Glial and immune dysregulation in glaucoma independent of retinal ganglion cell loss: a human post-mortem histopathology study

Glaucoma is characterized by progressive retinal ganglion cell (RGC) loss and optic nerve head (ONH) changes, but the roles of glial activation and immune responses remain unclear. This study examines gliosis, microglial diversity, and inflammation in postmortem retinal tissues. Postmortem retinal and ONH samples (total n = 50) from patients with open-angle glaucoma (G, n = 18) were compared with those from age-matched controls (n = 32), including healthy individuals (Ctrl) and disease controls (patients with early age-related macular degeneration [AMD] and diabetes mellitus [DM]). Immunostaining was performed to assess glial activation, blood–retinal barrier (BRB) integrity, and immune infiltration, which were quantified via ImageJ and Zen lite. Generalized estimating equations (GEEs) with Bonferroni correction accounted for intrapatient variability. G retinae presented significant RGC loss accompanied by widespread gliosis, with activation of microglia (Iba1), astrocytes (GFAP), and Müller cells (Vimentin). This gliotic response differed across conditions, with astrocyte activation being more prominent in DM and microglial activation predominating in AMD. In glaucoma, gliosis is evident even in early-stage disease, regardless of the severity of retinal ganglion cell (RGC) loss or structural changes in the ONH. Furthermore, microglia showed a marked shift in morphological diversity, transitioning to hyperramified, bushy, and amoeboid forms, along with an increased distribution of activation markers such as CD45, CD11b, and CD163. Additionally, biochemical evidence of alterations to the BRB integrity, characterized by reduced tight junction protein expression, facilitates immune cell infiltration, as indicated by the minimal and inconsistent presence of CD3/CD4+ T cells. Gliosis persisted regardless of RGC loss severity, suggesting that gliosis progresses independently of neuronal degeneration. Unlike AMD and DM, where specific glial subtypes dominate, glaucoma exhibits widespread gliosis. Microglial heterogeneity indicates the existence of a continuum of functional states. Furthermore, dysregulation of the BRB, inconsistent immune infiltration, and multimodal microglial activation indicate that the inflammatory response in glaucoma patients is driven primarily by resident microglia, with limited interactions with infiltrating immune cells. These findings highlight the need for further research into glial modulation as a potential therapeutic strategy.