Amyloid Precursor Protein Synthesis Research Articles

Novel Anticholinesterases Based on the Molecular Skeletons of Furobenzofuran and Methanobenzodioxepine

Reductive cyclization of 5-hydroxy-3-methyl-3-methoxycarbonylmethylenebenzofuran-2(3H)-one (4) gave 5-hydroxy-3a-methyl-2,3,3a,8a-tatrahydrofuro[2,3-b]benzofuran (5) and the rearrangement product 7-hydroxy-4,5-dihydro-2,5-methano-1,3-benzodioxepine (6). Reaction of compounds 5 and 6 with different isocyanates provided two series novel carbamates (7-12) whose structures were confirmed by X-ray crystallography. These were assessed for anticholinesterase action against freshly prepared human enzyme and proved to be potent inhibitors of either acetyl- (AChE) or butyrylcholinesterase (BChE) with specific compounds exhibiting remarkable selectivity. Because the two series of carbamates (7-12) differ in their phenolic moieties, their respective potency and selectivity for AChE versus BChE was governed by their N-substituted groups. This same characteristic was also present in a series of physovenine analogues (1, 13, 15, 17) and physostigmine analogues (2, 14, 16, 18). These structure-activity relations proved valuable in elucidating the mechanisms underpinning the interaction between carbamate-based cholinesterase inhibitors and their enzyme target. In addition, because physostigmine analogues have demonstrated activity in lowering the Alzheimer's disease protein, amyloid precursor protein (APP), examples of the two new series of carbamates were characterized in culture assays of quantifying cell viability and synthesis of APP.

Soluble form of amyloid precursor protein regulates proliferation of progenitors in the adult subventricular zone.

The amyloid precursor protein (APP) is a type I transmembrane protein of unknown physiological function. Its soluble secreted form (sAPP) shows similarities with growth factors and increases the in vitro proliferation of embryonic neural stem cells. As neurogenesis is an ongoing process in the adult mammalian brain, we have investigated a role for sAPP in adult neurogenesis. We show that the subventricular zone (SVZ) of the lateral ventricle, the largest neurogenic area of the adult brain, is a major sAPP binding site and that binding occurs on progenitor cells expressing the EGF receptor. These EGF-responsive cells can be cultured as neurospheres (NS). In vitro, EGF provokes soluble APP (sAPP) secretion by NS and anti-APP antibodies antagonize the EGF-induced NS proliferation. In vivo, sAPP infusions increase the number of EGF-responsive progenitors through their increased proliferation. Conversely, blocking sAPP secretion or downregulating APP synthesis decreases the proliferation of EGF-responsive cells, which leads to a reduction of the pool of progenitors. These results reveal a new function for sAPP as a regulator of SVZ progenitor proliferation in the adult central nervous system.

Regulation of APP Synthesis and Secretion by Neuroimmunophilin Ligands and Cyclooxygenase Inhibitors

We and others previously showed that both the synthesis of the amyloid precursor protein (APP) and its processing (i.e., to amyloidogenic A beta peptides; soluble nonamyloidogenic APPs; and other APP fragments) are regulated by neurotransmitters. Transmitters that elevate cellular cAMP levels (like norepinephrine and prostaglandins, which act on beta-adrenergic receptors and prostaglandin E2 receptors respectively) enhance APP synthesis and the formation of amyloidogenic APP holoprotein. Transmitters that stimulate phosphatidylinositol hydrolysis (by activating muscarinic m1 or m3 receptors, serotoninergic 5HT2a or 5HT2c receptors, or metabotropic glutamate receptors of subtypes 1 or 5) increase the conversion of APP to soluble APPs, and decrease the formation of A beta. These findings suggest that drugs that regulate the activity of neurotransmitter receptors might be useful in preventing the excessive formation of A beta or other amyloid precursors in Alzheimer's disease. We now show that neuroimmunophilin ligands (like cyclosporin A or FK-506) and nonsteroidal antiinflammatory agents (NSAIDs), including cyclooxygenase (COX)-2 inhibitors, can also prevent APP overexpression and the overproduction of amyloidogenic peptides. We observe that the enhancement of APP overexpression by prostaglandin E2 is inhibited by neuroimmunophilin ligands like cyclosporin A or FK-506 (tacrolimus). We also find that the NSAIDs, which reduce prostaglandin synthesis by inhibiting COX-1 and -2 enzymes, might also be expected to lower APP levels. Our present data confirm that these drugs, as well as drugs that selectively inhibit COX-2, reduce the levels of amyloidogenic APP holoprotein in cultured neurons or in cultured astrocytes. We previously showed that elevations in cAMP, perhaps generated in response to prostaglandins, can suppress APPs secretion. The NSAIDs and COX inhibitors also increased levels of soluble APPs in the media of cultured astrocytes and neurons, perhaps acting by inhibition of prostaglandin production. Since APP holoprotein can be amyloidogenic, while APPs may be neurotrophic, our findings suggest that some neuroimmunophilin ligands, NSAIDs and COX-2 inhibitors might suppress amyloid formation and enhance neuronal regeneration in Alzheimer's disease.

Copper inhibits β-amyloid production and stimulates the non-amyloidogenic pathway of amyloid-precursor-protein secretion

Previous studies have demonstrated that amyloid precursor protein (APP) can bind and reduce Cu(II) to Cu(I), leading to oxidative modification of APP. In the present study we show that adding copper to Chinese-hamster ovary (CHO) cells greatly reduced the levels of amyloid Aβ peptide (Aβ) both in parental CHO-K1 and in copper-resistant CHO-CUR3 cells, which have lower intracellular copper levels. Copper also caused an increase in the secretion of the APP ectodomain, indicating that the large decrease in Aβ release was not due to a general inhibition in protein secretion. There was an increase in intracellular full-length APP levels which paralleled the decrease in Aβ generation, suggesting the existence of two distinct regulating mechanisms, one acting on Aβ production and the other on APP synthesis. Maximal inhibition of Aβ production and stimulation of APP secretion was achieved in CHO-K1 cells at about 10 μM copper and in CHO-CUR3 cells at about 50 μM copper. This dose ‘window of opportunity’ at which copper promoted the non-amyloidogenic pathway of APP was confirmed by an increase in the non-amyloidogenic p3 fragment produced by α-secretase cleavage. Our findings suggest that copper or copper agonists might be useful tools to discover novel targets for anti-Alzheimer drugs and may prove beneficial for the prevention of Alzheimer's disease.

Copper inhibits β-amyloid production and stimulates the non-amyloidogenic pathway of amyloid-precursor-protein secretion

Previous studies have demonstrated that amyloid precursor protein (APP) can bind and reduce Cu(II) to Cu(I), leading to oxidative modification of APP. In the present study we show that adding copper to Chinese-hamster ovary (CHO) cells greatly reduced the levels of amyloid Abeta peptide (Abeta) both in parental CHO-K1 and in copper-resistant CHO-CUR3 cells, which have lower intracellular copper levels. Copper also caused an increase in the secretion of the APP ectodomain, indicating that the large decrease in Abeta release was not due to a general inhibition in protein secretion. There was an increase in intracellular full-length APP levels which paralleled the decrease in Abeta generation, suggesting the existence of two distinct regulating mechanisms, one acting on Abeta production and the other on APP synthesis. Maximal inhibition of Abeta production and stimulation of APP secretion was achieved in CHO-K1 cells at about 10 microM copper and in CHO-CUR3 cells at about 50 microM copper. This dose 'window of opportunity' at which copper promoted the non-amyloidogenic pathway of APP was confirmed by an increase in the non-amyloidogenic p3 fragment produced by alpha-secretase cleavage. Our findings suggest that copper or copper agonists might be useful tools to discover novel targets for anti-Alzheimer drugs and may prove beneficial for the prevention of Alzheimer's disease.

Translation of the Alzheimer Amyloid Precursor Protein mRNA Is Up-regulated by Interleukin-1 through 5′-Untranslated Region Sequences

The amyloid precursor protein (APP) has been associated with Alzheimer's disease (AD) because APP is processed into the beta-peptide that accumulates in amyloid plaques, and APP gene mutations can cause early onset AD. Inflammation is also associated with AD as exemplified by increased expression of interleukin-1 (IL-1) in microglia in affected areas of the AD brain. Here we demonstrate that IL-1alpha and IL-1beta increase APP synthesis by up to 6-fold in primary human astrocytes and by 15-fold in human astrocytoma cells without changing the steady-state levels of APP mRNA. A 90-nucleotide sequence in the APP gene 5'-untranslated region (5'-UTR) conferred translational regulation by IL-1alpha and IL-1beta to a chloramphenicol acetyltransferase (CAT) reporter gene. Steady-state levels of transfected APP(5'-UTR)/CAT mRNAs were unchanged, whereas both base-line and IL-1-dependent CAT protein synthesis were increased. This APP mRNA translational enhancer maps from +55 to +144 nucleotides from the 5'-cap site and is homologous to related translational control elements in the 5'-UTR of the light and and heavy ferritin genes. Enhanced translation of APP mRNA provides a mechanism by which IL-1 influences the pathogenesis of AD.

Prostaglandin E2Stimulates Amyloid Precursor Protein Gene Expression: Inhibition by Immunosuppressants

Amyloid plaques that accumulate in the brains of patients with Alzheimer's disease (AD) are primarily composed of aggregates of amyloid peptides that are derived from the amyloid precursor protein (APP). Overexpression of APP in cell cultures increases the formation of amyloidogenic peptides and causes neurodegeneration and cognitive dysfunction in transgenic mice. We now report that activation of prostaglandin E2 (PGE2) receptors increases cAMP formation and stimulates overexpression of APP mRNA and holoprotein in primary cultures of cortical astrocytes. Levels of glial fibrillary acidic protein were also increased by PGE2 treatment, suggesting that these cultured astrocytes resemble reactive astrocytes found in vivo. The stimulation by PGE2 of APP synthesis was mimicked or blocked by activators or inhibitors, respectively, of protein kinase A. Actinomycin D or cycloheximide also inhibited the increase in APP holoprotein stimulated by PGE2. Treatment of astrocytes with 8-Bromo-cAMP or forskolin for 24 hr also stimulated APP overexpression in cultured astrocytes. The immunosuppressants cyclosporin A and FK-506 inhibited the increase in APP mRNA and holoprotein levels caused by PGE2 or by other treatments that elevated cellular cAMP levels; the inhibitory effect of FK-506 but not of cyclosporin A was attenuated by rapamycin. These results suggest that prostaglandins produced by brain injury or inflammation can activate APP transcription in astrocytes and that immunosuppressants may be used to prevent APP overexpression and possibly the pathophysiological processes underlying AD.

The microbial alkaloid toxin staurosporine blocks the phorbol ester–induced increase in β‐amyloid precursor protein in PC12 cells

AbstractThe amyloid precursor protein (APP) is abnormally cleaved during the progression of Alzheimer's disease, resulting in production of the toxic beta‐amyloid peptide, which forms neuritic plaques in the brain. To develop a pharmacological approach for treatment of Alzheimer's disease, natural compounds which may inhibit APP synthesis and/or beta‐amyloid production are required. Staurosporine, a toxin isolated from Streptomyces staurospores bacteria, is widely used as a protein kinase C inhibitor in signal transduction research. Using rat pheochromocytoma PC12 sympathetic neurons, which express APP, we characterised staurosporine effect on APP level by western blotting, using an anti‐APP monoclonal antibody. PC12 APP levels were increased or decreased upon exposure to either 50–200 nM or 10–20 nM phorbol 12‐myristate 13‐acetate (PMA, a protein kinase C activator), respectively. An apparent relationship was found between the change in APP level and a differential down regulation process of different PKC isoforms. The PMA‐induced increase in intracellular APP level was dose‐dependently inhibited by staurosporine (natural alkaloid) or GF 109203X (synthetic analogue), protein kinase C (PKC) inhibitors. This inhibition was mainly observed upon treatment of the cells before the exposure to PMA. These results suggest PKC regulation of APP levels in PC12 cells, and provide staurosporine as a leader compound for the development of drugs to control the expression of APP in Alzheimer's research. Nat. Toxins 5:173–179, 1997. © 1998 Wiley‐Liss, Inc.

Amyloid Precursor Protein Metabolism in Primary Cell Cultures of Neurons, Astrocytes, and Microglia

Amyloid precursor protein (APP) gives rise by proteolytic processing to the amyloid beta peptide (A beta) found abundantly in cerebral senile plaques of individuals with Alzheimer's disease. APP is highly expressed in the brain. To assess the source of cerebral A beta, the metabolism of APP was investigated in the major cell types of the newborn rat cerebral cortex by pulse/chase labeling and immunoprecipitation of the APP and APP metabolic fragments. We describe a novel C-terminally truncated APP isoform that appears to be made only in neurons. The synthesis, degradation, and metabolism of APP were quantified by phosphorimaging in neurons, astrocytes, and microglia. The results show that although little APP is metabolized through the amyloidogenic pathways in each of the three cultures, neurons appear to generate more A beta than astrocytes or microglia.