Localization of Phosphorylated ERK/MAP Kinases to Mitochondria and Autophagosomes in Lewy Body Diseases

We previously found that sustained ERK activation contributes to toxicity elicited by the parkinsonian neurotoxin 6‐hydroxydopamine. In addition, substantia nigra neurons from patients with incidental Lewy body disease, Parkinson's disease (PD), and diffuse Lewy body dementia (DLB) display abnormal phospho‐ERK accumulations in the form of discrete cytoplasmic granules. In this study, we investigated the subcellular localization of phospho‐ERK immunoreactive granules using double label confocal microscopy and immunoelectron microscopy. A small percentage of phospho‐ERK granules colocalized with the early endosome marker Rab5, but not with cathepsin D, 20S proteasome β‐subunit, or cytochrome P450 reductase. Phospho‐ERK immunoreactivity was often associated with mitochondrial proteins (MnSOD, 60 kDa and 110 kDa mitochondrial antigens), and some vesicular‐appearing phospho‐ERK granules appeared to envelop enlarged mitochondria by confocal laser scanning microscopy. Ultrastructural immuno‐gold studies revealed phospho‐ERK labeling in mitochondria and in association with bundles of ∼10 nm fibrils. Heavily labeled mitochondria were observed within autophagosomes. As mitochondrial pathology may play a pivotal role in Parkinson's and other related neurodegenerative diseases, these studies suggest a potential interaction between dysfunctional mitochondria, autophagy, and ERK signaling pathways.