Glu2.53(90) of the GnRH receptor is part of the conserved G protein-coupled receptor structure and does not form a salt-bridge with Lys3.32(121)

Restoring function to inactivating G protein-coupled receptor variants in the hypothalamic-pituitary-gonadal axis1

G protein-coupled receptors (GPCRs) are central to the functioning of the hypothalamic-pituitary-gonadal axis (HPG axis) and include the rhodopsin-like GPCR family members, neurokinin 3 receptor, kappa-opioid receptor, kisspeptin 1 receptor, gonadotropin-releasing hormone receptor, and the gonadotropin receptors, luteinizing hormone/choriogonadotropin receptor and follicle-stimulating hormone receptor. Unsurprisingly, inactivating variants of these receptors have been implicated in a spectrum of reproductive phenotypes, including failure to undergo puberty, and infertility. Clinical induction of puberty in patients harbouring such variants is possible, but restoration of fertility is not always a realisable outcome, particularly for those patients suffering from primary hypogonadism. Thus, novel pharmaceuticals and/or a fundamental change in approach to treating these patients are required. The increasing wealth of data describing the effects of coding-region genetic variants on GPCR function has highlighted that the majority appear to be dysfunctional as a result of misfolding of the encoded receptor protein, which, in turn, results in impaired receptor trafficking through the secretory pathway to the cell surface. As such, these intracellularly retained receptors may be amenable to 'rescue' using a pharmacological chaperone (PC)-based approach. PCs are small, cell permeant molecules hypothesised to interact with misfolded intracellularly retained proteins, stabilising their folding and promoting their trafficking through the secretory pathway. In support of the use of this approach as a viable therapeutic option, it has been observed that many rescued variant GPCRs retain at least a degree of functionality when 'rescued' to the cell surface. In this review, we examine the GPCR PC research landscape, focussing on the rescue of inactivating variant GPCRs with important roles in the HPG axis, and describe what is known regarding the mechanisms by which PCs restore trafficking and function. We also discuss some of the merits and obstacles associated with taking this approach forward into a clinical setting.

Gonadotropin-Releasing Hormone and GnRH Receptor: Structure, Function and Drug Development

BACKGROUND

Gonadotropin-Releasing Hormone (GnRH) is a key element in sexual maturation and regulation of the reproductive cycle in the human organism. GnRH interacts with the pituitary cells through the activation of the Gonadotropin Releasing Hormone Receptors (GnRHR). Any impairments/dysfunctions of the GnRH-GnRHR complex lead to the development of various cancer types and disorders. Furthermore, the identification of GnRHR as a potential drug target has led to the development of agonist and antagonist molecules implemented in various treatment protocols. The development of these drugs was based on the information derived from the functional studies of GnRH and GnRHR.

OBJECTIVE

This review aims at shedding light on the versatile function of GnRH and GnRH receptor and offers an apprehensive summary regarding the development of different agonists, antagonists and non-peptide GnRH analogues.

CONCLUSION

The information derived from these studies can enhance our understanding of the GnRH-GnRHR versatile nature and offer valuable insight into the design of new more potent molecules.