Inclusions containing ubiquitinated proteins are a hallmark of many neurological disorders such as Alzheimer's (AD), Parkinson's (PD), and Huntington's diseases. Covalent binding of ubiquitin to proteins is known to mark them for degradation by the ubiquitin/proteasome pathway. This ATP-dependent pathway plays a major role in the breakdown of abnormal proteins, which should be rapidly removed. Although the relationship between accumulation of ubiquitinated proteins and neurodegeneration is poorly understood, recently identified mutations in ubiquitin and in an enzyme of the ubiquitin/proteasome pathway were found to be closely associated with sporadic AD and familial PD, respectively. We propose that ubiquitin-protein aggregates must result from a malfunction or overload of the ubiquitin/proteasome pathway or from structural changes in protein substrates halting their degradation, and that failure to eliminate ubiquitinated proteins disrupts cellular homeostasis contributing to degeneration. Therefore, it is of the utmost importance to identify stress conditions that jeopardize the functioning of the ubiquitin/proteasome pathway and lead to accumulation of ubiquitinated proteins in neuronal cells. The goals of this project are: (i) to identify stress conditions that interfere with the proper functioning of the ubiquitin/proteasome pathway and understand the biochemical mechanisms by which they disrupt homeostasis; (ii) to study genetic regulatory pathways affected by these conditions and establish how they change expression of enzymes of the ubiquitin/proteasome pathway as well as of related proteins involved in the pathological process; (iii) test the therapeutic effectiveness of antioxidants and inhibitors o some of these regulatory pathways, in preventing accumulation of ubiquitinated proteins and neurodegeneration. To better understand the role played by the ubiquitin/proteasome pathway in neurodegeneration we will establish a stable neuronal cell line in which the activity of its proteolytic moiety, the 20S proteasome, is compromised by a mutation in the active site of one of its catalytic subunits. The proposed studies will yield insights into a poorly understood aspect of neurodegeneration, and more specifically identify novel therapeutic targets for prevention of the accumulation of ubiquitinated proteins in stressed neuronal cells.
