A significant barrier to harnessing the power of cell-surface glycosaminoglycans (GAGs) to modulate glial cell-line-derived neurotrophic factor (GDNF) signaling is the difficulty in accessing key GAG structures involved. Here, we report tailored GDNF signaling using synthetic polyproline-based GAG mimetics (PGMs). PGMs deliver the much needed proactive programmability for GDNF recognition and effectively modulate GDNF-mediated neuronal processes in a cellular context.