The roles between M2a cells and CHI3L1 in IDD was demonstrated by Li et al. through rat IDD models: M2a cells generated CHI3L1 protein and acted on the underlying receptor IL-13R, mediating ECM degradation in NP cells through ERK and JNK-specific pathways rather than p38 pathways. Here, CHI3L1 is linked to intervertebral disk degenerative disorder.