Preferential activation of HIF-2α adaptive signalling in neuronal-like cells in response to acute hypoxia

GLUT3/SLC2A3 Is an Endogenous Marker of Hypoxia in Prostate Cancer Cell Lines and Patient-Derived Xenograft Tumors

The microenvironment of solid tumors is dynamic and frequently contains pockets of low oxygen levels (hypoxia) surrounded by oxygenated tissue. Indeed, a compromised vasculature is a hallmark of the tumor microenvironment, creating both spatial gradients and temporal variability in oxygen availability. Notably, hypoxia associates with increased metastasis and poor survival in patients. Therefore, to aid therapeutic decisions and better understand hypoxia’s role in cancer progression, it is critical to identify endogenous biomarkers of hypoxia to spatially phenotype oncogenic lesions in human tissue, whether precancerous, benign, or malignant. Here, we characterize the glucose transporter GLUT3/SLC2A3 as a biomarker of hypoxic prostate epithelial cells and prostate tumors. Transcriptomic analyses of non-tumorigenic, immortalized prostate epithelial cells revealed a highly significant increase in GLUT3 expression under hypoxia. Additionally, GLUT3 protein increased 2.4-fold in cultured hypoxic prostate cell lines and was upregulated within hypoxic regions of xenograft tumors, including two patient-derived xenografts (PDX). Finally, GLUT3 out-performs other established hypoxia markers; GLUT3 staining in PDX specimens detects 2.6–8.3 times more tumor area compared to a mixture of GLUT1 and CA9 antibodies. Therefore, given the heterogeneous nature of tumors, we propose adding GLUT3 to immunostaining panels when trying to detect hypoxic regions in prostate samples.

Hypoxia-inducible Factor 2α Exerts Neuroprotective Effects by Promoting Angiogenesis via the VEGF/Notch Pathway after Intracerebral Hemorrhage Injury in Rats

Angiogenesis after intracerebral hemorrhage (ICH) injury can effectively alleviate brain damage and improve neurological function. Hypoxia-inducible factor 2α (HIF-2α) is an important angiogenic regulator and exhibits protective effects in several neurological diseases; however, its role in ICH has not yet been reported. Hence, in the present study, we explored whether HIF-2α reduces ICH injury by promoting angiogenesis. In addition, we explored the role of the vascular endothelial growth factor (VEGF)/Notch pathway in HIF-2α-mediated angiogenesis. We injected 50 μL of autologous blood taken from the femoral artery into the right striatum of healthy male adult Sprague-Dawley rats to create an autologous-blood-induced rat model of ICH. Lentiviral vectors were injected to both overexpress and knock down HIF-2α expression. VEGF receptor 2 (VEGFR2) and Notch-specific inhibitors were injected intraperitoneally to block VEGFR2- and Notch-mediated signaling after lentiviral injections. Our data showed that HIF-2α overexpression reduced neurological-damage scores and brain-water content, suggesting it had a protective effect on ICH injury. In addition, overexpression of HIF-2α promoted angiogenesis, increased focal cerebral blood flow (CBF), and reduced neuronal damage, whereas HIF-2α knockdown resulted in the opposite effects. Furthermore, we found that HIF-2α-mediated angiogenesis was blocked by a Notch-specific inhibitor. Likewise, the HIF-2α-mediated increase in phospho-VEGFR-2, cleaved-Notch1 and Notch1 expression was reversed via a VEGFR2-specific inhibitor. Taken together, our results indicate that HIF-2α promotes angiogenesis via the VEGF/Notch pathway to attenuate ICH injury. Moreover, our findings may contribute to the development of a novel strategy for alleviating ICH injury via HIF-2α-mediated upregulation of angiogenesis.

Hypoxia-inducible factor (HIF) prolyl hydroxylase inhibitors induce autophagy and have a protective effect in an in-vitro ischaemia model

This study compared effects of five hypoxia-inducible factor (HIF) prolyl hydroxylases (PHD) inhibitors on PC12 cells and primary rat neurons following oxygen-glucose deprivation (OGD). At 100 µM, the PHD inhibitors did not cause cytotoxicity and apoptosis. MTT activity was only significantly reduced by FG4592 or Bayer 85-3934 in PC12 cells. The PHD inhibitors at 100 µM significantly increased the LC3-II/LC3-I expression ratio and downregulated p62 in PC12 cells, so did FG4592 (30 µM) and DMOG (100 µM) in neurons. HIF-1α was stabilised in PC12 cells by all the PHD inhibitors at 100 µM except for DMOG, which stabilised HIF-1α at 1 and 2 mM. In primary neurons, HIF-1α was stabilised by FG4592 (30 µM) and DMOG (100 µM). Pretreatment with the PHD inhibitors 24 hours followed by 24 hour reoxygenation prior to 6 hours OGD (0.3% O₂) significantly reduced LDH release and increased MTT activity compared to vehicle (1% DMSO) pretreatment. In conclusion, the PHD inhibitors stabilise HIF-1α in normoxia, induce autophagy, and protect cells from a subsequent OGD insult. The new class of PHD inhibitors (FG4592, FG2216, GSK1278863, Bay85-3934) have the higher potency than DMOG. The interplay between autophagy, HIF stabilisation and neuroprotection in ischaemic stroke merits further investigation.

The Arginase Pathway in Neonatal Brain Hypoxia-Ischemia

Brain damage after hypoxia-ischemia (HI) occurs in an age-dependent manner. Neuroprotective strategies assumed to be effective in adults might have deleterious effects in the immature brain. In order to create effective therapies, the complex pathophysiology of HI in the developing brain requires exploring new mechanisms. Critical determinants of neuronal survival after HI are the extent of vascular dysfunction, inflammation, and oxidative stress, followed later by tissue repair. The key enzyme of these processes in the human body is arginase (ARG) that acts via the bioavailability of nitric oxide, and the synthesis of polyamines and proline. ARG is expressed throughout the brain in different cells. However, little is known about the effect of ARG in pathophysiological states of the brain, especially hypoxia-ischemia. Here, we summarize the role of ARG during neurodevelopment as well as in various brain pathologies.