Influencing early stages of neuromuscular junction formation through glycocalyx engineering.

Achieving molecular control over the formation of synaptic contacts in the nervous system can provide important insights into their regulation and can offer means for creating well-defined in vitro systems to evaluate modes of therapeutic intervention. Agrin-induced clustering of acetylcholine receptors (AChRs) at postsynaptic sites is a hallmark of the formation of the neuromuscular junction, a synapse between motoneurons and muscle cells. In addition to the cognate agrin receptor, LRP4 (low-density lipoprotein receptor related protein-4), muscle cell surface heparan sulfate (HS) glycosaminoglycans (GAGs) have been proposed to contribute to AChR clustering by acting as agrin co-receptors. Here, we provide direct evidence for the role of HS GAGs in agrin recruitment to the surface of myotubes as well as their functional contributions towards AChR clustering. We also demonstrate that engineering of the myotube glycocalyx using synthetic HS GAG polymers can replace native HS structures to gain control over agrin-mediated AChR clustering.