Nilotinib-induced autophagic changes increase endogenous parkin level and ubiquitination, leading to amyloid clearance.

UNLABELLED: Alzheimer's disease (AD) is a neurodegenerative disorder associated with amyloid accumulation and autophagic changes. Parkin is an E3 ubiquitin ligase involved in proteasomal and autophagic clearance. We previously demonstrated decreased parkin solubility and interaction with the key autophagy enzyme beclin-1 in AD, but tyrosine kinase inhibition restored parkin-beclin-1 interaction. In the current studies, we determined the mechanisms of nilotinib-induced parkin-beclin-1 interaction, which leads to amyloid clearance. Nilotinib increased endogenous parkin levels and ubiquitination, which may enhance parkin recycling via the proteasome, leading to increased activity and interaction with beclin-1. Parkin solubility was decreased and autophagy was altered in amyloid expressing mice, suggesting that amyloid stress affects parkin stability, leading to failure of protein clearance via the lysosome. Isolation of autophagic vacuoles revealed amyloid and parkin accumulation in autophagic compartments but nilotinib decreased insoluble parkin levels and facilitated amyloid deposition into lysosomes in wild type, but not parkin(-/-) mice, further underscoring an essential role for endogenous parkin in amyloid clearance. These results suggest that nilotinib boosts the autophagic machinery, leading to increased level of endogenous parkin that undergoes ubiquitination and interacts with beclin-1 to facilitate amyloid clearance. These data suggest that nilotinib-mediated autophagic changes may trigger parkin response via increased protein levels, providing a therapeutic strategy to reduce Aß and Tau in AD. KEY MESSAGE: Parkin solubility (stability) is decreased in AD and APP transgenic mice. Nilotinib-induced autophagic changes increase endogenous parkin level. Increased parkin level leads to ubiquitination and proteasomal recycling. Re-cycling decreases insoluble parkin and increases parkin-beclin-1 interaction. Beclin-1-parkin interaction enhances amyloid clearance.

Ubiquitination increases parkin activity to promote autophagic α-synuclein clearance.

Parkinson's disease (PD) is a movement disorder associated with genetic and age related causes. Although autosomal recessive early onset PD linked to parkin mutations does not exhibit α-Synuclein accumulation, while autosomal dominant and sporadic PD manifest with α-Synuclein inclusions, loss of dopaminergic substantia nigra neurons is a common denominator in PD. Here we show that decreased parkin ubiquitination and loss of parkin stability impair interaction with Beclin-1 and alter α-Synuclein degradation, leading to death of dopaminergic neurons. Tyrosine kinase inhibition increases parkin ubiquitination and interaction with Beclin-1, promoting autophagic α-Synuclein clearance and nigral neuron survival. However, loss of parkin via deletion increases α-Synuclein in the blood compared to the brain, suggesting that functional parkin prevents α-Synuclein release into the blood. These studies demonstrate that parkin ubiquitination affects its protein stability and E3 ligase activity, possibly leading to α-Synuclein sequestration and subsequent clearance.

Tyrosine kinase inhibition increases functional parkin-Beclin-1 interaction and enhances amyloid clearance and cognitive performance.

Tyrosine kinase inhibitors (TKIs) are effective therapies for leukaemia. Alzheimer is a neurodegenerative disease characterized by accumulation of ß-amyloid (plaques) and hyper-phosphorylated Tau (tangles). Here we show that AD animals have high levels of insoluble parkin and decreased parkin-Beclin-1 interaction, while peripheral administration of TKIs, including Nilotinib and Bosutinib, increases soluble parkin leading to amyloid clearance and cognitive improvement. Blocking Beclin-1 expression with shRNA or parkin deletion prevents tyrosine kinase (TK) inhibition-induced amyloid clearance, suggesting that functional parkin-Beclin-1 interaction mediates amyloid degradation. Isolation of autophagic vacuoles (AVs) in AD mouse brain shows accumulation of parkin and amyloid, consistent with previous results in AD brains, while Bosutinib and Nilotinib increase parkin-Beclin-1 interaction and result in protein deposition in the lysosome. These data suggest that decreased parkin solubility impedes parkin-Beclin-1 interaction and amyloid clearance. We identified two FDA-approved anti-cancer drugs as potential treatment for AD.

Fractalkine Mediates Communication between Pathogenic Proteins and Microglia: Implications of Anti-Inflammatory Treatments in Different Stages of Neurodegenerative Diseases.

The role of inflammation in neurodegenerative diseases has been widely demonstrated. Intraneuronal protein accumulation may regulate microglial activity via the fractalkine (CX3CL1) signaling pathway that provides a mechanism through which neurons communicate with microglia. CX3CL1 levels fluctuate in different stages of neurodegenerative diseases and in various animal models, warranting further investigation of the mechanisms underlying microglial response to pathogenic proteins, including Tau, ß-amyloid (Aß), and α-synuclein. The temporal relationship between microglial activity and localization of pathogenic proteins (intra- versus extracellular) likely determines whether neuroinflammation mitigates or exacerbates disease progression. Evidence in transgenic models suggests a beneficial effect of microglial activity on clearance of proteins like Aß and a detrimental effect on Tau modification, but the role of CX3CL1 signaling in α-synucleinopathies is less clear. Here we review the nature of fractalkine-mediated neuronmicroglia interaction, which has significant implications for the efficacy of anti-inflammatory treatments during different stages of neurodegenerative pathology. Specifically, it is likely that anti-inflammatory treatment in early stages of disease during intraneuronal accumulation of proteins could be beneficial, while anti-inflammatory treatment in later stages when proteins are secreted to the extracellular space could exacerbate disease progression.