III. Anti-aging interventions
III.A. Diet restriction
Diet restriction: fully effective in fat hyperinsulinemic mice
Using the C57BL/6J Lepob/Lepob (ob/ob) mouse, which produces no leptin, we investigated the relationship between body fat and diet restriction (DR). Under DR, we reduced the fat of ob/ob mice to 48% of the total body weight, which still is about 4 times the fat composition of ad lib-fed normal controls. Nonetheless, these ob/ob mice lived as long as diet restricted genetic controls (Harrison et al., 1984; 1991). This demonstrates that the extremely large stores of fat in DR ob/ob mice — and their high levels of circulating insulin — did not prevent them from gaining the full benefit of DR.
Diet restriction: retards stem cell aging
In BALB/cByJ mice, hematopoietic stem cells (HSC) age more rapidly than those in the C57BL/6J (Chen et al, 2000; Yuan et al, 2005). Hemopoietic deficiencies appear with age, while marrow concentrations of cells with HSC antigenic markers and competitive repopulation functions are reduced by half. Strikingly, the strong correlations over time, which demonstrate clonal stability during long-term competitive repopulation, disappear in old BALB marrow. DR for 24 months alleviates hematopoietic deficiencies and increases concentrations of marrow cells with HSC markers. Surprisingly, HSC competitive repopulation in old diet restricted BALB mice was better than that in young adults. Degrees of repopulation by marrow from these donors also correlated well over time, demonstrating clonal stability. DR for 5 months improved HSC function to a much smaller degree. (Chen et al., 2003)
III.B. Corticosterone
Because DR elevates circulating corticosterone, and because chronic corticosterone supplements are used for hypophosectomized rodents in studies in which life span is increased, we evaluated effects of chronic corticosterone treatment in normal mice. Results show that chronic physiological elevation of corticosterone increases maximum life span in B6CBA F1 males by about 10%. We conclude that the effects of DR on life span could be partly, but not entirely, mediated by chronic elevation of circulating corticosterone (Flurkey et al., in prep).
Figure III.B. Effect of corticosterone on life span.
III.C. Intervention Testing Program (ITP)
As part of a multi-center project, with funding from the National Institutes of Aging, we are testing simple chemical interventions, administered through food, to determine if they retard aging and increase life span in mice. We will consider an intervention successful if it reduces chronic inflammation, increases insulin sensitivity, and reduces susceptibility to oxidative damage, all of which are well-known indicators of retarded aging. We will test the most successful interventions in combinations at all centers.
We produced mice for the study by breeding 2 F1 hybrids (cByB6F1/J females and C3D2F1/J males) that represent 4 diverse genotypes in a 4-way cross first used by Miller et al. (1999) to study life spans. Thus, the tested populations represent great genetic diversity, yet are reproducible. We are including a group of diet restricted 4-way cross mice as positive controls because diet restriction is the "gold standard" for treatments that retard aging and increase life span.
Although one of the most important criteria of retarded aging is increased maximum life span, we are conducting longitudinal studies of aging in individual biological systems that can be monitored without harm to the mice: proportions of blood T cell subsets, voluntary activity, plasma IGF, glucose, insulin, and thyroid hormone. We also will test pathologies at death.
III.D. Environmental enrichment and husbandry
Igloos and tunnel cages: Using our 4-way cross mouse model (CZECHxMOLF F1 females by WSBxSKIVE Fa males), we are studying the effects of social dynamics by monitoring the effects of large group housing in tunnel cages that include "igloo-like" enclosures with room for only 2 mice. Although the density (number of mice per unit of cage space) remains the same as with standard housing, the tunnel cages provide extra space in which the mice can maneuver. Experiments are ongoing.
Figure III.D. Mouse "igloo" and tunnel connection. The left photo shows a red "igloo" and the connection to the other mouse box. The right photo details the connection between the two boxes.
