Antidepressant actions of histone deacetylase inhibitors

Abstract

Persistent symptoms of depression suggest the involvement of stable molecular adaptations in brain, which may be reflected at the level of chromatin remodeling. We find that chronic social defeat stress in mice causes a transient decrease, followed by a persistent increase, in levels of acetylated histone H3 in the nucleus accumbens, an important limbic brain region. This persistent increase in H3 acetylation is associated with decreased levels of histone deacetylase 2 (HDAC2) in the nucleus accumbens. Similar effects were observed in the nucleus accumbens of depressed humans studied postmortem. These changes in H3 acetylation and HDAC2 expression mediate long-lasting positive neuronal adaptations, since infusion of HDAC inhibitors into the nucleus accumbens, which increases histone acetylation, exerts robust antidepressant-like effects in the social defeat paradigm and other behavioral assays. HDAC inhibitor [N-(2-aminophenyl)-4-[N-(pyridine-3-ylmethoxy-carbonyl)aminomethyl]benzamide (MS-275)] infusion also reverses the effects of chronic defeat stress on global patterns of gene expression in the nucleus accumbens, as determined by microarray analysis, with striking similarities to the effects of the standard antidepressant fluoxetine. Stress-regulated genes whose expression is normalized selectively by MS-275 may provide promising targets for the future development of novel antidepressant treatments. Together, these findings provide new insight into the underlying molecular mechanisms of depression and antidepressant action, and support the antidepressant potential of HDAC inhibitors and perhaps other agents that act at the level of chromatin structure.

Figure 1.

Chronic social defeat stress in mice and clinical depression are associated with increased levels of acetylated H3 in the NAc. A, Brain sections were collected from C57BL/6J mice at 1 h, 24 h, or 10 d after chronic (10 d) social defeat or control conditions. acH3K14, and total levels of histone H1 as a control, were then quantified using immunohistochemical analysis in the NAc (indicated by the square). Shown here is a representative section collected 10 d after the last social defeat stress or control condition. B, Acetylated H3 is dynamically regulated after chronic defeat stress: acH3K14 (normalized to total H1) is decreased 1 h after the final stress episode but significantly increased 24 h and 10 d later compared with nondefeated controls. Differences between nonstressed controls and chronically defeated mice at each time point are denoted by triple asterisks (***) to indicate significance at p < 0.001. C, Increased levels of acH3K14 in the NAc 15 d after chronic social defeat stress are also evident by Western blot (left) Similarly, clinical depression is accompanied by an increase in levels of acH3K14 in the NAc compared with matched controls (right) (*p < 0.05, **p < 0.01). Error bars indicate SEM.

Figure 2.

Chronic social defeat stress in mice and clinical depression are associated with decreased levels of HDAC2 in the NAc. A, Chronic (10 d) social defeat stress decreases mRNA levels of HDAC2, but not of HDAC1 or HDAC3, in the NAc relative to nondefeated controls examined 24 h after the last defeat episode (**p < 0.01). B, Likewise, HDAC2 protein levels are significantly decreased 15 d after the last social defeat episode (left) and also downregulated in human postmortem NAc collected from a clinically depressed population compared with matched controls (right) (*p < 0.05). Error bars indicate SEM.

Figure 3.

HDAC inhibitors have robust antidepressant-like effects when infused into the NAc. After chronic (10 d) social defeat stress or control conditions, separate groups of mice were fitted with subcutaneous minipumps and bilateral guide cannulae to receive a continuous infusion of the HDAC inhibitor MS-275 or SAHA, or vehicle, into the NAc. A, On experimental day 15 (5 d after surgery), each mouse was examined for total time spent within the “interaction zone” when a social target was present. When receiving vehicle infusion, stressed mice spent significantly less time engaged in social interaction when compared with nondefeated controls. In contrast, the infusion of either MS-275 (100 μm) or SAHA (100 μm) restored the amount of time spent interacting socially. B, Over the next 4 d, preference for a sweetened 1% sucrose solution (over water alone) was examined across these same groups. Defeated mice infused with vehicle had a reduced preference for sucrose compared with their controls, and this effect of stress was reversed by the MS-275 (100 μm) infusion. C, On the next day, a forced-swim test was conducted. Chronic stress increased the total duration of immobility recorded within vehicle-treated mice. MS-275 (100 μm) and SAHA (100 μm) both decreased the duration of stress-induced immobility during this test. D, During 2.5 min of exposure to an open field, no differences in distance traveled were observed across the various treatment groups. Differences between vehicle and drug infusions in socially defeated mice are denoted by an asterisk (*) and double asterisks (**) to indicate significance at p < 0.05 or 0.01, respectively. Differences between vehicle-treated nondefeated controls and socially defeated groups are denoted by a pound sign (#) to indicate significance at p < 0.05. Error bars indicate SEM.

Figure 4.

Continuous infusion of MS-275 (100 μm) or SAHA (100 μm) into the NAc significantly increases acetylated H3 in vivo. acH3K14 was quantified directly where the HDAC inhibitor was delivered after 10 continuous days of treatment via immunohistochemistry (A) and Western blotting (B) (*p < 0.01, SAHA; **p < 0.001, MS-275). Error bars indicate SEM.

Figure 5.

Gene expression arrays provide novel insight into the molecular mechanisms of antidepressant action in the NAc. Extending previous reports, chronic (10 d) social defeat stress induces a unique pattern of gene expression in the NAc that is mostly reversed by fluoxetine or MS-275 administration. Vehicle or MS-275 (100 μm infusion into the NAc), or placebo or fluoxetine (20 mg · kg⁻¹ · d⁻¹, subcutaneous pellet) were administered for 10 continuous days after chronic (10 d) social defeat stress or control conditions, and representative patterns of gene expression in the NAc were analyzed using Illumina microarrays. A, Chronic stress-induced genomic regulation is mostly reversed by MS-275 or fluoxetine, with differences between the two treatments indicated by the red bars and similarities indicated by blue bars. B, Within MS-275-treated mice, gene expression is robustly regulated in both nonstressed controls (∼435 genes) and defeated mice (∼413). In contrast, fluoxetine regulates a large number of genes in previously stressed mice only (∼206), with many fewer genes regulated in nonstressed controls (∼84). C, When analyzing only those genes that are upregulated by fluoxetine after chronic stress, MS-275 regulates many of them in a similar way (above the top blue bar), although some are differently regulated. In much the same way, fluoxetine similarly regulates a sizable percentage of the MS-275-regulated genes (above the bottom blue bar).

Figure 6.

Molecular pathway analysis of genes regulated in the NAc by the HDAC inhibitor MS-275 after chronic social defeat stress. Examples of highly regulated molecular pathways include genes that encode presynaptic vesicular proteins, plasma membrane receptors, intracellular signaling molecules, proteins that regulate the actin cytoskeleton, and the transcriptional regulatory machinery.