Monitoring Endoplasmic\nReticulum Peroxynitrite Fluctuations\nin Primary Tendon-Derived Stem Cells and Insights into Tendinopathy

Tendinopathy is one of the most prevalent\nmusculoskeletal\ndisorders,\nsignificantly affecting the quality of life of patients. Treatment\noutcomes can be improved with an early diagnosis and timely targeted\ninterventions. Increasing evidence indicates that ROS and endoplasmic\nreticulum (ER) stress play key roles in modulating the differentiation\nprocesses of tendon-derived stem cells (TDSCs), thereby contributing\nto the initiation and progression of tendinopathy. However, the relationship\nbetween ONOO<sup>–</sup> and the differentiation process, as\nwell as the various stages of tendinopathy, remains unexplored. Herein,\nwe developed two highly specific and sensitive fluorescent probes\n(<b>Rod-Cl</b> and <b>Rod-Br</b>) for detecting ONOO<sup>–</sup> in the ER. <b>Rod-Br</b> can detect basal levels\nof ONOO<sup>–</sup> in the ER of TDSCs and measure ONOO<sup>–</sup> levels in primary TDSCs stimulated by interleukin-1β\nover various durations, allowing for comparisons between chondrogenic\nand osteogenic differentiation and ER stress levels. Additionally,\nwe examined ONOO<sup>–</sup> variations in different stages\nof tendinopathy and treatment rat models in vivo and discussed the\npotential mechanisms. This research provides a robust tool for analyzing\nONOO<sup>–</sup> dynamics in the tenogenic and osteogenic differentiation\nof TDSCs, offering new insights into the pathophysiology and treatment\nof tendinopathy.