CD34 defines an osteoprogenitor cell population in mouse bone marrow stromal cells

Bone marrow stromal cells (BMSCs, also known as bone marrow-derived mesenchymal stem cells) and their progenitors have been identified based on retrospective functional criteria. CD markers are employed to define cell populations with distinct functional characteristics. However, defining and prospective isolation of BMSCs and committed progenitors are lacking. Here, we compared the transcriptome profile of CD markers expressed at baseline and during the course of osteoblast and adipocyte differentiation of two well-characterized osteogenic-committed murine BMSCs (mBMSC(Bone)) and adipogenic-committed mBMSCs (mBMSC(Adipo)), respectively. Bioinformatic analysis revealed the presence of a core set of canonical mBMSC CD markers with comparable expression levels in mBMSC(Bone) and mBMSC(Adipo) at baseline and during their differentiation. We identified 11 CD markers that are differentially expressed between mBMSC(Adipo) and mBMSC(Bone). Among these, we identified osteoprogenitor-associated CD markers expressed only in mBMSC(Bone): CD34, CD54, CD73, CD132, CD200, CD227 and adipoprogenitor-associated CD markers expressed only in mBMSC(Adipo): CD53, CD80, CD134, CD141 and CD212. FACS analysis confirmed these results. We selected CD34 for further analysis. CD34 was expressed at baseline of mouse stromal cell line ST2, primary mBMSCs, mBMSC(Bone) and its expression decreased during osteoblast differentiation. FACS-sorted CD34(+) primary mBMSCs exhibited higher expression of 70% osteoblast-associated genes, and formed significantly higher heterotopic bone in vivo when implanted subcutaneously in immune-deficient mice compared with CD34(-) primary mBMSCs. Our results demonstrate that a set of CD markers can distinguish osteoprogenitor versus adipoprogenitor populations of mBMSCs. CD34 is suitable for prospective isolation of mouse bone marrow osteoprogenitors.