Conference Agenda

The cerebral cortex contains an extraordinary diversity of excitatory projection neuron (PN) and inhibitory interneurons (IN), wired together to form complex circuits. Spatiotemporally coordinated execution of intrinsic molecular programs by PNs and INs and activity-dependent processes, contribute to cortical development and cortical microcircuits formation. Alterations of these delicate processes have often been associated with neurological/neurodevelopmental disorders. However, despite the groundbreaking discovery that spontaneous activity in the embryonic brain can shape regional identities of distinct territories, it is still unclear whether this early activity contributes to defining subtype-specific neuronal fate. In this study, we combined in utero genetic perturbations and pharmacological inhibition of selected ion channels (i.e HCN1) with RNA-sequencing and live imaging technologies to identify the activity-regulated processes controlling the development of different cortical PN classes, their wiring, and the acquisition of subtype-specific features. Moreover, we generated human induced pluripotent stem cells (iPSCs) from patients affected by a severe, rare, and untreatable form of developmental epileptic encephalopathy caused by single-point mutations in the HCN1 channel. By differentiating cortical organoids from patient-derived iPSCs we create human models of early electrical alterations for studying HCN1 mutation-derived molecular, structural, and functional consequences during cortical development. Our preliminary results point out at HCN1 channel as a possible modulator of spontaneous electrical activity in the developing cerebral cortex and propose HCN-current as a potential pacemaker signal to initiate cortical wave propagation during development.

We explore the role of integrin αVβ3 in cortical plasticity. This extracellular matrix receptor plays a crucial role in mediating both biochemical and mechanical signals. Recent evidence has linked its deficiency to autism spectrum disorder (ASD) in humans. Our research reveals that integrin αVβ3 is selectively expressed in pyramidal neurons within deep cortical circuits. Furthermore, constitutive and conditional KO mouse models for this receptor exhibit specific impairments in social memory and an increased susceptibility to seizures. To gain insight into the underlying mechanisms, we have conducted synaptic proteomic and bioinformatics analyses, which identify distinct alterations in AMPA-type and group 1 metabotropic (mGluR1/5) glutamate receptors. Through electrophysiological and pharmacological investigations, we uncover an inversion in the law governing mGluR1/5-dependent long-term potentiation (LTP) and long-term depression (LTD) within the medial prefrontal cortex. These electrophysiological alterations are accompanied by changes in basal and activity-dependent phosphorylation levels of AMPA receptors. Remarkably, treatment with the competitive mGluR5 antagonist MPEP enables a complete rescue of the behavioral impairments observed in integrin αVβ3 KO mouse models. These findings highlight the functional significance of integrin αVβ3 for cortical circuit plasticity and serve as a rational foundation for the development of targeted therapies for ASD.

Cajal-Retzius (CR) cells are a transient cell type important for brain development. During prenatal development, they release Reelin, a protein critical for neuronal migration. But while in most brain areas CR cells disappear soon after birth, in the hippocampus they persist for several months. What then is the function of CR cells in the postnatal development of the hippocampus? To understand how CR cells’ persistence influences the maturation of hippocampal circuits, we are combining a specific transgenic mouse line with viral vector injection to selectively ablate CR cells from the postnatal hippocampus. We find that this manipulation results in layer-specific changes in the dendritic complexity and spine density of CA1 pyramidal cells. In addition, transcriptomic and proteomic analyses reveal significant alterations in the expression of synapse related genes and proteins across development. Interestingly, we observe severe effects on the expression levels of Latrophilin-2, a postsynaptic guidance molecule known for its role in regulating entorhinal-hippocampal connectivity. Preliminary data also indicate deficits in hippocampal-dependent learning. Our results reveal a critical role for CR cells in the establishment of the hippocampal network.

Background: TBC1D24 is a gene mutated in a broad spectrum of neurodevelopmental disorders, from mild epilepsy to severe epileptic encephalopathy. TBC1D24 regulates neuronal development, synaptic vesicle trafficking and synaptic function; yet the molecular mechanisms mediating these complex roles and their relation to brain dysfunction are largely unknown. TBC1D24 is unique in containing the conserved TBC and TLDc domains; TLDc proteins have been recently described as interactors of the V-ATPase proton pump.

Experimental approach: We evaluated the Tbc1d24/V-ATPase interaction in neurons by immunoprecipitation and cell staining experiments. Using Tbc1d24 knockout neurons, we investigated V-ATPase expression and assembly state by Western blot analysis and fractionation experiments. Cell staining and live imaging experiments were performed to evaluate intracellular organelle acidification and autophagy process. Synaptic specific probes were used to evaluate synaptic autophagy and synaptic vesicles pH.

Key findings: Tbc1d24 interacts with the V-ATPase cytosolic domain in the brain. Loss of Tbc1d24 leads to decreased V-ATPase assembly with impaired intracellular organelles acidification and autophagic clearance. This phenotype is accompanied by defects in synaptic ultrastructure, synaptic autophagy and synaptic vesicle pH.

Conclusions: We uncover a novel function for TBC1D24 as a regulator of V-ATPase activity in neurons and suggest pH dysregulation as a key cellular mechanism that underpins the synaptic defects and pathogenesis in TBC1D24-related disorders.