Nano-mechanical Compliance of Muller Cells Investigated by Atomic Force Microscopy

It has been known that a single Muller cell displays a large variation in the cytoskeletal compositions along its cell body, suggesting different mechanical properties in different segments. Muller cells are thought to be involved in many retinal diseases such as retinoschisis, which can be facilitated by a mechanical stress. Thus, mapping of mechanical properties on localized nano-domains of Muller cells could provide essential information for understanding their structural functions in the retina and roles in their pathological progresses. Using Atomic Force Microscopy (AFM) - based bio-nano-mechanics, we have investigated the local variations of the mechanical properties of Muller cells in vitro. We have a particular interest in identifying elastic moduli in regions closer to three distinctive segments of the cells - process, endfoot, and soma. Using the modified spherical AFM probes, we were able to accurately determine mechanical properties, i.e., elastic moduli from the obtained force-distance curves. We found that the regions closer to soma were mechanically more compliant than regions closer to endfoot and process of Muller cells. We found that this lateral heterogeneity of the mechanical compliance within a single Muller cell is consistent with reports from other cell types. The local variation in mechanical compliances along a single Muller cell may support their diverse mechanical functions in the retina such as a soft mechanical embedding, mechanosensing, and neurotrophic functions for neurons.