Topographical Differences in Stress Vulnerability in Experimental Parkinson\u27s Disease

Parkinson\u27s disease is characterized by the progressive spread of protein misfolding stress, or proteotoxicity, across the brain. During this protracted process, the allocortex of the temporal lobe develops protein inclusions before the neocortex in the frontal and parietal lobes. In the present study we tested the hypothesis that the staged appearance of proteotoxicity in allocortex followed by neocortex is the result of intrinsic vulnerability differences. We microdissected the neocortex and multiple subregions of the allocortex from rat brains and plated the primary neo- and allocortical neurons for parallel in vitro studies. Cells were then exposed to a number of Parkinson\u27s disease-mimicking toxins and cellular viability was measured by three independent and unbiased assays that we have validated as linear and highly sensitive. As expected, neocortex was more resistant to loss of proteasomal degradation of proteins than three allocortical subregions: entorhinal cortex, piriform cortex, and hippocampus. Neocortex was also more resistant to α-synucleinopathy than hippocampal allocortex. Entorhinal allocortex exhibited lower protein degradative activity than neocortex and greater stress-induced increases in misfolded proteins. Entorhinal allocortex also expressed higher stress-sensitive changes in heat shock proteins (Hsps) such as Hsp70 and Hsc70, suggesting that allocortex needs to rely more on chaperone defenses. In support of this hypothesis, simultaneous loss of Hsp70/Hsc70 and proteasome activity was far more toxic in allocortex than neocortex, whereas facilitation of Hsp70/Hsc70 activity was protective only in neocortex. Neocortex exhibited higher levels of the antioxidants glutathione and ceruloplasmin, and loss of glutathione synthesis rendered neocortex as vulnerable to proteotoxicity as allocortex. Consistent with these observations, allocortex was protected against proteotoxicity by facilitating glutathione synthesis with N-acetyl cysteine. Finally, as aging is a natural model of protein misfolding stress, the levels of select heat shock proteins, proteasome subunits, and glutathione were examined in neocortex and allocortex in vivo as a function of age. Our findings suggest that the cerebral cortex is more heterogenous than previous in vitro studies of this brain region have acknowledged and that the staged appearance of protein inclusions in Parkinson\u27s disease is at least partly determined by topographic differences in intrinsic vulnerability to protein misfolding stress