Presynaptic Control of Glycine Transporter 2 (GlyT2) by Physical and Functional Association with Plasma Membrane Ca2+-ATPase (PMCA) and Na+-Ca2+ Exchanger (NCX)

Background: GlyT2 is crucial for glycinergic neurotransmission, but only a few interacting partners for this protein are known. Results: PMCA2/3 and NCX1 interact with GlyT2 and modulate its activity in lipid raft subdomains. Conclusion: Functional interaction of GlyT2 with PMCA2/3 and NCX1 helps Na+ and Ca2+ local homeostasis in glycinergic terminals. Significance: Learning how GlyT2 is regulated might help with developing new therapies for hyperekplexia or neuropathic pain. Fast inhibitory glycinergic transmission occurs in spinal cord, brainstem, and retina to modulate the processing of motor and sensory information. After synaptic vesicle fusion, glycine is recovered back to the presynaptic terminal by the neuronal glycine transporter 2 (GlyT2) to maintain quantal glycine content in synaptic vesicles. The loss of presynaptic GlyT2 drastically impairs the refilling of glycinergic synaptic vesicles and severely disrupts neurotransmission. Indeed, mutations in the gene encoding GlyT2 are the main presynaptic cause of hyperekplexia in humans. Here, we show a novel endogenous regulatory mechanism that can modulate GlyT2 activity based on a compartmentalized interaction between GlyT2, neuronal plasma membrane Ca2+-ATPase (PMCA) isoforms 2 and 3, and Na+/Ca2+-exchanger 1 (NCX1). This GlyT2PMCA2,3NCX1 complex is found in lipid raft subdomains where GlyT2 has been previously found to be fully active. We show that endogenous PMCA and NCX activities are necessary for GlyT2 activity and that this modulation depends on lipid raft integrity. Besides, we propose a model in which GlyT2PMCA2-3NCX complex would help Na+/K+-ATPase in controlling local Na+ increases derived from GlyT2 activity after neurotransmitter release.