Biomedical subjects

J Eidenmüller

Publications and source records attributed to J Eidenmüller.

4 recordsLinked to original sources

PubMed2001

Phosphorylation-mimicking glutamate clusters in the proline-rich region are sufficient to simulate the functional deficiencies of hyperphosphorylated tau protein.

The microtubule-associated tau proteins represent a family of closely related phosphoproteins that become enriched in the axons during brain development. In Alzheimer's disease (AD), tau aggregates somatodendritically in paired helical filaments in a hyperphosphorylated form. Most of the sites that are phosphorylated to a high extent in paired helical filament tau are clustered in the proline-rich region (P-region; residues 172--251) and the C-terminal tail region (C-region; residues 368--441) that flank tau's microtubule-binding repeats. This might point to a role of a region-specific phosphorylation cluster for the pathogenesis of AD. To determine the functional consequences of such modifications, mutated tau proteins were produced in which a P- or C-region-specific phosphorylation cluster was simulated by replacement of serine/threonine residues with glutamate. We show that a phosphorylation-mimicking glutamate cluster in the P-region is sufficient to block microtubule assembly and to inhibit tau's interaction with the dominant brain phosphatase protein phosphatase 2A isoform AB alpha C. P-region-specific mutations also decrease tau aggregation into filaments and decrease tau's process-inducing activity in a cellular transfection model. In contrast, a phosphorylation-mimicking glutamate cluster in the C-region is neutral with regard to these activities. A glutamate cluster in both the P- and C-regions induces the formation of SDS-resistant conformational domains in tau and suppresses tau's interaction with the neural membrane cortex. The results indicate that modifications in the proline-rich region are sufficient to induce the functional deficiencies of tau that have been observed in AD. They suggest that phosphorylation of the proline-rich region has a crucial role in mediating tau-related changes during disease.

Binding Sites↗

PubMed2000

Structural and functional implications of tau hyperphosphorylation: information from phosphorylation-mimicking mutated tau proteins.

Abnormal tau-immunoreactive filaments are a hallmark of tauopathies, including Alzheimer's disease (AD). A higher phosphorylation ("hyperphosphorylation") state of tau protein may represent a critical event. To determine the potential role of tau hyperphosphorylation in these disorders, mutated tau proteins were produced where serine/threonine residues known to be highly phosphorylated in tau filaments isolated from AD patients were substituted for glutamate to simulate a paired helical filament (PHF)-like tau hyperphosphorylation. We demonstrate that, like hyperphosphorylation, glutamate substitutions induce compact structure elements and SDS-resistant conformational domains in tau protein. Hyperphosphorylation-mimicking glutamate-mutated tau proteins display a complete functional loss in its ability to promote microtubule nucleation which can partially be overcome by addition of the osmolyte trimethylamine N-oxide (TMAO), which is similar to phosphorylated tau. In addition, glutamate-mutated tau proteins fail to interact with the dominant brain protein phosphatase 2A isoform ABalphaC, and exhibit a reduced ability to assemble into filaments. Interestingly, wild-type tau and phosphorylation-mimicking tau similarly bind to microtubules when added alone, but the mutated tau is almost completely displaced from the microtubule surface by equimolar concentrations of wild-type tau. The data indicate that glutamate-mutated tau proteins provide a useful model for analyzing the functional consequences of tau hyperphosphorylation. They suggest that several mechanisms contribute to the abnormal tau accumulation observed during tauopathies, in particular a selective displacement of hyperphosphorylated tau from microtubules, a functional loss in promoting microtubule nucleation, and a failure to interact with phosphatases.

Actin Cytoskeleton↗

PubMed2000

Interaction of tau with the neural membrane cortex is regulated by phosphorylation at sites that are modified in paired helical filaments.

The axonal microtubule-associated phosphoprotein tau interacts with neural plasma membrane (PM) components during neuronal development (Brandt, R., Léger, J., and Lee, G. (1995) J. Cell Biol. 131, 1327-1340). To analyze the mechanism and potential regulation of tau's PM association, a method was developed to isolate PM-associated tau using microsphere separation of surface-biotinylated cells. We show that tau's PM association requires an intact membrane cortex and that PM-associated tau and cytosolic tau are differentially phosphorylated at sites detected by several Alzheimer's disease (AD) diagnostic antibodies (Ser(199)/Ser(202), Thr(231), and Ser(396)/Ser(404)). In polar neurons, the association of endogenous tau phosphoisoforms with the membrane cortex correlates with an enrichment in the axonal compartment. To test for a direct effect of AD-specific tau modifications in determining tau's interactions, a phosphomutant that simulates an AD-like hyperphosphorylation of tau was produced by site-directed mutagenesis of Ser/Thr residues to negatively charged amino acids (Glu). These mutations completely abolish tau's association with the membrane cortex; however, the construct retains its capability to bind to microtubules. The data suggest that a loss of tau's association with the membrane cortex as a result of phosphorylation at sites that are modified during disease contributes to somatodendritic tau accumulation, axonal microtubule disintegration, and neuronal death characteristic for AD.

Actins↗

PubMed2000

Herpes simplex virus-mediated expression of the axonal protein tau in human model neurons (NT2-N cells).

The establishment of axonal-somatodendritic polarity is an important event during neuronal development. The analysis of the underlying molecular events requires experimental models that display characteristic steps in the development of polarity and that are accessible for experimental manipulations. Here we show that human model neurons (NT2-N cells) can be efficiently infected with an amplicon-based herpes simplex virus (HSV) system that expresses the axonal microtubule-associated protein tau. We demonstrate that the neurons express a high level of exogenous tau, which persists for several days, thus allowing us to analyze the morphological effects of the expressed protein. The intracellular interactions of tau and the effects on the microtubule structure of infected neurons, which were processed for immunocytochemistry, were determined using laser scanning microscopy (LSM). Exogenous tau expression does not result in an increased axon growth of the neurons but promotes neuronal microtubule assembly as indicated by an increased amount of total microtubule polymer as well as a labile, detyrosinated microtubule subpopulation. In contrast, tau expression does not induce a significant microtubule stabilization as judged from the quantitation of acetylated microtubule staining 24 hours after infection. The data demonstrate that HSV-mediated expression of proteins in human model neurons provides a useful system for analysis of the effect of neuronal proteins on the morphology and cytoskeletal organization of terminally differentiated polar neurons. In addition, it suggests a role for tau as a factor which locally promotes tubulin polymerization while the dynamics of axonal microtubules are preserved.

Axons↗