An ITGA11 expressing subpopulation as predictor for the donor-specific osteogenic capacity of stromal cells
Stromal progenitor cells of bone marrow origin are non-hematopoietic cells that give rise to osteoblasts and adipocytes in the postnatal organism. Marrow stromal cells (also known as mesenchymal stem cells - MSCs) are currently being employed in a large number of clinical trials for regenerative purposes post in vitro expansion. However, the clinical outcome has been variable, which might in part be due to the heterogeneity of the cells and the lack of a defined cell product with a molecular signature that favors tissue regeneration. In this study, we determined the cellular heterogeneity of primary stromal cultures and examined how inter-donor variation in subpopulation composition contributes to the differentiation potential of primary cultures. We profiled 136,014 stromal progenitors from 26 donors and identified 5 subpopulations that were linked to distinct bone-related pathways and genetic traits of bone mineral density and morphology. Abundancy of one cluster characterized by high expression of ITGA11 (integrin alpha-11) and genes related to matrix function, collagen organization, and elevated expression upon lineage commitment was positively correlated with osteoblastic differentiation capacity in vitro. In addition, ITGA11 protein expression in progenitor cells was a predictive marker for matrix mineralization in vitro and ectopic bone formation in vivo. Sorting stromal progenitors into ITGA11high and ITGA11low cells established cultures with high and low osteoblastic differentiation potential and revealed transcriptional differences reflective of the subpopulation-specific signature, which was not affected by siRNA mediated knockdown of ITGA11 expression. Our findings corroborate the presence of an extensive donor-dependent cellular heterogeneity that persists in cultured stromal cells, and that ITGA11 can be employed as a marker for isolating cells with high bone-forming potential, a feature likely to benefit clinical trials of bone regeneration. Overall design: 10x Genomics single cell RNA-seq expression profiles of 21 primary cell cultures that have been tested for their osteogenic and adipogenic differentiation capacity in vitro. Bulk RNA-seq of primary cultures from 5 donors subjected to control or ITGA11 knockdown or subjected to sorting into low and high ITGA11 surface expression.