42 research outputs found
Deficiency of Sphingosine-1-phosphate Lyase Impairs Lysosomal Metabolism of the Amyloid Precursor Protein
Progressive accumulation of the amyloid Ī² protein in extracellular plaques is a neuropathological hallmark of Alzheimer disease. Amyloid Ī² is generated during sequential cleavage of the amyloid precursor protein (APP) by Ī²- and Ī³-secretases. In addition to the proteolytic processing by secretases, APP is also metabolized by lysosomal proteases. Here, we show that accumulation of intracellular sphingosine-1-phosphate (S1P) impairs the metabolism of APP. Cells lacking functional S1P-lyase, which degrades intracellular S1P, strongly accumulate full-length APP and its potentially amyloidogenic C-terminal fragments (CTFs) as compared with cells expressing the functional enzyme. By cell biological and biochemical methods, we demonstrate that intracellular inhibition of S1P-lyase impairs the degradation of APP and CTFs in lysosomal compartments and also decreases the activity of Ī³-secretase. Interestingly, the strong accumulation of APP and CTFs in S1P-lyase-deficient cells was reversed by selective mobilization of Ca(2+) from the endoplasmic reticulum or lysosomes. Intracellular accumulation of S1P also impairs maturation of cathepsin D and degradation of Lamp-2, indicating a general impairment of lysosomal activity. Together, these data demonstrate that S1P-lyase plays a critical role in the regulation of lysosomal activity and the metabolism of APP
Statins in unconventional secretion of insulin-degrading enzyme and degradation of the amyloid-Ī² peptide.
Population-based studies demonstrated that statins might decrease the risk of developing Alzheimer's disease (AD). Statins inhibit the 3-hydroxy-3-methyl-glutaryl-coenzyme-A reductase and thereby de novo synthesis of cholesterol. Cell culture and animal studies indicated that cholesterol affects the proteolytic processing of the amyloid precursor protein and the generation of amyloid-Ī² (AĪ²). Recently, we have demonstrated that statins can also stimulate the degradation of AĪ². The statin-induced clearance of AĪ² could be attributed to increased release of the insulin-degrading enzyme (IDE) via an exosome-related unconventional secretory pathway. Interestingly, this statin-induced secretion of exosome-associated IDE was independent of cellular cholesterol concentrations, but rather caused by impairment of isoprenoid biosynthesis and protein prenylation. We further identified a new hexapeptide sequence in the C-terminal region of IDE, named the SlyX motif that is critically involved in IDE secretion. Taken these findings together, the increased clearance of AĪ² by stimulated secretion of IDE might contribute to the protective effects of statins against AD
Comparative transcriptome profiling of amyloid precursor protein family members in the adult cortex
<p>Abstract</p> <p>Background</p> <p>The Ī²-amyloid precursor protein (APP) and the related Ī²-amyloid precursor-like proteins (APLPs) undergo complex proteolytic processing giving rise to several fragments. Whereas it is well established that AĪ² accumulation is a central trigger for Alzheimer's disease, the physiological role of APP family members and their diverse proteolytic products is still largely unknown. The secreted APPsĪ± ectodomain has been shown to be involved in neuroprotection and synaptic plasticity. The Ī³-secretase-generated APP intracellular domain (AICD) functions as a transcriptional regulator in heterologous reporter assays although its role for endogenous gene regulation has remained controversial.</p> <p>Results</p> <p>To gain further insight into the molecular changes associated with knockout phenotypes and to elucidate the physiological functions of APP family members including their proposed role as transcriptional regulators, we performed DNA microarray transcriptome profiling of prefrontal cortex of adult wild-type (WT), APP knockout (APP<sup>-/-</sup>), APLP2 knockout (APLP2<sup>-/-</sup>) and APPsĪ± knockin mice (APP<sup>Ī±/Ī±</sup>) expressing solely the secreted APPsĪ± ectodomain. Biological pathways affected by the lack of APP family members included neurogenesis, transcription, and kinase activity. Comparative analysis of transcriptome changes between mutant and wild-type mice, followed by qPCR validation, identified co-regulated gene sets. Interestingly, these included heat shock proteins and plasticity-related genes that were both down-regulated in knockout cortices. In contrast, we failed to detect significant differences in expression of previously proposed AICD target genes including <it>Bace1</it>, <it>Kai1</it>, <it>Gsk3b</it>, <it>p53</it>, <it>Tip60</it>, and <it>Vglut2</it>. Only <it>Egfr </it>was slightly up-regulated in APLP2<sup>-/- </sup>mice. Comparison of APP<sup>-/- </sup>and APP<sup>Ī±/Ī± </sup>with wild-type mice revealed a high proportion of co-regulated genes indicating an important role of the C-terminus for cellular signaling. Finally, comparison of APLP2<sup>-/- </sup>on different genetic backgrounds revealed that background-related transcriptome changes may dominate over changes due to the knockout of a single gene.</p> <p>Conclusion</p> <p>Shared transcriptome profiles corroborated closely related physiological functions of APP family members in the adult central nervous system. As expression of proposed AICD target genes was not altered in adult cortex, this may indicate that these genes are not affected by lack of APP under resting conditions or only in a small subset of cells.</p
Elevation in Sphingomyelin Synthase Activity Is Associated with Increases in Amyloid-Beta Peptide Generation
Expression of B4GALNT1, an essential glycosyltransferase for the synthesis of complex gangliosides, suppresses BACE1 degradation and modulates APP processing
Insulin-degrading enzyme is not secreted from cultured cells
Abstract Insulin-degrading enzyme (IDE) functions in the catabolism of bioactive peptides. Established roles include degrading insulin and the amyloid beta peptide (AĪ²), linking it to diabetes and Alzheimerās disease. IDE is primarily located in the cytosol, and a longstanding question is how it gains access to its peptide substrates. Reports suggest that IDE secreted by an unconventional pathway participates in extracellular hydrolysis of insulin and AĪ². We find that IDE release from cultured HEK-293 or BV-2 cells represents only ~1% of total cellular IDE, far less than has been reported previously. Importantly, lactate dehydrogenase (LDH) and other cytosolic enzymes are released at the same relative level, indicating that extracellular IDE results from a loss of cell integrity, not secretion. Lovastatin increases IDE release from BV-2 cells as reported, but this release is mirrored by LDH release. Cell viability assays indicate lovastatin causes a loss of cell integrity, explaining its effect on IDE release. IDE is present in an exosome-enriched fraction from BV-2 cell conditioned media, however it represents only ~0.01% of the total cellular enzyme and is unlikely to be a significant source of IDE. These results call into question the secretion of IDE and its importance in extracellular peptide degradation
Nitric Oxide Decreases the Enzymatic Activity of Insulin Degrading Enzyme in APP/PS1 Mice
peer reviewedNitric oxide has been implicated in the regulation of enzyme activity, particularly the activity of metalloproteinases. Since the inducible form of the nitric oxide synthase (NOS2), is upregulated in Alzheimer's disease, we investigated the activity of two amyloid Ī² degrading enzymes, IDE and neprilysin. In vitro we demonstrated that the activity of IDE was inhibited by *NO donor Sin-1, whereas activity of neprilysin remained unaffected. In vivo the activity of insulin-degrading enzyme was lowered in APP/PS1 mice, but not in APP/PS1/NOS2(-/-) mice. These data suggest that NOS2 upregulation impairs amyloid Ī² degradation through negative regulation of IDE activity and thus loss of NOS2 activity will positively influence amyloid Ī² clearance