Negative effects of lifespan extending intervention on resilience in mice

Abstract

One key goal of basic aging research is the development of reliable assays of both current and future health. These assays could dramatically accelerate progress toward developing health-extending interventions by obviating the need for full lifespan studies, especially if they were informative relatively early in life. One potential approach is the assessment of physiological resilience, defined as the ability to recover from an adverse event. Here, using CB6F1 mice, we evaluated four potential resilience assays, each quantifying recovery from a physiological challenge with clear relevance to humans. The challenges were: (1) anesthesia recovery, (2) restoration of hemoglobin levels after a blood draw, (3) speed of wound healing, and (4) survival after pathogen exposure. We evaluated how each changed with age and with interventions known to extend health in males only (17α-estradiol) or both sexes (calorie restriction). We found that three of the four (recovery from anesthesia, blood draw, and pathogen exposure) showed significant and expected age effects, but wound healing did not. None of the three age-sensitive assays responded to the health-extending interventions in the way we expected, and for some assays, including anesthesia response, interventions actually worsened outcomes. Possible explanations are: (1) our interventions were too brief, (2) the ages we evaluated were too young, (3) our assays did not capture important features of organismal resilience, or (4) organismal resilience is not as clearly related to current or future health as hypothesized. Future studies are needed to determine which of these interpretations is valid and to determine whether other resilience metrics may be more informative about current and future health.

Fig 1. Impact of age on putative resilience assays.

(A) Anesthesia recovery displays a significant increase with age (p = 0.004) but not sex (p = 0.36). (B) Ear punch wound healing does not change with age or sex. (C, D) Recovery from blood draw shows a trend towards an age effect (p = 0.081), but no impact of sex (p = 0.36). (E, F) Exposure to a standardized dose of S. pneumoniae pathogen reveals both age and sex effects on survival (p = 0.0009 for both). * = p <0.05.

Fig 2. Impact of EST supplementation.

Body weight (A) and percent body fat (B) at baseline (12 months old) and after 3 and 8 months of supplementation (15 and 20 months old, respectively). Note that EST-fed males never return to baseline body weight even though controls continue to gain weight. Effect seems to be due to reduced fat mass. There was no impact of EST feeding on female body weight or composition. Contrary to our hypothesis, EST-fed males (C) are not more resilient than females to anesthesia. For blood draw (D & E), red dashed lines indicated EST-fed animals, and males showed significantly lower Hemoglobin levels after eight months EST treatment. * = p <0.05.

Fig 3. Behavioral impact of EST supplementation.

Open field (A, B). There were provocative but very marginal sex-dependent effects of diet total distance traveled (A) (p = 0.09), but no trace of an effect of sex and diet interacting on time spent in the central zone (B). The cage wire hang test (C) did have a trend towards a (p = 0.07) sex-dependent effect of diet EST-fed males improving whereas females did not and a similarly marginal (p = 0.04) sex-dependent effect of diet on quality of nest building (D). * = p <0.05.

Fig 4. Impact of 8 weeks of calorie restriction (CR).

(A) impact of CR on body weight. (B) Anesthesia recovery under CR was not statistically different from controls for either males or females (p = 0.14). (C) Wound healing under CR also did not differ significantly (p = 0.34) in either sex. * = p <0.05.