Positive feedback loop PU.1-IL9 in Th9 promotes rheumatoid arthritis development

Area of Science:

• Immunology
• Rheumatology
• Molecular Biology

Background:

• T helper 9 (Th9) cells, characterized by PU.1 and interleukin-9 (IL-9) production, are implicated in autoimmune diseases.
• The specific role of the PU.1-IL-9 axis in rheumatoid arthritis (RA) pathogenesis requires further elucidation.

Purpose of the Study:

• To investigate the relationship between PU.1, IL-9, and RA pathogenesis.
• To explore the therapeutic potential of targeting the PU.1-IL-9 axis in RA.

Main Methods:

• Quantified PU.1 and IL-9 levels in RA patients using ELISA, Western blotting, and immunohistochemistry.
• Utilized knockout mouse models (PU.1, IL-9, IL-9R) and therapeutic interventions (PU.1 inhibitor, IL-9 blocking antibody) in arthritis models (CAIA, CIA).
• Conducted in vitro studies with siRNAs and recombinant IL-9, alongside mechanistic investigations (luciferase reporter, Western blotting, Chip-qPCR).

Main Results:

• Elevated IL-9 expression in RA patients correlated positively with clinical disease markers.
• Targeting PU.1 and IL-9 significantly reduced inflammation in collagen antibody-induced arthritis (CAIA) and collagen-induced arthritis (CIA) models.
• In vitro studies confirmed IL-9's pro-inflammatory role, particularly in activating macrophages and fibroblast-like synoviocytes, revealing a positive feedback loop where PU.1 activates IL-9 transcription and IL-9 induces PU.1 via the IL-9R-JAK1/STAT3 pathway.

Conclusions:

• The PU.1-IL-9 axis forms a critical positive feedback loop contributing to Th9 cell dysregulation in RA.
• Targeting the PU.1-IL-9 signaling axis represents a potential therapeutic strategy for managing rheumatoid arthritis.