Pathogenic Forms of Tau Inhibit Kinesin-Dependent Axonal Transport Through a Tau-Dependent Mechanism Involving Activation of Axonal Phosphotransferases

Aggregated filamentous forms of hyperphosphorylated tau (a microtubule-associated protein) represent pathological hallmarks of Alzheimer’s disease (AD) and other tauopathies. While axonal transport dysfunction is thought to represent a primary pathogenic factor in AD and other neurodegenerative diseases, the direct molecular link between pathogenic forms of tau and deficits in axonal transport remain unclear. Recently, we demonstrated that filamentous, but not soluble, forms of wild-type tau inhibit anterograde, kinesin-based fast axonal transport (FAT) by activating axonal protein phosphatase 1 (PP1) and glycogen synthase kinase 3 (GSK3), independent of microtubule binding. Here, we demonstrate that amino acids 2-18 of tau, comprising a phosphatase-activating domain (PAD), are necessary and sufficient for activation of this pathway in axoplasms isolated from squid giant axons. Various pathogenic forms of tau displaying increased exposure of PAD inhibited anterograde FAT in squid axoplasm. Importantly, immunohistochemical studies using a novel PAD-specific monoclonal antibody in human postmortem tissue indicated that increased PAD exposure represents an early pathogenic event in AD that closely associates in time with AT8 immunoreactivity, an early marker of pathological tau. We propose a model of pathogenesis in which disease-associated changes in tau conformation lead to increased exposure of PAD, activation of PP1-GSK3 and inhibition of FAT. Results from these studies reveal a novel role for tau in modulating axonal phosphotransferases and provide a molecular basis for a toxic gain-of-function associated with pathogenic forms of tau

Additional file 3: of Lewy body-like alpha-synuclein inclusions trigger reactive microgliosis prior to nigral degeneration

Figure S3. Antigen-presenting MHC-IIir microglia are not associated with peak of intraneuronal inclusions of pSyn in the striatum. Progression of pSyn pathology and MHC-IIir microglia in the striatum. (a) At 2 months p.i., pSyn inclusions are localized to neurites, presumably representing terminals from the SNc. (b–c) Over time pSyn inclusions become primarily localized to the soma of striatal neurons. (d) Abundant MHC-IIir microglia in the striatum primarily localized around the α-syn PFF injection site at 2 months. (e–f) MHC-IIir microglia in the striatum are largely absent during continuing accumulation of intraneuronal pSyn inclusions at 4 months (e) and 6 months (f) p.i. (g) Intrastriatal injection of PBS results abundant MHC-IIir microglia in the striatum localized near the site of injection at 2 months p.i., although appearing less abundant than MHC-IIir microglia in the striatum of α-syn PFF rats at the same time point (d). (h) MHC-IIir microglia are similarly absent from the parenchyma by 4 months (h) and 6 months p.i (i). Scale bars A–I = 50 μm. Abbreviations: p.i. = postinjection; PFFs = pre-formed alpha-synuclein fibrils; PBS = phosphate-buffered saline; pSyn = α-syn phosphorylated at serine 129, MHC-IIir = major-histocompatibility complex-II immunoreactive. (TIF 112368 kb

Additional file 1: of Lewy body-like alpha-synuclein inclusions trigger reactive microgliosis prior to nigral degeneration

Figure S1. Unilateral intrastriatal injection of α-syn PFFs, but not RSA or PBS, induces bilateral cortical and unilateral SNc Lewy-body like inclusions of phosphorylated α-syn (pSyn). (a) pSyn pathology is observed bilaterally in cortical areas after unilateral injection of α-syn PFFs, namely in layers 2/3 and orbital and agranular insular cortices. (b) Injection of PBS or (c) RSA did not induce pSyn accumulation. (d) pSyn accumulation in the ipsilateral substantia nigra pars compacta (SNc) at 2 months postinjection, with no evidence of pSyn inclusions in the contralateral SNc. Scale bars (A–D) = 50 μm. Abbreviations: α-syn = alpha-synuclein; PFFs = pre-formed alpha-synuclein fibrils; PBS = phosphate-buffered saline; RSA = rat serum albumin; pSyn = α-syn phosphorylated at serine 129. (TIF 117729 kb

Additional file 3: of Lewy body-like alpha-synuclein inclusions trigger reactive microgliosis prior to nigral degeneration

Figure S3. Antigen-presenting MHC-IIir microglia are not associated with peak of intraneuronal inclusions of pSyn in the striatum. Progression of pSyn pathology and MHC-IIir microglia in the striatum. (a) At 2 months p.i., pSyn inclusions are localized to neurites, presumably representing terminals from the SNc. (b–c) Over time pSyn inclusions become primarily localized to the soma of striatal neurons. (d) Abundant MHC-IIir microglia in the striatum primarily localized around the α-syn PFF injection site at 2 months. (e–f) MHC-IIir microglia in the striatum are largely absent during continuing accumulation of intraneuronal pSyn inclusions at 4 months (e) and 6 months (f) p.i. (g) Intrastriatal injection of PBS results abundant MHC-IIir microglia in the striatum localized near the site of injection at 2 months p.i., although appearing less abundant than MHC-IIir microglia in the striatum of α-syn PFF rats at the same time point (d). (h) MHC-IIir microglia are similarly absent from the parenchyma by 4 months (h) and 6 months p.i (i). Scale bars A–I = 50 μm. Abbreviations: p.i. = postinjection; PFFs = pre-formed alpha-synuclein fibrils; PBS = phosphate-buffered saline; pSyn = α-syn phosphorylated at serine 129, MHC-IIir = major-histocompatibility complex-II immunoreactive. (TIF 112368 kb

Additional file 2: of Lewy body-like alpha-synuclein inclusions trigger reactive microgliosis prior to nigral degeneration

Figure S2. Unilateral intrastriatal injection of α-syn PFFs induces widespread accumulation of Lewy-body like inclusions of phosphorylated α-syn (pSyn). Representative images illustrating the time course of pSyn pathology in regions innervating the striatum. (a–c) pSyn pathology in the ipsilateral agranular insular cortex localized to both the soma and neurites at 2 months p.i. (postinjection) that over time becomes primarily localized to the soma; scale bar = 50 μm, inset = 10 μm. (d–f) Ipsilateral accumulation of pSyn in the substantia nigra peaks at 2 months and becomes less abundant over time as neurons degenerate; scale bar = 200 μm, inset = 25 μm. (g–i) In contrast to other areas, pSyn in the striatum is primarily localized to neurites at 2 months and becomes more abundant and localized to the soma over time, scale bar = 50 μm, inset = 10 μm. Abbreviations: α-syn = alpha-synuclein; PFFs = pre-formed alpha-synuclein fibrils; pSyn = α-syn phosphorylated at serine 129; p.i. = postinjection. (TIF 33472 kb