Role of cartilage-derived anti-angiogenic factor, chondromodulin-I, duringendochondral bone formation

Objective: Cartilage is a typical avasclar tissue that exhibits powerful re sistance to angiogenesis or vascular invasion. We previously identified a c artilage-specific 25 kDa glycosylated protein, chondromodulin-I (ChM-I), as anti-angiogenic factor. Taking advantage of ectopic bone formation and xen ograft tumour model by human chondrosarcoma cell line OUMS-27, we examined how ChM-I is involved in switching of angiogenesis in cartilage. Design: Gene expression pattern of ChM-I was examined in 4-week-old mice an d mouse embryos by northern blot analysis and in situ hybridization. To eva luate the effect of ChM-I on ectopic bone formation, guanidine extracts of demineralized bone matrix were mixed with the ChM-I-bound heparin-Sepharose beads and were implanted onto the fasciae of back muscle of 6-week old nud e mice. To analyse the effect of ChM-I on tumour angiogenesis, the level of ChM-I mRNA in cartilaginous tumours was assessed by competitive PCR, and c ompared with that of articular cartilage. Then, human chondrosarcoma OUMS-2 7 cells were inoculated into the back of nude mice to form a tumour about 4 5 mm(3) in size. Recombinant ChM-I protein was administrated into OUMS-27 x enograft tumours for the initial 5 days to study its effect against tumour- angiogenesis. Results: ChM-I gene was specifically expressed in cartilage of 4-week-old m ice. Eye and thymus were also identified as minor expression sites. However , during endochondral bone development, cartilage changes its character fro m anti-angiogenic into angiogenic prior to the replacement of calcified car tilage by bone. In embryos, ChM-I mRNA was expressed in proliferative and u pper hypertrophic cartilage zones in the developing cartilaginous bone rudi ments, but completely abolished in lower hypertrophic and calcified cartila ge zones. Purified ChM-I protein apparently inhibited vascular invasion int o cartilage induced by the implantation of demineralized bone matrix in nud e mice, leading to the inhibition of replacement of cartilage. The level of ChM-I transcripts in the lower-grade chondrosarcomas was substantially red uced to several hundreds or less in the lower-grade chondrosarcomas, compar ed with that of articular cartilage or other benign cartilage tumours. The local administration of recombinant human ChM-I almost completely blocked t umour angiogenesis and growth in the human chondrosarcoma xenografts in mic e. Conclusions: ChM-I is involved in the anti-angiogenic property of cartilage and its absence creates a permissive microenvironment for vascular invasio n into cartilage under physiological and pathological conditions. (C) 2001 OsteoArthritis Research Society International.