Cellular prion protein mediates impairment of synaptic plasticity by amyloid-beta oligomers.

A pathological hallmark of Alzheimer's disease is an accumulation of insoluble plaque containing the amyloid-beta peptide of 40-42 amino acid residues. Prefibrillar, soluble oligomers of amyloid-beta have been recognized to be early and key intermediates in Alzheimer's-disease-related synaptic dysfunction. At nanomolar concentrations, soluble amyloid-beta oligomers block hippocampal long-term potentiation, cause dendritic spine retraction from pyramidal cells and impair rodent spatial memory. Soluble amyloid-beta oligomers have been prepared from chemical syntheses, transfected cell culture supernatants, transgenic mouse brain and human Alzheimer's disease brain. Together, these data imply a high-affinity cell-surface receptor for soluble amyloid-beta oligomers on neurons-one that is central to the pathophysiological process in Alzheimer's disease. Here we identify the cellular prion protein (PrP(C)) as an amyloid-beta-oligomer receptor by expression cloning. Amyloid-beta oligomers bind with nanomolar affinity to PrP(C), but the interaction does not require the infectious PrP(Sc) conformation. Synaptic responsiveness in hippocampal slices from young adult PrP null mice is normal, but the amyloid-beta oligomer blockade of long-term potentiation is absent. Anti-PrP antibodies prevent amyloid-beta-oligomer binding to PrP(C) and rescue synaptic plasticity in hippocampal slices from oligomeric amyloid-beta. Thus, PrP(C) is a mediator of amyloid-beta-oligomer-induced synaptic dysfunction, and PrP(C)-specific pharmaceuticals may have therapeutic potential for Alzheimer's disease.

Novel neurotrophic factor CDNF protects and rescues midbrain dopamine neurons in vivo.

In Parkinson's disease, brain dopamine neurons degenerate most prominently in the substantia nigra. Neurotrophic factors promote survival, differentiation and maintenance of neurons in developing and adult vertebrate nervous system. The most potent neurotrophic factor for dopamine neurons described so far is the glial-cell-line-derived neurotrophic factor (GDNF). Here we have identified a conserved dopamine neurotrophic factor (CDNF) as a trophic factor for dopamine neurons. CDNF, together with its previously described vertebrate and invertebrate homologue the mesencephalic-astrocyte-derived neurotrophic factor, is a secreted protein with eight conserved cysteine residues, predicting a unique protein fold and defining a new, evolutionarily conserved protein family. CDNF (Armetl1) is expressed in several tissues of mouse and human, including the mouse embryonic and postnatal brain. In vivo, CDNF prevented the 6-hydroxydopamine (6-OHDA)-induced degeneration of dopaminergic neurons in a rat experimental model of Parkinson's disease. A single injection of CDNF before 6-OHDA delivery into the striatum significantly reduced amphetamine-induced ipsilateral turning behaviour and almost completely rescued dopaminergic tyrosine-hydroxylase-positive cells in the substantia nigra. When administered four weeks after 6-OHDA, intrastriatal injection of CDNF was able to restore the dopaminergic function and prevent the degeneration of dopaminergic neurons in substantia nigra. Thus, CDNF was at least as efficient as GDNF in both experimental settings. Our results suggest that CDNF might be beneficial for the treatment of Parkinson's disease.

Memory impairment in transgenic Alzheimer mice requires cellular prion protein.

Soluble oligomers of the amyloid-beta (Abeta) peptide are thought to play a key role in the pathophysiology of Alzheimer's disease (AD). Recently, we reported that synthetic Abeta oligomers bind to cellular prion protein (PrP(C)) and that this interaction is required for suppression of synaptic plasticity in hippocampal slices by oligomeric Abeta peptide. We hypothesized that PrP(C) is essential for the ability of brain-derived Abeta to suppress cognitive function. Here, we crossed familial AD transgenes encoding APPswe and PSen1DeltaE9 into Prnp-/- mice to examine the necessity of PrP(C) for AD-related phenotypes. Neither APP expression nor Abeta level is altered by PrP(C) absence in this transgenic AD model, and astrogliosis is unchanged. However, deletion of PrP(C) expression rescues 5-HT axonal degeneration, loss of synaptic markers, and early death in APPswe/PSen1DeltaE9 transgenic mice. The AD transgenic mice with intact PrP(C) expression exhibit deficits in spatial learning and memory. Mice lacking PrP(C), but containing Abeta plaque derived from APPswe/PSen1DeltaE9 transgenes, show no detectable impairment of spatial learning and memory. Thus, deletion of PrP(C) expression dissociates Abeta accumulation from behavioral impairment in these AD mice, with the cognitive deficits selectively requiring PrP(C).

Genetic variants of Nogo-66 receptor with possible association to schizophrenia block myelin inhibition of axon growth.

In schizophrenia, genetic predisposition has been linked to chromosome 22q11 and myelin-specific genes are misexpressed in schizophrenia. Nogo-66 receptor 1 (NGR or RTN4R) has been considered to be a 22q11 candidate gene for schizophrenia susceptibility because it encodes an axonal protein that mediates myelin inhibition of axonal sprouting. Confirming previous studies, we found that variation at the NGR locus is associated with schizophrenia in a Caucasian case-control analysis, and this association is not attributed to population stratification. Within a limited set of schizophrenia-derived DNA samples, we identified several rare NGR nonconservative coding sequence variants. Neuronal cultures demonstrate that four different schizophrenia-derived NgR1 variants fail to transduce myelin signals into axon inhibition, and function as dominant negatives to disrupt endogenous NgR1. This provides the first evidence that certain disease-derived human NgR1 variants are dysfunctional proteins in vitro. Mice lacking NgR1 protein exhibit reduced working memory function, consistent with a potential endophenotype of schizophrenia. For a restricted subset of individuals diagnosed with schizophrenia, the expression of dysfunctional NGR variants may contribute to increased disease risk.

Neuralized-2: expression in human and rodents and interaction with Delta-like ligands.

Delta-Notch signaling is a universal cell-cell communication pathway crucial for numerous developmental and physiological processes. Several proteins interact with and regulate the Notch pathway, including the E3 ubiquitin ligase Neuralized (Neur) that influences the stability and activity of Notch ligands. In mammals there are two homologs of Neur, Neur1 and Neur2, that both can interact with Notch ligands Delta-like1 and Jagged1. Here, we show that Neur2, in contrast to Neur1, is highly expressed during embryonic development of the brain and several non-neural tissues and its mRNA levels subside postnatally. In the hippocampal neurons of the adult brain Neur2 transcripts, in contrast to Neur1, are excluded from the dendrites. Neur2 protein has a predominantly cytoplasmic localization. We also show that in addition to Delta-like1, Neur1 and Neur2 interact with another Notch ligand, Delta-like4.

Cellular prion protein as a therapeutic target in Alzheimer's disease.

Soluble oligomeric species of amyloid-ß (Aß) peptide are presumed to be drivers of synaptic impairment, and the resulting cognitive dysfunction in Alzheimer's disease. In 2009, cellular prion protein (PrPC) was identified in a genome-wide screen as a high-affinity receptor for Aß oligomers, and since then, many studies have explored the role of PrPC in Alzheimer's disease. Herein, I systematically assess the current level of target validation for PrPC in Alzheimer's disease and the merits of the identified approaches to therapeutically affect the PrPC:Aß oligomer-interaction. The interaction of Aß oligomers with PrPC in mice impairs hippocampal long-term potentiation, memory, and learning in a manner that involves Fyn, tau, and glutamate receptors. Furthermore, PrPC acts to catalyze the formation of certain Aß oligomeric species in the synapse and may mediate the toxic effects of other ß-sheet rich oligomers as well. Therapeutic approaches utilizing soluble PrPC ectodomain or monoclonal antibodies targeting PrPC can at least partially prevent the neurotoxic effects of Aß oligomers in mice.

Antibody engineering and therapeutics, The Annual Meeting of the Antibody Society: December 8-12, 2013, Huntington Beach, CA.

The 24th Antibody Engineering & Therapeutics meeting brought together a broad range of participants who were updated on the latest advances in antibody research and development. Organized by IBC Life Sciences, the gathering is the annual meeting of The Antibody Society, which serves as the scientific sponsor. Preconference workshops on 3D modeling and delineation of clonal lineages were featured, and the conference included sessions on a wide variety of topics relevant to researchers, including systems biology; antibody deep sequencing and repertoires; the effects of antibody gene variation and usage on antibody response; directed evolution; knowledge-based design; antibodies in a complex environment; polyreactive antibodies and polyspecificity; the interface between antibody therapy and cellular immunity in cancer; antibodies in cardiometabolic medicine; antibody pharmacokinetics, distribution and off-target toxicity; optimizing antibody formats for immunotherapy; polyclonals, oligoclonals and bispecifics; antibody discovery platforms; and antibody-drug conjugates.

LRRTM3 is dispensable for amyloid-ß production in mice.

Neuronal LRRTM3 (leucine-rich repeat transmembrane 3) protein has been reported to promote amyloid-ß protein precursor (AßPP) processing and LRRTM3 is a candidate gene in late-onset Alzheimer's disease. To address the role of LRRTM3 in AßPP processing and amyloid-ß (Aß) production in vivo, we analyzed amyloidogenic processing of AßPP in the brains of LRRTM3-deficient mice and transgenic AßPP/PS1 mice with or without LRRTM3. We did not find differences between the genotypes in the levels of Aß or AßPP C-terminal fragments indicating that LRRTM3 is not an essential regulator of Aß production in adult mice. Moreover, Aß levels in primary cortical neurons were similar between the genotypes, indicating that LRRTM3 is not required for Aß generation in developing mice.

An unbiased expression screen for synaptogenic proteins identifies the LRRTM protein family as synaptic organizers.

Delineating the molecular basis of synapse development is crucial for understanding brain function. Cocultures of neurons with transfected fibroblasts have demonstrated the synapse-promoting activity of candidate molecules. Here, we performed an unbiased expression screen for synaptogenic proteins in the coculture assay using custom-made cDNA libraries. Reisolation of NGL-3/LRRC4B and neuroligin-2 accounts for a minority of positive clones, indicating that current understanding of mammalian synaptogenic proteins is incomplete. We identify LRRTM1 as a transmembrane protein that induces presynaptic differentiation in contacting axons. All four LRRTM family members exhibit synaptogenic activity, LRRTMs localize to excitatory synapses, and artificially induced clustering of LRRTMs mediates postsynaptic differentiation. We generate LRRTM1(-/-) mice and reveal altered distribution of the vesicular glutamate transporter VGLUT1, confirming an in vivo synaptic function. These results suggest a prevalence of LRR domain proteins in trans-synaptic signaling and provide a cellular basis for the reported linkage of LRRTM1 to handedness and schizophrenia.

Characterization of myelin ligand complexes with neuronal Nogo-66 receptor family members.

Nogo, MAG, and OMgp are myelin-associated proteins that bind to a neuronal Nogo-66 receptor (NgR/NgR1) to limit axonal regeneration after central nervous system injury. Within Nogo-A, two separate domains are known interact with NgR1. NgR1 is the founding member of the three-member NgR family, whereas Nogo-A (RTN4A) belongs to a four-member reticulon family. Here, we systematically mapped the interactions between these superfamilies, demonstrating novel nanomolar interactions of RTN2 and RTN3 with NgR1. Because RTN3 is expressed in spinal cord white matter, it may have a role in myelin inhibition of axonal growth. Further analysis of the Nogo-A and NgR1 interactions revealed a novel third interaction site between the proteins, suggesting a trivalent Nogo-A interaction with NgR1. We also confirmed here that MAG binds to NgR2, but not to NgR3. Unexpectedly, we found that OMgp interacts with MAG with a higher affinity compared with NgR1. To better define how these multiple structurally distinct ligands bind to NgR1, we examined a series of Ala-substituted NgR1 mutants for ligand binding activity. We found that the core of the binding domain is centered in the middle of the concave surface of the NgR1 leucine-rich repeat domain and surrounded by differentially utilized residues. This detailed knowledge of the molecular interactions between NgR1 and its ligands is imperative when assessing options for development of NgR1-based therapeutics for central nervous system injuries.

A novel gene family encoding leucine-rich repeat transmembrane proteins differentially expressed in the nervous system.

Leucine-rich repeat containing proteins are involved in protein-protein interactions and they regulate numerous cellular events during nervous system development and disease. Here we have isolated and characterized a new four-membered family of genes from human and mouse, named LRRTMs, that encode putative leucine-rich repeat transmembrane proteins. Human and mouse LRRTMs are highly conserved, and orthologous genes exist in other vertebrates but not in invertebrates. All LRRTMs, except LRRTM4, are located in the introns of different alpha-catenin genes, suggesting coevolution of these two gene families. We show by in situ hybridization and RT-PCR that LRRTM mRNAs are predominantly expressed in the nervous system and that each LRRTM possesses a specific, partially nonoverlapping expression pattern. The structure and expression profile of LRRTM mRNAs suggest that they may have a role in the development and maintenance of the vertebrate nervous system.

Two novel mammalian Nogo receptor homologs differentially expressed in the central and peripheral nervous systems.

The regenerative capacity of the adult mammalian central nervous system is restricted by the myelinating oligodendrocytes that form a nonpermissive environment for axonal growth. Currently only the Nogo receptor (NgR), in complex with p75(NTR) neurotrophin receptor is known to be involved in this inhibitory signalling in neurons. NgR is a common receptor for the three inhibitory myelin proteins Nogo-A, OMgp, and MAG. Here we describe two novel Nogo receptor gene homologs named NGRL2 and NGRL3 from human and mouse that, like NGR, encode putative leucine-rich repeat containing GPI-anchored proteins. We show by in situ hybridisation and by RT-PCR that NGRL mRNAs are predominantly expressed in the neurons of the embryonic and adult central and peripheral nervous systems, and that they together with NGR possess distinct and partially nonoverlapping expression patterns. We also show that all four members of the reticulon family, including Nogo-A, are widely expressed in the nervous system, and therefore are possible ligands for the NgRLs.