Glycogen synthase kinase-3beta phosphorylates protein tau and rescues the axonopathy in the central nervous system of human four-repeat tau transgenic mice

Protein tau filaments in brain of patients suffering from Alzheimer's disease, frontotemporal dementia, and other tauopathies consist of protein tau that is hyperphosphorylated. The responsible kinases operating in vivo in neurons still need to be identified. Here we demonstrate that glycogen synthase kinase-3beta (GSK-3beta) is an effective kinase for protein tau in cerebral neurons in vivo in adult GSK-3beta and GSK-3beta x human tau40 transgenic mice. Phosphorylated protein tau migrates slower during electrophoretic separation and is revealed by phosphorylation-dependent anti-tau antibodies in Western blot analysis. In addition, its capacity to bind to re-assembled paclitaxel (Taxol((R)))-stabilized microtubules is reduced, compared with protein tau isolated from mice not overexpressing GSK-3beta. Co-expression of GSK-3beta reduces the number of axonal dilations and alleviates the motoric impairment that was typical for single htau40 transgenic animals (Spittaels, K., Van den Haute, C., Van Dorpe, J., Bruynseels, K., Vandezande, K., Laenen, I., Geerts, H., Mercken, M., Sciot, R., Van Lommel, A., Loos, R., and Van Leuven, F. (1999) Am. J. Pathol. 155, 2153-2165). Although more hyperphosphorylated protein tau is available, neither an increase in insoluble protein tau aggregates nor the presence of paired helical filaments or tangles was observed. These findings could have therapeutic implications in the field of neurodegeneration, as discussed.

Differential response of a(2)-macroglobulin-deficient mice in models of lethal TNF-induced inflammation

Tumor necrosis factor (TNF) is an essential mediator in the pathogenesis of Gram-negative septic shock. Injection of TNF into normal mice leads to systemic, lethal inflammation, which is indistinguishable from lipopolysaccharide (LPS)-induced lethal inflammation. alpha(2)-macroglobulin (A2M) is a major positive acute phase protein with broad-spectrum protease-inhibitory activity. Mouse A2M-deficient (MAM-/-) mice were significantly protected against lethal systemic inflammation induced by TNF. The protection is not due to faster clearance of the injected TNF. The induction of tolerance to TNF-induced lethality by repetitive administration of small doses of human TNF for five consecutive days was equally efficient in both mutant mice compared to wild-type mice. In D-(+)-galactosamine (GalN)-sensitized mice, TNF induces lethal inflammatory hepatitis. MAM(-/-) mice are equally sensitive to the lethal combination of TNF/GalN. Furthermore, interleukin-1-induced desensitization to TNF/GalN was not impaired in MAM(-/-) mice. We conclude that MAM plays a mediating role in TNF-induced lethal shock and that MAM deficiency does not reduce changes in efficiency of tolerance and desensitization to TNF and TNF/GalN-induced lethality, respectively.

Purification and structural analysis of an abundant thaumatin-like protein from ripe banana fruit

The pulp of ripe bananas (Musa acuminata) contains an abundant thaumatin-like protein (TLP). Characterization of the protein and molecular cloning of the corresponding gene from banana demonstrated that the native protein consists of a single polypeptide chain of 200 amino acid residues. Molecular modelling further revealed that the banana thaumatin-like protein (Ban-TLP) adopts an overall fold similar to that of thaumatin and thaumatin-like PR-5 proteins. Although the banana protein exhibits an electrostatically polarized surface, which is believed to be essential for the antifungal properties of TLPs, it is apparently devoid of antifungal activity towards pathogenic fungi. It exhibits a low but detectable in vitro endo-beta-1,3-glucanase (EC 3.2.1.x) activity. As well as being present in fruits, Ban-TLP also occurs in root tips where its accumulation is enhanced by methyl jasmonate treatment of plants. Pulp of plantains (Musa acuminata) also contains a very similar TLP, which is even more abundant than its banana homologue. Our results demonstrate for the first time that fruit-specific (abundant) TLPs are not confined to dicots but occur also in fruits of monocot species. The possible role of the apparent widespread accumulation of fruit-specific TLPs is discussed.

Prominent axonopathy and disruption of axonal transport in transgenic mice expressing human apolipoprotein E4 in neurons of brain and spinal cord

The epsilon 4 allele of the human apolipoprotein E gene (ApoE4) constitutes an important genetic risk factor for Alzheimer's disease. Recent experimental evidence suggests that human ApoE is expressed in neurons, in addition to being synthesized in glial cells. Moreover, brain regions in which neurons express ApoE seem to be most vulnerable to neurofibrillary pathology. The hypothesis that the expression pattern of human ApoE might be important for the pathogenesis of Alzheimer's disease was tested by generating transgenic mice that express human ApoE4 in neurons or in astrocytes of the central nervous system. Transgenic mice expressing human ApoE4 in neurons developed axonal degeneration and gliosis in brain and in spinal cord, resulting in reduced sensorimotor capacities. In these mice, axonal dilatations with accumulation of synaptophysin, neurofilaments, mitochondria, and vesicles were documented, suggesting impairment of axonal transport. In contrast, transgenic mice expressing human ApoE4 in astrocytes remained normal throughout life. These results suggest that expression of human ApoE in neurons of the central nervous system could contribute to impaired axonal transport and axonal degeneration. The possible contribution of hyperphosphorylation of protein Tau to the resulting phenotype is discussed.

Trypanosoma cruzi: acute infection affects expression of alpha-2-macroglobulin and A2MR/LRP receptor differently in C3H and C57BL/6 mice

Although a complete cellular and humoral immune response is elicited in Chagas' disease, recent data suggest that other natural elements of innate immunity may also contribute to the initial host primary defense. alpha-Macroglobulins are a family of plasma proteinase inhibitors that are acute-phase reactants in Trypanosoma cruzi-infected mice and humans. Mice contain a tetrameric alpha-2-macroglobulin (MAM) and a monomeric murinoglobulin (MUG). Heterogeneity in their reactions was observed in murine T. cruzi-infected plasma A2M levels despite an overall increase. In addition, up-regulation of the A2M receptor (A2MR/LRP) was observed in peritoneal macrophages during T. cruzi infection. Here, we show that during T. cruzi infection (Y strain), the MAM and MUG hepatic mRNA levels and the corresponding plasma protein levels were up-regulated in C3H and C57BL/6 (B6) mice, but with different kinetics. On the contrary, A2MR/LRP mRNA levels increased in acutely infected C3H mice, but decreased in B6 mice, in both liver and heart. Immunocytochemistry of infected B6 heart cryosections confirmed a less intense endothelium labeling by the fluoresceinated ligand for A2MR/LRP. On the other hand, infected B6 spleen cells displayed higher F-A2M-FITC binding and MAC1 expression, confirming higher A2MR/LRP expression in macrophages. In uninfected mice, as well as after T. cruzi infection, higher A2M plasma levels were measured in C3H mice than in B6 mice. The lower tissue T. cruzi parasitism found in C3H-infected mice could reflect an inhibitory effect of A2M on parasite invasion. Our present data further contribute to clarifying aspects of the role of A2MR/LRP in a model of acute Chagas' disease in different mouse strains.

No evidence for cholinergic problems in apolipoprotein E knockout and apolipoprotein E4 transgenic mice

The varepsilon4 allele of the apolipoprotein E gene constitutes the major genetic risk factor to develop Alzheimer's disease. If and how this protein contributes to the pathological cascade of Alzheimer's disease is not known. The varepsilon4 allele particularly affects the cholinergic defect, which is one of the most consistent neurotransmitter problems in an Alzheimer's disease brain. We have analysed several parameters of the cholinergic system in brain of apolipoprotein E knockout mice as well as in transgenic mice overexpressing human apolipoprotein E4. We analysed the distribution of cholinergic fibers, the number and morphology of cholinergic neurons and the enzymatic activity of acetylcholinesterase and choline acetyltransferase in different brain regions. Finally, we analysed the distribution and the binding parameters of [3H]hemicholinium-3, a specific marker for the high affinity choline transporter in different brain sections and regions. This extensive effort failed to show any consistent difference in the cholinergic parameters studied, in either the apolipoprotein E4 transgenic mice or in the apolipoprotein E knockout mice, compared to age-matched non-transgenic mice. We conclude that the apolipoprotein E4 is not deleterious per se for the cholinergic system in mouse brain.

Aging increased amyloid peptide and caused amyloid plaques in brain of old APP/V717I transgenic mice by a different mechanism than mutant presenilin1

Aging of transgenic mice that overexpress the London mutant of amyloid precursor protein (APP/V717I) (Moechars et al., 1999a) was now demonstrated not to affect the normalized levels of alpha- or beta-cleaved secreted APP nor of the beta-C-terminal stubs. This indicated that aging did not markedly disturb either alpha- or beta-secretase cleavage of APP and failed to explain the origin of the massive amounts of amyloid peptides Abeta40 and Abeta42, soluble and precipitated as amyloid plaques in the brain of old APP/V717I transgenic mice. We tested the hypothesis that aging acted on presenilin1 (PS1) to affect gamma-secretase-mediated production of amyloid peptides by comparing aged APP/V717I transgenic mice to double transgenic mice coexpressing human PS1 and APP/V717I. In double transgenic mice with mutant (A246E) but not wild-type human PS1, brain amyloid peptide levels increased and resulted in amyloid plaques when the mice were only 6-9 months old, much earlier than in APP/V717I transgenic mice (12-15 months old). Mutant PS1 increased mainly brain Abeta42 levels, whereas in aged APP/V717I transgenic mice, both Abeta42 and Abeta40 increased. This resulted in a dramatic difference in the Abeta42/Abeta40 ratio of precipitated or plaque-associated amyloid peptides, i.e., 3.11+/-0.22 in double APP/V717I x PS1/A246E transgenic mice compared with 0.43 +/- 0.07 in aged APP/V717I transgenic mice, and demonstrated a clear difference between the effect of aging and the effect of the insertion of a mutant PS1 transgene. In conclusion, we demonstrate that aging did not favor amyloidogenic over nonamyloidogenic processing of APP, nor did it exert a mutant PS1-like effect on gamma-secretase. Therefore, the data are interpreted to suggest that parenchymal and vascular accumulation of amyloid in aging brain resulted from failure to clear the amyloid peptides rather than from increased production.

Fruit-specific lectins from banana and plantain

One of the predominant proteins in the pulp of ripe bananas (Musa acuminata L.) and plantains (Musa spp.) has been identified as a lectin. The banana and plantain agglutinins (called BanLec and PlanLec, respectively) were purified in reasonable quantities using a novel isolation procedure, which prevented adsorption of the lectins onto insoluble endogenous polysaccharides. Both BanLec and PlanLec are dimeric proteins composed of two identical subunits of 15 kDa. They readily agglutinate rabbit erythrocytes and exhibit specificity towards mannose. Molecular cloning revealed that BanLec has sequence similarity to previously described lectins of the family of jacalin-related lectins, and according to molecular modelling studies has the same overall fold and three-dimensional structure. The identification of BanLec and PlanLec demonstrates the occurrence of jacalin-related lectins in monocot species, suggesting that these lectins are more widespread among higher plants than is actually believed. The banana and plantain lectins are also the first documented examples of jacalin-related lectins, which are abundantly present in the pulp of mature fruits but are apparently absent from other tissues. However, after treatment of intact plants with methyl jasmonate, BanLec is also clearly induced in leaves. The banana lectin is a powerful murine T-cell mitogen. The relevance of the mitogenicity of the banana lectin is discussed in terms of both the physiological role of the lectin and the impact on food safety.

Modeling Alzheimer's disease in transgenic mice: effect of age and of presenilin1 on amyloid biochemistry and pathology in APP/London mice

In transgenic mice that overexpress mutant Amyloid Precursor Protein [V717I], or APP/London (APP/Lo) (1999a. Early phenotypic changes in transgenic mice that overexpress different mutants of Amyloid Precursor Protein in brain. J. Biol. Chem. 274, 6483-6492; 1999b. Premature death in transgenic mice that overexpress mutant Amyloid precursor protein is preceded by severe neurodegeneration and apoptosis. Neuroscience 91, 819-830) the AD related phenotype of plaque and vascular amyloid pathology is late (12-15 months). This typical and diagnostic pathology is thereby dissociated in time from early symptoms (3-9 months) that include disturbed behavior, neophobia, aggression, glutamate excitotoxicity, defective cognition and decreased LTP. The APP/Lo transgenic mice are therefore a very interesting model to study early as well as late pathology, including the effect of age. In ageing APP*Lo mice, brain soluble and especially "insoluble" amyloid peptides dramatically increased, while normalized levels of secreted APPsalpha and APPsbeta, as well as cell-bound beta-C-stubs, remained remarkably constant, indicating normal alpha- and beta-secretase processing of APP. In double transgenic mice, i.e. APP/LoxPS1, clinical mutant PS1[A246E] but not wild-type human PS1 increased Abeta, and plaques and vascular amyloid developed at age 6-9 months. The PS1 mutant caused increasing Abeta42 production, while ageing did not. Amyloid deposits are thus formed, not by overproduction of Abeta, but by lack of clearance and/or degradation in the brain of ageing APP/Lo transgenic mice. The clearance pathways of the cerebral amyloid peptides are therefore valuable targets for fundamental research and for therapeutic potential. Although hyper-phosphorylated protein tau was evident in swollen neurites around the amyloid plaques, neurofibrillary pathology is not observed and the "tangle" aspect of AD pathology is therefore still missing from all current transgenic "amyloid" models. Also the "ApoE4" risk for late onset AD remains a problem for modeling in transgenic mice. We have generated transgenic mice that overexpress human ApoE4 (2000. Expression of Human Apolipoprotein E4 in neurons causes hyperphosphorylation of Protein tau in the brains of transgenic mice. Am. J. Pathol. 156 (3) 951-964) or human protein tau (1999. Prominent axonopathy in the brain and spinal cord of transgenic mice overexpressing four-repeat human tau protein. Am. J. Pathol. 155, 2153-2165) in their neurons. Both develop a similar although not identical axonopathy, with progressive degeneration of nerves and with muscle wasting resulting in motoric problems. Remarkably, ApoE4 transgenic mice are, like the tau transgenic mice, characterized by progressive hyper-phosphorylation of protein tau also in motor neurons which explains the motoric defects. Further crossing with the APP/Lo transgenic mice is ongoing to yield "multiple" transgenic mouse strains to study new aspects of amyloid and tau pathology.

Abnormal glutamate transport function in mutant amyloid precursor protein transgenic mice

Recent studies have shown that amyloid precursor protein (APP), which plays a central role in Alzheimer's disease (AD), protects against excitotoxic neuronal injuries by regulating the function of the glial glutamate transporters. The mechanisms underlying these effects and their relationship to the neurodegenerative process in AD are under intense scrutiny. In this context, the main objective of the present study was to determine if overexpression of mutant human APP in transgenic mouse brains results in altered functioning of the excitatory amino acid transporters (EAATs). Transgenic mice expressing the 695 amino acid form of the human APP from the Thy-1 promoter showed a significant decrease in B(max) and K(D) for aspartate uptake when compared to nontransgenic controls. This decrease in glutamate transporter activity was associated with decreased protein expression of glial specific glutamate transporters, EAAT1 and 2, but did not affect mRNA levels. These results suggest that expression of mutant forms of APP disturbs astroglial transport of excitatory amino acids at the posttranscriptional level leading, in turn, to increased susceptibility to glutamate toxicity.

Acetylcholinesterase-positive fiber deafferentation and cell shrinkage in the septohippocampal pathway of aged amyloid precursor protein london mutant transgenic mice

Several lines of evidence implicate a cholinergic deficit in Alzheimer's disease (AD). Transgenic mice that overexpress clinical mutants of the human amyloid precursor protein (APP) have been generated that recapitulate many aspects of AD. We now analyzed the cholinergic system in aged APP/London transgenic mice. The major finding was the reorganization of acetylcholinesterase-positive fibers within the hippocampus and the reduced size of cholinergic cells in the medial septum. The reduction of acetylcholinesterase-positive fibers in the subiculum together with increased fiber density in the CA1 and in the dentate gyrus suggests a synaptic sprouting compensatory mechanism within the hippocampus. In the cortex, amyloid plaques were associated with intense acetylcholinesterase activity and surrounded by dystrophic acetylcholinesterase-positive fibers. Nevertheless, the overall pattern of cholinergic innervation was unchanged. These results demonstrate that overexpression of APP/London caused, besides amyloid plaques in aged mouse brain, also cholinergic deafferentation and cholinergic cell shrinkage.

Characterization and molecular cloning of two different type 2 ribosome-inactivating proteins from the monocotyledonous plant Polygonatum multiflorum

Leaves of the monocotyledonous plant Polygonatum multiflorum L. (Solomon's seal) contain besides a monocot mannose-binding lectin two galactose/N-acetylgalactosamine (Gal/GalNAc)-binding type 2 ribosome-inactivating proteins (RIPs). Both RIPs were purified using a combination of classical protein purification techniques and affinity chromatography. Although both RIPs consist of protomers of 65 kDa, the P. multiflorum RIP monomer (PMRIPm) occurs as a monomer of approximately 60 kDa, whereas the tetramer (PMRIPt) is a tetramer of 240 kDa. Both RIPs exhibit similar RNA N-glycosidase activity but differ in their specific agglutination activity and carbohydrate-binding specificity, PMRIPt being a GalNAc-specific lectin whereas PMRIPm is Gal/GalNAc-specific. Toxicity tests indicated that both Polygonatum RIPs exhibit a very low cytotoxicity towards human and animal cells. Analysis of the genomic clones encoding both RIPs revealed a high degree of sequence similarity to other type 2 RIPs. Molecular modelling confirmed that both Polygonatum RIPs have a similar structure to ricin.

Expression of human apolipoprotein E4 in neurons causes hyperphosphorylation of protein tau in the brains of transgenic mice

Epidemiological studies have established that the epsilon 4 allele of the ApoE gene (ApoE4) constitutes an important risk factor for Alzheimer's disease and might influence the outcome of central nervous system injury. The mechanism by which ApoE4 contributes to the development of neurodegeneration remains unknown. To test one hypothesis or mode of action of ApoE, we generated transgenic mice that overexpressed human ApoE4 in different cell types in the brain, using four distinct gene promoter constructs. Many transgenic mice expressing ApoE4 in neurons developed motor problems accompanied by muscle wasting, loss of body weight, and premature death. Overexpression of human ApoE4 in neurons resulted in hyperphosphorylation of the microtubule-associated protein tau. In three independent transgenic lines from two different promoter constructs, increased phosphorylation of protein tau was correlated with ApoE4 expression levels. Hyperphosphorylation of protein tau increased with age. In the hippocampus, astrogliosis and ubiquitin-positive inclusions were demonstrated. These findings demonstrate that expression of ApoE in neurons results in hyperphosphorylation of protein tau and suggests a role for ApoE in neuronal cytoskeletal stability and metabolism.

Behavioral disturbances without amyloid deposits in mice overexpressing human amyloid precursor protein with Flemish (A692G) or Dutch (E693Q) mutation

The contribution of mutations in the amyloid precursor protein (APP) gene known as Flemish (APP/A692G) and Dutch (APP/E693Q) to the pathogenesis of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis of the Dutch type, respectively, was studied in transgenic mice that overexpress the mutant APP in brain. These transgenic mice showed the same early behavioral disturbances and defects and increased premature death as the APP/London (APP V717I), APP/Swedish (K670N, M671L), and other APP transgenic mice described previously. Pathological changes included intense glial reaction, extensive microspongiosis in the white matter, and apoptotic neurons in select areas of the brain, while amyloid deposits were absent, even in mice over 18 months of age. This contrasts with extensive amyloid deposition in APP/London transgenic mice and less pronounced amyloid deposition in APP/Swedish transgenic mice generated identically. It demonstrated, however, that the behavioral deficiencies and the pathological changes in brain resulting from an impaired neuronal function are caused directly by APP or its proteolytic derivative(s). These accelerate or impinge on the normal process of aging and amyloid deposits per se are not essential for this phenotype.

Purification, characterization and structural analysis of an abundant beta-1,3-glucanase from banana fruit

An abundant, catalytically active beta-1,3-endoglucanase (EC 3.2.1. 39) has been isolated from the pulp of ripe bananas. Biochemical analysis of the purified protein, molecular modelling, and molecular cloning of the corresponding gene indicate that this banana enzyme closely resembles previously characterized plant beta-glucanases with respect to its amino-acid sequence, structure and biological activity. The results described in this paper demonstrate both the occurrence of an abundant active beta-1,3-endoglucanases in fruits and also readdress the question of the possible involvement of these enzymes in the ripening and/or softening process.

Major protein of resting rhizomes of Calystegia sepium (hedge bindweed) closely resembles plant RNases but has no enzymatic activity

The most abundant protein of resting rhizomes of Calystegia sepium (L.) R.Br. (hedge bindweed) has been isolated and its corresponding cDNA cloned. The native protein consists of a single polypeptide of 212 amino acid residues and occurs as a mixture of glycosylated and unglycosylated isoforms. Both forms are derived from the same preproprotein containing a signal peptide and a C-terminal propeptide. Analysis of the deduced amino acid sequence indicated that the C. sepium protein shows high sequence identity and structural similarity with plant RNases. However, no RNase activity could be detected in highly purified preparations of the protein. This apparent lack of activity results most probably from the replacement of a conserved His residue, which is essential for the catalytic activity of plant RNases. Our findings not only demonstrate the occurrence of a catalytically inactive variant of an S-like RNase, but also provide further evidence that genes encoding storage proteins may have evolved from genes encoding enzymes or other biologically active proteins.

Lipoprotein receptor-related protein in brain and in cultured neurons of mice deficient in receptor-associated protein and transgenic for apolipoprotein E4 or amyloid precursor protein

The role of the receptor-associated protein in controlling the expression of the low-density lipoprotein receptor-related protein was analysed in brain and in cultured neurons of receptor-associated protein - / - mice. In addition, the effect of two important ligands of lipoprotein receptor-related protein in brain, i.e. apolipoprotein E and amyloid precursor protein, was examined by crossing the receptor-associated protein - / - mice with transgenic mice overexpressing these proteins specifically in neurons. The immunohistochemical localization of lipoprotein receptor-related protein and receptor-associated protein in wild-type mouse brain was demonstrated to be congruent over all structures, including the cortex and hippocampus. In primary hippocampal neurons, lipoprotein receptor-related protein was distributed somatodendritically and receptor-associated protein was concentrated perinuclearly. In hippocampal neurons from receptor-associated protein - / - mice, lipoprotein receptor-related protein was redistributed over the cell body at the expense of the dendrites. In the absence of receptor-associated protein, maturation of lipoprotein receptor-related protein is slow, resulting in accumulation of the uncleaved 600,000 mol. wt precursor. Neither the added expression of apolipoprotein E4 nor that of amyloid precursor protein in cultured neurons influenced the maturation of lipoprotein receptor-related protein, in either the presence or absence of receptor-associated protein. This result shows that receptor-associated protein is not needed to allow co-expression of lipoprotein receptor-related protein with these ligands in neurons. Furthermore, the typical ramified neuronal morphology of cultured primary neurons and the histology and architecture of the brain were normal in receptor-associated protein - / - mice and in all of the double transgenic mice. Finally, we demonstrated that the survival of receptor-associated protein - /- hippocampal neurons was normal and unaffected by the genotype of the glial feeder cells, whether they were derived from wild-type mice or from mice deficient in receptor-associated protein or apolipoprotein E. These results show that, despite the dramatic effect on maturation and cellular localization of lipoprotein receptor-related protein, the absence of receptor-associated protein did not result in any notable physiological, functional or morphological effects.

Prominent axonopathy in the brain and spinal cord of transgenic mice overexpressing four-repeat human tau protein

Mutations in the human tau gene cause frontotemporal dementia and parkinsonism linked to chromosome 17. Some mutations, including mutations in intron 10, induce increased levels of the functionally normal four-repeat tau protein isoform, leading to neurodegeneration. We generated transgenic mice that overexpress the four-repeat human tau protein isoform specifically in neurons. The transgenic mice developed axonal degeneration in brain and spinal cord. In the model, axonal dilations with accumulation of neurofilaments, mitochondria, and vesicles were documented. The axonopathy and the accompanying dysfunctional sensorimotor capacities were transgene-dosage related. These findings proved that merely increasing the concentration of the four-repeat tau protein isoform is sufficient to injure neurons in the central nervous system, without formation of intraneuronal neurofibrillary tangles. Evidence for astrogliosis and ubiquitination of accumulated proteins in the dilated part of the axon supported this conclusion. This transgenic model, overexpressing the longest isoform of human tau protein, recapitulates features of known neurodegenerative diseases, including Alzheimer's disease and other tauopathies. The model makes it possible to study the interaction with additional factors, to be incorporated genetically, or with other biological triggers that are implicated in neurodegeneration.

Analysis of expression of genes involved in apolipoprotein E-based lipoprotein metabolism in pregnant mice deficient in the receptor-associated protein, the low density lipoprotein receptor, or apolipoprotein E

Mice deficient in receptor-associated protein (RAP) were phenotypically normal, but in contrast to results previously reported in RAP(-/-) mice, nearly 50% of the offspring died at or shortly after birth. To attempt to determine the reason for this, we analyzed the regulation of expression of genes involved in apolipoprotein E (apoE)-based mechanisms in RAP-deficient mice and compared this to results in mice deficient in low density lipoprotein receptor (LDLR) or apoE. The major finding concerned a large increase in hepatic lipoprotein receptor-related protein (LRP) mRNA and LDLR mRNA levels in pregnant RAP knockout mice. This is in contrast to the down-regulation of LRP mRNA and LDLR mRNA, which is normally seen in wild-type mice. Also in LDLR knockout mice, a significant up-regulation in expression of LRP mRNA was demonstrated. In apoE knockout mice, hepatic LRP mRNA did not change significantly, while hepatic LDLR mRNA expression was increased. In placenta and uterus, the deficiency of RAP did not markedly affect the expression of LRP and LDLR. Lipoprotein lipase mRNA and apoE mRNA increased during pregnancy in all mice, independent of their genetic status. The current study does not directly explain the increased mortality of RAP(-/-) pups. The data demonstrate, however, important relative changes in expression of the genes analyzed, an indication that LRP and LDLR play an important role in lipid metabolism during pregnancy.

Presenilin 2 deficiency causes a mild pulmonary phenotype and no changes in amyloid precursor protein processing but enhances the embryonic lethal phenotype of presenilin 1 deficiency

Mutations in the homologous presenilin 1 (PS1) and presenilin 2 (PS2) genes cause the most common and aggressive form of familial Alzheimer's disease. Although PS1 function and dysfunction have been extensively studied, little is known about the function of PS2 in vivo. To delineate the relationships of PS2 and PS1 activities and whether PS2 mutations involve gain or loss of function, we generated PS2 homozygous deficient (-/-) and PS1/PS2 double homozygous deficient mice. In contrast to PS1(-/-) mice, PS2(-/-) mice are viable and fertile and develop only mild pulmonary fibrosis and hemorrhage with age. Absence of PS2 does not detectably alter processing of amyloid precursor protein and has little or no effect on physiologically important apoptotic processes, indicating that Alzheimer's disease-causing mutations in PS2, as in PS1, result in gain of function. Although PS1(+/-) PS2( -/-) mice survive in relatively good health, complete deletion of both PS2 and PS1 genes causes a phenotype closely resembling full Notch-1 deficiency. These results demonstrate in vivo that PS1 and PS2 have partially overlapping functions and that PS1 is essential and PS2 is redundant for normal Notch signaling during mammalian embryological development.

alpha2-macroglobulin- and murinoglobulin-1- deficient mice. A mouse model for acute pancreatitis

Mice deficient in either or both mouse alpha2-macroglobulin (MAM) and murinoglobulin-1 (MUG1) were generated and proved phenotypically normal under standard conditions. Acute pancreatitis was induced with a diet deficient in choline and methionine, supplemented with ethionine. The mortality was less than 25% in wild-type mice, as opposed to at least 56% in knockout mice, and was highest (70%) in MAM-/- mice, with earliest onset at 2 days. Plasma amylase and lipase levels were increased, but pancreatic tissue appeared histologically variable in individual mice. The clinical symptoms were most severe in MAM-/- mice and, surprisingly, were not aggravated in the double knockout mice, suggesting that the lack of proteinase inhibition capacity was not the major problem. Therefore, we analyzed the expression of 21 different cytokines and polypeptide factors in the pancreas of all experimental groups of mice. Interleukin-1-receptor antagonist mRNA was consistently induced by the diet in the pancreas of MAM-/- mice, and transforming growth factor-beta, tumor necrosis factor-alpha, tumor necrosis factor-beta, beta-lymphotoxin, and interferon-gamma mRNA levels were also increased. The data demonstrate the important role of alpha2-macroglobulin (A2M) in acute pancreatitis as both a proteinase inhibitor and a cytokine carrier. Mice deficient in MAM and/or MUG thus offer new experimental models for defining in vivo the role of the macroglobulins in pancreatitis and in other normal and pathological processes.

Developmental expression of wild-type and mutant presenilin-1 in hippocampal neurons from transgenic mice: evidence for novel species-specific properties of human presenilin-1

Presenilins 1 (PS1) and 2 (PS2) are multispanning transmembrane proteins associated with familial Alzheimer disease (FAD). They are developmentally regulated, being expressed at highest levels during neuronal differentiation and are sustained at a lower level throughout life. We investigated the distribution and metabolism of endogenous murine PS1 as well as human wild-type (wtPS1) and the familial AD Met146Leu (M146L) mutant presenilins in dissociated cultures of hippocampal neurons derived from control and transgenic mice. We found that the PS1 endoproteolytic fragments and, to a lesser extent, the full-length protein, were expressed as early as day 3 post-plating. Both species increased until the cells were fully differentiated at day 12. Confocal microscopy revealed that presenilin is present in the Golgi and endoplasmic reticulum and, as in punctate, vesicle-like structures within developing neurites and growth cones. Using a human-specific PS1 antibody, we were able to independently examine the distribution of the transgenic protein which, although similar to the endogenous, showed some unique qualities. These included (i) some heterogeneity in the proteolytic fragments of human PS1; (ii) significantly reduced levels of full-length human PS1, possibly as a result of preferential processing; and (iii) a more discrete intracellular distribution of human PS1. Colocalization with organelle-specific proteins revealed that PS1 was located in a diffuse staining pattern in the MAP2-positive dendrites and in a punctate manner in GAP43-positive axons. PS1 showed considerable overlap with GAP43, particularly at the growth cones. Similar patterns of PS1 distribution were detected in cultures derived from transgenic animals expressing human wild-type or mutant presenilins. The studies demonstrate that mutant presenilins are not grossly different in their processing or distribution within cultured neurons, which may represent more physiological models as compared to transfection systems. Our data also suggest that the molecular pathology associated with PS1 mutations results from subtle alterations in presenilin function, which can be further investigated using these transgenic neuronal cell culture models.

Premature death in transgenic mice that overexpress a mutant amyloid precursor protein is preceded by severe neurodegeneration and apoptosis

A mutant amyloid precursor protein (APP/RK) designed to interfere with processing by alpha-secretase caused a severe phenotype in transgenic mice, including behavioural abnormalities, i.e. neophobia, aggression, hypersensitivity to kainic acid, hyposensitivity to N-methyl-D-aspartate, and premature death [Moechars D. et al. (1996) Eur. molec. Biol. Org. J. 15, 1265-1274]. We now demonstrated that the APP/RK transgene did not disturb the expression of several other genes, i.e. endogenous amyloid precursor protein and amyloid precursor protein-like proteins, members of the low density lipoprotein receptor lipoprotein receptor family and several of their ligands, including apolipoprotein E, but expression of alpha-2-macroglobulin was never detected. Neither amyloid deposits nor neurofibrillary tangles were detected in the brain of APP/RK transgenic mice, even when 15-months-old. The tendency for seizures and hyposensitivity for N-methyl-D-aspartate was not due to or reflected in the distribution of the three major types of glutamate receptors. The major and consistent finding in transgenic APP/RK mice that died prematurely was extensive neurodegeneration and apoptosis, mainly in hippocampus and cortex, and accompanied by astrocytosis throughout the brain. Reduced synaptic density and dendritic damage was only observed in three transgenic mice that were killed shortly after positive observation of seizures. In addition, the distribution of cathepsin D and ubiquitin was abnormal in these mice.

Isolation and partial characterisation of galactose-specific lectins from African yam beans, Sphenostyles stenocarpa Harms

A new galactose-specific lectin was isolated from African yam bean (Sphenostyles stenocarpa Harms) by affinity chromatography on galactose-Sepharose 4B. SDS-PAGE analysis resulted in four polypeptide bands of approximately 27, 29, 32 and 34 kDa, respectively. Based on the analysis of carbohydrate content and native PAGE, it is likely that the Sphenostyles lectin is a tetrameric glycoprotein with M(r) of approximately 122 kDa. N-terminal protein sequencing of purified lectins from four different Sphenostyles accessions shows that the four polypeptides have largely identical amino acid sequences. The sequences contain the conserved consensus sequence F-F-LILG characteristic of legume lectins, as well as Phaseolus vulgaris proteins in the arcelin-alpha-amylase inhibitor gene family. The lectin agglutinates both rabbit and human erythrocytes, but with a preference for blood types A and O. Using Western blotting, the lectin was shown to accumulate rapidly during seed development, but levels dropped slightly as seeds attained maturity. This is the first time a lectin has been purified from the genus Sphenostyles. The new lectin was assigned the abbreviation LECp.SphSte.se.Hga1.