Free intracellular calcium in aging and Alzheimer's disease

Age-related changes in large-conductance calcium-activated potassium channels in mammalian circadian clock neurons

Aging impairs the function of the suprachiasmatic nucleus (SCN, the central mammalian clock), leading to a decline in the circadian rhythm of many physiological processes, including sleep-wake rhythms. Recent studies have found evidence of age-related changes in the circadian regulation of potassium currents; these changes presumably lead to a decrease in the SCN's electrical rhythm amplitude. Current through large-conductance Ca(2+)-activated K(+) (BK) channels promote rhythmicity in both SCN neuronal activity and behavior. In many neuron types, changes in BK activity are correlated with changes in intracellular Ca(2+) concentration ([Ca(2+)]i). We performed patch-clamp recordings of SCN neurons in aged mice and observed that the circadian modulation of BK channel activity was lost because of a reduction in BK currents during the night. This reduced current diminished the afterhyperpolarization, depolarized the resting membrane potential, widened the action potential, and increased [Ca(2+)]i. These data suggest that reduced BK current increases [Ca(2+)]i by altering the action potential waveform, possibly contributing to the observed age-related phenotype.

The prevention of dementia

OBJECTIVE

Dementia is prevalent in older adults and the population is ageing. Many factors have been associated with dementia and anything that may aid the prevention of dementia is of importance.

METHOD

The literature in this area was evaluated and information relating to the various factors that may impact upon the prevention of dementia is presented below.

RESULTS

Factors that have been associated with a possible increased risk of developing dementia include high blood pressure, (at least in midlife), high body mass index, smoking and possibly diabetes although the evidence is mixed. There is currently no clear evidence with regard to cholesterol and metabolic syndrome although both may be implicated. Having education and maintaining a Mediterranean diet, including vegetable, fruit and fish intake, have been linked to a lower incidence of dementia as has low to moderate alcohol intake. Although care must be taken with the latter given the different characteristics of the studies reporting on alcohol and dementia.

CONCLUSION

It may be that risk and protective factors vary with age, however, in the absence of prophylactic treatment it seems likely that the maintenance of a healthy lifestyle may represent the best option with regard to the prevention of dementia.

Age-related impairment of human T lymphocytes' activation: specific differences between CD4(+) and CD8(+) subsets

The relevance of physiological immune aging is of great interest with respect to determining disorders with pathologic immune function in aging individuals. In recent years, the relevance of changes in peripheral lymphocytes in age-associated neurologic diseases has become more evident. Due to the lack of immunological studies, covering more than one event after mitogenic activation, we envisaged a new concept in the present study, aiming to investigate several events, starting from T cell receptor (TCR) ligation up to T cell proliferation. In addition, we addressed the question whether changes are present in the subsets (CD4, CD8) with aging. Phosphorylation of tyrosine residues declines with increasing age in CD4(+) cells. Fewer levels of CD69 positive cells after 4 h mitogenic activation, altered expression of cytokines (IL2, IFN-gamma and TNF-alpha; 22 h) and lower proliferation (72 h) were determined in aging. Moreover, it could be shown that CD8(+) lymphocytes react more effectively to mitogenic stimulation with reference to CD69 expression and proliferation in both age groups (<35 and >60 years old). These data indicate that T cell activation, mediated by TCR engagement, is significantly impaired in aging and both subsets are affected. However, bypassing the TCR does not fully restore T cell function, indicating that there are more mechanisms involved than impaired signal transduction through TCR only. The results will be discussed in relation to their relevance in neurodegenerative and psychiatric disorders.

Vitamin K-dependent proteins in the developing and aging nervous system

Although the warfarin embryopathy syndrome, with its neurologic and bone abnormalities, has been known for decades, the role of vitamin K in the brain has not been studied systematically. Recently, it was demonstrated that vitamin K-dependent carboxylase expression is temporally regulated in a tissue-specific manner with high expression in the nervous system during the early embryonic stages and with liver expression after birth and in adult animals. This finding, along with the discovery of wide distribution of the novel vitamin K-dependent growth factor, Gas6, in the central nervous system, provides compelling evidence of a biologic role of vitamin K during the development of the nervous system. In animals and bacteria, vitamin K was observed to influence the brain sulfatide concentration and the activity and synthesis of an important enzyme involved in brain sphingolipids biosynthesis. Taken together, previous research results point to a possible role of vitamin K in the nervous system, especially during its development. Hence, the knowledge of the biologic role of vitamin K in the brain may be important for unveiling the mechanisms of normal and pathologic development and aging of the nervous system. The role of the vitamin K-dependent protein Gas6 in activation of signal transduction events in the brain in light of the age-related changes in the nervous system is also discussed.

Calcium ion transients in neutrophils from patients with sporadic Alzheimer's disease

Abnormalities involving intracellular calcium homeostasis have been detected in Alzheimer's disease brain and fibroblasts as well as presenilin-1 mutation-bearing cells. In the present study we investigated inositol(1,4,5)trisphosphate-mediated calcium transients as well as calcium responses via mechanisms not related to surface receptors in Alzheimer's disease polymorphonuclear (PMN) granulocytes, using the tripeptide formyl-methionyl-leucyl-phenyl alanine (fMLP) and calcium ionophore ionomycin, respectively. fMLP elicited a biphasic response with an initial, fast increase in intracellular free calcium concentrations followed by a second, lower phase with no significant differences in either maximal response or time course between Alzheimer's disease granulocytes and controls. Similarly, the calcium signal elicited after ionomycin exposure was unchanged in Alzheimer's disease PMN. In conclusion, these results indicate that calcium mobilization from intracellular stores and via cross-membrane mechanisms is intact in Alzheimer's disease granulocytes.

Multiple behavioral anomalies in GluR2 mutant mice exhibiting enhanced LTP

We have previously disrupted the ionotropic glutamate receptor type 2 gene (GluR2) using gene targeting in embryonic stem cells and generated mice which lacked the GluR2 gene product. Neurophysiological analyses of these mice showed a markedly enhanced long-term potentiation (LTP) and a 9-fold increase in kainate induced Ca2+ permeability in the hippocampus. Here, we analyze the behavioral and neuroanatomical consequences of GluR2 deficiency in homozygous null mutant and age-matched littermate control mice. We show that despite unaltered gross brain morphology, several aspects of behavior were abnormal in the mutants. Object exploration, rearing, grooming and locomotion were altered in the novel arena. Eye-closure reflex, motor performance on the rotating rod and spatial and non-spatial learning performance in the water maze were also abnormal in the mutants. These abnormalities together with the widespread expression pattern of GluR2 in most excitatory CNS pathways suggest that the absence of GluR2 leads to neurological phenotypes associated with not only the hippocampus but several other brain regions potentially including the cortex and cerebellum. We speculate that GluR2 mutant mice suffer from an overall non-specifically increased excitability that may alter cognitive functions ranging from stimulus processing to motivation and learning.

Alzheimer's alpha-secretase may be a calcium-dependent protease

Proteolytic processing of beta-amyloid precursor protein (APP) is believed to be fundamental to the understanding of Alzheimer's disease. The identities and the regulatory elements of the proteases involved in the process, known as alpha/beta/gamma secretases, are unclear. In this study, by examining reported data, we found some indications suggesting that the putative alpha-secretase may be a calcium-dependent protease, and that this enzyme may play a primary role in the regulation of APP processing. Based on this, we proposed a model for the membrane orientations of the secretases for further discussions.

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.