Evidence revealing deregulation of the KLF11-MAO A pathway in association with chronic stress and depressive disorders

Abstract

The biochemical pathways underlying major depressive disorder (MDD) and chronic stress are not well understood. However, it has been reported that monoamine oxidase A (MAO A, a major neurotransmitter-degrading enzyme) is significantly increased in the brains of human subjects affected with MDD and rats exposed to chronic social defeat (CSD) stress, which is used to model depression. In the current study, we compared the protein levels of a MAO A-transcriptional activator, Kruppel-like factor 11 (KLF11 , also recognized as transforming growth factor-beta-inducible early gene 2) between the brains of 18 human subjects with MDD and 18 control subjects. We found that, indeed, the expression of KLF11 is increased by 36% (p<0.02) in the postmortem prefrontal cortex of human subjects with MDD compared with controls. We also observed a positive correlation between KLF11 levels and those of its target gene, MAO A, both in association with MDD. KLF11 protein expression was also increased by 44% (p<0.02) in the frontal cortex of KLF11 wild-type mice (Klf11(+/+)) vs Klf11(-/-) when both exposed to CSD stress. In contrast, locomotor activities, central box duration and sucrose preference were significantly reduced in the stressed Klf11(+/+) mice, suggesting that Klf11(+/+) mice are more severely affected by the stress model compared with Klf11(-/-) mice. These results serve to assign an important role of KLF11 in upregulating MAO A in MDD and chronic social stress, suggesting that inhibition of the pathways regulated by this transcription factor may aid in the therapeutics of neuropsychiatric illnesses. Thus, the new knowledge derived from the current study extends our understanding of transcriptional mechanisms that are operational in the pathophysiology of common human diseases and thus bears significant biomedical relevance.

Figure 1

Western blot analysis of KLF11 (TIEG2) protein levels in the human postmortem prefrontal cortex of 18 subjects with major depressive disorder (MDD) vs 18 non-affected, psychiatrically normal control subjects. (a) A representative immunoblot showing three healthy controls and three MDD subjects is shown. β-actin was used as the loading control. (b) Quantitative analysis. Each KLF11 band was evaluated by its relative intensity and normalized to the density of β-actin. Graphs of the average optical density of KLF11/actin for the individual subjects (solid circles or squares) and mean values (horizontal lines) are shown.

Figure 2

Western blot analysis of MAO A in the human postmortem prefrontal cortex of 18 subjects with major depressive disorder (MDD) vs 18 non-affected control subjects. (a) Quantitative analysis. Each MAO A band was evaluated by its relative intensity and normalized to the density of β-actin. Graphs of the average optical density of MAO A/actin for the individual subjects (solid circles or squares) and mean values (horizontal lines) are shown. (b) Graphic representation demonstrating the positive correlation between KLF11 and MAO A levels in psychiatrically normal control subjects (black circles) and subjects with MDD. (c) Representative images showing cell phenotype-specific localization of MAO A in neurons (NeuN positive) and astrocytes (GFAP positive) in the prefrontal cortex of the postmortem human brain.

Figure 3

Analysis of KLF11 in the frontal cortex of seven mice following exposure to chronic social defeat (CSD) stress vs seven control mice. (a) Quantitative analysis. Real-time RT-PCR results of KLF11 mRNA are shown for mice exposed to CSD stress. (b) Quantitative analysis. (A) A representative immunoblot of KLF11 and β-actin is shown for three control mice and three stressed mice is shown. (B) Each KLF11 band was assessed based on its relative intensity and normalized to β-actin.

Figure 4

Analysis of MAO A in the frontal cortex of KLF11-wild-type and knockout mice following exposure to chronic social defeat (CSD) stress. (a) Quantitative analysis. Real-time RT-PCR results assessing MAO A mRNA are shown. (b) Quantitative analysis. Catalytic activity levels are illustrated for both control and stressed mice.

Figure 5

Evaluation of the depressive behaviors. (a) Immobility, (b) total distance traveled, and (c) time in central box in open-field tests and (d) sucrose preference of KLF11-wild-type and knockout mice following exposure to chronic social defeat (CSD) stress. Open-field tests were performed 1 day after the sucrose preference tests that were performed on day 10 of the chronic social defeat procedure and compared with baseline.