Background: Gangliosides are receptors for bacterial toxins. Results: Alpha-toxin from Clostridium perfringens specifically interacts with GM1a. Conclusion: Trp-84 and Tyr-85 of alpha-toxin are the residues that interact with GM1a, leading to activation of TrkA in A549 cells. Significance: These results define the role of GM1a-TrkA as a receptor for alpha-toxin.
Clostridium perfringens alpha-toxin elicits various immune responses such as the release of cytokines, chemokines, and superoxide via the GM1a/TrkA complex. Alpha-toxin possesses phospholipase C (PLC) hydrolytic activity that contributes to signal transduction in the pathogenesis of gas gangrene. Little is known about the relationship between lipid metabolism and TrkA activation by alpha-toxin. Using live-cell fluorescence microscopy, we monitored transbilayer movement of diacylglycerol (DAG) with the yellow fluorescent protein-tagged C1AB domain of protein kinase C-γ (EYFP-C1AB). DAG accumulated at the marginal region of the plasma membrane in alpha toxin-treated A549 cells, which also exhibited GM1a clustering and TrkA phosphorylation. Annexin V binding assays showed that alpha-toxin induced the exposure of phosphatidylserine on the outer leaflet of the plasma membrane. However, H148G, a variant toxin which binds cell membrane and has no enzymatic activity, did not induce DAG translocation, GM1a clustering, or TrkA phosphorylation. Alpha-toxin also specifically activated endogenous phospholipase Cγ-1 (PLCγ-1), a TrkA adaptor protein, via phosphorylation. U73122, an endogenous PLC inhibitor, and siRNA for PLCγ-1 inhibited the formation of DAG and release of IL-8. GM1a accumulation and TrkA phosphorylation in A549 cells treated with alpha-toxin were also inhibited by U73122. These results suggest that the flip-flop motion of hydrophobic lipids such as DAG leads to the accumulation of GM1a and TrkA. We conclude that the formation of DAG by alpha-toxin itself (first step) and activation of endogenous PLCγ-1 (second step) leads to alterations in membrane dynamics, followed by strong phosphorylation of TrkA.
Digital breast tomosynthesis (DBT) imaging uses two types of image reconstruction. methods, i.e., filtered back projection (FBP) method and an iterative reconstruction (IR) method. Although the effect of the difference in the image reconstruction method on the image quality has been reported, these studies were performed using different apparatus or conditions. In this study, we examined the effect of image reconstruction on the image quality using the same equipment under the same conditions. Method: We measured reflection artifact, sharpness, signal detection ability, and granularity using DBT-photographed images by both the FBP and the IR methods. Result: Although the difference between the two methods was subtle for granularity, IR was found to be superior to FBP in all items tested. Conclusion: This study suggested the clinical usefulness of IR over FBP.
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