Chronic overexpression of the calcineurin inhibitory gene DSCR1 (Adapt78) is associated with Alzheimer's disease

Molecular and cellular mechanisms elucidating neurocognitive basis of functional impairments associated with intellectual disability in Down syndrome

Down syndrome, the most common genetic cause of intellectual disability, is associated with brain disorders due to chromosome 21 gene overdosage. Molecular and cellular mechanisms involved in the neuromorphological alterations and cognitive impairments are reported herein in a global model. Recent advances in Down syndrome research have lead to the identification of altered molecular pathways involved in intellectual disability, such as Calcineurin/NFATs pathways, that are of crucial importance in understanding the molecular basis of intellectual disability pathogenesis in this syndrome. Potential treatments in mouse models of Down syndrome, including antagonists of NMDA or GABA(A) receptors, and microRNAs provide new avenues to develop treatments of intellectual disability. Nevertheless, understanding the links between molecular pathways and treatment strategies in human beings requires further research.

Communication breaks-Down: from neurodevelopment defects to cognitive disabilities in Down syndrome

Down syndrome (DS) is the leading cause of genetically-defined intellectual disability and congenital birth defects. Despite being one of the first genetic diseases identified, only recently, thanks to the phenotypic analysis of DS mouse genetic models, we have begun to understand how trisomy may impact cognitive function. Cognitive disabilities in DS appear to result mainly from two pathological processes: neurogenesis impairment and Alzheimer-like degeneration. In DS brain, suboptimal network architecture and altered synaptic communication arising from neurodevelopmental impairment are key determinants of cognitive defects. Hypocellularity and hypoplasia start at early developmental stages and likely depend upon impaired proliferation of neuronal precursors, resulting in reduction of numbers of neurons and synaptic contacts. The impairment of neuronal precursor proliferation extends to adult neurogenesis and may affect learning and memory. Neurodegenerative mechanisms also contribute to DS cognitive impairment. Early onset Alzheimer disease occurs with extremely high incidence in DS patients and is causally-related to overexpression of beta-amyloid precursor protein (betaAPP), which is one of the triplicated genes in DS. In this review, we will survey the available findings on neurodevelopmental and neurodegenerative changes occurring in DS throughout life. Moreover, we will discuss the potential mechanisms by which defects in neurogenesis and neurodegenerative processes lead to altered formation of neural circuits and impair cognitive function, in connection with findings on pharmacological treatments of potential benefit for DS.

Interleukin-11 in endometrial adenocarcinoma is regulated by prostaglandin F2alpha-F-prostanoid receptor interaction via the calcium-calcineurin-nuclear factor of activated T cells pathway and negatively regulated by the regulator of calcineurin-1

Interleukin-11 (IL-11) up-regulates the proliferative and invasive capacity of many cancers. Coexpression of glycoprotein 130 (GP130) and IL-11 receptor alpha (IL-11Ralpha) is necessary for high-affinity binding of IL-11 to IL-11Ralpha. This study investigated the expression of IL-11 and role of prostaglandin F(2alpha)-F-prostanoid receptor (FP receptor) signaling in the modulation of IL-11 expression in endometrial adenocarcinoma cells. Localization of IL-11, IL-11Ralpha, and GP130 expression was performed by immunohistochemistry. IL-11 and regulator of calcineurin 1 isoform 4 (RCAN1-4) mRNA and protein expression were determined by real-time RT-PCR and/or enzyme-linked immunosorbent assay/Western blot analysis using Ishikawa endometrial adenocarcinoma cells stably expressing the FP receptor (FPS cells) and endometrial adenocarcinoma explants. IL-11 mRNA expression was significantly elevated in endometrial adenocarcinoma samples compared with normal endometrium and increased with tumor grade. IL-11 protein expression localized with FP receptor, IL-11Ralpha, and GP130 in the neoplastic glandular epithelium of endometrial adenocarcinomas. Prostaglandin F(2alpha)-FP receptor signaling significantly elevated the expression of IL-11 mRNA and protein in a Gq-protein kinase C-calcium-calcineurin-nuclear factor of activated T cells-dependent manner in FPS cells. The calcineurin signaling pathway is known to be controlled by the RCAN (RCAN1-4). Indeed, RCAN1-4 expression was significantly elevated in well-differentiated endometrial adenocarcinoma compared with normal endometrium and was found to decrease with tumor grade and negatively regulate IL-11 expression in vitro. This study has highlighted a new mechanism regulating IL-11 expression in endometrial adenocarcinoma cells by the FP receptor via the calcium-calcineurin-nuclear factor of activated T cells pathway.

Knockdown of RCAN1.4 Increases Susceptibility to FAS-mediated and DNA-damage-induced Apoptosis by Upregulation of p53 Expression

Despite the potential importance of the human regulator of calcineurin 1 (RCAN-1) gene in the modulation of cell survival under stress, little is known about its role in death-inducing signal pathways. In this study, we addressed the effects of RCAN1.4 knockdown on cellular susceptibility to apoptosis and the activation of death pathway proteins. Transfection of siRNAs against RCAN1.4 resulted in enhanced Fas- and etoposide-induced apoptosis, which was associated with increased expression and translocation of Bax to mitochondria. Our results suggest that enhanced expression and activation of p53 was responsible for the upregulation of Bax and the increased sensitivity to apoptosis, which could be reversed by p53 knockdown. To explain the observed upregulation of p53, we propose a downregulation of the ubiquitin ligase HDM2, probably translationally. These findings show the importance of appropriate RCAN1.4 expression in the modulation of cell survival and reveal a link between RCAN1.4 and p53.

Cognitive decline in Alzheimer's disease is associated with selective changes in calcineurin/NFAT signaling

Upon activation by calcineurin, the nuclear factor of activated T-cells (NFAT) translocates to the nucleus and guides the transcription of numerous molecules involved in inflammation and Ca(2+) dysregulation, both of which are prominent features of Alzheimer's disease (AD). However, NFAT signaling in AD remains relatively uninvestigated. Using isolated cytosolic and nuclear fractions prepared from rapid-autopsy postmortem human brain tissue, we show that NFATs 1 and 3 shifted to nuclear compartments in the hippocampus at different stages of neuropathology and cognitive decline, whereas NFAT2 remained unchanged. NFAT1 exhibited greater association with isolated nuclear fractions in subjects with mild cognitive impairment (MCI), whereas NFAT3 showed a strong nuclear bias in subjects with severe dementia and AD. Similar to NFAT1, calcineurin-Aalpha also exhibited a nuclear bias in the early stages of cognitive decline. But, unlike NFAT1 and similar to NFAT3, the nuclear bias for calcineurin became more pronounced as cognition worsened. Changes in calcineurin/NFAT3 were directly correlated to soluble amyloid-beta (Abeta((1-42))) levels in postmortem hippocampus, and oligomeric Abeta, in particular, robustly stimulated NFAT activation in primary rat astrocyte cultures. Oligomeric Abeta also caused a significant reduction in excitatory amino acid transporter 2 (EAAT2) protein levels in astrocyte cultures, which was blocked by NFAT inhibition. Moreover, inhibition of astrocytic NFAT activity in mixed cultures ameliorated Abeta-dependent elevations in glutamate and neuronal death. The results suggest that NFAT signaling is selectively altered in AD and may play an important role in driving Abeta-mediated neurodegeneration.

Omic analyses unravels global molecular changes in the brain and liver of a rat model for chronic Sake (Japanese alcoholic beverage) intake

The effects of chronic administration of Sake (Japanese alcoholic beverage, Nihonshu) on brain and liver of female F334 (Fisher) rats were surveyed via global omic analyses using DNA microarray, 2-DE, and proton nuclear magnetic resonance. Rats weaned at 4 wk of age were given free access to Sake (15% alcohol), instead of water. At 13 months of age, and 24 h after withdrawal of Sake supply, rats were sacrificed, and the whole brain and liver tissues dissected for analyses. In general, molecular changes in brain were found to be less than those in liver. Transcriptomics data revealed 36 and 9, and 80 and 62 up- and down-regulated genes, in the brain and liver, respectively, with binding and catalytic activity gene categories the most prominently changed. Results suggested Sake-induced fragility of brain and liver toxicity/damage, though no significant abnormalities in growth were seen. At protein level, a striking decrease was found in the expression of NADH dehydrogenase (ubiquinone) Fe-S protein 1 in brain, suggesting attenuation of mitochondrial metabolism. In liver, results again suggested an attenuation of mitochondrial function and, in addition, glycoproteins with unknown function were induced at protein and gene levels, suggesting possible changes in glycoprotein binding in that organ. Metabolomic analysis of brain revealed significant increases in valine, arginine/ornithine, alanine, glutamine, and choline with decreases in isoleucine, N-acetyl aspartate, taurine, glutamate, and gamma aminobutyric acid. Our results provide a detailed inventory of molecular components of both brain and liver after Sake intake, and may help to better understand effects of chronic Sake drinking.

Down syndrome critical region 1 enhances the proteolytic cleavage of calcineurin

Down syndrome critical region 1 (DSCR1), an oxidative stress-response gene, interacts with calcineurin and represses its phosphatase activity. Recently it was shown that hydrogen peroxide inactivates calcineurin by proteolytic cleavage. Based on these facts, we investigated whether oxidative stress affects DSCR1- mediated inactivation of calcineurin. We determined that overexpression of DSCR1 leads to increased proteolytic cleavage of calcineurin. Convertsely, knockdown of DSCR1 abolished calcineurin cleavage upon treatment with hydrogen peroxide. The PXIIXT motif in the COOH-terminus of DSCR1 is responsible for both binding and cleavage of calcineurin. The knockdown of overexpressed DSCR1 in DS fibroblast cells also abrogated calcineurin proteolysis by hydrogen peroxide. These results suggest that DSCR1 has the ability to inactivate calcineurin by inducing proteolytic cleavage of calcineurin upon oxidative stress.

Role of protein phosphatases and mitochondria in the neuroprotective effects of estrogens

In the present treatise, we provide evidence that the neuroprotective and mito-protective effects of estrogens are inexorably linked and involve the ability of estrogens to maintain mitochondrial function during neurotoxic stress. This is achieved by the induction of nuclear and mitochondrial gene expression, the maintenance of protein phosphatases levels in a manner that likely involves modulation of the phosphorylation state of signaling kinases and mitochondrial pro- and anti-apoptotic proteins, and the potent redox/antioxidant activity of estrogens. These estrogen actions are mediated through a combination of estrogens receptor (ER)-mediated effects on nuclear and mitochondrial transcription of protein vital to mitochondrial function, ER-mediated, non-genomic signaling and non-ER-mediated effects of estrogens on signaling and oxidative stress. Collectively, these multifaceted, coordinated action of estrogens leads to their potency in protecting neurons from a wide variety of acute insults as well as chronic neurodegenerative processes.

Degradation of regulator of calcineurin 1 (RCAN1) is mediated by both chaperone-mediated autophagy and ubiquitin proteasome pathways

Regulator of calcineurin 1 (RCAN1), a gene identified from the critical region of Down syndrome, has been implied in pathogenesis of Alzheimer's disease (AD). RCAN1 expression was shown to be increased in AD brains; however, the mechanism of RCAN1 gene regulation is not well defined. The present study was designed to investigate the molecular mechanism of RCAN1 protein degradation. In addition to being degraded through the ubiquitin proteasome pathway, we found that lysosomal inhibition markedly increased RCAN1 protein expression in a time- and dosage-dependent manner. Inhibition of macroautophagy reduced RCAN1 expression, indicating that RCAN1 degradation is not through a macroautophagy pathway. However, disruption of chaperone-mediated autophagy (CMA) increased RCAN1 expression. Two CMA recognition motifs were identified in RCAN1 protein to mediate its degradation through a CMA-lysosome pathway. A promoter assay further demonstrated that inhibition of RCAN1 degradation in cells reduced calcineurin-NFAT activity. Dysfunctions of ubiquitin-proteasome and autophagy-lysosome pathways have been implicated in neurodegenerative diseases. Therefore, elucidation of RCAN1 degradation by a ubiquitin proteasome pathway and CMA-lysosome pathway in the present study may greatly advance our understanding of AD pathogenesis.

Down syndrome--recent progress and future prospects

Down syndrome (DS) is caused by trisomy of chromosome 21 (Hsa21) and is associated with a number of deleterious phenotypes, including learning disability, heart defects, early-onset Alzheimer's disease and childhood leukaemia. Individuals with DS are affected by these phenotypes to a variable extent; understanding the cause of this variation is a key challenge. Here, we review recent research progress in DS, both in patients and relevant animal models. In particular, we highlight exciting advances in therapy to improve cognitive function in people with DS and the significant developments in understanding the gene content of Hsa21. Moreover, we discuss future research directions in light of new technologies. In particular, the use of chromosome engineering to generate new trisomic mouse models and large-scale studies of genotype–phenotype relationships in patients are likely to significantly contribute to the future understanding of DS.

Regulator of calcineurin (RCAN1-1L) is deficient in Huntington disease and protective against mutant huntingtin toxicity in vitro

Our work suggests an important new link between the RCAN1 gene and Huntington disease. Huntington disease is caused by expansion of glutamine repeats in the huntingtin protein. How the huntingtin protein with expanded polyglutamines (mutant huntingtin) causes the disease is still unclear, but phosphorylation of huntingtin appears to be protective. Increased huntingtin phosphorylation can be produced either by inhibition of the phosphatase calcineurin or by activation of the Akt kinase. The RCAN1 gene encodes regulators of calcineurin, and we now demonstrate, for the first time, that RCAN1-1L is depressed in Huntington disease. We also show that RCAN1-1L overexpression can protect against mutant huntingtin toxicity in an ST14A cell culture model of Huntington disease and that increased phosphorylation of huntingtin via calcineurin inhibition, rather than via Akt induction or activation, is the likely mechanism by which RCAN1-1L may be protective against mutant huntingtin. These findings suggest that RCAN1-1L "deficiency" may actually play a role in the etiology of Huntington disease. In addition, our results allow for the possibility that controlled overexpression of RCAN1-1L in the striatal region of the brain might be a viable avenue for therapeutic intervention in Huntington disease patients (and perhaps other polyglutamine expansion disorders).

Two key genes closely implicated with the neuropathological characteristics in Down syndrome: DYRK1A and RCAN1

The most common genetic disorder Down syndrome (DS) displays various developmental defects including mental retardation, learning and memory deficit, the early onset of Alzheimer's disease (AD), congenital heart disease, and craniofacial abnormalities. Those characteristics result from the extra-genes located in the specific region called nDown syndrome critical region (DSCR)' in human chromosome 21. In this review, we summarized the recent findings of the DYRK1A and RCAN1 genes, which are located on DSCR and thought to be closely associated with the typical features of DS patients, and their implication to the pathogenesis of neural defects in DS. DYRK1A phosphorylates several transcriptional factors, such as CREB and NFAT, endocytic complex proteins, and AD-linked gene products. Meanwhile, RCAN1 is an endogenous inhibitor of calcineurin A, and its unbalanced activity is thought to cause major neuronal and/or non-neuronal malfunction in DS and AD. Interestingly, they both contribute to the learning and memory deficit, altered synaptic plasticity, impaired cell cycle regulation, and AD-like neuropathology in DS. By understanding their biochemical, functional and physiological roles, we hope to get important molecular basis of DS pathology, which would consequently lead to the basis to develop the possible therapeutic tools for the neural defects in DS. [BMB reports 2009; 42(1): 6-15].

Transcription enhancer factor 3 (TEF3) mediates the expression of Down syndrome candidate region 1 isoform 1 (DSCR1-1L) in endothelial cells

The Down syndrome candidate region 1 gene (DSCR1) can be expressed as four isoforms, one of which is the well-studied isoform 4 (DSCR1-4) that is induced by VEGF-A(165) to provide a negative feedback loop in the VEGF-A(165)-induced angiogenesis. We reported previously that another DSCR1 isoform, DSCR1-1L, was also up-regulated by VEGF-A(165) in cultured endothelial cells and in several in vivo models of pathological angiogenesis and that different from DSCR1-4, DSCR1-1L overexpression alone induced cultured endothelial cell proliferation and promoted angiogenesis in Matrigel assays. It was reported recently that tumor growth was greatly repressed in DSCR1 knock-out mice. Although DSCR1-4 transcription was primarily regulated by NFAT, the mechanism regulating DSCR1-1L expression was still unknown. We developed human DSCR1-1L promoter-driven luciferase system and found that deletion of a putative conserved M-CAT site located 1426-bp upstream of the translation start site blunted promoter activity. We further showed that knockdown of TEF3, not other members of TEF family inhibited VEGF-A(165)-induced DSCR1-1L expression. We also demonstrated that TEF3 directly interacted with the putative M-CAT site in the DSCR1-1L promoter in vitro and in vivo. Finally, overexpression of TEF3 isoform 1, not isoform 3, in HUVEC was sufficient to induce DSCR1-1L expression even in the absence of VEGF-A(165) stimulation. Taken together, we elucidated a novel function of transcriptional factor TEF3. TEF3 was required for DSCR1-1L expression through binding to the M-CAT site in its promoter and could be an attractive target for anti-angiogenesis therapy.

Calcium/calcineurin signaling in primary cortical astrocyte cultures: Rcan1-4 and cyclooxygenase-2 as NFAT target genes

The calcineurin/nuclear factor of activated T cells (NFAT) signaling pathway mediates important cell responses to calcium, but its activity and function in astrocytes have remained unclear. We show that primary cortical astrocyte cultures express the regulatory and catalytic subunits of the phosphatase calcineurin as well as the calcium-regulated NFAT family members (NFATc1, c2, c3, and c4). NFATs are activated by calcium-mobilizing agents in astrocytes, and this activation is blocked by the calcineurin inhibitor cyclosporine A. Microarray screening identified cyclooxygenase-2 (Cox-2), which is implicated in brain injury, and Rcan 1-4, an endogenous calcineurin inhibitor, as genes up-regulated by calcineurin-dependent calcium signals in astrocytes. Mobilization of intracellular calcium with ionophore potently augments the promoter activity and mRNA and protein expression of Rcan 1-4 and Cox-2 induced by combined treatment with phorbol esters. Moreover, Rcan 1-4 expression is efficiently induced by calcium mobilization alone. For both the genes, the calcium signal component is dependent on calcineurin and is replicated by exogenous expression of a constitutively active NFAT, strongly suggesting that the calcium-induced gene activation is mediated by NFATs. Finally, we report that calcineurin-dependent expression of Cox-2 and Rcan 1-4 is induced by physiological calcium mobilizing agents, such as thrombin, agonists of purinergic and glutamate receptors, and L-type voltage-gated calcium channels. These findings provide insights into calcium-initiated gene transcription in astrocytes, and have implications for the regulation of calcium responses in astrocytes.

Crosstalk between calcium and redox signaling: from molecular mechanisms to health implications

Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

Mental retardation and associated neurological dysfunctions in Down syndrome: a consequence of dysregulation in critical chromosome 21 genes and associated molecular pathways

Down syndrome (DS), affecting 1/700 live births, is the major genetic cause of mental retardation (MR), a cognitive disorder with hard impact on public health. DS brain is characterized by a reduced cerebellar volume and number of granular cells, defective cortical lamination and reduced cortical neurons, malformed dendritic trees and spines, and abnormal synapses. These neurological alterations, also found in trisomic mouse models, result from gene-dosage effects of Human Chromosome 21 (HC21) on the expression of critical developmental genes. HC21 sequencing, mouse ortholog gene identification and DS mouse model generation lead to determine HC21 gene functions and the effects of protein-dosage alterations in neurodevelopmental and metabolic pathways in DS individuals. Trisomic brain transcriptome of DS patients and trisomic mouse models identified some molecular changes determined by gene-overdosage and associated dysregulation of some disomic gene expression in DS brains. These transcriptional variations cause developmental alterations in neural patterning and signal transduction pathways that may lead to defective neuronal circuits responsible for the pathogenesis of MR in DS. Recently, the first altered molecular pathway responsible of some DS phenotypes, including neurological and cognitive disorders has been identified. In this pathway, two critical HC21 genes (DYRK1A and DSCR1) act synergistically to control the phosphorylation levels of NFATc and NFATc-regulated gene expression. Interestingly, the NFATc mice show neurological dysfunctions similar to those seen in DS patients and trisomic mouse models. Treatment of DS mouse model Ts65Dn with GABA(A) antagonists allowed post-drug rescue of cognitive defects, indicating a hopeful direction in clinical therapies for MR in children with DS.

Upregulation of DSCR1 (RCAN1 or Adapt78) in the peri-infarct cortex after experimental stroke

Down syndrome candidate region 1 (DSCR1; also known as RCAN1 or Adapt78) has been shown to be induced by calcium overload and oxidative stress which are included in the pathogenic hallmarks of the ischemic diseases. After ischemic stroke, inflammatory responses play an important role in the exacerbation of neuronal loss. In this study, we investigated the expression pattern of DSCR1 in the mouse cortex after transient middle cerebral artery occlusion (MCAO). Then, in vitro studies were taken to address whether inflammatory mediators could induce DSCR1. Male C57BL/6 mice were subjected to transient MCAO for 35 min and sacrificed at 6, 24, and 72 h after the reperfusion. The expression of DSCR1 began to increase in layer VI of the peri-infarct cortex at 24 h and was prominently enhanced at 72h after transient MCAO. Moreover, real-time reverse transcriptase-polymerase chain reaction and immunohistochemistry showed that the induction of the DSCR1 isoform 4 (DSCR1-4) mRNA preceded the expression of the DSCR1 protein. In in vitro studies, tumor necrosis factor alpha and interleukin-1beta (IL-1beta) were found to induce strong upregulation of DSCR1-4 mRNA. Furthermore, western blot analysis revealed that overexpression of DSCR1-4 in SK-N-SH neuroblastoma cells attenuated IL-1beta-induced cyclooxygenase 2 and intercellular adhesion molecule 1 expression. These results demonstrate upregulation of DSCR1 in the mouse peri-infarct cortex following transient MCAO. In addition, our results suggest that inflammatory mediators such as TNFalpha and IL-1beta can induce DSCR1-4 transcription, which may be associated with the alleviation of inflammatory processes.

NF-kappaB-inducing kinase phosphorylates and blocks the degradation of Down syndrome candidate region 1

Down syndrome, the most frequent genetic disorder, is characterized by an extra copy of all or part of chromosome 21. Down syndrome candidate region 1 (DSCR1) gene, which is located on chromosome 21, is highly expressed in the brain of Down syndrome patients. Although its cellular function remains unknown, DSCR1 expression is linked to inflammation, angiogenesis, and cardiac development. To explore the functional role of DSCR1 and the regulation of its expression, we searched for novel DSCR1-interacting proteins using a yeast two-hybrid assay. Using a human fetal brain library, we found that DSCR1 interacts with NF-kappaB-inducing kinase (NIK). Furthermore, we demonstrate that NIK specifically interacts with and phosphorylates the C-terminal region of DSCR1 in immortalized hippocampal cells as well as in primary cortical neurons. This NIK-mediated phosphorylation of DSCR1 increases its protein stability and blocks its proteasomal degradation, the effects of which lead to an increase in soluble and insoluble DSCR1 levels. We show that an increase in insoluble DSCR1 levels results in the formation of cytosolic aggregates. Interestingly, we found that whereas the formation of these inclusions does not significantly alter the viability of neuronal cells, the overexpression of DSCR1 without the formation of aggregates is cytotoxic.

DSCR1/RCAN1 regulates vesicle exocytosis and fusion pore kinetics: implications for Down syndrome and Alzheimer's disease

Genes located on chromosome 21, over-expressed in Down syndrome (DS) and Alzheimer's disease (AD) and which regulate vesicle trafficking, are strong candidates for involvement in AD neuropathology. Regulator of calcineurin activity 1 (RCAN1) is one such gene. We have generated mutant mice in which RCAN1 is either over-expressed (RCAN1(ox)) or ablated (Rcan1-/-) and examined whether exocytosis from chromaffin cells, a classic cellular model of neuronal exocytosis, is altered using carbon fibre amperometry. We find that Rcan1 regulates the number of vesicles undergoing exocytosis and the speed at which the vesicle fusion pore opens and closes. Cells from both Rcan1-/- and RCAN1(ox) mice display reduced levels of exocytosis. Changes in single-vesicle fusion kinetics are also evident resulting in the less catecholamine released per vesicle with increasing Rcan1 expression. Acute calcineurin inhibition did not replicate the effect of RCAN1 overexpression. These changes are not due to alterations in Ca2+ entry or the readily releasable vesicle pool size. Thus, we illustrate a novel regulator of vesicle exocytosis, Rcan1, which influences both exocytotic rate and vesicle fusion kinetics. If Rcan1 functions similarly in neurons then overexpression of this protein, as occurs in DS and AD brains, will reduce both the number of synaptic vesicles undergoing exocytosis and the amount of neurotransmitter released per fusion event. This has direct implications for the pathogenesis of these diseases as sufficient levels of neurotransmission are required for synaptic maintenance and the prevention of neurodegeneration and vesicle trafficking defects are the earliest hallmark of AD neuropathology.

The Down syndrome critical region protein RCAN1 regulates long-term potentiation and memory via inhibition of phosphatase signaling

Regulator of calcineurin 1 (RCAN1/MCIP1/DSCR1) regulates the calmodulin-dependent phosphatase calcineurin. Because it is located on human chromosome 21, RCAN1 has been postulated to contribute to mental retardation in Down syndrome and has been reported to be associated with neuronal degeneration in Alzheimer's disease. The studies herein are the first to assess the role of RCAN1 in memory and synaptic plasticity by examining the behavioral and electrophysiological properties of RCAN1 knock-out mice. These mice exhibit deficits in spatial learning and memory, reduced associative cued memory, and impaired late-phase long-term potentiation (L-LTP), phenotypes similar to those of transgenic mice with increased calcineurin activity. Consistent with this, the RCAN1 knock-out mice display increased enzymatic calcineurin activity, increased abundance of a cleaved calcineurin fragment, and decreased phosphorylation of the calcineurin substrate dopamine and cAMP-regulated phosphoprotein-32. We propose a model in which RCAN1 plays a positive role in L-LTP and memory by constraining phosphatase signaling.

Risk of vascular anomalies with Down syndrome

OBJECTIVE

Patients with Down syndrome have a reduced risk of developing solid tumors. This protective effect has been attributed to increased gene dosage from an additional copy of chromosome 21, and elevated expression of endostatin has been implicated. We hypothesized that vascular anomalies, including infantile hemangioma, an angiogenesis-dependent vascular tumor, and vascular malformations might be similarly inhibited in patients with Down syndrome.

PATIENTS AND METHODS

The Children's Hospital Boston Vascular Anomalies Center database was searched for patients with Down syndrome between 1999 and 2007. In addition, the records of patients with Down syndrome treated at Children's Hospital Boston and the National Birth Defects Center between 1985 and 2007 were reviewed to find concurrent vascular anomalies. Two-sided exact binomial tests were used to evaluate whether patients with vascular anomalies are at reduced risk for Down syndrome or if patients with Down syndrome are at less risk for vascular anomalies compared with the general population. Ninety-five-percent confidence intervals were calculated on the basis of the risk of Down syndrome (1 in 800) and vascular anomalies (1 in 22) in the general population.

RESULTS

Two of the 7354 patients evaluated in our vascular anomalies unit had Down syndrome. Both patients had a lymphatic malformation: one in the orbit and the other in the lower extremity. Six of the 633 patients with Down syndrome had a vascular anomaly (infantile hemangioma [n = 4] or lymphatic malformation [n = 2]). The risk of concurrent Down syndrome and vascular anomalies was different from the corresponding risk in the general population.

CONCLUSIONS

Patients with Down syndrome have a reduced risk of vascular anomalies compared with the general population. Elevated expression of antiangiogenic proteins may protect these patients from developing vascular anomalies, as well as solid tumors.

Mental retardation in Down syndrome: From gene dosage imbalance to molecular and cellular mechanisms

Down syndrome (DS), the most frequent genetic disorder leading to mental retardation (MR), is caused by three copies of human chromosome 21 (HC21). Trisomic and transgenic mouse models for DS allow genetic dissection of DS neurological and cognitive disorders in view to identify genes responsible for these phenotypes. The effects of the gene dosage imbalance on DS phenotypes are explained by two hypotheses: the "gene dosage effect" hypothesis claims that a DS critical region, containing a subset of dosage-sensitive genes, determines DS phenotypes, and the "amplified developmental instability" hypothesis holds that HC21 trisomy determines general alteration in developmental homeostasis. Transcriptome and expression studies showed different up- or down-expression levels of genes located on HC21 and the other disomic chromosomes. HC21 genes, characterized by their overexpression in brain regions affected in DS patients and by their contribution to neurological and cognitive defects when overexpressed in mouse models, are proposed herein as good candidates for MR. In this article, we propose a new molecular and cellular mechanism explaining MR pathogenesis in DS. In this model, gene dosage imbalance effects on transcriptional variations are described considering the nature of gene products and their functional relationships. These transcriptional variations may affect different aspects of neuronal differentiation and metabolism and finally, determine the brain neuropathologies and mental retardation in DS.

Differential expression of members of the RCAN family of calcineurin regulators suggests selective functions for these proteins in the brain

RCANs, also called Down Syndrome Critical Region-1 (DSCR1)-like proteins, Modulatory Calcineurin Interacting Proteins (MCIPs) or calcipressins, are regulators of calcineurin, a Ca(2+)-dependent protein phosphatase involved in several neuronal functions. Despite the potential importance of the RCAN proteins in brain physiology, very little is known about their relative abundance and distribution patterns in the central nervous system. In this study we report the expression and distribution of RCAN mRNA transcripts and proteins in the mouse brain. RT-PCR and Western blot analysis showed that all Rcan mRNAs (Rcan1-1, Rcan1-2, Rcan2-1, Rcan2-3 and Rcan3) and their corresponding protein products (RCAN1-L, RCAN1-S, RCAN2-L, RCAN2-S and RCAN3) are present in every adult mouse brain region examined. All protein isoforms are also expressed in these same brain regions at early postnatal stages. Within regions, RCAN1-L, RCAN1-S, RCAN2-L and RCAN3 are differentially expressed depending on the region and developmental stage, whereas RCAN2-S is distributed homogeneously. Detailed immunohistochemical analysis revealed significant differences in the cellular and subcellular distributions of RCAN proteins. In the adult, RCAN1 was mainly expressed in the neuropil throughout the brain. Although at lower levels, RCAN3 was also detected throughout the neuropil. In contrast, RCAN2 was highly expressed in scattered neurons, in both the nucleus and the cytoplasm. Interestingly, RCAN2 is the only member of the RCAN family that was detected in glial cells. Finally, the expression patterns of RCANs at early postnatal stages differed from those of the adult, in different brain areas, in both their distributions and relative abundance, suggesting that the expression of these proteins could be regulated during neuronal differentiation. The nonoverlapping expression patterns of the RCAN proteins shown here highlight the existence of different physiological scenarios and therefore suggest different RCAN functional activities in the brain, depending on the cellular context and developmental stage.

Calmodulin Inhibitor-induced Apoptosis was Prevented by Glycogen Synthase Kinase-3 Inhibitors in PC12 Cells

Calmodulin is known to transduce Ca(2+) signals by interacting with specific target proteins. In order to determine the role of calmodulin in regulating neuronal survival and death, we examined, whether calmodulin inhibitors induce caspase-dependent apoptotic cell death, and whether glycogen synthase kinase-3 is involved in calmodulin inhibitor-induced cell death in PC12 cells. W13, a calmodulin specific inhibitor increased apoptotic cell death with morphological changes characterized by cell shrinkage and nuclear condensation of fragmentation. Glycogen synthase kinase-3 inhibitors prevented calmodulin inhibitor-induced apoptosis. In addition, nerve growth factor and cycloheximide, a protein synthesis inhibitor, completely blocked cell death. Moreover, caspase-3 activation was accompanied by calmodulin inhibitor-induced cell death and inhibited by nerve growth factor. These results suggest that calmodulin inhibitors induce caspase-dependent apoptosis, and the activation of glycogen synthase kinase-3 is involved in the death of PC12 cells.

Calcium homeostasis and modulation of synaptic plasticity in the aged brain

The level of intracellular Ca2+ plays a central role in normal and pathological signaling within and between neurons. These processes involve a cascade of events for locally raising and lowering cytosolic Ca2+. As the mechanisms for age-related alteration in Ca2+ dysregulation have been illuminated, hypotheses concerning Ca2+ homeostasis and brain aging have been modified. The idea that senescence is due to pervasive cell loss associated with elevated resting Ca2+ has been replaced by concepts concerning changes in local Ca2+ levels associated with neural activity. This article reviews evidence for a shift in the sources of intracellular Ca2+ characterized by a diminished role for N-methyl-D-aspartate receptors and an increased role for intracellular stores and voltage-dependent Ca2+ channels. Physiological and biological models are outlined, which relate a shift in Ca2+ regulation with changes in cell excitability and synaptic plasticity, resulting in a functional lesion of the hippocampus.

Overexpression of DSCR1 blocks zinc-induced neuronal cell death through the formation of nuclear aggregates

The Down syndrome (DS) candidate region gene 1 (DSCR1) is localized near DS critical region on chromosome 21 and is overexpressed in the brains of DS patients. Although DSCR1 was known for a modulator of calcineurin, the overexpression of DSCR1 is thought to play a role in neuronal cell death. Zinc, one of the most abundant transition metals in the brain, may also contribute to selective neuronal cell death when present in excessive amounts. In the present study, we investigated the effect of DSCR1 overexpression on zinc-induced cell death in hippocampal neuroprogenitor cells. The overexpression of DSCR1 caused apoptotic cell death without an apparent formation of intracellular protein inclusions. Upon exposure to zinc, soluble DSCR1 levels were significantly decreased and insoluble levels were enhanced to a similar extent, which were partially caused by the zinc-induced inhibition of proteasomal activity and a consequently diminished degradation of DSCR1. Furthermore, zinc treatment induced the formation of nuclear DSCR1 aggregates, which blocked zinc-induced cell death. These findings indicate that, although the up-regulation of DSCR1 levels exerts a cytotoxic effect, the addition of zinc leads to the formation of cytoprotective nuclear aggregates in neuronal cells.

Identification and dissection of Ca(2+)-binding sites in the extracellular domain of Ca(2+)-sensing receptor

Ca(2+)-sensing receptors (CaSRs) represent a class of receptors that respond to changes in the extracellular Ca(2+) concentration ([Ca(2+)](o)) and activate multiple signaling pathways. A major barrier to advancing our understanding of the role of Ca(2+) in regulating CaSRs is the lack of adequate information about their Ca(2+)-binding locations, which is largely hindered by the lack of a solved three-dimensional structure and rapid off rates due to low Ca(2+)-binding affinities. In this paper, we have reported the identification of three potential Ca(2+)-binding sites in a modeled CaSR structure using computational algorithms based on the geometric description and surface electrostatic potentials. Mutation of the predicted ligand residues in the full-length CaSR caused abnormal responses to [Ca(2+)](o), similar to those observed with naturally occurring activating or inactivating mutations of the CaR, supporting the essential role of these predicted Ca(2+)-binding sites in the sensing capability of the CaSR. In addition, to probe the intrinsic Ca(2+)-binding properties of the predicted sequences, we engineered two predicted continuous Ca(2+)-binding sequences individually into a scaffold protein provided by a non-Ca(2+)-binding protein, CD2. We report herein the estimation of the metal-binding affinities of these predicted sites in the CaSR by monitoring aromatic-sensitized Tb(3+) fluorescence energy transfer. Removing the predicted Ca(2+)-binding ligands resulted in the loss of or significantly weakened cation binding. The potential Ca(2+)-binding residues were shown to be involved in Ca(2+)/Ln(3+) binding by high resolution NMR and site-directed mutagenesis, further validating our prediction of Ca(2+)-binding sites within the extracellular domain of the CaSR.

Beta-amyloid causes downregulation of calcineurin in neurons through induction of oxidative stress

Calcineurin is an abundant cytosolic protein that is implicated in the modulation of glutamate release. Here we show that the expression level of this enzyme is reduced in primary neuronal cultures treated with beta-amyloid. Parallel experiments in ETNA cell lines expressing SOD1 suggested that the effect of beta-amyloid on calcineurin expression is mediated by oxidative stress. The relevance of the in vitro experiments was assessed by analysis of tissue from patients with Alzheimer's disease (AD) and tissue from two strains of transgenic mice that mimic aspects of AD. The tissue from the AD brains displayed a pronounced downregulation of calcineurin immunoreactivity in profiles that were negative for glial fibrillary acidic protein (GFAP). In the hippocampus of the transgenic animals (which were analyzed in an early stage of the disease) the downregulation of calcineurin was restricted to mossy fiber terminals. A downregulation of the presynaptic pool of calcineurin may contribute to the dysregulation of glutamate release that is considered a hallmark of AD.

RCAN1 (DSCR1) increases neuronal susceptibility to oxidative stress: a potential pathogenic process in neurodegeneration

Oxidative stress (OS) underlies neuronal dysfunction in many neurodegenerative disorders. Regulator of Calcineurin 1 (RCAN1 or DSCR1) is a dose-sensitive gene whose overexpression has been linked to Down syndrome (DS) and Alzheimer's disease (AD) neuropathology and to the response of cells to stress stimuli. Here, we show that RCAN1 mRNA and protein expression are sensitive to OS in primary neurons, and we evaluate the involvement of RCAN1 dosage in neuronal death induced by OS. We find that Rcan1(-/-) neurons display an increased resistance to damage by H(2)O(2), which can be reverted by RCAN1 overexpression or by exogenous inhibitors of calcineurin. Although increased intracellular Ca(2+) concentration is an important factor in OS-mediated cell death, our results show that Ca(2+) loading after exposure to H(2)O(2) was similar in Rcan1(+/+) and Rcan1(-/-) neurons. Our data further suggest that CaN and NFAT signaling protect against OS in both Rcan1(+/+) and Rcan1(-/-) neurons. To explain the observed differential vulnerability, we therefore propose a mechanism downstream of H(2)O(2)-mediated Ca(2+) entry, involving calcineurin-NFAT signaling. These findings highlight the importance of RCAN1 gene dosage in the modulation of cell survival and death pathways and suggest that changes in the amount of RCAN1 could represent an important mechanism for regulating susceptibility to neurodegeneration, especially in DS and AD.

RCAN1-1L is overexpressed in neurons of Alzheimer's disease patients

At least two different isoforms of RCAN1 mRNA are expressed in neuronal cells in normal human brain. Although RCAN1 mRNA is elevated in brain regions affected by Alzheimer's disease, it is not known whether the disease affects neuronal RCAN1, or if other cell types (e.g. astrocytes or microglia) are affected. It is also unknown how many protein isoforms are expressed in human brain and whether RCAN1 protein is overexpressed in Alzheimer's disease. We explored the expression of both RCAN1-1 and RCAN1-4 mRNA isoforms in various cell types in normal and Alzheimer's disease postmortem samples, using the combined technique of immunohistochemistry and in situ hybridization. We found that both exon 1 and exon 4 are predominantly expressed in neuronal cells, and no significant expression of either of the exons was observed in astocytes or microglial cells. This was true in both normal and Alzheimer's disease brain sections. We also demonstrate that RCAN1-1 mRNA levels are approximately two-fold higher in neurons from Alzheimer's disease patients versus non-Alzheimer's disease controls. Using western blotting, we now show that there are three RCAN1 protein isoforms expressed in human brain: RCAN1-1L, RCAN1-1S, and RCAN1-4. We have determined that RCAN1-1L is expressed at twice the level of RCAN1-4, and that there is very minor expression of RCAN1-1S. We also found that the RCAN1-1L protein is overexpressed in Alzheimer's disease patients, whereas RCAN1-4 is not. From these results, we conclude that RCAN1-1 may play a role in Alzheimer's disease, whereas RCAN1-4 may serve another purpose.

Down syndrome candidate region 1 isoform 1 mediates angiogenesis through the calcineurin-NFAT pathway

Down syndrome candidate region 1 (DSCR1) is one of more than 50 genes located in a region of chromosome 21 that has been implicated in Down syndrome. DSCR1 can be expressed as four isoforms, one of which, isoform 4 (DSCR1-4), has recently been found to be strongly induced by vascular endothelial growth factor A (VEGF-A(165)) and to provide a negative feedback loop that inhibits VEGF-A(165)-induced endothelial cell proliferation in vitro and angiogenesis in vivo. We report here that another DSCR1 isoform, DSCR1-1L, is also up-regulated by VEGF-A(165) in cultured endothelial cells and is strongly expressed in several types of pathologic angiogenesis in vivo. In contrast to DSCR1-4, the overexpression of DSCR1-1L induced the proliferation and activation of the transcription factor NFAT in cultured endothelial cells and promoted angiogenesis in Matrigel assays in vivo, even in the absence of VEGF-A. Similarly, small interfering RNAs specific for DSCR1-1L and DSCR1-4 had opposing inhibitory and stimulatory effects, respectively, on these same functions. DSCR1-4 is thought to inhibit angiogenesis by inactivating calcineurin, thereby preventing activation and nuclear translocation of NFAT, a key transcription factor. In contrast, DSCR1-1L, regulated by a different promoter than DSCR1-4, activates NFAT and its proangiogenic activity is inhibited by cyclosporin, an inhibitor of calcineurin. In sum, DSCR1-1L, unlike DSCR1-4, potently activates angiogenesis and could be an attractive target for antiangiogenesis therapy.

Alzheimer's disease and endocytic dysfunction: clues from the Down syndrome-related proteins, DSCR1 and ITSN1

Down syndrome (DS) is a genetically-based disorder which results in multiple conditions for sufferers. Amongst these is a common early incidence of Alzheimer's disease (AD) which usually affects DS individuals by their mid 40s. This fact provides a clue that one or more of the genes located on chromosome 21 may be involved in the onset of AD. Current evidence suggests that endosomal disorders may underlie the earliest pathology of AD, preceding the classical pathological markers of beta-amyloid plaque deposition and neurofibrillary tangles. Therefore, any genes involved in endocytosis and vesicle trafficking which are over-expressed in DS are novel candidates in the pathogenesis of AD. Intersectin-1 (ITSN1) and Down syndrome candidate region 1 (DSCR1) are two such genes. Extensive in vitro data and data from Drosophila indicates that the over-expression of either of these genes or their products results in inhibition or ablation of endocytosis in neuronal as well as non-neuronal cells. This review discusses in detail the known and potential roles of ITSN1 and DSCR1 in DS, AD, endocytosis and vesicle trafficking.

Down syndrome candidate region 1 increases the stability of the IkappaBalpha protein: implications for its anti-inflammatory effects

Down syndrome candidate region 1 (DSCR1), an endogenous inhibitor of calcineurin, inhibits the expression of genes involved in the inflammatory response. To elucidate the molecular basis of these anti-inflammatory effects, we analyzed the role of DSCR1 in the regulation of NF-kappaB transactivation using glioblastoma cells stably transfected with DSCR1.4 or its truncation mutants (DSCR1.4-(1-133) and DSCR1.4-(134-197)). Overexpression of DSCR1.4 significantly attenuated the induction of cyclooxygenase-2 (COX-2) expression by phorbol 12-myristate 13-acetate (PMA) via a calcineurin-independent mechanism. Experiments using inhibitors of the signaling molecules for NF-kappaB activation showed that NF-kappaB is responsible for the induction of COX-2. Full-length and truncated DSCR1.4 decreased the steady-state activity of NF-kappaB as well as PMA-induced activation of NF-kappaB, which correlated with attenuation of COX-2 induction. DSCR1.4 did not affect the PMA-stimulated phosphorylation or degradation kinetics of IkappaBalpha; however, DSCR1.4 significantly decreased the basal turnover rate of IkappaBalpha and consequently up-regulated its steady-state level. In the same context, knockdown of endogenous DSCR1.4 increased the turnover rate of IkappaBalpha as well as COX-2 induction. These results suggest that DSCR1 attenuates NF-kappaB-mediated transcriptional activation by stabilizing its inhibitory protein, IkappaBalpha.

Analysis of the cerebellar proteome in a transgenic mouse model of inherited prion disease reveals preclinical alteration of calcineurin activity

Inherited prion diseases are linked to insertional and point mutations in the prion protein (PrP) gene, which favor conversion of PrP into a conformationally altered, pathogenic isoform. The cellular mechanism by which this process causes neurological dysfunction is unknown. Transgenic (Tg) (PG14) mice express a mouse PrP homolog of a nine-octapeptide insertion associated with an inherited prion disorder. These mice develop a progressive neurological syndrome characterized by ataxia and cerebellar atrophy due to synaptic degeneration in the molecular layer and massive apoptosis of granule neurons. To investigate the molecular events that may contribute to neurological dysfunction, we carried out a differential proteomic analysis of cerebella from Tg(PG14) mice at the preclinical, onset, and symptomatic phases of their neurological illness. 2-D maps of cerebellar proteins from Tg(PG14) mice were compared to those obtained from age-matched Tg(WT) mice that express wild-type PrP and remain healthy. Proteins whose levels were significantly modified in at least one stage of the Tg(PG14) disease were identified by PMF. Analysis detected a preclinical decrease of the calcium/calmodulin-dependent phosphatase calcineurin (CaN) in granule neurons, suggesting that dysregulation of CaN activity induced by mutant PrP may be responsible for the cerebellar dysfunction in Tg(PG14) mice.

RCAN1 (DSCR1 or Adapt78) stimulates expression of GSK-3beta

The RCAN1 protein (previously called calcipressin 1 or MCIP1) binds to calcineurin, a serine/threonine phosphatase (PP2B), and inhibits its activity. Here we demonstrate that regulated overexpression of an RCAN1 transgene (this gene was previously called DSCR1 or Adapt78) also stimulates expression of the GSK-3beta kinase, which can antagonize the action of calcineurin. We also show that GSK-3beta is regulated by RCAN1 at a post-transcriptional level. In humans, high RCAN1 expression is found in the brain, where at least two mRNA isoforms have been reported. Therefore, we further investigated expression of the various RCAN1 isoforms, resulting from differential splicing and alternative promotors in human brain. We detected at least three distinct RCAN1s: RCAN1-1 Short at 31 kDa (RCAN1-1S), RCAN1-1 Long at 38 kDa (RCAN1-1 L), and RCAN1-4. Furthermore, the levels of RCAN1-1S, but not RCAN1-1 L or RCAN1-4 correlated with the levels of GSK-3beta. This suggests that RCAN1-1S might induce production of GSK-3beta in vivo. While RCAN1s can regulate calcineurin and GSK-3beta, it has also been shown that calcineurin and GSK-3beta can regulate RCAN1s. Here we propose a new model (incorporating all these findings) in which cells maintain an equilibrium between RCAN1s, calcineurin, and GSK-3beta.

Free radical biology and medicine: it's a gas, man!

We review gases that can affect oxidative stress and that themselves may be radicals. We discuss O(2) toxicity, invoking superoxide, hydrogen peroxide, and the hydroxyl radical. We also discuss superoxide dismutase (SOD) and both ground-state, triplet oxygen ((3)O(2)), and the more energetic, reactive singlet oxygen ((1)O(2)). Nitric oxide ((*)NO) is a free radical with cell signaling functions. Besides its role as a vasorelaxant, (*)NO and related species have other functions. Other endogenously produced gases include carbon monoxide (CO), carbon dioxide (CO(2)), and hydrogen sulfide (H(2)S). Like (*)NO, these species impact free radical biochemistry. The coordinated regulation of these species suggests that they all are used in cell signaling. Nitric oxide, nitrogen dioxide, and the carbonate radical (CO(3)(*-)) react selectively at moderate rates with nonradicals, but react fast with a second radical. These reactions establish "cross talk" between reactive oxygen (ROS) and reactive nitrogen species (RNS). Some of these species can react to produce nitrated proteins and nitrolipids. It has been suggested that ozone is formed in vivo. However, the biomarkers that were used to probe for ozone reactions may be formed by non-ozone-dependent reactions. We discuss this fascinating problem in the section on ozone. Very low levels of ROS or RNS may be mitogenic, but very high levels cause an oxidative stress that can result in growth arrest (transient or permanent), apoptosis, or necrosis. Between these extremes, many of the gasses discussed in this review will induce transient adaptive responses in gene expression that enable cells and tissues to survive. Such adaptive mechanisms are thought to be of evolutionary importance.

Calcineurin inhibitors cause an acceleration of the neurological phenotype in a mouse transgenic for the human Huntington's disease mutation

Calcineurin (CaN) is a Ca(2+)- and calmodulin-dependent protein serine-threonine phosphatase that is thought to play an important role in the neuronal response to changes in the intracellular Ca(2+) concentration. CaN has been implicated in numerous physiological processes including learning and memory. Decreases in CaN expression are thought to be responsible for some of the pathological features seen in brain ischemia, Down's syndrome and Alzheimer's disease. In this study, we examined the possibility of CaN playing a role in the progressive neurological phenotype of the R6/2 mouse of Huntington's disease. We studied the effects of the CaN inhibitors cyclosporin A and FK506 on the progressive neurological phenotype in the R6/2 mouse. We found that an immunosuppressive dose of both drugs dramatically accelerated the main features of the neurological phenotype in R6/2 mice. This was unlikely to be due solely to the immunosuppressive action of these drugs, since treatment with cyclophosphamide, an immunosuppressant drug with a mechanism of action that is not mediated via CaN, did not have deleterious effects on the R6/2 mouse. If anything, cyclophosphamide improved the neurological symptoms in the R6/2 mice. Together, our data suggest a central role for CaN in the deleterious phenotype of the R6/2 mouse. Treatments aimed at preventing the loss of CaN or stimulating its function may be beneficial in the treatment of HD.

Altered gene expression profiles reveal similarities and differences between Parkinson disease and model systems

Parkinson disease (PD) targets dopaminergic neurons in the substantia nigra, resulting in motor disturbances such as resting tremor, bradykinesia, and rigidity. Pathogenic processes likely occur over several decades, in that an overwhelming percentage of neurons are already dead at the time of clinical diagnosis. For this reason, the usage of animal model systems to discover the early steps in the pathologic cascade is required. These include exposure to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which selectively kills dopamine neurons in the substantia nigra, and genetic models incorporating mutations in the alpha-synuclein gene that cause disease in human patients. Through the evaluation of these models at multiple time points, it is possible to discover novel gene expression changes that may underlie disease pathogenesis. Specifically, the authors hypothesize that animal models of PD and human PD brains share a gene expression profile that signifies certain aspects of pathogenesis and/or recovery-resistance. To test this and similar hypotheses, the authors and others have utilized new microarray technology that enables the sampling of thousands of genes' expression level in one assay. Because the technology is fairly new and results can vary depending on methods used, results must be evaluated with care. Multiple array and data-mining options can be used to make the most accurate inferences as to differentially expressed genes in each set of samples. The authors developed a fusion classifier approach whereby individual data-mining algorithms generate lists of significant genes. The lists are subsequently queried, and only genes unanimously called significant are retained for further validation. Although the authors' approach identified hundreds of differentially expressed genes in each of three PD systems, only a few were common between the human and animal substantia nigra. These were related to dopamine phenotype, synaptic function, and the mitochondrial metabolism, implicating the presynaptic terminal as a primary site of injury. The time course of the authors' experiments indicates that if the synaptic changes could be prevented, this may alleviate some cell death, in that these changes precede neuronal loss.

Restoration of DSCR1 to disomy in the trisomy 16 mouse model of Down syndrome does not correct cardiac or craniofacial development anomalies

The Down syndrome critical region 1 (DSCR1) gene is located in syntenic regions of human chromosome 21 and mouse chromosome 16 and encodes a regulatory protein in the calcineurin/NFAT pathway. DSCR1 expression in the embryonic brain, craniofacial structures, and heart is consistent with a role in contributing to Down syndrome developmental anomalies. In the trisomy 16 (Ts16) murine model of Down syndrome, expression of DSCR1 isoforms is elevated and NFAT transcriptional activity is decreased in the developing heart and brain. The individual contribution of DSCR1 to Down syndrome-related anomalies was examined by specific restoration of DSCR1 to disomic levels in Ts16 embryos. However, genetic restoration of DSCR1 did not rescue major morphological abnormalities in cardiac or craniofacial development. These data demonstrate that trisomy of DSCR1 alone does not significantly contribute to developmental defects in Ts16 mice and underscore the complexity of developmental anomalies associated with Down syndrome.

Drosophila melanogaster homolog of Down syndrome critical region 1 is critical for mitochondrial function

Mitochondrial dysfunction has emerged as a common theme that underlies numerous neurological disorders, including Down syndrome. Down syndrome cultures and tissues show mitochondrial damage such as impaired mitochondrial enzyme activities, defective mitochondrial DNA repairs and accumulation of toxic free radicals, but the cause of mitochondrial dysfunction remains elusive. Here we demonstrate that the Drosophila melanogaster homolog of human Down syndrome critical region gene 1 (DSCR1), nebula (also known as sarah, sra), has a crucial role in the maintenance of mitochondrial function and integrity. We report that nebula protein is located in the mitochondria. An alteration in the abundance of nebula affects mitochondrial enzyme activities, mitochondrial DNA content, and the number and size of mitochondria. Furthermore, nebula interacts with the ADP/ATP translocator and influences its activity. These results identify nebula/DSCR1 as a regulator of mitochondrial function and integrity and further suggest that an increased level of DSCR1 may contribute to the mitochondrial dysfunction seen in Down syndrome.

The role of calcineurin in amyloid-beta-peptides-mediated cell death

Amyloid beta-peptide (Abeta) is widely held to be associated with Alzheimer's disease. It was previously demonstrated by our group that Abeta induces cell death by an apoptotic process. We report here that activation of the caspase-3 apoptotic cascade is regulated by calcineurin-mediated BAD dephosphorylation. Calcineurin inhibitors were also proven to be effective by preventing the loss of mitochondrial membrane potential (Delta Psim) induced by Abeta, not allowing cytochrome c release from mitochondria and subsequently caspase-3 activation. Considering the results presented, we argue that calcineurin activation and BAD dephosphorylation are upstream in premitochondrial signaling events leading to caspase-3 activation in Abeta-peptide-treated cells.

Depolarization of neural cells induces transcription of the Down syndrome critical region 1 isoform 4 via a calcineurin/nuclear factor of activated T cells-dependent pathway

In this study we showed that the transcriptional regulation of Down syndrome critical region isoform 4 (DSCR1.4) is mediated by the calcineurin/nuclear factor of activated T cells (NFAT) pathway in neural cells. Stimuli that elicit an increase in the intracellular concentrations of calcium, such as membrane depolarization, induced de novo transcription of DSCR1.4, with mRNA expression peaking after 4 h and then declining. Action via the physiologically relevant L-type calcium channel was confirmed by blockade with nifedipine and verapamil. This calcium-dependent transcription of DSCR1.4 was inhibited by the calcineurin inhibitors cyclosporin A and FK506. Deletional analysis showed that the calcium- and calcineurin-dependent activation is mediated by the promoter region between nucleotides -350 and -166, a region that contains putative NFAT-binding motifs. Exogenous NFATc2 potently augmented the DSCR1.4 promoter transcriptional activity, and the involvement of endogenous NFAT signaling pathway in DSCR1.4 transcription was confirmed by the suppression of depolarization-inducible promoter activity with the NFAT inhibitor peptide VIVIT. Exogenous overexpression of DSCR1 protein (calcipressin 1) resulted in the inhibition of the transcription of DSCR1.4 and NFAT-dependent signaling. These findings suggest that calcineurin-dependent induction of DSCR1.4 product may represent an important auto-regulatory mechanism for the homeostatic control of NFAT signaling in neural cells.

Expression level of sarah, a homolog of DSCR1, is critical for ovulation and female courtship behavior in Drosophila melanogaster

To better understand the genetic bases of postmating responses in Drosophila melanogaster females, we screened a collection of P{GS} insertion lines and identified two insertions in sarah (sra), whose misexpression in the nervous system induced high levels of ovulation in virgins. The gene sra encodes a protein similar to human Down syndrome critical region 1 (DSCR1). The ovulation phenotype was reproduced in transgenic virgins expressing UAS-sra in the nervous system. The flies also extruded the ovipositor toward courting males as seen in wild-type mated females, supporting the notion that ovulation and behavioral patterns are physiologically coupled. The sra insertions were found to be hypomorphic alleles with reduced expression levels. Females homozygous for these alleles show: (1) spontaneous ovulation in virgins, (2) sterility with impaired meiotic progression, and (3) compromised postmating responses with lower ovulation level, higher remating rate, and shorter period for restoration of receptivity. No obvious defects were observed in the homozygous males. The gene sra is predominantly expressed in oocytes, nurse cells, and the nervous system. Taken together, these results indicate that the expression level of sra is critical for ovulation and female courtship behavior, including their postmating changes.

PP2B isolated from human brain preferentially dephosphorylates Ser-262 and Ser-396 of the Alzheimer disease abnormally hyperphosphorylated tau

PP2B is one of the major serine/threonine phosphatases in the brain. We quantitated the dephosphorylation of various sites of Alzheimer disease abnormally hyperphosphorylated tau by PP2B purified from six (three Alzheimer and three control) autopsied human brains. The purified PP2B was essentially homogenous holoenzyme as determined by SDS-PAGE, Western blot analyses and biochemical characterization. Purified PP2B from all six brains efficiently dephosphorylated (32)P-tau with specific activities ranging from 684-1286 pmol (32)Pi/mg/min. Estimated by dot-blot analyses, the purified PP2B (on average from six brains) dephosphorylated Alzheimer tau at pS199, pT217, pS262, pS396 and pS422 by 38%, 32%, 63%, 78%, and 32%, respectively. Dephosphorylation of tau at pT181, pS202, pT205, pT212, pS214, and pS404 by PP2B was undetectable. The preferential dephosphorylation of Ser262 and Ser396 by PP2B suggests a possible involvement of this phosphatase in Alzheimer neurofibrillary degeneration.