A novel fluorescent-based assay reveals that thrombopoietin signaling and Bcl-XL influence, respectively, platelet and erythrocyte lifespans

Objective: The factors determining platelet and erythrocyte lifespan are not completely understood, despite extensive study. The lack of success may be attributed to the methods used to measure lifespan kinetics, all of which require processing of cells prior to analysis, and the inconsistent and potentially inappropriate use of mathematical models for data analysis. The aims of this study were to establish an in vivo platelet and erythrocyte labeling method using carboxyfluorescein diacetate succinimidyl ester (CFSE), determine the most appropriate mathematical model for lifespan analysis, and apply both to the study of factors that control platelet and erythrocyte lifespans. Materials and Methods: Control, c-mpl knockout (KO), and Bcl-XL mutant mice were injected with CFSE and platelet and erythrocyte fluorescence followed over time. Datasets were analyzed using linear, exponential, multiple-hit, and lognormal mathematical models. Results: In vivo CFSE labeling of platelets and erythrocytes requires no postcollection processing, proved stable, nontoxic, nonimmunogenic, and the lifespans were highly reproducible. Mathematical modeling revealed the lognormal model gave a robust fit to control and extreme datasets when either extrinsic or intrinsic factors determined lifespan. Using these methods, platelet lifespans were found to be significantly shortened in thrombopoietin-receptor-deficient mice independent of blood loss, and the antiapoptotic protein Bcl-XL was shown to play a role in prolonging erythrocyte lifespans. Conclusions: The simultaneous study of platelet and erythrocyte lifespans using in vivo CFSE labeling with lognormal modeling yielded insight into common intrinsic and extrinsic platelet and erythrocyte lifespan determinants and provides an improved methodology for use in this field of research