Hypoxia-inducible factor 1 transcriptional activity in endothelial cells is required for acute phase cardioprotection induced by ischemic preconditioning

Human iPSC-derived myocardium-on-chip with capillary-like flow for personalized medicine

The heart wall tissue, or the myocardium, is one of the main targets in cardiovascular disease prevention and treatment. Animal models have not been sufficient in mimicking the human myocardium as evident by the very low clinical translation rates of cardiovascular drugs. Additionally, current in vitro models of the human myocardium possess several shortcomings such as lack of physiologically relevant co-culture of myocardial cells, lack of a 3D biomimetic environment, and the use of non-human cells. In this study, we address these shortcomings through the design and manufacture of a myocardium-on-chip (MOC) using 3D cell-laden hydrogel constructs and human induced pluripotent stem cell (hiPSC) derived myocardial cells. The MOC utilizes 3D spatially controlled co-culture of hiPSC derived cardiomyocytes (iCMs) and hiPSC derived endothelial cells (iECs) integrated among iCMs as well as in capillary-like side channels, to better mimic the microvasculature seen in native myocardium. We first fully characterized iCMs using immunostaining, genetic, and electrochemical analysis and iECs through immunostaining and alignment analysis to ensure their functionality, and then seeded these cells sequentially into the MOC device. We showed that iECs could be cultured within the microfluidic device without losing their phenotypic lineage commitment, and align with the flow upon physiological level shear stresses. We were able to incorporate iCMs within the device in a spatially controlled manner with the help of photocrosslinkable polymers. The iCMs were shown to be viable and functional within the device up to 7 days, and were integrated with the iECs. The iCMs and iECs in this study were derived from the same hiPSC cell line, essentially mimicking the myocardium of an individual human patient. Such devices are essential for personalized medicine studies where the individual drug response of patients with different genetic backgrounds can be tested in a physiologically relevant manner.

WDR26 promotes mitophagy of cardiomyocytes induced by hypoxia through Parkin translocation

Myocardial ischemia is a heart condition caused by reduction of blood flow to the heart, preventing heart from receiving enough oxygen. Myocardial ischemia is the most common cause of death globally. Heart ischemic preconditioning (IPC) has a protective effect against myocardial cell death induced by ischemia and ischemia-reperfusion injury. WDR26 has recently been identified as a protein that is increased following rat cardiac IPC. WDR26 can promote the proliferation of H9c2 cells and protect cardiomyocytes against oxidative stress through inhibiting apoptosis. However, its role in myocardial ischemia is unclear. The aim of this study was to explore the role of WDR26 in myocardial ischemia and H9c2 cell hypoxia. Our results showed that WDR26 is induced by myocardial ischemia and H9c2 cell hypoxia. WDR26 protects H9c2 cells against hypoxia injury through inhibiting LDH release and increasing cell viability. WDR26 promotes hypoxia-induced autophagy in hypoxia of H9c2 cells. We further demonstrated that in H9c2 cell hypoxia, WDR26 increases mitochondrial membrane potential, thereby increases Parkin translocation of mitochondria. After Parkin is translocated at mitochondria, WDR26 can increase mitochondrial protein ubiquitination in hypoxia of H9c2 cells. WDR26 is a mediator of response to hypoxia, and WDR26 plays an important role in hypoxia-mediated autophagy and mitophagy. This study provides novel insights into the protective role of WDR26 in cardiomyocyte injury during hypoxia. WDR26 may serve as a potential target for the treatment of myocardial ischemia.

Molecular Characterization of Reactive Oxygen Species in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (I/R) injury is experienced by individuals suffering from cardiovascular diseases such as coronary heart diseases and subsequently undergoing reperfusion treatments in order to manage the conditions. The occlusion of blood flow to the tissue, termed ischemia, can be especially detrimental to the heart due to its high energy demand. Several cellular alterations have been observed upon the onset of ischemia. The danger created by cardiac ischemia is somewhat paradoxical in that a return of blood to the tissue can result in further damage. Reactive oxygen species (ROS) have been studied intensively to reveal their role in myocardial I/R injury. Under normal conditions, ROS function as a mediator in many cell signaling pathways. However, stressful environments significantly induce the generation of ROS which causes the level to exceed body's antioxidant defense system. Such altered redox homeostasis is implicated in myocardial I/R injury. Despite the detrimental effects from ROS, low levels of ROS have been shown to exert a protective effect in the ischemic preconditioning. In this review, we will summarize the detrimental role of ROS in myocardial I/R injury, the protective mechanism induced by ROS, and potential treatments for ROS-related myocardial injury.

Admission hypoxia-inducible factor 1α levels and in-hospital mortality in patients with acute decompensated heart failure

BACKGROUND

Hypoxia-inducible factor 1 (HIF-1) is a critical regulator for cellular oxygen balance. Myocardial hypoxia can induce the increased expression of HIF-1α. Our goals were to evaluate the value of HIF-1α in predicting death of patients with acute decompensated heart failure (ADHF) and describe the in vivo relationship between serum HIF-1α and N-terminal-pro-brain natriuretic peptide (NT-proBNP) levels.

METHOD

We included 296 patients who were consecutively admitted to the emergency department for ADHF. The primary end point was in-hospital death. The patients were categorized as HFrEF (patients with reduced systolic function) and HFpEF (patients with preserved systolic function) groups.

RESULTS

In our patients, the median admission HIF-1α level was 2.95 ± 0.85 ng/ml. The HIF-1α level was elevated significantly in HFrEF patients and deceased patients compared with HFpEF patients and patients who survived. The HIF-1α level was positively correlated with NT-proBNP and cardiac troponin T levels, and negatively correlated with left ventricular ejection fraction and systolic blood pressure. Kaplan-Meier curves revealed a significant increase in in-hospital mortality in ADHF patients with higher HIF-1α levels. Multivariable Cox regression analysis showed that HIF-1α levels were not correlated with the short-term prognosis of ADHF patients.

CONCLUSIONS

This is the first study to evaluate the circulating levels of HIF-1α in ADHF patients. Serum HIF-1α levels may reflect a serious state in patients with ADHF. Due to the limitations of the study, serum HIF-1α levels were not correlated with the in-hospital mortality based on regression analysis. Further studies are needed to demonstrate the diagnostic and/or prognostic role of HIF-1α as a risk biomarker in patients with ADHF.

Physiologic hypoxia and oxygen homeostasis in the healthy intestine. A Review in the Theme: Cellular Responses to Hypoxia

In recent years, the intestinal mucosa has proven to be an intriguing organ to study tissue oxygenation. The highly vascularized lamina propria juxtaposed to an anaerobic lumen containing trillions of metabolically active microbes results in one of the most austere tissue microenvironments in the body. Studies to date have determined that a healthy mucosa contains a steep oxygen gradient along the length of the intestine and from the lumen to the serosa. Advances in technology have allowed multiple independent measures and indicate that, in the healthy mucosa of the small and large intestine, the lumen-apposed epithelia experience Po2 conditions of <10 mmHg, so-called physiologic hypoxia. This unique physiology results from a combination of factors, including countercurrent exchange blood flow, fluctuating oxygen demands, epithelial metabolism, and oxygen diffusion into the lumen. Such conditions result in the activation of a number of hypoxia-related signaling processes, including stabilization of the transcription factor hypoxia-inducible factor. Here, we review the principles of mucosal oxygen delivery, metabolism, and end-point functional responses that result from this unique oxygenation profile.

Differential Tissue-Specific Function of Adora2b in Cardioprotection

The adenosine A2b receptor (Adora2b) has been implicated in cardioprotection from myocardial ischemia. As such, Adora2b was found to be critical in ischemic preconditioning (IP) or ischemia/reperfusion (IR) injury of the heart. Whereas Adora2b is present on various cells types, the tissue-specific role of Adora2b in cardioprotection is still unknown. To study the tissue-specific role of Adora2b signaling on inflammatory cells, endothelia, or myocytes during myocardial ischemia in vivo, we intercrossed floxed Adora2b mice with Lyz2-Cre(+), VE-cadherin-Cre(+), or myosin-Cre(+) transgenic mice, respectively. Mice were exposed to 60 min of myocardial ischemia with or without IP (four times for 5 min) followed by 120 min of reperfusion. Cardioprotection by IP was abolished in Adora2b(f/f)-VE-cadherin-Cre(+) or Adora2b(f/f)-myosin-Cre(+), indicating that Adora2b signaling on endothelia or myocytes mediates IP. In contrast, primarily Adora2b signaling on inflammatory cells was necessary to provide cardioprotection in IR injury, indicated by significantly larger infarcts and higher troponin levels in Adora2b(f/f)-Lyz2-Cre(+) mice only. Cytokine profiling of IR injury in Adora2b(f/f)-Lyz2-Cre(+) mice pointed toward polymorphonuclear neutrophils (PMNs). Analysis of PMNs from Adora2b(f/f)-Lyz2-Cre(+) confirmed PMNs as one source of identified tissue cytokines. Finally, adoptive transfer of Adora2b(-/-) PMNs revealed a critical role of Adora2b on PMNs in cardioprotection from IR injury. Adora2b signaling mediates different types of cardioprotection in a tissue-specific manner. These findings have implications for the use of Adora2b agonists in the treatment or prevention of myocardial injury by ischemia.

IRF-5-Mediated Inflammation Limits CD8+ T Cell Expansion by Inducing HIF-1α and Impairing Dendritic Cell Functions during Leishmania Infection

Inflammation is known to be necessary for promoting, sustaining, and tuning CD8⁺ T cell responses. Following experimental Leishmania donovani infection, the inflammatory response is mainly induced by the transcription factor IRF-5. IRF-5 is responsible for the activation of several genes encoding key pro-inflammatory cytokines, such as IL-6 and TNF. Here, we investigate the role of IRF-5-mediated inflammation in regulating antigen-specific CD8⁺ T cell responses during L. donovani infection. Our data demonstrate that the inflammatory response induced by IRF-5 limits CD8⁺ T cell expansion and induces HIF-1α in dendritic cells. Ablation of HIF-1α in CD11c⁺ cells resulted into a higher frequency of short-lived effector cells (SLEC), enhanced CD8⁺ T cell expansion, and increased IL-12 expression by splenic DCs. Moreover, mice with a targeted depletion of HIF-1α in CD11c⁺ cells had a significantly lower splenic parasite burden, suggesting that induction of HIF-1α may represent an immune evasive mechanism adopted by Leishmania parasites to establish persistent infections.

Inflammation is essential for inducing, sustaining, and regulating CD8⁺ T cell responses. The transcription factor IRF-5 is mainly responsible for initiating the inflammatory response following experimental Leishmani donovani infection. IRF-5 activates several genes encoding key pro-inflammatory cytokines, such as IL-6 and TNF. In this study, we investigate the role of IRF-5-mediated inflammation in regulating antigen-specific CD8⁺ T cell responses during L. donovani infection. Our data demonstrate that the inflammatory response induced by IRF-5 limits the expansion CD8⁺ T cell. This negative effect is mediated by the induction of HIF-1α in dendritic cells. Indeed, we observed a significant increase in CD8⁺ T cell expansion in mice lacking HIF-1α expression in dendritic cells. Moreover, these mice had a significantly lower parasite burden in the spleen, suggesting that induction of HIF-1α may represent an immune evasive mechanism adopted by Leishmania parasites to establish persistent infections.

Kidney injury is independent of endothelial HIF-1α

Hypoxia-inducible transcription factors (HIFs) control cellular adaptation to low oxygen. In the kidney, activation of HIF is beneficial during injury; however, the specific contribution of HIF-1α in renal endothelial cells (EC) remains elusive. Since EC display tissue-specific heterogeneity, we investigated how HIF-1α affects key functions of glomerular EC in vitro and its contribution to renal development and pathophysiological adaptation to acute or chronic renal injury in vivo. Loss of HIF-1α in glomerular EC induces hypoxic cell death and reduces hypoxic adhesion of macrophages in vitro. In vivo, HIF-1α expression in EC in mouse kidneys is detectable but limited. Accordingly, EC-specific ablation of HIF-1α does not lead to developmental or phenotypical abnormalities in the kidney. Renal function and expression of adhesion molecules during acute ischemic kidney injury is independent of HIF-1α in EC. Likewise, inflammation and development of fibrosis after unilateral ureteric obstruction is not influenced by endothelial HIF-1α. Taken together, although HIF-1α exerts effects on glomerular EC in vitro, endothelial HIF-1α does not influence renal development and pathophysiological adaptation to kidney injury in vivo. This implies a profound difference of the hypoxic response of the renal vascular bed compared to other organs, such as the heart. This has implications for the development of pharmacological strategies targeting the endothelial hypoxic response pathways.

KEY MESSAGE

HIF-1α controls hypoxic survival and adhesion on endothelial cells (EC) in vitro. In vivo, HIF-1α expression in renal EC is low. Deletion of HIF-1α in EC does not affect kidney development and function in mice. Renal function after acute and chronic kidney injury is independent of HIF-1α in EC. Data suggest organ-specific regulation of HIF-1α function in EC.

Hypoxia disrupts proteostasis in Caenorhabditis elegans

Oxygen is fundamentally important for cell metabolism, and as a consequence, O₂ deprivation (hypoxia) can impair many essential physiological processes. Here, we show that an active response to hypoxia disrupts cellular proteostasis – the coordination of protein synthesis, quality control, and degradation that maintains the functionality of the proteome. We have discovered that specific hypoxic conditions enhance the aggregation and toxicity of aggregation-prone proteins that are associated with neurodegenerative diseases. Our data indicate this is an active response to hypoxia, rather than a passive consequence of energy limitation. This response to hypoxia is partially antagonized by the conserved hypoxia-inducible transcription factor, hif-1. We further demonstrate that exposure to hydrogen sulfide (H₂S) protects animals from hypoxia-induced disruption of proteostasis. H₂S has been shown to protect against hypoxic damage in mammals and extends lifespan in nematodes. Remarkably, our data also show that H₂S can reverse detrimental effects of hypoxia on proteostasis. Our data indicate that the protective effects of H₂S in hypoxia are mechanistically distinct from the effect of H₂S to increase lifespan and thermotolerance, suggesting that control of proteostasis and aging can be dissociated. Together, our studies reveal a novel effect of the hypoxia response in animals and provide a foundation to understand how the integrated proteostasis network is integrated with this stress response pathway.

Developing functional musculoskeletal tissues through hypoxia and lysyl oxidase-induced collagen cross-linking

The inability to recapitulate native tissue biomechanics, especially tensile properties, hinders progress in regenerative medicine. To address this problem, strategies have focused on enhancing collagen production. However, manipulating collagen cross-links, ubiquitous throughout all tissues and conferring mechanical integrity, has been underinvestigated. A series of studies examined the effects of lysyl oxidase (LOX), the enzyme responsible for the formation of collagen cross-links. Hypoxia-induced endogenous LOX was applied in multiple musculoskeletal tissues (i.e., cartilage, meniscus, tendons, ligaments). Results of these studies showed that both native and engineered tissues are enhanced by invoking a mechanism of hypoxia-induced pyridinoline (PYR) cross-links via intermediaries like LOX. Hypoxia was shown to enhance PYR cross-linking 1.4- to 6.4-fold and, concomitantly, to increase the tensile properties of collagen-rich tissues 1.3- to 2.2-fold. Direct administration of exogenous LOX was applied in native cartilage and neocartilage generated using a scaffold-free, self-assembling process of primary chondrocytes. Exogenous LOX was found to enhance native tissue tensile properties 1.9-fold. LOX concentration- and time-dependent increases in PYR content (∼ 16-fold compared with controls) and tensile properties (approximately fivefold compared with controls) of neocartilage were also detected, resulting in properties on par with native tissue. Finally, in vivo subcutaneous implantation of LOX-treated neocartilage in nude mice promoted further maturation of the neotissue, enhancing tensile and PYR content approximately threefold and 14-fold, respectively, compared with in vitro controls. Collectively, these results provide the first report, to our knowledge, of endogenous (hypoxia-induced) and exogenous LOX applications for promoting collagen cross-linking and improving the tensile properties of a spectrum of native and engineered tissues both in vitro and in vivo.

The role of HIFs in ischemia-reperfusion injury

The reduction or cessation of the blood supply to an organ results in tissue ischemia. Ischemia can cause significant tissue damage, and is observed as a result of a thrombosis, as part of a disease process, and during surgery. However, the restoration of the blood supply often causes more damage to the tissue than the ischemic episode itself. Research is therefore focused on identifying the cellular pathways involved in the protection of organs from the damage incurred by this process of ischemia reperfusion (I/R). The hypoxia-inducible factors (HIFs) are a family of heterodimeric transcription factors that are stabilized during ischemia. The genes that are expressed downstream of HIF activity enhance oxygen-independent ATP generation, cell survival, and angiogenesis, amongst other phenotypes. They are, therefore, important factors in the protection of tissues from I/R injury. Interestingly, a number of the mechanisms already known to induce organ protection against I/R injury, including preconditioning, postconditioning, and activation of signaling pathways such as adenosine receptor signaling, converge on the HIF system. This review describes the evidence for HIFs playing a role in I/R protection mediated by these factors, highlights areas that require further study, and discuss whether HIFs themselves are good therapeutic targets for protecting tissues from I/R injury.

Hypoxia-inducible factor-1α mediates up-regulation of neprilysin by histone deacetylase-1 under hypoxia condition in neuroblastoma cells

Hypoxia-inducible factor (HIF)-1 is the key transcriptional activator mediating both adaptive and pathological responses to hypoxia. The purpose of this study was to find the role of HIF-1 in regulating neprilysin (NEP) at the early stage of hypoxia and explore the underlying mechanism. In this study, we demonstrated that both NEP mRNA and protein levels in neuroblastoma cells were elevated in early stages of hypoxia. Over-expression of HIF-1α gene increased NEP mRNA/protein levels, as well as enzyme activity while knockdown of HIF-1α decreased them. Meanwhile, HIF-1α was shown to bind to histone deacetylase (HDAC)-1 and reduced the association of HDAC-1 with NEP promoter, thus activating NEP gene transcription in a de-repression way. In summary, our results indicated that hypoxia in the early stages would up-regulate NEP expression, in which interaction of HIF-1α and HDAC-1 may play a role. This study suggested that NEP up-regulation might be an adaptive response to hypoxia, which was mediated by HIF-1α binding to HDAC-1 at the early stage of hypoxia.

Concise review: genetic dissection of hypoxia signaling pathways in normal and leukemic stem cells

Adult hematopoiesis depends on rare multipotent hematopoietic stem cells (HSCs) that self-renew and give rise to progenitor cells, which differentiate to all blood lineages. The strict regulation of the fine balance between self-renewal and differentiation is essential for normal hematopoiesis and suppression of leukemia development. HSCs and progenitor cells are commonly assumed to reside within the hypoxic BM microenvironment, however, there is no direct evidence supporting this notion. Nevertheless, HSCs and progenitors do exhibit a hypoxic profile and strongly express Hif-1α. Although hypoxia signaling pathways are thought to play important roles in adult HSC maintenance and leukemogenesis, the precise function of Hif-dependent signaling in HSCs remains to be uncovered. Here we discuss recent gain-of-function and loss-of-function studies that shed light on the complex roles of hypoxia-signaling pathways in HSCs and their niches in normal and malignant hematopoiesis. Importantly, we comment on the current and often contrasting interpretations of the role of Hif-dependent signaling in stem cell functions.

Pivotal role of mast cell carboxypeptidase A in mediating protection against small intestinal ischemia-reperfusion injury in rats after ischemic preconditioning

AIM OF THE STUDY

Mast cell (MC) degranulation contributes to the protection mediated by ischemic preconditioning (IPC); however, the precise mechanisms underlying this protection remain largely unknown. Mast cell carboxypeptidase A (MC-CPA) is released solely from MCs and plays a critical role in degrading toxins and endothelin 1 (ET-1). The present study sought to explore whether MC-CPA is involved in the process of IPC in a rodent model of small intestinal ischemia reperfusion (IIR) injury.

MATERIALS AND METHODS

IIR injuries were induced in Sprague-Dawley rats by clamping the superior mesenteric artery for 60 min followed by reperfusion for 2 h. One cycle of 10 min intestinal ischemia and 10 min of reperfusion was used in the IPC group, and the MC stabilizer cromolyn sodium and MC potato carboxypeptidase inhibitor were administered before the start of IPC. At the end of experiment, intestine tissue was obtained for assays of the MC-CPA3, tumor necrosis factor-α, interleukin-6, and ET-1 contents and myeloperoxidase activities. Intestinal histologic injury scores and MC degranulation were assessed. Apoptosis indices and cleaved caspase- 3 protein expressions were quantified.

RESULTS

IIR resulted in severe injury, as evidenced by significant increases in injury scores and MC-CPA3, tumor necrosis factor-α, interleukin-6, and ET-1 contents that were accompanied with concomitant elevations in cleaved caspase 3 expression, apoptosis indices, and myeloperoxidase activities. IPC induced a significant increase in MC-CPA3, induced MC degranulation, and attenuated IIR injury by downregulating IIR-induced biochemical changes, whereas cromolyn sodium and potato carboxypeptidase inhibitor abolished the IPC-mediated changes.

CONCLUSIONS

These data suggest that IPC protected against IIR injury via the MC degranulation-mediated release of MC-CPA.

HIF and pulmonary vascular responses to hypoxia

In the lung, acute reductions in oxygen lead to hypoxic pulmonary vasoconstriction, whereas prolonged exposures to hypoxia result in sustained vasoconstriction, pulmonary vascular remodeling, and the development of pulmonary hypertension. Data from both human subjects and animal models implicate a role for hypoxia-inducible factors (HIFs), oxygen-sensitive transcription factors, in pulmonary vascular responses to both acute and chronic hypoxia. In this review, we discuss work from our laboratory and others supporting a role for HIF in modulating hypoxic pulmonary vasoconstriction and mediating hypoxia-induced pulmonary hypertension, identify some of the downstream targets of HIF, and assess the potential to pharmacologically target the HIF system.

Erythromycin pretreatment induces tolerance against focal cerebral ischemia through up-regulation of nNOS but not down-regulation of HIF-1α in rats

The purpose of this study was to determine whether the antibiotic erythromycin induces tolerance against focal cerebral ischemia, and the possible underlying mechanism including the involvement of neuronal nitric oxide synthase (nNOS) and hypoxia-inducible factor-1α (HIF-1α). In rat focal cerebral ischemia models, we found that erythromycin preconditioning could significantly decrease the cerebral infarct volume and brain edema. Meanwhile, the neurological deficits from day 4 through 7 after surgery were also remarkably decreased after erythromycin preconditioning. Moreover, erythromycin preconditioning induced significantly increased nNOS levels and decreased HIF-1α levels in both mRNA and protein expression. This study for the first time indicated that erythromycin preconditioning could induce focal brain ischemic tolerance and attenuate brain injury of subsequent transient focal cerebral ischemia. The potential mechanism may be due to up-regulation of nNOS, but the HIF-1α system was not involved.

Role of hypoxia inducible factor-1α in remote limb ischemic preconditioning

Remote ischemic preconditioning (RIPC) has emerged as a feasible and attractive therapeutic procedure for heart protection against ischemia/reperfusion (I/R) injury. However, its molecular mechanisms remain poorly understood. Hypoxia inducible factor-1α (HIF-1α) is a transcription factor that plays a key role in the cellular adaptation to hypoxia and ischemia. This study's aim was to test whether RIPC-induced cardioprotection requires HIF-1α upregulation to be effective. In the first study, wild-type mice and mice heterozygous for HIF1a (gene encoding the HIF-1α protein) were subjected to RIPC immediately before myocardial infarction (MI). RIPC resulted in a robust HIF-1α activation in the limb and acute cardioprotection in wild-type mice. RIPC-induced cardioprotection was preserved in heterozygous mice, despite the low HIF-1α expression in their limbs. In the second study, the role of HIF-1α in RIPC was evaluated using cadmium (Cd), a pharmacological HIF-1α inhibitor. Rats were subjected to MI (MI group) or to RIPC immediately prior to MI (R-MI group). Cd was injected 18 0min before RIPC (Cd-R-MI group). RIPC induced robust HIF-1α activation in rat limbs and significantly reduced infarct size (IS). Despite Cd's inhibition of HIF-1α activation, RIPC-induced cardioprotection was preserved in the Cd-R-MI group. RIPC applied immediately prior to MI increased HIF-1α expression and attenuated IS in rats and wild-type mice. However, RIPC-induced cardioprotection was preserved in partially HIF1a-deficient mice and in rats pretreated with Cd. When considered together, these results suggest that HIF-1α upregulation is unnecessary in acute RIPC.

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-1β. 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.

The role of angiogenic factors in fibroid pathogenesis: potential implications for future therapy

BACKGROUND

It is well established that tumors are dependent on angiogenesis for their growth and survival. Although uterine fibroids are known to be benign tumors with reduced vascularization, recent work demonstrates that the vasculature of fibroids is grossly and microscopically abnormal. Accumulating evidence suggests that angiogenic growth factor dysregulation may be implicated in these vascular and other features of fibroid pathophysiology.

METHODS

Literature searches were performed in PubMed and Google Scholar for articles with content related to angiogenic growth factors and myometrium/leiomyoma. The findings are hereby reviewed and discussed.

RESULTS

Multiple growth factors involved in angiogenesis are differentially expressed in leiomyoma compared with myometrium. These include epidermal growth factor (EGF), heparin-binding-EGF, vascular endothelial growth factor, basic fibroblast growth factor, platelet-derived growth factor, transforming growth factor-β and adrenomedullin. An important paradox is that although leiomyoma tissues are hypoxic, leiomyoma feature down-regulation of key molecular regulators of the hypoxia response. Furthermore, the hypoxic milieu of leiomyoma may contribute to fibroid development and growth. Notably, common treatments for fibroids such as GnRH agonists and uterine artery embolization (UAE) are shown to work at least partly via anti-angiogenic mechanisms.

CONCLUSIONS

Angiogenic growth factors play an important role in mechanisms of fibroid pathophysiology, including abnormal vasculature and fibroid growth and survival. Moreover, the fibroid's abnormal vasculature together with its aberrant hypoxic and angiogenic response may make it especially vulnerable to disruption of its vascular supply, a feature which could be exploited for treatment. Further experimental studies are required in order to gain a better understanding of the growth factors that are involved in normal and pathological myometrial angiogenesis, and to assess the potential of anti-angiogenic treatment strategies for uterine fibroids.

Hypoxia-inducible factor 1 and cardiovascular disease

Cardiac function is required for blood circulation and systemic oxygen delivery. However, the heart has intrinsic oxygen demands that must be met to maintain effective contractility. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that functions as a master regulator of oxygen homeostasis in all metazoan species. HIF-1 controls oxygen delivery, by regulating angiogenesis and vascular remodeling, and oxygen utilization, by regulating glucose metabolism and redox homeostasis. Analysis of animal models suggests that by activation of these homeostatic mechanisms, HIF-1 plays a critical protective role in the pathophysiology of ischemic heart disease and pressure-overload heart failure.

Oxygen sensing, hypoxia-inducible factors, and disease pathophysiology

Hypoxia-inducible factors (HIFs) are transcriptional activators that function as master regulators of oxygen homeostasis, which is disrupted in disorders affecting the circulatory system and in cancer. The role of HIFs in these diseases has been elucidated by clinical studies and by analyses of mouse models. HIFs play a protective role in the pathophysiology of myocardial ischemia due to coronary artery disease, limb ischemia due to peripheral arterial disease, pressure-overload heart failure, wound healing, and chronic rejection of organ transplants. In contrast, HIFs contribute to the pathogenesis of pulmonary arterial hypertension, systemic hypertension associated with sleep apnea, ocular neovascularization, hereditary erythrocytosis, and cancer.

In vivo electroporation of constitutively expressed HIF-1α plasmid DNA improves neovascularization in a mouse model of limb ischemia

OBJECTIVE

Hypoxia-inducible factor-1 alpha (HIF-1α) is a transcription factor that stimulates angiogenesis during tissue ischemia. In vivo electroporation (EP) enhances tissue DNA transfection. We hypothesized that in vivo EP of plasmid DNA encoding a constitutively expressed HIF-1α gene enhances neovascularization compared with intramuscular (IM) injection alone.

METHODS

Left femoral artery ligation was performed in mice assigned to three groups: (1) HIF-EP (n = 13); (2) HIF-IM (n = 14); and (3) empty plasmid (pVAX)-EP (n = 12). A single dose of HIF-1α or pVAX DNA (20 μL of 5 μg/μL each) was injected into the ischemic adductor muscle followed by EP (groups one and three). Mice in group two received IM injection of HIF-1α plasmid DNA alone. From preligation to days 0, 3, 7, 14, and 21 postligation, limb perfusion recovery quantified by laser Doppler perfusion imager, limb function, and limb necrosis were measured. On day 21, the surviving mice (4-5 per group) were sacrificed and adductor muscle tissues stained for necrosis using hematoxylin and eosin, capillary density (anti-CD31 antibodies), and collateral vessels via anti-α-smooth muscle actin antibodies.

RESULTS

In vivo EP of HIF-1α DNA significantly improved limb perfusion (HIF-EP: 1.03 ± 0.15 vs HIF-IM: 0.78 ± 0.064; P < .05, vs pVAX-EP: 0.41 ± 0.019; P < .001), limb functional recovery (HIF-EP: 3.5 ± 0.58 vs HIF-IM, 2.4 ± 1.14; P < .05, vs pVAX-EP: 2.4 ± 1.14; P < .001), and limb autoamputation on day 21 (HIF-EP: 77% ± 12% vs HIF-IM: 43% ± 14%; P < .05 vs pVAX-EP: 17% ± 11%; P < .01). Adductor muscle tissue necrosis decreased (HIF-EP: 20.7% ± 1.75% vs HIF-IM: 44% ± 3.73; P < .001, vs pVAX-EP: 60.05% ± 2.17%; P < .0001), capillary density increased (HIF-EP: 96.83 ± 5.72 vessels/high-powered field [hpf] vs HIF-IM: 62.87 ± 2.0 vessels/hpf; P < .001, vs pVAX-EP: 39.37 ± 2.76 vessels/hpf; P < .0001), collateral vessel formation increased (HI-EP: 76.33 ± 1.94 vessels/hpf vs HIF-IM: 37.5 ± 1.56 vessels/hpf; P < .0001, vs pVAX-EP: 18.5 ± 1.34 vessels/hpf; P < .00001), and the vessels were larger (HIF-EP: 15,521.67 ± 1298.16 μm(2) vs HIF-IM: 7788.87 ± 392.04 μm(2); P < .001 vs pVAX-EP: 4640.25 ± 614.01 μm(2); P < .0001).

CONCLUSIONS

In vivo EP-mediated delivery of HIF-1α plasmid DNA improves neovascularization in a mouse model of limb ischemia and is a potentially suitable nonviral, noninvasive intervention to facilitate therapeutic angiogenesis in critical limb ischemia.

Prolyl 4-hydroxylases, master regulators of the hypoxia response

A decrease in oxygenation is a life-threatening situation for most organisms. An evolutionarily conserved efficient and rapid hypoxia response mechanism activated by a hypoxia-inducible transcription factor (HIF) is present in animals ranging from the simplest multicellular phylum Placozoa to humans. In humans, HIF induces the expression of more than 100 genes that are required to increase oxygen delivery and to reduce oxygen consumption. As its name indicates HIF is found at protein level only in hypoxic cells, whereas in normoxia, it is degraded by the proteasome pathway. Prolyl 4-hydroxylases, enzymes that require oxygen in their reaction, are the cellular oxygen sensors regulating the stability of HIF. In normoxia, 4-hydroxyproline residues formed in the α-subunit of HIF by these enzymes lead to its ubiquitination by the von Hippel-Lindau E3 ubiquitin ligase and immediate destruction in proteasomes thus preventing the formation of a functional HIF αβ dimer. Prolyl 4-hydroxylation is inhibited in hypoxia, facilitating the formation of the HIF dimer and activation of its target genes, such as those for erythropoietin and vascular endothelial growth factor. This review starts with a summary of the molecular and catalytic properties and individual functions of the four HIF prolyl 4-hydroxylase isoenzymes. Induction of the hypoxia response via inhibition of the HIF prolyl 4-hydroxylases may provide a novel therapeutic target in the treatment of hypoxia-associated diseases. The current status of studies aiming at such therapeutic approaches is introduced in the final part of this review.

Attenuating myocardial ischemia by targeting A2B adenosine receptors

Myocardial ischemia is associated with profound tissue hypoxia due to an imbalance in oxygen supply and demand, and studies of hypoxia-elicited adaptive responses during myocardial ischemia revealed a cardioprotective role for the signaling molecule adenosine. In ischemic human hearts, the A2B adenosine receptor (ADORA2B) is selectively induced. Functional studies in genetic models show that ADORA2B signaling attenuates myocardial infarction by adapting metabolism towards more oxygen efficient utilization of carbohydrates. This adenosine-mediated cardio-adaptive response involves the transcription factor hypoxia-inducible factor HIF1α and the circadian rhythm protein PER2. In this article, we discuss advances in the understanding of adenosine-elicited cardioprotection with particular emphasis on ADORA2B, its downstream targets, and the implications for novel strategies to prevent or treat myocardial ischemia.

Metabolic preconditioning of mammalian cells: mimetic agents for hypoxia lack fidelity in promoting phosphorylation of pyruvate dehydrogenase

Induction of HIF-1α by oxygen limitation promotes increased phosphorylation and catalytic depression of mitochondrial pyruvate dehydrogenase (PDH) and an enhanced glycolytic poise in cells. Cobalt chloride and desferrioxamine are widely used as mimics for hypoxia because they increase the levels of HIF-1α. We evaluated the ability of these agents to elicit selected physiological responses to hypoxia as a means to metabolically precondition mammalian cells, but without the detrimental effects of hypoxia. We show that, while CoCl(2) does increase HIF-1α in a dose-dependent manner, it unexpectedly and strikingly decreases PDH phosphorylation at E1α sites 1, 2, and 3 (Ser(293), Ser(300), and Ser(232), respectively) in HepG2 cells. This same effect is also observed for site 1 in mouse NIH/3T3 fibroblasts and J774 macrophages. CoCl(2) unexpectedly decreases the mRNA expression for PDH kinase-2 in HepG2 cells, which likely explains the dephosphorylation of PDH observed. And nor does desferrioxamine promote the expected increase in PDH phosphorylation. Dimethyloxaloylglycine (a prolyl hydroxylase inhibitor) performs better in this regard, but failed to promote the stronger effects seen with hypoxia. Consequently, CoCl(2) and desferrioxamine are unreliable mimics of hypoxia for physiological events downstream of HIF-1α stabilization. Our study demonstrates that mimetic chemicals must be chosen with caution and evaluated thoroughly if bona fide cellular outcomes are to be promoted with fidelity.