Lipid metabolic reprogramming mediated by circulating Nrg4 alleviates metabolic dysfunction-associated steatotic liver disease during the early recovery phase after sleeve gastrectomy

Abstract

Background: The metabolic benefits of bariatric surgery that contribute to the alleviation of metabolic dysfunction-associated steatotic liver disease (MASLD) have been reported. However, the processes and mechanisms underlying the contribution of lipid metabolic reprogramming after bariatric surgery to attenuating MASLD remain elusive.

Methods: A case-control study was designed to evaluate the impact of three of the most common adipokines (Nrg4, leptin, and adiponectin) on hepatic steatosis in the early recovery phase following sleeve gastrectomy (SG). A series of rodent and cell line experiments were subsequently used to determine the role and mechanism of secreted adipokines following SG in the alleviation of MASLD.

Results: In morbidly obese patients, an increase in circulating Nrg4 levels is associated with the alleviation of hepatic steatosis in the early recovery phase following SG before remarkable weight loss. The temporal parameters of the mice confirmed that an increase in circulating Nrg4 levels was initially stimulated by SG and contributed to the beneficial effect of SG on hepatic lipid deposition. Moreover, this occurred early following bariatric surgery. Mechanistically, gain- and loss-of-function studies in mice or cell lines revealed that circulating Nrg4 activates ErbB4, which could positively regulate fatty acid oxidation in hepatocytes to reduce intracellular lipid deposition.

Conclusions: This study demonstrated that the rapid effect of SG on hepatic lipid metabolic reprogramming mediated by circulating Nrg4 alleviates MASLD.

Keywords: Early postoperative recovery phase; Fatty acid oxidation; Lipid metabolic reprogramming; Metabolic dysfunction-associated steatotic liver disease; Neuregulin-4; Sleeve gastrectomy.

Fig. 1

A Dynamics of BMI between the pre-SG group (n = 40) and post-SG group (n = 40). The color scale is shown on the right. B The image above shows the changes in the CT scan before and after SG. The image below shows the comparison of LSRs across the control, pre-SG, and post-SG groups. Profiles of the adipokines (Nrg4 (C), leptin (D), and adiponectin (E)) in the control, pre-SG, and post-SG groups and correlations between the adipokines and clinical parameters, including the LSR and BMI. The symbol Δ represents the post-SG group minus the pre-SG group. LSR, liver/spleen CT value ratio; BMI, body mass index. The data are presented as the means ± SDs. Each data point represents an individual patient

Fig. 2

A Schematic diagram of rodent model construction and sample collection. B Surgical schematic diagram of sleeve gastrectomy (SG). C Body weight after SG in two groups of mice at 2 and 4 weeks post-surgery. D Representative images of morphology and H&E and Oil Red O staining of liver tissue sections from two groups of mice at 2 weeks and 4 weeks post-surgery. Scale bar, 1 cm or 100 μm. E Comparisons of the relative area of lipid droplets among the different groups of mice at 2 weeks and 4 weeks post-surgery. F–H Serum levels of the adipokines Nrg4 (F), leptin (G), and lipocalin (H) in 2 groups of mice. n = 5. * indicates p < 0.05, ²* indicates p < 0.01, ³* indicates p < 0.001, ⁴* indicates p < 0.0001. The color indicates the compared group. I–K Correlation analysis between adipokine levels and the relative area of lipid droplets

Fig. 3

Gene deletion of Nrg4 increased susceptibility to MASLD and decreased the therapeutic effect of SG. A Schematic diagram of the rodent model construction. B Representative images of mouse liver tissue section morphology and H&E and Oil Red O staining. C Comparisons of the relative area of lipid droplets among the different groups of mice. D Comparisons of the serum Nrg4 concentration among different mouse models. * indicates p < 0.05, ²* indicates p < 0.01, ³* indicates p < 0.001, ⁴* indicates p < 0.0001. The color indicates the compared group. E Correlation analysis between Nrg4 and the relative area of lipid droplets in different mouse models

Fig. 4

A PCA result of sample clustering based on DEGs. B Schematic diagram of the identification of Nrg4-associated genes. C Functional analysis of Nrg4-associated genes

Fig. 5

Characterization of the Nrg4 overexpression system in liver cell lines. A Oil Red O staining was used to analyze the metabolic status of control and Nrg4-overexpressing cells treated with different concentrations of OA. Scale bar, 50 μm. B Quantitative analysis of lipid droplets in panel A. C Cell viability of hepatocytes in panel A. D Western blot analysis of key proteins involved in fatty acid oxidation in control and Nrg4-overexpressing cell lines. * indicates p < 0.05, ²* indicates p < 0.01, ³* indicates p < 0.001, ⁴* indicates p < 0.0001. The color indicates the compared group

Fig. 6

Western blot analysis of key proteins involved in fatty acid oxidation in the MASLD mouse models

Fig. 7

Schematic diagram of the rapid effect of SG on hepatic lipid metabolic reprogramming mediated by circulating Nrg4 for MASLD alleviation