calyculin-a and Nerve-Degeneration

In the present treatise, we provide evidence that the neuroprotective and mito-protective effects of estrogens are inexorably linked and involve the ability of estrogens to maintain mitochondrial function during neurotoxic stress. This is achieved by the induction of nuclear and mitochondrial gene expression, the maintenance of protein phosphatases levels in a manner that likely involves modulation of the phosphorylation state of signaling kinases and mitochondrial pro- and anti-apoptotic proteins, and the potent redox/antioxidant activity of estrogens. These estrogen actions are mediated through a combination of estrogens receptor (ER)-mediated effects on nuclear and mitochondrial transcription of protein vital to mitochondrial function, ER-mediated, non-genomic signaling and non-ER-mediated effects of estrogens on signaling and oxidative stress. Collectively, these multifaceted, coordinated action of estrogens leads to their potency in protecting neurons from a wide variety of acute insults as well as chronic neurodegenerative processes.

Topics: Animals; Calcineurin; Endoplasmic Reticulum; Enzyme Activation; Estrogens; Gene Expression Regulation; Humans; Marine Toxins; Mitochondria; Nerve Degeneration; Neuroprotective Agents; Oxazoles; Oxidation-Reduction; Oxidative Stress; Phosphoprotein Phosphatases; Signal Transduction

Abnormal phosphorylation and aggregation of the microtubule-associated protein Tau are hallmarks of various neurodegenerative diseases, such as Alzheimer disease. Molecular mechanisms that regulate Tau phosphorylation are complex and currently incompletely understood. We have developed a novel live cell reporter system based on protein-fragment complementation assay to study dynamic changes in Tau phosphorylation status. In this assay, fusion proteins of Tau and Pin1 (peptidyl-prolyl cis-trans-isomerase 1) carrying complementary fragments of a luciferase protein serve as a sensor of altered protein-protein interaction between Tau and Pin1, a critical regulator of Tau dephosphorylation at several disease-associated proline-directed phosphorylation sites. Using this system, we identified several structurally distinct GABA(A) receptor modulators as novel regulators of Tau phosphorylation in a chemical library screen. GABA(A) receptor activation promoted specific phosphorylation of Tau at the AT8 epitope (Ser-199/Ser-202/Thr-205) in cultures of mature cortical neurons. Increased Tau phosphorylation by GABA(A) receptor activity was associated with reduced Tau binding to protein phosphatase 2A and was dependent on Cdk5 but not GSK3β kinase activity.

Topics: Alzheimer Disease; Animals; Cell Line, Tumor; Cyclin-Dependent Kinase 5; Cytoskeleton; Enzyme Inhibitors; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Marine Toxins; Mice; Naphthoquinones; Nerve Degeneration; Neuroblastoma; NIMA-Interacting Peptidylprolyl Isomerase; Oxazoles; Peptidylprolyl Isomerase; Phosphorylation; Protein Kinase Inhibitors; Protein Phosphatase 2; Purines; Rats; Receptors, GABA-A; Roscovitine; tau Proteins; Tauopathies

The activity of protein phosphatase (PP)-2A and PP-1 decreased in the brains of Alzheimer's disease and inhibition of the phosphatases led to spatial memory deficit in rats. However, the molecular basis underlying memory impairment of the phosphatase inhibition is elusive. In the present study, we observed a selective inhibition of PP-2A and PP-1 with Calyculin A (CA) not only caused hyperphosphorylation of cytoskeletal proteins, but also impaired the transport of pEGFP-labeled neurofilament-M subunit in the axon-like processes of neuroblastoma N2a cells and resulted in accumulation of neurofilament in the cell bodies. To analyze the morphological alteration of the cells during inhibition of the phosphatases, we established a cell model showing steady outgrowth of axon-like cell processes and employed a stereological system to analyze the retraction of the processes. We found CA treatment inhibited outgrowth of the cell processes and prolonged treatment with CA caused retraction of the processes and meanwhile, the early neurodegenerative varicosities were also obvious in the CA-treated cells. We conclude suppression of PP-2A and PP-1 by CA not only damages intracellular transport but also leads to cell degeneration, which may serve as the functional and structural elements for the memory deficits induced by suppression of the phosphatases.

Topics: Animals; Axonal Transport; Axons; Brain; Cell Differentiation; Cell Line, Tumor; Enzyme Inhibitors; Image Cytometry; Marine Toxins; Memory Disorders; Mice; Nerve Degeneration; Neurites; Neurofilament Proteins; Oxazoles; Phosphoprotein Phosphatases