Alzheimer disease (AD) is a complex pathology related to multiple causes including oxidative stress. Brain-derived neurotrophic factor (BDNF) is a neutrotrophic factor essential for the survival and differentiation of neurons and is considered a key target in the pathophysiology of various neurodegenerative diseases, as for example AD. Contrarily to BDNF, the precursor form of BDNF (proBDNF) induces apoptosis through the specific interaction with p75 and its co-receptor, Sortilin.We used hippocampal tissue and cerebrospinal fluid from AD patients and controls. to study the localization and the levels of proBDNF, p75 and Sortilin as well as the post-traduccional modifications of proBDNF induced by Radical Oxygen Species, by immunofluorescence and Western blot. Differentiation and survival were assessed on differentiated mouse hippocampal neurons derived from postnatal neural stem cells from WT animals or from the transgenic AD animal model APP/PS1∆E9, based on mutations of familiar AD. In AD patients we observe a significative increase of proBDNF and Sortilin expression and a significative increase of the ratio proBDNF/BDNF in their cerebrospinal fluid compared to controls. In addition, the proBDNF of AD patients is modified by ROS-derived advanced glycation end products, which prevent the processing of the proBDNF to the mature BDNF, leading to an increase of pathogenicity and a decrease of trophic effects. The cerebrospinal fluid from AD patients, but not from controls, induces apoptosis in differentiated hippocampal neurons mainly by the action of AGE-modified proBDNF present in the cerebrospinal fluid of the patients. This effect is triggered by the activation and processing of p75 that stimulate the internalization of the intracellular domain (ICD) within the nucleus causing apoptosis. Induction of apoptosis and p75 ICD internalization by AD patients-derived proBDNF is further enhanced in neuron cultures from the AD model expressing the APP/PS1∆E9 transgene.Our results indicate the importance of proBDNF neurotoxic signaling in AD pathology essentially by three mechanisms: i) by an increase of proBDNF stability due to ROS-induced post-traductional modifications; ii) by the increase of expression of the p75 co-receptor, Sortilin and iii) by the increase of the basal levels of p75 processing found in AD.Electronic supplementary materialThe online version of this article (10.1186/s13041-018-0411-6) contains supplementary material, which is available to authorized users.

EphA/ephrin signaling regulates axon growth and guidance of neurons, but whether this process occurs also independently of ephrins is unclear. We show that presenilin-1 (PS1)/γ-secretase is required for axon growth in the developing mouse brain. PS1/γ-secretase mediates axon growth by inhibiting RhoA signaling and cleaving EphA3 independently of ligand to generate an intracellular domain (ICD) fragment that reverses axon defects in PS1/γ-secretase- and EphA3-deficient hippocampal neurons. Proteomic analysis revealed that EphA3 ICD binds to non-muscle myosin IIA (NMIIA) and increases its phosphorylation (Ser1943), which promotes NMIIA filament disassembly and cytoskeleton rearrangement. PS1/γ-secretase-deficient neurons show decreased phosphorylated NMIIA and NMIIA/actin colocalization. Moreover, pharmacological NMII inhibition reverses axon retraction in PS-deficient neurons suggesting that NMIIA mediates PS/EphA3-dependent axon elongation. In conclusion, PS/γ-secretase-dependent EphA3 cleavage mediates axon growth by regulating filament assembly through RhoA signaling and NMIIA, suggesting opposite roles of EphA3 on inhibiting (ligand-dependent) and promoting (receptor processing) axon growth in developing neurons.

Neuron migration is a hallmark of nervous system development that allows gathering of neurons from different origins for assembling of functional neuronal circuits. Cortical inhibitory interneurons arise in the ventral telencephalon and migrate tangentially forming three transient migratory streams in the cortex before reaching the final laminar destination. Although migration defects lead to the disruption of inhibitory circuits and are linked to aspects of psychiatric disorders such as autism and schizophrenia, the molecular mechanisms controlling cortical interneuron development and final layer positioning are incompletely understood. Here, we show that mouse embryos with a double deletion of FLRT2 and FLRT3 genes encoding cell adhesion molecules exhibit an abnormal distribution of interneurons within the streams during development, which in turn, affect the layering of somatostatin1 interneurons postnatally. Mechanistically, FLRT2 and FLRT3 proteins act in a noncell-autonomous manner, possibly through a repulsive mechanism. In support of such a conclusion, double knockouts deficient in the repulsive receptors for FLRTs, Unc5B and Unc5D, also display interneuron defects during development, similar to the FLRT2/FLRT3 mutants. Moreover, FLRT proteins are chemorepellent ligands for developing interneurons in vitro, an effect that is in part dependent on FLRT-Unc5 interaction. Together, we propose that FLRTs act through Unc5 receptors to control cortical interneuron distribution in a mechanism that involves cell repulsion.

The forebrain includes the cerebral cortex, the thalamus, and the striatum and globus pallidus (GP) in the subpallium. The formation of these structures and their interconnections by specific axonal tracts take place in a precise and orchestrated time and spatial-dependent manner during development. However, the knowledge of the molecular and cellular mechanisms that are involved is rather limited. Moreover, while many extracellular cues and specific receptors have been shown to play a role in different aspects of nervous system development, including neuron migration and axon guidance, examples of intracellular signaling effectors involved in these processes are sparse. In the present work, we have shown that the atypical RhoGTPase, Rnd3, is expressed very early during brain development and keeps a dynamic expression in several brain regions including the cortex, the thalamus, and the subpallium. By using