Loss-of-Function Mutations in the Human Luteinizing Hormone Receptor Predominantly Cause Intracellular Retention

Abstract

Mutations in G protein-coupled receptors (GPCRs) have been identified for many endocrine hormone signaling deficiencies. Inactivating mutations can impair ligand binding, receptor activation/ coupling to signaling pathways, or can cause receptor misfolding and consequent impaired expression at the cell membrane. Here we examine the cell surface expression, ligand binding, and signaling of a range of mutant human luteinizing hormone receptors (LHRs) identified as causing reproductive dysfunction in human patients. The data obtained reveal how mutations in GPCRs can have diverse and severely deleterious effects on receptor function. Furthermore, it was found that impaired functionality of the majority of the mutant LHRs was due to reduced expression at the cell surface (14/20) while only two mutations caused impaired binding affinity and two impaired in signaling. An additional two mutations were found to cause no impairment of receptor function. These data demonstrate that the majority of LHR mutations lead to intracellular retention and highlight the potential for novel pharmacological chaperone therapeutics that can "rescue" expression/function of retained mutant GPCRs. (Endocrinology 157: 4364 -4377, 2016) T he hypothalamic-pituitary-gonadal axis governs the endocrine control of reproduction. GnRH released from the hypothalamus binds the GnRH receptor on gonadotrope cells in the anterior pituitary, stimulating secretion of the gonadotropins, LH and FSH. LH and FSH enter the circulation and activate their cognate receptors LHR/LHCGR and FSHR in the gonads, to stimulate gametogenesis and the production/secretion of the sex steroid hormones. Perturbation of the hypothalamicpituitary-gonadal axis is associated with reproductive phenotypes, such as Leydig cell hypoplasia (LCH) in males (manifesting as a continuum of disorders from micropenis and hypospadias [Class II LCH], through to pseudohermaphroditism [Class I LCH]), and amenorrhea, and ovarian cysts in females (1). LCH is a 46,XY disorder, characterized by high circulating levels of LH with impaired male gonadal development. In some cases, LCH can be attributed to inactivating mutations in the LHR gene. In 46,XX patients inactivating LHR mutations can result in infertility, oligo-/amenorrhea, and/or empty follicle syn-

Novel Compound Heterozygous Variants in the <i>LHCGR</i> Gene in a Genetically Male Patient with Female External Genitalia

“…Gender assignment for LCH patients is influenced by genital appearance, surgical options, fertility potential and the views of the family, and can be difficult (11). Timing of gender assignment can also be controversial, especially when the psychological age is taken into consideration.…”

Novel Compound Heterozygous Variants in the LHCGR Gene in a Genetically Male Patient with Female External Genitalia

“…We first excluded harmful variant in the SRY gene. By performing WES, we identified a compound heterozygous variants in the patient, with a novel missense variant Gender assignment for LCH patients can be difficult, which is influenced by genital appearance, surgical options, fertility potential, and the views of the family (11). Timing of gender assignment can be controversial, especially when the psychological age is taken into consideration.…”

Glycoprotein G-protein Coupled Receptors in Disease: Luteinizing Hormone Receptors and Follicle Stimulating Hormone Receptors

“…As with FSHRs, mutations in LHRs (Table 2) can affect the trafficking of the receptor to the plasma membrane and produce disorders in fertility, similar to those seen with the expression of inactivating receptor mutations [64]. Because of the role of LHRs in male gonad development, males expressing inactivating LHR mutations can exhibit micropenis, hypospadias, delayed puberty, and Leydig cell hypoplasia with lower LHR expression.…”