Christopher Corbo

Phosphorylation of Tau at Thr212, Thr231, and Ser262 Combined Causes Neurodegeneration

Abnormal hyperphosphorylation of the microtubule-associated protein Tau is a hallmark of Alzheimer disease and related diseases called tauopathies. As yet, the exact mechanism by which this pathology causes neurodegeneration is not understood. The present study provides direct evidence that Tau abnormal hyperphosphorylation causes its aggregation, breakdown of the microtubule network, and cell death and identifies phosphorylation sites involved in neurotoxicity. We generated pseudophosphorylated Tau proteins by mutating Ser/Thr to Glu and, as controls, to Ala. These mutations involved one, two, or three pathological phosphorylation sites by site-directed mutagenesis using as backbones the wild type or FTDP-17 mutant R406W Tau. Pseudophosphorylated and corresponding control Tau proteins were expressed transiently in PC12 and CHO cells. We found that a single phosphorylation site alone had little influence on the biological activity of Tau, except Thr212, which, upon mutation to Glu in the R406W background, induced Tau aggregation in cells, suggesting phosphorylation at this site along with a modification on the C-terminal of the protein facilitates self-assembly of Tau. The expression of R406W Tau pseudophosphorylated at Thr212, Thr231, and Ser262 triggered caspase-3 activation in as much as 85% of the transfected cells, whereas the corresponding value for wild type pseudophosphorylated Tau was 30%. Cells transfected with pseudophosphorylated Tau became TUNEL-positive.

Molecular mechanism of prion-like tau-induced neurodegeneration

Accumulation of hyperphosphorylated tau and the disruption of microtubules are correlated with synaptic loss and pathology of Alzheimers disease (AD). Impaired cognitive function and pathology of AD is correlated with this lesion. This review looks at the mechanism of neurodegeneration, the prion‐like behavior of tau in its interaction with normal MAPs in correlation with tau hyperphosphorylation.

Use of different morphological techniques to analyze the cellular composition of the adult zebrafish optic tectum.

Cellular composition of the adult zebrafish (Danio rerio) optic tectal cortex was examined in this study. Morphological techniques such as 1μm thick serial plastic sections stained with osmium tetroxide and toluidine blue, modified rapid Golgi silver impregnation, GFAP immunohistochemistry, confocal microscopy, as well as scanning and transmission electron microscopy were used. Neuronal and glial components are described and the layers of the cortex are revisited. Specific neuronal arrangements as well as unique glial/ependymal cells are described. A three dimensional rendering of the astrocytic fiber arrangement in the marginal zone is presented and a composite drawing summarizes the cellular composition of the optic tectum. Microsc. Res. Tech. 2011.

Novel therapeutics based on tau/microtubule dynamics: WO2008084483

Background: The present patent deals with the generation of peptides derived from the activity-dependent peptide and tau mimetic to study its effect on microtubule stability, its ability to bind to tubulin and MAPs, as well as promoting cell survival. Objective: To analyze these peptides and their effects as potential therapeutic elements for neurodegenerative diseases. Methods: We review the action of the peptides described by Gozes and collaborators and compare the effectiveness with those already reported in the literature for Alzheimers disease. Conclusion: The research of Dr. Gozes and collaborators has shown that the addition of picomolar concentration of the peptides promotes cell survival, by interacting with tubulin and stabilizing the microtubules. Based on the results, these peptides seem to be very attractive candidates for therapeutical intervention in neurodegenerative diseases.

Hyperphosphorylation of Tau Associates With Changes in Its Function Beyond Microtubule Stability

Tau is a neuronal microtubule associated protein whose main biological functions are to promote microtubule self-assembly by tubulin and to stabilize those already formed. Tau also plays an important role as an axonal microtubule protein. Tau is an amazing protein that plays a key role in cognitive processes, however, deposits of abnormal forms of tau are associated with several neurodegenerative diseases, including Alzheimer disease (AD), the most prevalent, and Chronic Traumatic Encephalopathy (CTE) and Traumatic Brain Injury (TBI), the most recently associated to abnormal tau. Tau post-translational modifications (PTMs) are responsible for its gain of toxic function. Alonso et al. (1996) were the first to show that the pathological tau isolated from AD brains has prion-like properties and can transfer its toxic function to the normal molecule. Furthermore, we reported that the pathological changes are associated with tau phosphorylation at Ser199 and 262 and Thr212 and 231. This pathological version of tau induces subcellular mislocalization in cultured cells and neurons, and translocates into the nucleus or accumulated in the perinuclear region of cells. We have generated a transgenic mouse model that expresses pathological human tau (PH-Tau) in neurons at two different concentrations (4% and 14% of the total endogenous tau). In this model, PH-Tau causes cognitive decline by at least two different mechanisms: one that involves the cytoskeleton with axonal disruption (at high concentration), and another in which the apparent neuronal morphology is not grossly affected, but the synaptic terminals are altered (at lower concentration). We will discuss the putative involvement of tau in proteostasis under these conditions. Understanding tau’s biological activity on and off the microtubules will help shed light to the mechanism of neurodegeneration and of normal neuronal function.

Quantitative analysis of the effect of phosphorylated tau on cellular microfilament networks

The purpose of this study is to analyze the effect of site-specific tau phosphorylation on cellular microfilaments networks. We examined cell images to study tau’s interaction with microfilaments in both wild type full-length (2N4R) tau and pathological human tau (PH-tau) when expressed in Chinese hamster ovarian fibroblasts (CHO). A custom ImageJ plugin was developed to provide quantitative analysis of the immunofluorescently labeled polymerized actin in cells expressing either of the above mentioned tau vectors. Using histograms of the pixel intensities of images, with userdefined thresholds, the code calculates the integrated densities and creates an output image to visualize the considered areas (those outside the thresholds are displayed as well). The data demonstrated the presence of an inverse correlation between the level of PH-tau expressed and the amount of total actin polymerization. Additionally, actin polymerization was not only interrupted by the presence of PH-tau but also punctate staining was also detected (as opposed to the normal fibril structure). These observations were not detected in cells expressing wild type tau. The visualization helped reveal some image acquisition anomalies such as varying levels of fluorescent staining as well as standardized image collection. The results should aid in a further understanding the mechanism of cellular degeneration induced by the hyperphosphorylation of MAP tau. Keywords: Microfilaments, Medical