Oral Communications

SAN2022 Meeting

Andrea Aguilar-Arredondo, Damiana Giacomini, Alejandro Schinder

Leloir Institute Foundation, Neural plasticity lab

Presenting Author: Aguilar Arredondo, Andrea

GABAergic signaling is crucial for the development and function of adult-born granule cells (aGCs). Parvalbumin interneurons (PV-INs) exert perisomatic inhibition onto aGCs that becomes functionally mature at 6 weeks of neuronal age. The molecular mechanisms orchestrating the establishment of this synapse are unknown. We investigated whether neuroligin-2 (NL2), a postsynaptic adhesion molecule involved in the development of inhibitory contacts, plays a role in perisomatic GABAergic synaptogenesis in aGCs. Using confocal microscopy, we first characterized the development of synapses formed by PV-INs expressing tdTomato onto aGCs expressing GFP, by measuring the size of perisomatic appositions at different time points. We observed a substantial increase in synaptic size from 2 to 4 weeks, with no further changes at later times. We next delivered a retrovirus expressing a shRNA against NL2 and monitored the effect of NL2 knockdown on the PV-IN to GC synapse. We found smaller synaptic contacts accompanied by an important reduction of perisomatic appositions of the vesicular GABA transporter VGAT, suggesting impaired synaptic function. Moreover, we analyzed the expression of the presynaptic active zone protein bassoon, which showed a reduction in the number of puncta within terminals of PV-INs contacting aGCs in shNL2 expressing cells. Our results reveal NL2 as a critical player in the delayed functional maturation of perisomatic inhibition in aGCs of the adult brain.

Benjamín I. de la Cruz-Thea, María F. Harman, Mauricio G. Martín

Instituto de Investigaciones Médicas Mercedes y Martín Ferreyra (INIMEC-CONICET-UNC), Universidad Nacional de Córdoba, Córdoba, Argentina.

Presenting Author: de la Cruz-Thea, Benjamín Isaías

Aging is associated to epigenetic alterations which lead to diminished expression of memory-related genes. One of the most important changes is the decrease in histone acetylation produced by the Histone Deacetylase 2 (HDAC2) activity. This process has been described as determinant for memory loss during aging. In this work we demonstrate that aging triggers the accumulation of HDAC2 in regulatory regions of the BDNF gene, a key transcription factor for synaptic plasticity. We found that the transcriptional co-repressor Chromodomain Y like protein (CDYL), which interacts with HDAC2 in hippocampal extracts, is accumulated in the nucleus of old neurons. The co-accumulation of CDYL and HDAC2 was also observed in slices of old transgenic Thy-1(GFP) mice brain. Considering that CDYL degradation is triggered by synaptic activity, our data suggest that CDYL accumulation can be due to impaired NMDA receptor activity as a consequence of cholesterol depletion in old neurons. Moreover, we found that CDYL silencing in primary culture of cortical neurons induces a decrease in the levels of HDAC2 when compared to controls, highlighting the fact that CDYL accumulation could both recruit HDAC2 to BDNF promoter and regulate HDAC2 expression or stability through a still undescribed mechanism. The findings herein contribute to the understanding of the epigenetic processes underlying synaptic impairment during aging.

Natalia G. Armando 1°, Simon P. Heister 2°, Sebastián Giusti 1°, Damián Refojo 1°

1.IBioBA – Max Planck Partner Institute, Buenos Aires, Argentina
2.Max Planck Institute of Psychiatry, Munich, Germany

Presenting Author: Armando, Natalia Giannina

The COP9 signalosome (CSN) is a protein complex that regulates protein degradation by removing the ubiquitin-like modifier Nedd8 from cullin-based E3 ubiquitin ligases. The ubiquitin-proteasome system was found to be critically involved in many neuronal processes, but the role of CSN in neurons is still unclear. We aimed to characterize the impact of CSN loss-of-function in several stages of neuronal development using the Cre-loxP system to knock out (KO) the catalytic subunit 5 of the CSN (CSN5). We observed that the constitutive KO of CSN5 in proliferating neuroblasts leads to mid-term embryonic lethality. The KO in early postmitotic neurons proved lethal at postnatal day 1. However, neuron viability was not affected in KO CSN5 neurons from the developing cortex generated by in utero electroporation technique. Moreover, the loss of CSN5 in mature principal neurons of the forebrain did not affect mice viability or relevant behavioral alterations. We analyzed morphological changes of mature neurons in vivo, using a genetically-labelled sparse subset of neurons. Here, we report a reduction in total dendritic length and arborization complexity compared to control littermates, whereas spine density on apical dendrites remains unaffected. Our findings suggest that CSN-reliant regulatory mechanisms exhibit developmental stage-dependent activity patterns in the brain and are indispensable in early developmental stages.

Javier Andrés Muñiz 1°, Carolina Lucia Facal 1°, Ezequiel Pereyra 1°, German Falasco 3°, Indiana Páez Paz 1°, Juan Ferrario 2°, Ana Damianich 1°, M. Elena Avale 1°

1.Laboratorio de Terapéutica Experimental en Procesos Neurodegenerativos – INGEBI
2.Neurobiología de la enfermedad de Parkinson – Instituto de Biociencias, Biotecnologia y Biologia Translacional
3.Laboratorio de Imagen Preclínica, Centro de Imagen Molecular – FLENI

Presenting Author: Muñiz, Javier Andrés Muñiz

Tau is a microtubule-associated protein predominantly expressed in neurons, which participates in microtubule polymerization and axonal transport. The alternative splicing of exon 10 (E10) in the Tau transcript produces protein isoforms with three (3R) or four (4R) microtubule binding repeats, which are expressed in equal amounts in the normal adult human brain. Here aimed to characterize early phenotypes of htau mice, at 3, 6 and 12 months old, to establish the time course of the progression state of tau pathology and identify the brain nuclei involved in these phenotypes. We performed behavioral tests to identify cognitive deficits, anxiety phenotypes, motor impulsivity and loss of behavioral inhibition. In addition, we assessed electrophysiological neuronal activity during the time course of pathological phenotypes, as well as molecular and histological markers. Finally, using an RNA trans-splicing strategy to modulate E10 inclusion (Sonia/ani) we demonstrate that local shifting of 3R to 4R tau into the striatum of htau mice improved some of the htau phenotypes. Together, our results suggest that tau isoforms imbalance could develop early phenotypes that can be identified to generate elaborate strategies to restore the isoform balance.

Ana Paula De Vincenti 1°, Antonela Bonafina 1°, Fernanda Ledda 2°, Gustavo Paratcha 1°

1.Laboratorio de neurociencia molecular y celular, Instituto de biología celular y neurociencias “Prof. E De Robertis” (IBCN), Universidad de Buenos Aires-CONICET
2.Fundación Instituto Leloir, Instituto de investigaciones bioquímicas de Buenos Aires, CONICET

Presenting Author: De Vincenti, Ana Paula

The mammalian cerebral cortex is a highly organized structure responsible for cognitive, sensory and motor functions. It’s development requires coordination of crucial processes such as cell proliferation, migration, differentiation and acquisition of layer specific identities. Many extracellular cues and intrinsic factors have been identified as regulators of this process. However, further investigation is needed to understand how this complex architecture is achieved. In this work, we show that Leucine-rich repeats and immunoglobulin-like domains proteins (Lrig) are expressed in the embryonic neocortex during the period of neurogenesis. We identified a member of Lrig family as a regulator of cortical cell proliferation and self-renewal, disrupting mitogenic activity of trophic factors. We show that genetic ablation of Lrig modifies the population of proliferating cortical precursors in vivo, which in turn gives rise to an abnormal number of excitatory neurons in mice postnatal cortex. These results indicate that Lrig plays a key physiological role functioning as a homeostatic regulator of glutamatergic cortical neurogenesis.

Agustín Solano 1°, Gonzalo Lerner 1°, Pedro Caffaro 1°, Luis Alberto Riquelme 1°, Daniel Perez-Chada 2°, Valeria Della-Maggiore 1°

1.CONICET-Universidad de Buenos Aires, IFIBIO Houssay, Buenos Aires, Argentina
2.Internal Medicine, Pulmonary and Sleep Service, Austral Univ. Hosp., Pilar, Argentina

Presenting Author: Solano, Agustín

Strong evidence suggests that sleep benefits declarative memories (DM). However, its contribution to motor learning is controversial. Recently, we showed that learning a motor adaptation (MA) task shortly before sleep enhances the delta power and the coupling between spindles and slow oscillations (SO), similarly to what is observed in DM. Here, we tested the hypothesis that the beneficial effect of sleep in MA depends on its overlap with the consolidation window. First, we tracked MA memory retention through a 24h window. We found that it decayed initially and stabilized at 6h post training, and remained constant overnight (p<0.001), suggesting that sleep does not benefit MA if the time proximity between learning and sleep is not controlled. To control the interval between learning and sleep we then tracked the time course of MA memory consolidation using an anterograde interference protocol. We found that release from interference started about 6h post learning (p<0.001), implying that MA consolidates within such a time window. Finally, we trained two groups of subjects so that sleep occurred outside (~14h; group T-14h) or inside (~10min; group T-10min) the consolidation window, and recorded EEG overnight. We found that T-10min retained 30% more than T-14h (p<0.05). This sleep benefit was accompanied by an increment in the spindle-SO coupling and delta band power over the brain hemisphere contralateral to the trained hand (p<0.05), supporting our hypothesis.

Graciela Ines Kearney, Lidia Szczupak

1.Instituto de Fisiología, Biología Molecular y Neurociencias (UBA-CONICET)

Presenting Author: Kearney, Graciela Ines

In animal motor behaviors, the segments along the antero-posterior axis perform movements in a coordinated manner. Leeches are an outstanding model to analyze the underlying neuronal network controlling this function because the 21 segments that compose the body are virtually identical, simplifying the question on intersegmental coordination to that on interactions among iterated units. Leeches crawl over solid surfaces through successive elongation and contraction body waves. Each segment bears all the neurons required to produce this rhythmic motor pattern and dopamine evokes fictive crawling in isolated midbody ganglia. Coordinated rhythmic motor pattern can be also elicited in chains of 3 ganglia. The pattern of activity in both experimental conditions is highly similar, and fits behavioral parameters. Within the chain, the intersegmental interactions give rise to a global network, turning each segmental circuit refractory to local perturbations. To analyze the nature of these intersegmental signals, we used a chamber that allows chemical compartmentalization of the chain. Application of dopamine in a single ganglion elicited crawling in anterior and/or posterior ganglia. These results show that local crawling oscillators provide excitatory drive bidirectionally, which operates tonically upon neighboring circuits spreading the rhythmic activity.