Application of Optical Tweezers to Understand the Effect of Renal Ciliary Length Alterations on Ciliary Biomechanics
Authors: Nag Subhra , Resnick Andrew 
Published: June 2021

A renal primary cilium act as a cellular mechanosensor. Fluid flow causes bending of renal cilia resulting in the increased intracellular concentration calcium ion, a second messenger which initiates downstream cell signaling pathways. Better understanding of ciliary biomechanics can help to interpret how ciliary mechanotransduction may be impaired in ciliopathies, such as polycystic kidney disease. Fluid flow in kidney tubules can generate three separate forces: shear and stretch acting on renal tubule wall or epithelial cell layers, and hydrodynamic drag which acts on protruding structures i.e., primary cilia. As compared to direct fluid flow experiments, optical trapping method has the advantage that it can isolate and evaluate only the effects of hydrodynamic drag on ciliary biomechanics, avoiding any background effects of shear and stretch forces acting on cellular layers. Optical tweezers technique is non‐invasive and non‐contact measurement and allow accurate measurement due to the ability to control a trapped primary cilium at a time. Thus, using optical tweezers biomechanical properties of an individual cilium can be correlated with bio‐physiological features of the cilium, such as length and spatial distribution.

As reported previously by other research groups, kidney transplantation and ischemia‐reperfusion injury can affect renal ciliary lengths. Previous cell culture studies have shown presence or absence of fluid flow affects ciliary lengths of mouse kidney cortical duct epithelial cells. Stabilization of hypoxia inducible factor (HIF) 1α by cobalt chloride (CoCl2) can affect renal ciliary lengths [1] and can also alter bending modulus of the cilia [2]. We aim to understand the significance of altered ciliary length on the kidney cellular function and diseases. In this study, using optical trapping method we aim to understand if ciliary lengths are related to ciliary biomechanics and flow sensing. We used Mardin‐Darby Canine Kidney (MDCK) epithelial cells which were differentiated by serum starvation to generate primary cilia. We determined the mean square displacement (MSD) values of optically trapped cilia and correlated with ciliary lengths. The MSD value measures the displacement of a particle (i.e., tip of a cilium) from the initial position and long‐time section of MSD relies on the spring constant. MSD values can represent ability of cilia to deflect in response to fluid flow. Currently, we are trying to manipulate ciliary lengths using HIF stabilizer CoCl2 in the presence or absence of HIF inhibitors: chetomin and echinomycin. We anticipate that chetomin or echinomycin may restrict alterations of ciliary length by CoCl2 and may maintain the MSD value of cilia to a base level i.e., without any HIF stabilization. These findings can establish a direct connection between the ciliary length and ciliary flow‐sensing. Thus, this study aims to test whether renal epithelial ciliary lengths are altered in order to adjust the ciliary biomechanical properties or flow‐sensing function as a cellular response to adapt adverse physiological conditions, such as lack of fluid flow and localized hypoxia.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.