Hypoxia sensing through -adrenergic receptors

The effect of the four pharmacological pillars of heart failure on haemoglobin level

Anaemia, a condition characterized by low levels of haemoglobin, is frequently observed in patients with heart failure (HF). Guideline-directed medical therapy improves HF outcomes by using medications like beta blockers, angiotensin-converting enzyme inhibitors, and angiotensin receptor blockers, along with mineralocorticoid receptor antagonists and sodium-glucose cotransporter 2 inhibitors. In this study, we aimed to review the pathophysiology of anaemia in patients with HF and present the current evidence regarding the relationship between the main recommended medications for these patients and haemoglobin levels. The authors conducted a comprehensive search in the medical literature for relevant original clinical articles in which the four pharmacological pillars of HF were given to the patients; we, then, assessed whether the association of use of these medications and haemoglobin level or development of anaemia was provided. These common medications have been shown in the literature that may exacerbate or ameliorate anaemia. Besides, it has been shown that even in the case that they result in the development of anaemia, their use is associated with positive effects that outweigh this potential harm. The literature also suggests that among patients receiving medications with negative effects on the level of haemoglobin, there was no difference in the rate of mortality between anaemic and non-anaemic patients when both were on treatment for anaemia; this point highlights the importance of the detection and treatment of anaemia in these patients. Further research is needed to explore these relationships and identify additional strategies to mitigate the risk of anaemia in this population.

Timolol maleate, a β blocker eye drop, improved edema in a retinal vein occlusion model

Purpose

To investigate the therapeutic effects of eye drops, namely, timolol maleate, a β-adrenergic receptor antagonist, and latanoprost, a prostaglandin F2α analog, on retinal edema in a murine retinal vein occlusion (RVO) model.

Methods

An RVO model was established using laser-induced RVO in mice, which were administered timolol maleate and latanoprost eye drops several times after venous occlusion. Subsequently, the thickness of the inner nuclear layer (INL) and the expression levels of such genes as Vegf and Atf4, which are stress markers of the endoplasmic reticulum, were examined. Primary human cultured retinal microvascular endothelial cells (HRMECs) were treated with timolol under hypoxic conditions, after which the gene expression pattern was investigated. Importantly, an integrated stress response inhibitor (ISRIB) was used in the RVO model, he known ISRIB, which suppresses the expression of ATF4 in retinal edema.

Results

Increased INL thickness was suppressed by timolol eye drops, as were the expressions of Vegf and Atf4, in the RVO model. However, latanoprost eye drops did not induce any change in INL thickness. In HRMECs, hypoxic stress and serum deprivation increased the Vegf and Atf4 expressions; in response, treatment with timolol suppressed the Vegf expression. Furthermore, the ISRIB decreased the Vegf expression pattern and edema formation, which are associated with RVO.

Conclusions

These results indicate that timolol eye drops may be a potential option for RVO treatment.

Hypoxia Sensing of β-Adrenergic Receptor Is Regulated by Endosomal PI3Kγ

BACKGROUND

Impaired beta-adrenergic receptor (β1 and β2AR) function following hypoxia underlies ischemic heart failure/stroke. Activation of PI3Kγ (phosphoinositide 3-kinase γ) by beta-adrenergic receptor leads to feedback regulation of the receptor by hindering beta-adrenergic receptor dephosphorylation through inhibition of PP2A (protein phosphatase 2A). However, little is known about PI3Kγ feedback mechanism in regulating hypoxia-mediated β1 and β2AR dysfunction and cardiac remodeling.

METHODS

Human embryonic kidney 293 cells or mouse adult cardiomyocytes and C57BL/6 (WT) or PI3Kγ knockout (KO) mice were subjected to hypoxia. Cardiac plasma membranes and endosomes were isolated and evaluated for β1 and β2AR density and function, PI3Kγ activity and β1 and β2AR-associated PP2A activity. Metabolic labeling was performed to assess β1 and β2AR phosphorylation and epinephrine/norepinephrine levels measured post-hypoxia.

RESULTS

Hypoxia increased β1 and β2AR phosphorylation, reduced cAMP, and led to endosomal accumulation of phosphorylated β2ARs in human embryonic kidney 293 cells and WT cardiomyocytes. Acute hypoxia in WT mice resulted in cardiac remodeling and loss of adenylyl cyclase activity associated with increased β1 and β2AR phosphorylation. This was agonist-independent as plasma and cardiac epinephrine and norepinephrine levels were unaltered. Unexpectedly, PI3Kγ activity was selectively increased in the endosomes of human embryonic kidney 293 cells and WT hearts post-hypoxia. Endosomal β1- and β2AR-associated PP2A activity was inhibited upon hypoxia in human embryonic kidney 293 cells and WT hearts showing regulation of beta-adrenergic receptors by PI3Kγ. This was accompanied with phosphorylation of endogenous inhibitor of protein phosphatase 2A whose phosphorylation by PI3Kγ inhibits PP2A. Increased β1 and β2AR-associated PP2A activity, decreased beta-adrenergic receptor phosphorylation, and normalized cardiac function was observed in PI3Kγ KO mice despite hypoxia. Compared to WT, PI3Kγ KO mice had preserved cardiac response to challenge with β1AR-selective agonist dobutamine post-hypoxia.

CONCLUSIONS

Agonist-independent activation of PI3Kγ underlies hypoxia sensing as its ablation leads to reduction in β1- and β2AR phosphorylation and amelioration of cardiac dysfunction.

The β3 adrenoceptor in proliferative retinopathies: "Cinderella" steps out of its family shadow

In the retina, hypoxic condition leads to overgrowing leaky vessels resulting in altered metabolic supply that may cause impaired visual function. Hypoxia-inducible factor-1 (HIF-1) is a central regulator of the retinal response to hypoxia by activating the transcription of numerous target genes, including vascular endothelium growth factor, which acts as a major player in retinal angiogenesis. In the present review, oxygen urge by the retina and its oxygen sensing systems including HIF-1 are discussed in respect to the role of the beta-adrenergic receptors (β-ARs) and their pharmacologic manipulation in the vascular response to hypoxia. In the β-AR family, β1- and β2-AR have long been attracting attention because their pharmacology is intensely used for human health, while β3-AR, the third and last cloned receptor is no longer increasingly emerging as an attractive target for drug discovery. Here, β3-AR, a main character in several organs including the heart, the adipose tissue and the urinary bladder, but so far a supporting actor in the retina, has been thoroughly examined in respect to its function in retinal response to hypoxia. In particular, its oxygen dependence has been taken as a key indicator of β3-AR involvement in HIF-1-mediated responses to oxygen. Hence, the possibility of β3-AR transcription by HIF-1 has been discussed from early circumstantial evidence to the recent demonstration that β3-AR acts as a novel HIF-1 target gene by playing like a putative intermediary between oxygen levels and retinal vessel proliferation. Thus, targeting β3-AR may implement the therapeutic armamentarium against neovascular pathologies of the eye.

Occlusion preconditioned mice are resilient to hypobaric hypoxia-induced myocarditis and arrhythmias due to enhanced immunomodulation, metabolic homeostasis, and antioxidants defense

Background

Sea-level residents experience altitude sickness when they hike or visit altitudes above ~2,500 m due to the hypobaric hypoxia (HH) conditions at such places. HH has been shown to drive cardiac inflammation in both ventricles by inducing maladaptive metabolic reprogramming of macrophages, which evokes aggravated proinflammatory responses, promoting myocarditis, fibrotic remodeling, arrhythmias, heart failure, and sudden deaths. The use of salidroside or altitude preconditioning (AP) before visiting high altitudes has been extensively shown to exert cardioprotective effects. Even so, both therapeutic interventions have geographical limitations and/or are inaccessible/unavailable to the majority of the population as drawbacks. Meanwhile, occlusion preconditioning (OP) has been extensively demonstrated to prevent hypoxia-induced cardiomyocyte damage by triggering endogenous cardioprotective cascades to mitigate myocardial damage. Herein, with the notion that OP can be conveniently applied anywhere, we sought to explore it as an alternative therapeutic intervention for preventing HH-induced myocarditis, remodeling, and arrhythmias.

Methods

OP intervention (6 cycles of 5 min occlusion with 200 mmHg for 5 min and 5 min reperfusion at 0 mmHg - applying to alternate hindlimb daily for 7 consecutive days) was performed, and its impact on cardiac electric activity, immunoregulation, myocardial remodeling, metabolic homeostasis, oxidative stress responses, and behavioral outcomes were assessed before and after exposure to HH in mice. In humans, before and after the application of OP intervention (6 cycles of 5 min occlusion with 130% of systolic pressure and 5 min reperfusion at 0 mmHg - applying to alternate upper limb daily for 6 consecutive days), all subjects were assessed by cardiopulmonary exercise testing (CPET).

Results

Comparing the outcomes of OP to AP intervention, we observed that similar to the latter, OP preserved cardiac electric activity, mitigated maladaptive myocardial remodeling, induced adaptive immunomodulation and metabolic homeostasis in the heart, enhanced antioxidant defenses, and conferred resistance against HH-induce anxiety-related behavior. Additionally, OP enhanced respiratory and oxygen-carrying capacity, metabolic homeostasis, and endurance in humans.

Conclusions

Overall, these findings demonstrate that OP is a potent alternative therapeutic intervention for preventing hypoxia-induced myocarditis, cardiac remodeling, arrhythmias, and cardiometabolic disorders and could potentially ameliorate the progression of other inflammatory, metabolic, and oxidative stress-related diseases.

Reciprocal Regulation of MAGED2 and HIF-1α Augments Their Expression under Hypoxia: Role of cAMP and PKA Type II

Hypoxia stabilizes the transcription factor HIF-1α, which promotes the transcription of many genes essential to adapt to reduced oxygen levels. Besides proline hydroxylation, expression of HIF-1α is also regulated by a range of other posttranslational modifications including phosphorylation by cAMP-dependent protein kinase A (PKA), which stabilizes HIF-1α. We recently demonstrated that MAGED2 is required for cAMP generation under hypoxia and proposed that this regulation may explain the transient nature of antenatal Bartter syndrome (aBS) due to MAGED2 mutations. Consequently, we sought to determine whether hypoxic induction of HIF-1α requires also MAGED2. In HEK293 and HeLa cells, MAGED2 knock-down impaired maximal induction of HIF-1α under physical hypoxia as evidenced by time-course experiments, which showed a signification reduction of HIF-1α upon MAGED2 depletion. Similarly, using cobalt chloride to induce HIF-1α, MAGED2 depletion impaired its appropriate induction. Given the known effect of the cAMP/PKA pathway on the hypoxic induction of HIF-1α, we sought to rescue impaired HIF-1α induction with isoproterenol and forskolin acting upstream and downstream of Gαs, respectively. Importantly, while forskolin induced HIF-1α above control levels in MAGED2-depleted cells, isoproterenol had no effect. To further delineate which PKA subtype is involved, we analyzed the effect of two PKA inhibitors and identified that PKA type II regulates HIF-1α. Interestingly, MAGED2 mRNA and protein were also increased under hypoxia by a cAMP mimetic. Moreover, MAGED2 protein expression also required HIF-1α. Thus, our data provide evidence for reciprocal regulation of MAGED2 and HIF-1α under hypoxia, revealing therefore a new regulatory mechanism that may further explain the transient nature of aBS caused by MAGED2 mutations.

MAGED2 Is Required under Hypoxia for cAMP Signaling by Inhibiting MDM2-Dependent Endocytosis of G-Alpha-S

Mutations in MAGED2 cause transient Bartter syndrome characterized by severe renal salt wasting in fetuses and infants, which leads to massive polyhydramnios causing preterm labor, extreme prematurity and perinatal death. Notably, this condition resolves spontaneously in parallel with developmental increase in renal oxygenation. MAGED2 interacts with G-alpha-S (Gαs). Given the role of Gαs in activating adenylyl cyclase at the plasma membrane and consequently generating cAMP to promote renal salt reabsorption via protein kinase A (PKA), we hypothesized that MAGED2 is required for this signaling pathway under hypoxic conditions such as in fetuses. Consistent with that, under both physical and chemical hypoxia, knockdown of MAGED2 in renal (HEK293) and cancer (HeLa) cell culture models caused internalization of Gαs, which was fully reversible upon reoxygenation. In contrast to Gαs, cell surface expression of the β2-adrenergic receptor, which is coupled to Gαs, was not affected by MAGED2 depletion, demonstrating specific regulation of Gαs by MAGED2. Importantly, the internalization of Gαs due to MAGED2 deficiency significantly reduced cAMP generation and PKA activity. Interestingly, the internalization of Gαs was blocked by preventing its endocytosis with dynasore. Given the role of E3 ubiquitin ligases, which can be regulated by MAGE-proteins, in regulating endocytosis, we assessed the potential role of MDM2-dependent ubiquitination in MAGED2 deficiency-induced internalization of Gαs under hypoxia. Remarkably, MDM2 depletion or its chemical inhibition fully abolished Gαs-endocytosis following MAGED2 knockdown. Moreover, endocytosis of Gαs was also blocked by mutation of ubiquitin acceptor sites in Gαs. Thus, we reveal that MAGED2 is essential for the cAMP/PKA pathway under hypoxia to specifically regulate Gαs endocytosis by blocking MDM2-dependent ubiquitination of Gαs. This may explain, at least in part, the transient nature of Bartter syndrome caused by MAGED2 mutations and opens new avenues for therapy in these patients.

β3-Adrenoceptor, a novel player in the round-trip from neonatal diseases to cancer: Suggestive clues from embryo

The role of the β-adrenoceptors (β-ARs) in hypoxia-driven diseases has gained visibility after the demonstration that propranolol promotes the regression of infantile hemangiomas and ameliorates the signs of retinopathy of prematurity (ROP). Besides the role of β2-ARs, preclinical studies in ROP have also revealed that β3-ARs are upregulated by hypoxia and that they are possibly involved in retinal angiogenesis. In a sort of figurative round trip, peculiarities typical of ROP, where hypoxia drives retinal neovascularization, have been then translated to cancer, a disease equally characterized by hypoxia-driven angiogenesis. In this step, investigating the role of β3-ARs has taken advantage of the assumption that cancer growth uses a set of strategies in common with embryo development. The possibility that hypoxic induction of β3-ARs may represent one of the mechanisms through which primarily embryo (and then cancer, as an astute imitator) adapts to grow in an otherwise hostile environment, has grown evidence. In both cancer and embryo, β3-ARs exert similar functions by exploiting a metabolic shift known as the Warburg effect, by acquiring resistance against xenobiotics, and by inducing a local immune tolerance. An additional potential role of β3-AR as a marker of stemness has been suggested by the finding that its antagonism induces cancer cell differentiation evoking that β3-ARs may help cancer to grow in a nonhospital environment, a strategy also exploited by embryos. From cancer, the round trip goes back to neonatal diseases for which new possible interpretative keys and potential pharmacological perspectives have been suggested.

Adrenergic-Angiogenic Crosstalk in Head and Neck Cancer: Mechanisms and Therapeutic Implications

Head and neck squamous cell carcinomas (HNSCC) are loco-regionally aggressive tumors that often lead to debilitating changes in appearance, speech, swallowing and respiratory function in patients. It is therefore critical to develop novel targeted treatment strategies that can effectively target multiple components within the tumor microenvironment. In this regard, there has been an increased recognition of the role of neural signaling networks as mediators of disease progression in HNSCC. Here, we summarize the current knowledge on the mechanisms of adrenergic signaling in HNSCC specifically focusing on neurovascular crosstalk and the potential of targeting the adrenergic-angiogenic axis through repurposing of FDA-approved drugs against HNSCC.

The effects of normoxic endurance exercise on erythropoietin (EPO) production and the impact of selective β1 and non-selective β1 + β2 adrenergic receptor blockade

PURPOSE

Habitual endurance exercise results in increased erythropoiesis, which is primarily controlled by erythropoietin (EPO), yet studies demonstrating upregulation of EPO via a single bout of endurance exercise have been equivocal. This study compares the acute EPO response to 30 min of high versus 90 min of moderate-intensity endurance exercise and whether that response can be upregulated via selective adrenergic receptor blockade.

METHODS

Using a counterbalanced, cross-over design, fifteen participants (age 28 ± 8) completed two bouts of running (30-min, high intensity vs 90-min, moderate intensity) matched for overall training stress. A separate cohort of fourteen participants (age 31 ± 6) completed three bouts of 30-min high-intensity cycling after ingesting the preferential β₁-adrenergic receptor (AR) antagonist bisoprolol, the non-preferential β₁ + β₂ antagonist nadolol or placebo. Venous blood was collected before, during, and after exercise, and serum EPO levels were determined by ELISA.

RESULTS

No detectable EPO response was observed during or after high intensity running, however, in the moderate-intensity trial EPO was significantly elevated at both during-exercise timepoints (+ 6.8% ± 2.3% at 15 min and + 8.7% ± 2.2% at 60 min). No significant change in EPO was observed post-cycling or between the trials involving βAR blockade.

CONCLUSION

Neither training mode (running or cycling), nor beta-blockade significantly influenced the EPO response to 30 min of high-intensity exercise, however, 90 min of moderate-intensity running elevated EPO during exercise, returning to baseline immediately post-exercise. Identifying the optimal mode, duration and intensity required to evoke an EPO response to exercise may help tailor exercise prescriptions designed to maximize EPO response for both performance and clinical applications.

Metabolism in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is characterized by impaired regulation of pulmonary hemodynamics and vascular growth. Alterations of metabolism and bioenergetics are increasingly recognized as universal hallmarks of PAH, as metabolic abnormalities are identified in lungs and hearts of patients, animal models of the disease, and cells derived from lungs of patients. Mitochondria are the primary organelle critically mediating the complex and integrative metabolic pathways in bioenergetics, biosynthetic pathways, and cell signaling. Here, we review the alterations in metabolic pathways that are linked to the pathologic vascular phenotype of PAH, including abnormalities in glycolysis and glucose oxidation, fatty acid oxidation, glutaminolysis, arginine metabolism, one-carbon metabolism, the reducing and oxidizing cell environment, and the tricarboxylic acid cycle, as well as the effects of PAH-associated nuclear and mitochondrial mutations on metabolism. Understanding of the metabolic mechanisms underlying PAH provides important knowledge for the design of new therapeutics for treatment of patients.

Highlighting the Potential for Chronic Stress to Minimize Therapeutic Responses to Radiotherapy through Increased Immunosuppression and Radiation Resistance

Ionizing radiation has been used in the treatment of cancer for more than 100 years. While often very effective, there is still a great effort in place to improve the efficacy of radiation therapy for controlling the progression and recurrence of tumors. Recent research has revealed the close interaction between nerves and tumor progression, especially nerves of the autonomic nervous system that are activated by a variety of stressful stimuli including anxiety, pain, sleep loss or depression, each of which is likely to be increased in cancer patients. A growing literature now points to a negative effect of chronic stressful stimuli in tumor progression. In this review article, we present data on the potential for adrenergic stress to influence the efficacy of radiation and in particular, its potential to influence the anti-tumor immune response, and the frequency of an "abscopal effect" or the shrinkage of tumors which are outside an irradiated field. We conclude that chronic stress can be a major impediment to more effective radiation therapy through mechanisms involving immunosuppression and increased resistance to radiation-induced tumor cell death. Overall, these data highlight the potential value of stress reduction strategies to improve the outcome of radiation therapy. At the same time, objective biomarkers that can accurately and objectively reflect the degree of stress in patients over prolonged periods of time, and whether it is influencing immunosuppression and radiation resistance, are also critically needed.

Impairment of Hypoxia-Induced CA IX by Beta-Blocker Propranolol-Impact on Progression and Metastatic Potential of Colorectal Cancer Cells

The coexistence of cancer and other concomitant diseases is very frequent and has substantial implications for treatment decisions and outcomes. Beta-blockers, agents that block the beta-adrenergic receptors, have been related also to cancers. In the model of multicellular spheroids formed by colorectal cancer cells we described a crosstalk between beta-blockade by propranolol and tumour microenvironment. Non-selective beta-blocker propranolol decreased ability of tumour cells to adapt to hypoxia by reducing levels of HIF1α and carbonic anhydrase IX in 3D spheroids. We indicated a double action of propranolol in the tumour microenvironment by inhibiting the stability of HIF1α, thus mediating decrease of CA IX expression and, at the same time, by its possible effect on CA IX activity by decreasing the activity of protein kinase A (PKA). Moreover, the inhibition of β-adrenoreceptors by propranolol enhanced apoptosis, decreased number of mitochondria and lowered the amount of proteins involved in oxidative phosphorylation (V-ATP5A, IV-COX2, III-UQCRC2, II-SDHB, I-NDUFB8). Propranolol reduced metastatic potential, viability and proliferation of colorectal cancer cells cultivated in multicellular spheroids. To choose the right treatment strategy, it is extremely important to know how the treatment of concomitant diseases affects the superior microenvironment that is directly related to the efficiency of anti-cancer therapy

Emerging cellular and molecular determinants of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF), the most common form of idiopathic interstitial pneumonia, is a progressive, irreversible, and typically lethal disease characterized by an abnormal fibrotic response involving vast areas of the lungs. Given the poor knowledge of the mechanisms underpinning IPF onset and progression, a better understanding of the cellular processes and molecular pathways involved is essential for the development of effective therapies, currently lacking. Besides a number of established IPF-associated risk factors, such as cigarette smoking, environmental factors, comorbidities, and viral infections, several other processes have been linked with this devastating disease. Apoptosis, senescence, epithelial-mesenchymal transition, endothelial-mesenchymal transition, and epithelial cell migration have been shown to play a key role in IPF-associated tissue remodeling. Moreover, molecules, such as chemokines, cytokines, growth factors, adenosine, glycosaminoglycans, non-coding RNAs, and cellular processes including oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, hypoxia, and alternative polyadenylation have been linked with IPF development. Importantly, strategies targeting these processes have been investigated to modulate abnormal cellular phenotypes and maintain tissue homeostasis in the lung. This review provides an update regarding the emerging cellular and molecular mechanisms involved in the onset and progression of IPF.

Adipocyte-conditioned medium induces resistance of breast cancer cells to lapatinib

Background

The existence of a cross-talk between peritumoral adipocytes and cancer cells has been increasingly investigated. Several studies have shown that these adipocytes protect tumor cells from the effect of anticancer agents.

Methods

To investigate a potential protective effect of adipocyte-conditioned medium on HER2 positive breast cancer cells exposed to tyrosine kinase inhibitors (TKI) such as lapatinib, we analyzed the sensitivity of HER2 positive breast cancer models in vitro and in vivo on SCID mice in the presence or absence of adipocytes or adipocyte-conditioned medium.

Results

Conditioned medium from differentiated adipocytes reduced the in vitro sensitivity of the HER2+ cell lines BT474 and SKBR3 to TKI. Particularly, conditioned medium abrogated P27 induction in tumor cells by lapatinib but this was observed only when conditioned medium was present during exposure to lapatinib. In addition, resistance was induced with adipocytes derived from murine NIH3T3 or human hMAD cells but not with fibroblasts or preadipocytes. In vivo studies demonstrated that the contact of the tumors with adipose tissue reduced sensitivity to lapatinib. Soluble factors involved in this resistance were found to be thermolabile. Pharmacological modulation of lipolysis in adipocytes during preparation of conditioned media showed that various lipolysis inhibitors abolished the protective effect of conditioned media on tumor cells, suggesting a role for adipocyte lipolysis in the induction of resistance of tumor cells to TKI.

Conclusions

Overall, our results suggest that contact of tumor cells with proximal adipose tissue induces resistance to anti HER2 small molecule inhibitors through the production of soluble thermolabile factors, and that this effect can be abrogated using lipolysis inhibitors.

Intermittent Hypoxia Triggers Early Cardiac Remodeling and Contractile Dysfunction in the Time-Course of Ischemic Cardiomyopathy in Rats

BACKGROUND Sleep-disordered breathing is associated with a poor prognosis (mortality) in patients with ischemic cardiomyopathy. The understanding of mechanisms linking intermittent hypoxia (IH), the key feature of sleep-disordered breathing, to ischemic cardiomyopathy progression is crucial for identifying specific actionable therapeutic targets. The aims of the present study were (1) to evaluate the impact of IH on the time course evolution of cardiac remodeling and contractile dysfunction in a rat model of ischemic cardiomyopathy; and (2) to determine the impact of IH on sympathetic activity, hypoxia inducible factor-1 activation, and endoplasmic reticulum stress in the time course of ischemic cardiomyopathy progression. METHODS AND RESULTS Ischemic cardiomyopathy was induced by a permanent ligature of the left coronary artery in male Wistar rats (rats with myocardial infarction). Rats with myocardial infarction were then exposed to either IH or normoxia for up to 12 weeks. Cardiac remodeling and function were analyzed by Sirius red and wheat germ agglutinin staining, ultrasonography, and cardiac catheterization. Sympathetic activity was evaluated by spectral analysis of blood pressure variability. Hypoxia-inducible factor-1α activation and burden of endoplasmic reticulum stress were characterized by Western blots. Long-term IH exposure precipitated cardiac remodeling (hypertrophy and interstitial fibrosis) and contractile dysfunction during the time course evolution of ischemic cardiomyopathy in rodents. Among associated mechanisms, we identified the early occurrence and persistence of sympathetic activation, associated with sustained hypoxia-inducible factor-1α expression and a delayed pro-apoptotic endoplasmic reticulum stress. CONCLUSIONS Our data provide the demonstration of the deleterious impact of IH on post-myocardial infarction remodeling and contractile dysfunction. Further studies are needed to evaluate whether targeting sympathetic nervous system or HIF-1 overactivities could limit these effects and improve management of coexisting ischemic cardiomyopathy and sleep-disordered breathing.

The pVHL neglected functions, a tale of hypoxia-dependent and -independent regulations in cancer

The von Hippel–Lindau protein (pVHL) is a tumour suppressor mainly known for its role as master regulator of hypoxia-inducible factor (HIF) activity. Functional inactivation of pVHL is causative of the von Hippel–Lindau disease, an inherited predisposition to develop different cancers. Due to its impact on human health, pVHL has been widely studied in the last few decades. However, investigations mostly focus on its role in degrading HIFs, whereas alternative pVHL protein–protein interactions and functions are insistently surfacing in the literature. In this review, we analyse these almost neglected functions by dissecting specific conditions in which pVHL is proposed to have differential roles in promoting cancer. We reviewed its role in regulating phosphorylation as a number of works suggest pVHL to act as an inhibitor by either degrading or promoting downregulation of specific kinases. Further, we summarize hypoxia-dependent and -independent pVHL interactions with multiple protein partners and discuss their implications in tumorigenesis.

Estrogen receptor (ESR1 and ESR2)-mediated activation of eNOS-NO-cGMP pathway facilitates high altitude acclimatization

Higher levels of circulatory nitric oxide (NO) and NO metabolites reportedly facilitate high altitude acclimatization. But the underlying factors and molecular pathways promoting NO production at high altitude has been poorly characterized. Studying healthy lowlanders at sea level (C, lowlander) and high altitude (3500 m, after day 1, 4 and 7 of ascent), we report higher protein levels of eNOS and eNOS^Ser1177, higher plasma levels of BH₄, NOx (nitrate and nitrites), cGMP and lower levels of endogenous eNOS inhibitor ADMA during healthy high altitude acclimatization. Our qRT-PCR-based gene expression studies identified higher levels of eNOS/NOS3 mRNA along with several other eNOS pathway genes like CALM1, SLC7A1 and DNM2. In addition, we observed higher mRNA levels of estrogen (E2) receptors ERα/ESR1 and ERβ/ESR2 at high altitude that transcriptionally activates NOS3. We also observed higher mRNA level of membrane receptor ERBB2 that phosphorylates eNOS at Ser1177 and thus augments NO availability. Evaluating E2 biosynthesis at high altitude, we report higher plasma levels of CYP11A1, CYP19A1, E2, lower levels of testosterone (T) and T/E2 ratio as compared to sea level. Correlation studies revealed moderate positive correlation between E2 and NOx (R = 0.68, p = 0.02) after day 4 and cGMP (R = 0.69, p = 0.02) after day 7 at high altitude. These findings suggest a causative role of E2 and its receptors ESR1 and ESR2 in augmenting eNOS activity and NO availability during healthy high altitude ascent. These results will aid in better understanding of NO production during hypobaric hypoxia and help in designing better high altitude acclimatization protocols.

Yes-associated protein (YAP) and transcriptional coactivator with a PDZ-binding motif (TAZ): a nexus between hypoxia and cancer

Hypoxia is a common feature of solid tumors. As transcription factors, hypoxia-inducible factors (HIFs) are the master regulators of the hypoxic microenvironment; their target genes function in tumorigenesis and tumor development. Intriguingly, both yes-associated protein (YAP) and its paralog transcriptional coactivator with a PDZ-binding motif (TAZ) play fundamental roles in the malignant progression of hypoxic tumors. As downstream effectors of the mammalian Hippo pathway, YAP and/or TAZ (YAP/TAZ) are phosphorylated and sequestered in the cytoplasm by the large tumor suppressor kinase 1/2 (LATS1/2)-MOB kinase activator 1 (MOB1) complex, which restricts the transcriptional activity of YAP/TAZ. However, dephosphorylated YAP/TAZ have the ability to translocate to the nucleus where they induce transcription of target genes, most of which are closely related to cancer. Herein we review the tumor-related signaling crosstalk between YAP/TAZ and hypoxia, describe current agents and therapeutic strategies targeting the hypoxia–YAP/TAZ axis, and highlight questions that might have a potential impact in the future.

GRK2-Dependent HuR Phosphorylation Regulates HIF1α Activation under Hypoxia or Adrenergic Stress

Adaptation to hypoxia is a common feature in solid tumors orchestrated by oxygen-dependent and independent upregulation of the hypoxia-inducible factor-1α (HIF-1α). We unveiled that G protein-coupled receptor kinase (GRK2), known to be overexpressed in certain tumors, fosters this hypoxic pathway via phosphorylation of the mRNA-binding protein HuR, a central HIF-1α modulator. GRK2-mediated HuR phosphorylation increases the total levels and cytoplasmic shuttling of HuR in response to hypoxia, and GRK2-phosphodefective HuR mutants show defective cytosolic accumulation and lower binding to HIF-1α mRNA in hypoxic Hela cells. Interestingly, enhanced GRK2 and HuR expression correlate in luminal breast cancer patients. GRK2 also promotes the HuR/HIF-1α axis and VEGF-C accumulation in normoxic MCF7 breast luminal cancer cells and is required for the induction of HuR/HIF1-α in response to adrenergic stress. Our results point to a relevant role of the GRK2/HuR/HIF-1α module in the adaptation of malignant cells to tumor microenvironment-related stresses.

Hypoxia and the hypoxia inducible factor 1α activate protein kinase A by repressing RII beta subunit transcription

Overactivation of the cAMP signal transduction pathway plays a central role in the pathogenesis of endocrine tumors. Genetic aberrations leading to increased intracellular cAMP or directly affecting PKA subunit expression have been identified in inherited and sporadic endocrine tumors, but are rare indicating the presence of nongenomic pathological PKA activation. In the present study, we examined the impact of hypoxia on PKA activation using human growth hormone (GH)-secreting pituitary tumors as a model of an endocrine disease displaying PKA-CREB overactivation. We show that hypoxia activates PKA and enhances CREB transcriptional activity and subsequently GH oversecretion. This is due to a previously uncharacterized ability of HIF-1α to suppress the transcription of the PKA regulatory subunit 2B (PRKAR2B) by sequestering Sp1 from the PRKAR2B promoter. The present study reveals a novel mechanism through which the transcription factor HIF-1α transduces environmental signals directly onto PKA activity, without affecting intracellular cAMP concentrations. By identifying a point of interaction between the cellular microenvironment and intracellular enzyme activation, neoplastic, and nonneoplastic diseases involving overactivated PKA pathway may be more efficiently targeted.

Integrative proteomics and phosphoproteomics in pulmonary arterial hypertension

Pulmonary arterial endothelial cells (PAEC) are mechanistically linked to origins of pulmonary arterial hypertension (PAH). Here, global proteomics and phosphoproteomics of PAEC from PAH (n = 4) and healthy lungs (n = 5) were performed using LC-MS/MS to confirm known pathways and identify new areas of investigation in PAH. Among PAH and control cells, 170 proteins and 240 phosphopeptides were differentially expressed; of these, 45 proteins and 18 phosphopeptides were located in the mitochondria. Pathologic pathways were identified with integrative bioinformatics and human protein-protein interactome network analyses, then confirmed with targeted proteomics in PAH PAEC and non-targeted metabolomics and targeted high-performance liquid chromatography of metabolites in plasma from PAH patients (n = 30) and healthy controls (n = 12). Dysregulated pathways in PAH include accelerated one carbon metabolism, abnormal tricarboxylic acid (TCA) cycle flux and glutamate metabolism, dysfunctional arginine and nitric oxide pathways, and increased oxidative stress. Functional studies in cells confirmed abnormalities in glucose metabolism, mitochondrial oxygen consumption, and production of reactive oxygen species in PAH. Altogether, the findings indicate that PAH is typified by changes in metabolic pathways that are primarily found in mitochondria.

Interdependence of hypoxia and β-adrenergic receptor signaling in pulmonary arterial hypertension

The β-adrenergic receptor (βAR) exists in an equilibrium of inactive and active conformational states, which shifts in response to different ligands and results in downstream signaling. In addition to cAMP, βAR signals to hypoxia-inducible factor 1 (HIF-1). We hypothesized that a βAR-active conformation (R**) that leads to HIF-1 is separable from the cAMP-activating conformation (R*) and that pulmonary arterial hypertension (PAH) patients with HIF-biased conformations would not respond to a cAMP agonist. We compared two cAMP agonists, isoproterenol and salbutamol, in vitro. Isoproterenol increased cAMP and HIF-1 activity, while salbutamol increased cAMP and reduced HIF-1. Hypoxia blunted agonist-stimulated cAMP, consistent with receptor equilibrium shifting toward HIF-activating conformations. Similarly, isoproterenol increased HIF-1 and erythropoiesis in mice, while salbutamol decreased erythropoiesis. βAR overexpression in cells increased glycolysis, which was blunted by HIF-1 inhibitors, suggesting increased βAR leads to increased hypoxia-metabolic effects. Because PAH is also characterized by HIF-related glycolytic shift, we dichotomized PAH patients in the Pulmonary Arterial Hypertension Treatment with Carvedilol for Heart Failure trial (NCT01586156) based on right ventricular (RV) glucose uptake to evaluate βAR ligands. Patients with high glucose uptake had more severe disease than those with low uptake. cAMP increased in response to isoproterenol in mononuclear cells from low-uptake patients but not in high-uptake patients' cells. When patients were treated with carvedilol for 1 wk, the low-uptake group decreased RV systolic pressures and pulmonary vascular resistance, but high-uptake patients had no physiologic responses. The findings expand the paradigm of βAR activation and uncover a novel PAH subtype that might benefit from β-blockers.

Predisposing factors to heart failure in diabetic nephropathy: a look at the sympathetic nervous system hyperactivity

Diabetes mellitus (DM) and heart failure (HF) are frequent comorbidities among elderly patients. HF, a leading cause of mortality and morbidity worldwide, is characterized by sympathetic nervous system hyperactivity. The prevalence of diabetes mellitus (DM) is rapidly growing and the risk of developing HF is higher among DM patients. DM is responsible for several macro- and micro-angiopathies that contribute to the development of coronary artery disease (CAD), peripheral artery disease, retinopathy, neuropathy and diabetic nephropathy (DN) as well. Independently of CAD, chronic kidney disease (CKD) and DM increase the risk of HF. Individuals with diabetic nephropathy are likely to present a distinct pathological condition, defined as diabetic cardiomyopathy, even in the absence of hypertension or CAD, whose pathogenesis is only partially known. However, several hypotheses have been proposed to explain the mechanism of diabetic cardiomyopathy: increased oxidative stress, altered substrate metabolism, mitochondrial dysfunction, activation of renin-angiotensin-aldosterone system (RAAS), insulin resistance, and autonomic dysfunction. In this review, we will focus on the involvement of sympathetic system hyperactivity in the diabetic nephropathy.

Pulmonary arterial hypertension treatment with carvedilol for heart failure: a randomized controlled trial

BACKGROUND

Right-sided heart failure is the leading cause of death in pulmonary arterial hypertension (PAH). Similar to left heart failure, sympathetic overactivation and β-adrenoreceptor (βAR) abnormalities are found in PAH. Based on successful therapy of left heart failure with β-blockade, the safety and benefits of the nonselective β-blocker/vasodilator carvedilol were evaluated in PAH.

METHODS

PAH Treatment with Carvedilol for Heart Failure (PAHTCH) is a single-center, double-blind, randomized, controlled trial. Following 1-week run-in, 30 participants were randomized to 1 of 3 arms for 24 weeks: placebo, low-fixed-dose, or dose-escalating carvedilol. Outcomes included clinical measures and mechanistic biomarkers.

RESULTS

Decreases in heart rate and blood pressure with carvedilol were well tolerated; heart rate correlated with carvedilol dose. Carvedilol-treated groups had no decrease in exercise capacity measured by 6-minute walk, but had lower heart rates at peak and after exercise, and faster heart rate recovery. Dose-escalating carvedilol was associated with reduction in right ventricular (RV) glycolytic rate and increase in βAR levels. There was no evidence of RV functional deterioration; rather, cardiac output was maintained.

CONCLUSIONS

Carvedilol is likely safe in PAH over 6 months of therapy and has clinical and mechanistic benefits associated with improved outcomes. The data provide support for longer and larger studies to establish guidelines for use of β-blockers in PAH.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01586156FUNDING. This project was supported by NIH R01HL115008 and R01HL60917 and in part by the National Center for Advancing Translational Sciences, UL1TR000439.

Impact of paroxetine on proximal β-adrenergic receptor signaling

β-adrenergic receptors (βAR) regulate numerous functions throughout the body, however G protein-coupled receptor kinase (GRK)-dependent desensitization of βAR has long been recognized as a maladaptive process in the progression of various disease states. Thus, the development of small molecule inhibitors of GRKs for the study of these processes and as potential therapeutics has been at the forefront of recent research efforts. Via structural and biochemical analyses, the selective serotonin reuptake inhibitor (SSRI) paroxetine was identified as a GRK2 inhibitor that enhances βAR-dependent cardiomyocyte and cardiac contractility and reverses cardiac dysfunction and myocardial βAR expression in mouse models of heart failure. Despite these functional outcomes, consistent with diminished βAR desensitization, the proximal βAR signaling mechanisms sensitive to paroxetine have not been reported. In this study, we aimed to determine whether paroxetine prevents classic βAR desensitization-related signaling mechanisms at a molecular level. Therefore, via immunoblotting, radioligand binding, fluorescence resonance energy transfer (FRET) and microscopy assays, we have performed an assessment of the effect of paroxetine on proximal βAR signaling responses. Indeed, paroxetine treatment inhibited ligand-induced β2AR phosphorylation in a concentration-dependent manner. Additionally, for both β1AR and β2AR, paroxetine decreased ligand-induced βarrestin2 recruitment and subsequent receptor internalization. Thus, paroxetine inhibits βAR desensitization mechanisms consistent with GRK2 inhibition and provides a useful pharmacological tool for studying these proximal GPCR signaling responses.