Plasminogen (Plg), a classical fibrinolytic factor, is essential for maintaining homeostasis of blood coagulation, and has important roles in wound healing as well as pathophysiology of atherosclerosis, cancer and Alzheimer's disease. Recently, we have shown that the activation of the Plg fibrinolytic pathway is critical for hematopoietic regeneration from stem cells after myelosuppression. Here, we investigated the role of Plg in regulating erythropoiesis.
Male and female C57BL/6J mice with normal or homozygously disrupted Plg genes were used under steady state conditions and in a model of acute erythropoietic stress selectively induced by intravenous injection of the hemolytic drug phenylhydrazine hydrochloride. Orbital vein blood, bone marrow and spleen were obtained to determine erythropoietic parameters. In addition, testosterone concentrations were measured in murine serum.
Normochromic normocytic anemia was found in Plg-/- mice under steady state conditions. Microscopic evaluation of blood smears revealed the presence of altered erythrocytes, such as acanthocytes, echinocytes (burr cells) and to lesser extent schistocytes. In addition, flow cytometry of intravenously injected autologous erythrocytes, labeled with a fluorescent probe, showed significantly shortened erythrocyte lifespan, suggestive of hemolysis as a cause of the anemia. In concordance, there was an increase in plasma erythropoietin with augmented reticulocyte counts, erythroid burst forming units in bone marrow, and finally erythroid progenitors in spleens, which were significantly enlarged, suggestive of extramedullar erythropoiesis. Interestingly, the intensity of compensatory erythropoiesis was higher in Plg-/- female mice, resulting in lesser hematocrit decrease when compared to that observed in Plg-/- male mice. In addition, similar gender differences could be observed in a model of acute erythropoietic stress. Concretely, acute hemolytic anemia induced by intravenous injection of phenylhydrazine hydrochloride resulted in a significant erythrocyte recovery delay in Plg-/- male mice that, in contrast, was not as profound in Plg-/- female mice. To understand the reason for the observed gender differences, a competitive enzyme immunoassay was employed to measure serum concentrations of testosterone. As a result, a significant decrease in serum testosterone levels was detected in Plg-/- male mice.
In summary, we found that Plg plays important role in maintaining normal lifespan of erythrocytes by preventing their mechanical alteration by microangiopathy from abnormal fibrin deposition. In addition, given that testosterone is well known to regulate erythropoiesis, through increasing erythropoietin levels as well as having non-erythropoietin stimulating effects, our present results suggest that Plg might also play roles in regulating erythropoiesis through being important for normal testosterone production.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.