Biomedical subjects

R T Bronson

Publications and source records attributed to R T Bronson.

At least 55 records · Page 3Linked to original sources

PubMed1999

Lesion biomarkers of aging in B6C3F1 hybrid mice.

This study of B6C3F1 hybrid mice was designed to determine the effects of caloric restriction (CR) on age-related pathologic changes. These changes accompany and may, in part, account for the apparent effect of CR in slowing the rate of aging. The study also explored whether lesions observed in groups of animals killed at 6 month intervals can serve as biomarkers of aging. Approximately 30 mice of each sex and each of two diet groups--CR and ad libitum fed (AL)--and each of six age groups--6, 12, 18, 24, 30, and 36 months of age--from the Biomarkers of Aging Program of the National Institute on Aging were killed and all tissues from each were examined for the histological presence or absence of lesions. A total of 209 distinct lesions were observed, of which 51 occurred in at least 10% of the AL or CR mice. The average number of lesions per mouse increased linearly with age in all diet-sex groups except in male CR mice. This increase was significantly smaller in CR than in AL mice of both sexes. The number of distinct lesions also increased with age in both diet groups but much less rapidly in CR mice. Nearly all lesions, including neoplastic, and nonneoplastic proliferative and degenerative ones, occurred significantly less often in CR than in AL mice at all ages. Foci of leukocytes in the liver, however, occurred more frequently in CR mice. Lung adenomas in old female mice occurred with equal frequency in both diet groups. A parsimonious classification tree analysis showed that diet groups could have been distinguished at each age by an evaluation of relatively few lesions and tissues. Altogether, this study suggests strongly that the prevalence of many individual lesions, the total lesion burden, and the total types of lesions are good biomarkers of aging because they increase with age and reflect the effect of CR in slowing the aging process. The study also shows that lesions occur stochastically, randomly, and independently in genetically homogeneous mice raised in a nonvariable environment.

Aging↗

PubMed1999

Effects of genotype and diet on age-related lesions in ad libitum fed and calorie-restricted F344, BN, and BNF3F1 rats.

The effects of calorie restriction (CR) on age-related lesions in Brown Norway, Fischer 344, and BNF3F1 hybrid rats are presented. A logistic regression analysis of data from histologic samples from rats of each genotype, sex, and diet at 12, 18, 24, 30, and 36 months of age demonstrated the effects of age, diet, and sex on lesion prevalence in all three genotypes. CR reduced the prevalence of neoplastic, nonneoplastic proliferative, and degenerative lesions. All genotype-sex-age cohorts demonstrated a reduced average lesion burden with CR. Importantly, some lesions common to Brown Norway rats seldom occurred in Fischer 344 rats and vice versa. Some lesions that occurred in only one parental strain also occurred in BNF3F1 rats. Many traits occurred in all three genotypes but at significantly different prevalence rates. We suggest that the diseases and lesions that rats develop as they age are controlled by genes and environmental factors such as CR.

Adrenal Glands↗

PubMed1999

Wild-derived inbred mice have a novel basis of susceptibility to polyomavirus-induced tumors.

Polyomavirus induces a broad array of tumors when introduced into newborn mice of certain standard inbred strains, notably those bearing the H-2(k) haplotype. Susceptibility in these mice is conferred by an endogenous mouse mammary tumor virus superantigen (Mtv-7 sag) that acts to delete T cells required for polyomavirus-induced tumor immunosurveillance. In the present study we show that mice of two wild-derived inbred strains, PERA/Ei (PE) and CZECH II/Ei (CZ), are highly susceptible to polyomavirus but carry no detectable Mtv sag-related sequences and show no evidence of Vbeta deletion. C57BR/cdJ (BR) mice, which are H-2(k) but lack the endogenous Mtv-7, are highly resistant based on an effective anti-polyomavirus tumor immune response. When crossed with BR, both PE and CZ mice transmit their susceptibility in a dominant fashion, indicating a mechanism(s) that overrides the immune response of BR. Susceptibility in PE and CZ mice is not based on interference with antigen processing or presentation since cytotoxic T cells from BR can efficiently kill F(1)-derived tumor cells in vitro. The expected precursors of polyomavirus-specific cytotoxic T cells are present in both the wild inbred animals and their F(1) progeny. These findings indicate a novel basis of susceptibility that operates independently of endogenous superantigen and prevents the development of tumor immunity.

Animals↗

PubMed1999

Radiation-resistant and radiation-sensitive forms of host resistance to polyomavirus.

Newborn mice of several inbred strains develop few or no tumors following inoculation with highly tumorigenic strains of polyomavirus. Here we show that such resistant strains can be divided into two groups based on the responses of adult mice to radiation followed by virus inoculation. Most strains show a radiation-sensitive form of resistance (Rr-s) and develop tumors following radiation and virus challenge. This type of resistance has previously been recognized as immunological, based on T-cell responses against virus-encoded neoantigen(s) expressed in tumor cells. Other strains exhibit a radiation-resistant form of resistance (Rr-r) and fail to develop tumors when treated in the same manner. Three additional properties of Rr-r mice distinguish them from Rr-s mice: (i) survival of newborns following inoculation with a highly virulent and usually lethal strain of virus, (ii) resistance to virus spread in newborns inoculated with either tumorigenic or virulent virus strains, and (iii) dominant or semidominant transmission of resistance in crosses with a highly susceptible strain. The Rr-r phenotype reflects a constitutive nonimmunological type of resistance that is targeted to the virus and blocks its dissemination.

Animals↗

PubMed1998

A critical role for DNA end-joining proteins in both lymphogenesis and neurogenesis.

XRCC4 was identified via a complementation cloning method that employed an ionizing radiation (IR)-sensitive hamster cell line. By gene-targeted mutation, we show that XRCC4 deficiency in primary murine cells causes growth defects, premature senescence, IR sensitivity, and inability to support V(D)J recombination. In mice, XRCC4 deficiency causes late embryonic lethality accompanied by defective lymphogenesis and defective neurogenesis manifested by extensive apoptotic death of newly generated postmitotic neuronal cells. We find similar neuronal developmental defects in embryos that lack DNA ligase IV, an XRCC4-associated protein. Our findings demonstrate that differentiating lymphocytes and neurons strictly require the XRCC4 and DNA ligase IV end-joining proteins and point to the general stage of neuronal development in which these proteins are necessary.

Animals↗

PubMed1998

Hematopoietic cells from -spectrin-deficient mice are sufficient to induce thrombotic events in hematopoietically ablated recipients.

Thrombotic events are life-threatening complications of human hemolytic anemias such as paroxysmal nocturnal hemoglobinuria, sickle cell disease, and thalassemia. It is not clear whether these events are solely influenced by aberrant hematopoietic cells or also involve aberrant nonhematopoietic cells. Spherocytosis mutant (Spna1(sph)/Spna1(sph); for simplicity referred to as sph/sph) mice develop a severe hemolytic anemia postnatally due to deficiencies in -spectrin in erythroid and other as yet incompletely defined nonerythroid tissues. Thrombotic lesions occur in all adult sph/sph mice, thus providing a hematopoietically stressed model in which to assess putative causes of thrombus formation. To determine whether hematopoietic cells from sph/sph mice are sufficient to initiate thrombi, bone marrow from sph/sph or +/+ mice was transplanted into mice with no hemolytic anemia. One set of recipients was lethally irradiated; the other set was genetically stem cell deficient. All mice implanted with sph/sph marrow, but not +/+ marrow, developed severe anemia and histopathology typical of sph/sph mice. Histological analyses of marrow recipients showed that thrombi were present in the recipients of sph/sph marrow, but not +/+ marrow. The results indicate that the -spectrin-deficient hematopoietic cells of sph/sph mice are the primary causative agents of the thrombotic events.

Anemia, Hemolytic↗

PubMed1998

Dystrophic muscle in mice chimeric for expression of alpha5 integrin.

alpha5-deficient mice die early in embryogenesis (). To study the functions of alpha5 integrin later in mouse embryogenesis and during adult life we generated alpha5 -/-;+/+ chimeric mice. These animals contain alpha5-negative and positive cells randomly distributed. Analysis of the chimerism by glucose- 6-phosphate isomerase (GPI) assay revealed that alpha5 -/- cells contributed to all the tissues analyzed. High contributions were observed in the skeletal muscle. The perinatal survival of the mutant chimeras was lower than for the controls, however the subsequent life span of the survivors was only slightly reduced compared with controls (). Histological analysis of alpha5 -/-;+/+ mice from late embryogenesis to adult life revealed an alteration in the skeletal muscle structure resembling a typical muscle dystrophy. Giant fibers, increased numbers of nuclei per fiber with altered position and size, vacuoli and signs of muscle degeneration-regeneration were observed in head, thorax and limb muscles. Electron microscopy showed an increase in the number of mitochondria in some muscle fibers of the mutant mice. Increased apoptosis and immunoreactivity for tenascin-C were observed in mutant muscle fibers. All the alterations were already visible at late stages of embryogenesis. The number of altered muscle fibers varied in different animals and muscles and was often increased in high percentage chimeric animals. Differentiation of alpha5 -/- ES cells or myoblasts showed that in vitro differentiation into myotubes was achieved normally. However proper adhesion and survival of myoblasts on fibronectin was impaired. Our data suggest that a novel form of muscle dystrophy in mice is alpha5-integrin-dependent.

Animals↗

PubMed1998

Mice with a homozygous null mutation for the most abundant glutathione peroxidase, Gpx1, show increased susceptibility to the oxidative stress-inducing agents paraquat and hydrogen peroxide.

Glutathione peroxidases have been thought to function in cellular antioxidant defense. However, some recent studies on Gpx1 knockout (-/-) mice have failed to show a role for Gpx1 under conditions of oxidative stress such as hyperbaric oxygen and the exposure of eye lenses to high levels of H2O2. These findings have, unexpectedly, raised the issue of the role of Gpx1, especially under conditions of oxidative stress. Here we demonstrate a role for Gpx1 in protection against oxidative stress by showing that Gpx1 (-/-) mice are highly sensitive to the oxidant paraquat. Lethality was already detected within 24 h in mice exposed to paraquat at 10 mg.kg-1 (approximately (1)/(7) the LD50 of wild-type controls). The effects of paraquat were dose-related. In the 30 mg.kg-1-treated group, 100% of mice died within 5 h, whereas the controls showed no evidence of toxicity. We further demonstrate that paraquat transcriptionally up-regulates Gpx1 in normal cells, reinforcing a role for Gpx1 in protection against paraquat toxicity. Finally, we show that cortical neurons from Gpx1 (-/-) mice are more susceptible to H2O2; 30% of neurons from Gpx1 (-/-) mice were killed when exposed to 65 microM H2O2, whereas the wild-type controls were unaffected. These data establish a function for Gpx1 in protection against some oxidative stressors and in protection of neurons against H2O2. Further, they emphasize the need to elucidate the role of Gpx1 in protection against different oxidative stressors and in different disease states and suggest that Gpx1 (-/-) mice may be valuable for studying the role of H2O2 in neurodegenerative disorders.

Animals↗

PubMed1998

A very large protein with diverse functional motifs is deficient in rjs (runty, jerky, sterile) mice.

Three radiation-induced alleles of the mouse p locus, p6H, p25H, and pbs, cause defects in growth, coordination, fertility, and maternal behavior in addition to p gene-related hypopigmentation. These alleles are associated with disruption of the p gene plus an adjacent gene involved in the disorders listed. We have identified this adjacent gene, previously named rjs (runty jerky sterile), by positional cloning. The rjs cDNA is very large, covering 15,264 nucleotides. The predicted rjs-encoded protein (4,836 amino acids) contains several sequence motifs, including three RCC1 repeats, a structural motif in common with cytochrome b5, and a HECT domain in common with E6-AP ubiquitin ligase. On the basis of sequence homology and conserved synteny, the rjs gene is the single mouse homolog of a previously described five- or six-member human gene family. This family is represented by at least two genes, HSC7541 and KIAA0393, from human chromosome 15q11-q13. HSC7541 and KIAA0393 lie close to, or within, a region commonly deleted in most Prader-Willi syndrome patients. Previous work has suggested that the multiple phenotypes in rjs mice might be due to a common neuroendocrine defect. In addition to this proposed mode of action, alternative functions of the rjs gene are evaluated in light of its known protein homologies.

Amino Acid Sequence↗

PubMed1998

Impaired B-lymphopoiesis, myelopoiesis, and derailed cerebellar neuron migration in CXCR4- and SDF-1-deficient mice.

The chemokine stromal cell-derived factor 1, SDF-1, is an important regulator of leukocyte and hematopoietic precursor migration and pre-B cell proliferation. The receptor for SDF-1, CXCR4, also functions as a coreceptor for T-tropic HIV-1 entry. We find that mice deficient for CXCR4 die perinatally and display profound defects in the hematopoietic and nervous systems. CXCR4-deficient mice have severely reduced B-lymphopoiesis, reduced myelopoiesis in fetal liver, and a virtual absence of myelopoiesis in bone marrow. However, T-lymphopoiesis is unaffected. Furthermore, the cerebellum develops abnormally with an irregular external granule cell layer, ectopically located Purkinje cells, and numerous chromophilic cell clumps of abnormally migrated granule cells within the cerebellar anlage. Identical defects are observed in mice lacking SDF-1, suggesting a monogamous relationship between CXCR4 and SDF-1. This receptor-ligand selectivity is unusual among chemokines and their receptors, as is the function in migration of nonhematopoietic cells.

Animals↗

PubMed1998

Disease incidence and longevity are unaltered by dietary antioxidant supplementation initiated during middle age in C57BL/6 mice.

The ability of augmented antioxidant consumption to alter disease incidence, lesion burden and/or longevity was studied in adult male C57BL/6 mice. Mice were fed modified AIN76 diet or modified AIN76 supplemented with vitamin E, glutathione (GSH), vitamin E and GSH, melatonin or strawberry extract starting at 18 months of age. All the mice in this study were heavier than reference populations of male C57BL/6 mice fed NIH-07 or NIH-31, which were maintained without a mid-life change in diet. Fatty liver, focal kidney atrophy and proteinacious casts in the renal tubules were observed more frequently in this study population than in the reference populations. Lesion burden and incidence of specific lesions observed amongst the various groups in this study did not differ. There were no differences observed for longevity of any of the study groups. The longevity observed in this study was similar to that previously reported for male C57BL/6 mice. Thus, diet supplementation with antioxidants initiated during middle age did not appear to affect age-associated lesions patterns, lesion burden or longevity for ad libitum fed male C57BL/6 mice.

Aging↗

PubMed1998

Neuronal ceroid lipofuscinosis (nclf), a new disorder of the mouse linked to chromosome 9.

The neuronal ceroid lipofuscinoses (NCLs) comprise a set of at least 6 distinct human and an unknown number of animal diseases characterized by storage of proteolipids in lysosomes of many cell types. By unknown mechanisms, this accumulation leads to or is associated with severe neuronal and retinal degeneration. The genes for 3 human NCLs, infantile, late infantile, and juvenile, have been cloned. The first murine form of NCL, the motor neuron degeneration (mnd) mouse, has been described and mapped to proximal Chromosome 8. Here we describe a second genetic variant of NCL in the mouse, neuronal ceroid lipofuscinosis, nclf. These mice exhibited a phenotype that was almost exactly the same as that observed in mnd/mnd mice. Homozygous nclf mice developed progressive retinal atrophy early in life and become paralyzed at around 9 months of age. They accumulated luxol fast blue staining material in cytoplasm of neurons and many other cell types. Ultrastructurally, affected lysosomes had a "finger print pattern" with membranous material arranged in "pentalaminar" patterns. Affected mice developed severe cerebral gliosis in late stages of their disease. They also had severe Wallerian degeneration of long tracts in spinal cord and brain stem, lesions that accounted for the distinctive upper motor neuron signs displayed by both nclf/nclf and mnd/mnd mice. By crossing nclf/nclf mice with CAST/Ei mice, linkage analysis of nclf with respect to SSLP markers was performed, showing that nclf is located on Chromosome 9 between D9Mit164 and D9Mit165, in a region that is homologous with human Ch 15q21, where the gene for one variant of late infantile NCL, CLN6, recently has been mapped. The genes for two proteolipids known to be stored in lysosomes of animals and people with NCL were also mapped in this study and found not to map to the mnd or nclf loci nor to any mouse locus homologous to any known human NCL disease locus.

Animals↗

PubMed1998

Gene dosage-dependent embryonic development and proliferation defects in mice lacking the transcriptional integrator p300.

The transcriptional coactivator and integrator p300 and its closely related family member CBP mediate multiple, signal-dependent transcriptional events. We have generated mice lacking a functional p300 gene. Animals nullizygous for p300 died between days 9 and 11.5 of gestation, exhibiting defects in neurulation, cell proliferation, and heart development. Cells derived from p300-deficient embryos displayed specific transcriptional defects and proliferated poorly. Surprisingly, p300 heterozygotes also manifested considerable embryonic lethality. Moreover, double heterozygosity for p300 and cbp was invariably associated with embryonic death. Thus, mouse development is exquisitely sensitive to the overall gene dosage of p300 and cbp. Our results provide genetic evidence that a coactivator endowed with histone acetyltransferase activity is essential for mammalian cell proliferation and development.

Animals↗

PubMed1998

p21 is a critical CDK2 regulator essential for proliferation control in Rb-deficient cells.

Proliferation in mammalian cells is controlled primarily in the G1-phase of the cell cycle through the action of the G1 cyclin-dependent kinases, CDK4 and CDK2. To explore the mechanism of cellular response to extrinsic factors, specific loss of function mutations were generated in two negative regulators of G1 progression, p21 and pRB. Individually, these mutations were shown to have significant effects in G1 regulation, and when combined, Rb and p21 mutations caused more profound defects in G1. Moreover, cells deficient for pRB and p21 were uniquely capable of anchorage-independent growth. In contrast, combined absence of pRB and p21 function was not sufficient to overcome contact inhibition of growth nor for tumor formation in nude mice. Finally, animals with the genotype Rb+/-;p21(-/-) succumbed to tumors more rapidly than Rb+/- mice, suggesting that in certain contexts mutations in these two cell cycle regulators can cooperate in tumor development.

Animals↗

PubMed1998

A specific, nonproliferative role for E2F-5 in choroid plexus function revealed by gene targeting.

Homozygous E2F-5 knockout embryos and mice have been generated. Although embryonic development appeared normal, newborn mice developed nonobstructive hydrocephalus, suggesting excessive cerebrospinal fluid (CSF) production. Although the CSF-producing choroid plexus displayed normal cellular organization, it contained abundant electron-lucent epithelial cells, consistent with excessive CSF secretory activity. Moreover, E2F-5 CNS expression in normal animals was largely confined to the choroid plexus. Cell cycle kinetics were not perturbed in homozygous knockout embryo fibroblasts. Thus, E2F-5 is not essential for cell proliferation. Rather, it affects the secretory behavior of a differentiated neural tissue.

Alleles↗

PubMed1998

Mice heterozygous for a mutation at the Nf2 tumor suppressor locus develop a range of highly metastatic tumors.

A role for the membrane/cytoskeleton interface in the development and progression of cancer is established, yet poorly understood. The neurofibromatosis type II (NF2) tumor suppressor gene encodes a member of the ezrin/radixin/moesin (ERM) family of membrane/cytoskeleton linker proteins thought to be important for cell adhesion and motility. We report that in contrast to the narrow spectrum of benign tumors in human NF2 patients, Nf2 heterozygous mice develop a variety of malignant tumors. Using the fact that Nf2 is linked to the p53 tumor suppressor locus in the mouse we have also investigated the effects of genetic linkage of cancer-predisposing mutations on tumorigenesis and examined the genetic pathway to tumor formation involving Nf2 loss. Importantly, we observed a very high rate of metastasis associated with Nf2 deficiency, with or without loss of p53 function, and we provide experimental evidence supporting a role for Nf2 loss in metastatic potential. Together, our results suggest an important role for the NF2 tumor suppressor, and perhaps the ERM family in tumor formation and metastasis.

Animals↗

PubMed1998

Reduced fertility in female mice lacking copper-zinc superoxide dismutase.

Copper-zinc superoxide dismutase (CuZn-SOD) is believed to play a major role in the first line of antioxidant defense by catalyzing the dismutation of superoxide anion radicals to form hydrogen peroxide and molecular oxygen. Recent studies have shown that missense mutations in this gene contribute, evidently through a gain-of-function mechanism, to about 20% of familial amyotrophic lateral sclerosis. To define further the physiologic role of this enzyme, a model of mice deficient in this enzyme was generated using gene targeting technology. Mice lacking this enzyme were apparently healthy and displayed no increased sensitivity to hyperoxia. However, they exhibited a pronounced susceptibility to paraquat toxicity. Most surprisingly, female homozygous knock-out mice showed a markedly reduced fertility compared with that of wild-type and heterozygous knock-out mice. Further studies revealed that although these mice ovulated and conceived normally, they exhibited a marked increase in embryonic lethality. These data, for the first time, suggest a role of oxygen free radicals in causing abnormality of female reproduction in mammals.

Animals↗

PubMed1998

A test of the role of alpha5 integrin/fibronectin interactions in tumorigenesis.

Published data show that reduction or loss of fibronectin or its receptor, alpha5beta1 integrin, occurs frequently in tumors and transformed cells. Furthermore, restoration of these adhesion proteins has been reported to reduce tumorigenesis. These results suggest that fibronectin/alpha5beta1 interactions may act to suppress tumor development or progression. To test this hypothesis in the context of spontaneous tumor formation, we have analyzed tumor development in mice genetically altered in the genes for fibronectin or alpha5 integrin. Our results show that heterozygosity for either does not lead to an increased incidence of tumors, alteration in tumor spectrum, or increased levels of metastasis, even when the fibronectin or alpha5 mutations are combined with mutations in the p53 tumor suppressor gene that lead to spontaneous tumor formation and could also cause loss of heterozygosity. Furthermore, loss of heterozygosity for alpha5 was not a common concomitant of tumorigenesis or metastasis. Finally, chimeric animals containing high proportions of alpha5-null cells did not show an increased incidence of tumors or a change in tumor progression. We conclude that, in the genetic backgrounds studied here, loss of fibronectin or alpha5beta1 integrin does not contribute to tumorigenesis or metastasis.

Animals↗