Prevention of age-related changes in rat cortex transcription factor activator protein-1 by hypolipidemic drugs

Age-associated alterations in constitutively expressed cyclooxygenase-2 immunoreactivity and protein levels in the hippocampus

Cyclooxygenase-2 (COX-2) is a known inducible inflammatory mediator. COX-2 is constitutively expressed in the hippocampus and may regulate synaptic plasticity. The present study investigated the age‑associated alterations in white blood cell counts and hippocampal COX‑2 expression in healthy mice using immunohistochemical and western blot analyses at 1 month postnatal (PM1), PM3, PM6, PM12 and PM24. White blood cell counts were significantly decreased in the PM24 group when compared with the PM1 group. In addition, lymphocyte counts were decreased in the PM24 group when compared with all other groups. By contrast, monocyte, neutrophil and eosinophil counts were increased in the PM24 group; however, this did not reach statistical significance. COX‑2 expression was identified in the granule cells of the dentate gyrus and in the pyramidal cells of the hippocampal CA2/3 region. COX‑2 immunoreactivity was maintained until PM18, however, the levels significantly decreased by PM24. These results suggest that, despite alterations in the differential white blood cell counts, the significant decrease in constitutive COX‑2 expression in the hippocampus may be associated with degenerative age-associated alterations in synaptic plasticity in the hippocampus.

Increased expression of receptor for activated C kinase 1 in temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is characterized by spontaneous recurrent complex partial seizures. Increased neurogenesis and neuronal plasticity have been reported in animal models of MTLE, but not in detail in human MTLE cases. Here, we showed that receptor for activated C kinase 1 (RACK1) was expressed in the hippocampus and temporal cortex of the MTLE human brain. Interestingly, most of the cells expressing RACK1 in the epileptic temporal cortices co-expressed both polysialylated neural cell adhesion molecules, the migrating neuroblast marker, and the beta-tubulin isotype III, an early neuronal marker, suggesting that these cells may be post-mitotic neurons in the early phase of neuronal development. A subpopulation of RACK1-positive cells also co-express neuronal nuclei, a mature neuronal marker, suggesting that epilepsy may promote the generation of new neurons. Moreover, in the epileptic temporal cortices, the co-expression of both axonal and dendritic markers in the majority of RACK1-positive cells hints at enhanced neuronal plasticity. The expression of b-tubulin II (TUBB2B) associated with neuronal migration and positioning, was decreased. This study is the first to successfully identify a single population of cells expressing RACK1 in the human temporal cortex and the brain of the animal model, which can be up-regulated in epilepsy. Therefore, it is possible that these cells are functionally relevant to the pathophysiology of epilepsy.

RACK1 Function in Cell Motility and Protein Synthesis

The receptor for activated C kinase 1 (RACK1) serves as an adaptor for a number of proteins along the MAPK, protein kinase C, and Src signaling pathways. The abundance and near ubiquitous expression of RACK1 reflect its role in coordinating signaling molecules for many critical biological processes, from mRNA translation to cell motility to cell survival and death. Complete deficiency of Rack1 is embryonic lethal, but the recent development of genetic Rack1 hypomorphic mice has highlighted the central role that RACK1 plays in cell movement and protein synthesis. This review focuses on the importance of RACK1 in these processes and places the recent work in the larger context of understanding RACK1 function.

Cyclooxygenase-2 inhibitors modulate skin aging in a catalytic activity-independent manner

It has been proposed that the pro-inflammatory catalytic activity of cyclooxygenase-2 (COX-2) plays a key role in the aging process. However, it remains unclear whether the COX-2 activity is a causal factor for aging and whether COX-2 inhibitors could prevent aging. We here examined the effect of COX-2 inhibitors on aging in the intrinsic skin aging model of hairless mice. We observed that among two selective COX-2 inhibitors and one non-selective COX inhibitor studied, only NS-398 inhibited skin aging, while celecoxib and aspirin accelerated skin aging. In addition, NS-398 reduced the expression of p53 and p16, whereas celecoxib and aspirin enhanced their expression. We also found that the aging-modulating effect of the inhibitors is closely associated with the expression of type I procollagen and caveolin-1. These results suggest that pro-inflammatory catalytic activity of COX-2 is not a causal factor for aging at least in skin and that COX-2 inhibitors might modulate skin aging by regulating the expression of type I procollagen and caveolin-1.

Cyclooxygenase-2 immunoreactivity and protein level in the gerbil hippocampus during normal aging

Cyclooxygenases-2 (COX-2) is not only related to inflammation but also plays critical roles in brain development and synaptic signaling. In the present study, we investigated age-related changes in COX-2 immunoreactivity and protein levels in the gerbil hippocampus. In the hippocampal CA1 region (CA1) and dentate gyrus (DG), weak COX-2 immunoreactivity was observed at postnatal month 1 (PM 1), and COX-2 immunoreactivity was markedly increased at PM 18 and 24. In the CA2/3, COX-2 immunoreactivity was strong at PM 1. COX-2 immunoreactivities in the PM 3, 6 and 12 groups were decreased compared to that in the PM 1 group, and it was increased at PM 18 and 24. In addition, age-related changes in COX-2 levels were similar with immunohistochemical results in the CA2/3. These results suggest that COX-2 immunoreactivity and levels were high in the hippocampus of aged gerbils.

Selective COX-2 inhibitors modulate cellular senescence in human dermal fibroblasts in a catalytic activity-independent manner

It has been recently proposed that pro-inflammatory genes such as cyclooxygenase-2 (COX-2) play a key role in the aging process. However, it remains unclear whether the pro-inflammatory activity of COX-2 is involved in the aging process and whether COX-2 inhibitors prevent aging. We therefore examined the effect of COX-2 inhibitors on aging in the cellular senescence model of human dermal fibroblasts (HDFs). While the catalytic activity of COX-2 was observed to increase in the senescence process, we found that among three selective COX-2 inhibitors studied, only NS-398 inhibited the senescence whereas celecoxib and nimesulide accelerated the senescence. Non-selective COX inhibitors including aspirin, ibuprofen and flurbiprofen accelerated the senescence. The senescence-regulating effect of selective COX-2 inhibitors had no correlation with cellular reactive oxygen species levels, NF-kappaB activities or protein levels of p53 and p21. We instead found that selective COX-2 inhibitors regulate caveolin-1 expression at transcriptional levels, which was closely associated with the inhibitors' effect on the senescence. Collectively, these results suggest that COX-2 catalytic activity does not mediate HDF senescence and that selective COX-2 inhibitors modulate HDF senescence by a catalytic activity-independent mechanism.

Amla (Emblica officinalisGaertn.) prevents dyslipidaemia and oxidative stress in the ageing process

Amla (Emblica officinalisGaertn.) is widely used in Indian medicine for the treatment of various diseases. We have investigated the effects of amla on the lipid metabolism and protein expression involved in oxidative stress during the ageing process. SunAmla or ethyl acetate extract of amla, a polyphenol-rich fraction, was administered at a dose of 40 or 10 mg/kg body weight per d for 100 d to young rats aged 2 months and aged rats aged 10 months. The lipid levels, such as cholesterol and TAG, in serum and liver were markedly elevated in aged control rats, while they were significantly decreased by the administration of amla. The PPARα is known to regulate the transcription of genes involved in lipid and cholesterol metabolism. The PPARα protein level in liver was reduced in aged control rats. However, the oral administration of amla significantly increased the hepatic PPARα protein level. In addition, oral administration of amla significantly inhibited the serum and hepatic mitochondrial thiobarbituric acid-reactive substance levels in aged rats. Moreover, the elevated expression level of bax was significantly decreased after the oral administration of amla, while the level of bcl-2 led to a significant increase. Furthermore, the expressions of hepatic NF-κB, inducible NO synthase (iNOS), and cyclo-oxygenase-2 (COX-2) protein levels were also increased with ageing. However, amla extract reduced the iNOS and COX-2 expression levels by inhibiting NF-κB activation in aged rats. These results indicate that amla may prevent age-related hyperlipidaemia through attenuating oxidative stress in the ageing process.

Gene expression of cyclooxygenase-1 and Ca(2+)-independent phospholipase A(2) is altered in rat hippocampus during normal aging

Brain aging is associated with inflammatory changes. However, data on how the brain arachidonic acid (AA) metabolism is altered as a function of age are limited and discrepant. AA is released from membrane phospholipids by phospholipase A(2) (PLA(2)) and then further metabolized to bioactive prostaglandins and thromboxanes by cyclooxygenases (COX)-1 and -2. We examined the phospholipase A(2) (PLA(2))/COX-mediated AA metabolic pathway in the hippocampus and cerebral cortex of 4-, 12-, 24- and 30-month-old rats. A two-fold increase in brain thromboxane B(2) level in 24 and 30 months was accompanied by increased hippocampal COX-1 mRNA levels at 12, 24, and 30 months. COX-2 mRNA expression was significantly decreased only at 30 months. Hippocampal Ca(2+)-independent iPLA(2) mRNA levels were decreased at 24 and 30 months without any change in Ca(2+)-dependent PLA(2) expression. In the cerebral cortex, mRNA levels of COX and PLA(2) were not significantly changed. The specific changes in the AA cascade observed in the hippocampus may alter phospholipids homeostasis and possibly increase the susceptibility of the aging brain to neuroinflammation.

The different facets of protein kinases C: old and new players in neuronal signal transduction pathways

Signal transduction pathways are crucial for cell-to-cell communication. Various molecular cascades allow the translation of distinct stimuli, targeting the cell, into a language that the cell itself is able to understand, thus elaborating specific responses. Within this context, a strategic role is played by protein kinases which catalyze the phosphorylation of specific substrates. The serine/threonine protein kinase C (PKC) enzymes family (at least 10 isoforms) is implicated in the transduction of signals coupled to receptor-mediated hydrolysis of membrane phospholipids. Within this molecular pathway, protein-protein interactions play a critical role in directing the distinct activated PKCs towards selective subcellular compartments, in order to guarantee spatio-temporal and localized cellular responses. A space-specific modulation of biochemical events is particularly important during learning. Among the various mechanisms, the modulation of mRNA decay appears to be an efficient post-transcriptional way of controlling gene expression during learning, allowing changes to take place in selected neuronal regions, in particular at synaptic level. To this regard, recent studies have pointed out that PKC activation is also involved in a novel signalling cascade leading to the stabilization of specific mRNAs. This review will especially focus the attention on the implication of PKC in memory trace formation and how alterations within this molecular cascade may have consequences on physiological and pathological neuronal aging (i.e. Alzheimer's disease).

Ageing introduces a complex pattern of changes in several rat brain transcription factors depending on gender and anatomical localization

As ageing changes the activity of several transcription factors in the rat cortex, we were interested in determining whether similar changes also appear in the hippocampus of old rats. We determined by electrophoretic gel shift assays the binding activity of nuclear factor kappa B (NFkappaB), activator protein-1 (AP-1), peroxisome proliferator-activated receptor (PPAR), and liver X receptor (LXR) in cortex and hippocampus samples from young (3-month-old), and old (18-month-old) male and female Sprague-Dawley rats. NFkappaB activity increased in old male and female rats, though only in cortex samples, while AP-1 activity decreased only in the cortex and hippocampus of old female animals. LXR activity decreased in all conditions, except in old male cortexes; whereas PPAR activity only decreased in the hippocampus of old female rats. Decreases in AP-1 and PPAR activities restricted to old female rats did not result from an age-related decline in plasma 17beta-estradiol concentration, as their activities did not change in samples obtained from ovariectomized young female rats. Our results indicate that ageing induces a complex pattern of changes in the brain-binding activity of NFkappaB, AP-1, PPAR and LXR, depending on the anatomical origin of the samples (cortex or hippocampus), and the sex of the animals studied.

Regional protein levels of cytosolic phospholipase A2 and cyclooxygenase-2 in Rhesus monkey brain as a function of age

Limited evidence suggests that brain cytosolic phospholipase A(2) (cPLA(2)), which selectively releases arachidonic acid (AA) from membrane phospholipids, and cyclooxygenase-2 (COX-2), the rate-limiting enzyme for AA metabolism to prostanoids, change as a function of normal aging. In this study, we examined the protein levels of cPLA(2) and COX-2 enzymes in hippocampus, frontal pole and cerebellum from young (2-5 years old), middle-aged (8-11 years old) and old (23 years old) male and female Rhesus monkeys. In the cerebellum, cPLA(2) protein level was higher in the young brain as compared to levels seen at both middle-aged and old. Similarly, in the frontal pole, the young brain showed a higher level of COX-2 protein as compared to the levels seen at both older ages. For both, once an animal reached 8-11 years of age the levels appeared to remain relatively constant over the next decade. Immunohistochemistry of COX-2 protein within the brain demonstrated no significant change in the localization to neurons within the frontal pole. Qualitatively, a greater number of neurons were positively stained for COX-2 in the young brain than in the aged brain. Based on the previous reports of localization of cPLA(2) and COX-2 at post-synaptic sites in neurons results from the current study suggest that the elevated protein levels of the two enzymes seen in the younger brain is related to the greater potential for synaptic plasticity across multiple neurons as a function of age and that cPLA(2) and COX-2 may be considered as post-synaptic markers.

RACK1 has the nerve to act: structure meets function in the nervous system

The receptor for activated protein kinase C 1 (RACK1) is an intracellular adaptor protein. Accumulating evidence attributes to this member of the tryptophan-aspartate (WD) repeat family the role of regulating several major nervous system pathways. Structurally, RACK1 is a seven-bladed-beta-propeller, interacting with diverse proteins having distinct structural folds. When bound to the IP3 receptor, RACK1 regulates intracellular Ca2+ levels, potentially contributing to processes such as learning, memory and synaptic plasticity. By binding to the NMDA receptor, it dictates neuronal excitation and sensitivity to ethanol. When bound to the stress-induced acetylcholinesterase variant AChE-R, RACK1 is implicated in stress responses and behavior, compatible with reports of RACK1 modulations in brain ageing and in various neurodegenerative diseases. This review sheds new light on both the virtues and the variety of neuronal RACK1 interactions and their physiological consequences.