SREBP-regulated adipocyte lipogenesis is dependent on substrate availability and redox modulation of mTORC1
Clair Crewe, … , Jay D. Horton, Philipp E. Scherer
Clair Crewe, … , Jay D. Horton, Philipp E. Scherer
Published August 8, 2019; First published July 16, 2019
Citation Information: JCI Insight. 2019;4(15):e129397. https://doi.org/10.1172/jci.insight.129397.
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Categories: Research Article Endocrinology Metabolism

SREBP-regulated adipocyte lipogenesis is dependent on substrate availability and redox modulation of mTORC1

Abstract

The synthesis of lipid and sterol species through de novo lipogenesis (DNL) is regulated by 2 functionally overlapping but distinct transcription factors: the SREBPs and carbohydrate response element–binding protein (ChREBP). ChREBP is considered to be the dominant regulator of DNL in adipose tissue (AT); however, the SREBPs are highly expressed and robustly regulated in adipocytes, suggesting that the model of AT DNL may be incomplete. Here, we describe what we believe to be a new mouse model of inducible, adipocyte-specific overexpression of the insulin-induced gene 1 (Insig1), a negative regulator of SREBP transcriptional activity. Contrary to convention, Insig1 overexpression did block AT lipogenic gene expression. However, this was immediately met with a compensatory mechanism triggered by redox activation of mTORC1 to restore SREBP1 DNL gene expression. Thus, we demonstrate that SREBP1 activity sustains adipocyte lipogenesis, a conclusion that has been elusive due to the constitutive nature of current mouse models.

Authors

Clair Crewe, Yi Zhu, Vivian A. Paschoal, Nolwenn Joffin, Alexandra L. Ghaben, Ruth Gordillo, Da Young Oh, Guosheng Liang, Jay D. Horton, Philipp E. Scherer

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Figure 4

Acute suppression of AT DNL induces mitochondrial oxidative stress, resulting in mTORC1 activation.

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Acute suppression of AT DNL induces mitochondrial oxidative stress, resu...
(A) mRNA expression in sWAT of the citrate transporter (CiC) over the indicated dox treatment duration (n = 8–12). (B) Mice were injected with dox (2 mg/kg). At 3.5 hours after injection mice were gavaged with 1:1 glucose/fructose. At 4 hours after dox injection sWAT was harvested for determination of glycolytic and TCA cycle intermediate concentrations. (C) Wild-type mice were treated with and without 20% fructose in the drinking water for 12 hours. A representative Western blot and densitometry for pS6Ser240/244 and pAKTThr308 in sWAT (n = 5) are shown. (D) Protein carbonylation blot densitometry over the indicated time course of dox exposure (n = 4). (E) qPCR analysis of antioxidant genes in sWAT 8 hours after an injection of 2 mg/kg dox (n = 6). (F and H) Control or ad-Insig1 mice were injected with 5 mg/kg MitoQ or 250 mg/kg 2-DG and simultaneously supplied dox-supplemented diet for 24 hours. (F) Representative Western blot and densitometry of pS6Ser240/244 from the sWAT of control or ad-Insig1 mice treated with or without MitoQ or 2-DG (n = 3–4). (G) AT depots weights with MitoQ treatment. (H) An example Western blot for ACC and FASN levels in sWAT from control or ad-Insig1 mice treated with MitoQ or 2-DG and corresponding densitometry (n = 3–4). In this instance FASN was run on a separate gel from ACC and GAPDH although the biological sample presented is consistent. All data are presented as mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001 by 2-tailed Student’s t test. In all cases, for a given condition, representative Western blot images are from the same sample, although the target proteins may have been probed on separate membranes to facilitate clear visualization. All densitometry was conducted on samples run on the same gel.