Neuroprotective properties of anti-apoptotic BCL-2 proteins in 5xFAD mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is the most common cause of dementia. An early feature of the AD pathology is the dysregulation of intracellular Ca2+ signaling in neurons. In particular, increased Ca2+ release from endoplasmic reticulum-located Ca2+ channels, including inositol-1,4,5-trisphosphate type 1 receptors (IP3R1) and ryanodine receptors type 2 (RyR2), have been extensively reported. Known for its anti-apoptotic properties, Bcl-2 also has the ability to bind to and inhibit the Ca2+-flux properties of IP3Rs and RyRs. In this study, the hypothesis that the expression of Bcl-2 proteins can normalize dysregulated Ca2+ signaling in a mouse model of AD (5xFAD) and thereby prevent or slow the progression of AD was examined. Therefore, stereotactic injections of adeno-associated viral vectors expressing Bcl-2 proteins were performed in the CA1 region of the 5xFAD mouse hippocampus. In order to assess the importance of the association with IP3R1, the Bcl-2K17D mutant was also included in these experiments. This K17D mutation has been previously shown to decrease the association of Bcl-2 with IP3R1, thereby impairing its ability to inhibit IP3R1 while not affecting Bcl-2's ability to inhibit RyRs. Here, we demonstrate that Bcl-2 protein expression leads to synaptoprotective and amyloid-protective effects in the 5xFAD animal model. Several of these neuroprotective features are also observed by Bcl-2K17D protein expression, suggesting that these effects are not associated with Bcl-2-mediated inhibition of IP3R1. Potential mechanisms for this Bcl-2 synaptoprotective action may be related to its ability to inhibit RyR2 activity as Bcl-2 and Bcl-2K17D are equally potent in inhibiting RyR2-mediated Ca2+ fluxes. This work indicates that Bcl-2-based strategies hold neuroprotective potential in AD models, though the underlying mechanisms requires further investigation.

ATP13A2/PARK9 regulates endo-/lysosomal cargo sorting and proteostasis through a novel PI(3, 5)P2-mediated scaffolding function.

ATP13A2 (also called PARK9), is a transmembrane endo-/lysosomal-associated P5 type transport ATPase. Loss-of-function mutations in ATP13A2 result in the Kufor-Rakeb Syndrome (KRS), a form of autosomal Parkinson's disease (PD). In spite of a growing interest in ATP13A2, very little is known about its physiological role in stressed cells. Recent studies suggest that the N-terminal domain of ATP13A2 may hold key regulatory functions, but their nature remains incompletely understood. To this end, we generated a set of melanoma and neuroblastoma cell lines stably overexpressing wild-type (WT), catalytically inactive (D508N) and N-terminal mutants, or shRNA against ATP13A2. We found that under proteotoxic stress conditions, evoked by the proteasome inhibitor Bortezomib, endo-/lysosomal associated full-length ATP13A2 WT, catalytically-inactive or N-terminal fragment mutants, reduced the intracellular accumulation of ubiquitin-conjugated (Ub) proteins, independent of autophagic degradation. In contrast, ATP13A2 silencing increased the intracellular accumulation of Ub-proteins, a pattern also observed in patient-derived fibroblasts harbouring ATP13A2 loss-of function mutations. In treated cells, ATP13A2 evoked endocytic vesicle relocation and increased cargo export through nanovesicles. Expression of an ATP13A2 mutant abrogating PI(3,5)P2 binding or chemical inhibition of the PI(3,5)P2-generating enzyme PIKfyve, compromised vesicular trafficking/nanovesicles export and rescued intracellular accumulation of Ub-proteins in response to proteasomal inhibition. Hence, our study unravels a novel activity-independent scaffolding role of ATP13A2 in trafficking/export of intracellular cargo in response to proteotoxic stress.

α-Synuclein strains cause distinct synucleinopathies after local and systemic administration.

Misfolded protein aggregates represent a continuum with overlapping features in neurodegenerative diseases, but differences in protein components and affected brain regions. The molecular hallmark of synucleinopathies such as Parkinson's disease, dementia with Lewy bodies and multiple system atrophy are megadalton α-synuclein-rich deposits suggestive of one molecular event causing distinct disease phenotypes. Glial α-synuclein (α-SYN) filamentous deposits are prominent in multiple system atrophy and neuronal α-SYN inclusions are found in Parkinson's disease and dementia with Lewy bodies. The discovery of α-SYN assemblies with different structural characteristics or 'strains' has led to the hypothesis that strains could account for the different clinico-pathological traits within synucleinopathies. In this study we show that α-SYN strain conformation and seeding propensity lead to distinct histopathological and behavioural phenotypes. We assess the properties of structurally well-defined α-SYN assemblies (oligomers, ribbons and fibrils) after injection in rat brain. We prove that α-SYN strains amplify in vivo. Fibrils seem to be the major toxic strain, resulting in progressive motor impairment and cell death, whereas ribbons cause a distinct histopathological phenotype displaying Parkinson's disease and multiple system atrophy traits. Additionally, we show that α-SYN assemblies cross the blood-brain barrier and distribute to the central nervous system after intravenous injection. Our results demonstrate that distinct α-SYN strains display differential seeding capacities, inducing strain-specific pathology and neurotoxic phenotypes.

Depletion of RIPK3 or MLKL blocks TNF-driven necroptosis and switches towards a delayed RIPK1 kinase-dependent apoptosis.

In human cells, the RIPK1-RIPK3-MLKL-PGAM5-Drp1 axis drives tumor necrosis factor (TNF)-induced necroptosis through mitochondrial fission, but whether this pathway is conserved among mammals is not known. To answer this question, we analyzed the presence and functionality of the reported necroptotic axis in mice. As in humans, knockdown of receptor-interacting kinase-3 (RIPK3) or mixed lineage kinase domain like (MLKL) blocks TNF-induced necroptosis in L929 fibrosarcoma cells. However, repression of either of these proteins did not protect the cells from death, but instead induced a switch from TNF-induced necroptosis to receptor-interacting kinase-1 (RIPK1) kinase-dependent apoptosis. In addition, although mitochondrial fission also occurs during TNF-induced necroptosis in L929 cells, we found that knockdown of phosphoglycerate mutase 5 (PGAM5) and dynamin 1 like protein (Drp1) did not markedly protect the cells from TNF-induced necroptosis. Depletion of Pink1, a reported interactor of both PGAM5 and Drp1, did not affect TNF-induced necroptosis. These results indicate that in these murine cells mitochondrial fission and Pink1 dependent processes, including Pink-Parkin dependent mitophagy, apparently do not promote necroptosis. Our data demonstrate that the core components of the necrosome (RIPK1, RIPK3 and MLKL) are crucial to induce TNF-dependent necroptosis both in human and in mouse cells, but the associated mechanisms may differ between the two species or cell types.

Neurotransmitters involved in fast excitatory neurotransmission directly activate enteric glial cells.

BACKGROUND: The intimate association between glial cells and neurons within the enteric nervous system has confounded careful examination of the direct responsiveness of enteric glia to different neuroligands. Therefore, we aimed to investigate whether neurotransmitters known to elicit fast excitatory potentials in enteric nerves also activate enteric glia directly. METHODS: We studied the effect of acetylcholine (ACh), serotonin (5-HT), and adenosine triphosphate (ATP) on intracellular Ca(2+) signaling using aequorin-expressing and Fluo-4 AM-loaded CRL-2690 rat and human enteric glial cell cultures devoid of neurons. The influence of these neurotransmitters on the proliferation of glia was measured and their effect on the expression of c-Fos as well as glial fibrillary acidic protein (GFAP), Sox10, and S100 was examined by immunohistochemistry and quantitative RT-PCR. KEY RESULTS: Apart from ATP, also ACh and 5-HT induced a dose-dependent increase in intracellular Ca(2+) concentration in CRL-2690 cells. Similarly, these neurotransmitters also evoked Ca(2+) transients in human primary enteric glial cells obtained from mucosal biopsies. In contrast with ATP, stimulation with ACh and 5-HT induced early gene expression in CRL-2690 cells. The proliferation of enteric glia and their expression of GFAP, Sox10, and S100 were not affected following stimulation with these neurotransmitters. CONCLUSIONS & INFERENCES: We provide evidence that enteric glial cells respond to fast excitatory neurotransmitters by changes in intracellular Ca(2+). On the basis of our experimental in vitro setting, we show that enteric glia are not only directly responsive to purinergic but also to serotonergic and cholinergic signaling mechanisms.

Efficient and stable transduction of dopaminergic neurons in rat substantia nigra by rAAV 2/1, 2/2, 2/5, 2/6.2, 2/7, 2/8 and 2/9.

Dysfunction of the nigrostriatal system is the major cause of Parkinson's disease (PD). This brain region is therefore an important target for gene delivery aiming at disease modeling and gene therapy. Recombinant adeno-associated viral (rAAV) vectors have been developed as efficient vehicles for gene transfer into the central nervous system. Recently, several serotypes have been described, with varying tropism for brain transduction. In light of the further development of a viral vector-mediated rat model for PD, we performed a comprehensive comparison of the transduction and tropism for dopaminergic neurons (DNs) in the adult Wistar rat substantia nigra (SN) of seven rAAV vector serotypes (rAAV 2/1, 2/2, 2/5, 2/6.2, 2/7, 2/8 and 2/9). All vectors were normalized by titer and volume, and stereotactically injected into the SN. Gene expression was assessed non-invasively and quantitatively in vivo by bioluminescence imaging at 2 and 5 weeks after injection, and was found to be stable over time. Immunohistochemistry at 6 weeks following injection revealed the most widespread enhanced green fluorescence protein expression and the highest number of positive nigral cells using rAAV 2/7, 2/9 and 2/1. The area transduced by rAAV 2/8 was smaller, but nevertheless almost equal numbers of nigral cells were targeted. Detailed confocal analysis revealed that serotype 2/7, 2/9, 2/1 and 2/8 transduced at least 70% of the DNs. In conclusion, these results show that various rAAV serotypes efficiently transduce nigral DNs, but significant differences in transgene expression pattern and level were observed.

Neonatal neuronal overexpression of glycogen synthase kinase-3 beta reduces brain size in transgenic mice.

Glycogen synthase kinase-3beta (GSK-3beta) is important in neurogenesis. Here we demonstrate that the kinase influenced post-natal maturation and differentiation of neurons in vivo in transgenic mice that overexpress a constitutively active GSK-3beta[S9A]. Magnetic resonance imaging revealed a reduced volume of the entire brain, concordant with a nearly 20% reduction in wet brain weight. The reduced volume was most prominent for the cerebral cortex, without however, disturbing the normal cortical layering. The resulting compacted architecture was further demonstrated by an increased neuronal density, by reduced size of neuronal cell bodies and of the somatodendritic compartment of pyramidal neurons in the cortex. No evidence for apoptosis was obtained. The marked overall reduction in the level of the microtubule-associated protein 2 in brain and in spinal cord, did not affect the ultrastructure of the microtubular cytoskeleton in the proximal apical dendrites. The overall reduction in size of the entire CNS induced by constitutive active GSK-3beta caused only very subtle changes in the psychomotoric ability of adult and ageing GSK-3beta transgenic mice.

Coexpression of GSK-3beta corrects phenotypic aberrations of dorsal root ganglion cells, cultured from adult transgenic mice overexpressing human protein tau.

Coexpression of constitutively active GSK-3beta[S9A] rescued the axonal pathology induced by overexpression of human tau in transgenic mice (Spittaels et al., (2000) J. Biol. Chem. 275, 41340-41349). We isolated dorsal root ganglion (DRG) neuronal cultures from adult tau4R- and tau4R x GSK-3beta-transgenic mice to define the mechanisms at the cellular and subcellular level. DRG from tau4R-transgenics showed a reduced sprouting capacity while density and stability of microtubules in the axonal processes were significantly increased. Video-enhanced contrast microscopy demonstrated a dramatic inhibition of fast axonal transport. Coexpression of GSK-3beta increased tau phosphorylation and reversed the effects on microtubule stability and saltatory motion. In DRG from GSK-3beta single transgenics, increased tau phosphorylation was evident without any major effects on microtubule stability or axonal transport. These observations support the hypothesis that excess tau competed with motor-proteins for binding to microtubules and/or that a rigid microtubular system inhibits axonal transport.

Modelling Alzheimer's disease in multiple transgenic mice.

We have reported transgenic mice with neuronal overexpression of the clinical mutant beta-amyloid precursor protein (APP) known as London, which develop an AD-related phenotype [Moechers, Dewachter, Lorent, Reversé, Baekelandt, Nadiu, Tesseur, Spittaels, Van den Haute, Checler, et al. (1999) J. Biol. Chem. 274, 6483-6492]. Characterized early symptoms (3-9 months) include disturbed behaviour, neophobia, aggression, hypersensitivity to kainic acid, hyposensitivity to N-methyl-D-aspartate, defective cognition and memory, and decreased long-term potentiation. Late in life, at 12-15 months, amyloid plaques develop in the brain and correlate with increased levels of beta-amyloid (A beta)40/42 (the 40- and 42-amino-acid forms of A beta). The formation of amyloid plaques is dissociated in time from and not involved in the early phenotype. Hyperphosphorylated protein tau is present but no tangle pathology is observed. In double-transgenic mice, i.e. APP/London x Presenilin 1, the increased production of A beta 42 results in amyloid plaques developing by the age of 6 months. Transgenic mice with overexpression of either human apolipoprotein E4 (ApoE4) or human protein tau in central neurons develop severe axonopathy in the brain and spinal cord. Progressive degeneration of nerves and muscles is demonstrated by motor problems, wasting and premature death. Tau is hyperphosphorylated but there is no formation of filaments or neurofibrillary tangles. The tangle aspect of AD pathology is still missing from all current transgenic amyloid models. Its implementation will require insight into the cellular signalling pathways which regulate the microtubule-stabilizing function by phosphorylation of neuronal tau.

Coexpression of human cdk5 and its activator p35 with human protein tau in neurons in brain of triple transgenic mice.

The potential contribution of cyclin-dependent protein kinase 5 (cdk5) to hyperphosphorylate protein tau, as claimed in Alzheimer's disease, was investigated in vivo. We generated single, double, and triple transgenic mice that coexpress human cdk5 and its activator p35 as well as human protein tau in cerebral neurons. Whereas expression and increased cdk5-kinase activity was obtained, as measured in vitro and demonstrated in vivo, neither murine nor human protein tau was appreciably phosphorylated in the brain of double and triple transgenic mice. These mice behaved and reproduced normally. Silver impregnation and immunohistochemistry of brain sections demonstrated that neurofilament proteins became redistributed in apical dendrites of cortical neurons. This suggested a cytoskeletal effect, but no other relevant brain pathology became apparent. These observations indicate that cdk5/p35 is not a major protein tau kinase and that cdk5/p35 did not cause neurodegeneration in mouse brain, as opposed to cdk5/p25.

Prominent cerebral amyloid angiopathy in transgenic mice overexpressing the london mutant of human APP in neurons.

Deposition of amyloid beta-peptide (Abeta) in cerebral vessel walls (cerebral amyloid angiopathy, CAA) is very frequent in Alzheimer's disease and occurs also as a sporadic disorder. Here, we describe significant CAA in addition to amyloid plaques, in aging APP/Ld transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP) exclusively in neurons. The number of amyloid-bearing vessels increased with age, from approximately 10 to >50 per coronal brain section in APP/Ld transgenic mice, aged 13 to 24 months. Vascular amyloid was preferentially deposited in arterioles and ranged from small focal to large circumferential depositions. Ultrastructural analysis allowed us to identify specific features contributing to weakening of the vessel wall and aneurysm formation, ie, disruption of the external elastic lamina, thinning of the internal elastic lamina, interruption of the smooth muscle layer, and loss of smooth muscle cells. Biochemically, the much lower Abeta42:Abeta40 ratio evident in vascular relative to plaque amyloid, demonstrated that in blood vessel walls Abeta40 was the more abundant amyloid peptide. The exclusive neuronal origin of transgenic APP, the high levels of Abeta in cerebrospinal fluid compared to plasma, and the specific neuroanatomical localization of vascular amyloid strongly suggest specific drainage pathways, rather than local production or blood uptake of Abeta as the primary mechanism underlying CAA. The demonstration in APP/Ld mice of rare vascular amyloid deposits that immunostained only for Abeta42, suggests that, similar to senile plaque formation, Abeta42 may be the first amyloid to be deposited in the vessel walls and that it entraps the more soluble Abeta40. Its ability to diffuse for larger distances along perivascular drainage pathways would also explain the abundance of Abeta40 in vascular amyloid. Consistent with this hypothesis, incorporation of mutant presenilin-1 in APP/Ld mice, which resulted in selectively higher levels of Abeta42, caused an increase in CAA and senile plaques. This mouse model will be useful in further elucidating the pathogenesis of CAA and Alzheimer's disease, and will allow testing of diagnostic and therapeutic strategies.

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.

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.

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.

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.

[Blood gas determination in the newborn infant (prognostic and therapeutic value)]. / Gazométries sanguines chez le nouveau-né (intérêt pronostique et thérapeutique)

A study of 55 blood gas determinations performed on the umbilical vein blood in the new-born (determinations of pH, SAO2, PaCO2, O2 vol% of total blood, CO2 vol% of total plasma, hemoglobin, hematocrit and, in some cases, PaO2). The cases include: 26 girls, 23 boys, issued from 9 primiparas (mean age: 25 years) and 40 multiparas (mean age: 28 years). In 18 of these cases, the parturient woman was administered oxygen. In 6 cases the delivery was complicated. The comparison of the data obtained by means of blood gas determination with the Apgar test evidences the value of the determination of these biological parameters. Authors insist on the necessity to make a functional respiratory study in the pregnany woman exhibiting a chronic respiratory deficiency, and to perform a blood gas determination and an oxygen-therapy (with an hyperoxygenated gas mixture -- O2 60% -- N2 40%) during the labour in order to avoid a fetal anoxia and its consequences, always redoubtable.