Online Ph.D. Defense: “Importance of the Fibrinogen Alpha-C Connector in Fibrin Fiber Mechanical Properties and Automated Fiber Diameter Measurements in SEM Images of Fibrin Clots” — November 24, 2020 at 4 PM
Mr. Ali Daraei, Ph.D. Candidate
Mentor: Professor Martin Guthold
Department of Physics
Wake Forest University
Tuesday, November 24, 2020 at 4:00pm – 6:00 pm
(Private defense will follow public presentation.)
Via Video Conference (contact firstname.lastname@example.org for link information)
Fibrinogen is the key mechanical protein in blood coagulation since it is the building block of fibrin fibers, and these 100 nm thick fibers provide mechanical and structural stability to blood clots as they stem the flow of blood. The major structural and mechanical component of a blood clot is a meshwork of fibrin fibers. Therefore, to better understand blood clots and their behavior, it is critical to understand the fundamental mechanical and structural properties of the main constituents of a clot-fibrin fiber, and the molecular and physiological determinants of their mechanical properties. Fibrinogen has two large, intrinsically unfolded regions, termed alpha C regions, which comprise 27% of its molecular weight. The role of these unfolded regions has long puzzled scientists. We found that they contribute significantly to the mechanical properties of fibrin fibers, which, in turn, determine the stability of blood clots.
We used a nano-mechanical manipulation method, based on a combined atomic force and optical microscope, to determine the mechanical properties of native fibrin fibers, and of fibers formed from a variant in which the alpha C region was truncated (deleted). Compared to native fibrin fibers, fibers formed from the truncated variant showed dramatically different mechanical properties. The extensibility (fracture strain) was reduced by a factor of 1.7 (from 2.1 to 1.26) and the modulus (stiffness) decreased by a factor of 3 (from 3 MPa to 1 MPa).
We also evaluated the accuracy of a plug-in for the open-source, NIH-supported image analysis program ImageJ, called DiameterJ, in determining the diameters of fibers in Scanning Electron Microscopy (SEM) images. We found that for the SEM images with an optimal pixel size of 8-10 nm (13-16 pixels/fiber) several DiameterJ algorithms strongly correlated with the manual measurements. We also evaluated the emerging best subsets of the 24 algorithms on two patient data sets to see if the trends in samples from healthy individuals and patients that were detected by manual measurements can be reliably detected by these automated algorithms.
1. Daraei, A., Pieters, Baker, S., Ariens, R., M., Weisel, J., Litvinov, R., M.P.M. (Moniek) de Maat, de Lange, Z., Guthold, M., “Automated fiber diameter and porosity measurement of fibrin clots in SEM images”, In preparation for submission to Journal of Thrombosis and Haemostasis, Nov 2020.
2. Maksudov, F., Daraei, A., Guthold, M., Barsegov, V., “Theoretical modeling of experimental force-extension spectra and single fiber’s rupture.” In preparation for submission to Biomaterial, Nov 2020.
3. Daraei, A., Dement, T., Hudson, N., Guthold, M., “Intrinsically unfolded alpha-C region of fibrinogen is the major contributor to the mechanical strength of fibrin fibers”, In preparation for submission to Journal of Thrombosis and Haemostasis, Nov 2020.
4. Daraei, A., Dement, T., Hudson, N., Guthold, M., “Intrinsically unfolded alpha-C region of fibrinogen is major contributor to the mechanical strength of fibrin fibers”, peer-reviewed abstract, Biophysical Journal, 2020.
5. Daraei, A., Pieters, M., de Lange, Z., Guthold, M., “Automated Fiber Diameter and Porosity Measurement of Fibrin Clots in SEM Images”, peer-reviewed abstract, Biophysical Journal, 2020.