8 Triple phosphorylation of Ser202, Thr205, and Ser208 promotes tau mislocalization and aggregation, leading to the formation of NFT

8 Triple phosphorylation of Ser202, Thr205, and Ser208 promotes tau mislocalization and aggregation, leading to the formation of NFT. Comparative assessment of the epitopes recognized by antibodies AT8, CP13, and 7F2 demonstrates that CP13 and 7F2 are specific for tau phosphorylation at Ser202 and Thr205, respectively, independently of the phosphorylation state of adjacent phosphorylation sites. Supporting the involvement of pSer208 in tau pathology, a novel monoclonal antibody 3G12 specific for tau phosphorylation at Ser208 revealed strong reactivity of tau inclusions in the brains of PS19 and rTg4510 transgenic mouse models of tauopathy. 3G12 also labelled neurofibrillary tangles in brains of patients with AD but revealed differential staining compared to CP13 and 7F2 for other types of tau pathologies such as in neuropil threads and neuritic plaques in AD, tufted astrocytes in progressive supranuclear palsy and astrocytic plaques in corticobasal degeneration. These results support the hypothesis that tau phosphorylation at Ser208 strongly contributes to unique types of tau aggregation and may be a reliable marker for the presence of mature?neurofibrillary tangles. Keywords: Alzheimers disease, tau, Neurodegeneration, Neurofibrillary tangle, Microtubule-associated protein tau (MAPT), Protein aggregation, AT8, CP13, Microtubule binding, Prion-like seeding, Tauopathy Introduction Alzheimers disease (AD) is the most common form of age-related dementia and affects over 25 million people worldwide [66]. AD is pathologically defined by the presence of two major types of pathologic brain inclusions: 1) extracellular amyloid- (A) deposits in the form of plaques and cerebral amyloid angiopathy and 2) intracellular aggregates of tau protein that comprise neurofibrillary tangles (NFT) and neuropil threads [11, 40]. The amyloid cascade hypothesis suggests that the accumulation and deposition of A is the primary cause of AD [70]. However as the density of tau inclusions strongly correlates with cognitive decline [63], the tau hypothesis proposes that pathogenic tau is the main toxic factor that drives neurodegeneration in AD and other related diseases [43]. Mutations in the microtubule-associated protein tau (MAPT) gene cause different familial forms of frontotemporal lobar degeneration (FTLD) including Picks disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and globular MZ1 glial tauopathy (GGT) [23, 39, 80]. Tau is a microtubule-associated protein that is highly expressed in the distal axons of neurons in the central nervous system [9, 80]. Physiologically, tau binds directly to microtubules (MTs) and is important for regulating MT assembly, dynamics, and stability, which are all important for normal axonal transport of vesicles MZ1 and other molecules [42, 44, 83]. Tau protein can be alternatively spliced into six major isoforms found in the brains of humans and rodents [30, 31]. Variations in insertion of two N-terminal inserts of 29 amino acids generate 0?N, 1?N and 2?N isoforms. The presence or absence of exon 10 can lead to either three or four MT binding repeats to Mouse Monoclonal to Strep II tag generate either 3R or 4R isoforms. In AD, all six major tau isoforms aggregate to form pathological inclusions in a hyperphosphorylated state [29, 80]. Over 45 out of 85 total potential phosphorylation sites have been identified in AD brains by mass spectrometry and other methods [34C37, 60]. This aberrant hyperphosphorylation can cause tau to dissociate from MTs and decrease its ability to assemble and regulate MTs [22, 47, 49, 71]. Hyperphosphorylated tau may also be more prone to be mislocalized and to promote tau aggregation [2, 12, 32, 75]. Phosphorylation-specific tau antibodies such as AT8 are widely used to survey the distribution of tau pathology in AD brains, which follows a stereotypical pattern of progression as described in Braak staging C with NFT appearing to start in the entorhinal cortex and extending into the hippocampus and more MZ1 distant cortical regions in late stage disease [10, 11]. Although the AT8 antibody is very useful diagnostic tool, the exact epitope recognized by this antibody has not been completely resolved, since AT8 was originally created by immunizing mice with paired helical filaments of tau (PHF-tau) purified from AD brains [58]. Early characterization of the AT8 epitope indicated that it requires phosphorylation at Ser202 (pSer202) and Thr205 (pThr205) [8, 28]; however, AT8 also has some reactivity to tau phosphorylation at Ser199 [8]. Recent epitope mapping has revealed that tau pSer208 may also be a part of the classic AT8 epitope and the addition of pSer208 to pSer202/pThr205 can enhance AT8 binding [53,.