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Spectrin, red cell shape and deformability. I. Membrane curvature in genetic spectrin deficiency
Abstract:
Using novel microscopic techniques for observing individual cells in suspension, the shape and deformability of the erythrocytes of a spectrin-deficient strain of mouse were investigated in vitro (fresh and after fixation) and in vivo (intravital microscopy of the mesenteric capillaries). The animals were identical to those studied by Greenquist et al. [14]; however, in contrast to the descriptions by these authors, in the present study, spherical cells were seen only exceptionally. Instead, sphero-echinocytes, spherules with tethered microvesicles, myelin figures and occasional stomato-spherocytes were observed. This pleomorphy, also seen in scanning electron micrographs, can be explained by the fact that in the majority of these cells the membrane assumes an extremely positive outward curvature. After osmotic dehydration, all cells responded by developing progressive membrane protrusions with a positive curvature. Osmotic inflation led to reincorporation of the membrane tethers. After hypoosmolar lysis, the ghosts of the spectrum-deficient mouse cells also showed a pronounced tendency to assume shapes characterized by a progressively positive outward curvature. In vivo observation of the mouse erythrocytes using high magnification interference contrast optics confirmed this in vitro observation. Thus, it is concluded that spectrin deficiency does not primarily lead to spherocytosis: instead, the equilibrium shapes assumed are associated with membrane evaginations which are easily torn off from the main cell body by mechanical forces.
Insights
Spectrin deficiency in mouse erythrocytes causes abnormal cell shapes, not spherocytosis. These cells exhibit membrane evaginations prone to mechanical detachment, impacting red blood cell deformability.
Area of Science:
- Cell Biology
- Hematology
- Biophysics
Background:
- Spectrin is a key cytoskeletal protein in erythrocytes, essential for maintaining cell shape and mechanical stability.
- Previous studies suggested spectrin deficiency leads to spherocytosis, a condition characterized by spherical red blood cells.
- Understanding the precise morphological consequences of spectrin deficiency is crucial for diagnosing and treating related anemias.
Purpose of the Study:
- To investigate the in vitro and in vivo shape and deformability of erythrocytes from a spectrin-deficient mouse strain.
- To clarify the morphological abnormalities associated with spectrin deficiency, contrasting with previous findings.
- To elucidate the relationship between spectrin deficiency, cell shape, and membrane mechanics.
Main Methods:
- Utilized novel microscopic techniques for observing individual cells in suspension.
- Performed in vitro studies on fresh and fixed erythrocytes.
- Conducted in vivo intravital microscopy of mesenteric capillaries.
- Employed scanning electron microscopy and high magnification interference contrast optics.
Main Results:
- Spectrin-deficient erythrocytes exhibited pleomorphic shapes, including sphero-echinocytes, spherules with tethered microvesicles, myelin figures, and stomato-spherocytes, rather than uniform spherocytosis.
- The predominant shape abnormality involved an extreme positive outward curvature of the cell membrane.
- Cells showed progressive membrane protrusions upon osmotic dehydration and reincorporation of tethers upon osmotic inflation.
- Erythrocyte ghosts after hypoosmolar lysis also displayed a tendency towards positive outward curvature shapes.
- In vivo observations confirmed these in vitro findings, revealing membrane evaginations easily detached by mechanical forces.
Conclusions:
- Spectrin deficiency in mouse erythrocytes does not primarily cause spherocytosis.
- The observed abnormal shapes are characterized by membrane evaginations with a positive outward curvature.
- These evaginations are mechanically fragile and prone to detachment, contributing to altered red blood cell deformability and potential hemolytic anemia.