Blockade of HMG-CoA reductase activity causes changes in microtubule-stabilizing protein tau via suppression of geranylgeranylpyrophosphate formation: implications for Alzheimer's disease

Eur J Neurosci. 2003 Jan;17(1):93-102. doi: 10.1046/j.1460-9568.2003.02433.x.

Abstract

Histopathologically, Alzheimer's disease is characterized by plaques and tangles that develop progressively over time. Experimental data described a statin-induced decrease in beta-amyloid production, a major constituent of the plaques. Others reported data on statin-mediated changes in neuronal survival and cytoskeleton, including the microtubule-associated protein tau, a major constituent of the tangles. However, these latter reports remain contradictory. To clarify and extend our knowledge on the effect of statin on the cytoskeleton, we challenged rat primary neuron cultures by lovastatin and determined the metabolite that is critical for structural integrity and survival of neurons. During the blockade of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the neuritic network was affected and eventually was completely destroyed. This process was not part of the execution phase of apoptosis and was marked by alterations in the microfilament and microtubule system. The distribution and phosphorylation of protein tau changed. Immunoblot analysis and indirect immunofluorescence revealed a transient increase in tau phosphorylation, which ceased during the execution of apoptosis. All of these effects could be linked to the lack of the geranylgeranylpyrophosphate intermediate. Inhibition of the geranylgeranylation of Rho family GTPases (geranylgeranyl-transferase I) evoked similar changes in neurons. These data and our findings that statin treatment reduced the membrane-bound fraction of RhoA-GTPase in neurons suggest that reduced levels of functional small G proteins are responsible for the observed effects. Our data demonstrate that lovastatin concentrations able to suppress not only cholesterol but also geranylgeranylpyrophosphate formation may evoke phosphorylation of tau reminiscent of preclinical early stages of Alzheimer's disease and, when prolonged, apoptosis.

MeSH terms

  • Alzheimer Disease / enzymology
  • Alzheimer Disease / metabolism*
  • Animals
  • Apoptosis
  • Blotting, Western
  • Cell Culture Techniques
  • Cell Survival
  • Electrophoresis, Polyacrylamide Gel
  • Fluorescent Antibody Technique
  • Hippocampus / enzymology*
  • Hydroxymethylglutaryl CoA Reductases / drug effects*
  • Hydroxymethylglutaryl CoA Reductases / metabolism*
  • Hydroxymethylglutaryl-CoA Reductase Inhibitors / pharmacology*
  • In Situ Nick-End Labeling
  • Neurons / enzymology*
  • Phosphorylation / drug effects
  • Polyisoprenyl Phosphates / metabolism*
  • Rats
  • Rats, Wistar
  • tau Proteins / drug effects
  • tau Proteins / metabolism*

Substances

  • Hydroxymethylglutaryl-CoA Reductase Inhibitors
  • Polyisoprenyl Phosphates
  • tau Proteins
  • Hydroxymethylglutaryl CoA Reductases
  • geranylgeranyl pyrophosphate