The Arctic APP mutation (E693G) within the amyloid ß (Aß) domain of amyloid precursor protein (APP) leads to dementia with clinical features similar to Alzheimer's disease (AD), which is believed to be mediated via increased formation of protofibrils. We have generated a transgenic mouse model, TgAPParc, with neuron-specific expression of human amyloid precursor protein with the Arctic mutation (hAPParc), showing mild amyloid pathology with a relatively late onset. Here we performed a detailed analysis of the spatiotemporal progression of neuropathology in homozygous TgAPParc, focusing on intracellular Aß and diffuse Aß aggregates rather than amyloid plaques. We show that the neuropathology in homozygous TgAPParc mice starts with intracellular Aß aggregates, which is followed by diffuse extracellular Aß deposits in subiculum that later expands to brain regions receiving neuronal projections from regions already affected. Together this suggests that the pathology in TgAPParc mice affects interconnected brain regions and may represent a valuable tool to study the spread and progression of neuropathology in Alzheimer's disease.
BACKGROUND: The plasma membrane of hepatocytes can be divided in sinusoidal, lateral and apical membrane, each with functionally and structurally distinct features. The apical domain consists of the bile canalicular structures. The morphogenesis and the polarization of hepatocytes is still poorly known. EXPERIMENTAL DESIGN: We used HepG2 cells, a hepatoma cell line to study the formation of the bile canaliculi in the apical part of the cells. The cells were synchronized by using nocodazole. The formation of the bile canaliculi was monitored by using immunofluorescence microscopy, confocal laser scanning microscopy, and immunoelectron microscopy. Antibodies to alpha-fodrin and villin were used. Actin was visualized with rhodamine phalloidin. RESULTS: Confocal laser scanning microscopy showed accumulations of actin, villin and fodrin at the cell membranes 8 to 12 hours after the release of the nocodazole block. These sites probably represent areas destined to develop into bile canaliculi. Later, immature bile canaliculi were discerned that were located asymmetrically between adjacent cells. Transmission electron microscopy of serial sections showed that they were always connected with the surface of the cell. Mature bile canaliculi appeared between adjacent cells 48 hours after the release of the nocodazole block. They were round, vesicle-like structures lined with microvilli and sealed by tight junctions and desmosomes. They were usually seen between two juxtaposed cells, and often several cells contributed to their formation. Typically, mature bile canaliculi were delineated by a subplasmalemmal filamentous meshwork of fodrin and actin, resembling a terminal web of enterocytes. Actin and villin were also found in microvillar cores. CONCLUSIONS: The results show that (i) bile canaliculi are formed de novo between two or more juxtaposed cells; (ii) canalicular-formation is accompanied by a distinct accumulation of the membrane skeletal and microvillar proteins fodrin, actin and villin at the apical surfaces of the cells, suggesting that they play an important role in bile canaliculus morphogenesis, and that (iii) apical membrane differentiation in the cells contributing to the formation of a single canaliculus is an asymmetric process.
The authors collected ambient air along two highways in Oslo to investigate the annual variations in particulate matter (PM10) and the presence of latex as an outdoor allergen. PMI, was monitored for a period of five years, during which time the use of studded winter tires was reduced. The presence of latex and of common aeroallergens was examined directly on the collection filters with immunoelectron microscopy visualized in a scanning electron microscope. The annual variation in PM10 was similar over the five years of sampling, with increased mass concentrations in winter. Statistical analysis indicated no major effect from the change to nonstudded tires. The most important factors influencing the PM10 concentration were meteorological parameters like wind and rain. Immnunolabeling of the filters showed latex as an outdoor allergen that adhered to carbon aggregates from vehicle emission. The results also indicated cross-reactive epitopes among the common allergens investigated, which for sensitized subjects may add to the risk of developing latex allergy.
Transmission electron and confocal laser scanning (CLSM) microscopies with monoclonal anti-tetrodotoxin antibodies were used to locate tetrodotoxin (TTX) in tissues and gland cells of the ribbon worm Lineus alborostratus. CLSM studies have shown that the toxin is primarily localized in the cutis (special subepidermal layer) of the body wall and in the glandular epithelium of the proboscis. Immunoelectron micrographs have shown that only subepidermal bacillary gland cells type I in cutis and pseudocnidae-containing and mucoid gland cells manifested TTX-gold labeling. TTX was associated with the nuclear envelope, endoplasmic reticulum membrane, and secretory granules of TTX-positive gland cells. These studies indicate that ??? is brought into the cytoplasm of the glandular cells of the cutis and proboscis epithelium, where it is associated with membrane-enclosed organelles involved in protein secretion and then concentrated in glandular granules.
Endostatin, a proteolytic fragment of type XVIII collagen, has been shown to inhibit angiogenesis, tumor growth, and endothelial cell proliferation and migration. We analyzed its functions in vivo by generating transgenic mice in which it was overexpressed in the skin and lens capsule under the keratin K14 promoter. Opacity of the lens occurred at 4 months of age in the mouse line J4, with the highest level of endostatin expression. The lens epithelial cells appeared to lose contact with the capsule and began to vacuolize. In 1-year-old mice the lens epithelial cell layer had entirely degenerated, and instead, large plaques of spindle-shaped cells had formed in the anterior region of the lens. Moreover, a widening of the epidermal basement membrane (BM) zone of the skin was observed in electron microscopy. The epidermal BM was conspicuously altered in the J4 mice with high transgene expression, including clear broadening and occurrence of pearl-like protrusions in some areas, whereas the BM was more even in appearance but consistently broadened in the mouse line G20 with moderate transgene expression. In both lines the BM was continuous. Measurements indicated that the lamina densa was 78.54 +/- 53.10 nm in line J4, the large variation reflecting the protrusions of the lamina densa, and 44.24 +/- 11.52 nm in line G20, compared with 33.74 +/- 9.96 nm in wild-type adult mice. Immunoelectron microscopy of wild-type mouse skin type XVIII collagen showed a polarized orientation in the BMs, with the C-terminal endostatin region localized in the lamina densa and the N terminus in average approximately 40 nm more on the dermal side. Type XVIII collagen was dispersed in the transgenic skin, suggesting that the transgene-derived endostatin fragment displaces the full-length collagen XVIII. This may impair the anchoring of the lamina densa to the dermis and thereby lead to loosening of the BMs, resembling the previously observed situation in collagen XVIII-null mice.
BACKGROUND: Free radicals and antioxidant enzymes (AOEs) may play a critical role in cell proliferation and in the resistance of malignant cells against cytotoxic drugs and radiation. Malignant mesothelioma is a resistant tumor with high levels of manganese superoxide dismutase, a central superoxide scavenging AOE. In the current study, the authors assessed the expression and prognostic role of catalase, an important hydrogen peroxide scavenging AOE, in malignant pleural mesothelioma. METHODS: Catalase expression was investigated by immunohistochemistry in 5 cases of nonmalignant healthy pleura and in tumor tissue of 32 mesothelioma patients, and by Western blot in 7 continuous human mesothelioma cell lines. The distribution of catalase in mesothelioma cells was assessed by immunoelectron microscopy. Furthermore, to investigate the effect of catalase inhibition in the drug resistance of these cells in vitro, the authors exposed mesothelioma cells with the highest catalase level to epirubicin with and without aminotriazole pretreatment. RESULTS: Nonmalignant mesothelial cells showed no catalase immunoreactivity whereas most mesothelioma cases (24 of 32, 75%) were catalase positive, 17 cases (53%) showing moderate or high expression. Higher catalase expression in mesothelioma was associated with a better prognosis, mean survival rate from diagnosis being 6 and 24 months for negative/low expression and moderate/high expression, respectively. Furthermore, a coordinately high expression of both manganese-superoxide dismutase (Mn-SOD) and catalase predicted even more favorable outcome of the mesothelioma patients. Catalase also could be detected in all mesothelioma cell lines, the most resistant cell line showing the highest protein expression and compartmentalization of catalase mainly to peroxisomes. Aminotriazole inhibition of catalase had a marginal effect on the toxicity caused by epirubicin. CONCLUSIONS: Catalase may have multifactorial effects in malignant cells; high catalase and/or coordinated high expression of Mn-SOD and catalase may decrease tumor progression by modulating the cellular redox state, but enhanced antioxidant capacity of mesothelioma cells also may protect tumor cells against exogenous oxidants, at least in vitro.
Distribution of actin and fodrin, a nonerythroid analogue of spectrin, was studied in cytocentrifuge preparations and in tissue sections of normal and pathologic respiratory epithelium by using immunofluorescence and immunoelectron microscopy. In ciliated epithelial cells and in goblet cells of normal bronchial epithelium, fodrin and actin were located in the apical parts and along the lateral walls of the cells. In basal cells, fodrin and actin were also seen diffusely in the cytoplasm. Immunoelectron microscopy showed fodrin in close association with the basal bodies and rootlets of the cilia and microvilli in the ciliated cells. In alveolar epithelium, fodrin and actin were located at the apical membrane in type I pneumocytes and along the apical and lateral membranes in type II pneumocytes. In type II pneumocytes, fodrin was also seen in close association with the secretory vacuoles. In metaplastic and dysplastic bronchial epithelium, a diffuse cytoplasmic and a circumferential, membrane-associated staining for fodrin and actin was seen. In all types of carcinomas, fodrin was seen along the lateral walls and diffusely in the cytoplasm. The staining was more intense than in the normal cells. In immunoblotting of the normal bronchial epithelium, and peripheral lung and lung carcinomas, a single 240 kD band was recognized with antibodies to fodrin. The results show distinct differences in the distribution of fodrin in the various cell types of the respiratory epithelium. In ciliated cells, the close relationship with cytoskeleton suggests a role of fodrin in the establishment of the elaborate structural architecture of the apical compartment. In type II pneumocytes, on the other hand, fodrin probably plays a role in secretion of the surfactant. In basal cells, the diffuse distribution of fodrin probably reflects the high proliferative capacity of this cell compartment. Interestingly, a similar distribution was also seen in premalignant and malignant cells.
The distribution of the extracellular matrix proteins types III pN-collagen and IV collagen, laminin and tenascin was investigated in fetal, infant, and adult human spleens by using immuno-electron microscopy. The presence of type III pN-collagen was assessed by using an antibody against the aminoterminal propeptide of type III procollagen. All the proteins other than type III pN-collagen were found in reticular fibers throughout development. In the white pulp of the fetus aged 16 gestational weeks, only an occasional type III pN-collagen-containing fibril was present, although type III pN-collagen was abundant in the reticular fibers of the red pulp. Conversely, in adults, most of the reticular fibers of the white pulp, but not of the red pulp, were immunoreactive for type III pN-collagen. Ring fibers, the basement membranes of venous sinuses, were well developed in both infant and adult spleens. The first signs of their formation could be seen as a discontinuous basement membrane, which was immunoreactive for type IV collagen, laminin, and tenascin in the fetus aged 20 gestational weeks. Intracytoplasmic immunoreactivity for all the proteins studied was visible in the mesenchymal cells of the fetus aged 16 gestational weeks and in the reticular cells of the older fetuses, which also showed labeling for type IV collagen and laminin in the endothelial cells. The results suggest that proteins of the extracellular matrix are produced by these stationary cells.
Oulu Center for Cell-Matrix Research, Biocenter Oulu, Department of Medical Biochemistry and Molecular Biology, University of Oulu, and Department of Clinical Neurophysiology, Oulu University Hospital, FIN-90221 Oulu, Finland.
Although the Schwann cell basement membrane (BM) is required for normal Schwann cell terminal differentiation, the role of BM-associated collagens in peripheral nerve maturation is poorly understood. Collagen XV is a BM zone component strongly expressed in peripheral nerves, and we show that its absence in mice leads to loosely packed axons in C-fibers and polyaxonal myelination. The simultaneous lack of collagen XV and another peripheral nerve component affecting myelination, laminin a4, leads to severely impaired radial sorting and myelination, and the maturation of the nerve is permanently compromised, contrasting with the slow repair observed in Lama4-/- single knock-out mice. Moreover, the Col15a1-/-;Lama4-/- double knock-out (DKO) mice initially lack C-fibers and, even over 1 year of age have only a few, abnormal C-fibers. The Lama4-/- knock-out results in motor and tactile sensory impairment, which is exacerbated by a simultaneous Col15a1-/- knock-out, whereas sensitivity to heat-induced pain is increased in the DKO mice. Lack of collagen XV results in slower sensory nerve conduction, whereas the Lama4-/- and DKO mice exhibit increased sensory nerve action potentials and decreased compound muscle action potentials; x-ray diffraction revealed less mature myelin in the sciatic nerves of the latter than in controls. Ultrastructural analyses revealed changes in the Schwann cell BM in all three mutants, ranging from severe (DKO) to nearly normal (Col15a1-/-). Collagen XV thus contributes to peripheral nerve maturation and C-fiber formation, and its simultaneous deletion from neural BM zones with laminin a4 leads to a DKO phenotype distinct from those of both single knock-outs.
Type XIII collagen is a type II transmembrane protein found at many sites of cell adhesion in tissues. Homologous recombination was used to generate a transgenic mouse line (Col13a1(N/N)) that expresses N-terminally altered type XIII collagen molecules lacking the short cytosolic and transmembrane domains but retaining the large collagenous ectodomain. The mutant molecules were correctly transported to focal adhesions in cultured fibroblasts derived from the Col13a1(N/N) mice, but the cells showed decreased adhesion when plated on type IV collagen. These mice were viable and fertile, and in immunofluorescence stainings the mutant protein was located in adhesive tissue structures in the same manner as normal alpha1(XIII) chains. In immunoelectron microscopy of wild-type mice type XIII collagen was detected at the plasma membrane of skeletal muscle cells whereas in the mutant mice the protein was located in the adjacent extracellular matrix. Affected skeletal muscles showed abnormal myofibers with a fuzzy plasma membrane-basement membrane interphase along the muscle fiber and at the myotendinous junctions, disorganized myofilaments, and streaming of z-disks. The findings were progressive and the phenotype was aggravated by exercise. Thus type XIII collagen seems to participate in the linkage between muscle fiber and basement membrane, a function impaired by lack of the cytosolic and transmembrane domains.