Hepatic Fis1 regulates mitochondrial integrated stress response and improves metabolic homeostasis
Yae-Huei Liou, Jean Personnaz, David Jacobi, Nelson H. Knudsen, Mayer M. Chalom, Kyle A. Starost, Israel C. Nnah, Chih-Hao Lee
Yae-Huei Liou, Jean Personnaz, David Jacobi, Nelson H. Knudsen, Mayer M. Chalom, Kyle A. Starost, Israel C. Nnah, Chih-Hao Lee
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Research Article Metabolism

Hepatic Fis1 regulates mitochondrial integrated stress response and improves metabolic homeostasis

Abstract

Mitophagy and mitochondrial integrated stress response (ISR) are 2 primary protective mechanisms to maintain functional mitochondria. Whether these 2 processes are coordinately regulated remains unclear. Here we show that mitochondrial fission 1 protein (Fis1), which is required for completion of mitophagy, serves as a signaling hub linking mitophagy and ISR. In mouse hepatocytes, high fat diet (HFD) feeding induces unresolved oxidative stress, defective mitophagy and enhanced type I interferon (IFN-I) response implicated in promoting metabolic inflammation. Adenoviral-mediated acute hepatic Fis1 overexpression is sufficient to reduce oxidative damage and improve glucose homeostasis in HFD-fed mice. RNA-Seq analysis reveals that Fis1 triggers a retrograde mitochondria-to-nucleus communication upregulating ISR genes encoding anti-oxidant defense, redox homeostasis, and proteostasis pathways. Fis1-mediated ISR also suppresses expression of IFN-I–stimulated genes through activating transcription factor 5 (Atf5), which inhibits the transactivation activity of interferon regulatory factor 3 (Irf3) known to control IFN-I production. Metabolite analysis demonstrates that Fis1 activation leads to accumulation of fumarate, a TCA cycle intermediate capable of increasing Atf5 activity. Consequently, hepatic Atf5 overexpression or monomethyl fumarate (MMF) treatment improves glucose homeostasis in HFD-fed mice. Collectively, these results support the potential use of small molecules targeting the Fis1-Atf5 axis, such as MMF, to treat metabolic diseases.

Authors

Yae-Huei Liou, Jean Personnaz, David Jacobi, Nelson H. Knudsen, Mayer M. Chalom, Kyle A. Starost, Israel C. Nnah, Chih-Hao Lee

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Figure 1

Overnutrition induces oxidative stress and impairs mitophagy in the liver.

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Overnutrition induces oxidative stress and impairs mitophagy in the live...
(A) Liver mROS production in fasted/refed mice. Mice were fasted overnight, followed by a 5-hour fasting or refeeding. Liver mitochondria were stained with MitoSOX Red plus 20 mM sodium succinate (to induce mROS production) for FACS analysis. MFI, mean fluorescence intensity from FACS analysis. n = 3, experiments repeated twice. (B) mROS levels in liver mitochondria isolated at diurnal fasting (Zeitgeber time 2, or ZT2 = 8 am) and feeding (ZT14 = 8 pm) periods. Mice were fed a NC or HFD for 8 weeks. n = 3–5, experiments repeated twice. (C) Protein carbonyl content in livers of NC- or HFD-fed mice at ZT2, repeated twice. (D) LC3B and p62 immunoblotting in NC or HFD livers at ZT4 and ZT14. n = 2, repeated twice. Beta tubulin (Tubb) included for loading control. (E) LC3B and Fis1 immunoblotting in primary hepatocytes from NC- or HFD-fed mice with 10 μM valinomycin at indicated time points, repeated 3 times. (F) Relative expression of IFN-I signaling genes by real-time PCR. Primary hepatocytes from NC- or HFD-fed mice were transfected with/without 100 ng/well Poly I:C for 16 hours. n = 3, repeated 3 times. (G) Ifnb1 gene expression (n = 3) and IFN-β protein secretion (n = 6, normalized to cellular protein content) from the condition described in F. (H) LC3B immunoblotting in primary hepatocytes stimulated with 10 ng/mL IFN-β for 16 hours, followed by 10 μM valinomycin time course treatment. Tubb and beta actin (Actb): loading controls. Experiments repeated twice. Values are mean ± SEM. Significance of A–C were determined by unpaired, 2-tailed Student’s t test; and of F and G by 1-way ANOVA followed by Holm-Šidák multiple comparisons test. *P < 0.05; #P < 0.01; $P < 0.001.