Genetic studies conducted over the past four decades have provided us with a detailed catalog of genes that play critical roles in the etiology of Alzheimer’s Disease (AD) and Related Dementias (ADRDs). Despite this progress, as a field we have had only limited success in incorporating this rich complexity of human AD/ADRD genetics findings into our animal models of these diseases. Our group is playing a central role in the NIH efforts to directly address this problem by developing the first sets of AD/ADRD mouse lines that model the genetics of AD as closely as possible. To do this, we devised Gene Replacement (GR) technologies that allow us for the first time to generate mouse lines in which genes-of-interest are precisely and completely replaced by their human orthologs. Each set of models we make consists of a control line with a wt human allele, and variant lines that precisely match the human genomic sequence in the control line except for a high-impact pathogenic mutation that we specifically introduce.
We are actively working to generate mice with human alleles in three general categories: 1) genes in which high-impact rare variants cause early-onset Familial AD (FAD), 2) genes in which high-impact rare variants cause inherited forms of ADRD, and 3) genes identified as modifiers of the risk of developing dementia. We have to-date generated sets of GR lines that carry the full human alleles that encode TAU (MAPT-Gene Replacement, or MAPT-GR, with 190kb of human genomic sequence), Amyloid Precursor Protein (APP-GR, 344kb), Presenilin 1 (PSEN1-GR, 106kb), a-Synuclein (SNCA-GR, 158kb), C9orf72 (C9ort72-GR, 109kb), and the full gene cluster encoding APOE and related genes (APOE-GR, 47kb five-gene cluster). Additional projects in progress include mice with human alleles that encode Presenilin 2 (PSEN2-GR, 113kb), TDP-43 (TARDBP-GR, 65kb), TMEM106B (TMEM106B-GR, 97kb), TREM2 (TREM2-GR, 202kb six-gene cluster) and MS4A (MS4A-GR, 313kb six-gene cluster).
The full range of consequences of many AD pathogenic and risk variant sequences are only evident by their interactions with the products of genes either upstream or downstream in the AD pathogenic cascade. We are therefore generating mouse lines in which we combine multiple GR human alleles in the same animals, with the ultimate goal of recreating the human genetics and pathophysiology of AD as closely as is possible in a mouse.
Our GR models serve as experimental systems for probing the molecular dysfunctions caused by pathogenic AD mutations, identifying quantifiable early-stage endophenotypes directly linked to these mutations, and developing and testing therapeutic interventions for correcting these dysfunctions. These precisely matched sets of animal models allow us to evaluate the molecular impact of pathogenic mutations within the context of the human genomic sequence in which they occur in patients, and these mouse lines contain all potential human therapeutic targets ranging from the full genomic DNA sequences to all RNA transcription variants and protein products that they encode.
We are conducting in-depth characterization of our MAPT-GR set of mouse lines in collaborative projects with the Tim Ebner and Dezhi Liao research groups. We induce mild traumatic brain injury (mTBI) in the forebrains of MAPT-GR mice, and brain tissue is then examined for TAU phosphorylation and sub-cellular localization. Prior to mTBI, human TAU protein in MAPT-GR mice is unphosphorylated and primarily localized to axons. We find that TAU in neurons impacted by mTBI becomes phosphorylated and prominently mis-localized to the somatodendritic domain. TAU pathology is clearly detectable by day 3 post-mTBI, is fully developed by day 7, and in young animals is largely cleared by 1 month. We conclude that physical damage to axons activates a pair of kinases to phosphorylate TAU and that this phosphorylation is a necessary component of the process that then moves the modified TAU protein from the axon to the somatodendritic domain. We are currently working to determine the precise molecular details and consequences of this TAU phosphorylation/mis-localization pathway, and to explore its connection to other molecular pathways in the AD pathogenic cascade.
(For a comprehensive list of recent publications, refer to PubMed, a service provided by the National Library of Medicine.)
- Perissinotti PP, Martínez-Hernández E, He Y, Koob MD, Piedras-Rentería ES. Genetic deletion of KLHL1 leads to hyperexcitability in hypothalamic POMC neurons and lack of electrical responses to leptin. Front Neurosci. 2021 Sep 9;15:718464.
- Castro M, Venkateswaran N , Peters ST, Deyle DR, Bower M, Koob MD, Boeve BF, Vossel K. Case Report: Early-onset behavioral variant frontotemporal dementia in patient with retrotransposed full-length transcript of matrin-3 variant 5. Front Neurol. 2020 Dec 21;11:600468.
- Martínez-Hernández E, Zeglin A, Almazan E, Perissinotti P, He Y, Koob M, Martin JL, Piedras-Rentería ES. KLHL1 controls CaV3.2 expression in DRG neurons and mechanical sensitivity to pain. Front Mol Neurosci. 2020 Jan 8;12:315.
- Gamache JE, Kemper L, Steuer E, Leinonen-Wright K, Choquette JM, Hlynialuk C, Benzow K, Vossel KA, Xia W, Koob MD, Ashe KH. Developmental pathogenicity of 4-repeat human tau is lost with the P301L mutation in genetically matched tau-transgenic mice. J Neurosci. 2020;40(1):220-236.
- Gamache JE, Benzow K, Forster C, Kemper L, Hlyniakluk C, Furrow E, Ashe KH, Koob MD. Factors other than hTau overexpression that contribute to tauopathy-like phenotype in rTg4510 mice. Nat Commun. 2019;10:2479.
- Yoon YG, Koob MD. Intramitochondrial transfer and engineering of mammalian mitochondrial genomes in yeast. Mitochondrion. 2019 May;46:15-21.
- Perissinotti PP, Ethington EA, Almazan E, Martínez-Hernández E, Kalil J, Koob MD, Piedras-Rentería ES. Calcium current homeostasis and synaptic deficits in hippocampal neurons from Kelch-like 1 knockout mice. Front Cell Neurosci. 2015 Jan 7;8:444.
- Perissinotti PP, Ethington EG, Cribbs L, Koob MD, Martin J, Piedras-Rentería ES. Down-regulation of endogenous KLHL1 decreases voltage-gated calcium current density. Cell Calcium. 2014;55:269-280.
Former Graduate Students:
Julia Gamache (Ph.D. 2019, Neuroscience, University of Minnesota)