUSIONS

Spontaneous spheroids from AB-MSCs enhance stemness and pluripotency. HIF-1/2α plays an important role in the stemness regulation of spheroids. AB-MSC spheroids exhibit excellent multi-differentiation capability, which may be a potent therapy for craniomaxillofacial tissue regeneration.

The role of hypoxia-inducible factors in breast cancer stem cell specification

Breast tumor is heterogeneous cancer with high morbidity and mortality rates, particularly in developing countries. Despite new efforts to reduce the breast cancer implications, the number of newly diagnosed cases is increasing worldwide. It is believed that cancer stem cells (CSCs) are responsible for the implication of cancers including breast cancer. Although CSCs compose a small population in tumor bulks, they play a crucial role in tumor initiation, progression, metastasis, and chemotherapeutic resistance. These events are mediated by the hypoxia-inducible factor (HIF) pathway which regulates the transcription of genes involved in CSC maintenance and tumorigenesis. In this review, we discussed the mechanisms by which hypoxia- or chemotherapy-induced HIFs promote breast CSC specification.

Tumor hypoxia: From basic knowledge to therapeutic implications

Diminished oxygen availability, termed hypoxia, within solid tumors is one of the most common characteristics of cancer. Hypoxia shapes the landscape of the tumor microenvironment (TME) into a pro-tumorigenic and pro-metastatic niche through arrays of pathological alterations such as abnormal vasculature, altered metabolism, immune-suppressive phenotype, etc. In addition, emerging evidence suggests that limited efficacy or the development of resistance towards antitumor therapy may be largely due to the hypoxic TME. This review will focus on summarizing the knowledge about the molecular machinery that mediates the hypoxic cellular responses and adaptations, as well as highlighting the effects and consequences of hypoxia, especially for angiogenesis regulation, cellular metabolism alteration, and immunosuppressive response within the TME. We also outline the current advances in novel therapeutic implications through targeting hypoxia in TME. A deep understanding of the basics and the role of hypoxia in the tumor will help develop better therapeutic avenues in cancer treatment.

Hypoxia-Inducible Factors-Based Single Nucleotide Polymorphism in Breast Cancer with More Cancer Susceptibility

Hypoxia-inducible factors (HIFs) are a collection of transcriptional factors that engage in the regulation of oxygen homeostasis. They are hypoxia-responsive stress factors whose expression is linked to tumor growth and angiogenesis. HIF is a crucial player in the progression of breast cancer. Patients with high levels of hypoxia-inducible HIFs in their primary tumor biopsies had a higher chance of metastasis, the leading cause of breast cancer-related death. HIF polymorphisms have been shown in several epidemiological studies to influence breast cancer susceptibility. In the oxygendependent degradation domain, several short nucleotide polymorphisms (SNPs) of the HIF gene have been connected with higher HIF activity. To find SNP that make up the genetic diversity that underpins the phenotypic difference found between individuals in their susceptibility to cancer and the course of their disease, researchers used a variety of potential pathway-based approaches.

Conditioned media-integrated microneedles for hair regeneration through perifollicular angiogenesis

Androgenetic alopecia (AGA), the most prevalent type of hair loss in clinic, is induced partly by insufficient perifollicular vascularization. Here we designed a dissolvable microneedles (MNs) patch that was loaded with conditioned media (CM) derived from hypoxia-pretreated mesenchymal stem cells, which contained elevated HIF-1α. The CM-integrated MNs patch (designated as CM-MNs) can puncture the stratum corneum and deliver the pro-angiogenic factors directly into skin in a one-step and minimally invasive manner. Meanwhile, the administration of CM-MNs induced a certain mechanical stimulation on the skin, which can also promote neovascularization. With the combined effects of the pro-angiogenic factors in CM and the mechanical stimulation induced by MNs, CM-MNs successfully boosted perifollicular vascularization, and activated hair follicle stem cells, thereby inducing notably faster hair regeneration at a lower administration frequency on AGA mouse model compared with minoxidil. Furthermore, we proved that the inhibition of perifollicular angiogenesis restrained the awakening of hair follicle stem cells, elucidating the tight correlation between perifollicular angiogenesis and the activation of hair follicle stem cells. The innovative integration of CM and MNs holds great promise for clinical AGA treatment and indicates that boosting angiogenesis around hair follicles is an effective strategy against AGA.

Hypoxia-inducible factors: master regulators of hypoxic tumor immune escape

Hypoxia, a common feature of the tumor microenvironment in various types of cancers, weakens cytotoxic T cell function and causes recruitment of regulatory T cells, thereby reducing tumoral immunogenicity. Studies have demonstrated that hypoxia and hypoxia-inducible factors (HIFs) 1 and 2 alpha (HIF1A and HIF2A) are involved in tumor immune escape. Under hypoxia, activation of HIF1A induces a series of signaling events, including through programmed death receptor-1/programmed death ligand-1. Moreover, hypoxia triggers shedding of complex class I chain-associated molecules through nitric oxide signaling impairment to disrupt immune surveillance by natural killer cells. The HIF-1-galactose-3-O-sulfotransferase 1-sulfatide axis enhances tumor immune escape via increased tumor cell-platelet binding. HIF2A upregulates stem cell factor expression to recruit tumor-infiltrating mast cells and increase levels of cytokines interleukin-10 and transforming growth factor-β, resulting in an immunosuppressive tumor microenvironment. Additionally, HIF1A upregulates expression of tumor-associated long noncoding RNAs and suppresses immune cell function, enabling tumor immune escape. Overall, elucidating the underlying mechanisms by which HIFs promote evasion of tumor immune surveillance will allow for targeting HIF in tumor treatment. This review discusses the current knowledge of how hypoxia and HIFs facilitate tumor immune escape, with evidence to date implicating HIF1A as a molecular target in such immune escape. This review provides further insight into the mechanism of tumor immune escape, and strategies for tumor immunotherapy are suggested.

Renoprotective Role of Hypoxia-Inducible Factors and the Mechanism

BACKGROUND

The kidney requires abundant blood supply, and oxygen is transmitted by diffusion through blood vessels. Most physiological metabolism of the kidney depends on oxygen, so it is very sensitive to oxygen. An increasing pool of evidence suggests that hypoxia is involved in almost all acute and chronic kidney diseases (CKDs). Vascular damage, tubular injury, and fibrosis are the main pathologies associated during hypoxia. Hypoxia-inducible factors (HIFs) are the main mediators during hypoxia, but their functions remain controversial. This article reviewed recent studies and described its mechanisms on renoprotection.

SUMMARY

HIF is degraded rapidly during under normal oxygen. But under hypoxia, HIFs accumulate and many target genes are regulated by HIFs. Homeostasis during injury is maintained through these genes. Pretreatment of HIF can protect the kidney from acute hypoxia and can improve repair, but HIF's role in CKD and in renal tumor is still controversial. Due to its mechanism in kidney disease, many drugs toward HIFs are widely researched, even some of which have been used in clinical or in clinical research.

KEY MESSAGES

In this review, we described the known physiological mechanisms, target genes, and renal protective roles of HIFs, and we discussed several drugs that are researched due to such renal protective roles.

Adaptive cardiorespiratory changes to chronic continuous and intermittent hypoxia

This chapter reviews cardiorespiratory adaptations to chronic hypoxia (CH) experienced at high altitude and cardiorespiratory pathologies elicited by chronic intermittent hypoxia (CIH) occurring with obstructive sleep apnea (OSA). Short-term CH increases breathing (ventilatory acclimatization to hypoxia) and blood pressure (BP) through carotid body (CB) chemo reflex. Hyperplasia of glomus cells, alterations in ion channels, and recruitment of additional excitatory molecules are implicated in the heightened CB chemo reflex by CH. Transcriptional activation of hypoxia-inducible factors (HIF-1 and 2) is a major molecular mechanism underlying respiratory adaptations to short-term CH. High-altitude natives experiencing long-term CH exhibit blunted hypoxic ventilatory response (HVR) and reduced BP due to desensitization of CB response to hypoxia and impaired processing of CB sensory information at the central nervous system. Ventilatory changes evoked by long-term CH are not readily reversed after return to sea level. OSA patients and rodents subjected to CIH exhibit heightened CB chemo reflex, increased hypoxic ventilatory response, and hypertension. Increased generation of reactive oxygen species (ROS) is a major cellular mechanism underlying CIH-induced enhanced CB chemo reflex and the ensuing cardiorespiratory pathologies. ROS generation by CIH is mediated by nontranscriptional, disrupted HIF-1 and HIF-2-dependent transcriptions as well as epigenetic mechanisms.

Role of Endothelial Prolyl-4-Hydroxylase Domain Protein/Hypoxia-Inducible Factor Axis in Acute Kidney Injury

Ischemia reperfusion injury (IRI) results from a cessation or restriction of blood supply to an organ followed by reestablishment of perfusion and reoxygenation. In the kidney, IRI due to transplantation, cardiac surgery with cardiopulmonary bypass, and other major vascular surgeries contributes to acute kidney injury (AKI), a clinical condition associated with significant morbidity and mortality in hospitalized patients. In the postischemic kidney, endothelial damage promotes inflammatory responses and leads to persistent hypoxia of the renal tubular epithelium. Like other cell types, endothelial cells respond to low oxygen tension by multiple hypoxic signaling mechanisms. Key mediators of adaptation to hypoxia are hypoxia-inducible factors (HIF)-1 and -2, transcription factors whose activity is negatively regulated by prolyl-hydroxylase domain proteins 1 to 3 (PHD1 to PHD3). The PHD/HIF axis controls several processes determining injury outcome, including ATP generation, cell survival, proliferation, and angiogenesis. Here, we discuss recent advances in our understanding of the endothelial-derived PHD/HIF signaling and its effects on postischemic AKI.

Prolonged hypoxia switched on cancer stem cell-like plasticity in HepG2 tumourspheres cultured in serum-free media

Tumour hypoxia drives resistance and aggressiveness, and in large part, contributes to treatment failure thereby causing cancer-related deaths. The rapid and uncontrolled tumour growth develops not only a hypoxic niche but also a nutrient-deprived condition due to insufficient blood supply; together, these create a stressful tumour niche, further promoting higher aggressiveness and resistance features of cancer. However, how cellular responses in the prolonged stress is associated with cancer stem cells (CSCs), which is linked to these features, remains unclear. Here, we established HepG2 tumoursphere culture in a hypoxic and serum-free condition that recapitulated differential responses to prolonged tumour growth pressures, evident by their progressive changes in the morphology of tumoursphere formation over a course of 15-day culture. HepG2 tumourspheres formed larger sphere sizes of > 200 μm in hypoxic conditions, concomitant with higher cell yield and upregulation of PCNA marker at day 7, corresponding with higher self-renewal capacity when cultured in SFM compared to SM. Notably, prolonged growth of HepG2 tumourspheres for 15 days under hypoxic and SFM condition increased their sphere counts, yet significantly reduced their cell yield along with downregulation of PCNA expression. Gene expression analysis showed that HepG2 tumourspheres on day 15 exhibited enhanced expression of markers of quiescence, stemness, EMT, and chemoresistance. Interestingly, analysis of HIF1α and HIF2α and their target gene expression indicated complementary HIF expression with preferential upregulation of HIF2α was observed in HepG2 tumourspheres in prolonged hypoxic and serum-free conditions, suggesting HIF2α-dependency and plausibility of the HIF1α-HIF2α switch that govern their survival by promoting CSC-like programmes. Altogether, these findings suggest the implication of prolonged hypoxia and nutrient deprivation stress in promoting CSC-like programmes in cancer cells recapitulating their plasticity, hence having opened many research directions that enable development of effective targeting of CSCs and precision medicine for treating cancer.

Hypoxia boosts aerobic glycolysis of carcinoma：a complex process for tumor development

Hypoxia, a common feature in malignant tumors, is mainly caused by insufficient oxygen supply. Hypoxia is closely related to cancer development, affecting cancer invasion and metastasis, energy metabolism and other pathological processes, and is not conducive to cancer treatment and prognosis. Tumor cells exacerbate metabolic abnormalities to adapt to the hypoxic microenvironment, especially to enhance aerobic glycolysis. Glycolysis leads to an acidic microenvironment in cancer tissues, enhancing cancer metastasis, deterioration and drug resistance. Therefore, hypoxia is a therapeutic target that cannot be ignored in cancer treatment. The adaptation of tumor cells to hypoxia is mainly regulated by hypoxia inducible factors (HIFs), and the stability of HIFs is improved under hypoxic conditions. HIFs can promote the glycolysis of tumors by regulating glycolytic enzymes, transporters, and participates in regulating the TCA (tricarboxylic acid) cycle. In addition, HIFs indirectly affect glycolysis through its interaction with non-coding RNAs. Therefore, targeting hypoxia and HIFs are important tumor therapies.

Altered physiological response and gill histology in black rockfish, Sebastes schlegelii, during progressive hypoxia and reoxygenation

Hypoxia has gradually become common in aquatic ecosystems and imposes a significant challenge for fish farming. The loss of equilibrium (LOE), 50% lethal time (LT50), plasma cortisol, glucose, red blood cells (RBC), hemoglobin (Hb), gill histological alteration, and related parameters (lamellar length [SLL] and width [SLW], interlamellar distance [ID], basal epithelial thickness [BET], lamellar surface area [LA], and gill surface area [GSA]); respiratory rate; the proportion of the secondary lamellae available for gas exchange (PAGE); and hypoxia-inducible factor (hif-1α, hif-2α) mRNA expression were determined during progressive hypoxia and reoxygenation (R-0, R-12, R-24 h) to illustrate the underlying physiological response mechanisms in black rockfish Sebastes schlegelii. Results showed that the DO concentration significantly decreased during progressive hypoxia, while DO at LOE and LT50 were 2.42 ± 0.10 mg L^-1 and 1.67 ± 0.38 mg L^-1, respectively. Cortisol and glucose were significantly increased at LOE and LT50, with the highest levels observed at LT50, and then gradually recovered to normal within reoxygenation 24 h. RBC number and Hb results were like those of glucose. Hypoxia stress resulted in lamellar clubbing, hypertrophy, and hyperplasia. Respiratory frequency significantly increased at LOE and decreased at LT50. Lamellar perimeters, SLL, ID, LA, GSA, and PAGE, significantly increased at LOE and LT50, with the highest values observed at LT50. However, SLW and BET significantly decreased at LOE, LT50, and R-0. These parameters recovered to nearly normal levels at R-24 h. hif-1α mRNAs in gill and liver were significantly upregulated at LOE and LT50, and recovery to normal after reoxygenation 24 h. hif-2α mRNAs in gill was similar to that of hif-1α, whereas hepatic hif-2α mRNAs remained unchanged during hypoxia-reoxygenation. These results indicated that progressive hypoxia stress elevated RBC number, Hb, cortisol, and glucose levels, induced the alteration of gill morphology, increased LA and GSA, stimulated respiratory frequency and PAGE, and upregulated the transcription of hif-1α and hif-2α in gill and liver. Reoxygenation treatment for 24 h alleviated the stress mentioned above effects. These findings expand current knowledge on hypoxia tolerance in black rockfish Sebastes schlegelii.

2-Methoxyestradiol synergizes with Erlotinib to suppress hepatocellular carcinoma by disrupting the PLAGL2-EGFR-HIF-1/2α signaling loop

Erlotinib, an EGFR tyrosine kinase inhibitor has been introduced into cancer chemotherapy. However, the therapeutic effects of erlotinib in hepatocellular carcinoma (HCC) remain vaguely understood. Our previous study found that a hypoxia-mediated PLAGL2-EGFR-HIF-1/2α signaling loop in HCC decreased response to erlotinib. The current study has demonstrated that the combination of erlotinib and 2ME2 exerted synergistic antitumor effects against HCC. Further investigation showed that erlotinib increased the expression level of EGFR, HIF-2α, and PLAGL2, which contributes to the insensitivity of hypoxic HCC cells to erlotinib. The simultaneous exposure to 2ME2 effectively inhibited the expression level of EGFR, HIF-2α, and PLAGL2 that was induced by erlotinib. This contributes to the synergistic effect of the two therapeutic agents. Furthermore, the combination of erlotinib and 2ME2 induced apoptosis and inhibited the stemness of hypoxic HCC cells. Our findings potentially explain the mechanism of HCC insensitivity to erlotinib and provide a new strategy of combining EGFR and HIF1/2α inhibitors for HCC treatment.

Altered Behavioral Performance in the Neuron-Specific HIF-1- and HIF-2-Deficient Mice Following Chronic Hypoxic Exposure

Hypoxia-inducible factors (HIFs) are transcriptional regulators that mediate in mice for HIF-1 and HIF-2. The objective of this study was to investigate the effect of neuronal deletion of HIF-1 and HIF-2 in hypoxic adaptation by using the neuron-specific knockout (KO) mice. The floxed control and KO mice were used. Hypoxic mice were kept in a hypobaric chamber at a pressure of 300 torr (0.4 ATM, which was equivalent to 8% oxygen under normobaric condition) for 3 weeks. The littermate, normoxic control mice were housed in the same room next to the chamber to match ambient conditions. Body weights were monitored throughout the 3-week course. Cognitive function was measured using a Y-maze test; motor functions were measured using the rotarod test and the grip strength test. The hematocrit increased significantly at the end of 3-week hypoxic exposure in both control and KO mice. In the Y-maze test, the alternation rate (indicative of sustained cognition) trended lower in the KO mice compared to the controls following hypoxia (%, 51.3 ± 13.1, n = 6 vs. 63.2 ± 12.0, n = 8). In the rotarod test, the latency (seconds) in the KO mice was significantly lower compared to the controls (50.4 ± 5.7 vs. 77.1 ± 5.0, n = 3 each before hypoxia and 66.4 ± 3.4, n = 6 vs. 98.1 ± 15.4 after hypoxia, n = 3). The grip strength in the KO mice was similar compared to the control mice before hypoxia, but the strength of KO mice trended higher after hypoxic exposure. Our data suggest that deficiency of neuronal HIF-1 and HIF-2 may result in changes in behavioral performance and other adaptative responses to hypoxia.

In vitro temporal HIF-mediated deposition of osteochondrogenic matrix governed by hypoxia and osteogenic factors synergy

Musculoskeletal interfaces are naturally hypoxic. An understanding of key interactions occurring between different cell populations and their environment is critical for native tissue recapitulation. Here, an enthesis coculture model (preosteoblasts and tendon cells) was used to understand the influence of hypoxia (5% O₂ ) and osteogenic medium (OM) supplementation in cells' phenotype modulation. In single cultures, preosteoblasts were found to undergo osteogenic impairment, while tendon cells underwent a maturation process through extracellular matrix (ECM) rescue. When in co-culture, hypoxia and osteoinduction promoted a temporal chondro/osteogenic pathway activation, as observed by an early deposition of cartilaginous ECM associated with HIF1A stabilization and RUNX2 activation, and later hypertrophic differentiation resulting from HIF2A translocation and SOX9 activation. Moreover, the presence of OM under hypoxia was shown to influence the extracellular ROS/HIF1A interplay. Overall, this study revealed a link between biochemical factors and cell-cell crosstalk, providing a molecular framework for hypoxic control and modulation of cells' fate toward enthesis-like phenotypes.

Effect of sodium (S)-2-hydroxyglutarate in male, and succinic acid in female Wistar rats against renal ischemia-reperfusion injury, suggesting a role of the HIF-1 pathway

Background

Ischemia–reperfusion (IR) injury is the main cause of delayed graft function in solid organ transplantation. Hypoxia-inducible factors (HIFs) control the expression of genes related to preconditioning against IR injury. During normoxia, HIF-α subunits are marked for degradation by the egg-laying defective nine homolog (EGLN) family of prolyl-4-hydroxylases. The inhibition of EGLN stabilizes HIFs and protects against IR injury. The aim of this study was to determine whether the EGLN inhibitors sodium (S)-2-hydroxyglutarate [(S)-2HG] and succinic acid (SA) have a nephroprotective effect against renal IR injury in Wistar rats.

Methods

(S)-2HG was synthesized in a 22.96% yield from commercially available L-glutamic acid in a two-step methodology (diazotization/alkaline hydrolysis), and its structure was confirmed by nuclear magnetic resonance and polarimetry. SA was acquired commercially. (S)-2HG and SA were independently evaluated in male and female Wistar rats respectively after renal IR injury. Rats were divided into the following groups: sham (SH), nontoxicity [(S)-2HG: 12.5 or 25 mg/kg; SA: 12.5, 25, or 50 mg/kg], IR, and compound+IR [(S)-2HG: 12.5 or 25 mg/kg; SA: 12.5, 25, or 50 mg/kg]; independent SH and IR groups were used for each assessed compound. Markers of kidney injury (BUN, creatinine, glucose, and uric acid) and liver function (ALT, AST, ALP, LDH, serum proteins, and albumin), proinflammatory cytokines (IL-1β, IL-6, and TNF-α), oxidative stress biomarkers (malondialdehyde and superoxide dismutase), and histological parameters (tubular necrosis, acidophilic casts, and vascular congestion) were assessed. Tissue HIF-1α was measured by ELISA and Western blot, and the expression of Hmox1 was assessed by RT-qPCR.

Results

(S)-2HG had a dose-dependent nephroprotective effect, as evidenced by a significant reduction in the changes in the BUN, creatinine, ALP, AST, and LDH levels compared with the IR group. Tissue HIF-1α was only increased in the IR group compared to SH; however, (S)-2HG caused a significant increase in the expression of Hmox1, suggesting an early accumulation of HIF-1α in the (S)-2HG-treated groups. There were no significant effects on the other biomarkers. SA did not show a nephroprotective effect; the only changes were a decrease in creatinine level at 12.5 mg/kg and increased IR injury at 50 mg/kg. There were no effects on the other biochemical, proinflammatory, or oxidative stress biomarkers.

Conclusion

None of the compounds were hepatotoxic at the tested doses. (S)-2HG showed a dose-dependent nephroprotective effect at the evaluated doses, which involved an increase in the expression of Hmox1, suggesting stabilization of HIF-1α. SA did not show a nephroprotective effect but tended to increase IR injury when given at high doses.

Liver fibrogenesis: un update on established and emerging basic concepts

Liver fibrogenesis is defined as a dynamic and highly integrated process occurring during chronic injury to liver parenchyma that can result in excess deposition of extracellular matrix (ECM) components (i.e., liver fibrosis). Liver fibrogenesis, together with chronic inflammatory response, is then primarily involved in the progression of chronic liver diseases (CLD) irrespective of the specific etiology. In the present review we will first offer a synthetic and updated overview of major basic concepts in relation to the role of myofibroblasts (MFs), macrophages and other hepatic cell populations involved in CLD to then offer an overview of established and emerging issues and mechanisms that have been proposed to favor and/or promote CLD progression. A special focus will be dedicated to selected issues that include emerging features in the field of cholangiopathies, the emerging role of genetic and epigenetic factors as well as of hypoxia, hypoxia-inducible factors (HIFs) and related mediators.

Hypoxia: Turning vessels into vassals of cancer immunotolerance

Hypoxia is a universal feature of solid cancers caused by a mismatch between cellular oxygen supply and consumption. To meet the increased demand for oxygen, hypoxic cancer cells (CCs) induce a multifaceted process known as angiogenesis, wherein new vessels are formed by the sprouting of pre-existing ones. In addition to providing oxygen for growth and an exit route for dissemination, angiogenic vessels and factors are co-opted by CCs to enable the generation of an immunotolerant, hypoxic tumor microenvironment, leading to therapeutic failure and mortality. In this review, we discuss how hypoxia-inducible factors (HIFs), the mechanistic target of rapamycin (mTOR), and the unfolded protein response (UPR) control angiogenic factors serving both vascular and immunomodulatory functions in the tumor microenvironment. Possible therapeutic strategies, wherein targeting oxygen sensing might enhance anti-angiogenic and immunologically-mediated anti-cancer responses, are suggested.

New role for ceramide in hypoxia and insulin resistance

Ceramides are significant metabolic products of sphingolipids in lipid metabolism and are associated with insulin resistance and hepatic steatosis. In chronic inflammatory pathological conditions, hypoxia occurs, the metabolism of ceramide changes, and insulin resistance arises. Hypoxia-inducible factors (HIFs) are a family of transcription factors activated by hypoxia. In hypoxic adipocytes, HIF-1α upregulates pla2g16 (a novel HIF-1α target gene) gene expression to activate the NLRP3 inflammasome pathway and stimulate insulin resistance, and adipocyte-specific Hif1a knockout can ameliorate homocysteine-induced insulin resistance in mice. The study on the HIF-2α—NEU3—ceramide pathway also reveals the role of ceramide in hypoxia and insulin resistance in obese mice. Under obesity-induced intestinal hypoxia, HIF-2α increases the production of ceramide by promoting the expression of the gene Neu3 encoding sialidase 3, which is a key enzyme in ceramide synthesis, resulting in insulin resistance in high-fat diet-induced obese mice. Moreover, genetic and pathophysiologic inhibition of the HIF-2α—NEU3—ceramide pathway can alleviate insulin resistance, suggesting that these could be potential drug targets for the treatment of metabolic diseases. Herein, the effects of hypoxia and ceramide, especially in the intestine, on metabolic diseases are summarized.

Critical examination of mechanisms underlying the reduction in heart failure events with SGLT2 inhibitors: identification of a molecular link between their actions to stimulate erythrocytosis and to alleviate cellular stress

Sodium-glucose co-transporter 2 (SGLT2) inhibitors reduce the risk of serious heart failure events, even though SGLT2 is not expressed in the myocardium. This cardioprotective benefit is not related to an effect of these drugs to lower blood glucose, promote ketone body utilization or enhance natriuresis, but it is linked statistically with their action to increase haematocrit. SGLT2 inhibitors increase both erythropoietin and erythropoiesis, but the increase in red blood cell mass does not directly prevent heart failure events. Instead, erythrocytosis is a biomarker of a state of hypoxia mimicry, which is induced by SGLT2 inhibitors in manner akin to cobalt chloride. The primary mediators of the cellular response to states of energy depletion are sirtuin-1 and hypoxia-inducible factors (HIF-1α/HIF-2α). These master regulators promote the cellular adaptation to states of nutrient and oxygen deprivation, promoting mitochondrial capacity and minimizing the generation of oxidative stress. Activation of sirtuin-1 and HIF-1α/HIF-2α also stimulates autophagy, a lysosome-mediated degradative pathway that maintains cellular homoeostasis by removing dangerous constituents (particularly unhealthy mitochondria and peroxisomes), which are a major source of oxidative stress and cardiomyocyte dysfunction and demise. SGLT2 inhibitors can activate SIRT-1 and stimulate autophagy in the heart, and thereby, favourably influence the course of cardiomyopathy. Therefore, the linkage between erythrocytosis and the reduction in heart failure events with SGLT2 inhibitors may be related to a shared underlying molecular mechanism that is triggered by the action of these drugs to induce a perceived state of oxygen and nutrient deprivation.

Hypoxia: a barricade to conquer the pancreatic cancer

Pancreatic cancer (PC) remains one of the most extremely lethal malignancies worldwide due to late diagnosis and early metastasis, with a 1-year overall survival rate of approximately 20%. The hypoxic microenvironment, induced by intratumoral hypoxia, promotes tumor invasion and progression, leading to chemotherapy or radiotherapy resistance and eventual mortality after treatment of PC. However, the role of the hypoxic microenvironment in PC is complicated and requires further investigation. In this article, we review recent advances regarding the regulation of malignant behaviors in PC, which provide insight into the potential of hypoxic microenvironment activation therapy for the therapeutic agents.

The role of hypoxia-inducible factors in neovascular age-related macular degeneration: a gene therapy perspective

Understanding the mechanisms that underlie age-related macular degeneration (AMD) has led to the identification of key molecules. Hypoxia-inducible transcription factors (HIFs) have been associated with choroidal neovascularization and the progression of AMD into the neovascular clinical phenotype (nAMD). HIFs regulate the expression of multiple growth factors and cytokines involved in angiogenesis and inflammation, hallmarks of nAMD. This knowledge has propelled the development of a new group of therapeutic strategies focused on gene therapy. The present review provides an update on current gene therapies in ocular angiogenesis, particularly nAMD, from both basic and clinical perspectives.

Hypoxia and HIF activation as a possible link between sepsis and thrombosis

Risk factors for thrombosis include hypoxia and sepsis, but the mechanisms that control sepsis-induced thrombus formation are incompletely understood. A recent article published in Thrombosis Journal: (i) reviews the role of endothelial cells in the pathogenesis of sepsis-associated microthrombosis; (ii) describes a novel ‘two-path unifying theory’ of hemostatic discorders; and (iii) refers to hypoxia as a consequence of microthrombus formation in sepsis patients. The current article adds to this review by describing how sepsis and thrombus formation could be linked through hypoxia and activation of hypoxia-inducible transcription factors (HIFs). In other words, hypoxia and HIF activation may be a cause as well as a consequence of thrombosis in sepsis patients. While microthrombosis reduces microvascular blood flow causing local hypoxia and tissue ischemia, sepsis-induced increases in HIF1 activation could conversely increase the expression of coagulant factors and integrins that promote thrombus formation, and stimulate the formation of pro-thrombotic neutrophil extracellular traps. A better understanding of the role of cell-specific HIFs in thrombus formation could lead to the development of novel prophylactic therapies for individuals at risk of thrombosis.

Caffeine is associated with improved alveolarization and angiogenesis in male mice following hyperoxia induced lung injury

Background

Caffeine therapy for apnea of prematurity reduces the incidence of bronchopulmonary dysplasia (BPD) in premature neonates. Several mechanisms, including improvement in pulmonary mechanics underly beneficial effects of caffeine in BPD. As vascular development promotes alveologenesis, we hypothesized that caffeine might enhance angiogenesis in the lung, promoting lung growth, thereby attenuating BPD.

Methods

C57Bl/6 mice litters were randomized within 12 h of birth to room air (RA) or 95%O₂ to receive caffeine (20 mg/kg/day) or placebo for 4 days and recovered in RA for 12wks. The lung mRNA and protein expression for hypoxia-inducible factors (HIF) and angiogenic genes performed on day 5. Lung morphometry and vascular remodeling assessed on inflation fixed lungs at 12wks.

Results

Caffeine and hyperoxia in itself upregulate HIF-2α and vascular endothelial growth factor gene expression. Protein expression of HIF-2α and VEGFR1 were higher in hyperoxia/caffeine and angiopoietin-1 lower in hyperoxia. An increase in radial alveolar count, secondary septal count, and septal length with a decrease in mean linear intercept indicate an amelioration of hyperoxic lung injury by caffeine. An increase in vessel surface area and a significant reduction in smooth muscle thickness of the pulmonary arterioles may suggest a beneficial effect of caffeine on vascular remodeling in hyperoxia, especially in male mice.

Conclusions

Postnatal caffeine by modulating angiogenic gene expression early in lung development may restore the pulmonary microvasculature and alveolarization in adult lung.

Involvement of A3 Adenosine Receptor in Neuroblastoma Progression via Modulation of the Hypoxic/Angiogenic Pathway

Neuroblastoma (NB) is the most common extracranial solid tumor of childhood. The clinical course may range from spontaneous regression towards ganglioneuroblastoma/ganglioneuroma or maturation to a very aggressive form characterized by an extensive hypoxic area. In solid tumors, extracellular microenvironment hypoxia induces the transcription of hypoxia-inducible factors (HIFs) leading to synthesis of pro-angiogenic factor, VEGF; also, it increases extracellular adenosine production from ATP breakdown. To date, the role of this nucleoside in the hypoxic/angiogenic pathway characterizing the core of cancer mass has not been investigated yet. Therefore, the aim of the present study was to analyze the adenosine effect on modulation of the HIF-1α/2α/VEGF pathway mediated through A₃ AR binding. To this end, we have used a selective A₃ AR agonist IB-MECA or antagonist VUF 5574 in an in vitro model of malignant undifferentiated and all-trans retinoic acid (RA)-differentiated SH-SY5Y cells, representing the benign form of NB. Our results have shown that specific A₃ AR stimulation induces HIF and VEGF expression through the activation of mitogen-activated protein kinase/Erk kinase signaling cascade. In conclusion, the data suggest that A₃ AR may represent a marker of NB malignancy as well as a drug target for treatment of this solid tumor. Graphical Abstract.

HER2 regulates HIF-2α and drives an increased hypoxic response in breast cancer

Background

Tumour hypoxia is a driver of breast cancer progression associated with worse prognosis and more aggressive disease. The cellular response to hypoxia is mediated by the hypoxia-inducible transcription factors HIF-1 and HIF-2, whose transcriptional activity is canonically regulated through their oxygen-labile HIF-α subunits. These are constitutively degraded in the presence of oxygen; however, HIF-1α can be stabilised, even at high oxygen concentrations, through the activation of HER receptor signalling. Despite this, there is still limited understanding on how HER receptor signalling interacts with HIF activity to contribute to breast cancer progression in the context of tumour hypoxia.

Methods

2D and 3D cell line models were used alongside microarray gene expression analysis and meta-analysis of publicly available gene expression datasets to assess the impact of HER2 overexpression on HIF-1α/HIF-2α regulation and to compare the global transcriptomic response to acute and chronic hypoxia in an isogenic cell line model of HER2 overexpression.

Results

HER2 overexpression in MCF7 cells leads to an increase in HIF-2α but not HIF-1α expression in normoxia and an increased upregulation of HIF-2α in hypoxia. Global gene expression analysis showed that HER2 overexpression in these cells promotes an exaggerated transcriptional response to both short-term and long-term hypoxia, with increased expression of numerous hypoxia response genes. HIF-2α expression is frequently higher in HER2-overexpressing tumours and is associated with worse disease-specific survival in HER2-positive breast cancer patients. HER2-overexpressing cell lines demonstrate an increased sensitivity to targeted HIF-2α inhibition through either siRNA or the use of a small molecule inhibitor of HIF-2α translation.

Conclusions

This study suggests an important interplay between HER2 expression and HIF-2α in breast cancer and highlights the potential for HER2 to drive the expression of numerous hypoxia response genes in normoxia and hypoxia. Overall, these findings show the importance of understanding the regulation of HIF activity in a variety of breast cancer subtypes and points to the potential of targeting HIF-2α as a therapy for HER2-positive breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1097-0) contains supplementary material, which is available to authorized users.

Promoting vascularization for tissue engineering constructs: current strategies focusing on HIF-regulating scaffolds

INTRODUCTION

Vascularization remains one of the greatest yet unmet challenges in tissue engineering. When engineered tissues are scaled up to therapeutically relevant dimensions, their demand of oxygen and nutrients can no longer be met by diffusion. Thus, there is a need for perfusable vascular structures. Hypoxia-inducible factors (HIF) act as transcriptional oxygen sensors and regulate a multitude of genes involved in adaptive processes to hypoxia, including angiogenesis. Thus, targeting HIFs is a promising strategy to induce vascularization of engineered tissues.

AREAS COVERED

Here we review current vascularization strategies and summarize the present knowledge regarding activation of HIF signaling by ions, iron chelating agents, α-Ketoglutarate (αKG) analogues, and the lipid-lowering drug simvastatin to induce angiogenesis. Specifically, we focus on the incorporation of HIF-activating agents into biomaterials and scaffolds for controlled release.

EXPERT OPINION

Vascularization of tissue constructs through activation of upstream regulators of angiogenesis offers advantages but also suffers from drawbacks. HIFs can induce a complete angiogenic program; however, this program appears to be too slow to vascularize larger constructs before cell death occurs. It is therefore crucial that HIF-activation is combined with cell protective strategies and prevascularization techniques to obtain fully vascularized, vital tissues of therapeutically relevant dimensions.

Genetic and metabolic hallmarks of clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is a malignancy characterized by deregulated hypoxia-inducible factor signaling, mutation of several key chromatin modifying enzymes, and numerous alterations in cellular metabolism. Pre-clinical studies have historically been limited to cell culture models, however, the identification of critical tumor suppressors and oncogenes from large-scale patient sequencing data has led to several new genetically engineered mouse models with phenotypes reminiscent of ccRCC. In this review, we summarize recent literature on these topics and discuss how they inform targeted therapeutic approaches for the treatment of ccRCC.

PACAP and VIP regulate hypoxia-inducible factors in neuroblastoma cells exposed to hypoxia

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two related peptides acting as neurotransmitters/neuromodulators in central and peripheral nervous system. They are also involved in cancer showing a controversial role. Particulary, they are implicated in neuroblastoma differentiation (NB). This pediatric tumor can evolve to a malignant metastatic disease or spontaneously regress towards a benign form, known as ganglioneuroblastoma/ganglioneuroma. A negative hallmark of neoplasia progression is represented by hypoxic microenvironment. Low oxygen tension induces activation of hypoxia-inducible factors (HIFs) promoting cells proliferation and metastasis formation. Moreover, HIFs trigger vascular endothelial growth factor (VEGF) release favouring high-risk NB phenotype development. In the present work, we have investigated for the first time, if PACAP and VIP interfere with NB differentiation through modulation of hypoxic/angiogenic process. To this end, we analyzed their effect in malignant undifferentiated and all-trans retinoic acid (RA) differentiated SH-SY5Y cells, representing the benign form of this tumor. Our results have suggested tha both peptides, but predominantly VIP, induce NB differentiation into benign form by regulating HIFs, VEGF and VEGFRs expression and distribution. All these data give new insight regarding PACAP/VIP regulatory role in NB progression.

Fatty acid-binding protein 4 regulates fatty infiltration after rotator cuff tear by hypoxia-inducible factor 1 in mice

BACKGROUND

Fatty infiltration in skeletal muscle is directly linked to loss of muscle strength and is associated with various adverse physical outcomes such as muscle atrophy, inflammation, insulin resistance, mobility impairments, and even mortality in the elderly. Aging, mechanical unloading, muscle injury, and hormonal imbalance are main causes of muscle fat accumulation, and the fat cells are derived from muscle stem cells via adipogenic differentiation. However, the pathogenesis and molecular mechanisms of fatty infiltration in muscles are still not fully defined. Fatty acid-binding protein 4 (FABP4) is a carrier protein for fatty acids and is involved in fatty acid uptake, transport, and lipid metabolism. Rotator cuff tear (RCT) usually occurs in the elderly and is closely related with fatty infiltration in injured muscle. To investigate potential mechanisms for fatty infiltration other than adipogenic differentiation of muscle stem cells, we examined the role of FABP4 in muscle fatty infiltration in an RCT mouse model.

METHODS

In the RCT model, we evaluated the expression of FABP4 by qRT-PCR, western blotting, and immunohistochemical analyses. Histological changes such as inflammation and fat accumulation in the injured muscles were examined immunohistochemically. To evaluate whether hypoxia induces FABP4 expression, the levels of FABP4 mRNA and protein in C3H10T1/2 cells after hypoxia were examined. Using a transient transfection assay in 293T cells, we assessed the promoter activity of FABP4 by hypoxia-inducible factors (HIFs). Additionally, we evaluated the reduction in FABP4 expression and fat accumulation using specific inhibitors for HIF1 and FABP4, respectively.

RESULTS

FABP4 expression was significantly increased after RCT in mice, and its expression was localized in the intramuscular fatty region. Rotator cuff tear-induced FABP4 expression was up-regulated by hypoxia. HIF1α, which is activated by hypoxia, augmented the promoter activity of FABP4, together with HIF1β. Hypoxia-induced FABP4 expression was significantly decreased by HIF1 inhibitor treatment. Furthermore, in RCT model mice, fat accumulation was remarkably reduced by FABP4 inhibitor treatment.

CONCLUSIONS

This study shows that RCT induces FABP4 expression, leading to fat accumulation in injured muscle. FABP4 transcription is regulated by the direct binding of HIF1 to the FABP4 promoter in the hypoxic condition induced by RCT. Fat accumulation in injured muscle was reduced by the inhibition of FABP4. Ultimately, in the RCT model, we identified a novel mechanism for fatty infiltration by FABP4, which differs from adipogenic differentiation of muscle stem cells, and we found that fatty infiltration might be regulated by inhibition of HIF1 or FABP4.

Nap Interferes with Hypoxia-Inducible Factors and VEGF Expression in Retina of Diabetic Rats

The retinal microvascular damage is a complication of diabetic retinopathy (DR). Hyperglycemia and hypoxia are responsible of aberrant vessel's proliferation. The cellular response to hypoxia is mediated through activation of hypoxia-inducible factors (HIFs). Among these, HIF-1α modulates expression of its target gene, VEGF, whose upregulation controls the angiogenic event during DR development. In a previous study, we have demonstrated that a small peptide, NAP, is able to protect retina from hyperglycemic insult. Here, we have demonstrated that its intraocular administration in a rat model of diabetic retinopathy has reduced expression of HIF-1α, HIF-2α, and VEGF by increasing HIF-3α levels. These data have been also confirmed by immunolocalization study by confocal microscopy. Although these evidences need to be further deepened to understand the molecular mechanism involved in the protective NAP action, the present data suggest that this small peptide may be effective to prevent the development of this ocular pathology.

Tuberous sclerosis complex protein 1 expression is affected by VHL Gene alterations and HIF-1α production in sporadic clear-cell renal cell carcinoma

Alterations in von Hippel-Lindau gene (VHL) do not determine deregulation of hypoxia-inducible factors (HIFs) in clear-cell renal carcinoma (ccRCC). Their effects on tuberous sclerosis proteins (TSC1/2) and heat shock protein 90 (Hsp90) expressions in sporadic ccRCC are unknown. Therefore, we analyze the impact of VHL alterations and HIF-α production on the expression of TSC proteins and Hsp90 in these tumors. Alterations in VHL gene region exhibited 37/47 (78.7%) tumors. Monoallelic inactivation (intragenic mutation or LOH) was found in 10 (21.3%) and biallelic inactivation (intragenic mutation plus LOH) in 27 (57.4%) ccRCCs. Tumorous expression of HIF-α mRNAs, HIF-α, Hsp90 and TSC2 were VHL independent; TSC2 was underexpressed in all tumors by immunostaining (P<0.001). Immunoblotting revealed that TSC1 production was lower in tumors with monoallelic VHL inactivation than in control (P=0.01) and tissues with biallelic VHL inactivation (P=0.019), while tumors lacking HIF-1α (16/47) concurrently overexpressed HIF-2α and underexpressed TSC1 in comparison to controls (P=0.01 for both) and HIF-1α positive tumors (P=0.015 and P=0.050). Significant portion of variability (56.4%) in tumor diameter was explained by oscillations in nuclear grade, and TSC1 and HIF-2α expression in VHL altered tumors. In conclusion, while TSC2 is broadly downregulated in sporadic ccRCC, TSC1 expression is reduced in two subsets of these tumors, those with monoallelic VHL gene inactivation and those with concurrent low HIF-1α and high HIF-2α expression. Hence, the involvement of nuclear grade, TSC1 and HIF-2α in the progression of VHL altered tumors, implies the interplay between pVHL and TSC1.

'Blood doping' from Armstrong to prehabilitation: manipulation of blood to improve performance in athletes and physiological reserve in patients

Haemoglobin is the blood’s oxygen carrying pigment and is encapsulated in red blood corpuscles. The concentration of haemoglobin in blood is dependent on both its total mass in the circulation (tHb-mass) and the total plasma volume in which it is suspended. Aerobic capacity is defined as the maximum amount of oxygen that can be consumed by the body per unit time and is one measure of physical fitness. Observations in athletes who have undergone blood doping or manipulation have revealed a closer relationship between physical fitness (aerobic capacity) and total haemoglobin mass (tHb-mass) than with haemoglobin concentration ([Hb]). Anaemia is defined by the World Health Organisation (WHO) as a haemoglobin concentration of <130 g/L for men and <120 g/L for women. Perioperative anaemia is a common problem and is associated with increased mortality and morbidity following surgery. Aerobic capacity is also associated with outcome following major surgery, with less fit patients having a higher incidence of mortality and morbidity after surgery. Taken together, these observations suggest that targeted preoperative elevation of tHb-mass may raise aerobic capacity both directly and indirectly (by augmenting preoperative exercise initiatives- ‘prehabilitation’) and thus improve postoperative outcome. This notion in turn raises a number of questions. Which measure ([Hb] or tHb-mass) has the most value for the description of oxygen carrying capacity? Which measure has the most utility for targeting therapies to manipulate haemoglobin levels? Do the newer agents being used for blood manipulation (to increase tHb-mass) in elite sport have utility in the clinical environment? This review explores the literature relating to blood manipulation in elite sport as well as the relationship between perioperative anaemia, physical fitness and outcome following surgery, and suggests some avenues for exploring this area further.

Hypoxia leads to abnormal epidermal differentiation via HIF-independent pathways

Atmospheric oxygen is important for the epidermis, as the skin epidermis is not greatly affected by blood circulation. Therefore, it is necessary to understand the effect of hypoxic signals on the epidermis as some environmental stimuli can induce skin hypoxia. Here, we investigated how hypoxia (1% O2) affected skin equivalents (SEs) and normal human epidermal keratinocytes. We found that hypoxia specifically decreased the protein levels of keratin 1 (K1)/keratin 10 (K10), a representative marker of the epidermal spinous layer in the epidermis. However, hypoxia-inducible factors, the major regulators of hypoxia, did not affect hypoxia-induced down-regulation of K1/K10. We also found that N-acetyl-l-cysteine (NAC), a reactive oxygen species scavenger, antagonized the hypoxia-induced reduction of K1/K10 in keratinocytes and SEs. In contrast to the findings for NAC, inhibitors that blocked reactive oxygen species generation did not cause recovery of K1/K10 protein levels under hypoxic conditions. Taken together, these results indicate that hypoxia leads to abnormal keratinocyte differentiation by down-regulating K1/K10 and that this phenomenon can be ameliorated by NAC.

PACAP Modulates Expression of Hypoxia-Inducible Factors in Streptozotocin-Induced Diabetic Rat Retina

Retinal hypoxia has been related to the pathogenesis of diabetic retinopathy. This event is mediated by the hypoxia-inducible factors (HIFs), including HIF-1α, HIF-2α, and HIF-3α. Previously, we have demonstrated the protective role of pituitary adenylate cyclase-activating peptide (PACAP) in the early phase of diabetic retinopathy. In the present work, we investigated whether PACAP effect in hyperglycemic retina is mediated through modulation of HIFs' expression. Diabetes was induced with a single injection of streptozotocin (STZ) in rats. After 1 week, a group of diabetic animals was treated with a single intravitreal injection of 100 μM PACAP or saline solution. Then, changes in HIFs' expression levels were evaluated in the retina after 3 weeks of hyperglycemia. The expression of HIF-1α and HIF-2α was significantly (p < 0.001 vs control) increased in diabetic rats as compared to controls. Instead, their expression levels were significantly (p < 0.001 vs STZ) decreased after PACAP intraocular administration, as detected by Western blot analysis. Conversely, the expression of HIF-3α was significantly (p < 0.001 vs control) downregulated in retinas of STZ-injected rats and significantly (p < 0.001 vs control) increased after PACAP treatment. These data were supported by the immunohistochemical analysis. HIFs were localized either in inner and outer retinal layers. Diabetes interferes with their distribution, which is changed following intravitreal injection of PACAP. The present results suggest that the protective effect of the peptide in diabetic retina might be also mediated through modulation of HIFs' expression.

2-Methoxyestradiol synergizes with sorafenib to suppress hepatocellular carcinoma by simultaneously dysregulating hypoxia-inducible factor-1 and -2. Cancer Lett. 2014;355:96-105. [PMID: 25218350 DOI: 10.1016/j.canlet.2014.09.011]

Sorafenib is the approved systemic drug of choice for advanced hepatocellular carcinoma (HCC), but has demonstrated limited benefits because of drug resistance. 2-Methoxyestradiol (2ME2) has been shown to be a promising anticancer drug against various types of cancers and acts by dysregulating hypoxia-inducible factor (HIF)-1. Hypoxic cancer cells are extremely resistant to therapies since they elicit strong survival ability due to the cellular adaptive response to hypoxia, which is controlled by HIF-1 and HIF-2. The present study has demonstrated that sorafenib downregulated the expression of HIF-1α, making the hypoxic response switch from HIF-1α- to HIF-2α-dependent pathways, resulting in upregulation of HIF-2α, which contributes to the insensitivity of hypoxic HCC cells to sorafenib. HIF-2α played a dominant role in regulating VEGF, thus sorafenib in turn increased the expression of VEGF (a downstream molecule of both HIF-1 and HIF-2) and cyclin D1 (a downstream molecule of HIF-2), but reduced the expression of LDHA (a downstream molecule of HIF-1), in hypoxic HCC cells. 2ME2 significantly reduced the expression of both HIF-1α and HIF-2α, and their downstream molecules, VEGF, LDHA and cyclin D1, rendering hypoxic HCC cells to increased sensitivity to 2ME2. 2ME2 also inhibited the nuclear translocation of HIF-1α and HIF-2α proteins, but had no effect on their mRNA expression. 2M2 synergized with sorafenib to suppress the proliferation and induction of apoptosis of HCC cells in vitro and in vivo, and inhibited tumoral angiogenesis. These results indicate that 2ME2 given in combination with sorafenib acts synergistically for treating HCC.

Regulation of the HIF-system in human macrophages--differential regulation of HIF-α subunits under sustained hypoxia

Macrophages are often associated to pathophysiological processes and were found at hypoxic areas. However, cell adaption greatly depends on hypoxia-inducible factors (HIF). Activation of these transcription factors is induced by heterodimerization of an α-(HIF-1α, -2α, -3α) and HIF-1β subunit. The main regulatory pathway is represented by α-subunit stability. Beside, little is known about the exact mechanisms of fine-tuning in Hif-regulation. The present study characterizes the hypoxia-induced regulation of HIF-1α and -2α in human macrophages. The hypoxic increase of both subunits is initially mediated by protein stabilization. Sustained hypoxia caused a distinct regulation of HIF-1α and -2α. The striking increase of HIF-2α protein expression was contrasted by a dramatic decrease of HIF-1α. The long-term downregulation of HIF-1α is due to downregulation of its mRNA. This decrease was accompanied by increased expression of ahif, a natural cis-antisense transcript of HIF-1α. The ahif-transcript was strongly inducible by hypoxia and rapidly degraded under reoxygenation. Using an adenoviral overexpression and siRNA silencing approach revealed that the targeted regulation of ahif is mediated by the HIF-system itself. Furthermore it could be shown that ahif indeed is able to modulate the hypoxic expression of HIF-1α and influences the expression of the HIF-target gene Enolase-2. Taken together, this study characterizes a new regulation process of the HIF-transcription factor-system in human macrophages under hypoxia. For the first time evidence is provided that ahif is regulated by the HIF-system and influences HIF-1α expression in primary human macrophages.

Hypoxia-inducible factor prolyl hydroxylases as targets for neuroprotection by "antioxidant" metal chelators: From ferroptosis to stroke

Neurologic conditions including stroke, Alzheimer disease, Parkinson disease, and Huntington disease are leading causes of death and long-term disability in the United States, and efforts to develop novel therapeutics for these conditions have historically had poor success in translating from bench to bedside. Hypoxia-inducible factor (HIF)-1α mediates a broad, evolutionarily conserved, endogenous adaptive program to hypoxia, and manipulation of components of the HIF pathway is neuroprotective in a number of human neurological diseases and experimental models. In this review, we discuss molecular components of one aspect of hypoxic adaptation in detail and provide perspective on which targets within this pathway seem to be ripest for preventing and repairing neurodegeneration. Further, we highlight the role of HIF prolyl hydroxylases as emerging targets for the salutary effects of metal chelators on ferroptosis in vitro as well in animal models of neurological diseases.

Regulation of the Hif-system by micro-RNA 17 and 20a - role during monocyte-to-macrophage differentiation

MiRNAs are a class of endogenous tiny RNAs that act as inhibitors of translation or promote RNA degradation by duplex-formation within the 3'-UTR of target mRNAs. They play an important role during a wide range of cellular processes by fine-tuning of gene expression. The differentiation of monocytes to macrophages plays a pivotal role in physiological as well as pathophysiological processes such as atherosclerosis. Monocytes which can be found in well-oxygenated blood migrate into areas with a high inflammation, such as the atherosclerotic plaque. There, they differentiate into macrophages. Interestingly, macrophages were found mainly at hypoxic sites of the plaque. Key regulators for the adaptation to hypoxia are the hypoxia-inducible factors (Hif). Therefore the aim of the present study was to investigate the regulation of the Hif-system by miRNAs during the process of monocyte differentiation. The present study shows that during the differentiation of monocytes into macrophages a dramatically change in the expression pattern of Hif-1α and Hif-2α took place. This was associated with a downregulation of microRNAs encoded by the miR-17-92 cluster. An in silico analysis of the 3'-UTR of Hif-α subunits for binding sites of miRNAs was performed using different miRNA databases in concert with a secondary structure prediction algorithm. This analysis revealed that both 3'-UTRs contain binding sites for miRNAs of the miR-17-92 cluster. Transfection of HeLa cells with miR-17 and miR-20a led to an inhibition of Hif-1α and -2α mRNA and protein expression and a lowered Hif DNA binding activity. Using a Luciferase-Reporter assay, it could be shown, that both Hif-α subunits are targeted by miR-17 and miR-20a. Furthermore, miR-overexpression in primary human macrophages demonstrates the important role of this microRNA-mediated regulation of the Hif-system for adaption of macrophages to hypoxia. In conclusion, the present study shows that the Hif-system is activated during monocyte-to-macrophage differentiation. This activation is in part mediated by a miRNA-dependent mechanism, which seems to be crucial for the adaption of macrophages to hypoxia.