Targeting of HIF-alpha to the von Hippel-Lindau ubiquitylation complex by O2-regulated prolyl hydroxylation

Hypoxia drives HIF2-dependent reversible macrophage cell cycle entry

Low-oxygen conditions (hypoxia) have been associated primarily with cell-cycle arrest in dividing cells. Macrophages are typically quiescent in G0 but can proliferate in response to tissue signals. Here we show that hypoxia (1% oxygen tension) results in reversible entry into the cell cycle in macrophages. Cell cycle progression is largely limited to G0-G1/S phase transition with little progression to G2/M. This cell cycle transitioning is triggered by an HIF2α-directed transcriptional program. The response is accompanied by increased expression of cell-cycle-associated proteins, including CDK1, which is known to phosphorylate SAMHD1 at T592 and thereby regulate antiviral activity. Prolyl hydroxylase (PHD) inhibitors are able to recapitulate HIF2α-dependent cell cycle entry in macrophages. Finally, tumor-associated macrophages (TAMs) in lung cancers exhibit transcriptomic profiles representing responses to low oxygen and cell cycle progression at the single-cell level. These findings have implications for inflammation and tumor progression/metastasis where low-oxygen environments are common.

VHL loss enhances antitumor immunity by activating the anti-viral DNA-sensing pathway

von Hippel-Lindau (VHL), known as a tumor suppressor gene, is frequently mutated in clear cell renal cell carcinoma (ccRCC). However, VHL mutation is not sufficient to promote tumor formation. In most cases other than ccRCC, VHL loss alters cellular homeostasis and causes cell stress and metabolic changes by stabilizing hypoxia-inducible factor (HIF) levels, resulting in a fitness disadvantage. In addition, the function of VHL in regulating immune response is still not well established. In this study, we demonstrate that VHL loss enhances the efficacy of anti-programmed death 1 (PD1) treatment in multiple murine tumor models in a T cell-dependent manner. Mechanistically, we discovered that upregulation of HIF1α/2α induced by VHL loss decreased mitochondrial outer membrane potential and caused the cytoplasmic leakage of mitochondrial DNA, which triggered cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) activation and induced type I interferons. Our study thus provided mechanistic insights into the role of VHL gene loss in boosting antitumor immunity.

MicroRNA-138 inhibits hypoxia-inducible factor 1α expression in breast cancer cells

BACKGROUND

Hypoxia, a critical feature during cancer development, leads to the stabilization and activation of the hypoxia-inducible factor 1-alpha (HIF-1α) to drive the expression of many target genes which in turn can promote many aspects of breast cancer biology, mainly metastasis and resistance to therapy. MicroRNAs are known to modulate the expression of many genes involved in breast cancer tumorigenesis. In this study, we examined the regulatory effect of miRNAs on HIF1α expression.

METHODS

MCF-7 and MDA-MB-231 were cultivated under normoxia or hypoxia conditions. TaqMan-Low Density Array (TLDA) was used to characterize the miRNA signatures. Wild-Type (WT) or mutated fragments of HIF-1α 3'UTR containing the miR-138 potential target site were cloned downstream of the Renilla luciferase gene in the psiCHECK-1 plasmid. Luciferase assays were then carried out. A lentiviral vector containing copGFP as a reporter gene was prepared and transduced into MCF-7 and MDA-MB-231 cells to assess the effect of identified deregulated miRNAs on HIF-1α expression.

RESULTS

Under hypoxic conditions, MCF-7 cells showed deregulated expression for 12 miRNAs. In the case of MDA-MB-231 cells, 16 miRNAs were deregulated in response to hypoxia. Interestingly, miR-138 that was downregulated in both MCF-7 and MDA-MB-231 cells cultivated under hypoxic conditions appeared to have a binding site in 3'UTR of HIF-1α. Moreover, our results indicated that miR-138 could down regulate HIF-1α expression, upon binding directly to its 3'UTR.

CONCLUSIONS

Interestingly, our data highlights miR-138 as a potential therapeutic target to reduce HIF-1α expression and subsequently restrain breast cancer invasion and metastasis.

Metabolic pathways for glucose and fructose: I synthesis and metabolism of fructose by ovine conceptuses†

Fructose, the most abundant hexose sugar in fetal fluids and the blood of sheep and other ungulates and cetaceans, is synthesized from glucose via the polyol pathway in trophectoderm and chorion. However, the cell-specific and temporal expression of enzymes for the synthesis and metabolism of fructose in sheep conceptuses (embryo and placental membranes) and placentomes has not been characterized. This study characterized key enzymes involved in fructose synthesis and metabolism by ovine conceptuses throughout pregnancy. Day 17 conceptuses expressed mRNAs for the polyol pathway (SORD and AKR1B1) and glucose and fructose metabolism (HK1, HK2, G6PD, OGT, and FBP), but not those required for gluconeogenesis (G6Pase or PCK). Ovine placentomes also expressed mRNAs for SORD, AKR1B1, HK1, and OGT. Fructose can be metabolized via the ketohexokinase (KHK) pathway, and isoforms, KHK-A and KHK-C, were expressed in ovine conceptuses from Day 16 of pregnancy and placentomes during pregnancy in a cell-specific manner. The KHK-A protein was more abundant in the trophectoderm and cotyledons of placentomes, while KHK-C protein was more abundant in the endoderm of Day 16 conceptuses and the chorionic epithelium in placentomes. Expression of KHK mRNAs in placentomes was greatest at Day 30 of pregnancy (P < 0.05), but not different among days later in gestation. These results provide novel insights into the synthesis and metabolism of fructose via the uninhibited KHK pathway in ovine conceptuses to generate ATP via the tricarboxylic cycle, as well as substrates for the pentose cycle, hexosamine biosynthesis pathway, and one-carbon metabolism required for conceptus development throughout pregnancy.

Transcriptional landscape of a hypoxia response identifies cell-specific pathways for adaptation

How the HIF-1 (Hypoxia-Inducible) transcription factor drives and coordinates distinct responses to low oxygen across diverse cell types is poorly understood. We present a multi-tissue single-cell gene-expression atlas of the hypoxia response of the nematode Caenorhabditis elegans . This atlas highlights how cell-type-specific HIF-1 responses overlap and diverge among and within neuronal, intestinal, and muscle tissues. Using the atlas to guide functional analyses of candidate muscle-specific HIF-1 effectors, we discovered that HIF-1 activation drives downregulation of the tspo-1 ( TSPO, Translocator Protein) gene in vulval muscle cells to modulate a hypoxia-driven change in locomotion caused by contraction of body-wall muscle cells. We further showed that in human cardiomyocytes HIF-1 activation decreases levels of TSPO and thereby alters intracellular cholesterol transport and the mitochondrial network. We suggest that TSPO-1 is an evolutionarily conserved mediator of HIF-1-dependent modulation of muscle and conclude that our gene-expression atlas can help reveal how HIF-1 drives cell-specific adaptations to hypoxia.

Acod1-mediated inhibition of aerobic glycolysis suppresses osteoclast differentiation and attenuates bone erosion in arthritis

OBJECTIVES

Metabolic changes are crucially involved in osteoclast development and may contribute to bone degradation in rheumatoid arthritis (RA). The enzyme aconitate decarboxylase 1 (Acod1) is known to link the cellular function of monocyte-derived macrophages to their metabolic status. As osteoclasts derive from the monocyte lineage, we hypothesised a role for Acod1 and its metabolite itaconate in osteoclast differentiation and arthritis-associated bone loss.

METHODS

Itaconate levels were measured in human peripheral blood mononuclear cells (PBMCs) of patients with RA and healthy controls by mass spectrometry. Human and murine osteoclasts were treated with the itaconate derivative 4-octyl-itaconate (4-OI) in vitro. We examined the impact of Acod1-deficiency and 4-OI treatment on bone erosion in mice using K/BxN serum-induced arthritis and human TNF transgenic (hTNFtg) mice. SCENITH and extracellular flux analyses were used to evaluate the metabolic activity of osteoclasts and osteoclast progenitors. Acod1-dependent and itaconate-dependent changes in the osteoclast transcriptome were identified by RNA sequencing. CRISPR/Cas9 gene editing was used to investigate the role of hypoxia-inducible factor (Hif)-1α in Acod1-mediated regulation of osteoclast development.

RESULTS

Itaconate levels in PBMCs from patients with RA were inversely correlated with disease activity. Acod1-deficient mice exhibited increased osteoclast numbers and bone erosion in experimental arthritis while 4-OI treatment alleviated inflammatory bone loss in vivo and inhibited human and murine osteoclast differentiation in vitro. Mechanistically, Acod1 suppressed osteoclast differentiation by inhibiting succinate dehydrogenase-dependent production of reactive oxygen species and Hif1α-mediated induction of aerobic glycolysis.

CONCLUSION

Acod1 and itaconate are crucial regulators of osteoclast differentiation and bone loss in inflammatory arthritis.

Multi-omic Analyses Shed Light on The Genetic Control of High-altitude Adaptation in Sheep

Sheep were domesticated in the Fertile Crescent and then spread globally, where they have been encountering various environmental conditions. The Tibetan sheep has adapted to high altitudes on the Qinghai-Tibet Plateau over the past 3000 years. To explore genomic variants associated with high-altitude adaptation in Tibetan sheep, we analyzed Illumina short-reads of 994 whole genomes representing ∼ 60 sheep breeds/populations at varied altitudes, PacBio High fidelity (HiFi) reads of 13 breeds, and 96 transcriptomes from 12 sheep organs. Association testing between the inhabited altitudes and 34,298,967 variants was conducted to investigate the genetic architecture of altitude adaptation. Highly accurate HiFi reads were used to complement the current ovine reference assembly at the most significantly associated β-globin locus and to validate the presence of two haplotypes A and B among 13 sheep breeds. The haplotype A carried two homologous gene clusters: (1) HBE1, HBE2, HBB-like, and HBBC, and (2) HBE1-like, HBE2-like, HBB-like, and HBB; while the haplotype B lacked the first cluster. The high-altitude sheep showed highly frequent or nearly fixed haplotype A, while the low-altitude sheep dominated by haplotype B. We further demonstrated that sheep with haplotype A had an increased hemoglobin-O2 affinity compared with those carrying haplotype B. Another highly associated genomic region contained the EGLN1 gene which showed varied expression between high-altitude and low-altitude sheep. Our results provide evidence that the rapid adaptive evolution of advantageous alleles play an important role in facilitating the environmental adaptation of Tibetan sheep.

Hypoxia- and Postirradiation reoxygenation-induced HMHA1/ARHGAP45 expression contributes to cancer cell invasion in a HIF-dependent manner

BACKGROUND

Cancer cells in severely hypoxic regions have been reported to invade towards tumour blood vessels after surviving radiotherapy in a postirradiation reoxygenation- and hypoxia-inducible factor (HIF)-dependent manner and cause recurrence. However, how HIF induces invasiveness of irradiated and reoxygenated cancer cells remains unclear.

METHODS

Here, we identified human minor histocompatibility antigen 1 (HMHA1), which has been suggested to function in cytoskeleton dynamics and cellular motility, as a responsible factor and elucidated its mechanism of action using molecular and cellular biology techniques.

RESULTS

HMHA1 expression was found to be induced at the transcription initiation level in a HIF-dependent manner under hypoxia. Boyden chamber invasion assay revealed that the induction of HMHA1 expression is required for the increase in invasion of hypoxic cancer cells. Reoxygenation treatment after ionising radiation in vitro that mimics dynamic changes of a microenvironment in hypoxic regions of tumour tissues after radiation therapy further enhanced HMHA1 expression and invasive potential of HMHA1 wildtype cancer cells in ROS- and HIF-dependent manners, but not of HMHA1 knockout cells.

CONCLUSION

These results together provide insights into a potential molecular mechanism of the acquisition of invasiveness by hypoxic cancer cells after radiotherapy via the activation of the ROS/HIF/HMHA1 axis.

Hypoxia research, where to now?

Investigating how cells and organisms sense and respond to O2 levels is essential to our understanding of physiology and pathology. This field has advanced considerably since the discovery of the major transcription factor family, hypoxia-inducible factor (HIF), and the enzymes that control its levels: prolyl hydroxylases (PHDs). However, with its expansion, new complexities have emerged. Herein we highlight three main areas where, in our opinion, the research community could direct some of their attention. These include non-transcriptional roles of HIFs, specificity and O2 sensitivity of 2-oxoglutarate-dependent dioxygenases (2-OGDDs), and new tools and methods to detect O2 concentrations in cells and organs. A greater understanding of these areas would answer big questions and help drive our knowledge of cellular responses to hypoxia forward.

Decreasing mitochondrial fission ameliorates HIF-1α-dependent pathological retinal angiogenesis

Angiogenesis plays a critical role in many pathological processes, including irreversible blindness in eye diseases such as retinopathy of prematurity. Endothelial mitochondria are dynamic organelles that undergo constant fusion and fission and are critical signalling hubs that modulate angiogenesis by coordinating reactive oxygen species (ROS) production and calcium signalling and metabolism. In this study, we investigated the role of mitochondrial dynamics in pathological retinal angiogenesis. We showed that treatment with vascular endothelial growth factor (VEGF; 20 ng/ml) induced mitochondrial fission in HUVECs by promoting the phosphorylation of dynamin-related protein 1 (DRP1). DRP1 knockdown or pretreatment with the DRP1 inhibitor Mdivi-1 (5 μM) blocked VEGF-induced cell migration, proliferation, and tube formation in HUVECs. We demonstrated that VEGF treatment increased mitochondrial ROS production in HUVECs, which was necessary for HIF-1α-dependent glycolysis, as well as proliferation, migration, and tube formation, and the inhibition of mitochondrial fission prevented VEGF-induced mitochondrial ROS production. In an oxygen-induced retinopathy (OIR) mouse model, we found that active DRP1 was highly expressed in endothelial cells in neovascular tufts. The administration of Mdivi-1 (10 mg·kg-1·d-1, i.p.) for three days from postnatal day (P) 13 until P15 significantly alleviated pathological angiogenesis in the retina. Our results suggest that targeting mitochondrial fission may be a therapeutic strategy for proliferative retinopathies and other diseases that are dependent on pathological angiogenesis.

Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

UFM1 inhibits hypoxia-induced angiogenesis via promoting proteasome degradation of HIF-1α

Angiogenesis is crucial for blood flow recovery and ischemic tissue repair of peripheral artery disease (PAD). Exploration of new mechanisms underlying angiogenesis will shed light on the treatment of PAD. Ubiquitin-fold modifier 1 (UFM1), a newly identified ubiquitin-like molecule, has been discovered to be involved in various pathophysiological processes. However, the role of UFM1 in the pathogenesis of PAD, especially in endothelial angiogenesis remains obscure, and we aimed to clarify this issue in this study. We initially found UFM1 was significantly upregulated in gastrocnemius muscles of PAD patients and hind limb ischemia mice. And UFM1 was mainly colocalized with endothelial cells in ischemic muscle tissues. Further, elevated expression of UFM1 was observed in hypoxic endothelial cells. Subsequent genetic inhibition of UFM1 dramatically enhanced migration, invasion, adhesion, and tube formation of endothelial cells under hypoxia. Mechanistically, UFM1 reduced the stability of hypoxia-inducible factor-1α (HIF-1α) and promoted the von Hippel-Lindau-mediated K48-linked ubiquitin-proteasome degradation of HIF-1α, which in turn decreased angiogenic factor VEGFA expression and suppressed VEGFA related signaling pathway. Consistently, overexpression of UFM1 inhibited the angiogenesis of endothelial cells under hypoxic conditions, whereas overexpression of HIF-1α reversed this effect. Collectively, our data reveal that UFM1 inhibits the angiogenesis of endothelial cells under hypoxia through promoting ubiquitin-proteasome degradation of HIF-1α, suggesting UFM1 might serve as a potential therapeutic target for PAD.

The experimental significance of isorhamnetin as an effective therapeutic option for cancer: A comprehensive analysis

Isorhamnetin (C16H12O7), a 3'-O-methylated derivative of quercetin from the class of flavonoids, is predominantly present in the leaves and fruits of several plants, many of which have traditionally been employed as remedies due to its diverse therapeutic activities. The objective of this in-depth analysis is to concentrate on Isorhamnetin by addressing its molecular insights as an effective anticancer compound and its synergistic activity with other anticancer drugs. The main contributors to Isorhamnetin's anti-malignant activities at the molecular level have been identified as alterations of a variety of signal transduction processes and transcriptional agents. These include ROS-mediated cell cycle arrest and apoptosis, inhibition of mTOR and P13K pathway, suppression of MEK1, PI3K, NF-κB, and Akt/ERK pathways, and inhibition of Hypoxia Inducible Factor (HIF)-1α expression. A significant number of in vitro and in vivo research studies have confirmed that it destroys cancerous cells by arresting cell cycle at the G2/M phase and S-phase, down-regulating COX-2 protein expression, PI3K, Akt, mTOR, MEK1, ERKs, and PI3K signaling pathways, and up-regulating apoptosis-induced genes (Casp3, Casp9, and Apaf1), Bax, Caspase-3, P53 gene expression and mitochondrial-dependent apoptosis pathway. Its ability to suppress malignant cells, evidence of synergistic effects, and design of drugs based on nanomedicine are also well supported to treat cancer patients effectively. Together, our findings establish a crucial foundation for understanding Isorhamnetin's underlying anti-cancer mechanism in cancer cells and reinforce the case for the requirement to assess more exact molecular signaling pathways relating to specific cancer and in vivo anti-cancer activities.

Genetic and Molecular Biomarkers in Aggressive Pheochromocytomas and Paragangliomas

Pheochromocytomas and paragangliomas (PPGLs) are rare neoplasms producing catecholamines that occur as hereditary syndromes in 25-40% of cases. To date, PPGLs are no longer classified as benign and malignant tumors since any lesion could theoretically metastasize, even if it occurs only in a minority of cases (approximately 10-30%). Over the last decades, several attempts were made to develop a scoring system able to predict the risk of aggressive behavior at diagnosis, including the risk of metastases and disease recurrence; unfortunately, none of the available scores is able to accurately predict the risk of aggressive behavior, even including clinical, biochemical, and histopathological features. Thus, life-long follow-up is required in PPGL patients. Some recent studies focusing on genetic and molecular markers (involved in hypoxia regulation, gene transcription, cellular growth, differentiation, signaling pathways, and apoptosis) seem to indicate they are promising prognostic factors, even though their clinical significance needs to be further evaluated. The most involved pathways in PPGLs with aggressive behavior are represented by Krebs cycle alterations caused by succinate dehydrogenase subunits (SDHx), especially when caused by SDHB mutations, and by fumarate hydratase mutations that lead to the activation of hypoxia pathways and DNA hypermethylation, suggesting a common pathway in tumorigenesis. Conversely, PPGLs showing mutations in the kinase cascade (cluster 2) tend to display less aggressive behavior. Finally, establishing pathways of tumorigenesis is also fundamental to developing new drugs targeted to specific pathways and improving the survival of patients with metastatic disease. Unfortunately, the rarity of these tumors and the scarce number of cases enrolled in the available studies represents an obstacle to validating the role of molecular markers as reliable predictors of aggressiveness.

Cathepsins L and B target HIF1α for oxygen-independent proteolytic cleavage

The oxygen-labile transcription factor called hypoxia-inducible factor (HIF) is responsible for the cellular and organismal adaptive response to reduced oxygen availability. Deregulation of HIF is associated with the pathogenesis of major human diseases including cardiovascular disease and cancer. Under normoxia, the HIFα subunit is hydroxylated on conserved proline residues within the oxygen-dependent degradation domain (ODD) that labels HIFα for proteasome-mediated degradation. Despite similar oxygen-dependent degradation machinery acting on HIF1α and HIF2α, these two paralogs have been shown to exhibit unique kinetics under hypoxia, which suggests that other regulatory processes may be at play. Here, we characterize the protease activity found in rabbit reticulocytes that specifically cleaves the ODD of HIF1α but not HIF2α. Notably, the cleavage product is observed irrespective of the oxygen-dependent prolyl-hydroxylation potential of HIF1α, suggesting independence from oxygen. HIF1α M561T substitution, which mimics an evolutionary substitution that occurred during the duplication and divergence of HIF1α and HIF2α, diminished the cleavage of HIF1α. Protease inhibitor screening suggests that cysteine proteases cathepsins L and B preferentially cleave HIF1αODD, thereby revealing an additional layer of differential HIF regulation.

N-terminal cysteine acetylation and oxidation patterns may define protein stability

Oxygen homeostasis is maintained in plants and animals by O2-sensing enzymes initiating adaptive responses to low O2 (hypoxia). Recently, the O2-sensitive enzyme ADO was shown to initiate degradation of target proteins RGS4/5 and IL32 via the Cysteine/Arginine N-degron pathway. ADO functions by catalysing oxidation of N-terminal cysteine residues, but despite multiple proteins in the human proteome having an N-terminal cysteine, other endogenous ADO substrates have not yet been identified. This could be because alternative modifications of N-terminal cysteine residues, including acetylation, prevent ADO-catalysed oxidation. Here we investigate the relationship between ADO-catalysed oxidation and NatA-catalysed acetylation of a broad range of protein sequences with N-terminal cysteines. We present evidence that human NatA catalyses N-terminal cysteine acetylation in vitro and in vivo. We then show that sequences downstream of the N-terminal cysteine dictate whether this residue is oxidised or acetylated, with ADO preferring basic and aromatic amino acids and NatA preferring acidic or polar residues. In vitro, the two modifications appear to be mutually exclusive, suggesting that distinct pools of N-terminal cysteine proteins may be acetylated or oxidised. These results reveal the sequence determinants that contribute to N-terminal cysteine protein modifications, with implications for O2-dependent protein stability and the hypoxic response.

To Erase or Not to Erase: Non-Canonical Catalytic Functions and Non-Catalytic Functions of Members of Histone Lysine Demethylase Families

Histone lysine demethylases (KDMs) play an essential role in biological processes such as transcription regulation, RNA maturation, transposable element control, and genome damage sensing and repair. In most cases, their action requires catalytic activities, but non-catalytic functions have also been shown in some KDMs. Indeed, some strictly KDM-related proteins and some KDM isoforms do not act as histone demethylase but show other enzymatic activities or relevant non-enzymatic functions in different cell types. Moreover, many studies have reported on functions potentially supported by catalytically dead mutant KDMs. This is probably due to the versatility of the catalytical core, which can adapt to assume different molecular functions, and to the complex multi-domain structure of these proteins which encompasses functional modules for targeting histone modifications, promoting protein-protein interactions, or recognizing nucleic acid structural motifs. This rich modularity and the availability of multiple isoforms in the various classes produced variants with enzymatic functions aside from histone demethylation or variants with non-catalytical functions during the evolution. In this review we will catalog the proteins with null or questionable demethylase activity and predicted or validated inactive isoforms, summarizing what is known about their alternative functions. We will then go through some experimental evidence for the non-catalytical functions of active KDMs.

VHL suppresses UBE3B-mediated breast tumor growth and metastasis

Protein homeostasis is predominantly governed through post-translational modification (PTM). UBE3B, identified as an oncoprotein, exhibits elevated protein levels in breast cancer. However, the impact of PTM on UBE3B remains unexplored. In this study, we show that VHL is a bona fide E3 ligase for UBE3B. Mechanistically, VHL directly binds to UBE3B, facilitating its lysine 48 (K48)-linked polyubiquitination at K286 and K427 in a prolyl hydroxylase (PHD)-independent manner. Consequently, this promotes the proteasomal degradation of UBE3B. The K286/427R mutation of UBE3B dramatically abolishes the inhibitory effect of VHL on breast tumor growth and lung metastasis. Additionally, the protein levels of UBE3B and VHL exhibit a negative correlation in breast cancer tissues. These findings delineate an important layer of UBE3B regulation by VHL.

Multiple roles for hypoxia inducible factor 1-alpha in airway epithelial cells during mucormycosis

During pulmonary mucormycosis, inhaled sporangiospores adhere to, germinate, and invade airway epithelial cells to establish infection. We provide evidence that HIF1α plays dual roles in airway epithelial cells during Mucorales infection. We observed an increase in HIF1α protein accumulation and increased expression of many known HIF1α-responsive genes during in vitro infection, indicating that HIF1α signaling is activated by Mucorales infection. Inhibition of HIF1α signaling led to a substantial decrease in the ability of R. delemar to invade cultured airway epithelial cells. Transcriptome analysis revealed that R. delemar infection induces the expression of many pro-inflammatory genes whose expression was significantly reduced by HIF1α inhibition. Importantly, pharmacological inhibition of HIF1α increased survival in a mouse model of pulmonary mucormycosis without reducing fungal burden. These results suggest that HIF1α plays two opposing roles during mucormycosis: one that facilitates the ability of Mucorales to invade the host cells and one that facilitates the ability of the host to mount an innate immune response.

Reduced vacuolar ATPase protects mice from Friend virus infection - an unintended but instructive effect in Hif-2afl mice

During acute viral infections, innate immune cells invade inflamed tissues and face hypoxic areas. Hypoxia-inducible factors (HIFs) adapt cellular responses towards these conditions. We wanted to investigate the effects of a loss of HIF-2α in macrophages during acute Friend murine leukemia retrovirus (FV) infection in C57BL/6 mice using a Cre/loxP system. Remarkably, mice with floxed Hif-2a (Hif-2afl; Hif-2a is also known as Epas1) did not show any signs of FV infection independent of Cre activity. This prevented a detailed analysis of the role of macrophage HIF-2α for FV infection but allowed us to study a model of unexpected FV resistance. Hif-2afl mice showed a significant decrease in the expression of the Atp6v1e2 gene encoding for the E2 subunit of the vacuolar H+-ATPase, which resulted in a decreased acidification of lysosomes and limited virus entry into the cell. These findings highlight that the insertion of loxP sites is not always without functional consequences and has established a phenotype in the floxed Hif-2a mouse, which is not only unexpected, but unwanted and is of relevance for the use of this mouse strain in (at least virus) experiments.

Biomimetic Nano-Regulator that Induces Cuproptosis and Lactate-Depletion Mediated ROS Storm for Metalloimmunotherapy of Clear Cell Renal Cell Carcinoma

Herein, a ccRCC targeting nanodrug is designed to enhance chemodynamic therapy (CDT) as well as activate cuproptosis and tumor immunotherapy via ccRCC cell membrane modifying CuO@Gd2O3 yolk-like particles (CGYL) loaded with lactate oxidase (LOx) (mCGYL-LOx). Benefiting from the homologous targeting effect of Renca cell membranes, the mCGYS-LOx can be effectively internalized by Renca cells, open the "gate", and then release LOx and copper (Cu) ions. LOx can catalyze excessive lactate in Renca cells into H2O2, following that the produced H2O2 is further converted by Cu ions to the highly toxic ·OH, contributing to tumor CDT. Meanwhile, the excessive Cu ions effectively trigger tumor cuproptosis. These synergistic effects induce the release of damage associated molecular patterns (DAMPs) and activate immunogenic cell death (ICD), leading to DC maturation and infiltration of immune effector cells. Moreover, LOx-mediated lactate consumption downregulates the expression of PD-L1, crippling tumor immune escape. In addition, the mCGYL-LOx improves T1-weighted MRI signal, allowing for accurate diagnosis of ccRCC. This study demonstrates that the mCGYL-LOx has great potential for improving therapy of ccRCC via the synergistic actions of CDT and cuproptosis as well as immunotherapy.

Deleting the ribosomal prolyl hydroxylase OGFOD1 protects mice against diet-induced obesity and insulin resistance

Type 2 diabetes predisposes patients to heart disease, which is the primary cause of death across the globe. Type 2 diabetes often accompanies obesity and is defined by insulin resistance and abnormal glucose handling. Insulin resistance impairs glucose uptake and results in hyperglycemia, which damages tissues such as kidneys, liver, and heart. 2-oxoglutarate (2-OG)- and iron-dependent oxygenases (2-OGDOs), a family of enzymes regulating various aspects of cellular physiology, have been studied for their role in obesity and diet-induced insulin resistance. However, nothing is known of the 2-OGDO family member 2-oxoglutarate and iron-dependent prolyl hydroxylase domain containing protein 1 (OGFOD1) in this setting. OGFOD1 deletion leads to protection in cardiac ischemia-reperfusion injury and cardiac hypertrophy, which are two cardiac events that can lead to heart failure. Considering the remarkable correlation between heart disease and diabetes, the cardioprotection observed in OGFOD1-knockout mice led us to challenge these knockouts with high-fat diet. Wildtype mice fed a high-fat diet developed diet-induced obesity, insulin resistance, and glucose intolerance, but OGFOD1 knockout mice fed this same diet were resistant to diet-induced obesity and insulin resistance. These results support OGFOD1 down-regulation as a strategy for preventing obesity and insulin handling defects.

Sphingosine d18:1 promotes nonalcoholic steatohepatitis by inhibiting macrophage HIF-2α

Non-alcoholic steatohepatitis (NASH) is a severe type of the non-alcoholic fatty liver disease (NAFLD). NASH is a growing global health concern due to its increasing morbidity, lack of well-defined biomarkers and lack of clinically effective treatments. Using metabolomic analysis, the most significantly changed active lipid sphingosine d18:1 [So(d18:1)] is selected from NASH patients. So(d18:1) inhibits macrophage HIF-2α as a direct inhibitor and promotes the inflammatory factors secretion. Male macrophage-specific HIF-2α knockout and overexpression mice verified the protective effect of HIF-2α on NASH progression. Importantly, the HIF-2α stabilizer FG-4592 alleviates liver inflammation and fibrosis in NASH, which indicated that macrophage HIF-2α is a potential drug target for NASH treatment. Overall, this study confirms that So(d18:1) promotes NASH and clarifies that So(d18:1) inhibits the transcriptional activity of HIF-2α in liver macrophages by suppressing the interaction of HIF-2α with ARNT, suggesting that macrophage HIF-2α may be a potential target for the treatment of NASH.

Evaluating the safety and efficacy of vadadustat for the treatment of anemia associated with chronic kidney disease

INTRODUCTION

The breakthrough in erythropoietin-stimulating agents in the 1990s improved the prognosis and treatment of complications in chronic kidney disease patients and renal anemia. Discovery of the novel molecular mechanisms for hypoxia-inducible factor (HIF) transcription factor under hypoxic conditions has led to the development of oral drugs, HIF-Prolyl Hydroxylase inhibitors (HIF-PHIs), that constantly activate erythropoietin by inhibiting prolyl hydroxylase. HIF-PHIs have gained rapid approval in Asian countries, including Japan, with six distinct types entering clinical application.

AREAS COVERED

This article provides a comprehensive review of the latest literature, with a particular focus on the effectiveness and safety of vadadustat.

EXPERT OPINION

A phase 3, randomized, open-label, clinical trial (PRO2TECT) demonstrated that vadadustat had the prespecified non-inferiority for hematologic efficacy as compared with darbepoetin alfa in non-dialysis-dependent patients not previously treated with ESA. However, vadadustat did not show non-inferiority in major adverse cardiovascular events in the non-US/non-Europe patients. It may partly because of imbalances of the baseline eGFR level in those countries. In dialysis-dependent patients, a phase 3 clinical trial (INNO2VATE) showed vadadustat was non-inferior to darbepoetin alfa in cardiovascular safety and maintenance of hemoglobin levels. Adverse events including cancer, retinopathy, thrombosis, and vascular calcification should be evaluated in future clinical studies.

Regulation of the HIF switch in human endothelial and cancer cells

Hypoxia-inducible factors (HIFs) are transcription factors that reprogram the transcriptome for cells to survive hypoxic insults and oxidative stress. They are important during embryonic development and reprogram the cells to utilize glycolysis when the oxygen levels are extremely low. This metabolic change facilitates normal cell survival as well as cancer cell survival. The key feature in survival is the transition between acute hypoxia and chronic hypoxia, and this is regulated by the transition between HIF-1 expression and HIF-2/HIF-3 expression. This transition is observed in many human cancers and endothelial cells and referred to as the HIF Switch. Here we discuss the mechanisms involved in the HIF Switch in human endothelial and cancer cells which include mRNA and protein levels of the alpha chains of the HIFs. A major continuing effort in this field is directed towards determining the differences between normal and tumor cell utilization of this important pathway, and how this could lead to potential therapeutic approaches.

P4HA2 activates mTOR via hydroxylation and targeting P4HA2-mTOR inhibits lung adenocarcinoma cell growth

Mammalian target of rapamycin (mTOR) kinase functions as a central regulator of cell growth and metabolism, and its complexes mTORC1 and mTORC2 phosphorylate distinct substrates. Dysregulation of mTOR signaling is commonly implicated in human diseases, including cancer. Despite three decades of active research in mTOR, much remains to be determined. Here, we demonstrate that prolyl 4-hydroxylase alpha-2 (P4HA2) binds directly to mTOR and hydroxylates one highly conserved proline 2341 (P2341) within a kinase domain of mTOR, thereby activating mTOR kinase and downstream effector proteins (e.g. S6K and AKT). Moreover, the hydroxylation of P2341 strengthens mTOR stability and allows mTOR to accurately recognize its substrates such as S6K and AKT. The growth of lung adenocarcinoma cells overexpressing mTORP2341A is significantly reduced when compared with that of cells overexpressing mTORWT. Interestingly, in vivo cell growth assays show that targeting P4HA2-mTOR significantly suppresses lung adenocarcinoma cell growth. In summary, our study reveals an undiscovered hydroxylation-regulatory mechanism by which P4HA2 directly activates mTOR kinase, providing insights for therapeutically targeting mTOR kinase-driven cancers.

MFN2 suppresses the accumulation of lipid droplets and the progression of clear cell renal cell carcinoma

Dissolving the lipid droplets in tissue section with alcohol during a hematoxylin and eosin (H&E) stain causes the tumor cells to appear like clear soap bubbles under a microscope, which is a key pathological feature of clear cell renal cell carcinoma (ccRCC). Mitochondrial dynamics have been reported to be closely associated with lipid metabolism and tumor development. However, the relationship between mitochondrial dynamics and lipid metabolism reprogramming in ccRCC remains to be further explored. We conducted bioinformatics analysis to identify key genes regulating mitochondrial dynamics differentially expressed between tumor and normal tissues and immunohistochemistry and Western blot to confirm. After the target was identified, we created stable ccRCC cell lines to test the impact of the target gene on mitochondrial morphology, tumorigenesis in culture cells and xenograft models, and profiles of lipid metabolism. It was found that mitofusin 2 (MFN2) was downregulated in ccRCC tissues and associated with poor prognosis in patients with ccRCC. MFN2 suppressed mitochondrial fragmentation, proliferation, migration, and invasion of ccRCC cells and growth of xenograft tumors. Furthermore, MFN2 impacted lipid metabolism and reduced the accumulation of lipid droplets in ccRCC cells. MFN2 suppressed disease progression and improved prognosis for patients with ccRCC possibly by interrupting cellular lipid metabolism and reducing accumulation of lipid droplets.

The Role of Hyperbaric Oxygen Therapy in Neuroregeneration and Neuroprotection: A Review

Neurogenesis is a high energy-demanding process, which is why blood vessels are an active part of the neurogenic niche since they allow the much-needed oxygenation of progenitor cells. In this regard, although neglected for a long time, the "oxygen niche" should be considered an important intervenient in adult neurogenesis. One possible hypothesis for the failure of numerous neuroprotective trials is that they relied on compounds that target a highly specific neuroprotective pathway. This approach may be too limited, given the complexity of the processes that lead to cell death. Therefore, research should adopt a more multifactorial approach. Among the limited range of agents with multimodal neuromodulatory capabilities, hyperbaric oxygen therapy has demonstrated effectiveness in reducing secondary brain damage in various brain injury models. This therapy functions not only as a neuroprotective mechanism but also as a powerful neuroregenerative mechanism.

Hypoxia-associated autophagy flux dysregulation in human cancers

A general feature of cancer is hypoxia, determined as low oxygen levels. Low oxygen levels may cause cells to alter in ways that contribute to tumor growth and resistance to treatment. Hypoxia leads to variations in cancer cell metabolism, angiogenesis and metastasis. Furthermore, a hypoxic tumor microenvironment might induce immunosuppression. Moreover, hypoxia has the potential to impact cellular processes, such as autophagy. Autophagy refers to the catabolic process by which damaged organelles and toxic macromolecules are broken down. The abnormal activation of autophagy has been extensively recorded in human tumors and it serves as a regulator of cell growth, spread to other parts of the body, and resistance to treatment. There is a correlation between hypoxia and autophagy in human malignancies. Hypoxia can regulate the activity of AMPK, mTOR, Beclin-1, and ATGs to govern autophagy in human malignancies. Furthermore, HIF-1α, serving as an indicator of low oxygen levels, controls the process of autophagy. Hypoxia-induced autophagy has a crucial role in regulating the growth, spread, and resistance to treatment in human malignancies. Hypoxia-induced regulation of autophagy can impact other mechanisms of cell death, such as apoptosis. Chemoresistance and radioresistance have become significant challenges in recent years. Hypoxia-mediated autophagy plays a crucial role in determining the response to these therapeutic treatments.

Advance in Iron Metabolism, Oxidative Stress and Cellular Dysfunction in Experimental and Human Kidney Diseases

Kidney diseases pose a significant global health issue, frequently resulting in the gradual decline of renal function and eventually leading to end-stage renal failure. Abnormal iron metabolism and oxidative stress-mediated cellular dysfunction facilitates the advancement of kidney diseases. Iron homeostasis is strictly regulated in the body, and disturbance in this regulatory system results in abnormal iron accumulation or deficiency, both of which are associated with the pathogenesis of kidney diseases. Iron overload promotes the production of reactive oxygen species (ROS) through the Fenton reaction, resulting in oxidative damage to cellular molecules and impaired cellular function. Increased oxidative stress can also influence iron metabolism through upregulation of iron regulatory proteins and altering the expression and activity of key iron transport and storage proteins. This creates a harmful cycle in which abnormal iron metabolism and oxidative stress perpetuate each other, ultimately contributing to the advancement of kidney diseases. The crosstalk of iron metabolism and oxidative stress involves multiple signaling pathways, such as hypoxia-inducible factor (HIF) and nuclear factor erythroid 2-related factor 2 (Nrf2) pathways. This review delves into the functions and mechanisms of iron metabolism and oxidative stress, along with the intricate relationship between these two factors in the context of kidney diseases. Understanding the underlying mechanisms should help to identify potential therapeutic targets and develop novel and effective therapeutic strategies to combat the burden of kidney diseases.

Advances in Engineered Nanoparticles for the Treatment of Ischemic Stroke by Enhancing Angiogenesis

Angiogenesis, or the formation of new blood vessels, is a natural defensive mechanism that aids in the restoration of oxygen and nutrition delivery to injured brain tissue after an ischemic stroke. Angiogenesis, by increasing vessel development, may maintain brain perfusion, enabling neuronal survival, brain plasticity, and neurologic recovery. Induction of angiogenesis and the formation of new vessels aid in neurorepair processes such as neurogenesis and synaptogenesis. Advanced nano drug delivery systems hold promise for treatment stroke by facilitating efficient transportation across the the blood-brain barrier and maintaining optimal drug concentrations. Nanoparticle has recently been shown to greatly boost angiogenesis and decrease vascular permeability, as well as improve neuroplasticity and neurological recovery after ischemic stroke. We describe current breakthroughs in the development of nanoparticle-based treatments for better angiogenesis therapy for ischemic stroke employing polymeric nanoparticles, liposomes, inorganic nanoparticles, and biomimetic nanoparticles in this study. We outline new nanoparticles in detail, review the hurdles and strategies for conveying nanoparticle to lesions, and demonstrate the most recent advances in nanoparticle in angiogenesis for stroke treatment.

Cholesterol accumulation impairs HIF-1α-dependent immunometabolic reprogramming of LPS-stimulated macrophages by upregulating the NRF2 pathway

Lipid accumulation in macrophages (Mφs) is a hallmark of atherosclerosis. Yet, how lipid loading modulates Mφ inflammatory responses remains unclear. We endeavored to gain mechanistic insights into how pre-loading with free cholesterol modulates Mφ metabolism upon LPS-induced TLR4 signaling. We found that activities of prolyl hydroxylases (PHDs) and factor inhibiting HIF (FIH) are higher in cholesterol loaded Mφs post-LPS stimulation, resulting in impaired HIF-1α stability, transactivation capacity and glycolysis. In RAW264.7 cells expressing mutated HIF-1α proteins resistant to PHDs and FIH activities, cholesterol loading failed to suppress HIF-1α function. Cholesterol accumulation induced oxidative stress that enhanced NRF2 protein stability and triggered a NRF2-mediated antioxidative response prior to and in conjunction with LPS stimulation. LPS stimulation increased NRF2 mRNA and protein expression, but it did not enhance NRF2 protein stability further. NRF2 deficiency in Mφs alleviated the inhibitory effects of cholesterol loading on HIF-1α function. Mutated KEAP1 proteins defective in redox sensing expressed in RAW264.7 cells partially reversed the effects of cholesterol loading on NRF2 activation. Collectively, we showed that cholesterol accumulation in Mφs induces oxidative stress and NRF2 stabilization, which when combined with LPS-induced NRF2 expression leads to enhanced NRF2-mediated transcription that ultimately impairs HIF-1α-dependent glycolytic and inflammatory responses.

OTUB2 silencing promotes ovarian cancer via mitochondrial metabolic reprogramming and can be synthetically targeted by CA9 inhibition

Ovarian cancer is an aggressive gynecological tumor characterized by a high relapse rate and chemoresistance. Ovarian cancer exhibits the cancer hallmark of elevated glycolysis, yet effective strategies targeting cancer cell metabolic reprogramming to overcome therapeutic resistance in ovarian cancer remain elusive. Here, we revealed that epigenetic silencing of Otubain 2 (OTUB2) is a driving force for mitochondrial metabolic reprogramming in ovarian cancer, which promotes tumorigenesis and chemoresistance. Mechanistically, OTUB2 silencing destabilizes sorting nexin 29 pseudogene 2 (SNX29P2), which subsequently prevents hypoxia-inducible factor-1 alpha (HIF-1α) from von Hippel-Lindau tumor suppressor-mediated degradation. Elevated HIF-1α activates the transcription of carbonic anhydrase 9 (CA9) and drives ovarian cancer progression and chemoresistance by promoting glycolysis. Importantly, pharmacological inhibition of CA9 substantially suppressed tumor growth and synergized with carboplatin in the treatment of OTUB2-silenced ovarian cancer. Thus, our study highlights the pivotal role of OTUB2/SNX29P2 in suppressing ovarian cancer development and proposes that targeting CA9-mediated glycolysis is an encouraging strategy for the treatment of ovarian cancer.

HIF2α-dependent inhibition of mitochondrial clustering of glutaminase suppresses clear cell renal cell carcinoma

Clear cell renal cell carcinomas (ccRCC) are largely driven by HIF2α and are avid consumers of glutamine. However, inhibitors of glutaminase1 (GLS1), the first step in glutaminolysis, have not shown benefit in phase III trials, and HIF2α inhibition, recently FDA-approved for treatment of ccRCC, shows great but incomplete benefits, underscoring the need to better understand the roles of glutamine and HIF2α in ccRCC. Here, we report that glutamine deprivation rapidly redistributes GLS1 into isolated clusters within mitochondria across diverse cell types, excluding ccRCC. GLS1 clustering is rapid (1-3 hours) and reversible, is specifically driven by the level of intracellular glutamate, and is mediated by mitochondrial fission. Clustered GLS1 has markedly enhanced glutaminase activity and promotes cell death under glutamine-deprived conditions. We further show that HIF2α prevents GLS1 clustering, independently of its transcriptional activity, thereby protecting ccRCC cells from cell death induced by glutamine deprivation. Reversing this protection, by genetic expression of GLS1 mutants that constitutively cluster, enhances ccRCC cell death in culture and suppresses ccRCC growth in vivo . These finding provide multiple insights into cellular glutamine handling, including a novel metabolic pathway by which HIF2α promotes ccRCC, and reveals a potential therapeutic avenue to synergize with HIF2α inhibition in the treatment of ccRCC.

Mammalian pexophagy at a glance

Peroxisomes are highly plastic organelles that are involved in several metabolic processes, including fatty acid oxidation, ether lipid synthesis and redox homeostasis. Their abundance and activity are dynamically regulated in response to nutrient availability and cellular stress. Damaged or superfluous peroxisomes are removed mainly by pexophagy, the selective autophagy of peroxisomes induced by ubiquitylation of peroxisomal membrane proteins or ubiquitin-independent processes. Dysregulated pexophagy impairs peroxisome homeostasis and has been linked to the development of various human diseases. Despite many recent insights into mammalian pexophagy, our understanding of this process is still limited compared to our understanding of pexophagy in yeast. In this Cell Science at a Glance article and the accompanying poster, we summarize current knowledge on the control of mammalian pexophagy and highlight which aspects require further attention. We also discuss the role of ubiquitylation in pexophagy and describe the ubiquitin machinery involved in regulating signals for the recruitment of phagophores to peroxisomes.

Immune consequences of exercise in hypoxia: A narrative review

Immune outcomes are key mediators of many health benefits of exercise and are determined by exercise type, dose (frequency/duration, intensity), and individual characteristics. Similarly, reduced availability of ambient oxygen (hypoxia) modulates immune functions depending on the hypoxic dose and the individual capacity to respond to hypoxia. How combined exercise and hypoxia (e.g., high-altitude training) sculpts immune responses is not well understood, although such combinations are becoming increasingly popular. Therefore, in this paper, we summarize the impact on immune responses of exercise and of hypoxia, both independently and together, with a focus on specialized cells in the innate and adaptive immune system. We review the regulation of the immune system by tissue oxygen levels and the overlapping and distinct immune responses related to exercise and hypoxia, then we discuss how they may be modulated by nutritional strategies. Mitochondrial, antioxidant, and anti-inflammatory mechanisms underlie many of the adaptations that can lead to improved cellular metabolism, resilience, and overall immune functions by regulating the survival, differentiation, activation, and migration of immune cells. This review shows that exercise and hypoxia can impair or complement/synergize with each other while regulating immune system functions. Appropriate acclimatization, training, and nutritional strategies can be used to avoid risks and tap into the synergistic potentials of the poorly studied immune consequences of exercising in a hypoxic state.

Hypoxia-Inducible Factor-Dependent and Independent Mechanisms Underlying Chemoresistance of Hypoxic Cancer Cells

In hypoxic regions of malignant solid tumors, cancer cells acquire resistance to conventional therapies, such as chemotherapy and radiotherapy, causing poor prognosis in patients with cancer. It is widely recognized that some of the key genes behind this are hypoxia-inducible transcription factors, e.g., hypoxia-inducible factor 1 (HIF-1). Since HIF-1 activity is suppressed by two representative 2-oxoglutarate-dependent dioxygenases (2-OGDDs), PHDs (prolyl-4-hydroxylases), and FIH-1 (factor inhibiting hypoxia-inducible factor 1), the inactivation of 2-OGDD has been associated with cancer therapy resistance by the activation of HIF-1. Recent studies have also revealed the importance of hypoxia-responsive mechanisms independent of HIF-1 and its isoforms (collectively, HIFs). In this article, we collate the accumulated knowledge of HIF-1-dependent and independent mechanisms responsible for resistance of hypoxic cancer cells to anticancer drugs and briefly discuss the interplay between hypoxia responses, like EMT and UPR, and chemoresistance. In addition, we introduce a novel HIF-independent mechanism, which is epigenetically mediated by an acetylated histone reader protein, ATAD2, which we recently clarified.

Targeting hypoxia signaling pathways in angiogenesis

Oxygen (O2) supply is constantly maintained by the vascular network for a proper tissue oxygenation. Hypoxia is the result of an increased O2 demand and/or decreased supply and is common in both physiological conditions and human diseases. Angiogenesis is one of the adaptive responses to hypoxia and is mainly regulated by the hypoxia-inducible factors, HIFs. These heterodimeric transcription factors are composed of one of three O2-dependent α subunits (HIF-1, HIF-2, and HIF-3) and a constitutively expressed O2-insensitive subunit (HIF-1β). Among them HIF-1α is the most characterized and its activity is tightly controlled. Under hypoxia, its intracellular accumulation triggers the transcription of several genes, involved in cell survival/proliferation, autophagy, apoptosis, cell metabolism, and angiogenesis. HIF pathway is also modulated by specific microRNAs (miRNAs), thus resulting in the variation of several cellular responses, including alteration of the angiogenic process. The pro-angiogenic activity of HIF-1α is not restricted to endothelial cells, as it also affects the behavior of other cell types, including tumor and inflammatory/immune cells. In this context, exosomes play a crucial role in cell-cell communication by transferring bio-active cargos such as mRNAs, miRNAs, and proteins (e.g., VEGFA mRNA, miR210, HIF-1α). This minireview will provide a synopsis of the multiple factors able to modulate hypoxia-induced angiogenesis especially in the tumor microenvironment context. Targeting hypoxia signaling pathways by up-to-date approaches may be relevant in the design of therapeutic strategies in those pathologies where angiogenesis is dysregulated.

The Role of Oxygen Homeostasis and the HIF-1 Factor in the Development of Neurodegeneration

Understanding the molecular underpinnings of neurodegeneration processes is a pressing challenge for medicine and neurobiology. Alzheimer's disease (AD) and Parkinson's disease (PD) represent the most prevalent forms of neurodegeneration. To date, a substantial body of experimental evidence has strongly implicated hypoxia in the pathogenesis of numerous neurological disorders, including AD, PD, and other age-related neurodegenerative conditions. Hypoxia-inducible factor (HIF) is a transcription factor that triggers a cell survival program in conditions of oxygen deprivation. The involvement of HIF-1α in neurodegenerative processes presents a complex and sometimes contradictory picture. This review aims to elucidate the current understanding of the interplay between hypoxia and the development of AD and PD, assess the involvement of HIF-1 in their pathogenesis, and summarize promising therapeutic approaches centered on modulating the activity of the HIF-1 complex.

HIF1α-dependent uncoupling of glycolysis suppresses tumor cell proliferation

Hypoxia-inducible factor-1α (HIF1α) attenuates mitochondrial activity while promoting glycolysis. However, lower glycolysis is compromised in human clear cell renal cell carcinomas, in which HIF1α acts as a tumor suppressor by inhibiting cell-autonomous proliferation. Here, we find that, unexpectedly, HIF1α suppresses lower glycolysis after the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) step, leading to reduced lactate secretion in different tumor cell types when cells encounter a limited pyruvate supply such as that typically found in the tumor microenvironment in vivo. This is because HIF1α-dependent attenuation of mitochondrial oxygen consumption increases the NADH/NAD+ ratio that suppresses the activity of the NADH-sensitive GAPDH glycolytic enzyme. This is manifested when pyruvate supply is limited, since pyruvate acts as an electron acceptor that prevents the increment of the NADH/NAD+ ratio. Furthermore, this anti-glycolytic function provides a molecular basis to explain how HIF1α can suppress tumor cell proliferation by increasing the NADH/NAD+ ratio.

Pin1-Catalyzed Conformation Changes Regulate Protein Ubiquitination and Degradation

The unique prolyl isomerase Pin1 binds to and catalyzes cis-trans conformational changes of specific Ser/Thr-Pro motifs after phosphorylation, thereby playing a pivotal role in regulating the structure and function of its protein substrates. In particular, Pin1 activity regulates the affinity of a substrate for E3 ubiquitin ligases, thereby modulating the turnover of a subset of proteins and coordinating their activities after phosphorylation in both physiological and disease states. In this review, we highlight recent advancements in Pin1-regulated ubiquitination in the context of cancer and neurodegenerative disease. Specifically, Pin1 promotes cancer progression by increasing the stabilities of numerous oncoproteins and decreasing the stabilities of many tumor suppressors. Meanwhile, Pin1 plays a critical role in different neurodegenerative disorders via the regulation of protein turnover. Finally, we propose a novel therapeutic approach wherein the ubiquitin-proteasome system can be leveraged for therapy by targeting pathogenic intracellular targets for TRIM21-dependent degradation using stereospecific antibodies.

Detrimental Roles of Hypoxia-Inducible Factor-1α in Severe Hypoxic Brain Diseases

Hypoxia stabilizes hypoxia-inducible factors (HIFs), facilitating adaptation to hypoxic conditions. Appropriate hypoxia is pivotal for neurovascular regeneration and immune cell mobilization. However, in central nervous system (CNS) injury, prolonged and severe hypoxia harms the brain by triggering neurovascular inflammation, oxidative stress, glial activation, vascular damage, mitochondrial dysfunction, and cell death. Diminished hypoxia in the brain improves cognitive function in individuals with CNS injuries. This review discusses the current evidence regarding the contribution of severe hypoxia to CNS injuries, with an emphasis on HIF-1α-mediated pathways. During severe hypoxia in the CNS, HIF-1α facilitates inflammasome formation, mitochondrial dysfunction, and cell death. This review presents the molecular mechanisms by which HIF-1α is involved in the pathogenesis of CNS injuries, such as stroke, traumatic brain injury, and Alzheimer's disease. Deciphering the molecular mechanisms of HIF-1α will contribute to the development of therapeutic strategies for severe hypoxic brain diseases.

EPAS1 expression contributes to maintenance of the primordial follicle pool in the mouse ovary

Oxygen availability can have profound effects on cell fate decisions and survival, in part by regulating expression of hypoxia-inducible factors (HIFs). In the ovary, HIF expression has been characterised in granulosa cells, however, any requirement in oocytes remains relatively undefined. Here we developed a Hif2a/Epas1 germline-specific knockout mouse line in which females were fertile, however produced 40% fewer pups than controls. No defects in follicle development were detected, and quality of MII oocytes was normal, as per assessments of viability, intracellular reactive oxygen species, and spindle parameters. However, a significant diminishment of the primordial follicle pool was evident in cKO females that was attributed to accelerated follicle loss from postnatal day 6 onwards, potentially via disruption of the autophagy pathway. These data demonstrate the importance of HIF signalling in oocytes, particularly at the primordial follicle stage, and lend to the importance of controlling oxygen tension in the development of in vitro growth and maturation approaches for assisted reproduction.

The Clinical Significance and Involvement in Molecular Cancer Processes of Chemokine CXCL1 in Selected Tumors

Chemokines play a key role in cancer processes, with CXCL1 being a well-studied example. Due to the lack of a complete summary of CXCL1's role in cancer in the literature, in this study, we examine the significance of CXCL1 in various cancers such as bladder, glioblastoma, hemangioendothelioma, leukemias, Kaposi's sarcoma, lung, osteosarcoma, renal, and skin cancers (malignant melanoma, basal cell carcinoma, and squamous cell carcinoma), along with thyroid cancer. We focus on understanding how CXCL1 is involved in the cancer processes of these specific types of tumors. We look at how CXCL1 affects cancer cells, including their proliferation, migration, EMT, and metastasis. We also explore how CXCL1 influences other cells connected to tumors, like promoting angiogenesis, recruiting neutrophils, and affecting immune cell functions. Additionally, we discuss the clinical aspects by exploring how CXCL1 levels relate to cancer staging, lymph node metastasis, patient outcomes, chemoresistance, and radioresistance.

Scutellarin activates IDH1 to exert antitumor effects in hepatocellular carcinoma progression

Isochlorate dehydrogenase 1 (IDH1) is an important metabolic enzyme for the production of α-ketoglutarate (α-KG), which has antitumor effects and is considered to have potential antitumor effects. The activation of IDH1 as a pathway for the development of anticancer drugs has not been attempted. We demonstrated that IDH1 can limit glycolysis in hepatocellular carcinoma (HCC) cells to activate the tumor immune microenvironment. In addition, through proteomic microarray analysis, we identified a natural small molecule, scutellarin (Scu), which activates IDH1 and inhibits the growth of HCC cells. By selectively modifying Cys297, Scu promotes IDH1 active dimer formation and increases α-KG production, leading to ubiquitination and degradation of HIF1a. The loss of HIF1a further leads to the inhibition of glycolysis in HCC cells. The activation of IDH1 by Scu can significantly increase the level of α-KG in tumor tissue, downregulate the HIF1a signaling pathway, and activate the tumor immune microenvironment in vivo. This study demonstrated the inhibitory effect of IDH1-α-KG-HIF1a on the growth of HCC cells and evaluated the inhibitory effect of Scu, the first IDH1 small molecule agonist, which provides a reference for cancer immunotherapy involving activated IDH1.

Cullin-RING ligases employ geometrically optimized catalytic partners for substrate targeting

Cullin-RING ligases (CRLs) ubiquitylate specific substrates selected from other cellular proteins. Substrate discrimination and ubiquitin transferase activity were thought to be strictly separated. Substrates are recognized by substrate receptors, such as Fbox or BCbox proteins. Meanwhile, CRLs employ assorted ubiquitin-carrying enzymes (UCEs, which are a collection of E2 and ARIH-family E3s) specialized for either initial substrate ubiquitylation (priming) or forging poly-ubiquitin chains. We discovered specific human CRL-UCE pairings governing substrate priming. The results reveal pairing of CUL2-based CRLs and UBE2R-family UCEs in cells, essential for efficient PROTAC-induced neo-substrate degradation. Despite UBE2R2's intrinsic programming to catalyze poly-ubiquitylation, CUL2 employs this UCE for geometrically precise PROTAC-dependent ubiquitylation of a neo-substrate and for rapid priming of substrates recruited to diverse receptors. Cryo-EM structures illuminate how CUL2-based CRLs engage UBE2R2 to activate substrate ubiquitylation. Thus, pairing with a specific UCE overcomes E2 catalytic limitations to drive substrate ubiquitylation and targeted protein degradation.

Investigational new drugs for the treatment of chronic renal failure: an overview of the literature

INTRODUCTION

Chronic kidney disease (CKD) is widespread throughout the world, with a high social and health impact. It is considered a 'silent killer' for its sudden onset without symptoms in the early stages of the disease. The main goal of nephrologists is to slow the progression of kidney disease and treat the associated symptoms with a range of new medications.

AREAS COVERED

The aim of this systematic review is to analyze the new investigational drugs for the treatment of chronic renal failure. Data were obtained from the available scientific literature and from the ClinicalTrials.gov website.

EXPERT OPINION

Among the drugs currently being researched, SGLT2 inhibitors appear to be the most promising drugs for the treatment of CKD, has they have slower progression of CKD and protection of cardiorenal function. An important role in the future of CKD treatment is played by autologous cell-therapy, which appears to be a new frontier in the treatment of CKD. Other therapeutic strategies are currently being investigated and have been shown to slow the progression of CKD. However, further studies are needed to determine whether these approaches may offer benefits in slowing the progression of CKD in the near future.

Tumor metabolic crosstalk and immunotherapy

Tumor cells must resist the host's immune system while maintaining growth under harsh conditions of acidity and hypoxia, which indicates that tumors are more robust than normal tissue. Immunotherapeutic agents have little effect on solid tumors, mostly because of the tumor density and the difficulty of penetrating deeply into the tissue to achieve the theoretical therapeutic effect. Various therapeutic strategies targeting the tumor microenvironment (TME) have been developed. Immunometabolic disorders play a dominant role in treatment resistance at both the TME and host levels. Understanding immunometabolic factors and their treatment potential may be a way forward for tumor immunotherapy. Here, we summarize the metabolism of substances that affect tumor progression, the crosstalk between the TME and immunosuppression, and some potential tumor-site targets. We also summarize the progress and challenges of tumor immunotherapy.

HIF-1α Mediates Immunosuppression and Chemoresistance in Colorectal Cancer by Inhibiting CXCL9, -10 and -11

Uncertainty exists regarding the mechanisms by which hypoxia-inducible factors (HIFs) control CD8+T-cell migration into tumor microenvironments. Here, we found that HIF-1α knockdown or overexpression resulted in increased or decreased CXCL9, -10, and -11 expression in vitro, respectively. Gene Set Variation Analysis revealed that elevated HIF-1α levels correlated with a poor prognosis, severe pathological stage, and an absence of CD8+ T cells in the tumor microenvironment in colorectal cancer (CRC) patients. HIF-1α was inversely associated with pathways beneficial to anti-tumor immunotherapy and cytokine/chemokine function. In vivo, inhibiting HIF-1α or its upstream regulator BIRC2 significantly suppressed tumor growth and promoted CD8+ T-cell infiltration. CXCR3 neutralizing antibodies reversed these effects, implicating the involvement of CXCL9, -10, and -11/CXCR3 axis. The presence of HIF-1α weakened the upregulation of CXCL9, -10, and -11 by bleomycin and doxorubicin. Combining HIF-1α inhibition with bleomycin promoted CD8+ T-cell infiltration and tumor suppression in vivo. Moreover, doxorubicin could upregulate CXCL9, -10 and -11 by suppressing HIF-1α. Our findings highlight the potential of HIF-1α inhibition to improve CRC microenvironments and increase chemotherapy sensitivity.

Biochemistry of the hypoxia-inducible factor hydroxylases

The hypoxia-inducible factors are α,β-heterodimeric transcription factors that mediate the chronic response to hypoxia in humans and other animals. Protein hydroxylases belonging to two different structural subfamilies of the Fe(II) and 2-oxoglutarate (2OG)-dependent oxygenase superfamily modify HIFα. HIFα prolyl-hydroxylation, as catalysed by the PHDs, regulates HIFα levels and, consequently, α,β-HIF levels. HIFα asparaginyl-hydroxylation, as catalysed by factor inhibiting HIF (FIH), regulates the transcriptional activity of α,β-HIF. The activities of the PHDs and FIH are regulated by O2 availability, enabling them to act as hypoxia sensors. We provide an overview of the biochemistry of the HIF hydroxylases, discussing evidence that their kinetic and structural properties may be tuned to their roles in the HIF system. Avenues for future research and therapeutic modulation are discussed.