Steroid hormones play important roles in virtually every aspect of cellular metabolism, including the regulation of carbohydrate, lipid and protein metabolism and immune function (glucocorticoids), as well as salt and water balance and blood pressure regulation (mineralocorticoids). They are also critically involved in the maintenance of secondary sex characteristics, reproductive functions and muscle and bone growth (testosterone, progestins and estrogens). Thus, understanding steroid hormone production has important implications for almost every feature related to normal human health, but also to most diseases, making it quite relevant for the VA. The common precursor of steroid hormone biosynthesis is cholesterol, with the rate-limiting step being the transfer of cholesterol from the outer to the inner mitochondrial membrane. Though cholesterol trafficking for steroid hormone production has been the subject of intense investigation, the mechanisms how cholesterol traffics to the outer mitochondrial membrane remain incompletely understood. The overall goal of this proposal is to elucidate the mechanisms underlying the trafficking of cholesterol for steroidogenesis. The overall goal will be achieved by testing 2 major hypotheses. First, we propose the novel hypothesis that cholesteryl esters selectively transferred from HDL traverse the plasma membrane via SR-B1 and at the cytoplasmic side behave as micro-lipid droplets, acquiring lipid droplet- associated proteins that then direct the cholesteryl esters (micro-lipid droplets) to coalesce into mature lipid droplets or to fuse with existing cytoplasmic lipid droplets. This will be accomplished by tracing the movement of cholesteryl esters contained within HDL into lipid droplets in adrenal and gonadal cells in which specific cytosolic proteins have been knocked down or inhibited. Second, we hypothesize that the pathways through which cholesterol is transported from the plasma membrane, the endoplasmic reticulum, and lipid droplets to mitochondria each involves different mechanisms that comprise both vesicular and non- vesicular means.
This aim will be accomplished using several different approaches. First, a novel cell-free in vitro reconstitution assay we have developed for cholesterol transport to mitochondria containing isolated mitochondria and recombinant StAR will be used to assess the efficiency of cholesterol delivery from the plasma membrane, the endoplasmic reticulum and lipid droplets in the presence of specific recombinant proteins, including SNAREs. Second, we will knockdown specific plasma membrane and endoplasmic reticulum proteins in granulosa and adrenal cells to assess their impact on cholesterol transport to mitochondria. Third, we will use SNARE mutant mice to compare cholesterol homeostasis and movement to mitochondria and steroidogenesis in vivo. The results from these studies should provide insights into the critical biological process of steroid hormone production.

Public Health Relevance

Steroid hormones (cortisol, estrogen, testosterone) are made in the adrenal glands, ovaries and testes. These hormones are involved in almost every aspect of normal human function, including metabolism, blood pressure, sex, reproduction, and bone and muscle strength. Thus, understanding steroids has relevance to the entire Veteran population, as well as to the general population at large. All of these steroid hormones are made in the body from cholesterol; however, it is not at all well understood how cholesterol moves through the cell to be able to be made into steroids. The current proposal is designed to develop a basic understanding how cholesterol does move through the cell and is made into steroid hormones.

Agency
National Institute of Health (NIH)
Institute
Veterans Affairs (VA)
Type
Non-HHS Research Projects (I01)
Project #
2I01BX000398-09
Application #
9348976
Study Section
Endocriniology A (ENDA)
Project Start
2009-04-01
Project End
2021-03-31
Budget Start
2017-04-01
Budget End
2018-03-31
Support Year
9
Fiscal Year
2017
Total Cost
Indirect Cost
Name
Veterans Admin Palo Alto Health Care Sys
Department
Type
Independent Hospitals
DUNS #
046017455
City
Palo Alto
State
CA
Country
United States
Zip Code
94304
Shen, Wen-Jun; Asthana, Shailendra; Kraemer, Fredric B et al. (2018) Scavenger receptor B type 1: expression, molecular regulation, and cholesterol transport function. J Lipid Res 59:1114-1131
Singh, Amar Bahadur; Dong, Bin; Kraemer, Fredric B et al. (2018) Farnesoid X Receptor Activation by Obeticholic Acid Elevates Liver Low-Density Lipoprotein Receptor Expression by mRNA Stabilization and Reduces Plasma Low-Density Lipoprotein Cholesterol in Mice. Arterioscler Thromb Vasc Biol 38:2448-2459
Kraemer, Fredric B; Shen, Wen-Jun; Azhar, Salman (2017) SNAREs and cholesterol movement for steroidogenesis. Mol Cell Endocrinol 441:17-21
Hu, Zhigang; Shen, Wen-Jun; Kraemer, Fredric B et al. (2017) Regulation of adrenal and ovarian steroidogenesis by miR-132. J Mol Endocrinol 59:269-283
Han, Lu; Shen, Wen-Jun; Bittner, Stefanie et al. (2017) PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part II: PPAR-?/? and PPAR-?. Future Cardiol 13:279-296
Han, Lu; Shen, Wen-Jun; Bittner, Stefanie et al. (2017) PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part I: PPAR-?. Future Cardiol 13:259-278
Ueno, Masami; Suzuki, Jinya; Hirose, Masamichi et al. (2017) Cardiac overexpression of perilipin 2 induces dynamic steatosis: prevention by hormone-sensitive lipase. Am J Physiol Endocrinol Metab 313:E699-E709
Lin, Ye; Hou, Xiaoming; Shen, Wen-Jun et al. (2016) SNARE-Mediated Cholesterol Movement to Mitochondria Supports Steroidogenesis in Rodent Cells. Mol Endocrinol 30:234-47
Casado, María E; Pastor, Oscar; García-Seisdedos, David et al. (2016) Hormone-sensitive lipase deficiency disturbs lipid composition of plasma membrane microdomains from mouse testis. Biochim Biophys Acta 1861:1142-1150
Zhang, Haiyan; Shen, Wen-Jun; Li, Yihang et al. (2016) Microarray analysis of gene expression in liver, adipose tissue and skeletal muscle in response to chronic dietary administration of NDGA to high-fructose fed dyslipidemic rats. Nutr Metab (Lond) 13:63

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