Abstract
Extracellular vesicles (EVs) are newly appreciated regulators of tissue homeostasis and a means of intercellular communication. Reports have investigated the role of EVs and their cargoes in cellular regulation and have tried to fine-tune their biotechnological use, but to date very little is known on their function in bone biology. To investigate the relevance of EV-mediated communication between bone cells, we isolated EVs from primary mouse osteoblasts and assessed membrane integrity, size, and structure by transmission electron microscopy (TEM) and fluorescence-activated cell sorting (FACS). EVs actively shuttled loaded fluorochromes to osteoblasts, monocytes, and endothelial cells. Moreover, osteoblast EVs contained mRNAs shared with donor cells. Osteoblasts are known to regulate osteoclastogenesis, osteoclast survival, and osteoclast function by the pro-osteoclastic cytokine, receptor activator of nuclear factor κ-B ligand (Rankl). Osteoblast EVs were enriched in Rankl, which increased after PTH treatment. These EVs were biologically active, supporting osteoclast survival. EVs isolated from rankl-/- osteoblasts lost this pro-osteoclastic function, indicating its Rankl-dependence. They integrated ex vivo into murine calvariae, and EV-shuttled fluorochromes were quickly taken up by the bone upon in vivo EV systemic administration. Rankl-/- mice lack the osteoclast lineage and are negative for its specific marker tartrate-resistant acid phosphatase (TRAcP). Treatment of rankl-/- mice with wild-type osteoblast EVs induced the appearance of TRAcP-positive cells in an EV density-dependent manner. Finally, osteoblast EVs internalized and shuttled anti-osteoclast drugs (zoledronate and dasatinib), inhibiting osteoclast activity in vitro and in vivo. We conclude that osteoblast EVs are involved in intercellular communication between bone cells, contribute to the Rankl pro-osteoclastic effect, and shuttle anti-osteoclast drugs, representing a potential means of targeted therapeutic delivery. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.
Highlights
Extracellular vesicles (EVs) represent a large group of complex membrane structures ranging from 40 nm to 1000 nm in diameter.[1,2,3,4,5,6] They are phospholipidic bilayers encompassing cellular constituents, classified mainly according to their size and mechanisms of biogenesis.[1,7] EVs generally comprise two different classes: small exosomes, of endocytic origin, and microvesicles, arising by budding from the plasma membrane.When EVs were first observed, they were considered a product of cellular wasting and nonspecific debris.[2]
To investigate whether physiologic cell-to-cell communication in bone cells could involve EVs, we focused on osteoblasts, the active matrix-forming cell type in the bone, examining clues of intercellular communication based on EV exchange
Because we noted that PTH increased EV production by osteoblasts (Fig. 1C), and given that PTH is a well-known inducer of receptor activator of nuclear factor k-B ligand (Rankl) expression,(30) we evaluated the proportion of osteoblast-derived EVs which were Rankl-positive following treatment with 1 Â 10–7M rhParaThyroid Hormone (rhPTH)
Summary
Extracellular vesicles (EVs) represent a large group of complex membrane structures ranging from 40 nm to 1000 nm in diameter.[1,2,3,4,5,6] They are phospholipidic bilayers encompassing cellular constituents, classified mainly according to their size and mechanisms of biogenesis.[1,7] EVs generally comprise two different classes: small exosomes, of endocytic origin, and microvesicles, arising by budding from the plasma membrane.When EVs were first observed, they were considered a product of cellular wasting and nonspecific debris.[2]. Bone is a dynamic tissue hosting finely tuned metabolic processes aimed at guaranteeing the health of the bone tissue itself and that of other organs.[23] To this aim, bone harbors an intricate and strictly synchronized remodeling process in which the bone-forming cells (osteoblasts), the bone-resorbing cells (osteoclasts), and the bone-sensing cells (osteocytes) have an intimate crosstalk, with coordinated and controlled coupling. This relationship induces a tightly regulated influence on the activities and functions of these cells. Since the first pivotal molecule in osteoblast-osteoclast coupling was identified,(24,25) more and more pathways and communication mechanisms between bone cells have been brought to light
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
