A beta3-adrenergic-leptin-melanocortin circuit regulates behavioral and metabolic changes induced by chronic stress

Abstract

Background: Obesity has been associated with an increased risk of developing several psychiatric illnesses, including major depression and posttraumatic stress disorder. Likewise, these stress-related disturbances are associated with a higher rate of obesity; yet, the neurobiological mechanisms linking obesity and stress remain incompletely understood.

Methods: Following exposure to chronic social defeat stress (CSDS), mice were given free access to either regular chow or a Western-style diet high in triglycerides and cholesterol. Comprehensive metabolic and behavioral testing was then conducted.

Results: Mice subjected to CSDS and then fed a high-fat diet for 30 days display severe behavioral deficits accompanied by redistribution of body fat. Stressed mice have decreased adipose tissue as well as decreased serum leptin levels compared with control mice. Pharmacological inhibition of beta(3)-adrenergic signaling during CSDS normalizes these metabolic abnormalities but worsens behavioral symptoms. Furthermore, mice subjected to CSDS display central leptin resistance including reduced expression of pro-opiomelanocortin in hypothalamus. Administration of a central melanocortin agonist worsens stress-induced behavioral deficits, while mice lacking the melanocortin-4 receptor display attenuated symptoms.

Conclusions: These results indicate that chronic signaling through beta(3)-adrenergic receptors during social stress is an adaptive response that improves behavioral function. However, these responses come at the expense of central leptin resistance and melanocortin signaling alterations that contribute to significant and long-lasting metabolic abnormalities.

Figure 1. Metabolic effects of CSDS

C57BL/6 mice were subjected to CSDS (n=25) or non-aggressive encounters (control, n = 34) for ten days and then randomized into groups receiving either regular chow or HFD for 30 days. CSDS increases (A) social avoidance at day 39 [significant defeat effect (F_1,55 = 41.76, p<0.0001, and (B) body weight [significant group × day_RM interaction (F_{18, 391} = 2.36, p=0.0015)]. A sub-group of animals (n = 6/group) were further analyzed for (C) food intake [significant defeat effect (F_{1, 20} = 8.81, p=0.0076)], (D) body composition [significant defeat × diet interaction effect (F_{1, 20} = 5.81, p=0.0257), and (E) leptin [significant defeat × diet interaction (F_{1, 20} = 26.11, p<0.0001)]. Data are presented as mean±SEM, with * indicating significant differences (*p<0.05, **p<0.01, ***p<0.001). RM (repeated measure).

Figure 2. β₃-AR signaling in CSDS

C57BL/6 mice (n=10/group) were given twice daily injections of the β₃-AR antagonist SR59230A (5 mg/kg i.p.) or vehicle during CSDS or control encounters. (A) Food intake [significant defeat effect (F_{1, 36} =4.17, p=0.0484) and significant treatment effect (F_{1, 36} =6.59, p=0.0146)] and (B) body composition [significant treatment effect (F_{1, 36} =5.92, p=0.0201)]. (C) Leptin levels (n=7/group) [significant treatment effect (F_{1, 24} =5.14, p=0.0075)]. (D) SR59230A worsens social avoidance behavior on Day 11 [significant defeat effect (F_{1, 36}=30.22, p<0.0001)]. C57BL/6 mice were given injections of the β₃-AR agonist CL316243 (1 mg/kg i.p., n=5) or saline (n=6) once daily for ten days. (E) CL316243 effect on food intake [significant treatment × day_RM interaction (F_{8, 81} = 2.54, p=0.0163)]. (F) Body composition [p=0.005 by Student’s t-test], and (G) leptin levels [p=0.0493 by Student’s t-test]. Data are presented as mean±SEM, with * indicating significant differences (*p<0.05, **p<0.01, ***p<0.001). RM (repeated measure).

Figure 3. Leptin resistance after CSDS

C57BL/6 mice subjected to CSDS (n=10/group) or control encounters (n=10/group) were given leptin (1 mg/kg i.p.) twice daily for four days. (A) Body weight [significant effect of leptin × day_RM (F_{9, 144} = 4.77, p<0.0001). (B) Food intake [significant effect for leptin (F_{1, 36} = 10.19, p=0.0029) and defeat (F_{1, 36} = 14.86, p=0.0005)]. (C) Social interaction scores on day 15 [significant effect of defeat (F_{1, 36} = 5.81, p=0.0211)]. (D) Sucrose preference after leptin treatment [significant effect of defeat (F_1,35 = 16.94, p=0.0002)]. (E) Hypothalamic expression of POMC, NPY, and AgRP (n=7/group) determined by qPCR on day 15 [POMC: significant effect of defeat (F_{1, 24} = 196.82, p<0.0001), NPY: significant effect of leptin × defeat (F_{1, 24} = 72.17, p<0.0001), AgRP: significant effect of leptin × defeat (F_{1, 24} = 59.60, p<0.0001). In a separate experiment, mice were subjected to CSDS (n=9/group) or control encounters (n=9/group) and given a single injection of leptin (1 mg/kg). (F) Levels of phosphorylated STAT3 [p=0.004 by Student’s t-test]. Data are presented as mean±SEM, with * indicating significant differences (*p<0.05, **p<0.01, **p<0.001). RM (repeated measure).

Figure 4. Melanocortin signaling in anxiety and depression

C57BL/6 mice subjected to CSDS (n=10/group) or control encounters (n=10/group) were given MT II (50 μg i.p.) four times daily for two days. (A) Body weight change [significant effect of treatment (F_{1, 36} = 52.59, p<0.0001)] and (B) food intake [significant effect of treatment (F_{1, 36} = 5.41, p=0.0257)] on Days 11 and 12. (C) Social interaction scores on day 13 (n=18 control-saline, n=16 control-MTII, n=19 social defeat-saline, n=18 social defeat-MTII) [significant effect for defeat (F_{1, 67} = 89.59, p<0.0001) and MT II (F_{1, 67} = 8.80, p=0.0042). A cohort of wild-type (n=7) and MC4R-null (n=9) littermates were tested in rodent models of depression and anxiety including (D) time spent on open arm of elevated plus maze (p=0.027 by Student’s t-test), (E) immobility in the forced swim test (p=0.0478), and (F) social avoidance after CSDS [significant defeat effect (F_{1, 26} =38.45, p<0.0001) and significant genotype effect (F_{1, 26} = 8.47, p=0.0073)]. Data are presented as mean±SEM, * indicating significant differences (*p<0.05, **p<0.01, ***p<0.001).