The enhancer landscape predetermines the skeletal regeneration capacity of stromal cells

Abstract

Multipotent stromal cells are considered attractive sources for cell therapy and tissue engineering. Despite numerous experimental and clinical studies, broad application of stromal cell therapeutics is not yet emerging. A major challenge is the functional diversity of available cell sources. Here, we investigated the regenerative potential of clinically relevant human stromal cells from bone marrow (BMSCs), white adipose tissue, and umbilical cord compared with mature chondrocytes and skin fibroblasts in vitro and in vivo. Although all stromal cell types could express transcription factors related to endochondral ossification, only BMSCs formed cartilage discs in vitro that fully regenerated critical-size femoral defects after transplantation into mice. We identified cell type–specific epigenetic landscapes as the underlying molecular mechanism controlling transcriptional stromal differentiation networks. Binding sites of commonly expressed transcription factors in the enhancer and promoter regions of ossification-related genes, including Runt and bZIP families, were accessible only in BMSCs but not in extraskeletal stromal cells. This suggests an epigenetically predetermined differentiation potential depending on cell origin that allows common transcription factors to trigger distinct organ-specific transcriptional programs, facilitating forward selection of regeneration-competent cell sources. Last, we demonstrate that viable human BMSCs initiated defect healing through the secretion of osteopontin and contributed to transient mineralized bone hard callus formation after transplantation into immunodeficient mice, which was eventually replaced by murine recipient bone during final tissue remodeling. Stromal cells vary in their tissue-specific differentiation potential because of their differing epigenetic enhancer signatures. Enhancing bone ossification Musculoskeletal tissue engineering approaches require a reliable source of precursor cells. Hochmann et al . report that despite having some transcriptional similarities, the inherent differentiation potential of different stromal cell types is constrained by their enhancer landscapes. In contrast to stromal cells derived from white adipose tissue or umbilical cord, only bone marrow–derived cells had an epigenetic signature permitting their differentiation into functional hypertrophic cartilage discs capable of ameliorating a critical-size bone defect model after transplantation into mice. These findings have ramifications for the development of regenerative cell–based musculoskeletal therapies. —CAC