Kindlin-3 deficiency leads to impaired erythropoiesis and erythrocyte cytoskeleton.

Kindlin-3 (K3) is critical for activation of integrin adhesion receptors in hematopoietic cells. In humans and mice, K3 deficiency is associated with impaired immunity, bleeding, bone development and aberrant erythrocyte shape. To delineate how K3 deficiency (K3KO) contributes to anemia and misshaped erythrocytes, mice deficient in erythroid- (K3KO\EpoR-cre) or myeloid cell K3 (K3KO\Lyz2cre), knock-in mice expressing K3 mutant (Q597W598/AA) with reduced integrin activation function (K3KI) and control K3 WT mice were studied. Both K3-deficient strains and K3KI mice showed anemia at baseline, reduced response to erythropoietin stimulation and compromised recovery following phenylhydrazine (PHZ)-induced hemolytic anemia as compared to K3WT. Erythroid K3KO and K3 (Q597W598/AA) showed arrested erythroid differentiation at proerythroblast stage, while macrophage K3KO showed decreased erythroblast numbers at all developmental stages of terminal erythroid differentiation due to reduced erythroblastic island (EBI) formation attributable to decreased expression and activation of erythroblast integrin α4β1 and macrophage αVβ3. Peripheral blood smears of K3KO\EpoR-cre mice but not of the other mouse strains showed numerous aberrant tear drop-shaped erythrocytes. K3 deficiency in these erythrocytes led to disorganized actin cytoskeleton, reduced deformability and increased osmotic fragility. Mechanistically, K3 directly interacted with F-actin through an actin-binding site K3-LK48. Taken together, these findings document that erythroid and macrophage K3 are critical contributors to erythropoiesis in integrin-dependent manner while F-actin binding to K3 maintains the membrane cytoskeletal integrity and erythrocyte biconcave shape. The dual function of K3 in erythrocytes and in erythroblastic islands establish an important functional role for K3 in normal erythroid function.