Meprin β knockout reduces brain Aβ levels and rescues learning and memory impairments in the APP/lon mouse model for Alzheimer’s disease

β-Site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1) is the major described β-secretase to generate Aβ peptides in Alzheimer’s disease (AD). However, all therapeutic attempts to block BACE1 activity and to improve AD symptoms have so far failed. A potential candidate for alternative Aβ peptides generation is the metalloproteinase meprin β, which cleaves APP predominantly at alanine in p2 and in this study we can detect an increased meprin β expression in AD brain. Here, we report the generation of the transgenic APP/lon mouse model of AD lacking the functional Mep1b gene (APP/lon × Mep1b−/−). We examined levels of canonical and truncated Aβ species using urea-SDS-PAGE, ELISA and immunohistochemistry in brains of APP/lon mouse × Mep1b−/−. Additionally, we investigated the cognitive abilities of these mice during the Morris water maze task. Aβ1-40 and 1–42 levels are reduced in APP/lon mice when meprin β is absent. Immunohistochemical staining of mouse brain sections revealed that N-terminally truncated Aβ2–x peptide deposition is decreased in APP/lon × Mep1b−/− mice. Importantly, loss of meprin β improved cognitive abilities and rescued learning behavior impairments in APP/lon mice. These observations indicate an important role of meprin β within the amyloidogenic pathway and Aβ production in vivo

Mechanisms causing imprinting defects in familial Beckwith-Wiedemann syndrome with Wilms' tumour

The imprinted expression of the IGF2 and H19 genes is controlled by the Imprinting Centre 1 (IC1) at chromosome 11p15.5. This is a methylation-sensitive chromatin insulator that works by binding the zinc-finger protein CTCF in a parent-specific manner. Microdeletions abolishing some of the CTCF target sites (CTSs) of IC1 have been associated with the Beckwith-Wiedemann syndrome (BWS). However, the link between these mutations and the molecular and clinical phenotypes was debated. We have identified two novel families with IC1 deletions, in which individuals with the clinical features of the BWS are present in multiple generations. By analysing the methylation pattern at the IGF2 - H19 locus together with the clinical phenotypes in the individuals with maternal and those with paternal transmission of five different deletions, we demonstrate that maternal transmission of 1.4-1.8 kb deletions in the IC1 region co-segregates with the hypermethylation of the residual CTSs and BWS phenotype with complete penetrance, whereas normal phenotype is observed upon paternal transmission. Although gene expression could not be assayed in all cases, the methylation detected at the IGF2 DMR2 and H19 promoter suggests that IC1 hypermethylation is consistently associated with biallelic activation of IGF2 and biallelic silencing of H19. Comparison of these deletions with a 2.2 kb one previously reported by another group indicates that the spacing of the CTSs on the deleted allele is critical for the gain of the abnormal methylation and penetrance of the clinical phenotype. Furthermore, we observe that the hypermethylation resulting from the deletions is always mosaic, suggesting that the epigenetic defect at the IGF2-H19 locus is established post-zygotically and may cause body asymmetry and heterogeneity of the clinical phenotype. Finally, the IC1 microdeletions are associated with a high incidence of Wilms' tumour, making their molecular diagnosis particularly important for genetic counselling and tumour surveillance at follow-up

Frequent LPA KIV-2 Variants Lower Lipoprotein(a) Concentrations and Protect Against Coronary Artery Disease

Background: Lipoprotein(a) (Lp(a)) concentrations are a major independent risk factor for coronary artery disease (CAD) and are mainly determined by variation in LPA. Up to 70% of the LPA coding sequence is located in the hypervariable kringle IV type 2 (KIV-2) region. It is hardly accessible by conventional technologies, but may contain functional variants. Objectives: This study sought to investigate the new, very frequent splicing variant KIV-2 4733G>A on Lp(a) and CAD. Methods: We genotyped 4733G>A in the GCKD (German Chronic Kidney Disease) study (n = 4,673) by allele-specific polymerase chain reaction, performed minigene assays, identified proxy single nucleotide polymorphisms and used them to characterize its effect on CAD by survival analysis in UK Biobank (n = 440,234). Frequencies in ethnic groups were assessed in the 1000 Genomes Project. Results: The 4733G>A variant (38.2% carrier frequency) was found in most isoform sizes. It reduces allelic expression without abolishing protein production, lowers Lp(a) by 13.6 mg/dL (95% CI: 12.5-14.7; P A and 4925G>A, another KIV-2 splicing mutation, reduces Lp(a) by 31.8 mg/dL and most importantly narrows the interquartile range by 9-fold (from 42.1 to 4.6 mg/dL) when compared to the wild type. In UK Biobank 4733G>A alone and compound heterozygosity with 4925G>A reduced HR for CAD by 9% (95% CI: 7%-11%) and 12% (95% CI: 7%-16%) (both P < 0.001). Frequencies in ethnicities differ notably. Conclusions: Functional variants in the previously inaccessible LPA KIV-2 region cooperate in determining Lp(a) variance and CAD risk. Even a moderate but lifelong genetic Lp(a) reduction translates to a noticeable CAD risk reduction