Coding mutations in NUS1 contribute to Parkinson's disease.

Whole-exome sequencing has been successful in identifying genetic factors contributing to familial or sporadic Parkinson's disease (PD). However, this approach has not been applied to explore the impact of de novo mutations on PD pathogenesis. Here, we sequenced the exomes of 39 early onset patients, their parents, and 20 unaffected siblings to investigate the effects of de novo mutations on PD. We identified 12 genes with de novo mutations (MAD1L1, NUP98, PPP2CB, PKMYT1, TRIM24, CEP131, CTTNBP2, NUS1, SMPD3, MGRN1, IFI35, and RUSC2), which could be functionally relevant to PD pathogenesis. Further analyses of two independent case-control cohorts (1,852 patients and 1,565 controls in one cohort and 3,237 patients and 2,858 controls in the other) revealed that NUS1 harbors significantly more rare nonsynonymous variants (P = 1.01E-5, odds ratio = 11.3) in PD patients than in controls. Functional studies in Drosophila demonstrated that the loss of NUS1 could reduce the climbing ability, dopamine level, and number of dopaminergic neurons in 30-day-old flies and could induce apoptosis in fly brain. Together, our data suggest that de novo mutations could contribute to early onset PD pathogenesis and identify NUS1 as a candidate gene for PD.

Polymorphisms of HOMER1 gene are associated with piglet splay leg syndrome and one significant SNP can affect its intronic promoter activity in vitro.

BACKGROUND: In our previous genome-wide association study (GWAS) on the piglet splay leg (PSL) syndrome, the homer scaffolding protein 1 (HOMER1) was detected as a candidate gene. The aim of this work was to further verify the candidate gene by sequencing the gene and find the significantly associated mutation. Then we preliminarily analyzed the effect of the significant SNP on intronic promoter activity. This research provided a reference for further investigation of the pathogenesis of PSL. RESULT: We investigated the 19 SNPs on HOMER1 and found 12 SNPs significant associated with PSL, including 8 SNPs resided in the potential intronic promoter region in intron 4. The - 663~ - 276 bp upstream the exon 5 had promoter activity and it could be an intronic promoter that regulated the transcription of HOMER1-205 transcript. The promoter activity of the - 663~ - 276 bp containing the rs339135425 and rs325197091 mutant alleles was significantly higher than of the wild type (P < 0.05). The G allele of rs325197091 (A > G) may create a new binding site of transcription factor aryl hydrocarbon receptor nuclear translocator (ARNT) and could enhance HOMER1 intronic promoter activity. CONCLUSIONS: HOMER1 gene was associated with the PSL, and the rs325197091 could influence HOMER1 intronic promoter activity in vitro.

Novel roles for AhR and ARNT in the regulation of alcohol dehydrogenases in human hepatic cells.

The mechanisms by which pollutants participate in the development of diverse pathologies are not completely understood. The pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) activates the AhR (aryl hydrocarbon receptor) signaling pathway. We previously showed that TCDD (25 nM, 30 h) decreased the expression of several alcohol metabolism enzymes (cytochrome P450 2E1, alcohol dehydrogenases ADH1, 4 and 6) in differentiated human hepatic cells (HepaRG). Here, we show that, as rapidly as 8 h after treatment (25 nM TCDD) ADH expression decreased 40 % (p < 0.05). ADH1 and 4 protein levels decreased 40 and 27 %, respectively (p < 0.05), after 72 h (25 nM TCDD). The protein half-lives were not modified by TCDD which suggests transcriptional regulation of expression. The AhR antagonist CH-223191 or AhR siRNA reduced the inhibitory effect of 25 nM TCDD on ADH1A, 4 and 6 expression 50-100 % (p < 0.05). The genomic pathway (via the AhR/ARNT complex) and not the non-genomic pathway involving c-SRC mediated these effects. Other AhR ligands (3-methylcholanthrene and PCB 126) decreased ADH1B, 4 and 6 mRNAs by more than 78 and 55 %, respectively (p < 0.01). TCDD also regulated the expression of ADH4 in the HepG2 human hepatic cell line, in primary human hepatocytes and in C57BL/6J mouse liver. In conclusion, activation of the AhR/ARNT signaling pathway by AhR ligands represents a novel mechanism for regulating the expression of ADHs. These effects may be implicated in the toxicity of AhR ligands as well as in the alteration of ethanol or retinol metabolism and may be associated further with higher risk of liver diseases or/and alcohol abuse disorders.

Hypoxia-inducible factor 1 is required for remote ischemic preconditioning of the heart.

Both preclinical and clinical studies suggest that brief cycles of ischemia and reperfusion in the arm or leg may protect the heart against injury following prolonged coronary artery occlusion and reperfusion, a phenomenon known as remote ischemic preconditioning. Recent studies in mice indicate that increased plasma interleukin-10 (IL-10) levels play an important role in remote ischemic preconditioning induced by clamping the femoral artery for 5 min followed by 5 min of reperfusion for a total of three cycles. In this study, we demonstrate that remote ischemic preconditioning increases plasma IL-10 levels and decreases myocardial infarct size in wild-type mice but not in littermates that are heterozygous for a knockout allele at the locus encoding hypoxia-inducible factor (HIF) 1α. Injection of a recombinant adenovirus encoding a constitutively active form of HIF-1α into mouse hind limb muscle was sufficient to increase plasma IL-10 levels and decrease myocardial infarct size. Exposure of C2C12 mouse myocytes to cyclic hypoxia and reoxygenation rapidly increased levels of IL-10 mRNA, which was blocked by administration of the HIF-1 inhibitor acriflavine or by expression of short hairpin RNA targeting HIF-1α or HIF-1ß. Chromatin immunoprecipitation assays demonstrated that binding of HIF-1 to the Il10 gene was induced when myocytes were subjected to cyclic hypoxia and reoxygenation. Taken together, these data indicate that HIF-1 activates Il10 gene transcription and is required for remote ischemic preconditioning.

Hypoxia-inducible regulation of placental BOK expression.

BOK (BCL-2-related ovarian killer) is a member of the pro-apoptotic BCL-2 family that is highly expressed in the human placenta. BOK excess causes increased trophoblast autophagy and apoptosis in pre-eclampsia, a pathological condition of hypoxia and oxidative stress. In the present study, we identified an HRE (hypoxia-response element) at the junction of exon-1 and intron-1 (+229 to +279) in the human BOK gene, as well as an antisense transcript driven by a promoter located in intron-2. The isolated BOK-HRE bound hypoxia-inducible HIF (hypoxia-inducible factor) proteins in vitro as well as in trophoblastic JEG3 cells and was functional in its natural position as well as in front of a heterologous promoter. Being a reverted repeat, the BOK-HRE functioned in both orientations. This directionless feature of the BOK-HRE facilitates hypoxia regulation via HIF of both BOK and its antisense transcript as demonstrated by RNAi knockdown of the HIF system. Although the antisense transcript was expressed in several human carcinoma cell lines, including choriocarcinoma-derived JEG3 cells, no antisense-regulated mechanism for BOK expression was noted. Taken together, these findings indicate that hypoxia-induced expression of BOK in placental cells is regulated via HIF and is not affected by its antisense transcript.

A cyclic peptide inhibitor of HIF-1 heterodimerization that inhibits hypoxia signaling in cancer cells.

Hypoxia inducible factor-1 (HIF-1) is a heterodimeric transcription factor that acts as the master regulator of cellular response to reduced oxygen levels, thus playing a key role in the adaptation, survival, and progression of tumors. Here we report cyclo-CLLFVY, identified from a library of 3.2 million cyclic hexapeptides using a genetically encoded high-throughput screening platform, as an inhibitor of the HIF-1α/HIF-1ß protein-protein interaction in vitro and in cells. The identified compound inhibits HIF-1 dimerization and transcription activity by binding to the PAS-B domain of HIF-1α, reducing HIF-1-mediated hypoxia response signaling in a variety of cell lines, without affecting the function of the closely related HIF-2 isoform. The reported cyclic peptide demonstrates the utility of our high-throughput screening platform for the identification of protein-protein interaction inhibitors, and forms the starting point for the development of HIF-1 targeted cancer therapeutics.

Hypoxia-inducible factor-1ß (HIF-1ß) is upregulated in a HIF-1α-dependent manner in 518A2 human melanoma cells under hypoxic conditions.

Solid tumors include hypoxic areas due to excessive cell proliferation. Adaptation to low oxygen levels is mediated by the hypoxia-inducible factor (HIF) pathway promoting invasion, metastasis, metabolic alterations, chemo-resistance and angiogenesis. The transcription factor HIF-1, the major player within this pathway consists of HIF-1α and HIF-1ß. The alpha subunit is continuously degraded under normoxia and becomes stabilized under reduced oxygen supply. In contrast, HIF-1ß is generally regarded as constitutively expressed and being present in excess within the cell. However, there is evidence that the expression of this subunit is more complex. The aim of this study was to investigate the role of HIF-1ß in human melanoma cells. Among a panel of five different cell lines, in 518A2 cells exposed to the hypoxia-mimetic cobalt chloride HIF-1ß was rapidly elevated on protein level. Knockdown experiments performed under cobalt chloride-exposure and hypoxia revealed that this effect was mediated by HIF-1α. The non-canonical relationship between these subunits was further confirmed by pharmacologic inhibition of HIF-1α and by expression of a dominant-negative HIF mutant. Overexpression of HIF-1α showed a time delay in HIF-1ß induction, thus arguing for HIF-1ß de novo synthesis rather than protein stabilization by heterodimerization. A Hen's egg test-chorioallantoic membrane model of angiogenesis and invasion indicated a local expression of HIF-1ß and implies a biological relevance of these findings. In summary, this study demonstrates the HIF-1α-dependent regulation of HIF-1ß under hypoxic conditions for the first time. The results indicate a novel cell specific mechanism which might prevent HIF-1ß to become a limiting factor.

Mechanistic target of rapamycin (mTOR) dependent regulation of thioredoxin interacting protein (TXNIP) transcription in hypoxia.

Thioredoxin interacting protein (TXNIP), first identified as an inhibitor of thioredoxin, is also a tumor suppressor as well as an inhibitor of lipogenesis. TXNIP is known to be transcriptionally regulated in response to nutrients such as glucose and stress signals, including endoplasmic reticulum stress and lactic acidosis. In this study, we characterized the transcriptional regulation of TXNIP in response to hypoxia. Using a hepatocellular carcinoma cell line, we have found that TXNIP mRNA expression is regulated in a biphasic manner in hypoxia whereby TXNIP expression showed an initial rapid decrease, followed by an increase under prolonged hypoxia. Interestingly, we have shown that TXNIP induction in prolonged hypoxia is independent of the Hypoxia-Inducible Factor (HIF) transcription factor. The effect of hypoxia on TXNIP expression is mediated via the inhibition of the 4E-BP1/eIF4E axis of mechanistic target of rapamycin (mTORC1). Thus, we found that inhibiting mTORC1-dependent 4E-BP1 phosphorylation mimics the effect of hypoxia on TXNIP expression. Furthermore, overexpressing eIF4E prevents the induction of TXNIP in hypoxia. Our results suggest that mTORC1 may be an important regulator of hypoxia-dependent gene expression.

IFN-γ attenuates hypoxia-inducible factor (HIF) activity in intestinal epithelial cells through transcriptional repression of HIF-1ß.

Numerous studies have revealed that hypoxia and inflammation occur coincidentally in mucosal disorders, such as inflammatory bowel disease. During inflammation, epithelial-expressed hypoxia-inducible factor (HIF) serves an endogenously protective function. In this study, we sought to explore how mucosal immune responses influence HIF-dependent end points. Guided by a screen of relevant inflammatory mediators, we identified IFN-γ as a potent repressor of HIF-dependent transcription in human intestinal epithelial cells. Analysis of HIF levels revealed that HIF-1ß, but not HIF-1α, is selectively repressed by IFN-γ in a JAK-dependent manner. Cloning and functional analysis of the HIF-1ß promoter identified a prominent region for IFN-γ-dependent repression. Further studies revealed that colonic IFN-γ and HIF-1ß levels were inversely correlated in a murine colitis model. Taken together, these studies demonstrated that intestinal epithelial HIF is attenuated by IFN-γ through transcriptional repression of HIF-1ß. These observations are relevant to the pathophysiology of colitis (i.e., that loss of HIF signaling during active inflammation may exacerbate disease pathogenesis).

Inhibition of ARNT severely compromises endothelial cell viability and function in response to moderate hypoxia.

Hypoxia inducible factor (HIF) is a master heterodimeric transcriptional regulator of oxygen (O(2)) homeostasis critical to proper angiogenic responses. Due to the distinctive coexpression of HIF-1α and HIF-2α subunits in endothelial cells, our goal was to examine the genetic elimination of HIF transcriptional activity in response to physiological hypoxic conditions by using a genetic model in which the required HIF-ß subunit (ARNT, Aryl hydrocarbon Receptor Nuclear Translocator) to HIF transcriptional responses was depleted. Endothelial cells (ECs) and aortic explants were isolated from Arnt ( loxP/loxP ) mice and infected with Adenovirus-Cre/GFP or control-GFP. We observed that moderate levels of 2.5 % O(2) promoted vessel sprouting, growth, and branching in control aortic ring assays while growth from Adenovirus-Cre infected explants was compromised. Primary Adenovirus-Cre infected EC cultures featured adverse migration and tube formation phenotypes. Primary pulmonary or cardiac ARNT-deleted ECs also failed to proliferate and survive in response to 8 or 2.5 % O(2) and hydrogen peroxide treatment. Our data demonstrates that ARNT promotes EC migration and vessel outgrowth and is indispensible for the proliferation and preservation of ECs in response to the physiological environmental cue of hypoxia. Thus, these results demonstrate that ARNT plays a critical intrinsic role in ECs and support an important collaboration between HIF-1 and HIF-2 transcriptional activity in these cells.

Recent Advances in the Discovery of HIF-1α-p300/CBP Inhibitors as Anti-Cancer Agents.

Hypoxia-inducible factor-1 (HIF-1), a heterodimeric (containing α and ß subunits) transcription factor, is involved in hypoxia response pathway that regulates the expression of many tumorrelated genes. The stabilized HIF-1 heterodimer couples to the general co-activators p300/CBP (CREB binding protein), forming an active transcription factor to initiate hypoxic responses. Inhibiting the transcription factor-coactivator HIF-1α-p300/CBP interaction represents an attractive approach for blocking hypoxia pathway in tumors. Recently, diverse HIF-1α-p300/CBP inhibitors have been designed and their anti-tumor activities have been evaluated. The developments of inhibitors of HIF-1α- p300/CBP are discussed in this review. An outline of structures and biological activities of these inhibitors can be traced, along with the approaches for inhibitors discovery. The challenges in identifying novel and selective potent inhibitors of HIF-1α-p300/CBP are also put forward.

Effects of sequential exposure to water accommodated fraction of crude oil and chlorpyrifos on molecular and biochemical biomarkers in rainbow trout.

Fish can be simultaneously or sequentially exposed to various kinds of pollutants, resulting in combined effects. Polycyclic aromatic hydrocarbons induce cytochrome P450 monooxygenase 1A (CYP1A) expression, which catalyzes the conversion of the organophosphorus insecticide chlorpyrifos (CPF) into its most active derivative, CPF-oxon. CPF-oxon inhibits CYP1A and other enzymes, including carboxylesterases (CEs) and acetylcholinesterase (AChE). We studied the effects of an in vivo exposure to crude oil water accommodated fraction (WAF) followed by an ex vivo exposure of liver tissue to CPF on the expression of Cyp1a, AhR and ARNT mRNA, CYP1A protein and on the activity of biomarker enzymes in the rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout were exposed to WAF (62 µg L-1 TPH) for 48 h. Then, liver was dissected out, sliced and exposed to 20 µg L-1 CPF ex vivo for 1 h. Liver tissue was analyzed for mRNA and protein expression and for CEs, AChE, glutathione S-transferase (GST) and CYP1A (EROD) activity. WAF induced Cyp1a mRNA and CYP1A protein expression by 10-fold and 2.5-8.3-fold, respectively, with no effect of CPF. WAF induced AhR expression significantly (4-fold) in control but not in CPF treated liver tissue. ARNT mRNA expression was significantly lowered (5-fold) by WAF. CPF significantly reduced liver EROD activity, independently of WAF pre-treatment. CEs activity was significantly inhibited in an additive manner following in vivo exposure to WAF (42%) and ex vivo exposure to CPF (19%). CPF exposure inhibited AChE activity (37%) and increased GST activity (42%).

(Aryloxyacetylamino)benzoic acid analogues: A new class of hypoxia-inducible factor-1 inhibitors.

Structural modification of a compound discovered during screening using an HRE-dependent reporter assay has revealed a novel class of HIF-1 inhibitors, which potently inhibit the HIF-1alpha protein accumulation and its target gene expression under hypoxic conditions in human hepatocellular carcinoma Hep3B cells.

HIFing the brakes: therapeutic opportunities for treatment of human malignancies.

The unfortunate ability of tumor cells to survive and expand in an uncontrolled manner has captivated the attention of clinicians and basic scientists alike. The molecular mechanisms that tumor cells use to grow are the very same pathways used in normal cell growth and differentiation. One important pathway conferring a growth advantage on tumor cells is the epidermal growth factor receptor (EGFR) pathway. Signaling through the EGFR leads to activation of the phosphatidylinositol 3-kinase and Akt pathway and to increased activity of multiple effectors, including hypoxia-inducible factors (HIFs), which are cellular transcription factors involved in environmental stress response. The target genes that HIF members stimulate that are relevant to tumor growth include transcriptional activators and repressors and cytokines and growth factors, as well as their receptors. In this Perspective, findings from several recent studies are discussed in terms of their effect on the signal transducers, target genes, and tumor properties that are ultimately affected during EGFR-stimulated HIF signaling in cancer cells.

Inhibition of hypoxia-induced angiogenesis by sodium butyrate, a histone deacetylase inhibitor, through hypoxia-inducible factor-1alpha suppression.

Hypoxia-inducible factor-1 (HIF-1) plays a pivotal role in cellular response to low oxygen concentration, such as angiogenesis in tumors. Here, we found that a histone deacetylase inhibitor, sodium butyrate, inhibits the hypoxia-induced induction and activity of HIF-1alpha in HT1080 human fibrosarcoma cells. Moreover, sodium butyrate also suppressed the hypoxia-stimulated angiogenic effects and downregulated HIF-1alpha and vascular endothelial growth factor expression in vascular endothelial cells. These findings suggest that sodium butyrate may play important roles in tumor suppression via inhibition of HIF-1alpha mediated angiogenesis under hypoxic conditions.

Hypoxia-inducible factor-1 inhibition in combination with temozolomide treatment exhibits robust antitumor efficacy in vivo.

PURPOSE: Inhibiting hypoxia-inducible factor-1 (HIF-1) represents a unique mechanism for cancer therapy. It is conceived that HIF-1 inhibitors may synergize with many classes of cancer therapeutic agents, such as angiogenesis inhibitors and cytotoxic drugs, to achieve a more robust tumor response. However, these hypotheses have not been rigorously tested in tumor models in vivo. The present study was carried out to evaluate the antitumor efficacy of combining HIF-1 inhibition with angiogenesis inhibitors or cytotoxic agents. EXPERIMENTAL DESIGN: Using a D54MG-derived tumor model that allows knockdown of HIF-1alpha on doxycycline treatment, we examined the tumor responses to chemotherapeutic agents, including the angiogenesis inhibitor ABT-869 and cytotoxic agents 1,3-bis(2-chloroethyl)-1-nitrosourea and temozolomide, in the presence or absence of an intact HIF-1 pathway. RESULTS: Surprisingly, inhibiting HIF-1 in tumors treated with the angiogenesis inhibitor ABT-869 did not produce much added benefit compared with ABT-869 treatment alone, suggesting that the combination of an angiogenesis inhibitor with a HIF-1 inhibitor may not be a robust therapeutic regimen. In contrast, the cytotoxic drug temozolomide, when used in combination with HIF-1alpha knockdown, exhibited a superadditive and likely synergistic therapeutic effect compared with the monotherapy of either treatment alone in the D54MG glioma model. CONCLUSIONS: Our results show that the DNA alkylating agent temozolomide exhibits robust antitumor efficacy when used in combination with HIF-1 inhibition in D54MG-derived tumors, suggesting that the combination of temozolomide with HIF-1 inhibitors might be an effective regimen for cancer therapy. In addition, our results also show that the RNA interference-based inducible knockdown model can be a valuable platform for further evaluation of the combination treatment of other cancer therapeutics with HIF-1 inhibition.

A rationally designed small molecule that inhibits the HIF-1alpha-ARNT heterodimer from binding to DNA in vivo.

Modern drug development is focused on two steps: the identification of new molecular targets and the development of drugs that affect these targets. A molecular target can be an enzymatic activity or a macromolecular interface that is important in a disease pathway. Current drugs on the market are biased toward targeting cell surface receptors and intracellular enzymatic activities. However, macromolecular interfaces can also serve as potential molecular targets. A recent paper from Kaelin and Dervan's groups examined an underused molecular target-transcription factor DNA binding. To specifically disrupt transcriptional activation, they used a rationally designed small molecule that binds specifically in the minor groove of a DNA sequence that in vivo is bound by a bHLH heterodimer transcription factor.

Blocking expression of AHR2 and ARNT1 in zebrafish larvae protects against cardiac toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The zebrafish (Danio rerio) has become an attractive vertebrate model for studying developmental processes, and is emerging as a model system for studying the mechanisms by which xenobiotic compounds perturb normal development. Embryos treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) shortly after fertilization exhibit a range of adverse effects on the heart: an early reduction in cardiac myocyte number, followed by a change in heart looping and morphology, with an apparent compaction of the ventricle and overall decrease in heart size. These changes are accompanied by impaired cardiac function including a decrease in cardiac output and eventually irreversible ventricular standstill. The mechanisms involved in mediating effects of TCDD on the heart remain unknown. However, it is widely accepted that aryl hydrocarbon receptor (AHR) activation mediates endpoints of TCDD toxicity in vertebrates. In zebrafish, there are multiple forms of AHR and AHR nuclear translocator protein (ARNT) raising the question about whether different endpoints of TCDD toxicity are mediated by different components of the AHR/ARNT pathway. To address this question we used morpholino oligonucleotide technology to specifically block the expression of zfAHR2, zfARNT1, zfARNT2, and zfCYP1A, and assessed the previously described effects of TCDD on heart morphology, size, and function in the developing morphants. We report that blocking zfAHR2 and zfARNT1 expression provided protection against the TCDD-mediated alteration in heart morphology, reduced cardiac myocyte number, decreased cardiac output and ventricular standstill in zebrafish larvae, while the zfarnt2 and zfcyp1a morpholinos did not block the TCDD-induced cardiac toxicity.

Differential suppression of the aryl hydrocarbon receptor nuclear translocator-dependent function by an aryl hydrocarbon receptor PAS-A-derived inhibitory molecule.

The aryl hydrocarbon receptor (AhR) heterodimerizes with the aryl hydrocarbon receptor nuclear translocator (Arnt) for transcriptional regulation. We generated three N-terminal deletion constructs of the human AhR of 12-24 kDa in size--namely D1, D2, and D3--to suppress the Arnt function. We observed that all three deletions interact with the human Arnt with similar affinities. D2, which contains part of the AhR PAS-A domain and interacts with the PAS-A domain of Arnt, inhibits the formation of the AhR gel shift complex. D2 suppresses the 3-methylcholanthrene-induced, dioxin response element (DRE)-driven luciferase activity in Hep3B cells and exogenous Arnt reverses this D2 suppression. D2 suppresses the induction of CYP1A1 at both the message and protein levels in Hep3B cells; however, the CYP1B1 induction is not affected. D2 suppresses the recruitment of Arnt to the cyp1a1 promoter but not to the cyp1b1 promoter, partly because the AhR/Arnt heterodimer binds better to the cyp1b1 DRE than to the cyp1a1 DRE. Interestingly, D2 has no effect on the cobalt chloride-induced, hypoxia inducible factor-1 (HIF-1)-dependent expression of vegf, aldolase c, and ldh-a messages. Our data reveal that the flanking sequences of the DRE contribute to the binding affinity of the AhR/Arnt heterodimer to its endogenous enhancers and the function of AhR and HIF-1 can be differentially suppressed by the D2 inhibitory molecule.

Targeting the hypoxia-sensing pathway in clinical hematology.

Hypoxia-inducible factors (HIFs) are oxygen-sensitive transcription factors regulated by oxygen-dependent prolyl hydroxylase domain (PHD) enzymes and are key to cell adaptation to low oxygen. The hematopoietic stem cell (HSC) niche in the bone marrow is highly heterogeneous in terms of microvasculature and thus oxygen concentration. The importance of hypoxia and HIFs in the hematopoietic environment is becoming increasingly recognized. Many small compounds that inhibit PHDs have been developed, enabling HIFs to be pharmacologically stabilized in an oxygen-independent manner. The use of PHD inhibitors for therapeutic intervention in hematopoiesis is being increasingly investigated. PHD inhibitors are well established to increase erythropoietin production to correct anemia in hemodialysis patients. Pharmacological stabilization of HIF-1α protein with PHD inhibitors is also emerging as an important regulator of HSC proliferation and self-renewal. Administration of PHD inhibitors increases quiescence and decreases proliferation of HSCs in the bone marrow in vivo, thereby protecting them from high doses of irradiation and accelerating hematological recovery. Recent findings also show that stabilization of HIF-1α increases mobilization of HSCs in response to granulocyte colony-stimulating factor and plerixafor, suggesting that PHD inhibitors could be useful agents to increase mobilization success in patients requiring transplantation. These findings highlight the importance of the hypoxia-sensing pathway and HIFs in clinical hematology.