Mechanical Engineering Professor Investigates Sickle Cell Disease

By John Giardina

Until recently, the pairing of molecular biology and mechanical engineering would have been viewed as highly unusual. But thanks to an explosion of imaging and simulation techniques over the past few decades, there is an opportunity to view biology at the molecular and even nano-levels through the eyes of an engineer. Dr. George Lykotrafitis, assistant professor in the Department of Mechanical Engineering, has made full use of this opportunity. Using state-of-the-art instruments, Dr. Lykotrafitis researches the intricacies of sickle cell anemia, a debilitating, painful disease affecting one in every 5,000 Americans, which unleashes a myriad of health complications and reduces by half the life expectancy of afflicted individuals. The rate is even higher in developing regions of the world.

Sickle cell anemia, or sickle cell disease, involves a genetic mutation that alters the genetic code of hemoglobin, a protein on red blood cells tasked with carrying oxygen throughout the body. Normally, red blood cells are highly elastic and able to alter their shape to pass easily through capillaries. But mutated hemoglobin proteins link together to form a network of stiff polymer fibers. These long fibers distort the shape, strength and elasticity of the cell, and along with increased red blood cell adherence to the blood vessels make it difficult for red blood cells to squeeze through tiny capillaries and often producing vessel blockages or tears. This can reduce oxygen flow, which can severely damage organs and cause intense pain if left unchecked. Furthermore, the defining sickle shape of the red blood cells decreases the surface area to which oxygen can bind, increasing oxygen deprivation. Finally, the lifespan of sickle cells is much less than that of normal red blood cells, resulting in anemia and further reduction in oxygen flow throughout the body.

In studying sickle cell anemia, Dr. Lykotrafitis aims to quantify the different characteristics of the membranes of erythrocytes with sickle cell anemia. He is particularly interested in studying the elasticity of the cell membrane and the presence of certain proteins on the cell membrane that encourage adhesion to proteins on the inner lining of blood vessels. Using different tests to study these characteristics, he is able to advance our understanding of the disease. He says, “What we do here, basically, is quantify. Then with that baseline, we can see how drugs affect specific cells.”

A critical tool Dr. Lykotrafitis employs in examining cell membranes is atomic force microscopy (AFM). In contrast with a standard optical microscope, which uses light to illuminate a surface, an AFM “feels” the surface and enables researchers to measure the texture and elasticity of the membrane. In AFM, an extremely small needle moves systematically up and down along the entire surface it is scanning, recording the texture of the surface by assigning the specific position on the sample with a corresponding “altitude.” In the end, it creates a kind of topographic map of the surface, showing the shape and texture of the membrane. This provides a detailed, three-dimensional image that cannot be produced with an optical microscope. While the AFM is scanning, it can also measure the elasticity of the membrane. The needle will basically push into the membrane, using the amount of force it takes to push down to calculate a measure for the stiffness of the membrane. Beyond determining the shape and elasticity of the cell, an AFM can also quantify the presence of certain proteins on the cell membrane, which adhere to the lining of blood vessels, causing blockages in blood vessels and decreased oxygen flow. Recent studies have suggested that sickle cell disease increases the expression of these proteins. For this application, the needle on the AFM is coated with an antibody that corresponds to the protein. When the antibody-laden needle touches one of the target proteins, it binds to it. When the AFM raises the needle, it encounters, first, resistance, and, then, as the bond breaks, the needle swings upward with greater force than normal. This then indicates that a target protein is located at that point on the membrane. After the whole cell is scanned, the AFM can map the concentration of the protein across the membrane.

Dr. Lykotrafitis joined UConn in 2009 after conducting post-doctoral studies under Dr. Subra Suresh at MIT. He earned two doctoral degrees, one from the National Technical University of Athens, Greece in applied mathematics and physical sciences and another from Caltech in mechanical engineering. Dr. Lykotrafitis hopes his research will unveil important clues to sickle cell disease, a disease with a well-known genetic origin but with virtually no cure. “For example,” he says, “it is not even known how much red blood cell adhesion plays a role in sickle cell disease.” Hopefully, with the help of Dr. Lykotrafitis’ work, that question, among many others, will be answered, blazing a path that may lead to the development of effective therapies and remedies for alleviating the effects of a brutal and devastating disease. Read more about Dr. Lykotrafitis’ research here.

Published: February 3, 2011