Adult Stem Cells for Bone Regeneration and Repair

Abstract

The regeneration of bone fractures, resulting from trauma, osteoporosis or tumors, is a major problem in our super-aging society. Bone regeneration is one of the main topics of concern in regenerative medicine. In recent years, stem cells have been employed in regenerative medicine with interesting results due to their self-renewal and differentiation capacity. Moreover, stem cells are able to secrete bioactive molecules and regulate the behavior of other cells in different host tissues. Bone regeneration process may improve effectively and rapidly when stem cells are used. To this purpose, stem cells are often employed with biomaterials/scaffolds and growth factors to accelerate bone healing at the fracture site. Briefly, this review will describe bone structure and the osteogenic differentiation of stem cells. In addition, the role of mesenchymal stem cells for bone repair/regrowth in the tissue engineering field and their recent progress in clinical applications will be discussed.

Keywords: bone; differentiation; regenerative medicine; repair; stem cell.

FIGURE 1

Representation of bone structure. Two types of osseous tissue can be identified: compact bone and trabecular bone. Bone tissue is subjected to bone remodeling, a life-dominant process that plays an important role in bone mass balance and mineral homeostasis. During bone remodeling osteoclasts, derived from hematopoietic stem cells, resorb old, or damaged bone. Subsequently, osteoblasts, derived from mesenchymal stem cells, are recruited to the damaged area in order to replace bone removed by osteoclasts. Instead, osteocytes derived from osteoblasts suspend their activity when buried in the bone matrix.

FIGURE 2

Strategies for MSCs based therapy. MSCs can be isolated from different sources [e.g., amniotic fluid (AF-MSCs), dental pulp tissue (DPSCs), placental-derived MSCs (PD-MSCs), bone marrow tissue (BM-MSCs), and adipose tissue (ADSCs)] with or without culture expansion before clinical application. MSCs can be introduced intravenously by systemic infusion or local injection into fracture site (direct approach), or loaded on scaffold (e.g., ceramics, polymers, and composite) before the implantation into damaged area.

FIGURE 3

Cytoskeleton analysis of human ADSCs. Cytoskeleton analysis by phalloidin TRITC (tetramethylrhodamineisothiocyanate) staining of human ADSCs grown on the biomaterial (magnification 40x). Cellular nuclei were stained with 0.5 mg/ml DAPI.