Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Anatomy and Cell Biology

Supervisor

Duennwald, Martin L.

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease associated with protein misfolding and dysregulated cellular protein quality control mechanisms. Molecular chaperones, and heat shock proteins (Hsp), are key players in maintaining cellular protein quality control. DNAJC7 is an understudied cytosolic Hsp40 that works together with Hsp70 and Hsp90 to regulate proper protein folding or degradation. Of note, mutations in the gene encoding DNAJC7 were discovered to cause familial ALS. We asked whether ALS-associated mutations in DNAJC7 compromise its function as a chaperone, which may cause the toxic accumulation of misfolded proteins. This study attempts to uncover the functions of DNAJC7 in folding ALS-associated proteins, TDP-43 and FUS, using a yeast model, mammalian cultured cells, and human pathological tissue. Furthermore, we engineered DNAJC7 mutations to be used in future studies. We propose that DNAJC7 may be involved in the proper folding of TDP-43 and FUS by allowing these proteins to be passed from Hsp90 to Hsp70 and thus prevent their misfolding and the ensuing toxicity.

Summary for Lay Audience

Amyotrophic lateral sclerosis (ALS) is a fatal disease that affects nerve cells in the brain and spinal cord, eventually leading to complete loss of muscle function. Unfortunately, there is no cure for ALS, however, scientists have discovered a promising link between improperly folded proteins within the nerve cell and nerve cell dysfunction. Proteins are the functional molecules of the cell as they are responsible for our growth, development, and daily functioning. Thus, when proteins become improperly folded, they can no-longer preform their function, which can lead to massive problems for the survivability of the cell. Thankfully, this is not a concern in healthy individuals as they have maintenance mechanisms within the cell that are responsible for either re-folding these misfolded proteins or destroying them. Conversely, these maintenance mechanisms are compromised in individuals with ALS, thus, the misfolded proteins accumulate within the nerve cell, preventing the neuron from functioning properly. Chaperone proteins are the key players in maintenance mechanisms as they are responsible for refolding misfolded proteins. In this thesis we explore the role of DNAJC7, a chaperone protein that becomes abnormally altered in ALS individuals. Little is known about DNAJC7 and how it functions normally within the nerve cell, let alone how the altered forms of DNAJC7 may affect its function in ALS individuals. We began our studies in a yeast model, which allows us to isolate DNAJC7 and visualize how it functions in a simplified manner before studying its role in more complex organisms (e.g. mice). Interestingly, we discovered that DNAJC7 may play a key role in properly folding or degrading two well-studied proteins, TDP-43 and FUS, that have been shown to misfold in ALS individuals. Thus, we speculate that the altered DNAJC7 found in ALS individuals is unable to refold or degrade TDP-43 and FUS, leading to the accumulation of these proteins in the nerve cell and ultimately nerve cell dysfunction. In this study we engineered the ALS altered forms of DNAJC7 to be used in future experiments. Overall, this thesis provides new information about an understudied chaperone protein, DNAJC7, and engineered ALS-associated altered forms of DNAJC7.

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