Ubiquitin Proteasome Dysfunction as a biomarker for Neurodegenerative Disease
Authors: Karteek Kadimisetty, Kathleen Sheets, Jess Dhillon, Dahmane Ouazia
The ubiquitin-proteasome system (UPS), chaperone mediated-autophagy (CMA), and mitophagy constitute the protein quality control system of the cell. Since damaged proteins are rarely repaired, the failure of protein quality control is particularly difficult to overcome in terminally differentiated cells (e.g., neurons). UPS dysfunction likely plays a key causative role in Alzheimer’s disease (AD) and Parkinson’s disease (PD); for example, mutations in the ubiquitin ligase parkin lead to loss of mitophagy, destruction of dopaminergic neurons and, thus, to Parkinson’s Disease. Numerous developmental neuronal defects and neuromuscular pathologies are attributed to mutations in UPS genes. LifeSensors has studied the consequences of these mutations by screening brain tissues, serum, and CSF of healthy individuals (postmortem) and age-matched AD patients. Because antibodies against ubiquitin or target proteins are ineffective due to low affinity, epitope masking, and an inability to discriminate among various poly-ubiquitin chains, LifeSensors developed high-affinity chain selective polyubiquitin binding tools called TUBEs (Tandem Ubiquitin Binding Entities) to isolate ubiquitylated proteins. These enriched ubiquitylated protein fractions were analyzed by mass spectrometry-based proteomics to identify candidate markers for UPS dysfunction in neurons; comparing brain tissues from healthy individuals and AD patients, we uncovered numerous proteins with altered ubiquitylation patterns in the disease state. For example, the Tau protein is heavily ubiquitylated at multiple sites in AD, while Tau from normal brain is essentially ubiquitin-free; other unique ubiquitylated biomarkers were identified for AD. We are currently investigating CSF and plasma samples from AD and PD patients to establish a panel of unique ubiquitylated markers with reference to control samples. The goal of this study is to develop a diagnostic panel of ubiquitylation signatures using pan-selective and linkage-selective TUBEs for blood-based early diagnosis of AD/PD.