Unsaturated Fatty Acids Disrupt Smad Signaling in Gonadotrope Cells Leading to Inhibition of FSHβ Gene Expression

Abstract

Reproductive function is highly dependent on nutritional input. We recently provided evidence that the unsaturated ω6 fatty acid (FA), linoleic acid (linoleic), interferes with transcription and secretion of the gonadotropin LH, highlighting the existence of a lipid sensing in pituitary gonadotropes. Here, we show, using a combination of in vivo and in vitro models, that linoleic differentially regulates Lhb and Fshb expression. Central exposure of rats to linoleic over 7 days was associated with increase of Lhb but not Fshb transcript levels. Consistently, exposure of rat pituitary cells or LβT2 cells to linoleic increased Lhb, whereas it dramatically decreased Fshb transcript levels without affecting its stability. This effect was also induced by ω9 and ω3-polyunsaturated FA but not by saturated palmitic acid. Analysis of the underlying mechanisms in LβT2 cells using small interfering RNA revealed that early growth response protein 1 mediates linoleic stimulation of Lhb expression. Furthermore, we demonstrated that linoleic counteracts activin and bone morphogenetic protein-2 stimulation of Fshb expression. Using Western blotting and Smad-responsive reporter gene assays, linoleic was shown to decrease basal Smad2/3 phosphorylation levels as well as activin- and bone morphogenetic protein-2-dependent activation of Smad, uncovering a new FA-sensitive signaling cascade. Finally, the protein phosphatase magnesium-dependent 1A was shown to mediate linoleic inhibition of basal Smad phosphorylation and Fshb expression, identifying protein phosphatase magnesium-dependent 1A as a new target of FA in gonadotropes. Altogether, this study provides a novel mechanism by which FAs target gene expression and underlines the relevant role of pituitary gonadotropes in mediating the effects of nutritional FA on reproductive function.

Long-chain unsaturated fatty acids reduce the transcriptional activity of the rat follicle-stimulating hormone β-subunit gene

“…Long-chain fatty acids (LCFAs) may act as metabolic signals in the regulation of reproductive functions. This is supported by findings that peripheral or central lipoprivation suppresses pulsatile LH secretion [ 15 , 16 ], and central exposure to linoleic acid increases Lhb mRNA expression levels in rats [ 17 ]. Interestingly, LCFAs are supposed to have some influence on the synthesis and secretion of gonadotropic hormones at the pituitary level, since a free fatty acid (FFA) cocktail directly increases Lhb mRNA levels and suppresses Fshb mRNA levels in the gonadotropic cell line LβT2 [ 18 ] and linoleic acid increases LH release and Lhb mRNA levels in both LβT2 cells and rat primary cultured pituitary cells [ 19 ].…”

“…1 ). In previous studies, the role of LCFAs on the transcription of gonadotropin hormone subunit genes has been examined using concentrations in the range of several hundred micromolars of LCFAs [ 17 , 18 , 19 ]. In this study, however, the low concentration of 10 µM unsaturated LCFAs repressed the expression of Fshb .…”

“…2 ). Previous studies have shown that an FFA cocktail or linoleic acid reduces basal Fshb mRNA levels by disrupting the effects of activin on transcription of Fshb in LβT2 cells [ 17 , 18 ]. LβT2 cells have been reported to produce activin endogenously to maintain basal Fshb expression [ 36 ].…”

“…Garrel et al . [ 17 , 19 ] reported that linoleic acid treatment induced an increase in the Lhb mRNA levels, while it had no effect on Cga mRNA levels in LβT2 cells or rat anterior pituitary cells. The inconsistency may depend on the difference in experimental methods used.…”

Cellular distribution of Egr1 transcription in the male rat pituitary gland

“…These include insulin and fatty acids (Buggs et al 2006, Garrel et al 2014, indicating a potential role in mediating the effects of nutritional status and possibly obesity on reproductive capacity (shown in Brothers et al (2010)). In addition, there is evidence that EGR1 mediates the effects of glucocorticoids/stress at the Lhb gene promoter (Breen et al 2012).…”