Activation Of Hypoxia-inducible Factor Research Articles

Exploring transcriptomic mechanisms underlying pulmonary adaptation to diverse environments in Indian rams.

The Changthangi sheep thrive at high altitudes in the cold desert regions of Ladakh, India while Muzaffarnagri sheep are well-suited to the low altitude plains of northern India. This study investigates the molecular mechanisms of pulmonary adaptation to diverse environments by analyzing gene expression profiles of lung tissues through RNA sequencing. Four biological replicates of lung tissue from each breed were utilized to generate the transcriptomic data. Differences in gene expression analysis revealed discrete expression profiles in lungs of each breed. In Changthangi sheep, genes related to immune responses, particularly cytokine signaling, were significantly enriched. Pathway analysis highlighted the activation of NF-kB signaling, a key mediator of inflammation and immune response. Additionally, the gene network analysis indicated a strong association between cytokine signaling, hypoxia-inducible factor (HIF) and NF-kB activation, suggesting a coordinated response to hypoxic stress in lungs of Changthangi sheep. In Muzaffarnagri sheep, the gene expression profiles were enriched for pathways related to energy metabolism, homeostasis and lung physiology. Key pathways identified include collagen formation and carbohydrate metabolism, both of which are crucial for maintaining lung function and structural integrity. Gene network analysis further reinforced this by revealing a strong connection between genes associated with lung structure and function. Our findings shed light on the valuable insights into gene expression mechanisms that enable these sheep breeds to adapt to their respective environments and contribute to a better understanding of high altitude adaptation in livestock.

Hypoxia drives estrogen receptor β-mediated cell growth via transcription activation in non-small cell lung cancer.

Non-small cell lung cancer (NSCLC) is a highly malignant tumor with a poor prognosis. Hypoxia conditions affect multiple cellular processes promoting the adaptation and progression of cancer cells via the activation of hypoxia-inducible factors (HIF) and subsequent transcription activation of their target genes. Preliminary studies have suggested that estrogen receptor β (ERβ) might play a promoting role in the progression of NSCLC. However, the precise mechanisms, particularly its connection to HIF-1α-mediated modulation under hypoxia, remain unclear. Our findings demonstrated that the overexpression of ERβ, not ERα, increased cell proliferation and inhibition of apoptosis in NSCLC cells and xenografts. Tissue microarray staining revealed a strong correlation between the protein expression of HIF-1α and ERβ. HIF-1α induced ERβ gene transcription and protein expression in CoCl2-induced hypoxia, 1% O2 incubation, or HIF-1α overexpressing cells. ChIP identified HIF-1α binding to a hypoxia response element in the ESR2 promoter. The suppression of HIF-1α and ERβ both in vitro and in vivo effectively reduced the tumor growth, thus emphasizing the promising prospects of targeting HIF-1α and ERβ as a therapeutic approach for the treatment of NSCLC. KEY MESSAGES: ERβ, not ERα, increases cell proliferation and inhibition of apoptosis in NSCLC cells and xenografts. A strong correlation exists between the protein expression of HIF-1α and ERβ. HIF-1α induced ERβ gene transcription and protein expression in hypoxic cells via binding to HRE in the ESR2 promoter. The suppression of HIF-1α and ERβ both in vitro and in vivo effectively reduced the NSCLC tumor growth.

Hypoxia-mediated rescue of retinal ganglion cells deficient in mitochondrial complex I is independent of the hypoxia-inducible factor pathway

Continuous exposure to environmental hypoxia (11% O2) has been shown to markedly slow the progressive degeneration of retinal ganglion cells (RGCs) in a mouse model of mitochondrial optic neuropathy with RGC-specific deletion of the key mitochondrial complex I accessory subunit ndufs4. As a first step toward identifying the therapeutic mechanism of hypoxia in this model, we conducted a series of experiments to investigate the role of the hypoxia-inducible factor (HIF) regulatory pathway in RGC neuroprotection. Vglut2-Cre; ndufs4loxP/loxP mice were crossed with strains bearing floxed alleles of the negative HIF regulatory vhl or of the two major HIF α-subunit isoforms, Hif1α and Hif2α. Deletion of vhl within ndufs4-deficient RGCs failed to prevent RGC degeneration under normoxia, indicating that HIF activation is not sufficient to achieve RGC rescue. Furthermore, the rescue of ndufs4-deficient RGCs by hypoxia remained robust despite genetic inactivation of Hif1α and Hif2α. Our findings demonstrate that the HIF pathway is entirely dispensable to the rescue of RGCs by hypoxia. Future efforts to uncover key HIF-independent molecular pathways induced by hypoxia in this mouse model may be of therapeutic relevance to mitochondrial optic neuropathies such as Leber hereditary optic neuropathy.

Endothelial PHD2 deficiency induces apoptosis resistance and inflammation via AKT activation and AIP1 loss independent of HIF2α.

In hypoxic and pseudohypoxic rodent models of pulmonary hypertension (PH), hypoxia-inducible factor (HIF) inhibition attenuates disease initiation. However, HIF activation alone, due to genetic alterations or use of inhibitors of prolyl hydroxylase domain (PHD) enzymes, has not been definitively shown to cause PH in humans, indicating the involvement of other mechanisms. Given the association between endothelial cell dysfunction and PH, the effects of pseudohypoxia and its underlying pathways were investigated in primary human lung endothelial cells. PHD2 silencing or inhibition, while activating HIF2α, induced apoptosis-resistance and IFN/STAT activation in endothelial cells, independent of HIF signaling. Mechanistically, PHD2 deficiency activated AKT and ERK, inhibited JNK, and reduced AIP1 (ASK1-interacting protein 1), all independent of HIF2α. Like PHD2, AIP1 silencing affected these same kinase pathways and produced a similar dysfunctional endothelial cell phenotype, which was partially reversed by AKT inhibition. Consistent with these in vitro findings, AIP1 protein levels in lung endothelial cells were decreased in Tie2-Cre/Phd2 knockout mice compared with wild-type controls. Lung vascular endothelial cells from patients with pulmonary arterial hypertension (PAH) showed IFN/STAT activation. Lung tissue from both SU5416/hypoxia PAH rats and patients with PAH all showed AKT activation and dysregulated AIP1 expression. In conclusion, PHD2 deficiency in lung vascular endothelial cells drives an apoptosis-resistant and inflammatory phenotype, mediated by AKT activation and AIP1 loss independent of HIF signaling. Targeting these pathways, including PHD2, AKT, and AIP1, holds the potential for developing new treatments for endothelial dysfunction in PH.NEW & NOTEWORTHY HIF activation alone does not conclusively lead to human PH, suggesting that HIF-independent signaling may also contribute to hypoxia-induced PH. This study demonstrated that PHD2 silencing-induced pseudohypoxia in human lung endothelial cells suppresses apoptosis and activates STAT, effects that persist despite HIF2α inhibition or knockdown and are attributed to AKT and ERK activation, JNK inhibition, and AIP1 loss. These findings align with observations in lung endothelial cells and tissues from PAH rodent models and patients.

Long-Term Excretion of Roxadustat in Urine.

Roxadustat (FG-4592), an orally active hypoxia-inducible factor prolyl hydroxylase stabilizer, has been shown to enhance erythropoiesis by increasing endogenous erythropoietin. It is indicated for the treatment of anemia and chronic kidney disease and is approved for clinical use in several countries, including the European Union, Japan and others. Due to its reasonably anticipated performance-enhancing effect in athletes, roxadustat is prohibited for use in sports at all times. A few cases of adverse analytical findings in routine doping controls have been reported worldwide, some of which were claimed to be the result of contaminated dietary supplements. The present study offers new data demonstrating the long-term excretion pattern of roxadustat. Even after a single-dose administration, roxadustat can remain detectable in urine for 8 months, albeit at very low concentrations (<10 pg/mL). Following three times a week treatment with 70 to 100 mg of roxadustat, the drug was still detectable in the urine of anemic patients for between 9 and 18 months after treatment was discontinued. Lastly, an athlete who admitted use of roxadustat for almost a year (50 mg 3 to 5 times a week) has now tested positive multiple times over the course of 15 months (the first test being 12 months after the drug was discontinued), with an estimated concentration of roxadustat between 3 and 8 pg/mL. Altogether, these findings indicate the unusually prolonged terminal excretion kinetics of roxadustat, a property that testing authorities should consider in their results management process.

The mitochondrial Na+/Ca2+ exchanger NCLX is implied in the activation of hypoxia-inducible factors

Eukaryotic cells and organisms depend on oxygen for basic living functions, and they display a panoply of adaptations to situations in which oxygen availability is diminished (hypoxia). A number of these responses in animals are mediated by changes in gene expression programs directed by hypoxia-inducible factors (HIFs), whose main mechanism of stabilization and functional activation in response to decreased cytosolic oxygen concentration was elucidated two decades ago. Human acute responses to hypoxia have been known for decades, although their precise molecular mechanism for oxygen sensing is not fully understood. It is already known that a redox component, linked with reactive oxygen species (ROS) production of mitochondrial origin, is implied in these responses. We have recently described a mechanism by which the mitochondrial sodium/calcium exchanger, NCLX, participates in mitochondrial electron transport chain regulation and ROS production in response to acute hypoxia.Here we show that NCLX is also implied in the response to hypoxia mediated by the HIFs. By using a NCLX inhibitor and interference RNA we show that NCLX activity is necessary for HIF-α subunits stabilization in hypoxia and for HIF-1-dependent transcriptional activity. We also show that hypoxic mitochondrial ROS production is not required for HIF-1α stabilization under all circumstances, suggesting that the basal cytosolic redox state or other mechanism(s) could be operating in the NCLX-mediated response to hypoxia that operates through HIF-α stabilization. This finding provides a link between acute and medium-term responses to hypoxia, reinforcing a central role of mitochondrial cell signalling in the response to hypoxia.

Hypoxia in Human Obesity: New Insights from Inflammation towards Insulin Resistance-A Narrative Review.

Insulin resistance (IR), marked by reduced cellular responsiveness to insulin, and obesity, defined by the excessive accumulation of adipose tissue, are two intertwined conditions that significantly contribute to the global burden of cardiometabolic diseases. Adipose tissue, beyond merely storing triglycerides, acts as an active producer of biomolecules. In obesity, as adipose tissue undergoes hypertrophy, it becomes dysfunctional, altering the release of adipocyte-derived factors, known as adipokines. This dysfunction promotes low-grade chronic inflammation, exacerbates IR, and creates a hyperglycemic, proatherogenic, and prothrombotic environment. However, the fundamental cause of these phenomena remains unclear. This narrative review points to hypoxia as a critical trigger for the molecular changes associated with fat accumulation, particularly within visceral adipose tissue (VAT). The activation of hypoxia-inducible factor-1 (HIF-1), a transcription factor that regulates homeostatic responses to low oxygen levels, initiates a series of molecular events in VAT, leading to the aberrant release of adipokines, many of which are still unexplored, and potentially affecting peripheral insulin sensitivity. Recent discoveries have highlighted the role of hypoxia and miRNA-128 in regulating the insulin receptor in visceral adipocytes, contributing to their dysfunctional behavior, including impaired glucose uptake. Understanding the complex interplay between adipose tissue hypoxia, dysfunction, inflammation, and IR in obesity is essential for developing innovative, targeted therapeutic strategies.

VHL synthetic lethality screens uncover CBF-β as a negative regulator of STING.

Clear cell renal cell carcinoma (ccRCC) represents the most common form of kidney cancer and is typified by biallelic inactivation of the von Hippel-Lindau ( VHL ) tumour suppressor gene. Here, we undertake genome-wide CRISPR/Cas9 screening to reveal synthetic lethal interactors of VHL , and uncover that loss of Core Binding Factor β (CBF-β) causes cell death in VHL -null ccRCC cell lines and impairs tumour establishment and growth in vivo . This synthetic relationship is independent of the elevated activity of hypoxia inducible factors (HIFs) in VHL -null cells, but does involve the RUNX transcription factors that are known binding partners of CBF-β. Mechanistically, CBF-β loss leads to upregulation of type I interferon signalling, and we uncover a direct inhibitory role for CBF-β at the STING locus controlling Interferon Stimulated Gene expression. Targeting CBF-β in kidney cancer both selectively induces tumour cell lethality and promotes activation of type I interferon signalling.

In Silico Exploration of AHR-HIF Pathway Interplay: Implications for Therapeutic Targeting in ccRCC.

The oxygen-sensing pathway is a crucial regulatory circuit that defines cellular conditions and is extensively exploited in cancer development. Pathogenic mutations in the von Hippel-Lindau (VHL) tumour suppressor impair its role as a master regulator of hypoxia-inducible factors (HIFs), leading to constitutive HIF activation and uncontrolled angiogenesis, increasing the risk of developing clear cell renal cell carcinoma (ccRCC). HIF hyperactivation can sequester HIF-1β, preventing the aryl hydrocarbon receptor (AHR) from correctly activating gene expression in response to endogenous and exogenous ligands such as TCDD (dioxins). In this study, we used protein-protein interaction networks and gene expression profiling to characterize the impact of VHL loss on AHR activity. Our findings reveal specific expression patterns of AHR interactors following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and in ccRCC. We identified several AHR interactors significantly associated with poor survival rates in ccRCC patients. Notably, the upregulation of the androgen receptor (AR) and retinoblastoma-associated protein (RB1) by TCDD, coupled with their respective downregulation in ccRCC and association with poor survival rates, suggests novel therapeutic targets. The strategic activation of the AHR via selective AHR modulators (SAhRMs) could stimulate its anticancer activity, specifically targeting RB1 and AR to reduce cell cycle progression and metastasis formation in ccRCC. Our study provides comprehensive insights into the complex interplay between the AHR and HIF pathways in ccRCC pathogenesis, offering novel strategies for targeted therapeutic interventions.

Oxygen-controllable injectable hydrogel alleviates intervertebral disc degeneration by balancing extracellular matrix metabolism

Nucleus pulposus (NP) cells, situated at the core of intervertebral discs, have acclimated to a hypoxic environment, orchestrating the equilibrium of extracellular matrix metabolism (ECM) under the regulatory influence of hypoxia inducible factor-1α (HIF-1α). Neovascularization and increased oxygen content pose a threat, triggering ECM degradation and intervertebral disc degeneration (IVDD). To address this, our study devised an oxygen-controllable strategy, introducing laccase into an injectable and ultrasound-responsive gelatin/agarose hydrogel. Laccase-mediated reactions were employed to deplete oxygen, establishing a hypoxic microenvironment that upregulated HIF-1α expression. The activation of hypoxia-inducible factors significantly enhanced the expression of aggrecan and collagen II, concurrently suppressing Matrix metalloproteinases (MMP13) and A Disintegrin and Metalloproteinase with Thrombospondin motifs (ADAMTS5) levels, thereby restoring the equilibrium of ECM metabolism. Simultaneously, the hydrogel facilitated the recruitment of stem cells into the NP through the controlled release of ATI2341, activating C-X-C chemokine receptor type 4 (CXCR4). Moreover, ultrasound amplification enhanced ATI2341 release, promoting the migration of NP stem cells. The hydrogel's efficacy in mitigating metabolic imbalances and inhibiting IVDD progression was substantiated in a rat puncture IVDD model through hydrogel injection into the discs. In conclusion, this hypoxia-inducible hydrogel, responsive to thermal stimuli from ultrasound, presents a promising avenue for IVDD treatment.

Benzothiazole derivatives in the design of antitumor agents.

Benzothiazoles are a class of heterocycles with multiple applications as anticancer, antibiotic, antiviral, and anti-inflammatory agents. Benzothiazole is a privileged scaffold in drug discovery programs for modulating a variety of biological functions. This review focuses on the design and synthesis of new benzothiazole derivatives targeting hypoxic tumors. Cancer is a major health problem, being among the leading causes of death. Tumor-hypoxicareas promote proliferation, malignancy, and resistance to drug treatment, leading to the dysregulation of key signaling pathways that involve drug targets such as vascular endothelial growth factor, epidermal growth factor receptor, hepatocyte growth factor receptor, dual-specificity protein kinase, cyclin-dependent protein kinases, casein kinase2, Rho-related coil formation protein kinase, tunica interna endothelial cell kinase, cyclooxygenase-2, adenosine kinase, lysophosphatidic acid acyltransferases, stearoyl-CoA desaturase, peroxisome proliferator-activated receptors, thioredoxin, heat shock proteins, and carbonic anhydrase IX/XII. In turn, they regulate angiogenesis, proliferation, differentiation, and cell survival, controlling the cell cycle, inflammation, the immune system, and metabolic alterations. A wide diversity of benzothiazoles were reported over the last years to interfere with various proteins involved in tumorigenesis and, more specifically, in hypoxic tumors. Many hypoxic targets are overexpressed as a result of the hypoxia-inducible factor activation cascade and may not be present in normal tissues, providing a potential strategy for selectively targeting hypoxic cancers.

Hypoxia-induced Factor-1α and its Role in Endometrial Cancer.

The transcription factor hypoxia inducible factor-1 (HIF-1) is one of the main factors in the cell's response to a lack of oxygen. Hypoxia is a typical feature of a growing cancerous tumor. Increased activity of HIF-1 is observed in many cancers, including endometrial cancer. HIF-1 functions as a heterodimer consisting of three subunits HIF-1α, HIF-2α, and HIF-3α and one subunit β. HIF-1α is a subunit that is sensitive to oxygen concentration and is constitutively expressed. The HIF-1α gene is highly polymorphic. Literature data suggest that single nucleotide polymorphisms (SNPs) of the HIF-1α gene may be risk factors for endometrial cancer. A better understanding of the molecular mechanisms of cancer development, progression and prognosis, including the role of SNPs, could lead to the development of new anti-cancer therapies.

ZBTB7A forms a heterodimer with ZBTB2 and inhibits ZBTB2 homodimerization required for full activation of HIF-1

Hypoxia-inducible factor 1 (HIF-1), recognized as a master transcription factor for adaptation to hypoxia, is associated with malignant characteristics and therapy resistance in cancers. It has become clear that cofactors such as ZBTB2 are critical for the full activation of HIF-1; however, the mechanisms downregulating the ZBTB2-HIF-1 axis remain poorly understood. In this study, we identified ZBTB7A as a negative regulator of ZBTB2 by analyzing protein sequences and structures. We found that ZBTB7A forms a heterodimer with ZBTB2, inhibits ZBTB2 homodimerization necessary for the full expression of ZBTB2-HIF-1 downstream genes, and ultimately delays the proliferation of cancer cells under hypoxic conditions. The Cancer Genome Atlas (TCGA) analyses revealed that overall survival is better in patients with high ZBTB7A expression in their tumor tissues. These findings highlight the potential of targeting the ZBTB7A-ZBTB2 interaction as a novel therapeutic strategy to inhibit HIF-1 activity and improve treatment outcomes in hypoxia-related cancers.

The ‘ABC’ of split-nanoluciferase HIF heterodimerization bioassays: Applications, Benefits & Considerations

Hypoxia-inducible factors (HIF) are interesting targets for multiple therapeutic indications. While HIF activation is desired for the treatment of anemia-related and ischemic diseases, HIF inhibition is of tremendous interest to anti-cancer drug development. Different signaling events within the HIF pathway are being targeted by drug discovery programs, with a special interest in HIF-selective (possibly also HIF1/2 isoform-selective) compounds. In this study, we applied recently developed cell-based split-nanoluciferase HIF heterodimerization assays to study the effects of compounds, targeting HIF activity by various mechanisms of action. This study shows that the application of similar or diverse assay protocols allows to detect various influences on HIF heterodimerization as a key signaling event in the oxygen sensing pathway: increased HIF heterodimerization (roxadustat, MG-132), decreased HIF heterodimerization (PX-478, ibuprofen) and direct (HIF isoform-selective) heterodimerization inhibiting effects (PT-2385). Changes in treatment time and in the assay protocol allowed to assess direct and indirect effects on HIFα-HIFβ heterodimerization. In addition to the evaluation of applications of these new bioassays regarding pharmacological characterizations, benefits and considerations are discussed related to the use of cellular, luminescent-based bioassays. Briefly, benefits include the bidirectional nature of the biological readout, the upstream mechanism of detection, the differentiation between HIF1 and HIF2 effects and the simulation of various conditions. Specific and general considerations include cell-based, technical and disease/drug-related aspects (e.g., non-specific effects, color interference). In summary, the versatility of these bioassays offers benefits in widespread applications regarding drug discovery and pharmacological characterization of various therapeutics, applying either the same or optimized experimental protocols.

Activation of PERK/eIF2α/ATF4/CHOP branch of endoplasmic reticulum stress response and cooperation between HIF-1α and ATF4 promotes Daprodustat-induced vascular calcification.

Introduction: Vascular calcification is accelerated in patients with chronic kidney disease (CKD) and increases the risk of cardiovascular events. CKD is frequently associated with anemia. Daprodustat (DPD) is a prolyl hydroxylase inhibitor for the treatment of CKD-associated anemia that enhances erythropoiesis through the activation of the hypoxia-inducible factor 1 (HIF-1) pathway. Studies showed that DPD promotes osteogenic differentiation of human aortic smooth muscle cells (HAoSMCs) and increases aorta calcification in mice with CKD. HIF-1 activation has been linked with endoplasmic reticulum (ER) stress; therefore, here we investigated the potential contribution of ER stress, particularly activating transcription factor 4 (ATF4), to the pro-calcification effect of DPD. Methods: Here, we used an adenine-induced CKD mouse model and HAoSMCs as an in vitro vascular calcification model to study the effect of DPD. Results: DPD treatment (15mg/kg/day) corrects anemia but increases the expression of hypoxia (Glut1, VEGFA), ER stress (ATF4, CHOP, and GRP78), and osteo-/chondrogenic (Runx2, Sox9, BMP2, and Msx2) markers and accelerates aorta and kidney calcification in CKD mice. DPD activates the PERK/eIF2α/ATF4/CHOP pathway and promotes high phosphate-induced osteo-/chondrogenic differentiation of HAoSMCs. Inhibition of ER stress with 4-PBA or silencing of ATF4 attenuates HAoSMC calcification. DPD-induced ATF4 expression is abolished in the absence of HIF-1α; however, knockdown of ATF4 does not affect HIF-1α expression. Conclusion: We concluded that DPD induces ER stress in vitro and in vivo, in which ATF4 serves as a downstream effector of HIF-1 activation. Targeting ATF4 could be a potential therapeutic approach to attenuate the pro-calcific effect of DPD.

Deubiquitinating enzyme mutagenesis screens identify a USP43-dependent HIF-1 transcriptional response

The ubiquitination and proteasome-mediated degradation of Hypoxia Inducible Factors (HIFs) is central to metazoan oxygen-sensing, but the involvement of deubiquitinating enzymes (DUBs) in HIF signalling is less clear. Here, using a bespoke DUBs sgRNA library we conduct CRISPR/Cas9 mutagenesis screens to determine how DUBs are involved in HIF signalling. Alongside defining DUBs involved in HIF activation or suppression, we identify USP43 as a DUB required for efficient activation of a HIF response. USP43 is hypoxia regulated and selectively associates with the HIF-1α isoform, and while USP43 does not alter HIF-1α stability, it facilitates HIF-1 nuclear accumulation and binding to its target genes. Mechanistically, USP43 associates with 14-3-3 proteins in a hypoxia and phosphorylation dependent manner to increase the nuclear pool of HIF-1. Together, our results highlight the multifunctionality of DUBs, illustrating that they can provide important signalling functions alongside their catalytic roles.

Revisiting reactive oxygen species production in hypoxia.

Cellular responses to hypoxia are crucial in various physiological and pathophysiological contexts and have thus been extensively studied. This has led to a comprehensive understanding of the transcriptional response to hypoxia, which is regulated by hypoxia-inducible factors (HIFs). However, the detailed molecular mechanisms of HIF regulation in hypoxia remain incompletely understood. In particular, there is controversy surrounding the production of mitochondrial reactive oxygen species (ROS) in hypoxia and how this affects the stabilization and activity of HIFs. This review examines this controversy and attempts to shed light on its origin. We discuss the role of physioxia versus normoxia as baseline conditions that can affect the subsequent cellular response to hypoxia and highlight the paucity of data on pericellular oxygen levels in most experiments, leading to variable levels of hypoxia that might progress to anoxia over time. We analyze the different outcomes reported in isolated mitochondria, versus intact cells or whole organisms, and evaluate the reliability of various ROS-detectingtools. Finally, we examine the cell-type and context specificity of oxygen's various effects. We conclude that while recent evidence suggests that the effect of hypoxia on ROS production is highly dependent on the cell type and the duration of exposure, efforts should be made to conduct experiments under carefully controlled, physiological microenvironmental conditions in order to rule out potential artifacts and improve reproducibility in research.

Teleocidin B-4, a PKC Activator, Upregulates Hypoxia-Inducible Factor 1 (HIF-1) Activity by Promoting the Accumulation of HIF-1α Protein via the PKCα/mTORC Signaling Pathway.

Hypoxia-inducible factor 1 (HIF-1) signaling is upregulated in an oxygen-dependent manner under hypoxic conditions. Activation of HIF-1 signaling increases the expression of HIF-1 target genes involved in cell survival, proliferation, and angiogenesis. Therefore, compounds that activate HIF-1 signaling have therapeutic potential in ischemic diseases. Screening for compounds that activate HIF-1 activity identified a microbial metabolite, teleocidin B-4, a PKC activator. Other PKC activators, such as TPA and 10-Me-Aplog-1, also activated HIF-1 activity. PKC activators induced HIF-1α protein accumulation through PKCα/mTORC activation. These results suggest that PKC activators without tumor-promoting activity have potential as therapeutic agents via HIF-1 target gene activation.

Induction of DEPP1 by HIF Mediates Multiple Hallmarks of Ischemic Cardiomyopathy.

HIF (hypoxia inducible factor) regulates many aspects of cardiac function. We and others previously showed that chronic HIF activation in the heart in mouse models phenocopies multiple features of ischemic cardiomyopathy in humans, including mitochondrial loss, lipid accumulation, and systolic cardiac dysfunction. In some settings, HIF also causes the loss of peroxisomes. How, mechanistically, HIF promotes cardiac dysfunction is an open question. We used mice lacking cardiac pVHL (von Hippel-Lindau protein) to investigate how chronic HIF activation causes multiple features of ischemic cardiomyopathy, such as autophagy induction and lipid accumulation. We performed immunoblot assays, RNA sequencing, mitochondrial and peroxisomal autophagy flux measurements, and live cell imaging on isolated cardiomyocytes. We used CRISPR-Cas9 gene editing in mice to validate a novel mediator of cardiac dysfunction in the setting of chronic HIF activation. We identify a previously unknown pathway by which cardiac HIF activation promotes the loss of mitochondria and peroxisomes. We found that DEPP1 (decidual protein induced by progesterone 1) is induced under hypoxia in a HIF-dependent manner and localizes inside mitochondria. DEPP1 is both necessary and sufficient for hypoxia-induced autophagy and triglyceride accumulation in cardiomyocytes ex vivo. DEPP1 loss increases cardiomyocyte survival in the setting of chronic HIF activation ex vivo, and whole-body Depp1 loss decreases cardiac dysfunction in hearts with chronic HIF activation caused by VHL loss in vivo. Our findings identify DEPP1 as a key component in the cardiac remodeling that occurs with chronic ischemia.

Tumor promoting effect of PDLIM2 downregulation involves mitochondrial ROS, oncometabolite accumulations and HIF-1α activation

BackgroundCancer is characterized by dysregulated cellular metabolism. Thus, understanding the mechanisms underlying these metabolic alterations is important for developing targeted therapies. In this study, we investigated the pro-tumoral effect of PDZ and LIM domain 2 (PDLIM2) downregulation in lung cancer growth and its association with the accumulation of mitochondrial ROS, oncometabolites and the activation of hypoxia-inducible factor-1 (HIF-1) α in the process.MethodsDatabases and human cancer tissue samples were analyzed to investigate the roles of PDLIM2 and HIF-1α in cancer growth. DNA microarray and gene ontology enrichment analyses were performed to determine the cellular functions of PDLIM2. Seahorse assay, flow cytometric analysis, and confocal microscopic analysis were employed to study mitochondrial functions. Oncometabolites were analyzed using liquid chromatography–mass spectrometry (LC–MS). A Lewis lung carcinoma (LLC) mouse model was established to assess the in vivo function of PDLIM2 and HIF-1α.ResultsThe expression of PDLIM2 was downregulated in lung cancer, and this downregulation correlated with poor prognosis in patients. PDLIM2 highly regulated genes associated with mitochondrial functions. Mechanistically, PDLIM2 downregulation resulted in NF-κB activation, impaired expression of tricarboxylic acid (TCA) cycle genes particularly the succinate dehydrogenase (SDH) genes, and mitochondrial dysfunction. This disturbance contributed to the accumulation of succinate and other oncometabolites, as well as the buildup of mitochondrial reactive oxygen species (mtROS), leading to the activation of hypoxia-inducible factor 1α (HIF-1α). Furthermore, the expression of HIF-1α was increased in all stages of lung cancer. The expression of PDLIM2 and HIF-1α was reversely correlated in lung cancer patients. In the animal study, the orally administered HIF-1α inhibitor, PX-478, significantly reduces PDLIM2 knockdown-promoted tumor growth.ConclusionThese findings shed light on the complex action of PDLIM2 on mitochondria and HIF-1α activities in lung cancer, emphasizing the role of HIF-1α in the tumor-promoting effect of PDLIM2 downregulation. Additionally, they provide new insights into a strategy for precise targeted treatment by suggesting that HIF-1α inhibitors may serve as therapy for lung cancer patients with PDLIM2 downregulation.