Gonadotropin-releasing hormone receptor

Genes

There are two major forms of the GNRHR, each encoded by a separate gene (GNRHR and GNRHR2).

Alternative splicing of the GNRHR gene, GNRHR, results in multiple transcript variants encoding different isoforms. More than 18 transcription initiation sites in the 5' region and multiple polyA signals in the 3' region have been identified for GNRHR.

Regulation

The GnRHR responds to GnRH as well as to synthetic GnRH agonists. Agonists stimulate the receptor, however prolonged exposure leads to a downregulation effect resulting in hypogonadism, an effect that is often medically utilized. GnRH antagonists block the receptor and inhibit gonadotropin release. GnRHRs are further regulated by the presence of sex hormones as well as activin and inhibin.

Ligands

Agonists

Peptides

• Azagly-nafarelin
• Buserelin
• Deslorelin
• Fertirelin
• GnRH
• Gonadorelin
• Goserelin
• Histrelin
• Lecirelin
• Leuprorelin
• Nafarelin
• Peforelin
• Triptorelin

Antagonists

Peptides

• Abarelix
• Cetrorelix
• Degarelix
• Ganirelix
• Ozarelix

Non-peptides

• Elagolix
• Linzagolix
• Opigolix
• Relugolix
• Sufugolix

Pharmacoperones

Current research is looking into pharmacoperones, or chemical chaparones that promote the shuttling of mature Gonadotropin-releasing hormone receptor (GNRHR) protein to the cell surface, leading to a functional protein. Gonadotropin-releasing hormone receptor function has been shown to be deleteriously effected by point mutations in its gene. Some of these mutations, when expressed, cause the receptor to remain in the cytosol. An approach to rescue receptor function utilizes pharmacoperones or molecular chaperones, which are typically small molecules that rescue misfolded proteins to the cell surface. These interact with the receptor to restore cognate receptor function devoid of antagonist or agonist activity. This approach, when effective, should increase therapeutic reach. Pharmacoperones have been identified that restore function of Gonadotropin-releasing hormone receptor.

Clinical implications

Defects in the GnRHR are a cause of hypogonadotropic hypogonadism (HH).

Normal puberty begins between ages 8 and 14 in girls and between 9 and 14 in boys. Puberty, however, for some children can come much sooner (precocious puberty) or much later (delayed puberty). In some cases puberty never occurs and thereby contributes to the estimated 35-70 million infertile couples worldwide. Among children, the abnormally early or late onset of puberty exerts intense emotional and social stress that too often goes untreated.

The timely onset of puberty is regulated by many factors and one factor that is often referred to as the master regulator of puberty and reproduction is GnRH. This peptide hormone is produced in the hypothalamus but gets secreted and acts upon GnRHRs in the anterior pituitary to exert its effects on reproductive maturation.

Understanding how GnRHR functions has been key to developing clinical strategies to treat reproductive-related disorders.