Ca2+ and mitochondria as substrates for deficits in synaptic plasticity in normal brain ageing

Biological markers of age-related memory deficits: treatment of senescent physiology

In humans, age-related memory impairments begin in mid-life and cognitive weakening continues with advancing age. An important aspect of defining memory decline is the distinction between dementia as a result of neurological diseases, such as Alzheimer's disease, and memory loss not specifically associated with disease. Within the population of elderly without dementia, there is considerable variability in memory. This variability is likely to be a result of the interaction of genetic make-up and environment, which influences several processes for cell maintenance and repair including oxidative damage and cholesterol metabolism, leading to disruption of Ca(2+) homeostasis, and ultimately Ca(2+)-dependent processes that underlie memory. In humans, several methods have been employed to distinguish biological markers of aging that may predict cognitive decline. Memory deficits associated with normal aging and Alzheimer's disease have been linked to a decrease in the volume of brain structures, such as the hippocampus and to genetic markers, such as apolipoprotein E. In this regard, examination of CSF for biomarkers of disease can help in differentiating normal aging from Alzheimer's disease. Measures of oxidative stress and cholesterol in plasma correlate with memory deficits; research suggests that treatments that reduce oxidative stress or cholesterol through exercise, diet or the use of antioxidant vitamins may delay cognitive decline.Nevertheless, to date, very little treatment is available to reverse memory deficits in later life. In this regard it is important to identify individuals at risk for memory deficits in order to discriminate different mechanisms of brain aging and develop treatments. Considerable effort is driving research to develop accurate biological markers of brain aging. In turn, these markers will provide information on mechanisms of aging and cognitive decline and point to potential treatments. Accordingly, the effectiveness of treatment needs to be verified for both cognitive changes and biological markers that are specific for age-related memory deficits.

Early and simultaneous emergence of multiple hippocampal biomarkers of aging is mediated by Ca2+-induced Ca2+ release

Age-dependent changes in multiple Ca2+-related electrophysiological processes in the hippocampus appear to be consistent biomarkers of aging, and several also correlate with cognitive decline. These findings have led to the hypothesis that a common mechanism of Ca2+ dyshomeostasis underlies aspects of aging-dependent brain impairment. However, some key predictions of this view remain untested, including that multiple Ca2+-related biomarkers should emerge concurrently during aging and their onset should also precede/coincide with initial signs of cognitive decline. Moreover, blocking a putative common source of dysregulated Ca2+ should eliminate aging differences. Here, we tested these predictions using combined electrophysiological, imaging, and pharmacological approaches in CA1 neurons to determine the ages of onset (across 4-, 10-, 12-, 14-, and 23-month-old F344 rats) of several established biomarkers, including the increases in the slow afterhyperpolarization, spike accommodation, and [Ca2+]i rise during repetitive synaptic stimulation. In addition, we tested the hypothesis that altered Ca2+-induced Ca2+ release (CICR) from ryanodine receptors, which can be triggered by L-type Ca2+ channels, provides a common source of dysregulated Ca2+ in aging. Results showed that multiple aging biomarkers were first detectable at about the same age (12 months of age; approximately midlife), sufficiently early to influence initial cognitive decline. Furthermore, selectively blocking CICR with ryanodine slowed the Ca2+ rise during synaptic stimulation more in aged rat neurons and, notably, reduced or eliminated aging differences in the biomarkers. Thus, this study provides the first evidence that altered CICR plays a role in driving the early and simultaneous emergence in hippocampus of multiple Ca2+-related biomarkers of aging.

Effects of aging on Ca2+ signaling in murine mesenteric arterial smooth muscle cells

Pathophysiological changes in arterial smooth muscle structure and function occur with aging and there are a number of reports illustrating reductions in vascular responsiveness with aging. While much is known about arterial remodeling and functional adaptations with aging, very little is known about the biophysical adaptations in individual arterial myocytes. Cytosolic Ca2+ signaling, involving activation of L-type Ca2+ channels on the plasma membrane as well as InsP3 and ryanodine receptors on the sarcoplasmic reticulum, is integral to vascular tone and reactivity. Thus, we tested the hypothesis that aging results in reductions in the functional expression of L-type channels and temporal aspects of ryanodine receptor and InsP3 receptor Ca2+ signaling, in mesenteric arterial smooth muscle cells isolated from 6 and 30 months old C57Bl/6 mice. Comparisons of L-type current activity were made using dialyzed, whole-cell voltage-clamp techniques and Ba2+ as charge carrier. Ca2+ signaling was measured using fura-2 fluorescence microscopy techniques. Cell morphological changes were also investigated using electrophysiological and immunocytochemical approaches. The amplitudes of L-type Ca2+ currents were increased in older mice, but this was associated with membrane surface area increases of approximately 50%, due to increases in cell length not cell width. Consequently, L-type Ca2+ current densities were preserved with age, indicating functional channel expression was unchanged. In contrast, aging was associated with decrements in Ca2+ signaling in response to either ryanodine receptor stimulation by caffeine or InsP3 receptor activation with phenylephrine. These changes with aging may be related to the previously reported depression in myogenic reactivity.

Association of refractory complex partial seizures with a polymorphism of ApoE genotype

Apolipoprotein E (ApoE) is a constituent of many types of lipoproteins that play a role in metabolism of cholesterol and lipids in the body as well as in the brain. ApoE is synthesised in astrocytes and microglia and enter to neurons through LDL, LRP and VLDL receptors. Recently it was shown that ApoE is also produced in neurons. ApoE has a role in modulating learning and memory, structural plasticity, mobilization of cholesterol in repair, growth and maintenance of myelin and neuronal membranes during development and aging, and cell death after ischemic, convulsive, or other type of brain injury. The aim of this research was to investigate the possible association of ApoE gene polymorphism with the development of resistance to pharmacological therapy in patients with partial complex seizures with or without secondary generalization. In this prospective matched-pair controlled study, 60 patients with cryptogenic epilepsy with complex partial seizures, with or without secondary generalization, who have been suffering for five or more years, were studied. The first group comprised 30 patients refractory to the current therapy, while the second group consisted of patients with well-controlled seizures. The refractory and non-refractory groups of patients differed significantly in their phenotypes. Phenotype E3/4 was six times more frequent in refractory group than among non-refractory group. The lack of response was shown to be significantly associated with the presence of epsilon4 allele. This study provided evidence that the presence of epsilon4 allele is more often associated with a lack of response to current antiepileptic drugs as compared to epsilon2 and epsilon3 alleles.