Elucidating the Influence of Microglia on Retinal Ganglion Cells in a Human Pluripotent Stem Cell Model

Abstract

Glaucoma is a complex disease that leads to irreversible blindness, characterized by the loss of retinal ganglion cells (RGCs), which are the cells that transmit visual information from your eye into your brain. Evidence suggests that microglia, the resident immune cells in the central nervous system, may have a detrimental role in the onset and the progression of glaucoma. Microglia become activated in response to damage, pathogens and toxins and are initially thought to be beneficial to RGCs. However, when these cells are activated for excessive periods of time, they are thought to be harmful to RGCs. Thus, we sought to develop novel human pluripotent stem cell (hPSC)-derived microglia, astrocyte and RGC co-cultures to determine how microglia activation modulates RGC phenotypes in a human cellular model. Healthy and LPS-activated microglia were first co-cultured with RGCs for up to 3 weeks and the effects of microglia upon RGCs were assessed. Additionally, healthy and LPS-activated microglia were also co-cultured with astrocytes and RGCs for up to three weeks to assess if LPS-treated microglia can activate astrocytes and the effects this would have on RGCs. Results showed that when co-cultured with RGCs alone for 1 week, microglia activation is initially beneficial to RGCs. However, when co-cultured with RGCs for 3 weeks, microglia activation leads to RGC damage. Consequently, when astrocytes are present, microglia activation is harmful to RGCs in both short-term and long-term co-cultures, suggesting an additional role for microglia modulation of astrocytes, further leading to neurodegeneration. Taken together, our results have allowed for the precise study of how individual cell types are adversely affected in disease-relevant states, how microglia can directly influence RGCs, and how multiple co-cultures of human microglia, astrocytes and RGCs allows for a more sophisticated investigation of cellular interactions in disease states relevant to glaucoma.