Expression of heat-shock-proteins in the differentiation process of chondrocytes.

To know the role of HSP70 in chondrocytes, HSP70 expressions under heat stress or in a non-stress condition were examined by using electrophoresis, immunohistochemistry, and in situ hybridization. As a result, HSP70 was observed in proliferating chondrocytes in the micro-mass cultures without heat stress. In this culture, chondrocytes maintained the terminal differentiation potency. On the other hand, HSP70 did not appear in the chondrocytes in the logarithmic growth phase of the monolayer culture. In growth plates in vivo, HSP70 expressions in the chondrocytes located in the resting and hypertrophic zones were observed with immunohistochemistry. Appearance of HSP70 mRNA was also confirmed by in situ hybridization in the proliferating zone of growth plate. HSP70 can be expressed not only in chondrocytes under heat stress but also in the cells without stress, and the expression would be related to the terminal differentiation of chondrocytes. HSP70 is surmised to promote hypertrophy and calcification by stopping protein synthesis in chondrocytes which possess terminal differentiation potency.