Expression of APP in brains of transgenic mice containing the entire human APP gene

A major component of amyloid deposits found in Alzheimer disease and Down syndrome is the beta/A4 peptide, which is derived from the Alzheimer amyloid protein precursor (APP). Recent evidence indicates that increases in APP expression and/or beta/A4 peptide accumulation may underlie the amyloidosis characteristic of these diseases. In the present study, transgenic mice carrying the entire human APP gene were studied for expression of human APP. Significant expression of human APP protein was observed in these animals, and this expression paralleled the expression of endogenous APP. These results, which represent a first demonstration of significant human APP expression in transgenic animals, support the use of such animals to study human APP expression and processing in vivo and possibly as models for the amyloidosis associated with Alzheimer disease.

Protein phosphorylation inhibits production of Alzheimer amyloid beta/A4 peptide

The major component of amyloid plaque cores and cerebrovascular amyloid deposits found in Alzheimer disease is the beta/A4 peptide, which is derived from the Alzheimer amyloid protein precursor (APP). Recent evidence suggests that abnormalities in beta/A4 peptide production or beta/A4 peptide aggregation may underlie cerebral amyloidosis. In the present study, treatment of cells with phorbol dibutyrate, which activates protein kinase C, and/or okadaic acid, which inhibits protein phosphatases 1 and 2A, reduced beta/A4 peptide production by 50-80%. These effects were observed with APP695 and APP751 expressed in stably transfected CHO cells, as well as with endogenous APP in human glioma (Hs 683) cells. Phorbol dibutyrate also decreased beta/A4 peptide production in cells expressing various mutant forms of APP associated with familial Alzheimer disease, one of which was reported to manifest greatly increased beta/A4 peptide production in cultured cells. Mastoparan and mastoparan X, compounds which can activate phospholipase C and hence protein kinase C, also decreased beta/A4 peptide production in CHO cells stably transfected with APP695. A model is presented in which decreases in beta/A4 peptide production can be achieved by accelerating the metabolism of APP through a nonamyloidgenic secretory pathway.

Protein phosphorylation regulates relative utilization of processing pathways for Alzheimer beta/A4 amyloid precursor protein

The Alzheimer amyloid precursor protein (APP) is a phosphoprotein, and the phosphorylation state of APP at Ser655 can be regulated by protein kinase C, calcium/calmodulin-dependent protein kinase II, and okadaic acid-sensitive protein phosphatases. Other enzymes may also play a role at Ser655 of APP and, perhaps, at other residues. Signal transduction via protein phosphorylation regulates APP metabolism. In particular, APP processing via the nonamyloidogenic secretory cleavage pathway is increased following the activation of protein kinase C or the inactivation of okadaic acid-sensitive protein phosphatases. The mechanism(s) by which protein phosphorylation regulates APP secretory cleavage include (among others): substrate activation, substrate redistribution, protease activation and/or protease redistribution. Current experimental evidence will be discussed, addressing the relative importance of each of these possibilities and the implications for these events in the modulation of beta/A4-amyloidogenesis.

Cholinergic agonists and interleukin 1 regulate processing and secretion of the Alzheimer beta/A4 amyloid protein precursor

Activation of protein kinase C by phorbol esters is known to accelerate the processing and secretion of the beta/A4 amyloid protein precursor. We have now examined various first messengers that increase protein kinase C activity of target cells for their ability to affect beta/A4 amyloid protein precursor metabolism. Acetylcholine and interleukin 1, which are altered in Alzheimer disease, were shown to increase processing of the beta/A4 amyloid protein precursor via the secretory cleavage pathway. Cholinergic agonists stimulated secretion in human glioma and neuroblastoma cells as well as in PC12 cells transfected with the M1 receptor, while interleukin 1 stimulated secretion in human endothelial and glioma cells.

The nature and metabolism of potentially amyloidogenic carboxyl-terminal fragments of the Alzheimer beta/A4-amyloid precursor protein: some technical notes

The proteolytic processing and secretion of APP are regulated by protein phosphorylation, especially via protein kinase C and protein phosphatases 1 and/or 2A. Our studies of these regulatory mechanisms have led us to perform extensive experimentation on the metabolism of APP carboxyl-terminal fragments, using as our system either untransfected, undifferentiated rat pheochromocytoma (PC12) cells or APP-baculovirus infected Sf9 cells. We have not assayed APP fragments for biological activity in either system. However, we have made potentially relevant observations regarding APP carboxyl-terminal fragment trafficking. In this note, we review our published and unpublished data in relation to published reports from other laboratories using related systems.

Protein phosphorylation regulates secretion of Alzheimer beta/A4 amyloid precursor protein

Extracellular deposition of the beta/A4 amyloid peptide is a characteristic feature of the brain in patients with Alzheimer disease. beta/A4 amyloid is derived from the amyloid precursor protein (APP), an integral membrane protein that exists as three major isoforms (APP695, APP751, and APP770). Secreted forms of APP found in blood plasma and cerebrospinal fluid arise by proteolytic cleavage of APP within the beta/A4 amyloid domain, precluding the possibility of amyloidogenesis for that population of molecules. In the present study, we have demonstrated that treatment of PC12 cells with phorbol ester produces a severalfold increase in secretion of APP695, APP751, and APP770. This increase is augmented by simultaneous treatment with the protein phosphatase inhibitor okadaic acid. These data indicate that protein phosphorylation regulates intra-beta/A4 amyloid cleavage and APP secretion. These and other results suggest that APP molecules can normally follow either of two processing pathways: regulated secretion or proteolytic degradation unassociated with secretion.

Chloroquine inhibits intracellular degradation but not secretion of Alzheimer beta/A4 amyloid precursor protein

The metabolic fate of the Alzheimer beta/A4 amyloid precursor protein (APP) includes intraamyloid proteolysis that leads to the production of secreted N-terminal and cell-associated C-terminal fragments. The cellular sites at which this processing occurs are not known. We have examined the route of APP processing in metabolically labeled PC12 cells. The lysosomotropic drug chloroquine exerted inhibitory effects on the degradation of mature APP holoprotein. In addition, recovery of a C-terminal fragment resulting from normal intraamyloid cleavage was significantly increased in the presence of chloroquine, suggesting that further degradation of the C-terminal fragment was inhibited. Chloroquine had virtually no effect on APP maturation (N- and O-glycosylation and tyrosine sulfation) or secretion. Treatment with either monensin (which inhibits distal Golgi function) or brefeldin A (which causes resorption of the Golgi into the endoplasmic reticulum and fusion of the trans-Golgi network with the endosomal system) prevented normal APP maturation and abolished APP secretion and recovery of C-terminal fragments, indicating that intact Golgi function is necessary for APP maturation and processing. Our results suggest that a substantial proportion of APP is degraded in an intracellular acidic compartment but that the coupled APP cleavage/secretion event occurs in a chloroquine-insensitive compartment. The observations are consistent with the existence of multiple cellular routes for the trafficking and proteolysis of APP.

Processing of Alzheimer beta/A4 amyloid precursor protein: modulation by agents that regulate protein phosphorylation

The turnover and processing of the Alzheimer beta/A4 amyloid precursor protein (beta APP) has been studied in PC12 cells after treatment with agents that regulate protein phosphorylation. Phorbol 12,13-dibutyrate, an agent that stimulates protein kinase C, decreased the levels of mature beta APP and increased the levels of 15- and 19-kDa peptides. These peptides appeared to be COOH-terminal fragments of beta APP, which arose when phorbol 12,13-dibutyrate increased the rate of proteolytic processing of mature forms of beta APP. Okadaic acid, an inhibitor of protein phosphatases 1 and 2A, also led to decreased levels of mature beta APP and increased levels of the 15- and 19-kDa peptides. H-7, an inhibitor of protein kinase C and of several other protein kinases, apparently decreased the rate of proteolytic processing of mature beta APP. The sizes of the putative COOH-terminal fragments observed after treatment with either phorbol 12,13-dibutyrate or okadaic acid suggest that one or both may contain the entire beta/A4 region of beta APP and thus be amyloidogenic. Our results support the hypothesis that abnormal protein phosphorylation may play a role in the development of the cerebral amyloidosis that accompanies Alzheimer disease.

In vivo protein phosphorylation in Drosophila mutants defective in learning and memory

Polypeptides phosphorylated in vivo in Drosophila mutants defective in learning and memory, were characterized by polyacrylamide gel electrophoresis of subcellular fractions obtained by phase partitioning in Triton X-114 [3]. In the mutants turnip, dunce and Shaker, one or more bands at a molecular weight range of 50-80 kDa had altered 32P incorporation. Some of these bands were altered in more than one mutant. In the mutant rutabaga no significant differences from wild-type were observed. The data suggest that phosphoproteins that could be potentially related to learning mechanisms might be identified in some learning mutants.

A quantitative model for the kinetics of cAMP-dependent protein kinase (type II) activity. Long-term activation of the kinase and its possible relevance to learning and memory

Using computer simulation we have modeled the kinetics of cAMP-dependent protein kinase, type II, following transient pulses of cAMP. We show that under the appropriate physiological conditions, the kinase can remain activated 20 min or longer after the cessation of adenylate cyclase activation, in a process we term long-term activation. Long-term activation depends in part on the state of phosphorylation of the regulatory subunit, because phosphorylation of the regulatory subunit regulates the affinity of this subunit for the catalytic subunit. We have used our model to simulate experiments that have been performed on the kinetic and steady state activities of cAMP-dependent protein kinase and have found good agreement between the simulations and the experimental data. The effects of the activity of phosphodiesterase, adenylate cyclase, and protein phosphatase on the kinetics of cAMP-dependent protein kinase have been modeled, as have the effects of different ratios of regulatory subunit to catalytic subunit. We have also simulated the activation of the cAMP-dependent protein kinase in Drosophila learning and memory mutants having primary or secondary defects in the cAMP cascade. We make predictions regarding the behavior of different mutants, which are in line with the experimental data. The model corroborates the assumption that the cAMP cascade may play a role in learning and short-term memory.

A microtiter-based assay for protein kinase activity suitable for the analysis of large numbers of samples, and its application to the study of Drosophila learning mutants

We have developed a microtiter-based assay for protein kinase activity which depends on the immobilization of substrate proteins to nitrocellulose. The technique makes use of a filtration manifold, allowing as much as a 10-fold increase in efficiency as compared to other protein kinase assays. We have used this assay to measure cAMP-dependent protein kinase (PKA) in Drosophila learning and memory mutants, with exogenous and endogenous substrates. An alteration was found in the affinity of PKA in the mutant turnip. The procedure should be useful for rapid screening of mutants and drugs and could be adapted to additional types of protein kinases as well as protein phosphatases.

In vitro protein phosphorylation in head preparations from normal and mutant Drosophila melanogaster

We have characterized protein phosphorylation in vitro in subcellular fractions from Drosophila melanogaster heads. Optimal conditions for the incorporation of 32P into proteins, and its dependence on ATP, divalent cations, and cyclic nucleotides have been determined, as well as the effect of inhibitors of ATPase, protein phosphatase, and protein kinase on protein phosphorylation. Among these inhibitors, Zn2+ was found to affect the incorporation of 32P into specific bands and p-hydroxymercuribenzoate was found to be most suited for freezing the activity of both kinases and phosphatases. Cyclic AMP-dependent protein kinase (cAMP-dPK) activity was present in both supernatant (S2) and particulate (P2) fractions, with the majority (60-85%, depending on the homogenization medium) being associated with S2, as determined by phosphorylation of exogenous synapsin I. cAMP-dPK catalyzed the phosphorylation of at least 18 endogenous polypeptides in S2 and at least 10 endogenous polypeptides in P2. These proteins could be classified on the basis of the extent of stimulation of phosphorylation by cyclic nucleotides, dependence on cyclic nucleotide concentration, and rate of phosphorylation. A phosphoprotein of 51 kilodaltons (pp51) was a major component of the S2 and P2 fractions and displayed properties expected from the regulatory subunit of the cAMP-dPK, R-II. A phosphoprotein doublet of approximately 37 kilodaltons (pp37) was stimulated to the largest extent by cAMP in the P2 and S2 fractions. The phosphorylation of several proteins in both fractions was significantly lowered by the mammalian Walsh inhibitor of cAMP-dPK, whereas in some cases the stimulation of phosphorylation of the same proteins by exogeneous cAMP was relatively small. Phosphoproteins from two learning mutants known to be deficient in cAMP metabolism, dnc and rut, were analyzed for their extent of phosphorylation in the presence of a stable cAMP analogue; no significant differences from normal were detected, suggesting that the genetic defect in cAMP metabolism is not accompanied by constituent abnormalities in phosphorylated substrates in the adult fly, and that the physiological defects in these mutants result from aberrations in the interaction of the cAMP cascade with normal substrates. The majority of Ca2+/calmodulin kinase activity (80-90%, depending on the homogenization procedure) was associated with S2, as revealed by phosphorylation of exogenous synapsin I. Two endogenous substrates for this kinase in P2 had molecular masses of approximately 45 and 87 kilodaltons. At least 11 substrates for the Ca2+/calmodulin-dependent kinase were detected in S2.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of electromyography to quantify muscle pain

This study was designed to determine the feasibility of using electromyography (EMG) to quantify muscle pain in patients suffering from chronic myofacial pain dysfunction (MPD). Ten patients were carefully selected to include those having mild to severe pain, but not any major psychological or other physiological dysfunction. Measurements of perceived pain and EMG frequency and amplitude were recorded before and after standard analgesic therapy. EMG recordings were collected bilaterally from the masseter and anterior temporalis muscles during the resting, swallowing, clenching and chewing modes of activity. Multiple regression (R) analysis indicated that changes in perceived pain are correlated with changes in the EMG and can be determined by using the following formula: delta P = (delta F) (0.405) + C where P = perceived pain level, F = EMG frequency, and C = 1.533. By computing the Phi coefficients, the highest correlation between EMG recordings and subjective pain ratings was demonstrated in the resting mode. In this mode, 64% (multiple R = 0.80) of the variance in perceived pain difference scores from pre- to post-therapy tests could be determined. A significant relationship exists between the change in perceived pain and the EMG (t = 2.525, p less than 0.05), whether pain levels increase or decrease. The implementation of this method to quantify expected changes in pain due to muscle spasm in uncomplicated individuals is discussed.

A comparison of centric relation with maximum intercuspation based on quantitative electromyography

The study concerned the nature of the alterations, if any, in muscle activity demonstrable when the mandible shifts from maximum intercuspation into its most retruded physiological relation (i.e. centric relation). An integrator-averager was used to determine micro V average amplitude from masseter and temporal muscles in two maxillo-mandibular positions, centric relation and maximum intercuspation, and three modes, first contact occlusion, chewing and swallowing. Vertical reference marks on the cuspids were used to quantitate horizontal deviation from maximum intercuspation to centric relation. Data were obtained from twelve subjects and analysed for variance. Results demonstrated a significant increase in micro V in all centric relation positions. Statistics yielded an F value of 5.88258 with a probability of 0.005. Results suggest critical limitations in reliance on centric relation as a reference position during clinical therapy.