Related Experiment Video
Updated: Jun 17, 2026

Software-Assisted Quantitative Measurement of Osteoarthritic Subchondral Bone Thickness
Published on: March 18, 2022
Binding characteristics of the osteoarthritis-associated protein asporin
Ikuyo Kou1, Masahiro Nakajima, Shiro Ikegawa
1Laboratory for Bone and Joint Diseases, Center for Genomic Medicine, RIKEN, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Abstract:
Asporin is an extracellular matrix (ECM) protein that regulates cartilage matrix gene expression and cartilage formation by modulating the transforming growth factor-beta (TGF-beta) signaling pathway. Our previous studies have indicated that asporin binds to TGF-beta1 directly and inhibits TGF-beta1-mediated expression of cartilage matrix genes. However, it is still unknown how asporin interacts with TGF-beta1 and influences its activity. Using competition assays, we determined that amino acids 159-205 of asporin mediate its interaction with TGF-beta1 and effectively repress TGF-beta1-induced cartilage matrix gene expression. Asporin also has a binding ability to type II collagen in vitro, but its binding pattern is different from that of TGF-beta1. In contrast with previous in vivo findings, asporin did not affect the interaction between TGF-beta1 and the TGF-beta type II receptor (TbetaRII) by itself or in the presence of type II collagen in vitro. However, in the presence of heparin/heparan sulfate, asporin inhibits the interaction between TGF-beta and TbetaRII in vitro. These findings suggest that asporin is one of the important cartilage matrix proteins that binds to the ECM and TGF-beta1 and thereby modulates interactions between TGF-beta and its signaling receptors.
Related Concept Videos
Structural Protein Function
Collagen, the most abundant protein in mammals, is found throughout the body. In connective tissue, such as skin, ligaments, and tendons, it provides tensile strength and elasticity. In bones and teeth, it mineralizes to form...
Structural Protein Function
Collagen, the most abundant protein in mammals, is found throughout the body. In connective tissue, such as skin, ligaments, and tendons, it provides tensile strength and elasticity. In bones and teeth, it mineralizes to form...
Structural Joints: Synovial Joints
Cytoskeletal Accessory Proteins
The JAK-STAT Signaling Pathway
Bone as Supporting Connective Tissue
Bone Matrix
Bone, or osseous tissue, is a connective tissue that has a large amount of two different types of matrix material. The organic matrix is similar to the matrix material found in other connective tissues, including some amount of collagen and elastic fibers. This gives strength and flexibility to the tissue. The inorganic matrix consists of mineral salts— mostly calcium salts— that give the...