HERV-W upregulation expression in bipolar disorder and schizophrenia: unraveling potential links to systemic immune/inflammation status

Bipolar disorder (BD) and schizophrenia (SZ) are the two main mental disorders with unknown etiology that significantly impact individuals’ quality of life. The potential pro-inflammatory role in their pathogenesis is postulated and Human Endogenous Retrovirus W (HERV-W) is an emerging candidate to modulate this pathogenic finding. HERVs, ancient retroviruses in the human genome, may play roles in inflammation and disease pathogenesis. Despite HERVs’ involvement in autoimmune diseases, their influence on mental disorders remains underexplored. Therefore, the aim of this study was to assess the level of HERV-W-env expression and the systemic inflammatory profile through the concentration of IL-2, IL-4, IL-6, IL-10, TNF-α and INF-γ cytokines in BD and SZ patients. All participants showed HERV-W-env expression, but its expression was higher in mental disorder patients (p < 0.01) than in control. When separated, SZ individuals exhibited higher HERV-W expression than the control group (p < 0.01). Higher serum levels of TNF-α and IL-10 were found in BD (p = 0.0001 and p = 0.001, respectively) and SZ (p = 0.01) and p = 0.01, respectively) than in the control group, while SZ showed decreased levels IFN-γ and IL-2 as compared to controls (p = 0.05) and BD patients (p = 0.05), respectively. Higher TNF-α/IL-4 and TNF-α/IL-10 ratios, and lower IFN-γ/IL-10 were observed in BD and SZ patients than controls. Significant negative correlation between HERV-W-env expression and IL-10 (r=-0.47 p < 0.05), as well as positive correlations between HERV-W-env expression and TNF-α/IL-10 or IFN-γ/IL-10 ratios (r = 0.48 p < 0.05 and r = 0.46 p < 0.05, respectively) were found in BD patients. These findings suggest not only a potential link between HERV-W-env expression both in BD and SZ, but also a possible involvement of systemic inflammatory status in BD patients.