IL-1β modulates inflammatory response of human bone marrow-derived MSCs and neutrophil recruitment in vitro via NF-kB-associated signaling

The variable clinical outcomes of mesenchymal stromal cell (MSC)-based therapy in acute respiratory distress syndrome (ARDS) are attributed to a variety of factors, including host microenvironmental factors. Interleukin-1β (IL-1β) has been linked to the development and progression of ARDS, and we have previously found that IL-1β could be used to predict MSC activation in vitro. However, the exact mechanisms through which IL-1β alters the MSC function and its interaction with the host immune cells remains unknown. Therefore, the aim of this study was to assess how IL-1β alters MSC function, with a specific focus on MSC-neutrophil interaction.

Human bone marrow-derived MSCs were exposed to 20 ng/ml IL-1β for 1 or 24 h. Following exposure, MSCs were analyzed using bulk RNA sequencing and key secretome proteins were measured in their conditioned medium. A transwell culture system was used to evaluate the neutrophil recruitment capacity of IL-1β-exposed MSCs, with or without NF-kB inhibition. MSCs exposed to serum free medium were used as controls in all experiments.

The sequencing data revealed that genes involved in response to biotic stimuli and immune response were altered in MSCs exposed to IL-1β compared to control cells. In particular, genes essential for neutrophil recruitment were significantly upregulated after IL-1β exposure. The functional in vitro studies further validated these results, demonstrating that MSCs exposed to IL-1β had a significantly higher neutrophil recruitment capacity compared to unstimulated MSCs. Finally, inhibition of the NF-kB pathway resulted in a significant decrease of the MSC's capacity to recruit neutrophils to levels similar as to the unstimulated control MSCs.

These data provide mechanistic insight into how inflammatory factors present in the host microenvironment might affect the interaction between MSCs and immune cells. This further highlights the need to understand the MSC mode of action, and to map out how the MSC fate might change in different host environments after administration.