osteoprogenitor

Osteoprogenitor cells, also called osteogenic precursor cells, are a population of cells in bone tissue that are committed to the osteoblast lineage and capable of differentiating into osteoblasts. They originate from mesenchymal stem cells and are found in several anatomical niches including the periosteum, endosteum, and bone marrow. In the osteogenic program, the transcription factors Runx2 (Cbfa1) and Osterix (Sp7) are essential; without them, osteoblast differentiation fails. Osteoprogenitors respond to bone morphogenetic proteins and Wnt signaling, as well as mechanical stimuli, by proliferating and differentiating into mature osteoblasts that synthesize type I collagen and non-collagenous proteins, form osteoid, and later become mineralized.

Some osteoblasts become osteocytes embedded in the mineralized matrix and some may re-enter a quiescent state or contribute to remodeling activity. The pool of osteoprogenitors can be depleted with age or disease, reducing bone formation and healing capacity. Markers of osteoprogenitors are characteristic of the osteoblast lineage, including alkaline phosphatase activity and expression of osteogenic transcription factors Runx2 and Osterix; they are distinct from hematopoietic cells. They are essential during growth, bone remodeling, and fracture repair, supplying new osteoblasts to form and renew bone tissue. In regenerative medicine, osteoprogenitors are investigated for bone repair and tissue-engineering applications.