@article {2328, title = {APOE4 Affects Basal and NMDAR-Mediated Protein Synthesis in Neurons by Perturbing Calcium Homeostasis.}, journal = {J Neurosci}, volume = {41}, year = {2021}, month = {2021 Oct 20}, pages = {8686-8709}, abstract = {

Apolipoprotein E (APOE), one of the primary lipoproteins in the brain has three isoforms in humans, APOE2, APOE3, and APOE4. APOE4 is the most well-established risk factor increasing the predisposition for Alzheimer{\textquoteright}s disease (AD). The presence of the APOE4 allele alone is shown to cause synaptic defects in neurons and recent studies have identified multiple pathways directly influenced by APOE4. However, the mechanisms underlying APOE4-induced synaptic dysfunction remain elusive. Here, we report that the acute exposure of primary cortical neurons or synaptoneurosomes to APOE4 leads to a significant decrease in global protein synthesis. Primary cortical neurons were derived from male and female embryos of Sprague Dawley (SD) rats or C57BL/6J mice. Synaptoneurosomes were prepared from P30 male SD rats. APOE4 treatment also abrogates the NMDA-mediated translation response indicating an alteration of synaptic signaling. Importantly, we demonstrate that both APOE3 and APOE4 generate a distinct translation response which is closely linked to their respective calcium signature. Acute exposure of neurons to APOE3 causes a short burst of calcium through NMDA receptors (NMDARs) leading to an initial decrease in protein synthesis which quickly recovers. Contrarily, APOE4 leads to a sustained increase in calcium levels by activating both NMDARs and L-type voltage-gated calcium channels (L-VGCCs), thereby causing sustained translation inhibition through eukaryotic translation elongation factor 2 (eEF2) phosphorylation, which in turn disrupts the NMDAR response. Thus, we show that APOE4 affects basal and activity-mediated protein synthesis responses in neurons by affecting calcium homeostasis. Defective protein synthesis has been shown as an early defect in familial Alzheimer{\textquoteright}s disease (AD). However, this has not been studied in the context of sporadic AD, which constitutes the majority of cases. In our study, we show that Apolipoprotein E4 (APOE4), the predominant risk factor for AD, inhibits global protein synthesis in neurons. APOE4 also affects NMDA activity-mediated protein synthesis response, thus inhibiting synaptic translation. We also show that the defective protein synthesis mediated by APOE4 is closely linked to the perturbation of calcium homeostasis caused by APOE4 in neurons. Thus, we propose the dysregulation of protein synthesis as one of the possible molecular mechanisms to explain APOE4-mediated synaptic and cognitive defects. Hence, the study not only suggests an explanation for the APOE4-mediated predisposition to AD, it also bridges the gap in understanding APOE4-mediated pathology.

}, issn = {1529-2401}, doi = {10.1523/JNEUROSCI.0435-21.2021}, author = {Ramakrishna, Sarayu and Jhaveri, Vishwaja and Konings, Sabine C and Nawalpuri, Bharti and Chakraborty, Sumita and Holst, Bj{\o}rn and Schmid, Benjamin and Gouras, Gunnar K and Freude, Kristine K and Muddashetty, Ravi S} } @article {2362, title = {Astrocytic reactivity triggered by defective autophagy and metabolic failure causes neurotoxicity in frontotemporal dementia type 3.}, journal = {Stem Cell Reports}, volume = {16}, year = {2021}, month = {2021 Nov 09}, pages = {2736-2751}, abstract = {

Frontotemporal dementia type 3 (FTD3), caused by a point mutation in the charged multivesicular body protein 2B (CHMP2B), affects mitochondrial ultrastructure and the endolysosomal pathway in neurons. To dissect the astrocyte-specific impact of mutant CHMP2B expression, we generated astrocytes from human induced pluripotent stem cells (hiPSCs) and confirmed our findings in CHMP2B mutant mice. Our data provide mechanistic insights into how defective autophagy causes perturbed mitochondrial dynamics with impaired glycolysis, increased reactive oxygen species, and elongated mitochondrial morphology, indicating increased mitochondrial fusion in FTD3 astrocytes. This shift in astrocyte homeostasis triggers a reactive astrocyte phenotype and increased release of toxic cytokines, which accumulate in nuclear factor kappa b (NF-κB) pathway activation with increased production of CHF, LCN2, and C3 causing neurodegeneration.

}, issn = {2213-6711}, doi = {10.1016/j.stemcr.2021.09.013}, author = {Chandrasekaran, Abinaya and Dittlau, Katarina Stoklund and Corsi, Giulia I and Haukedal, Henriette and Doncheva, Nadezhda T and Ramakrishna, Sarayu and Ambardar, Sheetal and Salcedo, Claudia and Schmidt, Sissel I and Zhang, Yu and Cirera, Susanna and Pihl, Maria and Schmid, Benjamin and Nielsen, Troels Tolstrup and Nielsen, J{\o}rgen E and Kolko, Miriam and Kobol{\'a}k, Julianna and Dinny{\'e}s, Andr{\'a}s and Hyttel, Poul and Palakodeti, Dasaradhi and Gorodkin, Jan and Muddashetty, Ravi S and Meyer, Morten and Aldana, Blanca I and Freude, Kristine K} } @article {1602, title = {Generation of a set of isogenic, gene-edited iPSC lines homozygous for all main APOE variants and an APOE knock-out line.}, journal = {Stem Cell Res}, volume = {34}, year = {2019}, month = {2019 Jan}, pages = {101349}, abstract = {

Alzheimer{\textquoteright}s disease (AD) is the most frequent neurodegenerative disease amongst the elderly. The SNPs rs429358 and rs7412 in the APOE gene are the most common risk factor for sporadic AD, and there are three different alleles commonly referred to as APOE-ε2, APOE-ε3 and APOE-ε4. Induced pluripotent stem cells (iPSCs) hold great promise to model AD as such cells can be differentiated in vitro to the required cell type. Here we report the use of CRISPR/Cas9 technology employed on iPSCs from a healthy individual with an APOE-ε3/ε4 genotype to obtain isogenic APOE-ε2/ε2, APOE-ε3/ε3, APOE-ε4/ε4 lines as well as an APOE-knock-out line.

}, issn = {1876-7753}, doi = {10.1016/j.scr.2018.11.010}, author = {Schmid, Benjamin and Prehn, Kennie R and Nimsanor, Natakarn and Garcia, Blanca Irene Aldana and Poulsen, Ulla and J{\o}rring, Ida and Rasmussen, Mikkel A and Clausen, Christian and Mau-Holzmann, Ulrike A and Ramakrishna, Sarayu and Muddashetty, Ravi and Steeg, Rachel and Bruce, Kevin and Mackintosh, Peter and Ebneth, Andreas and Holst, Bj{\o}rn and Cabrera-Socorro, Alfredo} } @article {1609, title = {Generation of two iPSC lines with either a heterozygous V717I or a heterozygous KM670/671NL mutation in the APP gene.}, journal = {Stem Cell Res}, volume = {34}, year = {2019}, month = {2019 Jan}, pages = {101368}, abstract = {

Alzheimer{\textquoteright}s disease (AD) is the most common form of dementia, affecting millions of people worldwide. Mutations in the genes PSEN1, PSEN2 or APP are known to cause familial forms of AD with an early age of onset. In this study, specific pathogenic mutations in the APP gene were introduced into an iPSC line from a healthy individual by the use of CRISPR-Cas9. The study resulted in the generation of two new cell lines, one carrying the V717I APP mutation and one with the KM670/671NL APP mutation.

}, issn = {1876-7753}, doi = {10.1016/j.scr.2018.101368}, author = {Frederiksen, Henriette R and Holst, Bj{\o}rn and Ramakrishna, Sarayu and Muddashetty, Ravi and Schmid, Benjamin and Freude, Kristine} }