Guy Lacombe

Age-related impairment of p56lck and ZAP-70 activities in human T lymphocytes activated through the TcR/CD3 complex

Cellular immune responses decrease with aging. Lymphocytes of aged individuals do not perform as well as cells from young subjects in a number of in vitro assays including cell proliferation, cytokine production, and protection against apoptosis. Here, we have tested the hypothesis that a decrease in T cell responses in tymphocytes from elderly subjects could parallel a decrease in the activity of protein tyrosine kinases (PTK) associated with signal transduction in T lymphocytes. We report that anti-CD3-triggered T lymphocyte proliferation was significantly decreased in T lymphocytes from elderly subjects, but the decrease was not due to an alteration of the percentage or mean fluorescence intensities of CD3, CD4, and CD45. Of significance, the activities of p56lck and ZAP-70 in vitro were significantly decreased in T lymphocytes from elderly subjects compared to young individuals. However, the level of expression of the two kinases did not change with aging. The activity of p59fyn did not show changes with aging, suggesting that p59fyn did not compensate for the decreased activity of p56lck. We also found that the extent of tyrosine phosphorylation of the adaptor protein p95vav was similar in activated T lymphocytes from elderly and young subjects. Our results suggest that the altered cellular immune responses observed in T lymphocytes with aging may be the result, at least in part, of an alteration in early events associated with signal transduction through the TcR/CD3 complex that translates into decreased activities of p56lck and ZAP-70. Impairment in the activities of these twokey components of T cell signaling may contribute to reduced immune functions associated with aging.

Increased susceptibility of low‐density lipoprotein (LDL) to oxidation by γ‐radiolysis with age

The susceptibility to oxidation of freshly isolated LDL from healthy normolipidemic individuals in three age groups was estimated by exposure of LDL to ionizing radiation followed by analyses of vitamin E, TBARS, conjugated dienes, and fluorescent products. The results clearly showed that LDL from elderly subjects was the most susceptible to oxidative damage in vitro. In particular, the greater susceptibility of LDL from elderly subjects in comparison to that from young subjects may be attributed to the much lower (4‐fold) concentration of LDL vitamin E in the elderly subjects. The present study reinforces the notion that the susceptibility of LDL to oxidation increases with age.

Cellular distribution of protein kinase C isozymes in CD3-mediated stimulation of human T lymphocytes with aging

Protein kinase C (PKC) is involved in a variety of cellular responses, such as the expression and secretion of IL‐2, the regulation of cytotoxic killing and cell proliferation. It is known that these immune functions are altered with aging. Here, we show that anti‐CD3‐triggered T cell proliferation is significantly decreased with aging and that H7, an inhibitor of PKC, impairs the anti‐CD3‐induced T cell proliferation in a differential manner, lymphocytes of healthy young subjects being more sensitive to the PKC inhibitor than those of elderly subjects. We examined (Western blot) the presence and the cellular distribution of PKC isozymes in T lymphocytes of healthy young and elderly subjects in the resting state and after anti‐CD3 mAb stimulation using antibodies directed against PKC α, β, δ, ϵ and ζ isoforms in the cytosol and the plasma membrane fractions. These five PKC isotypes were present in human T cells of young and elderly subjects. However, their distribution between the cytosolic and membrane fractions varied according to the isozymes and the age of the subjects. In resting lymphocytes of young subjects, all the PKC isozymes were found in the cytosolic fraction, except PKC‐ζ. In resting lymphocytes of elderly subjects PKC‐δ and ‐ϵ were almost equally distributed between the cytosolic and the membrane fractions, whereas PKC‐α and ‐ζ were mainly found in the membrane fraction and PKC‐β was almost exclusively located in the cytosolic fraction. The translocation of PKC‐α, ‐β, ‐δ and ‐ϵ could be observed under anti‐CD3 mAb stimulation in lymphocytes of young subjects, while in the case of elderly subjects only the PKC β isoform was translocated. Our results suggest that the decreased availability of cytosolic PKC may contribute to the diminished PKC‐dependent responses to CD3‐triggered stimulation of human T lymphocytes with aging.

Cyclodextrin modulation of T lymphocyte signal transduction with aging

There is an alteration of the immune response in aging that leads to the increased incidence of infections, cancers and autoimmune disorders. The aim of the present study was to investigate whether there exists changes in signal transduction under the IL-2 receptor stimulation and the role of plasma membrane cholesterol in the activation of T cells with aging. We report age-related changes in the JAK-STAT signalling pathway that results in decreased tyrosine phosphorylation of STAT5. We present evidence for the importance of cholesterol content in regulating signalling pathways in T cells and in modulating their proliferation by using the plasma membrane cholesterol-depleting agent methyl-beta-cyclodexrin (MBCD). MBCD treatment (0.5 mM) induced a significant decrease in the cholesterol content of T cells of elderly subjects whereas it was increased in T cells of young subjects. MBCD induced changes in the phosphorylation of p56(lck), especially in T cells of elderly subjects. The proliferation of MBCD-treated T cells decreased in lymphocytes of young subjects but did not change in T cells of elderly subjects. These results suggest a role for plasma membrane cholesterol in the regulation of the TcR signalling pathways with differential effects related to aging. However, the data suggest that modulation of the plasma membrane cholesterol content alone may not be enough to restore signal transduction changes with aging.

Lower Brain 18F-Fluorodeoxyglucose Uptake But Normal 11C-Acetoacetate Metabolism in Mild Alzheimer's Disease Dementia

BACKGROUND The cerebral metabolic rate of glucose (CMRg) is lower in specific brain regions in Alzheimers disease (AD). The ketones, acetoacetate and β-hydroxybutyrate, are the brains main alternative energy substrates to glucose. OBJECTIVE To gain insight into brain fuel metabolism in mild AD dementia by determining whether the regional CMR and the rate constant of acetoacetate (CMRa and Ka, respectively) reflect the same metabolic deficit reported for cerebral glucose uptake (CMRg and Kg). METHODS Mild AD dementia (Mild AD; n = 10, age 76 y) patients were compared with gender- and age-matched cognitively normal older adults (Controls; n = 29, age 75 y) using a PET/MRI protocol and analyzed with both ROI- and voxel-based methods. RESULTS ROI-based analysis showed 13% lower global CMRg in the gray matter of mild AD dementia versus Controls (34.2 ± 5.0 versus 38.3 ± 4.7 μmol/100 g/min, respectively; p = 0.015), with CMRg and Kg in the parietal cortex, posterior cingulate, and thalamus being the most affected (p ≤ 0.022). Neither global nor regional CMRa or Ka differed between the two groups (all p ≥ 0.188). Voxel-based analysis showed a similar metabolic pattern to ROI-based analysis with seven clusters of significantly lower CMRg in the mild AD dementia group (uncorrected p ≤ 0.005) but with no difference in CMRa. CONCLUSION Regional brain energy substrate hypometabolism in mild AD dementia may be specific to impaired glucose uptake and/or utilization. This suggests a potential avenue for compensating brain energy deficit in AD dementia with ketones.

Multicenter Validation of an MMSE-MoCA Conversion Table

Accumulating evidence points to the superiority of the MoCA over the MMSE as a cognitive screening tool. To facilitate the transition from the MMSE to the MoCA in clinical and research settings, authors have developed MMSE‐MoCA conversion tables. However, it is unknown whether a conversion table generated from Alzheimers disease (AD) patients would apply to patients with other dementia subtypes like vascular dementia or frontotemporal dementia. Furthermore, the reliability and accuracy of MMSE‐MoCA conversion tables has not been properly evaluated.

A 3-Month Aerobic Training Program Improves Brain Energy Metabolism in Mild Alzheimer’s Disease: Preliminary Results from a Neuroimaging Study

BACKGROUND Aerobic training has some benefits for delaying the onset or progression of Alzheimers disease (AD). Little is known about the implication of the brains two main fuels, glucose and ketones (acetoacetate), associated with thesebenefits. OBJECTIVE To determine whether aerobic exercise training modifies brain energy metabolism in mild AD. METHODS In this uncontrolled study, ten patients with mild AD participated in a 3-month, individualized, moderate-intensity aerobic training on a treadmill (Walking). Quantitative measurement of brain uptake of glucose (CMRglu) and acetoacetate (CMRacac) using neuroimaging and cognitive testing were done before and after the Walking program. RESULTS Four men and six women with an average global cognitive score (MMSE) of 26/30 and an average age of 73 y completed the Walking program. Average total distance and treadmill speed were 8 km/week and 4 km/h, respectively. Compared to the Baseline, after Walking, CMRacac was three-fold higher (0.6±0.4 versus 0.2±0.1 μmol/100 g/min; p = 0.01). Plasma acetoacetate concentration and the blood-to-brain acetoacetate influx rate constant were also increased by 2-3-fold (all p≤0.03). CMRglu was unchanged after Walking (28.0±0.1 μmol/100 g/min; p = 0.96). There was a tendency toward improvement in the Stroop-color naming test (-10% completion time, p = 0.06). Performance on the Trail Making A&B tests was also directly related to plasma acetoacetate and CMRacac (all p≤0.01). CONCLUSION In mild AD, aerobic training improved brain energy metabolism by increasing ketone uptake and utilization while maintaining brain glucose uptake, and could potentially be associated with some cognitive improvement.

Impact of AP@LZ in the daily life of three persons with Alzheimer's disease: long-term use and further exploration of its effectiveness.

ABSTRACT AP@LZ is an electronic organiser that was designed to support the day-to-day activities of persons with Alzheimer’s disease. To assess the potential of this technology, three participants (NI, JB, RD) were approached to take part in the study. They benefited from a structured cognitive intervention to learn how to operate AP@LZ; the intervention included the following learning stages: Acquisition, Application and Adaptation. Pre- and post-intervention measures were collected. NI, for whom a longitudinal study was conducted, still continued to use AP@LZ 24 months post-intervention. JB and RD also showed a gradual improvement in their performance throughout the intervention phase (sessions 1 to 19 for JB: performance increased from 50 to 100%; sessions 1 to 25 for RD: from 56 to 89%). The results of the use of AP@LZ in activities of daily living suggest that the application was beneficial for three persons with Alzheimer’s disease whose profiles differed notably (age, cognitive and social profiles). Thus, results indicate that they were all able to learn how to operate AP@LZ’s functions and to use them in their activities of daily living. Cognitive intervention appears to play an important role for the promotion of learning and adoption of such technology.

Can an Infection Hypothesis Explain the Beta Amyloid Hypothesis of Alzheimer’s Disease?

Alzheimer’s disease (AD) is the most frequent type of dementia. The pathological hallmarks of the disease are extracellular senile plaques composed of beta-amyloid peptide (Aβ) and intracellular neurofibrillary tangles composed of pTau. These findings led to the “beta-amyloid hypothesis” that proposes that Aβ is the major cause of AD. Clinical trials targeting Aβ in the brain have mostly failed, whether they attempted to decrease Aβ production by BACE inhibitors or by antibodies. These failures suggest a need to find new hypotheses to explain AD pathogenesis and generate new targets for intervention to prevent and treat the disease. Many years ago, the “infection hypothesis” was proposed, but received little attention. However, the recent discovery that Aβ is an antimicrobial peptide (AMP) acting against bacteria, fungi, and viruses gives increased credence to an infection hypothesis in the etiology of AD. We and others have shown that microbial infection increases the synthesis of this AMP. Here, we propose that the production of Aβ as an AMP will be beneficial on first microbial challenge but will become progressively detrimental as the infection becomes chronic and reactivates from time to time. Furthermore, we propose that host measures to remove excess Aβ decrease over time due to microglial senescence and microbial biofilm formation. We propose that this biofilm aggregates with Aβ to form the plaques in the brain of AD patients. In this review, we will develop this connection between Infection – Aβ – AD and discuss future possible treatments based on this paradigm.

Orthostatic hypotension associated with executive dysfunction in mild cognitive impairment

INTRODUCTION Midlife hypertension is associated with dementia in longitudinal studies while chronic hypotension in the elderly is associated with dementia onset. Orthostatic hypotension could influence cognitive performance in the elderly. The objective of this study was to assess the relationship between orthostatic hypotension and cognitive functions. METHODS Consecutive participants with complete neuropsychological evaluation from a Memory Clinic were included. Orthostatic hypotension (OH) was defined by a fall≥20/10mmHg systolic/diastolic pressure. Participants were classified into one of 3 groups: 1) subjective cognitive impairment (SCI), 2) mild cognitive impairment (MCI), and 3) dementia. Neuropsychological tests were analyzed for patients with and without OH. RESULTS One hundred and twenty participants were included, of which 16 (13%) were classified as SCI, 42 (35%) as MCI, and 63 (52%) with dementia. Prevalence of OH was 0% for the SCI group, 26% (n=11) for the MCI group, and 38% (n=24) for the dementia group. Age, sex, education, and brief cognitive test scores (MMSE & MoCA) were not different between groups with or without OH. In the MCI group, OH was associated with lower cognitive performance in several executive functions tests: visual working memory (p<0.001), processing speed (p=0.006), Stroop flexibility (p=0.030) and Trail-Making Test part B (p=0.024). There was no difference in episodic memory performance. OH was associated with a diagnosis of hypertension and the use of antihypertensive medication. No differences were observed in vascular brain injury between groups with and without OH. CONCLUSIONS This study found that orthostatic hypotension prevalence is correlated to severity of cognitive deficits in a Memory Clinic. In MCI, OH is associated with lower performance in executive functions. OH could represent an under-recognized correlate of cognitive performance.