NH2-truncated human tau induces deregulated mitophagy in neurons by aberrant recruitment of Parkin and UCHL-1: implications in Alzheimer's disease

Disarrangement in functions and quality control of mitochondria at synapses are early events in Alzheimer's disease (AD) pathobiology. We reported that a 20-22 kDa NH2-tau fragment mapping between 26 and 230 amino acids of the longest human tau isoform (aka NH2htau): (i) is detectable in cellular and animal AD models, as well in synaptic mitochondria and cerebrospinal fluids (CSF) from human AD subjects; (ii) is neurotoxic in primary hippocampal neurons; (iii) compromises the mitochondrial biology both directly, by inhibiting the ANT-1-dependent ADP/ATP exchange, and indirectly, by impairing their selective autophagic clearance (mitophagy). Here, we show that the extensive Parkin-dependent turnover of mitochondria occurring in NH2htau-expressing post-mitotic neurons plays a pro-death role and that UCHL-1, the cytosolic Ubiquitin-C-terminal hydrolase L1 which directs the physiological remodeling of synapses by controlling ubiquitin homeostasis, critically contributes to mitochondrial and synaptic failure in this in vitro AD model. Pharmacological or genetic suppression of improper mitophagy, either by inhibition of mitochondrial targeting to autophagosomes or by shRNA-mediated silencing of Parkin or UCHL-1 gene expression, restores synaptic and mitochondrial content providing partial but significant protection against the NH2htau-induced neuronal death. Moreover, in mitochondria from human AD synapses, the endogenous NH2htau is stably associated with Parkin and with UCHL-1. Taken together, our studies show a causative link between the excessive mitochondrial turnover and the NH2htau-induced in vitro neuronal death, suggesting that pathogenetic tau truncation may contribute to synaptic deterioration in AD by aberrant recruitment of Parkin and UCHL-1 to mitochondria making them more prone to detrimental autophagic clearance.

Glucose-6-phosphate tips the balance in modulating apoptosis in cerebellar granule cells

A metabolic shift from oxidative phosphorylation to glycolysis (i.e. the Warburg effect) occurs in Alzheimer's disease accompanied by an increase of both activity and level of HK-I. The findings reported here demonstrate that in the early phase of apoptosis VDAC1 activity, but not its protein level, progressively decreases, in concomitance with the physical interaction of HK-I with VDAC1. In the late phase of apoptosis, glucose-6-phosphate accumulation in the cell causes the dissociation of the two proteins, the re-opening of the channel and the recovery of VDAC1 function, resulting in a reawakening of the mitochondrial function, thus inevitably leading to cell death.

Extracellular ADP prevents neuronal apoptosis via activation of cell antioxidant enzymes and protection of mitochondrial ANT-1

Apoptosis in neuronal tissue is an efficient mechanism which contributes to both normal cell development and pathological cell death. The present study explores the effects of extracellular ADP on low [K(+)]-induced apoptosis in rat cerebellar granule cells. ADP, released into the extracellular space in brain by multiple mechanisms, can interact with its receptor or be converted, through the actions of ectoenzymes, to adenosine. The findings reported in this paper demonstrate that ADP inhibits the proapoptotic stimulus supposedly via: i) inhibition of ROS production during early stages of apoptosis, an effect mediated by its interaction with cell receptor/s. This conclusion is validated by the increase in SOD and catalase activities as well as by the GSSG/GSH ratio value decrease, in conjunction with the drop of ROS level and the prevention of the ADP protective effect by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a novel functionally selective antagonist of purine receptor; ii) safeguard of the functionality of the mitochondrial adenine nucleotide-1 translocator (ANT-1), which is early impaired during apoptosis. This effect is mediated by its plausible internalization into cell occurring as such or after its hydrolysis, by means of plasma membrane nucleotide metabolizing enzymes, and resynthesis into the cell. Moreover, the findings that ADP also protects ANT-1 from the toxic action of the two Alzheimer's disease peptides, i.e. Aβ1-42 and NH2htau, which are known to be produced in apoptotic cerebellar neurons, further corroborate the molecular mechanism of neuroprotection by ADP, herein proposed.

Dissecting the molecular mechanism by which NH2htau and Aβ1-42 peptides impair mitochondrial ANT-1 in Alzheimer disease

To find out whether and how the adenine nucleotide translocator-1 (ANT-1) inhibition due to NH2htau and Aβ1-42 is due to an interplay between these two Alzheimer's peptides, ROS and ANT-1 thiols, use was made of mersalyl, a reversible alkylating agent of thiol groups that are oriented toward the external hydrophilic phase, to selectively block and protect, in a reversible manner, the -SH groups of ANT-1. The rate of ATP appearance outside mitochondria was measured as the increase in NADPH absorbance which occurs, following external addition of ADP, when ATP is produced by oxidative phosphorylation and exported from mitochondria in the presence of glucose, hexokinase and glucose-6-phosphate dehydrogenase. We found that the mitochondrial superoxide anions, whose production is induced at the level of Complex I by externally added Aβ1-42 and whose release from mitochondria is significantly reduced by the addition of the VDAC inhibitor DIDS, modify the thiol group/s present at the active site of mitochondrial ANT-1, impair ANT-1 in a mersalyl-prevented manner and abrogate the toxic effect of NH2htau on ANT-1 when Aβ1-42 is already present. A molecular mechanism is proposed in which the pathological Aβ-NH2htau interplay on ANT-1 in Alzheimer's neurons involves the thiol redox state of ANT-1 and the Aβ1-42-induced ROS increase. This result represents an important innovation because it suggests the possibility of using various strategies to protect cells at the mitochondrial level, by stabilizing or restoring mitochondrial function or by interfering with the energy metabolism providing a promising tool for treating or preventing AD.

A peptide containing residues 26-44 of tau protein impairs mitochondrial oxidative phosphorylation acting at the level of the adenine nucleotide translocator

Having confirmed that adenovirus-mediated overexpression of NH(2)-tau fragment lacking the first 25 aminoacids evokes a potent neurotoxic effect, sustained by protracted stimulation of NMDA receptors, in primary neuronal cultures we investigated whether and how chemically synthesized NH(2)-derived tau peptides, i.e. NH(2)-26-44 and NH(2)-1-25 fragments, affect mitochondrial function. We tested both fragments on each step of the processes leading to ATP synthesis via oxidative phosphorylation: i) electron flow via the respiratory chain from physiological substrates to oxygen with the activity of each individual complex of the respiratory chain investigated in some detail, ii) membrane potential generation arising from externally added succinate and iii) the activity of both the adenine nucleotide translocator and iv) ATP synthase. Oxidative phosphorylation is not affected by NH(2)-1-25 tau fragment, but dramatically impaired by NH(2)-26-44 tau fragment. Both cytochrome c oxidase and the adenine nucleotide translocator are targets of NH(2)-26-44 tau fragment, but adenine nucleotide translocator is the unique mitochondrial target responsible for impairment of oxidative phosphorylation by the NH(2)-26-44 tau fragment, which then exerts deleterious effects on cellular availability of ATP synthesized into mitochondria.

Molecular basis of cystic fibrosis in Lithuania: incomplete CFTR mutation detection by PCR-based screening protocols

Mutational analysis of the cystic fibrosis transmembrane regulator (CFTR) gene was performed in 98 unrelated CF chromosomes from 49 Lithuanian CF patients through a combined approach in which the p.F508del mutation was first screened by allele-specific PCR while CFTR mutations in nonp.F508del chromosomes have been screened for by denaturing gradient gel electrophoresis analysis. A CFTR mutation was characterized in 62.2% of CF chromosomes, two of which (2.0%) have been previously shown to carry a large gene deletion CFTRdele2,3(21 kb). The most frequent Lithuanian CF mutation is p.F508del (52.0%). Seven CFTR mutations, p.N1303K (2.0%), p.R75Q (1.0%), p.G314R (1.0%), p.R553X (4.2%), p.W1282X (1.0%), and g.3944delGT (1.0%), accounted for 10.1% of Lithuanian CF chromosomes. It was not possible to characterize 35.8% of the CF Lithuanian chromosomes. Analysis of intron 8 (TG)mTn and M470V polymorphic loci did not permit the characterization of the CFTR dysfunction underlying the CF phenotype in the patients for which no CFTR mutation was identified. Thus, screening of the eight CFTR mutations identified in this study and of the large deletion CFTRdele2,3(21 kb) allows the implementation of an early molecular or confirmatory CF diagnosis for 65% of Lithuanian CF chromosomes.

Non-radioactive detection of five common microsatellite markers for ATP7B gene in Wilson disease patients

Haplotype analysis using microsatellite markers is a useful indicator of specific mutations and is often exploited as the first large-scale screening technique to carry out the molecular characterization of the disease gene in probands from a specific population. However, the methodologies available are still cumbersome and require the use of either radioactive compounds or specialized equipment suitable to follow fluorescent dyes. Both these techniques may not be available for newly developing clinical laboratories. We have set up a sensitive and easy-to-use protocol to characterize five closely spaced, highly polymorphic microsatellite polymorphisms (CA repeats) that span the Wilson disease (WD) region, i.e. D13S316, D13S133, D13S301, D13S314, D13S315. The technique described here for the analysis of the WD gene microsatellite system relies on the quick detection method of silver staining, avoiding the use of toxic or sophisticated equipment. This approach could be the method of choice to implement molecular genetic testing in clinical laboratories, even those not especially equipped for DNA analysis and in particular in newly developed molecular genetics centers in countries whose population has not yet been characterized for WD-causing ATP7B gene mutations.

Glutamate neurotoxicity, oxidative stress and mitochondria

The excitatory neurotransmitter glutamate plays a major role in determining certain neurological disorders. This situation, referred to as 'glutamate neurotoxicity' (GNT), is characterized by an increasing damage of cell components, including mitochondria, leading to cell death. In the death process, reactive oxygen species (ROS) are generated. The present study describes the state of art in the field of GNT with a special emphasis on the oxidative stress and mitochondria. In particular, we report how ROS are generated and how they affect mitochondrial function in GNT. The relationship between ROS generation and cytochrome c release is described in detail, with the released cytochrome c playing a role in the cell defense mechanism against neurotoxicity.

Cytochrome c is released from mitochondria in a reactive oxygen species (ROS)-dependent fashion and can operate as a ROS scavenger and as a respiratory substrate in cerebellar neurons undergoing excitotoxic death

In rat cerebellar granule cells both reactive oxygen species production and release of cytochrome c take place during glutamate toxicity. This investigation was aimed (i) to ascertain whether and how these two processes are related and (ii) to gain insight into the role played by the released cytochrome c in the onset of neurotoxicity. Cytochrome c release takes place owing to the generation of reactive oxygen species both in glutamate-treated cerebellar granule cells and in sister control cultures incubated in the presence of the reactive oxygen species-generating system consisting of xanthine plus xanthine oxidase. In the early phase of neurotoxicity (30-min glutamate exposure) about 40% of the maximum (as measured at 3 h of glutamate exposure) cytochrome c release was found to occur in cerebellar granule cells from mitochondria that were essentially coupled and intact and that had a negligible production of oxygen free radicals. Contrarily, mitochondria from cells treated with glutamate for 3 h were mostly uncoupled and produced reactive oxygen species at a high rate. The cytosolic fraction containing the released cytochrome c was able to transfer electrons from superoxide anion to molecular oxygen via the respiratory chain and was found to partially prevent glutamate toxicity when added externally to cerebellar neurons undergoing necrosis. In the light of these findings, we propose that in the early phase of neurotoxicity, cytochrome c release can be part of a cellular and mitochondrial defense mechanism against oxidative stress.

Characterization of the CYP21 gene 5' flanking region in patients affected by 21-OH deficiency

In order to test the hypothesis that mutations in the 5' non-coding region of CYP21 gene could contribute to the various spectrum of disease presentation due to 21-OH deficiency, the 400bp nucleotide sequence upstream of the ATG codon of CYP21 gene has been characterized in 28 CAH patients who have previously been genotyped by screening for the ten most frequent CYP21 mutations. Six specific sequence variations (-4C-->T, -73C-->T, -295T-->C, -294A-->C, -283A-->G, -281T-->G) have been identified in this region of CYP21 gene in 3 out of 28 21-OH deficient patients for whom the coding region mutations have been previously identified. Three of these mutations, -295T-->C, -294A-->C, -283A-->G, are apparently generated by a gene-conversion event, thus giving first evidence that this mechanism also applies to the 5' untranslated region of CYP21 gene in 21-OH deficiency. Four other sequence changes, identified at nucleotide position -279, -331, -350 and -353, could be referred to as normal since they are present also in healthy subjects. It may not be excluded that some of the newly-identified single nucleotide changes in the regulatory region could have a modulatory effect on the CYP21 gene transcriptional activity thus affecting the clinical outcome.

Early release and subsequent caspase-mediated degradation of cytochrome c in apoptotic cerebellar granule cells

Cytochrome c (cyt c) release was investigated in cerebellar granule cells used as an in vitro neuronal model of apoptosis. We have found that cyt c is released into the cytoplasm as an intact, functionally active protein, that this event occurs early, in the commitment phase of the apoptotic process, and that after accumulation, this protein is progressively degraded. Degradation, but not release, is fully blocked by benzyloxycarbonyl-Val-Ala-Asp-fluoromethylchetone (z-VAD-fmk). On the basis of previous findings obtained in the same neuronal population undergoing excitotoxic death, it is hypothesized that release of cyt c may be part of a cellular attempt to maintain production of ATP via cytochrome oxidase, which is reduced by cytosolic NADH in a cytochrome b5-soluble cyt c-mediated fashion.

Characterisation of CAH alleles with non-radioactive DNA single strand conformation polymorphism analysis of the CYP21 gene

The major cause of congenital adrenal hyperplasia (CAH), a common recessive genetic disease, is the deficiency of steroid 21-hydroxylase (21OH), a microsomal enzyme encoded by the CYP21 gene. Although several CAH causing mutations have been identified in the CYP21 gene of patients with 21OH deficiency, genotyping of the 21OH locus is quite complex because of the high frequency of gene conversion and the presence of multiple mutations on single CAH alleles. In order to perform the complete characterisation of the CYP21 gene coding region more simply, we developed a highly sensitive, non-radioactive method allowing DNA single strand conformation polymorphism (DNA-SSCP) analysis. This method was applied to the characterisation of all the exons and intron-exon junctions of the CYP21 gene in five patients affected by the simple virilising form and one affected by the salt wasting form. In all samples showing SSCP signals, direct sequence analysis showed the presence of more than one single sequence variant. In particular, four mutations which are already known to cause the disease, 16 polymorphisms, and one newly identified C to T transition at position 849 were detected. A random sequence analysis, performed on 31 out of 81 exons showing a normal SSCP pattern, shows the method to be highly sensitive: no sequence variant was detected, thus confirming the validity of this non-radioactive DNA-SSCP analysis in characterising the CYP21 gene in patients with steroid 21OH deficiency. Notwithstanding the complete characterisation of all exons and exon/intron junctions of the CYP21 gene, no complete genotype/phenotype correlation was found in the panel of patients analysed, thus suggesting that characterisation of CAH alleles must be extended to outside the coding region of the CYP21 gene, most probably into the promoter region.

Detection of microsatellites by ethidium bromide staining. The analysis of an STR system in the human phenylalanine hydroxylase gene

The analysis of short tandem repeat (STR) systems usually relies on polyacrylamide gel electrophoresis analysis followed by visualization with silver staining or autoradiography. Both these techniques may not be suitable for clinical laboratories. We developed a simple procedure based on the visualization of STR alleles by ethidium bromide staining. The 4-bp STR system analysed is located in the human phenylalanine hydroxylase gene. Alleles differing by 4 bp are clearly separated independently of the size of the amplified fragments and homozygous samples are easily identified by comparison of the relative intensity of the electrophoretic bands. This method could be applied to the analysis of other STR systems located in different genetic loci by carefully changing the electrophoretic conditions.

Characterization of mitochondrial DNA in primary cardiomyopathies

With the aim of studying the involvement of the mitochondrial genome in the impairment of heart function, mitochondrial DNA was analyzed by modified primer shift-polymerase chain reaction in a panel of young patients affected by primary cardiomyopathies. Mitochondrial DNA molecules harboring the 7436 bp deletion were specifically found in cardiomyopathic patients as compared with a panel of control subjects. The 4977 bp deletion was commonly detected among the subjects analyzed whereas none of the specific tRNA gene point mutations generally associated with the cardiomyopathic trait were detected. The presence of the 7436 bp deletion as a consequence of a premature aging of the heart muscle, secondary to heart dysfunction, is discussed.

Specificity of zinc binding to myelin basic protein

Zn2+ appears to stabilize the myelin sheath but the mechanism of this effect is unknown. In a previous report we have shown that zinc binds to CNS myelin basic protein (MBP) in the presence of phosphate and this results in MBP aggregation. For this paper we used a solid phase zinc blotting assay to identify which myelin proteins bind zinc. MBP and a 58 kDa band were found to be the major targets of 65Zn binding. Moreover, using fluorescence, light scattering and electron microscopy we investigated the binding of zinc and other cations to purified MBP in solution. Among the cations tested for their ability to interfere with the binding of zinc, the most effective were cadmium, mercury and copper, but only cadmium and mercury increased the scattering intensity, whereas MBP aggregation was not inhibited by copper ions. Thus, the effect of zinc on the formation of MBP clusters seems to be specific.

Myelin basic protein interaction with zinc and phosphate: fluorescence studies on the water-soluble form of the protein

The interaction of myelin basic protein (MBP) with zinc and phosphate ions has been studied by using the emission properties of the single tryptophan residue of the protein (Trp-115). The studies have been carried out by means of both static and time-resolved fluorescence techniques. The addition of either zinc to MBP in the presence of phosphate or phosphate to MBP in the presence of zinc resulted in an increase of fluorescence intensity and a blue shift of the emission maximum wavelength. Furthermore, a concomitant increase in the scattering was also detected. Anisotropy decay experiments demonstrated that these effects are due to the formation of MBP molecules into large aggregates. A possible physiological role for such interaction is discussed.

A new detergent to purify CNS myelin basic protein isoforms in lipid-bound form

We have previously shown that CNS myelin basic protein (MBP) can be purified in the lipid-bound, native-like form by using a procedure based on myelin solubilization with detergents at pH above 7, and on the filter-like use of hydroxyapatite to separate non-adsorbed MBP from other myelin proteins. Here, we report on the isolation of MBP in the zwitterionic detergent 3-((3-cholamidopropyl)dimethylammonio)-1-propane sulfonate (CHAPS), which does not interfere at 280 nm and can be removed by dialysis. This detergent appears to improve MBP purification and to be suitable for fluorescence and reconstitution studies that can be useful to understand both structure and function of MBP in its natural environment.

On the spontaneous adherence of myelin basic protein to T lymphocytes

We have applied a double tagging system in order to study whether purified myelin basic protein is able to adhere to normal human peripheral T lymphocytes without the need to purify cells. Evaluation of myelin basic protein adherence to peripheral blood mononuclear cells was determined with biotinylated myelin basic protein and fluoresceinated avidin, and lymphocyte population was identified by the corresponding phycoerythrinated monoclonal antibody. The observed adherence of myelin basic protein to T lymphocytes was found to depend on protein conformation.

Spontaneous adhesiveness of lipid-free myelin basic protein to immune cells as detected by a double labelling technique

We have investigated whether immunocompetent cells have the capacity to interact directly with the myelin basic protein (MBP) of the central nervous system. To this end we have applied a double tagging system in order to study whether purified lipid-free MBP is able to bind to normal peripheral blood mononuclear cells (PBMC) without the need to purify the cells. Evaluation of MBP binding to PBMC was determined with biotinylated MBP and fluoresceinated avidin, and lymphocytes population was identified by the corresponding phycoerythrinated monoclonal antibody (MoAb). The contemporary use of MoAbs and avidin unambiguously showed that MBP is able to bind to both B and T lymphocytes. The biological significance of MBP adherence to immune cells still needs clarification.

Interaction of cations with lipid-free myelin basic protein. A spectroscopy study

The interaction of some divalent cations with myelin basic protein (MBP) in buffer and in model membranes was studied by using the static fluorescence of the intrinsic tryptophan residue of the protein. Results were indicative of Zn++ ability to bind to MBP. The observed binding could facilitate the interaction of MBP with lipids and have a role in stabilizing the myelin sheath.

Estimation of protein secondary structure from circular dichroism spectra: a critical examination of the CONTIN program

The computer program CONTIN uses the Provencher and Glöckner procedure to calculate protein secondary structure from circular dichroism spectra. We have tested this program with peptides and proteins in which unfolding was either induced by denaturing treatment or was already present. Results indicate that the program does not clearly discriminate between the ordered and the unordered states of a protein.

[Mechanical staplers in our surgical practice]

On the basis of our experience from 1981 to 1989, advantages of staplers in digestive surgery are reported. Complications such as bleeding and stenosis are not clinically important, however, in most cases, they can be avoided if the instruments are properly used.

T lymphocytes possess receptors for brain myelin small protein

In immunomediated demyelinating diseases, T cells are found in chronic lesions. To discover whether immunocompetent cells may interact with some myelin proteins, we purified myelin proteins in the lipid-bound native state and evaluated their binding to peripheral blood mononuclear cells (PMBC) isolated from healthy donors. To this end, myelin proteins were conjugated to biotin and added to PBMCs or purified CD4+ and CD8+ cells; then binding was detected using fluoresceinated avidin. In this article, we describe experiments carried out with a myelin protein recently discovered in the central nervous system. Our results show that this small, phosphatidylserine-binding protein can bind to human T cells.

Myelin basic protein ability to organize lipid bilayers: structural transition in bilayers of lysophosphatidylcholine micelles

Myelin basic protein isolated by a single step with the cationic detergent cethyltrimethylammonium bromide in a lipid-bound form is able to induce structural transition of lysophosphatydilcholine micelles into multi-laminar vesicles. This finding, observed through electron microscopy, is discussed in the light of the assumed ability of the basic protein to organize myelin lipids.

A new protein of the brain myelin: isolation and chemical characterization

An unknown protein has been isolated from bovine brain myelin. This protein, purified in the nonionic detergent n-octylpolydisperse oligooxyethylene, reveals on SDS gel electrophoresis a large number of bands in the higher MW region. However, chemical analysis and gel chromatography indicate the presence of a single, small protein containing large amounts of bound phosphatidylserine. N-terminal and C-terminal sequences, aminoacid composition, and the anomalous electrophoretic behaviour led us to exclude the protein as a fragment of other already known myelin proteins.

On the binding of brain myelin basic protein to chromatographic resins

Myelin basic protein, only in association with certain detergents, is able to bind irreversibly to the usual gel filtration media. While this binding is greatly advantageous in purification of proteolipid (the other major myelin protein), the question arises of the uncommon, nonphysiological behaviour of the basic protein. A relationship between binding property and basic protein structure is suggested.