Anatomical Heterogeneity of Skeletal Stem Cells and Its Implications for Cranial Bone Regeneration

Introduction: Bone is a complex organ composed of multiple cell types, including skeletal lineage cells, hematopoietic cells, and immune cells. These skeletal niche cells interact with skeletal stem cells (SSCs), the central hub of the bone niche, to maintain homeostasis. Since the identification of SSCs, increasing evidence has highlighted their heterogeneity, which is influenced by anatomical location. Cranial bones, derived from two distinct developmental origins compared to long bones, likely harbor cranial SSCs with unique genetic and functional attributes, which ultimately leads to variable regeneration capacity.

Methods: Using established surface markers, we FACS-isolated SSCs from parietal, occipital, nasal, mandibular, and femur as control. Bulk RNA sequencing was conducted to identify genetical heterogeneity within the SSCs. In vitro and in vivo differentiation assays were performed to identify the functional heterogeneity.

Results: We identified that cranial SSCs display diverse genetic features and functional activities that vary across different regions of the cranium, impacting their differentiation capacities (Fig1). Time-course analyses further revealed that SSCs increasingly outnumber progenitor cells with age, a trend that may serve as an important indicator of skeletal development and regenerative potential. Importantly, our findings demonstrate that SSC heterogeneity significantly influences bone regenerative capacity, particularly in response to Bone Morphogenetic Proteins (BMPs). We observed that the osteogenic response of SSCs to BMP-2 varies significantly by anatomical location, emphasizing the need for customized BMP-based therapies to enhance cranial bone regeneration at the stem cell level.

Conclusion: This study underscores the heterogeneity of SSCs in transcriptomic profiles and functional activity, ultimately shaping their regenerative potential.