Platelets in regenerative medicine

Stem and progenitor cells have evolved as the central cell type in regenerative medicine. This focussed approach may, however, sometimes narrow the point of view. Recently, platelets have been shown to strongly influence progenitor cell biology and to serve as regenerative cells themselves. Platelets represent an important recruitment factor for circulating progenitor cells. Furthermore, they modulate progenitor cell chemotaxis, migration and differentiation. Platelets are crucial for the regeneration of parenchymatous organs such as the liver. Moreover, in the clinical setting, platelets are already applied for the restoration of connective and bone tissue. However, also adverse effects can be mediated by platelets and progenitor cells exposed to platelets, including the induction of pro-inflammatory processes. This review gives an update on platelets as regenerative cells and as modulators of progenitor cell biology in (patho-) physiological conditions. Abundant data obtained during the last decade have linked progenitor and stem cells to tissue repair. Very recent accumulating results from different groups revealed that platelets may have a strong influence on central functions of these progenitor cells. Only little is known about the impact of platelets themselves on tissue regeneration. Therefore, this review highlights the role of platelets themselves as a potential effector cell for tissue regeneration and their impact on progenitor cell biology.