Hypoxia-inducible factor 1 levels vary exponentially over a physiologically relevant range of O2 tension

A Boolean network model of hypoxia, mechanosensing and TGF-β signaling captures the role of phenotypic plasticity and mutations in tumor metastasis

The tumor microenvironment aids cancer progression by promoting several cancer hallmarks, independent of cancer-related mutations. Biophysical properties of this environment, such as the stiffness of the matrix cells adhere to and local cell density, impact proliferation, apoptosis, and the epithelial to mesenchymal transition (EMT). The latter is a rate-limiting step for invasion and metastasis, enhanced in hypoxic tumor environments but hindered by soft matrices and/or high cell densities. As these influences are often studied in isolation, the crosstalk between hypoxia, biomechanical signals, and the classic EMT driver TGF-β is not well mapped, limiting our ability to predict and anticipate cancer cell behaviors in changing tumor environments. To address this, we built a Boolean regulatory network model that integrates hypoxic signaling with a mechanosensitive model of EMT, which includes the EMT-promoting crosstalk of mitogens and biomechanical signals, cell cycle control, and apoptosis. Our model reproduces the requirement of Hif-1α for proliferation, the anti-proliferative effects of strong Hif-1α stabilization during hypoxia, hypoxic protection from anoikis, and hypoxia-driven mechanosensitive EMT. We offer experimentally testable predictions about the effect of VHL loss on cancer hallmarks, with or without secondary oncogene activation. Taken together, our model serves as a predictive framework to synthesize the signaling responses associated with tumor progression and metastasis in healthy vs. mutant cells. Our single-cell model is a key step towards more extensive regulatory network models that cover damage-response and senescence, integrating most cell-autonomous cancer hallmarks into a single model that can, in turn, control the behavior of in silico cells within a tissue model of epithelial homeostasis and carcinoma.

Oxygen-carrying nanoemulsions and respiratory hyperoxia eliminate tumor hypoxia-induced immunosuppression

Hypoxia/hypoxia-inducible factor 1α-driven immunosuppressive transcription and cAMP-elevating signaling through A2A adenosine receptors (A2ARs) represent a major tumor-protecting pathway that enables immune evasion. Recent promising clinical outcomes due to the blockade of the adenosine-generating enzyme CD73 and A2AR in patients refractory to all other therapies have confirmed the importance of targeting hypoxia-adenosinergic signaling. We report a feasible approach to target the upstream stage of hypoxia-adenosinergic immunosuppression using an oxygen-carrying nanoemulsion (perfluorocarbon blood substitute). We show that oxygenation agent therapy (a) eliminates tumor hypoxia, (b) improves efficacy of endogenously developed and adoptively transferred T cells, and thereby (c) promotes regression of tumors in different anatomical locations. We show that both T cells and NK cells avoid hypoxic tumor areas and that reversal of hypoxia by oxygenation agent therapy increases intratumoral infiltration of activated T cells and NK cells due to reprogramming of the tumor microenvironment (TME). Thus, repurposing oxygenation agents in combination with supplemental oxygen may improve current cancer immunotherapies by preventing hypoxia-adenosinergic suppression, promoting immune cell infiltration and enhancing effector responses. These data also suggest that pretreating patients with oxygenation agent therapy may reprogram the TME from immunosuppressive to immune-permissive prior to adoptive cell therapy, or other forms of immunotherapy.

Redefining the role of hypoxia-inducible factors (HIFs) in oxygen homeostasis

Hypoxia-inducible factors (HIFs) are key regulators of intracellular oxygen homeostasis. The marked increase in HIFs activity in hypoxia as compared to normoxia, together with their transcriptional control of primary metabolic pathways, motivated the widespread view of HIFs as responsible for the cell's metabolic adaptation to hypoxic stress. In this work, we suggest that this prevailing model of HIFs regulation is misleading. We propose an alternative model focused on understanding the dynamics of HIFs' activity within its physiological context. Our model suggests that HIFs would not respond to but rather prevent the onset of hypoxic stress by regulating the traffic of electrons between catabolic substrates and oxygen. The explanatory power of our approach is patent in its interpretation of the Warburg effect, the tendency of tumor cells to favor anaerobic metabolism over respiration, even in fully aerobic conditions. This puzzling behavior is currently considered as an anomalous metabolic deviation. Our model predicts the Warburg effect as the expected homeostatic response of tumor cells to the abnormal increase in metabolic demand that characterizes malignant phenotypes. This alternative perspective prompts a redefinition of HIFs' function and underscores the need to explicitly consider the cell's metabolic activity in understanding its responses to changes in oxygen availability.

Harnessing transcriptional regulation of alternative end-joining to predict cancer treatment

Alternative end-joining (alt-EJ) is an error-prone DNA repair pathway that cancer cells deficient in homologous recombination rely on, making them vulnerable to synthetic lethality via inhibition of poly(ADP-ribose) polymerase (PARP). Targeting alt-EJ effector DNA polymerase theta (POLθ), which synergizes with PARP inhibitors and can overcome resistance, is of significant preclinical and clinical interest. However, the transcriptional regulation of alt-EJ and its interactions with processes driving cancer progression remain poorly understood. Here, we show that alt-EJ is suppressed by hypoxia while positively associated with MYC (myelocytomatosis oncogene) transcriptional activity. Hypoxia reduces PARP1 and POLQ expression, decreases MYC binding at their promoters, and lowers PARylation and alt-EJ-mediated DNA repair in cancer cells. Tumors with HIF1A mutations overexpress the alt-EJ gene signature. Inhibition of hypoxia-inducible factor 1α or HIF1A expression depletion, combined with PARP or POLθ inhibition, synergistically reduces the colony-forming capacity of cancer cells. Deep learning reveals the anticorrelation between alt-EJ and hypoxia across regions in tumor images, and the predictions for these and MYC activity achieve area under the curve values between 0.70 and 0.86. These findings further highlight the critical role of hypoxia in modulating DNA repair and present a strategy for predicting and improving outcomes centered on targeting alt-EJ.

100% oxygen mobilizes stem cells and up-regulates MIF and APRIL in humans: a new point on the hormetic dose curve

Introduction

The aim of the current study was to test normobaric 100% oxygen (NBO) (PiO2 = 713 mmHg) for stem cell mobilization and cytokine modulation. Although current oxygen therapy (PiO2 = 1,473-2,233 mmHg) is well known to mobilize stem cells and modulate cytokine, little is known about NBO and its place on the low dose stimulation phase of the hormetic dose curve of oxygen. We asked the question, will NBO mobilize stem cells and modulate cytokines. A positive outcome presents the potential to create and refine oxygen treatment protocols, expand access, and optimize patient outcomes.

Methods

Healthy 30-35-year-old volunteers were exposed to 100% normobaric oxygen for 60 min, M-F, for 10 exposures over 2 weeks. Venous blood samples were collected at four time points: 1) prior to the first exposure (serving as the control for each subject), 2) immediately after the first exposure (to measure the acute effect), 3) immediately before the ninth exposure (to measure the chronic effect), and 4) three days after the final exposure (to assess durability). Blinded scientists used flow cytometry to gate and quantify the Stem Progenitor Cells (SPCs).

Results

CD45dim/CD34+/CD133+ and CD45+/CD34+/CD133+ were significantly mobilized following nine daily one-hour exposures to normobaric 100% oxygen. Conversely CD45-/CD34+/CD133+, CD45-/CD34+/CD133- and CD45-/CD34-/CD133+ phenotypes were downregulated suggesting differentiation into more mature phenotypes. The CD133+ phenotype exhibited a maturing from CD45- to CD45dim stem cells. CD45-/CD34, CD45-/CD31 and CD45-/CD105 were downregulated with no changes in related CD45dim and CD45+ phenotypes. The cytokines "macrophage migration inhibitory factor" (MIF) and "a proliferation inducing ligand" (APRIL) were significantly upregulated.

Conclusion

This study demonstrates that 100% normobaric oxygen mobilizes stem cells and upregulates the expression of the inflammatory cytokines marking a new point on the low dose stimulation phase of the hormetic dose curve of oxygen.

Oxygen control in cell culture - Your cells may not be experiencing what you think!

Oxygen (O2)-controlled cell culture has been pivotal in studying mammalian mechanisms of O2 sensing, regulation, and utilization. We posit, however, that O2-controlled cell culture is paradoxically not controlling O2. There is overwhelming evidence that the pericellular O2 is lower than the surrounding gas phase due to cellular O2 consumption. Standard hypoxic cell culture is at high risk of inducing pericellular anoxia. We discuss the implications of poor O2 control for cellular O2 regulation mechanisms, bioenergetics, and redox signaling. We also highlight the evidence of frequent under-oxygenation in standard (i.e., normoxic) cell culture. This issue has been largely overlooked because strategies to control pericellular O2 have been lacking. Here, we propose a framework to control pericellular O2 based on our recent investigation into the nature of the gas/pericellular O2 gradient. Implementing this framework into standard practice will unlock quantitative O2 control in vitro, improving our ability to understand the role of O2 in biology.

Acute Three-Dimensional Hypoxia Regulates Angiogenesis

Hypoxia elicits a multitude of tissue responses depending on the severity and duration of the exposure. While chronic hypoxia is shown to impact development, regeneration, and cancer, the understanding of the threats of acute (i.e., short-term) hypoxia is limited mainly due to its transient nature. Here, a novel gelatin-dextran (Gel-Dex) hydrogel is established that decouples hydrogel formation and oxygen consumption and thus facilitates 3D sprouting from endothelial spheroids and, subsequently, induces hypoxia "on-demand." The Gel-Dex platform rapidly achieves acute moderate hypoxic conditions without compromising its mechanical properties. Acute exposure to hypoxia leads to increased endothelial cell migration and proliferation, promoting the total length and number of vascular sprouts. This work finds that the enhanced angiogenic response is mediated by reactive oxygen species, independently of hypoxia-inducible factors. Reactive oxygen species-dependent matrix metalloproteinases activity mediated angiogenic sprouting is observed following acute hypoxia. Overall, the Gel-Dex hydrogel offers a novel platform to study how "on-demand" acute moderate hypoxia impacts angiogenesis, with broad applicability to the development of novel sensing technologies.

A functional approach to homeostatic regulation

In this work, we present a novel modeling framework for understanding the dynamics of homeostatic regulation. Inspired by engineering control theory, this framework incorporates unique features of biological systems. First, biological variables often play physiological roles, and taking this functional context into consideration is essential to fully understand the goals and constraints of homeostatic regulation. Second, biological signals are not abstract variables, but rather material molecules that may undergo complex turnover processes of synthesis and degradation. We suggest that the particular nature of biological signals may condition the type of information they can convey, and their potential role in shaping the dynamics and the ultimate purpose of homeostatic systems. We show that the dynamic interplay between regulated variables and control signals is a key determinant of biological homeostasis, challenging the necessity and the convenience of strictly extrapolating concepts from engineering control theory in modeling the dynamics of homeostatic systems. This work provides a simple, unified framework for studying biological regulation and identifies general principles that transcend molecular details of particular homeostatic mechanisms. We show how this approach can be naturally applied to apparently different regulatory systems, contributing to a deeper understanding of homeostasis as a fundamental process in living systems.

Von Hippel-Lindau deficiency protects the liver against ischemia/reperfusion injury through the regulation of hypoxia-inducible factor 1α and 2α

BACKGROUND

Ischemia and reperfusion (I/R)-induced liver injury contributes to morbidity and mortality during hepatic surgery or liver transplantation. As a pivotal regulator of cancer and inflammation, the role of Von Hippel-Lindau (VHL) in hepatic I/R injury remains undetermined.

METHODS

We investigated the role of VHL in hepatic I/R injury by generating VHL conditional knockout (VHL-KO) mice. The downstream mechanisms of VHL were confirmed, and the role of HIF-2α in hepatic I/R injury was further investigated.

RESULTS

In this study, we discovered that VHL upregulation was associated with hepatic I/R injury in a mouse model. VHL gene knockout (VHL-KO) and overexpression (Ad-VHL) mice demonstrated that VHL aggravated liver injury, increased inflammation, and accelerated cell death in hepatic I/R injury. The VHL protein (pVHL) regulates a crucial control mechanism by targeting HIFα subunits for ubiquitin-mediated degradation. In vitro and in vivo studies demonstrated that VHL interacted with and repressed hypoxia-inducible factor 1α (HIF-1α) and hypoxia-inducible factor 2α (HIF-2α) expression during hepatic I/R injury. Notably, the inhibition of HIF-1α or 2α, as well as the concurrent inhibition of HIF-1α and 2α, abrogated the protective effect of VHL-KO. The severe stabilization of HIF-1α or 2α, as well as the simultaneous overexpression of HIF-1α and 2α, compensated for the detrimental effect of VHL.

CONCLUSIONS

Thus, we identified the VHL-HIF-1α/HIF-2α axis as an indispensable pathway that may be a novel target for mediating hepatic I/R injury.

The Potential Interplay Between HIF-1α, Angiogenic, and Autophagic Signaling During Intermittent Hypoxic Exposure and Exercise

Berkemeier, Quint N., Michael R. Deyhle, James J. McCormick, Kurt A. Escobar, and Christine M. Mermier. The potential interplay between HIF-1α, angiogenic, and autophagic signaling during intermittent hypoxic exposure and exercise High Alt Med Biol. 25:326-336, 2024.-Environmental hypoxia as a result of decreased barometric pressure upon ascent to high altitudes (>2,500 m) presents increased physiological demands compared with low altitudes, or normoxic environments. Competitive athletes, mountaineers, wildland firefighters, military personnel, miners, and outdoor enthusiasts commonly participate in, or are exposed to, forms of exercise or physical labor at moderate to high altitudes. However, the majority of research on intermittent hypoxic exposure is centered around hematological markers, and the skeletal muscle cellular responses to exercise in hypoxic environments remain largely unknown. Two processes that may be integral for the maintenance of cellular health in skeletal muscle include angiogenesis, or the formation of new blood vessels from preexisting vasculature and autophagy, a process that removes and recycles damaged and dysfunctional cellular material in the lysosome. The purpose of this review is to is to examine the current body of literature and highlight the potential interplay between low-oxygen-sensing pathways, angiogenesis, and autophagy during acute and prolonged intermittent hypoxic exposure in conjunction with exercise. The views expressed in this paper are those of the authors and do not reflect the official policy of the Department of Army, DOD, DOE, ORAU/ORISE or U.S. Government.

A closed-loop modular multiorgan-on-chips platform for self-sustaining and tightly controlled oxygenation

To mimic physiological microenvironments in organ-on-a-chip systems, physiologically relevant parameters are required to precisely access drug metabolism. Oxygen level is a critical microenvironmental parameter to maintain cellular or tissue functions and modulate their behaviors. Current organ-on-a-chip setups are oftentimes subjected to the ambient incubator oxygen level at 21%, which is higher than most if not all physiological oxygen concentrations. Additionally, the physiological oxygen level in each tissue is different ranging from 0.5 to 13%. Here, a closed-loop modular multiorgan-on-chips platform is developed to enable not only real-time monitoring of the oxygen levels but, more importantly, tight control of them in the range of 4 to 20% across each connected microtissue-on-a-chip in the circulatory culture medium. This platform, which consists of microfluidic oxygen scavenger(s), an oxygen generator, a monitoring/controller system, and bioreactor(s), allows for independent, precise upregulation and downregulation of dissolved oxygen in the perfused culture medium to meet the physiological oxygen level in each modular microtissue compartment, as needed. Furthermore, drug studies using the platform demonstrate that the oxygen level affects drug metabolism in the parallelly connected liver, kidney, and arterial vessel microtissues without organ-organ interactions factored in. Overall, this platform can promote the performances of organ-on-a-chip devices in drug screening by providing more physiologically relevant and independently adjustable oxygen microenvironments for desired organ types on a single- or a multiorgan-on-chip(s) configuration.

Origins and molecular effects of hypoxia in cancer

Hypoxia (insufficient O2) is a pivotal factor in cancer progression, triggering genetic, transcriptional, translational and epigenetic adaptations associated to therapy resistance, metastasis and patient mortality. In this review, we outline the microenvironmental origins and molecular mechanisms responsible for hypoxic cancer cell adaptations in situ and in vitro, whilst outlining current approaches to stratify, quantify and therapeutically target hypoxia in the context of precision oncology.

Mechanisms underlying the health benefits of intermittent hypoxia conditioning

Intermittent hypoxia (IH) is commonly associated with pathological conditions, particularly obstructive sleep apnoea. However, IH is also increasingly used to enhance health and performance and is emerging as a potent non-pharmacological intervention against numerous diseases. Whether IH is detrimental or beneficial for health is largely determined by the intensity, duration, number and frequency of the hypoxic exposures and by the specific responses they engender. Adaptive responses to hypoxia protect from future hypoxic or ischaemic insults, improve cellular resilience and functions, and boost mental and physical performance. The cellular and systemic mechanisms producing these benefits are highly complex, and the failure of different components can shift long-term adaptation to maladaptation and the development of pathologies. Rather than discussing in detail the well-characterized individual responses and adaptations to IH, we here aim to summarize and integrate hypoxia-activated mechanisms into a holistic picture of the body's adaptive responses to hypoxia and specifically IH, and demonstrate how these mechanisms might be mobilized for their health benefits while minimizing the risks of hypoxia exposure.

Hypoxia-inducible factor prolyl hydroxylase inhibitors for anaemia in chronic kidney disease: a clinical practice document by the European Renal Best Practice board of the European Renal Association

Anaemia is a common complication of chronic kidney disease (CKD) and is associated with poor long-term outcomes and quality of life. The use of supplemental iron, erythropoiesis-stimulating agents (ESAs) and blood transfusions has been the mainstay for treatment of anaemia in CKD for more than 3 decades. Despite available treatments, CKD patients with anaemia are undertreated and moderate-severe anaemia remains prevalent in the CKD population. Anaemia has consistently been associated with greater mortality, hospitalization, cardiovascular events and CKD progression in CKD patients, and the risk increases with anaemia severity. Hypoxia-inducible factor (HIF) prolyl hydroxylase (PH) inhibitors have a novel mechanism of action by mimicking the body's response to hypoxia and have emerged as an alternative to ESAs for treatment of anaemia in CKD. Their efficacy in correcting and maintaining haemoglobin has been demonstrated in >30 phase 3 clinical trials. Additionally, HIF activation results in various pleiotropic effects beyond erythropoiesis, with cholesterol reduction and improved iron homeostasis and potential anti-inflammatory effects. The long-term safety of these agents, particularly with respect to cardiovascular and thromboembolic events, and their possible effect on tumour growth needs to be fully elucidated. This article presents in detail the effects of HIF-PH inhibitors, describes their mechanisms of action and pharmacologic properties and discusses their place in the treatment of anaemia in CKD according to the available evidence.

High-Quality Three-Dimensionally Cultured Cells Using Interfaces of Diblock Copolymers Containing Different Ratios of Zwitterionic N-Oxides

To control three-dimensional (3D) cell spheroid formation, it is well-known the surface physicochemical and mechanical properties of cell culture materials are important; however, the formation and function of 3D cells are still unclear. This study demonstrated the precise control of the formation of 3D cells and 3D cell functions using diblock copolymers containing different ratios of a zwitterionic trimethylamine N-oxide group. The diblock copolymers were composed of poly(n-butyl methacrylate) (PBMA) as the hydrophobic unit for surface coating on a cell culture dish and stabilization in water, and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) as the precursor of N-oxide. The zwitterionic N-oxide converted from 0 to 100% using PDMAEMA. The wettability and surface zeta potential varied with different ratios of N-oxide diblock copolymer-coated surfaces, and the amount of protein adsorbed in the cell culture medium decreased monotonically with increasing N-oxide ratio. 3D cell spheroid formations were observed by seeding human umbilical cord mesenchymal stem cells (hUC-MSCs) in diblock copolymer-coated flat-bottom well plates, and the N-oxide ratio was over 40%. The cells proliferated in two-dimensions (2D) and did not form spheroids when the N-oxide ratio was less than 20%. Interestingly, the expression of undifferentiated markers of hUC-MSCs was higher on surfaces that adsorbed proteins to some extent and formed 50-150 μm spheroids in the range of 40-70% of N-oxide ratio. We revealed that a moderately protein-adsorbed surface allows precise control of spheroid formation and undifferentiated 3D cells and has potential applications for high-quality spheroids in regenerative medicine and drug screening.

Controlling Pericellular Oxygen Tension in Cell Culture Reveals Distinct Breast Cancer Responses to Low Oxygen Tensions

In oxygen (O2)-controlled cell culture, an indispensable tool in biological research, it is presumed that the incubator setpoint equals the O2 tension experienced by cells (i.e., pericellular O2). However, it is discovered that physioxic (5% O2) and hypoxic (1% O2) setpoints regularly induce anoxic (0% O2) pericellular tensions in both adherent and suspension cell cultures. Electron transport chain inhibition ablates this effect, indicating that cellular O2 consumption is the driving factor. RNA-seq analysis revealed that primary human hepatocytes cultured in physioxia experience ischemia-reperfusion injury due to cellular O2 consumption. A reaction-diffusion model is developed to predict pericellular O2 tension a priori, demonstrating that the effect of cellular O2 consumption has the greatest impact in smaller volume culture vessels. By controlling pericellular O2 tension in cell culture, it is found that hypoxia vs. anoxia induce distinct breast cancer transcriptomic and translational responses, including modulation of the hypoxia-inducible factor (HIF) pathway and metabolic reprogramming. Collectively, these findings indicate that breast cancer cells respond non-monotonically to low O2, suggesting that anoxic cell culture is not suitable for modeling hypoxia. Furthermore, it is shown that controlling atmospheric O2 tension in cell culture incubators is insufficient to regulate O2 in cell culture, thus introducing the concept of pericellular O2-controlled cell culture.

HIPK2 in Colon Cancer: A Potential Biomarker for Tumor Progression and Response to Therapies

Colon cancer, one of the most common and fatal cancers worldwide, is characterized by stepwise accumulation of specific genetic alterations in tumor suppressor genes or oncogenes, leading to tumor growth and metastasis. HIPK2 (homeodomain-interacting protein kinase 2) is a serine/threonine protein kinase and a "bona fide" oncosuppressor protein. Its activation inhibits tumor growth mainly by promoting apoptosis, while its inactivation increases tumorigenicity and resistance to therapies of many different cancer types, including colon cancer. HIPK2 interacts with many molecular pathways by means of its kinase activity or transcriptional co-repressor function modulating cell growth and apoptosis, invasion, angiogenesis, inflammation and hypoxia. HIPK2 has been shown to participate in several molecular pathways involved in colon cancer including p53, Wnt/β-catenin and the newly identified nuclear factor erythroid 2 (NF-E2) p45-related factor 2 (NRF2). HIPK2 also plays a role in tumor-host interaction in the tumor microenvironment (TME) by inducing angiogenesis and cancer-associated fibroblast (CAF) differentiation. The aim of this review is to assess the role of HIPK2 in colon cancer and the underlying molecular pathways for a better understanding of its involvement in colon cancer carcinogenesis and response to therapies, which will likely pave the way for novel colon cancer therapies.

Exploring the pathogenesis of pulmonary vascular disease

Pulmonary hypertension (PH) is a complex cardiopulmonary disorder impacting the lung vasculature, resulting in increased pulmonary vascular resistance that leads to right ventricular dysfunction. Pulmonary hypertension comprises of 5 groups (PH group 1 to 5) where group 1 pulmonary arterial hypertension (PAH), results from alterations that directly affect the pulmonary arteries. Although PAH has a complex pathophysiology that is not completely understood, it is known to be a multifactorial disease that results from a combination of genetic, epigenetic and environmental factors, leading to a varied range of symptoms in PAH patients. PAH does not have a cure, its incidence and prevalence continue to increase every year, resulting in higher morbidity and mortality rates. In this review, we discuss the different pathologic mechanisms with a focus on epigenetic modifications and their roles in the development and progression of PAH. These modifications include DNA methylation, histone modifications, and microRNA dysregulation. Understanding these epigenetic modifications will improve our understanding of PAH and unveil novel therapeutic targets, thus steering research toward innovative treatment strategies.

Quemeiteng granule relieves goiter by suppressing thyroid microvascular endothelial cell proliferation and angiogenesis via miR-217-5p-mediated targeting of FGF2-induced regulation of the ERK pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Goiters are enlargements of the thyroid gland and are a global public issue. Quemeiteng granule (QMTG) is a traditional Chinese medicine (TCM) formula used to treat goiter in Yunnan Province. However, the effectiveness and underlying mechanism of these treatments have not been fully elucidated.

AIM OF THE STUDY

This study aimed to investigate the therapeutic effects of QMTG on goiter and the downstream regulatory mechanisms.

MATERIALS AND METHODS

In this study, we first evaluated the antigoiter efficacy of QMTG through biochemical indices [body weight, thyroid coefficient, triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH)] and hematoxylin-eosin (HE) staining in a Propylthiouracil (PTU)-induced model. Based on microRNA sequencing (miRNA-seq) and bioinformatics analysis, key miRNA was screened out. A dual-luciferase reporter assay was performed to confirm the transcriptional regulation of the target gene by the miRNA. The viability of rat thyroid microvascular endothelial cells (RTMECs) and human thyroid microvascular endothelial cells (HTMECs) was assessed using the CCK-8 assays. The migration and angiogenesis of RTMECs and HTMECs were visualized through tube formation and wound scratch assays. Proteins involved in angiogenesis and the ERK pathway were assessed via Western blotting.

RESULTS

QMTG significantly increased body weight, decreased the thyroid coefficient, increased the levels of T3, T4, FT3 and FT4 and reduced TSH levels in rats with goiter. QMTG also promoted the morphological recovery of thyroid follicles. MiR-217-5p was identified as a key miRNA. Our studies revealed that miR-217-5p directly targets FGF2 and that QMTG promotes the recovery of thyroid hormone (TH) levels and morphological changes in the thyroid, suppresses thyroid microvascular endothelial cell vitality, tube formation and migration, and reduces the expression of VEGF, Ang-1 and VCAM-1 triggered by miR-217-5p, thereby inhibiting the Ras/MEK/ERK cascade through FGF2.

CONCLUSIONS

Our experiments demonstrated that the QMTG had therapeutic effects on goiter. These effects were attributed to the inhibition of ERK pathway-induced proliferation and angiogenesis through the targeting of FGF2 by miR-217-5p.

Regulation of Cancer-Associated miRNAs Expression under Hypoxic Conditions

Solid tumors frequently experience hypoxia or low O2 levels. In these conditions, hypoxia-inducible factor 1 alpha (HIF-1α) is activated and acts as a transcription factor that regulates cancer cell adaptation to O2 and nutrient deprivation. HIF-1α controls gene expression associated with various signaling pathways that promote cancer cell proliferation and survival. MicroRNAs (miRNAs) are 22-nucleotide noncoding RNAs that play a role in various biological processes essential for cancer progression. This review presents an overview of how hypoxia regulates the expression of multiple miRNAs in the progression of cancer cells.

Functional hypoxia reduces mitochondrial calcium uptake

Mitochondrial respiration extends beyond ATP generation, with the organelle participating in many cellular and physiological processes. Parallel changes in components of the mitochondrial electron transfer system with respiration render it an appropriate hub for coordinating cellular adaption to changes in oxygen levels. How changes in respiration under functional hypoxia (i.e., when intracellular O2 levels limit mitochondrial respiration) are relayed by the electron transfer system to impact mitochondrial adaption and remodeling after hypoxic exposure remains poorly defined. This is largely due to challenges integrating findings under controlled and defined O2 levels in studies connecting functions of isolated mitochondria to humans during physical exercise. Here we present experiments under conditions of hypoxia in isolated mitochondria, myotubes and exercising humans. Performing steady-state respirometry with isolated mitochondria we found that oxygen limitation of respiration reduced electron flow and oxidative phosphorylation, lowered the mitochondrial membrane potential difference, and decreased mitochondrial calcium influx. Similarly, in myotubes under functional hypoxia mitochondrial calcium uptake decreased in response to sarcoplasmic reticulum calcium release for contraction. In both myotubes and human skeletal muscle this blunted mitochondrial adaptive responses and remodeling upon contractions. Our results suggest that by regulating calcium uptake the mitochondrial electron transfer system is a hub for coordinating cellular adaption under functional hypoxia.

Circadian Clock and Hypoxia

The timing of life on Earth is remarkable: between individuals of the same species, a highly similar temporal pattern is observed, with shared periods of activity and inactivity each day. At the individual level, this means that over the course of a single day, a person alternates between two states. They are either upright, active, and communicative or they lie down in a state of (un)consciousness called sleep where even the characteristic of neuronal signals in the brain shows distinctive properties. The circadian clock governs both of these time stamps-activity and (apparent) inactivity-making them come and go consistently at the same approximate time each day. This behavior thus represents the meeting of two pervasive systems: the circadian clock and metabolism. In this article, we will describe what is known about how the circadian clock anticipates daily changes in oxygen usage, how circadian clock regulation may relate to normal physiology, and to hypoxia and ischemia that can result from pathologies such as myocardial infarction and stroke.

Long-term HIF-1α stabilization reduces respiration, promotes mitophagy, and results in retinal cell death

Ocular hypertension during glaucoma can lead to hypoxia, activation of the HIF transcription factors, and a metabolic shift toward glycolysis. This study aims to test whether chronic HIF activation and the attendant metabolic reprogramming can initiate glaucoma-associated pathology independently of ocular hypertension. HIF-1α stabilization was induced in mice for 2 and 4 weeks by inhibiting prolyl hydroxylases using the small molecule Roxadustat. HIF-1α stabilization and the expression of its downstream bioenergetic targets were investigated in the retina by immunofluorescence, capillary electrophoresis, and biochemical enzyme activity assays. Roxadustat dosing resulted in significant stabilization of HIF-1α in the retina by 4 weeks, and upregulation in glycolysis-associated proteins (GLUT3, PDK-1) and enzyme activity in both neurons and glia. Accordingly, succinate dehydrogenase, mitochondrial marker MTCO1, and citrate synthase activity were significantly decreased at 4 weeks, while mitophagy was significantly increased. TUNEL assay showed significant apoptosis of cells in the retina, and PERG amplitude was significantly decreased with 4 weeks of HIF-1α stabilization. A significant increase in AMPK activation and glial hypertrophy, concomitant with decreases in retinal ganglion cell function and inner retina cell death suggests that chronic HIF-1α stabilization alone is detrimental to retina metabolic homeostasis and cellular survival.

Redox-Mediated Rewiring of Signalling Pathways: The Role of a Cellular Clock in Brain Health and Disease

Metazoan signalling pathways can be rewired to dampen or amplify the rate of events, such as those that occur in development and aging. Given that a linear network topology restricts the capacity to rewire signalling pathways, such scalability of the pace of biological events suggests the existence of programmable non-linear elements in the underlying signalling pathways. Here, we review the network topology of key signalling pathways with a focus on redox-sensitive proteins, including PTEN and Ras GTPase, that reshape the connectivity profile of signalling pathways in response to an altered redox state. While this network-level impact of redox is achieved by the modulation of individual redox-sensitive proteins, it is the population by these proteins of critical nodes in a network topology of signal transduction pathways that amplifies the impact of redox-mediated reprogramming. We propose that redox-mediated rewiring is essential to regulate the rate of transmission of biological signals, giving rise to a programmable cellular clock that orchestrates the pace of biological phenomena such as development and aging. We further review the evidence that an aberrant redox-mediated modulation of output of the cellular clock contributes to the emergence of pathological conditions affecting the human brain.

Genomic Variation, Population History, and Long-Term Genetic Adaptation to High Altitudes in Tibetan Partridge (Perdix hodgsoniae)

Species residing across elevational gradients display adaptations in response to environmental changes such as oxygen availability, ultraviolet radiation, and temperature. Here, we study genomic variation, gene expression, and long-term adaptation in Tibetan Partridge (Perdix hodgsoniae) populations residing across the elevational gradient of the Tibetan Plateau. We generated a high-quality draft genome and used it to carry out downstream population genomic and transcriptomic analysis. The P. hodgsoniae populations residing across various elevations were genetically distinct, and their phylogenetic clustering was consistent with their geographic distribution. We identified possible evidence of gene flow between populations residing in <3,000 and >4,200 m elevation that is consistent with known habitat expansion of high-altitude populations of P. hodgsoniae to a lower elevation. We identified a 60 kb haplotype encompassing the Estrogen Receptor 1 (ESR1) gene, showing strong genetic divergence between populations of P. hodgsoniae. We identified six single nucleotide polymorphisms within the ESR1 gene fixed for derived alleles in high-altitude populations that are strongly conserved across vertebrates. We also compared blood transcriptome profiles and identified differentially expressed genes (such as GAPDH, LDHA, and ALDOC) that correlated with differences in altitude among populations of P. hodgsoniae. These candidate genes from population genomics and transcriptomics analysis were enriched for neutrophil degranulation and glycolysis pathways, which are known to respond to hypoxia and hence may contribute to long-term adaptation to high altitudes in P. hodgsoniae. Our results highlight Tibetan Partridges as a useful model to study molecular mechanisms underlying long-term adaptation to high altitudes.

Controlling pericellular oxygen tension in cell culture reveals distinct breast cancer responses to low oxygen tensions

Oxygen (O2) tension plays a key role in tissue function and pathophysiology. O2-controlled cell culture, in which the O2 concentration in an incubator's gas phase is controlled, is an indispensable tool to study the role of O2 in vivo. For this technique, it is presumed that the incubator setpoint is equal to the O2 tension that cells experience (i.e., pericellular O2). We discovered that physioxic (5% O2) and hypoxic (1% O2) setpoints regularly induce anoxic (0.0% O2) pericellular tensions in both adherent and suspension cell cultures. Electron transport chain inhibition ablates this effect, indicating that cellular O2 consumption is the driving factor. RNA-seq revealed that primary human hepatocytes cultured in physioxia experience ischemia-reperfusion injury due to anoxic exposure followed by rapid reoxygenation. To better understand the relationship between incubator gas phase and pericellular O2 tensions, we developed a reaction-diffusion model that predicts pericellular O2 tension a priori. This model revealed that the effect of cellular O2 consumption is greatest in smaller volume culture vessels (e.g., 96-well plate). By controlling pericellular O2 tension in cell culture, we discovered that MCF7 cells have stronger glycolytic and glutamine metabolism responses in anoxia vs. hypoxia. MCF7 also expressed higher levels of HIF2A, CD73, NDUFA4L2, etc. and lower levels of HIF1A, CA9, VEGFA, etc. in response to hypoxia vs. anoxia. Proteomics revealed that 4T1 cells had an upregulated epithelial-to-mesenchymal transition (EMT) response and downregulated reactive oxygen species (ROS) management, glycolysis, and fatty acid metabolism pathways in hypoxia vs. anoxia. Collectively, these results reveal that breast cancer cells respond non-monotonically to low O2, suggesting that anoxic cell culture is not suitable to model hypoxia. We demonstrate that controlling atmospheric O2 tension in cell culture incubators is insufficient to control O2 in cell culture and introduce the concept of pericellular O2-controlled cell culture.

In vivo optical imaging of tumor stromal cells with hypoxia-inducible factor activity

Tumors contain various stromal cells, such as immune cells, endothelial cells, and fibroblasts, which contribute to the development of a tumor-specific microenvironment characterized by hypoxia and inflammation, and are associated with malignant progression. In this study, we investigated the activity of intratumoral hypoxia-inducible factor (HIF), which functions as a master regulator of the cellular response to hypoxia and inflammation. We constructed the HIF activity-monitoring reporter gene hypoxia-response element-Venus-Akaluc (HVA) that expresses the green fluorescent protein Venus and modified firefly luciferase Akaluc in a HIF activity-dependent manner, and created transgenic mice harboring HVA transgene (HVA-Tg). In HVA-Tg, HIF-active cells can be visualized using AkaBLI, an ultra-sensitive in vivo bioluminescence imaging technology that produces an intense near-infrared light upon reaction of Akaluc with the D-luciferin analog AkaLumine-HCl. By orthotopic transplantation of E0771, a mouse triple negative breast cancer cell line without a reporter gene, into HVA-Tg, we succeeded in noninvasively monitoring bioluminescence signals from HIF-active stromal cells as early as 8 days after transplantation. The HIF-active stromal cells initially clustered locally and then spread throughout the tumors with growth. Immunohistochemistry and flow cytometry analyses revealed that CD11b+ F4/80+ macrophages were the predominant HIF-active stromal cells in E0771 tumors. These results indicate that HVA-Tg is a useful tool for spatiotemporal analysis of HIF-active tumor stromal cells, facilitating investigation of the roles of HIF-active tumor stromal cells in tumor growth and malignant progression.

Intracellular energy production and distribution in hypoxia

The hydrolysis of ATP is the primary source of metabolic energy for eukaryotic cells. Under physiological conditions, cells generally produce more than sufficient levels of ATP to fuel the active biological processes necessary to maintain homeostasis. However, mechanisms underpinning the distribution of ATP to subcellular microenvironments with high local demand remain poorly understood. Intracellular distribution of ATP in normal physiological conditions has been proposed to rely on passive diffusion across concentration gradients generated by ATP producing systems such as the mitochondria and the glycolytic pathway. However, subcellular microenvironments can develop with ATP deficiency due to increases in local ATP consumption. Alternatively, ATP production can be reduced during bioenergetic stress during hypoxia. Mammalian cells therefore need to have the capacity to alter their metabolism and energy distribution strategies to compensate for local ATP deficits while also controlling ATP production. It is highly likely that satisfying the bioenergetic requirements of the cell involves the regulated distribution of ATP producing systems to areas of high ATP demand within the cell. Recently, the distribution (both spatially and temporally) of ATP-producing systems has become an area of intense investigation. Here, we review what is known (and unknown) about intracellular energy production and distribution and explore potential mechanisms through which this targeted distribution can be altered in hypoxia, with the aim of stimulating investigation in this important, yet poorly understood field of research.

Environmental and behavioral regulation of HIF-mitochondria crosstalk

Reduced oxygen availability (hypoxia) can lead to cell and organ damage. Therefore, aerobic species depend on efficient mechanisms to counteract detrimental consequences of hypoxia. Hypoxia inducible factors (HIFs) and mitochondria are integral components of the cellular response to hypoxia and coordinate both distinct and highly intertwined adaptations. This leads to reduced dependence on oxygen, improved oxygen supply, maintained energy provision by metabolic remodeling and tapping into alternative pathways and increased resilience to hypoxic injuries. On one hand, many pathologies are associated with hypoxia and hypoxia can drive disease progression, for example in many cancer and neurological diseases. But on the other hand, controlled induction of hypoxia responses via HIFs and mitochondria can elicit profound health benefits and increase resilience. To tackle pathological hypoxia conditions or to apply health-promoting hypoxia exposures efficiently, cellular and systemic responses to hypoxia need to be well understood. Here we first summarize the well-established link between HIFs and mitochondria in orchestrating hypoxia-induced adaptations and then outline major environmental and behavioral modulators of their interaction that remain poorly understood.

Manipulation of iron status on cerebral blood flow at high altitude in lowlanders and adapted highlanders

Cerebral blood flow (CBF) increases during hypoxia to counteract the reduction in arterial oxygen content. The onset of tissue hypoxemia coincides with the stabilization of hypoxia-inducible factor (HIF) and transcription of downstream HIF-mediated processes. It has yet to be determined, whether HIF down- or upregulation can modulate hypoxic vasodilation of the cerebral vasculature. Therefore, we examined whether: 1) CBF would increase with iron depletion (via chelation) and decrease with repletion (via iron infusion) at high-altitude, and 2) explore whether genotypic advantages of highlanders extend to HIF-mediated regulation of CBF. In a double-blinded and block-randomized design, CBF was assessed in 82 healthy participants (38 lowlanders, 20 Sherpas and 24 Andeans), before and after the infusion of either: iron(III)-hydroxide sucrose, desferrioxamine or saline. Across both lowlanders and highlanders, baseline iron levels contributed to the variability in cerebral hypoxic reactivity at high altitude (R2 = 0.174, P < 0.001). At 5,050 m, CBF in lowlanders and Sherpa were unaltered by desferrioxamine or iron. At 4,300 m, iron infusion led to 4 ± 10% reduction in CBF (main effect of time p = 0.043) in lowlanders and Andeans. Iron status may provide a novel, albeit subtle, influence on CBF that is potentially dependent on the severity and length-of-stay at high altitude.

Hypoxia inducible factor-1α is an important regulator of macrophage biology

Hypoxia-inducible factor-1 (HIF-1), a heterodimeric transcription factor composed of the α and β subunits, regulates cellular adaptive responses to hypoxia. Macrophages, which are derived from monocytes, function as antigen-presenting cells that activate various immune responses. HIF-1α regulates the immune response, viability, migration, phenotypic plasticity, and metabolism of macrophages. Specifically, macrophage-derived HIF-1α can prevent excessive pro-inflammatory responses by attenuating the transcriptional activity of nuclear factor-kappa B in vivo and in vitro. HIF-1α modulates macrophage migration by inducing the release of various chemokines and providing necessary energy. HIF-1α promotes macrophage M1 polarization by targeting glucose metabolism. Additionally, HIF-1α induces the upregulation of glycolysis-related enzymes and intermediates of the tricarboxylic acid cycle and pentose phosphate pathway. HIF-1α promotes macrophage apoptosis, necroptosis and reduces autophagy. The current review highlights the mechanisms associated with the regulation of HIF-1α stabilization in macrophages as well as the role of HIF-1α in modulating the physiological functions of macrophages.

Harnessing EGLN1 Gene Editing to Amplify HIF-1α and Enhance Human Angiogenic Response

Therapeutic angiogenesis has been the focus of hundreds of clinical trials but approval for human treatment remains elusive. Current strategies often rely on the upregulation of a single proangiogenic factor, which fails to recapitulate the complex response needed in hypoxic tissues. Hypoxic oxygen tensions dramatically decrease the activity of hypoxia inducible factor prolyl hydroxylase 2 (PHD2), the primary oxygen sensing portion of the hypoxia inducible factor 1 alpha (HIF-1α) proangiogenic master regulatory pathway. Repressing PHD2 activity increases intracellular levels of HIF-1α and impacts the expression of hundreds of downstream genes directly associated with angiogenesis, cell survival, and tissue homeostasis. This study explores activating the HIF-1α pathway through Sp Cas9 knockout of the PHD2 encoding gene EGLN1 as an innovative in situ therapeutic angiogenesis strategy for chronic vascular diseases. Our findings demonstrate that even low editing rates of EGLN1 lead to a strong proangiogenic response regarding proangiogenic gene transcription, protein production, and protein secretion. In addition, we show that secreted factors of EGLN1 edited cell cultures may enhance human endothelial cell neovascularization activity in the context of proliferation and motility. Altogether, this study reveals that EGLN1 gene editing shows promise as a potential therapeutic angiogenesis strategy.

The Sweet Side of HIPK2

HIPK2 is an evolutionary conserved protein kinase which modulates many molecular pathways involved in cellular functions such as apoptosis, DNA damage response, protein stability, and protein transcription. HIPK2 plays a key role in the cancer cell response to cytotoxic drugs as its deregulation impairs drug-induced cancer cell death. HIPK2 has also been involved in regulating fibrosis, angiogenesis, and neurological diseases. Recently, hyperglycemia was found to positively and/or negatively regulate HIPK2 activity, affecting not only cancer cell response to chemotherapy but also the progression of some diabetes complications. The present review will discuss how HIPK2 may be influenced by the high glucose (HG) metabolic condition and the consequences of such regulation in medical conditions.

Quantitative Imaging of Hypoxic CAIX-Positive Tumor Areas with Low Immune Cell Infiltration in Syngeneic Mouse Tumor Models

Limited diffusion of oxygen in combination with increased oxygen consumption leads to chronic hypoxia in most solid malignancies. This scarcity of oxygen is known to induce radioresistance and leads to an immunosuppressive microenvironment. Carbonic anhydrase IX (CAIX) is an enzyme functioning as a catalyzer for acid export in hypoxic cells and is an endogenous biomarker for chronic hypoxia. The aim of this study is to develop a radiolabeled antibody that recognizes murine CAIX to visualize chronic hypoxia in syngeneic tumor models and to study the immune cell population in these hypoxic areas. An anti-mCAIX antibody (MSC3) was conjugated to diethylenetriaminepentaacetic acid (DTPA) and radiolabeled with indium-111 (¹¹¹In). CAIX expression on murine tumor cells was determined using flow cytometry, and in vitro affinity of [¹¹¹In]In-MSC3 was analyzed in a competitive binding assay. Ex vivo biodistribution studies were performed to determine in vivo radiotracer distribution. CAIX⁺ tumor fractions were determined by mCAIX microSPECT/CT, and the tumor microenvironment was analyzed using immunohistochemistry and autoradiography. We showed that [¹¹¹In]In-MSC3 binds to CAIX-expressing (CAIX⁺) murine cells in vitro and accumulates in CAIX⁺ areas in vivo. We optimized the use of [¹¹¹In]In-MSC3 for preclinical imaging such that it can be applied in syngeneic mouse models and showed that we can quantitatively distinguish between tumor models with varying CAIX⁺ fractions by ex vivo analyses and in vivo mCAIX microSPECT/CT. Analysis of the tumor microenvironment identified these CAIX⁺ areas as less infiltrated by immune cells. Together these data demonstrate that mCAIX microSPECT/CT is a sensitive technique to visualize hypoxic CAIX⁺ tumor areas that exhibit reduced infiltration of immune cells in syngeneic mouse models. In the future, this technique may enable visualization of CAIX expression before or during hypoxia-targeted or hypoxia-reducing treatments. Thereby, it will help optimize immuno- and radiotherapy efficacy in translationally relevant syngeneic mouse tumor models.

HIPK2 in Angiogenesis: A Promising Biomarker in Cancer Progression and in Angiogenic Diseases

Angiogenesis is the formation of new blood capillaries taking place from preexisting functional vessels, a process that allows cells to cope with shortage of nutrients and low oxygen availability. Angiogenesis may be activated in several pathological diseases, from tumor growth and metastases formation to ischemic and inflammatory diseases. New insights into the mechanisms that regulate angiogenesis have been discovered in the last years, leading to the discovery of new therapeutic opportunities. However, in the case of cancer, their success may be limited by the occurrence of drug resistance, meaning that the road to optimize such treatments is still long. Homeodomain-interacting protein kinase 2 (HIPK2), a multifaceted protein that regulates different molecular pathways, is involved in the negative regulation of cancer growth, and may be considered a "bona fide" oncosuppressor molecule. In this review, we will discuss the emerging link between HIPK2 and angiogenesis and how the control of angiogenesis by HIPK2 impinges in the pathogenesis of several diseases, including cancer.

Mint3 as a Potential Target for Cooling Down HIF-1α-Mediated Inflammation and Cancer Aggressiveness

Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor that plays a crucial role in cells adapting to a low-oxygen environment by facilitating a switch from oxygen-dependent ATP production to glycolysis. Mediated by membrane type-1 matrix metalloproteinase (MT1-MMP) expression, Munc-18-1 interacting protein 3 (Mint3) binds to the factor inhibiting HIF-1 (FIH-1) and inhibits its suppressive effect, leading to HIF-1α activation. Defects in Mint3 generally lead to improved acute inflammation, which is regulated by HIF-1α and subsequent glycolysis, as well as the suppression of the proliferation and metastasis of cancer cells directly through its expression in cancer cells and indirectly through its expression in macrophages or fibroblasts associated with cancer. Mint3 in inflammatory monocytes enhances the chemotaxis into metastatic sites and the production of vascular endothelial growth factors, which leads to the expression of E-selectin at the metastatic sites and the extravasation of cancer cells. Fibroblasts express L1 cell adhesion molecules in a Mint3-dependent manner and enhance integrin-mediated cancer progression. In pancreatic cancer cells, Mint3 directly promotes cancer progression. Naphthofluorescein, a Mint3 inhibitor, can disrupt the interaction between FIH-1 and Mint3 and potently suppress Mint3-mediated inflammation, cancer progression, and metastasis without causing marked adverse effects. In this review, we will introduce the potential of Mint3 as a therapeutic target for inflammatory diseases and cancers.

An overview of hyperbaric oxygen preconditioning against ischemic stroke

Ischemic stroke (IS) has become the second leading cause of morbidity and mortality worldwide, and the prevention of IS should be given high priority. Recent studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) may be a protective nonpharmacological method, but its underlying mechanisms remain poorly defined. This study comprehensively reviewed the pathophysiology of IS and revealed the underlying mechanism of HBO-PC in protection against IS. The preventive effects of HBO-PC against IS may include inducing antioxidant, anti-inflammation, and anti-apoptosis capacity; activating autophagy and immune responses; upregulating heat shock proteins, hypoxia-inducible factor-1, and erythropoietin; and exerting protective effects upon the blood-brain barrier. In addition, HBO-PC may be considered a safe and effective method to prevent IS in combination with stem cell therapy. Although the benefits of HBO-PC on IS have been widely observed in recent research, the implementation of this technique is still controversial due to regimen differences. Transferring the results to clinical application needs to be taken carefully, and screening for the optimal regimen would be a daunting task. In addition, whether we should prescribe an individualized preconditioning regimen to each stroke patient needs further exploration.

Value of whole-body dynamic 18F-FMISO PET/CT Patlak multi-parameter imaging for evaluating the early radiosensitizing effect of oleanolic acid on C6 rat gliomas

The purpose of this study was to investigate the value of tumour-to-muscle (T/M) ratios and Patlak Ki images extracted from whole-body dynamic ¹⁸F-fluoromisonidazole (FMISO) PET/CT Patlak multi-parameter imaging for evaluating the early radiosensitizing effect of oleanolic acid (OA). Twenty-four rats with C6 gliomas were divided into 4 groups and treated with OA (group B), radiotherapy (group C), both (group D) or neither (group A). Whole-body dynamic ¹⁸F-FMISO PET/CT scans were performed for 120 min before treatment and 24 h following the treatment course. The tumour samples were dissected for hematoxylin and eosin staining, and HIF-1α, Ki-67 and GLUT-1 immunohistochemical staining. PET images were analysed using kinetic modelling (Patlak Ki) and static analysis (T/M ratios), and correlated with immunohistochemical results. The changes in T/M ratios, Ki values and tumour volume before treatment and 24 h following the treatment course were compared, and the survival time of tumour-bearing rats was recorded. Kaplan-Meier analysis showed that OA combined with radiotherapy can inhibit tumour growth and prolong the survival time of tumour-bearing rats. Whole-body dynamic ¹⁸F-FMISO PET/CT showed that the Ki values in group D were significantly lower than those in group C, whilst there was no significant difference in T/M ratios between groups C and D. The Pearson correlation coefficient analysis showed that Ki values were significantly related to immunohistochemical results. Our study suggests that Patlak Ki images may add value to PET/CT static images for evaluating the early radio-sensitizing effect of OA.

Hypoxia signaling in cancer: Implications for therapeutic interventions

Hypoxia is a persistent physiological feature of many different solid tumors and a key driver of malignancy, and in recent years, it has been recognized as an important target for cancer therapy. Hypoxia occurs in the majority of solid tumors due to a poor vascular oxygen supply that is not sufficient to meet the needs of rapidly proliferating cancer cells. A hypoxic tumor microenvironment (TME) can reduce the effectiveness of other tumor therapies, such as radiotherapy, chemotherapy, and immunotherapy. In this review, we discuss the critical role of hypoxia in tumor development, including tumor metabolism, tumor immunity, and tumor angiogenesis. The treatment methods for hypoxic TME are summarized, including hypoxia-targeted therapy and improving oxygenation by alleviating tumor hypoxia itself. Hyperoxia therapy can be used to improve tissue oxygen partial pressure and relieve tumor hypoxia. We focus on the underlying mechanisms of hyperoxia and their impact on current cancer therapies and discuss the prospects of hyperoxia therapy in cancer treatment.

Large-scale perfused tissues via synthetic 3D soft microfluidics

The vascularization of engineered tissues and organoids has remained a major unresolved challenge in regenerative medicine. While multiple approaches have been developed to vascularize in vitro tissues, it has thus far not been possible to generate sufficiently dense networks of small-scale vessels to perfuse large de novo tissues. Here, we achieve the perfusion of multi-mm3 tissue constructs by generating networks of synthetic capillary-scale 3D vessels. Our 3D soft microfluidic strategy is uniquely enabled by a 3D-printable 2-photon-polymerizable hydrogel formulation, which allows for precise microvessel printing at scales below the diffusion limit of living tissues. We demonstrate that these large-scale engineered tissues are viable, proliferative and exhibit complex morphogenesis during long-term in-vitro culture, while avoiding hypoxia and necrosis. We show by scRNAseq and immunohistochemistry that neural differentiation is significantly accelerated in perfused neural constructs. Additionally, we illustrate the versatility of this platform by demonstrating long-term perfusion of developing neural and liver tissue. This fully synthetic vascularization platform opens the door to the generation of human tissue models at unprecedented scale and complexity.

ZBTB2 links p53 deficiency to HIF-1-mediated hypoxia signaling to promote cancer aggressiveness

Aberrant activation of the hypoxia-inducible transcription factor HIF-1 and dysfunction of the tumor suppressor p53 have been reported to induce malignant phenotypes and therapy resistance of cancers. However, their mechanistic and functional relationship remains largely unknown. Here, we reveal a mechanism by which p53 deficiency triggers the activation of HIF-1-dependent hypoxia signaling and identify zinc finger and BTB domain-containing protein 2 (ZBTB2) as an important mediator. ZBTB2 forms homodimers via its N-terminus region and increases the transactivation activity of HIF-1 only when functional p53 is absent. The ZBTB2 homodimer facilitates invasion, distant metastasis, and growth of p53-deficient, but not p53-proficient, cancers. The intratumoral expression levels of ZBTB2 are associated with poor prognosis in lung cancer patients. ZBTB2 N-terminus-mimetic polypeptides competitively inhibit ZBTB2 homodimerization and significantly suppress the ZBTB2-HIF-1 axis, leading to antitumor effects. Our data reveal an important link between aberrant activation of hypoxia signaling and loss of a tumor suppressor and provide a rationale for targeting a key mediator, ZBTB2, to suppress cancer aggressiveness.

Modeling hypoxia-related inflammation scenarios

Cells respond to hypoxia via the activation of three isoforms of Hypoxia Inducible Factors (HIFs), that are characterized by different activation times. HIF overexpression has many effects on cell behavior, such as change in metabolism, promotion of angiogenic processes and elicitation of a pro-inflammatory response. These effects are driving forces of malignant progression in cancer cells. In this work we study in detail hypoxia-induced dynamics of HIF1α and HIF2α, which are the most studied isoforms, comparing available experimental data on their evolution in tumor cells with the results obtained integrating the deduced mathematical model. Then, we examine the possible scenarios that characterize the link between hypoxia and inflammation via the activation of NFkB (Nuclear Factor k-light-chain-enhancer of activated B cells) when the dimensionless groups of parameters of the mathematical model change. In this way we are able to discuss why and when hypoxic conditions lead to acute or chronic inflammatory states.

The Latest Evidence of Erythropoietin in the Treatment of Glaucoma

Erythropoietin (EPO) is a circulating hormone conventionally considered to be responsible for erythropoiesis. In addition to facilitating red blood cell production, EPO has pluripotent potential, such as for cognition improvement, neurogenesis, and anti-fibrotic, anti-apoptotic, anti-oxidative, and anti-inflammatory effects. In human retinal tissues, EPO receptors (EPORs) are expressed in the photoreceptor cells, retinal pigment epithelium, and retinal ganglion cell layer. Studies have suggested its potential therapeutic effects in many neurodegenerative diseases, including glaucoma. In this review, we discuss the correlation between glaucoma and EPO, physiology and potential neuroprotective function of the EPO/EPOR system, and latest evidence for the treatment of glaucoma with EPO.

Inner ear organoids: progress and outlook, with a focus on the vascularization

The inner ear is a complex organ that encodes sound, motion, and orientation in space. Given the complexity of the inner ear, it is not surprising that treatments are relatively limited despite the fact that, in 2015, hearing loss was the fourth leading cause of years lived with disability worldwide. Inner ear organoid models are a promising tool to advance the study of multiple aspects of the inner ear to aid the development of new treatments and validate drug-based therapies. The blood supply of the inner ear plays a pivotal role in growth, maturation, and survival of inner ear tissues and their physiological functions. This vasculature cannot be ignored in order to achieve a truly in vivo-like model that mimics the microenvironment and niches of organ development. However, this aspect of organoid development has remained largely absent in the generation of inner ear organoids. The current review focuses on three-dimensional inner ear organoid and how recent technical progress in generating in vitro vasculature can enhance the next generation of these models.

Adaptive Responses to Hypoxia and/or Hyperoxia in Humans

Significance: Oxygen is indispensable for aerobic life, but its utilization exposes cells and tissues to oxidative stress; thus, tight regulation of cellular, tissue, and systemic oxygen concentrations is crucial. Here, we review the current understanding of how the human organism (mal-)adapts to low (hypoxia) and high (hyperoxia) oxygen levels and how these adaptations may be harnessed as therapeutic or performance enhancing strategies at the systemic level. Recent Advances: Hyperbaric oxygen therapy is already a cornerstone of modern medicine, and the application of mild hypoxia, that is, hypoxia conditioning (HC), to strengthen the resilience of organs or the whole body to severe hypoxic insults is an important preparation for high-altitude sojourns or to protect the cardiovascular system from hypoxic/ischemic damage. Many other applications of adaptations to hypo- and/or hyperoxia are only just emerging. HC-sometimes in combination with hyperoxic interventions-is gaining traction for the treatment of chronic diseases, including numerous neurological disorders, and for performance enhancement. Critical Issues: The dose- and intensity-dependent effects of varying oxygen concentrations render hypoxia- and/or hyperoxia-based interventions potentially highly beneficial, yet hazardous, although the risks versus benefits are as yet ill-defined. Future Directions: The field of low and high oxygen conditioning is expanding rapidly, and novel applications are increasingly recognized, for example, the modulation of aging processes, mood disorders, or metabolic diseases. To advance hypoxia/hyperoxia conditioning to clinical applications, more research on the effects of the intensity, duration, and frequency of altered oxygen concentrations, as well as on individual vulnerabilities to such interventions, is paramount. Antioxid. Redox Signal. 37, 887-912.

Computational Modeling and Imaging of the Intracellular Oxygen Gradient

Computational modeling can provide a mechanistic and quantitative framework for describing intracellular spatial heterogeneity of solutes such as oxygen partial pressure (pO₂). This study develops and evaluates a finite-element model of oxygen-consuming mitochondrial bioenergetics using the COMSOL Multiphysics program. The model derives steady-state oxygen (O₂) distributions from Fickian diffusion and Michaelis–Menten consumption kinetics in the mitochondria and cytoplasm. Intrinsic model parameters such as diffusivity and maximum consumption rate were estimated from previously published values for isolated and intact mitochondria. The model was compared with experimental data collected for the intracellular and mitochondrial pO₂ levels in human cervical cancer cells (HeLa) in different respiratory states and under different levels of imposed pO₂. Experimental pO₂ gradients were measured using lifetime imaging of a Förster resonance energy transfer (FRET)-based O₂ sensor, Myoglobin-mCherry, which offers in situ real-time and noninvasive measurements of subcellular pO₂ in living cells. On the basis of these results, the model qualitatively predicted (1) the integrated experimental data from mitochondria under diverse experimental conditions, and (2) the impact of changes in one or more mitochondrial processes on overall bioenergetics.

The Role of Inflammation in Cognitive Impairment of Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) has become a major worldwide public health concern, given its global prevalence. It has clear links with multiple comorbidities and mortality. Cognitive impairment is one related comorbidity causing great pressure on individuals and society. The clinical manifestations of cognitive impairment in OSAS include decline in attention/vigilance, verbal–visual memory loss, visuospatial/structural ability impairment, and executive dysfunction. It has been proven that chronic intermittent hypoxia (CIH) may be a main cause of cognitive impairment in OSAS. Inflammation plays important roles in CIH-induced cognitive dysfunction. Furthermore, the nuclear factor kappa B and hypoxia-inducible factor 1 alpha pathways play significant roles in this inflammatory mechanism. Continuous positive airway pressure is an effective therapy for OSAS; however, its effect on cognitive impairment is suboptimal. Therefore, in this review, we address the role inflammation plays in the development of neuro-impairment in OSAS and the association between OSAS and cognitive impairment to provide an overview of its pathophysiology. We believe that furthering the understanding of the inflammatory mechanisms involved in OSAS-associated cognitive impairment could lead to the development of appropriate and effective therapy.

Overcoming the Impact of Hypoxia in Driving Radiotherapy Resistance in Head and Neck Squamous Cell Carcinoma

Hypoxia is very common in most solid tumours and is a driving force for malignant progression as well as radiotherapy and chemotherapy resistance. Incidences of head and neck squamous cell carcinoma (HNSCC) have increased in the last decade and radiotherapy is a major therapeutic technique utilised in the treatment of the tumours. However, effectiveness of radiotherapy is hindered by resistance mechanisms and most notably by hypoxia, leading to poor patient prognosis of HNSCC patients. The phenomenon of hypoxia-induced radioresistance was identified nearly half a century ago, yet despite this, little progress has been made in overcoming the physical lack of oxygen. Therefore, a more detailed understanding of the molecular mechanisms of hypoxia and the underpinning radiobiological response of tumours to this phenotype is much needed. In this review, we will provide an up-to-date overview of how hypoxia alters molecular and cellular processes contributing to radioresistance, particularly in the context of HNSCC, and what strategies have and could be explored to overcome hypoxia-induced radioresistance.

Hypoxia: molecular pathophysiological mechanisms in human diseases

Hypoxia, a low O2 tension, is a fundamental feature that occurs in physiological events as well as pathophysiological conditions, especially mentioned for its role in the mechanism of angiogenesis, glucose metabolism, and cell proliferation/survival. The hypoxic state through the activation of specific mechanisms is an aggravating circumstance commonly noticed in multiple sclerosis, cancer, heart disease, kidney disease, liver disease, lung disease, and in inflammatory bowel disease. On the other hand, hypoxia could play a key role in tissue regeneration and repair of damaged tissues, especially by acting on specific tissue stem cells, but their features may result as a disadvantage when it is concerned for neoplastic stem cells. Furthermore, hypoxia could also have a potential role in tissue engineering and regenerative medicine due to its capacity to improve the performance of biomaterials. The current review aims to highlight the hypoxic molecular mechanisms reported in different pathological conditions to provide an overview of hypoxia as a therapeutic agent in regenerative and molecular therapy.

Graphical abstract