Upregulation of NADPH Oxidase 2 Contributes to Renal Fibrosis in pcy Mice: An Experimental Model of Nephronophthisis

<b><i>Background:</i></b> DBA/2FG-<i>pcy</i> (<i>pcy</i>) mice harbor a homozygous <i>Nphp3</i> missense mutation and develop nephronophthisis with renal interstitial fibrosis. Previous studies have shown that aberrant oxygen homeostasis contributes to the renal pathology in <i>pcy</i> mice, but the underlying molecular mechanism remains largely unknown. <b><i>Methods:</i></b> <i>pcy</i> mice and a control strain, DBA/2N (DBA) mice, were used. Renal levels of 62 mRNAs involved in oxygen homeostasis were investigated by real-time PCR, and the resulting data were used for extraction of pathological pathways. On the basis of the genes found to be upregulated and pathway analysis, further studies were performed using immunoblotting, immunohistochemistry, and pharmacological intervention. <b><i>Results:</i></b> In comparison with DBA mice, the levels of 18 mRNAs were altered by &#x3e;2-fold in <i>pcy</i> mice. Pathway analysis extracted molecular pathways related to oxidative stress, inflammation, and cell adhesion. As the levels of mRNAs relevant to the NADPH oxidase 2 (NOX2) pathway were prominently (4 genes &#x3e;5-fold) increased in <i>pcy</i> mice, we further analyzed the molecules related to this pathway. A time course study suggested that the pathway was gradually activated in <i>pcy</i> mice from at least 5 weeks of age. Immunohistochemistry study revealed that NOX2 protein was colocalized with a macrophage marker protein in the renal interstitium. Moreover, treatment of <i>pcy</i> mice with apocynin, an inhibitor of the NOX2 pathway, ameliorated the renal fibrosis. <b><i>Conclusion:</i></b> Our findings suggest that the activation of the NOX2 pathway, possibly mediated by macrophage infiltration, plays a pivotal role in progressive renal fibrosis in <i>pcy</i> mice.

Biological Functions and Regulatory Mechanisms of Hypoxia-Inducible Factor-1α in Ischemic Stroke

Ischemic stroke is caused by insufficient cerebrovascular blood and oxygen supply. It is a major contributor to death or disability worldwide and has become a heavy societal and clinical burden. To date, effective treatments for ischemic stroke are limited, and innovative therapeutic methods are urgently needed. Hypoxia inducible factor-1α (HIF-1α) is a sensitive regulator of oxygen homeostasis, and its expression is rapidly induced after hypoxia/ischemia. It plays an extensive role in the pathophysiology of stroke, including neuronal survival, neuroinflammation, angiogenesis, glucose metabolism, and blood brain barrier regulation. In addition, the spatiotemporal expression profile of HIF-1α in the brain shifts with the progression of ischemic stroke; this has led to contradictory findings regarding its function in previous studies. Therefore, unveiling the Janus face of HIF-1α and its target genes in different type of cells and exploring the role of HIF-1α in inflammatory responses after ischemia is of great importance for revealing the pathogenesis and identifying new therapeutic targets for ischemic stroke. Herein, we provide a succinct overview of the current approaches targeting HIF-1α and summarize novel findings concerning HIF-1α regulation in different types of cells within neurovascular units, including neurons, endothelial cells, astrocytes, and microglia, during the different stages of ischemic stroke. The current representative translational approaches focused on neuroprotection by targeting HIF-1α are also discussed.

Integration and Visualization of Regulatory Elements and Variations of the EPAS1 Gene in Human

Endothelial PAS domain-containing protein 1 (EPAS1), also HIF2α, is an alpha subunit of hypoxia-inducible transcription factor (HIF), which mediates cellular and systemic response to hypoxia. EPAS1 has an important role in the transcription of many hypoxia-responsive genes, however, it has been less researched than HIF1α. The aim of this study was to integrate an increasing number of data on EPAS1 into a map of diverse OMICs elements. Publications, databases, and bioinformatics tools were examined, including Ensembl, MethPrimer, STRING, miRTarBase, COSMIC, and LOVD. The EPAS1 expression, stability, and activity are tightly regulated on several OMICs levels to maintain complex oxygen homeostasis. In the integrative EPAS1 map we included: 31 promoter-binding proteins, 13 interacting miRNAs and one lncRNA, and 16 post-translational modifications regulating EPAS1 protein abundance. EPAS1 has been associated with various cancer types and other diseases. The development of neuroendocrine tumors and erythrocytosis was shown to be associated with 11 somatic and 20 germline variants. The integrative map also includes 12 EPAS1 target genes and 27 interacting proteins. The study introduced the first integrative map of diverse genomics, transcriptomics, proteomics, regulomics, and interactomics data associated with EPAS1, to enable a better understanding of EPAS1 activity and regulation and support future research.

High altitude exposure affects male reproductive parameters: Could it also affect the prostate?†

Living at high altitudes and living with prostatic illness are two different conditions closely related to a hypoxic environment. People at high altitudes exposed to acute, chronic, or intermittent hypobaric hypoxia turn on several mechanisms at the system, cellular and molecular level to cope with oxygen atmosphere scarcity maintaining the oxygen homeostasis. This exposure affects the whole organism and function of many systems, such as cardiovascular, respiratory, and reproductive. On the other hand, malignant prostate is related to the scarcity of oxygen in the tissue microenvironment due to its low availability and high consumption due to the swift cell proliferation rates. Based on the literature, this similarity in the oxygen scarcity suggests that hypobaric hypoxia, and other common factors between these two conditions, could be involved in the aggravation of the pathological prostatic status. However, there is still a lack of evidence in the association of this disease in males at high altitudes. This review aims to examine the possible mechanisms that hypobaric hypoxia might negatively add to the pathological prostate function in males who live and work at high altitudes. More profound investigations of hypobaric hypoxia’s direct action on the prostate could help understand this exposure’s effect and prevent worse prostate illness impact in males at high altitudes.

Organization of Retinal Microvessels: Assessment Using Optical Coherence Tomography Angiography

Background: The vast majority of oxygen required for outer retinal layer, including photoreceptors is provided by choriocapillaris with a little support of deep retinal capillaris. This organization may differ between individuals depending on the variability in photoreceptor density. Based on these, we evaluated the changes and interaction between the retinal capillary networks—organization of retinal microvessels—using optical coherence tomography angiography (OCTA) considering ocular perfusion pressure (OPP) and diurnal variations. Methods: Forty eyes of 40 healthy volunteers formed the sample for this cross-sectional study. Mean arterial pressure (mAP), OPP, and OCTA measures were noted at two different time points on a single day. Results: The mAP, OPP, superficial capillary plexus (SCP), deep capillary plexus (DCP), and choriocapillaris (CC) perfusion values showed no diurnal change (p>0.05). When compared the mAP and OPP with the SCP, DCP, and CC perfusion measurements, there was no significant relation between them (p>0.05). There was a significant moderate positive correlation between DCP and CC values in both morning and afternoon (r=0.422; p=0.007, r=0.493; p=0.001, respectively). Conclusion: The DCP and CC perfusion values show a significant moderate positive correlation. This correlation may suggest the role of DCP in the maintenance of oxygen homeostasis in outer retinal layers.

The Impact of COVID-19 Infection on Oxygen Homeostasis: A Molecular Perspective

The novel coronavirus (2019-nCoV/SARS-CoV-2) causes respiratory symptoms including a substantial pulmonary dysfunction with worsening arterial hypoxemia (low blood oxygenation), eventually leading to acute respiratory distress syndrome (ARDS). The impact of the viral infection on blood oxygenation and other elements of oxygen homeostasis, such as oxygen sensing and respiratory mitochondrial mechanisms, are not well understood. As a step toward understanding these mechanisms in the context of COVID-19, recent experiments revealed contradictory data on the impact of COVID-19 infection on red blood cells (RBCs) oxygenation parameters. However, structural protein damage and membrane lipid remodeling in RBCs from COVID-19 patients that may impact RBC function have been reported. Moreover, COVID-19 infection could potentially disrupt one, if not all, of the other major pathways of homeostasis. Understanding the nature of the crosstalk among normal homeostatic pathways; oxygen carrying, oxygen sensing (i.e., hypoxia inducible factor, HIF) proteins, and the mitochondrial respiratory machinery may provide a target for therapeutic interventions.

Regulation of Oxygen Homeostasis at the Intestinal Epithelial Barrier Site

The unique biology of the intestinal epithelial barrier is linked to a low baseline oxygen pressure (pO2), characterised by a high rate of metabolites circulating through the intestinal blood and the presence of a steep oxygen gradient across the epithelial surface. These characteristics require tight regulation of oxygen homeostasis, achieved in part by hypoxia-inducible factor (HIF)-dependent signalling. Furthermore, intestinal epithelial cells (IEC) possess metabolic identities that are reflected in changes in mitochondrial function. In recent years, it has become widely accepted that oxygen metabolism is key to homeostasis at the mucosae. In addition, the gut has a vast and diverse microbial population, the microbiota. Microbiome–gut communication represents a dynamic exchange of mediators produced by bacterial and intestinal metabolism. The microbiome contributes to the maintenance of the hypoxic environment, which is critical for nutrient absorption, intestinal barrier function, and innate and/or adaptive immune responses in the gastrointestinal tract. In this review, we focus on oxygen homeostasis at the epithelial barrier site, how it is regulated by hypoxia and the microbiome, and how oxygen homeostasis at the epithelium is regulated in health and disease.

Comparative Analysis of Metabolic Differences of Jersey Cattle in Different High-Altitude Areas

In high-altitude area, hypoxia is a serious stress for humans and other animals, disrupting oxygen homeostasis and thus affecting tissue metabolism. Up to now, there are few reports on the metabolic changes of dairy cows at different altitudes. In this experiment, metabonomics technology and blood biochemical indexes were used to study the metabolic changes of dairy cows in different altitudes. The results showed that the different metabolites were mainly enriched in amino acid metabolism and sphingolipid metabolism, and sphingolipid metabolism showed a negative correlation with increased altitude. The results of this study will enrich the hypoxia-adaptive mechanism of dairy cows in high-altitude areas and provide a theoretical basis for the nutritional regulation of performance and disease treatment of dairy cows in high-altitude areas.

Involvement of HIF-1α in the Detection, Signaling, and Repair of DNA Double-Strand Breaks after Photon and Carbon-Ion Irradiation

Hypoxia-Inducible Factor 1α (HIF-1α), which promotes cancer cell survival, is the main regulator of oxygen homeostasis. Hypoxia combined with photon and carbon ion irradiation (C-ions) stabilizes HIF-1α. Silencing HIF-1α under hypoxia leads to substantial radiosensitization of Head-and-Neck Squamous Cell Carcinoma (HNSCC) cells after both photons and C-ions. Thus, this study aimed to clarify a potential involvement of HIF-1α in the detection, signaling, and repair of DNA Double-Strand-Breaks (DSBs) in response to both irradiations, in two HNSCC cell lines and their subpopulations of Cancer-Stem Cells (CSCs). After confirming the nucleoshuttling of HIF-1α in response to both exposure under hypoxia, we showed that silencing HIF-1α in non-CSCs and CSCs decreased the initiation of the DSB detection (P-ATM), and increased the residual phosphorylated H2AX (γH2AX) foci. While HIF-1α silencing did not modulate 53BP1 expression, P-DNA-PKcs (NHEJ-c) and RAD51 (HR) signals decreased. Altogether, our experiments demonstrate the involvement of HIF-1α in the detection and signaling of DSBs, but also in the main repair pathways (NHEJ-c and HR), without favoring one of them. Combining HIF-1α silencing with both types of radiation could therefore present a potential therapeutic benefit of targeting CSCs mostly present in tumor hypoxic niches.

(H)IF applicable: promotion of neurogenesis by induced HIF-2 signalling after ischaemia

HIF-2 represents a tissue-specific isoform of the hypoxia-inducible factors (HIFs) which regulate oxygen homeostasis in the cell. In acute oxygen deficiency, HIF transcription factors ensure the timely restoration of adequate oxygen supply. Particularly in medical conditions such as stroke, which have a high mortality risk due to ischaemic brain damage, rapid recovery of oxygen supply is of extraordinary importance. Nevertheless, the endogenous mechanisms are often not sufficient to respond to severe hypoxic stress with restoring oxygenation and fail to protect the tissue. Herein, we analysed murine neurospheres without functioning HIF-2α and found that special importance in the differentiation of neurons can be attributed to HIF-2 in the brain. Other processes, such as cell migration and signal transduction of different signalling pathways, appear to be mediated to some extent via HIF-2 and illustrate the function of HIF-2 in brain remodelling. Without hypoxic stress, HIF-2 in the brain presumably focuses on the fine-tuning of the neural network. However, a therapeutically increase of HIF-2 has the potential to regenerate or replace destroyed brain tissue and help minimize the consequences of an ischaemic stroke.