Fig. 9

A schematic diagram of the microenvironment changes between the normal and the degenerated meniscus. The upper side visualizes the healthy tendon, where TC1, TC2 and TC3 are dominant tenocyte populations. In this situation, TSPC could differentiate into normal subsets of tenocytes and the aberrant proliferation of blood vessels is inhibited. The lower side visualizes the degenerated tendon where the orchestrated microenvironment balance is broken. In this situation, TSPC could differentiate into chondrocytes and osteocytes, which resulted in HO. The EC1 grew and formed new blood vessels in the diseased area. The vascular permeability increased and allowed more immune cells to infiltrate the degenerated tissue. Proliferating EC1 and Mac can also act on the diseased tenocytes by expressing osteogenic and chondrogenic genes (SPP1, FN1, XIST) to promote disease progression