Biology subjects

Martinsson, I.

Publications and source records attributed to Martinsson, I..

4 recordsLinked to original sources

bioRxiv2026

Preferential generation of pathological tau species in specific subtypes of entorhinal neurons: implications for Alzheimer's Disease.

Alzheimers Disease (AD) is distinguished by the presence of two key pathological features: amyloid plaques, accumulations of proteolytic products of Amyloid Precursor Protein, and neurofibrillary tangles (NFTs), intracellular aggregations of microtubule-associated protein tau. NFTs first appear in particular entorhinal cortex (EC) neurons (called pre-alpha neurons) in asymptomatic patients, then continue to spread through other connected brain regions as the disease progresses. This stereotypical progression of tauopathy through synaptically connected brain regions (i.e. Braak stages) not only suggests that the tauopathy in AD spreads transsynaptically, it also raises the question whether particular neuronal subtypes and/or brain regions are especially prone to tauopathy. We explored this question by overexpressing wildtype human tau protein (hTau) in a variety of entorhinal and neocortical neuronal subtypes. We then compared the tendencies of different neuronal cell types to develop different pathological tau species over time and found that tau pathology does indeed develop at markedly different rates in different neuronal subtypes. Perhaps unsurprisingly, the EC is particularly prone, with the likely rat cognates of the pre-alpha neurons (ECLII fan cells) among the first to express pathological tau label. Fan cells were not, however, the neurons with the greatest vulnerability to generate pathological tau species: subsets of ECLIII neurons were found to express disproportional amounts of pathological tau. This is of particular interest given that the next structures to develop AD-related tauopathy after the EC in patients are CA1 hippocampus and subiculum, where ECLIII neurons project, rather than the dentate gyrus and CA3, where ECLII fan cells project. These results demonstrate differential susceptibility of different neuronal subtypes to pathological tau species and suggest distinct roles for different entorhinal neuronal subtypes in the propagation of the tauopathy underlying AD-related neurodegeneration.

neuroscience↗

bioRxiv2022

Apolipoprotein E intersects with amyloid-β within neurons

Apolipoprotein E4 (ApoE4) is the most important genetic risk factor for Alzheimers disease (AD). Among the earliest changes in AD is endosomal enlargement in neurons, which was reported as enhanced in ApoE4 carriers. ApoE is thought to be internalized into endosomes of neurons, while {beta}-amyloid (A{beta}) accumulates within neuronal endosomes early in AD. However, it remains unknown whether ApoE and A{beta} intersect intracellularly. We show that internalized astrocytic ApoE localizes mostly to lysosomes in neuroblastoma cells and astrocytes, while in neurons it preferentially localizes to endosomes-autophagosomes of neurites. In AD transgenic neurons, astrocyte-derived ApoE intersects intracellularly with amyloid precursor protein (APP)/A{beta}. Moreover, ApoE4 increases the levels of endogenous and internalized A{beta}42 in neurons. Taken together, we demonstrate differential localization of ApoE in neurons, astrocytes and neuron-like cells, and show that internalized ApoE intersects with APP/A{beta} in neurons, which may be of considerable relevance to AD.

neuroscience↗

bioRxiv2022

Aβ/APP-induced hyperexcitability and dysregulation of homeostatic synaptic plasticity in models of Alzheimer's disease

The proper function of the nervous system is dependent on the appropriate timing of neuronal firing. Synapses continually undergo rapid activity-dependent modifications that require feedback mechanisms to maintain network activity within a window in which communication is energy efficient and meaningful. Homeostatic synaptic plasticity (HSP) and homeostatic intrinsic plasticity (HIP) are such negative feedback mechanisms. Accumulating evidence implicates that Alzheimers disease (AD)-related amyloid precursor protein (APP) and its cleavage product amyloid-beta (A{beta}) play a role in the regulation of neuronal network activity, and in particular HSP. AD features impaired neuronal activity with regional early hyper-activity and A{beta}-dependent hyperexcitability has also been demonstrated in AD transgenic mice. We demonstrate similar hyper-activity in AD transgenic neurons in culture that have elevated levels of both human APP and A{beta}. To examine the individual roles of APP and A{beta} in promoting hyperexcitability we used an APP construct that does not generate A{beta}, or elevated A{beta} levels independently of APP. Increasing either APP or A{beta} in wild type (WT) neurons leads to increased frequency and amplitude of calcium transients. Since HSP/HIP mechanisms normally maintain a setpoint of activity, we examined whether homeostatic synaptic/intrinsic plasticity was altered in AD transgenic neurons. Using methods known to induce HSP/HIP, we demonstrate that APP protein levels are regulated by chronic modulation of activity and show that AD transgenic neurons have an impaired response to global changes in activity. Further, AD transgenic compared to WT neurons failed to adjust the length of their axon initial segments (AIS), an adaptation known to alter excitability. Thus, we present evidence that both APP and A{beta} influence neuronal activity and that mechanisms of HSP/HIP are disrupted in neuronal models of AD.

neuroscience↗

bioRxiv2021

FRET-based screening in HEK293T identifies p38 MAPK and PKC inhibition as therapeutic targets for α-synuclein aggregation

Aggregation of -synuclein is associated with neurodegeneration and a hallmark pathology in synucleinopathies. These aggregates are thought to function as prion-like particles where the conformation of misfolded -synuclein determines the induced pathologys traits similar to prion diseases. Still, little is known about the molecular targets facilitating the conformation-specific biological effects, but their identification could form the basis for new therapeutic intervention. High-throughput screening (HTS) of annotated compound libraries could facilitate mechanistic investigation by identifying targets with impact on -synuclein aggregation. To this end, we developed a FRET-based cellular reporter in HEK293T cells, with sensitivity down to 6.5 nM -synuclein seeds. Using this model system, we identified GF109203X, SB202190, and SB203580 as inhibitors capable of preventing induction of - synuclein aggregation via inhibition of p38 MAPK and PKC, respectively. Our findings highlight the value HTS brings to the mechanistic investigation of -synuclein aggregation while simultaneously identifying novel therapeutic compounds.

molecular biology↗