Endocrine Abstracts

Luteinising hormone (LH) and the luteinising hormone receptor (LHR) have key roles in steroidogenesis and ovulation, thus are central targets for fertility treatment. The LHR is a G protein-coupled receptor that predominantly signals through Gαs, although under conditions of high ligand concentration and/or high receptor density, as occurs during the mid-cycle LH surge, can also signal via Gαq/11. Yet, how LHR delineates signal pathway activation to coordinate pleiotropic physiological roles remains unknown. GPCR di/oligomerisation is an important mechanism regulating receptor activity. Whilst mouse studies have demonstrated the physiological relevance of multi-receptor complexes for the LHR in males, the role of distinct LHR complexes in coordinating the complexities of LHR signalling and female reproduction remains unknown. Based on previous super-resolution imaging, molecular modelling predicted multiple transmembrane (TM) interfaces used in formation of multi-receptor LHR complexes. From this, peptides were designed against specific LHR transmembrane domains to allow disruption of different LHR complexes. By inhibiting specific transmembrane domain interactions singularly, and in combination, we have demonstrated that inhibiting formation of different LHR complexes has distinct effects on downstream signalling. Inhibiting TM1,2,4,5 and 6 together results in a 50% loss in cAMP signalling, whilst inhibiting TM1 or TM5 alone results in a 22% or 12% loss of cAMP, respectively. It has been proposed that membrane trafficking can position GPCRs in microdomains rich in signalling partners. Using single particle tracking we have demonstrated that following LH treatment LHR moves slower than untreated receptor, travels less total distance than untreated receptor and is more constricted in its movements, suggesting activated LHR is trafficked to specific membrane micro-compartments. Overall, we have demonstrated that formation of different LHR complexes is critical for LHR function, and that treatment with LH may constrict receptor movement to specific membrane microdomains prior to internalisation.