Mouse (Mus musculus) stocks derived from tropical islands: new models for genetic analysis of life-history traits

Founder effects, together with access to unoccupied ecological niches, may allow rodent populations on isolated islands to evolve constellations of life‐history traits that distinguish them from their mainland relatives, for example in body size, litter size, and longevity. In particular, low intrinsic mortality risks on islands with reduced predator numbers and not subject to harsh winter climates may in principle support the development of stocks with extended longevity. Conversely, the conditions under which laboratory rodents are typically bred are thought to select for genotypes that produce large, rapidly maturing races with high early reproductive rates but diminished longevity. To test these ideas, and to generate new mouse stocks suitable for genetic and molecular analysis of the processes that time life‐history events, we have developed specific pathogen‐free stocks from mice trapped from three distinct populations: the U.S. mainland (Idaho) and the tropical Pacific islands Majuro and Pohnpei. Mice from all three locations were found to be shorter and lighter, to have smaller litters, and to have higher faecal corticosterone levels than mice of a genetically heterogeneous stock derived from four common laboratory inbred strains. Among the wild‐derived stocks, mice from Pohnpei and Majuro were significantly lighter and shorter than Idaho‐derived animals, even in populations kept from birth under identical housing conditions. Litter size and reproductive success rates did not differ significantly among the three wild‐derived stocks. Although further work will be needed to see if, as predicted, the wild‐derived stocks differ from one another and from laboratory mice in longevity, these stocks provide useful tools for genetic dissection of factors that regulate body size and reproductive success.

T cell subset patterns that predict resistance to spontaneous lymphoma, mammary adenocarcinoma, and fibrosarcoma in mice

Aging leads to changes in the proportion of several T cell subsets in peripheral blood, but it is not yet known whether these changes have prognostic significance for late-life diseases. To examine this question, levels of T cell subsets were measured at 8 and 18 mo of age in the peripheral blood of mice of a genetically heterogeneous stock, and the mice were then subsequently evaluated for life span and for cause of death. The results indicate that mice whose T cell subset patterns look like those of old mice tend to die at earlier ages, regardless of the specific cause of death. At 18 mo, 39% of the variance within the set of seven measured subsets could be combined statistically into a single number, whose correlation with individual subsets suggested that it could be interpreted as an index of immunological aging. T cell subset pattern, as represented by this index, was a predictor of life span in mice dying of lymphoma, fibrosarcoma, mammary adenocarcinoma, or of all other causes considered together. Even as early as 8 mo of age, T cell subset patterns are significant predictors of all three forms of cancer, although at this age the association is stronger in mated female mice than in virgin mice. These results support two controversial hypotheses, which are not mutually exclusive: 1) early immune senescence might predispose to early death from cancer and 2) differences in aging rate, as monitored by tests of immune status, might accelerate or decelerate a wide range of late life neoplastic diseases.

Coordinated genetic control of neoplastic and nonneoplastic diseases in mice

Some models of aging imply that late-life diseases, though roughly synchronous, are the result of distinct pathophysiological processes, each in turn influenced by polymorphisms at multiple loci. Other models suggest that the dramatic increase in later life of multiple forms of illness might reflect the outcome of a unitary process, of so-far unknown biochemical nature, that proceeds at a species-specific rate to increase the risk of many forms of disease and disability in parallel. We have previously reported the results of genetic linkage analyses documenting the ability of alleles at D9Mit110, D10Mit15, and D12Mit167, and an allele pair at D2Mit58 and D16Mit182 to predict longevity in mice bred as the progeny of (BALB/cJ x C57BL/6J)F1 mothers and (C3H/HeJ x DBA/2J)F1 fathers (the UM-HET3 stock). Here we report the results of post hoc analyses to test the hypothesis that the genes that extend the life span of mice dying of neoplastic diseases also extend the life span of mice that die of nonneoplastic causes. In all four cases we find that the genotype associated with increased survival in mice dying of cancer is also associated for a similar degree of life span extension in mice dying of other causes. For D9Mit110 and the combination of D2Mit58 and D16Mit182, the difference is statistically significant in both the neoplastic and nonneoplastic mouse groups. The data support the hypothesis that many forms of late-life disease may be influenced by shared pathophysiologic mechanisms that are under coordinated genetic control.

Differential longevity in mouse stocks selected for early life growth trajectory

Small body size is associated with superior longevity in several intraspecies comparisons, including dogs bred for specific forms of work, mice and rats fed diets low in calories, rats fed diets low in methionine, and mutant mice whose levels of growth hormone and thyroid hormone are atypically low. To further investigate the interactions among body size, genetic endowment, and longevity, we measured the life span of female mice selectively bred from Institute for Cancer Research stock for differences in rate of body weight gain. These mice were selected for differential rates of growth either early (0-10 days) or later (26-56 days) in the first 2 months of life. The data show a good correlation between the average weight of the stock and its mean longevity, with low body size associated, as predicted, with longer life span. Weight at 3, 6, and 12 months, and weight at peak body weight, are all significant predictors of longevity (among stocks) in univariate regressions; weight at 6 months has the strongest association in stepwise multiple regression. There is no significant correlation between the life span for the stock and the proportion of deaths attributable to neoplasia in this group of mice. The data provide support for the hypothesis that genetic factors that influence early life growth trajectories can have a strong influence on life span. These size-selected mice provide useful tools for analysis of the genetic factors that influence life history parameters, including maturation and aging rates.

Lifelong treatment with oral DHEA sulfate does not preserve immune function, prevent disease, or improve survival in genetically heterogeneous mice

OBJECTIVES

To determine whether lifelong exposure to dehydroepiandrosterone sulfate extends the lifespan or retards immune senescence in mice.

DESIGN

Double-blind, placebo-controlled intervention trial.

SETTING

A specific pathogen-free rodent vivarium.

PARTICIPANTS

120 mice bred as a cross between CB6F1 females and C3D2F1 males.

INTERVENTION

DHEAS at 100 microg/mL in drinking water from weaning until death.

MEASUREMENT

Age at death, cause of death, antibody production after erythrocyte immunization, and T cell subset profiles in peripheral blood at ages 8 and 18 months.

RESULTS

DHEAS ingestion did not lead to a significant increase in mean or maximal longevity: the 95% confidence interval for DHEAS effect on mean lifespan ranged from +35 days to -80 days. There were no significant effects of DHEAS on incidence of lethal illnesses, except for a trend toward higher levels of mammary adenocarcinoma in DHEAS-treated females and mouse urinary syndrome in DHEAS-treated males. DHEAS treatment did not improve the ability of middle-aged mice to produce antibody to a foreign particulate antigen, and it did not alter the proportions of age-sensitive T cell subsets in middle-aged animals.

CONCLUSION

Although differences among species in pharmacokinetics complicate interpretation of studies in which DHEA or DHEAS is administered to rodents, our data provide no support for the idea that chronic exposure to this steroid retards immune senescence or prevents late life illness.

Exotic mice as models for aging research: polemic and prospectus

Most gerontological research using rodent models employs inbred strains, or F1 hybrids derived from them, rather than populations of genetically heterogeneous individuals. This study presents the argument that reliance on genetically homogeneous rodents, though sanctioned by tradition, may not be ideal for many sorts of investigations, and that use of heterogeneous mice and rats would allow researchers to reach robust conclusions that were less likely to reflect strain-specific idiosyncrasies. Segregating stocks, bred by backcross, F2 cross, or four-way cross procedures, would be an improvement over inbred and F1 stocks, providing inexpensive, arbitrarily large, and reproducible populations of genetically diverse test subjects. These stocks would not, however, recapture allelic variations that are likely to have been lost when wild-trapped mice and rats are selected inadvertently over dozens of generations for breeding success in laboratory conditions. Development of specific pathogen free stocks from wild-trapped progenitors particularly from populations selected for relevant evolutionary history and physiological characteristics, may be of great value for analysis of aging and late-life pathophysiology.

Lipoma in the Mediastinum of a Prairie Dog (Cynomys ludovicianus)

A large, firm lipoma was found in the cranial mediastinum of a 3-year-old female prairie dog (Cynomys ludovicianus). It encompassed the carotid arteries, jugular veins, and thymus, and compressed the esophagus and trachea. Localized compression caused dysphagia, weight loss, and dyspnea, which eventually resulted in death. Most reports on prairie dogs involve their use in research on gallbladder contractility and its role in formation of cholesterol gallstones. There are few reports on naturally developing diseases in prairie dogs, and reports of neoplasia consist of only hepatocellular carcinoma and epiglottal fibrosarcoma. Intrathoracic lipomas have been reported as rare tumors in human beings, dogs, and rats. We describe here an intrathoracic lipoma in a prairie dog and information about this type of tumor in other species.

CD4 memory T cell levels predict life span in genetically heterogeneous mice

Aging leads to changes in the relative proportions of several functionally distinct T cell subsets, including increases in the proportions of memory cells in the CD4 and CD8 subsets and in the proportion of T cells expressing the multiple-drug resistance pump P-glycoprotein. To see whether individual differences in T cell subset levels predict life span, we measured the levels of five age-sensitive T cell subsets, at 8 and again at 18 months of age, in the peripheral blood of genetically heterogeneous mice bred as the progeny of CB6F1 females and C3D2F1 males. The strongest immunological predictor of life span in univariate regression analyses was the proportion of CD4 memory cells measured at 18 months of age (P=0.003). CD4 memory cell levels remained strongly correlated with life span (P<0.0003) in a multiple regression analysis after adjustment for sex. The proportion of CD4 cells expressing P-glycoprotein was also correlated with life span (P<0.01), but only in male mice. Weaker relationships were observed between life span and 8-month tests of CD8 memory and CD8 P-glycoprotein levels, for CD4 naive cells at 18 months, and for the change in CD4 naive cells between 8 and 18 months of age; these were, however, near the margin of statistical significance and could reflect chance relationships. The relationship between CD4 memory cell levels and life span was similarly strong regardless of the cause of death in mice whose death was attributable to lymphoma, fibrosarcoma, mammary carcinoma, and other forms of terminal pathology. Additional work is needed to discriminate between two hypotheses: 1) that high levels of CD4 memory cell themselves predispose to disease and early death, particularly from neoplasia; or 2) that accumulation of CD4 memory cells is a biomarker of some underlying process-perhaps accelerated aging-that itself leads to early mortality.

Effector mechanisms responsible for gamma interferon-mediated host resistance to Legionella pneumophila lung infection: the role of endogenous nitric oxide differs in susceptible and resistant murine hosts

To facilitate identification of the effector mechanism(s) responsible for gamma interferon (IFN-gamma)-mediated host resistance to Legionella pneumophila, a murine model of legionellosis in BALB/c mice with a targeted disruption in the IFN-gamma gene (gamma knockout [GKO] mice) was developed. Immunocompetent BALB/c mice and GKO mice were inoculated intratracheally with virulent L. pneumophila (10(6) bacteria per mouse), and bacterial clearance and the pulmonary inflammatory response were assessed. L. pneumophila did not replicate in, and was rapidly cleared from, the lungs of immunocompetent BALB/c mice, demonstrating that immunocompetent BALB/c mice are resistant to replicative L. pneumophila pulmonary infections. In contrast, similarly infected GKO mice developed persistent, replicative intrapulmonary L. pneumophila infections with extrapulmonary dissemination of the bacteria to the spleen. Histopathologic and flow cytometric analysis of L. pneumophila-infected lung tissue demonstrated that while immunocompetent BALB/c mice develop multifocal pneumonitis which resolves, similarly infected GKO mice develop diffuse pneumonitis with persistent neutrophil recruitment into the lung. Intratracheal administration of exogenous IFN-gamma to L. pneumophila-infected GKO mice facilitated intrapulmonary clearance of the bacteria, confirming the pivotal role of IFN-gamma in innate host defenses to L. pneumophila lung infection in this murine host. The potential role of endogenous reactive nitrogen intermediates, including nitric oxide (NO), in IFN-gamma-mediated resistance to L. pneumophila pulmonary infections in immunocompetent BALB/c mice was subsequently assessed. Macrophage inducible nitric oxide synthetase (an enzyme responsible for the production of NO) was induced in alveolar cells from L. pneumophila-infected immunocompetent BALB/c mice (with maximal expression at 48 h postinfection) but was not induced in similarly infected GKO mice. However, administration of the NO synthetase inhibitor N-monomethyl-L-arginine did not significantly inhibit clearance of L. pneumophila from the lung of immunocompetent BALB/c mice (compared with that in similarly infected mice not administered N-monomethyl-L-arginine). In contrast, we have previously demonstrated that IFN-gamma-induced host resistance to replicative L. pneumophila lung infections in a susceptible murine host (A/J mice) is mediated, in part, by endogenous NO. Taken together, these studies identify a differing role of endogenous NO in IFN-gamma-mediated resistance to L. pneumophila pulmonary infection in susceptible and resistant murine hosts.

Coinoculation with Hartmannella vermiformis enhances replicative Legionella pneumophila lung infection in a murine model of Legionnaires' disease

The effect of inhaled amoebae on the pathogenesis of Legionnaires' disease was investigated in vivo. A/J mice, which are susceptible to replicative Legionella pneumophila infections, were inoculated intratracheally with L. pneumophila (10(6) bacteria per mouse) or were coinoculated with L. pneumophila (10(6) bacteria per mouse) and Hartmannella vermiformis (10(6) amoebae per mouse). The effect of coinoculation with H. vermiformis on bacterial clearance, histopathology, cellular recruitment into the lung, and intrapulmonary levels of cytokines including gamma interferon and tumor necrosis factor alpha was subsequently assessed. Coinoculation with H. vermiformis significantly enhanced intrapulmonary growth of L. pneumophila in A/J mice. Histopathologic and flow cytometric analysis of lung tissue demonstrated that while A/J mice inoculated with L. pneumophila alone develop multifocal pneumonitis which resolves with minimal mortality, mice coinoculated with H. vermiformis develop diffuse pneumonitis which is associated with diminished intrapulmonary recruitment of lymphocytes and mononuclear phagocytic cells and significant mortality. Furthermore, coinoculation of mice with H. vermiformis resulted in a fourfold enhancement in intrapulmonary levels of gamma interferon and tumor necrosis factor alpha compared with mice infected with L. pneumophila alone. The effect of H. vermiformis on intrapulmonary growth of L. pneumophila in a resistant host (i.e., BALB/c mice) was subsequently evaluated. While BALB/c mice do not develop replicative L. pneumophila infections following inoculation with L. pneumophila alone, there was an eightfold increase in intrapulmonary L. pneumophila in BALB/c mice coinoculated with H. vermiformis. These studies, demonstrating that intrapulmonary amoebae potentiate replicative L. pneumophila lung infection in both a susceptible and a resistant host, have significant implications with regard to the potential role of protozoa in the pathogenesis of pulmonary diseases due to inhaled pathogens and in the design of strategies to prevent and/or control legionellosis.

Replicative Legionella pneumophila lung infection in intratracheally inoculated A/J mice. A murine model of human Legionnaires' disease

The role of host immune responses in the pathogenesis of Legionnaires' disease is incompletely understood, due in part to the current lack of an animal model that is both susceptible to replicative Legionella pneumophila-induced lung infection and for which species-specific immunological reagents are available. We have developed a model of replicative L. pneumophila lung infection in intratracheally inoculated A/J mice. L. pneumophila was obtained in the exponential growth phase and inoculated into the trachea of 6- to 8-week-old female A/J mice. Microbiological and histopathological evidence of infection was demonstrated in mice inoculated with 10(6) colony-forming units. Development of an acute pneumonia that resembled human Legionnaires' disease coincided with exponential growth of the bacteria in the lung 24 to 48 hours after intratracheal inoculation of L. pneumophila. This was associated with increased plasma levels of interferon-gamma at 24 hours after inoculation. After 48 hours, the bacteria were gradually eliminated from the lung over the next 5 days, corresponding with resolution of the inflammatory response in the lung, thereby mimicking the outcome frequently seen in the immunocompetent human host. Treatment of animals with anti-interferon-gamma antibody enhanced bacterial replication and disease progression, indicating an important role of host immune response in resolution of the infection. Because of the availability of murine-specific reagents, this model of replicative L. pneumophila lung infection in A/J mice after intrapulmonary inoculation of L. pneumophila potentially provides an important tool for future studies investigating the role of host immune responses in the pathogenesis of Legionnaires' disease in the immunocompetent host.

Age-sensitive T cell phenotypes covary in genetically heterogeneous mice and predict early death from lymphoma

We have assessed several age-sensitive indicators of immune status in young (i.e., 6 to 11-month-old) mice of a genetically heterogeneous population to see if these varied in parallel and to determine if one or more of the status indices predicted life span or cancer incidence. We report that the number of memory (i.e., CD44hi) T cells within the CD8 subset is correlated with number of memory cells in the CD4 population, and inversely correlated with the number of naive (i.e., CD45RBhi) CD4 cells at both 6 and 11 months of age, suggesting that the conversion of naive to memory cells may occur at similar rates in both T cell subsets. Mice that ranked high in the proportion of memory T cells (within the CD4 and CD8 pools) at 6 months of age tended to retain their ranking at 11 months, suggesting that the pace or extent of memory cell formation may be a consistent trait that distinguishes mice at least within a genetically heterogeneous population. Mice that at 6 months of age exhibited high levels of CD4 or CD8 memory T cells, low levels of naive CD4 cells, or low levels of T cells able to proliferate in response to Con A and IL-2 were found to be significantly more likely than their littermates to die within the first 18 months of life. Cases of follicular cell lymphoma, lymphocytic and lymphoblastic lymphoma, and hepatic hemangiosarcoma were seen within the group of mice dying at early ages.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hepatic arterial yttrium 90 glass microspheres in dogs

A 22-micron glass microsphere called TheraSphere (Theragenics Corp., Atlanta, GA) has been developed in which yttrium 89 oxide is incorporated into the glass matrix and is activated by neutron bombardment to form the beta-emitting isotope yttrium 90 (Y 90) before using the spheres as radiotherapeutic vehicles. The injection of up to 12 times (on a liver weight basis) the anticipated human dose of nonradioactive TheraSphere into the hepatic arteries of dogs was well tolerated and produced clinically silent alterations within centrolobular areas. The hepatic arterial (HA) injection of radioactive TheraSphere also produced portal changes similar to those observed in humans after external beam therapy. While the extent of damage increased with the delivered dose, radiation exposures in excess of 30,000 cGy did not cause total hepatic necrosis and were compatible with survival. No microspheres distributed to the bone marrow and absolutely no myelosuppression was encountered in any animal. Proposed hepatic exposures to humans of 5000 to 10,000 cGy by means of these microspheres, therefore, would appear to be feasible and tolerable. Radiotherapeutic microsphere administration preceded by regional infusion of a radiosensitizing agent and/or immediately following the redistribution of blood flow toward intrahepatic tumor by vasoactive agents can potentially yield a synergistic, highly selective attack on tumors confined to the liver.

Effects of hepatic arterial yttrium 90 glass microspheres in dogs

A 22-micron glass microsphere called TheraSphere (Theragenics Corp., Atlanta, GA) has been developed in which yttrium 89 oxide is incorporated into the glass matrix and is activated by neutron bombardment to form the beta-emitting isotope yttrium 90 (Y 90) before using the spheres as radiotherapeutic vehicles. The injection of up to 12 times (on a liver weight basis) the anticipated human dose of nonradioactive TheraSphere into the hepatic arteries of dogs was well tolerated and produced clinically silent alterations within centrolobular areas. The hepatic arterial (HA) injection of radioactive TheraSphere also produced portal changes similar to those observed in humans after external beam therapy. While the extent of damage increased with the delivered dose, radiation exposures in excess of 30,000 cGy did not cause total hepatic necrosis and were compatible with survival. No microspheres distributed to the bone marrow and absolutely no myelosuppression was encountered in any animal. Proposed hepatic exposures to humans of 5000 to 10,000 cGy by means of these microspheres, therefore, would appear to be feasible and tolerable. Radiotherapeutic microsphere administration preceded by regional infusion of a radiosensitizing agent and/or immediately following the redistribution of blood flow toward intrahepatic tumor by vasoactive agents can potentially yield a synergistic, highly selective attack on tumors confined to the liver.

Pathogenicity in mice of herpes simplex virus type 2 mutants unable to express glycoprotein C

Herpes simplex virus type 2 (HSV-2) mutants that were unable to express glycoprotein C (gC-2) were isolated. Deletions were made in a cloned copy of the gC-2 gene, and recombinant viruses containing these deletions were screened by using an immunoreactive plaque selection protocol. The viruses did not display a syncytial phenotype. Intravaginal inoculation of BALB/cJ mice with one of the HSV-2 gC-2- viruses produced local inflammation followed by a lethal spread of the viral infection into the nervous system in a manner identical to that produced by parental HSV-2 strain 333. Similarly, intracerebral inoculation of DBA-2 mice with the gC-2- virus produced a lethal neurological disease paralleling that caused by HSV-2 strain 333. These results indicate that gC-2 is not required for the spread of HSV-2 infections in mice.