Acute exercise-induced release of innate immune proteins via small extracellular vesicles changes with aerobic fitness and age

AIM

Physical exercise triggers the secretion of small extracellular vesicles (sEVs) into the circulation in humans, enabling signalling crosstalk between tissues. Exercise-derived EVs and their cargo have been proposed to mediate adaptations to exercise; however, our understanding of how exercise-derived EV protein cargo is modulated by factors such as aerobic fitness and age of an individual is currently unknown. Here, we examined the circulating sEV proteome following aerobic exercise in healthy males of different ages and aerobic fitness to understand exercise-induced EV response during the aging process.

METHODS

Twenty-eight healthy men completed a bout of 20-min cycling exercise at 70% estimated VO2peak . Small EVs were isolated from blood samples collected before and immediately after exercise, and then quantified using particle analysis and Western blotting. Small EV proteome was examined using quantitative proteomic analysis.

RESULTS

We identified a significant increase in 13 proteins in small plasma EVs following moderate-to-vigorous intensity exercise. We observed distinct changes in sEV proteome after exercise in young, mature, unfit, and fit individuals, highlighting the impact of aerobic fitness and age on sEV protein secretion. Functional enrichment and pathway analysis identified that the majority of the significantly altered sEV proteins are associated with the innate immune system, including proteins known to be damage-associated molecular patterns (DAMPs).

CONCLUSION

Together, our findings suggest that exercise-evoked acute stress can positively challenge the innate immune system through the release of signalling molecules such as DAMPs in sEVs, proposing a novel EV-based mechanism for moderate-to-vigorous intensity exercise in immune surveillance pathways.

First-in-human clinical trial of allogeneic, platelet-derived extracellular vesicles as a potential therapeutic for delayed wound healing

The release of growth factors, cytokines and extracellular matrix modifiers by activated platelets is an important step in the process of healthy wound healing. Extracellular vesicles (EVs) released by activated platelets carry this bioactive cargo in an enriched form, and may therefore represent a potential therapeutic for the treatment of delayed wound healing, such as chronic wounds. While EVs show great promise in regenerative medicine, their production at clinical scale remains a critical challenge and their tolerability in humans is still to be fully established. In this work, we demonstrate that Ligand-based Exosome Affinity Purification (LEAP) chromatography can successfully isolate platelet EVs (pEVs) of clinical grade from activated platelets, which retain the regenerative properties of the parent cell. LEAP-isolated pEVs display the expected biophysical features of EV populations and transport essential proteins in wound healing processes, including insulin growth factor (IGF) and transforming growth factor beta (TGF-ß). In vitro studies show that pEVs induce proliferation and migration of dermal fibroblasts and increase dermal endothelial cells' angiogenic potential, demonstrating their wound healing potential. pEV treatment activates the ERK and Akt signalling pathways within recipient cells. In a first-in-human, double-blind, placebo-controlled, phase I clinical trial of healthy volunteer adults, designed primarily to assess safety in the context of wound healing, we demonstrate that injections of LEAP-purified pEVs in formulation buffer are safe and well tolerated (Plexoval II study, ACTRN12620000944932). As a secondary objective, biological activity in the context of wound healing rate was assessed. In this cohort of healthy participants, in which the wound bed would not be expected to be deficient in the bioactive cargo that pEVs carry, all wounds healed rapidly and completely and no difference in time to wound closure of the treated and untreated wounds was observed at the single dose tested. The outcomes of this study evidence that pEVs manufactured through the LEAP process can be injected safely in humans as a potential wound healing treatment, and warrant further study in clinical trials designed expressly to assess therapeutic efficacy in patients with delayed or disrupted wound healing.

Decidual mesenchymal stem/stromal cells from preeclamptic patients secrete endoglin, which at high levels inhibits endothelial cell attachment invitro

INTRODUCTION

In preeclampsia (PE), inadequate remodelling of spiral arterioles in the decidua basalis causes oxidative stress and subsequent increased release of antiangiogenic soluble endoglin (sENG) into the maternal circulation. Decidual mesenchymal stem/stromal cells (DMSCs) reside adjacent to endothelial cells in this vascular niche. Surprisingly, DMSCs express membrane-bound ENG (CD105). PE-affected DMSCs (PE-DMSCs) are abnormal and due to reduced extravillous invasion, more of them are present, but the significance of this is not known.

METHODS

DMSCs were isolated and characterised from normotensive control and severe-PE placentae. Extracellular vesicle (EV) types, shed microvesicles (sMV) and exosomes, were isolated from DMSC conditioned media (DMSC_CM), respectively. Secretion of ENG by DMSCs was assessed by ELISA of DMSC_CM, with and without EV depletion. The effects of reducing ENG concentration, by blocking antibody, on human umbilical vein endothelial cell (HUVEC) attachment were assessed by xCELLigence real-time functional assays.

RESULTS

ENG was detected in DMSC_CM and these levels significantly decreased when depleted of exosomes and sMV. There was no significant difference in the amount of ENG secreted by control DMSCs and PE-DMSCs. Blocking ENG in concentrated DMSC_CM, used to treat HUVECs, improved endothelial cell attachment.

DISCUSSION

In normotensive pregnancies, DMSC secretion of ENG likely has a beneficial effect on endothelial cells. However, in PE pregnancies, shallow invasion of the spiral arterioles exposes more PE-DMSC derived sources of ENG (soluble and EV). The presence of these PE-DMSCs in the vascular niche contributes to endothelial cell dysfunction.

Exercise increases the release of NAMPT in extracellular vesicles and alters NAD+ activity in recipient cells

Aging is associated with a loss of metabolic homeostasis, with cofactors such as nicotinamide adenine dinucleotide (NAD⁺) declining over time. The decrease in NAD⁺ production has been linked to the age‐related loss of circulating extracellular nicotinamide phosphoribosyltransferase (eNAMPT), the rate‐limiting enzyme in the NAD⁺ biosynthetic pathway. eNAMPT is found almost exclusively in extracellular vesicles (EVs), providing a mechanism for the distribution of the enzyme in different tissues. Currently, the physiological cause for the release of eNAMPT is unknown, and how it may be affected by age and physical exercise. Here, we show that release of small EVs into the bloodstream is stimulated following moderate intensity exercise in humans. Exercise also increased the eNAMPT content in EVs, most prominently in young individuals with higher aerobic fitness. Both mature fit and young unfit individuals exhibited a limited increase in EV‐eNAMPT release following exercise, indicating that this mechanism is related to both the age and physical fitness of a person. Notably, unfit mature individuals were unable to increase the release of eNAMPT in EVs after exercise, suggesting that lower fitness levels and aging attenuate this important signalling mechanism in the body. EVs isolated from exercising humans containing eNAMPT were able to alter the abundance of NAD⁺ and SIRT1 activity in recipient cells compared to pre‐exercise EVs, indicating a pathway for inter‐tissue signalling promoted through exercise. Our results suggest a mechanism to limit age‐related NAD⁺ decline, through the systemic delivery of eNAMPT via EVs released during exercise.

Functional changes in decidual mesenchymal stem/stromal cells are associated with spontaneous onset of labour

Ageing and parturition share common pathways, but their relationship remains poorly understood. Decidual cells undergo ageing as parturition approaches term, and these age-related changes may trigger labour. Mesenchymal stem/stromal cells (MSCs) are the predominant stem cell type in the decidua. Stem cell exhaustion is a hallmark of ageing, and thus ageing of decidual MSCs (DMSCs) may contribute to the functional changes in decidual tissue required for term spontaneous labour. Here, we determine whether DMSCs from patients undergoing spontaneous onset of labour (SOL-DMSCs) show evidence of ageing-related functional changes compared with those from patients not in labour (NIL-DMSCs), undergoing Caesarean section. Placentae were collected from term (37-40 weeks of gestation), SOL (n = 18) and NIL (n = 17) healthy patients. DMSCs were isolated from the decidua basalis that remained attached to the placenta after delivery. DMSCs displayed stem cell-like properties and were of maternal origin. Important cell properties and lipid profiles were assessed and compared between SOL- and NIL-DMSCs. SOL-DMSCs showed reduced proliferation and increased lipid peroxidation, migration, necrosis, mitochondrial apoptosis, IL-6 production and p38 MAPK levels compared with NIL-DMSCs (P < 0.05). SOL- and NIL-DMSCs also showed significant differences in lipid profiles in various phospholipids (phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylserine), sphingolipids (ceramide, sphingomyelin), triglycerides and acyl carnitine (P < 0.05). Overall, SOL-DMSCs had altered lipid profiles compared with NIL-DMSCs. In conclusion, SOL-DMSCs showed evidence of ageing-related reduced functionality, accumulation of cellular damage and changes in lipid profiles compared with NIL-DMSCs. These changes may be associated with term spontaneous labour.

Aromatic residues in the C-terminal helix of human apoC-I mediate phospholipid interactions and particle morphology

Human apolipoprotein C-I (apoC-I) is an exchangeable apolipoprotein that binds to lipoprotein particles in vivo. In this study, we employed a LC-MS/MS assay to demonstrate that residues 38-51 of apoC-I are significantly protected from proteolysis in the presence of 1,2-dimyristoyl-3-sn-glycero-phosphocholine (DMPC). This suggests that the key lipid-binding determinants of apoC-I are located in the C-terminal region, which includes F42 and F46. To test this, we generated site-directed mutants substituting F42 and F46 for glycine or alanine. In contrast to wild-type apoC-I (WT), which binds DMPC vesicles with an apparent Kd [Kd(app)] of 0.89 microM, apoC-I(F42A) and apoC-I(F46A) possess 2-fold weaker affinities for DMPC with Kd(app) of 1.52 microM and 1.58 microM, respectively. However, apoC-I(F46G), apoC-I(F42A/F46A), apoC-I(F42G), and apoC-I(F42G/F46G) bind significantly weaker to DMPC with Kd(app) of 2.24 microM, 3.07 microM, 4.24 microM, and 10.1 microM, respectively. Sedimentation velocity studies subsequently show that the protein/DMPC complexes formed by these apoC-I mutants sediment at 6.5S, 6.7S, 6.5S, and 8.0S, respectively. This is compared with 5.0S for WT apoC-I, suggesting the shape of the particles was different. Transmission electron microscopy confirmed this assertion, demonstrating that WT forms discoidal complexes with a length-to-width ratio of 2.57, compared with 1.92, 2.01, 2.16, and 1.75 for apoC-I(F42G), apoC-I(F46G), apoC-I(F42A/F46A), and apoC-I(F42G/F46G), respectively. Our study demonstrates that the C-terminal amphipathic alpha-helix of human apoC-I contains the major lipid-binding determinants, including important aromatic residues F42 and F46, which we show play a critical role in stabilizing the structure of apoC-I, mediating phospholipid interactions, and promoting discoidal particle morphology.

Electron capture dissociation of complexes of diacylglycerophosphocholine and divalent metal ions: competition between charge reduction and radical induced phospholipid fragmentation

Divalent metal complexes of phosphocholines, [Metal(II)(L)(n)](2+) (where Metal=Cu(2+), Co(2+), Mg(2+), and Ca(2+), L=1,2-dihexanoyl-sn-glycero-3-phosphocholine [6:0/6:0GPCho] and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine [16:0/18:1GPCho] and n=2-5), were formed upon electrospray ionization mass spectrometry (ESI/MS) of 8 mM solution of phosphocholine (L) with 4 mM metal salt (Metal). The electron capture dissociation (ECD) reactions of these [Metal(II)(L)(n)](2+) complexes were examined via Fourier-transform ion-cyclotron resonance mass spectrometry. A rich and complex chemistry was observed, including charge reduction and fragmentation involving losses of a methyl radical, trimethylamine, and the acyl chains. The predominant reaction channel was dependent on the size (n) of the complex, the metal and ligand used, and the size of the acyl chain. Thus charge reduction dominates the ECD spectra of the larger phosphocholine, 16:0/18:1GPCho, but is largely absent in the smaller 6:0/6:0GPCho. For complexes of 16:0/18:1GPCho, n=4-5, fragmentation from the head group mainly occurs via loss of the methyl radical and trimethylamine. At n=3, the relative abundance of fragments due to loss of acyl chain radicals increases. The abundances of ions arising from these radical losses increase further for the n=2 complexes, thereby providing information on the composition and position of the 16:0 and 18:1 acyl groups. Thus ECD of metal complexes provides structurally useful information on the phosphocholine, including the nature of the head group, the acyl chains, and the positions of the acyl chains.

Detection of the abundance of diacylglycerol and triacylglycerol molecular species in cells using neutral loss mass spectrometry

Triacylglycerols (TAGs) are neutral lipids present in all mammalian cells as energy reserves, and diacylglycerols (DAGs) are present as intermediates in phospholipid biosynthesis and as signaling molecules. The molecular species of TAGs and DAGs present in mammalian cells are quite complex, and previous investigations revealed multiple isobaric species having molecular weights at virtually every even mass between 600 and 900 Da, making it difficult to assess changes of individual molecular species after cell activation. A method has been developed, using tandem MS and neutral loss scanning, to quantitatively analyze changes in those glyceryl ester molecular species containing identical fatty acyl groups. This was carried out by neutral loss scanning of 18 common fatty acyl groups where the neutral loss corresponded to the free carboxylic acid plus NH(3). Deuterium-labeled internal standards were used to normalize the signal for each nominal [M+NH(4)](+) ion undergoing this neutral loss reaction. This method was applied in studies of TAGs in RAW 264.7 cells treated with the toll-like receptor 4 ligand Kdo(2)-lipid A. A 50:1-TAG containing 18:1 was found to increase significantly over a 24-h time course after Kdo(2)-lipid A exposure, whereas an isobaric 50:1-TAG containing 16:1 did not change relative to controls.

Size matters! Fragmentation chemistry of [Cu(L)n]2+ complexes of diacylglycerophosphocholines as a function of coordination number (n = 2-7)

[Cu(L)(n)](2+) complexes of 1,2-dihexanoyl-sn-glycero-3-phosphocholine (L = D6PC) are formed upon electrospray ionization mass spectrometry (ESI-MS) of an 8 mM solution of D6PC with 4 mM CuCl(2) in 10 mM ammonium acetate buffer, pH 6.1. The collision-induced dissociation (CID) reactions of the [Cu(L)(n)](2+) complexes were examined in a linear ion trap mass spectrometer. A rich fragmentation chemistry was observed, including: loss of a neutral ligand; intermolecular ligand-ligand S(N)2 methylation; metal ion induced ligand fragmentation via carboxylate abstraction; and phosphate abstraction. The dominant reaction channel depends on the size (n) of the complex. Thus loss of neutral ligand(s) is the sole reaction channel for n = 5-7. At n = 4, S(N)2 methylation and carboxylate abstraction start to compete with neutral ligand loss. At n = 2 the carboxylate abstraction and phosphate abstraction reactions dominate the CID spectrum. The carboxylate abstraction and phosphate abstraction reactions are likely to be driven via neighboring group pathways. PM3 calculations, carried out to compare competing neighboring pathways based on the relative stabilities of the product ions, suggest a preference for five-membered ring formation for ligand fragmentation involving both carboxylate and phosphate abstraction.

Letter: collision-induced dissociation of [metal(L)(2)](2+) complexes (metal = Cu, Ca and Mg) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine allows distinction of the acyl groups at the sn1 and sn2 positions

The collision induced dissociation (CID) spectra of the divalent metal complexes of 1-palmitoyl-2-oleoyl-sn- glycero-3-phosphocholine, [Metal(lI)(L)(2)](2+) (where metal = Cu(2+), Mg(2+) and Ca(2+), L = [16:0/18:1GPCho]), formed by electrospray ionization, reveal interesting metal dependant fragmentation chemistry. Six main classes of reaction are observed corresponding to: two competing carboxylate abstraction pathways (from the sn1 and sn2 positions); phosphate abstraction; competing losses of the two different carboxylic acids from the sn1 and sn2 positions; loss of a protonated ligand, [L + H](+). The relative ratios of the competing carboxylate abstraction reactions are dependant on the metal, with the Cu and Ca complexes favouring the abstraction of the larger carboxylate (18:1) and the Mg complex favoring the abstraction of the smaller carboxylate (16:0).

Sources of artefacts in the electrospray ionization mass spectra of saturated diacylglycerophosphocholines: from condensed phase hydrolysis reactions through to gas phase intercluster reactions

The mass spectra of diacylglycerophosphocholine phospholipids comprised of saturated fatty acids (1,2-dipentanoyl-sn-glycero-3-phosphocholine (D5PC); 1,2-dihexanoyl-sn-glycero-3-phosphocholine (D6PC), and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (D14PC)) are sensitive to the electrospray ionization (ESI) conditions. When fresh solutions of phospholipid in 10 mM ammonium acetate are subjected to ESI, protonated oligomeric clusters, [DxPCn + H]+ (x = 5, 6, and 14) are observed in the following different types of mass spectrometers: 3D-quadrupole ion trap; linear ion trap, and triple quadrupole. The formation of the protonated cluster ions is not unique to the ion trap instruments, although they tend to be more abundant in these instruments. As the ESI solutions age, new ions are observed, which correspond to acid-catalyzed solution phase deacylation reactions. The collision induced dissociation fragmentation reactions of the oligomer cluster ions exhibit a distinct dependence on the cluster size, with the larger clusters (n > 2) simply fragmenting via the loss of lipid monomers. In contrast, the fragmentation of the dimeric cluster ion is unique, resulting in a number of additional reactions including covalent bond formation via intermolecular cluster SN2 reactions and SN2 transfer of a methyl group. The nature of the charge has a significant role in the formation of products via these intermolecular cluster reactions. Changing the head group to phosphoethanolamine "switches off" the SN2 reactions, while changing the cation from a proton to either a sodium or a potassium ion, diminishes the intermolecular reactions relative to monomer loss. Semi empirical PM3 calculations on [D6PC2 + H]+ suggest that the SN2 reactions are thermodynamically favored over simple monomer loss. These results have important implications in the field of lipidomics.

Gas-Phase Synthesis and Reactivity of the Organomagnesates [CH3MgL2]- (L = Cl and O2CCH3): From Ligand Effects to Catalysis

Multistage mass spectrometry experiments combined with density functional theory (DFT) calculations were used to examine the gas-phase synthesis and ion-molecule reactions of the organomagnesates [CH(3)MgL(2)](-) (L = Cl and O(2)CCH(3)). Neutral species containing an acidic proton (HX) react with the [CH(3)MgL(2)](-) ions via addition with concomitant elimination of methane to form [XMgL(2)](-) ions. Kinetic measurements combined with DFT calculations revealed reduced reactivity of [CH(3)Mg(O(2)CCH(3))(2)](-) toward water, caused by the bidentate binding mode of acetate, which induces overcrowding of the Mg coordination sphere. The [CH(3)MgL(2)](-) ions reacted with (i) aldehydes with enolizable protons via enolization rather than the Grignard reaction and (ii) CH(3)CO(2)H to complete a catalytic cycle for the decarboxylation of acetic acid. Other electrophilic reagents such as pivaldehyde, benzaldehyde, methyl iodide, and trimethylborate are unreactive. DFT calculations on the competition between enolization and the Grignard reaction for [CH(3)MgCl(2)](-) ions reacting with acetaldehyde suggest that while the latter has a smaller barrier, it is entropically disfavored.

Dimethyl Cuprate Undergoes C−C Bond Coupling with Methyliodide in the Gas Phase but Dimethyl Argenate Does Not

Multistage mass spectrometry experiments have been used to synthesize and study the reactions of (CH3)2M-(M = Cu and Ag) with methyl iodide in the gas phase. While the dimethylcuprate ion (M = Cu) reacts with CH3I via C-C bond cross coupling, its silver congener is unreactive. The experimental results are consistent with MP2/6-31++G** ab initio calculations, which reveal that the preferred mechanism for Cu involves the formation of a T-shaped Cu transition state. [reaction: see text]

The effects of deafferentation and exogenous NGF on neurotrophins and neurotrophin receptor mRNA expression in the adult superior cervical ganglion

Levels of nerve growth factor (NGF) and neurotrophin-3 (NT-3) protein and neurotrophin receptor mRNA in adult sympathetic neurons were investigated following surgical removal of preganglionic input and/or in vivo administration of NGF. Expression of trkC and p75, but not trkA, was significantly decreased following a 3-week deafferentation of the superior cervical ganglion (SCG). Protein levels of NGF and NT-3 in the SCG were unchanged by deafferentation. A 2-week intracerebroventricular infusion of NGF without deafferentation resulted in enhanced mRNA levels of trkA, trkC, and p75 as well as significantly increased NGF and NT-3 protein in the SCG. When NGF infusion followed deafferentation, both trkA and p75 showed significant increases while trkC levels were similar to control values. NGF protein was not increased in the SCG when deafferentation preceded exogenous NGF, yet NT-3 was elevated and levels were similar to cases receiving NGF infusion only. These results support a role for preganglionic input in trkC and p75 expression in adult sympathetic neurons. The increased levels of NT-3 protein and trkC gene expression observed following NGF infusion suggest that NGF influences NT-3 regulation in adult sympathetic neurons. In addition, the present findings provide evidence that, when preganglionic input is removed prior to the NGF infusion, NT-3 effectively competes with NGF for trkA binding. Taken together, we propose that NT-3 may play a role in the robust sprouting of sympathetic cerebrovascular axons previously observed following NGF administration, particularly when deafferentation precedes the NGF infusion period.

Gas phase ion chemistry of charged silver(i) adenine ions via multistage mass spectrometry experiments and DFT calculationsGas phase ion chemistry of biomolecules, Part 38. For part 37, see ref. 1.Electronic supplementary information available: Tables (energies and bond lengths) and figures (MS spectra and optimised structures). See http://www.rsc.org/suppdata/dt/b3/b311656e/

Electrospray ionization (ESI) of solutions containing adenine and AgNO(3) yields polymeric [Ad(x)+ Ag(y)-zH]((y-z)+) species. Density functional theory (DFT) calculations have been used to examine potential structures for several of the smaller ions while multistage mass spectrometry experiments have been used to probe their unimolecular reactivity (via collision-induced dissociation (CID)) and bimolecular reactivity (via ion-molecule reactions with the neutral reagents acetonitrile, methanol, butylamine and pyridine). DFT calculations of neutral adenine tautomers and their silver ion adducts provide insights into the binding modes of adenine. We find that the most stable [Ad + Ag](+) ion does not correspond to the most stable neutral adenine tautomer, consistent with previous studies that have shown that transition metal ions can stabilize rare tautomeric forms of nucleobases. Both the charge and the stoichiometry of the [Ad(x)+ Ag(y)-zH]((y-z)+) complexes play pivotal roles in directing the types of fragmentation and ion-molecule reactions observed. Thus, [Ad(2)+ Ag(2)](2+) is observed to dissociate to [Ad + Ag](+) and to react with butylamine via proton transfer, while [Ad(2)+ Ag(2)- H](+) fragments via loss of neutral adenine to form the [Ad + Ag(2)- H](+) ion and does not undergo proton transfer to butylamine. DFT calculations on several isomeric [Ad(2)+ Ag(2)](2+) ions suggest that planar centrosymmetric cations, in which two adjacent silver atoms are bridged by two N7H adenine tautomers via N(3),N(9)-bidentate interactions, are the most stable. The [Ad + Ag(2)-H](+) ion adds two neutral reagents in ion-molecule reactions, consistent with the presence of two vacant coordination sites. It undergoes a silver atom loss to form the [Ad + Ag - H](+) radical cation, which in turn fragments quite differently to the even electron [Ad + Ag](+) ion. Several other pairs of radical cation/even electron adenine-silver complexes were also found to undergo different fragmentation reactions.

Formation of apatite layers on modified canasite glass-ceramics in simulated body fluid

Canasite glass-ceramics were modified by either increasing the concentration of calcium in the glass, or by the addition of P2O5. Samples of these novel materials were placed in simulated body fluid (SBF), along with a control material (commercial canasite), for periods ranging from 12 h to 28 days. After immersion, surface analysis was performed using thin film X-ray diffraction, Fourier transform infrared reflection spectroscopy, and scanning electron microscopy equipped with energy dispersive X-ray detectors. The concentrations of sodium, potassium, calcium, silicon, and phosphorus in the SBF solution were measured using inductively coupled plasma emission spectroscopy. No apatite was detected on the surface of commercial canasite, even after 28 days of immersion in SBF. A crystalline apatite layer was formed on the surface of a P2O5-containing canasite after 5 days, and after 3 days for calcium-enriched canasite. Ion release data suggested that the mechanism for apatite deposition was different for P2O5 and non-P2O5-containing glass-ceramics.

Targeted transgenic expression of beta(2)-adrenergic receptors to type II cells increases alveolar fluid clearance

Clearance of edema fluid from the alveolar space can be enhanced by endogenous and exogenous beta-agonists. To selectively delineate the effects of alveolar type II (ATII) cell beta(2)-adrenergic receptors (beta(2)-ARs) on alveolar fluid clearance (AFC), we generated transgenic (TG) mice that overexpressed the human beta(2)-AR under control of the rat surfactant protein C promoter. In situ hybridization showed that transgene expression was consistent with the distribution of ATII cells. TG mice expressed 4.8-fold greater beta(2)-ARs than nontransgenic (NTG) mice (939 +/- 113 vs. 194 +/- 18 fmol/mg protein; P < 0.001). Basal AFC in TG mice was approximately 40% greater than that in untreated NTG mice (15 +/- 1.4 vs. 10.9 +/- 0.6%; P < 0.005) and approached that of NTG mice treated with the beta-agonist formoterol (19.8 +/- 2.2%; P = not significant). Adrenalectomy decreased basal AFC in TG mice to 9.7 +/- 0.5% but had no effect on NTG mice (11.5 +/- 1.0%). Na(+)-K(+)-ATPase alpha(1)-isoform expression was unchanged, whereas alpha(2)-isoform expression was approximately 80% greater in the TG mice. These findings show that beta(2)-AR overexpression can be an effective means to increase AFC in the absence of exogenous agonists and that AFC can be stimulated by activation of beta(2)-ARs specifically expressed on ATII cells.

The alpha(1)- and alpha(2)-isoforms of Na-K-ATPase play different roles in skeletal muscle contractility

The Na-K-ATPase, which maintains the Na(+) and K(+) gradients across the plasma membrane, can play a major role in modulation of skeletal muscle contractility. Although both alpha(1)- and alpha(2)-isoforms of the Na-K-ATPase are expressed in skeletal muscle, the physiological significance of these isoforms in contractility is not known. Evaluation of the contractile parameters of mouse extensor digitorum longus (EDL) was carried out using gene-targeted mice lacking one copy of either the alpha(1)- or alpha(2)-isoform gene of the Na-K-ATPase. The EDL muscles from heterozygous mice contain approximately one-half of the alpha(1)- or alpha(2)-isoform, respectively, which permits differentiation of the functional roles of these isoforms. EDL from the alpha(1)(+/-) mouse shows lower force compared with wild type, whereas that from the alpha(2)(+/-) mouse shows greater force. The different functional roles of these two isoforms are further demonstrated because inhibition of the alpha(2)-isoform with ouabain increases contractility of alpha(1)(+/-) EDL. These results demonstrate that the Na-K-ATPase alpha(1)- and alpha(2)-isoforms may play different roles in skeletal muscle contraction.

The enhanced contractility of the phospholamban-deficient mouse heart persists with aging

J. P. Slack, I. L. Grupp, R. Dash, D. Holder, A. Schmidt, M. J. Gerst, T. Tamura, C. Tilgmann, P. F. James, R. Johnson, A. M. Gerdes and E. G. Kranias. The Enhanced Contractility of the Phospholamban-deficient Mouse Heart Persists with Aging. Journal of Molecular and Cellular Cardiology (2001) 33, 1031-1040. Phospholamban ablation in the mouse is associated with significant increases in cardiac contractility. To determine whether this hyperdynamic function persists through the aging process, a longitudinal examination of age-matched phospholamban-deficient and wild-type mice was employed. Kaplan-Meier survival curves indicated no significant differences between phospholamban-deficient and wild-type mice over the first year. Examination of cardiac function revealed significant increases in the rates of contraction (+dP/dt) and relaxation (-dP/dt) in phospholamban-deficient hearts compared with their wild-type counterparts at 3, 6, 12, 18 and 24 months of age. Quantitative immunoblotting indicated that the expression levels of the sarcoplasmic reticulum Ca(2+)-ATPase were not altered in wild-type hearts, while they were significantly decreased at 12 months (40%) and 18 months (20%) in phospholamban-deficient hearts. These findings on the persistence of hyperdynamic cardiac function over the long term suggest that phospholamban may constitute an important target for treatment in heart disease.

Sperm motility is dependent on a unique isoform of the Na,K-ATPase

The Na,K-ATPase, a member of the P-type ATPases, is composed of two subunits, alpha and beta, and is responsible for translocating Na(+) out of the cell and K(+) into the cell using the energy of hydrolysis of one molecule of ATP. The electrochemical gradient it generates is necessary for many cellular functions, including establishment of the plasma membrane potential and transport of sugars and ions in and out of the cell. Families of isoforms for both the alpha and beta subunits have been identified, and specific functional roles for individual isoforms are just beginning to emerge. The alpha4 isoform is the most recently identified Na, K-ATPase alpha isoform, and its expression has been found only in testis. Here we show that expression of the alpha4 isoform in testis is localized to spermatozoa and that inhibition of this isoform alone eliminates sperm motility. These data describe for the first time a biological function for the alpha4 isoform of the Na,K-ATPase, revealing a critical role for this isoform in sperm motility.

Identification of a specific role for the Na,K-ATPase alpha 2 isoform as a regulator of calcium in the heart

It is well accepted that inhibition of the Na,K-ATPase in the heart, through effects on the Na/Ca exchanger, raises the intracellular Ca2+ concentration and strengthens cardiac contraction. However, the contribution that individual isoforms make to this calcium regulatory role is unknown. Assessing the phenotypes of mouse hearts with genetically reduced levels of Na,K-ATPase alpha 1 or alpha 2 isoforms clearly demonstrates different functional roles for these isoforms in vivo. Heterozygous alpha 2 hearts are hypercontractile as a result of increased calcium transients during the contractile cycle. In contrast, heterozygous alpha 1 hearts are hypocontractile. The different functional roles of these two isoforms are further demonstrated since inhibition of the alpha 2 isoform with ouabain increases the contractility of heterozygous alpha 1 hearts. These results definitively illustrate a specific role for the alpha 2 Na,K-ATPase isoform in Ca2+ signaling during cardiac contraction.

Characterization of the fourth alpha isoform of the Na,K-ATPase

The Na,K-ATPase is a major ion transport protein found in higher eukaryotic cells. The enzyme is composed of two subunits, alpha and beta, and tissue-specific isoforms exist for each of these, alpha1, alpha2 and alpha3 and beta1, beta2 and beta3. We have proposed that an additional alpha isoform, alpha4, exists based on genomic and cDNA cloning. The mRNA for this gene is expressed in rats and humans, exclusively in the testis, however the expression of a corresponding protein has not been demonstrated. In the current study, the putative alpha4 isoform has been functionally characterized as a novel isoform of the Na,K-ATPase in both rat testis and in alpha4 isoform cDNA transfected 3T3 cells. Using an alpha4 isoform-specific polyclonal antibody, the protein for this novel isoform is detected for the first time in both rat testis and in transfected cell lines. Ouabain binding competition assays reveal the presence of high affinity ouabain receptors in both rat testis and in transfected cell lines that have identical KD values. Further studies of this high affinity ouabain receptor show that it also has high affinities for both Na+ and K+. The results from these experiments definitively demonstrate the presence of a novel isoform of the Na,K-ATPase in testis.

Isolation of animal cell mutants defective in long-chain fatty aldehyde dehydrogenase. Sensitivity to fatty aldehydes and Schiff's base modification of phospholipids: implications for Sj-ogren-Larsson syndrome

Using tritium suicide, we have isolated a variant of the Chinese hamster ovary cell line, CHO-K1, that is deficient in long-chain fatty alcohol:NAD+ oxidoreductase (FAO; EC 1.1.1.192). Specifically, it was the fatty aldehyde dehydrogenase component that was affected. The enzymatic deficiency found in this mutant strain, designated FAA. K1A, was similar to that displayed by fibroblasts from patients with Sjögren-Larsson syndrome (SLS), an inheritable neurocutaneous disorder. Complementation analyses suggested that the deficiency in fatty alcohol oxidation in the FAA.K1A cells and the SLS fibroblasts is a result of lesions in homologous genes. The FAA.K1A cells were unable to convert long chain fatty aldehydes to the corresponding fatty acids. This resulted in a hypersensitivity of the FAA.K1A cells to the cytotoxic effects of long chain fatty aldehydes. The difference between the mutant and wild-type cells was most obvious when using fatty aldehydes between 14 and 20 carbons, with the greatest difference between wild-type and mutant cells found when using octadecanal. Fibroblasts from a patient with SLS also displayed the hypersensitivity phenotype when compared with FAldDH+ human fibroblasts. In both CHO and human FAldDH- cell lines, addition of long chain fatty aldehydes to the medium caused a dramatic increase in aldehyde-modified phosphatidylethanolamine, presumably through Schiff's base addition to the primary amine of the ethanolamine head group. When 25 microM hexadecanal was added to the growth medium, approximately 10% of the phosphatidylethanolamine was found in the fatty aldehyde-modified form in FAA.K1A, although this was not observed in wild-type cells. Modified phosphatidylethanolamine could be detected in FAldDH- cells even when exogenous fatty aldehydes were not added to the medium. We propose a possible role for fatty aldehydes, or other aldehydic species, in mediating some of the symptoms associated with Sjögren-Larsson syndrome.

An animal cell mutant with a deficiency in acyl/alkyl-dihydroxyacetone-phosphate reductase activity. Effects on the biosynthesis of ether-linked and diacyl glycerolipids

In the accompanying paper (James, P. F., and Zoeller, R. A. (1997) J. Biol. Chem. 272, 23532-23539), we reported the isolation of a series of mutants from the fibroblast-like cell line, CHO-K1, that are deficient in the incorporation of the long chain fatty alcohol, hexadecanol, into complex lipids. All but one of these mutants, FAA. K1B, were deficient in long-chain-fatty alcohol oxidase (FAO) activity. We have further characterized this FAO+ isolate. FAA.K1B cells displayed a 40% decrease in [9,10-3H]hexadecanol uptake when compared with the parent strain. Although incorporation of hexadecanol into the phospholipid fraction was decreased by 52%, the cells accumulated label in alkylglycerol (20-fold over wild type). The increase in 1-alkylglycerol labeling corresponded to a 4-fold increase in alkylglycerol mass. Short term labeling with 32Pi showed a 45-50% decrease in overall phospholipid biosynthesis in FAA.K1B. Both diacyl- and ether-linked species were affected, suggesting a general defect in phospholipid biosynthesis. Mutant cells were able to partially compensate for the decreased biosynthesis by decreasing the turnover of the phospholipid pools. The primary lesion in FAA. K1B was identified as a 95% reduction in acyl/alkyl-dihydroxyacetone-phosphate reductase activity. Whole cell homogenates from FAA.K1B were unable to reduce either acyl-dihydroxyacetone phosphate (DHAP) or alkyl-DHAP, supporting the notion that the reduction of these two compounds is catalyzed by a single enzyme. These data suggest that the biosynthesis of diacyl phospholipids, in Chinese hamster ovary cells, begins with the acylation of dihydroxyacetone phosphate as well as glycero-3-phosphate and that the "DHAP pathway" contributes significantly to diacyl glycerolipid biosynthesis. Also, the severe reduction in acyl/alkyl-DHAP reductase activity in FAA.K1B resulted in only a moderate decrease in ether lipid biosynthesis. These latter data together with the observed increase in alkylglycerol levels support the existence of a shunt pathway that is able to partially bypass the enzymatic lesion.

Synthetic implant surfaces. 1. The formation and characterization of sol-gel titania films

Sol-gel has been used to prepare thin titania films. We have investigated the effects of dip rate, sintering temperature and time on the chemical composition of the films, their physical structure and thickness, and adherence to a silica substrate. Our aim has been to produce films that mimic as closely as possible the natural oxide layer that is found on titanium. These films are to be used as substrates in an in vitro model of osseointegration.

Isolation and characterization of a Chinese hamster ovary cell line deficient in fatty alcohol:NAD+ oxidoreductase activity

We have isolated a mutant Chinese hamster ovary cell line that is defective in long-chain fatty alcohol oxidation. The ability of the mutant cells to convert labeled hexadecanol to the corresponding fatty acid in vivo was reduced to 5% of the parent strain. Whole-cell homogenates from the mutant strain, FAA.1, were deficient in long-chain fatty alcohol:NAD+ oxidoreductase (FAO; EC 1.1.1.192) activity, which catalyzes the oxidation of hexadecanol to hexadecanoic acid, although the intermediate fatty aldehyde was formed normally. A direct measurement of fatty aldehyde dehydrogenase showed that the FAA.1 strain was defective in this component of FAO activity. FAA.1 is a two-stage mutant that was selected from a previously described parent strain, ZR-82, which is defective in ether lipid biosynthesis and peroxisome assembly. Because of combined defects in ether lipid biosynthesis and fatty alcohol oxidation, the ability of the FAA.1 cells to incorporate hexadecanol into complex lipids was greatly impaired, resulting in a 60-fold increase in cellular fatty alcohol levels. As the FAO deficiency in FAA.1 cells appears to be identical to the defect associated with the human genetic disorder Sjögren-Larsson syndrome, the FAA.1 cell line may be useful in studying this disease.