High hydrophobic amino acid exposure is responsible of the neurotoxic effects induced by E200K or D202N disease-related mutations of the human prion protein

Mutations in prion protein are thought to be causative of inherited prion diseases favoring the spontaneous conversion of the normal prion protein into the scrapie-like pathological prion protein. We previously reported that, by controlled thermal denaturation, human prion protein fragment 90-231 acquires neurotoxic properties when transformed in a β-rich conformation, resembling the scrapie-like conformation. In this study we generated prion protein fragment 90-231 bearing mutations identified in familial prion diseases (D202N and E200K), to analyze their role in the induction of a neurotoxic conformation. Prion protein fragment 90-231(wild type) and the D202N mutant were not toxic in native conformation but induced cell death only after thermal denaturation. Conversely, prion protein fragment 90-231(E200K) was highly toxic in its native structure, suggesting that E200K mutation per se favors the acquisition of a peptide neurotoxic conformation. To identify the structural determinants of prion protein fragment 90-231 toxicity, we show that while the wild type peptide is structured in α-helix, hPrP90-231 E200K is spontaneously refolded in a β-structured conformer characterized by increased proteinase K resistance and propensity to generate fibrils. However, the most significant difference induced by E200K mutation in prion protein fragment 90-231 structure in native conformation we observed, was an increase in the exposure of hydrophobic amino-acids on protein surface that was detected in wild type and D202N proteins only after thermal denaturation. In conclusion, we propose that increased hydrophobicity is one of the main determinants of toxicity induced by different mutations in prion protein-derived peptides.     

Elucidation of the Molecular Mechanisms of Action of the Natural Antimicrobial Peptide Subtilosin Against the Bacterial Vaginosis-associated Pathogen Gardnerella vaginalis

Subtilosin A is a 35-amino acid long cyclical peptide produced by Bacillus amyloliquefaciens that has potent antimicrobial activity against a variety of human pathogens, including the bacterial vaginosis-related Gardnerella vaginalis. The specific mode of action of subtilosin against G. vaginalis was elucidated by studying its effects on the proton motive force's (PMF) components: transmembrane electric potential (ΔΨ), transmembrane pH gradient (ΔpH), and intracellular ATP levels. The addition of subtilosin to G. vaginalis cells caused an immediate and total depletion of the ΔpH, but had no effect on the ΔΨ. Subtilosin also triggered an instant but partial efflux of intracellular ATP that was twofold higher than that of the positive control bacteriocin, nisin. Taken together, these data suggest that subtilosin inhibits G. vaginalis growth by creating transient pores in the cells' cytoplasmic membrane, leading to an efflux of intracellular ions and ATP and eventually cell death.     

The targeting of plasmalemmal ceramide to mitochondria during apoptosis

Ceramide is a key lipid mediator of cellular processes such as differentiation, proliferation, growth arrest and apoptosis. During apoptosis, ceramide is produced within the plasma membrane. Although recent data suggest that the generation of intracellular ceramide increases mitochondrial permeability, the source of mitochondrial ceramide remains unknown. Here, we determine whether a stress-mediated plasmalemmal pool of ceramide might become available to the mitochondria of apoptotic cells. We have previously established annexin A1--a member of a family of Ca(2+) and membrane-binding proteins--to be a marker of ceramide platforms. Using fluorescently tagged annexin A1, we show that, upon its generation within the plasma membrane, ceramide self-associates into platforms that subsequently invaginate and fuse with mitochondria. An accumulation of ceramide within the mitochondria of apoptotic cells was also confirmed using a ceramide-specific antibody. Electron microscopic tomography confirmed that upon the formation of ceramide platforms, the invaginated regions of the plasma membrane extend deep into the cytoplasm forming direct physical contacts with mitochondrial outer membranes. Ceramide might thus be directly transferred from the plasma membrane to the mitochondrial outer membrane. It is conceivable that this "kiss-of-death" increases the permeability of the mitochondrial outer membrane thereby triggering apoptosis.     

Targeted deletion of integrin-linked kinase reveals a role in T-cell chemotaxis and survival

Integrin-linked kinase (ILK) is a serine/threonine kinase that is important in cell-matrix interactions and cell signaling. To examine the role of ILK in leukocyte trafficking and survival, we generated T cell-specific ILK knockouts by breeding ILK(flox/flox) mice to transgenic mice expressing Cre recombinase under control of the Lck proximal promoter. Thymic T cells from Lck-Cre(+)/ILK(flox/flox) mice had a marked reduction (>95%) in ILK protein levels. Thymic cellularity was comparable in 3- to 4-week-old mice, but a threefold diminution of thymic T cells became evident by 6 to 8 weeks of age in the T cell-specific ILK knockout mice due to increased cell death of double-positive (DP) T cells. Analysis of peripheral T cells by quantitative PCR and by breeding Lck-Cre(+)/ILK(flox/flox) mice to a YFP-transgenic reporter strain demonstrated an approximate 20-fold enrichment of ILK-competent cells, suggesting these cells have a competitive advantage in trafficking to and/or survival in peripheral lymphatic organs. We explored mechanisms related to altered cell trafficking and survival that might explain the decreases in thymic cellularity and enrichment for ILK-competent cells in the spleen and lymph nodes. We observed a >50% reduction in chemotaxis of ILK-deficient T cells to the chemokines CXCL12 (stromal cell-derived factor [SDF]-1alpha) and CCL19 (macrophage inflammatory protein [MIP]-3beta), as well as enhanced apoptosis of ILK-deficient cells upon stress. Signaling studies in ILK-deficient T cells demonstrated diminished phosphorylation of Akt on the activating phosphorylation site, Ser 473, and a concordant decrease in Akt kinase activity following stimulation with the chemokine SDF-1. Rac1 activation was also markedly diminished in ILK-deficient T cells following chemokine stimulation. These data extend the role of ILK to immune-cell trafficking and survival via modulation of Akt- and Rac-dependent substrates, and have implications for cell recruitment in both homeostatic and pathological processes.     

Trabeculectomy with mitomycin C in glaucoma associated with uveitis

The patients with uveitic glaucoma are at high risk for failure following drainage surgery because of young age of these patients, preoperative long-term control of inflammation and postoperative complications. Twenty-two trabeculectomies performed in 22 patients with uveitic glaucoma were retrospectively evaluated to analyze the effect of intraoperative application of mitomycin C (MMC). Success rates, postoperative levels of intraocular pressure (IOP) and postoperative complications were studied. After a mean follow-up of 10.6 months (range, 5-28 months), 15 patients (68.2%) achieved IOP of 21mmHg or less without antiglaucoma medications. There were statistically significant reduction in IOP postoperatively during the period studied (p < 0.001). Early postoperative complications included chorioidal detachment (9.1%), shallow anterior chamber (9.1%), hyphema (13.6%), macular edema (4.5%) and raised IOP (27.3%). Late postoperative complications included exacerbation of uveitis (4.5%), macular edema (4.5%), cataract (22.7%) and raised IOP (31.8%). The eyes with raised IOP needed additional antiglaucoma medication. The results of this retrospective and uncontrolled study suggest that intraoperative application of MMC may be a good option for enhancement of short-term trabeculectomy success rates in patients with uveitic glaucoma.     

Full-thickeness anterior blepharotomy and transpalpebral fat decompression in Graves' orbitopathy

A chief morbidity of Graves eye disease is eyelid retraction and exophthalmus. Transpalpebral orbital fat removal accomplished with full thickness anterior blepharotomy was performed in 4 patients (5 orbits). Preoperative and postoperative ocular exposure symptoms, visual acuity, upper eyelid retraction and proptosis were evaluated. In all 5 operated orbits preoperative symptoms resolved; good results were achieved from the functional and cosmetic point of view. Full-thickness anterior blepharotomy combined with fat decompression is a safe and effective surgery for patients with upper eyelid retraction and exophthalmus due to enlarged orbital fat compartment.     

Evidence of involvement of leptin and IL-6 peptides in the action of interferon-beta in secondary progressive multiple sclerosis

Leptin is a peptide hormone which acts on cells of immune system by influencing the production of cytokines. Serum leptin levels and cytokine production by peripheral blood mononuclear cells (PBMC) were measured in 18 secondary progressive multiple sclerosis (SPMS) patients under IFN-beta-1b treatment. There were no overall effects on leptin, interleukin-6 (IL-6), IL-10 and IL-12 p40 after 2, 6 and 12 months of treatment. However, leptin and IL-6 decreased after 6 and 12 months of treatment in 12 patients who did not show progression of disability. Thus, our pilot data show that the beneficial effect of IFN-beta on some SPMS patients might be associated with the reduced levels of leptin and reduced IL-6 production by PBMC.