The combination of increased secretion of triglyceride (TG)-rich apolipoprotein B (apoB) lipoproteins (Lps) and hepatic steatosis, are characteristic concomitants of insulin resistance, the metabolic syndrome, and type 2 diabetes mellitus. The basis for increased secretion of apoB-Lps is complex, and includes altered regulation of apoB synthesis and transport in hepatocytes, increased delivery of fatty acids (FA) to the liver, and increased de novo hepatic lipogenesis (DNHL). Increased hepatic uptake of FA and increased DNHL are also critical for the development of hepatic steatosis. However, recent evidence from our laboratory, and others, indicate that endoplasmic reticulum (ER) stress and aberrant hepatic expression of PPAR32 may both play important roles in apoB-Lp secretion and the development of hepatic steatosis. The studies proposed in this application focus mainly on our very recent and exciting findings linking disordered FA metabolism to both ER stress and hepatic expression of PPAR32. Specifically, we have demonstrated that oleic acid (OA)-loading of cultured hepatoma cells can induce ER stress that can have, at lower doses of FA for shorter durations, a """"""""selective"""""""" effect on apoB100 secretion without affecting total protein synthesis or secretion of albumin or apoA-I. We have comparable in vivo data in mice. Higher doses or longer exposure to OA cause """"""""global"""""""" ER stress with inhibition of secretion of several proteins and reduced total protein synthesis. We propose a series of experiments to extend, in detail, these exciting findings. We will compare ER stress effects on apoB by OA and tunicamycin, characterize the pathways by which apoB is degraded during ER stress, examine the effects of palmitic acid (PA) and docosahexanoic acid (DHA), extend our investigations regarding the particular sensitivity of apoB100 to ER stress, demonstrate in vivo that inhibition of ER stress results in increased secretion of VLDL and reversal of steatosis, and examine the important link between ER stress and increased lipogenesis. In a parallel series of studies we will extend observations related to the role of aberrant hepatic expression of PPAR32 in steatosis. In particular, we will determine the role of C/EBPs in the expression of PPAR32 in liver, investigate the signaling pathways for insulin stimulation of PPAR32 expression, and compare the effects of different FAs. We will extend initial studies indicating that hepatic expression of PPAR32 may both increase DNHL and, by suppressing a neutral TG lipase, TGH2, reduce the incorporation of hepatic TG into apoB-containing Lps. Finally, we will assess recent data suggesting that PPAR32 expression in liver can be a response to ER stress, possibly via increased expression of C/EBP. Overall, our proposed studies should provide the basis for a unified model to explain the common association of increased (but not maximal) apoB secretion, increased hepatic DNHL, and steatosis in mice and people with insulin resistance. The combination of increased secretion of triglycerides and apolipoprotein B (apoB), and hepatic steatosis (fatty liver), are characteristic concomitants of insulin resistance, the metabolic syndrome, and type 2 diabetes mellitus. Recent evidence from our laboratory indicate that endoplasmic reticulum (ER) stress and aberrant hepatic expression of the nuclear receptor, PPAR2, which is typically found in fat, may both play important roles in the increased secretion of triglycerides and apoB, and in the development of hepatic steatosis.

Public Health Relevance

The studies proposed in this application will focus on these new discoveries and extend our knowledge about the roles of ER stress and PPAR2 in the regulation of hepatic lipid metabolism. We will use cell culture models and mice, conducting in vitro and in vivo studies. Overall, our proposed studies should provide evidence for a unified model to explain the common association of increased apoB secretion, increased hepatic DNHL, and steatosis in mice and people with insulin resistance.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL073030-08
Application #
7893230
Study Section
Special Emphasis Panel (ZRG1-EMNR-G (02))
Program Officer
Ershow, Abby
Project Start
2003-04-01
Project End
2012-06-30
Budget Start
2010-07-01
Budget End
2011-06-30
Support Year
8
Fiscal Year
2010
Total Cost
$402,500
Indirect Cost
Name
Columbia University (N.Y.)
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
621889815
City
New York
State
NY
Country
United States
Zip Code
10032
Kitade, Hironori; Sawamoto, Kazuki; Nagashimada, Mayumi et al. (2012) CCR5 plays a critical role in obesity-induced adipose tissue inflammation and insulin resistance by regulating both macrophage recruitment and M1/M2 status. Diabetes 61:1680-90
Ables, Gene P; Yang, Kryscilla Jian Zhang; Vogel, Silke et al. (2012) Intestinal DGAT1 deficiency reduces postprandial triglyceride and retinyl ester excursions by inhibiting chylomicron secretion and delaying gastric emptying. J Lipid Res 53:2364-79
Moon, Byoung C; Hernandez-Ono, Antonio; Stiles, Bangyan et al. (2012) Apolipoprotein B secretion is regulated by hepatic triglyceride, and not insulin, in a model of increased hepatic insulin signaling. Arterioscler Thromb Vasc Biol 32:236-46
Li, Guoping; Hernandez-Ono, Antonio; Crooke, Rosanne M et al. (2012) Antisense reduction of 11?-hydroxysteroid dehydrogenase type 1 enhances energy expenditure and insulin sensitivity independent of food intake in C57BL/6J mice on a Western-type diet. Metabolism 61:823-35
Liu, Li; Yu, Shuiqing; Khan, Raffay S et al. (2011) DGAT1 deficiency decreases PPAR expression and does not lead to lipotoxicity in cardiac and skeletal muscle. J Lipid Res 52:732-44
Uriel, Nir; Naka, Yoshifumi; Colombo, Paolo C et al. (2011) Improved diabetic control in advanced heart failure patients treated with left ventricular assist devices. Eur J Heart Fail 13:195-9
Caviglia, Jorge Matias; Gayet, Constance; Ota, Tsuguhito et al. (2011) Different fatty acids inhibit apoB100 secretion by different pathways: unique roles for ER stress, ceramide, and autophagy. J Lipid Res 52:1636-51
Li, Guoping; Hernandez-Ono, Antonio; Crooke, Rosanne M et al. (2011) Effects of antisense-mediated inhibition of 11?-hydroxysteroid dehydrogenase type 1 on hepatic lipid metabolism. J Lipid Res 52:971-81
Choi, Sung Hee; Ginsberg, Henry N (2011) Increased very low density lipoprotein (VLDL) secretion, hepatic steatosis, and insulin resistance. Trends Endocrinol Metab 22:353-63
Elam, Marshall; Lovato, Laura C; Ginsberg, Henry (2011) Role of fibrates in cardiovascular disease prevention, the ACCORD-Lipid perspective. Curr Opin Lipidol 22:55-61

Showing the most recent 10 out of 30 publications