Biology subjects

Kobro-Flatmoen, A.

Publications and source records attributed to Kobro-Flatmoen, A..

8 recordsLinked to original sources

bioRxiv2023

Intraneuronal binding of amyloid beta with reelin -implications for the onset of Alzheimer's disease

It was recently shown that in anteriolateral entorhinal cortex layer II neurons (ECLII neurons) in McGill-R-Thy1-APP homozygous transgenic rats (a model commonly used to study Alzheimers disease (AD)), the glycoprotein reelin and intracellular amyloid-{beta} (A{beta}) engage in a direct protein-protein interaction. Numerous studies of the human brain supported by experimental results from rodent and cell models point to a role for intracellular oligomeric A{beta} in the onset of AD. If reelin functions as a sink for intracellular A{beta} and if the binding to reelin makes A{beta} physiologically inert, it implies that reelin may prevent the neuron from being exposed to the detrimental effects typically associated with oligomeric A{beta}. Considering that reelin expression is extraordinarily high in the major subset of ECLII neurons compared to most other cortical neurons, such a protective role appears very difficult to reconcile with the fact that ECLII is clearly a major cradle for the onset of AD in humans. Here we show that this conundrum may be resolved if ECLII neurons have a much higher maximum production capacity of A{beta} than neurons expressing low levels of reelin. We provide a rationale for why this difference has evolved, and argue that the higher maximum production capacity of A{beta} in ECLII neurons may in a senescent A{beta}-inducing physiology predispose these neurons to initiate AD development. Author summaryAmyloid-{beta} is a small peptide that is widely recognized as one of the main culprits involved in the development of Alzheimers disease. It was recently shown that in the major subset of neurons in entorhinal cortex layer II, which expresses high levels of the protein reelin, amyloid-{beta} and reelin bind to each other. These neurons, which are strongly involved in memory formation, are among the first to die in subjects with Alzheimers disease. If intracellular amyloid-{beta}, which is clearly involved in the onset of the disease, becomes physiologically inert when it binds to reelin, it implies that reelin can prevent the neuron from being exposed to the detrimental effects of increased levels of amyloid-{beta}. Considering that reelin expression is extraordinarily high in ECLII neurons compared to most other cortical neurons, such a protective role appears very difficult to reconcile with the fact that ECLII constitute the predominant cortical site for initiation of Alzheimers disease. Here, we show that this paradox may be resolved if ECLII neurons have a much higher maximum amyloid-{beta} production capacity than neurons expressing low levels of reelin. We provide reasons why this difference has evolved and argue that it, in a senescent physiology, predisposes ECLII neurons to initiate the development of Alzheimers disease.

neuroscience↗

bioRxiv2023

Bnip3 expression is strongly associated with reelin-positive entorhinal cortex layer II neurons

In layer II of the entorhinal cortex, the principal neurons that project to the dentate gyrus and the CA3/2 hippocampal fields express the large glycoprotein reelin (Re+ ECLII-neurons). In rodents, neurons located at the dorsal extreme of the entorhinal cortex that thus border the rhinal fissure, express the highest levels, and the expression gradually decreases at levels successively further away from the rhinal fissure. Here we test two predictions following from the hypothesis that reelin expression is strongly correlated with neuronal metabolic rate. Since mitochondrial turnover rate serves as a proxy for energy expenditure, we predicted that the expression of the canonical promitophagic BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (Bnip3) would be upregulated in Re+ ECLII-neurons, and that the degree of upregulation would strongly correlate with the expression level of reelin in these neurons. We confirm both predictions, which implies that the energy requirement of Re+ ECLII-neurons is generally high, and that there is a systematic decrease in metabolic rate in these neurons as one moves successively away from the rhinal fissure. We tentatively suggest that the reasons for the high energy requirement of these neurons are their high rate of synaptic transmission and the high frequency by which they remold their synaptic contacts. This implies that the systematic variation in energy requirement of the neurons manifesting the observed reelin gradient ties in with the level of spatial and temporal detail by which they encode information about the external environment.

neuroscience↗

bioRxiv2023

Reverse Engineering of Feedforward Cortical-Hippocampal Neural Networks Relevant for Preclinical Disease Modelling

Engineered biological neural networks are indispensable models for investigation of neural function and dysfunction from the subcellular to the network level. Notably, advanced neuro-engineering approaches are of significant interest for their potential to replicate the topological and functional organization of brain networks. In this study, we reverse engineered feed-forward neural networks of primary cortical and hippocampal neurons, using a custom-designed multinodal microfluidic device with Tesla valve inspired microtunnels. By interfacing this device with nanoporous microelectrodes, we show that the reverse engineered multinodal neural networks exhibit capacity for both segregated and integrated functional activity, mimicking brain network dynamics. To advocate the broader applicability of our model system, we induced localized perturbations with amyloid beta to study the impact of pathology on network functionality. Additionally, we demonstrate long-term culturing of subregion- and layer specific neurons extracted from the entorhinal cortex and hippocampus of adult Alzheimer ss-model mice and rats. Our results thus highlight the potential of our approach for reverse engineering of anatomically relevant multinodal neural networks to study dynamic structure-function relationships in both healthy and pathological conditions.

neuroscience↗

bioRxiv2023

Intracellular Amyloid-β in the Normal Rat Brain and Human Subjects

Amyloid-beta (A{beta}) is a normal product of neuronal activity, and the two most common variants are 40 or 42 residues long. Of these, the 42 residue-version (A{beta}42) is normally less abundant but more prone to self-aggregate, and is thought to cause Alzheimers disease (AD). Much knowledge about AD-pathogenesis comes from the study of rodents made to model aspects of the disease by expressing AD-relevant human transgenes, like human amyloid precursor protein (APP) containing mutations that drive up A{beta} production or increase the A{beta}42/40 ratio and thereby causes AD. Yet, when it comes to the normal expression of A{beta}42 in rodent brains, surprisingly little is known. Here we characterize the expression of A{beta}42 throughout the brain of normal, outbred Wistar rats, including animals from 3-18 months of age. We find that intracellular A{beta}42 (iA{beta}42) is present in neurons located throughout the brain at all ages of normal Wistar rats, but that the levels vary greatly between brain regions. In cortex, we observe the highest levels of iA{beta}42 in neurons that are part of layer II of the entorhinal cortex (EC), along with neurons in the hippocampus, closely followed by neurons in the somatosensory cortex. Among subcortical structures, we observe the highest levels iA{beta}42 in the locus coeruleus. In order to explore whether the striking presence of iA{beta}42 in rat EC also holds true in human subject free of neurological disease, we examined EC of six such cases ranging from ages 20-88 years. In all six cases, we find that iA{beta}42 is present in EC layer II-neurons. Our findings support two conclusions about iA{beta}42. First, iA{beta}42 is present in neurons of wild-type Wistar rats and is restricted to the same structures where iA{beta} accumulates, and A{beta}-plaques form, in a much used AD model based on Wistar rats (the McGill-R-Thy1-APP rat model). The difference between wild-type Wistar rats and these AD model rats, with respect to A{beta}42, is therefore a quantitative one rather that a qualitative one. This indicates that the McGill rat model in fact models the underlying wild-type neuronal population-specific vulnerability to A{beta}42-accumulation. Second, because the McGill rat model closely mimics the human AD-associated spatiotemporal sequence of amyloid plaque deposition, this model may offer a useful representation of the pre-plaque neuronal accumulation of iA{beta}42. Our findings in human cases are in line with prior findings, and substantiate the notion that neurons in layer II of EC are vulnerable to accumulation of iA{beta}42.

pathology↗

bioRxiv2022

A combined DTI-fMRI approach for optimizing the delineation of posteromedial vs. anterolateral entorhinal cortex

In the entorhinal cortex (EC), attempts have been made to identify the human homologue regions of the medial (MEC) and lateral (LEC) subdivision using either functional magnetic resonance imaging (fMRI) or diffusion tensor imaging (DTI). However, there are still discrepancies between entorhinal subdivisions depending on the choice of connectivity seed regions and the imaging modality used. While DTI can be used to follow the white matter tracts of the brain, fMRI can identify functionally connected brain regions. In this study, we used both DTI and resting-state fMRI in 103 healthy adults to investigate both structural and functional connectivity between the EC and associated cortical brain regions. Differential connectivity with these regions was then used to predict the locations of the human homologues of MEC and LEC. Our results from combining DTI and fMRI support a subdivision into posteromedial (pmEC) and anterolateral (alEC) EC and reveal a confined border between the pmEC and alEC. Furthermore, the EC subregions obtained by either imaging modality showed similar distinct connectivity patterns: While pmEC showed increased connectivity preferentially with the default mode network, the alEC exhibited increased connectivity with regions in the dorsal attention and salience networks. Optimizing the delineation of the human homologues of MEC and LEC with a combined, cross-validated DTI-fMRI approach allows to define a likely border between the two subdivisions and has implications for both cognitive and translational neuroscience research.

neuroscience↗

bioRxiv2022

Microdissection and culturing of adult lateral entorhinal cortex layer II neurons from APP/PS1 Alzheimer model mice

BackgroundPrimary neuronal cultures enable cell-biological studies of Alzheimers disease (AD), albeit typically non-neuron-specific. The first cortical neurons affected in AD reside in layer II of the lateralmost part of the entorhinal cortex, and they undergo early accumulation of intracellular amyloid-{beta}, form subsequent tau pathology, and start degenerating pre-symptomatically. These vulnerable entorhinal neurons uniquely express the glycoprotein reelin and provide selective inputs to the hippocampal memory system. Gaining a more direct access to study these neurons is therefore highly relevant. New methodWe demonstrate a methodological approach for microdissection and long-term culturing of adult lateral entorhinal layer II-neurons from AD-model mice. ResultsWe maintain adult microdissected lateralmost entorhinal layer II-neurons beyond two months in culture. We show that they express neuronal markers, and that they are electrophysiologically active by 15 days in vitro and continuing beyond 2 months. Comparison with existing methodsPrimary neurons are typically harvested from embryonic or early postnatal brains because such neurons are easier to culture compared to adult neurons. Methods to culture adult primary neurons have been reported, however, to our knowledge, culturing of adult entorhinal subregion-specific primary neurons from AD-model animals has not been reported. ConclusionsOur methodological approach offers a window to study initial pathological changes in the AD disease-cascade. This includes the study of proteinopathy, single-neuron changes, and network-level dysfunction. HighlightsO_LIWe microdissect and culture neurons from layer II of the lateralmost part of the entorhinal cortex from adult AD model mice and littermate controls C_LIO_LIThese entorhinal neurons self-organize into networks, express reelin, NeuN and intracellular amyloid-{beta}. C_LIO_LIThe neurons are electrophysiologically active by day 15 in culture and remain viable beyond two months. C_LI

neuroscience↗

bioRxiv2022

Lowering levels of reelin in entorhinal cortex layer II-neurons results in lowered levels of intracellular amyloid-β.

Projection neurons in the anterolateral part of entorhinal cortex layer II (alEC LII) are the predominant cortical site for hyperphosphorylation of tau (p-tau) and formation of neurofibrillary tangles (NFTs) in brains of subjects with early-stage Alzheimers Disease (AD). A majority of alEC LII-neurons are unique among cortical excitatory neurons by expressing the protein reelin (Re+). In AD patients, and a rat model for AD overexpression mutated human APP, these Re+ excitatory projection-neurons are prone to accumulate intracellular amyloid-{beta} (iA{beta}). Biochemical pathways that involve reelin-signaling regulate levels of p-tau, and iA{beta} has been shown to impair such reelin-signaling. We therefore used the rat model and set out to assess whether accumulation of iA{beta} in Re+ alEC LII projection neurons relates to the fact that these neurons express reelin. Here we show that in Re+ alEC LII-neurons, reelin and iA{beta}42 engage in a direct protein-protein interaction, and that microRNA-mediated lowering of reelin-levels in these neurons leads to a concomitant reduction of non-fibrillar iA{beta} ranging across three levels of aggregation. Our experiments are carried out several months before plaque pathology emerges in the rat model, and the reduction of iA{beta} occurs without any substantial associated changes in human APP-levels. We propose a model positioning reelin in a sequence of changes in functional pathways in Re+ alEC LII-neurons, explaining the region and neuron-specific initiation of AD pathology. SignificanceAnterolateral entorhinal cortex layer II (EC LII) neurons are the predominant cortical site for hyperphosphorylation of tau (p-tau) and formation of neurofibrillary tangles (NFTs) in brains of subjects with early-stage Alzheimers disease (AD). The same neurons are prone to very early accumulation of non-fibrillary forms of amyloid-{beta} in the context of AD, and are unique among cortical excitatory neurons by expressing the protein reelin. We show that in such alEC LII-neurons, reelin and iA{beta}42 engage in a direct protein-protein interaction, and that selectively lowering levels of reelin leads to a concomitant reduction of non-fibrillar A{beta}. We propose a model positioning reelin in a sequence of changes in functional pathways in reelin-expressing EC LII neurons, explaining the region and neuron specific initiation of AD.

pathology↗

bioRxiv2021

Structural connectivity-based segmentation of the human entorhinal cortex

The medial (MEC) and lateral entorhinal cortex (LEC), widely studied in rodents, are well defined and characterized. In humans, however, the exact locations of their homologues remain uncertain. Previous functional magnetic resonance imaging (fMRI) studies have subdivided the human EC into posterior-medial (pmEC) and anterior-lateral (alEC) parts, but uncertainty remains about the choice of imaging modality and seed regions, in particular in light of a substantial revision of the classical model of EC connectivity based on novel insights from rodent anatomy. Here, we used structural, not functional imaging, namely diffusion tensor imaging (DTI) and probabilistic tractography to segment the human EC based on differential connectivity to other brain regions known to project selectively to MEC or LEC. We defined MEC as more strongly connected to presubiculum and retrosplenial cortex (RSC), and LEC as more strongly connected to distal CA1 and proximal subiculum (dCA1pSub) and orbitofrontal cortex (OFC). Although our DTI segmentation had a larger medial-lateral component than in previous fMRI studies, our results show that the human MEC and LEC homologues have a border oriented both towards the posterior-anterior and medial-lateral axes, supporting the differentiation between pmEC and alEC.

neuroscience↗