Theranostics 2021; 11(9):4381-4402. doi:10.7150/thno.53652

Research Paper

NAD+-boosting therapy alleviates nonalcoholic fatty liver disease via stimulating a novel exerkine Fndc5/irisin

Dong-Jie Li1,2,3*, Si-Jia Sun2,3*, Jiang-Tao Fu1*, Shen-Xi Ouyang2,3*, Qin-Jie Zhao4, Li Su5, Qing-Xi Ji2,3, Di-Ynag Sun1, Jia-Hui Zhu2,3, Guo-Yan Zhang2,3, Jia-Wei Ma2,3, Xiu-Ting Lan2,3, Yi Zhao2,3, Jie Tong2,3, Guo-Qiang Li1,6, Fu-Ming Shen2,3, Pei Wang1,2,3✉

1. Department of Pharmacology, School of Pharmacy, Second Military Medical University/Naval Medical University, Shanghai, China.
2. Department of Pharmacy, School of Medicine, Shanghai Tenth People's Hospital, Tongji University School of Medicine, Shanghai, China.
3. Tongji University School of Medicine, Shanghai, China.
4. Department of Organic Chemistry, School of Pharmacy, Second Military Medical University/Naval Medical University, Shanghai, China.
5. Institute of Translational Medicine, Shanghai University, Shanghai, China.
6. School of Life Science, East China Normal University, Shanghai, China.
*These authors contributed equally to this work.

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Citation:
Li DJ, Sun SJ, Fu JT, Ouyang SX, Zhao QJ, Su L, Ji QX, Sun DY, Zhu JH, Zhang GY, Ma JW, Lan XT, Zhao Y, Tong J, Li GQ, Shen FM, Wang P. NAD+-boosting therapy alleviates nonalcoholic fatty liver disease via stimulating a novel exerkine Fndc5/irisin. Theranostics 2021; 11(9):4381-4402. doi:10.7150/thno.53652. Available from https://www.thno.org/v11p4381.htm

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Abstract

Rationale: Nicotinamide adenine dinucleotide+ (NAD+)-boosting therapy has emerged as a promising strategy to treat various health disorders, while the underlying molecular mechanisms are not fully understood. Here, we investigated the involvement of fibronectin type III domain containing 5 (Fndc5) or irisin, which is a novel exercise-linked hormone, in the development and progression of nonalcoholic fatty liver disease (NAFLD).

Methods: NAD+-boosting therapy was achieved by administrating of nicotinamide riboside (NR) in human and mice. The Fndc5/irisin levels in tissues and blood were measured in NR-treated mice or human volunteers. The therapeutic action of NR against NAFLD pathologies induced by high-fat diet (HFD) or methionine/choline-deficient diet (MCD) were compared between wild-type (WT) and Fndc5-/- mice. Recombinant Fndc5/irisin was infused to NALFD mice via osmotic minipump to test the therapeutic action of Fndc5/irisin. Various biomedical experiments were conducted in vivo and in vitro to know the molecular mechanisms underlying the stimulation of Fndc5/irisin by NR treatment.

Results: NR treatment elevated plasma level of Fndc5/irisin in mice and human volunteers. NR treatment also increased Fndc5 expression in skeletal muscle, adipose and liver tissues in mice. In HFD-induced NAFLD mice model, NR displayed remarkable therapeutic effects on body weight gain, hepatic steatosis, steatohepatitis, insulin resistance, mitochondrial dysfunction, apoptosis and fibrosis; however, these actions of NR were compromised in Fndc5-/- mice. Chronic infusion of recombinant Fndc5/irisin alleviated the NAFLD pathological phenotypes in MCD-induced NAFLD mice model. Mechanistically, NR reduced the lipid stress-triggered ubiquitination of Fndc5, which increased Fndc5 protein stability and thus enhanced Fndc5 protein level. Using shRNA-mediated knockdown screening, we found that NAD+-dependent deacetylase SIRT2, rather than other sirtuins, interacts with Fndc5 to decrease Fndc5 acetylation, which reduces Fndc5 ubiquitination and stabilize it. Treatment of AGK2, a selective inhibitor of SIRT2, blocked the therapeutic action of NR against NAFLD pathologies and NR-induced Fndc5 deubiquitination/deacetylation. At last, we identified that the lysine sites K127/131 and K185/187/189 of Fndc5 may contribute to the SIRT2-dependent deacetylation and deubiquitination of Fndc5.

Conclusions: The findings from this research for the first time demonstrate that NAD+-boosting therapy reverses NAFLD by regulating SIRT2-deppendent Fndc5 deacetylation and deubiquitination, which results in a stimulation of Fndc5/irisin, a novel exerkine. These results suggest that Fndc5/irisin may be a potential nexus between physical exercise and NAD+-boosting therapy in metabolic pathophysiology.

Keywords: Fndc5, irisin, NAD+, SIRT2, nonalcoholic fatty liver disease, physical exercise