Fig 1: Diagram of the mechanism.During the pathogenic process, metabolic disorder stimulates FGF21 expression, which through its receptors, activates the ERK/MAPK signaling to induce EGR1 expression. The transcription factor of EGR1 binds to the SLCO4C1 promoter and up-regulates its expression in hepatocytes. The SLCO4C1 functions as a cAMP uptake transporter through the interaction of its Gln463 with cAMP, increasing intracellular cAMP levels that activate the PKA-CREB signaling to feedback down-regulate SREBP1 and downstream ACC1, FASN and SCD1 expression, inhibiting fatty acid synthesis. Accordingly, induction of SLCO4C1 overexpression by AAV8-mediated hepatic SLCO4C1 expression and/or increasing intracellular cAMP levels by the Forskolin treatment effectively prevent and mitigate the progression of MASLD. Therefore, SLCO4C1 is a therapeutic target for MASLD. Conceivably, our findings may aid in the design of therapeutic strategies for treating MASLD.
Fig 2: FGF21 enhances the activation of ERK/MAPK signaling and the activity of transcriptional factor Egr1 binding to the SLCO4C1 promoter in hepatocytes.A Cytokines stimulated Slco4c1 mRNA transcription in primary mouse hepatocytes (B) FGF21 expression levels in different hepatic cell types. C Hepatic Fgf21 mRNA levels in GAN diet fed mice. D Correlation analysis between hepatic Fgf21 and Slco4c1 mRNA levels (n = 6). E, F Treatment with FGF21 stimulated Slco4c1 mRNA and protein expression in primary mouse hepatocytes (G) Schematic illustration of the predicted transcription factors. H The predicted transcription factor mRNA transcripts in the FGF21-treated primary mouse hepatocytes. I, J Hepatic Egr1/2/3 mRNA transcripts and protein expression in the indicated groups of mice. (* p < 0.05, vs. Chow diet-WT) (K) Correlation between hepatic Slco4c1 and Egrs mRNA levels in the GAN diet-fed WT mice (n = 6). L A diagram illustrating the potential EGRs binding sites in human SLCO4C1 proximal promoter and the reporter constructs. M Luciferase activities in 293 T cells co-transfected with truncated SLCO4C1 promoters with, or without, plasmids for EGRs overexpression. N A schematic diagram displayed the EGR1-binding site in the SLCO4C1 promoter and its mutant. O Luciferase activity in 293 T cells co-transfected with the mutant Slco4c1 promoter and the plasmid for EGR1 overexpression. Relative levels of Egr1 mRNA (P) and protein (Q) expression in primary mouse hepatocytes treated with, or without, an ERK/MAPK inhibitor, and after stimulated by FGF21 were examined. R ChIP assay revealed that FGF21 increased Egr1 binding to the Slco4c1-59 promoters in primary mouse hepatocytes. Relative levels Slco4c1 mRNA (S) and protein (T) expression in primary mouse hepatocytes treated with, or without, an ERK/MAPK inhibitor, and after stimulated by FGF21 were examined. A n = 5 and M, O n = 3, Biological replicates; C, I, J Each dot represents one mouse sample; Statistics: unpaired two-tailed Student’s t test. R: n = 3 and E, F, H, P, Q, S, T n = 5, Biological replicates; Statistics: one-way ANOVA test, Multiple comparisons. *p < 0.05, **p < 0.01, *** p < 0.001, **** p < 0.0001. F: *p < 0.05 vs. FGF21 0 μg/ml; #p < 0.05 vs. FGF21 0.1 μg/ml. Q, T: *p < 0.05 vs. FGF21 0 μg/ml; #p < 0.05 vs. FGF21 1 μg/ml. All data statistics are presented as mean ± SD and 95% confidence interval.
Supplier Page from Sino Biological, Inc. for Human FGF21 Protein