IL-4 as a profibrotic mediator of cardiac fibroblast differentiation through ROS and TGF-β1 signaling

Cardiac fibroblast (CF) differentiation is crucial for the fibrotic pathologies that affect the heart, increasing CF secretory capacity and enhancing their contractile, migratory, and proliferative abilities, which favor heart stiffening and dysfunction. Therefore, identifying the mechanisms underlying this pathological process is crucial. In cardiac diseases, an acute inflammatory process occurs, characterized by the secretion of inflammatory cytokines that, over time, evolve into a reparative process aimed at restoring tissue integrity and organ function. Several anti-inflammatory molecules are released, including interleukin-4 (IL-4), which plays a significant role in fibrotic processes. However, the role of IL-4 and the mechanisms underlying CF differentiation remain unknown. In this work, we stimulated CF with 10 ng/mL IL-4, which increased the expression of CF differentiation markers, including collagen I and alpha-smooth muscle actin. Furthermore, IL-4 increased CF proliferation but reduced its migratory capacity. Additionally, IL-4 downregulated the antioxidant machinery in CF, reducing the expression of FoxO3a, catalase, and superoxide dismutase 2 (SOD2), increasing reactive oxygen species (ROS) levels, and promoting CF differentiation. In addition, IL-4 induces the synthesis and secretion of TGF-β1, and the inhibition of transforming growth factor beta 1 (TGF-β1) and SMAD3 prevents IL-4-induced CF differentiation. Finally, IL-4 reduces NF-κB activation, indicating its anti-inflammatory capacity. In contrast, the activation of NF-κB prevented the effect of IL-4 on CF differentiation. In conclusion, our results suggest that IL-4 is a novel profibrotic agent that induces CF differentiation, positioning it as an attractive pharmacological target for various heart pathologies involving cardiac fibrosis.