Kozyrina, A. N. | Search bioRxiv

bioRxiv2025

Age-associated Tissue Organisation Shifts Retinal Pigment Epithelium Actomyosin Plasticity in Phagocytosis

Tissue homeostasis relies on mechanical feedback loops balanced by cell loss and proliferation. However, maintaining this balance becomes particularly challenging in postmitotic tissues, where alternative mechanisms replace compensatory proliferation. In the postmitotic retinal pigment epithelium (RPE), these mechanisms include significant structural adaptations over time. Yet, how these adaptations relate to epithelial mechanical homeostasis and age-associated functional decline remains poorly understood. To establish the relationship between structural changes, mechanical homeostasis and function, we developed an in vitro reductionistic model mimicking age-related reduction in RPE cell density. Inducing large-scale apoptosis in postmitotic stem cell-derived RPE monolayers recapitulates structural hallmarks of aged tissue, such as reduced cell height, shortened microvilli and cytoskeletal reorganisation. This new structure acquires a new mechanical equilibrium, evidenced by tissue stiffening and enhanced junctional contractility. Functionally, the monolayers display impaired vision-supporting phagocytosis of photoreceptor outer segments. Mechanistically, modulation of actin nucleators, Arp2/3 and formins, demonstrates that apicolateral monolayer deformation is critical for phagocytosis and may be compromised in aged RPE. Our findings suggest that a shift in mechanical homeostasis due to cell loss is a major driver of age-related RPE functional decline. Importantly, we show that structural remodelling in ageing alone can compromise tissue function, independent of other stressors.

cell biology↗

bioRxiv2023

Laminin alpha 5 - induced mechanical homeostasis modulates retinal epithelium functionality

Epithelial cells are highly interconnected, whereby they acquire mesoscale mechanical properties to accomplish specific tissue functions. In homeostasis, this mechanical status can be summarised as mechanical homeostasis, regulated by the balance of intercellular tension and extracellular matrix adhesion forces. In the outer retina, the significance of this force balance and its consequences for vision remains poorly understood. We found that the density of basement membrane laminins modulates the level of retinal pigmented epithelium contractility, which directly controls its efficiency in phagocytosing photoreceptor outer segments. In vivo, the density gradient of laminins follows retinal functional demand, supporting the physiological role of laminins in controlling epithelial mechanical homeostasis. Our data suggest that laminin density and isoform heterogeneity can differentially engage integrins {beta}1 and {beta}4, the ratio of which determines the contribution of actin vs keratin cytoskeleton in balancing tissue mechanics. With this work, we suggest that the extracellular matrix-defined mechanical status of retinal pigmented epithelium is a novel parameter for visual function. SignificanceIn the retina, the retinal pigmented epithelium (RPE) is responsible for the daily phagocytosis of photoreceptor cell fragments, a process vital for visual function. Along the visual axis, there is a natural decrease in the ratio of photoreceptors to RPE cells, indicating a decrease in RPE functional demand. This study reveals that the density of laminins in RPE basement membrane also diminishes along this axis, critically influencing RPE function by regulating its contractility. For the first time, we demonstrate the presence of a laminin- defined mechanical gradient within the RPE, which determines its capacity to support photoreceptor cells. Our findings highlight the importance of mechanical properties as a key factor in visual function, offering new insights into retinal health and disease.

biophysics↗