Dysregulation of 14-3-3 proteins in neurodegenerative diseases with Lewy body or Alzheimer pathology

Objective: The highly conserved 14-3-3 proteins interact with key players involved in Parkinson's disease (PD) and other neurodegenerative disorders. We recently demonstrated that 14-3-3 phosphorylation is increased in PD models and that increased 14-3-3 phosphorylation reduces the neuroprotective effects of 14-3-3 proteins. Here, we investigated whether 14-3-3 phosphorylation is altered in postmortem brains from control, PD, Alzheimer's Disease (AD), Alzheimer's with Lewy Bodies (ADLB), Dementia with Lewy Bodies (DLB), and Progressive Supranuclear Palsy (PSP) subjects at three conserved sites: serine 58 (S58), serine 185 (S185), and serine 232 (S232). Methods: S58, S185, and S232 phosphorylation was measured by western blot analysis of Triton X-100 soluble and insoluble fractions from postmortem temporal cortex. Results: The ratio of soluble phospho-S232 to insoluble phospho-S232 was reduced by 32%, 60%, 37%, and 52% in PD, AD, ADLB, and DLB, respectively. S185 and S58 phosphorylation were mildly elevated in the soluble fraction in DLB. We also noted a dramatic reduction in soluble pan 14-3-3 levels by similar to 35% in AD, ADLB, and DLB. Lower ratios of soluble to insoluble S232 phosphorylation (pointing to higher insoluble pS232) correlated with lower soluble pan 14-3-3 levels, suggesting that S232 phosphorylation may promote insolubilization of 14-3-3s. The phospho-S232 ratio and soluble pan 14-3-3 levels correlated with clinical and pathological severity. Interpretation: These data reveal dysregulation of 14-3-3 proteins in neurodegeneration associated with Lewy body or Alzheimer pathology. S232 phosphorylation may drive insolubilization of 14-3-3s and thus contribute to the pathophysiology in neurodegenerative disorders associated with Lewy body or Alzheimer pathology.