Defense Date


Document Type


Degree Name

Doctor of Philosophy


Human and Molecular Genetics

First Advisor

Dr. L Ashley Cowart

Second Advisor

Dr. Sarah Spiegel

Third Advisor

Dr. Devanand Sarkar

Fourth Advisor

Dr. Jennifer Koblinski

Fifth Advisor

Dr. Jolene Windle


Sphingolipids play crucial roles in cellular functions and metabolic disorders, including non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC). The serine palmitoyltransferase (SPT) enzyme complex, consisting of SPTLC1 and SPTLC2 subunits, synthesizes canonical sphingolipids, while the SPTLC1 and SPTLC3 heterodimer generates non-canonical sphingolipids that remain relatively understudied. Previous studies, including research conducted in our lab, have demonstrated elevated expression of SPTLC3 in various liver disorders, such as NAFLD and HCC. However, the molecular mechanism underlying SPTLC3's function in the liver remains unknown. Therefore, the primary objective of this project is to investigate the role of SPTLC3 and its downstream non-canonical sphingolipids in liver biology.

To explore the impact of SPTLC3, we developed a novel mouse model with hepatocyte specific SPTLC3 depletion (referred to as SPT3-hKO). RNA sequencing analysis of SPT3-hKO mice revealed a significant influence of SPTLC3 on mitochondrial biology. Using Seahorse analysis, we observed an overall decrease in the oxygen consumption rate in SPTLC3-deficient hepatocytes, with Oroboros experiments indicating that this defect primarily affected mitochondrial complex I. Additionally, SPTLC3 deficiency led to lower levels of complex I products, including the NAD+/NADH ratio and ATP production, confirming the complex I defect. Interestingly, primary hepatocytes from SPTLC3-hKO mice exhibited elevated glycolytic rates, suggesting an increased reliance on glycolysis for energy production.

We corroborated the mitochondrial morphological changes through electron microscopy and observed reduced expression of complex I proteins in SPTLC3-deficient hepatocytes. Furthermore, when we blocked SPTLC3 expression in a human hepatocyte cell line (HC-3716), mitochondrial oxidation significantly decreased, while knockdown of SPTLC2 had no effect on mitochondrial function. Notably, the decrease in complex I activity was not attributed to changes in mitochondrial membrane fluidity; however, we observed a lower membrane potential following SPTLC3 knockdown. Based on current findings, we propose the hypothesis that non-canonical sphingolipids are crucial for maintaining mitochondrial membrane integrity, and blocking SPTLC3 impedes the proper transport of electrons from complex I to complex III via coenzyme Q (CoQ). This disruption in electron flow within the electron transport chain (ETC) likely contributes significantly to the observed complex I defect and reduction in membrane potential.

Collectively, these findings provide valuable insights into the intricate relationship between SPTLC3, mitochondrial membrane composition, complex I activity, and energy metabolism. Understanding the role of SPTLC3 and its associated sphingolipids in liver biology has the potential to uncover novel therapeutic targets for liver disorders, such as NAFLD and HCC, ultimately leading to the development of more effective treatment strategies in the future.


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Available for download on Sunday, July 30, 2028