TEK and intervertebral disk degenerative disorder: Sakai et al. further revealed that angiopoietin‐1, a ligand of Tie2, suppressed apoptosis and promoted the proliferation of Tie2+ cells, enabling the development of a strategy to stimulate ANG‐1 to enhance Tie2+ progenitor cells for prevention of IDD.117 Later, the usefulness of the surface marker Tie2 was validated in a bovine coccygeal model.119