"Valar morghulis": all red cells must die

Thrombospondin-1/CD47 signaling modulates transmembrane cation conductance, survival, and deformability of human red blood cells

BACKGROUND

Thrombospondin-1 (TSP-1), a Ca²⁺-binding trimeric glycoprotein secreted by multiple cell types, has been implicated in the pathophysiology of several clinical conditions. Signaling involving TSP-1, through its cognate receptor CD47, orchestrates a wide array of cellular functions including cytoskeletal organization, migration, cell-cell interaction, cell proliferation, autophagy, and apoptosis. In the present study, we investigated the impact of TSP-1/CD47 signaling on Ca²⁺ dynamics, survival, and deformability of human red blood cells (RBCs).

METHODS

Whole-cell patch-clamp was employed to examine transmembrane cation conductance. RBC intracellular Ca²⁺ levels and multiple indices of RBC cell death were determined using cytofluorometry analysis. RBC morphology and microvesiculation were examined using imaging flow cytometry. RBC deformability was measured using laser-assisted optical rotational cell analyzer.

RESULTS

Exposure of RBCs to recombinant human TSP-1 significantly increased RBC intracellular Ca²⁺ levels. As judged by electrophysiology experiments, TSP-1 treatment elicited an amiloride-sensitive inward current alluding to a possible Ca²⁺ influx via non-selective cation channels. Exogenous TSP-1 promoted microparticle shedding as well as enhancing Ca²⁺- and nitric oxide-mediated RBC cell death. Monoclonal (mouse IgG1) antibody-mediated CD47 ligation using 1F7 recapitulated the cell death-inducing effects of TSP-1. Furthermore, TSP-1 treatment altered RBC cell shape and stiffness (maximum elongation index).

CONCLUSIONS

Taken together, our data unravel a new role for TSP-1/CD47 signaling in mediating Ca²⁺ influx into RBCs, a mechanism potentially contributing to their dysfunction in a variety of systemic diseases. Video abstract.