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The environmental enrichment (EE) paradigm is regarded as a useful tool to create a physical and intellectual stimulation for laboratory rodents and has been used in a variety of Alzheimer disease (AD) mouse models. However, the results of these studies have been conflicting as EE had inconsistent effects on memory performance, Aβ deposition, inflammatory status and other pathological outcomes depending on the AD model. Here, we studied the influence of a lifelong EE on the widely used 5XFAD mouse model, representing the main pathological features of AD. Although 11 months of enriched housing led to an improved survival rate and a partial rescue of motor performance, no beneficial effects in terms of anxiety phenotype, working memory performance, Aβ plaque load, Aβ1–42 levels, endogenous APP processing and inflammatory status were observed in 5XFAD mice. Concordantly, no changes in expression levels of BACE1 or Aβ-degrading enzymes like neprilysin or insulin-degrading enzyme could be detected in active mice. The 5XFAD model develops a relatively fast and aggressive pathology and therefore presents a model for early onset familial AD. Our results suggest that an intervention like EE might be too mild to counteract the fast disease progression seen in this model. Therefore, our data provide evidence that the effects of physical and cognitive stimulation vary depending on the severity of the pathology of the model and therefore might be more beneficial in models developing a milder AD phenotype.

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder characterized by early intraneuronal amyloid-β (Aβ) accumulation, extracellular deposition of Aβ peptides, and intracellular hyperphosphorylated tau aggregates. These lesions cause dendritic and synaptic alterations and induce an inflammatory response in the diseased brain. Although the neuropathological characteristics of AD have been known for decades, the molecular mechanisms causing the disease are still under investigation. Studying gene expression changes in postmortem AD brain tissue can yield new insights into the molecular disease mechanisms. To that end, one can employ transgenic AD mouse models and the next-generation sequencing technology. In this study, a whole-brain transcriptome analysis was carried out using the well-characterized APP/PS1KI mouse model for AD. These mice display a robust phenotype reflected by working memory deficits at 6 months of age, a significant neuron loss in a variety of brain areas including the CA1 region of the hippocampus and a severe amyloid pathology. Based on deep sequencing, differentially expressed genes (DEGs) between 6-month-old WT or PS1KI and APP/PS1KI were identified and verified by qRT-PCR. Compared to WT mice, 250 DEGs were found in APP/PS1KI mice, while 186 DEGs could be found compared to PS1KI control mice. Most of the DEGs were upregulated in APP/PS1KI mice and belong to either inflammation-associated pathways or lysosomal activation, which is likely due to the robust intraneuronal accumulation of Aβ in this mouse model. Our comprehensive brain transcriptome study further highlights APP/PS1KI mice as a valuable model for AD, covering molecular inflammatory and immune responses.

Brain accumulation and aggregation of amyloid-β (Aβ) peptides is a critical step in the pathogenesis of Alzheimer's disease (AD). Full-length Aβ peptides (mainly Aβ1-40 and Aβ1-42) are produced through sequential proteolytic cleavage of the amyloid precursor protein (APP) by β- and γ-secretases. However, studies of autopsy brain samples from AD patients have demonstrated that a large fraction of insoluble Aβ peptides are truncated at the N-terminus, with Aβ4-x peptides being particularly abundant. Aβ4-x peptides are highly aggregation prone, but their origin and any proteases involved in their generation are unknown. We have identified a recognition site for the secreted metalloprotease ADAMTS4 (a disintegrin and metalloproteinase with thrombospondin motifs 4) in the Aβ peptide sequence, which facilitates Aβ4-x peptide generation. Inducible overexpression of ADAMTS4 in HEK293 cells resulted in the secretion of Aβ4-40 but unchanged levels of Aβ1-x peptides. In the 5xFAD mouse model of amyloidosis, Aβ4-x peptides were present not only in amyloid plaque cores and vessel walls, but also in white matter structures co-localized with axonal APP. In the ADAMTS4-/- knockout background, Aβ4-40 levels were reduced confirming a pivotal role of ADAMTS4 in vivo. Surprisingly, in the adult murine brain, ADAMTS4 was exclusively expressed in oligodendrocytes. Cultured oligodendrocytes secreted a variety of Aβ species, but Aβ4-40 peptides were absent in cultures derived from ADAMTS4-/- mice indicating that the enzyme was essential for Aβ4-x production in this cell type. These findings establish an enzymatic mechanism for the generation of Aβ4-x peptides. They further identify oligodendrocytes as a source of these highly amyloidogenic Aβ peptides.

Deregulated expression of MYC is a driver of colorectal carcinogenesis, suggesting that inhibiting MYC may have significant therapeutic value. The PI3K and mTOR pathways control MYC turnover and translation, respectively, providing a rationale to target both pathways to inhibit MYC. Surprisingly, inhibition of PI3K does not promote MYC turnover in colon carcinoma cells, but enhances MYC expression because it promotes FOXO-dependent expression of growth factor receptors and MAPK-dependent transcription of MYC. Inhibition of mTOR fails to inhibit translation of MYC, because levels of 4EBPs are insufficient to fully sequester eIF4E and because an internal ribosomal entry site element in the 5′-untranslated region of the MYC mRNA permits translation independent of eIF4E. A small-molecule inhibitor of the translation factor eIF4A, silvestrol, bypasses the signaling feedbacks, reduces MYC translation, and inhibits tumor growth in a mouse model of colorectal tumorigenesis. We propose that targeting translation initiation is a promising strategy to limit MYC expression in colorectal tumors. Significance: Inhibiting MYC function is likely to have a significant therapeutic impact in colorectal cancers. Here, we explore several strategies to target translation initiation in order to block MYC expression. We show that a small-molecule inhibitor of eIF4A inhibits MYC expression and suppresses tumor growth in vivo. Cancer Discov; 5(7); 768–81. ©2015 AACR. See related commentary by Castell and Larsson, p. 701. This article is highlighted in the In This Issue feature, p. 681

The deposition of amyloid-β (Aβ) is one of the major neuropathological hallmarks of Alzheimer's disease (AD). In the case of sporadic AD, an imbalance in Aβ in production and clearance seems to be the reason for an enhanced Aβ accumulation. Besides a systematic clearance through the blood-brain barrier, Aβ is cleared from the brain by Aβ-degrading enzymes. The metalloprotease neprilysin (NEP) is an important Aβ-degrading enzyme as shown by numerous in vitro, in vivo and reverse genetics studies. 5XFAD mice represent an early-onset AD mouse model which develops plaque pathology starting with 2 months of age in addition to robust behavioral deficits at later time points. By crossing 5XFAD mice with homozygous NEP-knock-out mice (NEP-/-), we show that hemizygous NEP deficiency aggravates the behavioral and neuropathological phenotype of 5XFAD mice. We found that 5XFAD mice per se showed strongly decreased NEP expression levels compared to wildtype mice, which was aggravated by NEP reduction. 5XFAD/NEP+/- mice demonstrated impairment in spatial working memory and increased astrocytosis in all studied brain areas, in addition to an overall increased level of soluble Aβ42 as well as region-specific increases in extracellular Aβ deposition. Surprisingly, in young mice, a more abundant cortical Aβ plaque pathology was observed in 5XFAD compared to 5XFAD/NEP+/- mice. Additionally, young 5XFAD/NEP+/- as well as hemi- and homozygous NEP knockout mice showed elevated levels of endothelin-converting enzyme 1 (ECE1), suggesting a mutual regulation of ECE1 and NEP at young ages. The present data indicate that NEP mainly degrades soluble Aβ peptides, which confirms previous observations. Increased ECE1 levels correlated well with the strongly reduced extracellular plaque load in young 5XFAD/NEP+/- mice and might suggest a reciprocal effect between ECE and NEP activities in Aβ degradation.

The in vitro and in vivo effects of pyrvinium pamoate (PP), a newly identified WNT signaling inhibitor, were evaluated against colon cancer cell lines and primary colon cancer samples.Antiproliferative activity of PP and its effects on protein and RNA levels of WNT targets were evaluated on adenomatous polyposis coli (APC (mut)) and β-catenin(mut) cell lines, one WNT(wt) colon cancer cell line, as well as six primary colon cancer samples with mutant APC in vitro. In addition, the effect of PP on the growth of liver metastasis was examined.PP blocked colon cancer cell growth in vitro in a dose-dependent manner with great differences in the inhibitory concentration (IC(50)), ranging from 0.6 × 10(-6) to 65 × 10(-6) mol/L for colon cancer cells with mutations in WNT signaling. In addition, PP demonstrated a cytotoxic effect on primary colon cancer samples. A combined cytotoxic effect of PP with 5-fluorouracil (5-FU) was observed for two cell lines. PP decreased messenger RNA (mRNA) and protein levels of known WNT target genes as c-MYC and thereby led to the induction of p21. PP inhibited the migration of HCT116 colon cancer cells in vitro and decreased tumor growth in vivo after intraportal injection of HCT116 cells in nude mice.PP displays promising anticancer activity against a broad panel of human colon cancer cell lines, as well as primary colon cancer samples. However, our findings do not demonstrate a predominant cytotoxic effect of PP on colon cancer cells with mutations in WNT signaling.