Date of Award

1-1-2021

Embargo Period

12-17-2023

Document Type

Dissertation - MUSC Only

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry and Molecular Biology

College

College of Graduate Studies

First Advisor

L. Ashley Cowart

Second Advisor

Amy D. Bradshaw

Third Advisor

Samar M. Hammad

Fourth Advisor

Amanda C. LaRue

Fifth Advisor

David T. Long

Sixth Advisor

Besim Ogretmen

Abstract

Sphingosine kinase 1 (SPHK1) has been identified as a regulator of key processes in many metabolic tissues, though its role in adipose tissue has not been well established. As SPHK1 has been shown to be elevated in obesity, we developed an adipocyte-specific knockout mouse (SK1fatKO) and conducted a high-fat diet study to investigate the role of SPHK1 in the adipocyte in the context of obesity. Alternative to the constitutive SPHK1 knockout mouse which is protected from obesity induced maladies, high-fat diet fed SK1fatKO mice were glucose intolerant, hyperinsulinemic, had liver steatosis and hypertrophic adipocytes. Interestingly, these mice were protected from adipose tissue inflammation. Additionally, RNA sequencing of the gonadal adipose tissue from SK1fatKO mice revealed decreased expression of many mature adipocyte markers. Paired with the adipocyte hypertrophy results, this indicated that SPHK1 depletion may interfere with adipogenesis. To better understand the mechanisms by which SPHK1 regulates adipogenesis, we utilized an in vitro approach using primary adipose derived stem cells. Under standard pro-adipogenic culture conditions, Sphk1 expression, along with sphingosine-1-phosphate (S1P) and SPHK activity levels, but not SPHK2 were determined to increase early in adipogenesis and decrease as the cells mature. Treatment with individual pro-adipogenic media components revealed that only dexamethasone, a synthetic glucocorticoid, induced Sphk1. This led us to investigate how SPHK1 is involved in glucocorticoid signaling in early adipogenesis. We found that expression of key genes in the adipogenesis pathway, C/EBPα and C/EBPδ were reduced in SPHK1-/- cells. Additionally, chronic treatment of SPHK1-/- mice with corticosterone in drinking water led to reduced adipose expansion compared to controls, along with altered adipogenic gene expression. These results highlight the importance of SPHK1 for adipose expansion and metabolism in the contexts of high-fat diet and glucocorticoid induced obesity.

Rights

All rights reserved. Copyright is held by the author.

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