N-terminal tau truncation in the pathogenesis of Alzheimer's disease (AD): Developing a novel diagnostic and therapeutic approach.

Tau truncation occurs at early stages during the development of human Alzheimer's disease (AD) and other tauopathy dementias. Tau cleavage, particularly in its N-terminal projection domain, is able to drive per se neurodegeneration, regardless of its pro-aggregative pathway(s) and in fragment(s)-dependent way. In this short review, we highlight the pathological relevance of the 20-22 kDa NH2-truncated tau fragment which is endowed with potent neurotoxic "gain-of-function" action(s), both in vitro and in vivo. An extensive comment on its clinical value as novel progression/diagnostic biomarker and potential therapeutic target in the context of tau-mediated neurodegeneration is also provided.

AD-Related N-Terminal Truncated Tau Is Sufficient to Recapitulate In Vivo the Early Perturbations of Human Neuropathology: Implications for Immunotherapy.

The NH2tau 26-44 aa (i.e., NH2htau) is the minimal biologically active moiety of longer 20-22-kDa NH2-truncated form of human tau-a neurotoxic fragment mapping between 26 and 230 amino acids of full-length protein (htau40)-which is detectable in presynaptic terminals and peripheral CSF from patients suffering from AD and other non-AD neurodegenerative diseases. Nevertheless, whether its exogenous administration in healthy nontransgenic mice is able to elicit a neuropathological phenotype resembling human tauopathies has not been yet investigated. We explored the in vivo effects evoked by subchronic intracerebroventricular (i.c.v.) infusion of NH2htau or its reverse counterpart into two lines of young (2-month-old) wild-type mice (C57BL/6 and B6SJL). Six days after its accumulation into hippocampal parenchyma, significant impairment in memory/learning performance was detected in NH2htau-treated group in association with reduced synaptic connectivity and neuroinflammatory response. Compromised short-term plasticity in paired-pulse facilitation paradigm (PPF) was detected in the CA3/CA1 synapses from NH2htau-impaired animals along with downregulation in calcineurin (CaN)-stimulated pCREB/c-Fos pathway(s). Importantly, these behavioral, synaptotoxic, and neuropathological effects were independent from the genetic background, occurred prior to frank neuronal loss, and were specific because no alterations were detected in the control group infused with its reverse counterpart. Finally, a 2.0-kDa peptide which biochemically and immunologically resembles the injected NH2htau was endogenously detected in vivo, being present in hippocampal synaptosomal preparations from AD subjects. Given that the identification of the neurotoxic tau species is mandatory to develop a more effective tau-based immunological approach, our evidence can have important translational implications for cure of human tauopathies.

AMPK is activated early in cerebellar granule cells undergoing apoptosis and influences VADC1 phosphorylation status and activity.

The neurodegeneration of cerebellar granule cells, after low potassium induced apoptosis, is known to be temporally divided into an early and a late phase. Voltage-dependent anion channel-1 (VDAC1) protein, changing from the closed inactive state to the active open state, is central to the switch between the early and late phase. It is also known that: (i) VDAC1 can undergo phosphorylation events and (ii) AMP-activated protein kinase (AMPK), the sensor of cellular stress, may have a role in neuronal homeostasis. In the view of this, the involvement of AMPK activation and its correlation with VDAC1 status and activity has been investigated in the course of cerebellar granule cells apoptosis. The results reported in this study show that an increased level of the phosphorylated, active, isoform of AMPK occurs in the early phase, peaks at 3 h and guarantees an increase in the phosphorylation status of VDCA1, resulting in a reduced activity of this latter. However this situation is transient in nature, since, in the late phase, AMPK activation decreases as well as the level of phosphorylated VDAC1. In a less phosphorylated status, VDAC1 fully recovers its gating activity and drives cells along the death route.

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.

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.

Glycolytic enzyme upregulation and numbness of mitochondrial activity characterize the early phase of apoptosis in cerebellar granule cells.

Alzheimer's disease (AD) and cancer proceed via one or more common molecular mechanisms: a metabolic shift from oxidative phosphorylation to glycolysis-corresponding to the activation of the Warburg effect-occurs in both diseases. The findings reported in this paper demonstrate that, in the early phase of apoptosis, glucose metabolism is enhanced, i.e. key proteins which internalize and metabolize glucose-glucose transporter, hexokinase and phosphofructokinase-are up-regulated, in concomitance with a parallel decrease in oxygen consumption by mitochondria and increase of L-lactate accumulation. Reversal of the glycolytic phenotype occurs in the presence of dichloroacetate, inhibitor of the pyruvate dehydrogenase kinase enzyme, which speeds up apoptosis of cerebellar granule cells, reawakening mitochondria and then modulating glycolytic enzymes. Loss of the adaptive advantage afforded by aerobic glycolysis, which occurs in the late phase of apoptosis, exacerbates the pathological processes underlying neurodegeneration, leading inevitably the cell to death. In conclusion, the data propose that both aerobic, i.e. Warburg effect, essentially due to the protective numbness of mitochondria, and anaerobic glycolysis, rather due to the mitochondrial impairment, characterize the entire time frame of apoptosis, from the early to the late phase, which mimics the development of AD.

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. Aß1-42 and NH2htau, which are known to be produced in apoptotic cerebellar neurons, further corroborate the molecular mechanism of neuroprotection by ADP, herein proposed.

AD-linked, toxic NH2 human tau affects the quality control of mitochondria in neurons.

Functional as well as structural alterations in mitochondria size, shape and distribution are precipitating, early events in progression of Alzheimer's Disease (AD). We reported that a 20-22kDa NH2-tau fragment (aka NH2htau), mapping between 26 and 230 amino acids of the longest human tau isoform, is detected in cellular and animal AD models and is neurotoxic in hippocampal neurons. The NH2htau -but not the physiological full-length protein- interacts with Aß at human AD synapses and cooperates with it in inhibiting the mitochondrial ANT-1-dependent ADP/ATP exchange. Here we show that the NH2htau also adversely affects the interplay between the mitochondria dynamics and their selective autophagic clearance. Fragmentation and perinuclear mislocalization of mitochondria with smaller size and density are early found in dying NH2htau-expressing neurons. The specific effect of NH2htau on quality control of mitochondria is accompanied by (i) net reduction in their mass in correlation with a general Parkin-mediated remodeling of membrane proteome; (ii) their extensive association with LC3 and LAMP1 autophagic markers; (iii) bioenergetic deficits and (iv) in vitro synaptic pathology. These results suggest that NH2htau can compromise the mitochondrial biology thereby contributing to AD synaptic deficits not only by ANT-1 inactivation but also, indirectly, by impairing the quality control mechanism of these organelles.

Mitochondrial respiratory chain Complexes I and IV are impaired by ß-amyloid via direct interaction and through Complex I-dependent ROS production, respectively.

Here we investigate the effect of ß-amyloid on mitochondrial respiratory function, i.e. mitochondrial oxygen consumption and membrane potential generation as well as the individual activities of both the mitochondrial Complexes I-IV, that compose mitochondrial electron transport chain, and the ATP synthase, by using homogenate from cerebellar granule cells, treated with low concentrations of ß-amyloid, and Alzheimer synaptic-enriched brain samples. We found that ß-amyloid caused both a selective defect in Complex I activity associated with an increase (5 fold) of intracellular reactive oxygen species and an impairment of Complex IV likely due to membrane lipid peroxidation. In addition, a 130% increase of the GSSG/GSH ratio was measured in Alzheimer brains with respect to age-matched controls. Knowing the mechanisms of action of ß-amyloid could allow to mitigate or even to interrupt the toxic cascade that leads a cell to death. The results of this study represent an important innovation because they offer the possibility to act at mitochondrial level and on specific sites to protect cells, for example by preventing the interaction of ß-amyloid with the identified targets, by stabilizing or by restoring mitochondrial function or by interfering with the energy metabolism.

Dissecting the molecular mechanism by which NH2htau and Aß1-42 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 Aß1-42 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 Aß1-42 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 Aß1-42 is already present. A molecular mechanism is proposed in which the pathological Aß-NH2htau interplay on ANT-1 in Alzheimer's neurons involves the thiol redox state of ANT-1 and the Aß1-42-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.

Endogenous Aß causes cell death via early tau hyperphosphorylation.

Alzheimer's disease (AD) is characterized by Aß overproduction and tau hyperphosphorylation. We report that an early, transient and site-specific AD-like tau hyperphosphorylation at Ser262 and Thr231 epitopes is temporally and causally related with an activation of the endogenous amyloidogenic pathway that we previously reported in hippocampal neurons undergoing cell death upon NGF withdrawal [Matrone, C., Ciotti, M.T., Mercanti, D., Marolda, R., Calissano, P., 2008b. NGF and BDNF signaling control amyloidogenic route and Ab production in hippocampal neurons. Proc. Natl. Acad. Sci. 105, 13138-13143]. Such tau hyperphosphorylation, as well as apoptotic death, is (i) blocked by 4G8 and 6E10 Aß antibodies or by specific ß and/or γ-secretases inhibitors; (ii) temporally precedes tau cleavage mediated by a delayed (6-12h after NGF withdrawal) activation of caspase-3 and calpain-I; (iii) under control of Akt-GSK3ß-mediated signaling. Finally, we show that such site-specific tau hyperphosphorylation causes tau detachment from microtubules and an impairment of mitochondrial trafficking. These results depict, for the first time, a rapid interplay between endogenous Aß and tau post-translational modifications which act co-ordinately to compromise neuronal functions in the same neuronal system, under physiological conditions as seen in AD brain.

Does the term 'trophic' actually mean anti-amyloidogenic? The case of NGF.

The term trophic is widely used to indicate a general pro-survival action exerted on target cells by different classes of extracellular messengers, including neurotrophins (NTs), a family of low-molecular-weight proteins whose archetypal member is the nerve growth factor (NGF). The pro-survival action exerted by NTs results from a coordinated activation of multiple metabolic pathways, some of which have only recently come to light. NGF has been shown to exert a number of different, experimentally distinguishable effects on neurons, such as survival, differentiation of target neurons, growth of nerve fibers and their guidance (tropism) toward the source of its production. We have proposed a more complete definition of the NGF trophic action that should also include its newly discovered property of inhibiting the amyloidogenic processing of amyloid precursor protein (APP), which is among the first hypothesized primary trigger of Alzheimer's disease (AD) pathogenesis. This inhibitory action appears to be mediated by a complex series of molecular events and by interactions among NGF receptors (TrkA and p75), APP processing and tau metabolic fate and function.

Nerve growth factor as a paradigm of neurotrophins related to Alzheimer's disease.

Converging lines of evidence on the possible connection between NGF signaling and Alzheimer's diseases (AD) are unraveling new facets which could depict this neurotrophin (NTF) in a more central role. AD animal models have provided evidence that a shortage of NGF supply may induce an AD-like syndrome. In vitro experiments, moreover, are delineating a possible temporal and causal link between APP amiloydogenic processing and altered post-translational tau modifications. After NGF signaling interruption, the pivotal upstream players of the amyloid cascade (APP, beta-secretase, and active form of gamma-secretase) are up-regulated, leading to an increased production of amyloid beta peptide (Abeta) and to its intracellular aggregation in molecular species of different sizes. Contextually, the Abeta released pool generates an autocrine toxic loop in the same healthy neurons. At the same time tau protein undergoes anomalous, GSKbeta-mediated, phosphorylation at specific pathogenetic sites (Ser262 and Thr 231), caspase(s) and calpain- I- mediated truncation, detachment from microtubules with consequent cytoskeleton collapse and axonal transport impairment. All these events are inhibited when the amyloidogenic processing is reduced by beta and gamma secretase inhibitors or anti-Abeta antibodies and appear to be causally correlated to TrkA, p75CTF, Abeta, and PS1 molecular association in an Abeta-mediated fashion. In this scenario, the so-called trophic action exerted by NGF (and possibly also by other neurotrophins) in these targets neurons is actually the result of an anti-amyloidogenic activity.

SP protects cerebellar granule cells against beta-amyloid-induced apoptosis by down-regulation and reduced activity of Kv4 potassium channels.

The tachykinin endecapeptide substance P (SP) has been demonstrated to exert a functional role in neurodegenerative disorders, including Alzheimer's disease (AD). Aim of the present study was to evaluate the SP neuroprotective potential against apoptosis induced by the neurotoxic beta-amyloid peptide (A beta) in cultured rat cerebellar granule cells (CGCs). We found that SP protects CGCs against both A beta(25-35)- and A beta(1-42)-induced apoptotic CGCs death as revealed by live/dead cell assay, Hoechst staining and caspase(s)-induced PARP-1 cleavage, through an Akt-dependent mechanism. Since in CGCs the fast inactivating or A-type K(+) current (I(KA)) was potentiated by A beta treatment through up-regulation of Kv4 subunits, we investigated whether I(KA) and the related potassium channel subunits could be involved in the SP anti-apoptotic activity. Patch-clamp experiments showed that the A beta-induced increase of I(KA) current amplitude was reversed by SP treatment. In addition, as revealed by Western blot analysis and immunofluorescence studies, SP prevented the up-regulation of Kv4.2 and Kv4.3 channel subunits expression. These results indicate that SP plays a role in the regulation of voltage-gated potassium channels in A beta-mediated neuronal death and may represent a new approach in the understanding and treatment of AD.

Apoptosis and in vitro Alzheimer disease neuronal models.

Alzheimer disease (AD) is a human neurodegenerative disease characterized by co-existence of extracellular senile plaques (SP) and neurofibrillary tangles (NFT) associated with an extensive neuronal loss, primarily in the cerebral cortex and hippocampus. Several studies suggest that caspase(s)-mediated neuronal death occurs in cellular and animal AD models as well as in human brains of affected patients, although an etiologic role of apoptosis in such neurodegenerative disorder is still debated. This review summarizes the experimental evidences corroborating the possible involvement of apoptosis in AD pathogenesis and discusses the usefulness of ad hoc devised in vitro approaches to study how caspase(s), amyloidogenic processing and tau metabolism might reciprocally interact leading to neuronal death.

Involvement of cannabinoid CB1- and CB2-receptors in the modulation of exocrine pancreatic secretion.

The role of the cannabinoid system in the regulation of exocrine pancreatic secretion was investigated by studying the effects of the synthetic CB1- and CB2-receptors agonist, WIN55,212, on amylase secretion in isolated lobules and acini of guinea pig and rat, and the expression of CB-receptors in rat pancreatic tissue by immuno-chemistry and Western-blot analysis in both basal and cerulein (CK)-induced pancreatitis condition. In pancreatic lobules of guinea pig and rat, WIN55,212 significantly inhibited amylase release stimulated by KCl depolarization through inhibition of presynaptic acetylcholine release, but did not modify basal, carbachol- or CK-stimulated amylase secretion. The effect of WIN55,212 was significantly reduced by pre-treatment with selective CB1- and CB2-receptor antagonists. The antagonists, when given alone, did not affect the KCl-evoked response. Conversely, WIN55,212 was unable to affect basal and CK- or carbachol-stimulated amylase release from pancreatic acini of guinea pig and rat. Immunofluorescent staining of rat pancreatic tissues showed that CB1- and CB2-receptors are expressed in lobules and in acinar cells and their presence in acinar cells was also shown by Western-blot analysis. After CK-induced pancreatitis, the expression of CB1-receptors in acinar cells was not changed, whilst a down-regulation of CB2-receptors was observed. In conclusion, the present study shows that WIN55,212 inhibits amylase release from guinea pig and rat pancreatic lobules and, for the first time, that cannabinoid receptors are expressed in lobules of the rat pancreas, suggesting an inhibitory presynaptic role of this receptor system. Finally, in rat pancreatic acinar cells, CB1- and CB2-receptors, expressed both in basal conditions and after CK-induced pancreatitis but inactive on amylase secretion, have an unknown role both in physiological and pathological conditions.

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.

Identification of a caspase-derived N-terminal tau fragment in cellular and animal Alzheimer's disease models.

Biochemical modifications of tau proteins have been proposed to be among the earliest neurobiological changes in Alzheimer's disease (AD) and correlate better with cognitive symptoms than do beta-amyloid plaques. We have recently reported that adenovirus-mediated overexpression of the NH2 26-230aa tau fragment evokes a potent NMDA-mediated neurotoxic effect in primary neuronal cultures. In order to assess whether such N-terminal tau fragment(s) are indeed produced during apoptosis or neurodegeneration in vivo, we attempted to ascertain their presence in cell and animal models using an anti-tau antibody directed against the N-terminal sequence of human protein located downstream of the caspase(s)-cleavage site DRKD(25)-QGGYTMHQDQ. We provide biochemical evidence that a caspase(s)-cleaved NH2-terminal tau fragment of 20-22 kDa, consistent with the size of the NH2 26-230aa neurotoxic fragment of tau, is generated in vitro in differentiated human SH-SY5Y cells undergoing apoptosis by BDNF withdrawal or following treatment with staurosporine. In addition this NH2-terminally cleaved tau fragment, whose expression correlates with a significant up-regulation of caspase(s) activity, is also specifically detected in vivo in the hippocampus of 15 month-old AD11 transgenic mice, a model in which a progressive AD-like neurodegeneration is induced by the expression of transgenic anti-NGF antibodies. The results support the idea that aberrant activation of caspase(s), following apoptotic stimuli or neurodegeneration insults, may produce one or more toxic NH2 tau fragments, that further contribute to propagate and increase cellular dysfunctions in AD.

Substance P provides neuroprotection in cerebellar granule cells through Akt and MAPK/Erk activation: evidence for the involvement of the delayed rectifier potassium current.

In the current study, we have evaluated the ability of substance P (SP) and other neurokinin 1 receptor (NK1) agonists to protect, in a dose- and time-dependent manner, primary cultures of rat cerebellar granule cells (CGCs) from serum and potassium deprivation-induced cell death (S-K5). We also established the presence of SP high affinity NK1 transcripts and the NK1 protein localization in the membrane of a sub-population of CGCs. Moreover, SP significantly and dose-dependently reduced the Akt 1/2 and Erk1/2 dephosphorylation induced by S-K5 conditions, as demonstrated by Western blot analysis. Surprisingly, in SP-treated CGCs caspase-3 activity was not inhibited, while the calpain-1 activity was moderately reduced. Corroborating this result, SP blocked calpain-mediated cleavage of tau protein, as demonstrated by the reduced appearance of a diagnostic fragment of 17 kDa by Western blot analysis. In addition, SP induced a significant reduction of the delayed rectifier K+ currents (Ik) in about 42% of the patched neurons, when these were evoked with depolarizing potential steps. Taken together, the present results demonstrate that the activation of NK1 receptors expressed in CGCs promote the neuronal survival via pathways involving Akt and Erk activation and by inhibition of Ik which can contribute to the neuroprotective effect of the peptide.

Role of N-terminal tau domain integrity on the survival of cerebellar granule neurons.

Although the role of the microtubule-binding domain of the tau protein in the modulation of microtubule assembly is widely established, other possible functions of this protein have been poorly investigated. We have analyzed the effect of adenovirally mediated expression of two fragments of the N-terminal portion - free of microtubule-binding domain - of the tau protein in cerebellar granule neurons (CGNs). We found that while the expression of the tau (1-230) fragment, as well as of full-length tau, inhibits the onset of apoptosis, the tau (1-44) fragment exerts a powerful toxic action on the same neurons. The antiapoptotic action of tau (1-230) is exerted at the level of Akt-mediated activation of the caspase cascade. On the other hand, the toxic action of the (1-44) fragment is not prevented by inhibitors of CGN apoptosis, but is fully inhibited by NMDA receptor antagonists. These findings point to a novel, physiological role of the N-terminal domain of tau, but also underlay that its possible proteolytic truncation mediated by apoptotic proteases may generate a highly toxic fragment that could contribute to neuronal death.