The lipoprotein receptor-related protein-1 (LRP) adapter protein GULP mediates trafficking of the LRP ligand prosaposin, leading to sphingolipid and free cholesterol accumulation in late endosomes and impaired efflux

One of the conserved functional pathways linked to engulfment of apoptotic corpses involves two membrane proteins low density lipoprotein receptor-related protein-1 (LRP) and ABCA1 and the LRP adapter protein GULP. Because LRP and ABCA1 play roles in cellular lipid trafficking and efflux, here we addressed whether the third member, the LRP adapter protein GULP, also affects cellular lipid transport. Several lines of evidence show that overexpression of GULP causes glycosphingolipid and free cholesterol accumulation in the late endosome/lysosome compartment that is accompanied by down-regulation of ABCA1 and decreased efflux. Conversely, knockdown of endogenous GULP expression promoted cholesterol flux through the late endosomes and up-regulation of ABCA1, even in the context of a disease state such as Niemann-Pick Type C disease. Mechanistically, we were able to show that trafficking of the LRP ligands alpha2-macroglobulin and prosaposin, a protein cofactor necessary for glycosphingolipid degradation, are impaired in cells expressing full-length GULP protein, resulting in glycosphingolipid and free cholesterol accumulation in the late endosome/lysosome compartment. On the other hand, knockdown of endogenous GULP results in enhanced targeting of prosaposin and enhanced clearance of glycosphingolipids and cholesterol from the late endosomes. Taken together, these data reveal that GULP/LRP/ABCA1 represents a triad of molecules involved in engulfment and cellular lipid homeostasis.     

Entomopathogenic Nematodes Are Not an Alternative to Fenamiphos for Management of Plant-Parasitic Nematodes on Golf Courses in Florida

With the cancellation of fenamiphos in the near future, alternative nematode management tactics for plant-parasitic nematodes (PPN) on golf courses need to be identified. The use of entomopathogenic nematodes (EPN) has been suggested as one possible alternative. This paper presents the results of 10 experiments evaluating the efficacy of EPN at managing PPN on turfgrasses and improving turf performance. These experiments were conducted at various locations throughout Florida over the course of a decade. In different experiments, different EPN species were tested against different species of PPN. Separate experiments evaluated multiple rates and applications of EPN, compared different EPN species, and compared single EPN species against multiple species of PPN. In a few trials, EPN were associated with reductions in certain plant-parasite species, but in other trials were associated with increases. In most trials, EPN had no effect on plant parasites. Because EPN were so inconsistent in their results, we conclude that EPN are not acceptable alternatives to fenamiphos by most turf managers in Florida at this time.     

Parameterization of individual-based models: comparisons with deterministic mean-field models

The relating of deterministic, mean-field models into network models, where epidemic spread occurs between interconnected susceptible and infectious individuals or populations, requires careful consideration. Here, we discuss models that consider differently the manner in which contact rate and infectiousness change over time, with different algorithms suitable for different underlying processes. Though these models give coincidental results to the mean-field in the case of large, highly connected networks, the results when sparsely connected networks are considered may differ. Different subsets of the parameters from the mean-field epidemic (R(0), generation time, infectiousness, etc.) are preserved in each case. Despite these differences, simulated epidemics generated under some model architectures are insensitive to the average degree of contact amongst nodes, k. Model-based estimates of k may be model dependent, and must therefore be viewed with caution.     

Alterations of behavior and spatial learning after unilateral entorhinal ablation of rats

The entorhinal cortex (EC) is the key input and output structure of the hippocampus. It plays a crucial role in sensory processing, memory and learning, as well as in mechanisms of epileptic seizures. Our previous studies on the 4-aminopyridin induced epilepsy model of rats showed that ablation of unilateral EC prompted weakening of limbic seizure manifestation, thus the possibility of therapeutical benefit of this kind of surgery can be risen. Open field, elevated plus-maze and Morris water-maze test were performed to analyze changes of the basal activity level, exploratory behavior, and spatial memory capacity, respectively, of adult Wistar rats having undergone left EC excision. Compared with the sham-operated control group, rats with lesions of the EC showed enhanced locomotor activity in the open-field test. The elevated plus-maze test revealed higher frequency of entries and more time spent in the open arms. Morris water-maze test suggested impairment of the spatial learning capacity following left lateral EC lesion. Therefore, our data showed that EC lesions induced hyperactivity, increased exploratory behavior, and impaired spatial learning. Entorhinal cortex ablation, as a potential method for controlling epileptic seizures has multiple effects on animals' behavior and spatial learning. To determine the cost-benefit ratio of a potential surgical intervention needs further experimental and human investigations.     

Effect of acidic extracellular pH on the receptor-mediated endocytosis of peroxidase-antiperoxidase (PAP) immune complex in rat peritoneal macrophages

The effect of acidic extracellular medium on the uptake of peroxidase-antiperoxidase (PAP) immune complex in rat peritoneal macrophages was studied with the electron microscope. The acidic extracellular medium resulted in acidification of the cytosol in a relatively short period of time as was shown with 5(6) carboxyfluorescein as indicator. At pH 5.5 PAP was internalized. Some of the ligand was found in endosomes; however, a considerable quantity was still present at the cell surface after 5 min internalization. By 30 min the surface was cleared of PAP and the ligand was detectable almost exclusively in endosomes. PAP was never found in lysosomes which were identified by previous loading with cationized ferritin. We conclude that a pH shift of the cytoplasm results in inhibition of endosome-lysosome fusion.     

Reappearance of immune complex binding sites on macrophages after internalization and its inhibition by monensin

Receptor-mediated endocytosis of IgG and immune complexes in macrophages is terminated with digestion of the ligand in lysosomes. However, there are controversial data on whether Fc receptors are degraded together with the ligand or recycled to the cell surface. In the present study, rat peritoneal macrophages were incubated at 4 degrees C with rat peroxidase-antiperoxidase (PAP) complex for 1 h, washed and warmed up to 37 degrees C for different time periods and reincubated with new PAP at 4 degrees C. In another series of experiments, the cells were preincubated with 50 nM monensin, then cooled to 4 degrees C and reincubated with PAP in the presence of monensin. The cells were fixed and processed for electron microscopy at different stages of the experiments. Quantitative data were obtained by measuring PAP-binding membrane lengths on electron micrographs (morphometry) and by determining surface-bound PAP with spectrophotometry. In macrophages which had bound PAP at 4 degrees C and were warmed up for 5 min, the PAP was cleared from the cell surface and was found in endosome-like structures. When reincubated with PAP at 4 degrees C, such cells again bound the ligand on the cell surface, mainly in labyrinthic invaginations of the plasma membrane (synonyms: lacunae, caveolar indentations). Macrophages which had been warmed up for longer periods (30 and 60 min) showed the bound ligand all along the plasma membrane. Treatment of cells with monensin did not affect internalization of PAP, however, it decreased the ligand binding ability of macrophages considerably. These findings led us to assume an Fc receptor replenishment from a cytoplasmic pool.