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.     

Role of accelerated style senescence in pathogen defense

Plants, like animals, suffer from a variety of diseases that are transmitted via their sexual organs. In many species, the flowers senesce rapidly after pollination or fertilization. In ongoing studies of the impacts of a transposon insertional mutation in the gene that encodes the most abundant isoform of a major group-1 pollen allergen of maize, we found that pollen tubes with the mutant allele grow significantly slower in vivo than pollen with the wild-type allele. Here, we report that under field conditions, maize silks (styles) pollinated with pollen bearing the slower-growing mutant allele take significantly longer to senesce, and the resulting ears (infructescences) have dramatically higher incidence of "fungal ear rot" disease than silks pollinated with pollen bearing the wild-type allele. Because ear rot fungi gain access to the developing ear by growing on and through the silks, we propose that accelerated senescence of silks after fertilization is a defense against pathogens such as those causing ear rot. In addition, we divided the silks on each ear into two halves and experimentally varied the type of pollen (wild type, mutant, unpollinated) that was placed onto each half of the silks. Senescence of unpollinated silks was accelerated when ovaries on the other half of the ear were fertilized.     

SIRTain regulators of premature senescence and accelerated aging

The sirtuin proteins constitute class III histone deacetylases (HDACs). These evolutionarily conserved NAD⁺-dependent enzymes form an important component in a variety of cellular and biological processes with highly divergent as well as convergent roles in maintaining metabolic homeostasis, safeguarding genomic integrity, regulating cancer metabolism and also inflammatory responses. Amongst the seven known mammalian sirtuin proteins, SIRT1 has gained much attention due to its widely acknowledged roles in promoting longevity and ameliorating age-associated pathologies. The contributions of other sirtuins in the field of aging are also gradually emerging. Here, we summarize some of the recent discoveries in sirtuins biology which clearly implicate the functions of sirtuin proteins in the regulation of premature cellular senescence and accelerated aging. The roles of sirtuins in various cellular processes have been extrapolated to draw inter-linkage with anti-aging mechanisms. Also, the latest findings on sirtuins which might have potential effects in the process of aging have been reviewed.     

Post-traumatic osteoarthritis: the role of accelerated chondrocyte senescence

Joint injuries frequently lead to progressive joint degeneration that causes the clinical syndrome of post-traumatic osteoarthritis. The pathogenesis of osteoarthritis remains poorly understood, but patient age is a significant risk factor for progressive joint degeneration. We have found that articular cartilage chondrocytes show strong evidence of senescence with increasing age, including synthesis of smaller more irregular aggrecans; increased expression of lysosomal beta-galactosidase and telomere erosion; and decreased proteoglycan synthesis, response to the anabolic cytokine IGF-I, proliferative capacity, and mitochondrial function. These observations help explain the strong association between age and joint degeneration, but they do not explain how joint injury increases the risk of joint degeneration in younger individuals. We hypothesized that excessive loading of articular surfaces due to acute joint trauma or post-traumatic joint instability, incongruity or mal-alignment increases release of reactive oxygen species, and that the increased oxidative stress on chondrocytes accelerates chondrocyte senescence thereby decreasing the ability of the cells to maintain or restore the tissue. To test this hypothesis, we exposed human articular cartilage chondrocytes from young adults to mechanical and oxidative stress. We found that shear stress applied to cartilage explants in a triaxial pressure vessel increased release of reactive oxygen species and oxidative stress induced chondrocyte senescence (as measured by expression of lysosomal beta-galactosidase, nuclear and mitochondrial DNA damage and decreased mitochondrial function). These observations support the hypothesis that joint injury accelerates chondrocyte senescence and that this acceleration plays a role in the joint degeneration responsible for post-traumatic osteoarthritis.     

Increased expression of Rab5a correlates directly with accelerated maturation of Listeria monocytogenes phagosomes

Previous studies have shown that Listeria monocytogenes (LM) modulates phagocytic membrane traffic. Here we explore whether Rab5a, a GTPase associated with phagosome-endosome fusion, is related to phagosome maturation and to the intracellular survival of LM. Stable transfection of Rab5a cDNA into macrophages accelerates intracellular degradation of LM. Morphological studies confirmed that phagosome maturation and phagosome-lysosome fusion is enhanced by overexpression of Rab5a. Down-regulation experiments using antisense oligonucleotides targeted to the Rab5a mRNA efficiently reduced Rab5a synthesis, reduced phagosome-endosome traffic, blocked phagosome-lysosome fusion, and extended intraphagosomal survival of LM. Down-regulation of Rab5a had no effect on LM internalization. Down-regulation of Rab5c had no effect on phagosome maturation and phagosome-lysosome fusion. The results indicate that Rab5a controls early phagosome-endosome interactions and governs the maturation of the early phagosome leading to phagosome-lysosome fusion.     

Molecular cloning, expression, and regulation of hippocampal amyloid precursor protein of senescence accelerated mouse (SAMP8).

Alzheimer's disease (AD) is associated with increased expression of amyloid precursor protein (APP) with a consequent deposition of amyloid beta peptide (Abeta) which forms characteristic senile plaques. We have noticed that the senescence accelerated mouse (SAMP8), a strain of mouse that exhibits age-dependent defects such as loss of memory and retention at an early age of 8-12 months, also produces increased amounts of APP and Abeta similar to those observed in Alzheimer's disease (AD). In order to investigate if this is due to mutations in APP similar to those observed in AD, and to develop molecular probes that regulate its expression, APP cDNA was cloned from the hippocampus of 8-month-old SAMP8 mouse. The nucleotide sequence is 99.7% homologous with that of mouse and rat, 88.7% with monkey, and 89.2% with human homologues. At the amino acid level, the homology was 99.2% and 97.6% with rodent and primate sequences, respectively. A single amino acid substitution of Alanine instead of Valine at position 300 was unique to SAMP8 mouse APP. However, no mutations similar to those reported in human familial AD were observed. When the cDNA was expressed in HeLa cells, glycosylated mature APP could be detected by immunoblotting technique. The expression could be regulated in a time- and concentration-dependent manner by using an antisense oligonucleotide specific to APP mRNA. Such regulation of APP expression may have a therapeutic application in vivo.     

Neurodegenerative alterations induced by MPTP neurotoxin in senescence accelerated mice essay

Behavioral modifications and alterations in biochemical pathways induced by neurotoxin MPTP in Senescence Accelerated Mice (SAM) brains are discussed. MPTP injections lead to specific injuries of dophaminergic neurons and to reinforcement of oxidative stress conditions. The ability of neuropeptide carnosine to protect animals from oxidative injuries induced by MPTP injections is also described.