Striatal phosphoproteins in Parkinson disease and progressive supranuclear palsy

This study was undertaken to evaluate the levels of cAMP-regulated phosphoproteins in the striatum of patients with neurodegenerative diseases of the dopaminergic system. Postmortem samples of caudate nucleus and putamen from 24 control subjects, 23 patients with Parkinson disease, and 13 patients with progressive supranuclear palsy were studied with immunoblotting techniques. The levels of tyrosine hydroxylase were reduced in patients with Parkinson disease (levels were 24% and 10% of controls in caudate nucleus and putamen, respectively) and with progressive supranuclear palsy (levels were 11% and 6% of controls in caudate nucleus and putamen, respectively). Five phosphoproteins, which are present in striatal neurons and are likely to play a role in the postsynaptic actions of dopamine, were measured. These included ARPP-16, ARPP-19, ARPP-21 (cAMP-regulated phosphoproteins of Mr 16,000, 19,000, and 21,000, respectively), DARPP-32 (dopamine- and cAMP-regulated phosphoprotein of Mr 32,000), and phosphatase inhibitor I. The levels of these phosphoproteins were inversely correlated with postmortem delay. In brains of patients with Parkinson disease or progressive supranuclear palsy with postmortem delays comparable to those of controls, the levels of these proteins as well as those of synaptic (synapsin I and synaptophysin) and glial (glial fibrillary acidic protein and myelin basic protein) markers were not significantly modified. We conclude that the levels of several phosphoproteins involved in signal transduction in striatal neurons are not altered in Parkinson disease and progressive supranuclear palsy. This observation supports the view that the striatal output neurons are intact in both diseases.