TREM-1 and DAP12 expression in monocytes of patients with severe psychiatric disorders. EGR3, ATF3 and PU.1 as important transcription factors

Abstract INTRODUCTION: Immune activation is a characteristic of schizophrenia (SCZ), bipolar disorder (BD) and unipolar major depressive disorder (MDD). The triggering receptor expressed on myeloid cells 1 (TREM-1), its' adaptor molecule DAP12 and their transcription factor (TF) PU.1 are important key genes in inflammation and expressed in activated monocytes and microglia. AIM: To test: (1) if the expressions of TREM-1, DAP12 and PU.1 are increased in monocytes of patients with severe psychiatric disorders and (2) if PU.1 and the TFs ATF3 and EGR3 (which have been found as prominent increased monocyte genes in previous studies) are involved in the regulation of TREM-1 and DAP12 expression. METHODS: Using Q-PCR, we studied the gene expression of TREM-1, DAP12, PU.1, ATF3 and EGR3 in the monocytes of 73 patients with severe psychiatric disorders (27 recent onset SCZ patients, 22 BD patients and 24 MDD patients) and of 79 healthy controls (HC). Using in silico TF binding site prediction and in vivo chromatin immunoprecipitation (ChIP), we studied the actual binding of EGR3, ATF3 and PU.1 to the promoter regions of TREM-1 and DAP12. CONCLUSION: In this study, we provide evidence that TREM-1 gene expression is significantly increased in monocytes of SCZ and BD patients and that the TREM-1 gene is a target gene of the TFs ATF3 and EGR3. In MDD patients, PU.1 gene expression was increased with a tendency for TREM-1 gene over expression. Our observations support the concept that monocytes are in a pro-inflammatory state in severe psychiatric conditions and suggest differences in monocyte inflammatory set points between SCZ, BD and MDD.

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