In Parkinson's disease, the intraneuronal inclusions (Lewy bodies) in substantia nigra neurons contain aggregated α-synuclein. The biochemical mechanism of α-synuclein aggregation involves:
- A Hyperphosphorylation of α-synuclein at Ser129 promoting insoluble fibril formation — this can spread cell-to-cell as prion-like propagation ✓
- B Ubiquitination of α-synuclein leading to proteasomal degradation failure and nuclear inclusion formation
- C Glutamine expansion in SNCA gene causing polyglutamine aggregation analogous to Huntington's
- D Mitochondrial import failure causing α-synuclein accumulation in the IMS
Explanation
In PD, ~90% of α-synuclein in Lewy bodies is phosphorylated at Ser129 (pSer129-α-syn), which promotes misfolding, oligomerization, and fibril formation. The prion-like propagation hypothesis (Braak staging) proposes that pathological α-synuclein fibrils can be released from neurons and taken up by neighboring cells, seeding misfolding of endogenous α-synuclein — explaining the stereotyped caudal-to-rostral spread of Lewy pathology from olfactory bulb/dorsal motor nucleus → substantia nigra → neocortex. This is distinct from polyglutamine disorders (CAG expansion) and explains why PD pathology appears as a prion-like disease.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.