Different roles of membrane potentials in electrotaxis and chemotaxis of dictyostelium cells

Many types of cells migrate directionally in direct current (DC) electric fields (EFs), a phenomenon termed galvanotaxis or electrotaxis. The directional sensing mechanisms responsible for this response to EFs, however, remain unknown. Exposing cells to an EF causes changes in plasma membrane potentials (V(m)). Exploiting the ability of Dictyostelium cells to tolerate drastic V(m) changes, we investigated the role of V(m) in electrotaxis and, in parallel, in chemotaxis. We used three independent factors to control V(m): extracellular pH, extracellular [K(+)], and electroporation. Changes in V(m) were monitored with microelectrode recording techniques. Depolarized V(m) was observed under acidic (pH 5.0) and alkaline (pH 9.0) conditions as well as under higher extracellular [K(+)] conditions. Electroporation permeabilized the cell membrane and significantly reduced the V(m), which gradually recovered over 40 min. We then recorded the electrotactic behaviors of Dictyostelium cells with a defined V(m) using these three techniques. The directionality (directedness of electrotaxis) was quantified and compared to that of chemotaxis (chemotactic index). We found that a reduced V(m) significantly impaired electrotaxis without significantly affecting random motility or chemotaxis. We conclude that extracellular pH, [K(+)], and electroporation all significantly affected electrotaxis, which appeared to be mediated by the changes in V(m). The initial directional sensing mechanisms for electrotaxis therefore differ from those of chemotaxis and may be mediated by changes in resting V(m).

Co-culture systems for vascularization--learning from nature

The endothelial cell (EC) is practically ubiquitous in the human body and forms the inner cellular lining of the entire cardiovascular system. Following tissue injury, the microcirculation becomes the stage for both the inflammatory response and the subsequent healing reaction to restore physiological function to the damaged tissue. The advent of the multidisciplinary field of Regenerative Medicine (RegMed), of which Tissue Engineering (TE) and drug delivery using modern stimuli-responsive or interactive biomaterials are important components, has opened up new approaches to the acceleration of the healing response. A central and rate-limiting role in the latter is played by the process of vascularization or neovascularization, so that it is not surprising that in RegMed concepts have been developed for the drug- and gene-delivery of potent stimuli such as vascular-endothelial growth factor (VEGF) to promote neovessel development. However, not all of these novel materials can be tested in vivo, and in vitro co-culture model systems using human primary cells are being developed to pre-evaluate and determine which of the RegMed concepts exhibit the most promising potential for success after implantation. This review describes some of the growing number of in vitro co-cultures model systems that are being used to study cell-cell and cell-material interactions at the cellular and molecular levels to determine which materials are best suited to integrate into the host, promote a rapid vascularization and fit into the regenerative process without disturbing or slowing the normal healing steps.

Sphingosine-1-phosphate lyase deficiency produces a pro-inflammatory response while impairing neutrophil trafficking

Sphingosine-1-phosphate (S1P) lyase catalyzes the degradation of S1P, a potent signaling lysosphingolipid. Mice with an inactive S1P lyase gene are impaired in the capacity to degrade S1P, resulting in highly elevated S1P levels. These S1P lyase-deficient mice have low numbers of lymphocytes and high numbers of neutrophils in their blood. We found that the S1P lyase-deficient mice exhibited features of an inflammatory response including elevated levels of pro-inflammatory cytokines and an increased expression of genes in liver associated with an acute-phase response. However, the recruitment of their neutrophils into inflamed tissues was impaired and their neutrophils were defective in migration to chemotactic stimulus. The IL-23/IL-17/granulocyte-colony stimulating factor (G-CSF) cytokine-controlled loop regulating neutrophil homeostasis, which is dependent on neutrophil trafficking to tissues, was disturbed in S1P lyase-deficient mice. Deletion of the S1P4 receptor partially decreased the neutrophilia and inflammation in S1P lyase-deficient mice, implicating S1P receptor signaling in the phenotype. Thus, a genetic block in S1P degradation elicits a pro-inflammatory response but impairs neutrophil migration from blood into tissues.

Glial innate immunity generated by non-aggregated alpha-synuclein in mouse: differences between wild-type and Parkinson's disease-linked mutants

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized pathologically by the presence in the brain of intracellular protein inclusions highly enriched in aggregated alpha-synuclein (α-Syn). Although it has been established that progression of the disease is accompanied by sustained activation of microglia, the underlying molecules and factors involved in these immune-triggered mechanisms remain largely unexplored. Lately, accumulating evidence has shown the presence of extracellular α-Syn both in its aggregated and monomeric forms in cerebrospinal fluid and blood plasma. However, the effect of extracellular α-Syn on cellular activation and immune mediators, as well as the impact of familial PD-linked α-Syn mutants on this stimulation, are still largely unknown.

METHODS AND FINDINGS

In this work, we have compared the activation profiles of non-aggregated, extracellular wild-type and PD-linked mutant α-Syn variants on primary glial and microglial cell cultures. After stimulation of cells with α-Syn, we measured the release of Th1- and Th2- type cytokines as well as IP-10/CXCL10, RANTES/CCL5, MCP-1/CCL2 and MIP-1α/CCL3 chemokines. Contrary to what had been observed using cell lines or for the case of aggregated α-Syn, we found strong differences in the immune response generated by wild-type α-Syn and the familial PD mutants (A30P, E46K and A53T).

CONCLUSIONS

These findings might contribute to explain the differences in the onset and progression of this highly debilitating disease, which could be of value in the development of rational approaches towards effective control of immune responses that are associated with PD.

The effect of tert-butyl hydroperoxide on hepatic transcriptome expression patterns in the striped sea bream (Lithognathus mormyrus; Teleostei)

The study was aimed at examining the effects of tert-butyl hydroperoxide (tBHP) on hepatic transcriptome expression patterns of the teleost fish Lithognathus mormyrus. tBHP is an organic hydro-peroxide, widely used as a model pro-oxidant. It generates the reactive oxygen species (ROS) tert-butoxyl and tert-butylperoxyl. Complementary DNAs of tBHP-treated vs control fish were applied onto a previously produced cDNA microarray of approximately 1500 unique sequences. The effects of the tBHP application were demonstrated by leukocyte infiltration into the liver and by differential expression of various genes, some already known to be involved in ROS-related responses. Indicator genes of putative ROS effects were: aldehyde dehydrogenase 3A2, Heme oxygenase and the hemopexin-like protein. Putative indicators of transendothelial leukocyte migration and function were: p22phox, Rac1 and CD63-like genes. Interestingly, 7-dehydrocholesterol reductase was significantly down-regulated in response to all treatments. Several non-annotated genes revealed uniform directions of differential expression in response to all treatments.

Leucocyte/endothelium interactions and microvessel permeability: coupled or uncoupled?

In response to infections or tissue injury, circulating leucocytes adhere to and migrate from the vessel lumen to interstitial inflammatory sites to combat invading pathogens. However, these defensive actions may also cause host tissue injury and microvascular dysfunction through oxidative bursts or enzyme release. For decades, the interaction between leucocytes and microvessel walls has been considered as a critical event leading to organ dysfunction. Extensive investigations have therefore focused on blocking specific adhesive ligands to prevent tissue injury. However, anti-adhesion therapies have shown limited success in preventing vascular dysfunction in clinical trials. Numerous studies have demonstrated temporal and spatial dissociations of leucocyte adhesion and/or emigration from permeability increases. The mechanisms that initiate the adhesion cascade have been found to be distinct from those that trigger the leucocyte oxidative burst responsible for increasing microvessel permeability. Recent studies demonstrated that endothelial activation by inflammatory mediators is critical for initiating platelet adhesion and platelet-dependent leucocyte recruitment resulting in augmented increases in microvessel permeability. These new developments suggest that targeting endothelial activation via directly enhancing endothelial barrier function might be a more efficient strategy than focusing on anti-adhesion or platelet/leucocyte depletion to prevent vascular damage during inflammation. Owing to space limitations and the wide range of studies in the field, this article will not serve as a comprehensive review. Instead, it will highlight the emerging evidence of adhesion-uncoupled permeability changes and establish a basis for re-evaluating the coupled relationship between leucocyte/platelet activation and microvessel permeability to achieve a better understanding of permeability regulation during inflammation.