Protein homeostasis is a state of dynamic equilibrium in which protein production and proper folding is balanced against the protein degradation pathways such that the proteome enables cells to function normally. The accumulation of misfolded, aggregated proteins in neurodegenerative diseases is evidence for stress in the protein homeostasis dynamic and this can lead to cell dysfunction and death. One mechanism for coping with the accumulation of misfolded proteins in the endoplasmic reticulum (ER) is ER associated degradation (ERAD). The ERAD system is composed of an intricate assembly of positive and negative regulators that control the flow of substrates into the ubiquitin-proteosome pathway. Several lines of evidence implicate abnormalities in ERAD as pathophysiological contributors to neuronal dysfunction and death in models of neurodegenerative disease. I hypothesize that loss of function of select components of the ERAD pathway will suppress the toxic actions of mutant proteins such as superoxide dismutase (SOD1) or TAR DNA binding protein of 43 kDa molecular weight (TDP43).
In specific aim #1, I will use C. elegans models of mutant SOD and mutant TDP43 toxicity to undertake a directed screen of ERAD components that modify toxicity. Genes will be interrogated using genetic nulls, multiple alleles when possible and nervous system specific RNAi. In Preliminary studies we have found that null alleles of two ERAD genes suppress mutant SOD or mutant TDP43 phenotypes. The strongest suppressor of toxicity was rad-23 and in specific aim #2 we will determine the molecular mechanism by which reduction of rad23 suppresses the toxicity of mutant SOD and mutant TDP43 in a mammalian tissue culture model system. I will test the hypothesis that loss of rad23A accelerates the degradation of misfolded proteins. Together these studies will identify new targets and pathways for intervention to combat neurodegenerative disease.
Proteins must fold into a proper three-dimensional shape to function normally in cells and misfolded proteins accumulate in nerve cells in adult onset neurodegenerative diseases. In this proposal we will identify genes that reduce the burden of misfolded proteins, or their toxic actions, in neurons.
