Prospective isolation of human bone marrow stromal cell subsets: A comparative study between Stro-1-, CD146- and CD105-enriched populations

Stro-1 has proved an efficacious marker for enrichment of skeletalstem and progenitor cells although isolated populations remain heterogeneous, exhibitingvariable colony-forming efficiency and osteogenic differentiation potential. Theemerging findings that skeletal stem cells originate from adventitial reticular cellshave brought two further markers to the fore including CD146 and CD105 (both primarilyendothelial and perivascular). This study has compared CD146-, CD105- and Stro-1(individual and in combination)-enriched human bone marrow stromal cell subsets andassessed whether these endothelial/perivascular markers offer further selection overconventional Stro-1. Fluorescent cell sorting quantification showed that CD146 and CD105both targeted smaller (2.22% ± 0.59% and 6.94% ± 1.34%, respectively) and potentiallydifferent human bone marrow stromal cell fractions compared to Stro-1 (16.29% ± 0.78%).CD146+, but not CD105+, cells exhibited similar alkaline phosphatase–positivecolony-forming efficiency in vitro and collagen/proteoglycan deposition in vivo toStro-1+ cells. Molecular analysis of a number of select osteogenic and potentialosteo-predictive genes including ALP, CADM1, CLEC3B, DCN, LOXL4, OPN, POSTN and SATB2showed Stro-1+ and CD146+ populations possessed similar expression profiles. A discretehuman bone marrow stromal cell fraction (2.04% ± 0.41%) exhibited positiveimmuno-labelling for both Stro-1 and CD146. The data presented here show that CD146+populations are comparable but not superior to Stro-1+ populations. However, this studydemonstrates the critical need for new candidate markers with which to isolatehomogeneous skeletal stem cell populations or skeletal stem cell populations whichexhibit homogeneous in vitro/in vivo characteristics, for implementation within tissueengineering and regenerative medicine strategies