Salusin­α alleviates lipid metabolism disorders via regulation of the downstream lipogenesis genes through the LKB1/AMPK pathway.

Lipid metabolism disorders are a major cause of several chronic metabolic diseases which seriously affect public health. Salusin­α, a vasoactive peptide, has been shown to attenuate lipid metabolism disorders, although its mechanism of action has not been reported. To investigate the effects and potential mechanisms of Salusin­α on lipid metabolism, Salusin­α was overexpressed or knocked down using lentiviral vectors. Hepatocyte steatosis was induced by free fatty acid (FFA) after lentiviral transfection into HepG2 cells. The degree of lipid accumulation was assessed using Oil Red O staining and by measuring several biochemical indices. Subsequently, bioinformatics was used to analyze the signaling pathways that may have been involved in lipid metabolism disorders. Finally, semi­quantitative PCR and western blotting were used to verify the involvement of the liver kinase B1 (LKB1)/AMPK pathway. Compound C, an inhibitor of AMPK, was used to confirm this mechanism's involvement further. The results showed that Salusin­α significantly attenuated lipid accumulation, inflammation and oxidative stress. In addition, Salusin­α increased the levels of LKB1 and AMPK, which inhibited the expression of sterol regulatory element binding protein­1c, fatty acid synthase and acetyl­CoA carboxylase. The addition of Compound C abrogated the Salusin­α­mediated regulation of AMPK on downstream signaling molecules. In summary, overexpression of Salusin­α activated the LKB1/AMPK pathway, which in turn inhibited lipid accumulation in HepG2 cells. This provides insights into the potential mechanism underlying the mechanism by which Salusin­α ameliorates lipid metabolism disorders while identifying a potential therapeutic target.

Overexpression of salusin­ß downregulates adipoR1 expression to prevent fatty acid oxidation in HepG2 cells.

Salusin­ß and adiponectin receptor 1 (adipoR1) serve important roles in the development of certain cardiovascular diseases and lipid metabolism. However, to the best of our knowledge, the relationship between salusin­ß and adipoR1, and their underlying mechanisms of action, currently remain unclear. In the present study, lentiviral vectors designed to overexpress salusin­ß or knock down salusin­ß expression were used in 293T and HepG2 cells. Semi­quantitative PCR was performed to investigate the relationship between salusin­ß and adipoR1 mRNA expression in 293T cells. Western blotting was used to assess the protein expression levels of adipoR1, adenosine monophosphate­activated protein kinase (AMPK), acetyl­CoA carboxylase (ACC) and carnitine palmitoyl transferase 1A (CPT­1A) in transfected HepG2 cells. Simultaneously, HepG2 cells were treated with an adipoR1 inhibitor (thapsigargin) or agonist (AdipoRon) and the resultant changes in the expression levels of the aforementioned proteins were observed. Oil Red O staining and measurements of cellular triglyceride levels were performed to assess the extent of lipid accumulation in HepG2 cells. The results demonstrated that salusin­ß overexpression downregulated adipoR1 expression and inhibited the phosphorylation of AMPK and ACC, which led to decreased CPT­1A protein expression. By contrast, salusin­ß knockdown increased adipoR1 expression and promoted the phosphorylation of AMPK and ACC, which conversely enhanced CPT­1A protein expression. Treatment with adipoR1 agonist, AdipoRon, reversed the effects of salusin­ß overexpression. In addition, salusin­ß overexpression enhanced intracellular lipid accumulation in HepG2 cells induced by free fatty acid treatment. These findings highlighted the potential regulatory role of salusin­ß in adipoR1­mediated signaling pathways. To conclude, the present study provided insights into the regulation of fatty acid metabolism by the liver. In particular, salusin­ß may serve as a potential target for the therapeutic intervention of metabolic disorders of lipids.

Overexpression of salusin­α upregulates AdipoR2 and activates the PPARα/ApoA5/SREBP­1c pathway to inhibit lipid synthesis in HepG2 cells.

Salusin­α and adiponectin, are vasoactive peptides with numerous similar biological effects related to lipid metabolism. Adiponectin has been shown to reduce fatty acid oxidation and to inhibit lipid synthesis of liver cells through its receptor, adiponectin receptor 2 (AdipoR2), but whether salusin­α is able to interact with AdipoR2, was not previously reported. To investigate this, in vitro experiments were carried out. The overexpression and interference recombinant plasmids were constructed with salusin­α. The lentiviral expression systems of salusin­α overexpression and interference were respectively synthesized in 293T cells, and 293T cells were infected with the lentivirus. Finally, the association between salusin­α and AdipoR2 was analyzed by semi­quantitative PCR. Subsequently, HepG2 cells were also infected with these viruses. The expression levels of AdipoR2, peroxisome proliferator­activated receptor­α (PPARα), apolipoprotein A5 (ApoA5) and sterol regulatory element­binding transcription factor 1 (SREBP­1c) were detected by western blotting, and AdipoR2 inhibitor (thapsigargin) and agonist [4­phenyl butyric acid (PBA)] were used to observe the resultant changes in the aforementioned molecules. The results obtained revealed that the overexpression of salusin­α increased the level of AdipoR2 in 293T and HepG2 cells, led to an upregulation of the levels of PPARα and ApoA5, and inhibited the expression of SREBP­1c, whereas the salusin­α interference lentivirus exerted the opposite effects. Notably, thapsigargin inhibited the expression of AdipoR2, PPARα and ApoA5 in HepG2 cells of pHAGE­Salusin­α group, and caused an increase in the level of SREBP­1c, whereas the opposite effects were observed in pLKO.1­shSalusin­α#1 group upon treatment with PBA. Taken together, these data demonstrated that overexpression of salusin­α upregulated AdipoR2, which in turn activated the PPARα/ApoA5/SREBP­1c signaling pathway to inhibit lipid synthesis in HepG2 cells, thereby providing theoretical data on which to base the clinical application of salusin­α as a novel peptide for molecular intervention in fatty liver disease.