Updated Mechanisms of IL-6 in Human Endothelial Cells.

Interleukin-6 (IL-6) is a pleiotropic cytokine primarily involved in inflammation and vascular remodeling. While it is known to influence angiogenesis, the formation of new blood vessels, the underlying mechanisms and downstream targets in endothelial cells (ECs) remain poorly understood. This study aimed to explore the angiogenic effect of IL-6 in human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells (HMEC-1 cells) and to gain insights into the mechanistic pathways involved. We found that IL-6 promoted EC migration in a wound healing assay and stimulated tube formation in both cell types, while also enhancing blood vessel formation in the chicken chorioallantoic membrane assay. Proteomic analysis of IL-6-treated HUVECs identified pentraxin 3 (PTX3) as an IL-6-responsive factor. Subsequent validations using ELISA, qRT-PCR, and western blot confirmed increased PTX3 expression in HUVECs but revealed a downregulation in HMEC-1 cells, indicating a cell-type-specific regulatory effect of IL-6. To further elucidate the cellular response to IL-6, we assessed the expression of the IL-6 receptor subunits, IL-6Rα and gp130, in both EC types following IL-6 stimulation. qRT-PCR revealed increased gp130 gene expression, but flow cytometry showed no change in cell surface expression, while IL-6Rα surface expression increased in both EC types, supporting sustained IL-6 signaling. Overall, these findings provide updated insights into the pro-angiogenic actions of IL-6 and how it regulates PTX3 expression in human ECs.