A new murine model of accelerated senescence

The role of mitochondria in brain aging and the effects of melatonin

Melatonin is an endogenous indoleamine present in different tissues, cellular compartments and organelles including mitochondria. When melatonin is administered orally, it is readily available to the brain where it counteracts different processes that occur during aging and age-related neurodegenerative disorders. These aging processes include oxidative stress and oxidative damage, chronic and acute inflammation, mitochondrial dysfunction and loss of neural regeneration. This review summarizes age related changes in the brain and the importance of oxidative/nitrosative stress and mitochondrial dysfunction in brain aging. The data and mechanisms of action of melatonin in relation to aging of the brain are reviewed as well.

Diastolic dysfunction is associated with cardiac fibrosis in the senescence-accelerated mouse

Diastolic heart failure is a major cause of mortality in the elderly population. It is often preceded by diastolic dysfunction, which is characterized by impaired active relaxation and increased stiffness. We tested the hypothesis that senescence-prone (SAMP8) mice would develop diastolic dysfunction compared with senescence-resistant controls (SAMR1). Pulsed-wave Doppler imaging of the ratio of blood flow velocity through the mitral valve during early (E) vs. late (A) diastole was reduced from 1.3 ± 0.03 in SAMR1 mice to 1.2 ± 0.03 in SAMP8 mice (P < 0.05). Tissue Doppler imaging of the early (E') and late (A') diastolic mitral annulus velocities found E' reduced from 25.7 ± 0.9 mm/s in SAMR1 to 21.1 ± 0.8 mm/s in SAMP8 mice and E'/A' similarly reduced from 1.1 ± 0.02 to 0.8 ± 0.03 in SAMR1 vs. SAMP8 mice, respectively (P < 0.05). Invasive hemodynamics revealed an increased slope of the end-diastolic pressure-volume relationship (0.5 ± 0.05 vs. 0.8 ± 0.14; P < 0.05), indicating increased left ventricular chamber stiffness. There were no differences in systolic function or mean arterial pressure; however, diastolic dysfunction was accompanied by increased fibrosis in the hearts of SAMP8 mice. In SAMR1 vs. SAMP8 mice, interstitial collagen area increased from 0.3 ± 0.04 to 0.8 ± 0.09% and perivascular collagen area increased from 1.0 ± 0.11 to 1.6 ± 0.14%. Transforming growth factor-β and connective tissue growth factor gene expression were increased in the hearts of SAMP8 mice (P < 0.05 for all data). In summary, SAMP8 mice show increased fibrosis and diastolic dysfunction similar to those seen in humans with aging and may represent a suitable model for future mechanistic studies.

American ginseng improves neurocognitive function in senescence-accelerated mice: possible role of the upregulated insulin and choline acetyltransferase gene expression

AIM

To investigate the effects of American ginseng on neurocognitive function and glucose regulation in senescence-accelerated mice.

METHODS

Male senescence-resistant inbred strains (SAMR1) and senescence-prone inbred strains (SAMP10) mice were divided into five groups and fed either a control diet or an American ginseng-supplemented diet (1% or 2% g/g) from 6 weeks to 10 months of age. Bodyweight, levels of fasting plasma glucose (FPG) and grading scores were monitored every month and neurocognitive functions were evaluated at 9 months of age with a KUROBOX apparatus using a stress-free positive cue task. Gene expressions of peroxisome proliferator-activated receptor delta (PPAR-δ), insulin, choline acetyltransferase (ChAT) and amyloid precursor protein (APP) in the brain were measured by real-time quantitative reverse transcription polymerase chain reaction assays.

RESULTS

American ginseng decreased FPG in SAMR1 mice, but increased FPG in SAMP10 mice. Correct visit ratios were higher in both SAMR1 and SAMP10 strains consuming an American ginseng-supplemented diet. Gene upregulation of insulin and ChAT in the brain, but not of PPAR-δ or APP, was evident in American ginseng-fed groups.

CONCLUSION

Daily consumption of American ginseng induced an enhancement in neurocognitive function in senescence-accelerated mice, which could be related to the upregulation of insulin and ChAT gene expression in the brain. Geriatr Gerontol Int 2012; 12: 123-130.

Sildenafil ameliorates cognitive deficits and tau pathology in a senescence-accelerated mouse model

Aging is associated with a deterioration of cognitive performance and with increased risk of neurodegenerative disorders. In the present study we tested whether the specific phosphodiesterase 5 inhibitor sildenafil could ameliorate the age-dependent cognitive impairments shown by the senescence-accelerated mouse prone-8 (SAMP8). Sildenafil administration (7.5 mg/kg for 4 weeks) to 5-month-old SAMP8 mice attenuated spatial learning and memory impairments shown by these mice in the Morris Water Maze. Tau hyperphosphorylation (AT8 but not PHF-1 epitope) shown by SAMP8 mice at this age was also decreased in the hippocampus of sildenafil-treated mice, an effect probably related to a decrease in cyclin-dependent kinase 5 protein expression and activity (p25/p35 ratio). Interestingly, sildenafil also phosphorylated Akt, which was associated with an increase of glycogen synthase kinase-3β phosphorylation, providing a plausible explanation for the reductions in tau hyperphosphorylation (AT8 and PHF-1 epitopes) and attenuation of cognitive deficits shown by 9-month-old SAMP8 mice. Overall, sildenafil might be beneficial in age-related brain dysfunction and could be an emerging candidate for the treatment of other neurodegenerative diseases.

Aging-associated changes in physical performance and energy metabolism in the senescence-accelerated mouse

The aim of the study was to clarify the aging-associated changes in physical performance and energy metabolism in senescence-accelerated prone mouse (SAMP1). The endurance of aged SAMP1 was significantly lower by 28% than the age-matched senescence-resistant mouse (SAMR1). Oxygen consumption and fat oxidation in aged SAMP1 were lower by 19% and 22%, respectively. Peroxisome proliferator-activated receptor-γ coactivator-1β and medium-chain acyl coenzyme A dehydrogenase messenger RNA expression was significantly lower in aged SAMP1. Aged SAMP1 exhibited higher plasma glucose, insulin, leptin, and lower adiponectin concentrations. Aged SAMP1 also had higher malondialdehyde levels in plasma and tissues and lower peroxisome proliferator-activated receptor-γ messenger RNA and protein levels in adipose tissue. These results indicate that physical performance and energy expenditure decrease earlier with aging in SAMP1, accompanied by decreased fatty acid catabolism in muscle and liver and increased inflammation and oxidative stress in adipose tissue. SAMP1 could thus be a useful accelerated functional depression model for studying physical performance and energy metabolism.

Correlation between serum immunoglobulin G and hearing threshold among elderly subjects with age-related hearing loss

BACKGROUND AND PURPOSE

This study was based on the hypothesis that suboptimal immune response and low serum immunoglobulin G (IgG) may predispose to age-related hearing loss (ARHL), and the objective was to determine the serum levels of IgG and hearing thresholds of apparently healthy elderly subjects and assess their correlation.

METHOD

This prospective study involved 126 participants ≥ 60 years old who were found to be free of any medical conditions. Pure-tone averages for both the speech (500-2,000 Hz) and high frequencies (3,000-8,000 Hz) and serum IgG levels were determined. Using 30 dB as cut-off for hearing loss, the correlation with serum IgG was assessed.

RESULTS

There were 59 males and 67 females with a mean age ± SD of 67.0 ± 2.7 years. Speech frequency hearing loss was seen in 30.2%, while high-frequency hearing loss accounted for 74.6%. In the speech frequencies, the mean ± SD of serum IgG among subjects with normal hearing was 11.3 ± 3.9 g/l, while among those with hearing loss it was 8.3 ± 3.3 g/l (p = 0.01). In the high frequencies, the mean ± SD values of serum IgG among the subjects with normal hearing was 11.1 ± 2.3 g/l, while among those with hearing loss it was 8.7 ± 1.9 g/l (p = 0.01).

CONCLUSION

Low serum IgG may be a contributory factor to the development of ARHL among the elderly. However, a longitudinal study involving intervention with immunoglobulin supplementation may further confirm this role.

Expression of VGLUTs contributes to degeneration and acquisition of learning and memory

Vesicular glutamate transporters (VGLUTs), which include VGLUT1, VGLUT2 and VGLUT3, are responsible for the uploading of L-glutamate into synaptic vesicles. The expression pattern of VGLUTs determines the level of synaptic vesicle filling (i.e., glutamate quantal size) and directly influences glutamate receptors and glutamatergic synaptic transmission; thus, VGLUTs may play a key role in learning and memory in the central nervous system. To determine whether VGLUTs contribute to the degeneration or acquisition of learning and memory, we used an animal model for the age-related impairment of learning and memory, senescence-accelerated mouse/prone 8 (SAMP8). KM mice were divided into groups based on their learning and memory performance in a shuttle-box test. The expression of VGLUTs and synaptophysin (Syp) mRNA and protein in the cerebral cortex and hippocampus were investigated with real-time fluorescence quantitative PCR and western blot, respectively. Our results demonstrate that, in the cerebral cortex, protein expression of VGLUT1, VGLUT2, VGLUT3 and Syp was decreased in SAMP8 with age and increased in KM mice, which displayed an enhanced capacity for learning and memory. The protein expression of VGLUT2 and Syp was decreased in the hippocampus of SAMP8 with aging. The expression level of VGLUT1 and VGLUT2 proteins were highest in KM mouse group with a 76-100% avoidance score in the shuttle-box test. These data demonstrate that protein expression of VGLUT1, VGLUT2 and Syp decreases age-dependently in SAMP8 and increases in a learning- and memory-dependent manner in KM mice. Correlation analysis indicated the protein expression of VGLUT1, VGLUT2 and Syp has a positive correlation with the capacity of learning and memory.

Effects of Chinese herbal medicine Fuzhisan on autologous neural stem cells in the brain of SAMP-8 mice

Fuzhisan (FZS), a Chinese herbal complex prescription, has been used in the treatment of Alzheimer's disease (AD) for more than 16 years. However the underlying mechanism remains to be explored. The effects of the aqueous extract of FZS on the cognitive functions of the aged mice and the pharmacological basis for its therapeutic efficacy were investigated. The results showed that FZS improved impaired cognitive ability of aged SAMP-8 mice. FZS (2.4, 4.8 g/kg/d) increased hippocampal neurogenesis and the long-term survival of BrdU-labeled cells without affecting the proportion of BrdU-positive neurons and glial cells. FZS also increased the number of BrdU-positive cells in the subventricular zone (SVZ) of the lateral ventricles of 8-month-old SAMP-8 mice. These studies suggest that FZS upregulates neurogenesis by increasing proliferation of neural progenitor cells and prolonging survival of the newborn cells in the hippocampal DG. FZS may be beneficial for the treatment of senile dementia, especially Alzheimer's disease.

Analysis of neuronal nitric oxide synthase expression and increasing astrogliosis in the brain of senescence-accelerated-prone 8 mice

The senescence-accelerated mouse (SAM) is an autogenic senile murine model characterized by early cognitive impairment and age-related deterioration of learning and memory. The present study investigated the alternations of neuronal nitric oxide synthase (nNOS) expression in frontal cortex and hippocampus in the aging process of SAM-prone 8 (SAMP8) and SAM-resistant 1 (SAMR1) mice. The results demonstrated that the expression of nNOS was upregulated in the frontal cortex, but downregulated in the hippocampus in SAMP8. Further, age-related increases of astrogliosis were seen in the cortex and hippocampi of aged SAMP8 and SAMR1, as revealed by the expression of the astrocyte specific marker, glial fibrillary acidic protein (GFAP). Indeed, astrogliosis in aged SAMP8 was significantly greater than that of aged SAMR1. Our results suggest the possibility of a correlation between the downregulation of nitric oxide (NO) in the hippocampus and reported learning and memory deficits in SAMP8. However, the toxic effects of NO and age-related increases of astrogliosis, may have contributed to abnormal alterations in metabolism and neurochemical mechanisms in aged SAMP8.

Integrative physiology of the aging bone: insights from animal and cellular models

Age-related bone loss is a common worldwide phenomenon in the aging population, placing them at an increased risk of fractures. Fortunately, basic and translational studies have been pivotal in providing us with a mechanistic understanding of the cellular and molecular pathophysiology of this condition. This review focuses on the current concepts and paradigms of age-related bone loss and how various animal and cellular models have broadened our understanding in this fascinating but complex area. Changes in hormonal, neuronal, and biochemical cues with age and their effect on bone have been discussed. This review also outlines recent studies on the relationship between bone and fat in the marrow, as well as the fate of the marrow mesenchymal stromal cell population, which can give rise to either bone-forming osteoblasts or fat-forming adipocytic cells as a function of age.

Supplementation with the reduced form of Coenzyme Q10 decelerates phenotypic characteristics of senescence and induces a peroxisome proliferator-activated receptor-alpha gene expression signature in SAMP1 mice

Our present study reveals significant decelerating effects on senescence processes in middle-aged SAMP1 mice supplemented for 6 or 14 months with the reduced form (Q(10)H(2), 500 mg/kg BW/day) of coenzyme Q(10) (CoQ(10)). To unravel molecular mechanisms of these CoQ(10) effects, a genome-wide transcript profiling in liver, heart, brain and kidney of SAMP1 mice supplemented with the reduced (Q(10)H(2)) or oxidized form of CoQ(10) (Q(10)) was performed. Liver seems to be the main target tissue of CoQ(10) intervention, followed by kidney, heart and brain. Stringent evaluation of the resulting data revealed that Q(10)H(2) has a stronger impact on gene expression than Q(10), primarily due to differences in the bioavailability. Indeed, Q(10)H(2) supplementation was more effective than Q(10) to increase levels of CoQ(10) in the liver of SAMP1 mice. To identify functional and regulatory connections of the "top 50" (p<0.05) Q(10)H(2)-sensitive transcripts in liver, text mining analysis was used. Hereby, we identified Q(10)H(2)-sensitive genes which are regulated by peroxisome proliferator-activated receptor-alpha and are primarily involved in cholesterol synthesis (e.g. HMGCS1, HMGCL and HMGCR), fat assimilation (FABP5), lipoprotein metabolism (PLTP) and inflammation (STAT-1). These data may explain, at least in part, the decelerating effects on degenerative processes observed in Q(10)H(2)-supplemented SAMP1 mice.

Quantitative trait locus on chromosome X affects bone loss after maturation in mice

Genetic programming is known to affect the peak bone mass and bone loss after maturation. However, little is known about how polymorphic genes on chromosome X (Chr X) modulate bone loss after maturation. We previously reported a quantitative trait locus (QTL) on Chr X, designated Pbd3, which had a suggestive linkage to bone mass, in male SAMP2 and SAMP6 mice. In this study, we aimed to clarify the effects of Pbd3 on the skeletal phenotype. We generated a congenic strain, P2.P6-X, carrying a 45.6-cM SAMP6-derived Chr X interval on a SAMP2 genetic background. The effects of Pbd3 on the bone phenotype were determined by microcomputed tomography (microCT), whole-body dual-energy X-ray absorptiometry (DXA), serum bone turnover markers, and histomorphometric parameters. Both the bone area fraction (BA/TA) on microCT and whole-body DXA revealed reduced bone loss in P2.P6-X compared with that in SAMP2. The serum concentrations of bone turnover markers at 4 months of age were significantly lower in P2.P6-X than in SAMP2, but did not differ at 8 months of age. These results were observed in female mice, but not in male mice. In conclusion, a QTL within a segregated 45.6-cM interval on Chr X is sex-specifically related to the rate of bone loss after maturation.

The role of epigenetics in aging and autoimmunity

The decline in immunocompetence with age is accompanied by the increase in the incidence of autoimmune diseases. Aging of the immune system, or immunosenescence, is characterized by a decline of both T and B cell function, and paradoxically the presence of low-grade chronic inflammation. There is growing evidence that epigenetics, the study of inherited changes in gene expression that are not encoded by the DNA sequence itself, changes with aging. Interestingly, emerging evidence suggests a key role for epigenetics in human pathologies, including inflammatory and neoplastic disorders. Here, we will review the potential mechanisms that contribute to the increase in autoimmune responses in aging. In particular, we will discuss how epigenetic alterations, especially DNA methylation and histone acetylation, are accumulated during aging and how these events contribute to autoimmunity risk.

Animal models of ischemic stroke. Part one: modeling risk factors

Ischemic stroke is one of the leading causes of long-term disability and death in developed and developing countries. As emerging disease, stroke related mortality and morbidity is going to step up in the next decades. This is both due to the poor identification of risk factors and persistence of unhealthy habits, as well as to the aging of the population. To counteract the estimated increase in stroke incidence, it is of primary importance to identify risk factors, study their effects, to promote primary and secondary prevention, and to extend the therapeutic repertoire that is currently limited to the very first hours after stroke. While epidemiologic studies in the human population are essential to identify emerging risk factors, adequate animal models represent a fundamental tool to dissect stroke risk factors to their molecular mechanism and to find efficacious therapeutic strategies for this complex multi- factorial disorder. The present review is organized into two parts: the first part deals with the animal models that have been developed to study stroke and its related risk factors and the second part analyzes the specific stroke models. These models represent an indispensable tool to investigate the mechanisms of cerebral injury and to develop novel therapies.

Probing the biology of Alzheimer's disease in mice

Alzheimer's disease (AD), the most common cause of dementia among the elderly, may either represent the far end of a continuum that begins with age-related memory decline or a distinct pathobiological process. Although mice that faithfully model all aspects of AD do not yet exist, current mouse models have provided valuable insights into specific aspects of AD pathogenesis. We will argue that transgenic mice expressing amyloid precursor protein should be considered models of accelerated brain aging or asymptomatic AD, and the results of interventional studies in these mice should be considered in the context of primary prevention. Studies in mice have pointed to the roles of soluble beta-amyloid (Abeta) oligomers and soluble tau in disease pathogenesis and support a model in which soluble Abeta oligomers trigger synaptic dysfunction, but formation of abnormal tau species leads to neuron death and cognitive decline severe enough to warrant a dementia diagnosis.

Neuroprotective effect of 3,5-di-O-caffeoylquinic acid on SH-SY5Y cells and senescence-accelerated-prone mice 8 through the up-regulation of phosphoglycerate kinase-1

As aged population dramatically increases in these decades, efforts should be made on the intervention for curing age-associated neurologic degenerative diseases such as Alzheimer's disease (AD). Caffeoylquinic acid (CQA), an antioxidant component and its derivatives are natural functional compounds isolated from a variety of plants. In this study, we determined the neuroprotective effect of 3,5-di-O-CQA on Abeta(1-42) treated SH-SY5Y cells using MTT assay. To investigate the possible neuroprotective mechanism of 3,5-di-O-CQA, we performed proteomics analysis, real-time PCR analysis and measurement of the intracellular ATP level. In addition, we carried out the measurement of escape latency time to find the hidden platform in Morris water maze (MWM), real-time PCR using senescence-accelerated-prone mice (SAMP) 8 and senescence-accelerated-resistant mice (SAMR) 1 mice. Results showed that 3,5-di-O-CQA had neuroprotective effect on Abeta (1-42) treated cells. The mRNA expression of glycolytic enzyme (phosphoglycerate kinase-1; PGK1) and intracellular ATP level were increased in 3,5-di-O-CQA treated SH-SY5Y cells. We also found that 3,5-di-O-CQA administration induced the improvement of spatial learning and memory on SAMP8 mice, and the overexpression of PGK1 mRNA. These findings suggest that 3,5-di-O-CQA has a neuroprotective effect on neuron through the upregulation of PGK1 expression and ATP production activation.

Effect of intermittent treatment with human Parathyroid Hormone 1-34 in SAMP6 senescence-accelerated mice

We examined trabecular and cortical bone in the senescence-accelerated mouse prone 6 (SAMP6) murine model of senile osteoporosis after treatment with human PTH 1-34. Sixteen-week-old female SAMP6 mice were assigned to control and PTH groups. PTH (20 microg/kg) was administered sc 3 times a week for 12 weeks. The control mouse strain, senescence-accelerated mouse resistant 1 (SAMR1), was used for comparison. The femoral metaphysis and diaphysis were used to measure bone mineral density (BMD), analyze the trabecular and the cortical structure by micro-computed tomography, and for conducting the bone strength test. PTH significantly attenuated the loss of BMD, improved the trabecular bone microstructure, and increased the bone strength in the femoral metaphysis. We did not find any differences in the bone strength of the femoral diaphysis after PTH treatment, although the cortical bone volume and cortical thickness were improved. Although the cortical thickness increased, the cortical bone density decreased, likely because of the increase of cortical porosity in the distal metaphysis after administration of PTH.

A senescence accelerated mouse model to study aging in the larynx

Objective: Age-related changes in the larynx lead to significant voice impairment and reduced quality of life. There is a need for aged animal models that have practical generation times to study the fundamental changes and new therapeutics for the aging voice. The senescence accelerated prone mouse strain (SAMP) animals experience rapid aging without any experimental manipulation. The main objective of this study was to demonstrate the use of senescence accelerated mice to study aging in the larynx.

Study Design: Murine model.

Setting: Department of Animal Resources, Emory University.

Subjects and Methods: Larynges from five senescence accelerated prone mice, five normal aging senescence resistant mice, and five C57BL/6 mice were harvested and processed for paraffin sections. Histomorphometry was performed for assessment of collagen and hyaluronic acid distribution. In addition, frozen laryngeal tissue was harvested for transcriptional and translational assessment of collagen-1, using real-time polymerase chain reaction with specific primers and Western blots. Myofibroblast assessment was performed by immunostaining for the presence of α-smooth muscle actin.

Results: The deposition of collagen increased at six months of age in the SAMP vocal fold, and the level of collagen-1 mRNA increased with age. The myofibroblast protein α-smooth muscle actin was also found at a higher concentration in the SAMP vocal tissue. In contrast, the levels of hyaluronic acid in the vocal folds of SAMP mice decreased with age when compared to age-matched C57BL/6 mice.

Conclusion: SAMP mice show accelerated, age-related changes in the vocal fold that were evident at as early as six months of age. The use of senescence accelerated mice offers promise as a model to study age-related laryngeal changes.

Drinking hydrogen water ameliorated cognitive impairment in senescence-accelerated mice

Hydrogen has been reported to have neuron protective effects due to its antioxidant properties, but the effects of hydrogen on cognitive impairment due to senescence-related brain alterations and the underlying mechanisms have not been characterized. In this study, we investigated the efficacies of drinking hydrogen water for prevention of spatial memory decline and age-related brain alterations using senescence-accelerated prone mouse 8 (SAMP8), which exhibits early aging syndromes including declining learning ability and memory. However, treatment with hydrogen water for 30 days prevented age-related declines in cognitive ability seen in SAMP8 as assessed by a water maze test and was associated with increased brain serotonin levels and elevated serum antioxidant activity. In addition, drinking hydrogen water for 18 weeks inhibited neurodegeneration in hippocampus, while marked loss of neurons was noted in control, aged brains of mice receiving regular water. On the basis of our results, hydrogen water merits further investigation for possible therapeutic/preventative use for age-related cognitive disorders.

Novel model of TH2-polarized chronic ileitis: the SAMP1 mouse

BACKGROUND

SAMP1/Yit mice develop spontaneous, segmental, transmural ileitis recapitulating many features of Crohn's disease (CD). The ileitic phenotype may have arisen during crosses of SAMP1 mice selected for the presence of skin lesions. We hereby describe that the original SAMP1 strain similarly develops ileitis. Our aim was to characterize the histopathological and immunological features of this model and assess its responsiveness to standard inflammatory bowel disease (IBD) therapy.

METHODS

The time course of histopathological features of ileitis was assessed. Immune compartments were characterized by flow cytometry. Ileal cytokine profiles and transcription factors were determined by real-time reverse-transcription polymerase chain reaction (RT-PCR). Finally, response to corticosteroid therapy and its effect on immune compartments and cellularity was evaluated.

RESULTS

Histological features and time course of disease were conserved, compared to those reported in SAMP1/Yit strains, with similar expansion of CD19+, CD4+, and CD8+ effector (CD44(high) CD62L(low)), and central memory lymphocytes (CD44(high)CD62L(high)). However, different from SAMP1/YitFc mice, analysis of ileal cytokine profiles revealed initial T(H)1 polarization followed by T(H)2-polarized profile accompanied by prominent eosinophilia during late disease. Lastly, corticosteroids attenuated ileitis, resulting in decreased lymphocyte subsets and cellularity of compartments.

CONCLUSIONS

Here we report that the ileitic phenotype of SAMP1-related strains was already present in the original SAMP1 strain. By contrast, the cytokine profile within the terminal ilea of SAMP1 is distinct from the mixed T(H)1/T(H)2 profile of SAMP1/YitFc mice during late disease, as it shows predominant T(H)2 polarization. Dissemination of these strains may advance our understanding of CD pathogenesis, which in 60% of patients involves the terminal ileum.

[Anti-aging studies on the senescence accelerated mouse (SAM) strains]

Senescence accelerated mouse (SAM), a murine model of accelerated senescence, was established by Toshio Takeda and colleagues. SAM consists of series of SAMP (prone) and SAMR (resistant) lines. All SAMP lines (from SAMP1 to SAMP11) are characterized by accelerated accumulation of senile features, earlier onset and faster progress of age-associated pathological phenotypes, such as amyloidosis, impaired immune response, senile osteoporosis and deficits in learning and memory. These SAMP lines are useful for evaluation of putative anti-aging therapies. For example, SAMP1 line is used to study the anti-aging effect of the antioxidant containing foods and various anti-oxidants, such as coenzyme Q10, vitamin C, lycopene. SAMP8 line exhibiting an early onset of impaired learning and memory is often used for test strategies for therapeutic intervention of dementia of early onset. SAMP6 is used as an animal model for developing new strategies for the treatment of osteoporosis in humans. Various lines of SAM (P1, P6, P8, P10 and R1) are now commercially available for research. In this review, I will briefly introduce various usages of SAM in anti-aging research.

Pathomechanism of cellular infiltration in the perivascular region of several organs in SAMP1/Yit mouse

We investigated the histological changes of extra-intestinal organs, such as the liver, kidney, lung and pancreas in SAMP1/Yit mice, a human Crohn's disease model, using immunohistochemical techniques. The perivascular cellular infiltration was detected around the small vessels after 30 weeks. These infiltrating cells consisted of many CD4-positive T-lymphocytes, and small numbers of CD8- positive T-lymphocytes and IgG-positive B-lymphocytes. MAdCAM-1 and VCAM-1 were detected in vascular endothelial cells in non-affected regions of 13 and 20 week-old, as well as in the affected regions showing perivascular cellular infiltration after 30 weeks. In addition, integrin alpha4beta7 was detected on these infiltrating cells in the perivascular regions after 30 week-old. LT-beta and IL-12, cytokines of the Th-1-type immune response, were not observed in these affected regions. However, IL-4, one of the cytokines of the Th-2-type immune response, was detected on the perivascular infiltrating cells after 30 week-old. These results revealed that the changes in extra-intestinal organs were mainly caused by infiltration of CD4-positive T-lymphocytes into the perivascular regions in SAMP1/Yit mice. These cellular infiltrations were thought to be initiated by adhesion of CD4-positive T-lymphocytes to the endothelial cells mediated by MAdCAM-1 and integrin beta7. Immunohistochemistry for Th related cytokines indicated that the perivascular cellular infiltration was developed by the Th-2-type immune response in the extra-intestinal organs of SAMP1/Yit mouse.

Site-specific bone loss in senescence-accelerated mouse (SAMP6): a murine model for senile osteoporosis

The senescence-accelerated mouse strain P6 (SAMP6) is a model of senile osteoporosis, which possesses many features of senile osteoporosis in humans. So far, little is known about the systemic bone microstructural changes that occur at multiple skeletal sites. In this study, we therefore, investigated site (vertebra, femur and tibia) dependence of bone microstructure and bone mineral density (BMD) in SAMP6 and the normal control mouse (SAMR1) at 5 and 12months of age using quantitative micro computed tomography (micro-CT) and image analysis software. As compared with SAMR1, the most prominent change in SAMP6 was the reduction of vertebral trabecular bone volume fraction (BV/TV) and trabecular BMD. Moderate decrease of trabecular bone mass was observed in the proximal tibia and distal femur. Increased marrow area and periosteal perimeter were investigated, though the cortical area and cortical thickness had no marked changes in the mid-tibial and mid-femoral cortical bones. These results indicate that bone microstructural properties in SAMP6 are remarkably heterogeneous throughout the skeleton, which is analogous to changes that occur in human bones. These findings further validate the relevance of SAMP6 as a model of senile osteoporosis.

Sex steroids during bone growth: a comparative study between mouse models for hypogonadal and senile osteoporosis

SUMMARY

In this study, the role of disturbed bone mineral acquisition during puberty in the pathogenesis of osteoporosis was studied. To this end, a mouse model for senile and hypogonadal osteoporosis was used. Longitudinal follow-up showed that bone fragility in both models results from deficient bone build-up during early puberty.

INTRODUCTION

Male osteoporosis may result from impaired bone growth. This study characterizes the mechanisms of deficient peak bone mass acquisition in models for senile (SAMP6) and hypogonadal (orchidectomized SAMR1) osteoporosis.

METHODS

Bone mineral acquisition was investigated longitudinally in SAMP6 and orchidectomized SAMR1 mice (eight to ten animals per group) using peripheral quantitative computed tomography and histomorphometry. Additionally, the effects of long-term 5alpha-dihydrotestosterone (DHT) and 17beta-estradiol (E2) replacement were studied. Statistical analysis was performed using ANOVA and Student's t test.

RESULTS

SAMP6 mice showed an early (4 weeks) medullary expansion of the cortex due to impaired endocortical bone formation (-43%). Despite compensatory periosteal bone formation (+47%), cortical thickness was severely reduced in 20-week-old SAMP6 versus SAMR1. Orchidectomy reduced periosteal apposition between 4 and 8 weeks of age and resulted in high bone turnover and less trabecular bone gain in SAMP6 and SAMR1. DHT and E2 stimulated periosteal expansion and trabecular bone in orchidectomized SAMP6 and SAMR1. E2 stimulated endocortical apposition in SAMP6. Moreover, sex steroid action occurred between 4 and 8 weeks of age.

CONCLUSION

Bone fragility in both models resulted from deficient bone build-up during early puberty. DHT and E2 improved bone mass acquisition in orchidectomized animals, suggesting a role for AR and ER in male skeletal development.

Omega-3 polyunsaturated fatty acids ameliorate the severity of ileitis in the senescence accelerated mice (SAM)P1/Yit mice model

Clinical studies using omega-3 polyunsaturated fatty acids (omega3-PUFA) to Crohn's disease (CD) are conflicting. Beneficial effects of dietary omega3-PUFA intake in various experimental inflammatory bowel disease (IBD) models have been reported. However, animal models of large intestinal inflammation have been used in all previous studies, and the effect of omega3 fat in an animal model of small intestinal inflammation has not been reported. We hypothesized that the effects of omega3 fat are different between large and small intestine. The aim of this study was to determine whether the direct effect of omega3 fat is beneficial for small intestinal inflammation. Senescence accelerated mice (SAM)P1/Yit mice showed remarkable inflammation of the terminal ileum spontaneously. The numbers of F4/80-positive monocyte-macrophage cells as well as beta7-integrin-positive lymphocytes in the intestinal mucosa were increased significantly compared with those in the control mice (AKR-J mice). The area of mucosal addressin cell adhesion molecule-1 (MAdCAM-1)-positive vessels was also increased. The degree of expression levels of monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-6 and interferon (IFN)-gamma mRNA were increased significantly compared with those in the control mice. The feeding of two different kinds of omega3 fat (fish-oil-rich and perilla-oil-rich diets) for 16 weeks to SAMP1/Yit mice ameliorated inflammation of the terminal ileum significantly. In both the omega3-fat-rich diet groups, enhanced infiltration of F4/80-positive monocytes/macrophages in intestinal mucosa of SAMP1/Yit mice cells and the increased levels of MCP-1, IL-6 and IFN-gamma mRNA expression were ameliorated significantly compared with those in the control diet group. The results suggest that omega3 fat is beneficial for small intestinal inflammation by inhibition of monocyte recruitment to inflamed intestinal mucosa.

Influence of long-term consumption of a Lactococcus lactis strain on the intestinal immunity and intestinal flora of the senescence-accelerated mouse

The senescence-accelerated mouse develops normally until 5-6 months of age and then displays rapid and irreversible advancement of senescence manifesting as clinical signs and gross lesions. To clarify the effect of lactic acid bacteria on the physiological changes with increasing age, heat-killed Lactococcus lactis G50 was administered to 1-month-old senescence-accelerated-prone mouse (SAMP)6 mice for 11 months, a senescence-accelerated mouse strain that develops senile osteoporosis. Mice fed G50 gained more weight than the control mice (not fed G50) during the feeding experiment. Faecal IgA levels in the mice fed G50 at 3 months were higher than those of the control mice but decreased to control levels with increasing age. The numbers of viable cells of Bacteroides sp., Lactobacillus sp., Staphylococcus sp., Enterococcus/Streptococcus sp. and Enterobacteriaceae sp. in faeces were similar for mice fed the G50 and control diets at any age, but strain G50 suppressed the intestinal growth of H2S-producing bacteria. Bone density of the thigh bone did not differ between aged G50 and control mice. Strain G50 would be a beneficial bacterium for the enhancement of intestinal immunity during youth and to suppress the growth of harmful intestinal bacteria. The applicability of strain G50 for the food and animal industries has been proposed in the present study.

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.

RAGE, LDL receptor, and LRP1 expression in the brains of SAMP8

SAMP8, senescence-accelerated mice with age-related deficits in memory and learning, are known to show age-related increases of amyloid precursor protein (APP) expression and to be under elevated oxidative stress. The receptor for advanced glycation end product (RAGE) is a representative influx transporter of APP or amyloid-beta (A beta) protein in cerebral vessels, while low-density lipoprotein receptor (LDLR) and LDL-related protein 1 (LRP1) are efflux transporters. These receptors play roles not only in clearance of A beta protein but also in control of oxidative stress. In this study, we examined the gene and protein expressions of these receptors, by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemical techniques. SAMR1 mice with lower expression of APP were as controls. The gene and protein expressions of RAGE were lower in SAMP8 brains than in SAMR1. Those of LDLR were higher in SAMP8 brains than those of SAMR1. There were no differences in the expressions of LRP1 between SAMP8 and SAMR1. Immunosignals of RAGE and LDLR were seen in the cytoplasm of CD34-positive endothelial cells and also in astrocytes, in both strains of mice. These findings suggest that the lower expression of RAGE and the higher expression of LDLR may contribute to clearance of toxic substances and, in addition, be related to elevated oxidative stress in SAMP8 brains.

Identification of histone methylation multiplicities patterns in the brain of senescence-accelerated prone mouse 8

Histone post-translational modifications (PTMs) are involved in diverse biological processes and methylation was regarded as a long-term epigenetic mark. Though aging represented one of the major risk factors for neurodegenerative diseases, no systematic investigations had correlated the patterns of histone PTMs in the brain with aging and the roles of such concerted histone PTMs in brain aging are still unknown. In this study, enzyme digestion, nano-LC, MALDI-TOF/TOF MS analysis and Western blotting were combined to investigate the defined methylation of core histones (H2A, H2B, H3 and H4) in the brain of 12-month-old senescence accelerated mouse prone 8 (SAMP8). The expression of several modified histones in the brain of 3-, and 12-month-old SAMP8 mice as well as that of the age-matched control senescence accelerated-resistant mouse (SAMR1) was compared. In the brain of 12-month-old SAMP8 mice, seven methylation sites (H3K24, H3K27, H3K36, H3K79, H3R128, H4K20 and H2A R89) were detected and most PTMs sites were located on histone H3. Mono-methylated H4K20 decreased significantly in the brain of 12-month-old SAMP8 mice. Methylated H3K27 and H3K36 coexisted in the aged brain with different methylation multiplicities. Di-methylated H3K79 expressed in the neurons of cerebral cortex and hippocampus. This study showed histone methylation patterns in the aged SAMP8 mice brain and provided the experimental evidences for further research on histone PTMs in the aged brain. We hope these results could initiate a platform for the exchange of comprehensive information concerning aging or neurodegenerative disease and help us interpret the change of gene expression and DNA repair ability at epigenetic level.

Effect of dietary unsaturated fatty acids on senile amyloidosis in senescence-accelerated mice

Effects of dietary oils on aging were investigated in senescence-accelerated mice. For 26 weeks, mice were fed purified diets containing 4% olive oil, safflower oil, perilla oil, or fish oil. Serum total, high-density lipoprotein cholesterol, and apolipoprotein A-II (ApoA-II) were significantly lower in the fish oil group than in the perilla oil group, and these were significantly lower than in the olive oil or safflower oil group. The olive oil and safflower oil groups had significantly fewer ApoA-II amyloid fibril (AApoAII) deposits and anti-single-strand DNA (ssDNA) antibodies than the fish oil or perilla oil group, and the fish oil diet induced significantly more AApoAII deposits and anti-ssDNA antibodies than did the perilla oil diet. Survival decreased earlier in the fish oil group than in the other groups (as seen in the survival curve). The results suggest that greater the degree of unsaturation of dietary fatty acids, greater is the tendency for accelerated senescence.

Abcb1a and Abcb1b expression in senescence-accelerated mouse (SAM)

It was recently reported that some strains of senescence-accelerated mouse (SAM) including SAMR1 had a spontaneous retroviral insertional mutation in the ATP-binding cassette, sub-family B, member 1A (Abcb1a) gene, while other strains including SAMP8 had not. The Abcb1 gene product, P-glycoprotein, is a representative efflux transporter of cerebral vessels. In this study, using brain samples of SAMR1, Abcb1a gene-mutant mice, and of SAMP8 without that mutation, we examined the gene expression of some representative ATP-binding cassettes, such as Abcb1a, Abcb1b, Abcc, and Abcg2, and the protein expression of P-glycoprotein by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemical techniques. The gene expression of Abcb1a was decreased in the brain samples of SAMR1 compared with those of SAMP8, while that of Abcb1b was increased in the samples of SAMR1 compared with those of SAMP8. There were no differences in the gene expression of Abcc and Abcg2 between the samples of SAMR1 and SAMP8. The protein expression of P-glycoprotein was decreased in the brain samples of SAMR1 compared with those of SAMP8. Immunosignals of P-glycoprotein were seen in vessels walls, mainly CD34-positive endothelial cells and partially astrocytic cells, in both mice. These findings indicate that SAMR1, Abcb1a-mutant mice, showed decreased expression of Abcb1a gene and P-glycoprotein and increased gene expression of Abcb1b, compared with those of SAMP8 without that mutation, suggesting no clear effect of increased gene expression of Abcb1b on decreased expression of P-glycoprotein. The combination of SAMR1 and SAMP8 may be a good tool to investigate which transporter, Abcb1a or Abcb1b, can be used in drug delivery into the brain.

Senescence accelerated mouse strain is sensitive to neurodegeneration induced by mild impairment of oxidative metabolism

Neuronal loss and impairment of oxidative metabolism are frequently observed in aging associated neurodegenerative diseases. Thiamine deficiency (TD) induces the region selective neuronal loss in the brain, which has been used to model neurodegeneration, accompanied by mild impairment of oxidative metabolism. C57BL/6 mice were commonly used animals for TD experiments; however, the individual variations among C57BL/6 mice in response to TD limited the consistence of brain pathology. The senescence accelerated prone 8 (SAMP8) mouse strain exhibits age-related morphological changes in the brain and deficits in learning and memory. In this study, we compared the effects of TD on SAMP8 mice, senescence accelerated resistant 1 (SAMR1) mice and C57BL/6 mice. TD-induced body weight loss in SAMP8 mice was much greater than in SAMR1 and C57BL/6 mice. In addition, earlier and more severe loss of neurons in the submedial thalamic nucleus (SmTN) of the thalamus was detected in the SAMP8 mice. After 8 days of TD (TD8), the loss of NeuN-positive neurons in the SmTN of SAMP8, SAMR1 and C57BL/6 mice was 65%, 50%, and 36%, respectively. TD also caused accumulation of amyloid precursor protein (APP) in the thalamus. After TD10, APP immunoreactivity in the thalamus of SAMP8 was much more intense than that of SAMR1 and C57BL/6 mice. These results suggest that SAMP8 mice are sensitive to TD and therefore offer a useful model for studying aging related neurodegeneration caused by the impairment of oxidative metabolism.

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.

Effect of dietary n-3 polyunsaturated fatty acids on brain lipid fatty acid composition, learning ability, and memory of senescence-accelerated mouse

Animal studies have shown that a deficiency in brain of the n-3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) is associated with memory loss and diminished cognitive function. The senescence-accelerated prone 8 (SAMP8) mouse develops impairments in learning and memory at 8-12 months of age. The effect of diet supplemented with n-3 PUFA on brain phospholipid DHA status, learning, and memory ability in aged SAMP8 mice was investigated. At the age of 10 months, SAMP8 mice were fed either a low-DHA or a high-DHA diet for 8 weeks. In comparison to SAMP8 mice fed the low-DHA diet, those fed a high-DHA diet had improved acquisition and retention in a T-maze foot shock avoidance test and a higher proportion of DHA in hippocampal and amygdala phospholipids. This study demonstrates that, in mature animals, DHA is incorporated into brain phospholipids and that dietary n-3 PUFA is associated with delay in cognitive decline.

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.