Binding of AP-2 adaptor complex to brain membrane is regulated by phosphorylation of proteins

Evidence on differential role for alpha 1 and alpha 2 subtypes of AP-2 adaptin in the Central Nervous System

Two subtypes of alpha (α)subunits , α1and α2, belonging to AP-2 complex have been described in the central nervous system (CNS). The specific role of each subtype is still unclear. In this study, we evaluated the expression and interaction with cell membranes of both subtypes in the postnatal developing cerebral cortex and cerebellum in two rat strains that display distinct developmental features. We observed that α2 displays higher variations than α1 during development, and at lesser extent in the rats with delayed rate of development. Additionally, by in vitro binding assays we evaluated the interaction of α subunits with bovine brain membranes. Both subtypes displayed clear differences in their performance, maximum binding of α1 was higher and α2 reached it faster than α1. In addition, both subtypes displayed different binding to membranes when bivalent cations or nucleotides were added. We conclude that both subtypes interact differently with membranes and that they may play different roles in clathrin-mediated endocytosis in the CNS.

Castration causes an increase in lysosomal size and upregulation of cathepsin D expression in principal cells along with increased secretion of procathepsin D and prosaposin oligomers in adult rat epididymis

In the epididymis, lysosomal proteins of the epithelial cells are normally targeted from the Golgi apparatus to lysosomes for degradation, although their secretion into the epididymal lumen has been documented and associated with sperm maturation. In this study, cathepsin D (CatD) and prosaposin (PSAP) were examined in adult epididymis of control, and 2-day castrated rats without (Ct) and with testosterone replacement (Ct+T) to evaluate their expression and regulation within epididymal epithelial cells. By light microscope-immunocytochemistry, a quantitative increase in size of lysosomes in principal cells of Ct animals was noted from the distal initial segment to the proximal cauda. Androgen replacement did not restore the size of lysosomes to control levels. Western blot analysis revealed a significant increase in CatD expression in the epididymis of Ct animals, which suggested an upregulation of its expression in principal cells; androgens restored levels of CatD to that of controls. In contrast, PSAP expression in Ct animals was not altered from controls. Additionally, an increase in procathepsin D levels was noted from samples of the epididymal fluid of Ct compared to control animals, accompanied by an increased complex formation with PSAP. Moreover, an increased oligomerization of prosaposin was observed in the epididymal lumen of Ct rats, with changes reverted to controls in Ct+T animals. Taken together these data suggest castration causes an increased uptake of substrates that are acted upon by CatD in lysosomes of principal cells and in the lumen by procathepsin D. These substrates may be derived from apoptotic cells noted in the lumen of proximal regions and possibly by degenerating sperm in distal regions of the epididymis of Ct animals. Exploring the mechanisms by which lysosomal enzymes are synthesized and secreted by the epididymis may help resolve some of the issues originating from epididymal dysfunctions with relevance to sperm maturation.

Neurotoxins from Clostridium botulinum (serotype A) isolated from the soil of Mendoza (Argentina) differ from the A-Hall archetype and from that causing infant botulism

The type A of neurotoxin produced by Clostridium botulinum is the prevalent serotype in strains of Mendoza. The soil is the main reservoir for C.botulinum and is possibly one of the infection sources in infant botulism. In this study, we characterized and compared autochthonous C. botulinum strains and their neurotoxins. Bacterial samples were obtained from the soil and from fecal samples collected from children with infant botulism. We first observed differences in the appearance of the colonies between strains from each source and with the A Hall control strain. In addition, purified neurotoxins of both strains were found to be enriched in a band of 300 kDa, whereas the A-Hall strain was mainly made up of a band of ∼600 kDa. This finding is in line with the lack of hemagglutinating activity of the neurotoxins under study. Moreover, the proteolytic activity of C. botulinum neurotoxins was evaluated against SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins from rat brain. It was observed that both, SNAP 25 (synaptosomal-associated protein 25) and VAMP 2 (vesicle-associated membrane protein) were cleaved by the neurotoxins isolated from the soil strains, whereas the neurotoxins from infant botulism strains only induced a partial cleavage of VAMP 2. On the other hand, the neurotoxin from the A-Hall strain was able to cleave both proteins, though at a lesser extent. Our data indicate that the C.botulinum strain isolated from the soil, and its BoNT, exhibit different properties compared to the strain obtained from infant botulism patients, and from the A-Hall archetype.

Testosterone influences the expression and distribution of the cation-dependent mannose-6-phosphate receptor in rat epididymis. Implications in the distribution of enzymes

The mammalian epididymis plays a role in sperm maturation through its secretory activity. Among the proteins secreted by the epithelium, there are significant amounts of acid hydrolases. In most cell types, the normal distribution of lysosomal enzymes is mediated by mannose-6-phosphate receptors (MPRs). In this study, we analysed the expression and distribution of the cation-dependent MPR (CD-MPR) in epididymis from control, castrated or castrated rats with testosterone replacement. It was observed that expression of CD-MPR increased due to castration in all regions of the epididymis, which was reversed by injection of testosterone. We also measured the activity of α-mannosidase and observed that the castration tends to increase the retention of this enzyme in the tissue, which is reversed by the hormone replacement. In corpus, this resulted in a reduced secretion of the enzyme. Immunohistochemistry showed that CD-MPR has a supranuclear location (different from the cation-independent MPR), most likely in principal cells, and low reactivity in other cell types. The signal in castrated animals was more intense and tended to redistribute towards the apical cytoplasm. Thus, we concluded that expression and distribution of CD-MPR is affected by decrease of testosterone in rat epididymis, and this could change the distribution of lysosomal enzymes.

Expression of coat proteins changes during postnatal development in selected areas of the rat brain

It is well known that clathrin-mediated endocytosis is crucial for the normal functioning and integrity of neurons in the central nervous system. In this study we attempted to correlate the expression of coat proteins with development in different areas of rat brain. By Western blot, we studied the expression of AP-2, GGA1 and GGA2 in striatum, cerebellum, brain stem, cerebral cortex and hippocampus of newborn rats and during post-natal development; 5, 15, 30, 60, 90 or 150 days after birth. We observed that the expression of the α2 subunit of AP-2 increased substantially between the 15th and 30th day after birth in all areas studied, excepting the cerebellum and cortex. On the other hand, the expression of the α1 subunit does not change significantly during the development in any of the areas under study. We also noted that the expression of the μ2 subunit did not follow the pattern of α2 during development. In general terms, the expression of GGA1 and GGA2 followed a similar pattern to that of AP-2, although these proteins increased significantly in the cerebral cortex from the 15th day after birth. Moreover, presenilin-1, a protein associated with aging and neurodegeneration, shows an expression pattern similar to coat proteins in the striatum and cortex. These results suggest that proteins that conform the intracellular transport machinery in the brain cells seems to accompany development, according to the maturation of the different brain areas.

Acute intrastriatal administration of quinolinic acid affects the expression of the coat protein AP-2 and its interaction with membranes

Clathrin-coated vesicle endocytosis is thought to be crucial for the maintenance of synaptic transmission and for the cell plasticity at the nervous system. In this study, we demonstrated that acute intrastriatal administration of quinolinic acid (QUIN), an agonist of the N-methyl-D: -aspartate receptor, induces a decrease of the coat protein AP-2 expression and affects their interaction with membranes. By western blot analysis we observed that at 24 h after QUIN intrastriatal injection, alpha1 subunit of AP-2 and alpha2, at lesser extent, were reduced in the striatal membranes. The decrease of both subunits expression was extended to 48 h after treatment, although the soluble proteins were mostly affected. Other areas of the brain were not affected by the treatment, except the cerebellum, where a significant increase of soluble AP-2 (both subunits) was observed at 48 h after injection. Another coat protein, as the phosphoprotein AP-180, was not affected by the injection of QUIN. We also confirmed that QUIN injection causes increasing loss of striatal neurons after the administration of the toxin. We concluded that QUIN may affect the endocytotic machinery of the striatum, by inducing changes in the AP-2 behaviour. Consequently, the internalization of NMDAR and/or AMPAR may be affected, by QUIN, contributing to the excitotoxic effect of the drug.