Monitoring Endoplasmic Reticulum Peroxynitrite Fluctuations in Primary Tendon-Derived Stem Cells and Insights into Tendinopathy

Tendinopathy is one of the most prevalent musculoskeletal disorders, significantly affecting the quality of life of patients. Treatment outcomes can be improved with an early diagnosis and timely targeted interventions. Increasing evidence indicates that ROS and endoplasmic reticulum (ER) stress play key roles in modulating the differentiation processes of tendon-derived stem cells (TDSCs), thereby contributing to the initiation and progression of tendinopathy. However, the relationship between ONOO- and the differentiation process, as well as the various stages of tendinopathy, remains unexplored. Herein, we developed two highly specific and sensitive fluorescent probes (Rod-Cl and Rod-Br) for detecting ONOO- in the ER. Rod-Br can detect basal levels of ONOO- in the ER of TDSCs and measure ONOO- levels in primary TDSCs stimulated by interleukin-1β over various durations, allowing for comparisons between chondrogenic and osteogenic differentiation and ER stress levels. Additionally, we examined ONOO- variations in different stages of tendinopathy and treatment rat models in vivo and discussed the potential mechanisms. This research provides a robust tool for analyzing ONOO- dynamics in the tenogenic and osteogenic differentiation of TDSCs, offering new insights into the pathophysiology and treatment of tendinopathy.