Rescue of hypogonadotropic hypogonadism-causing and manufactured GnRH receptor mutants by a specific protein-folding template: Misrouted proteins as a novel disease etiology and therapeutic target

In the present study, we demonstrate pharmacological rescue (assessed by ligand binding and restoration of receptor coupling to effector) of five naturally occurring GnRH receptor (GnRHR) mutants ((TI)-I-32, (EK)-K-90, (CY)-Y-200, (CY)-Y-279, and (LR)-R-266), identified from patients with hypogonadotropic hypogonadism, as well as rescue of other defective receptors intentionally manufactured with internal or terminal deletions or substitutions at sites expected to be involved in establishment of tertiary receptor structure. The pharmacological agent used is a small, membrane-permeant molecule, originally designed as an orally active, nonpeptide receptor antagonist, but is believed to function as a folding template, capable of correcting the structural defects caused by the mutations and thereby restoring function. After rescue, this agent can be demonstrably removed. The rescued receptor, now stabilized in the plasma membrane, couples ligand binding to activation of the appropriate effector system. For comparison, low-, intermediate-, or high-affinity peptide antagonists of GnRHR (that do not penetrate the cell) were unable to effect rescue, as was a non. binding peptidomimetic congener of the rescue agent; this latter effect demonstrates specificity of the rescue agent. Our findings, taken in concert with an earlier study showing rescue of a mutant by modifications to the receptor structure that enhance plasma membrane expression of the GnRHR, suggest that mutant GnRHRs have frequently not lost intrinsic functionality and are subject to rescue by techniques that enhance membrane expression. The present findings demonstrate the efficacy of an approach based on pharmacological rescue and suggest the basis of new approaches for intervention in this and similar diseases.