Organotypic Epigenetic Signature Predicts Bone and Marrow Niche Forming Capacity of Stromal Progenitors in a Novel Mouse Model in Vivo.

Abstract 2987

Mesenchymal stem/progenitor cells (MSPCs) from numerous tissues are currently tested in clinical trials despite a limited understanding of their in vivo behavior. In this study we used MSPCs from adult and fetal tissues to select the appropriate source for clinical application. We asked whether MSPCs derived from human bone marrow (BM), white adipose tissue (WAT) and umbilical cord (UC), compared to skin fibroblasts, bear an equivalent bone and marrow niche formation potential with of in vivo. Furthermore we evaluated attraction and engraftment of murine as well as human hematopoietic stem/progenitor cells (HSPCs) into newly formed MSPC-derived niches. To elucidate potential mechanisms responsible for a tissue-specific MSPC potential after transplantation gene expression profiling and DNA methylation analysis on a novel high resolution 450K-CpG methylation array were employed.

MSPCs were transplanted subcutaneously to test for their spontaneous bone and marrow niche formation potential in immune-deficient NSG mice (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ). BM-derived MSPC transplantation reproducibly led to the development of mature bone (17/17 donors) through an endochondral ossification process leading to subsequent marrow niche formation. Additionally, these newly formed hematopoietic microenvironments attracted complete mouse hematopoiesis including immature lineage negative, Sca-1 positive, c-kit positive (LSK) HSPCs. Non-BM derived MSPCs completely lacked bone and marrow niche-forming potential and did not attract hematopoietic cells (0/9 donors). Induction of human hematopoietic chimerism through transplantation of umbilical cord blood (UCB)-derived human CD34+ HSPCs in advance of subcutaneous ectopic bone and marrow development resulted in immigration of re-transplantable human hematopoiesis into extra-medullary ossicles. Comparative 450K-CpG methylation array profiling of MSPCs revealed a tissue-specific epigenetic signature virtually corresponding to the in vivo differentiation. MSPCs from BM but neither fibroblasts nor MSPCs from WAT or UC showed epigenetically imprinted human bone and marrow niche (HuNiche) formation capacity favoring BM-MSPCs for skeletal regeneration. This novel HuNiche model should be ideally suited for studying normal and malignant hematopoiesis regulation in an ectopic human marrow with subsequent human hematopoietic engraftment that mimics clinical BM transplantation reality.