Contactin-associated protein 1 (Caspr1) regulates the traffic and synaptic content of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors.

Glutamate receptors of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type mediate fast excitatory synaptic transmission in the CNS. Synaptic strength is modulated by AMPA receptor binding partners, which regulate receptor synaptic targeting and functional properties. We identify Contactin-associated protein 1 (Caspr1) as an AMPA receptor interactor. Caspr1 is present in synapses and interacts with AMPA receptors in brain synaptic fractions. Coexpression of Caspr1 with GluA1 increases the amplitude of glutamate-evoked currents. Caspr1 overexpression in hippocampal neurons increases the number and size of synaptic GluA1 clusters, whereas knockdown of Caspr1 decreases the intensity of synaptic GluA1 clusters. Hence, Caspr1 is a regulator of the trafficking of AMPA receptors to synapses.

The Metabolomic Signature of Opa1 Deficiency in Rat Primary Cortical Neurons Shows Aspartate/Glutamate Depletion and Phospholipids Remodeling.

Pathogenic variants of OPA1, which encodes a dynamin GTPase involved in mitochondrial fusion, are responsible for a spectrum of neurological disorders sharing optic nerve atrophy and visual impairment. To gain insight on OPA1 neuronal specificity, we performed targeted metabolomics on rat cortical neurons with OPA1 expression inhibited by RNA interference. Of the 103 metabolites accurately measured, univariate analysis including the Benjamini-Hochberg correction revealed 6 significantly different metabolites in OPA1 down-regulated neurons, with aspartate being the most significant (p < 0.001). Supervised multivariate analysis by OPLS-DA yielded a model with good predictive capability (Q2cum = 0.65) and a low risk of over-fitting (permQ2 = -0.16, CV-ANOVA p-value 0.036). Amongst the 46 metabolites contributing the most to the metabolic signature were aspartate, glutamate and threonine, which all decreased in OPA1 down-regulated neurons, and lysine, 4 sphingomyelins, 4 lysophosphatidylcholines and 32 phosphatidylcholines which were increased. The phospholipid signature may reflect intracellular membrane remodeling due to loss of mitochondrial fusion and/or lipid droplet accumulation. Aspartate and glutamate deficiency, also found in the plasma of OPA1 patients, is likely the consequence of respiratory chain deficiency, whereas the glutamate decrease could contribute to the synaptic dysfunction that we previously identified in this model.

Myosin 1b promotes axon formation by regulating actin wave propagation and growth cone dynamics.

Single-headed myosin 1 has been identified in neurons, but its function in these cells is still unclear. We demonstrate that depletion of myosin 1b (Myo1b), inhibition of its motor activity, or its binding to phosphoinositides impairs the formation of the axon, whereas overexpression of Myo1b increases the number of axon-like structures. Myo1b is associated with growth cones and actin waves, two major contributors to neuronal symmetry breaking. We show that Myo1b controls the dynamics of the growth cones and the anterograde propagation of the actin waves. By coupling the membrane to the actin cytoskeleton, Myo1b regulates the size of the actin network as well as the stability and size of filopodia in the growth cones. Our data provide the first evidence that a myosin 1 plays a major role in neuronal symmetry breaking and argue for a mechanical control of the actin cytoskeleton both in actin waves and in the growth cones by this myosin.