Biology subjects

Viana da Silva, S.

Publications and source records attributed to Viana da Silva, S..

3 recordsLinked to original sources

bioRxiv2025

Deep mapping of the endomembrane system of cerebellar Purkinje neurons

Neuronal function relies on the precise spatial organization of intracellular membrane-bounded organelles involved in anabolism and Ca2+ sequestration, such as the Golgi apparatus, mitochondria and the endoplasmic reticulum (ER), along with structures involved in catabolism, such as lysosomes. Despite their known roles in energy supply, calcium homeostasis, and proteostasis, our understanding of how the anabolism-linked organelles are structurally arranged within neurons remains incomplete. Due to the tremendous complexity in the morphologies and fine structural features and interwoven nature of these intracellular organelles, particularly the ER, our understanding of their structural organization is limited, particularly, with regard to quantitative assessments of their sites of interaction and accurate measures of their volumetric proportions inside of a single large neuron. To approach this challenge, we used serial block-face scanning electron microscopy (SBEM) to generate large-scale 3D EM volumes and electron tomography on high-pressure frozen tissue of the rodent cerebellum, including the largest cells in the vertebrate brain, the cerebellar Purkinje neuron as well as the most abundant cell type in the vertebrate brain, the much smaller cerebellar granule neuron. We reconstructed the neuronal ultrastructure of these different cell types, focusing on the ER, mitochondria and membrane contact sites, to then characterize intracellular motifs and organization principles in detail, providing a first full map to quantitatively describe a neuronal endoarchitectome. At the gross level organization, we found that the intracellular composite of organelles are cell type specific features, with specific differences between Purkinje neurons and Granule cells. At the level of fine structure, we mapped ultrastructural domains within Purkinje neurons where ER and mitochondria associate directly. In addition to cell type specific differences, we observed significant subcellular regional variation, particularly within the axon initial segment (AIS) of Purkinje neurons, where we identified ultrastructural domains with sharply contrasting distributions of ER and mitochondria. These findings suggest a finely tuned spatial organization of organelles that may underpin the distinct functional demands along the axon. We expect that our subcellular map, along with the methods developed to obtain these maps, will facilitate future studies in health, aging and disease to characterize defined features, by developing a framework for quantitative analysis of the neuronal ultrastructure.

neuroscience↗

bioRxiv2022

Localized APP pathology in the hippocampus is sufficient to result in progressive disorganization of the timing of neuronal firing patterns

Deficits in spatial navigation are among the early symptoms in Alzheimers disease patients, consistent with the hippocampal formation as the site for spatial computations and disease onset. Although the correspondence between the early symptoms and brain regions that are affected early in the disease has been recognized, it is not clear whether progressive cognitive decline is solely caused by a spreading pathology or whether a focal pathology can by itself cause aberrant neuronal activity in a larger network. These possibilities cannot be distinguished in standard disease models which broadly express APP across brain regions. We therefore generated a mouse model in which the expression of mutant human APP was limited to hippocampal CA3 cells (CA3-APP mice). We first asked whether the limited pathology in CA3 can result in memory deficits and found impaired performance of CA3-APP mice in a hippocampus-dependent memory task. By then recording in the CA1 region, we asked to what extent neuronal activity patterns emerged in a brain region which received projections from APP-expressing CA3 cells, but did itself not show any primary pathology. While the spatial firing patterns of CA1 cells were preserved, we observed a reduced theta oscillation frequency in the local field potential and in a subpopulation of principal cells in CA1. Furthermore, CA1 interneurons showed decreased theta oscillation frequencies, and this effect was even more pronounced in CA3 interneurons, which also do not directly express APP. Pathology that is highly localized and limited to presynaptic cells is thus sufficient to cause aberrant firing patterns in postsynaptic neuronal networks, which indicates that disease progression is not only from a spreading molecular pathology but also mediated by progressive physiological dysfunction.

neuroscience↗

bioRxiv2020

Aβ-induced synaptic injury is mediated by presynaptic expression of amyloid precursor protein (APP) in hippocampal neurons

The patterns of A{beta}-induced synaptic injury were examined after targeting of the amyloid precursor protein (APP) preferentially to either CA1 or CA3 neurons using Cre-lox technology combined with tetracycline-regulated expression. Both CA1- and CA3-APP-expressing transgenic mouse lines exhibited reduction in long-term potentiation (LTP) only when APP was expressed in neurons presynaptic to the recording site, whereas LTP remained comparable to wild-type mice when APP was expressed in postsynaptic neurons. As quantified by both light and electron microscopy, this orientation-specific impairment in synaptic plasticity was mirrored by synaptic loss in regions receiving axonal inputs from neurons expressing APP. Furthermore, A(plaque deposition also occurred only in the postsynaptic axonal fields of APP-expressing neurons. These deficits were reversed not only with doxycycline to inhibit APP expression but also with {gamma}-secretase and Fyn kinase inhibitors, supporting the interpretation that the observed synaptic injury was mediated by A{beta}. Taken together, these results demonstrate that APP/A{beta}-induced synaptic toxicity is preferentially initiated by signaling of presynaptically expressed APP to the postsynaptic compartment.

neuroscience↗