Glycerol-3-phosphate acyltransferase-4-deficient mice are protected from diet-induced insulin resistance by the enhanced association of mTOR and rictor

TY - JOUR

T1 - Glycerol-3-phosphate acyltransferase-4-deficient mice are protected from diet-induced insulin resistance by the enhanced association of mTOR and rictor

AU - Zhang, Chongben

AU - Cooper, Daniel E

AU - Grevengoed, Trisha J

AU - Li, Lei O

AU - Klett, Eric L

AU - Eaton, James M

AU - Harris, Thurl E

AU - Coleman, Rosalind A

N1 - Copyright © 2014 the American Physiological Society.

PY - 2014/8/1

Y1 - 2014/8/1

N2 - Glycerol-3-phosphate acyltransferase (GPAT) activity is highly induced in obese individuals with insulin resistance, suggesting a correlation between GPAT function, triacylglycerol accumulation, and insulin resistance. We asked whether microsomal GPAT4, an isoform regulated by insulin, might contribute to the development of hepatic insulin resistance. Compared with control mice fed a high fat diet, Gpat4-/- mice were more glucose tolerant and were protected from insulin resistance. Overexpression of GPAT4 in mouse hepatocytes impaired insulin-suppressed gluconeogenesis and insulin-stimulated glycogen synthesis. Impaired glucose homeostasis was coupled to inhibited insulin-stimulated phosphorylation of Akt(Ser473) and Akt(Thr308). GPAT4 overexpression inhibited rictor's association with the mammalian target of rapamycin (mTOR), and mTOR complex 2 (mTORC2) activity. Compared with overexpressed GPAT3 in mouse hepatocytes, GPAT4 overexpression increased phosphatidic acid (PA), especially di16:0-PA. Conversely, in Gpat4-/- hepatocytes, both mTOR/rictor association and mTORC2 activity increased, and the content of PA in Gpat4-/- hepatocytes was lower than in controls, with the greatest decrease in 16:0-PA species. Compared with controls, liver and skeletal muscle from Gpat4-/--deficient mice fed a high-fat diet were more insulin sensitive and had a lower hepatic content of di16:0-PA. Taken together, these data demonstrate that a GPAT4-derived lipid signal, likely di16:0-PA, impairs insulin signaling in mouse liver and contributes to hepatic insulin resistance.

AB - Glycerol-3-phosphate acyltransferase (GPAT) activity is highly induced in obese individuals with insulin resistance, suggesting a correlation between GPAT function, triacylglycerol accumulation, and insulin resistance. We asked whether microsomal GPAT4, an isoform regulated by insulin, might contribute to the development of hepatic insulin resistance. Compared with control mice fed a high fat diet, Gpat4-/- mice were more glucose tolerant and were protected from insulin resistance. Overexpression of GPAT4 in mouse hepatocytes impaired insulin-suppressed gluconeogenesis and insulin-stimulated glycogen synthesis. Impaired glucose homeostasis was coupled to inhibited insulin-stimulated phosphorylation of Akt(Ser473) and Akt(Thr308). GPAT4 overexpression inhibited rictor's association with the mammalian target of rapamycin (mTOR), and mTOR complex 2 (mTORC2) activity. Compared with overexpressed GPAT3 in mouse hepatocytes, GPAT4 overexpression increased phosphatidic acid (PA), especially di16:0-PA. Conversely, in Gpat4-/- hepatocytes, both mTOR/rictor association and mTORC2 activity increased, and the content of PA in Gpat4-/- hepatocytes was lower than in controls, with the greatest decrease in 16:0-PA species. Compared with controls, liver and skeletal muscle from Gpat4-/--deficient mice fed a high-fat diet were more insulin sensitive and had a lower hepatic content of di16:0-PA. Taken together, these data demonstrate that a GPAT4-derived lipid signal, likely di16:0-PA, impairs insulin signaling in mouse liver and contributes to hepatic insulin resistance.

KW - Animals

KW - Carrier Proteins

KW - Cells, Cultured

KW - Diet, High-Fat

KW - Female

KW - Glycerol-3-Phosphate O-Acyltransferase

KW - Hepatocytes

KW - Hypoglycemic Agents

KW - Insulin

KW - Insulin Resistance

KW - Male

KW - Mice

KW - Mice, Inbred C57BL

KW - Mice, Knockout

KW - Obesity

KW - Phosphatidic Acids

KW - Recombinant Proteins

KW - Second Messenger Systems

KW - Signal Transduction

KW - TOR Serine-Threonine Kinases

U2 - 10.1152/ajpendo.00034.2014

DO - 10.1152/ajpendo.00034.2014

M3 - Journal article

C2 - 24939733

SN - 0193-1849

VL - 307

SP - E305-15

JO - American Journal of Physiology - Endocrinology and Metabolism

JF - American Journal of Physiology - Endocrinology and Metabolism

IS - 3

ER -