Pathologically stiff erythrocytes impede contraction of blood clots

Background: Blood clot contraction, volume shrinkage of the clot, is driven by platelet contraction and accompanied by compaction of the erythrocytes and their gradual shape change from biconcave to polyhedral, with the resulting cells named polyhedrocytes.

Objectives: Here, we examined the role of erythrocyte rigidity on clot contraction and erythrocyte shape transformation.

Methods: We used an optical tracking methodology that allowed us to quantify changes in contracting clot size over time.

Results and conclusions: Erythrocyte rigidity has been shown to be increased in sickle cell disease (SCD), and in our experiments erythrocytes from SCD patients were 4-fold stiffer than those from healthy subjects. On average, the final extent of clot contraction was reduced by 53% in the clots from the blood of patients with SCD compared to healthy individuals, and there was significantly less polyhedrocyte formation. To test if this reduction in clot contraction was due to the increase in erythrocyte rigidity, we used stiffening of erythrocytes via chemical cross-linking (glutaraldehyde), rigidifying Wright^b antibodies (Wr^b ), and naturally more rigid llama ovalocytes. Results revealed that stiffening erythrocytes result in impaired clot contraction and fewer polyhedrocytes. These results demonstrate the role of erythrocyte rigidity in the contraction of blood clots and suggest that the impaired clot contraction/shrinkage in SCD is due to the reduced erythrocyte deformability, which may be an underappreciated mechanism that aggravates obstructiveness of erythrocyte-rich (micro)thrombi in SCD.