Concise review: polarity in stem cells, disease, and aging

Abstract

Adult somatic stem cells are central to homeostasis in tissues that present with a high cellular turnover like the skin, intestine, and the hematopoietic system. It is thought that polarity is particularly important with respect to fate decisions on stem cell division (symmetric or asymmetric) as well as for the maintenance of stem cell adhesion and quiescence (interaction with the niche). Consequently the failure to establish or regulate stem cell polarity might result in disease or tissue attrition. Members of the family of small RhoGTPases are known to exert an important role in regulating cell polarity. We summarize and discuss here recent views on the role of cell polarity in somatic stem cell function, aging, and disease, concluding that targeting cell polarity might be a novel approach to ameliorate or even revert aberrant somatic stem cell function.

Figure 1

Stem cells and polarity. (A): Polarized quiescent stem cell. Polarity can be intrinsically established inside the cell. (B): An adherent polarized stem cell. Stem cell polarity can be established or maintained and reinforced upon adhesion to the niche. (C): Migrating polarized stem cell. (D): Polarized stem cells on division can distribute proteins symmetrically or asymetrically.

Figure 2

Polarized (A) and not polarized (B) HSCs. The picture is representative of tubulin (blue) and Numb (green) localization in freshly isolated mouse Lineage⁻ c-kit⁺ Sca-1⁺ CD34⁻ Flk2⁻ HSCs (long-term repopulating HSCs) from (A) young (2- to 4-month old) and (B) aged (24- to 26-month old) C57BL/6 mice. Scale bar = 5 μm. Abbreviation: HSC, hematopoietic stem cell.