Osteoprogenitor cells are types of cells that work in the growth or repair of bones. These cells originate from stem cells and are created by progenitor cells. Also known as preosteoblasts, osteoprogenitor cells are found in the bone marrow. The bone marrow is comprised of several cellular layers, and it is one of these layers that house these preosteoblast cells.
Osteoblast cells play a vital role in the formation and repair of bones. They secrete collagen fibers that help to harden bone. Osteoprogenitor cells have the capability of developing into osteoblasts. Each cell starts as a mesenchymal cell in the marrow. It then grows from a progenitor cell to an osteoprogenitor cell. From this point, the cells develop into the osteoblasts and begin growth or repair through either intramembranous ossification or endochondral ossification.
Intramembranous ossification uses osteoprogenitor cells to directly create bones. Many bones are formed in this manner during a child's development. Bones that form while a baby is still in the womb, such as the cranium, fall into this group. Some forms of bone repair will also use intramembranous ossification, depending on the level of movement the bone needs.
Endochondral ossification uses osteoprogenitor cells to create cartilage. This method forms the long bones of the body, such as the femur bone in the thigh. Chondrocytes, which are cartilage cells, regenerate rapidly and calcify to strengthen the extracellular matrix of existing cartilage cells. An osteoprogenitor cell cannot create or repair bone that is calcified. To allow access, other cells are brought in by blood cells to break down the calcified matrix enough for the osteoprogenitor cell group to create bone.
Osteoprogenitor cells are found in the inner layer of the periosteum. The periosteum is the part of the bone that is used for tendons, ligaments, and muscles. This outer membrane provides an attachment point. There is also an osteoprogenitor cell concentration in the endosteum. The endosteum lines the internal surfaces within the bones.
Some bone grafts rely on mesenchymal progenitor cells. An embryo contains these cells that contribute to the development of blood and lymphatic vessels, connective tissues, and blood. The progenitor cells are used to stimulate osteoprogenitor cells when a patient does not have a large enough amount of progenitor cells to properly heal bones. Dental reconstructions are one instance of this use, and patients who suffer from extreme or chronic bone damage may also benefit from stimulation through the use of progenitor cells.