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1.  Glutamatergic Transmission Aberration: A Major Cause of Behavioral Deficits in a Murine Model of Down's Syndrome 
The Journal of Neuroscience  2014;34(15):5099-5106.
Trisomy 21, or Down's syndrome (DS), is the most common genetic cause of intellectual disability. Altered neurotransmission in the brains of DS patients leads to hippocampus-dependent learning and memory deficiency. Although genetic mouse models have provided important insights into the genes and mechanisms responsible for DS-specific changes, the molecular mechanisms leading to memory deficits are not clear. We investigated whether the segmental trisomy model of DS, Ts[Rb(12.1716)]2Cje (Ts2), exhibits hippocampal glutamatergic transmission abnormalities and whether these alterations cause behavioral deficits. Behavioral assays demonstrated that Ts2 mice display a deficit in nest building behavior, a measure of hippocampus-dependent nonlearned behavior, as well as dysfunctional hippocampus-dependent spatial memory tested in the object-placement and the Y-maze spontaneous alternation tasks. Magnetic resonance spectra measured in the hippocampi revealed a significantly lower glutamate concentration in Ts2 as compared with normal disomic (2N) littermates. The glutamate deficit accompanied hippocampal NMDA receptor1 (NMDA-R1) mRNA and protein expression level downregulation in Ts2 compared with 2N mice. In concert with these alterations, paired-pulse analyses suggested enhanced synaptic inhibition and/or lack of facilitation in the dentate gyrus of Ts2 compared with 2N mice. Ts2 mice also exhibited disrupted synaptic plasticity in slice recordings of the hippocampal CA1 region. Collectively, these findings imply that deficits in glutamate and NMDA-R1 may be responsible for impairments in synaptic plasticity in the hippocampus associated with behavioral dysfunctions in Ts2 mice. Thus, these findings suggest that glutamatergic deficits have a significant role in causing intellectual disabilities in DS.
PMCID: PMC3983795  PMID: 24719089
Down's syndrome; glutamate; LTP; NMDA receptors; spatial memory
2.  Therapeutic effects of remediating autophagy failure in a mouse model of Alzheimer disease by enhancing lysosomal proteolysis 
Autophagy  2011;7(7):788-789.
The extensive autophagic-lysosomal pathology in Alzheimer disease (AD) brain has revealed a major defect in the proteolytic clearance of autophagy substrates. Autophagy failure contributes on several levels to AD pathogenesis and has become an important therapeutic target for AD and other neurodegenerative diseases. We recently observed broad therapeutic effects of stimulating autophagic-lysosomal proteolysis in the TgCRND8 mouse model of AD that exhibits defective proteolytic clearance of autophagic substrates, robust intralysosomal amyloid-β peptide (Aβ) accumulation, extracellular β-amyloid deposition and cognitive deficits. By genetically deleting the lysosomal cysteine protease inhibitor, cystatin B (CstB), to selectively restore depressed cathepsin activities, we substantially cleared Aβ, ubiquitinated proteins and other autophagic substrates from autolysosomes/lysosomes and rescued autophagic-lysosomal pathology, as well as reduced total Aβ40/42 levels and extracellular amyloid deposition, highlighting the underappreciated importance of the lysosomal system for Aβ clearance. Most importantly, lysosomal remediation prevented the marked learning and memory deficits in TgCRND8 mice. Our findings underscore the pathogenic significance of autophagic-lysosomal dysfunction in AD and demonstrate the value of reversing this dysfunction as an innovative therapeutic strategy for AD.
PMCID: PMC3359468  PMID: 21464620
autophagy; lysosome; cathepsin; cystatin B; proteolysis; Alzheimer disease; transgenic
3.  Reversal of autophagy dysfunction in the TgCRND8 mouse model of Alzheimer's disease ameliorates amyloid pathologies and memory deficits 
Brain  2010;134(1):258-277.
Autophagy, a major degradative pathway for proteins and organelles, is essential for survival of mature neurons. Extensive autophagic-lysosomal pathology in Alzheimer’s disease brain contributes to Alzheimer’s disease pathogenesis, although the underlying mechanisms are not well understood. Here, we identified and characterized marked intraneuronal amyloid-β peptide/amyloid and lysosomal system pathology in the Alzheimer’s disease mouse model TgCRND8 similar to that previously described in Alzheimer’s disease brains. We further establish that the basis for these pathologies involves defective proteolytic clearance of neuronal autophagic substrates including amyloid-β peptide. To establish the pathogenic significance of these abnormalities, we enhanced lysosomal cathepsin activities and rates of autophagic protein turnover in TgCRND8 mice by genetically deleting cystatin B, an endogenous inhibitor of lysosomal cysteine proteases. Cystatin B deletion rescued autophagic-lysosomal pathology, reduced abnormal accumulations of amyloid-β peptide, ubiquitinated proteins and other autophagic substrates within autolysosomes/lysosomes and reduced intraneuronal amyloid-β peptide. The amelioration of lysosomal function in TgCRND8 markedly decreased extracellular amyloid deposition and total brain amyloid-β peptide 40 and 42 levels, and prevented the development of deficits of learning and memory in fear conditioning and olfactory habituation tests. Our findings support the pathogenic significance of autophagic-lysosomal dysfunction in Alzheimer’s disease and indicate the potential value of restoring normal autophagy as an innovative therapeutic strategy for Alzheimer’s disease.
PMCID: PMC3009842  PMID: 21186265
autophagy; lysosome; cystatin B; cathepsin; Alzheimer’s disease
4.  Induction of Autophagy by Cystatin C: A Mechanism That Protects Murine Primary Cortical Neurons and Neuronal Cell Lines 
PLoS ONE  2010;5(3):e9819.
Cystatin C (CysC) expression in the brain is elevated in human patients with epilepsy, in animal models of neurodegenerative conditions, and in response to injury, but whether up-regulated CysC expression is a manifestation of neurodegeneration or a cellular repair response is not understood. This study demonstrates that human CysC is neuroprotective in cultures exposed to cytotoxic challenges, including nutritional-deprivation, colchicine, staurosporine, and oxidative stress. While CysC is a cysteine protease inhibitor, cathepsin B inhibition was not required for the neuroprotective action of CysC. Cells responded to CysC by inducing fully functional autophagy via the mTOR pathway, leading to enhanced proteolytic clearance of autophagy substrates by lysosomes. Neuroprotective effects of CysC were prevented by inhibiting autophagy with beclin 1 siRNA or 3-methyladenine. Our findings show that CysC plays a protective role under conditions of neuronal challenge by inducing autophagy via mTOR inhibition and are consistent with CysC being neuroprotective in neurodegenerative diseases. Thus, modulation of CysC expression has therapeutic implications for stroke, Alzheimer's disease, and other neurodegenerative disorders.
PMCID: PMC2843718  PMID: 20352108
5.  Proteins that bind to the RERMS region of β amyloid precursor protein 
The main objective of this study was to investigate the biological function of β amyloid precursor protein (APP), in particular its nerve growth factor-like activity. We hypothesize that the extracellular domain containing the sequence RERMS, amino acids 328-332 of APP695, represents the active site for this function. Binding assays using peptide fragments of this domain have demonstrated specific and saturable binding to the cell surface with affinity in the low nanomolar range. This induced our quest for an APP-specific receptor. We chose different peptide fragments of the RERMS domain as ligands and displacing agents on affinity columns to purify APP binding molecules. Amino acid microsequencing yielded partial sequences of serum albumin, actin, two novel proteins of 41 and 63 kDa and human Collapsin Response Mediator Protein-2 (hCRMP-2). Because both APP and hCRMP-2 promote neuronal outgrowth and use a common signaling pathway, APP could be acting through a semaphorin receptor as well.
PMCID: PMC1896148  PMID: 17335780
β Amyloid Precursor Protein (APP); Neurotropic Activity; Receptor Candidates; Lipid Rafts; Semaphorin Family

Results 1-5 (5)