A Novel Role for PIEZO1 in Calcium Homeostasis during Erythropoiesis

In erythrocytes, the mechanosensitive ion transporter PIEZO1 is crucial to maintain cellular volume homeostasis during circulation. Gain of function mutations in the PIEZO1 gene lead to prolonged Ca²⁺ influx resulting in hereditary xerocytosis (HX). This rare disorder of erythrocyte hydration is characterized by dehydration caused by increased Gardos channel activation. HX patients display a mild to moderate degree of hemolysis, which is generally compensated by an increased reticulocyte count. In addition to its function in erythrocytes we found that PIEZO1 RNA is also expressed at the proerythroblast stage suggesting a role during erythropoiesis. We therefore hypothesize that disturbed Ca²⁺ homeostasis due to inappropriate PIEZO1 channel function leads to defects in erythroid differentiation.

Primary erythroblasts were cultured from peripheral blood mononuclear cells from an HX patient, heterozygous for the previously reported c.6262C>G p.Arg2088Gly mutation in PIEZO1 (Glogowska, 2017 Blood 130(16): 1845-1856). Primary erythroblasts displayed a twofold decreased proliferation compared to healthy controls. Incubating erythroblasts from a healthy control with the PIEZO1 agonist Yoda1 led to a dose dependent decrease in erythroblast proliferation, thereby recapitulating the patient's phenotype. In addition, Yoda1 treatment was accompanied with increased cell death and reduced enucleation. In HX patient's erythroblasts basal Ca²⁺ levels were higher compared to control cells. In agreement with this, Yoda1-induced PIEZO1 activation led to a dose dependent Ca²⁺ influx. Yoda1 caused Erk1/2 and SAPK/JNK phosphorylation as well as NFATc2 dephosphorylation, suggesting that PIEZO1 triggers calcium-dependent signal transduction, possibly via calcineurin activation. Indeed, Yoda1-induced NFATc2 dephosphorylation was blocked and SAPK/JNK phosphorylation was inhibited upon pre-incubation of erythroblasts with the calcineurin inhibitor FK506.

In conclusion, we found that PIEZO1 has a role in regulating Ca²⁺ homeostasis during erythropoiesis possibly through activation of calcineurin. Inappropriate PIEZO1 channel activation in erythroid cells results in cell death and proliferation/differentiation defects. This novel feature adds to the complexity of the phenotypic expression of HX.