Membrane alterations in irreversibly sickled cells: hemoglobin--membrane interaction

Area of Science:

• Hematology
• Cell Biology
• Biophysics

Background:

• Irreversibly sickled cells (ISCs) are a hallmark of sickle cell disease, characterized by persistent elongated shapes.
• Their abnormal biophysical properties stem from acquired alterations in the erythrocyte membrane.

Purpose of the Study:

• To investigate the ultrastructural and molecular changes in the membranes of ISCs.
• To elucidate the role of hemoglobin-membrane interactions in ISC formation.

Main Methods:

• Freeze-etch electron microscopy of in vitro and in vivo ISCs.
• Diaminobenzidine staining of ISC ghosts.
• Scanning electron microscopy.
• Polyacrylamide gel electrophoresis of ISC membranes.

Main Results:

• Microbodies containing hemoglobin were observed on the internal surface of ISC membranes, obscuring spectrin.
• Intramembranous particles aggregated over these microbodies.
• Membrane-hemoglobin S interaction promoted microspherulation and membrane loss.
• Membrane-bound hemoglobin increased significantly in ISCs, correlating with adenosine triphosphate depletion.
• Alterations in membrane protein composition, including heteropolymer formation and changes in bands 4.1, 7, 8, and globin, were identified.

Conclusions:

• Hemoglobin S interaction with the erythrocyte membrane is a critical factor in ISC generation.
• Cross-linked membrane protein polymers contribute to the biophysical abnormalities and shape distortion of ISCs.
• These findings offer a unified concept for the determinants of ISC genesis in sickle cell disease.