Hg2+ and small-sized polyethylene glycols have inverse effects on membrane permeability, while both impair neutrophil cell motility

Immune profile of hyaluronic acid hydrogel polyethylene glycol crosslinked: An in vitro evaluation in human polymorphonuclear leukocytes

Neauvia hydrogel (N-Gel) is a hyaluronic acid-based dermal filler, cross-linked with polyethylene glycol. This filler contains sodium hyaluronate at different concentrations, poly(ethylene glycol) diglycidyl ether cross-linked, glycine, and l-prolyne. Assessing any effects of N-Gel on immunity and inflammation is of crucial importance. The aim of the study was to characterize the ability of N-Gel to modulate human polymorphonuclear leukocyte (PMN) functions, including migration, oxidative metabolism, and production of proinflammatory mediators. N-Gel was tested on isolated human PMN. Spontaneous and N-formylmethionyl-leucyl-phenylalanine (fMLP)-stimulated migration were examined using the Boyden Chamber technique, whereas the oxidative metabolism was assessed through spectrofluorometric measurement of reactive oxygen species (ROS) production under resting conditions and after stimulation with fMLP. Tumor necrosis factor (TNF)-α and interleukin (IL)-8 mRNA levels were measured by real-time PCR after stimulation with fMLP or Escherichia coli lipopolysaccharide. This study showed that N-Gel reduced fMLP-induced migration and ROS production without affecting these functions in resting cells. In addition, incubation of PMN with N-Gel effectively reduced both TNF-α and IL-8 mRNA levels. N-Gel modulates critical functions of human PMN such as migration and oxidative metabolism, indicating its potential as an anti-inflammatory agent.

Aquaporin water channels in the nervous system

The aquaporins (AQPs) are plasma membrane water-transporting proteins. AQP4 is the principal member of this protein family in the CNS, where it is expressed in astrocytes and is involved in water movement, cell migration and neuroexcitation. AQP1 is expressed in the choroid plexus, where it facilitates cerebrospinal fluid secretion, and in dorsal root ganglion neurons, where it tunes pain perception. The AQPs are potential drug targets for several neurological conditions. Astrocytoma cells strongly express AQP4, which may facilitate their infiltration into the brain, and the neuroinflammatory disease neuromyelitis optica is caused by AQP4-specific autoantibodies that produce complement-mediated astrocytic damage.

Aquaporin 9 phosphorylation mediates membrane localization and neutrophil polarization

Neutrophils are of prime importance in the host innate defense against invading microorganisms by using two primary mechanisms-locomotion toward and phagocytosis of the prey. Recent research points to pivotal roles for water channels known as AQPs in cell motility. Here, we focused on the role of AQP9 in chemoattractant-induced polarization and migration of primary mouse neutrophils and neutrophil-like HL60 cells. We found that AQP9 is phosphorylated downstream of fMLFR or PMA stimulation in primary human neutrophils. The dynamics of AQP9 were assessed using GFP-tagged AQP9 constructs and other fluorescent markers through various live-cell imaging techniques. Expression of WT or the phosphomimic S11D AQP9 changed cell volume regulation as a response to hyperosmotic changes and enhanced neutrophil polarization and chemotaxis. WT AQP9 and S11D AQP9 displayed a very dynamic distribution at the cell membrane, whereas the phosphorylation-deficient S11A AQP9 failed to localize to the plasma membrane. Furthermore, we found that Rac1 regulated the translocation of AQP9 to the plasma membrane. Our results show that AQP9 plays an active role in neutrophil volume regulation and migration. The display of AQP9 at the plasma membrane depends on AQP9 phosphorylation, which appeared to be regulated through a Rac1-dependent pathway.

Membrane water permeability related to antigen-presenting function of dendritic cells

Aquaporin 5 (AQP5) is one of the water channel proteins which participate in a wide array of physiological processes and are primary determinants of membrane osmotic water permeability. The AQP5 gene is located in human chromosome 12q, the same region as the location of the major asthma susceptibility loci. In this study we try to determine whether the AQP5 knock-out has some effect on allergen-induced asthma. With a mouse asthma model induced by ovalbumin (OVA), we found that deletion of AQP5 reduced some major characteristic features of asthma, such as less inflammation cell infiltration in lung tissues, lower cytokine expression and fewer inflammation cells in bronchoalveolar lavage fluids compared with those from wild-type (WT) mice. Because it was found that mice injected intratracheally with OVA-pulsed dendritic cells (DCs), the AQP5 gene knock-out (AQP5(-/-)) ones presented fewer inflammation cells. Because DCs are major antigen-presenting cells that play an important role in antigen-induced asthma, we also probed into the possible effect of gene knock-out on DCs. Surprisingly, reverse transcription-polymerase chain reaction and fluorescence activated cell sorter analysis showed high levels of AQP5 on the surface of DCs from in vivo or bone marrow monocyte-derived DCs (mDC) in vitro. Immature mDC from AQP5 knock-out mice (AQP5(-/-)) showed decreased expression of CD80 and CD86 and endocytosis ability compared with that from WT, but the difference disappeared after mDCs matured with lipopolysaccharide. AQP5-mediated water transmembrane may play some role in the function of DCs. However, the mechanism of the effect of AQP5 on the DCs' function needs to be investigated further.

Filopodia are induced by aquaporin-9 expression

Understanding filopodial formation in motile cells is a pertinent task in cell biology. In the present study we show that expression of the human water channel aquaporin-9 (AQP9) in different cell lines induces the formation of numerous filopodial extensions. Several lines of evidence support the role of aquaporins functioning both as a water channel and signaling participant. The number of filopodia is decreased by site-directed serine substitutions in putative PKC-binding or -phosphorylation sites at amino acid position 11 and 222 in AQP9. The filopodial phenotype obtained with wild-type AQP9 is associated with elevated levels of active Cdc42, while serine-deleted mutants have reduced levels of GTP-Cdc42. Co-transfection with inhibitory N-WASP CRIB completely abolishes wild-type AQP9-induced filopodia formation. Active PKC(zeta) phosphorylates wild-type AQP9 and myristoylated PKC(zeta) pseudosubstrate inhibits the formation of filopodia in AQP9-expressing cells. Expression of wild-type AQP9, but not mock or serine substituted mutants, increases sensitivity to hypo-osmolaric conditions, yielding a rapid morphological rounding of cells and cell death starting as early as 24 h post-transfection. We propose that increased water influx through AQP9 is critically involved in the formation of membrane protrusions, and that AQP9-induced actin polymerization is augmented by activation of Cdc42 and PKC(zeta).

Height changes associated with pigment aggregation in Xenopus laevis melanophores

Melanophores are pigment cells found in the skin of lower vertebrates. The brownish-black pigment melanin is stored in organelles called melanosomes. In response to different stimuli, the cells can redistribute the melanosomes, and thereby change colour. During melanosome aggregation, a height increase has been observed in fish and frog melanophores across the cell centre. The mechanism by which the cell increases its height is unknown. Changes in cell shape can alter the electrical properties of the cell, and thereby be detected in impedance measurements. We have in earlier studies of Xenopus laevis melanophores shown that pigment aggregation can be revealed as impedance changes, and therefore we were interested in investigating the height changes associated with pigment aggregation further. Accordingly, we quantified the changes in cell height by performing vertical sectioning with confocal microscopy. In analogy with theories explaining the leading edge of migrating cells, we investigated the possibility that the elevation of plasma membrane is caused by local swelling due to influx of water through HgCl2-sensitive aquaporins. We also measured the height of the microtubule structures to assess whether they are involved in the height increase. Our results show that pigment aggregation in X. laevis melanophores resulted in a significant height increase, which was substantially larger when aggregation was induced by latrunculin than with melatonin. Moreover, the elevation of the plasma membrane did not correlate with influx of water through aquaporins or formation of new microtubules, Rather, the accumulation of granules seemed to drive the change in cell height.