Roles of the endoplasmic reticulum stress transducer OASIS in fracture healing.

A new type of endoplasmic reticulum (ER) stress transducer, Old Astrocyte Specifically Induced Substance (OASIS), which is induced by bone morphogenetic protein-2 (BMP2), has been reported to activate the transcription of type I collagen and contribute to the secretion of bone matrix proteins in osteoblasts. Here, we examined the role of OASIS in fracture healing using the fracture models in wild-type (WT) and OASIS(-/-) mice. We found that the expression of OASIS mRNA was induced after fracture. Micro-computed tomography indicated that the callus density of OASIS(-/-) mice was less than that of WT mice, and the newly formed bone in OASIS(-/-) mice exhibited a decrease of the bone volume by bone morphometric analysis. Biomechanically, the callus bone strength of OASIS(-/-) mice was inferior to that of WT mice. Based on RT-PCR, in situ hybridization, immunohistochemical, and electrophoretic analyses, it was clarified that the synthesis of type I collagen was impaired in OASIS(-/-) mice. Electron microscopic analysis revealed that OASIS(-/-) osteoblasts in the fracture callus contained the abnormal expansion of the ERs, similar to OASIS(-/-) osteoblasts in the normal skeletal development. Thus, OASIS may play a role in bone formation through the expression of type I collagen and the secretion of bone matrix proteins in fracture healing.