Effect of high altitude and in vivo adenosine/(β)-adrenergic receptor blockade on ATP and 2,3BPG concentrations in red blood cells of avian embryos

Environmental gradients of selection for an alpine-obligate bird, the white-tailed ptarmigan (Lagopus leucura)

The warming climate will expose alpine species adapted to a highly seasonal, harsh environment to novel environmental conditions. A species can shift their distribution, acclimate, or adapt in response to a new climate. Alpine species have little suitable habitat to shift their distribution, and the limits of acclimation will likely be tested by climate change in the long-term. Adaptive genetic variation may provide the raw material for species to adapt to this changing environment. Here, we use a genomic approach to describe adaptive divergence in an alpine-obligate species, the white-tailed ptarmigan (Lagopus leucura), a species distributed from Alaska to New Mexico, across an environmentally variable geographic range. Previous work has identified genetic structure and morphological, behavioral, and physiological differences across the species' range; however, those studies were unable to determine the degree to which adaptive divergence is correlated with local variation in environmental conditions. We used a genome-wide dataset generated from 95 white-tailed ptarmigan distributed throughout the species' range and genotype-environment association analyses to identify the genetic signature and environmental drivers of local adaptation. We detected associations between multiple environmental gradients and candidate adaptive loci, suggesting ptarmigan populations may be locally adapted to the plant community composition, elevation, local climate, and to the seasonality of the environment. Overall, our results suggest there may be groups within the species' range with genetic variation that could be essential for adapting to a changing climate and helpful in guiding conservation action.

Critical developmental windows for morphology and hematology revealed by intermittent and continuous hypoxic incubation in embryos of quail (Coturnix coturnix)

Hypoxia during embryonic growth in embryos is frequently a powerful determinant of development, but at least in avian embryos the effects appear to show considerable intra- and inter-specific variation. We hypothesized that some of this variation may arise from different protocols that may or may not result in exposure during the embryo’s critical window for hypoxic effects. To test this hypothesis, quail embryos (Coturnix coturnix) in the intact egg were exposed to hypoxia (~15% O₂) during “early” (Day 0 through Day 5, abbreviated as D0-D5), “middle” (D6-D10) or “late” (D11-D15) incubation or for their entire 16–18 day incubation (“continuous hypoxia”) to determine critical windows for viability and growth. Viability, body mass, beak and toe length, heart mass, and hematology (hematocrit and hemoglobin concentration) were measured on D5, D10, D15 and at hatching typically between D16 and D18 Viability rate was ~50–70% immediately following the exposure period in the early, middle and late hypoxic groups, but viability improved in the early and late groups once normoxia was restored. Middle hypoxia groups showed continuing low viability, suggesting a critical period from D6-D10 for embryo viability. The continuous hypoxia group experienced viability reaching <10% after D15. Hypoxia, especially during late and continuous hypoxia, also inhibited growth of body, beak and toe when measured at D15. Full recovery to normal body mass upon hatching occurred in all other groups except for continuous hypoxia. Contrary to previous avian studies, heart mass, hematocrit and hemoglobin concentration were not altered by any hypoxic incubation pattern. Although hypoxia can inhibit embryo viability and organ growth during most incubation periods, the greatest effects result from continuous or middle incubation hypoxic exposure. Hypoxic inhibition of growth can subsequently be “repaired” by catch-up growth if a final period of normoxic development is available. Collectively, these data indicate a critical developmental window for hypoxia susceptibility during the mid-embryonic period of development.

Ca²+-regulatory proteins in cardiomyocytes from the right ventricle in children with congenital heart disease

BACKGROUND

Hypoxia and hypertrophy are the most frequent pathophysiological consequence of congenital heart disease (CHD) which can induce the alteration of Ca2+-regulatory proteins and inhibit cardiac contractility. Few studies have been performed to examine Ca2+-regulatory proteins in human cardiomyocytes from the hypertrophic right ventricle with or without hypoxia.

METHODS

Right ventricle tissues were collected from children with tetralogy of Fallot [n = 25, hypoxia and hypertrophy group (HH group)], pulmonary stenosis [n = 25, hypertrophy group (H group)], or small isolated ventricular septal defect [n = 25, control group (C group)] during open-heart surgery. Paraffin sections of tissues were stained with 3,3'-dioctadecyloxacarbocyanine perchlorate to measure cardiomyocyte size. Expression levels of Ca2+-regulatory proteins [sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), ryanodine receptor (RyR2), sodiumcalcium exchanger (NCX), sarcolipin (SLN) and phospholamban (PLN)] were analysed by means of real-time PCR, western blot, or immunofluorescence. Additionally, phosphorylation level of RyR and PLN and activity of protein phosphatase (PP1) were evaluated using western blot.

RESULTS

Mild cardiomyocyte hypertrophy of the right ventricle in H and HH groups was confirmed by comparing cardiomyocyte size. A significant reduction of SERCA2a in mRNA (P<0.01) was observed in the HH group compared with the C group. The level of Ser16-phosphorylated PLN was down-regulated (P<0.01) and PP1 was increased (P<0.01) in the HH group compared to that in the C group.

CONCLUSIONS

The decreased SERCA2a mRNA may be a biomarker of the pathological process in the early stage of cyanotic CHD with the hypertrophic right ventricle. A combination of hypoxia and hypertrophy can induce the adverse effect of PLN-Ser16 dephosphorylation. Increased PP1 could result in the decreased PLN-Ser16 and inhibition of PP1 is a potential therapeutic target for heart dysfunction in pediatrics.

Hypoxic incubation creates differential morphological effects during specific developmental critical windows in the embryo of the chicken (Gallus gallus)

Hypoxia inhibits vertebrate development, but the magnitude and timing of organ-specific effects are poorly understood. Chick embryos were exposed continuously to hypoxia (15% O2) throughout Days 1-6, 6-12, 12-18 or Days 1-18 of development, followed by morphometric measurements of major organ systems. Early hypoxic exposure reduced eye mass and beak length when measured in middle development. Liver, brain, heart, kidneys, stomach, intestines and skeletal long bones were not affected by hypoxia at any developmental stage. The chorioallantoic membrane (CAM) mass was unchanged by hypoxic exposure in early or mid-development, but CAM mass on Day 18 increased strikingly (40 and 60% in late and continuous populations, respectively) in response to hypoxic exposure. The increase in CAM mass presumably enhances oxygen delivery, thus minimizing the detrimental effects of hypoxia on development and growth. Hypoxic exposure at key critical windows in development thus results in differential effects on organ development, some of which can subsequently be repaired through additional incubation (yolk mass, eye mass, beak length).

Avian embryos in hypoxic environments

Avian embryos at high altitude do not benefit of the maternal protection against hypoxia as in mammals. Nevertheless, avian embryos are known to hatch successfully at altitudes between 4,000 and 6,500 m. This review considers some of the processes that bring about the outstanding modifications in the pressure differences between the environment and mitochondria of avian embryos in hypoxic environments. Among species, some maintain normal levels of oxygen consumption ( VO2) have a high oxygen carrying capacity, lower the air cell-arterial pressure difference ( PAO2 - PaO2 ) with a constant pH. Other species decrease VO2, increase only slightly the oxygen carrying capacity, have a higher PAO2 - PaO2 difference than sea-level embryos and lower the PCO2 and pH. High altitude embryos, and those exposed to hypoxia have an accelerated decline of erythrocyte ATP levels during development and an earlier stimulation of 2,3-BPG synthesis. A higher Bohr effect may ensure high tissue PO2 in the presence of the high-affinity hemoglobin. Independently of the strategy used, they serve together to promote suitable rates of development and successful hatching of high altitude birds in hypoxic environments.

An electrochemical investigation of effect of ATP on hemoglobin

The titratable potentiometric response of hemoglobin (Hb) induced by adenosine-5'-triphosphate (ATP) is observed. The concentration-dependent effect of ATP on the anaerobic redox reaction of the protein at pH 7.0 reflects that ATP will induce stabilization of the reduced state and destabilization of the R-like (met Fe(III)) state of the metHb, when ATP concentration is lower than 3.0 mM. But when ATP concentration is between 4 and 7 mM, shift of the oxidation potential may also be observed. With reference to the study of adenosine, adenosine-5'-monophosphate, adenosine-5'-diphosphate and 2,3-diphosphoglycerate, the allosteric effect of ATP on Hb is discussed extensively. This study has given an electrochemical approach to the investigation of effect of ATP, an in vivo allosteric effector, on Hb in the physiological concentration range.

Erythroid pyrimidine 5'-nucleotidase: cloning, developmental expression, and regulation by cAMP and in vivo hypoxia

A characteristic process of terminal erythroid differentiation is the degradation of ribosomal RNA into mononucleotides. The pyrimidine mononucleotides can be dephosphorylated by pyrimidine 5'-nucleotidase (P5N-I). In humans, a lack of this enzyme causes hemolytic anemia with ribosomal structures and trinucleotides retained in the red blood cells (RBCs). Although the protein/nucleotide sequence of P5N-I is known in mammals, the onset and regulation of P5N-I during erythroid maturation is unknown. However, in circulating chicken embryonic RBCs, the enzyme is induced together with carbonic anhydrase (CAII) and 2,3-bisphosphoglycerate (2,3-BPG) by norepinephrine (NE) and adenosine, which are released by the embryo under hypoxic conditions. Here, we present the chicken P5N-I sequence and the gene expression of P5N-I during RBC maturation; the profile of gene expression follows the enzyme activity with a rise between days 13 and 16 of embryonic development. The p5n-I expression is induced (1) in definitive but not primitive RBCs by stimulation of beta-adrenergic/adenosine receptors, and (2) in definitive RBCs by hypoxic incubation of the chicken embryo. Since embryonic RBCs increase their hemoglobin-oxygen affinity by degradation of nucleotides such as uridine triphosphate (UTP) and cytidine triphosphate (CTP), the induction of p5n-I expression can be seen as an adaptive response to hypoxia.

Hypoxia, hormones, and red blood cell function in chick embryos

The red blood cell function of avian embryos is regulated by cAMP. Adenosine A(2A) and beta-adrenergic receptor activation during hypoxic conditions cause changes in the hemoglobin oxygen affinity and CO(2) transport. Furthermore, experimental evidence suggests a general involvement of cAMP in terminal differentiation of avian erythroblasts.

NTP pattern of avian embryonic red cells: role of RNA degradation and AMP deaminase/5'-nucleotidase activity

During terminal erythroid differentiation, degradation of RNA is a potential source for nucleotide triphosphates (NTPs) that act as allosteric effectors of hemoglobin. In this investigation, we assessed the developmental profile of RNA and purine/pyrimidine trinucleotides in circulating embryonic chick red blood cells (RBC). Extensive changes of the NTP pattern are observed which differ significantly from what is observed for adult RBC. The biochemical mechanisms have not been identified yet. Therefore, we studied the role of AMP deaminase and IMP/GMP 5'-nucleotidase, which are key enzymes for the regulation of the purine nucleotide pool. Finally, we tested the effect of major NTPs on the oxygen affinity of embryonic/adult hemoglobin. The results are as follows. 1) Together with ATP, UTP and CTP serve as allosteric effectors of hemoglobin. 2) Degradation of erythroid RNA is apparently a major source for NTPs. 3) Developmental changes of nucleotide content depend on the activities of key enzymes (AMP deaminase, IMP/GMP 5'-nucleotidase, and pyrimidine 5'-nucleotidase). 4) Oxygen-dependent hormonal regulation of AMP deaminase adjusts the red cell ATP concentration and therefore the hemoglobin oxygen affinity.

cAMP and in vivo hypoxia induce tob, ifr1, and fos expression in erythroid cells of the chick embryo

During avian embryonic development, terminal erythroid differentiation occurs in the circulation. Some of the key events, such as the induction of erythroid 2,3-bisphosphoglycerate (2,3-BPG), carbonic anhydrase (CAII), and pyrimidine 5'-nucleotidase (P5N) synthesis are oxygen dependent (Baumann R, Haller EA, Schöning U, and Weber M, Dev Biol 116: 548-551, 1986; Dragon S and Baumann R, Am J Physiol Regulatory Integrative Comp Physiol 280: R870-R878, 2001; Dragon S, Carey C, Martin K, and Baumann R, J Exp Biol 202: 2787-2795, 1999; Dragon S, Glombitza S, Götz R, and Baumann R, Am J Physiol Regulatory Integrative Comp Physiol 271: R982-R989, 1996; Dragon S, Hille R, Götz R, and Baumann R, Blood 91: 3052-3058, 1998; Million D, Zillner P, and Baumann R, Am J Physiol Regulatory Integrative Comp Physiol 261: R1188-R1196, 1991) in an indirect way: hypoxia stimulates the release of norepinephrine (NE)/adenosine into the circulation (Dragon et al., J Exp Biol 202: 2787-2795, 1999; Dragon et al., Am J Physiol Regulatory Integrative Comp Physiol 271: R982-R989, 1996). This leads via erythroid beta-adrenergic/adenosine A(2) receptor activation to a cAMP signal inducing several proteins in a transcription-dependent manner (Dragon et al., Am J Physiol Regulatory Integrative Comp Physiol 271: R982-R989, 1996; Dragon et al., Blood 91: 3052-3058, 1998; Glombitza S, Dragon S, Berghammer M, Pannermayr M, and Baumann R, Am J Physiol Regulatory Integrative Comp Physiol 271: R973-R981, 1996). To understand how the cAMP-dependent processes are initiated, we screened an erythroid cDNA library for cAMP-regulated genes. We detected three genes that were strongly upregulated (>5-fold) by cAMP in definitive and primitive red blood cells. They are homologous to the mammalian Tob, Ifr1, and Fos proteins. In addition, the genes are induced in the intact embryo during short-term hypoxia. Because the genes are regulators of proliferation and differentiation in other cell types, we suggest that cAMP might promote general differentiating processes in erythroid cells, thereby allowing adaptive modulation of the latest steps of erythroid differentiation during developmental hypoxia.

Chronic hypoxia alters the physiological and morphological trajectories of developing chicken embryos

Chicken embryos were chronically exposed to hypoxia (P(O(2)) approximately 110 mmHg) during development, and assessed for detrimental metabolic and morphological effects. Eggs were incubated in one of four groups: control (i.e. 151 mmHg), or treated with continuous 110 mmHg (15% O(2)) during days 1-6 (H1-6), 6-12 (H6-12), or 12-18 (H12-18) with normoxia during the remaining incubation. Metabolism (V(O(2))), body mass, hemoglobin (Hb) and hematocrit (Hct) were measured in embryos on days 12 and 18 of incubation and in day-old hatchlings. Ability to maintain V(O(2)) was acutely measured during a step-wise decrease in P(O(2)) from normoxia to hypoxia (55 mmHg). On day 12, V(O(2)) of H1-6 eggs were significantly lower than in the control and H6-12 eggs. P(crit) in H6-12 eggs was lower than in control and H1-6 eggs. Body mass of H1-6 and H6-12 embryos on day 12 was significantly lower than in control embryos, while in H6-12 embryos, Hct and Hb were higher. On day 18, H6-12 embryos had significantly lower V(O(2)) than control eggs. Body mass of H6-12 and H12-18 embryos was significantly lower than control embryos. Hct and Hb did not differ between treatments. In hatchlings, mass, Hb and Hct had returned to values statistically identical to controls. However, H6-12 embryos had significantly lower V(O(2)). Long-term hypoxia altered V(O(2)) when hypoxic incubation occurred during the middle third of incubation, but not during earlier or later incubation. Thus, chronic hypoxic exposure during critical periods in development altered the developmental physiological trajectories and modified the phenotypes of the developing embryos.

Haemoglobin function in vertebrates: evolutionary changes in cellular regulation in hypoxia

The evolution of erythrocytic hypoxia responses is reviewed by comparing the cellular control of haemoglobin-oxygen affinity in agnathans, teleost fish and terrestrial vertebrates. The most ancient response to hypoxic conditions appears to be an increase in cell volume, which increases the haemoglobin-oxygen affinity in lampreys. In teleost fish, an increase of cell volume in hypoxic conditions is also evident. The volume increase is coupled to an increase in erythrocyte pH. These changes are caused by an adrenergic activation of sodium/proton exchange across the erythrocyte membrane. The mechanism is important in acute hypoxia and is followed by a decrease in cellular adenosine triphosphate (ATP) and guanosine triphosphate (GTP) concentrations in continued hypoxia. In hypoxic bird embryos, the ATP levels are also reduced. The mechanisms by which hypoxia decreases cellular ATP and GTP concentrations remains unknown, although at least in bird embryos cAMP-dependent mechanisms have been implicated. In mammals, hypoxia responses appear to occur mainly via modulation of cellular organic phosphate concentrations. In moderate hypoxia, 2,3-diphosphoglycerate levels are increased as a result of alkalosis caused by increased ventilation.

The potential role of adenosine in the pathophysiology of the insulin resistance syndrome

An increased intracellular availability of the co-enzyme A esters of long-chain fatty acids is thought to underlie many aspects of the insulin resistance syndrome. However, the cause of clustering of a hyperdynamic circulation, sympathetic activation, hypertension, hyperuricaemia, and a raised haematocrit in the insulin resistance syndrome remains to be elucidated. We propose a mechanism that expands the etiological role of long-chain fatty acids. By inhibiting adenine nucleotide translocators, elevated intracellular concentrations of the co-enzyme A esters of long-chain fatty acids impair mitochondrial oxidative phosphorylation. This is expected to result in a chronic systemic increase in extracellular adenosine concentrations. As adenosine stimulates the sympathetic nervous system, induces systemic vasodilatation, stimulates erythropoiesis, and induces renal vasoconstriction with renal sodium retention, increased extracellular ADO concentrations may be the common denominator explaining the above-mentioned and still unexplained phenomena associated with the insulin resistance syndrome. Along the same lines, hyperuricaemia can be explained by the fact that adenosine is broken down to urate and because of increased renal urate retention.

Erythroid carbonic anhydrase and hsp70 expression in chick embryonic development: role of cAMP and hypoxia

In the second half of avian embryonic development cAMP affects major aspects of red blood cell (RBC) function. At day 13/14, progressive developmental hypoxia causes the release of norepinephrine and erythroid beta-adrenergic receptor stimulation initiates the coordinate induction of adaptive key events of erythroid differentiation like carbonic anhydrase (CAII) and 2,3-biphosphoglycerate synthesis. Although cAMP-dependent regulation of CAII protein synthesis has been described in detail, no data exist about the transcriptional regulation in embryonic RBC. Here we report that after day 12 of embryonic development, the caII mRNA is accumulating. Hypoxic incubation at day 10 as well as in vitro incubation of isolated RBC with cAMP-elevating agonists strongly induces erythroid caII expression. The induction of caII occurs fast and does not require new protein synthesis. By screening several late erythroid genes, we could identify hsp70 as another cAMP-induced gene in definitive RBC. Because caII (but not hsp70) is also induced by cAMP in primitive RBC, the signal may regulate key events of late primitive and definitive erythropoiesis.