Biomedical subjects

Masanori Hosokawa

Publications and source records attributed to Masanori Hosokawa.

At least 19 recordsLinked to original sources

PubMed2006

Secreted frizzled-related protein 4 is a negative regulator of peak BMD in SAMP6 mice.

UNLABELLED: We segregated a QTL for peak BMD on Chr 13 by generating congenic sublines of the senescence-accelerated mouse SAMP6. Sfrp 4 within this locus was responsible for lower BMD of SAMP6. INTRODUCTION: Our genome-wide linkage study using SAMP6 and SAMP2 showed a significant quantitative trait locus (QTL) for peak BMD on chromosome (Chr) 13. To verify the gene that regulates peak BMD, we generated a congenic strain, P6.P2-Pbd2(b), which carried a 15-cM SAMP2 interval on an osteoporotic SAMP6 background, and showed that this Pbd2 locus increased peak BMD in SAMP6. MATERIALS AND METHODS: To narrow down this interval, we generated a new congenic subline P6.P2-13. We studied the effect of this locus on morphological and histomorphological features in vivo and on osteoblasts in vitro. The levels of expression of all genes in the segregated interval were examined, and we clarified the effect of the candidate gene, secreted frizzled-related protein (Sfrp4), on osteoblasts in vitro. RESULTS: The new congenic strain, P6.P2-13, retained the 2.4-Mb SAMP2 interval on the SAMP6 background, and 11 genes existed in this interval. In morphometrical analysis, P6.P2-13 increased the bone area fraction (BA/TA) by 6.6% at the diaphysial cortex (p < 0.001) and increased the trabecular bone volume (BV/TV) by 54.2% at the distal metaphysis (p < 0.05) in the femora compared with those of SAMP6. The bone formation rate of P6.P2-13 was markedly increased at the periosteal surface of femoral cortex and that was caused by a higher proliferation rate of osteoblasts in P6.P2-13 compared with those in SAMP6. Quantitative RT-PCR analysis of calvaria tissue showed approximately 40-fold higher levels of expression of Sfrp4 in SAMP6 than in P6.P2-13. Taken together with the result that recombinant Sfrp4 suppressed the proliferation of osteoblasts, we hypothesized that Sfrp4 inhibited the proliferation of osteoblasts through its antagonistic effect on Wnt signaling. TCF/beta-catenin-dependent reporter activity in osteoblasts derived from SAMP6 showed lower responsiveness for the Wnt ligand, Wnt3A, than that in osteoblasts from P6.P2-13. CONCLUSIONS: In SAMP6 mice, Sfrp4 negatively regulates bone formation and decreases BMD through the inhibition of Wnt signaling.

3T3 Cells↗

PubMed2006

Transmission of amyloidosis in offspring of mice with AApoAII amyloidosis.

Pre-existing amyloid fibrils can induce further polymerization of endogenous precursor proteins in vivo. Thus, transmission of amyloid fibrils (AApoAII) may induce a conformational change in endogenous apolipoprotein A-II and accelerate amyloid deposition in mouse senile amyloidosis. To characterize transmissibility, we examined amyloidosis in the offspring of AApoAII-injected mother mice that possessed the amyloidogenic Apoa2(c) allele of the apolipoprotein A-II gene. At 4 months of age, amyloid deposits were detected in the intestines of offspring born from and nursed by amyloid fibril-injected mothers, with intensity of deposition increasing thereafter. No amyloid deposits were detected in the offspring of noninjected control mothers. Accelerated amyloidosis was also observed in offspring born from mothers without injection but nursed by amyloid fibril-injected mothers. However, this was not observed in offspring born from amyloid fibril-injected mothers but nursed by control mothers. This fostering excluded vertical transmission through the placenta, suggesting the presence of factors that accelerate amyloidosis during the nursing period. In addition, milk obtained from amyloid fibril-injected mothers induced AApoAII amyloidosis in young mice, and transmission electron microscopy detected noodle-like amyloid fibrils in milk of amyloid fibril-injected mothers. These results provide important insight into the etiology and pathogenesis of amyloid diseases.

Alleles↗

PubMed2005

Different adaptive traits to cold exposure in young senescence-accelerated mice.

A reduced adaptation to cold is a prominent feature in aged mammals, including humans. The accelerated senescence-prone strain of mice (SAMP) has been studied as an animal model for several age-associated disorders and in the acceleration of senescence. Recent studies revealed that SAMP strains have dysfunctional hyperactive mitochondria and are under a higher oxidative stress status from a young age. To investigate whether young SAMP mice show impaired cold adaptation abilities, we performed cold-exposure experiments. There were no strain differences in baseline body temperature and lowest reached temperature during cold exposure. SAMP1 mice took longer times to reach their lowest temperature in comparison to SAMR1 mice. SAMR1 mice showed an elevation in temperature following cold exposure, whereas SAMP1 mice did not. Behavioral observations demonstrated that SAMP1 mice moved more actively than SAMR1 during cold exposure. However, mRNA levels of uncoupling protein 1 (UCP1), a heat generating protein, as well as plasma norepinephrine levels, were higher in SAMP1 than in SAMR1 mice. This newly found physiological phenotype in SAMP1 mice provides us with a tool to clarify the genetic mechanism which accelerates the senescence process and helps us develop medical means which will bring mankind to a healthy old age.

Adaptation, Physiological↗

PubMed2005

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

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

Animals↗

PubMed2005

Differential cooperative enzymatic activities of protein disulfide isomerase family in protein folding.

Endoplasmic reticulum (ER)p61, ERp72, and protein disulfide isomerase (PDI), which are members of the PDI family protein, are ubiquitously present in mammalian cells and are thought to participate in disulfide bond formation and isomerization. However, why the 3 different members need to be colocalized in the ER remains an enigma. We hypothesized that each PDI family protein might have different modes of enzymatic activity in disulfide bond formation and isomerization. We purified PDI, ERp61, and ERp72 proteins from rat liver microsomes and compared the effects of each protein on the folding of bovine pancreatic trypsin inhibitor (BPTI). ERp61 and ERp72 accelerated the initial steps more efficiently than did PDI. ERp61 and ERp72, however, accelerated the rate-limiting step less efficiently than did PDI. PDI or ERp72 did not impede the folding of BPTI by each other but rather catalyzed the folding reaction cooperatively with each other. These data suggest that differential enzymatic activities of ERp proteins and PDI represent a complementary contribution of these enzymes to protein folding in the ER.

Animals↗

PubMed2005

Functional characterization of 3 thioredoxin homology domains of ERp72.

Folding of secretory proteins is associated with the formation and isomerization of disulfide bonds. ERp72, a protein disulfide isomerase (PDI) family member, possesses 3 thioredoxin homology domains, but the participation of each domain in disulfide-bond formation and isomerization remains to be determined. We analyzed the function of individual domains in the insulin reduction assay system by site-directed mutagenesis with cysteine-to-serine replacement. All domains contributed to apparent steady-state binding (Km) and catalysis at saturating substrate concentrations (kcat) but in different manners. A mutant ERp72 with mutations in domains 1 and 2 (ERp72-mut-1+2) exhibited reductions in kcat of 73.9% when compared with wild type, whereas ERp72-mut-1+3 (mutations in domains 1 and 3) and ERp72-mut-2+3 (mutations in domains 2 and 3) exhibited less substantial reductions in kcat. ERp72-mut-1+3 and ERp72-mut-2+3 showed elevations in Km of 89.9% and 96.2%, respectively, when compared with wild type, whereas ERp72-mut-1+2 exhibited smaller elevations in Km. These results suggest that domains 1 and 2 make greater contributions to catalyzing efficacy and domain 3 to binding affinity. Domain 2 is involved in binding affinity, in combination with domain 3, in addition to its own contribution to catalyzing efficacy. This assignment of functions to individual domains is similar to that observed in other PDI domains, which is consistent with the high sequence homology between ERp and PDI domains.

Amino Acid Sequence↗

PubMed2004

Induction of AApoAII amyloidosis by various heterogeneous amyloid fibrils.

Preformed amyloid fibrils accelerate conformational changes of amyloid precursor proteins and result in rapid extension of amyloid fibrils in vitro. We injected various kinds of amyloid fibrils into mice with amyloidogenic apoAII gene (Apoa2(C)). The most severe amyloid depositions were detected in the tissues of mice injected with mouse AApoAII(C) amyloid fibrils. Mild amyloid depositions were also detected in the tissues of mice that were injected with other types of fibrils, including synthetic peptides and recombinant proteins. However, no amyloid depositions were found in mice that were injected with non-amyloid fibril proteins. These results demonstrated that a common structure of amyloid fibrils could serve as a seed for amyloid fibril formation in vivo.

Amyloid↗

PubMed2004

Consistency of low bone density across bone sites in SAMP6 laboratory mice.

The development of bone densitometry has made it clear that there are discrepancies in bone density at various measurement sites in a given individual. This study examined the consistency of bone density measurements across various sites in a strain of laboratory mouse (senescence-accelerated mouse; SAM). A systemic evaluation of the bone density was performed by dual-energy X-ray absorptiometry (DXA) on SAMP6 (P6) mice, a strain with low peak bone density, as measured by microphotodensitometry of the femoral bones, whereas the SAMP2 (P2) and SAMR1 (R1) strains have high peak bone density. We modified Jilka's method to more comprehensively measure the whole body and additional regions of interest (ROIs; head, right foreleg, left foreleg, right hindleg, left hindleg, spine, and tail). The age-related changes in the total (whole-body) BMD showed a common pattern among the strains studied, and the peak value was seen at 4 months old. P6 showed the lowest peak BMD. A detailed comparison of the bone density between P6 and P2 at the age of 4 months revealed significantly lower regional BMD values for P6 in all seven ROIs. The strain difference in BMD could not be attributed to a difference in size. In conclusion, P6 mice showed low bone density not only in their femurs but also in the subregions and over their entire body. This strain can be potentially useful in the investigation of the genetic basis of senile osteoporosis.

Absorptiometry, Photon↗

PubMed2004

Tissue distribution, biochemical properties, and transmission of mouse type A AApoAII amyloid fibrils.

In mouse strains with the amyloidogenic apolipoprotein A-II (ApoA-II) gene (Apoa2c), the type C ApoA-II protein (APOAIIC) associates to form amyloid fibrils AApoAII(C) that lead to development of early onset and systemic amyloidosis with characteristic heavy amyloid deposits in the liver and spleen. We found age-associated heavy deposition of amyloid fibrils [AApoAII(A)] composed of type A ApoA-II protein (APOAIIA) in BDF1 and C57BL/6 mice reared at one of our institutes. AApoAII(A) fibrils were deposited in the intestine, lungs, tongue, and stomach but not in the liver or spleen. AApoAII(A) fibrils were isolated, and morphological, biochemical, and structural characteristics distinct from those seen in AApoAII(C) and mouse AA amyloid fibrils were found. Transmission electron and atomic force microscopy showed that the majority of isolated AApoAII(A) amyloid fibrils featured fine, protofibril-like shapes. AApoAII(A) fibrils have a much weaker affinity for thioflavine T than for AApoAII(C), whereas APOAIIA protein contains less of the beta-pleated sheet structure than does APOAIIC. The injection of AApoAII(A) fibrils induced amyloid deposition in C57BL/6 and DBA2 mice (Apoa2a) as well as in R1.P1-Apoa2c mice (Apoa2c), but AApoAII(A) induced more severe amyloidosis in Apoa2a strains than in the Apoa2c strain. It was found that AApoAII(A) fibrils isolated from mice with mildly amyloidogenic APOAIIA protein have distinct characteristics. Induction of amyloidosis by heterologous amyloid fibrils clearly showed interactions between amyloid protein monomers and fibrils having different primary structures.

Alleles↗

PubMed2003

Age-related loss of synapses in the frontal cortex of SAMP10 mouse: a model of cerebral degeneration.

SAMP10 mouse is a model of brain aging in which senescence is characterized by cerebral atrophy most prominent in the frontal cortex, deterioration in performance of learning and memory tasks, and alterations of the central dopaminergic system. The present study investigates age-related changes in the expression of synapse-related proteins to determine whether the number of synapses is decreased in SAMP10 mice. We quantified expression levels of synaptophysin, a presynaptic protein, and of PSD-95, a postsynaptic protein in various brain regions by immunoblotting. Both synapse-related proteins (52% of synaptophysin and 55% of PSD-95) were lost from the anterior cerebral cortex in SAMP10 mice at age 10-12 months compared with those in mice at age 3 months. Synaptophysin was lost by 30% from the posterior cerebral cortex of SAMP10 mice at age 15-16 months. The level of synaptophysin, but not of PSD-95 decreased by about 25% in the brain stem of SAMP10 mice aged 7 and 10-12 months. A loss of synapse-related proteins was not significant in other brain regions. Age-related loss of synaptophysin or PSD-95 was not evident in normal aging control SAMR1 mice that do not develop brain atrophy. In summary, synapses were lost with aging in SAMP10 mice and the synaptic loss was most prominent in the anterior cerebral neocortex. Since a loss of neocortical synapses is the primary correlate with the intellectual decline in human neurodegenerative diseases, SAMP10 mouse is a useful model with which to study the mechanisms underlying synaptic loss in human neurodegenerative dementias.

Aging↗

PubMed2003

Dietary fat modulation of apoA-II metabolism and prevention of senile amyloidosis in the senescence- accelerated mouse.

Senescence-accelerated mouse-prone (SAMP1; SAMP1@Umz) is an animal model of senile amyloidosis with apolipoprotein A-II (apoA-II) amyloid fibril (AApoAII) deposits. This study was undertaken to investigate the effects of dietary fats on AApoAII deposits in SAMP1 mice when purified diets containing 4% fat as butter, safflower oil, or fish oil were fed to male mice for 26 weeks. The serum HDL cholesterol was significantly lower (P < 0.01) in mice on the diet containing fish oil (7.4 +/- 3.0 mg/dl) than in mice on the butter diet (38.7 +/- 12.5 mg/dl), which in turn had significantly lower (P < 0.01) HDL levels than mice on the safflower oil diet (51.9 +/- 5.6 mg/dl). ApoA-II was also significantly lower (P < 0.01) in mice on the fish oil diet (7.6 +/- 2.7 mg/dl) than on the butter (26.9 +/- 7.3 mg/dl) or safflower oil (21.6 +/- 3.7 mg/dl) diets. The mice fed fish oil had a significantly greater ratio (P < 0.01) of apoA-I to apoA-II, and a smaller HDL particle size than those fed butter and safflower oil. Severe AApoAII deposits in the spleen, heart, skin, liver, and stomach were shown in the fish oil group compared with those in the butter and safflower oil groups (fish oil > butter > safflower oil group, P < 0.05). These findings suggest that dietary fats differ in their effects on serum lipoprotein metabolism, and that dietary lipids may modulate amyloid deposition in SAMP1 mice.

Aging, Premature↗

PubMed2003

Amyloidosis modifier genes in the less amyloidogenic a/j mouse strain.

Apolipoprotein A-II is deposited as an amyloid fibril in aged mice (senile AApoAII amyloidosis). Although mouse strains with the apolipoprotein A-II c allele (Apoa2(c)) generally develop early-onset and severe senile amyloidosis, the A/J strain shows significantly less amyloid deposition. To identify genes that modify spontaneous amyloidosis development in the A/J mouse, we performed a genome-wide screening using hybrid mice derived from A/J and SAMP1 mice, which have Apoa2(c) and age-associated severe amyloid deposition. Our genetic analysis revealed that the lower levels of amyloidosis in the A/J strain were polygenically controlled. We found two chromosome locations associated with amyloidosis. One of these regions was in the chromosome 19 telomeric region, where the A/J alleles modify amyloidosis in an additive manner. The second region was in the chromosome 4 telomeric region, where the A/J alleles modify amyloidosis in a dominant manner. Perlecan and group II secretory phospholipase A2, located on the significantly linked region of chromosome 4, were compared in this study. These findings are for understanding the genetic mechanism of amyloidosis-related diseases and their prevention.

Amyloid↗

PubMed2003

Polymorphisms of mouse apolipoprotein A-II: seven alleles found among 41 inbred strains of mice.

In mice, apolipoprotein A-II (apoA-II) associates to form amyloid fibrils in an age-associated manner. We determined the complete nucleotide sequences of the apoA-II gene (Apoa2) cDNA in 41 inbred strains of mice including Mus musculus domesticus (laboratory mouse), Mus musculus castaneus, Mus musculus molossinus, Mus musculus musculus and Mus spretus. Among these strains we identified 7 alleles (Apoa2a1, Apoa2a2, Apoa2b, Apoa2c, Apoa2d, Apoa2e and Apoa2f). Polymorphisms of nucleotides at 15 positions were detected and amino acid substitutions were found at 8 positions. Apoa2a1 was found in all mouse subspecies, but Apoa2b and Apoa2c were found only in Mus musculus domesticus. Two strains of Mus spretus have the unique alleles Apoa2e and Apoa2f which resemble Apoa2c. We confirmed that VICS in which we found severe amyloidosis here and other amyloidoneic strains in published reports have Apoa2c allele. We determined the plasma concentrations of total and HDL cholesterol in the strains of Mus musculus domesticus with the Apoa2a1, Apoa2b and Apoa2c alleles. Significantly higher concentrations of plasma cholesterol were observed in mouse strains with the Apoa2b allele. These findings provide fundamental data on mouse Apoa2 alleles. Furthermore, differences in these alleles likely have considerable influence on traits related to amyloidosis and lipid metabolism.

Alleles↗

PubMed2002

Induction of protein conformational change in mouse senile amyloidosis.

Aggregated amyloid fibrils can induce further polymerization of precursor proteins in vitro, thus providing a possible basis for propagation or transmission in the pathogenesis of amyloidoses. Previously, we postulated that the transmission of amyloid fibrils induces conformational changes of endogenous amyloid protein in mouse senile amyloidosis (Xing, Y., Nakamura, A., Chiba, T., Kogishi, K., Matsushita, T., Fu, L., Guo Z., Hosokawa, M., Mori, M., and Higuchi, K. (2001) Lab. Invest. 81, 493-499). To further characterize this transmissibility, we injected amyloid fibrils (AApoAII(C)) of amyloidogenic C type apolipoprotein A-II (APOAIIC) intravenously into 2-month-old SAMR1 mice, which have B type apolipoprotein A-II (APOAIIB), and develop few if any amyloid deposits spontaneously. 10 months after amyloid injection, deposits were detected in the tongue, stomach, intestine, lungs, heart, liver, and kidneys. The intensity of deposition increased thereafter, whereas no amyloid was detected in distilled water-injected SAMR1 mice, even after 20 months. The deposited amyloid was composed of endogenous APOAIIB with a different amyloid fibril conformation. The injection of these amyloid fibrils of APOAIIB (AApoAII(B)) induced earlier and more severe amyloidosis in SAMR1 mice than the injection of AApoAII(C) amyloid fibrils. Thus, AApoAII(C) from amyloidogenic mice could induce a conformational change of less amyloidogenic APOAIIB to a different amyloid fibril structure, which could also induce amyloidosis in the less amyloidogenic strain. These results provide important insights into the pathogenesis of amyloid diseases.

Amyloid↗

PubMed2002

Deterioration in learning and memory of inferential tasks for evaluation of transitivity and symmetry in aged SAMP8 mice.

This study examined age-dependent deficits in the learning and memory of inferential tasks, using an established senescence-accelerated mouse model in age-related brain dysfunction (SAMP8) and its genetically related inbred strain (SAMR1). The mice learned two sets of nonspatial odor-odor pairs by association learning successively (i.e., A-->B, X-->Y, then B-->C, Y-->Z). They were tested in transitive inference (i.e., A-->C, X-->Z) and symmetrical inference (i.e., C-->B, Z-->Y). In the probe test of A-->C, X-->Z transitive inference, 1-month-old SAMP8 and control SAMR1 at the same age significantly chose the alternative based on transitive inference, but 4- and 7-month-old SAMP8 performed at a random chance level, in comparison with unambiguous inference by control SAMR1 at the same ages. During the test of C-->B, Z-->Y symmetrical inference, SAMP8 at 1 month of age made errors as frequently as control SAMR1 at the same age, but SAMP8 at 4 and 7 months of age made more errors than SAMR1 at the same ages. At 4 and 7 months of age, SAMP8 made more errors than 1-month-old SAMP8. Control SAMR1 did not show such an age-related deficient. These results indicate that SAMP8 mice have age-related learning and memory deficits in the ability to perform inferential tasks. Age-related hippocampal dysfunction is suggested to be the cause of these age-related deficits in old SAMP8 mice during the performance of inferential tasks mediated by declarative memory.

Aging↗

PubMed2002

A congenic mouse and candidate gene at the Chromosome 13 locus regulating bone density.

Previously, we identified two significant quantitative trait loci (QTLs) specifying the peak relative bone mass (bone mass corrected for bone size) on chromosomes (Chrs) 11 and 13 by interval mapping in two mouse strains, SAMP2 and SAMP6. The latter strain is an established murine model of senile osteoporosis and exhibits a significantly lower peak relative bone mass than SAMP2 mice. We recently designated the Chr 13 locus as Pbd2 (Peak bone density 2) and constructed a congenic strain, P6.P2-Pbd2(b), which carried a single genomic interval from the Chr 13 of SAMP2 on a SAMP6-derived osteoporotic background. In this study, we have constructed a congenic strain, P2.P6-Pbd2(a), carrying a SAMP6-derived susceptible interval on a SAMP2-derived resistance background. This congenic strain had a lower bone density than the background strain, SAMP2, based on three measurement methods, each utilizing a different principle for evaluating bone density: MD, DXA, and pQCT. Next, a candidate gene approach was used to find polymorphisms of Bmp6 (bone morphogenetic protein 6). The CAG trinucleotide repeat numbers in exon 1 of this gene differ among SAM strains. We found an association of CAG repeat length with relative peak bone mass in mice.

Animals↗

PubMed2002

A higher oxidative status accelerates senescence and aggravates age-dependent disorders in SAMP strains of mice.

The SAM strain of mice is actually a group of related inbred strains consisting of series of SAMP (accelerated senescence-prone, short-lived) and SAMR (accelerated senescence-resistant, longer-lived) strains. Comparing with the SAMR strains, the SAMP strains of mice show a more accelerated senescence process, shorter lifespan, and an earlier onset and more rapid progress of age-associated pathological phenotypes similar to several geriatric disorders observed in humans, including senile osteoporosis, degenerative joint disease, age-related deficits in learning and memory, olfactory bulb and forebrain atrophy, presbycusis and retinal atrophy, senile amyloidosis, immunosenescence, senile lungs, and diffuse medial thickening of the aorta. The higher oxidative stress observed in the SAMP strains of mice are partly caused by mitochondrial dysfunction, and may be one cause of the senescence acceleration and age-dependent alterations in cell structure and function, including neuronal cell degeneration. This senescence acceleration is also observed during senescence/crisis in cultures of isolated fibroblast-like cells from SAMP strains of mice, and was associated with a hyperoxidative status. These observations suggest that the SAM strains are useful tools in the attempt to understand the mechanisms of age-dependent degeneration of cells and tissues, and their aggravation, and to develop clinical interventions.

Aging↗

PubMed2002

Insufficient interleukin-2 production from splenic CD4+ T cells causes impaired cell proliferation and early apoptosis in SAMP1, a strain of senescence-accelerated mouse.

We examined the proliferative and cytokine-producing activities of CD4+ T cells from young mice of the senescence-accelerated mouse strain SAMP1, which had shown markedly low T-dependent antibody-producing responses. When splenic T cells were cultured with concanavalin A (Con A), the percentage of CD4+ cells decreased earlier in SAMP1 than in C3H/He mice. At 40 hr of culture, the percentage of BrdU-labelled proliferating CD4+ cells increased strongly in C3H/He, but only slightly in SAMP1. When purified CD4+ T cells were cultured with Con A, the percentage of 5-bromo-2'-deoxyuridine (BrdU)-labelled cells peaked at around 48 hr of culture in both strains, but decreased significantly at 64 hr in SAMP1. The production of interleukin (IL)-2 but not IL-4 or interferon-gamma (IFN-gamma) was significantly lower in SAMP1 than in C3H/He at 48 hr of culture. IL-2 production was also markedly low in SAMP1, even under the stimulation of anti-CD3 with anti-CD28 antibodies. The frequency of cells producing IL-2 was significantly lower in SAMP1 than in C3H/He at 6-24 hr of culture with Con A. The percentage of annexin-positive and propidium iodide (PI)-negative apoptotic cells was significantly higher in SAMP1 than in C3H/He at 96 hr of culture. Exogenous IL-2 prevented the decrease in BrdU-labelled cells and the increase in apoptotic cells in the SAMP1 cell culture. These results indicate that SAMP1 CD4+ T cells cannot produce IL-2 at levels sufficient to support cell proliferation and survival. This may account for the weak T-dependent antibody response in SAMP1 mice.

Aging, Premature↗