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Deletion of Smurf1 attenuates liver steatosis via stabilization of p53

Abstract

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease, characterized by excessive hepatic lipid accumulation. Recently, we demonstrated that Smad ubiquitination regulatory factor 1 (Smurf1) deficiency significantly alleviates mouse hepatic steatosis. However, the mechanism of Smurf1-regulating hepatic lipid accumulation requires further exploration and clarification. Hence, this study explores the potential mechanism of Smurf1 in hepatic steatosis. In this study, hepatic Smurf1 proteins in NAFLD patients and healthy individuals were determined using immunohistochemical staining. Control and NAFLD mouse models were established by feeding Smurf1-knockout (KO) and wild-type mice with either a high-fat diet (HFD) or a chow diet (CD) for eight weeks. Oleic acid (OA)-induced steatotic hepatocytes were used as the NAFLD mode cells. Lipid content in liver tissues was analyzed. Smurf1-MDM2 interaction, MDM2 and p53 ubiquitination, and p53 target genes expression in liver tissues and hepatocytes were analyzed. We found that hepatic Smurf1 is highly expressed in NAFLD patients and HFD-induced NAFLD mice. Its deletion attenuates hepatocyte steatosis. Mechanistically, Smurf1 interacts with and stabilizes mouse double minute 2 (MDM2), promoting p53 degradation. In Smurf1-deficient hepatocytes, an increase in p53 suppresses SREBP-1c expression and elevates the expression of both malonyl-CoA decarboxylase (MCD) and lipin1 (Lpin1), two essential proteins in lipid catabolism. Contrarily, the activities of these three proteins and hepatocyte steatosis are reversed by p53 knockdown in Smurf1-deficient hepatocytes. This study shows that Smurf1 is involved in the pathogenesis of NAFLD by balancing de novo lipid synthesis and lipolysis.

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Fig. 1: Smurf1 is highly expressed in the livers of NAFLD patients.
Fig. 2: Smurf1 depletion attenuates HFD-induced NAFLD.
Fig. 3: Smurf1 downregulates p53 protein by stabilizing MDM2.
Fig. 4: Smurf1 interacts with MDM2 and prevents its ubiquitination and degradation.
Fig. 5: Smurf1 deficiency inhibits p53 ubiquitination dependent on MDM2.
Fig. 6: Smurf1 depletion downregulates SREBP-1c mRNA level and upregulates MCD and Lpin1 mRNA levels in hepatocytes.
Fig. 7: Smurf1 knockout decreases SREBP-1c protein level and increases MCD and Lpin1 protein levels in hepatocytes.
Fig. 8: Smurf1 deficiency downregulates SREBP-1c and upregulates MCD and Lpin1 via the MDM2-p53 pathway.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

Pictures of liver, proteasome, and its degradation products in “Fig. 8D” were created with BioRender (https://app.biorender.com/user/signin).

Funding

This work was supported by the Chinese National Natural Science Foundation Projects (Grant no. 81570515).

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Y.Z., P.X. and W.A. performed study concept and design; W.L. and Y.Z. and P.X. performed development of methodology and writing, review and revision of the paper; W.L., X.Z., C. Z. and L.L. provided acquisition, analysis and interpretation of data, and statistical analysis; W.A., P.X., Y.Z. and J.Z. provided technical and material support. All authors read and approved the final paper.

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Correspondence to Ping Xie, Yutao Zhan or Wei An.

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All procedures involving human liver samples and blood samples were approved by the Ethics Committee of Beijing Youan Hospital and conducted following the principles of the Declaration of Helsinki. Informed consent in writing was obtained from each patient.

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Lin, W., Zhang, X., Zhang, C. et al. Deletion of Smurf1 attenuates liver steatosis via stabilization of p53. Lab Invest (2022). https://doi.org/10.1038/s41374-022-00802-x

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