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. 2013 Jun 6;50(5):686-98.
doi: 10.1016/j.molcel.2013.05.012.

SIRT4 coordinates the balance between lipid synthesis and catabolism by repressing malonyl CoA decarboxylase

Gaëlle Laurent  1 , Natalie J German, Asish K Saha, Vincent C J de Boer, Michael Davies, Timothy R Koves, Noah Dephoure, Frank Fischer, Gina Boanca, Bhavapriya Vaitheesvaran, Scott B Lovitch, Arlene H Sharpe, Irwin J Kurland, Clemens Steegborn, Steven P Gygi, Deborah M Muoio, Neil B Ruderman, Marcia C Haigis
Affiliations

SIRT4 coordinates the balance between lipid synthesis and catabolism by repressing malonyl CoA decarboxylase

Gaëlle Laurent et al. Mol Cell. .

Abstract

Lipid metabolism is tightly controlled by the nutritional state of the organism. Nutrient-rich conditions increase lipogenesis, whereas nutrient deprivation promotes fat oxidation. In this study, we identify the mitochondrial sirtuin, SIRT4, as a regulator of lipid homeostasis. SIRT4 is active in nutrient-replete conditions to repress fatty acid oxidation while promoting lipid anabolism. SIRT4 deacetylates and inhibits malonyl CoA decarboxylase (MCD), an enzyme that produces acetyl CoA from malonyl CoA. Malonyl CoA provides the carbon skeleton for lipogenesis and also inhibits fat oxidation. Mice lacking SIRT4 display elevated MCD activity and decreased malonyl CoA in skeletal muscle and white adipose tissue. Consequently, SIRT4 KO mice display deregulated lipid metabolism, leading to increased exercise tolerance and protection against diet-induced obesity. In sum, this work elucidates SIRT4 as an important regulator of lipid homeostasis, identifies MCD as a SIRT4 target, and deepens our understanding of the malonyl CoA regulatory axis.

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Figures

Figure 1
Figure 1. SIRT4 regulates lipid metabolism
(A) Lipogenesis was measured using 14C-acetate (n=3), (B) Triglyceride levels (n=6), and (C) Oil Red O staining (n=6) were determined using F442A adipocytes stably expressing empty vector control (CTL, open bar), SIRT4 (red bar) or the catalytic inactive mutant of SIRT4, SIRT4H162Y (red striped bar). (D) Lipogenesis was measured using 14C-acetate in WT (open bar) and SIRT4 KO (blue bar) primary adipocyte lines (n=3). (E) Fatty acid oxidation (FAO) was measured in C2C12 cells expressing control shRNA (shNT, open bar) or shRNAs targeted against SIRT4 (blue bars) (n=3). (F) FAO was measured in C2C12 cells overexpressing empty vector control, SIRT4 or SIRT4H162Y (n=3). (G) FAO was determined using WT and SIRT4 KO primary MEF lines (n=3). Levels of SIRT4 protein were determined by Western blotting using antibodies to SIRT4 and tubulin as a loading control. In each panel, data represent mean ± SEM. (*) p < 0.05; (**) p < 0.01, (***) p < 0.001.
Figure 2
Figure 2. SIRT4 interacts and represses MCD activity
(A) Schematic of the regulation of lipid homeostasis and malonyl CoA by acetyl-CoA carboxylase (ACC) and malonyl CoA decarboxylase (MCD). (B) Sirtuin-MCD interactions were assessed by cotransfecting expression vectors for SIRT3, SIRT4 or SIRT5 (FLAG-tagged at the C-terminus) with an expression vector for C-terminal HA-tagged MCD in HEK293T cells. HA-tagged MCD was immunoprecipitated and interactions were detected by immunoblotting with antibodies against FLAG. (C) Expression vectors containing SIRT4 or SIRT4H162Y (FLAG-tagged) were co-transfected with C-terminal HA-tagged MCD in HEK293T cells, and SIRT4-MCD binding was assessed by immunoprecipitation of MCD-HA and Western blotting with FLAG antibodies. (D) The subcellular localization of SIRT4-HA (green) and MCD-FLAG (red) stably overexpressed in immortalized MEFs was examined by immunofluorescence using HA and FLAG antibodies and the mitochondrial marker Mitotracker (pseudo-colored in blue). (E) FAO rates were assessed in WT and SIRT4 KO primary MEFs treated with control shRNA (shNT) or two shRNAs against MCD (sh1 and sh2) as indicated (n=3). (F) Relative MCD activity in SIRT4 WT and SIRT4 KO immortalized MEFs treated or not with nicotinamide (NAM; striped bars) (n=3). (G–H) Relative MCD activity in C2C12 (n=3) (G) or in F442A cells (n=3) (H) overexpressing empty vector control, SIRT4 or SIRT4H162Y. Levels of SIRT4 and MCD proteins were determined by Western blotting using antibodies for SIRT4 and MCD and tubulin as a loading control. In each panel, data represent mean ± SEM. (*) p < 0.05; (**) p < 0.01, (***) p < 0.001. See also Figure S1.
Figure 3
Figure 3. SIRT4 deacetylates MCD
(A) MCD acetylation was measured in WT immortalized MEFs before or after treatment with NAM. FLAG-tagged MCD was stably overexpressed in WT MEFs treated with (+) or without (−) NAM and immunoprecipitated using antibodies against FLAG. MCD acetylation levels were assessed with antibodies against acetyl-lysine (AcK). (B) MCD acetylation was assessed using WT and SIRT4 KO MEFs as described for panel A. (C) MCD acetylation was measured in C2C12 cells stably overexpressing FLAG-tagged MCD and SIRT4 or SIRT4H162Y. After immunoprecipitation of MCD with anti-FLAG antibodies, acetylation was measured as for panel A. (D) In vitro deacetylation assay was performed using immunopurified MCD and SIRT4. FLAG-MCD was immunoprecipitated from MEFs and incubated with FLAG-SIRT4 and FLAG-SIRT4H162Y immunoprecipitated from HEK293 cells and MCD acetylation status assessed by Western blot. (E) Recombinant SIRT4 was incubated with synthesized acetylated peptides of MCD and peptide deacetylation was assessed using mass spectrometry. Acetylated peptide from pyruvate dehydrogenase (PDH) was included as a negative control (n=3). (F) Acetylated peptide was incubated with SIRT4 and NAD+ concentrations were varied as indicated. Peptide deacetylation levels were analyzed by LC-MS. (G) Constructs encoding MCD, MCD K471R or MCD K471Q were expressed in HEK 293T cells and MCD activity was measured (n=4). (H–I) Retrovirus used to generate stable C2C12 (H) and F442A (I) cell lines overexpressing MCD, MCD K471R or MCD K471Q where FAO rates and lipogenesis were assessed (n=3). In each panel, data represent mean ± SEM. (*) p < 0.05; (**) p < 0.01, (***) p < 0.001. See also Figure S2 and S6.
Figure 4
Figure 4. SIRT4 deacetylates MCD in vivo during the fed state controlling malonyl CoA levels
(A) Schematic of the regulation of lipid homeostasis during fed and fasted state. (B–C) Muscle (soleus) and WAT were harvested from mice under fed or fasted conditions and analyzed for SIRT4 expression by Western blot and normalized to tubulin. Images were quantified (right panels) for the SIRT4/tubulin ratio using Image J. (D–E) Muscle (soleus) and WAT extracts from WT mice fed or fasted were immunoprecipitated with a monoclonal AcK antibody and blotted for MCD. (F–G) Muscle (soleus) and WAT extracts from WT and SIRT4 KO fed mice were immunoprecipitated with a monoclonal AcK antibody and blotted for MCD. (H–I) Relative MCD activity in muscle (quadriceps) and WAT from WT and SIRT4 KO fed mice (n=4 per genotype). (K–L) Malonyl CoA levels were measured in muscle (quadriceps) and WAT from WT (open and grey bars) and SIRT4 KO (dark and light blue bars) mice under fed and fasted conditions (n=4 per genotype, per condition). In each panel, data represent mean ± SEM. (*) p < 0.05; (**) p < 0.01, (***) p < 0.001.
Figure 5
Figure 5. SIRT4 KO mice display an altered lipid metabolism in vivo
(A) Triglyceride composition from WAT from WT and SIRT4 KO fed and fasted mice (n=3 mice per genotype, per condition). (B–C) Skeletal Muscle (quadriceps) phospholipid and triglyceride composition from WT and SIRT4 KO fed and fasted mice (n=3 mice per genotype, per condition). (D–E) Exercise tolerance assays were performed on WT and SIRT4 KO mice (n=11–14 per genotype). (F–G) RER in WT and SIRT4 KO mice during exercise (F) and recovery (G) (n=11–14). (H–J) De novo lipogenesis in vivo was measured by determining incorporation of deuterated water into palmitate in WAT (H), liver (I), and plasma (J) (n=6 per genotype). In each panel, data represent mean ± SEM. (*) p < 0.05; (**) p < 0.01, (***) p < 0.001. See also Figure S3.
Figure 6
Figure 6. SIRT4 KO mice are protected from diet-induced weight gain
(A) Body weight of WT and SIRT4 KO mice on a low fat diet (LFD) and high fat diet (HFD) (n=10–12 per genotype). (B) Representative images of CT-scan of WT and SIRT4 KO mice on a HFD with fat mass highlighted. Red represents the highest value in the range of WAT density and in blue the lowest. (C) Percentage of fat mass analyzed by CT-scan of WT and SIRT4 KO mice on a HFD (n=6 per genotype). (D) Epididymal WAT weights from WT and SIRT4 KO mice on a HFD (n=6 per genotype). (E) Representative hematoxylin and eosin staining slides of WAT of WT and SIRT4 KO mice under LFD and HFD. Scale bar is 50 μM. (F) Food intake in WT and SIRT4 KO mice on a HFD (n=6 per genotype). (G–I) Energy expenditure in WT and SIRT4 KO mice on a HFD (n=6 per genotype). (J) WAT extracts from WT and SIRT4 KO mice under HFD were immunoprecipitated with a monoclonal AcK antibody and Western blotted for MCD. (K) MCD activity in WAT of WT and SIRT4 KO mice under HFD. (L) Malonyl CoA levels in WAT of WT and SIRT4 KO mice under HFD. In each panel, data represent mean ± SEM. (*) p < 0.05; (**) p < 0.01, (***) p < 0.001. See also Figures S4 and S5.
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