<Original Articles>Expression of Heat-Shock-Proteins in the Differentiation Process of Chondrocytes

Abstract

To know the role of HSP70 in chondrocytes, HSP70 expressions under heat stress or in a nonstress 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.

軟骨細胞との関連が注目されている熱ショック蛋白質の発現を, 遠沈管培養軟骨細胞と骨端軟骨板を用いて, in vitro および in vivo で検索した. 温熱ストレス下のラﾂト軟骨細胞では, 少なくとも3種類の熱ショック蛋白質の発現がみとめられ, そのうち HSP70 の誘導量が最大であった. 非ストレス下では, 遠沈管培養軟骨細胞のうち肥大軟骨細胞様細胞への分化能を有すると考えられる細胞に HSP70 の発現が認められた骨端軟骨板においては, 肥大軟骨細胞で HSP70 が誘導されていた. また, HSP70 mRNA は肥大層に隣接する増殖層および静止層の軟骨細胞で観察された. このことは, 肥大軟骨細胞への分化能を有する軟骨細胞では, すでに HSP70 mRNA が誘導されていることを示している. これらの結果から, HSP70 の発現が軟骨細胞の分化と関係していることが推察された.