abs: IL-1b in Tendon Injury Enhances MSC Function
_{Large Animal Scientific Abstracts}

Mesenchymal stem cell (MSC) therapy has improved tissue architecture and reinjury rates in equine tendon injury. However, recent insight indicates therapy can be enhanced as MSCs exposed to tissue inflammation (deemed MSC licensing) have additional reparative effect. Previously, our laboratory identified interleukin (IL)-1b and IL-6 as the predominant cytokines present in surgically induced equine superficial digital flexor tendon injury, both at a peak concentration of 2 ng/ml. Therefore, the study objective was to evaluate changes in MSC gene and protein expression following in vitro licensing with IL-1b and IL-6 at this concentration. Bone marrow-derived MSCs were grown for 72 hours in standard MSC media (naïve control) or in standard media containing IL-1b or IL-6 at 2 ng/ml as licensed MSCs. RNA was isolated and outsourced for RNA sequencing. Supernatant was collected and protein expression determined via ELISA. IL-1b licensing, but not IL-6, induced MSC expression of numerous significant differentially expressed genes (DEGs) that could enhance tendon healing through vascular development (ANGPTL4, VEGF), ECM remodeling (COL5A1/A2, ADAMTS4/5, TIMP1/3), and immunomodulation (IL6, PTGS2, NOS2).  Additionally, downstream protein expression was confirmed, and compared to naïve cells, a significant increase in IL-6 (p=0.0126), VEGF (p=0.0162), and PGE-2 (p=0.0193) were measured in culture supernatants of IL-1b licensed MSCs. These data suggest that MCSs exposed to IL-1b at a concentration found in acute tendon injury could impart additional reparative benefit to the healing tendon compared to their naïve counterparts. These data support further work examining the in vitro interaction of IL-1b licensed MSCs and tenocytes