**7. Conclusion and outlook**

186 Blood Cell – An Overview of Studies in Hematology

**Spectrin Membrane Cytoskeleton**

permission, from (Kim, Higgins et al.,2012).

**6.7. Other conditions altering RBC deformability** 

**Normal Cell membrane**

**Transmembrane PS**

**Unexposed transmembrane segment**

**(a)**

**protein**

5 μm

**(b) (c) (d)**

**Figure 14.** (a) Illustration showing structural modifications inside a sickle RBC. Modified, with permission, from (Barabino, Platt et al.,2010). (b-d) Typical morphologies of sickle RBCs measured by DPM; (b) echinocyte, (c) discocyte, and (d) crescent-shaped irreversibly sickled cell. Reproduced, with

There are still many pathophysiological conditions that affect the deformabiltiy of RBCs, which are not covered in the above sections. Several hereditary disorders associated with formation of RBC membrane structures and Hb protein can result into altered RBC deformability. Thalassemias, causing the formation of abnormal Hb molecules due to the limited synthesis of the globin chain, results into loss of RBC deformability. Thalassemia is thus often accompanied by the destruction of a large number of RBCs in spleen, accompanying with the enlargement of spleen. In addition, abnormal Hb molecules in thalassemia often caues the formation of Heinz bodies, inclusions within RBCs composed of denatured Hb, and it causes the local rigidification of RBC membrane (Reinhart, Sung et al., 1986). Ektacytometer study measured that RBCs in hereditary spherocytosis showed markedly diminished deformability while their surface/volume ratio was normal (Nakashima and Beutler,1979). RBCs from the patients with homozygous hereditary elliptocytosis exhibits marked abnormalities in deformability and membrane fragility; these changes are closely related to the reduced levels of band 4.1 proteins (Tchernia, Mohandas et al.,1981). Since band 4.1 plays an important role in the modulation of spectrin-actin interaction, it has been suggested to be closely related to the maintenance of normal

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3 [μm]

**Abnormal cell membrane**

**Transmembrane protein**

**Exposed** 

**PS flip**

**transmembrane segment**

**Hb polymer**

> We have highlighted techniques for studying RBC deformabilty. Due to various deformability test techniques developed in the last years, our understandings on pathophysiology of RBCs have been significantly improved. Recent advances have enabled the precise measurements of various biomechanical properties of RBCs under systemically controlled conditions that mimic complex *in vivo* physiological environments. However, three major technical issues should be resolved in order to bring a much significant impact. First, the molecular mechanisms on RBC deformability should be directly accessed and studied. Employing biochemical assays such as molecular imaging and genetic knock-out methods, the relation between molecule-level changes and cellular-level deformability alterations can be studied. Second, such measurements should be performed at individual cell levels. Profiling mechanical, chemical, and biological properties at the cellular levels and their correlations may allow accessing to unexplored regimes of diseases mechanisms. Third, interactions between cell-to-protein, cell-to-cell, and cell-to-vessel should be considered, since these interactions can be affected and *in turn* modify RBC deformability. As more knowledge is gained about the pathophysiology of RBCs and their circulation through biomechanical studies, the potential for the development of novel diagnostic and treatment strategies for various RBC-related disease will become real and answer to important questions in hematology.
