An altered peripheral IL6 response in major depressive disorder

Area of Science:

• Neuroscience
• Immunology
• Genetics

Background:

• Major depressive disorder (MDD) is a prevalent psychiatric condition with a 17% lifetime prevalence.
• Emerging evidence indicates MDD is a systemic disease, not solely a brain dysfunction, with peripheral inflammation playing a key role.
• Elevated cytokine and chemokine levels in MDD patients partially normalize with antidepressant treatment, highlighting inflammation's central role.

Purpose of the Study:

• To investigate if peripheral tissues from MDD patients exhibit an aberrant transcriptional response to pro-inflammatory cytokines.
• To compare the response of dermal fibroblast cultures from MDD patients and controls to Interleukin-6 (IL6), Interleukin-1 beta (IL1β), and Tumor Necrosis Factor alpha (TNFα).

Main Methods:

• Dermal fibroblast cultures derived from MDD patients and healthy controls were treated with IL6, IL1β, TNFα, or vehicle.
• Quantitative PCR was employed to assess the expression levels of inflammation-responsive genes following RNA isolation and cDNA synthesis.

Main Results:

• Baseline expression of tested genes was comparable between MDD patients and controls.
• MDD patient fibroblasts demonstrated a diminished transcriptional response to IL6 across oxidative stress, mitochondrial function, and lipid metabolism gene sets.
• A significant increase in IL6 receptor gene transcript levels was observed in MDD fibroblasts, both at baseline and upon IL6 stimulation.
• IL6 stimulation led to increased SOCS3 induction in MDD fibroblasts, a mechanism that dampens IL6 receptor signaling.

Conclusions:

• MDD is associated with an altered transcriptional response to IL6 in peripheral tissues.
• This aberrant IL6 response may contribute to the pathophysiology of MDD.
• These findings suggest potential novel therapeutic targets for MDD focused on modulating the IL6 signaling pathway.