Permissive epigenetic regulatory mechanisms at the histone level are enhanced in postmortem dorsolateral prefrontal cortex of individuals with schizophrenia

Abstract

Background: Susceptibility to schizophrenia is determined by interactions between genes and environment, possibly via epigenetic mechanisms. Schizophrenia has been associated with a restrictive epigenome, and histone deacetylase (HDAC) inhibitors have been postulated as coadjuvant agents to potentiate the efficacy of current antipsychotic drugs. We aimed to evaluate global histone posttranslational modifications (HPTMs) and HDAC expression and activity in the dorsolateral prefrontal cortex (DLPFC) of individuals with schizophrenia.

Methods: We used postmortem DLPFC samples of individuals with schizophrenia and controls matched for sex, age, and postmortem interval. Schizophrenia samples were classified into antipsychotic-treated or antipsychotic-free subgroups according to blood toxicology. Expression of HPTMs and HDAC was quantified by Western blot. HDAC activity was measured with a fluorometric assay.

Results: H3K9ac, H3K27ac, and H3K4me3 were globally enhanced in the DLPFC of individuals with schizophrenia (+24%-42%, p < 0.05). HDAC activity (-17%, p < 0.01) and HDAC4 protein expression (-20%, p < 0.05) were downregulated in individuals with schizophrenia. Analyses of antipsychotic-free and antipsychotic-treated subgroups revealed enhanced H3K4me3 and H3K27ac (+24%-49%, p < 0.05) and reduced HDAC activity in the antipsychotic-treated, but not in the antipsychotic-free subgroup.

Limitations: Special care was taken to control the effect of confounding factors: age, sex, postmortem interval, and storage time. However, replication studies in bigger cohorts might strengthen the association between permissive HPTMs and schizophrenia.

Conclusion: We found global HPTM alterations consistent with an aberrantly permissive epigenome in schizophrenia. Further studies to elucidate the significance of enhanced permissive HPTMs in schizophrenia and its association with the mechanism of action of antipsychotic drugs are encouraged.

Figure 1

Immunodensity of histone H3 (A) and H4 (B) posttranslational modifications in the dorsolateral prefrontal cortex of individuals with schizophrenia (SZ) and matched controls (CTL). The data shown are mean values of 3–4 independent experiments and are expressed as corrected immunodensity values normalized for β-actin and for either histone H3 or H4 immunodensity as well as to a standard sample (STD) loaded in the same gel. Representative images of studied histone posttranslational modification (HPTM) immunodensities in antipsychotic (AP)-free, AP-treated individuals, and in matched controls are shown. Data correspond to 21 individuals with schizophrenia (11 antipsychoticfree, 10 antipsychotic-treated) and 21 matched controls. *p < 0.05 v. matched controls (2-tailed paired t test). **p < 0.01 v. matched controls (2-tailed paired t test).

Figure 2

(A) Histone deacetylase (HDAC) activity in the dorsolateral prefrontal cortex of individuals with schizophrenia (SZ) and matched controls (CTL) adjusted to Michaelis–Menten nonlinear regression model. Values are expressed as converted substrate in nM every minute per μg protein. HDAC activity parameters for (B) maximal velocity (V_max) and (C) Michaelis constant (K_M). Data correspond to 18 individuals with schizophrenia (10 antipsychotic [AP]-free, 8 antipsychotic-treated) and 18 matched controls.*p < 0.05 v. matched controls (2-tailed paired t test). **p < 0.01 v. matched controls (2-tailed paired t test).

Figure 3

Protein expression levels of (A) histone deacetylase 1 (HDAC1), (B) HDAC2, and (C) HDAC4 in the dorsolateral prefrontal cortex of individuals with schizophrenia (SZ) and matched controls (CTL). The data shown are mean values of 3–4 independent experiments and are expressed as corrected immunodensity values normalized for β-actin as well as to a standard sample (STD) loaded in the same gel. Representative images of studied HDAC immunodensity in antipsychotic (AP)-free and antipsychotic-treated individuals and in matched controls are shown. Data correspond to 21 individuals with schizophrenia (11 antipsychotic-free, 10 antipsychotic-treated) and 21 matched controls. *p < 0.05 v. matched controls (2-tailed paired t test).