ReviewMatrix vesicles: Are they anchored exosomes?

- Matrix vesicles are unique extracellular membrane-bound microparticles that serve as initial sites for mineralization.
- Exosomes, a product of the endosomal pathway, share many characteristics of matrix vesicles.
- Analyses of size, morphology and lipid and protein content indicate that matrix vesicles and exosomes are homologous structures.
- Processing of exosomes in vertebrate hard tissues explain in part how cells control the earliest stages of mineral deposition.
- The exosome concept suggests a new mechanism for the transfer of signaling molecules between cells within the growth plate.

Numerous studies have documented that matrix vesicles are unique extracellular membrane-bound microparticles that serve as initial sites for mineral formation in the growth plate and most other vertebrate mineralizing tissues. Microparticle generation is not confined to hard tissues, as cells in soft tissues generate similar structures; numerous studies have shown that a common type of extracellular particle, termed an exosome, a product of the endosomal pathway, shares many characteristics of matrix vesicles. Indeed, analyses of size, morphology and lipid and protein content indicate that matrix vesicles and exosomes are homologous structures. Such a possibility impacts our understanding of the biogenesis, processing and function of matrix vesicles (exosomes) in vertebrate hard tissues and explains in part how cells control the earliest stages of mineral deposition. Moreover, since exosomes influence a spectrum of functions, including cell-cell communication, it is suggested that this type of microparticle may provide a mechanism for the transfer of signaling molecules between cells within the growth plate and thereby regulate endochondral bone development and formation.