Novel Mouse Model for Tissue-specific Extracellular Vesicle Isolation and Characterization

Extracellular vesicles (EVs) are key mediators of intercellular communication, with important roles in numerous physiological and pathological processes, including profound effects on bone metabolism. These small membrane-bound vesicles are produced and released in the extracellular environment by virtually all cell types, including cells in the osteogenic lineage such as bone marrow-derived mesenchymal stem cells (MSCs), osteoblasts, osteoclasts and osteocytes. EVs serve as potent carriers of bioactive molecules, such as nucleic acids, proteins, lipids and metabolites, where they can influence recipient cells through fusion with target cell membranes to deliver these functional biomolecules. However, once released, the source cell of the EV is difficult to ascertain with any certainty. To overcome this obstacle, we developed a conditional (e.g. Cre-mediated) mouse model that expresses an EV tag, containing a fusion of CD81 and multiple C-terminal tags, termed the “Snorkel-tag”. By crossing with a Cre of interest, representing a specific cell-type or tissue, the specific EV subpopulations that are released can be isolated using antibody affinity columns. We crossed the CAGS-Snorkel mouse with Prx1- and Ocn-Cre, representing cell-types in the early vs late stages of osteoblast differentiation, isolated EVs from bone marrow plasma, and treated mouse bone marrow stromal cells (mBMSCs) with Prx1-EVs, Ocn-EVs or All-EVs (isolated using a Pan EV Isolation Kit [Miltenyi Biotec]) for 3 days and performed bulk RNA-sequencing. We found unique transcriptional and pathway signatures elicited by the different EV subpopulations in the mBMSCs, suggesting that EVs from diverse sources have distinct biological activities. Mouse Models: We crossed the CAGS-Snorkel mouse with either the Prx1-Cre (n=5, 2 male/3 female) or Ocn-Cre (n=5, 2 male/3 female).To serve as a control EV sample, we also used wild-type (WT) mice (n=5, 2 male/3 female). For each group (Prx1-EVs, Ocn-Evs, All-EVs), bone marrow plasma was collected from the n=5 mice per group and pooled to generate a single bone marrow plasma sample for each group. All mice were in the C57BL/6N background and all mice were 6 months old at sacrifice. EV Isolation and RNA sequencing: EVs were isolated from the pooled bone marrow plasma from these mice using an HA-antibody magnetic-bead affinity column and mouse bone marrow stromal cells (mBMSCs) were treated with these EV subpopulations for 3 days. RNA was isolated from the EV-treated mBMSCs using the Rneasy Plus Kit (Qiagen) and bulk mRNA-sequencing was performed.