the invention of this technology and current research with clinical applications are also discussed.
Bone Marrow Aspiration
Bone marrow is the soft tissue in the joints of the bones. It contains a reserve of hematopoietic stem cells, mesenchymal stem cells, and osteoprogenitor cells with the potential to differentiate into bone cells. In order to avoid immune rejection, the stem cells are usually isolated from the patient and then later used for therapy. The procedures for isolating human bone marrow cells are standardized. The cells are usually aspirated from the hip joints. The aspirated cells are then passed through a 70 mm filter, which removes accidental bone particles that might have mixed in with the aspirate. Once the cells are isolated, they are spun down to remove the cells from the serum. The stem cells are then plated in petri dishes – which provide a surface for the cells to attach and divide. A medium with the hormones, amino acids, and other essential chemicals, such as metals (magnesium and calcium), that are required for growth is added. The medium nourishes these cells, which then rapidly divide. This proliferation results in the expansion of the population of the cells, which is necessary because a significant amount of dividing cells is required to facilitate regeneration at the wound site. The stem cells derived from the bone are a heterogeneous mixture and contain cells that are not stem cells. The stem cells that are cultured in vitro are then tested for their ability to differentiate into bone cells. Osteogenicity is induced with BMP and other hormones. At day 14, the expression of osteogenic protein markers is tested. The RNA is isolated from these cells and the gene expression profile is tested. It is essential to test the osteogenic potential of the cells before prepping them for therapy.
Current research methodologies have devised effective mechanisms to increase the yield of stem cells, enabling efficient therapies. A significant drawback in the aforementioned method is that it involves centrifugation, which is time consuming and inefficient. This group of researchers has identified a non-woven fabric that is 9 μm apart. The cells obtained from the bone marrow are filtered, and then stem cells are allowed to grow on these biomaterials in the lab. These fabrics with the stem cells growing can then be directly applied at the wound site. This model was tested in vivo in murine models and was found to be effective. This is now waiting for verification in human subjects.
Liposuction
Another significant source of pluripotent stem cells that can differentiate into bone cells are the aspirates of liposuction. The fat of the human body contains pluripotent cells that can be induced to form bone. Human liposuction aspirate is a heterogeneous population of cells that contains a subpopulation of pluripotent cells called processed lipo aspirate (PLA) cells. These cells have the capacity to differentiate to bone. This is a faster and much more efficient mechanism than bone marrow aspirate, which requires a painful and more time-consuming process of extraction. An average of 45 percent of PLA cells have osteogenic potential—the ability to form bone—and this eliminates the necessity for time-consuming processes where the stem cells have to be expanded in labs.
PLA cells are processed in lab before they can be plated to differentiate them into bone. They are washed several times with saline solutions and then treated with collagenase. Collagenase is the enzyme that breaks apart the cells, making them individual. The collagenase reaction is stopped by adding serum, and the cells are then plated. After they attach to the bottom of the petri dish, the cells are treated with BMP or bone morphogenic protein, which induces the formation of bone. Once the cells are differentiated, they are either directly applied to the wound site or are implanted with biomaterials.
Embryonic Stem Cells
Embryonic stem cells are derived directly from the embryo. An embryo is formed from the union of an egg and a sperm. The one cell zygote then undergoes mitosis to develop into the embryo. The 60 cells stage is the blastocyst stage, in which the inner cell mass contains pluripotent stem cells with the capability of developing into the three different germ layers. The cells from the ICM are aspirated to develop in vitro for various research and therapeutic purposes. The embryos that are generated as a surplus in IVF are used to aspirate cells from the blastocyst. The blastocyst phase is two weeks before implantation into the uterus. There are several concerns regarding the use of embryonic stem cells for research purposes. The rules and ethical issues vary from country to country. The European Union and the United States have very different stands on this issue. Thus the use of embryonic stem cells for research depends on the country in which the research is being performed.
The stem cells are also isolated from the genital ridge of the fetus from five to eight weeks. These cells are called embryonic fetal stem cells and are multipotent cells capable of developing into bone cells. Some of the other sources of stem cells are from the femur of the developing fetus. These bone stem cells can be isolated from the fetus at between approximately 9 and 14 weeks, and these cells can be used for treatment in vivo. Most of these procedures are carried out with fetuses in the third trimester. They are performed on fetuses obtained from voluntary interruption or termination of pregnancies. In some countries, use of the fetus in such cases is considered an organ donation, and this enables bypass of many ethical issues and concerns. Besides stem cells, cells with specific lineage commitments are also isolated for other research purposes.
Dental Pulp
There is a constant search for new isolation strategies that yield stem cells of great quality and quantity. Periodontal ligament, deciduous and permanent teeth are also great sources of stem cells. In sum, dental pulp is a source of pluripotent stem cells, and it is highly accessible. These cells are called pulp derived stem cells or PDSCs. The isolation process is very simple, and PDSCs are shown to be adherent to plastic surfaces. This facilitates easy propagation in vitro. They are proven to self-renew and possess plasticity, making them the ideal candidate for stem cell therapy. They are multipotent and have the capacity to differentiate into several cell types, such as adipocytes, chondrocytes, osteoblasts, neural cell progenitors, and myotubes. Thus, these cells are a great source of stem cells for osteoinduction.
The different sources of stem cells for differentiation into bone shows the advancement of cellular therapy in the field of regeneration. While this is exciting, one important consideration is that PDSCs have a malignant tendency with their capability to self-renew and differentiate into other cell types. The viability of cells with respect to genome stability, absence of mutations, and intact cellular pathways such as DNA repair pathways must be tested before they can be used for therapy purposes. Stem cells are double-edged swords; while they are extremely useful tools, even a small amount of imprudence leads to dangerous outcomes.
Sharanya Kumar
Independent Scholar
See Also: Bone: Cell Types Composing the Tissue; Bone: Development and Regeneration Potential; Bone: Existing or Potential Regenerative Medicine Strategies; Bone: Major Pathologies; Bone: Stem and Progenitor Cells in Adults; Bone Marrow Transplants.
Further Readings
Arvidson, K., B. M. Abdallah, L. A. Applegate, et al. “Bone Regeneration and Stem Cells.” Journal of Cellular and Molecular Medicine, v.1/4 (2011).
Dawson, J. I., et al. “Concise Review: Bridging the Gap: Bone Regeneration Using Skeletal Stem Cell-Based Strategies—Where Are We Now?” Stem Cells, v.32/1 (2014).
Bone: Development and Regeneration Potential
Bone: Development and Regeneration Potential
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Bone: Development and Regeneration Potential
Bones are the solid, firm structures that make up the vertebrate skeleton. They are complex living organs that form the supportive framework of the body and are comprised of mineral matrix, marrow, blood vessels, nerves, and cartilage. A typical adult human body has 206 distinct bones with the largest