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Syntaxin 4a Regulates Matrix Vesicle‐Mediated Bone Matrix Production by Osteoblasts
Author(s) -
Kawai Shinji,
Michikami Ikumi,
Kitagaki Jirouta,
Hata Kenji,
Kiyonari Hiroshi,
Abe Takaya,
Amano Atsuo,
Wakisaka Satoshi
Publication year - 2017
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.3056
Subject(s) - microbiology and biotechnology , osteoblast , chemistry , secretion , extracellular matrix , endocrinology , bone morphogenetic protein 2 , medicine , vesicle , bone cell , matrix (chemical analysis) , biology , in vitro , biochemistry , membrane , chromatography
Osteoblasts secrete matrix vesicles and proteins to bone surfaces, but the molecular mechanisms of this secretion system remain unclear. The present findings reveal the roles of important genes in osteoblasts involved in regulation of extracellular matrix secretion. We especially focused on “soluble N‐ethylmaleimide‐sensitive factor (NSF) attachment protein receptor” (SNARE) genes and identified notable Syntaxin 4a ( Stx4a ) expression on the basolateral side of the plasma membrane of osteoblasts. Furthermore, Stx4a overexpression was found to increase mineralization by osteoblastic cells, whereas Stx4a knockdown reduced levels of mineralization. Also, BMP‐4 and IGF‐1 induced the localization of Stx4a to the basolateral side of the cells. To examine the function of Stx4a in osteoblasts, we generated osteoblast‐specific Stx4a conditional knockout mice, which demonstrated an osteopenic phenotype due to reduced matrix secretion. Bone mineral density, shown by peripheral quantitative computed tomography (pQCT), was reduced in the femur metaphyseal and diaphyseal regions of Stx4a osteoblast‐specific deficient mice, whereas bone parameters, shown by micro–computed tomography (μCT) and bone histomorphometric analysis, were also decreased in trabecular bone. In addition, primary calvarial cells from those mice showed decreased mineralization and lower secretion of matrix vesicles. Our findings indicate that Stx4a plays a critical role in bone matrix production by osteoblasts. © 2016 American Society for Bone and Mineral Research.