Deregulated Transcription and Proteostasis in Adult mapt Knockout Mouse

Transcriptomics and phosphoproteomics were carried out in the cerebral cortex of B6.Cg-Mapttm1(EGFP)Klt (tau knockout: tau-KO) and wild-type (WT) 12 month-old mice to learn about the effects of tau ablation. Compared with WT mice, tau-KO mice displayed reduced anxiety-like behavior and lower fear expression induced by aversive conditioning, whereas recognition memory remained unaltered. Cortical transcriptomic analysis revealed 69 downregulated and 105 upregulated genes in tau-KO mice, corresponding to synaptic structures, neuron cytoskeleton and transport, and extracellular matrix components. RT-qPCR validated increased mRNA levels of col6a4, gabrq, gad1, grm5, grip2, map2, rab8a, tubb3, wnt16, and an absence of map1a in tau-KO mice compared with WT mice. A few proteins were assessed with Western blotting to compare mRNA expression with corresponding protein levels. Map1a mRNA and protein levels decreased. However, ¿-tubulin III and GAD1 protein levels were reduced in tau-KO mice. Cortical phosphoproteomics revealed 121 hypophosphorylated and 98 hyperphosphorylated proteins in tau-KO mice. Deregulated phosphoproteins were categorized into cytoskeletal (n = 45) and membrane proteins, including proteins of the synapses and vesicles, myelin proteins, and proteins linked to membrane transport and ion channels (n = 84), proteins related to DNA and RNA metabolism (n = 36), proteins connected to the ubiquitin-proteasome system (UPS) (n = 7), proteins with kinase or phosphatase activity (n = 21), and 22 other proteins related to variegated pathways such as metabolic pathways, growth factors, or mitochondrial function or structure. The present observations reveal a complex altered brain transcriptome and phosphoproteome in tau-KO mice with only mild behavioral alterations. The project leading to these results received funding from the “la Caixa” Foundation (ID 100010434) under the agreements LCF/PR/HR19/52160007, HR18-00452 to IF. We thank the CERCA Programme/Generalitat de Catalunya for institutional support. The Proteomics Platform of Navarrabiomed is a member of Proteored (PRB3-ISCIII), supported by grant PT17/0019/009 to J.F.-I. of the PE I + D + I 2013-2016 funded by ISCIII and FEDER. This work was funded by a grant from the Spanish Ministry of Science, Innovation, and Universities (Ref. PID2019-110356RB-I00) to J.F.-I. and E.S. and the Department of Economic and Business Development from the Government of Navarra (Ref. 0011-1411-2020-000028) to E.S.