Shuji Matsuda

Gadd45|[beta]| mediates the NF-|[kappa]|B suppression of JNK signalling by targeting MKK7/JNKK2

NF-κB/Rel transcription factors control apoptosis, also known as programmed cell death. This control is crucial for oncogenesis, cancer chemo-resistance and for antagonizing tumour necrosis factor α (TNFα)-induced killing. With regard to TNFα, the anti-apoptotic activity of NF-κB involves suppression of the c-Jun N-terminal kinase (JNK) cascade. Using an unbiased screen, we have previously identified Gadd45β/Myd118, a member of the Gadd45 family of inducible factors, as a pivotal mediator of this suppressive activity of NF-κB. However, the mechanisms by which Gadd45β inhibits JNK signalling are not understood. Here, we identify MKK7/JNKK2 — a specific and essential activator of JNK — as a target of Gadd45β, and in fact, of NF-κB itself. Gadd45β binds to MKK7 directly and blocks its catalytic activity, thereby providing a molecular link between the NF-κB and JNK pathways. Importantly, Gadd45β is required to antagonize TNFα-induced cytotoxicity, and peptides disrupting the Gadd45β/MKK7 interaction hinder the ability of Gadd45β, as well as of NF-κB, to suppress this cytotoxicity. These findings establish a basis for the NF-κB control of JNK activation and identify MKK7 as a potential target for anti-inflammatory and anti-cancer therapy.

BRI2 Inhibits Amyloid β-Peptide Precursor Protein Processing by Interfering with the Docking of Secretases to the Substrate

Genetic alterations of amyloid β-peptide (Aβ) production caused by mutations in the Aβ precursor protein (APP) cause familial Alzheimers disease (AD). Mutations in BRI2, a gene of undefined function, are linked to familial British and Danish dementias, which are pathologically and clinically similar to Alzheimers disease. We report that BRI2 is a physiological suppressor of Aβ production. BRI2 restrict docking of γ-secretase to APP and access of α- and β-secretases to their cleavage APP sequences. Alterations of BRI2 by gene targeting or transgenic expression regulate Aβ levels and AD pathology in mouse models of AD. Competitive inhibition of APP processing by BRI2 may provide a new approach to AD therapy and prevention.

β- but not γ-secretase proteolysis of APP causes synaptic and memory deficits in a mouse model of dementia.

A mutation in the BRI2/ITM2b gene causes loss of BRI2 protein leading to familial Danish dementia (FDD). BRI2 deficiency of FDD provokes an increase in amyloid‐β precursor protein (APP) processing since BRI2 is an inhibitor of APP proteolysis, and APP mediates the synaptic/memory deficits in FDD. APP processing is linked to Alzheimer disease (AD) pathogenesis, which is consistent with a common mechanism involving toxic APP metabolites in both dementias. We show that inhibition of APP cleavage by β‐secretase rescues synaptic/memory deficits in a mouse model of FDD. β‐cleavage of APP yields amino‐terminal‐soluble APPβ (sAPPβ) and β‐carboxyl‐terminal fragments (β‐CTF). Processing of β‐CTF by γ‐secretase releases amyloid‐β (Aβ), which is assumed to cause AD. However, inhibition of γ‐secretase did not ameliorate synaptic/memory deficits of FDD mice. These results suggest that sAPPβ and/or β‐CTF, rather than Aβ, are the toxic species causing dementia, and indicate that reducing β‐cleavage of APP is an appropriate therapeutic approach to treating human dementias. Our data and the failures of anti‐Aβ therapies in humans advise against targeting γ‐secretase cleavage of APP and/or Aβ.

JNK-interacting protein-1 promotes transcription of Aβ protein precursor but not Aβ precursor-like proteins, mechanistically different than Fe65

Processing of the amyloid β protein precursor (AβPP) by the β and γ secretases leads to the production of two small peptides, amyloid β and the AβPP intracellular domain (AID, or called elsewhere AICD). Whereas the role of amyloid β in the pathogenesis of Alzheimers disease has been studied extensively, only recently has information begun to accumulate as to the role of AID. Functions identified for AID include its ability to trigger apoptosis and a role in regulating gene transcription, particularly in combination with the AβPP binding protein Fe65. Here, we report that AID in combination with Janus kinase interacting protein-1 (JIP-1) can activate gene expression. We demonstrate that the mechanism is different from activation in combination with Fe65 by first showing that although Fe65 enters the nucleus in the absence of full-length AβPP, JIP-1 does not. Additionally, JIP-1-induced activation is Tip60 independent, whereas a complex with AID, Fe65, and Tip60 is formed for Fe65-induced activation. Finally, and probably most interestingly, we show that although the AβPP family members APLP1 and APLP2 (for amyloid β precursor-like protein) can cause activation in combination with Fe65, APLP1 and APLP2 show little or no activation in combination with JIP-1. This activity for the AID fragment may help explain the unique functions of AβPP relative to its other family members, and changes in gene expression found in Alzheimers disease.

Danish dementia mice suggest that loss of function and not the amyloid cascade causes synaptic plasticity and memory deficits

According to the prevailing “amyloid cascade hypothesis,” genetic dementias such as Alzheimer’s disease and familial Danish dementia (FDD) are caused by amyloid deposits that trigger tauopathy, neurodegeneration, and behavioral/cognitive alterations. To efficiently reproduce amyloid lesions, murine models of human dementias invariably use transgenic expression systems. However, recent FDD transgenic models showed that Danish amyloidosis does not cause memory defects, suggesting that other mechanisms cause Danish dementia. We studied an animal knock-in model of FDD (FDDKI/+) genetically congruous with human cases. FDDKI/+ mice present reduced Bri2 levels, impaired synaptic plasticity and severe hippocampal memory deficits. These animals show no cerebral lesions that are reputed characteristics of human dementia, such as tangles or amyloid plaques. Bri2+/− mice exhibit synaptic and memory deficits similar to FDDKI/+ mice, and memory loss of FDDKI/+ mice is prevented by expression of WT BRI2, indicating that Danish dementia is caused by loss of BRI2 function. Together, the data suggest that clinical dementia in Danish patients occurs via a loss of function mechanism and not as a result of amyloidosis and tauopathy.

APP heterozygosity averts memory deficit in knockin mice expressing the Danish dementia BRI2 mutant

An autosomal dominant mutation in the BRI2/ITM2B gene causes familial Danish dementia (FDD). Analysis of FDDKI mice, a mouse model of FDD genetically congruous to the human disease since they carry one mutant and one wild‐type Bri2/Itm2b allele, has shown that the Danish mutation causes loss of Bri2 protein, synaptic plasticity and memory impairments. BRI2 is a physiological interactor of Aβ‐precursor protein (APP), a gene associated with Alzheimer disease, which inhibits processing of APP. Here, we show that APP/Bri2 complexes are reduced in synaptic membranes of FDDKI mice. Consequently, APP metabolites derived from processing of APP by β‐, α‐ and γ‐secretases are increased in Danish dementia mice. APP haplodeficiency prevents memory and synaptic dysfunctions, consistent with a role for APP metabolites in the pathogenesis of memory and synaptic deficits. This genetic suppression provides compelling evidence that APP and BRI2 functionally interact, and that the neurological effects of the Danish form of BRI2 only occur when sufficient levels of APP are supplied by two alleles. This evidence establishes a pathogenic sameness between familial Danish and Alzheimers dementias.

BRI3 Inhibits Amyloid Precursor Protein Processing in a Mechanistically Distinct Manner from Its Homologue Dementia Gene BRI2

Alzheimer disease (AD) is characterized by senile plaques, which are mainly composed of β amyloid (Aβ) peptides. Aβ is cleaved off from amyloid precursor protein (APP) with consecutive proteolytic processing: β-secretase, followed by γ-secretase. Here, we show that BRI3, a member of the BRI gene family that includes the familial British and Danish dementia gene BRI2, interacts with APP and serves as an endogenous negative regulator of Aβ production. BRI3 colocalizes with APP along neuritis in differentiated N2a cells; endogenous BRI3-APP complexes are readily detectable in mouse brain extract; reducing endogenous BRI3 levels by RNA interference results in increased Aβ secretion. BRI3 resembles BRI2, because BRI3 overexpression reduces both α- and β-APP cleavage. We propose that BRI3 inhibits the various processing of APP by blocking the access of α- and β-secretases to APP. However, unlike BRI2, the binding of BRI3 to the β-secretase cleaved APP C-terminal fragment is negligible and BRI3 does not cause the massive accumulation of this APP fragment, suggesting that, unlike BRI2, BRI3 is a poor γ-cleavage inhibitor. Competitive inhibition of APP processing by BRI3 may provide a new approach to AD therapy and prevention.

Generation and initial characterization of FDD knock in mice.

Background Mutations in the integral membrane protein 2B [1], also known as BRI2 [2], a type II trans-membrane domain protein cause two autosomal dominant neurodegenerative diseases, Familial British and Danish Dementia [3]. In these conditions, accumulation of a C-terminal peptide (ABri and ADan) cleaved off from the mutated precursor protein by the pro-protein convertase furin [4], leads to amyloid deposition in the walls of blood vessels and parenchyma of the brain. Recent advances in the understanding of the generation of amyloid in Alzheimers disease has lead to the finding that BRI2 interacts with the Amyloid Precursor Protein (APP), decreasing the efficiency of APP processing to generate Aβ [5], [6], [7]. The interaction between the two precursors, APP and BRI2, and possibly between Aβ and ABri or ADan, could be important in influencing the rate of amyloid production or the tendency of these peptides to aggregate. Methodology/Principal Findings We have generated the first BRI2 Danish Knock-In (FDDKI) murine model of FDD, expressing the pathogenic decamer duplication in exon 6 of the BRI2 gene. FDDKI mice do not show any evident abnormal phenotype, with normal brain histology and no detectable amyloid deposition in blood vessel walls or parenchyma. Conclusions/Significance This new murine mouse model will be important to further understand the interaction between APP and BRI2, and to provide insights into the molecular basis of FDD.

CD74 interacts with APP and suppresses the production of Aβ

BackgroundAlzheimer disease (AD) is characterized by senile plaques, which are mainly composed of β amyloid (Aβ) peptides. Aβ is cleaved off from amyloid precursor protein (APP) with consecutive proteolytic processing by β-secretase and γ-secretase.ResultsHere, we show that CD74, the invariant chain of class II major histocompatibility complex, interacts with APP and serves as a negative regulator of Aβ. CD74 resembles other APP interacters such as BRI2 and BRI3, since all of them reduce the level of Aβ. However, unlike BRIs, CD74 does not reduce the secretion of sAPPα or sAPPβ. Interestingly, in HeLa cells, over expression of CD74 steers APP, but not Notch, to large vacuoles created by CD74.ConclusionTaken together, we propose that CD74 inhibits Aβ production by interacting with and derailing normal trafficking of APP.

Proteomic characterization of a mouse model of familial Danish dementia.

A dominant mutation in the ITM2B/BRI2 gene causes familial Danish dementia (FDD) in humans. To model FDD in animal systems, a knock-in approach was recently implemented in mice expressing a wild-type and mutant allele, which bears the FDD-associated mutation. Since these FDDKI mice show behavioural alterations and impaired synaptic function, we characterized their synaptosomal proteome via two-dimensional differential in-gel electrophoresis. After identification by nanoliquid chromatography coupled to electrospray-linear ion trap tandem mass spectrometry, the differentially expressed proteins were classified according to their gene ontology descriptions and their predicted functional interactions. The Dlg4/Psd95 scaffold protein and additional signalling proteins, including protein phosphatases, were revealed by STRING analysis as potential players in the altered synaptic function of FDDKI mice. Immunoblotting analysis finally demonstrated the actual downregulation of the synaptosomal scaffold protein Dlg4/Psd95 and of the dual-specificity phosphatase Dusp3 in the synaptosomes of FDDKI mice.