Potassium channel dysfunction in fibroblasts identifies patients with Alzheimer disease

In vitro patch-clamp studies in skin fibroblasts

We have conducted single-channel patch-clamp experiments in skin fibroblasts maintained in culture. Two different cell lines, a mouse 3T3-L1 cell line and a human B17 cell line, were selected for these pilot studies. Recordings were made from both cell-attached and excised inside-out patches at room temperature. In the case of the 3T3-L1 cells, the success rate in obtaining good seals (> 1Gomega) was low, and channel openings in either cell-attached or excised patches were rare. We have, however, identified a channel in a cell-attached configuration with a slope conductance of 39 pS in symmetrical K+ solutions. In the case of the human B17 cells, good quality seals were more readily obtained. One principal type of channel opening was identified. In cell-attached patches, the prevalent type of channel in symmetrical K+ solutions had a conductance of 187 pS. This channel was activated by strong depolarization, and there was usually more than one active channel in the patch. It was blocked by extracellular tetraethylammonium (20 mM), and persisted when external Cl- was replaced by aspartate. In excised inside-out patches bathed in symmetrical K+, this channel was activated by an increase in Ca+ applied to the intracellular face. A large conductance channel (175 pS) was also observed in excised inside-out patches, with a reverse physiological K+ gradient. This channel had a reversal potential > 40 mV and appeared not to be voltage-dependent under these recording conditions (2 mM Ca(2+)i). We conclude that the channel we have identified in these cells belongs to the maxi-K+ channel class.

Alzheimer's-specific effects of soluble beta-amyloid on protein kinase C-alpha and -gamma degradation in human fibroblasts

Alzheimer's disease (AD) is a multifactorial disease in which beta-amyloid peptide (betaAP) plays a critical role. We report here that the soluble fraction 1-40 of betaAP differentially degrades protein kinase C-alpha and -gamma (PKCalpha and PKCgamma) isoenzymes in normal (age-matched controls, AC) and AD fibroblasts most likely through proteolytic cascades. Treatment with nanomolar concentrations of betaAP(1-40) induced a 75% decrease in PKCalpha, but not PKCgamma, immunoreactivity in AC fibroblasts. In the AD fibroblasts, a 70% reduction of the PKCgamma, but not PKCalpha, immunoreactivity was observed after betaAP treatment. Preincubation of AC or AD fibroblasts with 50 microM lactacystine, a selective proteasome inhibitor, prevented beta-AP(1-40)-mediated degradation of PKCalpha in the AC cells, and PKCgamma in the AD fibroblasts. The effects of betaAP(1-40) on PKCalpha in AC fibroblasts were prevented by inhibition of protein synthesis and reversed by PKC activation. A 3-hr treatment with 100 nM phorbol 12-myristate 13-acetate restored the PKCalpha signal in treated AC cells but it did not reverse the effects of betaAP(1-40) on PKCgamma in the AD fibroblasts. Pretreatment with the protein synthesis inhibitor, cycloheximide (CHX, 100 microM), inhibited the effects of betaAP(1-40) on PKCalpha and blocked the rescue effect of phorbol 12-myristate 13-acetate in AC fibroblasts but did not modify PKCgamma immunoreactivity in AD cells. These results suggest that betaAP(1-40) differentially affects PKC regulation in AC and AD cells via proteolytic degradation and that PKC activation exerts a protective role via de novo protein synthesis in normal but not AD cells.

Fibroblast models of neurological disorders: fluorescence measurement studies

Biochemical studies of human fibroblasts from patients with neurological disorders have revealed a wealth of information on how such disorders occur. In this review, Gerald Connolly describes how recently developed fluorescence video imaging techniques have been used to study the physiology of skin fibroblasts isolated from patients with certain neurological disorders, including those produced by Alzheimer's disease, Lesch-Nyhan syndrome, mitochondrial disorders, amyotrophic lateral sclerosis and lysosomal disorders. The results of these studies indicate disruptions in cell homeostasis, particularly specific changes in Ca2+ homeostasis and autofluorescence, which mirror changes thought to occur in the CNS of neurologically impaired patients. More extensive studies of these 'systemic changes' using new fluorescent indicators, combined with advances in imaging techniques, are predicted to increase the potential usefulness of human skin fibroblasts as experimental models and to help diagnose and treat neurological disorders.

Presenilins upregulate functional K+ channel currents in mammalian cells

Mutations in presenilin 1 (PS-1) and presenilin 2 (PS-2) have been linked to early onset, autosomal dominant Alzheimer's disease. Neither the normal function(s) of the presenilins nor their role(s) in mediating the devastating neurological and pathological changes associated with Alzheimer's Disease, however, are well understood. The results of the experiments described here demonstrate that expression of wild-type PS-1 or PS-2 increases outward K+ current densities in HEK-293 cells relative to untransfected or mock-transfected cells. Western blot analysis reveals that there is a marked increase in full-length, rather than processed, presenilins in transiently transfected HEK-293 cells, suggesting that full-length PS-1 (or PS-2) underlies the observed increases in outward K+ current densities. Consistent with this hypothesis, EXpression of an N-terminal proteolytic fragment of PS-1 is without effects on the membrane properties of HEK-293 cells. Mean outward K+ current densities are also shown to be increased in HEK-293 cells expressing the exon 9 splice site PS-1 mutation (deltaex9/PS-1), a mutant that does not undergo proteolytic processing. In HEK- 293 cells transiently transfected with a missense (G209V) PS-1 mutant, however, mean K+ current densities were not significantly different from controls. Expression of wild-type PS-1 in neonatal rat ventricular myocytes also results in increased outward K+ currents, whereas no detectable effects on membrane currents were seen in PS-1-transfected COS-7 cells. These results suggest that the presenilins do not actually form K+ channels, but rather that these proteins upregulate functional K+ channel expression either directly by associating with K+ channel pore-forming subunits or indirectly by increasing the synthesis, assembly, and/or transport of these subunits. The observation that PS-1 and PS-2 are highly expressed in neurons, localized to the endoplasmic reticulum, suggests that the presenilins could regulate neuronal K+ channel expression; mutations in PS-1/PS-2 would then be expected to result in profound changes in neuronal excitability and contribute to the cognitive decline commonly associated with Alzheimer's Disease.

Bradykinin-induced amyloid precursor protein secretion: a protein kinase C-independent mechanism that is not altered in fibroblasts from patients with sporadic Alzheimer's disease

We treated human skin fibroblasts with bradykinin (BK) and observed a concentration-dependent increase in the release of soluble amyloid precursor protein (sAPP). The estimated EC50 for the observed effect is 2.8 nM, which is of the same order of magnitude as the reported Kd of BK binding in human skin fibroblasts. The effect of BK on sAPP secretion appears to be dependent on interaction of the ligand with the B2 type of BK receptors but independent of activation of protein kinase C. We also show that sAPP release after BK treatment in fibroblasts from patients with sporadic Alzheimer's disease is not different from control cells and is paralleled by equivalent levels of inositol trisphosphate production. A discussion of the differences from previously published work focuses on the possible divergent alterations in transduction systems in fibroblasts from patients with familial and sporadic Alzheimer's disease. Our results are the first example of receptor-mediated sAPP release in human skin fibroblasts and the first demonstration of the co-existence of protein kinase C-dependent and -independent mechanisms in these cells.

Influence of potassium channel modulators on cognitive processes in mice

1. The effect of i.c.v. administration of different potassium channel openers (minoxidil, pinacidil, cromakalim) and potassium channel blockers (tetraethylammonium, apamin, charybdotoxin, gliquidone, glibenclamide) on memory processes was evaluated in the mouse passive avoidance test. 2. The administration of minoxidil (10 microg per mouse i.c.v.), pinacidil (5-25 microg per mouse i.c.v.) and cromakalim (10-25 microg per mouse i.c.v.) immediately after the training session produced an amnesic effect. 3. Tetraethylammonium (TEA; 1-5 microg per mouse i.c.v.), apamin (10 ng per mouse i.c.v.), charybdotoxin (1 microg per mouse i.c.v.), gliquidone (3 microg per mouse i.c.v.) and glibenclamide (1 microg per mouse i.c.v.), administered 20 min before the training session, prevented the potassium channel opener-induced amnesia. 4. At the highest effective doses, none of the drugs impaired motor coordination, as revealed by the rota rod test, or modified spontaneous motility and inspection activity, as revealed by the hole board test. 5. These results suggest that the modulation of potassium channels plays an important role in the regulation of memory processes. On this basis, the potassium channel blockers could be useful in the treatment of cognitive deficits.

Age-related alteration of PKC, a key enzyme in memory processes: physiological and pathological examples

Brain aging is characterized by a progressive decline of the cognitive and memory functions. It is becoming increasingly clear that protein phosphorylation and, in particular, the activity of the calcium-phospholipid-dependent protein kinase C (PKC) may be one of the fundamental cellular changes associated with memory function. PKC is a multigene family of enzymes highly expressed in brain tissues. The activation of kinase C is coupled with its translocation from the cytosol to different intracellular sites and recent studies have demonstrated the key role played by several anchoring proteins in this mechanism. PKC-phosphorylating activity appears to be impaired during senescence at brain level in a strain-dependent fashion in rodents. Whereas the levels of the various isoforms do not show age-related alterations, the enzyme translocation upon phorbol-ester treatment is deficitary among all strains investigated. Anchoring proteins may contribute to this activation deficit. We discuss also modifications of the PKC system in Alzheimer's disease that may be related to pathological alterations in neurotransmission. A better insight of the different factors controlling brain-PKC activation may be important not only for elucidating the molecular basis of neuronal transmission, but also for identifying new approaches for correcting or even preventing age-dependent changes in brain function.

A reproducible procedure for primary culture and subsequent maintenance of multiple lines of human skin fibroblasts

Cultured fibroblasts are a valuable tool to study many cellular processes and their modification by aging. Fibroblasts are a useful cell type in which to study many diseases, including those of the nervous system, in which a strong genetic component is suspected. Fibroblasts permit the study of multiple, dynamic processes in living cells, while avoiding the effect of the dying process and post-mortem artifacts that limit other approaches. For results to be comparable across time in one laboratory or consistent between laboratories, the detailed culture techniques require meticulous care and replicability. Lack of attention to detail in initial stages can lead to selection of different cell populations. Small variations in othe variables such as batches of serum can significantly alter growth rates and comparisons of cells from controls and Alzheimer patients. The aim of this paper is to present a detailed protocol for comparison of multiple cell lines from many patients. An example of using this approach to study growth and phase out (i.e., senescence) of cells from Alzheimer patients is presented. This procedure represents a modification of an earlier protocol (Cristofalo and Charpentier, 1980).

Peripheral markers in testing pathophysiological hypotheses and diagnosing Alzheimer's disease

Alterations in amyloid precursor protein (APP) metabolism, calcium regulation, oxidative metabolism, and transduction systems have been implicated in Alzheimer's disease (AD). Limitations to the use of postmortem brain for examining molecular mechanisms underscore the need to develop a human tissue model representative of the pathophysiological processes that characterize AD. The use of peripheral tissues, particularly of cultured skin fibroblasts derived from AD patients, could complement studies of autopsy samples and provide a useful tool with which to investigate such dynamic processes as signal transduction systems, ionic homeostasis, oxidative metabolism, and APP processing. Peripheral cells as well as body fluids (i.e., plasma and CSF) could also provide peripheral biological markers for the diagnosis of AD. The criteria required for a definite diagnosis of AD presently include clinical criteria in association with histopathologic evidence obtained from biopsy or autopsy. Thus, the use of peripheral markers as a diagnostic tool, either to predict or at least to confirm a diagnosis, may be of great importance.

Characterization of the acetylcholine-reducing effect of the amyloid-beta peptide in mouse SN56 cells

We previously reported that the amyloid-beta protein (Abeta) reduces the synthesis of acetylcholine (ACh) in a mouse septal cell line, SN56, without causing death of the cells. Here, we report that the ACh-reducing effect of either Abeta 1-28 or Abeta 1-42 (100 nM; 48 h) in SN56 cells can be prevented by a co-treatment with the tyrosine kinase inhibitors, genistein (75 microM) and tyrphostin A25 (50 microM). Treatment of the cells with either of these inhibitors alone increased ACh levels. An enhancement of the cellular ACh content was also obtained with aphidicolin, a compound which inhibits DNA synthesis. However, co-treatment of the cells for 48 h with aphidicolin (500 nM) and Abeta 1-42 (100 nM) did not prevent the reduction in ACh levels caused by the peptide. Furthermore, this effect could not prevented by a pre-treatment with vitamin E (50 microg/ml). These results suggest that the ACh-reducing effect of Abeta in SN56 cells is dependent on tyrosine phosphorylation, but is not dependent on DNA synthesis and may not be mediated by free radicals.

Abnormalities in Alzheimer's disease fibroblasts bearing the APP670/671 mutation

Abnormalities in cultured fibroblasts from familial Alzheimer's Disease (FAD) cases uniquely enable the determination of how gene defects alter cell biology in living tissue from affected individuals. The current study focused on measures of calcium regulation and oxidative metabolism in fibroblast lines from controls and FAD individuals with the Swedish APP670/671 mutation. Bombesin-induced elevations in calcium in APP670/671 mutation-bearing lines were reduced by 40% (p < 0.05), a striking contrast to the 100% increase seen in sporadic AD and presenilin-1 (PS1) mutation-bearing cells in previously published studies. The APP670/671 mutation-bearing lines did not exhibit the exaggerated 4-bromo-A23187 releasable pool of calcium following 10 nM bradykinin, the enhanced sensitivity of calcium stores to low concentrations of bradykinin, nor the reduced activity of alpha-ketoglutarate dehydrogenase previously reported in cells from sporadic AD and mutant PS1 FAD. Thus, an altered regulation of internal calcium stores is common to all AD lines, but the calcium pool affected and the polarity of the alteration varies, apparently in association with particular gene mutations. Comparison of signal transduction in cell lines from multiple, genetically characterized AD families will allow testing of the hypothesis that these various pathogenic FAD abnormalities that lead to AD converge at the level of abnormal signal transduction.

G protein subunit levels in fibroblasts from familial Alzheimer's disease patients: lower levels of high molecular weight Gs alpha isoform in patients with decreased beta-adrenergic receptor stimulated cAMP formation

Abnormalities in G protein linked signal transduction pathways have been detected in fibroblasts from individuals with familial and sporadic Alzheimer's disease. The present study used Gs alpha, Gi alpha, Gq alpha and Go alpha G protein subunit antisera, immunoblotting and densitometry to quantify levels of these proteins in control fibroblasts and in fibroblasts from individuals with familial Alzheimer's disease (FAD). The FAD fibroblasts were from individuals with the APPK670N,M671L mutation, different presenilin 1 (PS1) mutations and one fibroblast cell line from an individual with FAD of unknown genetic aetiology. Results revealed a significant reduction in the large Gs alpha subunit in fibroblasts with the PS1 mutations and in the fibroblast cell line of unknown genetic aetiology, when compared to control levels. This decrease was not apparent in the APPK670N,M671L FAD fibroblasts. Immunoreactivity for Go alpha was not detected in any of the fibroblast cell lines. No differences were observed in Gi alpha or Gq alpha levels when comparing any of the control and Alzheimer's disease fibroblast groups. WE conclude that with the exception of decreased levels of the large Gs alpha subunit, gross alterations in the levels of the Gi alpha, Gq alpha and Go alpha are not associated with the G protein-coupled signal transduction disturbances described previously for some of these FAD fibroblasts.

Cysteine proteinases are responsible for characteristic transketolase alterations in Alzheimer fibroblasts

Cultured fibroblasts from patients affected by Alzheimer's disease (AD) exhibited peculiar alterations of the enzyme transketolase (TK). Abnormalities (dubbed alkaline bands, ab) consisted of enzyme forms having unusually high pl and were proposed as a marker of the disease in living patients. The mechanisms of TK-ab expression were investigated with the use of cysteine proteinase inhibitors and purified preparations of either rat liver or human cysteine proteinases. The cysteine proteinase inhibitors N-acetyl-leu-leu-norleucinal (ALLN), L-trans-Epoxy-succinyl-leucylamido(4-guanidino)butane (E-64), and egg white cystatin added to AD cells just prior to extraction abolished TK abnormalities. Moreover, 1 day incubation of AD cultures with either ALLN (10 micrograms/ml), NH4Cl (10 mM), or KCl (30 mM) prevented TK-ab generation, due, presumably, to an impairment of lysosomal functions. Isolated rat liver cysteine proteinases were able to degrade TK in normal extracts and reproduce the characteristic TK-ab of AD fibroblasts. Moreover, pure human cathepsin H was also shown to partially induce an Alzheimer-like TK pattern and cleave normal TK to a 35 kDa fragment as spontaneously occurring in AD fibroblasts. The explanation of mechanisms of TK-ab formation provided evidence for an underlying imbalance of proteolysis in AD fibroblasts due to a relative increase/derangement of the cysteine proteinases cathepsins which might be also involved in the reported abnormal processing of multiple cellular components.

Impaired calcium regulation in subcortical vascular encephalopathy

BACKGROUND AND PURPOSE

A number of clinical observations and first in vitro findings indicate that chronic cerebral ischemia influences immunologic status, such as the proliferative response of T lymphocytes. The purpose of the present report was to assess (1) whether changes of immune function are likewise detectable in patients with progressive subcortical vascular encephalopathy (SVE) by investigating the [Ca2+]i homeostasis of lymphocytes and (2) whether differences exist in calcium regulation between lymphocytes from SVE patients and from Alzheimer's disease (AD) patients. This is of great interest, since specific changes have been reported recently in AD patients.

METHODS

[Ca2+]i was recorded in 26 patients with SVE, 26 age-matched nondemented control subjects, and 26 age-matched patients with AD. Basal [Ca2+]i and [Ca2+]i after lymphocyte activation with the mitogen phytohemagglutinin (PHA) were measured with the fura 2 method. In addition, modulation of the Ca2+ signaling by the peptide beta-amyloid and the potassium channel blocker tetraethylammonium was studied.

RESULTS

Basal [Ca2+]i was not different between patients and control subjects. After stimulation with PHA, however, a significant reduction of the Ca2+ response could be observed in lymphocytes of SVE patients compared with control subjects and with AD patients, providing evidence that the Ca2+ homeostasis of lymphocytes is impaired in SVE. The effect of the peptide beta-amyloid, the major constituent of senile plaques in AD brain, on Ca2+ signaling was similar in SVE patients and nondemented control subjects but typically reduced in cells of AD patients. Potassium channels were not involved in the impaired Ca2+ response of SVE lymphocytes after cell activation.

CONCLUSIONS

[Ca2+]i is not only one of the most important second messengers in signal transduction of many cells but also an early event in the signal cascade of cell proliferation as a reaction to antigen recognition. This mechanism seems to be impaired in SVE. These findings may result in new insights regarding the pathogenesis of this disease and the possible involvement of inflammatory or immunologic disturbances.

Ionic effects of the Alzheimer's disease beta-amyloid precursor protein and its metabolic fragments

Alzheimer's disease is a progressive dementia characterized in part by deposition of proteinaceous plaques in various areas of the brain. The main plaque protein component is beta-amyloid, a metabolic product of the beta-amyloid precursor protein. Substantial evidence has implicated beta-amyloid (and other amyloidogenic fragments of the precursor protein) with the neurodegeneration observed in Alzheimer's disease. Recently, beta-amyloid precursor protein and its amyloidogenic metabolic fragments have been shown to alter cellular ionic activity, either through interaction with existing channels or by de novo channel formation. Such alteration in ionic homeostasis has also been linked with cellular toxicity and might provide a molecular mechanism underlying the neurodegeneration seen in Alzheimer's disease.

Defective protein kinase C alpha leads to impaired secretion of soluble beta-amyloid precursor protein from Alzheimer's disease fibroblasts

The present study shows that cultured fibroblasts from sporadic AD patients present: a) reduced (-30%) cytosolic protein kinase C (PKC) activity; b) increased KD of phorbol ester binding (+94%) in cytosolic fractions; c) reduced (-30%) soluble protein kinase C alpha immunoreactivity; d) lower (-27.5%) basal soluble APP secretion and e) reduced soluble APP secretion in response to low phorbol ester concentrations (over threefold difference using 9 nM phorbol-12,13-dibutyrate-PdBu). Since the PKC-stimulated secretion of APP leads to the cleavage of the precursor within the amyloidogenic beta-A4 fragment, the reduced PKC activity in AD patients may lead to accumulation of potentially amyloidogenic or toxic APP fragments. A defect in the secretion of soluble amyloid beta-protein precursor is indeed suggested by literature data on familial AD fibroblasts as well as by the reported results.

Activation of K+ channels and suppression of neuronal activity by secreted beta-amyloid-precursor protein

The Alzheimer's beta-amyloid precursor protein (beta-APP) is widely expressed in neural cells, and in neurons secreted forms of beta-APP (sAPPs) are released from membrane-spanning holo-beta APP in an activity-dependent manner. Secreted APPs can modulate neurite outgrowth, synaptogenesis, synaptic plasticity and cell survival; a signal transduction mechanism of sAPPs may involve modulation of intracellular calcium levels ([Ca2+]i). Here we use whole-cell perforated patch and single-channel patch-clamp analysis of hippocampal neurons to demonstrate that sAPPs suppress action potentials and hyperpolarize neurons by activating high-conductance, charybdotoxin-sensitive K+ channels. Activation of K+ channels by sAPPs was mimicked by a cyclic GMP analogue and sodium nitroprusside and blocked by an antagonist of cGMP-dependent kinase and a phosphatase inhibitor, suggesting that the effect is mediated by cGMP and protein dephosphorylation. Calcium imaging studies indicate that activation of K+ channels mediates the ability of sAPPs to decrease [Ca2+]i. Modulation of neuronal excitability may be a major mechanism by which beta-APP regulates developmental and synaptic plasticity in the nervous system.

Cloning of a gene bearing missense mutations in early-onset familial Alzheimer's disease

Some cases of Alzheimer's disease are inherited as an autosomal dominant trait. Genetic linkage studies have mapped a locus (AD3) associated with susceptibility to a very aggressive form of Alzheimer's disease to chromosome 14q24.3. We have defined a minimal cosegregating region containing the AD3 gene, and isolated at least 19 different transcripts encoded within this region. One of these transcripts (S182) corresponds to a novel gene whose product is predicted to contain multiple transmembrane domains and resembles an integral membrane protein. Five different missense mutations have been found that cosegregate with early-onset familial Alzheimer's disease. Because these changes occurred in conserved domains of this gene, and are not present in normal controls, they are likely to be causative of AD3.

Alzheimer and beta-amyloid-treated fibroblasts demonstrate a decrease in a memory-associated GTP-binding protein, Cp20

The two proteins most consistently identified in the brains of patients with Alzheimer disease (AD) have been beta-amyloid and tau, whose roles in the physiology or pathophysiology of brain cells are not fully understood. To identify other protein(s) involved in AD that have been implicated in physiological contexts, we undertook to analyze a specific memory-associated protein, Cp20, in fibroblasts from AD and control donors. Cp20, a GTP-binding protein that is a member of the ADP-ribosylation factor family, was significantly decreased in fibroblasts from AD patients. Normal control fibroblasts exposed to 10 nM beta-amyloid, the same concentration that induced AD-like K+ changes in control fibroblasts, showed a similar decrease in Cp20. Since it has been previously demonstrated that Cp20 is a potent regulator of K+ channels, these findings suggest that changes in this memory-associated protein may explain previously observed differences in AD K+ channels and suggest a pathophysiologic involvement linked to soluble beta-amyloid metabolism that could contribute to the characteristic memory loss of AD.

Abnormal calcium homeostasis and mitochondrial polarization in a human encephalomyopathy

Patients with several inherited human encephalomyopathies exhibit systemic and neurological symptoms in association with specific mitochondrial mutations. The mechanisms by which these mitochondrial mutations result in cellular injury have not been elucidated. One potential cause of neuronal vulnerability is an inability to effectively buffer intracellular calcium. We report that fibroblasts from patients with one specific inherited encephalomyopathy, MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome, have elevated levels of ionized calcium and cannot normally sequester calcium influxes. Quantitative fluorescence imaging demonstrated that this abnormality was associated with a relative decrease in mitochondrial membrane potential compared to control fibroblasts. This documentation of pathological calcium homeostasis in a genetic neurological disease extends the calcium hypothesis of toxic cell injury to human mitochondrial encephalomyopathies.

Molecular mechanisms of memory and the pathophysiology of Alzheimer's disease

Research on molecular and biophysical mechanisms of associative learning and memory storage identified a number of key elements that are phylogenetically conserved. In both vertebrates and invertebrates, K+ channels, PKC, Cp20, and intracellular Ca2+ regulation play a fundamental role in memory mechanisms. Because memory loss is the hallmark and perhaps the earliest sign of Alzheimer's disease, we hypothesized that these normal memory mechanisms might be altered in AD. With the use of a variety of experimental methodologies, our results revealed that one of the critical elements in memory storage, K+ channels, are dysfunctional in AD fibroblasts. Moreover, beta-amyloid induced the same K+ dysfunction in normal cells. Intracellular Ca2+ release, also associated with molecular memory mechanisms, was found altered in fibroblasts from patients with AD. The results therefore strongly suggest that biophysical and molecular mechanisms of associative learning could be altered in AD and that they may contribute to the memory loss observed early in the disease.

Tau-like immunoreactivity in Alzheimer and control skin fibroblasts

The presence of the microtubule-associated protein tau in skin fibroblasts derived from Alzheimer patients and normal controls was investigated using a panel of well-characterized anti-tau antibodies against epitopes spanning the tau protein from the amino to the carboxyl end. The antibodies immunolabeled a fine, fibrillar cytoplasmic network in all skin fibroblasts. Disruption of the microtubule network with colchicine did not affect the immunolabeling of the fibrillar network nor did treatment with cytochalasin B known to disrupt the microfilament network. Immunoelectron microscopy with the anti-tau antibodies revealed colocalization of the label with the 10 nm intermediate filaments. Furthermore, immunoblots found no reactivity against purified vimentin, suggesting that the antibodies recognize an intermediate filament-associated protein. The findings indicate the presence of tau or a protein with considerable homology to tau in fibroblasts associated with intermediate filaments and not microtubules.

Comorbidity of other chronic age-dependent diseases in dementia

This study compares the prevalence rates of 5 common age-dependent diseases in non-demented and demented subjects. Control and dementia populations were approximately age-matched and their numbers also approximated. Prevalence rates for hypertension, myocardial infarction (MI), stroke, cancer and diabetes were determined. The rates of two or more coexisting diseases in the same patient were also compared. Two populations were studied: one was designated the autopsy series, and the other the hospital series. In the autopsy series, the rate of cardiomegaly/hypertension was 1.3 times higher in the control than in the dementia population, and for MI it was 1.7 times higher in the former than in the latter. The rate for stroke was higher in the control group by only a factor of 1.1, for cancer by only a factor of 1.2, and for diabetes the rates were almost identical in the two populations. The rate differences were statistically significant only with respect to cardiomegaly and MI. When the non-vascular and vascular dementias were compared, the rates in the latter were higher by only a factor of 1.3 for cardiomegaly, stroke, cancer and diabetes; for MIs, the rates were about the same in the two dementia categories. The data for two or more coexisting diseases were almost identical in control and dementia autopsy populations. In the hospital series, the hypertension rate was 1.6 times higher in the control than in the Alzheimer's disease (AD) group; for MI, the control group was higher by a factor of 1.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Soluble beta-amyloid induction of Alzheimer's phenotype for human fibroblast K+ channels

Although beta-amyloid is the main constituent of neurite plaques and may play a role in the pathophysiology of Alzheimer's disease, mechanisms by which soluble beta-amyloid might produce early symptoms such as memory loss before diffuse plaque deposition have not been implicated. Treatment of fibroblasts with beta-amyloid (10 nM) induced the same potassium channel dysfunction previously shown to occur specifically in fibroblasts from patients with Alzheimer's disease--namely, the absence of a 113-picosiemen potassium channel. A tetraethylammonium-induced increase of intracellular concentrations of calcium, [Ca2+]i, a response that depends on functional 113-picosiemen potassium channels, was also eliminated or markedly reduced by 10 nM beta-amyloid. Increased [Ca2+]i induced by high concentrations of extracellular potassium and 166-picosiemen potassium channels were unaffected by 10 nM beta-amyloid. In Alzheimer's disease, then, beta-amyloid might alter potassium channels and thus impair neuronal function to produce symptoms such as memory loss by a means other than plaque formation.

Internal Ca2+ mobilization is altered in fibroblasts from patients with Alzheimer disease

The recent demonstration of K+ channel dysfunction in fibroblasts from Alzheimer disease (AD) patients and past observations of Ca(2+)-mediated K+ channel modulation during memory storage suggested that AD, which is characterized by memory loss and other cognitive deficits, might also involve dysfunction of intracellular Ca2+ mobilization. Bombesin-induced Ca2+ release, which is inositol trisphosphate-mediated, is shown here to be greatly enhanced in AD fibroblasts compared with fibroblasts from control groups. Bradykinin, another activator of phospholipase C, elicits similar enhancement of Ca2+ signaling in AD fibroblasts. By contrast, thapsigargin, an agent that releases Ca2+ by direct action on the endoplasmic reticulum, produced no differences in Ca2+ increase between AD and control fibroblasts. Depolarization-induced Ca2+ influx data previously demonstrated the absence of between-group differences of Ca2+ pumping and/or buffering. There was no correlation between the number of passages in tissue culture and the observed Ca2+ responses. Furthermore, cells of all groups were seeded and analyzed at the same densities. Radioligand binding experiments indicated that the number and affinity of bombesin receptors cannot explain the observed differences. These and previous observations suggest that the differences in bombesin and bradykinin responses in fibroblasts and perhaps other cell types are likely to be due to alteration of inositol trisphosphate-mediated release of intracellular Ca2+.