Social stress shortens lifespan in mice

Abstract

Stress and low socioeconomic status in humans confer increased vulnerability to morbidity and mortality. However, this association is not mechanistically understood nor has its causation been explored in animal models thus far. Recently, cellular senescence has been suggested as a potential mechanism linking lifelong stress to age-related diseases and shorter life expectancy in humans. Here, we established a causal role for lifelong social stress on shortening lifespan and increasing the risk of cardiovascular disease in mice. Specifically, we developed a lifelong chronic psychosocial stress model in which male mouse aggressive behavior is used to study the impact of negative social confrontations on healthspan and lifespan. C57BL/6J mice identified through unbiased cluster analysis for receiving high while exhibiting low aggression, or identified as subordinate based on an ethologic criterion, had lower median and maximal lifespan, and developed earlier onset of several organ pathologies in the presence of a cellular senescence signature. Critically, subordinate mice developed spontaneous early-stage atherosclerotic lesions of the aortic sinuses characterized by significant immune cells infiltration and sporadic rupture and calcification, none of which was found in dominant subjects. In conclusion, we present here the first rodent model to study and mechanistically dissect the impact of chronic stress on lifespan and disease of aging. These data highlight a conserved role for social stress and low social status on shortening lifespan and increasing the risk of cardiovascular disease in mammals and identify a potential mechanistic link for this complex phenomenon.

Keywords: aggression; atherosclerosis; healthspan; lifespan; senescence; stress.

Figure 1

Effect of contextual aggression on survival. (a) Diagram of the lifelong chronic psychosocial stress (LCPS) model. (b) Dendrogram of the experimental population based on aggression exhibited and received by experimental subjects in the course of the 4‐week CPS phase and the statistically identified clusters (C1, N = 58, C2, N = 49, C3, N = 51, C4, N = 14). (c) Scatterplot of the amount of aggression exhibited and received by experimental subjects during the 4‐week CPS highlighting the four statistically identified clusters and associated individual probability density plots that exemplify the probability of receiving and exhibiting a given amount of aggression by individuals within each cluster. (d) Average amount of aggression exhibited [F(3,142) = 184.76, p < .0001, different letters represent statistically significant binary differences at post hoc level] and received [F(3,142) = 188.06, p < .0001] by the four clusters. (e) Survival probability as affected by aggression cluster (log‐rank test, χ² = 13.6 on 3 degrees of freedom, p < .01; Bonferroni corrected p value for binary comparisons = 0.0083). (f) Age at which 90%, etc. of the population survived, the percent survival at median and maximum (10%) survival as well as Cox regression model examining the contribution of cluster of aggression or achieved status on survival. (likelihood ratio test = 11.36 on 3 degrees of freedom, p = .009915: C2 vs. C1 p = .024, C3 vs. C1, ns, C4 vs. C1, ns) (HR, hazard ratio; CI, confidence interval)

Figure 2

Achieved subordinate status shortens lifespan in mice. (a) Average amount of aggression exhibited [F(1,115) = 309.35, p < .0001)] and received [F(1,115) = 176.1, p < .0001] by individual according to the achieved status (subordinate = 61, dominant = 56). (b, c) Survival probability and distribution of mortality frequencies as affected by the achieved status (log‐rank test, χ² = 8.9 on 1 degrees of freedom, p < .01). (d) Age at which 90%, etc. of the population survived, the percent survival at median and maximum (10%) survival as well as Cox regression model examining the contribution of achieved status on survival (HR, hazard ratio; CI, confidence interval). *p < .05

Figure 3

Achieved status impacts healthspan in mice. (a–f) Healthspan parameters during the 4 weeks of chronic psychosocial stress (CPS) exposure: (a) 4‐hr fasting glucose [diet: F(1,112) = 20.82, p < .0001; achieved status: F(1,112) = 14.59, p < .001]. (b) body weight gain [diet: F(1,113) = 186.71, p < .0001; achieved status: F(1,113) = 4.21, p < .05], (c) fat mass gain [diet: F(1,113) = 132.56, p < .0001]; (d) fat‐free mass gain; (e) food intake [diet: F(1,113) = 111.16, p < .0001; achieved status: F(1,113) = 12.12, p < .0001]; (f) food efficiency [diet: F(1,113) = 134.26, p < .0001; achieved status: F(1,113) = 7.90, p < .01]; (g–l) Healthspan parameters during the entire duration of the study: (g) 4‐hr fasting glucose after; (h) body weight; (i) fat mass; (j) fat‐free mass [achieved status: F(1,108) = 5.73, p < .05]; (k) food intake [diet: F(1,107) = 4.41, p < .05; achieved status: F(1,107) = 6.62, p < .05]; (STD, standard diet; HFD, high‐fat diet). While data are presented for the entire study duration (g–k), they were statistically analyzed only until 12 months after stress (shaded areas), a point upon which the number of missing samples started exceeding 5% thus affecting the analytical power [78]; missing data from animals not surviving to 12 months after stress (3.76%) were not treated nor included in this analysis. Different letters represent statistical differences between groups. (l) Fecal corticosterone metabolites [F(1,50) = 19.8, p < .0001]. N = 8/group. *p < .05, #p < .06. Data represent group mean ± SEM

Figure 4

Achieved status affects the onset of aging‐associated organ lesions and cellular markers of senescence. (a, b) Heat map of organ‐specific lesions, age‐dependent distribution of macroscopic dissectible lesions in proportion to their prevalence within each organ, and survival probability as a function of the number of macroscopic dissectible lesions as detected at time of necropsy in dominant and subordinate mice. (c, d) Cell senescence markers in spleen and liver of dominant and subordinate mice [p16^Ink4a, HMGB1 (high mobility group box 1), p53] N = 8/group. *p < .05, ^# p < .06. Data represent group mean ± SEM

Figure 5

Early‐stage atherosclerotic lesions of the aortic sinuses are found exclusively in subordinate mice. Exemplar slides stained with Movat's staining showing the presence of rupture (a, top red arrow), immune cells infiltration (a, bottom red arrow, b and d) as well as calcification as confirmed by Alizarin stain (b, e). Inflammation was verified by Mac‐2 staining (c, red arrow) and quantified with a Mac‐2 score [f, F(1,14) = 5.76, p < .05]. (g) Quantification of fibrosis in the mouse myocardium using Picrosirius Red stain (representative images are shown in Figure S6). (h) Liver expression of lipid cholesterol metabolism markers [iodothyronine deiodinase 1 (Dio1), sterol regulatory element‐binding protein 2 (Srebp2), lipase C (Lipc), peroxisome proliferator‐activated receptor alpha (PPAR‐α), carnitine palmitoyltransferase 1α [(Cpt1α)]. N = 8/group *p < .05, ^# p < .07