Kim, William David

The neuronal ceroid lipofuscinoses (NCLs), collectively referred to as Batten disease, are a group of neurodegenerative diseases that affect all ages, primarily children. Batten disease is caused by mutations in 1 of the 13 ceroid lipofuscinosis neuronal (CLN) genes (CLN1-CLN8, CLN10-CLN14), each of which causes an NCL subtype when mutated. One of the NCL subtypes, CLN5 disease, is caused by mutations in the CLN5 gene. CLN5 is a soluble lysosomal protein that localizes to the endoplasmic reticulum (ER), the Golgi complex, the cytoplasm, and extracellularly. CLN5 has four putative molecular functions, including as a ceramide synthase, glycoside hydrolase, depalmitoylase, and bis(monoacylglycerol)phosphate synthase. CLN5 plays various roles within the cell, such as lipid metabolism, autophagy, and proteasome degradation. However, the function and the exact pathway in which CLN5 is involved are unclear. In addition, CLN5 is a secreted protein that, as shown via bioinformatics analysis, contains a signal peptide sequence. Furthermore, there are currently 70 CLN5 disease-causing mutations reported in the NCL mutation database. 12 CLN5 disease-causing mutations have been studied thus far in terms of their cellular impact, as well as the release of CLN5 to a certain extent. However, there is a lack of research into the functionality of the signal peptide in CLN5 and an in-depth analysis of the molecular impact of mutations in CLN5 disease. Consequently, this Ph.D. thesis focused on using comparative transcriptomics to reveal biological pathways affected by cln5-deficiency, revealing mechanisms that regulate the secretion of Cln5 and CtsD, and using Dictyostelium to gain insights into the molecular effects of mutations in CLN5 disease. Comparative transcriptomics reveal many differentially expressed genes that are linked to phenotypes observed in cln5-deficient cells and identified pathways affected in other CLN5 disease models, such as autophagy. Furthermore, novel findings, like affected expression of lysosomal enzymes and pathways, including secretion, are identified within the comparative transcriptomics analysis. Subsequently, this research also shows the secretory role of the signal peptide in Cln5 and CtsD. Finally, this Ph.D. thesis revealed that mutations in CLN5 disease affect the lysosomal biology and secretion of Cln5 and other lysosomal enzymes.

Author Keywords: Batten disease, CLN5, Dictyostelium discoideum, Enzymes, Lysosome, Secretion