Philip T. T. Ly

Valproic acid inhibits Aβ production, neuritic plaque formation, and behavioral deficits in Alzheimer's disease mouse models

Neuritic plaques in the brains are one of the pathological hallmarks of Alzheimers disease (AD). Amyloid β-protein (Aβ), the central component of neuritic plaques, is derived from β-amyloid precursor protein (APP) after β- and γ-secretase cleavage. The molecular mechanism underlying the pathogenesis of AD is not yet well defined, and there has been no effective treatment for AD. Valproic acid (VPA) is one of the most widely used anticonvulsant and mood-stabilizing agents for treating epilepsy and bipolar disorder. We found that VPA decreased Aβ production by inhibiting GSK-3β–mediated γ-secretase cleavage of APP both in vitro and in vivo. VPA treatment significantly reduced neuritic plaque formation and improved memory deficits in transgenic AD model mice. We also found that early application of VPA was important for alleviating memory deficits of AD model mice. Our study suggests that VPA may be beneficial in the prevention and treatment of AD.

Valproic acid inhibits Ab production, neuritic plaque formation, and behavioral deficits in Alzheimer's disease mouse models

Qing et al. 2008. J. Exp. Med. doi:10.1084/jem.20081588 [OpenUrl][1][Abstract/FREE Full Text][2] [1]: {openurl}?query=rft_id%253Dinfo%253Adoi%252F10.1084%252Fjem.20081588%26rft_id%253Dinfo%253Apmid%252F18955571%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%

Inhibition of GSK3β-mediated BACE1 expression reduces Alzheimer-associated phenotypes

Deposition of amyloid β protein (Aβ) to form neuritic plaques in the brain is the pathological hallmark of Alzheimers disease (AD). Aβ is generated from sequential cleavages of the β-amyloid precursor protein (APP) by the β- and γ-secretases, and β-site APP-cleaving enzyme 1 (BACE1) is the β-secretase essential for Aβ generation. Previous studies have indicated that glycogen synthase kinase 3 (GSK3) may play a role in APP processing by modulating γ-secretase activity, thereby facilitating Aβ production. There are two highly conserved isoforms of GSK3: GSK3α and GSK3β. We now report that specific inhibition of GSK3β, but not GSK3α, reduced BACE1-mediated cleavage of APP and Aβ production by decreasing BACE1 gene transcription and expression. The regulation of BACE1 gene expression by GSK3β was dependent on NF-κB signaling. Inhibition of GSK3 signaling markedly reduced Aβ deposition and neuritic plaque formation, and rescued memory deficits in the double transgenic AD model mice. These data provide evidence for regulation of BACE1 expression and AD pathogenesis by GSK3β and that inhibition of GSK3 signaling can reduce Aβ neuropathology and alleviate memory deficits in AD model mice. Our study suggests that interventions that specifically target the β-isoform of GSK3 may be a safe and effective approach for treating AD.

NF-κB signaling inhibits ubiquitin carboxyl-terminal hydrolase L1 gene expression.

J. Neurochem. (2011) 116, 1160–1170.

Detection of Neuritic Plaques in Alzheimer's Disease Mouse Model

Alzheimers disease (AD) is the most common neurodegenerative disorder leading to dementia. Neuritic plaque formation is one of the pathological hallmarks of Alzheimers disease. The central component of neuritic plaques is a small filamentous protein called amyloid β protein (Aβ)1, which is derived from sequential proteolytic cleavage of the beta-amyloid precursor protein (APP) by β-secretase and γ-secretase. The amyloid hypothesis entails that Aγ-containing plaques as the underlying toxic mechanism in AD pathology2. The postmortem analysis of the presence of neuritic plaque confirms the diagnosis of AD. To further our understanding of Aγ neurobiology in AD pathogenesis, various mouse strains expressing AD-related mutations in the human APP genes were generated. Depending on the severity of the disease, these mice will develop neuritic plaques at different ages. These mice serve as invaluable tools for studying the pathogenesis and drug development that could affect the APP processing pathway and neuritic plaque formation. In this protocol, we employ an immunohistochemical method for specific detection of neuritic plaques in AD model mice. We will specifically discuss the preparation from extracting the half brain, paraformaldehyde fixation, cryosectioning, and two methods to detect neurotic plaques in AD transgenic mice: immunohistochemical detection using the ABC and DAB method and fluorescent detection using thiofalvin S staining method.

Down-regulation of MIF by NFκB under hypoxia accelerated neuronal loss during stroke

Neuronal apoptosis is one of the major causes of poststroke neurological deficits. Inflammation during the acute phase of stroke results in nuclear translocation of NFκB in affected cells in the infarct area. Macrophage migration inhibitory factor (MIF) promotes cardiomyocyte survival in mice following heart ischemia. However, the role of MIF during stroke remains limited. In this study, we showed that MIF expression is down‐regulated by 0.75 ± 0.10‐fold of the control in the infarct area in the mouse brains. Two functional cis‐acing NFκB response elements were identified in the human MIF promoter. Dual activation of hypoxia and NFκB signaling resulted in significant reduction of MIF promoter activity to 0.86 ± 0.01‐fold of the control. Furthermore, MIF reduced caspase‐3 activation and protected neurons from oxidative stressand in vitro ischemia/reperfusion‐induced apoptosis. H2O2 significantly induced cell death with 12.81 ± 0.58‐fold increase of TUNEL‐positive cells, and overexpression of MIF blocked the H2O2‐induced cell death. Disruption of the MIF gene in MIF‐knockout mice resulted in caspase‐3 activation, neuronal loss, and increased infarct development during stroke in vivo. The infarct volume was increased from 6.51 ± 0.74% in the wild‐type mice to 9.07 ± 0.66% in the MIF‐knockout mice. Our study demonstrates that MIF exerts a neuronal protective effect and that down‐regulation of MIF by NFκB‐mediated signaling under hypoxia accelerates neuronal loss during stroke. Our results suggest that MIF is an important molecule for preserving a longer time window for stroke treatment, and strategies to maintain MIF expression at physiological level could have beneficial effects for stroke patients.—Zhang, S., Zis, O., Ly, P. T. T., Wu, Y., Zhang, S., Zhang, M., Cai, F., Bucala, R., Shyu, W.‐C., Song, W. Down‐regulation of MIF by NFκB under hypoxia accelerated neuronal loss during stroke. FASEB J. 28, 4394–4407 (2014). www.fasebj.org

Aberrant Expression of RCAN1 in Alzheimer's Pathogenesis: A New Molecular Mechanism and a Novel Drug Target

AD, a devastating neurodegenerative disorder, is the most common cause of dementia in the elderly. Patients with AD are characterized by three hallmarks of neuropathology including neuritic plaque deposition, neurofibrillary tangle formation, and neuronal loss. Growing evidences indicate that dysregulation of regulator of calcineurin 1 (RCAN1) plays an important role in the pathogenesis of AD. Aberrant RCAN1 expression facilitates neuronal apoptosis and Tau hyperphosphorylation, leading to neuronal loss and neurofibrillary tangle formation. This review aims to describe the recent advances of the regulation of RCAN1 expression and its physiological functions. Moreover, the AD risk factors-induced RCAN1 dysregulation and its role in promoting neuronal loss, synaptic impairments and neurofibrillary tangle formation are summarized. Furthermore, we provide an outlook into the effects of RCAN1 dysregulation on APP processing, Aβ generation and neuritic plaque formation, and the possible underlying mechanisms, as well as the potential of targeting RCAN1 as a new therapeutic approach.

Loss of activated CaMKII at the synapse underlies Alzheimer’s disease memory loss

memory loss. At the microscopic level, early symptoms of memory perturbation likely involves the loss of synapses, which is one of the strong correlates of cognitive integrity. Many studies also have demonstrated that memory loss originates from synaptic failure, which precedes neuronal death. However, the mechanism by which synaptic integrity becomes compromised has not been clearly defined. In this recent article, Reese and colleagues demonstrated that the dysregulation of the calcium-camodulin kinase IIa (CaMKII) activity at the dendritic arbor could underlie the pathology of memory loss seen in AD patients (Reese et al. 2011). Under physiological condition, the number of NMDAtype glutmate receptor is tightly associated with synaptic transmission. Moreover, NMDA receptors can either induce long-term potentiation (LTP) or long-term depression (LTD), depending on the extent of intracellular calcium rise in the dendritic spines and the activation of downstream signal transduction cascades (Kullmann and Lamsa 2007). The state of protein phosphorylation is highly important in regulating the integrity of the post-synaptic density. For example, protein phosphorylation of various glutamate receptors will facilitate trafficking and insertion into the synaptic site. Moreover, protein phosphorylation of docking proteins by protein kinases at the synapse will enhance protein–protein binding and formation of new spines. Conversely, protein dephosphorylation by phosphatase at the synapse could be involved in receptor desensitization and internalization. The extent of intracellular rise in calcium levels appears to be the most upstream regulator of protein phosphorylation/dephosphorylation events at the synapse. The induction of LTP requires a higher intracellular calcium rise and activation of a whole series of protein phosphorylation events that lead to synapse stabilization and recruitment of more glutamate receptor to the synaptic site. However, lower intracellular calcium and induction of protein phosphatases lead to glutamate receptor internalization is required for LTD. LTP promotes formation of more dendritic spines associated with learning and memory. In contrast, LTD induces spine shrinkage and synaptic loss. Deposition of amyloid b proteins (Ab) to form neuritic plaque is the hallmark of AD neuropathology. According to the amyloid hypothesis, AD is caused by the abnormal accumulation and aggregation of neurotoxic Ab in the brain. The current emerging concept hypothesizes that it is the soluble oligomeric form of Ab causing impaired synaptic transmission and cognitive functions, and accumulation of Ab triggers a complex cascade of molecular and cellular changes that translates to clinical signs observed in AD patients. Therefore, a thorough understanding of how Ab accumulates and how it compromises synaptic integrity will provide insights to the development of novel therapeutics for treating AD. Ab is derived through two sequential cleavages of the b-amyloid precursor protein. First, the b-secretase (BACE1) cleaves b-amyloid precursor protein at the Asp-1 b-site to generate a C99 fragment then followed by c-secretase cleavage within the transmembrane domain to release Ab (Li et al. 2006). Naturally Ab in brain lysates and cerebrospinal fluids are heterogenous in length, but the majority of research studies conducted used the relatively abundant forms of either 40 or 42 amino acids (Selkoe

Glial and Neuronal Protein Tyrosine Phosphatase Alpha (PTPα) Regulate Oligodendrocyte Differentiation and Myelination

CNS myelination defects occur in mice deficient in receptor-like protein tyrosine phosphatase alpha (PTPα). Here, we investigated the role of PTPα in oligodendrocyte differentiation and myelination using cells and tissues from wild-type (WT) and PTPα knockout (KO) mice. PTPα promoted the timely differentiation of neural stem cell-derived oligodendrocyte progenitor cells (OPCs). Compared to WT OPCs, KO OPC cultures had more NG2+ progenitors, fewer myelin basic protein (MBP)+ oligodendrocytes, and reduced morphological complexity. In longer co-cultures with WT neurons, more KO than WT OPCs remained NG2+ and while equivalent MBP+ populations of WT and KO cells formed, the reduced area occupied by the MBP+ KO cells suggested that their morphological maturation was impeded. These defects were associated with reduced myelin formation in KO OPC/WT neuron co-cultures. Myelin formation was also impaired when WT OPCs were co-cultured with KO neurons, revealing a novel role for neuronal PTPα in myelination. Canonical Wnt/β-catenin signaling is an important regulator of OPC differentiation and myelination. Wnt signaling activity was not dysregulated in OPCs lacking PTPα, but suppression of Wnt signaling by the small molecule XAV939 remediated defects in KO oligodendrocyte differentiation and enhanced myelin formation by KO oligodendrocytes. However, the myelin segments that formed were significantly shorter than those produced by WT oligodendrocytes, raising the possibility of a role for glial PTPα in myelin extension distinct from its pro-differentiating actions. Altogether, this study reveals PTPα as a molecular coordinator of oligodendroglial and neuronal signals that controls multiple aspects of oligodendrocyte development and myelination.

Genomic and Molecular Characterization of Alzheimer Disease

Alzheimer disease (AD) is the most common neurodegenerative disease that afflicts mankind. Tremendous efforts have been made in investigating the genetic underpinnings and molecular pathophysiology of this illness. The heritability of AD is estimated to be around 60% and about 5% of AD cases are familial with early-onset caused by gene mutations. Several genes including APP, PSEN1, PSEN2 and APOE e4 have been identified to be causative or associated with AD. This is an overview of AD from the perspective of some of the latest high throughput technological platforms, including genome-wide association studies (GWAS), transcriptomics, proteomics, metabolomics and epigenetics. These approaches are introduced briefly followed by discussion of some of the more significant endeavors and findings. These results, including putative gene loci, differentially expressed genes, epigenetic effects etc., may provide some of the pieces of the AD puzzle. However a systems approach towards the diverse findings from various platforms will most likely give us a quantum leap in the understanding of AD that should lead to breakthroughs in diagnosis, tracking the disease progress, drug discovery and development.