Tyrosine phosphorylation of tau accompanies disease progression in transgenic mouse models of tauopathy

AIM

Tau protein is a prominent component of paired helical filaments in Alzheimer's disease (AD) and other tauopathies. While the abnormal phosphorylation of tau on serine and threonine has been well established in the disease process, its phosphorylation on tyrosine has only recently been described. We previously showed that the Src family non-receptor tyrosine kinases (SFKs) Fyn and Src phosphorylate tau on Tyr18 and that phospho-Tyr18-tau was present in AD brain. In this study, we have investigated the appearance of phospho-Tyr18-tau, activated SFK and proliferating cell nuclear antigen (PCNA) during disease progression in a mouse model of human tauopathy.

METHODS

We have used JNPL3, which expresses human tau with P301L mutation, and antibodies specific for phospho-Tyr18-tau (9G3), ser/thr phosphorylated tau (AT8), activated SFK and PCNA. Antibody staining was viewed by either epifluorescence or confocal microscopy.

RESULTS

Phospho-Tyr18-tau appeared concurrently with AT8-reactive tau as early as 4 months in JNPL3. Some 9G3-positive cells also contained activated SFKs and PCNA. We also investigated the triple transgenic mouse model of AD and found that unlike the JNPL3 model, the appearance of 9G3 reactivity did not coincide with AT8 in the hippocampus, suggesting that the presence of APP/presenilin influences tau phosphorylation. Also, Thioflavin S-positive plaques were 9G3-negative, suggesting that phospho-Tyr18-tau is absent from the dystrophic neurites of the mouse triple transgenic brain.

CONCLUSIONS

Our results provide evidence for the association of tyrosine-phosphorylated tau with mechanisms of neuropathogenesis and indicate that SFK activation and cell cycle activation are also involved in JNPL3.

Simpler technique for measuring oxidative susceptibility by heparin affinity column isolation of lipoproteins

Variations in the in vitro oxidative susceptibility or resistance of lipoproteins have been used to test the effect of ingested antioxidants and may prove to be a marker for coronary artery disease. Here we describe a simple technique for isolating and oxidizing beta-lipoproteins that may have utility in the clinical laboratory. Electrophoretic profiles showed that beta-lipoproteins were separated from alpha-lipoproteins and essentially from most other serum proteins using heparin affinity columns. Lipoproteins were normalized in the reaction mixture by measuring apo B in the beta-lipoprotein eluate using an automated apo B method, which gave good recoveries of 106-112%. Copper mediated oxidation was monitored by measurement of conjugated dienes formation at 234 nm for 300 min. When the reaction mixture included beta-lipoprotein eluate containing 0.03 g/L of apoB and 5 micromol/L copper sulfate, conditions were effective for obtaining complete oxidation while allowing reproducible measurements, with between day coefficients of variation of 2.35%, 14.6%, and 10.5% for lag, propagation and plateau phases, respectively. Beta-lipoproteins isolated from serum were more susceptible to oxidation than beta-lipoproteins from plasma apparently due to inhibition of oxidation by fibrinogen which co-eluted with beta-lipoprotein from plasma. For this reason, we recommend using serum preserved with EDTA for this assay.

Mechanized lipoprotein(a) assay as a marker for coronary artery disease illustrates the usefulness of high lipoprotein(a) levels

Only a few simple lipoprotein(a) [Lp(a)] assays are available in kit form for use in clinical laboratories. The present study compares the analytical and clinical performance of a mechanized immunonephelometric method to enzyme-linked immunosorbent assay. Clinical performance was evaluated by measuring lipoprotein markers in 191 patients, with the extent of stenosis defined by angiography. Analytically, both methods showed little or no correlation with cholesterol, high density lipoprotein cholesterol, elevated triglycerides, apo A-I and apo B, while they showed good agreement with one another (r = 0.88). The methods showed comparable well known differences between black and white persons. Logistic regression indicated that Lp(a) was a weak but independent marker for coronary artery disease (CAD). Receiver operator characteristic curve analysis showed an association with CAD only at higher Lp(a) concentrations. We conclude that Lp(a) at higher concentrations may be a contributory marker for CAD and that mechanized nephelometric assays for it can be used in the clinical laboratory.

Implementation of a successful on-call system in clinical chemistry

Successful practice of clinical pathology depends on a wide variety of laboratory, clinical, and managerial decisions. The skills needed to make these decisions can most effectively be learned by residents and fellows in pathology using a service-oriented on-call approach. We report our experience implementing an on-call system in the clinical chemistry laboratory at the University of Louisville Hospital (Ky). We detail the guidelines used to establish this system and the elements required for its successful implementation. The system emphasizes a laboratory-initiated approach to linking laboratory results to patient care. From inception of the program during late 1990 through 1995, the number of beeper calls (including clinician contacts) steadily increased and is currently 8 to 20 per week. The on-call system is active 24 hours per day, 7 days per week, thus representing activity on all three laboratory shifts. Types of responses were separated into administrative (12%), analytical (42%), clinical (63%), quality control or quality assurance (12%), and consultation (13%) categories. We also present 6 case reports as examples demonstrating multiple elements in these categories. In 23% of the calls, clinician contact was required and achieved by the fellow or resident on call for the laboratory. The on-call reports are documented and presented informally at weekly on-call report sessions. Emphasis is placed on learning and refinement of investigative skills needed to function as an effective laboratory director. Educational emphasis for the medical staff is in establishing awareness of the presence of the laboratory as an important interactive component of patient care. In addition, we found this program to be beneficial to the hospital and to the department of pathology in fulfilling its clinical service and teaching missions. Our experience may be helpful to other institutions establishing such a program.

Optimized automated apolipoprotein A-I assays as markers for coronary artery disease

BACKGROUND

Studies are divided as to whether or not apolipoprotein A-I (apo A-I) is a better marker for coronary artery disease (CAD) than high-density lipoprotein cholesterol. We hypothesized that the detergent Tween 20, which is thought to expose antigenic sites in apo A-I, would improve automated kit apo A-I assays as a diagnostic marker for CAD.

METHODS

Apolipoprotein A-I was assayed by two standard automated methods and by the same methods after serum samples and reagents had been treated with Tween 20. Serum samples were obtained from 226 consecutive male patients, age 40-70 years, presenting for angiography, except for defined exclusion characteristics. Patients were categorized into two groups on the basis of stenosis: (1) normal, all vessels <20% stenosis, n = 79, and (2) CAD, at least one vessel >70% stenosis, n = 147. Diagnostic accuracy was assessed by receiver operator characteristic stenosis curves and forward stepwise logistic regression, where adjustment was made for significant possible confounding characteristics and drugs.

RESULTS

The optimal concentration of Tween 20 was found to be 0.5%. Receiver operator characteristic curves showed a greater area for apo A-I with Tween (area = 0.63 to 0.64) as compared to apo A-I without Tween (area = 0.60 to 0.62). Logistic regression indicated that apo A-I with Tween was a significantly better marker than high-density lipoprotein cholesterol. Receiver operator characteristic curves indicated that the ratio of modified apo A-I to apo B gave a significant improvement in area over the ratio of high-density to low-density lipoprotein cholesterol.

CONCLUSIONS

Addition of Tween 20 to apo A-I assays improved diagnostic discrimination for CAD. The modified apo A-I assays were better markers than high-density lipoprotein cholesterol, and the ratio of apolipoproteins was significantly better markers than lipoprotein lipids. These findings may explain the discrepancies between studies comparing high-density lipoprotein cholesterol and apo A-I as markers for CAD. Our data suggest that a multicenter effort toward optimizing and clinically validating apo A-I test reagents may be worthwhile.

Effect of 2',3'-dideoxycytidine on oxidative phosphorylation in the PC12 cell, a neuronal model

Peripheral neuropathy induced by 2',3'-dideoxycytidine (ddC) could result from the previously shown inhibition of mtDNA replication by the action of ddC on the mitochondrial enzyme DNA polymerase gamma. Such inhibition would be expected to impair oxidative phosphorylation, and this was demonstrated in the present study for the PC12 cell, a model of a peripheral neuron. The dramatic rise in lactate formation upon exposure of the cell to ddC indicated that increased glycolysis was needed to produce ATP. A concomitant rise in O2 uptake indicated that oxidative phosphorylation had become uncoupled. When tested in a standard respiratory control system (isolated rat liver mitochondria), however, we found ddC not to be an uncoupler. Rather, the uncoupling most likely resulted from the failure of synthesis of one or more mitochondrial gene products necessary for oxidative phosphorylation. We also observed an important distinction between the manner in which ddC and 3'-azido-3'-deoxythymidine (AZT) act. ddC-exerted inhibition of oxidative phosphorylation was delayed for several days. This is consistent with the inhibition occurring indirectly, most likely as a result of the prior destruction of the mitochondrial genome, which encodes many of the components of the oxidative phosphorylation system. In contrast, we have shown previously that although AZT also impairs replication of the mitochondrial genome (in the Friend murine erythroleukemic cell), it also attacks directly an additional primary target leading to impairment of oxidative phosphorylation; its initial inhibition of this process is immediate, not occurring via inhibition of mitochondrial DNA replication.

Hemoglobin interference with urinary Bence Jones protein analysis on electrophoresis

Two cases are described which show that on urine protein electrophoresis a paraprotein owing to hemoglobin cannot be distinguished from a Bence Jones protein. A simple method is described for confirming the presence of hemoglobin: a densitometric scan of the electrophoretogram at 415 nm, in which hemoglobin absorbs in a band coincident with the restriction. Furthermore, it is shown that other serum proteins, elevated levels of bilirubin, and Bence Jones protein do not interfere with this detection system.

Cellular targets of 3'-azido-3'-deoxythymidine: an early (non-delayed) effect on oxidative phosphorylation

Previous results demonstrated that incubation of the Friend murine erythroleukemic cell with 5 microM AZT for several days leads to a decrease in the rate of cell growth, inhibition of mtDNA replication, reduction of mtDNA per cell and per mitochondrion, and an increase in mitochondria per cell. As shown here, such treatment also leads to changes in lactate and ATP synthesis and in O2 uptake, suggesting impairment of oxidative phosphorylation. Direct measurement of ATP synthesis in mitochondria isolated from AZT-treated cells confirmed this view. The most significant new finding in this paper, however, is that in addition to these delayed effects of AZT, similar but very rapidly appearing effects on oxidative phosphorylation were noted, with changes observed in the above parameters including mitochondrial proliferation. Some of these occurred as early as 3 hr, only 7% of the doubling time, after exposure of the cells to 5 microM AZT, a period too short for initiation of appreciable mtDNA-mediated effects. Studies on isolated mitochondria provided no evidence of the identity of the immediate target of AZT: AZT does not act as an uncoupler or inhibitor of respiratory control, and previous results failed to implicate adenylate kinase. We have also begun to address the question of the mechanism of AZT-induced mitochondrial proliferation. Initial experiments showed that AZT inhibited synthesis of total cytosolic protein but stimulated synthesis of those proteins imported into mitochondria from the cytoplasm. We also report that aminothymidine, a catabolite of AZT in liver capable of inhibiting cell growth, was not generated by Friend cells.

Relationships between triglycerides, lipoproteins, glucose and coronary artery disease

We examined the relationship of apolipoprotein B (apo B), glucose, triglycerides and other lipoprotein lipids to coronary artery disease (CAD). Using receiver-operating characteristic curves (ROC), we noticed that the triglyceride ROC curve crossed above other lipoprotein curves at a triglycerides level of approximately 1.4 g/l. We examined subgroups of < 1.4 g/l and > 1.4 g/l. ANOVA (F = 18.9, P < 0.0001) and stepwise logistic regression (P = 0.0002) indicated that triglycerides were the best predictor in the < 1.4 g/l group. The best markers in the > 1.4 g/l group were low density lipoprotein cholesterol and apo B. Glucose did not appear to significantly alter the predictive power of triglycerides. These data suggest that triglyceride appears to be an overall significant univariate marker for CAD because of its effect at lower concentrations. The strong relationship between CAD and triglycerides at low triglyceride levels may reflect increased levels of very low density lipoprotein metabolites in some individuals. We conclude that some triglyceride-rich particles are independently atherogenic, that glucose did not alter this relationship and that when the samples were split into those with high and low levels of triglycerides, triglycerides and apo B but not HDLC was a significant predictor of CAD.

Mechanisms of toxicity of 3'-azido-3'-deoxythymidine. Its interaction with adenylate kinase

Recent experiments from our laboratory have indicated that the inhibitory effect of 3'-azido-3'-deoxythymidine (AZT) on oxidative phosphorylation may occur directly, in addition to being brought about by its inhibition of mtDNA replication. We report here studies on the effect of AZT on adenylate kinase, an enzyme crucial to oxidative phosphorylation. AZT decreased the aromatic residues fluorescence of rabbit muscle adenylate kinase, indicating binding of AZT to the enzyme. Of three other enzymes studied as controls, AZT bound only to those that possessed ATP/ADP binding sites. Up to concentrations of 15 microM, AZT was a more potent effector of fluorescence quenching than were ATP, ADP, AMP, and the AZT control, deoxythymidine. AZT strongly inhibited adenylate kinase in the direction of ATP synthesis (Ki, 8 microM), the inhibition being of the partial competitive type, whereas deoxythymidine inhibition, also partially competitive, was much weaker (Ki, 90 microM). When measured in the direction of ADP synthesis, AZT failed to demonstrate any inhibition at concentrations up to 10 microM. Experiments on isolated intact rat liver mitochondria with the enzyme activity measured in both directions confirmed the isolated enzyme results. Respiratory control by these mitochondria was not affected by AZT. The finding of AZT affinity for ATP/ADP binding sites may open new avenues of approach to the study of AZT toxicity.

Usefulness of various lactate dehydrogenase isoenzyme 1 profiles after myocardial infarction

Isoenzyme profiles of lactate dehydrogenase (percent LD-1 of total LD, LD-1/LD-2 ratio, and absolute LD-1) have all been studied as late markers for myocardial infarction. It is known, however, that elevations of LD-5 frequently occur in this period as a result of liver congestion. Elevations of LD-5 may also occur as a result of complicating conditions. Such elevations could result in a reduced percent LD-1 of total LD, giving rise to false negatives. Receiver operating characteristic (ROC) curves were constructed for LD-1, LD-1/LD-2 and percent LD-1 of total LD from 285 specimens (124 patients) with suspected myocardial infarction. There was little difference in overall diagnostic power among the three assays. Using cutoffs determined from the ROC curves, 6 patients (18 specimens) were evaluated who appeared to be in the late period or who exhibited complicating conditions which could increase LD-5. In 14/18 specimens, increases in LD-5 resulted in false negatives by percent LD-1 of total LD. Only 5/18 specimens were false negatives by LD-1 or LD-1/LD-2. It is concluded that the percent LD-1 of total LD was affected by an increase in LD-5, and caution is recommended when using it.

Anti-human immunodeficiency virus type 1 therapy and peripheral neuropathy: prevention of 2',3'-dideoxycytidine toxicity in PC12 cells, a neuronal model, by uridine and pyruvate

A strategy for preventing or delaying the peripheral neuropathy induced by 2',3'-dideoxycytidine (ddC) therapy in patients with acquired immunodeficiency syndrome was suggested by findings, in two laboratories, that cultured avian and mammalian cells devoid of mitochondrial DNA continue to replicate at virtually normal rates, provided that the medium is supplemented with uridine and pyruvate. Inasmuch as it is likely that a depletion of mitochondrial DNA also takes place in neuronal cells exposed to ddC, we used PC12 cells, the neuronal model we have reported on previously, in an attempt to rescue these cells from the deleterious effects of ddC. We first show, using undifferentiated PC12 cells, that DNA replication is impaired in mitochondria isolated from cells grown in the presence of ddC. Then, using growth rate as a criterion of the well-being of the cells, we show that the addition of uridine and pyruvate to uninduced cells growing in the presence of ddC results in an average rescue efficiency of 51%, based on the uridine/pyruvate-treated control. This value increases considerably at substantially higher concentrations of uridine alone. Rescue efficiencies of differentiated cells, which do not proliferate, were assessed using neurite outgrowth and neurite survival as criteria. Here the rescue efficiency is 56%, based on the uridine/pyruvate-treated control. In addition, uridine and pyruvate prolong the viability of ddC-treated cells and maintain their healthy appearance; without these compounds, the ddC-treated cells have an abnormal morphology and die off quite rapidly.

Yeasts isolated from bumblebee honey from western Canada: identification with the aid of proton magnetic resonance spectra of their mannose-containing polysaccharides

Yeasts were isolated from bumblebee honey collected in the Pincher Creek region of southwestern Alberta and the Melfort and Saskatoon regions of central Saskatchewan. The predominant species isolated were Torulopsis bombicola n. sp., which produces hydroxy fatty acid sophorosides, a Candida species which resembles it in its assimilatory reactions but which does not produce sophorosides, and Saccharomyces rouxii. A few cultures of Debaryomyces phaffii and Candida reukaufii were isolated. The mannans or galactomannans formed by representatives of each group were extracted and their proton magnetic resonance spectra determined and used as an aid in identification of the different species.