Increased Mechanosensitivity of Aging Retinal Pigment Epithelial Cells

Abstract

Age related macular degeneration (AMD) is the leading cause of blindness for people over 65 around the world1. Progression of this disease is centered in the retina and its associated structures at the back of the eye. It is characterized by degeneration and breakdown of the retina, ultimately leading to a pathological healing response resulting in fibrotic lesions between the retina’s epithelial monolayer and its extracellular matrix, disrupting photoreceptor function. The Bruch’s membrane, or extracellular matrix associated with retinal pigment epithelial (RPE) cells, stiffens with patient age2. Higher ECM stiffness induces activity in mechanosensitive Rho/YAP pathways in RPE cells by polymerizing the contractile cytoskeletal protein F-actin. This process also leads to higher RPE cell contractility on stiffer substrates, indirectly demonstrating that aging is linked to RPE cell and microenvironmental mechanical properties3. This pathway also leads to epithelial-to-mesenchymal transition (EMT) or dedifferentiation in RPE cells, meaning they no longer perform the function of a healthy RPE cell4. Recent studies show that aging affects cellular mechanical properties such as contractility, but it is unclear how the aging process affects the mechanics of RPE cells directly. I hypothesized that there is a direct correlation between RPE cell contractility and age such that contractility changes with other mechanical properties in the aging retina. To test this, the contractility and cell area of human RPE cell lines from patients aged 29-94 were assessed using traction force microscopy (TFM) on compliant (5kPa) and stiff (10kPa) substrates. My data indicates that cell contractility in young patients is lower than that of aged patients, while cell spreading is lower in aged patients. Mechanosensitivity of aged cell lines, as measured by the average difference in contractility of each cell line on compliant and stiff substrates, is nearly double that of the young cell line. These data suggest RPE cells in aged patients are more sensitive to changes in the mechanical properties of tissues. This has implications in the understanding of AMD, as a necessarily age-related condition, and may identify additional therapeutic targets. Further investigation into the impact of increased contractility and mechanosensitivity in aged patients on RPE breakdown in AMD and other degenerative diseases of the retina is required to provide a complete understanding of the relationship between aging and retinal disease progression.