Photo by Don Boomer
From left to right: Study authors Velia Fowler, Alyson Smith, and Roberta Nowak
New research indicates that non-muscle myosin II-A (NMIIA) plays a key role in maintaining red blood cell (RBC) shape and deformability.
Researchers found evidence to suggest that NMIIA forms filaments in RBCs, and specialized regions at both ends of the filaments can pull on actin to control the stiffness of the cell membrane.
“You need active contraction on the cell membrane, similar to how muscles contract,” explained study author Velia Fowler, PhD, of The Scripps Research Institute in La Jolla, California.
“The myosin pulls on the actin to provide tension in the membrane, and then that tension maintains the biconcave shape.”
Dr Fowler and her colleagues described these findings in PNAS.
The researchers noted that RBC shape and deformability depend upon the membrane skeleton—a network of actin filaments (F-actin) cross-linked by spectrin tetramers.
And although NMII motors are known to exert force on F-actin networks to control cell shapes, no one had investigated a function for NMII contractility in the spectrin–F-actin network of RBCs. So Dr Fowler and her colleagues did just that.
The researchers said their work suggests NMIIA is the predominant RBC NMII isoform, and NMIIA motor activity regulates interactions with the spectrin–F-actin network to control RBCs’ shape and deformability.
Specifically, NMIIA forms bipolar filaments in RBCs, and these filaments associate with F-actins via their motor domains. It is through these interactions that NMIIA contractile forces promote membrane tension to maintain RBC shape and deformability.
To test these findings, the researchers treated RBCs with a compound called blebbistatin, which inhibits NMII motor activity.
After treatment, the team observed a decrease in NMIIA filaments associated with the RBC membrane and evidence of decreased membrane tension. The treated RBCs became elongated and showed a reduction in biconcavity as well as an increase in deformability.
The researchers believe this work could have applications for diseases in which RBCs are deformed. In fact, the team thinks inhibiting NMIIA in RBCs might prove useful for treating patients with sickle cell disease, as it could restore some elasticity to the patients’ RBCs.
Going forward, the researchers hope to learn more about what regulates NMIIA’s activity in RBCs and other cells.