Sex differences in the modulation of anxiety- and depression-like behaviors by matrix metalloproteinase-9 expression levels in mice

Abstract

Background: Major depressive disorder is one of the main causes of disability worldwide, but its etiopathology remains largely unknown, although several hypotheses have been proposed. Recent studies suggest a potential role for matrix metalloproteinase 9 (MMP-9) in depression, as it is overexpressed in the plasma of depressed patients and normalizes following chronic antidepressant treatment. This study aimed to characterize anxiety and depression-like behaviors in transgenic MMP-9 mice, as well as the expression of different neuroplasticity markers associated with depression, in both sexes.

Methods: In this study, we characterized the behavioral phenotypes of both MMP-9 knockout and MMP-9-overexpressing male and female mice. Here, we used a battery of tests to assess anxiety (open field, light‒dark box, elevated plus maze, and novelty‒suppressed feeding tests), depressive-like (tail suspension and social interaction tests), and cognitive (T-maze) behaviors.

Results: MMP-9 knockout female mice displayed increased innate anxiety (open field test), decreased behavioral despair (tail suspension test). Compared with control mice, female MMP-9 knockout mice presented increased levels of different neuroplasticity markers in the hippocampus. With respect to MMP-9-overexpressing mice, females presented decreased innate anxiety (elevated plus maze). Male MMP-9-overexpressing mice presented greater conflict-based anxiety (novelty-suppressed feeding test) than control mice did.

Conclusions: MMP-9 activity modifies anxiety- and depression-like behaviors, as well as neuroplasticity markers, in female but not in male mice. These findings reinforce the sex differences in the etiopathology of depression.

Keywords: Anxiety; Depression; Matrix metalloproteinase-9Transgenic mice; Neuroplasticity; Sex.

Fig. 1

Experimental timeline for behavioral tests. EPM: elevated plus maze; LDB: light-dark box; NSF: novelty-suppressed feeding; OFT: open field test; SIT: social interaction test; TST: tail suspension test; Hp: hippocampus; WB: Western blot

Fig. 2

Innate anxiety in MMP-9 KO (A–C) and MMP-9 OE (D–F) male and female mice. Time spent in the center (A and D) in the open field test, time spent in the open arms in the elevated plus maze (B and E), and time spent in the lit compartment in the light-dark box test (C and F). The data are expressed as the means ± SEMs. Two-way ANOVA followed by a Tukey’s post hoc test. *p < 0.05 and ***p < 0.001. n = 7–10 animals per group. OFT: open field test; EPM: elevated plus maze; LDB: light‒dark box test. WT: wild-type mice; KO: MMP-9 knockout mice; OE: MMP-9-overexpressing mice

Fig. 3

Conflict-based anxiety in MMP-9 KO (A) and MMP-9 OE (B) male and female mice assessed by the latency to feeding in the novelty-suppressed feeding test. The data are expressed as the means ± SEMs. Two-way ANOVA followed by a Tukey’s post hoc test. *p < 0.05. n = 7–10 animals per group. WT: wild-type mice; KO: MMP-9 knockout mice; OE: MMP-9-overexpressing mice

Fig. 4

Depressive-like behavior in MMP-9 KO (A and B) and MMP-9 OE (C and D) male and female mice. Immobility time in the tail suspension test (A and C) and social interaction time (B and D) in the social interaction test. The data are expressed as the means ± SEMs. Two-way ANOVA followed by a Tukey’s post hoc test. *p < 0.05. n = 7–10 animals per group. TST: tail suspension test; SIT: social interaction test; WT: wild-type; KO: MMP-9 knockout; OE: MMP-9-overexpressing

Fig. 5

Z-emotionality scores in MMP-9 KO (A and B) and MMP-9 OE (C and D) male and female mice. Z-emotionality of anxiety (A and C) and of depression (B and D). The results are expressed as the means ± S.E.M. Two-way ANOVA followed by a Tukey’s post hoc test. *p < 0.05, **p < 0.01 and ***p < 0.001. n = 14-20 animals per group. WT: wild-type mice; KO: MMP-9 knockout mice; OE: MMP-9-overexpressing mice

Fig. 6

Neuroplasticity markers expression in the hippocampus of male and female MMP-9 KO mice. BDNF (A), mTOR (B), phospho-mTOR (C), PSD95 (D), and synapsin I (E) expression in MMP-9 KO mice and their corresponding wild-type counterparts. Representative western blot bands are shown. The results are expressed as percentages versus the WT group and as the means ± S.E.M.s. Two-way ANOVA followed by a Tukey’s post hoc test. *p < 0.05, **p < 0.01. n = 7–8 animals per group. BDNF: brain-derived neurotrophic factor; mTOR: mammalian target of rapamycin; PSD95: postsynaptic density 95 protein; WT: wild-type; KO: MMP-9 knockout

Fig. 7

Neuroplasticity markers expression in the hippocampus of male and female MMP-9 OE mice. BDNF (A), mTOR (B), p-mTOR (C), PSD95 (D), and synapsin I (E) expression in MMP-9 OE mice and their corresponding wild-type counterparts. Representative western blot bands are shown. The results are expressed as percentages versus the WT group and as the means ± S.E.M.s. Two-way ANOVA followed by a Tukey’s post hoc test. n = 6–7 animals per group. BDNF: brain-derived neurotrophic factor; mTOR: mammalian target of rapamycin; PSD95: postsynaptic density 95 protein; WT: wild-type mice; OE: MMP-9-overexpressing mice