Metformin Inhibits Aromatase via an Extracellular Signal-Regulated Kinase-Mediated Pathway

Abstract

Metformin treatment, now widely prescribed in polycystic ovary syndrome, is aimed at correcting the associated insulin resistance, but it has also been shown to directly inhibit ovarian steroidogenesis. The mechanisms, however, by which metformin inhibits estradiol production in human granulosa cells remains unknown. Granulosa luteal cells were incubated with metformin, insulin, or combined metformin and insulin treatment, and aromatase mRNA expression was quantified using real-time RT-PCR. Enzyme activity was assessed by the conversion of (3)H-androstenedione to estrone and estradiol. Metformin's effect on the expression of specific untranslated first exon aromatase promoters was analyzed using semiquantitative PCR. The involvement of MAPK kinase (MEK)/ERK pathway was investigated by immunoblotting for aromatase, phosphorylated, and total ERK-1,2 from cells cultured as above with/without the MEK inhibitor PD98059. Metformin significantly inhibited basal and insulin-stimulated aromatase mRNA expression, with parallel results from the aromatase activity assay and protein assessment. This suppression was via down-regulation of aromatase promoter II, I.3, and 1.4 expression and was reversed by the addition of PD98059. Involvement of the ERK signaling pathway was demonstrated by the significant increase in phosphorylated ERK-1,2 with the combined metformin and insulin treatment. We have shown for the first time in human granulosa cells that metformin signficantly attenuated basal and insulin-stimulated P450 aromatase mRNA expression and activity, via silencing of key promoters. This occurred by activation of MEK/ERK pathway, which negatively regulated aromatase production. This is an important consideration given metformin's widespread use in polycystic ovary syndrome and may further support a possible therapeutic indication in estrogen-dependent breast tumors.

The insulin sensitiser metformin regulates chicken Sertoli and germ cell populations

“…In primary rat Leydig cell culture, the use of a natural AMPK ligand (curcumin; Zang et al 2006) decreases testosterone secretion through a reduction in cholesterol transport into the mitochondria and decreased conversion of progesterone into androstenedione (Svechnikov et al 2009). In females, metformin reduced progesterone and oestradiol (E 2 ) secretion by bovine granulosa cells, via downregulation of proteins involved in steroid production (Tosca et al 2006), and metformin reduced aromatase activity in human granulosa cells (Rice et al 2009). In our model, the decrease in serum testosterone levels was not associated with the overall growth rate of the treated birds, despite that testosterone is associated with muscle development and growth rate (Bhasin et al 2001).…”

Metformin decreases IGF1-induced cell proliferation and protein synthesis through AMP-activated protein kinase in cultured bovine granulosa cells

“…Metformin treatment is now widely prescribed in women with PCOS. Several studies have demonstrated that metformin is able to exert direct effects on the ovary, inhibiting progesterone and estradiol production by human granulosa cells (Mansfield et al 2003, Rice et al 2009). However, the effects and the molecular mechanism of metformin on the proliferation of granulosa cell are unknown.…”

Metformin: A Hopeful Promise in Aging Research

“…Metformin treatment had no effect on disease onset, progression or survival in male SOD1 G93A mice at any dose while eliciting a dose-dependent negative neurological response in females owing to metformin's ability to inhibit estrogen production (Rice et al 2009). Inhibition of estrogen can accelerate ALS progression and reduce life span in female SOD1 G93A mice (Choi et al 2008).…”