A hexavalent Coxsackievirus B vaccine is highly immunogenic and has a strong protective capacity in mice and nonhuman primates

Coxsackievirus B (CVB) enteroviruses are common human pathogens known to cause severe diseases including myocarditis, chronic dilated cardiomyopathy, and aseptic meningitis. CVBs are also hypothesized to be a causal factor in type 1 diabetes. Vaccines against CVBs are not currently available, and here we describe the generation and preclinical testing of a novel hexavalent vaccine targeting the six known CVB serotypes. We show that the vaccine has an excellent safety profile in murine models and nonhuman primates and that it induces strong neutralizing antibody responses to the six serotypes in both species without an adjuvant. We also demonstrate that the vaccine provides immunity against acute CVB infections in mice, including CVB infections known to cause virus-induced myocarditis. In addition, it blocks CVB-induced diabetes in a genetically permissive mouse model. Our preclinical proof-of-concept studies demonstrate the successful generation of a promising hexavalent CVB vaccine with high immunogenicity capable of preventing CVB-induced diseases.

Targeting of biotinylated compounds to its target tissue using a low-density lipoprotein receptor–avidin fusion protein

The very high binding affinity of avidin to biotin is one of the highest to occur in nature. We constructed a fusion protein composed of avidin and the endocytotic LDL receptor in order to target biotinylated molecules to cells of the desired tissues. In addition to the native avidin, charge-mutated and nonglycosylated avidins were utilized as part of the fusion proteins, in order to modify its properties. All of the fusion protein versions retained the biotin-binding capacity. Although the specificity was not increased, however, fusion proteins composed of natural avidin and nonglycosylated avidin bound most efficiently to the biotinylated ligands. Fluorescence microscopy and atomic force microscopy studies revealed the expression of the fusion protein on cell membranes, and demonstrated specific and high-affinity binding of biotin to the low-density lipoprotein receptor (LDLR)-avidin fusion protein in vitro. Additionally, systemically administered biotinylated ligand targeted with high specificity the intracerebral tumors of rats that were expressing fusion protein after the virus-mediated gene transfer. These results suggest that local gene transfer of the fusion protein to target tissues may offer a novel tool for the delivery of biotinylated molecules in vitro and in vivo for therapeutic and imaging purposes.

Entry of human parechovirus 1

Human parechovirus 1 (HPEV-1) is a prototype member of parechoviruses, a recently established picornavirus genus. Although there is preliminary evidence that HPEV-1 recognizes alpha(V) integrins as cellular receptors, our understanding of early events during HPEV-1 infection is still very limited. The aim of this study was to clarify the entry mechanisms of HPEV-1, including the attachment of the virus onto the host cell surface and subsequent internalization. In blocking experiments with monoclonal antibodies against different receptor candidates, antibodies against alpha(V) and beta(3) integrin subunits, in particular in combination, appeared to be the most efficient ones in preventing the HPEV-1 infection. To find out whether HPEV-1 uses clathrin-coated vesicles or other routes for the entry into the host cell, we carried out double-labeling experiments of virus-infected cells with anti-HPEV-1 antibodies and antibodies against known markers of the clathrin and the caveolin routes. At the early phase of infection (5 min postinfection [p.i.]) HPEV-1 colocalized with EEA1 (early endosomes), and later, after 30 min p.i., it colocalized with mannose-6-phosphate receptor (late endosomes), whereas no colocalization with caveolin-1 was observed. The data indicate that HPEV-1 utilizes the clathrin-dependent endocytic pathway for entry into the host cells. Interestingly, endocytosed HPEV-1 capsid proteins were observed in the endoplasmic reticulum and cis-Golgi network 30 to 60 min p.i. Depolymerization of microtubules with nocodazole inhibited translocation of the virus to the late endosomes but did not block HPEV-1 replication, suggesting that the RNA genome may be released early during the entry process.

Selective targeting of avidin/mannose 6-phosphate receptor chimeras to early or late endosomes

In this study we have used the Semliki forest virus expression system to transiently express chimeric proteins that contain transmembrane and cytoplasmic domains of the cation-independent mannose 6-phosphate receptor (CI-MPR) fused to chicken avidin. Immunofluorescence and electron microscopy studies showed that the chimeric protein with the entire cytoplasmic domain of CI-MPR was transported to late endosomes, where it accumulated. We made use of the biotin-binding capacity of lumenal avidin, and found that, in agreement with this distribution, the chimeric protein could be labelled with biotinylated HRP endocytosed for a long, but not a brief, period of time. However, truncation of the C-terminal tail distal to the rapid endocytosis motif (YKYSKV), caused the truncated chimera to be transported to, and accumulated within, early endosomes. This truncated chimera did not reach recycling early endosomes labelled with internalised transferrin, to any significant extent, but was accessible to biotinylated HRP internalised for 5 min (or for longer periods at 19 degrees C). Coinfection of these chimeras showed that they follow the same route from the TGN to the early endosomes. We conclude that the sequence distal to the endocytosis motif contains the signals which are required for efficient transport to late endosomes. Our results also suggest that the YKYSKV sequence close to the CI-MPR transmembrane segment is sufficient for targeting to sorting early endosomes.

The transmembrane protein p23 contributes to the organization of the Golgi apparatus

In previous studies we have shown that p23, a member of the p24-family of small transmembrane proteins, is highly abundant in membranes of the cis-Golgi network (CGN), and is involved in sorting/trafficking in the early secretory pathway. In the present study, we have further investigated the role of p23 after ectopic expression. We found that ectopically expressed p23 folded and oligomerized properly, even after overexpression. However, in contrast to endogenous p23, exogenous p23 molecules did not localize to the CGN, but induced a significant expansion of characteristic smooth ER membranes, where they accumulated in high amounts. This ER-derived, p23-rich subdomain displayed a highly regular morphology, consisting of tubules and/or cisternae of constant diameter, which were reminiscent of the CGN membranes containing p23 in control cells. The expression of exogenous p23 also led to the specific relocalization of endogenous p23, but not of other proteins, to these specialized ER-derived membranes. Relocalization of p23 modified the ultrastructure of the CGN and Golgi membranes, but did not affect anterograde and retrograde transport reactions to any significant extent. We conclude (i) that p23 has a morphogenic activity that contributes to the morphology of CGN-membranes; and (ii) that the presence of p23 in the CGN is necessary for the proper organization of the Golgi apparatus.

Endocytosis in skeletal muscle fibers

Defining the organization of endocytic pathway in multinucleated skeletal myofibers is crucial to understand the routing of membrane proteins, such as receptors and glucose transporters, through this system. Here we analyzed the organization of the endocytic trafficking pathways in isolated rat myofibers. We found that sarcolemmal-coated pits and transferrin receptors were concentrated in the I band areas. Fluid phase markers were taken up into vesicles in the same areas along the whole length of the fibers and were then delivered into structures around and between the nuclei. These markers also accumulated beneath the neuromuscular and myotendinous junctions. The recycling compartment, labeled with transferrin, appeared as perinuclear and interfibrillar dots that partially colocalized with the GLUT4 compartment. Low-density lipoprotein, a marker of the lysosome-directed pathway, was transported into sparsely distributed perinuclear and interfibrillar dots that contacted microtubules. A majority of these dots did not colocalize with internalized transferrin, indicating that the recycling and the lysosome-directed pathways were distinct. In conclusion, the I band areas were active in endocytosis along the whole length of the multinucleated myofibers. The sorting endosomes distributed in a cross-striated fashion while the recycling and late endosomal compartments showed perinuclear and interfibrillar localizations and followed the course of microtubules.

Intracellular route of canine parvovirus entry

The present study was designed to investigate the endocytic pathway involved in canine parvovirus (CPV) infection. Reduced temperature (18 degrees C) or the microtubule-depolymerizing drug nocodazole was found to inhibit productive infection of canine A72 cells by CPV and caused CPV to be retained in cytoplasmic vesicles as indicated by immunofluorescence microscopy. Consistent with previously published results, these data indicate that CPV enters a host cell via an endocytic route and further suggest that microtubule-dependent delivery of CPV to late endosomes is required for productive infection. Cytoplasmic microinjection of CPV particles was used to circumvent the endocytosis and membrane fusion steps in the entry process. Microinjection experiments showed that CPV particles which were injected directly into the cytoplasm, thus avoiding the endocytic pathway, were unable to initiate progeny virus production. CPV treated at pH 5.0 prior to microinjection was unable to initiate virus production, showing that factors of the endocytic route other than low pH are necessary for the initiation of infection by CPV.

Isoproterenol-induced redistribution of endosomes in cardiac myocytes

During myocardial infarction, it is well known that the cytoplasm of cardiac myocytes becomes more acidic due to lactate accumulation. The resulting necrosis is believed to result, at least in part, from the leakage of lysosomal enzymes into the cytoplasm. In addition, it has previously been shown that cytoplasm acidification in tissue culture cells can cause the redistribution of late endosomes and tubular lysosomes. In the present study, we have investigated whether lysosomal/endosomal structures were affected during isoproterenol-induced infarct-like myocardial necrosis in rat heart in vivo. In parallel, we treated rat primary myocyte cultures with a high dose of isoproterenol or low pH. We followed the fate of lysosomal enzymes, a lysosomal membrane glycoprotein and the cation-independent mannose 6-phosphate receptor. Lysosomes were intact until irreversible injury became evident suggesting that the lysosomal enzyme release concomitant with the leakage of cytoplasmic enzymes is merely a consequence of cell death. During the early phase of injury, when the myocyte cytoplasm was mildly acidified, late endosomes showed fragmentation and microtubule-dependent movement towards the periphery, while the subcellular distribution of lysosomes was unchanged. Both processes were also observed after mild artificial acidification of the cytoplasm. Our data show that late endosomes and lysosomal trafficking are affected early during isoproterenol-induced myocardial injury causing a pH-dependent redistribution of late endosomes.

Phosphomannosyl receptors of lysosomal enzymes of skeletal muscle in neuromuscular diseases

The phosphomannosyl receptor system is responsible for both the receptor-mediated endocytosis and the intracellular transport of lysosomal enzymes. In the present study this receptor system was examined in affected muscles of patients with various neuromuscular diseases. The total activity of beta-N-acetyl-glucosaminidase, a marker enzyme of lysosomal hydrolases, was significantly elevated in the patients with myopathies (polymyositis and muscular dystrophies) but only slightly increased in those with neurogenic muscle atrophies (amyotrophic lateral sclerosis, polyneuropathy or other neurogenic muscle disease). The increase was most prominent in the group of polymyositis. The content of phosphomannosyl receptors was increased in the patients with myogenic muscle disease but not in those with neurogenic disease. The receptor binding of lysosomal enzymes was saturable and inhibited with mannose 6-phosphate showing the typical characteristics of phosphomannosyl receptors. The characteristics of the receptors were very similar both to control and to diseased muscle samples. When surveying all the material, the content of phosphomannosyl receptors correlated highly significantly with the muscular activity of beta-N-acetylglucosaminidase, muscle atrophy index, and serum creatine kinase activity.

Effects of free fatty acids, lysophosphatides and phospholipase treatment on lipid peroxidation of myocardial homogenates and membrane fractions

The effects of various free fatty acids, lysophosphatides and phospholipase treatments on the enzymatic and the non-enzymatic lipid peroxidation capacities in the heart homogenates and subcellular fractions were studied. The results showed a dose related inhibition of both the enzymatic and non-enzymatic lipid peroxidation with free fatty acids. A significant inhibition occurred as early as at the concentration of 25-50 microM of several fatty acids both in homogenates and in organelle fractions. In general, the inhibition was greatest with cis-unsaturated, long-chain fatty acids. The inhibition was also induced by the pretreatment of the homogenates with phospholipase A2 but not with phospholipase C. The lysophosphatidyl cholines (16:0 and 18:1) had a stimulatory effect on the enzymatic lipid peroxidation capacity at the physiological concentrations. The results show that the stimulatory/inhibitory effect of various lipid amphiphiles on lipid peroxidation is strongly structure linked and the mitochondrial fraction is the most susceptible to the injury induced by lipid amphiphiles.

Morphological and enzymatic heterogeneity of suramin-induced lysosomal storage disease in some tissues of mice and rats

Suramin-induced lysosomal storage disease reproduced in the rat was extended to the mouse with the attempt to characterize enzymatically and morphologically heterogeneous responses of various organs to the drug. Suramin administration strikingly decreased (3-6 days afterward) the activity of beta-glucuronidase in all tissues studied (kidney, liver, heart, and skeletal muscle). The enzymatic responses were small in the activities of beta-N-acetyl-glucosaminidase. The activity of arylsulfatase A decreased to a varying degree in mouse tissues, but in rats the activity increased in liver and skeletal muscle. The activity of cathepsin D increased in rat tissues. Suramin induced morphological changes characteristic to lysosomal storage diseases in kidney and liver but not in heart and skeletal muscle of both mice and rats. Kidney was appreciably more susceptible to suramin than liver. The occurrence of lysosomal accumulations, membranous lamellar inclusions, and granular material were most prominent in tubular cells of kidney and in Kupffer cells of liver. These cells also presented intensive Alcian blue staining. Interestingly, the enzymatic and morphological responses did not correlate with each other, which may reflect differences in the regulation of lysosomal functions in various cell types.

Phosphomannosyl receptors of lysosomal enzymes in cardiac and skeletal muscles of young and old mice

The endogenous activity and the binding of high-uptake beta-N-acetylglucosaminidase were assayed in the membranes of heart and skeletal muscles of young (2 months) and old (15 months) NMRI-mice (Mus musculus) to evaluate the age-related changes in the phosphomannosyl receptors of lysosomal enzymes in muscular membranes. The total activities of beta-N-acetylglucosaminidase were significantly higher in cardiac and skeletal muscles of old than young mice. The total and the specific (inhibited by mannose-6-phosphate) binding of beta-N-acetylglucosaminidase to the membranes of cardiac muscle, but not to those of skeletal muscle, were higher in old mice than in young ones. The endogenous activity of beta-N-acetylglucosaminidase was significantly higher in the membranes of skeletal muscles of old mice than in those of young mice. The membranes of heart muscles did not show any difference in the endogenous activities. The saturation properties of the binding of beta-N-acetylglucosaminidase to the phosphomannosyl receptors were very similar in the membranes of heart and skeletal muscles of both age groups. We conclude that during aging the number of phosphomannosyl receptors of lysosomal enzymes increases in the membranes of heart muscle while the occupancy of phosphomannosyl receptors with endogenous ligands increases in the membranes of skeletal muscle.