Müller glia-mediated protection of retinal ganglion cells from ethambutol-induced neurotoxicity through brain-derived neurotrophic factor

Ethambutol (EMB)-associated optic neuropathy is the most common toxic optic neuropathy and poses a significant visual threat worldwide. This study aimed to investigate the neuroprotective roles of Müller glia, the most abundant macroglia in the retina, and their associated growth factors in supporting retinal ganglion cells (RGCs) under EMB-induced toxicity. Induced RGC-like cells (iRGCs), differentiated from human induced pluripotent stem cells, and Müller glial cell line MIO-M1 were used as cellular models. The response of iRGCs to EMB was investigated by using RNA sequencing. A transwell co-culture system was used to evaluate the protective effect of MIO-M1 cells on iRGC survival. Candidate trophic factors from MIO-M1 cells were measured by using quantitative RT-PCR. Brain-derived neurotrophic factor (BDNF) was identified as the major factor contributing to the neuroprotective effect from Müller glia. The effect of BDNF was further validated in both iRGCs and mouse retinal organotypic culture under EMB toxicity. Downstream signals of the BDNF pathway were investigated by Western blot. RNA sequencing revealed that EMB significantly disrupted neurotrophins and BDNF-associated pathways in iRGCs. Co-culture with MIO-M1 cells markedly enhanced the survival of iRGCs during EMB exposure. mRNA of BDNF and nerve growth factor (NGF) were elevated in MIO-M1 cells, while only BDNF improved the survival and morphological integrity of iRGCs under EMB treatment. Administration of BDNF also improved the survival of RGC in mouse retinal explants. The pro-survival effect of BDNF was suppressed by GNF5837, a pan-TRK inhibitor. Among the three downstream effectors of BDNF signaling, AKT was most prominently activated by BDNF in EMB-treated iRGCs, compared to ERK and PLCγ1. Furthermore, the protective effect of BDNF was blocked by the AKT inhibitor MK-2206 but not by the ERK inhibitor GDC-0094. Müller glia confer neuroprotection to RGCs under EMB-induced stress, primarily via BDNF signaling. AKT functions as the key downstream effector mediating this protective response. These findings suggest that the BDNF-AKT signaling may serve as a promising therapeutic target for EMB-associated optic neuropathy.