Retinal Müller glia alterations and their impact on ocular glymphatic clearance in an Alzheimer's disease mouse model

Background: Retinal amyloid-β (Aβ) accumulation has been detected in Alzheimer's disease (AD) and correlates with brain Aβ deposition, suggesting that the retina may reflect central disease processes. Impaired Aquaporin-4 (AQP4)-mediated glymphatic clearance contributes to Aβ accumulation in AD brains, but whether similar mechanisms affect the retina remains unclear. Objective: This study investigated glymphatic transport and Müller glia cell (MGC) remodeling in 3-month-old female 5xFAD mice. Methods: Fluorescent immunostaining of 5xFAD and wild-type (WT) retinas (n = 5 for each) of AQP4, glial fibrillary acidic protein (GFAP), and glutamine synthetase (GS) were performed to evaluate MGC function. To evaluate bulk glymphatic clearance rates along the optic nerve, intravitreal injections of fluorescent Aβ and cadaverine (interstitial fluid indicator) were performed (n = 5 for each WT, AD). Results: 5xFAD retinas showed upregulated AQP4 across all retina layers with increased perivascular localization, particularly in the peripheral retina. Indicators of more efficient perivascular Aβ clearance were observed in peripheral versus the central retina. Elevated GFAP in 5xFAD peripheral retinas indicated glial activation. Despite these changes, tracer-based assays showed no significant differences in bulk glymphatic flow. Conclusions: These findings suggest that retinal Aβ accumulation at this disease stage is unlikely driven by impaired glymphatic clearance but may result from enhanced local Aβ production. While later glymphatic dysfunction cannot be excluded, our results highlight the spatiotemporal dynamics of MGC remodeling and underscore the importance of a) focusing diagnostic imaging studies on the retinal periphery, and b) longitudinal evaluation of retinal amyloid plaque formation mechanisms.