Carbohydrate complexity and proportion of serum FSH isoforms reflect pituitary-ovarian activity in perimenopausal women and depot medroxyprogesterone acetate users

Heterogeneity and Dynamics of Vasculature in the Endocrine System During Aging and Disease

The endocrine system consists of several highly vascularized glands that produce and secrete hormones to maintain body homeostasis and regulate a range of bodily functions and processes, including growth, metabolism and development. The dense and highly vascularized capillary network functions as the main transport system for hormones and regulatory factors to enable efficient endocrine function. The specialized capillary types provide the microenvironments to support stem and progenitor cells, by regulating their survival, maintenance and differentiation. Moreover, the vasculature interacts with endocrine cells supporting their endocrine function. However, the structure and niche function of vasculature in endocrine tissues remain poorly understood. Aging and endocrine disorders are associated with vascular perturbations. Understanding the cellular and molecular cues driving the disease, and age-related vascular perturbations hold potential to manage or even treat endocrine disorders and comorbidities associated with aging. This review aims to describe the structure and niche functions of the vasculature in various endocrine glands and define the vascular changes in aging and endocrine disorders.

Recombinant FSH glycoforms are bioactive in mouse preantral ovarian follicles

Female reproductive aging is characterized by a rise in follicle-stimulating hormone (FSH) levels during peri-menopause. N-linked glycans are co-translationally attached to the Asn7 and Asn24 residues on the FSHβ subunit. Differences in the number of N-glycans on the FSHβ subunit result in distinct glycoforms: hypo-glycosylated (FSH21/18, glycans absent on either Asn24 or Asn7, respectively) or fully-glycosylated (FSH24, glycans present on both Asn7 and Asn24). The relative abundance of FSH glycoforms changes with advanced reproductive age, shifting from predominantly FSH21/18 in younger women to FSH24 in older women. Previous in vitro studies in granulosa cell lines and in vivo studies using Fshb-null mice showed these glycoforms elicit differential bioactivities. However, the direct effects of FSH glycoforms on the mouse ovarian follicle have not yet been determined. In this study, we isolated secondary follicles from pre-pubertal mice and treated them with 20- or 100 ng/mL purified recombinant FSH glycoforms for 1 h or 18-20 h. Analysis of phosphorylated PKA substrates showed that glycoforms were bioactive in follicles following 1-h treatment, although differential bioactivity was only observed with the 100 ng/mL dose. Treatment of follicles with 100 ng/mL of each glycoform also induced distinct expression patterns of FSH-responsive genes as assessed by qPCR, consistent with differential function. Our results, therefore, indicate that FSH glycoforms are bioactive in isolated murine follicles.

In vitro ovarian follicle growth: a comprehensive analysis of key protocol variables†

Folliculogenesis is a complex process that requires integration of autocrine, paracrine, and endocrine factors together with tightly regulated interactions between granulosa cells and oocytes for the growth and survival of healthy follicles. Culture of ovarian follicles is a powerful approach for investigating folliculogenesis and oogenesis in a tightly controlled environment. This method has not only enabled unprecedented insight into the fundamental biology of follicle development but also has far-reaching translational applications, including in fertility preservation for women whose ovarian follicles may be damaged by disease or its treatment or in wildlife conservation. Two- and three-dimensional follicle culture systems have been developed and are rapidly evolving. It is clear from a review of the literature on isolated follicle culture methods published over the past two decades (1980-2018) that protocols vary with respect to species examined, follicle isolation methods, culture techniques, culture media and nutrient and hormone supplementation, and experimental endpoints. Here we review the heterogeneity among these major variables of follicle culture protocols.

Hormonal Regulation of Follicle-Stimulating Hormone Glycosylation in Males

The Follicle-Stimulating Hormone plays an important role in the regulation of gametogenesis. It is synthesized and secreted as a family of glycoforms with differing oligosaccharide structure, biological action, and half-life. The presence of these oligosaccharides is absolutely necessary for the full expression of hormone bioactivity at the level of the target cell. The endocrine milieu modulates the glycosylation of this hormone. During male sexual development a progressive increase in FSH sialylation and in the proportion of glycoforms bearing complex oligosaccharides are the main features in this physiological condition. In late puberty, FSH oligosaccharides are largely processed in the medial- and trans-Golgi cisternae of the gonadotrope and remain without changes throughout adult life. In experimental models, the absence of gonads severely affects FSH sialylation; androgen administration is able to restore the characteristics observed under physiological conditions. The expression of ST6 beta-galactoside alpha-2,6-sialyltransferase 1 is hormonally regulated in the male rat; it decreases after short periods of castration but increases markedly at longer periods of androgen deprivation. Although ST3 beta-galactoside alpha-2,3-sialyltransferase 3 is expressed in the male rat pituitary it is not influenced by changes in the endocrine milieu. The oligosaccharide structure of FSH has an impact on the Sertoli cell endocrine activity. In more advanced stages of Sertoli cell maturation, both sialylation and complexity of the oligosaccharides are involved in the regulation of inhibin B production; moreover, FSH glycoforms bearing incomplete oligosaccharides may enhance the stimulatory effect exerted by gonadal growth factors. In this review, we discuss available information on variation of FSH glycosylation and its hormonal regulation under different physiological and experimental conditions, as well as the effect on Sertoli cell endocrine activity.

Role of FSH glycan structure in the regulation of Sertoli cell inhibin production

Variations in follicle-stimulating hormone (FSH) carbohydrate composition and structure are associated with important structural and functional changes in Sertoli cells (SCs) during sexual maturation. The aim of the present study was to investigate the impact of FSH oligosaccharide structure and its interaction with gonadal factors on the regulation of monomeric and dimeric inhibin production at different maturation stages of the SC. Recombinant human FSH (rhFSH) glycosylation variants were isolated according to their sialylation degree (AC and BA) and complexity of oligosaccharides (CO and HY). Native rhFSH stimulated inhibin α-subunit (Pro-αC) but did not show any effect on inhibin B (INHB) production in immature SCs isolated from 8-day-old rats. Activin A stimulated INHB and had a synergistic effect on FSH to stimulate Pro-αC. The less acidic/sialylated rhFSH charge analogues, BA, were the only charge analogue mix that stimulated INHB as well as the most potent stimulus for Pro-αC production. Native rhFSH stimulated both Pro-αC and INHB in SCs at a more advanced maturation stage, isolated from 20-day-old rats. In these cells, all rhFSH glycosylation variants increased INHB and Pro-αC production, even in the presence of growth factors. The BA preparation exerted a more marked stimulatory effect on INHB and Pro-αC than the AC. Glycoforms bearing high mannose and hybrid-type oligosaccharides, HY, stimulated INHB and Pro-αC more effectively than those bearing complex oligosaccharides, CO, even in the presence of gonadal growth factors. These findings demonstrate the modulatory effect of FSH oligosaccharide structure on the regulation of inhibin production in the male gonad.

Evaluation of in vivo bioactivities of recombinant hypo- (FSH21/18) and fully- (FSH24) glycosylated human FSH glycoforms in Fshb null mice

The hormone - specific FSHβ subunit of the human FSH heterodimer consists of N-linked glycans at Asn⁷ and Asn²⁴ residues that are co-translationally attached early during subunit biosynthesis. Differences in the number of N-glycans (none, one or two) on the human FSHβ subunit contribute to macroheterogeneity in the FSH heterodimer. The resulting FSH glycoforms are termed hypo-glycosylated (FSH^21/18, missing either an Asn²⁴ or Asn⁷ N-glycan chain on the β - subunit, respectively) or fully glycosylated (FSH²⁴, possessing of both Asn⁷ and Asn²⁴ N-linked glycans on the β - subunit) FSH. The recombinant versions of human FSH glycoforms (FSH^21/18 and FSH²⁴) have been purified and biochemically characterized. In vitro functional studies have indicated that FSH^21/18 exhibits faster FSH- receptor binding kinetics and is much more active than FSH²⁴ in every assay tested to date. However, the in vivo bioactivity of the hypo-glycosylated FSH glycoform has never been tested. Here, we evaluated the in vivo bioactivities of FSH glycoforms in Fshb null mice using a pharmacological rescue approach. In Fshb null female mice, both hypo- and fully-glycosylated FSH elicited an ovarian weight gain response by 48 h and induced ovarian genes in a dose- and time-dependent manner. Quantification by real time qPCR assays indicated that hypo-glycosylated FSH^21/18 was bioactive in vivo and induced FSH-responsive ovarian genes similar to fully-glycosylated FSH²⁴. Western blot analyses followed by densitometry of key signaling components downstream of the FSH-receptor confirmed that the hypo-glycosylated FSH^21/18 elicited a response similar to that by fully-glycosylated FSH²⁴ in ovaries of Fshb null mice. When injected into Fshb null males, hypo-glycosylated FSH^21/18 was more active than the fully-glycosylated FSH²⁴ in inducing FSH-responsive genes and Sertoli cell proliferation. Thus, our data establish that recombinant hypo-glycosylated human FSH^21/18 glycoform elicits bioactivity in vivo similar to the fully-glycosylated FSH. Our studies may have clinical implications particularly in formulating FSH-based ovarian follicle induction protocols using a combination of different human FSH glycoforms.

A human FSHB transgene encoding the double N-glycosylation mutant (Asn(7Δ) Asn(24Δ)) FSHβ subunit fails to rescue Fshb null mice

Follicle-stimulating hormone (FSH) is a gonadotrope-derived heterodimeric glycoprotein. Both the common α- and hormone-specific β subunits contain Asn-linked N-glycan chains. Recently, macroheterogeneous FSH glycoforms consisting of β-subunits that differ in N-glycan number were identified in pituitaries of several species and subsequently the recombinant human FSH glycoforms biochemically characterized. Although chemical modification and in vitro site-directed mutagenesis studies defined the roles of N-glycans on gonadotropin subunits, in vivo functional analyses in a whole-animal setting are lacking. Here, we have generated transgenic mice with gonadotrope-specific expression of either an HFSHB(WT) transgene that encodes human FSHβ WT subunit or an HFSHB(dgc) transgene that encodes a human FSHβ(Asn7Δ 24Δ) double N-glycosylation site mutant subunit, and separately introduced these transgenes onto Fshb null background using a genetic rescue strategy. We demonstrate that the human FSHβ(Asn7Δ 24Δ) double N-glycosylation site mutant subunit, unlike human FSHβ WT subunit, inefficiently combines with the mouse α-subunit in pituitaries of Fshb null mice. FSH dimer containing this mutant FSHβ subunit is inefficiently secreted with very low levels detectable in serum. Fshb null male mice expressing HFSHB(dgc) transgene are fertile and exhibit testis tubule size and sperm number similar to those of Fshb null mice. Fshb null female mice expressing the mutant, but not WT human FSHβ subunit-containing FSH dimer are infertile, demonstrate no evidence of estrus cycles, and many of the FSH-responsive genes remain suppressed in their ovaries. Thus, HFSHB(dgc) unlike HFSHB(WT) transgene does not rescue Fshb null mice. Our genetic approach provides direct in vivo evidence that N-linked glycans on FSHβ subunit are essential for its efficient assembly with the α-subunit to form FSH heterodimer in pituitary. Our studies also reveal that N-glycans on FSHβ subunit are essential for FSH secretion and FSH in vivo bioactivity to regulate gonadal growth and physiology.

Changes in pituitary function with ageing and implications for patient care

The pituitary gland has a role in puberty, reproduction, stress-adaptive responses, sodium and water balance, uterine contractions, lactation, thyroid function, growth, body composition and skin pigmentation. Ageing is marked by initially subtle erosion of physiological signalling mechanisms, resulting in lower incremental secretory-burst amplitude, more disorderly patterns of pituitary hormone release and blunted 24 h rhythmic secretion. Almost all pituitary hormones are altered by ageing in humans, often in a manner dependent on sex, body composition, stress, comorbidity, intercurrent illness, medication use, physical frailty, caloric intake, immune status, level of exercise, and neurocognitive decline. The aim of this article is to critically discuss the mechanisms mediating clinical facets of changes in the hypothalamic-pituitary axis during ageing, and the extent to which confounding factors operate to obscure ageing-related effects.

The glycan structure in recombinant human FSH affects endocrine activity and global gene expression in human granulosa cells

The aim of this study was to analyse the biological response to different recombinant human FSH (rhFSH) glycosylation variants on the endocrine activity and gene expression at whole-genome scale in human granulosa-like tumor cell line, KGN. The effects of differences in rhFSH sialylation and oligosaccharide complexity were determined on steroid hormone and inhibin production. A microarray approach was used to explore gene expression patterns induced by rhFSH glycosylation variants. Set enrichment analysis revealed that hormone sialylation and oligosaccharide complexity in rhFSH differentially affected the expression of genes involved in essential biological processes and molecular functions of KGN cells. The relevance of rhFSH oligosaccharide structure on steroidogenesis was confirmed assessing gene expression by real time-PCR. The results demonstrate that FSH oligosaccharide structure affects expression of genes encoding proteins, growth factors and hormones essential for granulosa cells function.

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

Granulosa cell (GC) inhibin A and B production is regulated by FSH and gonadal factors. This gonadotrophin is released as a mixture of glycoforms, which induce different biological responses in vivo and in vitro. Our aim was to determine the effect of recombinant human FSH (rhFSH) glycosylation variants on inhibin A and B production by rat GCs. Preparative isoelectro focusing was used to isolate more acidic/sialylated (pH <4.00) and less acidic/sialylated (pH >5.00) rhFSH charge analogues. Concanavalin A was used to isolate unbound and firmly bound rhFSH glycoforms on the basis of their oligosaccharide complexity. GCs, obtained from oestrogen-primed immature rats, were cultured with either native rhFSH or its glycosylation variants. Inhibin A and B were determined using specific ELISAs. Results were expressed as mean±s.e.m. Under basal conditions, inhibin A was the predominant dimer produced (inhibin A: 673±55; inhibin B: 80±4 pg/ml). More acidic/sialylated charge analogues stimulated inhibin B production when compared to inhibin A at all doses studied; by contrast, less acidic/sialylated charge analogues stimulated inhibin A production and elicited no effect on inhibin B. Glycoforms bearing complex oligosaccharides showed a potent stimulatory effect on inhibin B when compared to inhibin A production (i.e. dose 1 ng/ml: 4.9±0.5 vs 0.9±0.1-fold stimulation, P<0.001). Glycoforms bearing hybrid-type oligosaccharides favoured inhibin A production (i.e. dose 4 ng/ml 2.9±0.1 vs 1.6±0.1-fold stimulation, P<0.05). These results show that the sialylation degree as well as the complexity of oligosaccharides present in the rhFSH molecule may be considered additional factors that differentially regulate dimeric inhibin production by rat GCs.

Isolation of dipeptidyl peptidase IV (DP 4) isoforms from porcine kidney by preparative isoelectric focusing to improve crystallization

In the present studies we resolved the post-translational microheterogeneity of purified porcine dipeptidyl peptidase IV (DP 4) from kidney cortex. Applying SDS-homogeneous DP 4 onto an analytical agarose isoelectric focusing (IEF) gel, pH 4–6, activity staining resulted in at least 17 isoforms between pH 4.8–6.0. These could be separated into fractions with only two to six isoforms by means of preparative liquid-phase IEF, using a Rotofor cell. Starting off with three parallel Rotofor runs under the same conditions at pH 5–6, the fractions were pooled according to the specific activity of DP 4, pH and analytical IEF profile, and further refractionated without any additional ampholytes. Since excessive dilution of ampholytes and proteins was kept to the minimum, a second refractionation step could be introduced, resulting in pH gradients between 0.022 and 0.028 pH increments per fraction. By performing two consecutive refractionation steps, the high resolution necessary for the separation of DP 4 isoforms could be achieved. This represents an alternative method if isolation of isoforms with similar pI's results in precipitation and denaturation in presence of a narrow pH range. Furthermore, it demonstrates that preparative IEF is a powerful tool to resolve post-translational microheterogeneity of a purified protein required for crystallization processing.