Dietary protein restriction reduces circulating VLDL triglyceride levels via CREBH-APOA5–dependent and –independent mechanisms
J. Humberto Treviño-Villarreal, … , Luigi Fontana, James R. Mitchell
J. Humberto Treviño-Villarreal, … , Luigi Fontana, James R. Mitchell
Published November 2, 2018
Citation Information: JCI Insight. 2018;3(21):e99470. https://doi.org/10.1172/jci.insight.99470.
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Research Article Metabolism

Dietary protein restriction reduces circulating VLDL triglyceride levels via CREBH-APOA5–dependent and –independent mechanisms

Abstract

Hypertriglyceridemia is an independent risk factor for cardiovascular disease. Dietary interventions based on protein restriction (PR) reduce circulating triglycerides (TGs), but underlying mechanisms and clinical relevance remain unclear. Here, we show that 1 week of a protein-free diet without enforced calorie restriction significantly lowered circulating TGs in both lean and diet-induced obese mice. Mechanistically, the TG-lowering effect of PR was due, in part, to changes in very low–density lipoprotein (VLDL) metabolism both in liver and peripheral tissues. In the periphery, PR stimulated VLDL-TG consumption by increasing VLDL-bound APOA5 expression and promoting VLDL-TG hydrolysis and clearance from circulation. The PR-mediated increase in Apoa5 expression was controlled by the transcription factor CREBH, which coordinately regulated hepatic expression of fatty acid oxidation–related genes, including Fgf21 and Ppara. The CREBH-APOA5 axis activation upon PR was intact in mice lacking the GCN2-dependent amino acid–sensing arm of the integrated stress response. However, constitutive hepatic activation of the amino acid–responsive kinase mTORC1 compromised CREBH activation, leading to blunted APOA5 expression and PR-recalcitrant hypertriglyceridemia. PR also contributed to hypotriglyceridemia by reducing the rate of VLDL-TG secretion, independently of activation of the CREBH-APOA5 axis. Finally, a randomized controlled clinical trial revealed that 4–6 weeks of reduced protein intake (7%–9% of calories) decreased VLDL particle number, increased VLDL-bound APOA5 expression, and lowered plasma TGs, consistent with mechanistic conservation of PR-mediated hypotriglyceridemia in humans with translational potential as a nutraceutical intervention for dyslipidemia.

Authors

J. Humberto Treviño-Villarreal, Justin S. Reynolds, Alexander Bartelt, P. Kent Langston, Michael R. MacArthur, Alessandro Arduini, Valeria Tosti, Nicola Veronese, Beatrice Bertozzi, Lear E. Brace, Pedro Mejia, Kaspar Trocha, Gustavo S. Kajitani, Alban Longchamp, Eylul Harputlugil, Rose Gathungu, Susan S. Bird, Arnold D. Bullock, Robert S. Figenshau, Gerald L. Andriole, Andrew Thompson, Jöerg Heeren, C. Keith Ozaki, Bruce S. Kristal, Luigi Fontana, James R. Mitchell

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Figure 2

Protein restriction alters VLDL-TG consumption via changes in hepatic apolipoprotein expression.

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Protein restriction alters VLDL-TG consumption via changes in hepatic ap...
(A and B) Time-dependent clearance of radiolabeled TG from the following circulating lipoprotein particles: (A) [3H]-triolein-labeled recombinant lipoprotein particles injected into mice fed a complete (C) or protein-free (PF) diet (n = 7/group); or (B) [3H]-palmitate-labeled and purified VLDL particles from mice on C or PF diets, and injected into complete-fed mice (n = 4/group; multiple t tests between diet groups with Holm-Sidak post-hoc test). (C) Hepatic mRNA expression of apolipoprotein-encoding genes from mice on the indicated diet (n = 4–11/group; 2-tailed Student’s t test). (D) Immunoblot of hepatic APOA5 protein expression. Below, quantitation normalized to tubulin and expressed in arbitrary units (AU, n = 5/group; 2-tailed Student’s t test). (E) Representative confocal microscopic images taken with a 63× objective from livers of mice on the indicated diet showing the ER marker KDEL (green), APOA5 (red), nuclei (DNA stained with DAPI, blue) superimposed to differential interference contrast (DIC) image and a composite image. Scale bar: 20 μm. (F) Circulating VLDL-bound APOA5 levels in mice on the indicated diet, expressed as the ratio of serum APOA5 to APOB-100 as measured by ELISA (n = 5/group; Mann-Whitney U test). (G) Correlation analysis between serum TG and APOA5. Each dot represents an individual mouse; r, Pearson’s coefficient. (H) Fasted serum TG levels in whole body APOA5-KO or control FVB WT mice on the indicated diet (n = 4/group; 2-way ANOVA with Sidak post-hoc test between the indicated groups). Data expressed as mean ± SD; **P < 0.01, ***P < 0.001; ****P < 0.0001.