Abstract
Increased flux through the glycerolipid synthesis pathway impairs the ability of insulin to inhibit hepatic gluconeogenesis, but the exact mechanism remains unknown. To determine the mechanism by which glycerolipids impair insulin signaling, we overexpressed glycerol-3-phosphate acyltransferase-1 (GPAT1) in primary mouse hepatocytes. GPAT1 overexpression impaired insulin-stimulated phosphorylation of Akt-S473 and -T308, diminished insulin-suppression of glucose production, significantly inhibited mTOR complex 2 (mTORC2) activity and decreased the association of mTOR and rictor. Conversely, in hepatocytes from Gpat1 -/- mice, mTOR-rictor association and mTORC2 activity were enhanced. However, this increase in mTORC2 activity in Gpat1 -/- hepatocytes was ablated when rictor was knocked down. To determine which lipid intermediate was responsible for inactivating mTORC2, we overexpressed GPAT1, AGPAT, or lipin to increase the cellular content of lysophosphatidic acid (LPA), phosphatidic acid (PA), or diacylglycerol (DAG), respectively. The inhibition of mTOR/rictor binding and mTORC2 activity coincided with the levels of PA and DAG species that contained 16:0, the preferred substrate of GPAT1. Furthermore, di-16:0-PA strongly inhibited mTORC2 activity and disassociated mTOR/rictor in vitro. Taken together, these data reveal a signaling pathway by which phosphatidic acid synthesized via the glycerol-3-phosphate pathway inhibits mTORC2 activity by decreasing the association of rictor and mTOR, thereby down-regulating insulin action. These data demonstrate a critical link between nutrient excess, TAG synthesis, and hepatic insulin resistance.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1667-1672 |
| Number of pages | 6 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 109 |
| Issue number | 5 |
| DOIs | |
| State | Published - Jan 31 2012 |
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Keywords
- Hepatic steatosis
- Palmitate
- Triacylglycerol
ASJC Scopus subject areas
- General
Cite this
Glycerolipid signals alter mTOR complex 2 (mTORC2) to diminish insulin signaling. / Zhang, Chongben; Wendel, Angela A.; Keogh, Matthew R.; Harris, Thurl E.; Chen, Jie; Coleman, Rosalind A.
In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 109, No. 5, 31.01.2012, p. 1667-1672.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Glycerolipid signals alter mTOR complex 2 (mTORC2) to diminish insulin signaling
AU - Zhang, Chongben
AU - Wendel, Angela A.
AU - Keogh, Matthew R.
AU - Harris, Thurl E.
AU - Chen, Jie
AU - Coleman, Rosalind A.
PY - 2012/1/31
Y1 - 2012/1/31
N2 - Increased flux through the glycerolipid synthesis pathway impairs the ability of insulin to inhibit hepatic gluconeogenesis, but the exact mechanism remains unknown. To determine the mechanism by which glycerolipids impair insulin signaling, we overexpressed glycerol-3-phosphate acyltransferase-1 (GPAT1) in primary mouse hepatocytes. GPAT1 overexpression impaired insulin-stimulated phosphorylation of Akt-S473 and -T308, diminished insulin-suppression of glucose production, significantly inhibited mTOR complex 2 (mTORC2) activity and decreased the association of mTOR and rictor. Conversely, in hepatocytes from Gpat1 -/- mice, mTOR-rictor association and mTORC2 activity were enhanced. However, this increase in mTORC2 activity in Gpat1 -/- hepatocytes was ablated when rictor was knocked down. To determine which lipid intermediate was responsible for inactivating mTORC2, we overexpressed GPAT1, AGPAT, or lipin to increase the cellular content of lysophosphatidic acid (LPA), phosphatidic acid (PA), or diacylglycerol (DAG), respectively. The inhibition of mTOR/rictor binding and mTORC2 activity coincided with the levels of PA and DAG species that contained 16:0, the preferred substrate of GPAT1. Furthermore, di-16:0-PA strongly inhibited mTORC2 activity and disassociated mTOR/rictor in vitro. Taken together, these data reveal a signaling pathway by which phosphatidic acid synthesized via the glycerol-3-phosphate pathway inhibits mTORC2 activity by decreasing the association of rictor and mTOR, thereby down-regulating insulin action. These data demonstrate a critical link between nutrient excess, TAG synthesis, and hepatic insulin resistance.
AB - Increased flux through the glycerolipid synthesis pathway impairs the ability of insulin to inhibit hepatic gluconeogenesis, but the exact mechanism remains unknown. To determine the mechanism by which glycerolipids impair insulin signaling, we overexpressed glycerol-3-phosphate acyltransferase-1 (GPAT1) in primary mouse hepatocytes. GPAT1 overexpression impaired insulin-stimulated phosphorylation of Akt-S473 and -T308, diminished insulin-suppression of glucose production, significantly inhibited mTOR complex 2 (mTORC2) activity and decreased the association of mTOR and rictor. Conversely, in hepatocytes from Gpat1 -/- mice, mTOR-rictor association and mTORC2 activity were enhanced. However, this increase in mTORC2 activity in Gpat1 -/- hepatocytes was ablated when rictor was knocked down. To determine which lipid intermediate was responsible for inactivating mTORC2, we overexpressed GPAT1, AGPAT, or lipin to increase the cellular content of lysophosphatidic acid (LPA), phosphatidic acid (PA), or diacylglycerol (DAG), respectively. The inhibition of mTOR/rictor binding and mTORC2 activity coincided with the levels of PA and DAG species that contained 16:0, the preferred substrate of GPAT1. Furthermore, di-16:0-PA strongly inhibited mTORC2 activity and disassociated mTOR/rictor in vitro. Taken together, these data reveal a signaling pathway by which phosphatidic acid synthesized via the glycerol-3-phosphate pathway inhibits mTORC2 activity by decreasing the association of rictor and mTOR, thereby down-regulating insulin action. These data demonstrate a critical link between nutrient excess, TAG synthesis, and hepatic insulin resistance.
KW - Hepatic steatosis
KW - Palmitate
KW - Triacylglycerol
UR - http://www.scopus.com/inward/record.url?scp=84863115883&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84863115883&partnerID=8YFLogxK
U2 - 10.1073/pnas.1110730109
DO - 10.1073/pnas.1110730109
M3 - Article
C2 - 22307628
AN - SCOPUS:84863115883
VL - 109
SP - 1667
EP - 1672
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 5
ER -