Abnormalities of Red Cell membrane Lecture NO: 1st MBBS Dr Muhammad Ramzan

Red cell membrane abnormalities – the definition These are the inherited diseases due to mutations in various membranous or/and skeletal proteins of the red cell It results in ↓passive deformation, life span and premature removal of RBC from circulation by Haemolysis These include Hereditary Spherocytosis, Elliptocytosis and Somatocytosis Hereditary RBC membrane defects----. Wilma Barcellini.Blood Tranf2011. July;9(3):274- 277

Integrity of cell membrane – the background Mutation of skeletal proteins changes RBC shape Integrity of the Red cell membrane is maintained by the vertical interaction B/W Lipid Bilayer and membrane skeleton Mutation of the skeletal proteins leads to secondary defects in Spectrin assembly and unstable RBC membrane. 1 RBC changes from discoid to sphere; loses passive deformation, Trapped in capillaries, haemolyzed and results in anaemia 2 Pediatrics in Review; May 2004. VOLUME 25/ISSUE 5

RBC integrity - Vertical Interaction B/W Lipid Bilayer and cytoskeleton

Normal RBC – the morphology Passive deformation RBC is a biconcave disc like a rounded ball that appears wider at the ends and narrowest in the middle : when squeezed from 2 opposite ends Its average diameter is 7.8µm and 2µm in thickness ,However, Its thickness is < 1 mµ in the center Red cell has high surface area relative to cell volume that helps in rapid diffusion of respiratory gases Has the ability of passive deformation ( changes to < 1/3 of its diameter) ( Healthhype.com)

Red cell - Morphology

Red Cell – the characteristics

Red cell membrane - the characteristics the only structural component RBC is unique among the body cells that its plasma membrane accounts for all of its characteristics. These include: antigenic; transport (anions) and ability to undergo passive deformation(1/3) during its passage through: microvasculature especially in spleen)  ↑surface area relative to intracellular volume Helps in rapid diffusion of Respiratory gases Wilma Barcellini.Blood Tranfus. 2011. July;9(3):274- 277

Red Cell passive deformation 1/3 of its diameter It is the ability of the RBC to change and restores its shape after passing through microcirculation normally It is due to 1. excess of plasma membrane and is carried out without its stretching and 2. flexibility of Cytoskeleton Helps to complete the normal life span of RBC (120 days) 1 Prevents the RBC trapping, haemolysis and maintains blood flow 2 Red cell membrane; past, present and Future .2008 www.blood journal.org

Deformation of Red cell

Normal and damaged RBC

RBC membrane – the parts The red blood cell membrane consists of 3 basic components: A Lipid Bilayer, Trans membrane (integral) proteins and A Cytoskeleton network.   

RBC membrane – the parts

Lipid Bilayer – A semi permeable part of the plasma membrane The lipid Bilayer is a semi permeable compartment of the plasma membrane that separates 2 aqueous ones : The cytoplasm from the extracellular medium.  1 It consist of Phospholipids ; CH, CH esters, u FA and proteins 2 It is liquid in nature that allows the lateral movements of integral proteins (prevents vertical movements) 3 Maintains the fluidity of the cell membrane 4

Phospholipid Bilayer – A subunit of RBC membrane

Tran membrane/Integral proteins the types ` Transmembrane proteins cross the lipid Bilayer and have lateral mobility in the membrane Major ones are; Glycophorins ,Band3, Aquaporins and RHAG(Rhesus proteins) The red cell glucose transporters (GLUT-1) Band 3 is an ion transporter , a diamer Band 3 Tetramer; crosses the lipid Bilayer. Its Cytoplasmic domain interacts with the cytoskeleton via : Ankyrin and Spectrin

Trans membrane Proteins of RBC

Tran membrane proteins - the role Glycophorins, general proteins that contribute to Glycosalytion Glycophorin C crosses the Bilayer to interact with Protein 4.1 with in the junctional complex of Cytoskeleton Band 3 is an ion transporter(HCO3 for Cl++ ions) Aquaporin is a membrane water channel protein RH AG (Rhesus) proteins are associated with Band 3 and ABO blood group system The red cell Glucose transporter(GLUT1) is passive one and is present in other tissues also.

Red cell integral proteins

Red cell proteins – Band3

The Cytoskeleton – A network of skeletal and Cytoplasmic portions of Tran membrane proteins The cytoskeleton is an irregular hexagonal network of α and β Spectrin moles which are tied together mainly by the : Ankyrin, Actin; Band 3 and other Skeletal proteins at nodes called the junctional complexes. The skeleton makes a 2 D network which is very flexible and compressible and allows passive deformation of RBC

Red cell Cytoskeleton

Cytoskeleton - the Spectrin Spectrin is the major component of the cytoskeleton. Major role is: To provide support to the Lipid Bilayer 1 Maintains the cell shape . 2 Regulates the lateral movement of the Integral proteins 3 It interacts with the membrane and Skeletal proteins by vertical and horizontal interactions Dr Avinash Deo. February, 2014

Red cell Cytoskeleton

RBC – Cytoskeleton A hexagonal network

Disorders of RBC membrane the haemolytic anaemias These disorders comprise a group of hemolytic anaemias that present with different clinical and laboratory findings These include hereditary Spherocytosis; hereditary Elliptocytosis and hereditary Somatocytosis

Pathogenesis - Deformed RBC (spherical shape) loss of memb Pathogenesis - Deformed RBC (spherical shape) loss of memb. Surface area to intra cellular volume The primary cellular defect is the loss of membrane surface area relative to intracellular volume Defects in Spectrin assembly leads to the : Spherical shape of RBC from discoid one 1 Reduction in the ability of RBC for passive deformation 2 Lipids are lost from the lipid Bilayer as micro vesicles 3

Deformed RBC – the consequences Change in the shape of RBC (to spherical) loses its ability to move freely in micro circulation (Splenic) RBC are trapped, their membranes damaged that ↑ their chances for Haemolysis and : their premature removal from the circulation It results in haemolytic anaemia

Haemolytic anaemia

Hereditary Spherocytosis (HS) HS is the most common red cell membrane disorder in children Spherocytes are rounded Red cells that have lost the ability to change their shape (deformation) Spherocytes cannot move freely in capillaries with short lifespan Chronic haemolysis is the hallmark of HS HS is diagnosed by the presence of spherical RBC on the Peripheral blood smear

Hereditary Spherocytosis