Small Nucleolar RNAs U32a, U33, and U35a Are Critical Mediators of Liptoxic and Oxidative Stress
Date of Award
Doctor of Philosophy (PhD)
Obesity and diabetes are characterized by elevated serum triglycerides, and free fatty acids, due to insulin resistance. In these diseases, the capacity for lipid storage in adipose tissue is exceeded, leading to delivery of fatty acid substrates to non-adipose tissues and resulting in lipid accumulation. Ectopic lipid accumulation is associated with cellular dysfunction and cell death through the process of lipotoxicity, and this metabolic stress response has been implicated to play a key role in the pathogenesis of complications of diabetes and obesity. Though a variety of stress responses have been shown to mediate lipotoxicity, the precise molecular players linking deleterious lipid-accumulation and cellular dysfunction are still largely unknown.
To elucidate the molecular mechanisms of lipotoxicity, we used retroviral promoter trap mutagenesis to isolate a Chinese hamster ovary (CHO) cell line that is resistant to lipotoxic and oxidative stress. Proviral insertion in this mutant renders it haploinsufficient for ribosomal protein L13a (rpL13a). We show that loss of three box C/D small nucleolar RNAs (snoRNAs) encoded in the rpL13a locus in CHO cells is sufficient to confer resistance to lipotoxic and oxidative stress. Complementation of this phenotype is dependant on the expression of snoRNAs U32a, U33, and U35a from the rpL13a genomic locus. Furthermore, we demonstrate that lipotoxic and oxidative stress induce U32a, U33, and U35a snoRNA expression, and targeted depletion of snoRNAs confers resistance to lipotoxic and oxidative stress induced cell death in murine cells. Our findings demonstrate a novel role for snoRNAs U32a, U33, and U35a as critical mediators of lipotoxic and oxidative stress.
Canonical snoRNAs can serve as guides for the modification of ribosomal RNA in the nucleolus. However, our results suggest that rpL13a encoded snoRNAs do not mediate lipotoxic stress through this mechanism. We hypothesize that snoRNAs U32a, U33, and U35a function through interaction with mRNA transcripts in order to regulate gene expression that activates cellular stress responses. In conclusion, our work demonstrates a previously unappreciated role for snoRNAs as regulators of metabolic stress response pathways in mammalian cells.
Chair and Committee
Jean E. Schaffer
Peter Crawford, Kathleen Hall, Shin Imai, Jeff Milbrant, John Russell, Daniel Ory
Michel, Carlos, "Small Nucleolar RNAs U32a, U33, and U35a Are Critical Mediators of Liptoxic and Oxidative Stress" (2010). Arts & Sciences Electronic Theses and Dissertations. 103.