Novel frame-shift mutation in Slc5a2 encoding SGLT2 in a strain of senescence-accelerated mouse SAMP10

The senescence-accelerated mouse prone10 (SAMP10) strain, a model of aging, exhibits cognitive impairments and cerebral atrophy. We noticed that SAMP10/TaSlc mice, a SAMP10 substrain, have developed persistent glucosuria over the past few years. In the present study, we characterized SAMP10/TaSlc mice and further identified a spontaneous mutation in the Slc5a2 gene encoding sodium-glucose co-transporter (SGLT) 2. The mean concentration of urine glucose was high in SAMP10/TaSlc mice and increased further with advancing age, whereas other strains of senescence-accelerated mice, including SAMP1/SkuSlc, SAMP6/TaSlc and SAMP8/TaSlc or normal aging control SAMR1/TaSlc mice, exhibited no detectable glucose in urine. SAMP10/TaSlc mice consumed increasing amounts of food and water compared to SAMR1/TaSlc mice, suggesting the compensation of polyuria and the loss of glucose. Oral glucose tolerance tests showed decreased glucose reabsorption in the kidney of SAMP10/TaSlc mice. In addition, blood glucose levels decreased in an age-dependent fashion. The kidney was innately larger than that of control mice with no histological alterations. We examined the expression levels of glucose transporters in the kidney. Among SGLT1, SGLT2, glucose transporter (GLUT) 1 and GLUT2, we found a significant decrease only in the level of SGLT2. DNA sequencing of SGLT2 in SAMP10/TaSlc mice revealed a single nucleotide deletion of guanine at 1236, which resulted in a frameshift mutation that produced a truncated protein. We designate this strain as SAMP10/TaSlc-Slc5a2^slc (SAMP10-ΔSglt2). Recently, SGLT2 inhibitors have been demonstrated to be effective for the treatment of patients with type 2 diabetes (T2D). SAMP10-ΔSglt2 mice may serve as a unique preclinical model to study the link between aging-related neurodegenerative disorders and T2D.     

Proteomic analysis of specific brain proteins in aged SAMP8 mice treated with alpha-lipoic acid: implications for aging and age-related neurodegenerative disorders

Free radical-mediated damage to neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD) and aging. The senescence accelerated prone mouse strain 8 (SAMP8) exhibits age-related deterioration in memory and learning along with increased oxidative markers. Therefore, SAMP8 is a suitable model to study brain aging and, since aging is the major risk factor for AD and SAMP8 exhibits many of the biochemical findings of AD, perhaps as a model for and the early phase of AD. Our previous studies reported higher oxidative stress markers in brains of 12-month-old SAMP8 mice when compared to that of 4-month-old SAMP8 mice. Further, we have previously shown that injecting the mice with alpha-lipoic acid (LA) reversed brain lipid peroxidation, protein oxidation, as well as the learning and memory impairments in SAMP8 mice. Recently, we reported the use of proteomics to identify proteins that are expressed differently and/or modified oxidatively in aged SAMP8 brains. In order to understand how LA reverses the learning and memory deficits of aged SAMP8 mice, in the current study, we used proteomics to compare the expression levels and specific carbonyl levels of proteins in brains from 12-month-old SAMP8 mice treated or not treated with LA. We found that the expressions of the three brain proteins (neurofilament triplet L protein, alpha-enolase, and ubiquitous mitochondrial creatine kinase) were increased significantly and that the specific carbonyl levels of the three brain proteins (lactate dehydrogenase B, dihydropyrimidinase-like protein 2, and alpha-enolase) were significantly decreased in the aged SAMP8 mice treated with LA. These findings suggest that the improved learning and memory observed in LA-injected SAMP8 mice may be related to the restoration of the normal condition of specific proteins in aged SAMP8 mouse brain. Moreover, our current study implicates neurofilament triplet L protein, alpha-enolase, ubiquitous mitochondrial creatine kinase, lactate dehydrogenase B, and dihydropyrimidinase-like protein 2 in process associated with learning and memory of SAMP8 mice.     

Trimethylamine‐N‐oxide promotes brain aging and cognitive impairment in mice

Gut microbiota can influence the aging process and may modulate aging‐related changes in cognitive function. Trimethylamine‐N‐oxide (TMAO), a metabolite of intestinal flora, has been shown to be closely associated with cardiovascular disease and other diseases. However, the relationship between TMAO and aging, especially brain aging, has not been fully elucidated. To explore the relationship between TMAO and brain aging, we analysed the plasma levels of TMAO in both humans and mice and administered exogenous TMAO to 24‐week‐old senescence‐accelerated prone mouse strain 8 (SAMP8) and age‐matched senescence‐accelerated mouse resistant 1 (SAMR1) mice for 16 weeks. We found that the plasma levels of TMAO increased in both the elderly and the aged mice. Compared with SAMR1‐control mice, SAMP8‐control mice exhibited a brain aging phenotype characterized by more senescent cells in the hippocampal CA3 region and cognitive dysfunction. Surprisingly, TMAO treatment increased the number of senescent cells, which were primarily neurons, and enhanced the mitochondrial impairments and superoxide production. Moreover, we observed that TMAO treatment increased synaptic damage and reduced the expression levels of synaptic plasticity‐related proteins by inhibiting the mTOR signalling pathway, which induces and aggravates aging‐related cognitive dysfunction in SAMR1 and SAMP8 mice, respectively. Our findings suggested that TMAO could induce brain aging and age‐related cognitive dysfunction in SAMR1 mice and aggravate the cerebral aging process of SAMP8 mice, which might provide new insight into the effects of intestinal microbiota on the brain aging process and help to delay senescence by regulating intestinal flora metabolites.     

DHEAS improves learning and memory in aged SAMP8 mice but not in diabetic mice

Dehydroepiandrosterone sulfate (DHEAS) has been reported to improve memory in aged animals and suggested as a treatment for age-related dementias. The SAMP8 mouse, a model of Alzheimer's disease, has an age-related impairment in learning and memory and an increase in brain levels of amyloid precursor protein (APP) and amyloid beta protein (Abeta). Male SAMP8 mice also have a decrease in testosterone, to which DHEA is a precursor. Diabetes has been suggested as a model of aging and to be linked to Alzheimer's disease. Diabetics can have memory deficits and lower DHEAS levels. Here, we examined the effects of chronic oral DHEAS on acquisition and retention for T-maze footshock avoidance in 12 mo male SAMP8 mice and in CD-1 mice with streptozocin-induced diabetes. Learning and memory were improved in aged SAMP8 mice, but not in CD-1 mice with streptozocin-induced diabetes. These findings suggest that DHEAS is more effective in reversing the cognitive impairments associated with overexpression of Abeta than with diabetes.     

Regional differences in PACAP transport across the blood-brain barrier in mice: a possible influence of strain,amyloid beta protein,and age

The blood–brain barrier (BBB) controls the exchange of peptides and regulatory proteins between the central nervous system (CNS) and the blood. Transport across the BBB of such regulatory substances is altered in animal models of Alzheimer’s disease. These alterations could lead to cognitive impairments or diminish their therapeutic potential. Here, we measured the transport rate of radioactively labeled pituitary adenylate cyclase-activating polypeptide (PACAP) from blood into whole brain and into 11 brain regions in three groups of mice: young (2 months old) ICR, young (2 months old) SAMP8, and aged (12 months old) SAMP8 mice. The SAMP8 is a strain which develops impaired learning and memory with aging that correlates with an age-related increase in brain levels of amyloid β protein (AβP). PACAP is a powerful neurotrophin that may have a therapeutic role in neurodegenerative diseases. We found that I-PACAP crossed the BBB fastest at the hypothalamus and the hippocampus in all three groups. Slower transport rates into the whole brain, the olfactory bulb, the hypothalamus, and the hippocampus for aged SAMP8 mice was likely related to differences both from strain and expression of AβP with aging.     

Differential expression of the liver proteome in senescence accelerated mice

The senescence-accelerated mouse (SAM) is a useful animal model to study aging or age-associated disorders due to its inherited aging phenotype. To investigate proteins involved in the aging process in liver, we compared the young (4- or 20-week old) and the aged group (50-week-old) of SAMP8 (short life span) and SAMR1 (control) mice, and identified 85 differentially expressed distinct proteins comprising antioxidation, glucose/amino acid metabolism, signal transduction and cell cycle systems using proteomics tools. For the antioxidation system, the aged SAMP8 mice showed a large increase in glutathione peroxidase and decreases in glutathione-S-transferase and peroxiredoxin, ranging from 2.5- to 5-fold, suggesting lower detoxification potentials for oxidants in the aged SAMP8 liver. Similarly, levels of key glycolytic enzymes decreased greatly in the aged SAMP8 compared to SAMR1, indicating a disturbance in glucose homeostasis that may be closely related to the typical deficits in learning and memory of the aged SAMP8. Protein profiles of amino acid metabolic enzymes suggest that accumulation of glutamine and glutamate in tissues of the aged SAMP8 may be due to hyperexpression of ornithine aminotransferase and/or glutamate dehydrogenase. Decreases in levels of proteins involved in signal transduction/apoptosis (e.g., cathepsin B) in the aged SAMP8 may support the previously proposed negative relationship between apoptosis and aging. However, the changes described above were not markedly seen in the young group of both strains. For cell cycle systems, levels of selenium binding protein increased about four-fold with age in SAMP8. Yet, almost no change occurred in either the young or the aged SAMR1, which may explain problems associated with cell proliferation and tissue regeneration in the aged SAMP8. In conclusion, composite profiles of key proteins involved in age-related processes enable assessment of accelerated senescence and the appearance of senescence-related pathologies in the aged SAMP8.     

Effects of age on plasma levels of calcium-regulating hormones and bone status in male SAMP8 mice

This study was undertaken to examine whether the plasma levels of calcium-regulating hormones and bone status alter with age in male senescence accelerated mice (SAM), SAMP8. Age-matched senescence-resistant mice, SAMR1, were used as controls. The blood and femur samples were collected at 2.5 months of age (M) and then monthly from 3 to 12 M for physicochemical analyses, biochemical analyses, and the determination of hormones by radioimmunoassay. With advancing age, the plasma calcitonin (CT) levels decreased progressively, and the plasma parathyroid hormone (PTH) and 1,25-dihydroxycholecalciferol (1,25(OH)2D3) levels increased in both SAMR1 and SAMP8. The plasma calcium concentrations were maintained within a narrow range throughout the experimental period, while the plasma phosphorus (P) concentrations decreased with age in both strains. In contrast to SAMR1, the curves of age-related changes in the plasma CT levels and P concentrations were lower, and those in the plasma PTH levels were higher in SAMP8. The femoral bone densities and calcium contents increased gradually with age from the beginning of the experiment and peaked at 6 M in both strains, then declined. Those peaks were lower in SAMP8 than in SAMR1. These results indicate that the male SAMP8 develops osteoporotic signs earlier than SAMR1, and is proved to be a satisfactory animal model for longitudinal studies related to osteoporosis for men.     

Mitochondrial dysfunction in platelets and hippocampi of senescence-accelerated mice

Senescence-accelerated mice (SAM) strains are useful models to understand the mechanisms of age-dependent degeneration. In this study, measurements of the mitochondrial membrane potential (Δψ_m) of platelets and the Adenosine 5^′-triphosphate (ATP) content of hippocampi and platelets were made, and platelet mitochondria were observed in SAMP8 (faster aging mice) and SAMR1 (aging resistant control mice) at 2, 6 and 9 months of age. In addition, an Aβ-induced (Amyloid beta-protein) damage model of platelets was established. After the addition of Aβ, the Δψ_m of platelets of SAMP8 at 1and 6 months of age were measured. We found that platelet Δψ_m, and hippocampal and platelet ATP content of SAMP8 mice decreased at a relatively early age compared with SAMR1. The platelets of 6 month-old SAMP8 showed a tolerance to Aβ-induced damages. These results suggest that mitochondrial dysfunction might be one of the mechanisms leading to age-associated degeneration in SAMP mice at an early age and the platelets could serve as a biomarker for detection of mitochondrial function and age related disease.     

Effects of aging and dietary antler supplementation on the calcium-regulating hormones and bone status in ovariectomized SAMP8 mice

This study was conducted to investigate the effects of aging and long-term dietary antler supplementation on the calcium-regulating hormones and bone status in ovariectomized (Ovx) SAMP8 mice. The female SAMP8 mice were divided into four groups (in each group n = 6), Ovx or sham operated at the age of 2 months, and fed with 0.2% antler containing diet or control diet from the age of 2.5 months. The samples were collected at the age of 3, 6, 9, 12, and 15 months, respectively, for physicochemical analyses, biochemical analyses, and the determination of hormones by radioimmunoassay. The results showed that plasma calcium (Ca) concentrations were maintained in a narrow range in all groups throughout the whole experimental period. With aging and/or ovariectomy, plasma parathyroid hormone (PTH) and 1,25-dihydroxycholecalciferol (1,25-(OH)2-D3) levels increased, and plasma phosphorus (P) and calcitonin (CT) levels decreased, and the femoral bone densities and Ca contents increased during the earlier stage, and then decreased gradually in all groups. Plasma PTH and 1,25-(OH)2-D3 levels in the Ovx mice were significantly higher than those in the intact mice, and plasma P concentrations, plasma CT levels, femoral bone densities, and femoral Ca contents in the Ovx mice were significantly lower than those in the intact mice. In addition, the decreases of plasma P levels, plasma CT levels, femoral bone densities, and femoral Ca contents, and the increases of plasma PTH levels were moderated by antler administration in both Ovx and intact mice. However, there was no effect of the dietary antler supplementation on the plasma 1,25-(OH)2-D3 levels in the female mice. It is concluded that prolonged dietary antler supplementation has important positive effects on bone loss with age and/ or ovarian function deficiency.     

Adiposity-Related Biochemical Phenotype in Senescence-Accelerated Mouse Prone 6 (SAMP6)

Senescence-accelerated mouse prone 6 (SAMP6) is a model of senile osteoporosis. From 10 to 22 wk of age, SAMP6 mice were heavier than age-matched AKR/J and SAMR1 mice. Body mass indices of 10- and 25-wk-old SAMP6 mice were higher than those of age-matched AKR/J and SAMR1 mice, indicating obesity in the SAMP6 animals. We compared the blood biochemical values among SAMP6, SAMR1, and AKR/J mice to assess whether the SAMP6 strain has abnormal obesity-related parameters. Plasma glucose, triglyceride, insulin, and leptin levels were higher in 10-wk-old SAMP6 mice than in age-matched SAMR1 and AKR/J mice, whereas plasma glucagon and adiponectin levels in 25-wk-old SAMP6 were lower compared with those in age-matched SAMR1 and AKR/J. Total cholesterol levels in SAMR1 and SAMP6 mice at 10 and 25 wk of age were higher than those in AKR/J mice. Hepatic lipid levels were higher in 10- and 25-wk-old SAMP6 mice compared with age-matched AKR/J and SAMR1 animals. These results indicate that SAMP6 mice exhibit obesity and hyperlipidemia, suggesting that the SAMP6 strain is a potential tool for the study of hyperlipidemia.Abbreviations: BMI, body mass indexThe senescence-accelerated mouse strains were developed through selective breeding of AKR/J mice based on graded scores for senescence and pathologic phenotypes.⁴⁴ The 9 senescence-prone (SAMP) strains all have a shortened lifespan and display an early onset of senescence after normal development and maturation, whereas the 3 senescence-resistant (SAMR) strains are resistant to early senescence and serve as controls. Among the SAMP strains, SAMP8 and SAMP10 exhibit deficits in learning and memory at a relatively early stage in their lifespan.^6,30 In contrast, SAMP6 mice are considered to be a model of senile osteoporosis, with their low bone mass and slow bone loss;²⁴ the bone mineral density of SAMP6 mice decreases after 4 mo of age.^14,17Our regular measurement of body weight revealed that SAMP6 mice were significantly higher between 10 and 22 wk of age than were age-matched SAMR1 and AKR/J. Based on this observation, we decided to compare body mass indices (BMIs), blood biochemical values, and liver sections among mice of these strains at 10 and 25 wk of age, which respectively correspond to the beginning and end of a period of significant body weight gain in SAMP6 mice compared with age-matched SAMR1 and AKR/J. Increased BMIs of SAMP6 mice at 10- and 25 wk compared with those of age-matched AKR/J and SAMR1 animals would indicate obesity in the SAMP6. In addition, because osteoblasts and adipocytes are thought to share a common precursor cell, osteoporosis and enhanced adipogenesis may be related. For example, adipogenesis in the bone marrow increases with aging and during osteoporosis,^15,33,34 and increased bone turnover occurs in hypercholesterolemic or dyslipidemic patients.²² Therefore obesity in SAMP6 mice might be due at least in part to enhanced adipogenesis. We measured and compared blood biochemical values among SAMP6, SAMR1, and AKR/J (the founder for the SAM strains) mice to assess whether the SAMP6 strain has abnormalities in blood biochemical markers, such as triglycerides or cholesterol.     

Abnormal platelet amyloid-β precursor protein metabolism in SAMP8 mice: Evidence for peripheral marker in Alzheimer's disease

Senescence-accelerated mouse strains have proved to be an accelerated-aging model, which mimics numerous features with Alzheimer's disease (AD). Three, six, and nine-month senescence-accelerated resistant 1 and senescence-accelerated prone 8 (SAMP8) mice were used in the current study, to unravel potential mechanisms for dementia and explore new diagnostic approaches for AD. The amyloid-β (Aβ40) and Aβ42 levels were elevated in hippocampi and platelets from SAMP8, along with a reduced α-secretase expression and an enhanced β-secretase expression extent with age, compared to control mice. Furthermore, hippocampal Aβ40 and Aβ42 of SAMP8 were positively correlated with platelet of these mice with aging progression. In addition, β-γ-secretase-modulated proteolytic proceeding of amyloid precursor protein in platelet might work through the PI3K/Akt/GSK3β pathway. These results indicate that platelet could be a potential early marker in the periphery to study the age-correlative aggregation of the amyloid-β peptide in patients with AD, while still requiring the considerable study.     

Diabetes exacerbates amyloid and neurovascular pathology in aging‐accelerated mice

Mounting evidence supports a link between diabetes, cognitive dysfunction, and aging. However, the physiological mechanisms by which diabetes impacts brain function and cognition are not fully understood. To determine how diabetes contributes to cognitive dysfunction and age‐associated pathology, we used streptozotocin to induce type 1 diabetes (T1D) in senescence‐accelerated prone 8 (SAMP8) and senescence‐resistant 1 (SAMR1) mice. Contextual fear conditioning demonstrated that T1D resulted in the development of cognitive deficits in SAMR1 mice similar to those seen in age‐matched, nondiabetic SAMP8 mice. No further cognitive deficits were observed when the SAMP8 mice were made diabetic. T1D dramatically increased Aβ and glial fibrillary acidic protein immunoreactivity in the hippocampus of SAMP8 mice and to a lesser extent in age‐matched SAMR1 mice. Further analysis revealed aggregated Aβ within astrocyte processes surrounding vessels. Western blot analyses from T1D SAMP8 mice showed elevated amyloid precursor protein processing and protein glycation along with increased inflammation. T1D elevated tau phosphorylation in the SAMR1 mice but did not further increase it in the SAMP8 mice where it was already significantly higher. These data suggest that aberrant glucose metabolism potentiates the aging phenotype in old mice and contributes to early stage central nervous system pathology in younger animals.     

Scrapie infection activates the replication of ecotropic, xenotropic, and polytropic murine leukemia virus (MuLV) in brains and spinal cords of senescence-accelerated mice: implication of MuLV in progression of scrapie pathogenesis

Senescence-accelerated mice (SAMP8) have a short life span, whereas SAMR1 mice are resistant to accelerated senescence. Previously it has been reported that the Akv strain of ecotropic murine leukemia virus (E-MuLV) was detected in brains of SAMP8 mice but not in brains of SAMR1 mice. In order to determine the change of MuLV levels following scrapie infection, we analyzed the E-MuLV titer and the RNA expression levels of E-MuLV, xenotropic MuLV, and polytropic MuLV in brains and spinal cords of scrapie-infected SAM mice. The expression levels of the 3 types of MuLV were increased in scrapie-infected mice compared to control mice; E-MuLV expression was detected in infected SAMR1 mice, but only in the terminal stage of scrapie disease. We also examined incubation periods and the levels of PrPSc in scrapie-infected SAMR1 (sR1) and SAMP8 (sP8) mice. We confirmed that the incubation period was shorter in sP8 (210+/-5 days) compared to sR1 (235+/-10 days) after intraperitoneal injection. The levels of PrPSc in sP8 were significantly greater than sR1 at 210+/-5 days, but levels of PrPSc at the terminal stage of scrapie in both SAM strains were virtually identical. These results show the activation of MuLV expression by scrapie infection and suggest acceleration of the progression of scrapie pathogenesis by MuLV.     

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.     

The pentylenetetrazole-kindling model of epilepsy in SAMP8 mice: behavior and metabolism

This work describes a novel epilepsy model, combining pentylenetetrazole (PTZ) kindling with the senescence-accelerated mouse P8 (SAMP8) a model for aging. The 2- and 8-month-old SAMP8 mice were treated with PTZ, phenobarbital plus PTZ or saline every 48 h during a period of 40 days. Both 2- and 8-month-old PTZ-kindled mice showed a behavioral pattern that was very similar to severe chronic epilepsy with secondary generalized seizures. Two out of six 8-month-old animals died in the PTZ group. Interestingly, atypical absence seizures were limited to the 8-month-old PTZ group. Furthermore, 8-month-old mice were more sensitive to the sedative effect of phenobarbital. The concentrations of several amino acids were examined by HPLC. Lower levels of amino acids were found in the 8-month-old compared to the 2-month-old control animals. No biochemical changes were observed between the groups of 2-month-old animals, while in the 8-month-old animals both treatment groups showed significantly higher concentrations of GABA, glutamine and glutathione. Thus, it could be shown that cerebral metabolism of 8-month-old SAMP8 mice was more sensitive to PTZ and phenobarbital than metabolism of 2-month-old mice. Furthermore, it is suggested that glutamate metabolism in brains of 8-month-old SAMP8 mice is altered and that excessive glutamate is transformed, in considerable amounts, into glutamate related metabolites, possibly in astrocytes.     

Modulation of Macrophage Polarization and HMGB1-TLR2/TLR4 Cascade Plays a Crucial Role for Cardiac Remodeling in Senescence-Accelerated Prone Mice

The aim of this study was to investigate the role of macrophage polarization in aging heart. Macrophage differentiation is pathogenically linked to many inflammatory and immune disorders. It is often preceded by myocardial inflammation, which is characterized by increased cardiac damage and pro-inflammatory cytokine levels. Therefore, we investigated the hypothesis that senescence accelerated-prone (SAMP8) mice cardiac tissue would develop macrophage polarization compared with senescence-resistant control (SAMR1) mice. Both SAMP8 and SAMR1 mice were sacrificed when they became six month old. We evaluated, histo-pathological changes and modifications in protein expression by Western blotting and immuno-histochemical staining for M1 and M2 macrophage markers, high mobility group protein (HMG)B1 and its cascade proteins, pro-inflammatory factors and inflammatory cytokines in cardiac tissue. We observed significant upregulation of HMGB1, toll-like receptor (TLR)2, TLR4, nuclear factor (NF)κB p65, tumor necrosis factor (TNF)α, cyclooxygenase (COX)2, interferon (IFN)γ, interleukin (IL)-1β, IL-6 and M1 like macrophage specific marker cluster of differentiation (CD)68 expressions in SAMP8 heart. In contrast, M2 macrophage specific marker CD36, and IL-10 expressions were down-regulated in SAMP8 mice. The results from the study demonstrated that, HMGB1-TLR2/TLR4 signaling cascade and induction of phenotypic switching to M1 macrophage polarization in SAMP8 mice heart would be one of the possible reasons behind the cardiac dysfunction and thus it could become an important therapeutic target to improve the age related cardiac dysfunction.     

Effects of leptin on memory processing

Leptin is a peptide hormone secreted by adipose tissue. Studies have shown that leptin crosses the blood-brain barrier (BBB) by a saturable transport system where it acts within the hypothalamus to regulate food intake and energy expenditure. Leptin also acts in the hippocampus where it facilitates the induction of long-term potentiation and enhances NMDA receptor-mediated transmission. This suggests that leptin plays a role in learning and memory. Obese mice and rats, which have leptin receptor deficiency, have impaired spatial learning. In disease states such as diabetes, humans and animals develop leptin resistance at the BBB. This suggests that low leptin levels in the brain may be involved in cognitive deficits associated with diabetes. In the current study, the effects of leptin on post-training memory processing in CD-1 mice were examined. Mice were trained in T-maze footshock avoidance and step down inhibitory avoidance. Immediately after training, mice received bilateral injections of leptin into the hippocampus. Retention was tested 1 week later in the T-maze and 1 day later in step down inhibitory avoidance. Leptin administration improved retention of T-maze footshock avoidance and step down inhibitory avoidance. Leptin administered 24 h after T-maze training did not improve retention when tested 1 week after training. SAMP8 mice at 12 months of age have elevated amyloid-beta protein and impaired learning and memory. We examined the effect of leptin on memory processing in the hippocampus of 4 and 12 months old SAMP8 mice. Leptin improved retention in both 4 and 12 months old SAMP8 mice; 12 month SAMP8 mice required a lower dose to improve memory compared to 4 months SAMP8 mice. The current results indicate that leptin in the hippocampus is involved in memory processing and suggests that low levels of leptin may be involved in cognitive deficits seen in disease states where leptin transport into the CNS is compromised.     

Resistin-like molecule beta (RELMbeta/FIZZ2) is highly expressed in the ileum of SAMP1/YitFc mice and is associated with initiation of ileitis

SAMP1/Fc mice develop spontaneous ileitis that shares many features with human Crohn's disease. One of the earliest features of ileitis in SAMP1/Fc mice is an increase in the number of ileal goblet and intermediate cells. Resistin-like molecule beta (RELMbeta) is a goblet cell-specific, cysteine-rich peptide previously shown to function as part of the innate immune response. In this study, we examined the role of expression of RELMbeta in the initiation of ileal inflammation in SAMP1/Fc mice. RELMbeta was highly induced in the ilea of SAMP1/Fc mice beginning at age 5 wk, coincident with the histological appearance of inflammation. RELMbeta was found in ileal goblet cells and some intermediate and Paneth cells. Surprisingly, RELMbeta mRNA levels were significantly increased in the ilea of 80% of germ-free SAMP1/Fc mice examined compared with specific pathogen-free AKR control mice of similar age. Ileitis was observed in germfree SAMP1/Fc mice, although it was attenuated relative to specific pathogen-free SAMP1/Fc mice. These data suggest that neither the early induction of RELMbeta expression nor ileal inflammation requires the presence of viable intestinal flora. Neither was the induction of RELMbeta dependent on the major Th1 or Th2 cytokines. However, RELMbeta stimulated naive bone marrow-derived macrophages to secrete significant amounts of TNF-alpha, IL-6, and RANTES. Our data suggest that RELMbeta is involved in the initiation of ileitis in SAMP1/Fc mice and may act through the induction of proinflammatory cytokines from resident immune cells within the mucosa.     

The antioxidants alpha-lipoic acid and N-acetylcysteine reverse memory impairment and brain oxidative stress in aged SAMP8 mice

Oxidative stress may play a crucial role in age-related neurodegenerative disorders. Here, we examined the ability of two antioxidants, alpha-lipoic acid (LA) and N-acetylcysteine (NAC), to reverse the cognitive deficits found in the SAMP8 mouse. By 12 months of age, this strain develops elevated levels of Abeta and severe deficits in learning and memory. We found that 12-month-old SAMP8 mice, in comparison with 4-month-old mice, had increased levels of protein carbonyls (an index of protein oxidation), increased TBARS (an index of lipid peroxidation) and a decrease in the weakly immobilized/strongly immobilized (W/S) ratio of the protein-specific spin label MAL-6 (an index of oxidation-induced conformational changes in synaptosomal membrane proteins). Chronic administration of either LA or NAC improved cognition of 12-month-old SAMP8 mice in both the T-maze footshock avoidance paradigm and the lever press appetitive task without inducing non-specific effects on motor activity, motivation to avoid shock, or body weight. These effects probably occurred directly within the brain, as NAC crossed the blood-brain barrier and accumulated in the brain. Furthermore, treatment of 12-month-old SAMP8 mice with LA reversed all three indexes of oxidative stress. These results support the hypothesis that oxidative stress can lead to cognitive dysfunction and provide evidence for a therapeutic role for antioxidants.