Isolation and characterization of bone mesenchymal cell small extracellular vesicles using a novel mouse model.

ABSTRACT

Extracellular vesicles (EVs) are key mediators of cell-cell communication and are involved in transferring specific biomolecular cargo to recipient cells to regulate their physiological functions. A major challenge in the understanding of EV function in vivo is the difficulty ascertaining the origin of the EV particles. The recent development of the "Snorkel-tag", which includes EV-membrane-targeted CD81 fused to a series of extra-vesicular protein tags, can be used to mark EVs originating from a specific source for subsequent isolation and characterization. We developed an in vivo mouse model, termed "CAGS-Snorkel", which expresses the Snorkel-tag under the control of the Cre-lox system, and crossed this mouse with either Prx1-Cre (mesenchymal progenitors) or Ocn-Cre (osteoblasts/osteocytes) and isolated Snorkel-tagged EVs from the mouse bone marrow plasma using a magnetic bead affinity column. miRNA-sequencing was performed on the isolated EVs, and although similar profiles were observed, a few key miRNAs involved in bone metabolism (miR-106b-5p, miRs-19b-3p and miRs-219a-5p) were enriched in the Ocn-derived relative to the Prx1-derived EV subpopulations. To characterize the effects of these small EVs on a bone cell target, cultured mouse bone marrow stromal cells (mBMSCs) were treated with Prx1 or Ocn EVs, and mRNA-sequencing was performed. Pathways involved in ossification, bone development and extracellular matrix interactions were regulated by both EV subpopulations, whereas a few pathways including advanced glycation end-products (AGE) signaling, were uniquely regulated in the Ocn EV subpopulation, underlying important biological effects of specific EV subpopulations within the bone marrow microenvironment. These data demonstrate that EV isolation in vivo using the CAGS-Snorkel mouse model is a useful tool in characterizing the cargo and understanding the biology of tissue-specific EVs. Moreover, while bone mesenchymal cell populations share a common EV secretory profile, we uncover key differences based on the stage of osteoblastic differentiation that may have important biological consequences.

Extracellular vesicles (EVs) are small, lipid-based particles that are produced by all cells in the body, and function as a method of communication among different cells in a particular microenvironment. However, identification of the source of the EVs is difficult following export from the cell which the EV is produced. To facilitate the identification and characterization of the active molecules contained within EVs from a particular cell-type, we developed a new mouse model (CAGS-Snorkel) which allows for identification of the EV source cell using specific protein molecules on the EVs in only one particular cell- or tissue-type. As a proof-of-principle, we compared the microRNA EV cargo in cells from early bone cell progenitors and mature bone cells in the bone marrow microenvironment. We find that a number of microRNAs, molecules involved in the function and regulation of cellular processes, are expressed both in common and specifically within those two cell types. Notably, when purified EV subpopulations from these cell types were used to treat bone cell cultures, we find both common and unique gene expression and molecular pathway profiles. This work describes a new mouse model that will be useful in understanding how EVs function to carry important cellular information.