GABA Receptor Activation in Müller Glia as a Molecular Switch for Controlling VEGF-A in the Retina

GABA receptors are classically known for driving neuronal hyperpolarization and modulating synaptic transmission. In glial cells, however, GABA induces depolarization and triggers calcium-dependent signaling pathways. Müller glia, the principal retinal glial population, maintain retinal homeostasis and are the major source of neuroretinal VEGF-A, a key angiogenic factor in development and disease. Although GABA receptor (GABAR) activity has been proposed to influence retinal VEGF-A, it remains unclear whether this regulation occurs through Müller glial cells (MGC) and which mechanisms are involved. Here, we investigated how GABAR activation modulates VEGF-A in primary mouse MGC cultures. Cells were exposed to GABA and selective agonists or antagonists of GABA_A (muscimol, gabazine) and GABA_B receptors (baclofen, CGP55845). VEGF-A expression and secretion were analyzed by immunofluorescence, western blot, RT-qPCR, and ELISA. To assess Ca²⁺ involvement, we used Ca²⁺-free Ringer-Krebs solution and the L-type channel blocker nimodipine, and examined MAPK signaling with the ERK1/2 inhibitor FR180204. Our findings show that GABA and muscimol increased VEGF-A fluorescence intensity after 48 hours while reducing VEGF-A secretion, without altering Vegfa mRNA. Both effects were abolished by extracellular Ca²⁺ removal or nimodipine, indicating a Ca²⁺-dependent mechanism. FR180204 also attenuated GABA- and GABA_A-mediated effects, implicating MAPK signaling. Short-term assays revealed that GABA rapidly elevates VEGF-A protein and secretion within ∼30 minutes. Together, these findings identify a Ca²⁺- and GABA_A-dependent pathway through which Müller glia regulate VEGF-A production and release, providing new insight into glial signaling and neurotransmitter-driven modulation of retinal angiogenic factors.