Myocardial
fibrosis is a key pathological change in a variety of
heart diseases contributing to the development of
heart failure, arrhythmias, and
sudden death. Recent studies have shown that
relaxin prevents and reverses cardiac
fibrosis. Endogenous expression of
relaxin was elevated in the setting of
heart disease; the extent of such up-regulation, however, is insufficient to exert compensatory actions, and the mechanism regulating
relaxin expression is poorly defined. In the rat relaxin-1 (RLN1, Chr1) gene promoter region we found presence of repeated
guanine (G)-rich sequences, which allowed formation and stabilization of G-quadruplexes with the addition of a G-quadruplex interactive
ligand berberine. The G-rich sequences and the G-quadruplexes were localized adjacent to the binding motif of signal transducer and activator of transcription (STAT)3, which negatively regulates
relaxin expression. Thus, we hypothesized that the formation and stabilization of G-quadruplexes by
berberine could influence
relaxin expression. We found that
berberine-induced formation of G-quadruplexes did increase
relaxin gene expression measured at
mRNA and
protein levels. Formation of G-quadruplexes significantly reduced STAT3 binding to the promoter of
relaxin gene. This was associated with consequent increase in the binding of
RNA polymerase II and STAT5a to
relaxin gene promoter. In cardiac fibroblasts and rats treated with
angiotensin II,
berberine was found to suppress fibroblast activation,
collagen synthesis, and extent of cardiac
fibrosis through up-regulating
relaxin. The antifibrotic action of
berberine in vitro and in vivo was similar to that by exogenous
relaxin. Our findings document a novel therapeutic strategy for
fibrosis through up-regulating expression of endogenous
relaxin.