Endothelin‐1 inhibits TNFα‐induced iNOS expression in 3T3‐F442A adipocytes

Abstract

1 Endothelin-1 (ET-1) and tumor necrosis factor a (TNFa) by their action on adipocytes have been independently linked to the pathogenesis of insulino-resistance. In isolated adipocytes, TNFa induces the expression of the inducible nitric oxide synthase (iNOS). The purpose of the present work was, in the 3T3-F442A adipocyte cell line, to characterise TNFa-induced iNOS expression and to determine whether or not ET-1 could influence TNFa-induced iNOS expression and NO production. 2 In differentiated 3T3-F442A, treatment with TNFa (20 ng ml À1) induced the expression of a functional iNOS as demonstrated by nitrite assay, Western blot, reverse transcription -polymerase chain reaction and Northern blot analysis. TNFa-induced iNOS expression requires nuclear factor kB activation, but does not necessitate the activation of the PI-3 kinase/Akt and P38 -MAP kinase pathways. 3 ET-1, but not ET-3, inhibited the TNFa-induced expression of iNOS protein and mRNA as well as nitrite production. The effects of ET-1 were blocked by a specific ETA (BQ123, pA 2 7.4) but not by a specific ETB receptor antagonist (BQ788). 3T3-F442A adipocytes express the mRNAs for prepro-ET-1 and the ET-A receptor subtype, but not for the ET-B subtype. 4 The inhibitory effect of ET-1 was not affected by bisindolylmaleimide, SB 203580 or indomethacin, inhibitors of protein kinase C, p38-MAP kinase and cyclooxygenase, respectively, and was not associated with cAMP production. However, the effect of ET-1 was partially reversed by wortmannin, suggesting the involvement of PI3 kinase in the transduction signal of ET-1. 5 Differentiated 3T3-F442A adipocytes did not release ET-1 with or without exposure to TNFa, although the mRNA for preproET-1 was detected in both pre-and differentiated adipocytes. 6 Thus, these results confirm that adipocytes are a target for circulating ET-1 and demonstrate that the activation of the ETA receptor subtype can prevent TNFa-induced iNOS expression.

Heparin-Binding Epidermal Growth Factor-Like Growth Factor Inhibits Cytokine-Induced NF-κB Activation and Nitric Oxide Production via Activation of the Phosphatidylinositol 3-Kinase Pathway

“…We have used the PI3K inhibitor LY294002 to demonstrate that HB-EGF-mediated activation of PI3K is necessary for HB-EGF-induced suppression of NF-B activation and NO production induced by a combination of proinflammatory cytokines. The present demonstration that PI3K inhibition prevents the effects of HB-EGF on NF-B activation and NO production is reminiscent of the report demonstrating that endothelin-1-induced inhibition of iNOS expression in adipocytes is dependent on PI3K activation (40). Additionally, inhibition of PI3K induced the expression of iNOS in LPS stimulated microglial cells (8,9).…”

Maturation of the expression of adrenomedullin, endothelin-1 and nitric oxide synthases in adipose tissues from childhood to adulthood

“…It has been shown that ET-1 inhibits the induction of iNOS mRNA and protein by tumor necrosis factor alpha in adipocytes. 31 In a former study, the expression of iNOS in subcutaneous tissue was found to be 10-fold lower than eNOS, while iNOS protein was not detected in lean persons and only at low concentrations in obese patients, 23 nNOS being undetectable. Our iNOS levels were comparable to those of eNOS, which might be due to the operative setting (general anesthesia, laparotomy).…”

Nitrite augments glucose uptake in adipocytes through the protein kinase A-dependent stimulation of mitochondrial fusion

“…However, this concentration may increase significantly in inflammatory conditions or after exercise (51). For example, a greater than five-fold increase in adipocyte nitrite concentration has been reported after cytokine stimulation of iNOS (52). In these chronic inflammatory conditions, tissue nitrite concentration may approach the levels used in this study (50–100μM).…”