The influence of Chm-I knockout on ectopic cartilage regeneration and homeostasis maintenance.

Ectopic ossification of mesenchymal stem cell (MSC) regenerated cartilage has greatly restricted its application in repairing subcutaneous cartilage defects (such as nasal or auricular). Different from MSCs, chondrocytes can maintain stable chondrogenic phenotype in ectopic microenvironment, which was speculated to be related with the existence of antiangiogenic factors such as Chondromodulin-I (Chm-I). Therefore, the purpose of this study was to illustrate whether Chm-I was indispensable for stable ectopic chondrogenesis by chondrocyte, which may help to solve the problem of MSC ectopic ossification in the future. The current study demonstrated that Chm-I knockout did not obviously influence articular cartilage development in situ. However, native articular cartilage from Chm-I knockout (Chm-I(-/-), KO), but not wild-type (WT) mice, showed obvious ossification after subcutaneously implanted into nude mice for 16 days. Interestingly, cell morphology, cartilage-specific matrix expression, and pellet culture demonstrated that Chm-I knockout had no obvious influence on the phenotype, function, and chondrogenic ability of chondrocytes in vitro, except that cells in the WT group proliferated a little faster than those in the KO group. Nevertheless, Chm-I knockout directly interfered with in vivo ectopic cartilage regeneration when chondrocytes were subcutaneously injected into nude mice with matrigel. Moreover, Chm-I knockout obviously compromised ectopic stability of in vitro regenerated cartilage after subcutaneous implantation. These findings indicated that Chm-I was an indispensable factor for ectopic cartilage regeneration and the maintenance of cartilage homeostasis, which may provide a clue for solving the stability problem of MSC regenerated cartilage in ectopic niche. In addition, this study also provides a novel model based on tissue engineering strategy to properly evaluate the function of other targeted genes.