Identification of the salusin-β receptor using proteoliposomes embedded with endogenous membrane proteins

Overexpression of salusin‑β downregulates adipoR1 expression to prevent fatty acid oxidation in HepG2 cells

Salusin‑β 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 salusin‑β and adipoR1, and their underlying mechanisms of action, currently remain unclear. In the present study, lentiviral vectors designed to overexpress salusin‑β or knock down salusin‑β expression were used in 293T and HepG2 cells. Semi‑quantitative PCR was performed to investigate the relationship between salusin‑β and adipoR1 mRNA expression in 293T cells. Western blotting was used to assess the protein expression levels of adipoR1, adenosine monophosphate‑activated protein kinase (AMPK), acetyl‑CoA carboxylase (ACC) and carnitine palmitoyl transferase 1A (CPT‑1A) 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 salusin‑β overexpression downregulated adipoR1 expression and inhibited the phosphorylation of AMPK and ACC, which led to decreased CPT‑1A protein expression. By contrast, salusin‑β knockdown increased adipoR1 expression and promoted the phosphorylation of AMPK and ACC, which conversely enhanced CPT‑1A protein expression. Treatment with adipoR1 agonist, AdipoRon, reversed the effects of salusin‑β overexpression. In addition, salusin‑β overexpression enhanced intracellular lipid accumulation in HepG2 cells induced by free fatty acid treatment. These findings highlighted the potential regulatory role of salusin‑β in adipoR1‑mediated signaling pathways. To conclude, the present study provided insights into the regulation of fatty acid metabolism by the liver. In particular, salusin‑β may serve as a potential target for the therapeutic intervention of metabolic disorders of lipids.

ANGT_HUMAN[448–462], an Anorexigenic Peptide Identified using Plasma Peptidomics

The discovery of bioactive peptides is an important research target that enables the elucidation of the pathophysiology of human diseases and provides seeds for drug discovery. Using a large number of native peptides previously identified using plasma peptidomics technology, we sequentially synthesized selected sequences and subjected them to functional screening using human cultured cells. A 15-amino-acid residue proangiotensinogen-derived peptide, designated ANGT_HUMAN[448–462], elicited cellular responses and bound to cultured human cells. Synthetic fluorescent-labeled and biotinylated ANGT_HUMAN[448–462] peptides were rendered to bind to cell- and tissue-derived proteins and peptide-cell protein complexes were retrieved and analyzed using liquid chromatography-tandem mass spectrometry, revealing the β-subunit of ATP synthase as its cell-surface binding protein. Because ATP synthase mediates the effects of anorexigenic peptides, the ability of ANGT_HUMAN[448–462] to modulate eating behavior in mice was investigated. Both intraperitoneal and intracerebroventricular injections of low doses of ANGT_HUMAN[448–462] suppressed spontaneous food and water intake throughout the dark phase of the diurnal cycle without affecting locomotor activity. Immunoreactive ANGT_HUMAN[448–462], distributed throughout human tissues and in human-derived cells, is mostly co-localized with angiotensin II and is occasionally present separately from angiotensin II. In this study, an anorexigenic peptide, ANGT_HUMAN[448–462], was identified by exploring cell surface target proteins of the human native peptides identified using plasma peptidomics.

Knockdown of Salusin-β Improves Cardiovascular Function in Myocardial Infarction-Induced Chronic Heart Failure Rats

Salusin-β is a biologically active peptide with 20 amino acids that exerts several cardiovascular activity-regulating effects, such as regulating vascular endothelial function and the proliferation of vascular smooth muscle cells. However, the regulatory effects of salusin-β in myocardial infarction-induced chronic heart failure (CHF) are still unknown. The current study is aimed at investigating the effects of silencing salusin-β on endothelial function, cardiac function, vascular and myocardial remodeling, and its underlying signaling pathways in CHF rats induced by coronary artery ligation. CHF and sham-operated (Sham) rats were subjected to tail vein injection of adenoviral vectors encoding salusin-β shRNA or a control-shRNA. The coronary artery (CA), pulmonary artery (PA), and mesenteric artery (MA) were isolated from rats, and isometric tension measurements of arteries were performed. Compared with Sham rats, the plasma salusin-β, leptin and visfatin levels and the salusin-β protein expression levels of CA, PA, and MA were increased, while the acetylcholine- (ACh-) induced endothelium-dependent vascular relaxation of CA, PA, and MA was attenuated significantly in CHF rats and was improved significantly by salusin-β gene knockdown. Salusin-β knockdown also improved cardiac function and vascular and myocardial remodeling, increased endothelial nitric oxide synthase (eNOS) activity and nitric oxide (NO) levels, and decreased NAD(P)H oxidase activity, NOX-2 and NOX-4 expression, and reactive oxygen species (ROS) levels in arteries in CHF rats. The effects of salusin-β knockdown in CHF rats were attenuated significantly by pretreatment with the NOS inhibitor L-NAME. These results indicate that silencing salusin-β contributes to the improvement of endothelial function, cardiac function, and cardiovascular remodeling in CHF by inhibiting NAD(P)H oxidase-ROS generation and activating eNOS-NO production.

GIP_HUMAN[22-51] is a new proatherogenic peptide identified by native plasma peptidomics

We recently established a new plasma peptidomic technique and comprehensively identified a large number of low-molecular weight and low-abundance native peptides using a single drop of human plasma. To discover a novel polypeptide that potently modulates the cardiovascular system, we performed a bioinformatics analysis of the large-scale identification results, sequentially synthesized the selected peptide sequences, tested their biological activities, and identified a 30-amino-acid proatherogenic peptide, GIP_HUMAN[22-51], as a potent proatherosclerotic peptide hormone. GIP_HUMAN[22-51] has a common precursor with the glucose-dependent insulinotropic polypeptide (GIP) and is located immediately N-terminal to GIP. Chronic infusion of GIP_HUMAN[22-51] into ApoE-/- mice accelerated the development of aortic atherosclerotic lesions, which were inhibited by co-infusions with an anti-GIP_HUMAN[22-51] antibody. GIP_HUMAN[22-51] increased the serum concentrations of many inflammatory and proatherogenic proteins, whereas neutralising antibodies reduced their levels. GIP_HUMAN[22-51] induced IκB-α degradation and nuclear translocation of NF-κB in human vascular endothelial cells and macrophages. Immunoreactive GIP_HUMAN[22-51] was detected in human tissues but there was no colocalization with the GIP. The plasma GIP_HUMAN[22-51] concentration in healthy humans determined using a stable-isotope tagged peptide was approximately 0.6 nM. This study discovered a novel endogenous proatherogenic peptide by using a human plasma native peptidomic resource.

Suprabasin-derived bioactive peptides identified by plasma peptidomics

Identification of low-abundance, low-molecular-weight native peptides using non-tryptic plasma has long remained an unmet challenge, leaving potential bioactive/biomarker peptides undiscovered. We have succeeded in efficiently removing high-abundance plasma proteins to enrich and comprehensively identify low-molecular-weight native peptides using mass spectrometry. Native peptide sequences were chemically synthesized and subsequent functional analyses resulted in the discovery of three novel bioactive polypeptides derived from an epidermal differentiation marker protein, suprabasin. SBSN_HUMAN[279-295] potently suppressed food/water intake and induced locomotor activity when injected intraperitoneally, while SBSN_HUMAN[225-237] and SBSN_HUMAN[243-259] stimulated the expression of proinflammatory cytokines via activation of NF-κB signaling in vascular cells. SBSN_HUMAN[225-237] and SBSN_HUMAN[279-295] immunoreactivities were present in almost all human organs analyzed, while immunoreactive SBSN_HUMAN[243-259] was abundant in the liver and pancreas. Human macrophages expressed the three suprabasin-derived peptides. This study illustrates a new approach for discovering unknown bioactive peptides in plasma via the generation of peptide libraries using a novel peptidomic strategy.

A TOR2A Gene Product: Salusin-β Contributes to Attenuated Vasodilatation of Spontaneously Hypertensive Rats

PURPOSE

Attenuated vasodilatation of small arteries is a hallmark feature of hypertension. Salusin-β, which is a TOR2A gene product and an important vasoactive peptide, has a close relationship with cardiovascular disease. This study aimed to determinate the roles of salusin-β in vasodilatation, and its signal pathways in Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR).

METHODS

Isometric tension experiments were performed. Vasodilatation was induced by acetylcholine (ACh) or sodium nitroprusside (SNP).

RESULTS

Plasma salusin-β levels and their protein expressions in coronary artery (CA), mesenteric artery (MA), and pulmonary artery (PA) of SHR were much higher than that of WKY. Intravenous injection of salusin-β increased arterial blood pressure in SHR, while anti-salusin-β IgG decreased it. Salusin-β further deteriorated, while anti-salusin-β IgG improved, the attenuated ACh-induced relaxation, the decreased nitric oxide (NO) level, and endothelial nitric oxide synthase (eNOS) activity in arteries of SHR, and salusin-β had no significant effect on SNP-induced relaxation. The NAD(P)H oxidase activity and reactive oxygen species (ROS) level in arteries of SHR were much higher than that of WKY, which was further increased by salusin-β but reduced by anti-salusin-β IgG. ROS scavenger NAC or antioxidant apocynin significantly inhibited, while SOD inhibitor DETC aggravated, the effects of salusin-β, and the eNOS inhibitor L-NAME inhibited the effects of anti-salusin-β IgG.

CONCLUSIONS

These results indicated that enhanced salusin-β activity is involved in attenuated endothelium-dependent vasodilatation pathogenesis in SHR by activating NAD(P)H oxidase derived ROS generation and inhibiting eNOS activation and NO release.

Molecular form and concentration of serum α2-macroglobulin in diabetes

α₂-Macroglobulin is a highly abundant serum protein involved in the development of atherosclerosis and cardiac hypertrophy. However, its circulating molecular form and exact concentrations in human health/diseases are not known. Blue native-polyacrylamide gel electrophoresis of human serum was used to confirm the native conformation of α₂-macroglobulin. We created an enzyme-linked immunosorbent assay suitable for quantifying its circulating molecular form and undertook a cross-sectional study to measure its serum levels in 248 patients with diabetes mellitus and 59 healthy volunteers. The predominant circulating molecular form of α₂-macroglobulin was the tetramer, whereas its dimer was detectable in patients with high serum levels of α₂-macroglobulin. The serum α₂-macroglobulin concentration was not associated with glycated hemoglobin or any other glycemic variable as evaluated from 48-h continuous glucose monitoring, but showed close correlation with left ventricular posterior wall thickness, carotid artery intima-media thickness, urinary albumin:creatinine ratio (ACR) and brachial–ankle pulse wave velocity (baPWV). Multivariate analysis revealed only the ACR and baPWV to be independent variables influencing serum levels of α₂-macroglobulin. Thus, an increased ACR and baPWV are associated with higher serum concentrations of α₂-macroglobulin, and the latter may contribute to the mechanism by which albuminuria increases the risk of developing cardiovascular diseases.