Caveolin-1 in extracellular matrix vesicles secreted from osteoblasts.
Caveolin-1 is an essential and signature protein of caveolae, which are small invaginations of the plasma membrane enriched in cholesterol and sphingolipids. Although high levels of expression of caveolin-1 have been demonstrated in osteoblasts as well as endothelial cells, fibroblasts, and muscular cells, the role of caveolin-1 in osteoblasts has not been clarified. Here, we show that caveolin-1 is secreted from osteoblasts in the form of matrix vesicles; extracellular vesicles released from the plasma membrane of osteoblasts. In this study, caveolae and matrix vesicles were similarly enriched in cholesterol and sphingomyelin in fractions isolated from mineralizing MC3T3-E1 cells. Interestingly, in the MC3T3-E1 cells caveolin-1 was enriched in the matrix vesicle fraction as well as the caveolar membrane fraction, and the amount of caveolin-1 in the matrix vesicle fraction increased as differentiation progressed. Localization of caveolin-1 in matrix vesicles was also confirmed in murine tibia. Furthermore, overexpression of caveolin-1 enhanced matrix calcification in MC3T3-E1 cells, whereas knockdown of caveolin-1 diminished it. These results suggest that secreted caveolin-1 as a component of matrix vesicles may play an important role in osteoblast calcification.
Sawada
Naoki
N
Department of Clinical Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan.
Taketani
Yutaka
Y
Amizuka
Norio
N
Ichikawa
Masako
M
Ogawa
Chiharu
C
Nomoto
Kaori
K
Nashiki
Kunitaka
K
Sato
Tadatoshi
T
Arai
Hidekazu
H
Isshiki
Masashi
M
Segawa
Hiroko
H
Yamamoto
Hironori
H
Miyamoto
Ken-Ichi
K
Takeda
Eiji
E
D016475:3T3 Cells; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D002113:Calcification, Physiologic; D051242:Caveolin 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002784:Cholesterol / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D005109:Extracellular Matrix / Q000378:metabolism; D015870:Gene Expression; D051379:Mice; D016253:Microscopy, Immunoelectron; D010006:Osteoblasts / Q000378:metabolism* / Q000648:ultrastructure; D010710:Phosphates / Q000378:metabolism; D034622:RNA Interference; D022142:Secretory Vesicles / Q000378:metabolism; D013109:Sphingomyelins / Q000378:metabolism; D013977:Tibia / Q000378:metabolism / Q000648:ultrastructure
D051242:Caveolin 1; D017931:DNA Primers; D010710:Phosphates; D013109:Sphingomyelins; D002784:Cholesterol; D000469:Alkaline Phosphatase