SEC16B modulates high fat diet induced obesity in female but not male mice

As obesity and its associated complications continue to rise in the US, it is crucial to gain a better understanding of the complex cellular processes involved in lipid metabolism. Genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) in SEC16B gene to be associated with obesity in a variety of populations. SEC16B encodes a mammalian homolog of S. cerevisiae SEC16, which was first identified as a scaffold protein that organizes ER exit sites (ERES) in yeast. Previous studies have shown that SEC16 is involved in COPII coat assembly that allows for the packaging and delivery of proteins and lipids from the ER to the Golgi. While the function of SEC16B in ER transport is being defined, its potential roles in obesity have not been investigated. In this study, we aim to characterize the phenotype of a Sec16b knockout mouse model to further our knowledge of SEC16B in fat metabolism. We generated adipose-specific Sec16b knockout (AKO) mice by crossing Sec16b floxed mice with Adiponectin-Cre mice. Wild-type (WT) and AKO mice were challenged with a high-fat diet (HFD) and some females underwent ovariectomy surgery (OV). All mice groups were subjected to glucose and insulin tolerance tests. Metabolic rate was measured with indirect calorimetry using the Comprehensive Lab Animal Monitoring System (CLAMS). Body compositions (fat and lean mass) were measured with Echo MRI. Fat depots and the livers were collected for histology and gene expression analysis. Stromal vascular fraction (SVF) cells were harvested and differentiated in vitro. RNA sequencing was performed with gonadal white adipose tissues (gWAT) isolated from control and AKO female mice fed HFD. When challenged with a HFD, female AKO mice gained more body weight and showed less energy expenditure compared to their WT littermates. RNA seq analysis revealed dramatic decrease in the expression of Ucp-1 and Cidea, two genes involved in thermogenesis, in AKO mice. MRI analysis showed that the body weight difference was primarily due to increased body fat in AKO mice. In contrast, loss of Sec16b had no effect on HFD-induced obesity or energy expenditure in male mice. The AKO females also showed increased lipid accumulation in the liver and brown adipose tissue (BAT). Due to significant differences only seen in females, we next performed OV to examine if estrogen contributes to the different body weight gain in female AKO mice. Interestingly, the ovariectomized AKO mice had significantly less body weight gain compared to their WT counterparts upon HFD challenge. Furthermore, the ovariectomized AKO mice showed improved insulin sensitivity, increased metabolic rate, decreased body fat percentage, and reduced liver to body weight ratio compared to WT littermates. Histology analysis revealed less lipid accumulation in the BAT and livers of ovariectomized AKO mice. Surprisingly, the in vitro differentiation of SVF cells isolated from whole body Sec16b knockout and WT mice showed no differences in lipid droplet accumulation. Thus, estrogen likely contributes to the effect of Sec16b deficiency on obesity in females. Our studies revealed a novel regulatory mechanism of adiposity in females that involves the cooperation between SEC16B and estrogen. While further studies are be needed to elucidate the underlying mechanisms, these findings suggest that modulating SEC16B expression and estrogen may be beneficial for those with increased body fat and postmenopausal women.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nutritional Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Johnson, Kaylie

Contributors dc:contributor

• Wang, Bo
• Anakk, Sayeepriyadarshini
• Nakamura, Manabu

• Sec16b
• Estrogen
• Adipose Tissue
• Lipid Metabolism

Statement dc:rights

• Copyright 2023 Kaylie Johnson

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/120553

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F120553