Regulation of neuronal cytoskeletal protein phosphorylation in neurodegenerative diseases.

Neuronal cytoskeletal proteins such as neurofilaments (NFs) and tau are aberrantly and hyperphosphorylated in neurodegeneration. Under normal physiological conditions, NFs are synthesized in the cell bodies and phosphorylated and transported in the axonal compartment. However, under neurodegenerative disorders such as Alzheimer's disease (AD), spinal cord motor neuron inclusions of amyotrophic lateral sclerosis, Lewy bodies of Parkinson's disease, Pick's disease, Charcot-Marie-Tooth disease, and diabetic neuropathy, NFs are aberrantly and hyperphosphorylated in cell bodies. The proline directed protein kinases, such as cyclin-dependent protein kinase 5, mitogen activated protein kinase, and glycogen synthase kinase 3β, and the non proline-directed kinases, such as casein kinase 1, are deregulated in AD. Moreover, the reversible phosphorylation by protein phosphatase, PP2A, which mainly carries out the dephosphorylation of tau and NFs, is down regulated in AD brain. The aberrant phosphorylation of cytoskeletal proteins such as tau and NFs results in the axonal transport defects in neurodegeneration. The peptidyl-prolyl isomerase Pin1 plays a regulatory role in the post-phosphorylation mechanism of neuronal cytoskeletal proteins in AD brain. Possible therapeutic interventions for neurodegenerative disorders are (1) inhibition of proline-directed kinases, (2) activation of protein phosphatases such as PP2A, and (3) modulation of peptidyl-prolyl isomerases such as Pin1. Here, I discuss the regulation of neuronal cytoskeletal proteins under physiology and pathology.