The inhibition of the JNK2-Syntaxin-1A interaction neuroprotects against retinal degeneration
Retinal diseases (RDs) involve the degeneration of retinal cells, particularly retinal ganglion cells (RGCs), often driven by glutamate imbalance and aberrant signaling. We previously identified a presynaptic self-amplifying mechanism of glutamate overflow, where NMDA overstimulation activates JNK2-mediated phosphorylation of STX1A. To block this mechanism, a cell-permeable peptide, called JGRi1, was previously developed to disrupt the JNK2-STX1A interaction. Here, we investigated whether inhibition of this pathway by JGRi1 could provide neuroprotection in retinal degeneration. Here we showed that JGRi1 efficiently reached the mouse retina upon topical administration as eye drops and granted retinal protection. Using an ex vivo optic nerve cut (evONC) model, we demonstrated that JGRi1 preserved RGC viability, reduced phosphorylation of JNK and STX1A, and lowered glutamate release. In retinal wholemounts, JGRi1 similarly preserved RGC survival. Furthermore, in an NMDA-induced degeneration model, JGRi1 protected RGCs, reduced glutamate levels, disrupted the JNK2-STX1A interaction, and limited microglial infiltration. Collectively, our findings highlight the central role of the JNK2-STX1A pathway in retinal degeneration and identify JGRi1 as a promising neuroprotective tool. SYNOPSISGlutamate excitotoxicity drives retinal diseases via JNK2-dependent phosphorylation of STX1A, causing non-canonical presynaptic glutamate spillover (nPING). We developed JGRi1, a cell-permeable peptide that blocks the JNK2-STX1A interaction and prevents spillover. O_LIJGRi1 effectively reaches the retina via both ex vivo and in vivo topical administration, accumulating in the ganglion cell layer (GCL) and other retinal layers in a dose-dependent manner. C_LIO_LIJGRi1 protects retinal ganglion cells (RGCs) from degeneration in both evONC- and NMDA-induced models, reducing apoptosis, preserving retinal cytoarchitecture and axonal connectivity, and lowering glutamate spillover. C_LIO_LIJGRi1 counteracts the excitotoxic cascade by reducing JNK2 upregulation, STX1A phosphorylation, their interaction and co-localization, limiting SNARE complex formation, and dampening microglial activation. C_LI