Parkin Null Cortical Neuronal/Glial Cultures are Resistant to Amyloid-β_1-42 Toxicity: A Role for Autophagy?

Abstract

Dementia occurs often in late stages of Parkinson's disease (PD) but its cause is unknown. Likewise there is little information about the interaction between proteins that produce PD and those implicated in Alzheimer's disease (AD). Here we have investigated the interactions between parkin protein and the amyloid-β (Aβ)_1-42 peptide. We examined the effects of oligomeric Aβ_1-42 peptide on the survival, differentiation, and signaling pathways in cortical cultures from wild type (WT) and parkin null (PK-KO) mice. We discovered that PK-KO cells were more resistant than WT to Aβ_1-42. This peptide induced neuronal cell death, astrogliosis, microglial proliferation, and increased total and hyperphosphorylated tau and levels of chaperones HSP-70 and CHIP in WT, but not in Aβ-treated PK-KO cultures. Aβ_1-42 decreased proteasome activities in WT and PK-KO cultures, but the ubiquitination of proteins only increased in WT cultures. Aβ_1-42 induced a short activation of ERK1/2 and AKT signaling pathways, implicated in cell survival, in PK-KO-treated cells, and a shift in the autophagy marker LC3-II/LC3-I ratio. In addition, the percentage of cells immunoreactive to both HSC70 and LAMP-2A increased in PK-KO cultures versus WT and furthermore in PK-KO cultures treated with Aβ_1-42. Pre-treatment with inhibitors of glutathione synthesis or autophagy reverted the resistance to Aβ_1-42 of the PK-KO cultures. In conclusion, the loss of parkin protein triggers the compensatory mechanisms of cell protection against Aβ_1-42. Parkin suppression, therefore, is not a risk factor for dementia of AD type.