Selective Modulation of Follicle-Stimulating Hormone Signaling Pathways with Enhancing Equine Chorionic Gonadotropin/Antibody Immune Complexes

Abstract

The injection of equine chorionic gonadotropin (eCG) in dairy goats induces the production of anti-eCG antibodies (Abs) in some females. We have previously shown that Abs negatively modulate the LH and FSH-like bioactivities of eCG, in most cases, compromising fertility in treated females. Surprisingly, we found out that some anti-eCG Abs improved fertility and prolificity of the treated females, in vivo. These Abs, when complexed with eCG, enhanced LH and FSH ability to induce steroidogenesis on specific target cells, in vitro. In the present study, we analyzed the impact of three eCG/anti-eCG Ab-enhancing complexes on two transduction mechanisms triggered by the FSH receptor: guanine nucleotide-binding protein alphaS-subunit/cAMP/protein kinase A (PKA) and beta-arrestin-dependent pathways, respectively. In all cases, significant enhancing effects were observed on ERK phosphorylation compared with eCG alone. However, cAMP production and PKA activation induced by eCG could be differently modulated by Abs. By using a pharmacological inhibitor of PKA and small interfering RNA-mediated knock-down of endogenous beta-arrestin 1 and 2, we demonstrated that signaling bias was induced and was clearly dependent on the complexed Ab. Together, our data show that eCG/anti-eCG Ab-enhancing complexes can differentially modulate cAMP/PKA and beta-arrestin pathways as a function of the complexed Ab. We hypothesize that enhancing Abs may change the eCG conformation, the immune complex acquiring new "biased" pharmacological properties ultimately leading to the physiological effects observed in vivo. The modulation of ligand pharmacological properties by Abs opens promising research avenues towards the optimization of glycoprotein hormone biological activities and, more generally, the development of new therapeutics.

Are circulating gonadotropin isoforms naturally occurring biased agonists? Basic and therapeutic implications

“…However, these differential responses were not evident for all glycosylated variants, as we had tested several variants that did not exhibit dose-response relationships similar to the BV-hFSH and deglycosylated hFSH (Arey, data not shown). These observations were subsequently confirmed by others [15,63]. Interestingly, similar glycosylation-dependent signal biasing has been noted for other secreted glycoproteins [e.g.…”

“…This is supported by recent reports of ligand-induced selectivity in β-arrestin signaling and ERK activation by the FSHR. These observations demonstrated quite clearly the ability for biased signaling of the gonadotropin receptors [63]. Overall, these observations suggest that gonadotropin receptors, like many other GPCRs [44], induce a complex pattern of cell activation upon binding to their respective ligand even within the physiological context.…”

Novel pathways in gonadotropin receptor signaling and biased agonism

“…Recently, data have pointed to the instrumental role of β-arrestins as direct interactors with the FSH-R involved in the spatial and temporal organization of these signaling events [47][48][49]. These observations led to the concept that ligands with FSH activity could select only part of the signaling repertoire induced by the natural hormone, either G protein-dependent or β-arrestin-dependent [50,51]. Regarding gene regulation, the pattern of transcriptionally regulated genes through activation of PKA on the one hand and β-arrestins on the other, might be dictated primarily by modifications of chromatin accessibility, and to a lesser extent by recognition of consensus binding sites for specific transcription factors such as CREB.…”

“…Whether gonadotropins induce histone acetylation through β-arrestins still needs to be investigated, but it is tempting to speculate that both β-arrestin-and PKAmediated transcriptional events might each contribute to different parts of the whole FSH-regulated gene network. Further, it is expected that receptors impaired in their ability to couple to Gα s following mutations (Durand et al, in prep) or ligand-imposed constraints [50,51], as well as receptors weakly addressed to the plasma membrane [52], could still transcriptionally regulate part of the spectrum of FSH target genes. Recent evidences from our laboratory [53][54][55] and from other groups [56][57][58][59] have indicated that FSH and LH [60] could regulate genes in primary target cells at the level of mRNA translation as well.…”

“…Besides the PI3K pathway, biased extracellular signalregulated kinase (ERK) mitogen-activated protein kinase (MAPK) signaling has been shown to occur at the FSH-R bound to a modified agonist [50,51] or when its expression is severely reduced [52]. In this case, β-arrestins recruited to the agonist-bound receptor assemble a MAPK module, whereas G protein-dependent signaling is impaired.…”