Chapter 22: Stem Cells in Tissue Homeostasis and Regeneration

Stem Cells in Tissue Homeostasis and Regeneration explains how adult stem cells reside in specialized niches—microenvironments that regulate their behavior through signals such as Wnt, Notch, and BMP pathways. Examples include hematopoietic stem cells (HSCs) in bone marrow, epithelial stem cells in the gut and skin, and satellite cells in skeletal muscle. Asymmetric division and transit-amplifying cells are discussed as key mechanisms that balance renewal with differentiation. The chapter also highlights how tissue architecture and turnover rates vary—rapid in intestinal epithelia, moderate in liver and skin, and limited in neurons and cardiac muscle. Stem cell plasticity and transdifferentiation are introduced, along with the generation of induced pluripotent stem cells (iPSCs) through transcription factor reprogramming (e.g., Oct4, Sox2, Klf4, c-Myc). The therapeutic potential of stem cells is addressed in the context of regenerative medicine, including skin grafts, bone marrow transplantation, and disease modeling. Organoids and engineered tissues derived from stem cells are also mentioned as tools for drug screening and developmental studies. The chapter concludes with a discussion of how stem cell dysfunction contributes to aging, cancer, and degenerative diseases, emphasizing the need for careful regulation of self-renewal and differentiation to ensure tissue health.