Evaluation of GABA Production and Probiotic Activities of Enterococcus faecium BS5

Probiotics and Antimicrobial Proteins - Gamma-aminobutyric acid (GABA) is a principal inhibitory neurotransmitter in the central nervous system and is produced by irreversible decarboxylation of...     

Monolayer formation of human osteoblastic cells on vertically aligned multiwalled carbon nanotube scaffolds

Monolayer formation of SaOS‐2 (human osteoblast‐like cells) was observed on VACNT (vertically aligned multiwalled carbon nanotubes) scaffolds without purification or functionalization. The VACNT were produced by a microwave plasma chemical vapour deposition on titanium surfaces with nickel or iron as catalyst. Cell viability and morphology studies were evaluated by LDH (lactate dehydrogenase) release assay and SEM (scanning electron microscopy), respectively. The non‐toxicity and the flat spreading with monolayer formation of the SaOs‐2 on VACNT scaffolds surface indicate that they can be used for biomedical applications.     

Mammalian antimicrobial peptide influences control of cutaneous Leishmania infection

Cathelicidin-type antimicrobial peptides (CAMP) are important mediators of innate immunity against microbial pathogens acting through direct interaction with and disruption of microbial membranes and indirectly through modulation of host cell migration and activation. Using a mouse knock-out model in CAMP we studied the role of this host peptide in control of dissemination of cutaneous infection by the parasitic protozoan Leishmania. The presence of pronounced host inflammatory infiltration in lesions and lymph nodes of infected animals was CAMP-dependent. Lack of CAMP expression was associated with higher levels of IL-10 receptor expression in bone marrow, splenic and lymph node macrophages as well as higher anti-inflammatory IL-10 production by bone marrow macrophages and spleen cells but reduced production of the pro-inflammatory cytokines IL-12 and IFN-γ by lymph nodes. Unlike wild-type mice, local lesions were exacerbated and parasites were found largely disseminated in CAMP knockouts. Infection of CAMP knockouts with parasite mutants lacking the surface metalloprotease virulence determinant resulted in more robust disseminated infection than in control animals suggesting that CAMP activity is negatively regulated by parasite surface proteolytic activity. This correlated with the ability of the protease to degrade CAMP in vitro and co-localization of CAMP with parasites within macrophages. Our results highlight the interplay of antimicrobial peptides and Leishmania that influence the host immune response and the outcome of infection.     

Extracellular release of the glycosylphosphatidylinositol (GPI)-linked Leishmania surface metalloprotease, gp63, is independent of GPI phospholipolysis: implications for parasite virulence.

The major zinc metalloprotease of Leishmania (gp63), an important determinant of parasite virulence, is attached to the parasite surface via a glycosylphosphatidylinositol anchor. Here we report the spontaneous release of proteolytically active gp63 from a number of Leishmania isolates, causing cutaneous and visceral disease. To investigate the mechanism(s) of gp63 release, we transfected a gp63-deficient variant of Leishmania amazonensis with constructs expressing gp63 and various mutants thereof. Surprisingly, approximately half of wild type gp63 was found in the culture supernatant 12 h post-synthesis. Biochemical analysis of the extracellular gp63 revealed two forms of the protein, one that is released from the cell surface, and another, that apparently is directly secreted. Release of cell surface gp63 was significantly reduced when the proteolytic activity of the protein was inactivated by site-specific mutagenesis or inhibited by zinc chelation, suggesting that release involves autoproteolysis. The extracellular gp63 does not contain a glycosylphosphatidylinositol moiety or ethanolamine, indicating that phospholipolysis is not involved in the release process. Release of gp63 is also independent of glycosylation. The finding of proteolytically active, extracellular gp63 produced by multiple Leishmania isolates suggests a potential role of the extracellular enzyme in substrate degradation relevant to their survival in both the mammalian host and the insect vector.     

Immunophenotyping of human HT29 colon cancer cell primary tumours and their metastases in severe combined immunodeficient mice

The immunophenotype of HT29 human colon cancer cells implanted into severe combined immunodeficient mice was assessed in primary tumours and their metastases in the lungs using an indirect immunohistochemical method. After primary tumours were surgically removed, the metastases were given time to develop, thus paralleling the clinical situation. While vimentin was negative in both primary and secondary tumours, E-cadherin was present as membrane-bound labelling in the primary tumours only. Whereas the markers p53, MIB1, PCNA and CEA were consistently positive in both primary and metastatic tumours, CD44 variant 6 and CA125 were negative in metastases but positive in the primary tumours. There was a significant increase in the percentage of cells labelled for p53 in the primary tumours compared with the metastases. For the proliferation markers, there was no significant difference in labelling between primary tumours and metastases for MIB1. Of the cytokeratins examined, CK 20 gave the strongest and most consistent reaction in both primary and secondary tumours. The results indicate that, for certain immunohistochemical markers, results are the same in both primary tumours and metastases. Hence, in these cases, antigens that are expressed on the primary tumour as well as on the metastases can serve as target molecules for immunologically based forms of treatment of metastases. This revised version was published online in November 2006 with corrections to the Cover Date.     

Antimicrobial Peptide-induced Apoptotic Death of Leishmania Results from Calcium-de pend ent, Caspase-independent Mitochondrial Toxicity

α- and θ-defensin-, magainin-, and cathelicidin-type antimicrobial peptides (AMPs) can kill the pathogenic protozoan Leishmania. Comparative studies of a panel of AMPs have defined two distinct groups: those that induce nonapoptotic (Class I) and apoptotic (Class II) parasite killing based on their differential ability to induce phosphatidyl serine exposure, loss of mitochondrial membrane potential and decreased ATP production, induction of caspase-3/7 and -12 activity, and DNA degradation. Class II AMPs cause rapid influx of the vital stain SYTOX and an increase in intracellular Ca²⁺, whereas Class I AMPs cause a slow accumulation of SYTOX and do not affect intracellular Ca²⁺ levels. Inhibitors of cysteine or caspase proteases diminished fast influx of SYTOX through the surface membrane and DNA degradation but do not ablate the annexin V staining or the induction of apoptosis by Class II AMPs. This suggests that the changes in surface permeability in AMP-mediated apoptosis are related to the downstream events of intracellular cysteine/caspase activation or the loss of ATP. The activation of caspase-12-like activity was Ca²⁺-dependent, and inhibitors of voltage-gated and nonspecific Ca²⁺ channels diminished this activity. Flufenamic acid, a nonspecific Ca²⁺ inhibitor, completely ablated AMP-induced mitochondrial dysfunction and cell death, indicating the importance of dysregulation of Ca²⁺ in antimicrobial peptide-induced apoptosis.Leishmania are vector-borne protozoa that parasitize host macrophage phagolysosomes. Activated macrophages kill intracellular parasites in part by induction of apoptosis by nitric oxide in a caspase- and cysteine protease-independent manner (1, 2). Limited apoptosis of Leishmania within the sandfly vector, prior to infection of host, may be important to the establishment of infection (3, 4). In vitro Leishmania can undergo apoptosis by exposure to many different compounds that lead to alteration of surface the cell membrane causing enhanced annexin V staining, activation of caspase-like proteases, DNA laddering, and mitochondrial membrane depolarization. Our work has recently shown that antimicrobial peptide exposure of Leishmania can induce apoptosis, which occurs concomitant with activation of both caspase and cysteine protease activities (5).Antimicrobial peptides (AMPs)2 are structurally diverse highly cationic proteins between 10 and 50 amino acids and are components of the innate immune systems of organisms within all kingdoms. AMPs have a myriad of functions and are known to interact with and disrupt microbial surface membranes leading to cell death. Magainins are α-helical AMPs expressed in the skin of frogs, whereas cathelicidins are mammalian β-pleated sheet peptides, both of which can kill Leishmania at physiological concentrations (5). We have documented that magainins are quite apt at causing AMP-induced apoptosis of surface metalloprotease null mutants of L. major and that these exhibited features of apoptotic Leishmania induced by different stimuli (5). These two different structurally diverse classes of AMPs are known to interact with membranes in distinct ways (6), yet it is unknown whether we they can kill parasites via disparate mechanisms.Apoptosis of Leishmania induced by antimony, camptothecin, and hydrogen peroxide all induce significant increases in cytosolic calcium, which is toxic to mitochondrial membrane potential (7–9). Calcium-related cell death and mitochondrial toxicity are related to the activity of nonspecific calcium channels (7, 8, 10), which may be attributable to their location in the mitochondrial membrane (11, 12). Apoptosis of Leishmania is also associated with increases in caspase-like and cysteine protease activity (5, 7, 9, 13, 14). Caspase-3/7-like activation can be induced by a number of stimuli despite the absence of genes encoding caspases within the L. major genome (15). In addition, the ancestral metacaspase expressed by Leishmania donovani is a trypsin-like protease not inhibitible with caspase inhibitors (16). We and others have found that cysteine protease activity may be important for certain features of Leishmania apoptosis such as DNA degradation (5). It is quite clear that Leishmania can undergo apoptosis in caspase-dependent and caspase-independent pathways (17), yet we do not know what mode of apoptosis occurs upon AMP exposure.In the work presented here we show that two structurally diverse AMPs kill Leishmania differentially inducing either nonapoptotic or apoptotic cell death. We have characterized AMP-induced apoptotic cell death and found that although it is associated with the activation of caspase-3/7- and -12-like activities, these activities are not essential to apoptosis. Conversely we find that a dramatic increase in cytosolic Ca²⁺ correlates with the mitochondrial membrane dysfunction and the decline in ATP production and cell death and that this is completely inhibited by blockade of nonspecific calcium channels. Blockade of caspase and cysteine proteases affect surface membrane permeability changes and DNA degradation but do not prevent cell death, suggesting that AMP-induced apoptosis may be a caspase-independent process. These data provide a framework to understand the critical events in AMP-mediated apoptosis and may be helpful in the rational design of chemotherapeutic strategies for manipulation of cell death pathways in Leishmania.     

Molecular determinants of ciliary membrane localization of Trypanosoma cruzi flagellar calcium-binding protein

The flagellar calcium-binding protein (FCaBP) of Trypanosoma cruzi is localized to the flagellar membrane in all life cycle stages of the parasite. Myristoylation and palmitoylation of the N terminus of FCaBP are necessary for flagellar membrane targeting. Not all dually acylated proteins in T. cruzi are flagellar, however. Other determinants of FCaBP therefore likely contribute to flagellar specificity. We generated T. cruzi transfectants expressing the N-terminal 24 or 12 amino acids of FCaBP fused to GFP. Analysis of these mutants revealed that although amino acids 1-12 are sufficient for dual acylation and membrane binding, amino acids 13-24 are required for flagellar specificity and lipid raft association. Mutagenesis of several conserved lysine residues in the latter peptide demonstrated that these residues are essential for flagellar targeting and lipid raft association. Finally, FCaBP was expressed in the protozoan Leishmania amazonensis, which lacks FCaBP. The flagellar localization and membrane association of FCaBP in L. amazonensis suggest that the mechanisms for flagellar targeting, including a specific palmitoyl acyltransferase, are conserved in this organism.     

Comparisons of the molecular evolutionary process at rbcL and ndhF in the grass family (Poaceae)

We examine rate heterogeneity among evolutionary lineages of the grass family at two plasmid loci, ndhF and rbcL, and we introduce a method to determine whether patterns of rate heterogeneity are correlated between loci. We show both that rates of synonymous evolution are heterogeneous among grass lineages and that are heterogeneity is correlated between loci at synonymous sites. At nonsynonymous sites, the pattern of rate heterogeneity is not correlated between loci, primarily due to an aberrant pattern of rate heterogeneity at nonsynonymous sites of rbcL. We compare patterns of synonymous rate heterogeneity to predictors based on the generation time effect and the speciation rate hypotheses. Although there is some evidence for generation time effects, neither generation time effects nor speciation rates appear to be sufficient to explain patterns of rate heterogeneity in the grass plastid sequences.