FOXO1 expression in chondrocytes modulates cartilage production and removal in fracture healing.

Fracture healing is a multistage process characterized by inflammation, cartilage formation, bone deposition, and remodeling. Chondrocytes are important in producing cartilage that forms the initial anlagen for the hard callus needed to stabilize the fracture site. We examined the role of FOXO1 by selective ablation of FOXO1 in chondrocytes mediated by Col2α1 driven Cre recombinase. Experimental mice with lineage-specific FOXO1 deletion (Col2α1Cre+FOXO1L/L) and negative control littermates (Col2α1Cre-FOXO1L/L) were used for in vivo, closed fracture studies. Unexpectedly, we found that in the early phases of fracture healing, FOXO1 deletion significantly increased the amount of cartilage formed, whereas, in later periods, FOXO1 deletion led to a greater loss of cartilage. FOXO1 was functionally important as its deletion in chondrocytes led to diminished bone formation on day 22. Mechanistically, the early effects of FOXO1 deletion were linked to increased proliferation of chondrocytes through enhanced expression of cell cycle genes that promote proliferation and reduced expression of those that inhibit it and increased expression of cartilage matrix genes. At later time points experimental mice with FOXO1 deletion had greater loss of cartilage, enhanced formation of osteoclasts, increased IL-6 and reduced numbers of M2 macrophages. These results identify FOXO1 as a transcription factor that regulates chondrocyte behavior by limiting the early expansion of cartilage and preventing rapid cartilage loss at later phases.

Mucosal Immunity and the FOXO1 Transcription Factors.

FOXO1 transcription factors affect a number of cell types that are important in the host response. Cell types whose functions are modulated by FOXO1 include keratinocytes in the skin and mucosal dermis, neutrophils and macrophages, dendritic cells, Tregs and B-cells. FOXO1 is activated by bacterial or cytokine stimulation. Its translocation to the nucleus and binding to promoter regions of genes that have FOXO response elements is stimulated by the MAP kinase pathway and inhibited by the PI3 kinase/AKT pathway. Downstream gene targets of FOXO1 include pro-inflammatory signaling molecules (TLR2, TLR4, IL-1ß, and TNF-α), wound healing factors (TGF-ß, VEGF, and CTGF) adhesion molecules (integrins-ß1, -ß3, -ß6, αvß3, CD11b, CD18, and ICAM-1), chemokine receptors (CCR7 and CXCR2), B cell regulators (APRIL and BLYS), T-regulatory modulators (Foxp3 and CTLA-4), antioxidants (GPX-2 and cytoglobin), and DNA repair enzymes (GADD45α). Each of the above cell types are found in oral mucosa and modulated by bacteria or an inflammatory microenvironment. FOXO1 contributes to the regulation of these cells, which collectively maintain and repair the epithelial barrier, formation and activation of Tregs that are needed to resolve inflammation, mobilization, infiltration, and activation of anti-bacterial defenses in neutrophils, and the homing of dendritic cells to lymph nodes to induce T-cell and B-cell responses. The goal of the manuscript is to review how the transcription factor, FOXO1, contributes to the activation and regulation of key leukocytes needed to maintain homeostasis and respond to bacterial challenge in oral mucosal tissues. Examples are given with an emphasis on lineage specific deletion of Foxo1 to explore the impact of FOXO1 on cell behavior, inflammation and susceptibility to infection.

FOXO1 Deletion Reverses the Effect of Diabetic-Induced Impaired Fracture Healing.

Type 1 diabetes impairs fracture healing. We tested the hypothesis that diabetes affects chondrocytes to impair fracture healing through a mechanism that involves the transcription factor FOXO1. Type 1 diabetes was induced by streptozotocin in mice with FOXO1 deletion in chondrocytes (Col2α1Cre+FOXO1L/L) or littermate controls (Col2α1Cre-FOXO1L/L) and closed femoral fractures induced. Diabetic mice had 77% less cartilage and 30% less bone than normoglycemics evaluated histologically and by micro-computed tomography. Both were reversed with lineage-specific FOXO1 ablation. Diabetic mice had a threefold increase in osteoclasts and a two- to threefold increase in RANKL mRNA or RANKL-expressing chondrocytes compared with normoglycemics. Both parameters were rescued by FOXO1 ablation in chondrocytes. Conditions present in diabetes, high glucose (HG), and increased advanced glycation end products (AGEs) stimulated FOXO1 association with the RANKL promoter in vitro, and overexpression of FOXO1 increased RANKL promoter activity in luciferase reporter assays. HG and AGE stimulated FOXO1 nuclear localization, which was reversed by insulin and inhibitors of TLR4, histone deacetylase, nitric oxide, and reactive oxygen species. The results indicate that chondrocytes play a prominent role in diabetes-impaired fracture healing and that high levels of glucose, AGEs, and tumor necrosis factor-α, which are elevated by diabetes, alter RANKL expression in chondrocytes via FOXO1.

FOXO1 regulates VEGFA expression and promotes angiogenesis in healing wounds.

Angiogenesis is a critical aspect of wound healing. We investigated the role of keratinocytes in promoting angiogenesis in mice with lineage-specific deletion of the transcription factor FOXO1. The results indicate that keratinocyte-specific deletion of Foxo1 reduces VEGFA expression in mucosal and skin wounds and leads to reduced endothelial cell proliferation, reduced angiogenesis, and impaired re-epithelialization and granulation tissue formation. In vitro FOXO1 was needed for VEGFA transcription and expression. In a porcine dermal wound-healing model that closely resembles healing in humans, local application of a FOXO1 inhibitor reduced angiogenesis. This is the first report that FOXO1 directly regulates VEGFA expression and that FOXO1 is needed for normal angiogenesis during wound healing. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Microparticles Impair Hypotensive Cerebrovasodilation and Cause Hippocampal Neuronal Cell Injury after Traumatic Brain Injury.

Endothelin-1 (ET-1), tissue plasminogen activator (tPA), and extracellular signal-regulated kinases-mitogen activated protein kinase (ERK-MAPK) are mediators of impaired cerebral hemodynamics after fluid percussion brain injury (FPI) in piglets. Microparticles (MPs) are released into the circulation from a variety of cells during stress, are pro-thrombotic and pro-inflammatory, and may be lysed with polyethylene glycol telomere B (PEG-TB). We hypothesized that MPs released after traumatic brain injury impair hypotensive cerebrovasodilation and that PEG-TB protects the vascular response via MP lysis, and we investigated the relationship between MPs, tPA, ET-1, and ERK-MAPK in that process. FPI was induced in piglets equipped with a closed cranial window. Animals received PEG-TB or saline (vehicle) 30-minutes post-injury. Serum and cerebrospinal fluid (CSF) were sampled and pial arteries were measured pre- and post-injury. MPs were quantified by flow cytometry. CSF samples were analyzed with enzyme-linked immunosorbent assay. MP levels, vasodilatory responses, and CSF signaling assays were similar in all animals prior to injury and treatment. After injury, MP levels were elevated in the serum of vehicle but not in PEG-TB-treated animals. Pial artery dilation in response to hypotension was impaired after injury but protected in PEG-TB-treated animals. After injury, CSF levels of tPA, ET-1, and ERK-MAPK were all elevated, but not in PEG-TB-treated animals. PEG-TB-treated animals also showed reduction in neuronal injury in CA1 and CA3 hippocampus, compared with control animals. These results show that serum MP levels are elevated after FPI and lead to impaired hypotensive cerebrovasodilation via over-expression of tPA, ET-1, and ERK-MAPK. Treatment with PEG-TB after injury reduces MP levels and protects hypotensive cerebrovasodilation and limits hippocampal neuronal cell injury.

Exercise before scuba diving ameliorates decompression-induced neutrophil activation.

INTRODUCTION: The goals of this study were to investigate the difference in responses between a scuba dive preceded by aerobic exercise (EX) and a nonexercise control dive (CON) and to further evaluate the potential relation between venous gas emboli (VGE) and microparticles (MP). We hypothesized that exercise would alter the quantity and subtype of annexin V-positive MP and VGE. METHODS: Nineteen divers performed two dives to 18 m seawater for 41 min separated by at least 3 d, one of which was preceded by 60 min of treadmill interval exercise. Blood was obtained before exercise, before diving, and 15 min, 2 h, 4 h, and 24 h after surfacing. Intravascular bubbles were quantified by transthoracic echocardiography at 15, 40, 80, and 120 min. RESULTS: The median VGE remained unchanged between the two dives; however, there was a significant increase in VGE in the exercise dive at 40 and 80 min at rest. MP were significantly elevated by approximately 2 times at all time points after CON compared with those after EX. Markers of neutrophil and platelet activation were elevated by both dives, and these elevations were attenuated in the EX dive. CONCLUSIONS: We conclude that some of the differences observed between the EX and CON related to MP and platelet and neutrophil activation provide additional insight into the potential protective benefits of exercise; however, further study is needed to understand the mechanism and true potential of these benefits.

CD34+/CD45-dim stem cell mobilization by hyperbaric oxygen - changes with oxygen dosage.

Because hyperbaric oxygen treatment mobilizes bone marrow derived-stem/progenitor cells by a free radical mediated mechanism, we hypothesized that there may be differences in mobilization efficiency based on exposure to different oxygen partial pressures. Blood from twenty consecutive patients was obtained before and after the 1st, 10th and 20th treatment at two clinical centers using protocols involving exposures to oxygen at either 2.0 or 2.5 atmospheres absolute (ATA). Post-treatment values of CD34+, CD45-dim leukocytes were always 2-fold greater than the pre-treatment values for both protocols. Values for those treated at 2.5 ATA were significantly greater than those treated at 2.0 ATA by factors of 1.9 to 3-fold after the 10th and before and after the 20th treatments. Intracellular content of hypoxia inducible factors -1, -2, and -3, thioredoxin-1 and poly-ADP-ribose polymerase assessed in permeabilized CD34+ cells with fluorophore-conjugated antibodies were twice as high in all post- versus pre-treatment samples with no significant differences between 2.0 and 2.5 ATA protocols. We conclude that putative progenitor cell mobilization is higher with 2.5 versus 2.0 ATA treatments, and all newly mobilized cells exhibit higher concentrations of an array of regulatory proteins.

Oxidative Lung Damage Resulting from Repeated Exposure to Radiation and Hyperoxia Associated with Space Exploration.

BACKGROUND: Spaceflight missions may require crewmembers to conduct Extravehicular Activities (EVA) for repair, maintenance or scientific purposes. Pre-breathe protocols in preparation for an EVA entail 100% hyperoxia exposure that may last for a few hours (5-8 hours), and may be repeated 2-3 times weekly. Each EVA is associated with additional challenges such as low levels of total body cosmic/galactic radiation exposure that may present a threat to crewmember health and therefore, pose a threat to the success of the mission. We have developed a murine model of combined, hyperoxia and radiation exposure (double-hit) in the context of evaluating countermeasures to oxidative lung damage associated with space flight. In the current study, our objective was to characterize the early and chronic effects of repeated single and double-hit challenge on lung tissue using a novel murine model of repeated exposure to low-level total body radiation and hyperoxia. This is the first study of its kind evaluating lung damage relevant to space exploration in a rodent model. METHODS: Mouse cohorts (n=5-15/group) were exposed to repeated: a) normoxia; b) >95% O2 (O2); c) 0.25Gy single fraction gamma radiation (IR); or d) a combination of O2 and IR (O2+IR) given 3 times per week for 4 weeks. Lungs were evaluated for oxidative damage, active TGFß1 levels, cell apoptosis, inflammation, injury, and fibrosis at 1, 2, 4, 8, 12, 16, and 20 weeks post-initiation of exposure. RESULTS: Mouse cohorts exposed to all challenge conditions displayed decreased bodyweight compared to untreated controls at 4 and 8 weeks post-challenge initiation. Chronic oxidative lung damage to lipids (malondialdehyde levels), DNA (TUNEL, cleaved Caspase 3, cleaved PARP positivity) leading to apoptotic cell death and to proteins (nitrotyrosine levels) was elevated all treatment groups. Importantly, significant systemic oxidative stress was also noted at the late phase in mouse plasma, BAL fluid, and urine. Importantly, however, late oxidative damage across all parameters that we measured was significantly higher than controls in all cohorts but was exacerbated by the combined exposure to O2 and IR. Additionally, impaired levels of arterial blood oxygenation were noted in all exposure cohorts. Significant but transient elevation of lung tissue fibrosis (p<0.05), determined by lung hydroxyproline content, was detected as early as 2 week in mice exposed to challenge conditions and persisted for 4-8 weeks only. Interestingly, active TGFß1 levels in +BAL fluid was also transiently elevated during the exposure time only (1-4 weeks). Inflammation and lung edema/lung injury was also significantly elevated in all groups at both early and late time points, especially the double-hit group. CONCLUSION: We have characterized significant, early and chronic lung changes consistent with oxidative tissue damage in our murine model of repeated radiation and hyperoxia exposure relevant to space travel. Lung tissue changes, detectable several months after the original exposure, include significant oxidative lung damage (lipid peroxidation, DNA damage and protein nitrosative stress) and increased pulmonary fibrosis. These findings, along with increased oxidative stress in diverse body fluids and the observed decreases in blood oxygenation levels in all challenge conditions (whether single or in combination), lead us to conclude that in our model of repeated exposure to oxidative stressors, chronic tissue changes are detected that persist even months after the exposure to the stressor has ended. This data will provide useful information in the design of countermeasures to tissue oxidative damage associated with space exploration.

Carbon monoxide inhalation increases microparticles causing vascular and CNS dysfunction.

We hypothesized that circulating microparticles (MPs) play a role in pro-inflammatory effects associated with carbon monoxide (CO) inhalation. Mice exposed for 1h to 100 ppm CO or more exhibit increases in circulating MPs derived from a variety of vascular cells as well as neutrophil activation. Tissue injury was quantified as 2000 kDa dextran leakage from vessels and as neutrophil sequestration in the brain and skeletal muscle; and central nervous system nerve dysfunction was documented as broadening of the neurohypophysial action potential (AP). Indices of injury occurred following exposures to 1000 ppm for 1h or to 1000 ppm for 40 min followed by 3000 ppm for 20 min. MPs were implicated in causing injuries because infusing the surfactant MP lytic agent, polyethylene glycol telomere B (PEGtB) abrogated elevations in MPs, vascular leak, neutrophil sequestration and AP prolongation. These manifestations of tissue injury also did not occur in mice lacking myeloperoxidase. Vascular leakage and AP prolongation were produced in naïve mice infused with MPs that had been obtained from CO poisoned mice, but this did not occur with MPs obtained from control mice. We conclude that CO poisoning triggers elevations of MPs that activate neutrophils which subsequently cause tissue injuries.

Microparticles generated by decompression stress cause central nervous system injury manifested as neurohypophysial terminal action potential broadening.

The study goal was to use membrane voltage changes during neurohypophysial action potential (AP) propagation as an index of nerve function to evaluate the role that circulating microparticles (MPs) play in causing central nervous system injury in response to decompression stress in a murine model. Mice studied 1 h following decompression from 790 kPa air pressure for 2 h exhibit a 45% broadening of the neurohypophysial AP. Broadening did not occur if mice were injected with the MP lytic agent polyethylene glycol telomere B immediately after decompression, were rendered thrombocytopenic, or were treated with an inhibitor of nitric oxide synthase-2 (iNOS) prior to decompression, or in knockout (KO) mice lacking myeloperoxidase or iNOS. If MPs were harvested from control (no decompression) mice and injected into naive mice, no AP broadening occurred, but AP broadening was observed with injections of equal numbers of MPs from either wild-type or iNOS KO mice subjected to decompression stress. Although not required for AP broadening, MPs from decompressed mice, but not control mice, exhibit NADPH oxidase activation. We conclude that inherent differences in MPs from decompressed mice, rather than elevated MPs numbers, mediate neurological injury and that a component of the perivascular response to MPs involves iNOS. Additional study is needed to determine the mechanism of AP broadening and also mechanisms for MP generation associated with exposure to elevated gas pressure.

Bubbles, microparticles, and neutrophil activation: changes with exercise level and breathing gas during open-water SCUBA diving.

The study goal was to evaluate responses in humans following decompression from open-water SCUBA diving with the hypothesis that exertion underwater and use of a breathing mixture containing more oxygen and less nitrogen (enriched air nitrox) would alter annexin V-positive microparticle (MP) production and size changes and neutrophil activation, as well as their relationships to intravascular bubble formation. Twenty-four divers followed a uniform dive profile to 18 m of sea water breathing air or 22.5 m breathing 32% oxygen/68% nitrogen for 47 min, either swimming with moderately heavy exertion underwater or remaining stationary at depth. Blood was obtained pre- and at 15 and 120 min postdive. Intravascular bubbles were quantified by transthoracic echocardiography postdive at 20-min intervals for 2 h. There were no significant differences in maximum bubble scores among the dives. MP number increased 2.7-fold, on average, within 15 min after each dive; only the air-exertion dive resulted in a significant further increase to 5-fold over baseline at 2 h postdive. Neutrophil activation occurred after all dives. For the enriched air nitrox stationary at depth dive, but not for other conditions, the numbers of postdive annexin V-positive particles above 1 µm in diameter were correlated with intravascular bubble scores (correlation coefficients ∼0.9, P < 0.05). We conclude that postdecompression relationships among bubbles, MPs, platelet-neutrophil interactions, and neutrophil activation appear to exist, but more study is required to improve confidence in the associations.

Nitric-oxide synthase-2 linkage to focal adhesion kinase in neutrophils influences enzyme activity and ß2 integrin function.

This investigation was to elucidate the basis for augmentation of nitric-oxide synthesis in neutrophils exposed to hyperbaric oxygen. Hyperoxia increases synthesis of reactive species leading to S-nitrosylation of ß-actin, which causes temporary inhibition of ß(2) integrin adherence. Impaired ß(2) integrin function and actin S-nitrosylation do not occur in neutrophils from mice lacking type-2 nitric-oxide synthase (iNOS) or when incubated with 1400W, an iNOS inhibitor. Similarly, effects of hyperoxia were abrogated in cells depleted of focal adhesion kinase (FAK) by treatment with small inhibitory RNA and those exposed to a specific FAK inhibitor concurrent with hyperoxia. Nitric oxide production doubles within 10 min exposure to hyperoxia but declines to approximately half-maximum production over an additional 10 min. Elevated nitric oxide production did not occur after FAK depletion or inhibition, or when filamentous actin formation was inhibited by cytochalasin D. Intracellular content of iNOS triples over the course of a 45-min exposure to hyperoxia and iNOS dimers increase in a commensurate fashion. Confocal microscopy and immunoprecipitation demonstrated that co-localization/linkage of FAK, iNOS, and filamentous actin increased within 15 min exposure to hyperoxia but then decreased below the control level. Using isolated enzymes in ex vivo preparations an association between iNOS and filamentous actin mediated by FAK could be demonstrated and complex formation was impeded when actin was S-nitrosylated. We conclude that iNOS activity is increased by an FAK-mediated association with actin filaments but peak nitric oxide production is transient due to actin S-nitrosylation during exposure to hyperoxia.

Intramicroparticle nitrogen dioxide is a bubble nucleation site leading to decompression-induced neutrophil activation and vascular injury.

Inert gases diffuse into tissues in proportion to ambient pressure, and when pressure is reduced, gas efflux forms bubbles due to the presence of gas cavitation nuclei that are predicted based on theory but have never been characterized. Decompression stress triggers elevations in number and diameter of circulating annexin V-coated microparticles (MPs) derived from vascular cells. Here we show that ∼10% MPs from wild-type (WT) but not inflammatory nitric oxide synthase-2 (iNOS) knockout (KO) mice increase in size when exposed to elevated air pressure ex vivo. This response is abrogated by a preceding exposure to hydrostatic pressure, demonstrating the presence of a preformed gas phase. These MPs have lower density than most particles, 10-fold enrichment in iNOS, and generate commensurately more reactive nitrogen species (RNS). Surprisingly, RNS only slowly diffuse from within MPs unless particles are subjected to osmotic stress or membrane cholesterol is removed. WT mice treated with iNOS inhibitor and KO mice exhibit less decompression-induced neutrophil activation and vascular leak. Contrary to injecting naïve mice with MPs from wild-type decompressed mice, injecting KO MPs triggers fewer proinflammatory events. We conclude that nitrogen dioxide is a nascent gas nucleation site synthesized in some MPs and is responsible for initiating postdecompression inflammatory injuries.

Thioredoxin reductase linked to cytoskeleton by focal adhesion kinase reverses actin S-nitrosylation and restores neutrophil ß(2) integrin function.

The investigation goal was to identify mechanisms for reversal of actin S-nitrosylation in neutrophils after exposure to high oxygen partial pressures. Prior work has shown that hyperoxia causes S-nitrosylated actin (SNO-actin) formation, which mediates ß(2) integrin dysfunction, and these changes can be reversed by formylmethionylleucylphenylalanine or 8-bromo-cyclic GMP. Herein we show that thioredoxin reductase (TrxR) is responsible for actin denitrosylation. Approximately 80% of cellular TrxR is localized to the cytosol, divided between the G-actin and short filamentous actin (sF-actin) fractions based on Triton solubility of cell lysates. TrxR linkage to sF-actin requires focal adhesion kinase (FAK) based on immunoprecipitation studies. S-Nitrosylation accelerates actin filament turnover (by mechanisms described previously (Thom, S. R., Bhopale, V. M., Yang, M., Bogush, M., Huang, S., and Milovanova, T. (2011) Neutrophil ß(2) integrin inhibition by enhanced interactions of vasodilator stimulated phosphoprotein with S-nitrosylated actin. J. Biol. Chem. 286, 32854-32865), which causes FAK to disassociate from sF-actin. TrxR subsequently dissociates from FAK, and the physical separation from actin impedes denitrosylation. If SNO-actin is photochemically reduced with UV light or if actin filament turnover is impeded by incubations with cytochalasin D, latrunculin B, 8-bromo-cGMP, or formylmethionylleucylphenylalanine, FAK and TrxR reassociate with sF-actin and cause SNO-actin removal. FAK-TrxR association can also be demonstrated using isolated enzymes in ex vivo preparations. Uniquely, the FAK kinase domain is the site of TrxR linkage. We conclude that through its scaffold function, FAK influences TrxR activity and actin S-nitrosylation.

Temporal dynamics of microparticle elevation following subarachnoid hemorrhage.

OBJECT: Microparticles (MPs), small membrane fragments shed from various cell types, have been implicated in thrombosis, inflammation, and endothelial dysfunction. Their involvement in subarachnoid hemorrhage (SAH) and the development of cerebral infarction and clinical deterioration caused by delayed cerebral ischemia (DCI) remain ill defined. The authors sought to quantify the magnitude of elevations in MPs, delineate the temporal dynamics of elevation, and analyze the correlation between MPs and DCI in patients with SAH. METHODS: On the day of hemorrhage and on Days 1, 3, 5, 7, and 10 after hemorrhage, peripheral blood samples were drawn from 22 patients with SAH. Plasma samples were labeled with Annexin V and CD142, CD41a, CD235a, CD146, CD66b, or von Willebrand factor (vWF) and were quantified by flow cytometry. Clinical data, including the 3-month extended Glasgow Outcome Scale (GOS-E) scores, infarction as measured on MRI at 14 days after SAH, and vasospasm as measured by transcranial Doppler ultrasonography and angiography, were collected and compared with the MP burden. RESULTS: When averaged over time, all MP subtypes were elevated relative to controls. The CD235a+(erythrocyte)-, CD66b+(neutrophil)-, and vWF-associated MPs peaked on the day of hemorrhage and quickly declined. The CD142+(tissue factor [TF])-associated MPs and CD146+(endothelial cell)-associated MPs were significantly elevated throughout the study period. There was a strong negative correlation between TF-expressing and endothelial-derived MPs at Day 1 after SAH and the risk of infarction at Day 14 after SAH. CONCLUSIONS: Microparticles of various subtypes are elevated following SAH; however, the temporal profile of this elevation varies by subtype. Those subtypes closely associated with thrombosis and endothelial dysfunction, for example, CD145+(TF)-associated MPs and CD146+(endothelial cell)-associated MPs, had the most durable response and demonstrated a significant negative correlation with radiographic infarction at 14 days after SAH. Levels of these MPs predict infarction as early as Day 1 post-SAH.

Microparticle production, neutrophil activation, and intravascular bubbles following open-water SCUBA diving.

The goal of this study was to evaluate annexin V-positive microparticles (MPs) and neutrophil activation in humans following decompression from open-water SCUBA diving with the hypothesis that changes are related to intravascular bubble formation. Sixteen male volunteer divers followed a uniform profile of four daily SCUBA dives to 18 m of sea water for 47 min. Blood was obtained prior to and at 80 min following the first and fourth dives to evaluate the impact of repetitive diving, and intravascular bubbles were quantified by trans-thoracic echocardiography carried out at 20-min intervals for 2 h after each dive. MPs increased by 3.4-fold after each dive, neutrophil activation occurred as assessed by surface expression of myeloperoxidase and the CD18 component of ß(2)-integrins, and there was an increased presence of the platelet-derived CD41 protein on the neutrophil surface indicating interactions with platelet membranes. Intravascular bubbles were detected in all divers. Surprisingly, significant inverse correlations were found among postdiving bubble scores and MPs, most consistently at 80 min or more after the dive on the fourth day. There were significant positive correlations between MPs and platelet-neutrophil interactions after the first dive and between platelet-neutrophil interactions and neutrophil activation documented as an elevation in ß(2)-integrin expression after the fourth dive. We conclude that MPs- and neutrophil-related events in humans are consistent with findings in an animal decompression model. Whether there are causal relationships among bubbles, MPs, platelet-neutrophil interactions, and neutrophil activation remains obscure and requires additional study.

Microparticle enlargement and altered surface proteins after air decompression are associated with inflammatory vascular injuries.

Studies in a murine model have shown that decompression stress triggers a progressive elevation in the number of circulating annexin V-coated microparticles derived from leukocytes, erythrocytes, platelets, and endothelial cells. We noted that some particles appeared to be larger than anticipated, and size continued to increase for ≥24 h postdecompression. These observations led to the hypothesis that inert gas bubbles caused the enlargement and particle size could be reduced by hydrostatic pressure. After demonstrating pressure-induced particle size reduction, we hypothesized that annexin V-positive particle changes associated with decompression contributed to their proinflammatory potential. Intravenous injection of naive mice with particles isolated from decompressed mice, but not control mice, caused intravascular neutrophil activation; perivascular neutrophil sequestration and tissue injuries were documented as elevations of vascular permeability and activated caspase-3. These changes were not observed if mice were injected with particles that had been subjected to hydrostatic recompression or particles that had been emulsified by incubation with polyethylene glycol telomere B surfactant. Hydrostatic pressure and surfactant incubation also altered the pattern of proteins expressed on the surface of particles. We conclude that proinflammatory events and vascular damage are due to enlargement of annexin V-coated particles and/or changes in surface marker protein pattern associated with provocative decompression. Injection of annexin V-coated particles from decompressed mice will recapitulate the pathophysiological vascular changes observed following decompression stress.

Neutrophil beta2 integrin inhibition by enhanced interactions of vasodilator-stimulated phosphoprotein with S-nitrosylated actin.

Production of reactive species in neutrophils exposed to hyperoxia causes S-nitrosylation of ß-actin, which increases formation of short actin filaments, leading to alterations in the cytoskeletal network that inhibit ß(2) integrin-dependent adherence (Thom, S. R., Bhopale, V. M., Mancini, D. J., and Milovanova, T. N. (2008) J. Biol. Chem. 283, 10822-10834). In this study, we found that vasodilator-stimulated protein (VASP) exhibits high affinity for S-nitrosylated short filamentous actin, which increases actin polymerization. VASP bundles Rac1, Rac2, cyclic AMP-dependent, and cyclic GMP-dependent protein kinases in close proximity to short actin filaments, and subsequent Rac activation increases actin free barbed end formation. Using specific chemical inhibitors or reducing cell concentrations of any of these proteins with small inhibitory RNA abrogates enhanced free barbed end formation, increased actin polymerization, and ß(2) integrin inhibition by hyperoxia. Alternatively, incubating neutrophils with formylmethionylleucylphenylalanine or 8-bromo-cyclic GMP activates either cyclic AMP-dependent or cyclic GMP-dependent protein kinase, respectively, outside of the short F-actin pool and phosphorylates VASP on serine 153. Phosphorylated VASP abrogates the augmented polymerization normally observed with S-nitrosylated actin, VASP binding to actin, elevated Rac activity, and elevated formation of actin free barbed ends, thus restoring normal ß(2) integrin function.

Vasculogenic stem cell mobilization and wound recruitment in diabetic patients: increased cell number and intracellular regulatory protein content associated with hyperbaric oxygen therapy.

Diabetic patients undergoing hyperbaric oxygen therapies (HBO(2)T) for refractory lower extremity neuropathic ulcers exhibit more than a twofold elevation (p=0.004) in circulating stem cells after treatments and the post-HBO(2)T CD34(+) cell population contains two- to threefold higher levels of hypoxia inducible factors-1, -2, and -3, as well as thioredoxin-1 (p<0.003), than cells present in blood before HBO(2)T. Skin margins obtained from 2-day-old abdominal wounds exhibit higher expression of CD133, CD34, hypoxia inducible factor-1, and Trx-1 vs. margins from refractory lower extremity wounds and expression of these proteins in all wounds is increased due to HBO(2)T (p<0.003). HBO(2)T is known to mobilize bone marrow stem cells by stimulating nitric oxide synthase. We found that nitric oxide synthase activity is acutely increased in patients' platelets following HBO(2)T and remains elevated for at least 20 hours. We conclude that HBO(2) T stimulates vasculogenic stem cell mobilization from bone marrow of diabetics and more cells are recruited to skin wounds.