Differential effects of the charge variants of human follicle-stimulating hormone

Abstract

FSH is synthesized and secreted by the anterior pituitary gland in multiple molecular forms; the release of these isoforms depends on the endocrine status of the donor at the time of sample collection. In the present study, we analysed the possibility that the FSH charge isoforms may exert differential effects at the target cell. Seven FSH isoform mixes were isolated from pooled anterior pituitary glycoprotein extracts by high resolution chromatofocusing, followed by affinity chromatography, which removed nearly 90% of the LH that co-eluted with the FSH isoforms during chromatofocusing. The isoforms (isoform I, pH >7·10; II, pH range 6·60-6·20; III, pH 5·47-5·10; IV, pH 5·03-4·60; V, pH 4·76-4·12; VI, pH 4·05-3·82 and VII, pH <3·80) were then tested for their capacity to stimulate cAMP release, androgen aromatization and tissue-type plasminogen activator (tPA) enzyme activity and cytochrome P450 aromatase, tPA and inhibin -subunit mRNA production by rat granulosa cells in culture. cAMP and oestradiol production were determined by RIA, tPA enzyme activity by SDS-PAGE and zymography and all mRNAs by northern blot hybridization analysis and semiquantitative RT-PCR. All isoforms, with the exception of isoform I, stimulated synthesis and release of cAMP, oestrogen and tPA enzyme activity in a dosedependent manner; the potency of the less acidic isoforms (pH 6·60-4·60) was greater than that exhibited by the more acidic/sialylated analogs (pH 4·76 to <3·80; potencies II>III>IV>V>VII>VI). A similar trend was observed in terms of cytochrome P450 aromatase and tPA mRNA production. In contrast, when FSH-stimulated production of -inhibin mRNA was analysed, isoforms V-VII were significantly more potent (two-to threefold) than the less acidic/sialylated counterparts (II-IV). In contrast to isoforms II-VII (which behaved as FSH agonists), isoform I (elution pH >7·10) completely blocked P450 aromatase and tPA mRNA expression, without altering that of a constitutively expressed gene (glyceraldehyde-3-phosphate dehydrogenase). These results show for the first time that the naturally occurring human FSH isoforms may exhibit differential or even unique effects at the target cell level.

Effect of sialylation and complexity of FSH oligosaccharides on inhibin production by granulosa cells

“…In particular, a differential regulation induced by pituitary FSH charge analogues on inhibin a-subunit expression has been reported using a similar experimental model (Timossi et al 2000). Our results showed that the sialylation degree of rhFSH is involved in the differential secretion of a specific inhibin dimer.…”

Follicle-stimulating hormone isoforms and plasma concentrations of estradiol and inhibin A in dairy cows with ovulatory and non-ovulatory follicles during the first postpartum follicle wave

“…Inhibin A acts at the level of the pituitary to reduce FSH release (19), and locally at the level of the ovary to stimulate thecal androgen 190 production (23), but appears to inhibit granulosa cell estradiol synthesis (24). More acidic FSH isoforms were better at stimulating inhibin- subunit gene expression than less acidic isoforms in vitro (25). Our in vivo observations provide little support for this effect, as the more acidic isoforms were more abundant in the non-ovulatory cows, yet they had lower circulating inhibin…”

“…It has previously been demonstrated that a shift in the FSH isoform distribution occurs prior to ovulation in human beings (13,28) and cattle (10). Though less acidic isoforms have a short half-life in circulation (12), they have potent biological activities at the level of the ovary (11,29), and display a greater 205 capacity to induce aromatase expression than the more acidic isoforms (25). In the current study, we observed an increase in less acidic FSH isoforms during the final stages of follicle development in cows with an ovulatory follicle, associated with significantly greater circulating inhibin A and estradiol concentrations.…”

Structural and Functional Roles of FSH and LH as Glycoproteins Regulating Reproduction in Mammalian Species

“…Interestingly, a study by Timossi et al [104] revealed the relationship between FSH isoform and bioactivity may also be dynamic, with naturally occurring human FSH isoforms observed exhibiting differential or even unique effects at the target cell level.…”