Osteogenic capillaries - new aspect of endochondral ossification

2020 Fiscal Year Final Research Report

• Project/Area Number: 17H04015
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: General anatomy (including histology/embryology)
• Research Institution: Keio University
• Principal Investigator: MATSUO Koichi 慶應義塾大学, 医学部(信濃町), 教授 (40229422)
• Co-Investigator(Kenkyū-buntansha): 黒田 有希子 慶應義塾大学, 医学部(信濃町), 助教 (70455343)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 耳小骨 / 聴覚骨芽細胞 / ミネラリゼーション / 蝸牛

Outline of Final Research Achievements

Auditory ossicles in the middle ear and bony labyrinth of the inner ear are highly mineralized in adult mammals. Cellular mechanisms underlying formation of dense bone during development are unknown. Here, we found that osteoblast-like cells synthesizing highly mineralized hearing-related bones produce both type I and type II collagens as the bone matrix, while conventional osteoblasts and chondrocytes primarily produce type I and type II collagens, respectively. Furthermore, these osteoblast-like cells were not labeled in a "conventional osteoblast"-specific green fluorescent protein mouse line. Type II collagen-producing osteoblast-like cells were not chondrocytes as they express osteocalcin, localize along alizarin-labeled osteoid, and form osteocyte lacunae and canaliculi. Therefore, we conclude that these type II collagen-producing hypermineralizing osteoblasts (named auditory osteoblasts) represent a new osteoblast subtype.

Free Research Field

骨代謝学

Academic Significance and Societal Importance of the Research Achievements

耳小骨が硬いことにより音の伝導効率が良くなること、蝸牛骨が硬いことにより、蝸牛の構造的な安定性が増すものと考えられており、本研究はそのような硬い骨を生み出す骨芽細胞が、これまで知られていた骨芽細胞とは異なることを、いくつもの異なる研究手法を組み合わせて示した。実際に、骨の石灰化異常をきたす疾患では、難聴を認めるものも知られている。本研究は、骨代謝異常と難聴の関係を理解するための手がかりとなるものであるとともに、中耳や内耳で聴覚器を構成する骨組織に特化した骨芽細胞の存在が明らかになった。