Nogo-66 Restricts Synaptic Strengthening via Lingo1 and the ROCK2-Cofilin Pathway to Control Actin Dynamics.

Nogo-A restricts long-term potentiation (LTP) at the Schaffer collateral-CA1 pathway in the adult hippocampus via 2 extracellular domains: Nogo-A-Δ20 and Nogo-66. Nogo-66 signals via Nogo Receptor 1 (NgR1) to regulate synaptic function. Whether the NgR1 coreceptors Lingo1 and p75NTR are involved in the signaling in this context is still not known. Moreover, the intracellular cascade mediating the activity of Nogo-66 in restricting LTP is unexplored. We combine electrophysiology and biochemistry in acute hippocampal slices and demonstrate that a loss of function for Lingo1 results in a significant increase in LTP levels at the Schaffer collateral-CA1 pathway, and that Lingo1 is the NgR1 coreceptor mediating the role of Nogo-66 in restricting LTP. Our data show that p75NTR is not involved in mediating the Nogo-66 effect on LTP. Moreover, loss of function for p75NTR and NgR1 equally attenuate LTD, suggesting that p75NTR might mediate the NgR1-dependent regulation of LTD, independently of Nogo-66. Finally, our results indicate that Nogo-66 signaling limits LTP via the ROCK2-Cofilin pathway to control the dynamics of the actin cytoskeleton. The present results elucidate the signaling pathway activated by Nogo-66 to control LTP and contribute to the understanding of how Nogo-A stabilizes the neural circuits to limit activity-dependent plasticity events in the mature hippocampus.

Nogo-A controls structural plasticity at dendritic spines by rapidly modulating actin dynamics.

Nogo-A and its receptors have been shown to control synaptic plasticity, including negatively regulating long-term potentiation (LTP) in the cortex and hippocampus at a fast time scale and restraining experience-dependent turnover of dendritic spines over days. However, the molecular mechanisms and the precise time course mediating these actions of Nogo-A are largely unexplored. Here we show that Nogo-A signaling in the adult nervous system rapidly modulates the spine actin cytoskeleton within minutes to control structural plasticity at dendritic spines of CA3 pyramidal neurons. Indeed, acute Nogo-A loss-of-function transiently increases F-actin stability and results in an increase in dendritic spine density and length. In addition, Nogo-A acutely restricts AMPAR insertion and mEPSC amplitude at hippocampal synaptic sites. These data indicate a crucial function of Nogo-A in modulating the very tight balance between plasticity and stability of the neuronal circuitry underlying learning processes and the ability to store long-term information in the mature CNS. © 2016 Wiley Periodicals, Inc.

The DCR protein TTC3 affects differentiation and Golgi compactness in neurons through specific actin-regulating pathways.

In neuronal cells, actin remodeling plays a well known role in neurite extension but is also deeply involved in the organization of intracellular structures, such as the Golgi apparatus. However, it is still not very clear which mechanisms may regulate actin dynamics at the different sites. In this report we show that high levels of the TTC3 protein, encoded by one of the genes of the Down Syndrome Critical Region (DCR), prevent neurite extension and disrupt Golgi compactness in differentiating primary neurons. These effects largely depend on the capability of TTC3 to promote actin polymerization through signaling pathways involving RhoA, ROCK, CIT-N and PIIa. However, the functional relationships between these molecules differ significantly if considering the TTC3 activity on neurite extension or on Golgi organization. Finally, our results reveal an unexpected stage-dependent requirement for F-actin in Golgi organization at different stages of neuronal differentiation.

The sphingolipid receptor S1PR2 is a receptor for Nogo-a repressing synaptic plasticity.

Nogo-A is a membrane protein of the central nervous system (CNS) restricting neurite growth and synaptic plasticity via two extracellular domains: Nogo-66 and Nogo-A-Δ20. Receptors transducing Nogo-A-Δ20 signaling remained elusive so far. Here we identify the G protein-coupled receptor (GPCR) sphingosine 1-phosphate receptor 2 (S1PR2) as a Nogo-A-Δ20-specific receptor. Nogo-A-Δ20 binds S1PR2 on sites distinct from the pocket of the sphingolipid sphingosine 1-phosphate (S1P) and signals via the G protein G13, the Rho GEF LARG, and RhoA. Deleting or blocking S1PR2 counteracts Nogo-A-Δ20- and myelin-mediated inhibition of neurite outgrowth and cell spreading. Blockade of S1PR2 strongly enhances long-term potentiation (LTP) in the hippocampus of wild-type but not Nogo-A(-/-) mice, indicating a repressor function of the Nogo-A/S1PR2 axis in synaptic plasticity. A similar increase in LTP was also observed in the motor cortex after S1PR2 blockade. We propose a novel signaling model in which a GPCR functions as a receptor for two structurally unrelated ligands, a membrane protein and a sphingolipid. Elucidating Nogo-A/S1PR2 signaling platforms will provide new insights into regulation of synaptic plasticity.