Luca Giliberto

Oxidative stress mediates the pathogenic effect of different Alzheimer's disease risk factors

Alzheimers disease (AD) is a progressive neurodegenerative disorder affecting the elderly population. Mechanistically, the major cause of the disease bases on the altered processing of the amyloid-β (Aβ) precursor protein (APP), resulting in the accumulation and aggregation of neurotoxic forms of Aβ. Aβ derives from the sequential proteolytic cleavage of the β- and γ-secretases on APP. The causes of Aβ accumulation in the common sporadic form of AD are not completely known, but they are likely to include oxidative stress (OS). OS and Aβ are linked to each other since Aβ aggregation induces OS in vivo and in vitro, and oxidant agents increase the production of Aβ. Moreover, OS produces several effects that may contribute to synaptic function and cell death in AD. We and others have shown that the expression and activity of β-secretase (named BACE1; β-site APP cleaving enzyme) is increased by oxidant agents and by lipid peroxidation product 4-hydroxynonenal and that there is a significant correlation between BACE1 activity and oxidative markers in sporadic AD. OS results from several cellular insults such as aging, hyperglycemia, hypoxic insults that are all well known risk factors for AD development. Thus, our data strengthen the hypothesis that OS is a basic common pathway of Aβ accumulation, common to different AD risk factors.

Evidence that the Amyloid beta Precursor Protein-intracellular domain lowers the stress threshold of neurons and has a "regulated" transcriptional role

BackgroundRegulated intramembrane proteolysis of the β-amyloid precursor protein by the γ-secretase yields two peptides. One, amyloid-β, is the major component of the amyloid plaques found in Alzheimers disease patients. The other, APP IntraCellular Domain, has been involved in regulation of apoptosis, calcium flux and gene transcription. To date, a few potential target genes transcriptionally controlled by AID, alone or complexed with Fe65/Tip60, have been described. Although the reports are controversial: these include KAI1, Neprilysin, p53, EGFR, LRP and APP itself. Furthermore, p53 has been implicated in AID mediated susceptibility to apoptosis. To extend these findings, and assess their in vivo relevance, we have analyzed the expression of the putative target genes and of the total brain basal transriptoma in transgenic mice expressing AID in the forebrain. Also, we have studied the susceptibility of primary neurons from such mice to stress and pro-apoptotic agents.ResultsWe found that AID-target genes and the mouse brain basal transcriptoma are not influenced by transgenic expression of AID alone, in the absence of Fe65 over-expression. Also, experiments conducted on primary neurons from AID transgenic mice, suggest a role for AID in sensitizing these cells to toxic stimuli. Overall, these findings hint that a role for AID, in regulating gene transcription, could be induced by yet undefined, and possibly stressful, stimuli in vivo.ConclusionOverall, these data suggest that the release of the APP intracellular domain may modulate the sensitivity of neuronal cells to toxic stimuli, and that a transcriptional role of AID could be inscribed in signaling pathways thatare not activated in basal conditions.

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.

Memory Deficits Due to Familial British Dementia BRI2 Mutation Are Caused by Loss of BRI2 Function Rather than Amyloidosis

Familial dementias, which include Alzheimer disease (AD), familial British dementia (FBD), and familial Danish dementia (FDD), are caused by dominantly inherited autosomal mutations and are characterized by the production of amyloidogenic peptides, neurofibrillary tangles (NFTs) and neurodegeneration (St George-Hyslop and Petit, 2005; Garringer et al., 2009). The prevailing pathogenic theory, the “amyloid cascade hypothesis” (Hardy and Selkoe, 2002), posits that the accumulation of amyloidogenic peptides triggers tauopathy, neurodegeneration, and cognitive and behavioral changes. However, this hypothesis is yet to be validated, and causes of dementia may be multifaceted and involve other mechanisms, such as loss of function due to pathogenic mutations. Mouse models of human dementia invariably use transgenic expression systems (LaFerla and Oddo, 2005; McGowan et al., 2006; Vidal et al., 2009; Coomaraswamy et al., 2010) that do not reflect the genotypes of human disease and cannot replicate loss of function. Therefore, we generated a knock-in (KI) mouse model of FBD (FBDKI) genetically congruous with the human disease. FBD is caused by a missense mutation at the stop codon of the BRI2 gene (Vidal et al., 1999) and, like FBD patients, FBDKI mice carry this mutation in one of the two murine Bri2 alleles. We report that the British mutation drastically reduces expression of mature BRI2 in both KI mice and human FBD brains. This deficit is associated with severe hippocampal memory deficits in FBDKI mice. Remarkably, these animals showed no cerebral amyloidosis and tauopathy. Bri2 +/− mice present memory deficits similar to those in FBDKI animals. Collectively, these results indicate that the British BRI2 mutation underlies abnormal memory due to loss of BRI2 function and independently of histopathological alterations typically evident in advanced neurodegenerative disease.

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.

Plasma levels of insulin and amyloid β42 are correlated in patients with amnestic Mild Cognitive Impairment

Epidemiological and experimental data suggest that type 2 diabetes (DM2) and sporadic late-onset Alzheimers disease (AD) share a common mechanism, that is able to produce accumulation of insulin and amyloid beta 42 (Abeta42), the major pathogenic events respectively of the two conditions. In 71 non diabetic patients with amnestic mild cognitive impairment we found a significant linear correlation between fasting plasma levels of insulin and Abeta42 (R = +0.25, P < 0.05). The levels of both peptides were elevated in comparison to 48 age-matched cognitively normal controls. The correlation of insulin and Abeta42 plasma levels suggests a pathogenic link between DM2 and sporadic AD.