A new murine model of accelerated senescence

Long-lived lines of Caenorhabditis elegans can be used to establish predictive biomarkers of aging

Long-lived recombinant inbred lines, some of which have mean and maximum life spans up to 70% longer than wild type, were used in these analyses. Longer life results from a slower exponential rate of increase in mortality. General motor activity decreases with chronological age in all genotypes; this decay in general motor activity is a biomarker of aging in that it is a predictor of maximum life span. The aging process has also been dissected into component processes. The length of development and the length of reproduction are unrelated to increased life span; lengthened life is due entirely to an increase in post-reproductive life span. Development, reproduction, and life span are each under independent genetic control. General motor activity and life span share at least one common rate-determining genetic component.

Constitutional genetic markers of aging

Constitutional genetic markers of aging can be defined as members of that subset of genes that modulate the times of onset and/or the rates of progression of one or more of the processes of aging, or the response of the target cells, tissues and organisms to a particular process. These genetic factors are classified into: (1) those that control changes in structure and function that may be universally expressed in aging organisms or that are expressed in large taxonomic groups of organisms ("public markers") and (2) those that control changes that are species specific or that reflect polymorphisms or mutations within a species ("private markers"). Both spontaneous and experimentally induced genetic variation can identify and characterize such genetic elements. Recommendations for implementing such a program of research include (1) particularization of the aging phenotype, (2) further development of nonmammalian models amenable to genetic analysis, (3) systematic search for relevant spontaneous mutations in Mus musculus, (4) utilization of recombinant inbred, chimeric, transgenic and interspecific mice and (5) investigations of genetic concomitants of speciation.

Histopathologic observations on the senescence-accelerated mice (SAM) reared under specific pathogen free conditions

Five to 12 months old senescence-accelerated mice reared under specific pathogen free conditions (SPF SAM) were subjected to histopathologic examination. Senescence-prone SAM-P/1/Ta, P/3/Ta, and P/8/Ta exhibited marked depletion in thymic cortical lymphocytes which were associated with lymph follicle formation in the medulla, and marked infiltration of lymphocytes in the submaxillary gland, kidney, and other peripheral tissues. Morphometrical analysis of the adrenal gland revealed cortical atrophy and medullary hyperplasia in male SAM-P/8/Ta at 5 months of age. Other characteristic changes were marked vacuolation of the renal proximal tubules in male P/3/Ta and P/8/Ta mice, and degeneration of vascular wall in the testis of P/3/Ta mice. The pathogenesis of these changes appeared to be related to the adrenal lesions. Systemic amyloid deposition, one of the characteristic features of SAM housed in conventional facilities was not observed under the SPF condition. Acceleration of senescence in SPF SAM may arise from disorders of the thymus and adrenal.

Reexamination of the relationship between alcohol preference and brain monoamines in inbred strains of mice including senescence-accelerated mice

The relationship between voluntary alcohol consumption and brain monoamine levels was studied in the inbred strains of C57BL/6N, C57BL/6J, A/J, BALB/cA, CBA/N, C3H/He and DBA/2cr mice; the congeneric mouse strain, B10.Br/Sg, and the senescence accelerated mouse (SAM P1, SAM P2). The C57BL strains exhibited a high alcohol preference whereas the other strains exhibited a low alcohol preference. A clear positive relationship was found between alcohol intake (g/kg/day) and brain norepinephrine level (r = 0.683, p less than 0.05), and a clear negative relationship between alcohol intake and brain serotonin level (r = -0.628, p less than 0.05). The content of brain dopamine was not clearly correlated with alcohol intake (r = -0.206, p greater than 0.05). These findings suggest that in mice voluntary alcohol preference is influenced by brain norepinephrine and serotonin levels genetically.

High homology is present in the primary structures between murine senile amyloid protein (ASSAM) and human apolipoprotein A-II

The primary structure of a murine senile amyloid protein (ASSAM) was determined. The protein consists of a single polypeptide chain of 78 amino acid residues. The amino-terminus is blocked with pyrrolidone-carboxylic acid. The sequence differs from that of the known murine amyloid A protein and is highly homologous to human apolipoprotein (apo) A-II. The result indicates that the putative precursor of the senile amyloid protein is apo A-II in mice.

Molecular cloning and nucleotide sequence of cDNA for murine senile amyloid protein: nucleotide substitutions found in apolipoprotein A-II cDNA of senescence accelerated mouse (SAM)

cDNA clones encoding the murine senile amyloid protein (ASSAM) have been isolated from animal models of accelerated senescence (SAM-P/1) and from normal aging (SAM-R/1). Immunochemical and protein sequence studies revealed that apolipoprotein (apo) A-II is a serum precursor of ASSAM. A 17-base synthetic oligonucleotide based on residues 39-44 of ASSAM was used as a hybridization probe for screening newly constructed SAM-P/1 and SAM-R/1 liver cDNA libraries. The structure of murine apo A-II cDNA is of interest because of the amino acid substitution found in ASSAM and serum apo A-II of SAM-P; in SAM-R or other random bred slc:ICR mice, amino acid residue 5 of mature apo A-II is proline but, in SAM-P, this amino acid is changed to glutamine. This amino acid replacement is caused by two nucleotide substitutions (CCA for proline codon to CAG for glutamine codon). The third base mutation may not be relevant to the substitution of amino acid. Attention is directed to the relation of this amino acid substitution to the specific deposition of apo A-II, as a tissue amyloid fibril.

Age-related changes in learning and memory in the senescence-accelerated mouse (SAM)

Age-related changes in learning ability were studied in senescence-accelerated mice (SAM) reared under specific pathogen-free (SPF) conditions. SAM-P/8/Ta (SAM-P/8, senescence-prone substrain) showed an age-associated increase in spontaneous motor activity (SMA) compared with SAM-R/1/Ta (SAM-R/1, senescence-resistant substrain) in a novel environment when the activity was measured in the light period, although there was no significant difference in the dark period. In observations of the circadian rhythm of SMA, SAM-P/8 showed a significant increase in diurnal SMA. In SAM-P/8 mice, the acquisition of passive avoidance response was slightly but significantly impaired even at 2 months of age, compared with SAM-R/1 control; the impairment became obvious with aging. In a one-way active avoidance task, SAM-P/8 did not show any impairment in the acquisition of avoidance response at 2 and 4 months of age. However, significant impairment was observed in SAM-P/8 at 12 months of age. The impairments of avoidance tasks were not due to a decrease in shock sensitivity, as indicated by no significant change in the flinch-jump threshold. In a water-filled multiple T-maze task, there was no difference in the number of errors between the two groups. With regard to the performance time to reach the goal, however, SAM-P/8 showed a mild prolongation at 2 months of age, and the prolongation became marked with advancing age.(ABSTRACT TRUNCATED AT 250 WORDS)

Periodic acid-Schiff (PAS)-positive, granular structures increase in the brain of senescence accelerated mouse (SAM)

Abnormal granular structures, which stained positively with periodic acid-Schiff (PAS-positive granular structures; PGS), were observed in the brain of senescence accelerated mouse (SAM). They were small, round to ovoid, homogeneous structures measuring up to 5 microns in diameter and usually grouped in clusters. PGS were localized in the hippocampus, piriform cortices, olfactory tubercle, nucleus of the trapezoid body, and cerebellar cortices. Quantitative analysis revealed that PGS remarkably increased in the hippocampus of SAM-P/8, a substrain of SAM, with advancing age, although a few PGS also appeared in the aged control mice, SAM-R/1 and DDD. Their histochemical nature, morphological features and distribution pattern were different from those of corpora amylacea and other similar bodies. A close anatomical relationship between PGS and glial fibrillary acidic protein-positive astrocytes was inferred from immunohistochemical studies. PGS is considered to be one of the morphological manifestations of senescence in mice brains, and are found to occur more numerously in the brains of learning or memory deficit mice, SAM-P/8.

Age-related changes of activity of acid phosphatase in PHA-stimulated lymphocytes

Peripheral blood lymphocytes of 70-year-old individuals as well as spleen cells of 18-month-old Balb/c mice were characterized by diminished activity of acid phosphatase in relation to the activity of that enzyme in cells from young subjects. Simultaneously performed histochemical tests revealed that aging process in both species examined was accompanied by a reduction of the number of cells, disclosing the activity of acid phosphatase. Age-related differences with regard to the level of acid phosphatase became more pronounced after stimulation of cells with PHA. The decrease of acid phosphatase activity during aging is discussed in relation to the function of lymphocytes.

Amplification of extrachromosomal small circular DNAs in a murine model of accelerated senescence. A brief note

Extrachromosomal circular DNA complexes from peripheral blood lymphocytes from inbred mice of accelerated senescence, were detected by mica-press-adsorption method. In senescence-resistant series (SAM-R), polydisperse circular DNAs were observed at 7 weeks of age and a restricted size class of small circular forms of 0.4-0.8 microns in contour length was amplified several-fold at 26 months of age. In senescence-prone series (SAM-P), a similar amplification of small circular DNAs was observed at young age of 10 weeks and more progressive at 17 months of age.

Age-related changes of serum apoprotein SASSAM, apoprotein A-I and low-density lipoprotein levels in senescence accelerated mouse (SAM)

Age-related changes of serum concentration of apo SASSAM, an apoprotein of high density lipoprotein (HDL) which cross-reacts with antiserum against murine senile amyloid fibril protein (ASSAM) were estimated in senescence accelerated mouse (SAM-P) and in senescence resistant series (SAM-R), as a control, using a single radial immunodiffusion technique. Serum concentrations of apo A-I, a major apoprotein of HDL, and low density lipoprotein (LDL) were also measured. In SAM-P (SAM-P/1 and SAM-P/2) with a high incidence of senile systemic amyloidosis, we observed age-associated decreases in serum apo SASSAM levels. The concentrations of apo SASSAM at 16 months of age were below 40% of the concentration at 2 months of age, regardless of the sex. In contrast with SAM-P, we observed no age-associated decrease of serum apo SASSAM levels in SAM-R (SAM-R/1 and SAM-R/2) with a low incidence of amyloidosis. Serum apo SASSAM concentration was higher in SAM-R/1 than in any other strain of mice observed. Serum apo A-I concentration was highly and significantly correlated with the serum concentration of apo SASSAM and decreased with advancing age in SAM-P but not in SAM-R. Age-related changes of LDL were not observed in any strain, but the concentration was lower in the females. In old SAM-P (16 months' old), the concentration of apo SASSAM decreased to one-third of that in the young SAM-P (4 months' old) and the serum concentrations of albumin and total protein did not decrease, compared with those in the young mice. All these findings taken together suggest that abnormality of metabolism in apo SASSAM, putative precursor of ASSAM, might occur in SAM-P.

Grading score system: a method for evaluation of the degree of senescence in senescence accelerated mouse (SAM)

For evaluation of the degree of senescence in SAM-P, accelerated senescence prone mouse, formerly called SAM or prone series or P-series, consisting of SAM-P/1, SAM-P/2, SAM-P/3 and SAM-P/4 corresponding to P-1, P-2, P-3 and P-4 series, respectively, in the previous reports, and in SAM-R, accelerated senescence resistant mouse, formerly called resistant series or R-series, consisting of SAM-R/1, SAM-R/2 and SAM-R/3 corresponding to R-1, R-2 and R-3 series, respectively, in the previous reports, the grading score system was adopted. The items to be examined in this system include 11 categories selected from the clinical signs and gross lesions considered to be associated with the aging process. The degree of the senescence in each category was graded from 0 to 4 according to the detailed criteria devised in our laboratory. After 8 months of age each mouse was examined every 4 months, and some of the mice were examined after 2 months of age. In almost all categories, the grading score and incidence began to increase from 4 or 6 months of age and continued to increase with advancing age in both SAM-P and SAM-R. The increase, however, was more marked in SAM-P than in SAM-R. The slow but steady increase in the SAM-R levelled out at 24 months of age and was comparable to that at 12 months of age in SAM-P. In both SAM-P/1 at 8 months of age and SAM-R/2 at 12 months of age, there was a significant reverse correlation between total score of this grading score system and length of residual life after examination. Systematic and extensive studies using the grading score system showed that if the validity of the system is, based on "irreversibility" and "universality" of the changes in each category with advancing age, most categories are valid for evaluation of the degree of senescence. This grading score system is a unique, useful and convenient method for evaluation of the degree of senescence in mice.

Cataract and other ophthalmic lesions in senescence accelerated mouse (SAM). Morphology and incidence of senescence associated ophthalmic changes in mice

In a murine model of accelerated senescence (SAM), grading score and incidence in cataract, periophthalmic lesions, opacity and ulcer of the cornea were determined in mice from 4 to 24 months of age. From 4 to 6 months of age, incidence and grading score of these four categories began to increase in both the accelerated senescence prone (SAM) and resistant series with normal aging, and these increases continued with aging. As compared with the resistant series, there was a higher incidence and grading score of the four categories and a higher rate of increase in the prone series. The prone 3 series in particular showed a much higher incidence and grading score on cataract, the rate being 27.5% and 70.6% at 12 and 16 months, respectively. Histologically, the cataract was classified into two types. In one, degeneration of lens fibers, disintegration of lens cortex, and at an advanced stage, liquefaction of the lens cortex and proliferation of the anterior lens epithelial cells occurred. In the other type, lens fibers lost their distinct shapes and a homogenous mass formed at the anterior and posterior superficial cortex. The anterior lens epithelial cells had shrunk. There was an opacity and ulcer of the cornea with keratitis and the corneal epithelium was lost in case of the latter. Periophthalmic lesions included catarrhal changes of the skin of the eyelids and face and blepharitis. There were no lesions specific to each of the prone and resistant series. Thus, SAM should prove to be a suitable murine model for investigation of age-related ophthalmic lesions, including cataract in humans.

Isolation and characterization of senile amyloid--related antigenic substance (SASSAM) from mouse serum. Apo SASSAM is a low molecular weight apoprotein of high density lipoprotein

Sera obtained from senescence-accelerated mouse (SAM) and normal mice contained a substance that reacted with antiserum raised against ASSAM, a novel senile amyloid fibril protein isolated from the liver of SAM. This physiological substance, termed "SASSAM" (serum ASSAM-related antigenic substance), migrated to the albumin/prealbumin region in immunoelectrophoresis and the precipitation line formed with anti-ASSAM antiserum was stained positively with both Amide Black 10 B and Oil Red O/Fat Red 7B solutions, thereby suggesting that SASSAM is an alpha lipoprotein. Using Sephadex G-200 gel chromatography, SASSAM was eluted as a high mol wt form of approximately 200,000 daltons. Fractionation of lipoprotein from normal mouse serum by preparative ultra-centrifugation disclosed that SASSAM was found mainly in high density lipoprotein, HDL (the density is between 1.063 and 1.21 g/cm3). The largest amount of SASSAM was found in the HDL2 fraction (the density is between 1.063 and 1.125) and in this fraction SAA was not detected. Furthermore, ASSAM immunoreactivity appeared in the low mol wt proteins (below 10,000 daltons) of apo HDL separated in the buffer containing 8 M urea through Sephadex G-200. In 8 M urea sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), the major components of apolipoproteins in this position, possibly corresponding to apo C proteins, have the same molecular weight, 5,200 daltons, as ASSAM and this component was labeled by anti-ASSAM antiserum after transfer to nitrocellulose paper.

Spontaneous age-associated amyloidosis in senescence-accelerated mouse (SAM)

Morphological studies on spontaneous systemic amyloidosis were conducted on 222 senescence-accelerated mice (SAM) (P) and on 150 mice in the senescence-resistant series (R). Among the pathologic findings, amyloidosis showed the highest incidence in both SAM (79.7%) and R (32.7%). Although an extensive deposition of amyloid was evident in some aged mice in the R series, a more severe amyloidosis occurred with a higher incidence in the P series. There was a statistical significance between the incidence of amyloidosis and age, in both the P and R series. There were no differences in organ distribution and mode of amyloid deposition between the P and R series or between the sexes. In about 60% of the amyloid-positive cases in the 28 killed SAM and 7 mice in the R series, there were no signs of inflammation or neoplasm. The morphological features in SAM more closely resembled those seen in cases of murine spontaneous senile amyloidosis than the features seen in cases of experimentally induced amyloidosis. This model is expected to be a valuable tool with which to assess the relationship between amyloid deposition and the aging process or senescence, perhaps even cases of human senile amyloidosis.