Hypoxia causes IL-8 secretion, Charcot Leyden crystal formation, and suppression of corticosteroid-induced apoptosis in human eosinophils

BACKGROUND

Inflamed environments are typically hypercellular, rich in pro-inflammatory cytokines, and profoundly hypoxic. While the effects of hypoxia on neutrophil longevity and function have been widely studied, little is known about the consequences of this stimulus on eosinophils.

OBJECTIVE

We sought to investigate the effects of hypoxia on several key aspects of eosinophil biology, namely secretion, survival, and their sensitivity to glucocorticosteroids (GCS), agents that normally induce eosinophil apoptosis.

METHODS

Eosinophils derived from patients with asthma/atopy or healthy controls were incubated under normoxia and hypoxia, with or without glucocorticoids. Activation was measured by flow cytometry, ELISA of cultured supernatants, and F-actin staining; apoptosis and efferocytosis by morphology and flow cytometry; and GCS efficacy by apoptosis assays and qPCR.

RESULTS

Hypoxic incubation (3 kPa) caused (i) stabilization of HIF-2α and up-regulation of hypoxia-regulated genes including BNIP3 (BCL2/adenovirus E1B 19-kDa protein-interacting protein 3) and GLUT1 (glucose transporter 1); (ii) secretion of pre-formed IL-8, and Charcot Leyden crystal (CLC) formation, which was most evident in eosinophils derived from atopic and asthmatic donors; (iii) enhanced F-actin formation; (iv) marked prolongation of eosinophil lifespan (via a NF-κB and Class I PI3-kinase-dependent mechanism); and (v) complete abrogation of the normal pro-apoptotic effect of dexamethasone and fluticasone furoate. This latter effect was evident despite preservation of GCS-mediated gene transactivation under hypoxia.

CONCLUSION AND CLINICAL RELEVANCE

These data indicate that hypoxia promotes an eosinophil pro-inflammatory phenotype by enhancing eosinophil secretory function, delaying constitutive apoptosis, and importantly, antagonizing the normal pro-apoptotic effect of GCS. As eosinophils typically accumulate at sites that are relatively hypoxic, particularly during periods of inflammation, these findings may have important implications to understanding the behaviour of these cells in vivo.

Amblyomma americanum tick saliva insulin-like growth factor binding protein-related protein 1 binds insulin but not insulin-like growth factors

Silencing Amblyomma americanum insulin-like growth factor binding protein-related protein 1 (AamIGFBP-rP1) mRNA prevented ticks from feeding to repletion. In this study, we used recombinant (r)AamIGFBP-rP1 in a series of assays to obtain further insight into the role(s) of this protein in tick feeding regulation. Our results suggest that AamIGFBP-1 is an antigenic protein that is apparently exclusively expressed in salivary glands. We found that both males and females secrete AamIGFBP-rP1 into the host during feeding and confirmed that female ticks secrete this protein from within 24-48 h after attachment. Our data suggest that native AamIGFBP-rP1 is a functional insulin binding protein in that both yeast- and insect cell-expressed rAamIGFBP-rP1 bound insulin, but not insulin-like growth factors. When subjected to anti-blood clotting and platelet aggregation assays, rAamIGFBP-rP1 did not have any effect. Unlike human IGFBP-rP1, which is controlled by trypsinization, rAamIGFBP-rP1 is resistant to digestion, suggesting that the tick protein may not be under mammalian host control at the tick feeding site. The majority of tick-borne pathogens are transmitted 48 h after the tick has attached. Thus, the demonstrated antigenicity and secretion into the host within 24-48 h of the tick starting to feed makes AamIGFBP-rP1 an attractive target for antitick vaccine development.

Effect of self-assembled monolayers on charge injection and transport in poly(3-hexylthiophene)-based field-effect transistors at different channel length scales

Charge injection and transport in bottom-contact regioregular-poly(3-hexylthiophene) (rr-P3HT) based field-effect transistors (FETs), wherein the Au source and drain contacts are modified by self-assembled monolayers (SAMs), is reported at different channel length scales. Ultraviolet photoelectron spectroscopy is used to measure the change in metal work function upon treatment with four SAMs consisting of thiol-adsorbates of different chemical composition. Treatment of FETs with electron-poor (electron-rich) SAMs resulted in an increase (decrease) in contact metal work function because of the electron-withdrawing (-donating) tendency of the polar molecules. The change in metal work function affects charge injection and is reflected in the form of the modulation of the contact resistance, R(C). For example, R(C) decreased to 0.18 MΩ in the case of the (electron-poor) 3,5-bis-trifluoromethylbenzenethiol treated contacts from the value of 0.61 MΩ measured in the case of clean Au-contacts, whereas it increased to 0.97 MΩ in the case of the (electron-rich) 3-thiomethylthiophene treated contacts. Field-effect mobility values are observed to be affected in short-channel devices (<20 μm) but not in long-channel devices. This channel-length-dependent behavior of mobility is attributed to grain-boundary limited charge transport at longer channel lengths in these devices.

Is the molecular composition of K(ATP) channels more complex than originally thought?

ATP-sensitive K+ (K(ATP)) channels are abundantly expressed in the heart and may be involved in the pathogenesis of myocardial ischemia. These channels are heteromultimeric, consisting of four pore-forming subunits (Kir6.1, Kir6.2) and four sulfonylurea receptor (SUR) subunits in an octameric assembly. Conventionally, the molecular composition of K(ATP) channels in cardiomyocytes and pancreatic beta -cells is thought to include the Kir6.2 subunit and either the SUR2A or SUR1 subunits, respectively. However, Kir6.1 mRNA is abundantly expressed in the heart, suggesting that Kir6.1 and Kir6.2 subunits may co-assemble to form functional heteromeric channel complexes. Here we provide two independent lines of evidence that heteromultimerization between Kir6.1 and Kir6.2 subunits is possible in the presence of SUR2A. We generated dominant negative Kir6 subunits by mutating the GFG residues in the channel pore to a series of alanine residues. The Kir6.1-AAA pore mutant subunit suppressed both wt-Kir6.1/SUR2A and wt-Kir6.2/SUR2A currents in transfected HEK293 cells. Similarly, the dominant negative action of Kir6.2-AAA does not discriminate between either of the wild-type subunits, suggesting an interaction between Kir6.1 and Kir6.2 subunits within the same channel complex. Biochemical data support this concept: immunoprecipitation with Kir6.1 antibodies also co-precipitates Kir6.2 subunits and conversely, immunoprecipitation with Kir6.2 antibodies co-precipitates Kir6.1 subunits. Collectively, our data provide direct electrophysiological and biochemical evidence for heteromultimeric assembly between Kir6.1 and Kir6.2. This paradigm has profound implications for understanding the properties of native K(ATP)channels in the heart and other tissues.

Benefits of polyspecific associations for the Goeldi's monkey (Callimico goeldii)

Polyspecific associations are an important component of Callimico goeldii behavior and ecology. On average, Callimico goeldii was found in proximity to or in vocal contact with Saguinus troops (S. fuscicollis and S. labiatus) during 53% of all time intervals sampled. Polyspecific associations varied considerably between seasons, however, with association rates peaking during the wet-season month of February (89%) and declining in the dry season, with the lowest rate (13%) in July. The primary benefits of associations appear to be an increased use of the lower and middle canopy, and an increase in feeding behaviors during the wet season. Thus, Callimico goeldii appear to benefit most from associations during the wet season when fruits are its principal food source. Fruits are eaten more in the forest canopy than in the understory; thus, an increase in height use likely permits an increase in the fruit resources on which Callimico goeldii can forage and feed. In addition, Saguinus groups, with their smaller home ranges, are likely to be more knowledgeable than Callimico goeldii about the location and abundance of ripe fruits in their home ranges. Thus, Callimico goeldii may parasitize Saguinus for their fruit knowledge by following them through their ranges. In the dry season, limited dietary overlap between Callimico goeldii and Saguinus groups is likely to make associations less beneficial for Callimico goeldii as they adopt different foraging and ranging strategies.

Social organization, reproduction and rearing strategies of Callimico goeldii: new clues from the wild

The callitrichines are a specialized radiation of primates that are characterized in part by variable social systems and cooperative infant care. Callimico goeldii, unlike the other callitrichines, have single rather than twin offspring, reducing the need for allocare and permitting synchronous breeding within groups. Low mortality rates among offspring and unstable social groups are suggested to be possible factors that have led to single births among C. goeldii. Single offspring may benefit from greater maternal investment and more frequent food sharing than twin offspring, factors that may help to explain why C. goeldii reaches sexual maturity more rapidly than other callitrichines. In addition, increased breeding opportunities for young C. goeldii females may have selected for rapid maturation rates among this species. Postpartum ovulation and aseasonal resource availability appear to permit females to have biannual birth seasons, further increasing the potential reproductive output.

Amiodarone inhibits cardiac ATP-sensitive potassium channels

INTRODUCTION

ATP-sensitive K+ channels (K(ATP)) are expressed abundantly in cardiovascular tissues. Blocking this channel in experimental models of ischemia can reduce arrhythmias. We investigated the acute effects of amiodarone on the activity of cardiac sarcolemmal K(ATP) channels and their sensitivity to ATP.

METHODS AND RESULTS

Single K(ATP) channel activity was recorded using inside-out patches from rat ventricular myocytes (symmetric 140 mM K+ solutions and a pipette potential of +40 mV). Amiodarone inhibited K(ATP) channel activity in a concentration-dependent manner. After 60 seconds of exposure to amiodarone, the fraction of mean patch current relative to baseline current was 1.0 +/- 0.05 (n = 4), 0.8 +/- 0.07 (n = 4), 0.6 +/- 0.07 (n = 5), and 0.2 +/- 0.05 (n = 7) with 0, 0.1, 1.0, or 10 microM amiodarone, respectively (IC50 = 2.3 microM). ATP sensitivity was greater in the presence of amiodarone (EC50 = 13 +/- 0.2 microM in the presence of 10 microM amiodarone vs 43 +/- 0.1 microM in controls, n = 5; P < 0.05). Kinetic analysis showed that open and short closed intervals (bursting activity) were unchanged by 1 microM amiodarone, whereas interburst closed intervals were prolonged. Amiodarone also inhibited whole cell K(ATP) channel current (activated by 100 microM bimakalim). After a 10-minute application of amiodarone (10 microM), relative current was 0.71 +/- 0.03 vs 0.92 +/- 0.09 in control (P < 0.03).

CONCLUSION

Amiodarone rapidly inhibited K(ATP) channel activity by both promoting channel closure and increasing ATP sensitivity. These actions may contribute to the antiarrhythmic properties of amiodarone.

QLS motif in transmembrane helix VII of the glucose transporter family interacts with the C-1 position of D-glucose and is involved in substrate selection at the exofacial binding site

The liver-type (GLUT2) and brain-type (GLUT3) human facilitative glucose transporters exhibit distinct kinetics (Km values for deoxyglucose transport of approximately 11 mM and approximately 1.5 mM, respectively) and patterns of substrate transport (GLUT2 is capable of D-fructose transport, while GLUT3 is not). Using a range of chimeric glucose transporters comprised of regions of GLUT2 and GLUT3 studied by expression in Xenopus oocytes after microinjection of cRNA, we have proposed that the seventh putative transmembrane helix is intimately involved in the selection of transported substrate and that this region plays an important role in determining the Km for 2-deoxyglucose [Arbuckle, M. I., Kane, S., Porter, L. M., Seatter, M. J., and Gould, G. W. (1996) Biochemistry 35, 16519-16527]. Inspection of the predicted amino acid sequence of this region reveals that GLUTs 1, 3, and 4 (high-affinity glucose transporters) contain a conserved QLS motif in this helix (residues 277-279 in human GLUT3). In the glucose/fructose transporter (GLUT2) this motif is replaced by HVA. To study the role of the QLS motif in substrate selection, we have engineered substitutions in this region between GLUT2 and GLUT3. GLUT3 (QLS > HVA) exhibits a Km for deoxyglucose transport identical to that of native GLUT3 but increased sensitivity for inhibition of deoxyglucose transport by D-fructose. However, unlike native GLUT3, this species is capable of transporting D-fructose. Compared to wild-type GLUT2, GLUT2 (HVA > QLS) exhibits a lower Km for deoxyglucose transport (approximately 3 mM vs approximately 11 mM), the ability to transport D-fructose is reduced, and D-fructose is a less efficient inhibitor of deoxyglucose transport. Analysis of the ability of a range of glucose epimers and analogues to inhibit transport by these species suggests that the QLS motif interacts with the incoming D-glucose at the C-1 position; this may be a key interaction in the high-affinity recognition of the transported substrate. We further argue that this interaction acts as a molecular filter that is involved in the selection of the transported substrate.

Structure-function studies of the brain-type glucose transporter, GLUT3: alanine-scanning mutagenesis of putative transmembrane helix VIII and an investigation of the role of proline residues in transport catalysis

The brain-type glucose transporter (GLUT3) is a high-affinity transporter for D-glucose and D-galactose and is a member of a family of mammalian sugar transporters, each of which are proposed to adopt a secondary structure containing 12 transmembrane helices. In an effort to understand structure-function relationships within such transporters, we have employed alanine-scanning mutagenesis to examine the functional importance of each residue within putative transmembrane helix VIII of the human GLUT3 isoform. Each residue in this helix was replaced individually with alanine, and the functional properties of the mutants were examined by microinjection of in vitro transcribed mRNA into Xenopus oocytes. We show that substitution of residues 305, 306, 308-314, and 316-325 with alanine had minimal effect on the functional activity of the transporter, as determined by measurement of the Km for deoxyglucose transport and the Ki for maltose. In contrast, Asn-315 > Ala-315 exhibited a significant increase in the Km for deoxyglucose independently of any effect on the Ki for maltose. This data suggests that, despite the strong sequence conservation in this helix among the GLUT family, no individual residue is absolutely required for transport catalysis by this isoform. We have also examined the role of proline residues in transport catalysis mediated by GLUT3. Substitution of Pro-203 (helix VI), Pro-206, Pro-209 (cytoplasmic loop between helices VI and VII), Pro-381, Pro-383 and Pro-385 (helix X), Pro-399 (intracellular loop between helices X and XI), or Pro-451 (in the carboxy terminus, close to the end of helix XII) with alanine did not change the Km for deoxyglucose transport for any mutant. However, both Pro-381 and Pro-385 when mutated to alanine exhibited a reduction in the Ki for cytochalasin B. In addition, the Ki for maltose inhibition of deoxyglucose transport was increased for mutants Pro206Ala, Pro381Ala, Pro383Ala, and Pro451Ala. These results will be discussed in terms of proposed structural models for the transporters.

Structure-function analysis of liver-type (GLUT2) and brain-type (GLUT3) glucose transporters: expression of chimeric transporters in Xenopus oocytes suggests an important role for putative transmembrane helix 7 in determining substrate selectivity

The liver-type (GLUT2) and brain-type (GLUT3) human facilitative glucose transporters exhibit distinct kinetics (K(m) values for deoxyglucose transport of 11.2 +/- 1.1 and 1.4 +/- 0.06 mM, respectively) and patterns of substrate transport (GLUT2 is capable of D-fructose transport, GLUT3 is not) [Gould, G. W., Thomas, H. M., Jess, T. J., & Bell, G. I. (1991) Biochemistry 30, 5139-5145]. We have generated a range of chimeric glucose transporters composed of regions of GLUT2 and GLUT3 with a view to identifying the regions of the transporter which are involved in substrate recognition and binding. The functional characteristics of these chimeras were determined by expression in Xenopus oocytes after microinjection of cRNA. Replacement of the region from the start of putative transmembrane helix 7 to the C-terminus of GLUT3 with the corresponding region from GLUT2 results in a chimera with the ability to transport fructose and exhibits a K(m) for 2-deoxyglucose transport of close to that observed for wild-type GLUT2 (8.3 +/- 0.3 mM compared to 11.2 +/- 1.1 mM). Replacement of the region in GLUT3 from the end of helix 7 to the C-terminus with the corresponding region from GLUT2 resulted in a species which was unable to transport fructose and whose K(m) for 2-deoxyglucose was indistinguishable from wild-type GLUT3. We have determined the affinity for 2-deoxyglucose, D-fructose, and D-galactose of these and other chimeras. In addition, the Ki for maltose, a competitive inhibitor of 2-deoxyglucose transport, which binds to the exofacial sugar binding site was determined for these chimeras. The results obtained support a model in which the seventh putative transmembrane-spanning helix is intimately involved in the selection of transported substrate and in which this region plays an important role in determining the K(m) for 2-deoxyglucose. Additional data is presented which suggests that a region between the end of putative transmembrane helix 7 and the end of helix 10, together with sequences in the N-terminal half of the protein may also participate in substrate recognition and transport catalysis.

Inhibition of glyceraldehyde 3-phosphate dehydrogenase in boar spermatozoa by bromohydroxypropanone

In the presence of 3-bromo-1-hydroxypropanone (BOP), cauda epididymal sperm obtained from mature boars produced a carbonyl compound which is assumed to be (S)-3-bromolactaldehyde. Glyceraldehyde 3-phosphate dehydrogenase was rapidly inhibited which resulted in the accumulation of dihydroxyacetone phosphate and fructose-1,6-bisphosphate, and no accumulation of lactate when fructose was the substrate. The energy charge potential of the cells declined in the presence of BOP when either fructose or glycerol were substrates. It is suggested that BOP is transformed into (S)-3-bromolactaldehyde, which is the actual inhibitor of glyceraldehyde 3-phosphate dehydrogenase, thus demonstrating BOP to be the first brominated chemical to have an anti-glycolytic action on mature sperm in vitro.

Inhibition of glycolysis in boar spermatozoa by alpha-chlorohydrin phosphate appears to be mediated by phosphatase activity

(R,S)-alpha-chlorohydrin-1-phosphate, previously shown to have no anti-glycolytic activity on mature boar sperm in vitro, is a substrate for acid and/or neutral phosphatase(s) that are associated with washed sperm. The high phosphatase activity hydrolyses the ester to alpha-chlorohydrin which undergoes oxidation to (S)-3-chlorolactaldehyde, a specific inhibitor of sperm glyceraldehyde-3-phosphate dehydrogenase and triosephosphate isomerase, thereby exhibiting an anti-glycolytic action.