Quantification of Tau Protein Lysine Methylation in Aging and Alzheimer’s Disease

Abstract

Tau is a microtubule-associated protein that normally interacts in monomeric form with the neuronal cytoskeleton. In Alzheimer's disease, however, it aggregates to form the structural component of neurofibrillary lesions. The transformation is controlled in part by age-and diseaseassociated post-translational modifications. Recently we reported that tau isolated from cognitively normal human brain was methylated on lysine residues, and that high-stoichiometry methylation depressed tau aggregation propensity in vitro. However, whether methylation stoichiometry

SETD7-mediated lysine monomethylation is abundant on non-hyperphosphorylated nuclear Tau

“…We analyzed entorhinal cortex samples from donors classified as Braak stages 0-I as well as Braak stages III-IV to represent non-affected controls and early (often still clinically asymptomatic) AD, respectively (Table 1). This led to the identification of 12 phosphorylation sites which have been previously described, one novel acetylation site (Table 2) and 10 monomethylation sites, including 6 novel sites (K130, K150, K294, K298, K343, K438) and 4 described previously (K132, K259, K353, K385 (Funk et al, 2014, Huseby, Hoffman et al, 2019)). The majority of these methylated lysines is located in the repeat domains (Fig.…”

“…A recent study has suggested that Tau lysine methylation is altered in the human brain with age and differences potentially exist between control and AD patients (Huseby et al, 2019). To assess whether our sites of interest are differentially methylated between Braak 0-I and Braak III-IV patient brain samples, we used a sensitive electrochemiluminescence ELISA method using commercially available total Tau antibody-coated plates for capture and our novel methyl antibodies as detection antibodies.…”

“…While a few published studies have reported different lysine methylation events on Tau, the enzymes involved in these processes are unknown (Funk et al, 2014, Huseby et al, 2019, Thomas et al, 2012). We analyzed the Tau sequence for potential recognition sites for protein lysine methyltransferases and identified the consensus motif for SETD7 (SET Domain Containing 7) at aa130-132 (R/KSK(me), (Dhayalan, Kudithipudi et al, 2011)).…”

“…While recent mass spectrometry studies have described lysine methylation on the Tau protein in human brain samples derived from both AD patients and non-affected controls (Funk et al, 2014, Huseby et al, 2019, Thomas et al, 2012), protein lysine methyltransferases involved in this process or the functional consequences of Tau methylation in health and disease were so far unexplored. Here we show that Tau methylation at selected sites is more abundant in human AD brain samples compared to controls and increases with age in the rTg4510 mouse model of tauopathy.…”

“…Promoting nuclear localization of target proteins is a known function of lysine methylation, and has been reported among others also for non-histone targets of SETD7 such as p53 or the estrogen receptor (Chuikov, Kurash et al, 2004, Subramanian, Jia et al, 2008). Most lysine methylation sites so far identified on Tau are situated in the microtubule binding (MTB) domain (Funk et al, 2014, Huseby et al, 2019), and methylation may thus contribute to lower affinity of Tau for microtubules and facilitate its re-distribution to other subcellular compartments. Interestingly, a recent study reports preferential nuclear localization of an N279K Tau mutant associated with frontotemporal dementia, for which the novel lysine also falls within the MTB region (Ritter, Avila et al, 2018).…”