The SHP-1 expression is associated with cytokines and psychopathological status in unmedicated first episode schizophrenia patients

BACKGROUND: Recent lines of research have boosted awareness of the immunological facets of schizophrenia. However, associations with protein tyrosine phosphatase regulators have never been reported. The aim of our study was to investigate the expression and promoter status methylation of phosphatase SHP-1, a key negative regulator of the inflammatory process, in Peripheral blood mononuclear cells (PBMCs) of Schizophrenic patients. METHODS: We enrolled fifty-four (28 men and 26 women) unmedicated first episode subjects (SC) who met DSM-IV and thirty-eight (22 men and 16 women) healthy controls (HC). The SC psychopathological status was assessed using the Positive and Negative Syndrome Scale. We evaluated SHP-1 expression by Quantitative Real-time PCR (qPCR) and Western blotting (WB) methods and promoter status methylation through PCR bisulfate. IKK/NFkB signaling was detected by WB, and medium and plasma levels of pro-inflammatory cytokines (IL-1β, IL-2, and TNF-α) by the ELISA method. SHP-1 was silenced by treating cells with specific siRNA. RESULTS: We found a significantly lower level of SHP-1 gene expression in PBMCs from SC vs. HC, consistently with which the promoter region analyzed presented significant hypermethylation. Silencing of SHP-1 expression induced higher activation of IKK/NF-kB signaling and pro-inflammatory cytokine production in ex vivo PBMCs from both SC and HC. Linear regression among patients generated a model in which SHP-1 expression explained 30% of the clinical negative symptom variance (adjusted R(2)=0.30, ANOVA p<0.001). CONCLUSIONS: Our findings are the first to suggest that impairment of SHP-1 expression is involved in the physiopathology of schizophrenia, opening fruitful new avenues for ameliorating treatment at least of negative symptoms.