Stress and adrenergic function: HIF1α, a potential regulatory switch

Outcome of stress on G protein-coupled receptors and hypoxia inducible factor-1α

Stress drives neuroendocrine signals with detrimental effects to the intestinal homeostasis. The aim of this study was to evaluate the effect of stress on intestinal hypoxia response elements, including G protein-coupled receptor 41 (GPR41), GPR43, and hypoxia inducible factor (HIF)-1α. Groups of five BALB/c mice were subjected to acute (2 h per day) and chronic (2 h per day for 4 days) stress induced by restraint, and the results were compared to those of an unstressed control group. Whole mucosal samples from the colon were collected to evaluate the expression of GPR41, GPR43 and HIF-1α using Western blot chemiluminescent analysis. Compared to the control group, in the chronic stress group the expression of GPR43 (P = 0.0092) and HIF-1α (P < 0.0001) were significantly lower and the expression of GPR41 was similar (P = 0.9184); acute stress significantly increased HIF-1α expression (P = 0.0030) and increased GPR41 expression (P = 0.0937), without affecting GPR43 (P = 0.9184). These findings offer insights into the modulation of hypoxia response elements under stress conditions and their pharmacological implications for developing drugs that mitigate the effects of stress on intestinal homeostasis.

HIF2α regulates the synthesis and release of epinephrine in the adrenal medulla

The adrenal gland and its hormones regulate numerous fundamental biological processes; however, the impact of hypoxia signaling on adrenal function remains poorly understood. Here, we reveal that deficiency of HIF (hypoxia inducible factors) prolyl hydroxylase domain protein-2 (PHD2) in the adrenal medulla of mice results in HIF2α-mediated reduction in phenylethanolamine N-methyltransferase (PNMT) expression, and consequent reduction in epinephrine synthesis. Simultaneous loss of PHD2 in renal erythropoietin (EPO)-producing cells (REPCs) stimulated HIF2α-driven EPO overproduction, excessive RBC formation (erythrocytosis), and systemic hypoglycemia, which is necessary and sufficient to enhance exocytosis of epinephrine from the adrenal medulla. Based on these results, we propose that the PHD2-HIF2α axis in the adrenal medulla regulates the synthesis of epinephrine, whereas in REPCs, it indirectly induces the release of this hormone. Our findings are also highly relevant to the testing of small molecule PHD inhibitors in phase III clinical trials for patients with renal anemia. KEY MESSAGES: HIF2α and not HIF1α modulates PNMT during epinephrine synthesis in chromaffin cells. The PHD2-HIF2α-EPO axis induces erythrocytosis and hypoglycemia. Reduced systemic glucose facilitates exocytosis of epinephrine from adrenal gland.

Whole transcriptome analysis of adrenal glands from prenatal glucocorticoid programmed hypertensive rodents

Prenatal glucocorticoid exposure is associated with the development of hypertension in adults. We have previously demonstrated that antenatal dexamethosone (DEX) administration in Wistar-Kyoto dams results in offspring with increased blood pressure coupled with elevated plasma epinephrine levels. In order to elucidate the molecular mechanisms responsible for prenatal DEX-mediated programming of hypertension, a whole-transcriptome analysis was performed on DEX programmed WKY male adrenal glands using the Rat Gene 2.0 microarray. Differential gene expression (DEG) analysis of DEX-exposed offspring compared with saline-treated controls revealed 142 significant DEGs (109 upregulated and 33 downregulated genes). DEG pathway enrichment analysis demonstrated that genes involved in circadian rhythm signaling were most robustly dysregulated. RT-qPCR analysis confirmed the increased expression of circadian genes Bmal1 and Npas2, while Per2, Per3, Cry2 and Bhlhe41 were significantly downregulated. In contrast, gene expression profiling of Spontaneously Hypertensive (SHR) rats, a genetic model of hypertension, demonstrated decreased expression of Bmal1 and Npas2, while Per1, Per2, Per3, Cry1, Cry2, Bhlhe41 and Csnk1D were all upregulated compared to naïve WKY controls. Taken together, this study establishes that glucocorticoid programmed adrenals have impaired circadian signaling and that changes in adrenal circadian rhythm may be an underlying molecular mechanism responsible for the development of hypertension.

β-Adrenoceptor Activation in Breast MCF-10A Cells Induces a Pattern of Catecholamine Production Similar to that of Tumorigenic MCF-7 Cells

Adrenaline, which participates in the neuroendocrine response that occurs during stress and perimenopause, may be tumorigenic. This exploratory study aimed at investigating whether non-tumorigenic and tumorigenic human breast epithelial cell lines are able to synthesize adrenaline. The study was carried out in non-tumorigenic (MCF-10A) and tumorigenic (MCF-7) human breast cell lines. Expression of enzymes involved in adrenaline synthesis was characterized by RT-qPCR, immunocytochemistry and western blot. Catecholamines and analogue compounds were quantified by HPLC-ECD. Functional assessment of the impact of drugs on cells’ tumorigenic potential was assessed by determination of cell viability and clonogenic ability. Both MCF-10A and MCF-7 cells produce catecholamines, but the capacity to produce adrenaline is lower in MCF-10A cells. β-adrenoceptor activation increases the capacity of MCF-10A cells to produce adrenaline and favor both cell viability and colony formation. It is concluded that exposure of human breast epithelial cells to β-adrenoceptor agonists increases cell proliferation and the capacity to produce adrenaline, creating an autocrine potential to spread these adrenergic effects in a feed-forward loop. It is conceivable that these effects are related to tumorigenesis, bringing a new perspective to understand the claimed anticancer effects of propranolol and the increase in breast cancer incidence caused by stress or during perimenopause.

Phenylethanolamine N-methyltransferase gene polymorphisms associate with crisis pain in sickle cell disease patients

Aim: Phenylethanolamine N-methyltransferase (PNMT) catalyzes the conversion of sympathetic neurotransmitter norepinephrine to epinephrine. We examined the association of PNMT polymorphisms with acute and chronic pain in sickle cell disease (SCD). Methods: Utilization of emergency care owing to painful crisis was used as a marker for acute pain in 131 patients with SCD. Results: rs876493 A allele, rs2934965 T allele and rs2941523 G allele were significantly associated with decreased utilization (p ≤ 0.05). rs876493 A allele showed association with utilization in females (p = 0.003), not males (p = 0.803). rs2934965 T allele and rs2941523 G allele were predicted to cause loss of putative transcription factor binding sites. This is the first report of the association of PNMT polymorphisms with acute crisis pain in SCD. Together with our previous findings in catechol-o-methyltransferase, polymorphisms in catecholamine metabolizing enzymes appear to primarily influence acute pain in SCD.

Dry Fasting Physiology: Responses to Hypovolemia and Hypertonicity

OBJECTIVE

The aim of this study was to provide a deeper insight into dry fasting (DF) physiology.

DESIGN

Ten participants performed DF for 5 consecutive days.

METHODS

The following parameters were monitored daily: cortisol, aldosterone, high-sensitivity C-reactive protein (CRP), erythropoietin, albumin, uric acid, and vitamin C in serum; vasopressin (ADH), adrenocorticotropic hormone (ACTH), renin, angiotensin II, and total antioxidant capacity (TAC) in plasma; hematocrit and erythrocytes in whole blood; osmolality, noradrenaline, dopamine, adrenaline, Na+, and K+ in 24-h urine; waist circumference and body, urine, and stool weight.

RESULTS

The following parameters increased: ADH (60 ± 11%), ACTH (176 ± 34%), cortisol (495 ± 75%), urine osmolality (20 ± 4%), CRP (167 ± 77%), renin (315 ± 63%), angiotensin II (74 ± 21%), aldosterone (61 ± 21%), TAC (80.4 ± 17%), uric acid (103 ± 19%), albumin (18.4 ± 2.4%), erythrocytes (13.4 ± 2.2%), hematocrit (11 ± 1.8%), and the excretion of noradrenaline (40.3 ± 10%) and dopamine (17 ± 5%). The following parameters decreased: waist circumference (8.20 ± 0.61 cm), body weight (7.010 ± 0.3 kg), erythropoietin (65 ± 18%), and the excretion of adrenaline (38 ± 4%) and Na+ (60 ± 16%). The excretion of K+ remained unchanged. Vitamin C decreased, showing a half-life of 4.8 ± 0.7 days. The percent ratios of lost weight components were: urine (52.2 ± 3.7%), insensible water loss (32.2 ± 1.4%), stool (5 ± 0.3%), and respiratory gases, i.e., expired CO2 - incorporated O2 (10.6 ± 5.4%).

CONCLUSION

The mechanisms underlying the hypertonicity and hypovolemia compensation and the ratio analysis of lost weight components were presented. DF demonstrated short-term antioxidant, anti-ischemic, immune-stimulating, anti-edematous, and anti-inflammatory effects. The results may have an impact on developing new concepts for the treatment of edema, obesity, and inflammatory and ischemic diseases.

Impact of Extrinsic and Intrinsic Hypoxia on Catecholamine Biosynthesis in Absence or Presence of Hif2α in Pheochromocytoma Cells

Pheochromocytomas and paragangliomas (PPGLs) with activated pseudohypoxic pathways are associated with an immature catecholamine phenotype and carry a higher risk for metastasis. For improved understanding of the underlying mechanisms we investigated the impact of hypoxia and pseudohypoxia on catecholamine biosynthesis in pheochromocytoma cells naturally lacking Hif2α (MPC and MTT) or expressing both Hif1α and Hif2α (PC12). Cultivation under extrinsic hypoxia or in spheroid culture (intrinsic hypoxia) increased cellular dopamine and norepinephrine contents in all cell lines. To distinguish further between Hif1α- and Hif2α-driven effects we expressed Hif2α in MTT and MPC-mCherry cells (naturally lacking Hif2α). Presence of Hif2α resulted in similarly increased cellular dopamine and norepinephrine under hypoxia as in the control cells. Furthermore, hypoxia resulted in enhanced phosphorylation of tyrosine hydroxylase (TH). A specific knockdown of Hif1α in PC12 diminished these effects. Pseudohypoxic conditions, simulated by expression of Hif2α under normoxia resulted in increased TH phosphorylation, further stimulated by extrinsic hypoxia. Correlations with PPGL tissue data led us to conclude that catecholamine biosynthesis under hypoxia is mainly mediated through increased phosphorylation of TH, regulated as a short-term response (24–48 h) by HIF1α. Continuous activation of hypoxia-related genes under pseudohypoxia leads to a HIF2α-mediated phosphorylation of TH (permanent status).

Safflor yellow B reduces hypoxia-mediated vasoconstriction by regulating endothelial micro ribonucleic acid/nitric oxide synthase signaling

Hypoxia-induced generation of vasoconstrictors reduces cerebral blood flow (CBF) while nitric oxide (NO) synthase (NOS) and microRNAs (miRNA) in endothelial cells (ECs) suppress vasoconstriction. Safflor yellow B (SYB), a natural plant compound, previously attenuated angiotensin II-mediated injury of ECs and maintained endothelial function. This study investigated the putative involvement of NOS and miRNAs in SYB-mediated resistance to hypoxia-induced vasoconstriction. In vivo, chronic hypoxia was induced in rats, and SYB was administered intravenously. In vitro, rat primary aortic ECs were cultured under oxygen and glucose deprivation. After treatment with anti-microR-199a, as well as the NOS inhibitor, N(G)-nitro-L-arginine methyl ester, SYB, or both, cell viability, NO and peroxynitrite (ONOO-) levels, NOS expression, and miRNA levels were evaluated. SYB significantly alleviated hypoxia-mediated vasoconstriction and increased CBF endothelium-dependently. SYB upregulated miR-199a, increased EC viability, decreased endothelin-1 (ET-1) levels, inhibited protein kinase C (PKC) activity, and suppressed hypoxia inducible factor-1α (HIF-1α) expression. Furthermore, the SYB-mediated reduction of inducible NOS reduced ONOO- levels. In addition, SYB downregulated miR-138 and, thereby, enhanced S100A1 and endothelial NOS activity. Hypoxia-mediated regulation of miR-138 and miR-199a inhibited endothelial NOS expression and activation, which triggered ET-1 release and vasoconstriction. Therefore, SYB treatment reduced hypoxia-induced vasoconstriction through miR-199a/endothelial NOS signaling.

Potential antidepressant and resilience mechanism revealed by metabolomic study on peripheral blood mononuclear cells of stress resilient rats

Resilience is an active coping response to stress, which plays a very important role in major depressive disorder study. The molecular mechanisms underlying such resilience are poorly understood. Peripheral blood mononuclear cells (PBMCs) were promising objects in unveiling the underlying pathogenesis of resilience. Hereby we carried out successive study on PBMCs metabolomics in resilient rats of chronic unpredictable mild stress (CUMS) model. A gas chromatography-mass spectrometry (GC-MS) metabolomic approach coupled with principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) was used to detect differential metabolites in PBMCs of resilient rats. Ingenuity Pathways Analysis (IPA) was applied for pathway analysis. A set of differential metabolites including Malic acid, Ornithine, l-Lysine, Stigmasterol, Oleic acid, γ-Tocopherol, Adenosine and N-acetyl-d-glucosamine were significantly altered in resilient rats, meanwhile promoting antidepressant research. As revealed by IPA that aberrant energy metabolism, HIFα signaling, neurotransmitter, O-GlcNAcylation and cAMP signaling cascade in peripheral might be evolved in the pathogenesis of coping mechanism. The GC-MS based metabolomics may contribute to better understanding of resilience, as well as shedding light on antidepressant discovery.

Cellular density-dependent down-regulation of EP4 prostanoid receptors via the up-regulation of hypoxia-inducible factor-1α in HCA-7 human colon cancer cells

Increases in prostaglandin E₂ (PGE₂) and cyclooxygenase-2 (COX-2) levels are features of colon cancer. Among the different E-type prostanoid receptor subtypes, EP4 receptors are considered to play a crucial role in carcinogenesis by, for example, inducing COX-2 when stimulated with PGE₂. However, EP4 receptor levels and PGE₂-induced cellular responses are inconsistent among the cellular conditions. Therefore, the connections responsible for the expression of EP4 receptors were investigated in the present study by focusing on cell density-induced hypoxia-inducible factor-1α (HIF-1α). The expression of EP4 receptors was examined using immunoblot analysis, quantitative polymerase chain reaction, and reporter gene assays in HCA-7 human colon cancer cells with different cellular densities. The involvement of HIF-1α and its signaling pathways were also examined by immunoblot analysis, reporter gene assays, and with siRNA. We here demonstrated that EP4 receptors as well as EP4 receptor-mediated COX-2 expression levels decreased with an increase in cellular density. In contrast, HIF-1α levels increased in a cellular density-dependent manner. The knockdown of HIF-1α by siRNA restored the expression of EP4 receptors and EP4 receptor-mediated COX-2 in cells at a high density. Thus, the cellular density-dependent increase observed in HIF-1α expression levels reduced the expression of COX-2 by decreasing EP4 receptor levels. This novel regulation mechanism for the expression of EP4 receptors by HIF-1α may provide an explanation for the inconsistent actions of PGE₂. The expression levels of EP4 receptors may vary depending on cellular density, which may lead to the differential activation of their signaling pathways by PGE₂. Thus, cellular density-dependent PGE₂-mediated signaling may determine the fate/stage of cancer cells, i.e., the surrounding environments could define the fate/stage of malignancies associated with colon cancer.

Role of hypoxia and HIF2α in development of the sympathoadrenal cell lineage and chromaffin cell tumors with distinct catecholamine phenotypic features

Hypoxia has wide-ranging impact in normal physiology and disease processes. This stimulus evokes changes in gene expression mediated by transcription factors termed hypoxia-inducible factors (HIFs) that affect numerous processes: angiogenesis, cell survival, cellular metabolism, stem cell self-renewal and multipotency, migration, invasiveness, and metastatic progression in tumor cells. Over the past decade, increasing numbers of reports have emerged documenting differential roles of HIF1α and HIF2α in these processes. In cells of the sympathoadrenal lineage, both HIFs differentially mediate influences of hypoxia on catecholamine synthesis and secretion, but HIF2α signaling has particularly prominent functions in regulating developmental processes of growth and differentiation. This chapter discusses the role of HIF2α and HIF1α in the context of the development, phenotypic features, and functions of chromaffin cells. Moreover, current knowledge about tumor formation in cells of the sympathoadrenal lineage, leading to catecholamine-producing pheochromocytomas and paragangliomas, is analyzed in the light of the HIF2α signaling network.

Adaptive and maladaptive cardiorespiratory responses to continuous and intermittent hypoxia mediated by hypoxia-inducible factors 1 and 2

Hypoxia is a fundamental stimulus that impacts cells, tissues, organs, and physiological systems. The discovery of hypoxia-inducible factor-1 (HIF-1) and subsequent identification of other members of the HIF family of transcriptional activators has provided insight into the molecular underpinnings of oxygen homeostasis. This review focuses on the mechanisms of HIF activation and their roles in physiological and pathophysiological responses to hypoxia, with an emphasis on the cardiorespiratory systems. HIFs are heterodimers comprised of an O(2)-regulated HIF-1α or HIF-2α subunit and a constitutively expressed HIF-1β subunit. Induction of HIF activity under conditions of reduced O(2) availability requires stabilization of HIF-1α and HIF-2α due to reduced prolyl hydroxylation, dimerization with HIF-1β, and interaction with coactivators due to decreased asparaginyl hydroxylation. Stimuli other than hypoxia, such as nitric oxide and reactive oxygen species, can also activate HIFs. HIF-1 and HIF-2 are essential for acute O(2) sensing by the carotid body, and their coordinated transcriptional activation is critical for physiological adaptations to chronic hypoxia including erythropoiesis, vascularization, metabolic reprogramming, and ventilatory acclimatization. In contrast, intermittent hypoxia, which occurs in association with sleep-disordered breathing, results in an imbalance between HIF-1α and HIF-2α that causes oxidative stress, leading to cardiorespiratory pathology.

Impact of parturition on chemokine homing factor expression in the vaginal distention model of stress urinary incontinence

PURPOSE

Human childbirth simulated by vaginal distention is known to increase the expression of chemokines and receptors involved in stem cell homing and tissue repair. We hypothesized that pregnancy and parturition in rats contributes to the expression of chemokines and receptors after vaginal distention.

MATERIALS AND METHODS

We used 72 age matched female Lewis rats, including virgin rats with and without vaginal distention, and delivered rats with and without vaginal distention. Each rat was sacrificed immediately, or 3 or 7 days after vaginal distention and/or parturition, and the urethra was harvested. Relative expression of chemokines and receptors was determined by real-time polymerase chain reaction. Mixed models were used with the Bonferroni correction for multiple comparisons.

RESULTS

Vaginal distention up-regulated urethral expression of CCL7 immediately after injury in virgin and postpartum rats. Hypoxia inducible factor-1α and vascular endothelial growth factor were up-regulated only in virgin rats immediately after vaginal distention. CD191 expression was immediately up-regulated in postpartum rats without vaginal distention compared to virgin rats without vaginal distention. CD195 was up-regulated in virgin rats 3 days after vaginal distention compared to virgin rats without vaginal distention. CD193 and CXCR4 showed delayed up-regulation in virgin rats 7 days after vaginal distention. CXCL12 was up-regulated in virgin rats 3 days after vaginal distention compared to immediately after vaginal distention. Interleukin-8 and CD192 showed no differential expression.

CONCLUSIONS

Vaginal distention results in up-regulation of the chemokines and receptors expressed during tissue injury, which may facilitate the spontaneous functional recovery previously noted. Pregnancy and delivery up-regulated CD191 and attenuated the expression of hypoxia inducible factor-1α and vascular endothelial growth factor in the setting of vaginal distention, likely by decreasing hypoxia.

Epinephrine: a short- and long-term regulator of stress and development of illness : a potential new role for epinephrine in stress

Epinephrine (Epi), which initiates short-term responses to cope with stress, is, in part, stress-regulated via genetic control of its biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT). In rats, immobilization (IMMO) stress activates the PNMT gene in the adrenal medulla via Egr-1 and Sp1 induction. Yet, elevated Epi induced by acute and chronic stress is associated with stress induced, chronic illnesses of cardiovascular, immune, cancerous, and behavioral etiologies. Major sources of Epi include the adrenal medulla and brainstem. Although catecholamines do not cross the blood-brain barrier, circulating Epi from the adrenal medulla may communicate with the central nervous system and stress circuitry by activating vagal nerve β-adrenergic receptors to release norepinephrine, which could then stimulate release of the same from the nucleus tractus solitarius and locus coeruleus. In turn, the basal lateral amygdala (BLA) may activate to stimulate afferents to the hypothalamus, neocortex, hippocampus, caudate nucleus, and other brain regions sequentially. Recently, we have shown that repeated IMMO or force swim stress may evoke stress resiliency, as suggested by changes in expression and extinction of fear memory in the fear-potentiated startle paradigm. However, concomitant adrenergic changes seem stressor dependent. Present studies aim to identify stressful conditions that elicit stress resiliency versus stress sensitivity, with the goal of developing a model to investigate the potential role of Epi in stress-associated illness. If chronic Epi over expression does elicit illness, possibilities for alternative therapeutics exist through regulating stress-induced Epi expression, adrenergic receptor function and/or corticosteroid effects on Epi, adrenergic receptors and the stress axis.

Role of reactive oxygen species in the neural and hormonal regulation of the PNMT gene in PC12 cells

The stress hormone, epinephrine, is produced predominantly by adrenal chromaffin cells and its biosynthesis is regulated by the enzyme phenylethanolamine N-methyltransferase (PNMT). Studies have demonstrated that PNMT may be regulated hormonally via the hypothalamic-pituitary-adrenal axis and neurally via the stimulation of the splanchnic nerve. Additionally, hypoxia has been shown to play a key role in the regulation of PNMT. The purpose of this study was to examine the impact of reactive oxygen species (ROS) produced by the hypoxia mimetic agent CoCl₂, on the hormonal and neural stimulation of PNMT in an in vitro cell culture model, utilizing the rat pheochromocytoma (PC12) cell line. RT-PCR analyses show inductions of the PNMT intron-retaining and intronless mRNA splice variants by CoCl₂ (3.0- and 1.76-fold, respectively). Transient transfection assays of cells treated simultaneously with CoCl₂ and the synthetic glucocorticoid, dexamethasone, show increased promoter activity (18.5-fold), while mRNA levels of both splice variants do not demonstrate synergistic effects. Similar results were observed when investigating the effects of CoCl₂-induced ROS on the neural stimulation of PNMT via forskolin. Our findings demonstrate that CoCl₂-induced ROS have synergistic effects on hormonal and neural activation of the PNMT promoter.