Dephosphorylation of tau protein by calcineurin triturated into neural living cells

TauP301L disengages from the proteosome core complex and neurogranin coincident with enhanced neuronal network excitability

Tauopathies are characterised by the pathological accumulation of misfolded tau. The emerging view is that toxic tau species drive synaptic dysfunction and potentially tau propagation before measurable neurodegeneration is evident, but the underlying molecular events are not well defined. Human non-mutated 0N4R tau (tauWT) and P301L mutant 0N4R tau (tauP301L) were expressed in mouse primary cortical neurons using adeno-associated viruses to monitor early molecular changes and synaptic function before the onset of neuronal loss. In this model tauP301L was differentially phosphorylated relative to tauwt with a notable increase in phosphorylation at ser262. Affinity purification - mass spectrometry combined with tandem mass tagging was used to quantitatively compare the tauWT and tauP301L interactomes. This revealed an enrichment of tauP301L with ribosomal proteins but a decreased interaction with the proteasome core complex and reduced tauP301L degradation. Differences in the interaction of tauP301L with members of a key synaptic calcium-calmodulin signalling pathway were also identified, most notably, increased association with CaMKII but reduced association with calcineurin and the candidate AD biomarker neurogranin. Decreased association of neurogranin to tauP301L corresponded with the appearance of enhanced levels of extracellular neurogranin suggestive of potential release or leakage from synapses. Finally, analysis of neuronal network activity using micro-electrode arrays showed that overexpression of tauP301L promoted basal hyperexcitability coincident with these changes in the tau interactome and implicating tau in specific early alterations in synaptic function.

Zinc in Regulating Protein Kinases and Phosphatases in Neurodegenerative Diseases

Zinc is essential for human growth and development. As a trace nutrient, zinc plays important roles in numerous signal transduction pathways involved in distinct physiologic or pathologic processes. Protein phosphorylation is a posttranslational modification which regulates protein activity, degradation, and interaction with other molecules. Protein kinases (PKs) and phosphatases (PPs), with their effects of adding phosphate to or removing phosphate from certain substrates, are master regulators in controlling the phosphorylation of proteins. In this review, we summarize the disturbance of zinc homeostasis and role of zinc disturbance in regulating protein kinases and protein phosphatases in neurodegenerative diseases, with the focus of that in Alzheimer’s disease, providing a new perspective for understanding the mechanisms of these neurologic diseases.

Decoding the Phosphatase Code: Regulation of Cell Proliferation by Calcineurin

Calcineurin, a calcium-dependent serine/threonine phosphatase, integrates the alterations in intracellular calcium levels into downstream signaling pathways by regulating the phosphorylation states of several targets. Intracellular Ca²⁺ is essential for normal cellular physiology and cell cycle progression at certain critical stages of the cell cycle. Recently, it was reported that calcineurin is activated in a variety of cancers. Given that abnormalities in calcineurin signaling can lead to malignant growth and cancer, the calcineurin signaling pathway could be a potential target for cancer treatment. For example, NFAT, a typical substrate of calcineurin, activates the genes that promote cell proliferation. Furthermore, cyclin D1 and estrogen receptors are dephosphorylated and stabilized by calcineurin, leading to cell proliferation. In this review, we focus on the cell proliferative functions and regulatory mechanisms of calcineurin and summarize the various substrates of calcineurin. We also describe recent advances regarding dysregulation of the calcineurin activity in cancer cells. We hope that this review will provide new insights into the potential role of calcineurin in cancer development.

Gene therapy-mediated enhancement of protective protein expression for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is the leading form of dementia but lacks curative treatments. Current understanding of AD aetiology attributes the development of the disease to the misfolding of two proteins; amyloid-β (Aβ) and hyperphosphorylated tau, with their pathological accumulation leading to concomitant oxidative stress, neuroinflammation, and neuronal death. These processes are regulated at multiple levels to maintain homeostasis and avert disease. However, many of the relevant regulatory proteins appear to be downregulated in the AD-afflicted brain. Enhancement/restoration of these 'protective' proteins, therefore, represents an attractive therapeutic avenue. Gene therapy is a desirable means of achieving this because it is not associated with the side-effects linked to systemic protein administration, and sustained protein expression virtually eliminates compliance issues. The current article represents a focused and succinct review of the better established 'protective' protein targets for gene therapy enhancement/restoration rather than being designed as an exhaustive review incorporating less validated protein subjects. In addition, we will discuss how the risks associated with uncontrolled or irreversible gene expression might be mitigated through combining neuronal-specific promoters, inducible expression systems and localised injections. Whilst many of the gene therapy targets reviewed herein are yet to enter clinical trials, preclinical testing has thus far demonstrated encouraging potential for the gene therapy-based treatment of AD.

Chronic Presence of Oligomeric Aβ Differentially Modulates Spine Parameters in the Hippocampus and Cortex of Mice With Low APP Transgene Expression

Alzheimer’s disease is regarded as a synaptopathy with a long presymptomatic phase. Soluble, oligomeric amyloid-β (Aβ) is thought to play a causative role in this disease, which eventually leads to cognitive decline. However, most animal studies have employed mice expressing high levels of the Aβ precursor protein (APP) transgene to drive pathology. Here, to understand how the principal neurons in different brain regions cope with moderate, chronically present levels of Aβ, we employed transgenic mice expressing equal levels of mouse and human APP carrying a combination of three familial AD (FAD)-linked mutations (Swedish, Dutch, and London), that develop plaques only in old age. We analyzed dendritic spine parameters in hippocampal and cortical brain regions after targeted expression of EGFP to allow high-resolution imaging, followed by algorithm-based evaluation of mice of both sexes from adolescence to old age. We report that Aβ species gradually accumulated throughout the life of APP_SDL mice, but not the oligomeric forms, and that the amount of membrane-associated oligomers decreased at the onset of plaque formation. We observed an age-dependent loss of thin spines under most conditions as an indicator of a loss of synaptic plasticity in older mice. We further found that hippocampal pyramidal neurons respond to increased Aβ levels by lowering spine density and shifting spine morphology, which reached significance in the CA1 subfield. In contrast, the spine density in cortical pyramidal neurons of APP_SDL mice was unchanged. We also observed an increase in the protein levels of PSD-95 and Arc in the hippocampus and cortex, respectively. Our data demonstrated that increased concentrations of Aβ have diverse effects on dendritic spines in the brain and suggest that hippocampal and cortical neurons have different adaptive and compensatory capacity during their lifetime. Our data also indicated that spine morphology differs between sexes in a region-specific manner.

Inhibition of Calcineurin A by FK506 Suppresses Seizures and Reduces the Expression of GluN2B in Membrane Fraction

FK506, a calcineurin inhibitor, shows neuroprotective effects and has been associated with neurodegenerative diseases. Calcineurin A (CaNA), a catalytic subunit of calcineurin, mediates the dephosphorylation of various proteins. N-methyl-D-aspartate receptor (GluN) is closely related to epileptogenesis, and various phosphorylation sites of GluN2B, a regulatory subunit of the GluN complex, have different functions. Thus, we hypothesized that one of the potential anti-epileptic mechanisms of FK506 is mediated by its ability to promote the phosphorylation of GluN2B and reduce the expression of GluN2B in membrane fraction by down-regulating CaNA. CaNA expression was increased in the cortex of patients with temporal lobe epilepsy and pentylenetetrazol (PTZ)-induced epileptic models. CaNA was shown to be expressed in neurons using immunofluorescence staining. According to our behavioral observations, epileptic rats exhibited less severe seizures and were less sensitive to PTZ after a systemic injection of FK506. The levels of phosphorylated GluN2B were decreased in epileptic rats but increased after the FK506 treatment. Moreover, there was no difference in the total GluN2B levels before and after FK506 treatment. However, the expression of GluN2B in membrane fraction was suppressed after FK506 treatment. Based on these results, FK506 may reduce the severity and frequency of seizures by reducing the expression of GluN2B in membrane fraction.

Perturbed Calcineurin-NFAT Signaling Is Associated with the Development of Alzheimer's Disease

Down syndrome (DS), the most common genetic disorder, is caused by trisomy 21. DS is accompanied by heart defects, hearing and vision problems, obesity, leukemia, and other conditions, including Alzheimer's disease (AD). In comparison, most cancers are rare in people with DS. Overexpression of dual specificity tyrosine-phosphorylation-regulated kinase 1A and a regulator of calcineurin 1 located on chromosome 21 leads to excessive suppression of the calcineurin-nuclear factor of activated T cells (NFAT) signaling pathway, resulting in reduced expression of a critical angiogenic factor. However, it is unclear whether the calcineurin-NFAT signaling pathway is involved in AD pathology in DS patients. Here, we investigated the association between the calcineurin-NFAT signaling pathway and AD using neuronal cells. Short-term pharmacological stimulation decreased gene expression of tau and neprilysin, and long-term inhibition of the signaling pathway decreased that of amyloid precursor protein. Moreover, a calcineurin inhibitor, cyclosporine A, also decreased neprilysin activity, leading to increases in amyloid-β peptide levels. Taken together, our results suggest that a dysregulation in calcineurin-NFAT signaling may contribute to the early onset of AD in people with DS.

The protein serine/threonine phosphatases PP2A, PP1 and calcineurin: A triple threat in the regulation of the neuronal cytoskeleton

The microtubule, F-actin and neurofilament networks play a critical role in neuronal cell morphogenesis, polarity and synaptic plasticity. Significantly, the assembly/disassembly and stability of these cytoskeletal networks is crucially modulated by protein phosphorylation and dephosphorylation events. Herein, we aim to more closely examine the role played by three major neuronal Ser/Thr protein phosphatases, PP2A, PP1 and calcineurin, in the homeostasis of the neuronal cytoskeleton. There is strong evidence that these enzymes interact with and dephosphorylate a variety of cytoskeletal proteins, resulting in major regulation of neuronal cytoskeletal dynamics. Conversely, we also discuss how multi-protein cytoskeletal scaffolds can also influence the regulation of these phosphatases, with important implications for neuronal signalling and homeostasis. Not surprisingly, deregulation of these cytoskeletal scaffolds and phosphatase dysfunction are associated with many neurological diseases.

Region-specific dendritic simplification induced by Aβ, mediated by tau via dysregulation of microtubule dynamics: a mechanistic distinct event from other neurodegenerative processes

Background

Dendritic simplification, a key feature of the neurodegenerative triad of Alzheimer’s disease (AD) in addition to spine changes and neuron loss, occurs in a region-specific manner. However, it is unknown how changes in dendritic complexity are mediated and how they relate to spine changes and neuron loss.

Results

To investigate the mechanisms of dendritic simplification in an authentic CNS environment we employed an ex vivo model, based on targeted expression of enhanced green fluorescent protein (EGFP)-tagged constructs in organotypic hippocampal slices of mice. Algorithm-based 3D reconstruction of whole neuron morphology in different hippocampal regions was performed on slices from APP_SDL-transgenic and control animals. We demonstrate that induction of dendritic simplification requires the combined action of amyloid beta (Aβ) and human tau. Simplification is restricted to principal neurons of the CA1 region, recapitulating the region specificity in AD patients, and occurs at sites of Schaffer collateral input. We report that γ-secretase inhibition and treatment with the NMDA-receptor antagonist, CPP, counteract dendritic simplification. The microtubule-stabilizing drug epothilone D (EpoD) induces simplification in control cultures per se. Similar morphological changes were induced by a phosphoblocking tau construct, which also increases microtubule stability. In fact, low nanomolar concentrations of naturally secreted Aβ decreased phosphorylation at S262 in a cellular model, a site which is known to directly modulate tau-microtubule interactions.

Conclusions

The data provide evidence that dendritic simplification is mechanistically distinct from other neurodegenerative events and involves microtubule stabilization by dendritic tau, which becomes dephosphorylated at certain sites. They imply that treatments leading to an overall decrease of tau phosphorylation might have a negative impact on neuronal connectivity.

Enzymatic and thermodynamic analysis of calcineurin inhibition by RCAN1

Calcineurin (CN) is the target of the immunophilin-immunosuppressant complex, cyclophilin/cyclosporin A (CyP/CsA). RCAN1 has recently been shown to be an endogenous regulator of CN activity. We determined the enzymatic and thermodynamic aspects of CN inhibition by RCAN1. The IC50 values of isoforms RCAN1-1L and RCAN1-4 for CN were 2.7 μM and 2.6 μM, respectively. Two deletions in the CN catalytic subunit, one a deletion of Val314 in the Loop7 domain (ΔV314) and the other in the autoinhibitory domain (CNAabc), increased the sensitivity of CN to inhibition by RCAN1-1L. The IC50s of RCAN1-1L and RCAN1-4 for CN in homogenates of mouse brain were 141 nM and 100 nM, respectively. Using isothermal titration calorimetry (ITC), we found that the RCAN1-1L/CN or CyP/CsA/CN interactions were exothermic with a dissociation constant of 0.46 μM or 0.17 μM, respectively. Our ITC results show that the interactions between CN and its two inhibitors were both characterized by a favorable binding enthalpy change. We also confirmed that overexpression of RCAN1-1L could inhibit the transcriptional activation of an NFAT-dependent promoter in response to PMA and ionomycin by inhibiting CN activity in HEK293T cells. Our data should contribute to our understanding of the regulation of CN activity by endogenous inhibitors.

Aberrant behavioral sensitization by methamphetamine in junctophilin-deficient mice

Junctophilins (JPs) expressed in the endoplasmic/sarcoplasmic reticulum (ER/SR) interact with the plasma membrane, thereby constructing junctional membrane complexes (JMC). We here reported that double-knockout mice lacking both JP3 and JP4 (JP-DKO mice) exhibit aberrant synaptic plasticity in the corticostriatal circuits and irregular methamphetamine (METH)-induced behavioral sensitization when METH (1.0 mg/kg) was administrated six consecutive days and assessed the striatal glutamatergic population spike (PS) by stimulation of cortical white matter. When we assessed the striatal PS by stimulation of cortical white matter, the long-term depression (LTD) was observed in JP-DKO mouse striatum similar to that in control (JP-double hetero mice (JP-DHE mice)). Importantly, LTD converted to long-term potentiation (LTP) following chronic METH treatment concomitant with behavioral sensitization in JP-DHE mice. LTD in JP-DKO mice, however failed to convert to LTP with lacks of behavioral sensitization. LTP impairment in JP-DKO mice was restored by pretreatment with FK506, calcineurin (CaN) inhibitor, but not with apamin, SK channel inhibitor. In immunoblotting analyses, calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation was significantly increased following METH treatment in the striatum of JP-DHE mice. However, CaMKII autophosphorylation did not changed by METH treatment in the striatum of JP-DKO mouse. The increased CaMKII autophosphorylation was closely associated with elevated CaN activity in JP-DKO mice. The lack of increased CaMKII activity in JP-DKO mice was correlated with the impaired METH-induced behavioral sensitization. Thus, elevated CaN and aberrant CaMKII activities in the striatum of JP-DKO mice likely accounts for lack of METH-induced behavioral sensitization.

Effects of arsenite and UVA-1 radiation on calcineurin signaling

Calcineurin is a Ca(2+)-dependent serine/threonine phosphatase and the target of the immunosuppressive drugs cyclosporin and tacrolimus, which are used in transplant recipients to prevent rejection. Unfortunately, the therapeutic use of this drugs is complicated by a high incidence of skin malignancy, which has set off a number of studies into the role of calcineurin signaling in skin, particularly with respect to cell cycle control and DNA repair. Both UVA1 radiation and arsenic species are known to promote skin cancer development via production of reactive oxygen species. In light of the well-documented sensitivity of calcineurin to oxidative stress, we examined and compared the effects of UVA1 and arsenite on calcineurin signaling. In this paper, we show that physiologically relevant doses of UVA1 radiation and low micromolar concentrations of arsenite strongly inhibit calcineurin phosphatase activity in Jurkat and skin cells and decrease NFAT nuclear translocation in Jurkat cells. The effects on calcineurin signaling could be partly prevented by inhibition of NADPH oxidase in Jurkat cells or increased dismutation of superoxide in Jurkat and skin cells. In addition, both UVA1 and arsenite decreased NF-κB activity, although at lower concentrations, arsenite enhanced NF-κB activity. These data indicate that UVA1 and arsenite affect a signal transduction route of growingly acknowledged importance in skin and that calcineurin may serve as a potential link between ROS exposure and impaired tumor suppression.

Role of calcineurin in the VTA in rats behaviorally sensitized to methamphetamine

RATIONALE

Chronic psychostimulant administration increases locomotor activity, which is referred to as locomotor sensitization. Calcineurin has been suggested to participate in psychostimulant-induced sensitization, but the underlying neurobiological mechanism is poorly understood.

OBJECTIVES

This study was designed to examine whether calcineurin activity and its substrates participate in methamphetamine (METH)-induced locomotor sensitization in rats.

MATERIALS AND METHODS

Two weeks daily METH (1 mg/kg, i.p.) was administrated to rats to induce locomotor sensitization, activity of calcineurin and its substrates Synapsin and glycogen synthase kinase-3β (GSK-3β) were detected. The initiation and expression of locomotor sensitization were tested by inhibition of calcineurin activity systematically or locally in the ventral tegmental area (VTA).

RESULTS

Expression of the calcineurin A subunit (catalytic subunit) increased in the VTA but not prefrontal cortex, nucleus accumbens, or hippocampus in rats sensitized to METH. The calcineurin inhibitor cyclosporine A, systemically administered or microinfused into the VTA, suppressed the initiation but not expression of METH-induced locomotor sensitization. Chronic METH exposure upregulated the expression of the calcineurin A subunit in the VTA, which was negatively associated with downregulation of the phosphorylation of Synapsin and GSK-3β. Moreover, the related molecular changes were blocked by systemically administered cyclosporine A or microinjections into the VTA.

CONCLUSIONS

These data elucidate the critical role of calcineurin in the neurobiological mechanism underlying METH-induced locomotor sensitization, suggesting that calcineurin might participate in the initiation of METH-induced locomotor sensitization by negatively regulating the activity of Synapsin and GSK-3β in the VTA.

Progress in the development of new drugs in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease with a global prevalence estimated at 26.55 million in 2006. During the past decades, several agents have been approved that enhance cognition of AD patients. However, the effectiveness of these treatments are limited or controversial and they do not modify disease progression. Recent advances in understanding AD pathogenesis have led to the development of numerous compounds that might modify the disease process. AD is mainly characterized neuropathologically by the presence of two kinds of protein aggregates: extracellular plaques of Abeta-peptide and intracellular neurofibrillary tangles. Abeta and tau could interfere in an original way contributing to a cascade of events leading to neuronal death and transmitter deficits. Investigation for novel therapeutic approaches targeting the presumed underlying pathogenic mechanisms is major focus of research. Antiamyloid agents targeting production, accumulation, clearance, or toxicity associated with Abeta peptide, are some approaches under investigation to limit extracellular plaques of Abeta-peptide accumulation. We can state as an example: Abeta passive and active immunization, secretases modulation, Abeta degradation enhancement, or antiaggregation and antifibrillization agents. Tau-related therapies are also under clinical investigation but few compounds are available. Another alternative approach under development is neuroprotective agents such as antioxidants, anti-inflammatory drugs, compounds acting against glutamate mediated neurotoxicity. Neurorestorative approaches through neurotrophin or cell therapy also represent a minor avenue in AD research. Finally, statins, receptor for advanced glycation end products inhibitors, thiazolidinediones, insulin, and hormonal therapies are some other ways of research for a therapeutic approach of Alzheimer's disease. Taking into account AD complexity, it becomes clear that polypharmacology with drugs targeting different sites could be the future treatment approach and a majority of the recent drugs under evaluation seems to act on multiple targets. This article exposes general classes of disease-modifying therapies under investigation.

The polarity of the amino acid residue 118 of calcineurin B is closely linked to calcineurin enzyme activity

Calcineurin(Cn), a multifunctional regulator expressed in several tissues and organs, consists of CnA (catalytic subunit) and CnB (regulatory subunit). The crystal structure shows that the hydrophobic groove formed by 118-123 residues of CnB is necessary for its interactions with two different immunosuppressant-immunophilin complexes and with CnA. In this report, we focus on Met118 of CnB to study the association between conformational states of CnB and the phosphatase activity of Cn. We found that hydrophobicity in the region around site118 of CnB is essential for the Cn activity. Polar mutants significantly weakened the enzymatic activity compared with the nonpolar ones. The data showed that some modest alterations in the vicinity of site118 impaired the integrality and compactness of hydrophobic microenvironment, and this might explain why CnB mutants defective in hydrophobicity failed in activating Cn. This requirement of hydrophobic microenvironment around site118 in CnB suggests that, besides the mutations in the catalytic subunit CnA, which impairs Cn phosphatase activity, and had been identified to be associated with diseases such as Alzheimer's disease (AD), the mutations in CnB might also affect Cn enzymatic activity in vivo, and this might be helpful for our further research on mechanisms of diseases associated with Cn.

The neuroprotective effects of ginsenosides on calcineurin activity and tau phosphorylation in SY5Y cells

Calcineurin (CN) is a Ca(2+)/calmodulin-dependent protein phosphatase expressed at high levels in brain. Many findings have shown that calcineurin plays an important role in tau hyperphosphorylation, which is one of the neuropathologic features in the brains of Alzheimer's disease (AD). Based on the molecular screening model using p-nitrophenyl phosphate (p-NPP) as a substrate for preliminary screening and (32)P-labeled 19-residue phosphopeptide as a specific substrate for final determination, we found that the total ginsenoside extracts from stems and leaves of Panax ginseng (GSL) could enhance the phosphatase activity of purified CN. In the human neuroblastoma cells SY5Y, inhibition of CN by cyclosporine A (CsA) could induce hyperphosphorylation of tau at multiple sites, accompanied with oxidative stress. Pretreatment of the cells with GSL prior to CsA exposure could alleviate CsA-induced CN inhibition and tau hyperphosphorylation to some degree. Further oxidative parameters demonstrated that GSL caused increased SOD activity and content of SH significantly. It is speculated that GSL weakens CsA-induced CN inhibition through the antioxidant mechanisms. Although our results indicate that GSL may have neuroprotective effects on some characteristic features of AD, the chemical compositions of GSL and their potential for affecting the disease mechanism need to be further studied.

Infusion of FK506, a specific inhibitor of calcineurin, induces potent tau hyperphosphorylation in mouse brain

Calcineurin is a Ca2+/calmodulin-dependent protein phosphatase expressed at high levels in brain. Many electrophysiological and pharmacological findings have shown that calcineurin plays an important role in brain function. FK506 is always used as a specific calcineurin inhibitor in these researches. But these reports did not quantify the calcineurin activity in FK506-treated brain. Here we first investigated the inhibitory effect of FK506 injected into the mouse brain ventricle on CN activity. FK506 reduced calcineurin activity in a dose-dependent manner, without affecting its amount. Injection of 12.5 nmol FK506 also significantly enhanced the phosphorylation of tau at Ser-262 (12E8 site), Ser-198, Ser-199, and/or Ser-202 (Tau-1 site) and Ser-396 and/or Ser-404 (PHF-1 site), without affecting total tau. It is suggested that calcineurin plays an important role in tau phosphorylation, dependently of its activity. Compared with the effects of cyclosporin A, another specific inhibitor of CN in our previous study, we first evaluate that such infusion of FK506 is more effective than that of cyclosporin A on calcineurin inhibition and tau phosphorylation.

Tau binds both subunits of calcineurin, and binding is impaired by calmodulin

Calcineurin, an important protein Ser/Thr phosphatase which acts on tau in vivo, is a heterodimer of a catalytic subunit, calcineurin A, and a regulatory subunit, calcineurin B, and is unique in being regulated by calmodulin. Here, we find that both subunits of calcineurin bind tau, and calmodulin interferes with the association between calcineurin and tau. The domains of both subunits of calcineurin and tau involved in binding are mapped. We also investigate the functional consequences of the interactions between both subunits of calcineurin, tau and calmodulin, and reveal the interactions affect dephosphorylation of tau by calcineurin and contribute to the balance of phosphorylation and dephosphorylation of tau in vivo. Our findings may be of potential significance in neuronal physiology and also in neurodegenerative disorders. They shed some light on how the interactions might control the phosphorylation state of tau under physiological conditions, and provide new insights into the treatment of tauopathies such as Alzheimer's disease.

Inhibition of calcineurin by infusion of CsA causes hyperphosphorylation of tau and is accompanied by abnormal behavior in mice

Calcineurin is a Ca2+/calmodulin-dependent phosphatase that dephosphorylates numerous substrates in different neuronal compartments. Genetic and pharmacological studies have provided insight into its involvement in the brain. Cyclosporin A (CsA) is used as a specific calcineurin inhibitor in many pharmacological experiments. However, the calcineurin activity of CsA-treated brain has not been reported. To examine the relationship between calcineurin activity and brain function, we injected CsA into the left lateral ventricle of the mouse brain and assayed calcineurin activity. CsA reduced calcineurin activity in a dose-dependent manner, without affecting the amount of calcineurin protein. Assays of the effect of protein phosphatase inhibitors on CsA-injected mouse brain extracts and kinetic analysis revealed that CsA inhibited calcineurin activity in a non-competitive manner in vivo, in agreement with in vitro results. Injection of CsA led to enhanced phosphorylation of tau at Ser-262 (12E8 site), Ser-198, Ser-199, and/or Ser-202 (Tau-1 site) and Ser-396 and/or Ser-404 (PHF-1 site), as well as to impaired spatial memory, which are two characteristic features of Alzheimer's disease. We propose that inhibition of calcineurin may play an important role in Alzheimer's disease.

Pathological effects of glyoxalase I inhibition in SH-SY5Y neuroblastoma cells

In Alzheimer's disease (AD), in aging, and under conditions of oxidative stress, the levels of reactive carbonyl compounds continuously increase. Accumulating carbonyl levels might be caused by an impaired enzymatic detoxification system. The major dicarbonyl detoxifying system is the glyoxalase system, which removes methylglyoxal in order to minimize cellular impairment. Although a reduced activity of glyoxalase I was evident in aging brains, it is not known how raising the intracellular methylglyoxal level influences neuronal function and the phosphorylation pattern of tau protein, which is known to be abnormally hyperphosphorylated in AD. To simulate a reduced glyoxalase I activity, we applied an inhibitor of glyoxalase I, p-bromobenzylglutathione cyclopentyl diester (pBrBzGSCp(2)), to SH-SY5Y neuroblastoma cells to induce chronically elevated methylglyoxal concentrations. We have shown that 10 microM pBrBzGSCp(2) leads to a fourfold elevation of the methylglyoxal level after 24 hr. In addition, glyoxalase I inhibition leads to reduced cell viability, strongly retracted neuritis, increase in [Ca(2+)](i), and activation of caspase-3. However, pBrBzGSCp(2) did not lead to tau "hyper"-phosphorylation despite activation of p38 mitogen-activated protein kinase and c-Jun NH(2)-terminal kinase but rather activated protein phosphatases 2 and induced tau dephosphorylation at the Ser(202)/Thr(205) and Ser(396)/Ser(404) epitopes. Preincubation with the carbonyl scavenger aminoguanidine prevented tau dephosphorylation, indicating the specific effect of methylglyoxal. Also, pretreatment with the inhibitor okadaic acid prevented tau dephosphorylation, indicating that methylglyoxal activates PP-2A. In summary, our data suggest that a reduced glyoxalase I activity mimics some changes associated with neurodegeneration, such as neurite retraction and apoptotic cell death.

Down-regulation of muscarinic acetylcholine receptor M2 adversely affects the expression of Alzheimer's disease-relevant genes and proteins

Beta-amyloid peptides play a major role in the pathogenesis of Alzheimer's disease (AD). Therefore, preventing beta-amyloid formation by inhibition of the beta site amyloid precursor protein-cleaving enzyme (BACE) 1 is considered as a potential strategy to treat AD. Cholinergic mechanisms have been shown to control amyloid precursor protein processing and the number of muscarinic M2-acetylcholine receptors is decreased in brain regions of patients with AD enriched with senile plaques. Therefore, the present study investigates the effect of this M2 muscarinic receptor down-regulation by siRNA on total gene expression and on regulation of BACE1 in particular in SK-SH-SY5Y cells. This model system was used for microarray analysis after carbachol stimulation of siRNA-treated cells compared with carbachol stimulated, non-siRNA-treated cells. The same model system was used to elucidate changes at the protein level by using two-dimensional gels followed by Matrix Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF) analysis. Taken together, the results indicate that the M2 acetylcholine receptor down-regulation in brains of patients with AD has important effects on the expression of several genes and proteins with major functions in the pathology of AD. This includes beta-secretase BACE1 as well as several modulators of the tau protein and other AD-relevant genes and proteins. Moreover, most of these genes and proteins are adversely affected against the background of AD.

The effect of calcineurin activator, extracted from Chinese herbal medicine, on memory and immunity in mice

Calcineurin (CN) is a highly abundant phosphatase in the brain and it is the only Ca(2+)- and calmodulin-dependent protein serine/threonine phosphatase. There is considerable evidence to suggest that CN plays an essential role in activity-dependent modulation of synaptic efficacy. It has been shown recently that inhibitors of CN, such as CsA or FK506, impair memory formation in day-old chicks. In our present study, extract of Fructus cannabis (EFC) with activation of CN, extracted from Chinese traditional medicine, was used to determine the effects on memory and immunity. In the step-down-type passive avoidance test, the plant extract (0.2 g/kg) significantly improved amnesia induced by chemical drugs in mice, and greatly enhanced the ability of cell-mediated type hypersensitivity and nonspecific immune responses in normal mice. The present study provided pharmacological evidence for Chinese herbal medicine screening from molecular model.