Glycated bovine serum albumin for use in feeding trials with animal models - In vitro methodology and characterization of a glycated substrate for modifying feed pellets

This study investigated different methods to produce N^ε-carboxymethyl-lysine (CML)-enriched bovine serum albumin (BSA) as alternatives to the classical approach using glyoxylic acid (GA) and sodium cyanoborohydride (NaBH₃CN) which results in toxic hydrogen cyanide (HCN). The reaction of GA (6 mmol/L) and NaBH₃CN (21 mmol/L) to produce CML remained the most effective with CML yields of 24-35%, followed by 13-24% using 300 mmol/L glyoxal (GO). GA promoted specific modification of lysine to CML, and fewer structural modifications of the BSA molecule compared with GO, as evidenced by fluorescence and proteomic analyses. GO promoted greater arginine modification compared with GA (76 vs 23%). Despite structural changes to BSA with GO, murine fecal clearance of CML was similar to literature values. Hence, BSA glycation with 300 mmol/L glyoxal is a suitable alternative to GA and NaBH₃CN for generating CML-enriched protein free of HCN, but a CML-only fortification model remains to be described.

Intracellular acidification delays hormonal G2/M transition and inhibits G2/M transition triggered by thiophosphorylated MAPK in Xenopus oocytes

Xenopus oocyte maturation is analogous to G2/M transition and characterized by germinal vesicle breakdown (GVBD), spindle formation, activation of MPF and Mos-Xp42(Mpk1) pathways. It is accompanied prior to GVBD by a transient increase in intracellular pH. We determined that a well known acidifying compound, NH(4)Cl, delayed progesterone-induced GVBD in a dose-dependent manner. GVBD(50) was delayed up to 2.3-fold by 10 mM NH(4)Cl. Cyclin B2 phosphorylation, Cdk1 Tyr15 dephosphorylation as well as p39(Mos) accumulation, Xp42(Mpk1) and p90(Rsk) phosphorylation induced by progesterone were also delayed by incubation of oocyte in NH(4)Cl. The delay induced by NH(4)Cl was prevented by injection of MOPS buffer pH 7.7. In contrast to acidifying medium, alkalyzing treatment such as Tris buffer pH 9 injections, accelerated GVBD, MPF and Xp42(Mpk1) activation, indicating that pHi changes control early steps of G2/M dynamics. When injected in an immature recipient oocyte, egg cytoplasm triggers GVBD through MPF auto-amplification, independently of protein synthesis. In these conditions, GVBD and Xp42(Mpk1) activation were delayed by high concentration of NH(4)Cl, which never prevented or delayed MPF activation. Strickingly, NH(4)Cl strongly inhibited thiophosphorylated active MAPK-induced GVBD and MPF activation. Nevertheless, Tris pH 9 did not have any effects on egg cytoplasm- or active MAPK-induced GVBD. Taken together, our results suggest that dynamic of early events driving Xp42(Mpk1) and MPF activation induced by progesterone may be negatively or positively regulated by pH(i) changes. However Xp42(Mpk1) pathway was inhibited by acidification alone. Finally, MPF auto-amplification loop was not sensitive to pH(i) changes.

Female-enriched and thermosensitive expression of steroidogenic factor-1 during gonadal differentiation in Pleurodeles waltl

In the urodele amphibian Pleurodeles waltl, sex differentiation is genetically controlled, that is, ZZ male vs ZW female, but may be influenced by temperature, which induces a female-to-male sex reversal. We investigated whether steroidogenic factor 1 (SF-1) could be involved in Pleurodeles sex differentiation or in temperature-dependent sex reversal by cloning a Pleurodeles SF-1 cDNA and examining its developmental expression. The 468-amino-acid deduced protein is highly conserved in comparison with other species. In ZZ and ZW control larvae, SF-1 mRNA is detected at the first stage of the thermosensitive period (TSP) in the gonad-mesonephros-interrenal complex (GMI). By the end of TSP at stage 55, SF-1 is expressed in the gonad (Gd) and in the mesonephros-interrenal (MI) both in ZZ and ZW larvae. During this stage, a transient, ZW-specific increase of SF-1 transcription occurs not only in Gd but also in MI, this increase starting earlier in Gd than in MI. Therefore, in P. waltl, an SF-1 upregulation occurs after the onset of the ovarian-specific increase of aromatase mRNA expression. At the end of metamorphosis, the SF-1 transcription level in Gd and MI is nearly the same in both ZZ and ZW larvae. Besides, after long-term heat treatment leading to sex reversal, SF-1 mRNA upregulation is not observed in ZW larvae, in either Gd or MI. However, SF-1 expression is not decreased after a 48-h heat shock applied at the end of the TSP, suggesting that temperature has no inhibitory effect by itself in long-term heat treatment. Estradiol benzoate treatments show that, at the end of the TSP, SF-1 gene transcription could be controlled by the estrogen level. This is in accordance with the female-enriched SF-1 expression and the decreased SF-1 expression following long-term, sex-reversing heat treatment, which is known to decrease aromatase expression and activity. Thus, it is unlikely that SF-1 is directly involved in Pleurodeles temperature-dependent sex reversal.

Differential roles of p39Mos-Xp42Mpk1 cascade proteins on Raf1 phosphorylation and spindle morphogenesis in Xenopus oocytes

Fully-grown G2-arrested Xenopus oocytes resume meiosis upon hormonal stimulation. Resumption of meiosis is characterized by germinal vesicle breakdown, chromosome condensation, and organization of a bipolar spindle. These cytological events are accompanied by activation of MPF and the p39(Mos)-MEK1-Xp42(Mpk1)-p90(Rsk) pathways. The latter cascade is activated upon p39(Mos) accumulation. Using U0126, a MEK1 inhibitor, and p39(Mos) antisense morpholino and phosphorothioate oligonucleotides, we have investigated the role of the members of the p39(Mos)-MEK1-Xp42(Mpk1)-p90(Rsk) in spindle morphogenesis. First, we have observed at a molecular level that prevention of p39(Mos) accumulation always led to MEK1 phosphorylation defects, even when meiosis was stimulated through the insulin Ras-dependent pathway. Moreover, we have observed that Raf1 phosphorylation that occurs during meiosis resumption was dependent upon the activity of MEK1 or Xp42(Mpk1) but not p90(Rsk). Second, inhibition of either p39(Mos) accumulation or MEK1 inhibition led to the formation of a cytoplasmic aster-like structure that was associated with condensed chromosomes. Spindle morphogenesis rescue experiments using constitutively active Rsk and purified murine Mos protein suggested that p39(Mos) or p90(Rsk) alone failed to promote meiotic spindle organization. Our results indicate that activation of the p39(Mos)-MEK1-Xp42(Mpk1)-p90(Rsk) pathway is required for bipolar organization of the meiotic spindle at the cortex.

Steroids, aromatase and sex differentiation of the newt Pleurodeles waltl

In the newt Pleurodeles waltl, genetic sex determination obeys female heterogamety (female ZW, male ZZ). In this species as in most of non-mammalian vertebrates, steroid hormones play a key role in sexual differentiation of gonads. In that context, male to female sex reversal can be obtained by treatment of ZZ larvae with estradiol. Male to female sex reversal has also been observed following treatment of ZZ larvae with testosterone, a phenomenon that was called the "paradoxical effect". Female to male sex reversal occurs when ZW larvae are reared at 32 degrees C during a thermosensitive period (TSP) that takes place from stage 42 to stage 54 of development. Since steroids play an important part in sex differentiation, we focussed our studies on the estrogen-producing enzyme aromatase during normal sex differentiation as well as in experimentally induced sex reversal situations. Our results based on treatment with non-aromatizable androgens, aromatase activity measurements and aromatase expression studies demonstrate that aromatase (i) is differentially active in ZZ and ZW larvae, (ii) is involved in the paradoxical effect and (iii) might be a target of temperature. Thus, the gene encoding aromatase might be one of the master genes in the process leading to the differentiation of the gonad in Pleurodeles waltl.

Effect of cadmium on gonadogenesis and metamorphosis in Pleurodeles waltl (urodele amphibian)

In the amphibian Pleurodeles waltl, steroid hormones play a key role in sex differentiation. Since cadmium has been reported to block receptors of sex steroid hormones, we analyzed the effects of this heavy metal on Pleurodeles larvae gonadogenesis. At stage 42, larvae die in the presence of 10.9 microM Cd in the rearing tap water, with TL(50) of 46.3 h, but the concentration of 5.5 microM is tolerated for more than 60 days. When used at 5.5 microM cadmium accumulation measured by atomic absorption spectrophotometry (AAS) in total homogenates of larvae at stage 54 (after 77 days of exposure to the heavy metal) reached 58.1 microg/g of dry weight. At stage 54, we did not detect inhibitory effects on gonadogenesis in larvae reared in the presence of 5.5 microM Cd since stage 42. When the exposure to 5.5 microM Cd was lengthened after stage 54, metamorphosis was delayed and could not be completed. When larvae were exposed to 10.9 microM Cd from stage 54, metamorphosis did not occur and gonad development was stopped. Our study demonstrates a lack of a direct effect of cadmium on sex determination-differentiation but a strong inhibitory effect on metamorphosis, which impairs further gonadal development.

Effects of androgens on sex differentiation of the urodele Pleurodeles waltl

In nonmammalian vertebrates, steroids have been hypothesized to induce somatic sex differentiation, since manipulations of the steroidal environment of gonads have led to various degrees of sex reversal. Whereas the critical role of estrogens in ovarian differentiation is well documented, studies on androgens have produced a perplexing variety of results depending upon species variations and nature of androgens used. In this way, testosterone induces masculinization of females in some species but provokes paradoxical feminization of males in many other species such as the urodelan Pleurodeles waltl. In reptiles this phenomenon could be interpreted by conversion of exogenous testosterone to estradiol by aromatase. Treatments of Pleurodeles larvae with nonaromatizable androgens bring support to this hypothesis and suggest a role of androgens in sex differentiation. Dihydrotestosterone (DHT) could not induce the paradoxical feminization of ZZ larvae. In addition, DHT as well as 11beta-hydroxy-androstenedione could drive a functional male differentiation of ZW larvae. Moreover, other 5alpha reduced androgens also induced sex reversal of female larvae. Yet, the 5alpha reductase inhibitor CGP 53133 and antiandrogens such as flutamide or cyproterone acetate did not exert any effect on male sex differentiation of ZZ larvae. Though the precise role of androgens is still unknown, especially for 11-oxygenated androgens, our results suggest an implication in male sex differentiation. In this way, testosterone could play a pivotal role in being metabolized either into other androgens during testis differentiation or into estradiol during ovarian differentiation.

Differential expression of P450 aromatase during gonadal sex differentiation and sex reversal of the newt Pleurodeles waltl

A better understanding of vertebrate sexual differentiation could be provided by a study of models in which genetic sex determination (GSD) of gonads can be reversed by temperature. In the newt Pleurodeles waltl, a P450 aromatase cDNA was isolated from adult gonads, and the nucleotide or deduced amino acid sequences showed a high level of identity with various vertebrate species. In adults, aromatase expression was found in gonads and brain. In developing gonads, the expression was found to fit with the thermo-sensitive period (TSP) and was detected in both ZZ and ZW larvae, as well as in ZW submitted during the whole TSP to a masculinizing temperature. In the latter individuals, in situ hybridization and semi quantitative RT-PCR showed that, at the end of TSP, aromatase expression was at the same level than in normal ZZ larvae and was significantly lower than in normal ZW ones. Furthermore, temperature-induced down regulation did not occur when heating was performed at the end of TSP. Our results confirm the importance of aromatase regulation in female versus male differentiation and demonstrate that a down regulation of aromatase expression is involved in the process of sex reversal.

Modelling Alzheimer-specific abnormal Tau phosphorylation independently of GSK3beta and PKA kinase activities

In Alzheimer's disease, neurofibrillary degeneration results from the aggregation of abnormally phosphorylated Tau proteins into paired helical filaments. These Tau variants displayed specific epitopes that are immunoreactive with anti-phospho-Tau antibodies such as AT100. As shown in in vitro experiments, glycogen synthase kinase 3 beta (GSK3beta) and protein kinase A (PKA) may be key kinases in these phosphorylation events. In the present study, Tau was microinjected into Xenopus oocytes. Surprisingly, in this system, AT100 was generated without any GSK3beta and PKA contribution during the progesterone or insulin-induced maturation process. Our results demonstrate that a non-modified physiological process in a cell model can generate the most specific Alzheimer epitope of Tau pathology.

c-Mos proteolysis is independent of the CA(2+) rise induced by 6-DMAP in Xenopus oocytes

In Xenopus oocytes, metaphase II arrest is due to a cytostatic factor (CSF) that involves c-Mos, maintaining a high MPF (cdk1/cyclin B) activity in the cell. At fertilization, a rise in intracellular calcium triggers the proteolysis of both cyclin B and c-Mos. The kinase inhibitor 6-dimethylaminopurine (6-DMAP) is also able to release matured Xenopus oocytes from metaphase II block. This is characterized by c-Mos proteolysis without degradation of cyclin B. We hypothesized that 6-DMAP induced an increase in intracellular calcium. Using the calcium-sensitive fluorescent dye Fura-2, we observed a systematic increase in intracellular calcium following 6-DMAP application. In matured oocytes previously microinjected with the calcium chelator BAPTA, no calcium changes occurred after 6-DMAP addition; however, c-Mos was still proteolysed. In oocytes at the GVBD stage, c-Mos proteolysis occurred in response to 6-DMAP but not to calcium ionophore treatment. We suggest that c-Mos proteolysis is rather controlled by a phosphorylation-dependent process.

Differential effects of 6-DMAP, olomoucine and roscovitine on Xenopus oocytes and eggs

The effects of the new cyclin-dependent kinase inhibitors, roscovitine and olomoucine, on oocytes and eggs of Xenopus laevis were investigated and compared with those of 6-dimethylamino purine (6-DMAP). The inhibitory properties of 6-DMAP, olomoucine and roscovitine towards p34cdc2-cyclin B isolated from Xenopus eggs revealed K-IC50 values of 300, 40 and 10 microM respectively. The three compounds inhibited progesterone-induced maturation with M-IC50 values of 200, 100 and 20 microM. These values were consistent with the K-IC50 values but the ratio M-IC50/K-IC50 was higher for roscovitine and olomoucine than for 6-DMAP. The disappearance of spindle and condensed chromosomes without pronucleus formation was observed when 1 mM 6-DMAP was applied for 4 h at germinal vesicle breakdown or at metaphase II, whereas no effect was observed using 1 mM olomoucine or 50 microM roscovitine. Changes in the electrophoretic mobility of p34cdc2 and erk2 were observed only in homogenates of matured oocytes or eggs exposed for 4 h to 1 mM 6-DMAP. When the drugs were microinjected into matured oocytes, olomoucine (100 microM) and roscovitine (50 microM) induced pronucleus formation more efficiently than did 6-DMAP (100 microM). Taken together, these results demonstrate that Xenopus oocytes possess a lower permeability to olomoucine and roscovitine and that these new compounds are suitable for in vivo studies after germinal vesicle breakdown provided they are microinjected.

Activation of Xenopus eggs by the kinase inhibitor 6-DMAP suggests a differential regulation of cyclin B and p39(mos) proteolysis

In Xenopus eggs, metaphase II arrest is due to the cytostatic factor that maintains a high level of MPF activity. Kinases are important in this phenomenon since p39(mos) and MAPK play a part in the cytostatic activity whereas p34(cdc2) is the catalytic subunit of MPF. Fertilization induces a rise in intracellular calcium leading to egg activation that can be mimicked by calcium-increasing agents such as calcium ionophore. We have performed on Xenopus eggs a biochemical comparison of the effects of the kinase inhibitor 6-DMAP and the calcium ionophore. Both drugs were able to induce pronucleus formation but the underlying molecular events were different. The inactivation of MAPK occurred earlier in eggs exposed to 6-DMAP. Cyclins B1 and B2 were stable and p39(mos) was proteolysed in 6-DMAP-treated eggs while the three proteins underwent degradation in A23187-treated ones. These results suggest a differential regulation of ubiquitin-dependent proteolysis of cyclin B and p39(mos).

Inhibition of protein tyrosine phosphatases blocks calcium-induced activation of metaphase II-arrested oocytes of Xenopus laevis

We have studied the effect of a protein tyrosine phosphatases (PTP) inhibitor on calcium-induced activation of Xenopus laevis oocytes arrested at metaphase II. Ammonium molybdate microinjection blocked pronucleus formation following A23187 treatment while cortical granules still underwent exocytosis. Pronuclei still occurred in ammonium molybdate-injected oocytes following 6-DMAP addition. Changes that usually occurred following A23187 exposure were inhibited in the presence of ammonium molybdate in the oocyte: MAPK dephosphorylation, p34(cdc2) rephosphorylation and cyclin B2 and p39(mos) proteolysis. These results suggest that a PTP is involved in the activation of the ubiquitin-dependent degradation machinery.

Intra-M phase-promoting factor phosphorylation of cyclin B at the prophase/metaphase transition

Activation of Cdc2-cyclin B (or M phase-promoting factor (MPF)) at the prophase/metaphase transition proceeds in two steps: dephosphorylation of Cdc2 and phosphorylation of cyclin B. We here investigated the regulation of cyclin B phosphorylation using the starfish oocyte model. Cyclin B phosphorylation is not required for Cdc2 kinase activity; both the prophase complex dephosphorylated on Cdc2 with Cdc25 and the metaphase complex dephosphorylated on cyclin B with protein phosphatase 2A display high kinase activities. An in vitro assay of cyclin B kinase activity closely mimics in vivo phosphorylation as shown by phosphopeptide maps of in vivo and in vitro phosphorylated cyclin B. We demonstrate that Cdc2 itself is the cyclin B kinase; cyclin B phosphorylation requires Cdc2 activity both in vivo (sensitivity to vitamin K3, a Cdc25 inhibitor) and in vitro (copurification with Cdc2-cyclin B, requirement of Cdc2 dephosphorylation, and sensitivity to chemical inhibitors of cyclin-dependent kinases). Furthermore, cyclin B phosphorylation occurs as an intra-M phase-promoting factor reaction as shown by the following: 1) active Cdc2 is unable to phosphorylate cyclin B associated to phosphorylated Cdc2, and 2) cyclin B phosphorylation is insensitive to enzyme/substrate dilution. We conclude that, at the prophase/metaphase transition, cyclin B is mostly phosphorylated by its own associated Cdc2 subunit.

Effect of procaine on membrane potential and intracellular pH in Xenopus laevis oocytes

The effect of the local anaesthetic procaine on the intracellular pH, pHi, and electrophysiological properties of full-grown Xenopus oocytes was studied. In spite of its interference with both the pH-sensitive microelectrodes and fluorescent probe BCECF, we have shown that procaine induced an intracellular acidification rather than the alkalization commonly observed in most cells. The resting pHi of Xenopus oocytes loaded with BCECF was 7.36 +/- 0.04 (n = 16). Addition of 10 mM procaine to the bath at pH 7.5 caused pHi to decrease to a new steady state value of 6.97 +/- 0.05 (n = 9). A similar behaviour of pHi was observed with microelectrodes. Procaine also promoted a rise in membrane conductance and a membrane depolarization. These changes in membrane potential and conductance were not caused by the decrease in pHi since the addition of sodium propionate at pH 7.5 produced the same decrease of pHi as procaine, but resulted in only a slight depolarization with superimposed oscillations. Current measurements using two-electrode voltage clamp showed that the depolarization was associated with an inward current. No significant effect on this current was observed when replacing Cl, K or Na in the external medium. The absence of effect of Cl and K channel inhibitors argues against the involvement of Cl and K currents during the procaine response.

Ultrastructural localization of intracellular calcium stores in Xenopus ovarian follicles as revealed by cytochemistry and X-ray microanalysis

The ultrastructural localization of calcium in full-grown ovarian follicles of Xenopus laevis was demonstrated after fixation in the presence of fluoride ions and by means of energy dispersive X-ray microanalysis. In hormonally untreated follicles (prophase I-arrested oocytes), two calcium sites were detected: follicle cells and oocyte pigment granules. In follicle cells, calcium containing deposits were preferentially associated with macrovilli, which ended by gap junctions. In human chorionic gonadotropin treated follicles (meiotically reinitiated oocytes), deposits were only seen in follicle cells. This is the first report of the cytochemical detection of intracellular Ca2+ in follicle cells of amphibians. The possible involvements of these Ca2+ stores in mediating the hormonal control of meiotic maturation are discussed.

Procaine-induced maturation of Xenopus oocytes is mediated by a transient activation of M-phase promoting factor

We have recently shown that the incubation of Xenopus laevis oocytes in procaine-containing solutions induced germinal vesicle breakdown without white spot formation and, in some cases, with the appearance of spindle and chromosomes in the cytoplasm. The present study was performed to determine whether M-phase promoting factor was involved in this unusual maturation. Procaine failed to induce maturation in the presence of 6-dimethylamino purine or roscovitine, which are both known to inhibit p34cdc2 kinase. Histone H1 kinase activity was detected in procaine-treated oocytes but it was always lower than in progesterone-treated controls. A shift in p34cdc2 was observed in oocytes that had been exposed to procaine for 16 h, but it was not detected in those exposed for 24 h. Finally, cytoplasm transfer experiments demonstrated that the maturation promoting activity that occurred in oocytes incubated in procaine for 16 h could induce maturation of recipient stage VI oocytes. This transferable activity was weaker than that from progesterone-treated controls since only 30% of the recipients underwent germinal vesicle breakdown and only a few spindles were observed, which were not always correctly located. Taken together these results demonstrate that M-phase promoting factor is involved in the procaine maturing effect despite some differences compared with progesterone-treated oocytes which might explain the particular type of maturation induced by this substance. The discovery of the mechanisms by which procaine is able to activate M-phase promoting factor might now help in the understanding of some steps in progesterone-induced maturation that have still to be elucidated.

Xenopus oocyte maturation: cytoplasm alkalization is involved in germinal vesicle migration

In Xenopus laevis oocytes a transient increase in intracellular pH has been reported to occur during progesterone-induced maturation. Using a cytological approach, we have systematically analyzed germinal vesicle breakdown and meiotic spindle formation in various experimental conditions either preventing or promoting pHi changes. Injection of a neutral buffer (MOPS pH 6.9) induced a cytosolic acidification of 0.3 pH unit and inhibited by 30% the formation of the maturation white spot after progesterone exposure; in oocytes displaying a white spot, only half showed a spindle, often located far from the plasma membrane. Similar results were observed with a Na-free medium which prevents oocyte alkalization. Injection of an alkaline buffer (Tris pH 9) was able to induce migration of the germinal vesicle in 25% of the oocytes in the absence of progesterone, but failed to induce GVBD. Taken together, these results suggest that the increase in pHi observed during maturation may be involved in the migration of the germinal vesicle towards the plasma membrane. We also incubated oocytes in the presence of procaine, a weak base often used to artificially alkalize the oocyte cytoplasm. The changes induced by exposure to procaine were different from those resulting from alkaline buffer injection. Indeed procaine promoted GVBD, as well as spindle formation and chromosome condensation. However these events appeared without migration of the germinal vesicle, suggesting that the expected alkalization did not occur.

Abnormal Tau proteins in progressive supranuclear palsy. Similarities and differences with the neurofibrillary degeneration of the Alzheimer type

We have previously shown that abnormal Tau species are produced during the neurofibrillary degeneration of the Alzheimer type. These abnormal Tau proteins consist of a characteristic triplet named Tau 55, Tau 64 and Tau 69 which are constantly found in Alzheimer's disease (AD) and Downs syndrome brain regions with tangles. To determine if abnormal Tau species are also produced in other neurodegenerative conditions where intraneuronal filamentous Tau aggregates are observed, we have undertaken an immuno-blot study of brain homogenates from patients with progressive supranuclear palsy (PSP), a neurological disorder characterized by the presence of tangles in subcortical and cortical brain areas. We show here that abnormal Tau species are produced in PSP but that they are different from those in AD. Indeed, although Tau 64 and 69 were present in PSP brain homogenates, possibly as the result of an abnormal phosphorylation as in AD, they were detected in smaller amounts (three times lower) than in AD. In addition Tau 55 was undetected by the immunological tools, such as the absorbed anti-PHF antisera, which specifically label the abnormal Tau proteins. Also the two-dimensional analysis revealed different isoelectric properties. Our results suggest that the production of abnormal Tau species is a very important event during all types of neurofibrillary degeneration. The differences in the pathological Tau-variant profile that were observed between PSP and AD possibly reflect different etiopathogenetic pathways and might explain the formation of different types of filamentous Tau aggregates.

Expression of human Cu-Zn superoxide dismutase gene in transgenic mice: model for gene dosage effect in Down syndrome

It was suggested that increased Cu-Zn superoxide dismutase (SOD-1) might be involved in the various biological abnormalities found in Down's syndrome (DS) such as premature aging and Alzheimer-type neurological lesions. As a model system for testing this hypothesis we have developed two strains of transgenic mice carrying only one copy of the human SOD-1 gene. In the first strain (TG1), no expression has been found by northern blot analysis. The second strain (TG2) exhibited human SOD-1 mRNA and increased SOD-1 activity in the brain (1.93 fold), in the heart (1.69 fold), thymus (1.49 fold) and to a lesser extent in muscle (1.25 fold), liver (1.19 fold), kidney (1.18 fold), spleen (1.35 fold), lung (1.26 fold) and erythrocytes (1.09 fold). In this strain, increased SOD-1 activity in the brain did not induce modifications in the seleno-dependent glutathione peroxidase, glutathione reductase and glutathione S-transferase activities. In brain homogenates, we have focused our studies on Tau proteins which are known to be the major antigenic components of paired helical filaments (PHF), both in DS and Alzheimer's disease. Our results suggested that, in our experimental conditions, the overexpression of SOD-1 did not induce the modifications of Tau proteins similar to those seen during neurofibrillary degeneration.

Correlation between microscopical changes and Tau 64 and 69 biochemical detection in senile dementia of the Alzheimer type. Tau 64 and 69 are reliable markers of the neurofibrillary degeneration

We have recently reported that the immunoblot detection of two abnormally phosphorylated tau proteins, named Tau 64 and 69, in homogenates of cortical areas from patients with Alzheimer's disease (AD) was systematically associated with the presence of neurofibrillary tangles (NFT) and senile plaques (SP) in these areas. A blind study was performed to confirm that these proteins had a reliable diagnostic value and to study more precisely the correlation between Tau 64 and 69 and the presence of the characteristic lesions of AD. The density of NFT and of SP was evaluated on histological sections of gyrus supramarginalis from 17 patients with graded intellectual status. Immunodetection of Tau 64 and 69 was semiquantitatively evaluated by densitometry (reflectance mode) on immunoblots of homogenates of the same area on the contralateral hemisphere. The statistical analysis of results showed that Tau 64 and 69 were more strongly correlated with NFT than with SP. Moreover, semiquantitative evaluation of Tau 64 and 69 was correlated with the intellectual status (BTS score). Therefore, these pathological forms of tau proteins are reliable markers of the presence of NFT and SP in the neocortex and may be used as a diagnostic tool.

Pathological proteins Tau 64 and 69 are specifically expressed in the somatodendritic domain of the degenerating cortical neurons during Alzheimer's disease. Demonstration with a panel of antibodies against Tau proteins

Bundles of paired helical filaments (PHF) accumulate in the pyramidal neurons that degenerate during Alzheimer's disease. This neurofibrillary degeneration is highly correlated with clinical signs of dementia. During the degenerating process, Tau proteins, which are the major antigenic components of PHF, are abnormally phosphorylated and two pathological isoforms named Tau 64 and 69 are expressed. We have studied their immunoblot distribution in the cortical gray and white matter from different regions of normal and Alzheimer brains, to determine if the degenerating process preferentially affects the somatodendritic or the axonal domain. Two categories of antibodies were used. The first category consisted of anti-human native Tau, anti-Tau proteins from different vertebrates, anti-PHF, monoclonal antibody Alz-50 and an anti-C terminal repeated region of Tau. In control brains, these antibodies strongly detected normal Tau proteins in the gray matter while Tau immunodetection was weak in the white matter. In Alzheimer brain cortices, each antibody detected Tau 64 and 69 in gray matter extracts but not at all in white matter extracts. The second category of anti-Tau consisted of the anti-PHF saturated with normal brain protein extracts. This antiserum only probed the abnormally phosphorylated Tau proteins. It detected Tau 64 and 69 exclusively in the cortical gray matter of Alzheimer brains. Moreover, a 55-kDa Tau protein was also immunolabelled, which might be an intermediary form between normal Tau and Tau 64 and 69. Our results demonstrate that Tau proteins are normal and major components of the somatodendritic domain and that Tau pathology, reflected by the presence of Tau 64 and 69, affects preferentially this domain during Alzheimer's disease.

Phosphorylation of Tau proteins: a major event during the process of neurofibrillary degeneration. A comparative study between Alzheimer's disease and Down's syndrome

Six different brain areas from 6 patients with Down's syndrome (DS) of different ages were studied in respect of their Tau protein content using the western-blot technique. They were also studied histologically using a Palmgren (silver staining) method in order to reveal the presence of NFT and SP. The results of these studies show that Tau 64 and 69, two pathological Tau variants recently described in the brains of patients with Alzheimer's disease (AD), are also present in the brains of patients with DS. Alkaline phosphatase treatment demonstrates that their heavy molecular weight is due, as in AD, to an abnormal phosphorylation of Tau proteins. The results of this study show that the detection of Tau 64 and 69 in the brain of these patients is correlated with the presence of neurofibrillary tangles (NFT) and senile plaques (SP). These findings confirm that DS can act as a model for the study of the pathological events that occur in AD. Moreover, they suggest that the abnormal phosphorylation of Tau proteins, enhancing a shift of their electrophoretic mobility, might be an important step among the sequence of events that characterize neurofibrillary degeneration.

[Towards the development of an in vivo study model of Alzheimer-type neurofibrillary degeneration]

Progress in the search for the cause of Alzheimer's disease is considerably hampered by the lack of animal or in vitro model. We have shown that in Alzheimer's disease two pathological variants of Tau proteins, called Tau 64 and Tau 69, are regularly present in neural tissue undergoing neurofibrillary degeneration. Beside their diagnostic value, Tau 64 and Tau 69 might enable such a model to be devised at long last. It now seems possible to investigate for biochemical disorders capable of inducing the emergence of these two Tau proteins in neuron cultures or among transgenic animals. The innumerable pathogenetic tracks of Alzheimer's disease (aluminium, zinc, superoxide dismutase and free radicals, proteases and antiproteases, beta protein A4 precursor, etc.) should then be opened to exploration.

Qualitative and quantitative comparison of brain proteins in Alzheimer's disease

In human brain extracts, most proteins of pathological interest in Alzheimer's disease are insoluble and their analysis is often performed on denatured and reduced samples by immunoblotting after electrophoresis on polyacrylamide gel in presence of sodium dodecyl sulfate. Because we needed to accurately compare the concentration of several proteins in brain extracts to investigate the etiology of the disease, the quantitative aspect of immunoblotting was assessed and the results compared for a soluble component with those obtained by electroimmunoassay. Glial fibrillary acidic protein (GFAP) and Tau proteins were analysed by immunoblotting in brain homogenates treated with the Laemmli sample buffer from 10 control and 25 Alzheimer's disease brains. The linearity of densitometric measures of dilutions for one given sample was demonstrated. A 8 to 16-fold GFAP increase in Alzheimer brain was established. With regard to Tau proteins it was possible to show the presence of two pathological Tau variants (Tau 64 and 69) in all the Alzheimer brain homogenates, furthermore, the amount of Tau 64 and 69 was proportional to the presence of neurofibrillary degeneration. As far as alpha 1-antichymotrypsin is concerned, we showed, in a second set of brain samples (14 control and 12 Alzheimer brains), discrepancies between the results obtained by immunoblotting and by electroimmunoassay while for a given sample linearity of immunoblotting measures of dilutions of this sample was demonstrated. Quantitation by immunoblotting of such components which can be quantified using other procedures is uncertain whereas the interest of immunoblotting is undoubted for the insoluble proteins in the brain extracts.

Characterization of two pathological tau protein, variants in Alzheimer brain cortices

Tau proteins were detected in brain tissue homogenates from 10 patients with Alzheimer's disease versus 10 age-matched controls using the immunoblot technique and 2 polyclonal antibodies: anti-paired helical filaments (PHF) and anti-human native Tau proteins. In control brains, both antisera detected identically the normal set of Tau proteins, with molecular weight (MW) ranging from 45 to 62 kDa. Moreover, in association areas of neocortex from Alzheimer brains, the antisera detected 2 additional Tau variants of 64 and 69 kDa. Tau 64 and 69 were not found in regions of Alzheimer brains where the Alzheimer pathology was absent (caudate nucleus or cerebellum for example). The heavy MW of Tau 64 and 69 is due to their phosphorylation state as shown by the decrease of their MW after alkaline phosphatase treatment. Therefore, Tau 64 and Tau 69 are specific markers of the Alzheimer's disease neuronal degenerating process and their characterization demonstrates that an abnormal phosphorylation of Tau really occurs during the disease. Tau 64 and 69 were isolated with normal Tau proteins while the PHF were insoluble. Therefore, Tau proteins are likely to be abnormally phosphorylated prior to their incorporation in the PHF structure. Consequently, they might appear before the lesions and might be instrumental for the search of biochemical deregulations that precede the neurofibrillary degeneration.

Abnormal tau species are produced during Alzheimer's disease neurodegenerating process

Tau proteins were detected in human brain using two polyclonal antibodies: anti-paired helical filaments and anti-human native tau proteins. Both antisera detected identically the normal set of tau proteins in control brains. Moreover they detected two abnormal tau variants of 64 and 69 kDa exclusively in brain areas showing neurofibrillary tangles and senile plaques. Tau 64 and 69 were abnormally phosphorylated as revealed by the decrease in their molecular mass observed after alkaline phosphatase treatment. Therefore, tau 64 and 69 are specific markers of the neurofibrillary degeneration of the Alzheimer type and might be useful tools for studying the first pathological events that lead to neuronal death.