Plasma gelsolin modulates the production and fate of IL-1β-containing microparticles following high-pressure exposure and decompression

Abstract

Plasma gelsolin (pGSN) levels fall in association with diverse inflammatory conditions. We hypothesized that pGSN would decrease due to the stresses imposed by high pressure and subsequent decompression, and repletion would ameliorate injuries in a murine decompression sickness (DCS) model. Research subjects were found to exhibit a modest decrease in pGSN level while at high pressure and a profound decrease after decompression. Changes occurred concurrent with elevations of circulating microparticles (MPs) carrying interleukin (IL)-1β. Mice exhibited a comparable decrease in pGSN after decompression along with elevations of MPs carrying IL-1β. Infusion of recombinant human (rhu)-pGSN into mice before or after pressure exposure abrogated these changes and prevented capillary leak in brain and skeletal muscle. Human and murine MPs generated under high pressure exhibited surface filamentous actin (F-actin) to which pGSN binds, leading to particle lysis. In addition, human neutrophils exposed to high air pressure exhibit an increase in surface F-actin that is diminished by rhu-pGSN resulting in inhibition of MP production. Administration of rhu-pGSN may have benefit as prophylaxis or treatment for DCS.NEW & NOTEWORTHY Inflammatory microparticles released in response to high pressure and decompression express surface filamentous actin. Infusion of recombinant human plasma gelsolin lyses these particles in decompressed mice and ameliorates particle-associated vascular damage. Human neutrophils also respond to high pressure with an increase in surface filamentous actin and microparticle production, and these events are inhibited by plasma gelsolin. Gelsolin infusion may have benefit as prophylaxis or treatment for decompression sickness.

Keywords: decompression sickness; interleukin-1β; microparticles; neutrophils; oxidative stress.

Figure 1.

Changes in blood from human research subjects. The concentrations of pGSN and IL-1β were measured in plasma samples and blood-borne MPs were quantified preexposure, at-exposure, and postexposure to 300 kPa as described in methods. Individual data points are shown and below each plot are means ± SE, n = 6 for each sample, * indicates significantly different from preexposure, P < 0.05, RM ANOVA. IL-1β, interleukin-1β; MP, microparticles; RM, repeated-measures; pGSN, plasma gelsolin.

Figure 2.

Changes in mice. Male mice were exposed to air at ambient pressure (control) or for 2 h to 790 kPa air, decompressed and euthanized 2 h later (Deco). Where indicated air-exposed control mice were injected intravenously with 27 mg/kg rhu-pGSN (Control + Rhu-pGSN) and euthanized 4 h later. Other mice were injected with rhu-pGSN prior to pressurization (Rhu-pGSN + Deco) or immediately after decompression (Deco + Rhu-pGSN), and others injected intravenously with the carrier buffer used to suspend rhu-pGSN (Vehicle + Deco), and these groups euthanized 2 h after decompression. The concentrations of mouse pGSN and IL-1β were measured in plasma samples by mouse-specific ELISAs and blood-borne MPs were quantified as described in methods. Data are expressed as means ± SE, the (n) for each sample is shown, *indicates significantly different from control, P < 0.05, ANOVA. IL-1β, interleukin-1β; MP, microparticles; rhu-pGSN, recombinant human-plasma gelsolin; pGSN, plasma gelsolin.

Figure 3.

Biotinylation of MPs proteins. MPs from control and decompressed male mice were isolated, incubated with 200 mg/mL rhu-pGSN (shown as +pGSN) or just PBS, and then biotinylated as described in methods. MPs were then lysed in SDS buffer and protein from 45,500 MPs loaded into each lane for SDS-PAGE. Western blots probed for biotin and for β-actin are shown. Probing for IL-1β did not demonstrate bands (not shown). Molecular weight standards (in kDa) are shown at left. IL-1β, interleukin-1β; MP, microparticles; rhu-pGSN, recombinant human-plasma gelsolin; pGSN, plasma gelsolin.

Figure 4.

Biotinylated vs. nonbiotinylated MPs separation: MPs from control and decompressed male mice were isolated, biotinylated, and then lysed. Samples were incubated with magnetic streptavidin beads as described in methods and passed through a magnet to separate biotinylated (shown as +Biotin) from nonbiotinylated proteins (shown as −Biotin). Protein from 165,000 MPs was loaded into each lane for SDS-PAGE. Western blots probed for β-actin and biotin are shown. Probing for IL-1β did not demonstrate bands (not shown). Molecular weight standards (in kDa) are shown at left. IL-1β, interleukin-1β; MP, microparticles.

Figure 5.

Effect of rhu-pGSN on MPs from control and decompressed mice. Blood was obtained from control or decompressed male mice and centrifuged as described in methods. MPs suspensions were divided and where shown at time 0, 200 µg/mL rhu-pGSN was added. At 30-min intervals, samples were fixed. The number of remaining MPs and the percentage of particles that bound fluorescent phalloidin were quantified. Data are expressed as means ± SE, n = 5 for each sample, *indicates significantly different from the value at time 0, P < 0.05, RM-ANOVA. MP, microparticles; rhu-pGSN, recombinant human-plasma gelsolin; RM, repeated-measures; pGSN, plasma gelsolin.

Figure 6.

Effect of rhu-pGSN on human neutrophils and MPs. Neutrophils were isolated, incubated for 30 min in ambient air or at 790 kPa, and decompressed. At time 0 time, rhu-pGSN (200 µg/mL) was added and at 30-min intervals portions of samples were fixed and processed as described in methods to quantify MPs, binding of anti-gelsolin antibody and fluorescent phalloidin. Data are expressed as means ± SE, n = 4 for each sample, *indicates significantly different from the value at time 0, P < 0.05, RM-ANOVA. MP, microparticles; rhu-pGSN, recombinant human-plasma gelsolin; RM, repeated-measures; pGSN, plasma gelsolin.