Anesthesia promotes acute expression of genes related to Alzheimer’s disease and latent tau aggregation in transgenic mouse models of tauopathy

Abstract

Background Exposure to anesthesia in the elderly might increase the risk of dementia. Although the mechanism underlying the association is uncertain, anesthesia has been shown to induce acute tau hyperphosphorylation in preclinical models. We sought to investigate the impact of anesthesia on gene expression and on acute and long-term changes in tau biochemistry in transgenic models of tauopathy in order to better understand how anesthesia influences the pathophysiology of dementia. Methods We exposed mice with over-expressed human mutant tau (P301L and hyperdopaminergic COMTKO/P301L) to two hours of isoflurane and compared anesthetized mice to controls at several time points. We evaluated tau hyperphosphorylation with quantitative high-sensitivity enzyme-linked immunosorbent assay and performed differential expression and functional transcriptome analyses following bulk mRNA-sequencing. Results Anesthesia induced acute hyperphosphorylation of tau at epitopes related to Alzheimer’s disease (AD) in both P301L-based models. Anesthesia was associated with differential expression of genes in the neurodegenerative pathways (e.g., AD-risk genes ApoE and Trem2) and thermogenesis pathway, which is related to both mammalian hibernation and tau phosphorylation. One and three months after anesthesia, hyperphosphorylated tau aggregates were increased in the anesthetized mice. Conclusions Anesthesia may influence the expression of AD-risk genes and induce biochemical changes in tau that promote aggregation even after single exposure. Further preclinical and human studies are necessary to establish the relevance of our transcriptomic and biochemical findings in these preclinical models to the pathogenesis of dementia following anesthesia. Trial registration: Not applicable.

The Impact of Muscarinic Antagonism on Psychosis-Relevant Behaviors and Striatal [11C] Raclopride Binding in Tau Mouse Models of Alzheimer’s Disease

“…As the muscarinic receptor system has been shown to regulate extracellular concentrations of soluble tau [ 60 , 77 ], in order to determine whether scopolamine treatment increased soluble tau in the striatum, a region of dense expression of muscarinic receptors [ 78 ] soluble tau was measured in the P301L/COMTKO mice treated with scopolamine or saline. Soluble, rather than insoluble, tau in these mice was quantified, as we have found that 7 days (and even shorter) is a sufficient period to impact changes in soluble tau but insufficient time to impact aggregated tau in the P301L/COMTKO model [ 65 ]. Soluble tau (μg/mg protein) in the striatum was significantly increased in scopolamine-treated mice ( t = 2.643, p = 0.013, Figure 3 A).…”

“…In order to evaluate differentially expressed genes associated with treatment, as in our previously published work [ 65 ], following sacrifice after 1 week of exposure, total RNA was extracted from the brains of scopolamine-treated P301L/COMTKO mice and saline-treated P301L/COMTKO mice with an RNeasy Mini Kit (Qiagen, Hilden, Germany), according to the manufacturer’s protocol [ 65 ]. NanoDrop ND-100 Spectrophotometer was used to determine the concentration of RNA samples (NanoDrop Technologies, Wilmington, DE, USA), and BioAnalyzer RNA 2100 kit was used to test their integrity (Agilent Technologies, Santa Clara, CA, USA) [ 65 ]. RNA sequencing was performed with the Illumina mRNA TruSeq Stranded method on Illumina HiSeq (Illumina, San Diego, CA, USA) [ 65 ].…”

“…NanoDrop ND-100 Spectrophotometer was used to determine the concentration of RNA samples (NanoDrop Technologies, Wilmington, DE, USA), and BioAnalyzer RNA 2100 kit was used to test their integrity (Agilent Technologies, Santa Clara, CA, USA) [ 65 ]. RNA sequencing was performed with the Illumina mRNA TruSeq Stranded method on Illumina HiSeq (Illumina, San Diego, CA, USA) [ 65 ]. We used the RNA-seq Alignment app and Illumina BaseSpace Sequence Hub, together with the DRAGEN (Dynamic Read Analysis for Genomics) platform (version 3.9.0), to calculate the differential expression of genes in P301L/COMTKO mice under the two different treatment conditions.…”

“…The UCSC mm10 mus musculus (with RefSeq gene annotation) was the reference genome. Wald test p values below 0.05 for log 2 -fold-change (LFC) estimates of scopolamine-versus-saline treated mice were tested for false discovery in multiple comparisons utilizing the Benjamini–Hochberg procedure [ 65 ].…”

“…We utilized a high-sensitivity EILISA technique, developed in our lab, to quantify the total soluble tau (μg/mg protein) by utilizing monoclonal capture and detection tau antibodies [ 71 ]. Following sacrifice, as in our previously published work, the brains of P301L/COMTKO mice were removed, the forebrain was dissected from the hindbrain, and the striatum was dissected and prepared for quantitative tau biochemistry [ 65 , 72 ]. The striatum was homogenized using an appropriate volume of homogenizing buffer comprised of a solution of Tris-buffered saline, pH 7.4, containing: 10 mM NaF, 1 mM NaVO3, and 2 mM EGTA, with a complete Mini protease inhibitor cocktail (Roche Molecular Biochemicals, Indianapolis, IN, USA).…”