ABSTRACT
Death Blockers ................................................................................ 395 18.4 Conclusions and Future Directions ........................................................ 396 Acknowledgments .............................................................................................. 398 References ............................................................................................................. 398
18.1.1 Adult Stem Cells: Regenerative Potential
Stem cells are found in adult tissue at low frequencies and are capable of differentiating into specic tissues based on their differentiation potential, location, stimuli, and relocation (Huh et al. 2006). Multipotent stromal cells or mesenchymal stem cells (MSCs) present in the adult bone marrow are self-renewing clonal precursors of non-hematopoietic stromal tissue and are capable of differentiating into mesenchymal lineages of bone, cartilage, fat, tendon, muscle, endothelial cells, and marrow stroma (Pittenger et al. 1999). These can be obtained by marrow aspiration. There are also stem and progenitor cells found in adipose tissue, called adipose-derived stem cells (ASCs) obtained at a higher frequency compared to bone-marrow-derived stem cells, 0.5% compared to 0.01%. These cells which differ in expression of certain cell surface markers (Fraser et al. 2006) possess similar multilineage differentiation potential though there is a predilection toward fat tissue (Brayeld et al. 2010). ASCs are called by several other names in literature including processed lipoaspirate cells (LPA) and adipose-tissue-derived stromal cells. Likewise, the muscle also holds postnatal stem cells called musclederived stem cells (MDSCs); these cells can differentiate spontaneously into cardiac and skeletal muscle and by modication ex vivo with growth factors can differentiate into the osteogenic and chondrogenic lineages (Usas and Huard 2007). There also exist stem cells with more restricted differentiation ability like neural stem cells (NSCs) found in the adult hippocampus and lateral ventricle which can differentiate into neurons and glia (astrocytes and oligodendrocytes) (Massirer et al. 2011). There are other less well clinically characterized epithelial stem cells in tissues with high homeostasis, turnover rates, and regeneration such as the skin which form hair follicles (Zhang et al. 2009), sebaceous glands (Jensen et al. 2009), and epidermal cells (reviewed [Barker et al. 2010]). Other stem cells are found in the mammary and prostate glands (Shackleton et al. 2006; Stingl et al. 2006).
