Aldosterone Induced Galectin-3 Secretion In Vitro and In Vivo: From Cells to Humans (1)
Aldosterone induces macrophage activation and low grade inflammation, which may play an important role in cardiac fibrosis and myocardial dysfunction. Galectin-3 is a β-galactoside-binding animal lectin which is highly expressed and secreted by macrophages. Galectin-3 has been shown to be involved in fibrosis in various organs, including the lungs, liver, kidneys, and heart.
Galectin-3 was synthesized in the cultured RAW 264.7 cells with aldosterone stimulation in a dose-dependent manner. Aldosterone 10^−5 to 10^−7 M significantly induced galectin-3 secretion. After 12 hours of aldosterone (10^−6 M) stimulation, galectin-3 secretion in the cultured RAW 264.7 cells was significantly increased. Aldosterone 10^−6 M significantly induced galectin-3 mRNA expression in the cultured RAW-264.7 cells.
The secretion of galectin-3 after aldosterone stimulation was inhibited by pretreated with 10^−7 M spironolactone, but not by 10^−7 M RU-486. The secretion of galectin-3 was via mineralocorticoid receptors (MRs) rather than glucocorticoid receptors.
The induced secretion was blocked by LY294002, but not by PD98059, SB203580, Ro318220, or SP600125. This suggested that the induced secretion occurred via the PI3K/Akt pathway. p-Akt Western blotting revealed that the MRs were indeed upstream of the aldosterone-induced Akt phosphorylation. In transcriptional factor analysis, induction of galectin-3 secretion was blocked by the decoy ODN of NF-κB but not the decoy ODN of AP-1. NF-κB nuclear and cytosol Western blotting showed that MRs and PI3K/Akt were upstream of the aldosterone-induced NF-κB activation.
RAW 264.7 cells were pretreated with galectin-3 siRNA or control siRNA in order to knockdown the galectin-3 expression prior to aldosterone stimulation. The conditioned medium was collected and cultured with the human fibroblast cell line 293T. The aldosterone-induced galectin-3 expression was strongly suppressed by galectin-3 siRNA. there was no significant effect of aldosterone-induced galectin-3 on cell growth of the 293T or NIH/3T3 cells. aldosterone-induced galectin-3 significantly increased the expressions of fibronectin and procollagen (I) mRNA of the 293T and NIH/3T3 cells.
A novel signal transduction pathway of galectin-3 secretion by aldosterone in macrophage cell lines, and the impact of galectin-3 on collagen formation.
Galectin-3 interacts with various ligands in the extracellular matrix (ECM), including laminin, synexin, integrins, and collagen.