Abstract
(1) Background: It is known that sickle cells contain a higher amount of Ca2+ compared to healthy red blood cells (RBCs). The increased Ca2+ is associated with the most severe symptom of sickle cell disease (SCD), the vaso-occlusive crisis (VOC). The Ca2+ entry pathway received the name of Psickle but its molecular identity remains only partly resolved. We aimed to map the involved Ca2+ signaling to provide putative pharmacological targets for treatment. (2) Methods: The main technique applied was Ca2+ imaging of RBCs from healthy donors, SCD patients and a number of transgenic mouse models in comparison to wild-type mice. Life-cell Ca2+ imaging was applied to monitor responses to pharmacological targeting of the elements of signaling cascades. Infection as a trigger of VOC was imitated by stimulation of RBCs with lysophosphatidic acid (LPA). These measurements were complemented with biochemical assays. (3) Results: Ca2+ entry into SCD RBCs in response to LPA stimulation exceeded that of healthy donors. LPA receptor 4 levels were increased in SCD RBCs. Their activation was followed by the activation of Gi protein, which in turn triggered opening of TRPC6 and CaV2.1 channels via a protein kinase Cα and a MAP kinase pathway, respectively. (4) Conclusions: We found a new Ca2+ signaling cascade that is increased in SCD patients and identified new pharmacological targets that might be promising in addressing the most severe symptom of SCD, the VOC.
Highlights
In sickle cell disease (SCD) patients’ red blood cells (RBCs), the Ca2+ uptake is increased to approximately 300 μmol/(lcells h) during vaso-occlusive crisis (VOC), which is approximately 6-fold higher than in healthy RBCs [1,2]
Because TRPC6 has been reported to contribute to the increase in residual Ca2+ influx in RBC [37], we further investigated RBCs of TRPC6−/− mice [36,37]
Our results show that Ca2+ uptake evoked by lysophosphatidic acid (LPA) stimulation and well described in healthy RBCs [4,6,17,21,30] is markedly increased in SCD (Figure 1)
Summary
In sickle cell disease (SCD) patients’ red blood cells (RBCs), the Ca2+ uptake is increased to approximately 300 μmol/(lcells h) during vaso-occlusive crisis (VOC), which is approximately 6-fold higher than in healthy RBCs [1,2]. This Ca2+ overload is likely to be mechanistically involved in the generation of the VOC, e.g., favoring RBC dehydration that promotes crystallization of deoxyHbS. The increased Ca2+ may promote the perturbation of microcirculation with participation of even non-deoxygenated cells, independent of dehydration.
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