Senescence-accelerated mouse (SAM): a biogerontological resource in aging research

Long-term melatonin administration protects brain mitochondria from aging

We tested whether chronic melatonin administration in the drinking water would reduce the brain mitochondrial impairment that accompanies aging. Brain mitochondria from male and female senescent prone (SAMP8) mice at 5 and 10 months of age were studied. Mitochondrial oxidative stress was determined by measuring the levels of lipid peroxidation and nitrite, glutathione/glutathione disulfide ratio, and glutathione peroxidase and glutathione reductase activities. Electron transport chain activity and oxidative phosphorylation capability of mitochondria were also determined by measuring the activity of the respiratory chain complexes and the ATP content. The results support a significant age-dependent mitochondrial dysfunction with a diminished efficiency of the electron transport chain and reduced ATP production, accompanied by an increased oxidative/nitrosative stress. Melatonin administration between 1 and 10 months of age completely prevented the mitochondrial impairment, maintaining or even increasing ATP production. There were no major age-dependent differences between males in females, although female mice seemed to be somewhat more sensitive to melatonin treatment than males. Thus, melatonin administration as a single therapy maintained fully functioning brain mitochondria during aging, a finding with important consequences in the pathophysiology of brain aging.

Mitochondria and aging: innocent bystanders or guilty parties?

There are many theories of aging and a number of them encompass the role of mitochondria in this process. Mitochondrial DNA mutations and deletions have been shown to accumulate in many tissues in mammals during aging. However, there is little evidence that these mutations could affect the functioning of aging tissues.

H2O2-induced changes in astrocytic cultures from control and rapidly aging strains of mouse

The study compared the difference between the H2O2 treatment on astrocytic cultures from a rapidly aging strain of mouse (SAMP8) and its sister control (R1). A mild but statistically significant difference was observed in the numbers of dead cell between R1 and SAMP8 after H2O2 treatment. Cellular changes were equivalent in both strains after injury, including loss of cilia and side projections. Low total dose of H2O2 treatment (e.g., 400 microM for only 1 hour) caused increased cellular synthesis,while high total dose of H2O2 treatment (e.g., 200 microM for 4 hours) downregulated in intracellular synthesis and caused coagulation of microtubules.

Senescence-accelerated mouse (SAM) with special references to neurodegeneration models, SAMP8 and SAMP10 mice

The SAM strains, a group of related inbred strains consisting of senescence-prone inbred strains (SAMP) and senescence-resistant inbred strains (SAMR), have been successfully developed by selective inbreeding of the AKR/J strain of mice donated by the Jackson laboratory in 1968. The characteristic feature of aging common to the SAMP and SAMR is accelerated senescence and normal aging, respectively. Furthermore, SAMP and SAMR strains of mice manifest various pathobiological phenotypes spontaneously. Among SAMP strains, SAMP8 and SAMP10 mice show age-related behavioral deterioration such as deficits in learning and memory, emotional disorders (reduced anxiety-like behavior and depressive behavior) and altered circadian rhythm associated with certain pathological, biochemical and pharmacological changes. Here, the previous and recent literature on SAM mice are reviewed with an emphasis on SAMP8 and SAMP10 mice. A spontaneous model like SAM with distinct advantages over the gene-modified model is hoped by investigators to be used more widely as a biogerontological resource to explore the etiopathogenesis of accelerated senescence and neurodegenerative disorders.

Granulocyte macrophage--colony-stimulating factor-dependent proliferation is impaired in macrophages from senescence-accelerated mice

A senescence-accelerated (SAMP8) mouse model was used to determine the effect of aging on the immune system. We produced in vitro bone marrow-derived macrophages from SAMP8 mice and compared them against senescence-resistant, long-lived mice (SAMR1). Although macrophages from both strains of mice proliferated in a similar manner in response to monocyte-colony-stimulating factor (M-CSF), SAMP8 macrophages showed an impaired response to granulocyte macrophage-colony-stimulating factor (GM-CSF). Similar levels of external regulated kinases (ERK)1/2 and signaling transducer and activator of transcription 5 (STAT5) phosphorylation were observed in macrophages from both strains of mice. The lack of proliferation was not caused by the induction of apoptosis. Differentiation of bone marrow cells into dendritic cells was similar in both strains of mice, as was the induction of major histocompatibility complex (MHC) class II molecules by interferon-gamma (IFN-gamma). Finally, we determined the density of Langerhans cells in vivo in the skin of the two mouse strains, but no differences were found.

Evaluation of potential pro-survival pathways regulated by melatonin in a murine senescence model

We examined the effect of melatonin on pro-survival processes in three groups of mice. Untreated senescence-accelerated mice (SAMP8), melatonin-treated SAMP8 and untreated senescence-accelerated resistant mice (SAMR1) of 10 months old were studied. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) was supplied in the drinking water from the end of the first month until the end of the ninth month of life. Differences in the Akt/Erk1-2 pathway and downstream targets were examined and no significant changes were observed, except for beta-catenin. However, sirtuin 1 expression was significantly lower in SAMP8 than in SAMR1. In addition, acetylated p53 and NFkappaB expression were lower in SAMP8 than in SAMR1. These changes were prevented by melatonin. Moreover, the concentration/expression of alpha-secretase was lower and that of amyloid beta aggregates (Abeta) was higher in untreated SAMP8 than in SAMR1. Likewise, the levels of Bid were higher, whereas Bcl-2(XL) levels were lower in SAMP8 than in SAMR1. Melatonin reduced all these changes. We conclude that melatonin improves pro-survival signals and reduces pro-death signals in age-related impairments of neural processes.

Time-course of blood-brain barrier disruption in senescence-accelerated mouse prone 8 (SAMP8) mice

Senescence of the cerebrovascular system and an abnormal function of the blood-brain barrier have been related with Alzheimer's disease. We studied here the time-course of blood-brain barrier disruption in senescence-accelerated mouse prone 8 (SAMP8) mice, which is a murine model of senescence and is also considered a model of Alzheimer's disease. We used a previously described method that allows evaluating blood-brain barrier integrity by observing Evans blue extravasation from brain blood vessels. Three brain regions (cortex, hippocampus and hippocampal fissure) of SAMP8 brains were analyzed at 3, 6, 9, 12 and 15 months of age. Moreover, genetically related senescence-accelerated mouse resistant 1 (SAMR1) and ICR-CD1 mice were studied. Results indicate that Evans blue permeability in SAMP8 and SAMR1 increases from 6 to 15 months in the three studied regions. At 15 months of age, SAMP8 and SAMR1 mice showed higher Evans blue extravasation in CA1 and Fissure than ICR-CD1 mice. Further studies are required to understand the senescence process in SAMR1 mice, as blood-brain barrier alterations in old age have unexpectedly been observed. On the other hand, as blood-brain barrier permeability in SAMP8 mice increases with age, blood-brain barrier alterations may contribute to the cerebral pathology observed in this strain.

Dysfunction of astrocytes in senescence-accelerated mice SAMP8 reduces their neuroprotective capacity

Early onset increases in oxidative stress and tau pathology are present in the brain of senescence-accelerated mice prone (SAMP8). Astrocytes play an essential role, both in determining the brain's susceptibility to oxidative damage and in protecting neurons. In this study, we examine changes in tau phosphorylation, oxidative stress and glutamate uptake in primary cultures of cortical astrocytes from neonatal SAMP8 mice and senescence-accelerated-resistant mice (SAMR1). We demonstrated an enhancement of abnormally phosphorylated tau in Ser(199) and Ser(396) in SAMP8 astrocytes compared with that of SAMR1 control mice. Gsk3beta and Cdk5 kinase activity, which regulate tau phosphorylation, was also increased in SAMP8 astrocytes. Inhibition of Gsk3beta by lithium or Cdk5 by roscovitine reduced tau phosphorylation at Ser(396). Moreover, we detected an increase in radical superoxide generation, which may be responsible for the corresponding increase in lipoperoxidation and protein oxidation. We also observed a reduced mitochondrial membrane potential in SAMP8 mouse astrocytes. Glutamate uptake in astrocytes is a critical neuroprotective mechanism. SAMP8 astrocytes showed a decreased glutamate uptake compared with those of SAMR1 controls. Interestingly, survival of SAMP8 or SAMR1 neurons cocultured with SAMP8 astrocytes was significantly reduced. Our results indicate that alterations in astrocyte cultures from SAMP8 mice are similar to those detected in whole brains of SAMP8 mice at 1-5 months. Moreover, our findings suggest that this in vitro preparation is suitable for studying the molecular and cellular processes underlying early aging in this murine model. In addition, our study supports the contention that astrocytes play a key role in neurodegeneration during the aging process.

Senescence-dependent MutS alpha dysfunction attenuates mismatch repair

DNA damage and mutations in the genome increase with age. To determine the potential mechanisms of senescence-dependent increases in genomic instability, we analyzed DNA mismatch repair (MMR) efficiency in young and senescent human colonic fibroblast and human embryonic lung fibroblast. It was found that MMR activity is significantly reduced in senescent cells. Western blot and immunohistochemistry analysis revealed that hMSH2 and MSH6 protein (MutS alpha complex), which is a known key component in the MMR pathway, is markedly down-regulated in senescent cells. Moreover, the addition of purified MutS alpha to extracts from senescent cells led to the restoration of MMR activity. Semiquantitative reverse transcription-PCR analysis exhibited that MSH2 mRNA level is reduced in senescent cells. In addition, a decrease in E2F transcriptional activity in senescent cells was found to be crucial for MSH2 suppression. E2F1 small interfering RNA expression reduced hMSH2 expression and MMR activity in young human primary fibroblast cells. Importantly, expression of E2F1 in quiescent cells restored the MSH2 expression as well as MMR activity, whereas E2F1-infected senescent cells exhibited no restoration of MSH2 expression and MMR activity. These results indicate that the suppression of E2F1 transcriptional activity in senescent cells lead to stable repression of MSH2, followed by a induction of MutS alpha dysfunction, which results in a reduced cellular MMR capacity in senescent cells.

The senescence-accelerated mouse (SAM): a higher oxidative stress and age-dependent degenerative diseases model

The SAM strain of mice is actually a group of related inbred strains consisting of a series of SAMP (accelerated senescence-prone) and SAMR (accelerated senescence-resistant) strains. Compared with the SAMR strains, the SAMP strains show a more accelerated senescence process, a shorter lifespan, and an earlier onset and more rapid progress of age-associated pathological phenotypes similar to human geriatric disorders. The higher oxidative stress status observed in SAMP mice is partly caused by mitochondrial dysfunction, and may be a cause of this senescence acceleration and age-dependent alterations in cell structure and function. Based on our recent observations, we discuss a possible mechanism for mitochondrial dysfunction resulting in the excessive production of reactive oxygen species, and a role for the hyperoxidative stress status in neurodegeneration in SAMP mice. These SAM strains can serve as a useful tool to understand the cellular mechanisms of age-dependent degeneration, and to develop clinical interventions.

Age-related difference in nociceptive behavior between SAMP6 and SAMR1 strains

Senescence accelerated prone mouse 6 (SAMP6) mice have been known to be a model for accelerated aging. Compared with the normal control senescence accelerated resistant mouse 1 (SAMR1) mice, although the SAMP6 mice have normal bone mass at 4 months, they exhibit a significantly lower bone mass at 8 months. It was recently reported that SAMP6 has memory deficit at 4 months of age, indicating that the change of nervous function might be already detected at 4 months of age. To assess whether SAMP6 mice exhibit an age-related abnormality of nociceptive transmission, we examined a battery of tests using the von Frey test for mechanically induced response, the hot plate test for thermally induced response, and the formalin paw test for chemically induced response. SAMP6 and SAMR1 showed similar response patterns in the von Frey test and the hot plate test. In the formalin paw test, 1-month-old SAMP6 and SAMR1 had similar responses, while 4-month-old SAMP6 exhibited attenuated phase 2 response, but normal phase 1 response. These findings indicate that onset of age-related phenotypes in SAMP6 differs in different tissues. SAMP6 could be useful to delineate the involvement of age-related nociceptive mechanisms.

Age-related increase of superoxide generation in the brains of mammals and birds

Oxidative stress, an imbalance between endogenous levels of oxygen radicals and antioxidative defense, increases with aging. However, it is not clear which of these two factors is the more critical. To clarify the production of oxygen radicals increases with age, we examined oxygen radical-dependent chemiluminescent signals in ex vivo brain slices using a novel photonic imaging method. The chemiluminescent intensity was significantly decreased by the membrane permeable superoxide dismutase (SOD)/catalase mimic, but not by Cu,Zn-SOD. Inhibitors for complex I, III, and IV of the mitochondrial electron transport chain transiently enhanced the chemiluminescent signal. The superoxide-dependent chemiluminescent intensity in senescence accelerated mouse (SAM) brain tissues increases with age. Moreover, the slope of the age-dependent increase was steeper in SAMP10, a strain characterized by a short lifespan and atrophy in the frontal cerebral cortex, than the senescence-resistant strain SAMR1, which has a longer lifespan. An increase in chemiluminescence with age was also observed in C57/BL6 mice, Wistar rats, and pigeons, although levels of chemiluminescence were lower in the pigeons than murines. The rate of age-related increases of superoxide-dependent chemiluminescence was inversely related to the maximum lifespan of the animals. The activity of superoxide dismutase was unchanged during the aging process in the brain. This suggested that superoxide production itself may increase with age. We speculated that reactive oxygen may be a signal to determine the aging process.

Reduced expression of MAb6B4 epitopes on chondroitin sulfate proteoglycan aggrecan in perineuronal nets from cerebral cortices of SAMP10 mice: a model for age-dependent neurodegeneration

The accelerated senescence-prone SAMP10 mouse strain is a model for age-dependent neurodegeneration and is characterized by brain atrophy and deficits in learning and memory. Because perineuronal nets play an important role in the synaptic plasticity of adult brains, we examined the distributions of molecules that constitute perineuronal nets in SAMP10 mouse brain samples and compared them with those in control SAMR1 mouse samples. Proteoglycan-related monoclonal antibody 6B4 (MAb6B4) clearly immunostained perineuronal nets in SAMR1 mice cortices, but the corresponding immunostaining in SAMP10 mice was very faint. MAb6B4 recognizes phosphacan/PTPzeta in immature brains. However, this antibody recognized several protein bands, including a 400-kDa core glycoprotein from chondroitin sulfate proteoglycan in homogenates of mature cortices from SAMR1 mice. The 400-kDa band was also recognized by antiaggrecan antibodies. The aggrecan core glycoprotein band was also detectable in samples from SAMP10 mice, but this glycoprotein was faintly immunostained by MAb6B4. Because MAb6B4 recognized the same set of protein bands that the monoclonal antibody Cat-315 recognized in mature cerebral cortices of SAMR1 mice, the MAb6B4 epitope appears to be closely related to that of Cat-315 and presumably represents a novel type of oligosaccharide that attaches to aggrecans. The Cat-315 epitope colocalized with aggrecan in perineuronal nets from SAMR1 mouse brain samples, whereas its expression was prominently reduced in SAMP10 mouse brain samples. The biological significance of the MAb6B4/Cat-315 epitope in brain function and its relationship to the neurodegeneration and learning disabilities observed in SAMP10 mice remain to be elucidated.

Improved mitochondrial function and increased life span after chronic melatonin treatment in senescent prone mice

We investigated whether chronic melatonin administration influences mitochondrial oxidative stress and life span in mice. Diaphragmatic mitochondria from female senescent prone (SAMP8) and senescent resistant (SAMR1) mice at 5 and 10 months of age were studied. Mitochondrial oxidative stress was determined by measuring the levels of lipid peroxidation, glutathione and glutathione disulfide, and glutathione peroxidase and reductase activities. Mitochondrial function was assessed by measuring the activity of the respiratory chain complexes and the ATP content. The results suggest that the age-dependent mitochondrial oxidative damage in the diaphragm of SAMP8 mice was accompanied by a reduction in the electron transport chain complex activities and in ATP levels. Furthermore, melatonin administration between 1 and 10 months of age normalized the redox and the bioenergetic status of the mitochondria and increased the ATP levels. Melatonin also increased both half-life and longevity, mainly in SAMP8 group. These results suggest an age-related increase in mitochondria vulnerability to oxidation in SAM mice at 10 months of age that was counteracted by melatonin therapy. The effects of melatonin on mitochondrial physiology probably underline the ability of the indoleamine to increase maximal life span in these animals.

Activation of innate immunity system during aging: NF-kB signaling is the molecular culprit of inflamm-aging

Innate and adaptive immunity are the major defence mechanisms of higher organisms against inherent and environmental threats. Innate immunity is present already in unicellular organisms but evolution has added novel adaptive immune mechanisms to the defence armament. Interestingly, during aging, adaptive immunity significantly declines, a phenomenon called immunosenescence, whereas innate immunity seems to be activated which induces a characteristic pro-inflammatory profile. This process is called inflamm-aging. The recognition and signaling mechanisms involved in innate immunity have been conserved during evolution. The master regulator of the innate immunity is the NF-kB system, an ancient signaling pathway found in both insects and vertebrates. The NF-kB system is in the nodal point linking together the pathogenic assault signals and cellular danger signals and then organizing the cellular resistance. Recent studies have revealed that SIRT1 (Sir2 homolog) and FoxO (DAF-16), the key regulators of aging in budding yeast and Caenorhabditis elegans models, regulate the efficiency of NF-kB signaling and the level of inflammatory responses. We will review the role of innate immunity signaling in the aging process and examine the function of NF-kB system in the organization of defence mechanisms and in addition, its interactions with the protein products of several gerontogenes. Our conclusion is that NF-kB signaling seems to be the culprit of inflamm-aging, since this signaling system integrates the intracellular regulation of immune responses in both aging and age-related diseases.

Characterization of a new experimental model of osteoporosis in rabbits

To characterize an experimental model of osteoporosis in rabbits induced either by ovariectomy (OVX), glucocorticoids, or by a combination of both. Thirty-five rabbits were randomly allocated into five groups: bilateral OVX, daily methylprednisolone hemisuccinate (MPH) injections at a 1.5 mg/kg/day dose for 4 consecutive weeks (MPH group), or variable dose of MPH between 0.5 and 2 mg/kg/day in combination with OVX (OVX + MPH at low, medium, and high dose). Twenty-two animals were killed 6 weeks after OVX, and 13 were killed 16 weeks later. Dual-energy X-ray absorptiometry was obtained at baseline and 6 and 16 weeks after OVX. High-resolution magnetic resonance imaging (MRI) was carried out at 0 and 6 weeks after OVX. Glucose, total cholesterol, triglyceride, and oestradiol blood levels before and 16 weeks after OVX were determined. Bone mineral density (BMD) decreased significantly at lumbar spine in MPH and OVX + MPH medium-dose groups, and at global knee and subchondral bone of the knee in MPH, OVX + MPH low- and medium-dosage groups (P < 0.05). BMD variations in OVX rabbits were not significant in any of the three anatomical locations analyzed. BMD variation 16 weeks after OVX was significant at lumbar spine and global knee in the OVX + MPH medium-dose group and only at global knee in the OVX + MPH low-dose group (P < 0.05). MRI did not show bone or cartilage changes. Osteoporosis can be induced experimentally in rabbits through isolated MPH or by a combination of OVX and medium dose corticosteroid for 4 weeks. OVX alone was not sufficient to induce osteoporosis.

Kainate-induced mitochondrial oxidative stress contributes to hippocampal degeneration in senescence-accelerated mice

We have demonstrated that kainate (KA) induces a reduction in mitochondrial Mn-superoxide dismutase (Mn-SOD) expression in the rat hippocampus and that KA-induced oxidative damage is more prominent in senile-prone (SAM-P8) than senile-resistant (SAM-R1) mice. To extend this, we examined whether KA seizure sensitivity contributed to mitochondrial degeneration in these mouse strains. KA-induced seizure susceptibility in SAM-P8 mice paralleled prominent increases in lipid peroxidation and protein oxidation and was accompanied by significant impairment in glutathione homeostasis in the hippocampus. These findings were more pronounced in the mitochondrial fraction than in the hippocampal homogenate. Consistently, KA-induced decreases in Mn-SOD protein expression, mitochondrial transmembrane potential, and uncoupling protein (UCP)-2 expression were more prominent in SAM-P8 than SAM-R1 mice. Marked release of cytochrome c from mitochondria into the cytosol and a higher level of caspase-3 cleavage were observed in KA-treated SAM-P8 mice. Additionally, electron microscopic evaluation indicated that KA-induced increases in mitochondrial damage and lipofuscin-like substances were more pronounced in SAM-P8 than SAM-R1 animals. These results suggest that KA-mediated mitochondrial oxidative stress contributed to hippocampal degeneration in the senile-prone mouse.

Limbic structures are prone to age-related impairments in proteasome activity and neuronal ubiquitinated inclusions in SAMP10 mouse: a model of cerebral degeneration

AIMS

Neurodegenerative diseases are characterized by ubiquitinated inclusions in selective brain regions. Here we investigated whether the dysfunction of the ubiquitin proteasome system might be involved in the pathogenesis and regional selectivity of neuronal ubiquitinated inclusions using the SAMP10 strain of mouse, an inbred model of age-related cerebral degeneration.

METHODS

By comparing SAMP10 mice at various ages with SAMR1 and C57BL mice as normal brain ageing controls, we studied morphological features and distribution of inclusions. We measured tissue proteasome activity in different brain regions of mice at various ages by fluorogenic substrate assays. We induced inclusions in cultured neurones by inhibiting the proteasome and analysed changes in the dendritic morphology.

RESULTS

Inclusions were formed in association with lipofuscin in neuronal perikarya and occurred most frequently in the limbic-related forebrain structures. There were sparse inclusion-bearing neurones in the non-limbic forebrain. In aged SAMR1 and C57BL, there were far fewer inclusions in the limbic-related forebrain than in aged SAMP10. The proteasome activity in the limbic-related forebrain decreased much more rapidly and remarkably upon ageing (26% activity was detected in 17-month-old compared with 3-month-old mice) in SAMP10 than in SAMR1. The proteasome activity in the non-limbic forebrain did not change significantly with advancing age in either SAMP10 or SAMR1. Proteasomal inhibition enhanced the formation of ubiquitinated inclusions in cultured neurones. Neurones bearing inclusions had shortened neurites.

CONCLUSIONS

We propose that the regional selectivity of proteasomal impairment is causally related to the selectivity of inclusion formation and associated dendritic degeneration in neurones of ageing SAMP10 mice.

The effect of Ginkgo biloba on the cerebellum of aging SAMP mouse--a TUNEL, bcl-2, and fMRI study

EGb 761, an extract from Ginkgo biloba that possesses neuroprotective properties, was fed to a strain of fast aging mice (SAMP-8) beginning at 3 weeks of age until they were sacrificed at 3 months and 11 months, respectively, along with an age-matched control group without herbal feeding. The aim of the study was to determine (1) the status of apoptosis and the status of bcl-2, a molecule involved in the fate of cells following injury, in the cerebella of these mice and (2) to analyze the functional changes as shown by fMRI images. The data indicated that there were no differences in apoptosis between the mice fed with EGb 761 and the control group at the two time points of 3 and 11 months of age. For bcl-2 positive cells, there was a decrease in density only in the cerebella of 11-month-old mice fed with the herbal extract when compared with controls. Functional studies indicated that while no changes were observed in the 3-month-old mice fed with Ginkgo biloba, an expansion of activated sites, possibly related to "synaptic reorganization and pathway alteration," was observed in the 11-month-old mice.

Detecting genetic variation in microarray expression data

The use of high-density oligonucleotide arrays to measure the expression levels of thousands of genes in parallel has become commonplace. To take further advantage of the growing body of data, we developed a method, termed "GeSNP," to mine the detailed hybridization patterns in oligonucleotide array expression data for evidence of genetic variation. To demonstrate the performance of the algorithm, the hybridization patterns in data obtained previously from SAMP8/Ta, SAMP10/Ta, and SAMR1/Ta inbred mice and from humans and chimpanzees were analyzed. Genes with consistent strain-specific and species-specific hybridization pattern differences were identified, and approximately 90% of the candidate genes were independently confirmed to harbor sequence differences. Importantly, the quality of gene expression data was also improved by masking the probes of regions with putative sequence differences between species and strains. To illustrate the application to human disease groups, data from an inflammatory bowel disease study were analyzed. GeSNP identified sequence differences in candidate genes previously discovered in independent association and linkage studies and uncovered many promising new candidates. This approach enables the opportunistic extraction of genetic variation information from new or pre-existing gene expression data obtained with high-density oligonucleotide arrays.

Cell death in the Purkinje cells of the cerebellum of senescence accelerated mouse (SAMP(8))

The cerebella of SAMP(8) (accelerated aging mouse) and SAMR(1) controls were analyzed by Western Blotting of tyrosine hydroxylase and choline acetyltransferase, as well as by TUNEL and histological silver staining. Both tyrosine hydroxylase and choline acetyltransferase levels were higher in SAMR(1) than in SAMP(8). There was also an age-related decrease in enzyme levels in SAMP(8), with the reduction of tyrosine hydroxylase being more apparent. Concomitantly, there was an age-related increase of apoptosis in the medial neocerebellum and the vermis as revealed by TUNEL, with changes being significant in the SAMP(8) strain. Histologically, some Purkinje cells appeared to disappear during aging. Taken together, the data suggests that the aging SAMP(8) strain displays differential Purkinje cell death in the medial cerebellum and that some of the dying cells are likely to be catecholaminergic.

Differential gene expression profiles in the hippocampus of senescence-accelerated mouse

The senescence-accelerated mouse (SAM) is an animal model for studying senescence and age-associated disorders due to its inherited aging phenotype. The SAM/prone8 (SAMP8) is a useful animal model to investigate the fundamental mechanisms involved in age-related learning and memory deficits that may have relevance to age-associated AD, while SAM/resistant1 (SAMR1) shows normal. To identify genes rendering the cognitive deterioration with aging, the subtractive cDNA libraries containing 1924 clones with the positive ratio of 96.18% were generated and the microarray containing 3136 cDNA was prepared. The results of screening libraries by the microarray showed that of all 91 differentially expressed genes, 50 were over-expressed and 41 were low-expressed in SAMP8. Some of the identified genes were confirmed by the real time quantitative RT-PCR. These results indicated the profiles of gene expression in the hippocampus of SAMP8 and SAMR1 were significantly different, which may play important roles in the age-related cognitive deficit in SAMP8, suggesting those genes related to the cognitive deficient or pathology change in the brain of SAMP8 may be potential gene targets for Alzheimer's disease therapy.

Chronic melatonin treatment reduces the age-dependent inflammatory process in senescence-accelerated mice

It is hypothesized that, besides increased free radical production, aging is a process also related to inflammation. Thus, female and male senescence-accelerated (SAMP8) and senescence-resistant (SAMR1) mice of 5 and 10 months of age were studied to assess this hypothesis. Plasma from these mice was processed to determine nitric oxide (NO), and pro-inflammatory [interleukin (IL)-1beta, IL-2, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and granulocyte-macrophage colony-stimulating factor] and anti-inflammatory (IL-4, IL-5 and IL-10) cytokines. The results show the presence of an age-dependent increase in IFN-gamma and TNF-alpha and a reduction in IL-2 levels, with minor changes in the remaining cytokines. Moreover, age was associated with a significant increase in NO levels. Chronic melatonin administration between 1 and 10 months of age counteracted the age-dependent production of pro-inflammatory cytokines and NO, reducing them to the levels found at 5 months of age. Melatonin also reduced the levels of the anti-inflammatory cytokines. The results of this study suggest the existence of an inflammatory process during aging and further support that melatonin behaves as an essential molecule against aging, for its anti-inflammatory properties together with its antioxidative role reported elsewhere.

Chronic administration of melatonin reduces cerebral injury biomarkers in SAMP8

Certain effects of melatonin on senescence were investigated. The experimental model used was 10-month-old senescence-accelerated mouse prone 8 (SAMP8). The mice in the experiment were administered melatonin (10 mg/kg) from the age of 1 month. Results showed that chronic administration of melatonin decreased cell loss in the cerebral cortex and reduced oxidative damage in protein and lipids. There are several studies suggesting that the activation of the cdk5/p35 pathway at its cleavage to cdk5/p25 may play a role in hyperphosphorylation of tau during aging and neurodegenerative diseases. Melatonin not only reduced the cerebral aging disturbances, but also prevented tau hyperphosphorylation present in the experimental model used in this study. Melatonin reduced cdk5 expression, as well as the cleavage of p35 to p25. The other tau kinase studied, GSK3beta, showed a reduction in this activity in comparison with SAMP8 nontreated SAMP8. These data indicate that melatonin possesses neuroprotective properties against cerebral damage gated to senescence. Moreover, these data suggest that the cdk5/GSKbeta signaling cascade has a potential role as a target for neurodegenerative diseases related to aging.

Chronic melatonin treatment prevents age-dependent cardiac mitochondrial dysfunction in senescence-accelerated mice

Heart mitochondria from female senescence-accelerated (SAMP8) and senescence-resistant (SAMR1) mice of 5 or 10 months of age, were studied. Mitochondrial oxidative stress was determined by measuring the levels of lipid peroxidation, glutathione and glutathione disulfide and glutathione peroxidase and reductase activities. Mitochondrial function was assessed by measuring the activity of the respiratory chain complexes and ATP content. The results show that the age-dependent mitochondrial oxidative damage in the heart of SAMP8 mice was accompanied by a reduction in the electron transport chain complex activities and in ATP levels. Chronic melatonin administration between 1 and 10 months of age normalized the redox and the bioenergetic status of the mitochondria and increased ATP levels. The results support the presence of significant mitochondrial oxidative stress in SAM mice at 10 months of age, and they suggest a beneficial effect of chronic pharmacological intervention with melatonin, which reduces the deteriorative and functional oxidative changes in cardiac mitochondria with age.

Oxidation of guanine in liver and lung DNA of prematurely aging OXYS rats

Immunofluorescence assay was applied for determination of 8-oxoguanine (8-oxoG) in DNA. The 8-oxoG content in liver and lung DNA of 2- and 18-month-old Wistar rats was compared with that of prematurely aging OXYS rats. It was shown that for rats of both strains, 8-oxoG content in lung DNA compared with liver DNA was 1.7-2.0-fold and 1.3-1.7-fold higher for 2- and 18-month-old rats, respectively. However, the degree of oxidative damage in liver DNA of OXYS rats was 2.4- (p < 0.01) and 1.5-fold (p < 0.05) higher for 2- and 18-month-old animals, respectively, than that in liver DNA of Wistar rats. Oxidation of guanine in lung DNA of OXYS rats was 2- (p < 0.01) and 1.7-fold (p < 0.05) higher for 2- and 18-month-old animals, respectively, than that in lung DNA of Wistar rats. The data indicate that elevated DNA oxidative damage in various organs of OXYS rats may be an important factor of accelerated aging and progression of age-related diseases--cataract, macular dystrophy, hypertension, osteoporosis, cognitive and behavioral dysfunctions, and also lung and liver pathologies.

Long-term antioxidant supplementation attenuates oxidative stress markers and cognitive deficits in senescent-accelerated OXYS rats

Oxidative damage of biomolecules increases with age and is postulated to be a major causal factor of various neurodegenerative disorders. Consequently, the concept of neuroprotection by antioxidants has been developed. Recently we have shown that the behaviour of young senescent-accelerated OXYS rats is similar to the behaviour of old Wistar animals. To determine the role of oxidative stress in this phenomenon we investigated age-related changes in protein carbonyls (PrC), lipid peroxides (LP), reduced glutathione (GSH), alpha-tocopherol (TP) and SOD activity in the brain of OXYS and Wistar rats. We also studied the effect of long-term supplementation with bilberry extract (2g/kg of diet) and Vitamin E (140 mg/kg of diet) on oxidative stress markers and on learning in passive avoidance test. In both rat strains LP, PrC and TP increased with age and at 24 months PrC was significantly higher (p<0.0001) in OXYS rats. At 3 months GSH was higher and SOD activity was lower in OXYS rats than in Wistar rats. SOD activity decreased with age in OXYS whereas increased in Wistar rats. Cognitive impairments in OXYS rats were manifested earlier than significant differences in the level of brain oxidative stress markers between two strains. By contrast, differences in antioxidant systems of Wistar and OXYS rats were registered at 3 months. Antioxidants attenuated cognitive deficits in OXYS rats, providing evidence for therapeutic role of antioxidants. Nevertheless, the exact mechanisms of neuroprotective effects of antioxidants in vivo and the real impact of oxidative stress on the development of cognitive impairments in OXYS rats still needs to be further investigated.

Age-related disruptions of circadian rhythm and memory in the senescence-accelerated mouse (SAMP8)

Common complaints of the elderly involve impaired cognitive abilities, such as loss of memory and inability to attend. Although much research has been devoted to these cognitive impairments, other factors such as disrupted sleep patterns and increased daytime drowsiness may contribute indirectly to impaired cognitive abilities. Disrupted sleep-wake cycles may be the result of age-related changes to the internal (circadian) clock. In this article, we review recent research on aging and circadian rhythms with a focus on the senescence-accelerated mouse (SAM) as a model of aging. We explore some of the neurobiological mechanisms that appear to be responsible for our aging clock, and consider implications of this work for age-related changes in cognition.

Melatonin reduces oxidative stress in erythrocytes and plasma of senescence-accelerated mice

It has been suggested that oxidative stress is a feature of aging. The goal of the present study was to assess the oxidant effects related to aging and the protective role of exogenous melatonin in senescence-accelerated mice (SAMP8). Two groups of SAMP8 mice (males and females) were compared with their respective control groups of SAMR1 mice (senescence-resistant inbred strain) to determine their oxidative status without melatonin treatment. Four other groups of the same characteristics were treated with melatonin (10 mg/kg/day) in their drinking water. The melatonin concentration in the feeding bottles was titrated according to water consumption and body weight (i.e. 0.06 mg/mL for 30 g of body weight and 5 mL/day of water consumption). The treatment began when animals were 1-month old and continued for 9 months. When mice were 10-month old, they were anesthetized and blood was obtained. Plasma and erythrocytes were processed to examine oxidative stress markers: reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferase (GST), thiobarbituric acid reactive substances (TBARS), and hemolysis. The results showed greater oxidative stress in SAMP8 than in SAMR1, largely because of a decrease in GSH levels and to an increase in GSSG and TBARS with the subsequent induction of the antioxidant enzymes GPX and GR. Melatonin, as an antioxidant molecule, improved the glutathione-related parameters, prevented the induction of GPX in senescent groups, and promoted a decrease in SOD and TBARS in almost all the groups.

Oxidative damage in the livers of senescence-accelerated mice: a gender-related response

The prevalence of liver diseases emphasizes the need of animal models to research on the mechanism of disease pathogenesis. Furthermore, most of the liver pathologies have the oxidative stress as an important component. The senescence-accelerated mouse strain SAMP8 was proposed as a valuable animal model for the study of liver diseases. To gain a better understanding of the mechanisms underlying degenerative processes in SAMP8 mice livers, we studied the oxidative-induced damage in 5-month-old SAMP8 mice and SAMR1, senescence-accelerated-resistant mice. We found profound differences in the antioxidant response to aging between sexes, with males displaying lowest levels of main antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) in SAMP8; whereas females had no difference in their activities, except for GR, when compared with their SAMR1 controls. The results obtained show the binomial SOD/CAT as an important factor for counteracting reactive oxygen species-dependent damage. There were not pathological differences at the morphological level between both strains, although the decay in protection against free radicals had an immediate response by increasing lipid and protein oxidative damage in SAMP8 mice liver. At 5 months, both male and female SAMP8 mice confront the oxidative stress challenge to different extents. Indeed, proteins seem to be the most vulnerable biomolecule in SAMP8 male mice.

The Neurosecretory System Is Hypertrophied in Senescence-Accelerated Mice

The hypothalamic supraoptic and paraventricular nuclei form the neurosecretory system and synthesize the neurohormones oxytocin and arginine-vasopressin. The senescence-accelerated mouse is a model of rapid aging that displays senile amyloidosis and memory problems. This paper presents the characterization of the neurosecretory system and describes the presence of a bilateral constant cluster of neurosecretory neurons in these mice. The stereologic analysis revealed that these groups contain 197 +/- 18 cells (87% synthesize arginine-vasopressin and 13% oxytocin). The presence of these clusters of neurosecretory neurons suggests that these mice could present greater neurohormone synthesis, increasing the deleterious effects of accelerated aging in this strain.

Cerebral plasmalogens and aldehydes in senescence-accelerated mice P8 and R1: a comparison between weaned, adult and aged mice

In contrast with senescence-accelerated mice R1, SAM P8 show abnormal aging characteristics. Changes occurring during aging could be mainly caused by free radical reactions. The brain is a plasmalogen-rich tissue. These particular phospholipids may act as endogenous antioxidants, be oxidized and release long chain aldehydes and alpha-hydroxyaldehydes during oxidative stress. The aim of this study was to examine by GC/MS the age- and strain-related levels of plasmalogens, aldehydes and alpha-hydroxyaldehydes in brain homogenates of SAM P8 and R1 at weaning, 5 months and 9 months of age in order to better understand the differences between both strains. In SAM R1, the evolution of brain plasmalogen levels corresponded to characteristics of normal aging: an increase from weaned to adult mice followed by a decrease characterizing the normal loss of myelin. By contrast to SAM R1, there was no change in the plasmalogen content in SAM P8 brain. The levels of aldehydes and alpha-hydroxyaldehydes were similar for both strains, they remained constant between adult and aged mice. Specific changes in the aging of SAM P8 were not explained by cerebral levels of these oxidative products. Other mechanisms related to the toxicity of aldehydes and alpha-hydroxyaldehydes could be considered.

Age-related changes in the oestrous cycle and reproductive hormones in senescence-accelerated mouse

To investigate age-related changes in the oestrous cycle and reproductive hormone levels in senescence-accelerated mouse (SAM), we examined these parameters in 3-, 5-, 7-, 9- and 11-month-old female SAM-prone/8 (SAMP8) and SAM-resistant/1 (SAMR1) strains. Levels of beta-endorphin (beta-EP) and substance P (SP) in the hypothalamus were also measured. The oestrous cycle and dioestrus of 9-month-old SAMP8 mice were significantly prolonged compared with age-matched SAMR1 mice. Furthermore, the concentration of serum oestradiol was lower and the level of pituitary luteinising hormone was higher in SAMP8 mice compared with SAMR1 mice. This characterises the hypothalamus-pituitary-ovary (HPO) axis of the SAMP8 strain as hypergonadotropic-hypogonad. The levels of beta-EP and SP in the SAMP8 hypothalamus were lower than in the SAMR1 hypothalamus. These results indicate that the function of the HPO axis in SAMP8 mice declines early and this may be attributed, in part, to the decline in beta-EP and SP concentrations in the hypothalamus.

Soleus muscles of SAMP8 mice provide an accelerated model of skeletal muscle senescence

Animal models are valuable research tools towards effective prevention of sarcopenia and towards a better understanding of the mechanisms underlying skeletal muscle aging. We investigated whether senescence-accelerated mouse (SAM) strains provide valid models for skeletal muscle aging studies. Male senescence-prone mice SAMP6 and SAMP8 were studied at age 10, 25 and 60 weeks and compared with senescence-resistant strain, SAMR1. Soleus and EDL muscles were tested for in vitro contractile properties, phosphocreatine content, muscle mass and fiber-type distribution. Declined muscle mass and contractility were observed at 60 weeks, the differences being more pronounced in SAMP8 than SAMP6 and more pronounced in soleus than EDL. Likewise, age-related decreases in muscle phosphocreatine content and type-II fiber size were most pronounced in SAMP8 soleus. In conclusion, typical features of muscular senescence occur at relatively young age in SAMP8 and nearly twice as fast as compared with other models. We suggest that soleus muscles of SAMP8 mice provide a cost-effective model for muscular aging studies.

Cultured murine dermal fibroblast-like cells from senescence-accelerated mice as in vitro models for higher oxidative stress due to mitochondrial alterations

The senescence-accelerated mouse is a model for senescence acceleration, a higher oxidative stress status, and age-associated disorders. We studied whether fibroblasts cultured from accelerated senescence-prone SAMP11 mice could be used as in vitro models for oxidative stress in senescence. Dichlorofluorescein and hydroethidine assays demonstrated that cells from SAMP11 mice produced more reactive oxygen species than did cells from accelerated senescence-resistant SAMR1 mice. These differences were not due to the defective induction of antioxidants. Double labeling with hydroethidine and MitoTracker Green revealed that most of the reactive oxygen species were generated within the mitochondria. Nonyl acridine orange and JC-1 assays showed an increase in the mass of the mitochondria, especially those with low membrane potential, in SAMP11 cells. Ultrastructurally, mitochondria with degenerative morphology were increased in SAMP11 cells with longer culture periods. These results suggest that cells from SAMP11 mice are useful models for spontaneous higher oxidative stress in vitro due to dysfunctional mitochondria.

No effects of lifelong creatine supplementation on sarcopenia in senescence-accelerated mice (SAMP8)

Oral creatine supplementation can acutely ameliorate skeletal muscle function in older humans, but its value in the prevention of sarcopenia remains unknown. We evaluated the effects of lifelong creatine supplementation on muscle mass and morphology, contractility, and metabolic properties in a mouse model of muscle senescence. Male senescence-accelerated mice (SAMP8) were fed control or creatine-supplemented (2% of food intake) diet from the age of 10 to 60 wk. Soleus and extensor digitorum longus muscles were tested for in vitro contractile properties, creatine content, and morphology at weeks 25 and 60. Both muscle types showed reduced phosphocreatine content at week 60 that could not be prevented by creatine. Accordingly, age-associated decline in muscle mass and contractility was not influenced by treatment. Aged soleus muscles had fewer and smaller fast-twitch glycolytic fibers irrespective of treatment received. It is concluded that lifelong creatine supplementation is no effective strategy to prevent sarcopenia in senescence-accelerated mice.

Mechanisms of aging in senescence-accelerated mice

BACKGROUND

Progressive neurological dysfunction is a key aspect of human aging. Because of underlying differences in the aging of mice and humans, useful mouse models have been difficult to obtain and study. We have used gene-expression analysis and polymorphism screening to study molecular senescence of the retina and hippocampus in two rare inbred mouse models of accelerated neurological senescence (SAMP8 and SAMP10) that closely mimic human neurological aging, and in a related normal strain (SAMR1) and an unrelated normal strain (C57BL/6J).

RESULTS

The majority of age-related gene expression changes were strain-specific, with only a few common pathways found for normal and accelerated neurological aging. Polymorphism screening led to the identification of mutations that could have a direct impact on important disease processes, including a mutation in a fibroblast growth factor gene, Fgf1, and a mutation in and ectopic expression of the gene for the chemokine CCL19, which is involved in the inflammatory response.

CONCLUSION

We show that combining the study of inbred mouse strains with interesting traits and gene-expression profiling can lead to the discovery of genes important for complex phenotypes. Furthermore, full-genome polymorphism detection, sequencing and gene-expression profiling of inbred mouse strains with interesting phenotypic differences may provide unique insights into the molecular genetics of late-manifesting complex diseases.

Animal models for fracture treatment in osteoporosis

Demographic changes in the age structure of occidental populations are giving rise to osteoporosis and associated fractures, which are becoming a major public health burden. Various animal models have been established and used to investigate the pathogenesis of osteoporosis and to facilitate the preclinical testing of new treatment options such as antiresorptive drugs. Although osteoporosis can be induced in animals, spontaneous fractures without adequate trauma were only found in nonhuman primates. An animal model designed to investigate new ways to treat fractures of osteoporotic bone has to fulfill requirements that are very different from those of pharmacological testing. The aspects of major interest in orthopedic applications are bone fragility, efficacy of implant fixation and bone healing. Existing animal models for osteoporosis were critically reviewed focusing on these aspects. The advantages and disadvantages of the models with regard to their application in the testing of new fracture-fixation devices or biological approaches to stimulate bone healing are discussed. Ovariectomy alone does not cause the bone loss seen in osteoporotic human patients. New models to simulate fracture of osteoporotic bone need to be explored and used to address the specific aims of an experiment.

Sleep wake profile and EEG spectral power in young or old senescence accelerated mice

Changes occurring with age in cortical EEG and sleep-wake states architecture were examined in senescence accelerated prone (SAMP8) or senescence resistant (SAMR1) mice (age: 2 and 12 months) under baseline conditions or after a 4 h sleep deprivation (SD). In baseline conditions, an increase in slow wave sleep (SWS) amount (21-24%) occurs at the expense of the wakefulness (W) in old SAMP8 and SAMR1 mice versus young animals. In these conditions, SWS latency is reduced (67-72%). Moreover, in SAMP8 and SAMR1 mice, aging deteriorates paradoxical sleep (PS) architecture with more pronounced changes in SAMP8 (amount: -63%; episode duration: -44%; latency: +286%; circadian component loss; and EEG theta (theta) peak frequency (TPF): -1 Hz). During the 4 h recovery subsequent to a 4 h sleep deprivation, old SAMP8 mice exhibit an enhanced sensitivity resulting in SWS (+62%) and PS (+120%) rebounds, a characteristic of this inbred strain. Results obtained are discussed in line with the age-related learning and memory impairments existing in SAMP8 animals. In particular, the reduced cognitive performances described in old SAMP8 might be linked to the TPF deterioration during PS.

Spontaneous fos expression in the suprachiasmatic nucleus of young and old mice

The senescence-accelerated mouse (SAMP8) is an animal model of aging that displays an array of circadian rhythm disruptions as early as 7 months of age. The present study explored the physiological basis for age-related changes in circadian rhythms by measuring c-Fos immunostaining. Cellular activity in the SCN "core" and "shell" was examined for 2-, 7-, and 12-month-old SAMP8 at circadian times (CTs) 2 and 14. Consistent with previous studies in rats, we observed higher levels of cellular activity at CT2 than at CT14, and higher levels of activity in the "shell" than in the "core" of the SCN. However, there was no effect of age on the pattern of cellular activity in either the "core" or the "shell" of the SCN. These results are discussed in the context of current research on spontaneous and light-induced c-Fos expression in the SCN of rodents.

Seeking for senile-related gene expression in cerebral tissue of senescence-accelerated mouse

1. A better understanding of the molecular effect on aging in the brain may help reveal important aspects of organism aging, as well as the processes that lead to aging-related brain dysfunction. In this study, the aging-specific expression genes of the murine cerebrum were investigated by using the technique of DDRT-PCR in two senescence-accelerated mouse strains, SAMP10/Ta and SAMR1TA. 2. Through comparing gene expression profile among the age, 2, 4, 12, and 18 month of the SAMP10/Ta strain, four differential fragments have been found, and comparing gene expression profile between the two mouse strains, 24 fragments have been detected, 7 and 17 of them belong to SAMP10/Ta and SAMR1TA, respectively. 3. Sequencing analysis indicated that most of those fragments are homologous with some of certain gene cDNA that are related with senile. The data obtained from this study suggest that many genes are involved in the senile process and accelerate senescence phenotypic pathologies in SAMP10/Ta.

Caliban's heritance and the genetics of neuronal aging

Although current research on brain aging is dominated by Alzheimer's disease (AD), many other brain changes arise during middle age in humans and in rodent models that are independent of AD-like neurodegeneration. Differences and continuities between normal and pathological aspects of neuronal aging reveal the relative contributions and interactions of genetic and environmental factors. Apolipoprotein E alleles might be prototypes for genetic polymorphisms associated with functional changes that arise during middle age. Mice are valuable models for these aspects of aging because most genotypes show little neurodegeneration, and none accumulate beta-amyloid unless human transgenes are introduced. As further human genes are found to modify normal and pathological neuronal aging, this zoo of aging-animal variants will facilitate analysis both of pathways of age-related neuronal dysfunction and of environmental influences on these pathways.