Blocking Metabotropic Glutamate Receptor Subtype 7 via the Venus Flytrap Domain Promotes a Chronic Stress-Resilient Phenotype in Mice

Abstract

Chronic psychosocial stress participates prominently in the etiology of various psychiatric conditions and comorbid somatic pathologies; however, suitable pharmacotherapy of these disorders is still of high medical need. During the last few decades, research on mGlu receptors advanced remarkably and much attention was given to the mGlu7 subtype. Here, genetic mGlu7 ablation, short-term pharmacological mGlu7 blockade, as well as siRNA-mediated knockdown of mGlu7 were shown to result in an acute anti-stress, antidepressant- and anxiolytic-like phenotype in mice. Moreover, we recently revealed a prominent stress-protective effect of genetic mGlu7 ablation also with respect to chronic psychosocial stress. In addition, we are able to demonstrate in the present study that the chronic pharmacological blockade of mGlu7 interferes with various chronic stress-induced alterations. For this, we used the chronic subordinate colony housing (CSC), a mouse model of chronic male subordination, in combination with chronic treatment with the mGlu7-selective orthosteric-like antagonist XAP044 (7-hydroxy-3-(4-iodophenoxy)-4H-chromen-4-one). Interestingly, XAP044 dose-dependently ameliorates hypothalamic-pituitary-adrenal axis dysfunctions, thymus atrophy, as well as the CSC-induced increase in innate anxiety. Taken together, our findings provide further evidence for the role of mGlu7 in chronic psychosocial stress-induced alterations and suggests the pharmacological blockade of mGlu7 as a promising therapeutic approach for the treatment of chronic stress-related pathologies in men.

Keywords: XAP044; chronic psychosocial stress; chronic subordinate colony housing; mGlu7.

Figure 1

Experimental design of the chronic subordinate colony housing (CSC, 19 days) paradigm and effects of CSC exposure and i.c.v. drug-treatment on body weight. (A) Schematic illustration of the CSC paradigm. (B) Chemical structure of the used mGlu7-selective orthosteric-like antagonist XAP044. During 19 days of CSC, (C) body weight gain (day 20–day 1) (factor housing: F_1,147 = 0.197, p = 0.658; factor treatment: F_3,147 = 2.102, p = 0.102; housing*treatment interaction: F_3,147 = 0.718, p = 0.543) and (D) body weight development (factor time: F_6,528 = 104.692, p ≤ 0.001; factor treatment: F_3,88 = 1.176, p = 0.323; time*treatment interaction: F_18,528 = 5.979, p ≤ 0.001) were assessed in SHC and CSC mice treated either with VEH (5% DMSO) or XAP044 at different doses. White bar, SHC; black bar, CSC. n = 7–35 per treatment and housing group. Data represent the mean ± SEM. * p ≤ 0.05, ** p ≤ 0.01 VEH-CSC vs. VEH-SHC in (D); + p ≤ 0.05 XAP(100)-CSC vs. XAP(100)-SHC in (D); # p ≤ 0.05, ## p ≤ 0.01 XAP(100)-CSC vs. VEH-CSC in (C,D); two-way ANOVA followed by Bonferroni post hoc analysis or independent Student’s t-test (C) or repeated measures ANOVA, followed by Bonferroni post hoc analysis or independent Student’s t-test (D).

Figure 2

Effects of XAP044 treatment on CSC-induced physiological alterations and weight changes of lymphatic organs. On day 20, (A) absolute thymus weight (factor housing: F_1,146 = 16.481, p ≤ 0.001; factor treatment: F_3,146 = 3.252, p = 0.024; housing*treatment interaction: F_3,146 = 1.135, p = 0.337), (B) absolute spleen weight (factor housing: F_1,144 = 43.469, p ≤ 0.001; factor treatment: F_3,144 = 3.259, p = 0.023; housing*treatment interaction: F_3,144 = 1.317, p = 0.254) and (C) absolute pituitary weight (factor housing: F_1,139 = 0.762, p = 0.384; factor treatment: F_3,139 = 1.822, p = 0.146; housing*treatment interaction: F_3,139 = 0.699, p = 0.554) were assessed in mice treated either with VEH (5% DMSO) or XAP044 at different doses. White bar, SHC; black bar, CSC. n = 7–35 per treatment and housing group. Data represent the mean + SEM. * p ≤ 0.05, *** p ≤ 0.001 vs. respective SHC group; # p ≤ 0.05 vs. respective VEH group; ⁺⁺ p ≤ 0.05 vs. XAP(1); two-way ANOVA followed by Bonferroni post hoc analysis or independent Student’s t-test.

Figure 3

Effects of XAP044 treatment on CSC-induced HPA axis-related changes. On day 20, (A) absolute adrenal weight (factor housing: F_1,146 = 37.888, p ≤ 0.001; factor treatment: F_3,146 = 0.860, p = 0.464, housing*treatment interaction: F_3,146 = 1.783, p = 0.153), (B) basal morning plasma CORT levels (housing: F_1,137 = 0.074, p = 0.786; factor treatment: F_3,137 = 4.083, p = 0.008; housing*treatment interaction: F_3,137 = 0.462, p = 0.709) and (C) adrenal in vitro ACTH responsiveness (VEH: housing: F_1,131 = 8.337, p = 0.005; stimulation: F_1,131 = 48.465, p ≤ 0.001; housing*stimulation interaction: F_1,131 = 4.583, p = 0.034; XAP(1): housing: F_1,26 = 5.883, p = 0.023; stimulation: F_1,26 = 21.025, p ≤ 0.001; housing*stimulation interaction: F_1,26 = 1.482, p = 0.234; XAP(10): housing: F_1,92 = 6.054, p = 0.016; stimulation: F_1,92 = 39.208, p ≤ 0.001; housing*stimulation interaction: F_1,92 = 2.405, p = 0. 124; XAP(100): housing: F_1,48 = 0.343, p = 0.561; stimulation: F_1,48 = 93.461, p ≤ 0.001; housing*stimulation interaction: F_1,48 = 0.020, p = 0.887) were assessed in mice treated either with VEH (5% DMSO) or XAP044 at different doses. White bar, SHC; black bar, CSC. n = 6–35 per treatment and housing group. Data represent the mean + SEM. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001 vs. respective SHC group; # p ≤ 0.05 vs. XAP(10)-CSC in (B), # p ≤ 0.05, ### p ≤ 0.001 vs. respective basal stimulation in (C); two-way ANOVA followed by Bonferroni post hoc analysis or independent Student’s t-test.

Figure 4

Effects of XAP044 treatment on CSC-induced behavioral changes. In mice treated either with VEH (5% DMSO) or XAP044 at different doses, the percentage of time spent in the bright compartment indicative for the level of innate anxiety (A; factor housing: F_1,147 = 9.187, p = 0.003; factor treatment: F_3,147 = 0.852, p = 0. 468; housing*treatment interaction: F_3,147 = 2.624, p = 0.053) and the number of line crossings in the BC indicative for locomotor activity (B; factor housing: F_1,147 = 0.837, p = 0.362; factor treatment: F_3,147 = 1.600, p = 0.192; housing*treatment interaction: F_3,147 = 2.248, p = 0.085) were assessed on day 15 of CSC in the LDB. On day 18, the SIH response indicative for the level of physiological anxiety was assessed (C; factor housing: F_1,147 = 36.204, p ≤ 0.001; factor treatment: F_3,147 = 0.987, p = 0.401; housing*treatment interaction: F_3,147 = 1.001, p = 0.394). White bar, SHC; black bar, CSC. n = 8–36 per treatment and housing group. Data represent the mean + SEM. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001 vs. respective SHC group (A); two-way ANOVA followed by Bonferroni post hoc analysis.