Endothelin-1 induces lipolysis through activation of the GC/cGMP/Ca2+/ERK/CaMKIII pathway in 3T3-L1 adipocytes.

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide produced and secreted mainly by endothelial cells. Recent studies indicate that ET-1 can regulate lipid metabolism, which may increase the risk of insulin resistance. Our previous studies revealed that ET-1 induced lipolysis in adipocytes, but the underlying mechanisms were unclear. 3T3-L1 adipocytes were used to investigate the effect of ET-1 on lipolysis and the underlying mechanisms. Glycerol levels in the incubation medium and hormone-sensitive lipase (HSL) phosphorylation were used as indices for lipolysis. ET-1 significantly increased HSL phosphorylation and lipolysis, which were completely inhibited by ERK inhibitor (PD98059) and guanylyl cyclase (GC) inhibitor (LY83583). LY83583 reduced ET-1-induced ERK phosphorylation. A Ca2+-free medium and PLC inhibitor caused significant decreases in ET-1-induced lipolysis as well as ERK and HSL phosphorylation, and IP3 receptor activator (D-IP3) increased lipolysis. ET-1 increased cGMP production, which was not affected by depletion of extracellular Ca2+. On the other hand, LY83583 diminished the ET-1-induced Ca2+ influx. Transient receptor potential vanilloid-1 (TRPV-1) antagonist and shRNA partially inhibited ET-1-induced lipolysis. ET-1-induced lipolysis was completely suppressed by CaMKIII inhibitor (NH-125). These results indicate that ET-1 stimulates extracellular Ca2+ entry and activates the intracellular PLC/IP3/Ca2+ pathway through a cGMP-dependent pathway. The increased cytosolic Ca2+ that results from ET-1 treatment stimulates ERK and HSL phosphorylation, which subsequently induces lipolysis. ET-1 induces HSL phosphorylation and lipolysis via the GC/cGMP/Ca2+/ERK/CaMKIII signaling pathway in 3T3-L1 adipocytes.

The phosphatase activity of soluble epoxide hydrolase regulates ATP-binding cassette transporter-A1-dependent cholesterol efflux.

The contribution of soluble epoxide hydrolase (sEH) to atherosclerosis has been well defined. However, less is understood about the role of sEH and its underlying mechanism in the cholesterol metabolism of macrophages. The expression of sEH protein was increased in atherosclerotic aortas of apolipoprotein E-deficient mice, primarily in macrophage foam cells. Oxidized low-density lipoprotein (oxLDL) increased sEH expression in macrophages. Genetic deletion of sEH (sEH-/- ) in macrophages markedly exacerbated oxLDL-induced lipid accumulation and decreased the expression of ATP-binding cassette transporters-A1 (ABCA1) and apolipoprotein AI-dependent cholesterol efflux following oxLDL treatment. The down-regulation of ABCA1 in sEH-/- macrophages was due to an increase in the turnover rate of ABCA1 protein but not in mRNA transcription. Inhibition of phosphatase activity, but not hydrolase activity, of sEH decreased ABCA1 expression and cholesterol efflux following oxLDL challenge, which resulted in increased cholesterol accumulation. Additionally, oxLDL increased the phosphatase activity, promoted the sEH-ABCA1 complex formation and decreased the phosphorylated level of ABCA1 at threonine residues. Overexpression of phosphatase domain of sEH abrogated the oxLDL-induced ABCA1 phosphorylation and further increased ABCA1 expression and cholesterol efflux, leading to the attenuation of oxLDL-induced cholesterol accumulation. Our findings suggest that the phosphatase domain of sEH plays a crucial role in the cholesterol metabolism of macrophages.

Adipocytes play an etiological role in the podocytopathy of high-fat diet-fed rats.

Obesity is a risk factor that promotes progressive kidney disease. Studies have shown that an adipocytokine imbalance contributes to impaired renal function in humans and animals, but the underlying interplay between adipocytokines and renal injury remains to be elucidated. We aimed to investigate the mechanisms linking obesity to chronic kidney disease. We assessed renal function in high-fat (HF) diet-fed and normal diet-fed rats, and the effects of preadipocyte- and adipocyte-conditioned medium on cultured podocytes. HF diet-fed and normal diet-fed Sprague Dawley rats were used to analyze the changes in plasma BUN, creatinine, urine protein and renal histology. Additionally, podocytes were incubated with preadipocyte- or adipocyte-conditioned medium to investigate the effects on podocyte morphology and protein expression. In the HF diet group, 24 h urinary protein excretion (357.5 ± 64.2 mg/day vs 115.9 ± 12.4 mg/day, P < 0.05) and the urine protein/creatinine ratio were significantly higher (1.76 ± 0.22 vs 1.09 ± 0.15, P < 0.05), increased kidney weight (3.54 ± 0.04 g vs 3.38 ± 0.04 g, P < 0.05) and the glomerular volume and podocyte effacement increased by electron microscopy. Increased renal expression of desmin and decreased renal expression of CD2AP and nephrin were also seen in the HF diet group (P < 0.05). Furthermore, we found that adipocyte-conditioned medium-treated podocytes showed increased desmin expression and decreased CD2AP and nephrin expression compared with that in preadipocyte-conditioned medium-treated controls (P < 0.05). These findings show that adipocyte-derived factor(s) can modulate renal function. Adipocyte-derived factors play an important role in obesity-related podocytopathy.

Chronic endothelin-1 infusion causes adipocyte hyperplasia in rats.

OBJECTIVE: The aim of this study was to investigate the regulatory mechanism of endothelin-1 (ET-1), an endothelium-derived vasoconstrictor, on adipogenesis in vitro and in vivo. METHODS: 3T3-L1 preadipocytes were used to explore the mechanisms mediating ET-1 actions on preadipocyte proliferation and adipocyte differentiation. To investigate the in vivo effect of ET-1, male Sprague-Dawley rats were infused with ET-1 or saline for 4 weeks via intraperitoneally implanted osmotic pumps, and the fat pad weight and adipocyte size of adipose tissues were measured. RESULTS: ET-1 stimulated preadipocyte proliferation and increased the cell number at the mitotic clonal expansion stage of adipocyte differentiation via the endothelin A receptor (ETAR) and activation of the protein kinase C (PKC) pathway. ET-1, via ETAR, inhibited adipocyte differentiation partially through an ERK-dependent pathway. Furthermore, no significant difference in the body weight and fat pad weight was observed in either ET-1- or saline-infused rats. Compared with saline-infused rats, the adipocyte cell number was significantly increased but the adipocyte size was significantly decreased in ET-1-infused rats. CONCLUSIONS: Chronic ET-1 infusion increased the number of small adipocytes without the change of white adipose tissue mass in rats, which were associated with ET-1-stimulated preadipocyte proliferation, but not ET-1-suppressed adipocyte differentiation.

Resistin induces monocyte-endothelial cell adhesion by increasing ICAM-1 and VCAM-1 expression in endothelial cells via p38MAPK-dependent pathway.

Resistin, firstly reported as an adipocyte-specific hormone, is suggested to be an important link between obesity and diabetes. Recent studies have suggested an association between resistin and atherogenic processes. The adhesion of circulating monocytes to endothelial cells is a critical step in the early stages of atherosclerosis. The purpose of the present study was to investigate the effect of resistin on the adhesion of THP-1 monocytes to human umbilical vein endothelial cells (HUVECs) and the underlying mechanism. Our results showed that resistin caused a significant increase in monocyte adhesion. In exploring the underlying mechanisms of resistin action, we found that resistin-induced monocyte adhesion was blocked by inhibition of p38MAPK activation using SB203580 and SB202190. Furthermore, resistin increased the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) by HUVECs and these effects were also p38MAPK-dependent. Resistin-induced monocyte adhesion was also blocked by monoclonal antibodies against ICAM-1 and VCAM-1. Taken together, these results show that resistin increases both the expression of ICAM-1 and VCAM-1 by endothelial cells and monocyte adhesion to HUVECs via p38MAPK-dependent pathways.

Short-term regulation of tumor necrosis factor-alpha-induced lipolysis in 3T3-L1 adipocytes is mediated through the inducible nitric oxide synthase/nitric oxide-dependent pathway.

TNF-alpha has several effects on adipocytes that may be related to the development of type 2 diabetes in obese subjects. Many studies demonstrated that long-term treatment with TNF-alpha increases lipolysis in adipocytes. However, the short-term (<4 h) effects of TNF-alpha on lipolysis have not been well investigated. The aim of this study was to investigate the short-term regulatory mechanism of TNF-alpha-induced lipolysis in 3T3-L1 adipocytes. Well-differentiated 3T3-L1 adipocytes were used. Lipolysis was determined by measuring glycerol release. Expression of inducible nitric oxide (iNOS) and nitric oxide (NO) production were measured, respectively, by Western blots and the Griess reagent. A selective iNOS inhibitor (s-ethylisothiourea . HBr), an adenylyl cyclase inhibitor (SQ22536), and a guanylyl cyclase inhibitor (LY83583) were used to investigate the involvement of iNOS, cAMP, and cGMP in TNF-alpha-induced lipolysis. Transient transfection with iNOS short hairpin RNA was performed to confirm the involvement of iNOS in TNF-alpha-induced lipolysis. Phosphorylation of hormone-sensitive lipase (HSL) was measured by immunoprecipitation and Western blotting. Results showed that short-term TNF-alpha treatment significantly increased lipolysis, iNOS expression, and NO production in a time- and dose-dependent manner. Furthermore, treatment with the NO donor S-nitroso-N-acetylpenicillamine also stimulated lipolysis and HSL phosphorylation in 3T3-L1 adipocytes. Moreover, pretreatment with inhibitors of iNOS and guanylate cyclase, but not an adenylate cyclase inhibitor, abolished TNF-alpha-induced lipolysis and HSL phosphorylation. Suppression of TNF-alpha-induced iNOS expression using short hairpin RNA significantly reduced TNF-alpha-induced lipolysis. In conclusion, short-term TNF-alpha treatment induces lipolysis in 3T3-L1 adipocytes by increasing iNOS expression and NO production, which activates the guanylyl cyclase/cGMP-dependent pathway and induces phosphorylation of HSL.