Parkinson's disease (PD) is characterized by the accumulation of abnormal α-
synuclein in selected regions of the brain following a gradient of severity with
disease progression. Whether this is accompanied by globally altered
protein synthesis is poorly documented. The present study was carried out in PD stages 1-6 of Braak and middle-aged (MA) individuals without alterations in brain in the substantia nigra, frontal cortex area 8, angular gyrus, precuneus and putamen.
RESULTS: Reduced
mRNA expression of
nucleolar proteins nucleolin (NCL),
nucleophosmin (NPM1),
nucleoplasmin 3 (NPM3) and upstream binding
transcription factor (UBF), decreased NPM1 but not NPM3
nucleolar protein immunostaining in remaining neurons; diminished
18S rRNA,
28S rRNA; reduced expression of several mRNAs encoding
ribosomal protein (RP) subunits; and altered
protein levels of
initiation factor eIF3 and
elongation factor eEF2 of
protein synthesis was found in the substantia nigra in PD along with
disease progression. Although many of these changes can be related to neuron loss in the substantia nigra, selective alteration of certain factors indicates variable degree of vulnerability of mRNAs, rRNAs and
proteins in degenerating sustantia nigra. NPM1
mRNA and
18S rRNA was increased in the frontal cortex area 8 at stage 5-6; modifications were less marked and region-dependent in the angular gyrus and precuneus. Several RPs were abnormally regulated in the frontal cortex area 8 and precuneus, but only one RP in the angular gyrus, in PD. Altered levels of
eIF3 and eIF1, and decrease eEF1A and eEF2
protein levels were observed in the frontal cortex in PD. No modifications were found in the putamen at any time of the study except transient modifications in
28S rRNA and only one RP
mRNA at stages 5-6. These observations further indicate marked region-dependent and stage-dependent alterations in the cerebral cortex in PD. Altered solubility and α-
synuclein oligomer formation, assessed in total homogenate fractions blotted with anti-α-
synuclein oligomer-specific antibody, was demonstrated in the substantia nigra and frontal cortex, but not in the putamen, in PD. Dramatic increase in α-
synuclein oligomers was also seen in fluorescent-activated cell sorter (FACS)-isolated nuclei in the frontal cortex in PD.
CONCLUSIONS: Altered machinery of
protein synthesis is altered in the substantia nigra and cerebral cortex in PD being the frontal cortex area 8 more affected than the angular gyrus and precuneus; in contrast, pathways of
protein synthesis are apparently preserved in the putamen. This is associated with the presence of α-
synuclein oligomeric species in total homogenates; substantia nigra and frontal cortex are enriched, albeit with different band patterns, in α-
synuclein oligomeric species, whereas α-
synuclein oligomers are not detected in the putamen.