Adipose derived stem cell activation by macrophages and tendon fibroblasts

Tendon injuries are common, and healing often fails due to an over-exuberant inflammatory response and a lack of regeneration. Inflammatory cells play key roles in these processes, with a balance between classically activated pro-inflammatory M1 macrophages and alternatively activated inflammatory resolving M2 macrophages. Adipose-derived mesenchymal stem cells (ASCs) can dampen the pro-inflammatory effectsof macrophages, promote a regenerative environment, and enhance healing. Therefore, the goal of the study was to understand how ASCs are activated by macrophages in vitro. In vitro co-culture experiments were carried out with ASCs, macrophages, and tendon fibroblasts. RNA-seq and qRT-PCR were performed to determine expression patterns of activated ASCs. M1 macrophages prompted ASCs to upregulate pro-inflammatory signaling, matrix remodeling, and cytokine production pathways, while downregulating those related to cell adhesion and cell cycle. Conversely, TFs prompted ASCs to upregulate pathways involved in cell cycle and cytoskeleton remodeling, and to downregulate pathways associated with immune cell adhesion, inflammatory mediator production, and protein metabolism. The cell-specific activation profiles indicate a possible switch in ASC paracrine signaling depending on the context, from a pro-inflammatory pattern in response to M1 macrophages to a proliferative pattern in response to TFs. Understanding crosstalk between ASCs, TFs, and macrophages is essential for developing stem cell-based therapeutic strategies.