Splenectomy improves erythrocyte functionality in spherocytosis based on septin abundance but not maturation defects

Splenectomy improves clinical parameters of patients with hereditary spherocytosis but its potential benefit to red blood cell (RBC) functionality and the mechanism behind this benefit remain largely overlooked. We here compared 7 non-splenectomized and 12 splenectomized patients with mutations in the β-spectrin (SPTB) or the ankyrin (ANK1) gene. We showed that hematological parameters, spherocyte abundance, osmotic fragility, intracellular calcium and extracellular vesicle release were largely but not completely restored by splenectomy whereas cryohemolysis was not. Diseased RBCs exhibited decreases in β-spectrin and/or ankyrin contents and slight alterations in spectrin membrane distribution depending on the mutation. These modifications were found in both splenectomized and non-splenectomized patients and poorly correlated with RBC functionality alteration, suggesting additional alterations. Accordingly, we found increased abundance of septins, small GTP-binding cytoskeletal proteins. Septins-2,-7 and -8 but not -11 were less abundant upon splenectomy and correlated with the disease severity. Septin-2 membrane association was confirmed by immunolabeling. With the exception of cryohemolysis, all parameters of RBC morphology and functionality correlated with septin abundance. The increased septin content might result from RBC maturation defects evidenced by (i) the decrease in protein 4.2 and RhAG content in all patients, (ii) increased endoplasmic reticulum remnants and endocytosis proteins in non-splenectomized patients, and (iii) increased lysosomal and mitochondrial remnants in splenectomized patients. Our study paves the way for a better understanding of the involvement of septins in RBC membrane biophysical properties. In addition, the lack of restoration of septin-independent cryohemolysis by splenectomy may call into question its recommendation in some cases.