Anucleate platelets generate progeny

Abstract

Platelets are classified as terminally differentiated cells that are incapable of cellular division. However, we observe that anucleate human platelets, either maintained in suspension culture or captured in microdrops, give rise to new cell bodies packed with respiring mitochondria and ␣-granules. Platelet progeny formation also occurs in whole blood cultures. Newly formed platelets are structurally indistinguishable from normal platelets, are able to adhere and spread on extracellular matrix, and display normal signaldependent expression of surface Pselectin and annexin V. Platelet progeny formation is accompanied by increases in biomass, cellular protein levels, and protein synthesis in expanding populations. Platelet numbers also increase during ex vivo storage. These observations indicate that platelets have a previously unrecognized capacity for producing functional progeny, which involves a form of cell division that does not require a nucleus. Because this new function of platelets occurs outside of the bone marrow milieu, it raises the possibility that thrombopoiesis continues in the bloodstream. (Blood. 2010;115(18):3801-3809) IntroductionAfter they are shed from the cytoplasm of megakaryocytes, 1 platelets circulate in the bloodstream for 9 to 11 days. There is no evidence that these anucleate cytoplasts undergo cellular division, but recent studies by our group and others have identified unexpected cellular functions of platelets, 2-4 including the capacity to process pre-mRNA 2-5 and translate mRNA into protein. [6][7][8][9][10] Platelets also continue to synthesize protein for several days when they are stored ex vivo. 11 These findings indicate that, despite their terminally differentiated state, platelets are biosynthetically more sophisticated than previously thought. 12 They also suggest that platelets may be able to adjust their phenotypic composition in response to environmental cues.Here we show that platelets give rise to new cells that are structurally and functionally similar to their parent counterparts. The formation of platelet progeny is associated with increases in platelet biomass, protein synthetic events, and total intracellular protein. This heretofore undescribed proliferative capacity of platelets may have significant consequences for normal and pathologic thrombopoiesis in humans in addition to having clinical implications for transfusion medicine. Methods Platelet isolation and cultureAll studies were approved by the University of Utah Institutional Review Board committee (no. 392). Leukocyte-depleted platelets were isolated as previously described. 2,5 Washed platelets were resuspended at 100 000/L in serum-free M199 medium, placed in round-bottom polypropylene tubes (BD Biosciences), and cultured in a 37°C humidified incubator under gentle rotation (MacsMix, slow, 45°angle; Miltenyi). The same suspension culture conditions were also used for the whole blood studies shown in Figure 2A.Stored platelets were obtained from the ARUP Blood Transfusion Services at the University o...

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